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As oxygen is fundamental for oxidative phosphorylation, a shortage in O level likely alters ATP production rates. However, proton motive force and ATP production can be maintained by intracellular acidosis. Cytosolic protons that have accumulated with ATP hydrolysis and lactic acidosis can freely diffuse across the mitochondrial outer-membrane and acidify the inter-membrane space, hence directly contributing to the proton motive force and ATP production. | 1 | Applied and Interdisciplinary Chemistry |
The Haber process, also called the Haber–Bosch process, is the main industrial procedure for the production of ammonia. The German chemists Fritz Haber and Carl Bosch developed it in the first decade of the 20th century. The process converts atmospheric nitrogen (N) to ammonia (NH) by a reaction with hydrogen (H) using an iron metal catalyst under high temperatures and pressures. This reaction is slightly exothermic (i.e. it releases energy), meaning that the reaction is favoured at lower temperatures and higher pressures. It decreases entropy, complicating the process. Hydrogen is produced via steam reforming, followed by an iterative closed cycle to react hydrogen with nitrogen to produce ammonia.
The primary reaction is:
Before the development of the Haber process, it had been difficult to produce ammonia on an industrial scale, because earlier methods, such as the Birkeland–Eyde process and the Frank–Caro process, were too inefficient. | 0 | Theoretical and Fundamental Chemistry |
Ulloa returned to South America in 1758 as governor of Huancavelica, in Peru, and general manager of the quicksilver mines in the region. At the time, quicksilver (mercury) was of great practical importance because of its use in the extraction of silver and gold. Ulloa fought unsuccessfully against the deep-rooted corruption in the local administration and finally requested to be relieved of his post in 1764.
Following the defeat of France by Britain in the Seven Years War, France agreed in the secret Treaty of Fontainebleau to cede to Spain its remaining territories in North America. The Spanish Crown then appointed Ulloa as the first governor of Spanish Louisiana. Ulloa reached New Orleans, the major city and port of the region, on 5 March 1766. The French Creole colonists refused to recognize Spanish rule, leading to the Louisiana Rebellion of 1768. On 28 October, as riots broke out in New Orleans, the governor and his pregnant wife were taken to a Spanish vessel. The Superior Council voted that the governor leave within three days. He complied, departing on 1 November. The revolt was ultimately crushed in 1769 by forces under the command of the new Spanish governor, Alejandro OReilly, who succeeded in establishing definitively the control of the region by the Spanish Crown.
Between 1776 and 1778, in the context of the American Revolutionary War, in which Spain supported the fight against British rule of the Thirteen Colonies, Ulloa helped organize a fleet of the Viceroyalty of New Spain (present-day Mexico) and construction of a military shipyard in the Atlantic port of Veracruz. He was in command of the last great naval fleet to sail from Cádiz to the Americas. | 1 | Applied and Interdisciplinary Chemistry |
The shape correction function is a ratio of the surface area of a growing organism and that of an isomorph as function of the volume. The shape of the isomorph is taken to be equal to that of the organism for a given reference volume, so for that particular volume the surface areas are also equal and the shape correction function has value one.
For a volume and reference volume , the shape correction function equals:
* V0-morphs:
* V1-morphs:
* Isomorphs:
Static mixtures between a V0 and a V1-morph can be found as: for
The shape correction function is used in Dynamic Energy Budget theory to correct equations for isomorphs to organisms that change shape during growth. The conversion is necessary for accurately modelling food (substrate) acquisition and mobilization of reserve for use by metabolism. | 1 | Applied and Interdisciplinary Chemistry |
Raoults law ( law) is a relation of physical chemistry, with implications in thermodynamics. Proposed by French chemist François-Marie Raoult in 1887, it states that the partial pressure of each component of an ideal mixture of liquids' is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture. In consequence, the relative lowering of vapor pressure of a dilute solution of nonvolatile solute is equal to the mole fraction of solute in the solution.
Mathematically, Raoult's law for a single component in an ideal solution is stated as
where is the partial pressure of the component in the gaseous mixture above the solution, is the equilibrium vapor pressure of the pure component , and is the mole fraction of the component in the liquid or solid solution.
Where two volatile liquids A and B are mixed with each other to form a solution, the vapor phase consists of both components of the solution. Once the components in the solution have reached equilibrium, the total vapor pressure of the solution can be determined by combining Raoults law with Daltons law of partial pressures to give
In other words, the vapor pressure of the solution is the mole-weighted mean of the individual vapour pressures:
If a non-volatile solute B (it has zero vapor pressure, so does not evaporate) is dissolved into a solvent A to form an ideal solution, the vapor pressure of the solution will be lower than that of the solvent. In an ideal solution of a nonvolatile solute, the decrease in vapor pressure is directly proportional to the mole fraction of solute:
If the solute associates or dissociates in the solution, the expression of the law includes the van 't Hoff factor as a correction factor. | 0 | Theoretical and Fundamental Chemistry |
Viruses are so small that they can only be observed under an electron microscope. The structure of a virus is given by its coat of proteins, which surround the viral genome. Assembly of viral particles takes place spontaneously.
Over 50% of known plant viruses are rod-shaped (flexuous or rigid). The length of the particle is normally dependent on the genome but it is usually between 300 and 500 nm with a diameter of 15–20 nm. Protein subunits can be placed around the circumference of a circle to form a disc. In the presence of the viral genome, the discs are stacked, then a tube is created with room for the nucleic acid genome in the middle.
The second most common structure amongst plant viruses are isometric particles. They are 25–50 nm in diameter. In cases when there is only a single coat protein, the basic structure consists of 60 T subunits, where T is an integer. Some viruses may have 2 coat proteins that associate to form an icosahedral shaped particle.
There are three genera of Geminiviridae that consist of particles that are like two isometric particles stuck together.
A few number of plant viruses have, in addition to their coat proteins, a lipid envelope. This is derived from the plant cell membrane as the virus particle buds off from the cell. | 1 | Applied and Interdisciplinary Chemistry |
As explained in the general stream function article, definitions using an opposite sign convention – for the relationship between the Stokes stream function and flow velocity – are also in use. | 1 | Applied and Interdisciplinary Chemistry |
Since 2007, China has restricted exports of REEs (rare-earth elements) and imposed export tariffs, both to conserve resources and to give preference to Chinese manufacturers. In 2009, China supplied more than 96% of the world's REEs. Some outside China are concerned that because rare-earths are essential to some high-tech, renewable-energy, and defense-related technologies, the world should not be so reliant on a single supplier country
On September 22, 2010, China quietly enacted a ban on exports of rare-earths to Japan, a move suspected to be in retaliation for the Japanese arrest of a Chinese trawler captain in a territorial dispute. Because Japan and China are the only current sources for rare-earth magnetic material used in the US, a permanent disruption of Chinese rare-earth supply to Japan would leave China as the sole source. Jeff Green, a rare-earth lobbyist, said, "We are going to be 100 percent reliant on the Chinese to make the components for the defense supply chain." The House Committee on Science and Technology scheduled on September 23, 2010, the review of a detailed bill to subsidize the revival of the American rare-earths industry, including the reopening of the Mountain Pass mine.
After China doubled import duties on rare-earth concentrates to 25% as a result of the US-China trade war, MP Materials said, in May 2019, it will start its own partial processing operation in the United States, though full processing operations without Shenghe Resources have been delayed. According to Bloomberg, China in 2019 established a plan for restricting U.S. access to Chinese heavy rare earth elements, should the punitive step be deemed necessary. In 2022, the company announced that it had secured Department of Defense grants to support both light rare-earth elements (LREEs) and heavy rare earth elements (HREEs). The facility plans to begin separating NdPr oxide in early 2023. | 1 | Applied and Interdisciplinary Chemistry |
*A web application for determining molecular geometry indices on the basis of 3D structural files can be found [http://kchn.pg.gda.pl/geom/ here]. | 0 | Theoretical and Fundamental Chemistry |
The modern understanding of heat is often partly attributed to Thompsons 1798 mechanical theory of heat (An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction'), postulating a mechanical equivalent of heat.
A collaboration between Nicolas Clément and Sadi Carnot (Reflections on the Motive Power of Fire) in the 1820s had some related thinking along similar lines. In 1842, Julius Robert Mayer frictionally generated heat in paper pulp and measured the temperature rise. In 1845, Joule published a paper entitled The Mechanical Equivalent of Heat, in which he specified a numerical value for the amount of mechanical work required to "produce a unit of heat", based on heat production by friction in the passage of electricity through a resistor and in the rotation of a paddle in a vat of water. The theory of classical thermodynamics matured in the 1850s to 1860s. | 0 | Theoretical and Fundamental Chemistry |
Once quantitative counts of each transcript are available, differential gene expression is measured by normalising, modelling, and statistically analysing the data. Most tools will read a table of genes and read counts as their input, but some programs, such as cuffdiff, will accept binary alignment map format read alignments as input. The final outputs of these analyses are gene lists with associated pair-wise tests for differential expression between treatments and the probability estimates of those differences. | 1 | Applied and Interdisciplinary Chemistry |
While most magnetoelectric multiferroics developed to date have conventional transition-metal d-electron magnetism and a novel mechanism for the ferroelectricity, it is also possible to introduce a different type of magnetism into a conventional ferroelectric. The most obvious route is to use a rare-earth ion with a partially filled shell of f electrons on the A site. An example is EuTiO which, while not ferroelectric under ambient conditions, becomes so when strained a little bit, or when its lattice constant is expanded for example by substituting some barium on the A site. | 0 | Theoretical and Fundamental Chemistry |
If reaction sheet is not assumed to be thin, then there is a chance that one can find a value for in between zero and unity, although in reality, the reaction sheet is mostly thin compared to turbulent scales. Nevertheless, the general form the density function can be written as
where is the probability of finding the progress variable which is undergoing reaction (where transition from zero to unity is effected). Here, we have
where is negligible in most regions. | 1 | Applied and Interdisciplinary Chemistry |
Udayanas Nyayakusumanjali' gave the following nine arguments to prove the existence of creative God and also tried to refute the existing objections and questions by atheistic systems of charvaka, mimamsa, buddhists, jains and samkhya:
*Kāryāt (lit. "from effect"): The world is an effect, all effects have efficient cause, hence the world must have an efficient cause. That efficient cause is God.
*Āyojanāt (lit., from combination): Atoms are inactive. To form a substance, they must combine. To combine, they must move. Nothing moves without intelligence and source of motion. Since we perceive substance, some intelligent source must have moved the inactive atoms. That intelligent source is God.
*Dhŗtyādéḥ (lit., from support): Something sustains this world. Something destroys this world. Unintelligent Adrsta (unseen principles of nature) cannot do this. We must infer that something intelligent is behind. That is God.
*Padāt (lit., from word): Each word has meaning and represents an object. This representational power of words has a cause. That cause is God.
*Pratyayataḥ (lit, from faith): Vedas are infallible. Human beings are fallible. Infallible Vedas cannot have been authored by fallible human beings. Someone authored the infallible Vedas. That author is God.
*Shrutéḥ (lit., from scriptures): The infallible Vedas testify to the existence of God. Thus God exists.
*Vākyāt (lit., from precepts): Vedas deal with moral laws, the rights and the wrongs. These are divine. Divine injunctions and prohibitions can only come from a divine creator of laws. That divine creator is God.
*Samkhyāviśeşāt (lit., from the specialty of numbers): By rules of perception, only number "one" can ever be directly perceived. All other numbers other than one, are inferences and concepts created by consciousness. When man is born, his mind is incapable of inferences and concepts. He develops consciousness as he develops. The consciousness development is self-evident and proven because of man's ability with perfect numerical conception. This ability to conceive numerically perfect concepts must depend on something. That something is divine consciousness. So God must exist.
*Adŗşţāt (lit., from the unforeseen): Everybody reaps the fruits of his own actions. Merits and demerits accrue from his own actions. An Unseen Power keeps a balance sheet of the merit and demerit. But since this Unseen Power is Unintelligent, it needs intelligent guidance to work. That intelligent guide is God. | 1 | Applied and Interdisciplinary Chemistry |
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DWSIM is an open-source CAPE-OPEN compliant chemical process simulator for Windows, Linux and macOS. DWSIM is built on top of the Microsoft .NET and Mono Platforms and features a Graphical User Interface (GUI), advanced thermodynamics calculations, reactions support and petroleum characterization / hypothetical component generation tools.
DWSIM is able to simulate steady-state, vapor–liquid, vapor–liquid-liquid, solid–liquid and aqueous electrolyte equilibrium processes with the following Thermodynamic Models and Unit Operations:
* Thermodynamic models: [http://www.coolprop.org CoolProp], Peng–Robinson equation of state, Peng–Robinson-Strÿjek-Vera (PRSV2), Soave–Redlich–Kwong, Lee-Kesler, Lee-Kesler-Plöcker, UNIFAC(-LL), Modified UNIFAC (Dortmund), Modified UNIFAC (NIST), UNIQUAC, NRTL, Chao-Seader, Grayson-Streed, Extended UNIQUAC, Raoult's Law, IAPWS-IF97 Steam Tables, IAPWS-08 Seawater, Black-Oil and Sour Water;
* Unit operations: CAPE-OPEN Socket, Spreadsheet, Custom (IronPython Script), Mixer, Splitter, Separator, Pump, Compressor, Expander, Heater, Cooler, Valve, Pipe Segment, Shortcut Column, Heat exchanger, Reactors (Conversion, PFR, CSTR, Equilibrium and Gibbs), Distillation column, Simple, Refluxed and Reboiled Absorbers, Component Separator, Solids Separator, Continuous Cake Filter and Orifice plate;
* Utilities: Binary Data Regression, Phase Envelope, Natural Gas Hydrates, Pure Component Properties, True Critical Point, PSV Sizing, Vessel Sizing, Spreadsheet and Petroleum Cold Flow Properties;
* Tools: Hypothetical Component Generator, Bulk C7+/Distillation Curves Petroleum Characterization, Petroleum Assay Manager, Reactions Manager and Compound Creator;
* Process Analysis and Optimization: Sensitivity Analysis Utility, Multivariate Optimizer with bound constraints;
* Extras: Support for Runtime Python Scripts, Plugins and CAPE-OPEN Flowsheet Monitoring Objects. | 1 | Applied and Interdisciplinary Chemistry |
Pancratistatin occurs naturally in Hawaiian spider lily, a flowering plant within the family Amaryllidaceae. Pancratistatin is mostly found in the bulb tissues of spider lilies. It has been shown that the enrichment of atmospheric CO can enhance the production of antiviral secondary metabolites, including pancratistatin, in these plants. Pancratistatin can be isolated from the tropical bulbs of Hymenocallis littoralis in the order of 100 to 150 mg/kg when bulbs are obtained from the wild type in Hawaii. However, the compound has to be commercially extracted from field- and greenhouse-grown bulbs or from tissue cultures cultivated, for example, in Arizona, which generate lower levels of pancratistatin (a maximum of 22 mg/kg) even in the peak month of October. After October, when the bulb becomes dormant, levels of pancratistatin drop, down to only 4 mg/kg by May. Field-grown bulbs, which show monthly changes in pancratistatin content, generate somewhat smaller amounts (2–5 mg/kg) compared to those grown in greenhouses cultivated over the same period. There are about 40 different spider lily species worldwide and they are mainly native to the Andes of South America. | 0 | Theoretical and Fundamental Chemistry |
Although there are no set plans to search for biosignatures on Saturns sixth-largest moon, Enceladus, the prospects of biosignature discovery there are exciting enough to warrant several mission concepts that may be funded in the future. Similar to Jupiters moon Europa, there is much evidence for a subsurface ocean to also exist on Enceladus. Plumes of water vapor were first observed in 2005 by the Cassini mission and were later determined to contain salt as well as organic compounds. In 2014, more evidence was presented using gravimetric measurements on Enceladus to conclude that there is in fact a large reservoir of water underneath an icy surface. Mission design concepts include:
*Enceladus Life Finder (ELF)
*Enceladus Life Signatures and Habitability
* Enceladus Organic Analyzer
* Enceladus Explorer (En-Ex)
* Explorer of Enceladus and Titan (ET)
* Journey to Enceladus and Titan (JET)
* Life Investigation For Enceladus (LIFE)
* Testing the Habitability of Enceladus's Ocean (THEO)
All of these concept missions have similar science goals: To assess the habitability of Enceladus and search for biosignatures, in line with the strategic map for exploring the ocean-world Enceladus. | 1 | Applied and Interdisciplinary Chemistry |
Titanium undergoes allotropic transformation from its α-phase (hexagonal close-packed (hcp) structure at temperatures less than 882.5 °C) to its β-phase (body centered cubic, bcc) structure at temperatures above 882.3 °C). Alpha-phase titanium products typically exhibit medium to high strength with excellent creep strength, whereas beta-phase titanium products typically exhibit very high strength and low ductility. Foams created under thermal cycling conditions have been shown to exhibit increased porosity due to the density difference between allotropic phases. Davis et al. produced titanium foams with 41% porosity (as compared to 27% porosity through the normal HIP creep mechanism). Increases in overall ductility were also observed in foams created through thermal cycling. In a similar experiment, porosity of 44% was achieved and determined as the maximum achievable porosity under thermal cycling conditions. A later study also utilized exploitation of transformation superplasticity conditions through HIP, but in this case, the titanium powder in the precursor matrix was replaced with titanium wires to create anisotropic pores. The resulting anisotropic pores showed closer correlation with natural bone in that the foams exhibited higher elastic moduli, yield strength and deformation when subjected to longitudinally loaded forces than when loads were applied transversely. | 0 | Theoretical and Fundamental Chemistry |
In 2003 an alternative mechanism was devised by Nadine Abraham and Peter Palffy-Muhoray of Ohio, USA, that utilizes capillary action combined with evaporation to produce motion, but has no volatile working fluid. Their paper "A Dunking Bird of the Second Kind", was submitted to the American Journal of Physics, and published in June 2004. It describes a mechanism which, while similar to the original drinking bird, operates without a temperature difference. Instead it utilizes a combination of capillary action, gravitational potential difference and the evaporation of water to power the device.
This bird works as follows: it is balanced such that, when dry, it tips into a head-down position. The bird is placed next to a water source such that this position brings its beak into contact with water. Water is then lifted into the beak by capillary action (the authors used a triangular sponge) and carried by capillary action past the fulcrum to a larger sponge reservoir which they fashioned to resemble wings. When enough water has been absorbed by the reservoir, the now-heavy bottom causes the bird to tip into a head-up position. With the beak out of the water, eventually enough water evaporates from the sponge that the original balance is restored and the head tips down again. Although a small drop in temperature may occur due to evaporative cooling, this does not contribute to the motion of the bird. The device operates relatively slowly with 7 hours 22 minutes being the average cycle time measured. | 0 | Theoretical and Fundamental Chemistry |
Walsh originally constructed his diagrams by plotting what he described as "orbital binding energies" versus bond angles. What Walsh was actually describing by this term is unclear; some believe he was in fact referring to ionization potentials, however this remains a topic of debate. At any rate, the general concept he put forth was that the total energy of a molecule is equal to the sum of all of the "orbital binding energies" in that molecule. Hence, from knowledge of the stabilization or destabilization of each of the orbitals by an alteration of the molecular bond angle, the equilibrium bond angle for a particular state of the molecule can be predicted. Orbitals which interact to stabilize one configuration (ex. Linear) may or may not overlap in another configuration (ex. Bent), thus one geometry will be calculably more stable than the other.
Typically, core orbitals (1s for B, C, N, O, F, and Ne) are excluded from Walsh diagrams because they are so low in energy that they do not experience a significant change by variations in bond angle. Only valence orbitals are considered. However, one should keep in mind that some of the valence orbitals are often unoccupied. | 0 | Theoretical and Fundamental Chemistry |
Modern enantioselective synthesis typically applies a well-chosen homogeneous catalyst for key steps. The ligands on these catalysts confer chirality. The Josiphos family of privileged ligands provides especially high yields in enantioselective synthesis.
In the early 1990s, Antonio Togni began studying at the Ciba (now Novartis) Central Research Laboratories previously-known ferrocenyl ligands for a Au(I)-catalyzed aldol reaction. Tognis team began considering diphosphine ligands, and technician Josi Puleo prepared the first ligands with secondary phosphines. The team applied Puleos products in an Ru-catalyzed enamide hydrogenation synthesis; in a dramatic success, the reaction had e.e. >99% and a turnover frequency (TOF) 0.3 s. The same ligand proved useful in production of (S)-metolachlor, active ingredient in the most common herbicide in the United States. Synthesis requires enantioselective hydrogenation of an imine; after introduction of the catalyst, the reaction proceeds with 100% conversion, turnover number (TON) >7mil, and turnover frequency >0.5 ms. This process is the largest-scale application of enantioselective hydrogenation, producing over 10 kilotons/year of the desired product with 79% e.e.
Josiphos ligands also serve in non-enantioselective reactions: a Pd-catalyzed reaction of aryl chlorides and aryl vinyl tosylates with TON of 20,000 or higher, catalytic carbonylation, or Grignard and Negishi couplings A variety of Josiphos ligands are commercially available under licence from Solvias. The (R-S) and its enantiomer provide higher yields and enantioselectivities than the diastereomer (R,R).
The ferrocene scaffold has proved to be versatile. One structural parameter that influences reactivity is the bite angle. The P-M-P angle has an average value of 92.7°.
The general consensus for the naming is abbreviating the individual ligand as (R)-(S)-RPF-PR'. The substituent on the Cp is written in front of the F and the R on the chiral center after the F. | 0 | Theoretical and Fundamental Chemistry |
Denitrification is the utilization of nitrate () as a terminal electron acceptor. It is a widespread process that is used by many members of the Pseudomonadota. Many facultative anaerobes use denitrification because nitrate, like oxygen, has a high reduction potential. Many denitrifying bacteria can also use ferric iron () and some organic electron acceptors. Denitrification involves the stepwise reduction of nitrate to nitrite (), nitric oxide (NO), nitrous oxide (), and dinitrogen () by the enzymes nitrate reductase, nitrite reductase, nitric oxide reductase, and nitrous oxide reductase, respectively. Protons are transported across the membrane by the initial NADH reductase, quinones, and nitrous oxide reductase to produce the electrochemical gradient critical for respiration. Some organisms (e.g. E. coli) only produce nitrate reductase and therefore can accomplish only the first reduction leading to the accumulation of nitrite. Others (e.g. Paracoccus denitrificans or Pseudomonas stutzeri) reduce nitrate completely. Complete denitrification is an environmentally significant process because some intermediates of denitrification (nitric oxide and nitrous oxide) are important greenhouse gases that react with sunlight and ozone to produce nitric acid, a component of acid rain. Denitrification is also important in biological wastewater treatment where it is used to reduce the amount of nitrogen released into the environment thereby reducing eutrophication. Denitrification can be determined via a nitrate reductase test. | 1 | Applied and Interdisciplinary Chemistry |
The CK1 family of monomeric serine–threonine protein kinases is found in eukaryotic organisms from yeast to humans. Mammals have seven family members (sometimes referred to as isoforms, but encoded by distinct genes): alpha, beta 1, gamma 1, gamma 2, gamma 3, delta, and epsilon. Isoforms range from 22 to 55 kDa and have been identified in the membranes, nucleus, and cytoplasm of eukaryotes and additionally in the mitotic spindle in mammalian cells. The family members have the highest homology in their kinase domains (53%–98% identical) and differ from most other protein kinases by the presence of the sequence S-I-N instead of A-P-E in kinase domain VIII. The family members appear to have similar substrate specificity in vitro, and substrate selection is thought to be regulated in vivo via subcellular localization and docking sites in specific substrates. One consensus phosphorylation site is S/Tp-X-X-S/T, where S/Tp refers to a phospho-serine or phospho-threonine, X refers to any amino acid, and the underlined residues refer to the target site. Thus, this CKI consensus site requires priming by another kinase. CKI also phosphorylates a related unprimed site, which optimally contains a cluster of acidic amino acids N-terminal to the target S/T including an acidic residue at n − 3 and a hydrophobic region C-terminal to the target S/T. A single acidic residue in the n − 3 position is not sufficient for CKI phosphorylation. In contrast, in several important targets, NF-AT and beta-catenin, CKI does not require n − 3 priming but, instead, phosphorylates the first serine in the sequence S-L-S, which is followed by a cluster of acidic residues, albeit less efficiently than the optimal sites. | 1 | Applied and Interdisciplinary Chemistry |
In an X-ray tube, electrons are accelerated in a vacuum by an electric field towards a piece of metal called the "target". X-rays are emitted as the electrons slow down (decelerate) in the metal. The output spectrum consists of a continuous spectrum of X-rays, with additional sharp peaks at certain energies. The continuous spectrum is due to bremsstrahlung, while the sharp peaks are characteristic X-rays associated with the atoms in the target. For this reason, bremsstrahlung in this context is also called continuous X-rays.
The shape of this continuum spectrum is approximately described by Kramers' law.
The formula for Kramers' law is usually given as the distribution of intensity (photon count) against the wavelength of the emitted radiation:
The constant is proportional to the atomic number of the target element, and is the minimum wavelength given by the Duane–Hunt law.
The spectrum has a sharp cutoff at which is due to the limited energy of the incoming electrons. For example, if an electron in the tube is accelerated through 60 kV, then it will acquire a kinetic energy of 60 keV, and when it strikes the target it can create X-rays with energy of at most 60 keV, by conservation of energy. (This upper limit corresponds to the electron coming to a stop by emitting just one X-ray photon. Usually the electron emits many photons, and each has an energy less than 60 keV.) A photon with energy of at most 60 keV has wavelength of at least 21 pm, so the continuous X-ray spectrum has exactly that cutoff, as seen in the graph. More generally the formula for the low-wavelength cutoff, the Duane–Hunt law, is:
where is Planck's constant, is the speed of light, is the voltage that the electrons are accelerated through, is the elementary charge, and is picometres. | 0 | Theoretical and Fundamental Chemistry |
Due to the special property of photo-switchable fluorescence, Kaede protein possesses several advantages as an optical cell marker.
After the photoconversion, the photoconverted Kaede protein emits bright and stable red fluorescence. This fluorescence can last for months without anaerobic conditions. As this red state of Kaede is bright and stable compared to the green state, and because the unconverted green Kaede emits very low intensity of red fluorescence, the red signals provides contrast.
Besides, before the photoconversion, Kaede emits bright green fluorescence which enables the visualization of the localization of the non-photoacivated protein. This is superior to other fluorescent proteins such as PA-GFP and KFP1, which only show low fluorescence before photoactivation.
In addition, as both green and red fluorescence of Kaede are excited by blue light at 480 nm for observation, this light will not induce photoconversion. Therefore, illumination lights for observation and photoconversion can be separated completely. | 1 | Applied and Interdisciplinary Chemistry |
When the working fluid is a gas that is compressed and expanded but does not change phase, the refrigeration cycle is called a gas cycle. Air is most often this working fluid. As there is no condensation and evaporation intended in a gas cycle, components corresponding to the condenser and evaporator in a vapor compression cycle are the hot and cold gas-to-gas heat exchangers in gas cycles.
The gas cycle is less efficient than the vapor compression cycle because the gas cycle works on the reverse Brayton cycle instead of the reverse Rankine cycle. As such, the working fluid does not receive and reject heat at constant temperature. In the gas cycle, the refrigeration effect is equal to the product of the specific heat of the gas and the rise in temperature of the gas in the low temperature side. Therefore, for the same cooling load, a gas refrigeration cycle needs a large mass flow rate and is bulky.
Because of their lower efficiency and larger bulk, air cycle coolers are not often used nowadays in terrestrial cooling devices. However, the air cycle machine is very common on gas turbine-powered jet aircraft as cooling and ventilation units, because compressed air is readily available from the engines' compressor sections. Such units also serve the purpose of pressurizing the aircraft. | 0 | Theoretical and Fundamental Chemistry |
The decreasing electronegativity with increasingly heavy chalcogenides leads to a reversal of the dipole. In NO, oxygen is the more electronegative element. In NS, nitrogen is more electronegative. The NS radical is significantly more unstable and prone to catenation than NO. | 0 | Theoretical and Fundamental Chemistry |
For phonon-phonon scattering, effects by normal processes (processes which conserve the phonon wave vector - N processes) are ignored in favor of Umklapp processes (U processes). Since normal processes vary linearly with and umklapp processes vary with , Umklapp scattering dominates at high frequency. is given by:
where is the Gruneisen anharmonicity parameter, is the shear modulus, is the volume per atom and is the Debye frequency. | 0 | Theoretical and Fundamental Chemistry |
In enzymatic analysis (which is widely used in medical laboratories) the color reaction is preceded by a reaction catalyzed by an enzyme. As the enzyme is specific to a particular substrate, more accurate results can be obtained. Enzymatic analysis is always carried out in a buffer solution at a specified temperature (usually 37°C) to provide the optimum conditions for the enzymes to act. Examples follow. | 0 | Theoretical and Fundamental Chemistry |
* 2014 Monomers, polymers and articles containing the same from sugar derived compounds
* 2018 Isosorbide-based polymethacrylates | 1 | Applied and Interdisciplinary Chemistry |
Long non-coding RNA (LncRNA) are a type of RNA which is usually defined as transcripts which are greater than 200 base-pairs in length and not translated into proteins. This limitation distinguishes lncRNA from small non-coding RNAs which encompasses microRNAs (miRNAs), small interfering RNAs (siRNAs), Piwi-interacting RNAs (piRNAs), small nucleolar RNAs (snoRNAs), and other short RNAs. Long non-coding RNAs include lincRNAs, intronic ncRNAs, circular and linear ncRNA. | 1 | Applied and Interdisciplinary Chemistry |
Brassica species contain glucosinolates, which are sulfur-containing secondary compounds. Glucosinolates are composed of a β-thioglucose moiety, a sulfonated oxime and a side chain. The synthesis of glucosinolates starts with the oxidation of the parent amino acid to an aldoxime, followed by the addition of a thiol group (through conjugation with glutathione) to produce thiohydroximate. The transfer of a glucose and a sulfate moiety completes the formation of the glucosinolates.
The physiological significance of glucosinolates is still ambiguous, though they are considered to function as sink compounds in situations of sulfur excess. Upon tissue disruption glucosinolates are enzymatically degraded by myrosinase and may yield a variety of biologically active products such as isothiocyanates, thiocyanates, nitriles and oxazolidine-2-thiones. The glucosinolate-myrosinase system is assumed to play a role in plant-herbivore and plant-pathogen interactions.
Furthermore, glucosinolates are responsible for the flavor properties of Brassicaceae and recently
have received attention in view of their potential anti-carcinogenic properties.
Allium species contain γ-glutamylpeptides and alliins (S-alk(en)yl cysteine sulfoxides). The content of these sulfur-containing secondary compounds strongly depends on stage of development of the plant, temperature, water availability and the level of nitrogen and sulfur nutrition. In onion bulbs their content may account for up to 80% of the organic sulfur fraction. Less is known about the content of secondary sulfur compounds in the seedling stage of the plant.
It is assumed that alliins are predominantly synthesized in the leaves, from where they are subsequently transferred to the attached bulb scale. The biosynthetic pathways of synthesis of γ-glutamylpeptides and alliins are still ambiguous. γ-Glutamylpeptides can be formed from cysteine (via γ-glutamylcysteine or glutathione) and can be metabolized into the corresponding alliins via oxidation and subsequent hydrolyzation by γ-glutamyl transpeptidases.
However, other possible routes of the synthesis of γ-glutamylpeptides and alliins may not be excluded. Alliins and γ-glutamylpeptides are known to have therapeutic utility and might have potential value as phytopharmaceutics. The alliins and their breakdown products (e.g. allicin) are the flavor precursors for the odor and taste of species. Flavor is only released when plant cells are disrupted and the enzyme alliinase from the vacuole is able to degrade the alliins, yielding a wide variety of volatile and non-volatile sulfur-containing compounds. The physiological function of γ-glutamylpeptides and alliins is rather unclear. | 1 | Applied and Interdisciplinary Chemistry |
Cornstarch is a common thickening agent used in cooking. It is also a very good example of a shear-thickening system. When a force is applied to a 1:1.25 mixture of water and cornstarch, the mixture acts as a solid and resists the force. | 1 | Applied and Interdisciplinary Chemistry |
In the phosphatidylinositol signal pathway, the extracellular signal molecule binds with the G-protein receptor (G) on the cell surface and activates phospholipase C, which is located on the plasma membrane. The lipase hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into two second messengers: inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 binds with the IP3 receptor in the membrane of the smooth endoplasmic reticulum and mitochondria to open Ca channels. DAG helps activate protein kinase C (PKC), which phosphorylates many other proteins, changing their catalytic activities, leading to cellular responses.
The effects of Ca are also remarkable: it cooperates with DAG in activating PKC and can activate the CaM kinase pathway, in which calcium-modulated protein calmodulin (CaM) binds Ca, undergoes a change in conformation, and activates CaM kinase II, which has unique ability to increase its binding affinity to CaM by autophosphorylation, making CaM unavailable for the activation of other enzymes. The kinase then phosphorylates target enzymes, regulating their activities. The two signal pathways are connected together by Ca-CaM, which is also a regulatory subunit of adenylyl cyclase and phosphodiesterase in the cAMP signal pathway. | 1 | Applied and Interdisciplinary Chemistry |
Tip-enhanced Raman spectroscopy requires a confocal microscope, and a scanning probe microscope. The optical microscope is used to align the laser focal point with the tip coated with a SERS active metal. The three typical experimental configurations are bottom illumination, side illumination, and top illumination, depending on which direction the incident laser propagates towards the sample, with respect to the substrate. In the case of STM-TERS, only side and top illumination configurations can be applied, since the substrate is required to be conductive, therefore typically being non-transparent. In this case, the incident laser is usually linearly polarized and aligned parallel to the tip, in order to generate confined surface plasmon at the tip apex. The sample is moved rather than the tip so that the laser remains focused on the tip. The sample can be moved systematically to build up a series of tip enhanced Raman spectra from which a Raman map of the surface can be built allowing for surface heterogeneity to be assessed with up to 1.7 nm resolution. Subnanometer resolution has been demonstrated in certain cases allowing for submolecular features to be resolved.
In 2019, Yan group and Liu group at University of California, Riverside developed a lens-free nanofocusing technique, which concentrates the incident light from a tapered optical fiber to the tip apex of a metallic nanowire and collects the Raman signal through the same optical fiber. Fiber-in-fiber-out NSOM-TERS has been developed. | 0 | Theoretical and Fundamental Chemistry |
The German Institute for Standardization publishes a standard for pH measurement using pH meters, DIN 19263.
Very precise measurements necessitate that the pH meter is calibrated before each measurement. More typically calibration is performed once per day of operation. Calibration is needed because the glass electrode does not give reproducible electrostatic potentials over longer periods of time.
Consistent with principles of good laboratory practice, calibration is performed with at least two standard buffer solutions that span the range of pH values to be measured. For general purposes, buffers at pH 4.00 and pH 10.00 are suitable. The pH meter has one calibration control to set the meter reading equal to the value of the first standard buffer and a second control to adjust the meter reading to the value of the second buffer. A third control allows the temperature to be set. Standard buffer sachets, available from a variety of suppliers, usually document the temperature dependence of the buffer control. More precise measurements sometimes require calibration at three different pH values. Some pH meters provide built-in temperature-coefficient correction, with temperature thermocouples in the electrode probes. The calibration process correlates the voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale. Good laboratory practice dictates that, after each measurement, the probes are rinsed with distilled water or deionized water to remove any traces of the solution being measured, blotted with a scientific wipe to absorb any remaining water, which could dilute the sample and thus alter the reading, and then immersed in a storage solution suitable for the particular probe type. | 0 | Theoretical and Fundamental Chemistry |
Initially, copper is oxidized to the cuprous ion:
(1) Cu → Cu + e
The cuprous ion reacts with the chloride ion to form the insoluble white colored salt cuprous chloride:
(2) Cu + Cl → CuCl
The cuprous chloride reacts with atmospheric moisture and oxygen to form a green cupric chloride/cupric hydroxide compound and hydrochloric acid:
(3) 4 CuCl + 4 HO + O → CuCl·3 Cu(OH) + 2 HCl
The remaining copper is oxidised by air to the cuprous ion:
(4) Cu → Cu + e
The cuprous ion reacts with the chloride ion in the hydrochloric acid to form the insoluble white colored salt cuprous chloride:
(5) Cu + Cl → CuCl
The reaction then repeats from equation (3). It is the presence of two different white and green salts that lead to the fuzzy green appearance. | 1 | Applied and Interdisciplinary Chemistry |
The Haber–Bosch process relies on catalysts to accelerate N hydrogenation. The catalysts are heterogeneous, solids that interact with gaseous reagents.
The catalyst typically consists of finely divided iron bound to an iron oxide carrier containing promoters possibly including aluminium oxide, potassium oxide, calcium oxide, potassium hydroxide, molybdenum, and magnesium oxide. | 0 | Theoretical and Fundamental Chemistry |
In thermodynamics, thermal pressure (also known as the thermal pressure coefficient) is a measure of the relative pressure change of a fluid or a solid as a response to a temperature change at constant volume. The concept is related to the Pressure-Temperature Law, also known as Amontonss law or Gay-Lussacs law.
In general pressure, () can be written as the following sum: .
is the pressure required to compress the material from its volume to volume at a constant temperature . The second term expresses the change in thermal pressure . This is the pressure change at constant volume due to the temperature difference between and . Thus, it is the pressure change along an isochore of the material.
The thermal pressure is customarily expressed in its simple form as | 0 | Theoretical and Fundamental Chemistry |
An example of a medium lived is Cs, which has a half-life of 30 years. Caesium is released in bomb fallout and from the nuclear fuel cycle. A paper has been written on the radioactivity in oysters found in the Irish Sea, these were found by gamma spectroscopy to contain Ce, Ce, Ru, Ru, Cs, Zr and Nb. In addition, a zinc activation product (Zn) was found, this is thought to be due to the corrosion of magnox fuel cladding in cooling ponds. The concentration of all these isotopes in the Irish Sea attributable to nuclear facilities such as Sellafield has significantly decreased in recent decades.
An important part of the Chernobyl release was the caesium-137, this isotope is responsible for much of the long term (at least one year after the fire) external exposure which has occurred at the site. The caesium isotopes in the fallout have had an effect on farming. [http://www.uiar.org.ua/Eng/index.htm]
A large amount of caesium was released during the Goiânia accident where a radioactive source (made for medical use) was stolen and then smashed open during an attempt to convert it into scrap metal. The accident could have been stopped at several stages; first, the last legal owners of the source failed to make arrangements for the source to be stored in a safe and secure place; and second, the scrap metal workers who took it did not recognise the markings which indicated that it was a radioactive object.
Soudek et al. reported in 2006 details of the uptake of Sr and Cs into sunflowers grown under hydroponic conditions. The caesium was found in the leaf veins, in the stem and in the apical leaves. It was found that 12% of the caesium entered the plant, and 20% of the strontium. This paper also reports details of the effect of potassium, ammonium and calcium ions on the uptake of the radioisotopes.
Caesium binds tightly to clay minerals such as illite and montmorillonite; hence it remains in the upper layers of soil where it can be accessed by plants with shallow roots (such as grass). Hence grass and mushrooms can carry a considerable amount of Cs which can be transferred to humans through the food chain. One of the best countermeasures in dairy farming against Cs is to mix up the soil by deeply ploughing the soil. This has the effect of putting the Cs out of reach of the shallow roots of the grass, hence the level of radioactivity in the grass will be lowered. Also, after a nuclear war or serious accident, the removal of top few cm of soil and its burial in a shallow trench will reduce the long term gamma dose to humans due to Cs as the gamma photons will be attenuated by their passage through the soil. The more remote the trench is from humans and the deeper the trench is the better the degree of protection which will be afforded to the human population.
In livestock farming, an important countermeasure against Cs is to feed to animals a little prussian blue. This iron potassium cyanide compound acts as an ion-exchanger. The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of prussian blue per day. The prussian blue reduces the biological half-life (not to be confused with the nuclear half-life) of the caesium). The physical or nuclear half-life of Cs is about 30 years, which is a constant and can not be changed; however, the biological half-life will change according to the nature and habits of the organism for which it is expressed. Caesium in humans normally has a biological half-life of between one and four months. An added advantage of the prussian blue is that the caesium which is stripped from the animal in the droppings is in a form which is not available to plants. Hence, it prevents the caesium from being recycled. The form of prussian blue required for the treatment of humans or animals is a special grade. Attempts to use the pigment grade used in paints have not been successful. | 0 | Theoretical and Fundamental Chemistry |
Some fjords develop euxinia if the connection to the open ocean is constricted, similar to the case of the Black Sea. This constriction prohibits relatively dense, oxygen-rich oceanic water from mixing with the bottom water of the fjord, which leads to stable stratified layers in the fjord. Low salinity melt water forms a lens of fresh, low density water on top of a more dense mass of bottom water. Ground sources of sulfur are also an important cause for euxinia in fjords. | 0 | Theoretical and Fundamental Chemistry |
The Bodenstein number is calculated according to
where
* : flow velocity
* : length of the reactor
* : axial dispersion coefficient
It can also be determined experimentally from the distribution of the residence times. Assuming an open system:
holds, where
* : dimensionless variance
* : variance of the mean residence time
* : hydrodynamic residence time | 1 | Applied and Interdisciplinary Chemistry |
Matrai is originally from Chile. Matria has a B.A. from the Universidad de Concepción (1981), an M.S. (1984) and a Ph.D. (1988) from Scripps Institution of Oceanography and the University of California San Diego. Following her Ph.D. she moved to the University of Miami. She became a senior research scientist at Bigelow Laboratory for Ocean Sciences in 1995. | 0 | Theoretical and Fundamental Chemistry |
A helpful classification scheme for multiferroics into so-called type-I and type-II multiferroics was introduced in 2009 by D. Khomskii.
Khomskii suggested the term type-I multiferroic for materials in which the ferroelectricity and magnetism occur at different temperatures and arise from different mechanisms. Usually the structural distortion which gives rise to the ferroelectricity occurs at high temperature, and the magnetic ordering, which is usually antiferromagnetic, sets in at lower temperature. The prototypical example is BiFeO (T=1100 K, T=643 K), with the ferroelectricity driven by the stereochemically active lone pair of the Bi ion and the magnetic ordering caused by the usual superexchange mechanism. YMnO (T=914 K, T=76 K) is also type-I, although its ferroelectricity is so-called "improper", meaning that it is a secondary effect arising from another (primary) structural distortion. The independent emergence of magnetism and ferroelectricity means that the domains of the two properties can exist independently of each other. Most type-I multiferroics show a linear magnetoelectric response, as well as changes in dielectric susceptibility at the magnetic phase transition.
The term type-II multiferroic is used for materials in which the magnetic ordering breaks the inversion symmetry and directly "causes" the ferroelectricity. In this case the ordering temperatures for the two phenomena are identical. The prototypical example is TbMnO, in which a non-centrosymmetric magnetic spiral accompanied by a ferroelectric polarization sets in at 28 K. Since the same transition causes both effects they are by construction strongly coupled. The ferroelectric polarizations tend to be orders of magnitude smaller than those of the type-I multiferroics however, typically of the order of 10 μC/cm. The opposite effect has also been reported, in the Mott insulating charge-transfer salt –. Here, a charge-ordering transition to a polar ferroelectric case drives a magnetic ordering, again giving an intimate coupling between the ferroelectric and, in this case antiferromagnetic, orders. | 0 | Theoretical and Fundamental Chemistry |
Carbon subsulfide is an organic, sulfur-containing chemical compound with the formula and structure . This deep red liquid is immiscible with water but soluble in organic solvents. It readily polymerizes at room temperature to form a hard black solid. | 0 | Theoretical and Fundamental Chemistry |
During application, the building is enclosed and filled with the gas for a period of time, usually at least 16–18 hours, sometimes as long as 72 hours. The building must then be ventilated, generally for at least 6 hours, before occupants can return. California regulations are such that the tent will be on for three to five days, which includes ventilation. In the US, sulfuryl fluoride must be transported in a vehicle marked with "Inhalation Hazard 2" placards. Most states require a license or certification for the individual applying the fumigant.
The concentration is continuously monitored and maintained at the specified level using electronic equipment. Possible leakages are also checked by low range electronic detectors. Reentry to the home is allowed when the concentration level is at or below 5 ppm. Sulfuryl fluoride is colorless and odorless, however, during the fumigation process, a warning agent called chloropicrin is first released into the building to ensure that no occupants remain. Tent fumigation is the most effective treatment for the extermination of known and unknown infestations of wood-destroying insects. Heat is the only other approved method for whole structure treatment for termites in California. Sulfuryl fluoride provides no protection from future infestations, although heavy re-infestation can take several years since drywood termites have slower growing colonies than ground termites. | 1 | Applied and Interdisciplinary Chemistry |
One of the best studied graphite intercalation compounds, , is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite. is a superconductor with a very low critical temperature T = 0.14 K. Heating leads to the formation of a series of decomposition products as the K atoms are eliminated:
Via the intermediates (blue in color), , , ultimately the compound results.
The stoichiometry is observed for M = K, Rb and Cs. For smaller ions M = , , , , , and , the limiting stoichiometry is . Calcium graphite is obtained by immersing highly oriented pyrolytic graphite in liquid Li–Ca alloy for 10 days at 350 °C. The crystal structure of belongs to the Rm space group. The graphite interlayer distance increases upon Ca intercalation from 3.35 to 4.524 Å, and the carbon-carbon distance increases from 1.42 to 1.444 Å.
With barium and ammonia, the cations are solvated, giving the stoichiometry ((stage 1)) or those with caesium, hydrogen and potassium ((stage 1)).
In situ adsorption on free-standing graphene and intercalation in bilayer graphene of the alkali metals K, Cs, and Li was observed by means of low-energy electron microscopy.
Different from other alkali metals, the amount of Na intercalation is very small. Quantum-mechanical calculations show that this originates from a quite general phenomenon: among the alkali and alkaline earth metals, Na and Mg generally have the weakest chemical binding to a given substrate, compared with the other elements in the same group of the periodic table. The phenomenon arises from the competition between trends in the ionization energy and the ion–substrate coupling, down the columns of the periodic table. However, considerable Na intercalation into graphite can occur in cases when the ion is wrapped in a solvent shell through the process of co-intercalation. A complex magnesium(I) species has also been intercalated into graphite. | 0 | Theoretical and Fundamental Chemistry |
Ternary fission is a comparatively rare (0.2 to 0.4% of events) type of nuclear fission in which three charged products are produced rather than two. As in other nuclear fission processes, other uncharged particles such as multiple neutrons and gamma rays are produced in ternary fission.
Ternary fission may happen during neutron-induced fission or in spontaneous fission (the type of radioactive decay). About 25% more ternary fission happens in spontaneous fission compared to the same fission system formed after thermal neutron capture, illustrating that these processes remain physically slightly different, even after the absorption of the neutron, possibly because of the extra energy present in the nuclear reaction system of thermal neutron-induced fission.
Quaternary fission, at 1 per 10 million fissions, is also known (see below). | 0 | Theoretical and Fundamental Chemistry |
A cartilage-derived angiogenesis inhibitor is an angiogenesis inhibitor produced from cartilage. Examples include the peptide troponin I and chondromodulin I.
The antiangiogenic effect may be an inhibition of basement membrane degradation.
These inhibitory agents prevent vascular invasion, which is the proliferation of tumor cells in the blood or lymph vessels. They are usually highly expressed in cartilage and within chondrocytes. Their genetic transcription increases upon the expansion of cartilaginous regions.
Recent studies on Troponin I hypothesize that this protein performs its anti-proliferation effect on endothelial cells via interactions with a bFGF receptor. Neighboring studies on other anti-angiogenic factors are evolving, however, the general mechanism of action is still unknown today. | 1 | Applied and Interdisciplinary Chemistry |
The efficiency of solar-to-hydrogen (STH) of photocatalytic water splitting, however, has remained very low. | 0 | Theoretical and Fundamental Chemistry |
Poly(amidoamine), or PAMAM, is a class of dendrimer which is made of repetitively branched subunits of amide and amine functionality. PAMAM dendrimers, sometimes referred to by the trade name Starburst, have been extensively studied since their synthesis in 1985, and represent the most well-characterized dendrimer family as well as the first to be commercialized. Like other dendrimers, PAMAMs have a sphere-like shape overall, and are typified by an internal molecular architecture consisting of tree-like branching, with each outward layer, or generation, containing exponentially more branching points. This branched architecture distinguishes PAMAMs and other dendrimers from traditional polymers, as it allows for low polydispersity and a high level of structural control during synthesis, and gives rise to a large number of surface sites relative to the total molecular volume. Moreover, PAMAM dendrimers exhibit greater biocompatibility than other dendrimer families, perhaps due to the combination of surface amines and interior amide bonds; these bonding motifs are highly reminiscent of innate biological chemistry and endow PAMAM dendrimers with properties similar to that of globular proteins. The relative ease/low cost of synthesis of PAMAM dendrimers (especially relative to similarly-sized biological molecules such as proteins and antibodies), along with their biocompatibility, structural control, and functionalizability, have made PAMAMs viable candidates for application in drug development, biochemistry, and nanotechnology. | 0 | Theoretical and Fundamental Chemistry |
A Diffusion Ellipsoid is completely represented by the Diffusion Tensor, D. FA is calculated from the eigenvalues () of the diffusion tensor. The eigenvectors give the directions in which the ellipsoid has major axes, and the corresponding eigenvalues give the magnitude of the peak in that direction.
with being the mean value of the eigenvalues.
An equivalent formula for FA is
which is further equivalent to:
where R is the "normalized" diffusion tensor:
Note that if all the eigenvalues are equal, which happens for isotropic (spherical) diffusion, as in free water, the FA is . The FA can reach a maximum value of (this rarely happens in real data), in which case D has only one nonzero eigenvalue and the ellipsoid reduces to a line in the direction of that eigenvector. This means that the diffusion is confined to that direction alone. | 1 | Applied and Interdisciplinary Chemistry |
Like other β-lactam antibiotics, renal excretion of cefalexin is delayed by probenecid. It is also not recommended to take cefalexin with dofetilide, live Cholera vaccine, warfarin, and cholestyramine. Alcohol consumption reduces the rate at which it is absorbed. Cefalexin also interacts with metformin, an antidiabetic drug, and this can lead to higher concentrations of metformin in the body. Histamine H receptor antagonists like cimetidine and ranitidine may reduce the efficacy of cefalexin by delaying its absorption and altering its antimicrobial pharmacodynamics. Zinc and zinc supplements also interact with cefalexin and may reduce the amount of cefalexin in the body. | 0 | Theoretical and Fundamental Chemistry |
MIF with Borazocine linker was developed for hydrogen storage. Cu2I2Se6 has Se6 linkers. There are many MIFs with pnictogen linkers. | 0 | Theoretical and Fundamental Chemistry |
The above derivation can be used when dealing with the Eötvös number, a dimensionless quantity that represents the ratio between the buoyancy forces and surface tension of the liquid. Despite being introduced by Loránd Eötvös in 1886, he has since become fairly dissociated with it, being replaced with Wilfrid Noel Bond such that it is now referred to as the Bond number in recent literature.
The Bond number can be written such that it includes a characteristic length- normally the radius of curvature of a liquid, and the capillary length
with parameters defined above, and the radius of curvature.
Therefore the bond number can be written as
with the capillary length.
If the bond number is set to 1, then the characteristic length is the capillary length | 1 | Applied and Interdisciplinary Chemistry |
Another pharmaceutical that contains dextroamphetamine is commonly known by the brand name Adderall. It is available as immediate release (IR) tablets and extended release (XR) capsules. Adderall contains equal amounts of four amphetamine salts:
* One-quarter racemic (d,l-)amphetamine aspartate monohydrate
* One-quarter dextroamphetamine saccharate
* One-quarter dextroamphetamine sulfate
* One-quarter racemic (d,l-)amphetamine sulfate
Adderall has a total amphetamine base equivalence of 63%. While the enantiomer ratio by dextroamphetamine salts to levoamphetamine salts is 3:1, the amphetamine base content is 75.9% dextroamphetamine, 24.1% levoamphetamine. | 0 | Theoretical and Fundamental Chemistry |
Blood plasma is the liquid component of blood, which contains dissolved proteins, nutrients, ions, and other soluble components. In whole blood, red blood cells, white blood cells, and platelets are suspended within the plasma. The goal of plasma purification and processing is to extract specific materials that are present in blood, and use them for restoration and repair. There are several components that make up blood plasma, one of which is the protein albumin. Albumin is a highly water-soluble protein with considerable structural stability. It serves as a transportation device for materials such as hormones, enzymes, fatty acids, metal ions, and medicinal products. It is also used for therapeutic purposes, being essential in restoration and maintenance of circulating blood volume in imperative situations such as severe trauma or surgery. With little room for error, extremely pure samples that are lacking impurities needs to be at hand in good amount. Human blood plasma is important for the body so the nutrients etc. can be stored. | 0 | Theoretical and Fundamental Chemistry |
Fermentation is the metabolism of organic compounds in the absence of air. It involves substrate-level phosphorylation in the absence of a respiratory electron transport chain. The equation for the reaction of glucose to form lactic acid is:
: + 2 ADP + 2 P → 2 + 2 ATP + 2
Anaerobic respiration is respiration in the absence of . Prokaryotes can utilize a variety of electron acceptors. These include nitrate, sulfate, and carbon dioxide. | 1 | Applied and Interdisciplinary Chemistry |
Hennig Brand (; or ) was a German alchemist who lived and worked in Hamburg. In 1669, Brand accidentally discovered the chemical element phosphorus while searching for the "philosopher's stone", a substance which was believed to transmute base metals into gold. | 1 | Applied and Interdisciplinary Chemistry |
Discrete misorientations or the misorientation distribution can be fully described as plots in the Euler angle, axis/angle, or Rodrigues vector space. Unit quaternions, while computationally convenient, do not lend themselves to graphical representation because of their four-dimensional nature. For any of the representations, plots are usually constructed as sections through the fundamental zone; along φ in Euler angles, at increments of rotation angle for axis/angle, and at constant ρ (parallel to <001>) for Rodrigues. Due to the irregular shape of the cubic-cubic FZ, the plots are typically given as sections through the cubic FZ with the more restrictive boundaries overlaid.<br />
<br />
Mackenzie plots are a one-dimensional representation of the MD plotting the relative frequency of the misorientation angle, irrespective of the axis. Mackenzie determined the misorientation distribution for a cubic sample with a random texture. | 0 | Theoretical and Fundamental Chemistry |
Kidney impairment decreases the rate of elimination of levetiracetam from the body. Individuals with reduced kidney function may require dose adjustments. Kidney function can be estimated from the rate of creatinine clearance.
Dose adjustment of levetiracetam is not necessary in liver impairment. | 0 | Theoretical and Fundamental Chemistry |
Evans took a postdoctoral fellowship at the University of Texas at Arlington for the 1970–1971 academic year, followed by second fellowship at the University of Notre Dame in Indiana, where he worked with the organic chemist Ernest L. Eliel studying stereochemistry. Upon the completion of the fellowship, he was invited to be a research instructor at Dartmouth College in 1972, though they did not have the laboratory equipment he required to continue his research. Evans then joined the faculty of the University of North Carolina at Chapel Hill as an assistant professor of chemistry in 1974. He was the first African-American chemistry professor at the university. After 10 years at Chapel Hill, Evans became a full professor, and in 1992 was honored with a Kenan Professor chair.
Evans was a leading researcher in the field of organophosphorus chemistry, authoring more than 85 scientific articles on organosulfur and organophosphorus chemistry. His research led to a deeper understanding of the functions of organophosphate compounds and innovations in methods to produce chemical compounds for pharmaceutical drugs. Evans was inspired by William Standish Knowles, who in 1968 developed a method of asymmetric hydrogenation, which Evans used to develop alternative asymmetric synthesis methods as a way to produce single stereoisomers. Evans started experimenting with organophosphorus chemistry in 1970, developing a process using phosphorus atoms of organophosphate compounds as agents to produce specific stereoisomers. He also devised a method of asymmetric synthesis to synthesize alpha-amino phosphonic acids by adding phosphorus to sulfimides.
At the University of North Carolina Evans assembled a research team of undergraduates, graduate students, and postdoctoral fellows from around the world. In the 1980s, a Ford Foundation Fellowship allowed him to create ties between his research team and a research group at the Paul Sabatier University in France, where he spent a full sabbatical year. Later, with the help of a Fulbright Fellowship, he built ties with groups in Mexico, Poland, Germany, Greece, and Russia.
Evans championed recruiting minority applicants to UNC-Chapel Hill, while on the national front, he served on committees of the American Chemical Society, the National Institutes of Health, the National Science Foundation, and was chair of the U.S. National Committee of the International Union of Pure and Applied Chemistry. He also served on a council that advised the National Institute of General Medical Sciences. | 0 | Theoretical and Fundamental Chemistry |
In molecular biology, a reading frame is a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) molecule into a set of consecutive, non-overlapping triplets. Where these triplets equate to amino acids or stop signals during translation, they are called codons.
A single strand of a nucleic acid molecule has a phosphoryl end, called the 5′-end, and a hydroxyl or 3′-end. These define the 5′→3′ direction. There are three reading frames that can be read in this 5′→3′ direction, each beginning from a different nucleotide in a triplet. In a double stranded nucleic acid, an additional three reading frames may be read from the other, complementary strand in the 5′→3′ direction along this strand. As the two strands of a double-stranded nucleic acid molecule are antiparallel, the 5′→3′ direction on the second strand corresponds to the 3′→5′ direction along the first strand.
In general, at the most, one reading frame in a given section of a nucleic acid, is biologically relevant (open reading frame). Some viral transcripts can be translated using multiple, overlapping reading frames. There is one known example of overlapping reading frames in mammalian mitochondrial DNA: coding portions of genes for 2 subunits of ATPase overlap. | 1 | Applied and Interdisciplinary Chemistry |
Diffusers are typically connected to a piping system which is supplied with pressurized air by a blower. This system is commonly referred to as a diffused aeration system or aeration grid.
There are two main types of diffused aeration systems, retrievable and fixed grid, that are designed to serve different purposes. In the case of a plant with a single tank, a retrievable system is desirable, in order to avoid stopping operation of the plant when maintenance is required on the aeration system. Fixed systems, on the other hand, are typically less costly, and often more efficient because it is easier to make full use of the floor. | 1 | Applied and Interdisciplinary Chemistry |
In a real detector setup, some photons can and will undergo one or potentially more Compton scattering processes (e.g. in the housing material of the radioactive source, in shielding material or material otherwise surrounding the experiment) before entering the detector material. This leads to a peak structure that can be seen in the above shown energy spectrum of (Figure 1, the first peak left of the Compton edge), the so-called backscatter peak. The detailed shape of backscatter peak structure is influenced by many factors, such as the geometry of the experiment (source geometry, relative position of source, shielding and detector) or the type of the surrounding material (giving rise to different ratios of the cross sections of Photo- and Compton-effect).
The basic principle, however, is as follows:
* Gamma-ray sources emit photons isotropically
* Some photons will undergo a Compton scattering process in e.g. the shielding material or the housing of the source with a scattering angle close to 180° and some of these photons will subsequently be detected by the detector.
* The result is a peak structure with approximately the energy of the incident photon minus the energy of the Compton edge.
The backscatter peak usually appears wide and occurs at lower than 250 keV. | 0 | Theoretical and Fundamental Chemistry |
In 1967, Akira Fujishima discovered the Honda-Fujishima effect, (the photocatalytic properties of titanium dioxide).
Titanium dioxide| and other metal oxides are still most prominent catalysts for efficiency reasons. Including Strontium titanate| and Barium titanate|, this kind of semiconducting titanates, the conduction band has mainly titanium 3d character and the valence band oxygen 2p character. The bands are separated by a wide band gap of at least 3 eV, so that these materials absorb only UV radiation.
Change of the microstructure has also been investigated to further improve the performance. In 2002, Guerra (Nanoptek Corporation) discovered that high localized strain could be induced in semiconductor films formed on micro to nano-structured templates, and that this strain shifted the bandgap of the semiconductor, in the case of titanium dioxide, into the visible blue. It was further found (Thulin and Guerra, 2008) that the strain also favorably shifted the band-edges to overlay the hydrogen evolution potential, and further still that the strain improved hole mobility, for lower charge recombination rate and high quantum efficiency. Chandekar developed a low-cost scalable manufacturing process to produce both the nano-structured template and the strained titanium dioxide coating. Other morphological investigations include nanowire arrays or porous nanocrystalline photoelectrochemical cells. | 0 | Theoretical and Fundamental Chemistry |
ELS has been used to characterize the polydispersity, nanodispersity, and stability of single-walled carbon nanotubes in an aqueous environment with surfactants. The technique can be used in combination with dynamic light scattering to measure these properties of nanotubes in many different solvents. | 0 | Theoretical and Fundamental Chemistry |
Salbutamol is typically used to treat bronchospasm (due to any cause—allergic asthma or exercise-induced), as well as chronic obstructive pulmonary disease. It is also one of the most common medicines used in rescue inhalers (short-term bronchodilators to alleviate asthma attacks).
As a β agonist, salbutamol also has use in obstetrics. Intravenous salbutamol can be used as a tocolytic to relax the uterine smooth muscle to delay premature labor. While preferred over agents such as atosiban and ritodrine, its role has largely been replaced by the calcium channel blocker nifedipine, which is more effective and better tolerated.
Salbutamol has been used to treat acute hyperkalemia, as it stimulates potassium flow into cells, thus lowering the potassium in the blood. | 0 | Theoretical and Fundamental Chemistry |
The most popular way of generating a frequency comb is with a mode-locked laser. Such lasers produce a series of optical pulses separated in time by the round-trip time of the laser cavity. The spectrum of such a pulse train approximates a series of Dirac delta functions separated by the repetition rate (the inverse of the round-trip time) of the laser.
This series of sharp spectral lines is called a frequency comb or a frequency Dirac comb.
The most common lasers used for frequency-comb generation are Ti:sapphire solid-state lasers or Er:fiber lasers with repetition rates typically between 100 MHz and 1 GHz or even going as high as 10 GHz. | 0 | Theoretical and Fundamental Chemistry |
Iodosobenzene or iodosylbenzene is an organoiodine compound with the empirical formula . This colourless solid compound is used as an oxo transfer reagent in research laboratories examining organic and coordination chemistry. | 0 | Theoretical and Fundamental Chemistry |
In turbulent combustion, a quantity called the scalar dissipation rate with dimensional units of that of an inverse time is used to define a characteristic diffusion time. Its definition is given by
where is the diffusion coefficient of the scalar. Its stoichiometric value is . | 1 | Applied and Interdisciplinary Chemistry |
* Phosphofructokinase 1 catalyzes the first committed step of glycolysis.
* LpxC catalyzes the first committed step of lipid A biosynthesis.
* 8-amino-7-oxononanoate synthase catalyzes the first committed step in plant biotin synthesis.
* MurA catalyzes the first committed step of peptidoglycan biosynthesis.
*Aspartate transcarbamoylase catalyzes the committed step in the pyrimidine biosynthetic pathway in E. coli.
*3-deoxy-D-arabinose-heptulsonate 7-phosphate synthase catalyses the first committed step of the shikimate pathway responsible for the synthesis of the aromatic amino acids Tyrosine, Tryptophan and Phenylalanine in plants, bacteria, fungi and some lower eukaryotes.
*Citrate synthase catalyzes the addition of acetyl-CoA to oxaloacetate and is the first committed step of the Citric Acid Cycle.
*Acetyl-CoA carboxylase catalyzes the irreversible carboxylation of acetyl-CoA to malonyl-CoA in the first committed step of fatty acid biosynthesis.
*Glucose-6-phosphate dehydrogenase catalyzes the conversion of G6P into 6-phosphogluconolactone to produce NADPH in the first and committed step of the pentose phosphate pathway. | 1 | Applied and Interdisciplinary Chemistry |
Extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. In order to convert a metal oxide or sulphide to a purer metal, the ore must be reduced physically, chemically, or electrolytically. Extractive metallurgists are interested in three primary streams: feed, concentrate (metal oxide/sulphide) and tailings (waste).
After mining, large pieces of the ore feed are broken through crushing or grinding in order to obtain particles small enough, where each particle is either mostly valuable or mostly waste. Concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products.
Mining may not be necessary, if the ore body and physical environment are conducive to leaching. Leaching dissolves minerals in an ore body and results in an enriched solution. The solution is collected and processed to extract valuable metals. Ore bodies often contain more than one valuable metal.
Tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal. That concentrate would then be processed to separate the valuable metals into individual constituents. | 1 | Applied and Interdisciplinary Chemistry |
Nickel allergy is any of several allergic conditions provoked by exposure to the chemical element nickel. Nickel allergy often takes the form of nickel allergic contact dermatitis (Ni-ACD), a form of allergic contact dermatitis (ACD). Ni-ACD typically causes a rash that is red and itchy and that may be bumpy or scaly. The main treatment for it is avoiding contact with nickel-releasing metals, such as inexpensive jewelry. Another form of nickel allergy is a systemic form: systemic nickel allergy syndrome (SNAS) can mimic some of the symptoms of irritable bowel syndrome (IBS) and also has a dermatologic component. | 1 | Applied and Interdisciplinary Chemistry |
The earliest use of chromatography—passing a mixture through an inert material to create separation of the solution components based on differential adsorption—is sometimes attributed to German chemist Friedlieb Ferdinand Runge, who in 1855 described the use of paper to analyze dyes. Runge dropped spots of different inorganic chemicals onto circles of filter paper already impregnated with another chemical, and reactions between the different chemicals created unique color patterns. According to historical analysis of L. S. Ettre, however, Runge's work had "nothing to do with chromatography" (and instead should be considered a precursor of chemical spot tests such as the Schiff test).
In the 1860s, Christian Friedrich Schönbein and his student Friedrich Goppelsroeder published the first attempts to study the different rates at which different substances move through filter paper. Schönbein, who thought capillary action (rather than adsorption) was responsible for the movement, called the technique capillary analysis, and Goppelsroeder spent much of his career using capillary analysis to test the movement rates of a wide variety of substances. Unlike modern paper chromatography, capillary analysis used reservoirs of the substance being analyzed, creating overlapping zones of the solution components rather than separate points or bands.
Work on capillary analysis continued, but without much technical development, well into the 20th century. The first significant advances over Goppelsroeder's methods came with the work of Raphael E. Liesegang: in 1927, he placed filter strips in closed containers with atmospheres saturated by solvents, and in 1943 he began using discrete spots of sample adsorbed to filter paper, dipped in pure solvent to achieve separation. This method, essentially identical to modern paper chromatography, was published just before the independent—and far more influential—work of Archer Martin and his collaborators that inaugurated the widespread use of paper chromatography.
In 1897, the American chemist David Talbot Day (1859–1915), then serving with the U.S. Geological Survey, observed that crude petroleum generated bands of color as it seeped upwards through finely divided clay or limestone. In 1900, he reported his findings at the First International Petroleum Congress in Paris, where they created a sensation. | 1 | Applied and Interdisciplinary Chemistry |
The major statistical software packages do not cover dilution assays although a statistician should not have difficulties to write suitable scripts or macros to that end. Several special purpose software packages for dilution assays exist. | 1 | Applied and Interdisciplinary Chemistry |
is a dense, colourless liquid, although crude samples may be yellow or even red-brown. It is one of the rare transition metal halides that is a liquid at room temperature, vanadium tetrachloride| being another example. This property reflects the fact that molecules of weakly self-associate. Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. Its melting point is similar to that of Carbon tetrachloride|.
has a "closed" electronic shell, with the same number of electrons as the noble gas argon. The tetrahedral structure for is consistent with its description as a d metal center () surrounded by four identical ligands. This configuration leads to highly symmetrical structures, hence the tetrahedral shape of the molecule. adopts similar structures to Titanium tetrabromide| and Titanium tetraiodide|; the three compounds share many similarities. and react to give mixed halides , where x = 0, 1, 2, 3, 4. Magnetic resonance measurements also indicate that halide exchange is also rapid between and .
is soluble in toluene and chlorocarbons. Certain arenes form complexes of the type . reacts exothermically with donor solvents such as THF to give hexacoordinated adducts. Bulkier ligands (L) give pentacoordinated adducts . | 0 | Theoretical and Fundamental Chemistry |
The following have been named in his honour:
* Wollaston Medal
** List of Wollaston Medal recipients
* Wollaston, a lunar impact crater
* Wollaston Lake, Saskatchewan, Canada a 2,681 square kilometre (1,035 sq mi) freshwater lake
* Wollaston Islands, Chile are named for him
* Wollaston Foreland, NE Greenland.
* Wollaston Peninsula, Canada.
* Wollastonite, a chain silicate mineral
* Wollaston wire, extremely fine platinum wire
It has been mentioned that Wollaston has not received the renown which should complement his historical standing in world of science: his contemporaries Thomas Young, Humphry Davy and John Dalton have become far better-known.
Different reasons for this have been suggested, including that Wollaston himself was not systematic or conventional in presenting his discoveries, even publishing anonymously (initially) in the case of Palladium. Also, and perhaps more importantly for his modern legacy, privately held papers of his were inaccessible, and that his notebooks went missing shortly after his death and remained so for over a century; these were finally collated in the late 1960s at Cambridge University and the first comprehensive biography was completed by Melvyn Usselman in 2015, after over 30 years' research. | 1 | Applied and Interdisciplinary Chemistry |
Homer Eugene Le Grand Jr. (September 3, 1944, Charlotte, North Carolina – January 16, 2017, Melbourne, Australia) was an American-Australian historian of science. The Geological Society of London awarded him the 1995 Sue Tyler Friedman Medal. | 1 | Applied and Interdisciplinary Chemistry |
The atoms hydrogen, oxygen, and carbon co-exist naturally in specific proportions with their stable isotopes, 2H (or D), 18O and 13C respectively, in different proportions as shown in the figure 2 below.
The amount and distribution of the different isotopes in a molecule is influenced by:
* Environmental (climatic and geographical) conditions - for natural products
* Chemical or biochemical processes such as the photosynthetic metabolism in plants
This phenomenon is known as natural isotopic fractionation (see Figure 3). The resulting isotopic fingerprint can provide information on the origin - botanical, synthetic, geographical - of the molecule or product. | 0 | Theoretical and Fundamental Chemistry |
Jurins law, or capillary rise, is the simplest analysis of capillary action—the induced motion of liquids in small channels—and states that the maximum height of a liquid in a capillary tube is inversely proportional to the tubes diameter. Capillary action is one of the most common fluid mechanical effects explored in the field of microfluidics. Jurins law is named after James Jurin, who discovered it between 1718 and 1719. His quantitative law suggests that the maximum height of liquid in a capillary tube is inversely proportional to the tubes diameter. The difference in height between the surroundings of the tube and the inside, as well as the shape of the meniscus, are caused by capillary action. The mathematical expression of this law can be derived directly from hydrostatic principles and the Young–Laplace equation. Jurin's law allows the measurement of the surface tension of a liquid and can be used to derive the capillary length. | 1 | Applied and Interdisciplinary Chemistry |
Reporter genes are used in some cloning vectors to facilitate the screening of successful clones by using features of these genes that allow successful clone to be easily identified. Such features present in cloning vectors may be the lacZα fragment for α complementation in blue-white selection, and/or marker gene or reporter genes in frame with and flanking the MCS to facilitate the production of fusion proteins. Examples of fusion partners that may be used for screening are the green fluorescent protein (GFP) and luciferase. | 1 | Applied and Interdisciplinary Chemistry |
Aromatic nitriles are often prepared in the laboratory from the aniline via diazonium compounds. This is the Sandmeyer reaction. It requires transition metal cyanides. | 0 | Theoretical and Fundamental Chemistry |
Production cost of microalgae-biofuel through implementation of raceway pond systems is dominated by the operational cost which includes labour, raw materials, and utilities. In raceway pond system, during the cultivation process, electricity takes up the largest energy fraction of total operational energy requirements. It is used to circulate the microalgae cultures. It takes up an energy fraction ranging from 22% to 79%. In contrast, capital cost dominates the cost of production of microalgae-biofuel in PBRs. This system has a high installation cost though the operational cost is relatively lower than raceway pond systems.
Microalgae-biofuel production costs a larger amount of money compared to fossil fuel production. The cost estimation of producing microalgae-biofuel is around , which is considerably more expensive than conventional gasoline. However, when compared with electrification of the vehicle fleet – a key advantage of such biofuel is the avoidance of the costly distribution of large amounts of electrical energy (as is required to convert existing vehicle fleets to battery electric technology), therein allowing for the re-use of the existing liquid-fuel transportation infrastructure. Biofuel such as ethanol is also greatly more energy dense than current battery technologies (approximately 6x as much) further promoting its economic viability. | 0 | Theoretical and Fundamental Chemistry |
In chemistry, binding selectivity is defined with respect to the binding of ligands to a substrate forming a complex. Binding selectivity describes how a ligand may bind more preferentially to one receptor than another. A selectivity coefficient is the equilibrium constant for the reaction of displacement by one ligand of another ligand in a complex with the substrate. Binding selectivity is of major importance in biochemistry and in chemical separation processes. | 0 | Theoretical and Fundamental Chemistry |
Technically a perfect crystal must be infinite, so a finite size is an imperfection. Real crystals always exhibit imperfections of their order besides their finite size, and these imperfections can have profound effects on the properties of the material. André Guinier proposed a widely employed distinction between imperfections that preserve the long-range order of the crystal that he called disorder of the first kind and those that destroy it called disorder of the second kind. An example of the first is thermal vibration; an example of the second is some density of dislocations.
The generally applicable structure factor can be used to include the effect of any imperfection. In crystallography, these effects are treated as separate from the structure factor , so separate factors for size or thermal effects are introduced into the expressions for scattered intensity, leaving the perfect crystal structure factor unchanged. Therefore, a detailed description of these factors in crystallographic structure modeling and structure determination by diffraction is not appropriate in this article. | 0 | Theoretical and Fundamental Chemistry |
Methionine synthase regenerates methionine (Met) from homocysteine (Hcy). The overall reaction transforms 5-methyltetrahydrofolate (N-MeTHF) into tetrahydrofolate (THF) while transferring a methyl group to Hcy to form Met. Methionine Syntheses can be cobalamin-dependent and cobalamin-independent: Plants have both, animals depend on the methylcobalamin-dependent form.
In methylcobalamin-dependent forms of the enzyme, the reaction proceeds by two steps in a ping-pong reaction. The enzyme is initially primed into a reactive state by the transfer of a methyl group from N-MeTHF to Co(I) in enzyme-bound cobalamin (Cob), forming methyl-cobalamin(Me-Cob) that now contains Me-Co(III) and activating the enzyme. Then, a Hcy that has coordinated to an enzyme-bound zinc to form a reactive thiolate reacts with the Me-Cob. The activated methyl group is transferred from Me-Cob to the Hcy thiolate, which regenerates Co(I) in Cob, and Met is released from the enzyme. | 0 | Theoretical and Fundamental Chemistry |
Measurement of the abundance of clumped isotopes (doubly substituted isotopologues) of gases has been used in the field of stable isotope geochemistry to trace equilibrium and kinetic processes in the environment inaccessible by analysis of singly substituted isotopologues alone.
Currently measured doubly substituted isotopologues include:
*Carbon dioxide: COO
*Methane: CHD and CHD
*Oxygen: O and OO
*Nitrogen: N
*Nitrous oxide: NNO and NNO | 0 | Theoretical and Fundamental Chemistry |
Floral scent emissions of most flowering plants vary predictably throughout the day, following a circadian rhythm. This variation is controlled by light intensity. Maximal emissions coincide with peaks of the highest activity of visiting pollinators. For instance, snapdragon flowers, mostly pollinated by bees, have the highest emissions at noon, whereas nocturnally-visited tobacco plants have the highest emissions at night.
Floral scent emissions also vary along with floral development, with the highest emissions at anthesis, i.e. when the flower is fecund (highly fertile), and reduced emissions after pollination, probably due to mechanisms linked with fecundation. In tropical orchids, floral scent emission is terminated immediately following pollination, reducing the expenditure of energy on fragrance production. In petunia flowers, ethylene is released to stop the synthesis of benzenoid floral volatiles after successful pollination.
Abiotic factors, such as temperature, atmospheric concentration, hydric stress, and soil nutrient status also impact the regulation of floral scent. For instance, increased temperatures in the environment can increase the emission of VOCs in flowers, potentially altering communication between plants and pollinators.
Finally, biotic interactions may also affect the floral scent. Plant leaves attacked by herbivores emit new VOCs in response to the attack, the so-called herbivore-induced plant volatiles (HIPVs). Similarly, damaged flowers have a modified floral scent compared to undamaged ones. Micro-organisms present in nectar may alter floral scent emissions as well. | 1 | Applied and Interdisciplinary Chemistry |
Metabolites can be divided into two groups: those produced during the growth phase of the organism, called primary metabolites and those produced during the stationary phase, called secondary metabolites. Some examples of primary metabolites are ethanol, citric acid, glutamic acid, lysine, vitamins and polysaccharides. Some examples of secondary metabolites are penicillin, cyclosporin A, gibberellin, and lovastatin. | 1 | Applied and Interdisciplinary Chemistry |
When samples show elevated levels of indicator bacteria, further analysis is often undertaken to look for specific pathogenic bacteria. Species commonly investigated in the temperate zone include Salmonella typhi and Salmonella Typhimurium.
Depending on the likely source of contamination investigation may also extend to organisms such as Cryptosporidium spp.
In tropical areas analysis of Vibrio cholerae is also routinely undertaken. | 0 | Theoretical and Fundamental Chemistry |
Near Eastern development of bronze technology spread across Central Asia by way of the Eurasian Steppes, and with it came the knowledge and technology for tin prospection and extraction. By 2000 to 1500 BC Uzbekistan, Afghanistan, and Tajikistan appear to have exploited their sources of tin, carrying the resources east and west along the Silk Road crossing Central Asia. This trade link likely followed an existing trade route of lapis lazuli, a highly prized semi-precious blue gemstone, and chlorite vessels decorated with turquoise from Central Asia that have been found as far west as Egypt and that date to the same period.
In China, early tin was extracted along the Yellow River in Erlitou and Shang times between 2500 and 1800 BC. By Han and later times, China imported its tin from what is today Yunnan province. This has remained China's main source of tin throughout history and into modern times.
It is unlikely that Southeast Asian tin from Indochina was widely traded around the world in ancient times as the area was only opened up to Indian, Muslim, and European traders around 800 AD.
Indo–Roman trade relations are well known from historical texts such as Plinys Natural History' (book VI, 26), and tin is mentioned as one of the resources being exported from Rome to South Arabia, Somaliland, and India. | 1 | Applied and Interdisciplinary Chemistry |
Chrysoine resorcinol is a synthetic azo dye which was formerly used as a food additive. In Europe, it was banned as a food additive in 1977. In the US, it was banned in 1988.
Chrysoine resorcinol can be used as a pH indicator with a color change between pH 11 and pH 12.7.
In colorimetry, it has an absorption maximum of 387 nm. | 0 | Theoretical and Fundamental Chemistry |
Stearoyl-CoA is a coenzyme involved in the metabolism of fatty acids. Stearoyl-CoA is an 18-carbon long fatty acyl-CoA chain that participates in an unsaturation reaction. The reaction is catalyzed by the enzyme stearoyl-CoA desaturase, which is located in the endoplasmic reticulum. It forms a cis-double bond between the ninth and tenth carbons within the chain to form the product oleoyl-CoA. | 1 | Applied and Interdisciplinary Chemistry |
To process bastnäsite ore, it is finely ground and subjected to froth flotation to separate the bulk of the bastnäsite from the accompanying barite, calcite, and dolomite. Marketable products include each of the major intermediates of the ore dressing process: flotation concentrate, acid-washed flotation concentrate, calcined acid-washed bastnäsite, and finally a cerium concentrate, which was the insoluble residue left after the calcined bastnäsite had been leached with hydrochloric acid.
The lanthanides that dissolve as a result of the acid treatment are subjected to solvent extraction to capture the europium and purify the other individual components of the ore. A further product includes a lanthanide mix, depleted of much of the cerium, and essentially all of samarium and heavier lanthanides. The calcination of bastnäsite drives off the carbon dioxide content, leaving an oxide-fluoride, in which the cerium content oxidizes to the less-basic quadrivalent state. However, the high temperature of the calcination gives less-reactive oxide, and the use of hydrochloric acid, which can cause reduction of quadrivalent cerium, leads to an incomplete separation of cerium and the trivalent lanthanides. | 1 | Applied and Interdisciplinary Chemistry |
The tetrahedral molecule features C-I distances of 2.12 ± 0.02 Å. The molecule is slightly crowded with short contacts between iodine atoms of 3.459 ± 0.03 Å, and possibly for this reason, it is thermally and photochemically unstable.
Carbon tetraiodide crystallizes in tetragonal crystal structure (a 6.409, c 9.558 (.10 nm)).
It has zero dipole moment due to its symmetrically substituted tetrahedral geometry. | 0 | Theoretical and Fundamental Chemistry |
Its not certain when the Ottomans started using firearms, however its argued that they had been using cannons since the Battles of Kosovo (1389) and Nukap (1396) and most certainly by the 1420s. Some argue that field guns only entered service shortly after the Battle of Varna (1444) and more certainly used in the Second Battle of Kosovo (1448). Firearms, (especially grenades) were used in the 1683 siege of Vienna The arquebus reached them around 1425. | 1 | Applied and Interdisciplinary Chemistry |
Fibulin (FY-beau-lin) (now known as Fibulin-1 FBLN1) is the prototypic member of a multigene family, currently with seven members. Fibulin-1 is a calcium-binding glycoprotein. In vertebrates, fibulin-1 is found in blood and extracellular matrices. In the extracellular matrix, fibulin-1 associates with basement membranes and elastic fibers. The association with these matrix structures is mediated by its ability to interact with numerous extracellular matrix constituents including fibronectin, proteoglycans, laminins and tropoelastin. In blood, fibulin-1 binds to fibrinogen and incorporates into clots.
Fibulins are secreted glycoproteins that become incorporated into a fibrillar extracellular matrix when expressed by cultured cells or added exogenously to cell monolayers. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. The amino-terminal domain I of fibulin consists of three anaphylatoxin-like (AT) modules, each approximately 40 residues long and containing four or six cysteines. The structure of an AT module was determined for the complement-derived anaphylatoxin C3a, and was found to be a compact alpha-helical fold that is stabilized by three disulphide bridges in the pattern Cys14, Cys25 and Cys36 (where Cys is cysteine). The bulk of the remaining portion of the fibulin molecule is a series of nine EGF-like repeats. | 1 | Applied and Interdisciplinary Chemistry |
Multiple challenges exist in assessing exposure to pesticides in the general population, and many others that are specific to occupational exposures of agricultural workers. Beyond farm workers, estimating exposure to family members and children presents additional challenges, and may occur through "take-home" exposure from pesticide residues collected on clothing or equipment belonging to parent farm workers and inadvertently brought into the home. Children may also be exposed to pesticides prenatally from mothers who are exposed to pesticides during pregnancy. Characterizing children's exposure resulting from drift of airborne and spray application of pesticides is similarly challenging, yet well documented in developing countries. Because of critical development periods of the fetus and newborn children, these non-working populations are more vulnerable to the effects of pesticides, and may be at increased risk of developing neurocognitive effects and impaired development.
While measuring biomarkers or markers of biological effects may provide more accurate estimates of exposure, collecting these data in the field is often impractical and many methods are not sensitive enough to detect low-level concentrations. Rapid cholinesterase test kits exist to collect blood samples in the field. Conducting large scale assessments of agricultural workers in remote regions of developing countries makes the implementation of these kits a challenge. The cholinesterase assay is a useful clinical tool to assess individual exposure and acute toxicity. Considerable variability in baseline enzyme activity among individuals makes it difficult to compare field measurements of cholinesterase activity to a reference dose to determine health risk associated with exposure. Another challenge researchers face in deriving a reference dose is identifying health endpoints that are relevant to exposure. More epidemiological research is needed to identify critical health endpoints, particularly among populations who are occupationally exposed. | 1 | Applied and Interdisciplinary Chemistry |
An example of sorption of ligands occurs in metallic oxides and silicate surfaces. In a mineral surface, the metal ion acts as a Lewis acid, and the ligands act as the Lewis base. For ligands that have protons, the sorption is dependent on the pH.
In cases of where ligands affect the surface coordination by performing a redox reaction, the sorption phenomenon are then referred to as adsorption. This is of particular importance because different surfaces and ligands have varying redox intensity that can catalyze various reactions. | 0 | Theoretical and Fundamental Chemistry |
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