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To show the visitors how Birminghams iron industry developed, the main museum displays a wide range of Tannehill artifacts that have survived. Visitors, through paying a visit to the museum, can learn from the graphic exhibits how iron was made by 13 different iron companies and six rolling mills and how Alabamas iron-making industry made this state the arsenal of the Confederacy. Although Alabamas iron and steel industry experienced rapid growth during the post-war decades, Alabamas iron production had already occupied a central position in the countrys iron supply before the war ended. In the last two years of the Civil war, iron produced by Alabama furnaces accounted for 70% of the Confederate iron supply. To demonstrate the significant role Alabama played during the war , the museum displays a large number of wartime ironworks, including cookware, rifles and other weapons used by US soldiers (e.g. a 52 Cal. U.S. Spencer Repeater), cast-iron water pipes, CS artillery projectiles, the original parts of the Six Mile Bloomery Forge manufactured in 1860s, as well as a part of the Steve Phillips Collection. Notably, the artillery shells manufactured from 1862 to 1865 at the Naval Gun Works are also preserved in this museum, and this exhibition is considered as the Souths largest collection of artillery shells. In addition to the wartime iron relics, the museum preserves and demonstrates substantial numbers of historical artifacts that have witnessed the development of Alabama's iron and steel industry, such as a cast iron water pipe made in Birmingham during the 1880s.
The Iron and Steel Museum of Alabama not only displays iron relics but also preserves archaeological artifacts uncovered in this region. The site houses Walter B. Jones Centre for Industrial Archaeology, a state geologist and archeologist who devoted his lifetime to investigating Alabamas mineral and fossil fuel resources (Garrison, 2001) His geological and archaeological works are well preserved by many museums and historical institutions, including the University of Alabamas Jones Museum at Moundville Archaeological Park, as well as the Iron and Steel Museum of Alabama. In addition to the preservation of the archaeological works written by Walter Jones, the museum is further famous for its conservation of more than 10,000 archaeological artifacts that were discovered from 8 major on-site archaeological investigations from 1956 to 2008. It is noteworthy that the main museum building also houses a small research library. In this library, those who are interested in investigating the iron-making history in this country (e.g. historical researchers, scholars, and students) can find many historical archives, published materials, records, as well as first-hand accounts. | 1 | Applied and Interdisciplinary Chemistry |
*Hardware architecture: At the core of HIVE there exists a solid backbone hardware made of few redundant critical components and scalable compute and storage units. The diagram at the right demonstrates the connectivity and components assignations for such HIVE cluster. Core components providing the vital functions for HIVE cloud include
**web servers facing outside through the high-end secure firewall to support web-portal functionality;
**cloud servers are the core functional units orchestrating distributed storage and computations workflows through complex queuing and prioritization schemas;
**high availability drone hardware serves as a computational unit for scientific visualization and user interface support functionalities;
**ultra-fast inter-process communication storage units organize distributed computations data interchange staging arena.
**switches and firewall hardware organize the secure high performance network environment for HIVE cloud.
**permanent storage units each are designed to store hundreds of terabytes of NGS data and reference genomes as well as storage for computational results and personal user files.
Sub-clusters of scalable high performance high density compute cores are there to serve as a powerhouse for extra-large distributed parallelized computations of NGS algorithmics. System is extremely scalable and has deployment instances ranging from a single HIVE in a box appliance to massive enterprise level systems of thousands of compute units.
*Software architecture: HIVE software infrastructure consists of layers incrementally providing more functionality.
**The Kernel backbone layer provides integration with heterogeneous hardware and operating system platforms.
**HIVE cloud backbone supports distributed storage, security and computing environment.
**Science backbone represents set of low level scientific libraries to perform variety of scientific computations, mathematical apparatus for chemical, biological, statistical and other purely scientific concepts
**CGI and Java-script layers provide web-portal and web-application compatibility layers.
**Low level libraries provide Application Programming Interface (API) for developing tools and utilities.
**Integrated apps provide major NGS tool arsenal
**Web-apps and HIVE –portal provide web-portal functionality | 1 | Applied and Interdisciplinary Chemistry |
To begin HPTLC, a stationary phase has to be determined to separate different compounds within a mixture. Around 90% of all pharmaceutical separations are performed on normal phase silica gel; however, other stationary phases such as alumina can be used for samples with dissociating compounds and cellulose for ionic compounds. The reverse-phase HPTLC method (similar methodology to reverse-phase TLC) is used for compounds with high polarity. After the selection of the stationary phase, plates are generally washed with methanol and dried in an oven to remove excess solvent.
Selection for the mobile phase is one of the most important processes of HPTLC and follows a trial and error pathway. However, the PRISMA system stands as a guideline for finding the optimal mobile phase. The mobile phase is dependent on the absorptivity of the stationary phase and the composition of the compound of interest. The compound is first tested with solutions such as diethyl ether, ethanol, dichloromethane, chloroform for normal phase HPTLC, or solutions such as methanol, acetonitrile, and tetrahydrofuran for reverse phase HPTLC. The retardation factors (Rf) of the compounds with the selected solvent are then analyzed and the solvent that gives the largest Rf is chosen to be the mobile phase for the compound. Then, the mobile solvent strength is tested against hexane (for normal HPTLC) and water (for reverse-phase HPTLC) to determine the need for adjustment.
Notable HPTLC devices such as the Linomat 5 and the Automatic TLC Sampler 4 (ATS 4) by CAMAG function very similarly by having the automated spray-on sample application technique. This automated spray-on technique is useful to overcome the uncertainty in droplet size and position when the sample is applied to the TLC plate by hand. Additionally, automation provides high resolution and narrow bands since the solvent evaporates immediately as the sample makes contact with the plate. One approach to automation has been the use of piezoelectric devices and inkjet printers for applying the sample. Alternatively, the Nanomat 4 and ATS 4 by CAMAG are manually operated where the sample is applied via spot application using a capillary pipette.
Upon chromatographic detection, HPTLC plates are usually developed in saturated twin-trough chambers with filter paper for optimal outcomes. However, flat-bottom chambers and horizontal-development chambers are also used for specific compounds. A general mechanism for the HPTLC device goes as follows. A fitted filter paper is placed in the rear trough of the chamber and the mobile phase is poured through the rear trough to ensure complete solvent absorption of the filter paper. The chamber is then tilted to ~45° so both troughs are equal in solvent volume and left alone to equilibrate for ~20 mins. Finally, the HPTLC plate is placed in the chamber to develop. Between each sample reading, the mobile phase and filter paper are changed to ensure the best outcomes.
The spot capacity (analogous to peak capacity in HPLC) can be increased by developing the plate with two different solvents, using two-dimensional chromatography. The procedure begins with development of a sample loaded plate with first solvent. After removing it, the plate is rotated 90° and developed with a second solvent. | 0 | Theoretical and Fundamental Chemistry |
The lower rim of the cyclooctane B ring containing the first 5 carbon atoms was synthesized in a semisynthesis starting from naturally occurring L-serine (scheme 1). This route started with conversion of the amino group of the serine methyl ester (1) to the diol ester 2 via diazotization (sodium nitrite/sulfuric acid). After protection of the primary alcohol group to a (t-butyldimethyl) TBS silyl ether (TBSCl / imidazole) and that of the secondary alcohol group with a (Bn) benzyl ether (benzyl imidate, triflic acid), the aldehyde 3 was reacted with the methyl ester of isobutyric acid (4) in an Aldol addition to alcohol 5 with 65% stereoselectivity. This group was protected as a PMB (p-methoxybenzyl) ether (again through an imidate) in 6 which enabled organic reduction of the ester to the aldehyde in 7 with DIBAL.
Completing the cyclooctane ring required 3 more carbon atoms that were supplied by a C2 fragment in an aldol addition and a Grignard C1 fragment (scheme 2). A Mukaiyama aldol addition (magnesium bromide / toluene) took place between aldehyde 7 and ketene silyl acetal 8 with 71% stereoselectivity to alcohol 9 which was protected as the TBS ether 10 (TBSOTf, 2,6-lutidine). The ester group was reduced with DIBAL to an alcohol and then back oxidized to aldehyde 11 by Swern oxidation. Alkylation by methyl magnesium bromide to alcohol 12 and another Swern oxidation gave ketone 13. This group was converted to the silyl enol ether 14 (LHMDS, TMSCl) enabling it to react with NBS to alkyl bromide 15. The C20 methyl group was introduced as methyl iodide in a nucleophilic substitution with a strong base (LHMDS in HMPA) to bromide 16. Then in preparation to ring-closure the TBS ether was deprotected (HCl/THF) to an alcohol which was converted to the aldehyde 17 in a Swern oxidation. The ring-closing reaction was a Reformatskii reaction with Samarium(II) iodide and acetic acid to acetate 18. The stereochemistry of this particular step was of no consequence because the acetate group is dehydrated to the alkene 19 with DBU in benzene. | 0 | Theoretical and Fundamental Chemistry |
Herbert's wife Cathleen Synge Morawetz was a prolific mathematician at NYU. His sister Sonja Morawetz Sinclair revealed in 2017 she was a WW2 codebreaker after seven decades of secrecy by Bletchley Park Signals Intelligence. He helped organize the defection of Mikhail Barishnikov from the USSR 1974. His brother, Oskar Morawetz was a Canadian composer Oskar Morawetz. His brother John Morawetz was a Canadian businessman. | 0 | Theoretical and Fundamental Chemistry |
If the forces that bind A and B together are weak, ie for all r except very small r, . The reaction rate 9 simplifies even further to
This equation is true for a very large proportion of industrially relevant reactions in solution. | 0 | Theoretical and Fundamental Chemistry |
* Temperature (T) represents the average kinetic energy of the particles in a system. It's a measure of how hot or cold a system is.
* Pressure (P) is the force exerted by the particles of a system on a unit area of the container walls.
* Volume (V) refers to the space occupied by the system.
* Composition defines the amount of each component present for systems with more than one component (e.g., mixtures). | 0 | Theoretical and Fundamental Chemistry |
The liver is the main site of transferrin synthesis but other tissues and organs, including the brain, also produce transferrin. A major source of transferrin secretion in the brain is the choroid plexus in the ventricular system. The main role of transferrin is to deliver iron from absorption centers in the duodenum and white blood cell macrophages to all tissues. Transferrin plays a key role in areas where erythropoiesis and active cell division occur. The receptor helps maintain iron homeostasis in the cells by controlling iron concentrations.
The gene coding for transferrin in humans is located in chromosome band 3q21.
Medical professionals may check serum transferrin level in iron deficiency and in iron overload disorders such as hemochromatosis. | 1 | Applied and Interdisciplinary Chemistry |
The typical composition of KREEP includes about one percent, by mass, of potassium and phosphorus oxides, 20 to 25 parts per million of rubidium, and a concentration of the element lanthanum that is 300 to 350 times the concentrations found in carbonaceous chondrites. Most of potassium, phosphorus and rare-earth elements in KREEP basalts are incorporated in the grains of the phosphate minerals apatite and merrillite. | 0 | Theoretical and Fundamental Chemistry |
This is the chemistry associated with any part of the nuclear fuel cycle, including nuclear reprocessing. The fuel cycle includes all the operations involved in producing fuel, from mining, ore processing and enrichment to fuel production (Front-end of the cycle). It also includes the in-pile behavior (use of the fuel in a reactor) before the back end of the cycle. The back end includes the management of the used nuclear fuel in either a spent fuel pool or dry storage, before it is disposed of into an underground waste store or reprocessed. | 0 | Theoretical and Fundamental Chemistry |
These binding modes include μ-η,η-, μ-η,η-, and μ-η,η-. Depending on the degree of electron-transfer from the dimetal unit, these O ligands can again be described as peroxo or superoxo. Hemocyanin is an O-carrier that utilizes a bridging O2 binding motif. It features a pair of copper centers.
Salcomine, the cobalt(II) complex of salen ligand is the first synthetic O carrier. Solvated derivatives of the solid complex bind 0.5 equivalent of O:
:2 Co(salen) + O → [Co(salen)]O
Reversible electron transfer reactions are observed in some dinuclear O complexes. | 0 | Theoretical and Fundamental Chemistry |
Historically, pyrotechnic or explosive applications for traditional thermites have been limited due to their relatively slow energy release rates. Because nanothermites are created from reactant particles with proximities approaching the atomic scale, energy release rates are far greater.
MICs or super-thermites are generally developed for military use, propellants, explosives, incendiary devices, and pyrotechnics. Research into military applications of nano-sized materials began in the early 1990s. Because of their highly increased reaction rate, nano-thermitic materials are being studied by the U.S. military with the aim of developing new types of bombs several times more powerful than conventional explosives. Nanoenergetic materials can store more energy than conventional energetic materials and can be used in innovative ways to tailor the release of this energy. Thermobaric weapons are one potential application of nanoenergetic materials. | 0 | Theoretical and Fundamental Chemistry |
Gene knockouts (also known as gene deletion or gene inactivation) are a widely used genetic engineering technique that involves the targeted removal or inactivation of a specific gene within an organism's genome. This can be done through a variety of methods, including homologous recombination, CRISPR-Cas9, and TALENs.
One of the main advantages of gene knockouts is that they allow researchers to study the function of a specific gene in vivo, and to understand the role of the gene in normal development and physiology as well as in the pathology of diseases. By studying the phenotype of the organism with the knocked out gene, researchers can gain insights into the biological processes that the gene is involved in.
There are two main types of gene knockouts: complete and conditional. A complete gene knockout permanently inactivates the gene, while a conditional gene knockout allows for the gene to be turned off and on at specific times or in specific tissues. Conditional knockouts are particularly useful for studying developmental processes and for understanding the role of a gene in specific cell types or tissues.
Gene knockouts have been widely used in many different organisms, including bacteria, yeast, fruit flies, zebrafish, and mice. In mice, gene knockouts are commonly used to study the function of specific genes in development, physiology, and cancer research.
The use of gene knockouts in mouse models has been particularly valuable in the study of human diseases. For example, gene knockouts in mice have been used to study the role of specific genes in cancer, neurological disorders, immune disorders, and metabolic disorders.
However, gene knockouts also have some limitations. For example, the loss of a single gene may not fully mimic the effects of a genetic disorder, and the knockouts may have unintended effects on other genes or pathways. Additionally, gene knockouts are not always a good model for human disease as the mouse genome is not identical to the human genome, and mouse physiology is different from human physiology.
The KO technique is essentially the opposite of a gene knock-in. Knocking out two genes simultaneously in an organism is known as a double knockout (DKO). Similarly the terms triple knockout (TKO) and quadruple knockouts (QKO) are used to describe three or four knocked out genes, respectively. However, one needs to distinguish between heterozygous and homozygous KOs. In the former, only one of two gene copies (alleles) is knocked out, in the latter both are knocked out. | 1 | Applied and Interdisciplinary Chemistry |
Alexander Lyman Holley contributed significantly to the success of Bessemer steel in the United States. His A Treatise on Ordnance and Armor is an important work on contemporary weapons manufacturing and steel-making practices. In 1862, he visited Bessemers Sheffield works, and became interested in licensing the process for use in the US. Upon returning to the US, Holley met with two iron producers from Troy, New York, John F. Winslow and John Augustus Griswold, who asked him to return to the United Kingdom and negotiate with the Bank of England on their behalf. Holley secured a license for Griswold and Winslow to use Bessemers patented processes and returned to the United States in late 1863.
The trio began setting up a mill in Troy, New York in 1865. The factory contained a number of Holleys innovations that greatly improved productivity over Bessemers factory in Sheffield, and the owners gave a successful public exhibition in 1867. The Troy factory attracted the attention of the Pennsylvania Railroad, which wanted to use the new process to manufacture steel rail. It funded Holley's second mill as part of its Pennsylvania Steel subsidiary. Between 1866 and 1877, the partners were able to license a total of 11 Bessemer steel mills.
One of the investors they attracted was Andrew Carnegie, who saw great promise in the new steel technology after a visit to Bessemer in 1872, and saw it as a useful adjunct to his existing businesses, the Keystone Bridge Company and the Union Iron Works. Holley built the new steel mill for Carnegie, and continued to improve and refine the process. The new mill, known as the Edgar Thomson Steel Works, opened in 1875, and started the growth of the United States as a major world steel producer. Using the Bessemer process, Carnegie Steel was able to reduce the costs of steel railroad rails from $100 per ton to $50 per ton between 1873 and 1875. The price of steel continued to fall until Carnegie was selling rails for $18 per ton by the 1890s. Prior to the opening of Carnegie's Thomson Works, steel output in the United States totaled around 157,000 tons per year. By 1910, American companies were producing 26 million tons of steel annually.
William Walker Scranton, manager and owner of the Lackawanna Iron & Coal Company in Scranton, Pennsylvania, had also investigated the process in Europe. He built a mill in 1876 using the Bessemer process for steel rails and quadrupled his production.
Bessemer steel was used in the United States primarily for railroad rails. During the construction of the Brooklyn Bridge, a major dispute arose over whether crucible steel should be used instead of the cheaper Bessemer steel. In 1877, Abram Hewitt wrote a letter urging against the use of Bessemer steel in the construction of the Brooklyn Bridge. Bids had been submitted for both crucible steel and Bessemer steel; John A. Roeblings Sons submitted the lowest bid for Bessemer steel, but at Hewitts direction, the contract was awarded to J. Lloyd Haigh Co. | 1 | Applied and Interdisciplinary Chemistry |
The electronic properties of ordered, crystalline solids are determined by the distribution of the electronic states with respect to energy and momentum—the electronic band structure of the solid. Theoretical models of photoemission from solids show that this distribution is, for the most part, preserved in the photoelectric effect. The phenomenological three-step model for ultraviolet and soft X-ray excitation decomposes the effect into these steps:
# Inner photoelectric effect in the bulk of the material that is a direct optical transition between an occupied and an unoccupied electronic state. This effect is subject to quantum-mechanical selection rules for dipole transitions. The hole left behind the electron can give rise to secondary electron emission, or the so-called Auger effect, which may be visible even when the primary photoelectron does not leave the material. In molecular solids phonons are excited in this step and may be visible as satellite lines in the final electron energy.
# Electron propagation to the surface in which some electrons may be scattered because of interactions with other constituents of the solid. Electrons that originate deeper in the solid are much more likely to suffer collisions and emerge with altered energy and momentum. Their mean-free path is a universal curve dependent on electron's energy.
# Electron escape through the surface barrier into free-electron-like states of the vacuum. In this step the electron loses energy in the amount of the work function of the surface, and suffers from the momentum loss in the direction perpendicular to the surface. Because the binding energy of electrons in solids is conveniently expressed with respect to the highest occupied state at the Fermi energy , and the difference to the free-space (vacuum) energy is the work function of the surface, the kinetic energy of the electrons emitted from solids is usually written as .
There are cases where the three-step model fails to explain peculiarities of the photoelectron intensity distributions. The more elaborate one-step model treats the effect as a coherent process of photoexcitation into the final state of a finite crystal for which the wave function is free-electron-like outside of the crystal, but has a decaying envelope inside. | 0 | Theoretical and Fundamental Chemistry |
A separating funnel takes the shape of a cone with a hemispherical end. It has a stopper at the top and stopcock (tap), at the bottom. Separating funnels used in laboratories are typically made from borosilicate glass and their taps are made from glass or PTFE. Typical sizes are between 30 mL and 3 L. In industrial chemistry they can be much larger and for much larger volumes centrifuges are used. The sloping sides are designed to facilitate the identification of the layers. The tap-controlled outlet is designed to drain the liquid out of the funnel. On top of the funnel there is a standard taper joint which fits with a ground glass or Teflon stopper.
To use a separating funnel, the two phases and the mixture to be separated in solution are added through the top with the stopcock at the bottom closed. The funnel is then closed and shaken gently by inverting the funnel multiple times; if the two solutions are mixed together too vigorously emulsions will form. The funnel is then inverted and the stopcock carefully opened to release excess vapor pressure. The separating funnel is set aside to allow for the complete separation of the phases. The top and the bottom stopcock are then opened and the lower phase is released by gravitation. The top must be opened while releasing the lower phase to allow pressure equalization between the inside of the funnel and the atmosphere. When the bottom layer has been removed, the stopcock is closed and the upper layer is poured out through the top into another container. | 0 | Theoretical and Fundamental Chemistry |
The first edition was edited by John H. Perry who was a PhD physical chemist and chemical engineer for E. I. du Pont de Nemours & Co. W. S. Calcott (ChE) of DuPont was his assistant editor. It was published in 1934. The second edition was published in 1941. The third edition was edited by John H. Perry and published in 1950 The fourth edition was edited by Robert H. Perry, Cecil H. Chilton, and Sidney D. Kirkpatrick and published in 1963. The fifth edition was edited by Robert H. Perry and published in 1973. The sixth edition ("50th Anniversary Edition") was published in 1984 and edited by Robert H. Perry and Donald W. Green. The 1997 seventh edition was edited by Robert H. Perry and Donald W. Green. The 2640 page 2007–2008 eighth edition was edited by Don W. Green and Robert H. Perry. and published October 2007.
The 2018–2019 ninth edition was edited by Don W. Green and Marylee W. Southard Don Green, the handbooks editor-in-chief, holds a B.S. in petroleum engineering from the University of Tulsa, and M.S. and PhD. Degrees in chemical engineering from the University of Oklahoma. He is Editor of the 6th, 7th and 8th Editions of Perrys. On the other hand, Marylee Southard, the associate editor, holds B.S., M.S. and PhD Degrees in chemical engineering from the University of Kansas. She is new to the publication of Perry's, but has done significant work in inorganic chemicals production including process engineering, design and product development. | 1 | Applied and Interdisciplinary Chemistry |
In addition to storage, COF materials are exceptional at gas separation. For instance, COFs like imine-linked COF LZU1 and azine-linked COF ACOF-1 were used as a bilayer membrane for the selective separation of the following mixtures: H/CO, H/N, and H/CH. The COFs outperformed molecular sieves due to the inherent thermal and operational stability of the structures. It has also been shown that COFs inherently act as adsorbents, adhering to the gaseous molecules to enable storage and separation. | 0 | Theoretical and Fundamental Chemistry |
Improved versions of MPS method have been proposed for enhancement of numerical stability (e.g. [https://archive.today/20130105131748/http://www3.interscience.wiley.com/journal/2910/abstract Koshizuka et al., 1998]; [https://dx.doi.org/10.1002/fld.1106 Zhang et al., 2005]; [https://dx.doi.org/10.1016/j.fluiddyn.2005.12.002 Ataie-Ashtiani and Farhadi, 2006];[https://dx.doi.org/10.1002/fld.2132 Shakibaeina and Jin, 2009]; [https://doi.org/10.1016/j.cma.2019.112771 Jandaghian and Shakibaeinia, 2020]), momentum conservation (e.g. Hamiltonian MPS by [https://dx.doi.org/10.1016/j.cma.2006.12.006 Suzuki et al., 2007]; Corrected MPS by [https://dx.doi.org/10.1142/S0578563408001788 Khayyer and Gotoh, 2008]; Enhanced MPS by [https://doi.org/10.1016/j.cma.2019.112771 Jandaghian and Shakibaeinia, 2020]), mechanical energy conservation (e.g. Hamiltonian MPS by [https://dx.doi.org/10.1016/j.cma.2006.12.006 Suzuki et al., 2007]), pressure calculation (e.g. [https://dx.doi.org/10.1016/j.coastaleng.2008.10.004 Khayyer and Gotoh, 2009], [https://dx.doi.org/10.1002/fld.2207 Kondo and Koshizuka, 2010], [https://dx.doi.org/10.1016/j.apor.2010.01.001 Khayyer and Gotoh, 2010], [https://doi.org/10.1016/j.compfluid.2019.104235 Xu and Jin, 2019]), and for simulation of multiphase and granular flows ([http://ascelibrary.org/doi/10.1061/%28ASCE%29HY.1943-7900.0001275 Nabian and Farhadi 2016]; [https://doi.org/10.1017/jfm.2021.320 Xu and Jin, 2021]; [https://doi.org/10.1007/s11440-022-01766-4 Xu and Li, 2022]). | 1 | Applied and Interdisciplinary Chemistry |
Jun 1943. Further report on the use of aged chromate baths to specification DTD 911, Bath iii (30 minute hot chromate bath). Petch M K. RAE MR7147(A). Met/RTN/22
Feb 1944. Variations in corrosion properties over magnesium alloy sheet. Jones E R W Petch M K. RAE MR6858. Met/RTN/21, also in J. Inst. Metals, Nov. I946
Feb 1944. Protection of magnesium alloy sheet to specification DTD 118 by a modified form of the I.G. acid dip (bath iv of specification.DTD 911). Petch M K. RAE MR7588. Met/RTN/23
Mar 1944. Protection of magnesium alloys against corrosion by electrolytic chromate films. Petch M K. RAE MR3726(D). Met/RTN/17
Nov 1944. The protection of magnesium alloy components against corrosion by sprayed coatings of "Thickal" Latex. Petch M K. RAE MR7290. Met/RTN/22
1949. Some Observations on the Behaviour of Platinum/Platinum-Rhodium Thermocouples at High Temperatures. M K McQuillan. Journal of Scientific Instruments, Volume 26, Number 10
1956. Titanium - Metallurgy of the Rarer Metals – 4. by McQuillan MK.; Publisher: London, Butterworths, 1956.
1956. Titanium. McQuillan, A. D.; McQuillan, M. K.; Castle, J. G.Physics Today, vol. 9, issue 10, p. 24. Publication Date: 00/1956
1956. Titanium. Alan Dennis McQuillan; Marion Katharine McQuillan. Publisher: New York : Academic Press ; London : Butterworths Scientific Publications, 1956.
1957. Titanium. Alan D MacQuillan; Marion Katharine Macquillan. Publisher: London Butterworth [1957]
1958. Titan. Alan Denis McQuillan; Marion Katharine McQuillan; Sergej Georgievič Glazunov; Leonid Pavlovič Lužnikov.Language: Russian . Publisher: Moskva : Gosudarstvennoe Naučno-Tehničeskoe Izdatel'stvo Literatury po Černoj i Cvetnoj Metallurgii, 1958.
1978. McQuillan, Marion. Graduate Engineers in Production. Cranfield Inst of Tech, 1978.
1979. Graduate myth. Production Engineer (Volume: 58 , Issue: 4 , April 1979 ) | 1 | Applied and Interdisciplinary Chemistry |
Linear PPA is produced by anionic polymerization methods using a strong nucleophile as an initiator. This technique prevents the cyclization of the polymer chain as the propagating species have only one charged terminus that cannot backbite the other terminus which, in turn, is neutral in charge. Although processing linear PPA requires highly sensitive reaction conditions and is more time demanding, this type of polymer has many advantages over its cyclic counterpart. For instance, a control over the polymer's molar mass can easily be achieved by controlling the monomer and alcohol initiator ratios. Furthermore, it has been proven to be more thermally stable than its cyclic counterpart due to the presence of functionalized endcaps that stabilizes the polymer chain from depolymerization. For these reasons, it has been studied to a far greater extent than cyclic PPA. Various linear PPA with distinct end groups have been reported and studied for a variety of applications including sensing, drug delivery, and lithography. For instance, once these end groups are cleaved as a response to the exposure of PPA to a specific stimulus, the polymer will sequentially disassemble from head to tail through an unzipping reaction to form the monomer in short times that can be as low as a few minutes. | 0 | Theoretical and Fundamental Chemistry |
The Department of Chemistry at the University of Manchester is one of the largest Departments of Chemistry in the United Kingdom, with over 600 undergraduate and more than 200 postgraduate research students.
The department has comprehensive academic coverage across the chemical sciences and in all the core sub-disciplines of chemistry, with over 120 postdoctoral researchers. | 1 | Applied and Interdisciplinary Chemistry |
After obtaining his Ph.D., Negishi decided to become an academic researcher. Although he was hoping to work at a Japanese university, he could not find a position. In 1966 he resigned from Teijin, and became a postdoctoral associate at Purdue University, working under future Nobel laureate Herbert C. Brown. From 1968 to 1972 he was an instructor at Purdue.
In 1972, he became an assistant professor at Syracuse University, where began his lifelong study of transition metal–catalyzed reactions, and was promoted to associate professor in 1979. He returned to Purdue University as a full professor in the same year.
He discovered Negishi coupling, a process which condenses organic zinc compounds and organic halides under a palladium or nickel catalyst to obtain a C-C bonded product. For this achievement, he was awarded the Nobel Prize in Chemistry in 2010. Negishi also reported that organoaluminum compounds and organic zirconium compounds can be used for cross-coupling. He did not seek a patent for this coupling technology and explained his reasoning as follows: "If we did not obtain a patent, we thought that everyone could use our results easily."
In addition, Zr(CH) obtained by reducing zirconocene dichloride is also called Negishi reagent, which can be used in oxidative cyclisation reactions. The technique he developed is estimated to be used in a quarter of all reactions in the pharmaceutical industry.
By the time Negishi retired in 2019, he had published more than 400 academic papers. He was committed to instilling rigorous practices in his lab, emphasizing the need of keeping organized and comprehensive records. Before any separations, he asked his student to evaluate crude reaction mixtures in order to minimize loss of any useful scientific information. | 0 | Theoretical and Fundamental Chemistry |
With the experiments onboard of the EXPOSE facilities, various aspects of astrobiology were investigated that could not be sufficiently approached by use of laboratory facilities on ground. The chemical set of experiments is designed to reach a better understanding of the role of interstellar, cometary and planetary chemistry in the origin of life. Comets and meteorites are interpreted as exogenous sources of prebiotic molecules on the early Earth. All data achieved from the astrobiological experiments on both EXPOSE missions will add to the understanding of the origin and evolution of life on Earth and on the possibility of its distribution in space or origin elsewhere.
Data obtained from the studies on complex organics of cometary interest will support the interpretation of in-situ data obtained from the Rosetta mission after landing on Comet 67P/Churyumov–Gerasimenko in 2014, and samples analyzed by the Curiosity and ExoMars rovers on Mars. Finally the chemical experiments will contribute to the understanding of the chemical processes on Saturn's moon Titan and possible analogies to the prebiotic chemistry on the early Earth.
The biology experiments used the full extraterrestrial spectrum of solar UV radiation and suitable cut-off filters to study both, the role of the ozone layer in protecting our biosphere and the likelihood of resistant terrestrial microorganisms (extremophiles) to survive in outer space. The latter studies will provide experimental data to the lithopanspermia hypothesis, and they will provide basic data to planetary protection issues. To get better insight into the habitability of Mars, one set of samples was exposed to simulated Martian conditions (UV-radiation climate, pressure, atmosphere), with and without a protective cover of simulated Martian soil. The biological test samples selected are hardy representatives of various branches of life. | 1 | Applied and Interdisciplinary Chemistry |
GABA receptor antagonists are drugs that inhibit the action of GABA. In general these drugs produce stimulant and convulsant effects, and are mainly used for counteracting overdoses of sedative drugs.
Examples include bicuculline, securinine and metrazol, and the benzodiazepine GABA receptor antagonist flumazenil.
Other agents which may have GABA receptor antagonism include the antibiotic ciprofloxacin, tranexamic acid, thujone, ginkgo biloba, and kudzu. | 1 | Applied and Interdisciplinary Chemistry |
A thermal oscillator is a system where conduction along thermal gradients overshoots thermal equilibrium, resulting in thermal oscillations where parts of the system oscillate between being colder and hotter than average. | 0 | Theoretical and Fundamental Chemistry |
The InPAsSb quaternary alloy has been grown by both OMVPE and LPE. When lattice-matched to InAs, it has a bandgap in the range 0.3–0.55 eV. The benefits of such a low band gap have not been studied in depth. Therefore, cells incorporating InPAsSb have not been optimized and do not yet have competitive performance. The longest spectral response from an InPAsSb cell studied was 4.3 μm with a maximum response at 3 μm. For this and other low-bandgap materials, high IQE for long wavelengths is hard to achieve due to an increase in Auger recombination. | 0 | Theoretical and Fundamental Chemistry |
An indicator diagram is a chart used to measure the thermal, or cylinder, performance of reciprocating steam and internal combustion engines and compressors. An indicator chart records the pressure in the cylinder versus the volume swept by the piston, throughout the two or four strokes of the piston which constitute the engine, or compressor, cycle. The indicator diagram is used to calculate the work done and the power produced in an engine cylinder or used in a compressor cylinder.
The indicator diagram was developed by James Watt and his employee John Southern to help understand how to improve the efficiency of steam engines. In 1796, Southern developed the simple, but critical, technique to generate the diagram by fixing a board so as to move with the piston, thereby tracing the "volume" axis, while a pencil, attached to a pressure gauge, moved at right angles to the piston, tracing "pressure".
The gauge enabled Watt to calculate the work done by the steam while ensuring that its pressure had dropped to zero by the end of the stroke, thereby ensuring that all useful energy had been extracted. The total work could be calculated from the area between the "volume" axis and the traced line. The latter fact had been realised by Davies Gilbert as early as 1792 and used by Jonathan Hornblower in litigation against Watt over patents on various designs. Daniel Bernoulli had also had the insight about how to calculate work.
Watt used the diagram to make radical improvements to steam engine performance and long kept it a trade secret. Though it was made public in a letter to the Quarterly Journal of Science in 1822, it remained somewhat obscure, John Farey, Jr. only learned of it on seeing it used, probably by Watt's men, when he visited Russia in 1826.
In 1834, Émile Clapeyron used a diagram of pressure against volume to illustrate and elucidate the Carnot cycle, elevating it to a central position in the study of thermodynamics.
Later instruments for steam engine (illus.) used paper wrapped around a cylindrical barrel with a pressure piston inside it, the rotation of the barrel coupled to the piston crosshead by a weight- or spring-tensioned wire.
In 1869 the British marine engineer Nicholas Procter Burgh wrote a full book on the indicator diagram explaining the device step by step. He had noticed that "a very large proportion of the young members of the engineering profession look at an indicator diagram as a mysterious production."
Indicators developed for steam engines were improved for internal combustion engines with their rapid changes in pressure, resulting from combustion, and higher speeds. In addition to using indicator diagrams for calculating power they are used to understand the ignition, injection timing and combustion events which occur near dead-center, when the engine piston and indicator drum are hardly moving. Much better information during this part of the cycle is obtained by offsetting the indicator motion by 90 degrees to the engine crank, giving an offset indicator diagram. The events are recorded when the velocity of the drum is near its maximum and are shown against crank-angle instead of stroke. | 0 | Theoretical and Fundamental Chemistry |
Common examples of suspensions include:
*Mud or muddy water: where soil, clay, or silt particles are suspended in water.
*Flour suspended in water.
*Kimchi suspended on vinegar.
*Chalk suspended in water.
*Sand suspended in water. | 0 | Theoretical and Fundamental Chemistry |
The following table lists properties of selected radionuclides illustrating the range of properties and uses.
Key: Z = atomic number; N = neutron number; DM = decay mode; DE = decay energy; EC = electron capture | 0 | Theoretical and Fundamental Chemistry |
Process flowsheeting is the use of computer aids to perform steady-state heat and mass balancing, sizing and costing calculations for a chemical process. It is an essential and core component of process design.
The process design effort may be split into three basic steps
* Synthesis
* Analysis and
* Optimization. | 1 | Applied and Interdisciplinary Chemistry |
An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body. | 1 | Applied and Interdisciplinary Chemistry |
In 1999 Cédric Boissière and his team developed a two-step process whereby the hydrolysis at low pH (1 – 4) is completed before the condensation reaction is initiated by the addition of sodium fluoride (NaF). The two-step procedure includes the addition of a nonionic surfactant template to ultimately produce mesoporous silica particles. The main advantage of sequencing the hydrolysis and condensation reactions is the ability to ensure complete homogeneity of the surfactant and the precursor TEOS mixture. Consequently, the diameter and shape of the product particles as well as the pore size are determined solely by the reaction kinetics and the quantity of sodium fluoride introduced; higher relative fluoride levels produces a greater number of nucleation sites and hence smaller particles. Decoupling the hydrolysis and condensation process affords a level of product control that is substantially superior to that afforded by the one-step Stöber process, with particle size controlled nearly completely by the sodium fluoride-to-TEOS ratio.
The two-step Stöber process begins with a mixture of TEOS, water, alcohol, and a nonionic surfactant, to which hydrochloric acid is added to produce a microemulsion. This solution is allowed to stand until hydrolysis is complete, much like in the one-step Stöber process but with the hydrochloric acid replacing the ammonia as catalyst. Sodium fluoride is added to the resulting homogeneous solution, initiating the condensation reaction by acting as nucleation seed. The silica particles are collected by filtration and calcined to remove the nonionic surfactant template by combustion, resulting in the mesoporous silica product.
The selection of conditions for the process allows for control of pore sizes, particle diameter, and their distributions, as in the case of the one-step approach. Porosity in the modified process is controllable through the introduction of a swelling agent, the choice of temperature, and the quantity of sodium fluoride catalyst added. A swelling agent (such as mesitylene) causes increases in volume and hence in pore size, often by solvent absorption, but is limited by the solubility of the agent in the system. Pore size varies directly with temperature, bound by the lower out of the surfactant cloud point and the boiling point of water. Sodium fluoride concentration produces direct but non-linear changes in porosity, with the effect decreasing as the added fluoride concentration tends to an upper limit. | 0 | Theoretical and Fundamental Chemistry |
During the acute phase, the liver redirects protein synthesis, causing up-regulation of certain proteins and down-regulation of others. Measuring the serum level of proteins that are up- and down-regulated during the acute phase can reveal extremely important information about the patient's nutritional state. The most important up-regulated protein is C-reactive protein, which can rapidly increase 20- to 1,000-fold during the acute phase.
Hypermetabolism also causes expedited catabolism of carbohydrates, proteins, and triglycerides in order to meet the increased metabolic demands. | 1 | Applied and Interdisciplinary Chemistry |
Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of lowering energy requirements. However, such research has thus far failed to approach the efficiency and ease of the Haber process. Many compounds react with atmospheric nitrogen to give dinitrogen complexes. The first dinitrogen complex to be reported was (). Some soluble complexes do catalyze nitrogen fixation. | 1 | Applied and Interdisciplinary Chemistry |
Color superconductivity is a phenomenon where matter carries color charge without loss, on analogy to the way conventional superconductors can carry electric charge without loss. Color superconductivity is predicted to occur in quark matter if the baryon density is sufficiently high (i.e., well above the density and energies of an atomic nucleus) and the temperature is not too high (well below 10 kelvins). Color superconducting phases are to be contrasted with the normal phase of quark matter, which is just a weakly interacting Fermi liquid of quarks.
In theoretical terms, a color superconducting phase is a state in which the quarks near the Fermi surface become correlated in Cooper pairs, which condense. In phenomenological terms, a color superconducting phase breaks some of the symmetries of the underlying theory, and has a very different spectrum of excitations and very different transport properties from the normal phase. | 0 | Theoretical and Fundamental Chemistry |
* Base analog, which can substitute for DNA bases during replication and cause transition mutations. Some examples are 5-bromouracil and 2-aminopurine. | 0 | Theoretical and Fundamental Chemistry |
The (CSJ) is a learned society and professional association founded in 1878 in order to advance research in chemistry. The mission of the CSJ is to promote chemistry for science and industry in collaboration with other domestic and global societies. | 1 | Applied and Interdisciplinary Chemistry |
SWAT (soil and water assessment tool) is a river basin scale model developed to quantify the impact of land management practices in large, complex watersheds. SWAT is a public domain software enabled model actively supported by the USDA Agricultural Research Service at the [http://blackland.tamu.edu/ Blackland Research & Extension Center] in Temple, Texas, USA. It is a hydrology model with the following components: weather, surface runoff, return flow, percolation, evapotranspiration, transmission losses, pond and reservoir storage, crop growth and irrigation, groundwater flow, reach routing, nutrient and pesticide loading, and water transfer. SWAT can be considered a watershed hydrological transport model. This model is used worldwide and is continuously under development. As of July 2012, more than 1000 peer-reviewed articles have been published that document its various applications. | 1 | Applied and Interdisciplinary Chemistry |
Hyperthermophilic archaea encode pili structurally similar to the bacterial conjugative pili. However, unlike in bacteria, where conjugation apparatus typically mediates the transfer of mobile genetic elements, such as plasmids or transposons, the conjugative machinery of hyperthermophilic archaea, called Ced (Crenarchaeal system for exchange of DNA) and Ted (Thermoproteales system for exchange of DNA), appears to be responsible for the transfer of cellular DNA between members of the same species. It has been suggested that in these archaea the conjugation machinery has been fully domesticated for promoting DNA repair through homologous recombination rather than spread of mobile genetic elements. In addition to the VirB2-like conjugative pilus, the Ced and Ted systems include components for the VirB6-like transmembrane mating pore and the VirB4-like ATPase. | 1 | Applied and Interdisciplinary Chemistry |
In practice, for suction pressure below 100 mbar absolute, more than one ejector is used, usually with condensers between the ejector stages. Condensing of motive steam greatly improves ejector set efficiency; both barometric and shell-and-tube surface condensers are used.
In operation a two-stage system consists of a primary high-vacuum (HV) ejector and a secondary low-vacuum (LV) ejector. Initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to finally pull vacuum to the required pressure.
In operation a three-stage system consists of a primary booster, a secondary high-vacuum (HV) ejector, and a tertiary low-vacuum (LV) ejector. As per the two-stage system, initially the LV ejector is operated to pull vacuum down from the starting pressure to an intermediate pressure. Once this pressure is reached, the HV ejector is then operated in conjunction with the LV ejector to pull vacuum to the lower intermediate pressure. Finally the booster is operated (in conjunction with the HV & LV ejectors) to pull vacuum to the required pressure. | 1 | Applied and Interdisciplinary Chemistry |
Grain boundaries are the preferential site for segregation of impurities, which may form a thin layer with a different composition from the bulk and a variety of atomic structures that are distinct from the abutting crystalline phases. For example, a thin layer of silica, which also contains impurity cations, is often present in silicon nitride.
Grain boundary complexions were introduced by Ming Tang, Rowland Cannon, and W. Craig Carter in 2006.
These grain boundary phases are thermodynamically stable and can be considered as quasi-two-dimensional phase, which may undergo to transition, similar to those of bulk phases. In this case structure and chemistry abrupt changes are possible at a critical value of a thermodynamic parameter like temperature or pressure. This may strongly affect the macroscopic properties of the material, for example the electrical resistance or creep rates. Grain boundaries can be analyzed using equilibrium thermodynamics but cannot be considered as phases, because they do not satisfy Gibbs'definition: they are inhomogeneous, may have a gradient of structure, composition or properties. For this reasons they are defined as complexion: an interfacial material or stata that is in thermodynamic equilibrium with its abutting phases, with a finite and stable thickness (that is typically 2–20 Å). A complexion need the abutting phase to exist and its composition and structure need to be different from the abutting phase. Contrary to bulk phases, complexions also depend on the abutting phase. For example, silica rich amorphous layer present in SiN, is about 10 Å thick, but for special boundaries this equilibrium thickness is zero. Complexion can be grouped in 6 categories, according to their thickness: monolayer, bilayer, trilayer, nanolayer (with equilibrium thickness between 1 and 2 nm) and wetting. In the first cases the thickness of the layer will be constant; if extra material is present it will segregate at multiple grain junction, while in the last case there is no equilibrium thickness and this is determined by the amount of secondary phase present in the material. One example of grain boundary complexion transition is the passage from dry boundary to biltilayer in Au-doped Si, which is produced by the increase of Au. | 1 | Applied and Interdisciplinary Chemistry |
* Endogenous Expression of Oncogenic PI3K Mutation Leads to Activated PI3K Signaling and an Invasive Phenotype Poster Presented at AACR/EORTC Molecular Targets and Cancer Therapeutics, Boston, USA, Nov. 2009
* Endogenous Expression of Oncogenic PI3K Mutation Leads to accumulation of anti-apoptotic proteins in mitochondria Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010
* The use of ‘X-MAN’ isogenic cell lines to define PI3-kinase inhibitor activity profiles Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010
* The use of ‘X-MAN’ mutant PI3CA increases the expression of individual tubulin isoforms and promoted resistance to anti-mitotic chemotherapy drugs Poster Presented at AACR 2010, Washington, D.C., USA, April. 2010 | 1 | Applied and Interdisciplinary Chemistry |
Mutations that code for alterations of the conformational shape facilitate resistance of HIV to protease inhibitors. The locations of these mutations are primarily in the active site of the HIV protease enzyme as well as outside of the active site, including those at protease cleavage sites in the Gag-Pol polyprotein precursors. The cleavage sites have highly diverse sequences, so the protease recognizes its substrates not based on sequence but rather the conserved 3D shape the substrates share when bound at the active site. This conserved shape has been named the substrate envelope. The active site mutations have been shown to directly change the interactions of the inhibitors, and mostly occur at positions where inhibitors contact protease residues beyond the substrate envelope. The non-active site mutations are considered to affect by other mechanisms, like influencing dimer stability and conformational flexibility.
Over 100 single gene point mutations have been described, of which at least 26 are specific to protease inhibitors. Of these, there are about 15 primary or major mutations that are significant enough to change drug activity.
Many mutated residues have been found in HIV-1 protease which cause drug resistance, for example Leu33 changes to Ile, Val, or Phe; Val82 to Ala, Phe, Leu, or Thr; Ile84 to Val; and Leu90 to Met. Different mutations affects different protease inhibitors. For instance, mutations at Leu90 evidently affect saquinavir and nelfinavir while indinavir activity is affected by mutations at Met46, Val82, and Ile84, and fosamprenavir is affected when Ile50 changes to Val and at Ile84. A combination of mutations can render high-level drug resistance but single mutations normally do not equate with drug resistance to protease inhibitors.
The mutations can be divided into primary mutations and secondary mutations. Primary mutations often have only a small effect on resistance. The chemical structures of most protease inhibitors are quite similar, so it is not surprising that some primary mutations lead simultaneously to resistance to multiple protease inhibitors. Cross-resistance is one of the major problems of protease inhibitor treatment. Additional mutations emerging in the protease during continuous protease inhibitor therapy are commonly referred to as secondary mutations. This can lead to high-level protease inhibitor resistance.
The Stanford HIV RT and Protease Sequence Database (also called the “HIV Drug Resistance Database”) was formed in 1998 with HIV reverse transcriptase and protease sequences from persons with well-characterized antiretroviral treatment histories, and is publicly available to query resistance mutations and genotype-treatment, genotype-phenotype, and genotype-outcome correlations
Although the substrate envelope provides the general strategy of designing inhibitors that mimic the substrate and stay within the envelope to avoid resistance conferred by most active site mutations, there is no general strategy to tackle the problem of drug resistance, especially due to those away from the active site. Researches directed towards development of new therapies to cure AIDS are focused on avoiding cross-resistance to drugs that are already on the market. | 1 | Applied and Interdisciplinary Chemistry |
In chemistry, isomorphism has meanings both at the level of crystallography and at a molecular level. In crystallography, crystals are isomorphous if they have identical symmetry and if the atomic positions can be described with a set of parameters (unit cell dimensions and fractional coordinates) whose numerical values differ only slightly.
Molecules are isomorphous if they have similar shapes. The coordination complexes tris(acetylacetonato)iron (Fe(acac)) and tris(acetylacetonato)aluminium (Al(acac)) are isomorphous. These compounds, both of D symmetry have very similar shapes, as determined by bond lengths and bond angles. Isomorphous compounds give rise to isomorphous crystals and form solid solutions. Historically, crystal shape was defined by measuring the angles between crystal faces with a goniometer. Whereas crystals of Fe(acac) are deep red and crystals of Al(acac) are colorless, a solid solution of the two, i.e. FeAl(acac) will be deep or pale pink depending on the Fe/Al ratio, x.
Double sulfates, such as Tutton's salt, with the generic formula MM(SO).6HO, where M is an alkali metal and M is a divalent ion of Mg, Mn, Fe, Co, Ni, Cu or Zn, form a series of isomorphous compounds which were important in the nineteenth century in establishing the correct atomic weights of the transition elements. Alums, such as KAl(SO).12HO, are another series of isomorphous compounds, though there are three series of alums with similar external structures, but slightly different internal structures. Many spinels are also isomorphous.
In order to form isomorphous crystals two substances must have the same chemical formulation (i.e., atoms in the same ratio), they must contain atoms which have corresponding chemical properties and the sizes of corresponding atoms should be similar. These requirements ensure that the forces within and between molecules and ions are approximately similar and result in crystals that have the same internal structure. Even though the space group is the same, the unit cell dimensions will be slightly different because of the different sizes of the atoms involved. | 0 | Theoretical and Fundamental Chemistry |
* I. Zegkinoglou, A. Zendegani, I. Sinev, S. Kunze, H. Mistry, H. S. Jeon, J. Zhao, M. Hu, E. E. Alp, S. Piontek, M. Smialkowski, U.-P. Apfel, F. Körmann, J. Neugebauer, T. Hickel, B. Roldan Cuenya: Operando phonon studies of the protonation mechanism in highly active hydrogen evolution reaction pentlandite catalysts, JACS 2017, 139, 14360,
* H. Mistry, Y. Choi, A. Bagger, F. Scholten, C. Bonifacio, I. Sinev, N. J. Divins, I. Zegkinoglou, H. Jeon, K. Kisslinger, E. A. Stach, J. C. Yang, J. Rossmeisl, B. Roldan Cuenya: Enhanced carbon dioxide electroreduction to carbon monoxide over defect rich plasma-activated silver catalysts, Angew. Chem. 2017, 56, 11394,
* H. Mistry, A. Varela, C. S. Bonifacio, I. Zegkinoglou, I. Sinev, Y.-W. Choi, K. Kisslinger, E. A. Stach, J. C. Yang, P. Strasser, B. Roldan Cuenya, Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene, Nature Commun. 2016, 7, 12123, . | 0 | Theoretical and Fundamental Chemistry |
Internal conversion is a transition from a higher to a lower electronic state in a molecule or atom. It is sometimes called "radiationless de-excitation", because no photons are emitted. It differs from intersystem crossing in that, while both are radiationless methods of de-excitation, the molecular spin state for internal conversion remains the same, whereas it changes for intersystem crossing.
The energy of the electronically excited state is given off to vibrational modes of the molecule. The excitation energy is transformed into heat. | 0 | Theoretical and Fundamental Chemistry |
Cer6 is a LTR retrotransposon that is described from sequencing data in the chromosome III of C. elegans. | 1 | Applied and Interdisciplinary Chemistry |
The findings of the Apollo missions were the first articles of evidence to suggest the existence of a magma ocean on the Moon. The rocks in the samples acquired from the missions were found to be composed of a mineral called anorthite. Anorthite consists mostly of a variety of plagioclase feldspars, which are lower in density than magma. This discovery gave rise to the hypothesis that the rocks formed through an ascension to the surface of a magma ocean during the early life stages of the Moon. Additional evidence for the existence of the Lunar Magma Ocean includes the sources of mare basalts and KREEP (K for potassium, REE for rare-earth elements, and P for phosphorus). The existence of these components within the mostly anorthositic crust of the Moon are synonymous with the solidification of the Lunar Magma Ocean. Furthermore, the abundance of the trace element europium within the Moons crust suggests that it was absorbed from the magma ocean, leaving europium deficits in the mare basalt rock sources of the Moons crust. The lunar magma ocean was initially 200-300 km thick and the magma achieved a temperature of about 2000 K. After the early stages of the Moons accretion, the magma ocean was subjected to cooling caused by convection in the planets interior. | 0 | Theoretical and Fundamental Chemistry |
Metabolic pathways can be targeted for clinically therapeutic uses. Within the mitochondrial metabolic network, for instance, there are various pathways that can be targeted by compounds to prevent cancer cell proliferation. One such pathway is oxidative phosphorylation (OXPHOS) within the electron transport chain (ETC). Various inhibitors can downregulate the electrochemical reactions that take place at Complex I, II, III, and IV, thereby preventing the formation of an electrochemical gradient and downregulating the movement of electrons through the ETC. The substrate-level phosphorylation that occurs at ATP synthase can also be directly inhibited, preventing the formation of ATP that is necessary to supply energy for cancer cell proliferation. Some of these inhibitors, such as lonidamine and atovaquone, which inhibit Complex II and Complex III, respectively, are currently undergoing clinical trials for FDA-approval. Other non-FDA-approved inhibitors have still shown experimental success in vitro. | 1 | Applied and Interdisciplinary Chemistry |
Source:
If a solid body is modeled by a constant hard-core field, then
or
where
Here
For the hard solid potential
where is the position of the potential discontinuity. So, in this case | 0 | Theoretical and Fundamental Chemistry |
TLC plates are usually commercially available, with standard particle size ranges to improve reproducibility. They are prepared by mixing the adsorbent, such as silica gel, with a small amount of inert binder like calcium sulfate (gypsum) and water. This mixture is spread as a thick slurry on an unreactive carrier sheet, usually glass, thick aluminum foil, or plastic. The resultant plate is dried and activated by heating in an oven for thirty minutes at 110 °C. The thickness of the absorbent layer is typically around 0.1–0.25 mm for analytical purposes and around 0.5–2.0 mm for preparative TLC. Other adsorbent coatings include aluminium oxide (alumina), or cellulose. | 0 | Theoretical and Fundamental Chemistry |
The TFQI can be calculated with
from quantiles of FT4 and TSH concentration (as determined based on cumulative distribution functions). Per definition the TFQI has a mean of 0 and a standard deviation of 0.37 in a reference population. This explains the reference range of –0.74 to + 0.74. | 1 | Applied and Interdisciplinary Chemistry |
The equation of motion for Stokes flow can be obtained by linearizing the steady state Navier–Stokes equations. The inertial forces are assumed to be negligible in comparison to the viscous forces, and eliminating the inertial terms of the momentum balance in the Navier–Stokes equations reduces it to the momentum balance in the Stokes equations:
where is the stress (sum of viscous and pressure stresses), and an applied body force. The full Stokes equations also include an equation for the conservation of mass, commonly written in the form:
where is the fluid density and the fluid velocity. To obtain the equations of motion for incompressible flow, it is assumed that the density, , is a constant.
Furthermore, occasionally one might consider the unsteady Stokes equations, in which the term is added to the left hand side of the momentum balance equation. | 1 | Applied and Interdisciplinary Chemistry |
Like spin-lattice relaxation, spin-spin relaxation can be studied using a molecular tumbling autocorrelation framework. The resulting signal decays exponentially as the echo time (TE), i.e., the time after excitation at which readout occurs, increases. In more complicated experiments, multiple echoes can be acquired simultaneously in order to quantitatively evaluate one or more superimposed T decay curves. The relaxation rate experienced by a spin, which is the inverse of T, is proportional to a spins tumbling energy at the frequency difference between one spin and another; in less mathematical terms, energy is transferred between two spins when they rotate at a similar frequency to their beat frequency, in the figure at right. In that the beat frequency range is very small relative to the average rotation rate , spin-spin relaxation is not heavily dependent on magnetic field strength. This directly contrasts with spin-lattice relaxation, which occurs at tumbling frequencies equal to the Larmor frequency . Some frequency shifts, such as the NMR chemical shift, occur at frequencies proportional to the Larmor frequency, and the related but distinct parameter T' can be heavily dependent on field strength due to the difficulty of correcting for inhomogeneity in stronger magnet bores.
Assuming isothermal conditions, spins tumbling faster through space will generally have a longer T. Since slower tumbling displaces the spectral energy at high tumbling frequencies to lower frequencies, the relatively low beat frequency will experience a monotonically increasing amount of energy as increases, decreasing relaxation time. The figure at the left illustrates this relationship. It is worth noting again that fast tumbling spins, such as those in pure water, have similar T and T relaxation times, while slow tumbling spins, such as those in crystal lattices, have very distinct relaxation times. | 0 | Theoretical and Fundamental Chemistry |
The PDE nomenclature signifies the PDE family with an Arabic numeral, then a capital letter denotes the gene in that family, and a second and final Arabic numeral then indicates the splice variant derived from a single gene (e.g., PDE1C3: family 1, gene C, splicing variant 3).
The superfamily of PDE enzymes is classified into 11 families, namely PDE1-PDE11, in mammals. The classification is based on:
* amino acid sequences
* substrate specificities
* regulatory properties
* pharmacological properties
* tissue distribution
Different PDEs of the same family are functionally related despite the fact that their amino acid sequences can show considerable divergence. PDEs have different substrate specificities. Some are cAMP-selective hydrolases (PDE4, 7 and 8); others are cGMP-selective (PDE5, 6, and 9). Others can hydrolyse both cAMP and cGMP (PDE1, 2, 3, 10, and 11). PDE3 is sometimes referred to as cGMP-inhibited phosphodiesterase. Although PDE2 can hydrolyze both cyclic nucleotides, binding of cGMP to the regulatory GAF-B domain will increase cAMP affinity and hydrolysis to the detriment of cGMP. This mechanism, as well as others, allows for cross-regulation of the cAMP and cGMP pathways. PDE12 cleaves 2,5-phosphodiester bond linking adenosines of the 5'-triphosphorylated oligoadenylates. PDE12 is not a member of the cyclic nucleotide phosphodiesterase superfamily that contains PDE1 through PDE11. | 1 | Applied and Interdisciplinary Chemistry |
*Glutamate is the most common neurotransmitter. Most neurons secrete with glutamate or GABA. Glutamate is excitatory, meaning that the release of glutamate by one cell usually causes adjacent cells to fire an action potential. (Note: Glutamate is chemically identical to the MSG commonly used to flavor food.)
*GABA is an example of an inhibitory neurotransmitter.
* Monoamine neurotransmitters:
**Dopamine is a monoamine neurotransmitter. It plays a key role in the functioning of the limbic system, which is involved in emotional function and control. It also is involved in cognitive processes associated with movement, arousal, executive function, body temperature regulation, and pleasure and reward, and other processes.
**Norepinephrine, also known as noradrenaline, is a monoamine neurotransmitter that is involved in arousal, pain perception, executive function, body temperature regulation, and other processes.
**Epinephrine, also known as adrenaline, is a monoamine neurotransmitter that plays in fight-or-flight response, increases blood flow to muscles, output of the heart, pupil dilation, and glucose.
**Serotonin is a monoamine neurotransmitter that plays a regulatory role in mood, sleep, appetite, body temperature regulation, and other processes.
**Histamine is a monoamine neurotransmitter that is involved in arousal, pain, body temperature regulation, and appetite.
* Trace amines act as neuromodulators in monoamine neurons via binding to TAAR1.
*Acetylcholine assists motor function and is involved in memory.
*Nitric oxide functions as a neurotransmitter, despite being a gas. It is not grouped with the other neurotransmitters because it is not released in the same way.
*Endocannabinoids act in the endocannabinoid system to control neurotransmitter release in a host of neuronal tissues, including the hippocampus, amygdala, basal ganglia, and cerebellum.
* Eicosanoids act as neuromodulators via the Arachidonic acid cascade. | 1 | Applied and Interdisciplinary Chemistry |
The most commonly known solar cell is configured as a large-area p-n junction made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. n-type doping produces mobile electrons (leaving behind positively charged donors) while p-type doping produces mobile holes (and negatively charged acceptors) In practice, p-n junctions of silicon solar cells are not made in this way, but rather by diffusing an n-type dopant into one side of a p-type wafer (or vice versa).
If a piece of p-type silicon is placed in close contact with a piece of n-type silicon, then a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction). When the electrons diffuse into the p-type side, each one annihilates a hole, making that side net negatively charged (because now the number of mobile positive holes is now less than the number of negative acceptors). Similarly, holes diffusing to the n-type side make it more positively charged. However (in the absence of an external circuit) this diffusion current of carriers does not go on indefinitely because the charge build up on either side of the junction produces an electric field that opposes further diffusion of more charges. Eventually, an equilibrium is reached where the net current is zero, leaving a region either side of the junction where electrons and holes have diffused across the junction and annihilated each other called the depletion region because it contains practically no mobile charge carriers. It is also known as the space charge region, although space charge extends a bit further in both directions than the depletion region.
Once equilibrium is established, electron-hole pairs generated in the depletion region are separated by the electric field, with the electron attracted to the positive n-type side and holes to the negative p-type side, reducing the charge (and the electric field) built up by the diffusion just described. If the device is unconnected (or the external load is very high) then diffusion current would eventually restore the equilibrium charge by bringing the electron and hole back across the junction, but if the load connected is small enough, the electrons prefer to go around the external circuit in their attempt to restore equilibrium, doing useful work on the way. | 0 | Theoretical and Fundamental Chemistry |
In chromatography, internal standards are used to determine the concentration of other analytes by calculating response factor. The selected internal standard should have a similar retention time and derivatization. It must be stable and not interfere with the sample components. This mitigates the uncertainty that can occur in preparatory steps such as sample injection.
In gas chromatography-mass spectrometry (GC-MS), deuterated compounds with similar structures to the analyte commonly act as effective internal standards. However, there are non-deuterated internal standards such as norleucine, which is popular in the analysis of amino acids because it can be separated from accompanying peaks.
Selecting an internal standard for liquid chromatography-mass spectrometry (LC-MS) depends on the employed ionization method. The internal standard needs a comparable ionization response and fragmentation pattern to the analyte. LC-MS internal standards are often isotopically analogous to the structure of the analyte, using isotopes such as deuterium (H), C, N and O. | 0 | Theoretical and Fundamental Chemistry |
Inke Siewert (born 5 May 1980) is a professor for Inorganic Chemistry at University of Göttingen. Her research focuses on activation of small molecules by transition metal complexes and molecular electrochemistry. | 0 | Theoretical and Fundamental Chemistry |
A stationary hydraulic jump is the
type most frequently seen on rivers and on engineered features such as outfalls of dams and irrigation works. They occur when a flow of liquid at high velocity discharges into a zone of the river or engineered structure which can only sustain a lower velocity. When this occurs, the water slows in a rather abrupt rise (a step or standing wave) on the liquid surface.
Comparing the characteristics before and after, one finds:
The other stationary hydraulic jump occurs when a rapid flow encounters a submerged object which throws the water upward. The mathematics behind this form is more complex and will need to take into account the shape of the object and the flow characteristics of the fluid around it. | 1 | Applied and Interdisciplinary Chemistry |
Primer walking is a technique used to clone a gene (e.g., disease gene) from its known closest markers (e.g., known gene). As a result, it is employed in cloning and sequencing efforts in plants, fungi, and mammals with minor alterations. This technique, also known as "directed sequencing," employs a series of Sanger sequencing reactions to either confirm the reference sequence of a known plasmid or PCR product based on the reference sequence (sequence confirmation service) or to discover the unknown sequence of a full plasmid or PCR product by designing primers to sequence overlapping sections (sequence discovery service). | 1 | Applied and Interdisciplinary Chemistry |
Antiporters were discovered as scientists were exploring ion transport mechanisms across biological membranes. The early studies took place in the mid-20th century and were focused on the mechanisms that transported ions such as sodium, potassium, and calcium across the plasma membrane. Researchers made the observation that these ions were moved in opposite directions and hypothesized the existence of membrane proteins that could facilitate this type of transport.
In the 1960's, biochemist Efraim Racker made a breakthrough in the discovery of antiporters. Through purification from bovine heart mitochondria, Racker and his colleagues found a mitochondrial protein that could exchange inorganic phosphate for hydroxide ions. The protein is located in the inner mitochondrial membrane and transports phosphate ions for use in oxidative phosphorylation. It became known as the phosphate-hydroxide antiporter, or mitochondrial phosphate carrier protein, and was the first example of an antiporter identified in living cells.
As time went on, researchers discovered other antiporters in different membranes and in various organisms. This includes the sodium-calcium exchanger (NCX), another crucial antiporter that regulates intracellular calcium levels through the exchange of sodium ions for calcium ions across the plasma membrane. It was discovered in the 1970s and is now a well-characterized antiporter known to be found in many different types of cells.
Advances in the fields of biochemistry and molecular biology have enabled the identification and characterization of a wide range of antiporters. Understanding the transport processes of various molecules and ions has provided insight into cellular transport mechanisms, as well as the role of antiporters in various physiological functions and in the maintenance of homeostasis | 1 | Applied and Interdisciplinary Chemistry |
Understanding the interfacial energy of materials with different types of interphase boundaries (IPBs) provides valuable insights into several aspects of their behavior, including thermodynamic stability, deformation behavior, and phase evolution. | 1 | Applied and Interdisciplinary Chemistry |
Praseodymium(III) oxalate is used as an intermediate product in the synthesis of praseodymium. It is also applied to colour some glasses and enamels. If mixed with certain other materials, the compound paints glass intense yellow. | 0 | Theoretical and Fundamental Chemistry |
FCCS measures the coincident green and red intensity fluctuations of distinct molecules that correlate if green and red labeled particles move together through a predefined confocal volume. To perform fluorescence cross-correlation spectroscopy (FCCS), samples of interest are first labeled with fluorescent probes of different colours. The FCCS setup typically includes a confocal microscope, two laser sources, and two detectors. The confocal microscope is used to focus the laser beams and collect the fluorescence signals. The signals from the detectors are then collected and recorded over time. Data analysis involves cross-correlating the signals to determine the degree of correlation between the two fluorescent probes. This information can be used to extract data on the stoichiometry and binding constants of molecular complexes, as well as the timing and location of interactions within living cells. | 0 | Theoretical and Fundamental Chemistry |
As of 2014, the classical nucleation theory explained that the nucleation rate will correspond to the driving force One method for measuring the nucleation rate is through the induction time method. This process uses the stochastic nature of nucleation and determines the rate of nucleation by analysis of the time between constant supersaturation and when crystals are first detected. Another method includes the probability distribution model, analogous to the methods used to study supercooled liquids, where the probability of finding at least one nucleus at a given time is derived.
As of 2019, the early stages of nucleation and the rates associated with nucleation were modelled through multiscale computational modeling. This included exploration into an improved kinetic rate equation model and density function studies using the phase-field crystal model. | 0 | Theoretical and Fundamental Chemistry |
Sabatier's earliest research concerned the thermochemistry of sulfur and metallic sulfates, the subject for the thesis leading to his doctorate. In Toulouse, he continued his physical and chemical investigations to sulfides, chlorides, chromates and copper compounds. He also studied the oxides of nitrogen and nitrosodisulfonic acid and its salts and carried out fundamental research on partition coefficients and absorption spectra. Sabatier greatly facilitated the industrial use of hydrogenation. In 1897, building on the recent biochemical work of the American chemist, James Boyce, he discovered that the introduction of a trace amount of nickel (as a catalyst) facilitated the addition of hydrogen to molecules of most carbon compounds. | 0 | Theoretical and Fundamental Chemistry |
Both Kohlrausch's law and the Debye–Hückel–Onsager equation break down as the concentration of the electrolyte increases above a certain value. The reason for this is that as concentration increases the average distance between cation and anion decreases, so that there is more interactions between close ions. Whether this constitutes ion association is a moot point. However, it has often been assumed that cation and anion interact to form an ion pair. So, an "ion-association" constant , can be derived for the association equilibrium between ions A and B:
: A + B AB with =
Davies describes the results of such calculations in great detail, but states that should not necessarily be thought of as a true equilibrium constant, rather, the inclusion of an "ion-association" term is useful in extending the range of good agreement between theory and experimental conductivity data. Various attempts have been made to extend Onsager's treatment to more concentrated solutions.
The existence of a so-called conductance minimum in solvents having the relative permittivity under 60 has proved to be a controversial subject as regards interpretation. Fuoss and Kraus suggested that it is caused by the formation of ion triplets, and this suggestion has received some support recently.
Other developments on this topic have been done by Theodore Shedlovsky, E. Pitts, R. M. Fuoss, Fuoss and Shedlovsky, Fuoss and Onsager. | 0 | Theoretical and Fundamental Chemistry |
Lee received her BA summa cum laude in Chemistry at Cornell University in 1990. She obtained her PhD in organic chemistry at Harvard University in 1994.
From 1995 to 1997, Lee was a NIH Postdoctoral Research Fellow at UCLA in the lab of Kendall N. Houk.
Lee also teaches classes in organic chemistry for undergraduate students and advanced organic chemistry for graduate students. | 0 | Theoretical and Fundamental Chemistry |
A caisson closure involves sealing the gap with a caisson, essentially a large concrete box. This method was first applied in the Netherlands for mending dike breaches resulting from Allied assaults on Walcheren in 1944. The following year, at Rammekens, surplus caissons (Phoenix caissons) sourced from England, originally used for constructing the Mulberry harbours post-Normandy landings by Allied troops, were repurposed for dike repairs.
In the aftermath of the 1953 storm disaster, the closure of numerous breaches with caissons was contemplated. Given the uncertainty surrounding the final sizes of the gaps and the time-consuming nature of caisson construction, a decision was made shortly after February 1, 1953, to pre-fabricate a considerable quantity of relatively small caissons. These were strategically employed across various sites, and later, within the Delta Works.
A limited supply of larger Phoenix caissons from the Mulberry harbours was also utilized for sealing a few extensive dike breaches, notably at Ouwerkerk and Schelphoek. | 1 | Applied and Interdisciplinary Chemistry |
The Regional Scale Nodes is connected into the OOI Cyberinfrastructure.
The Cyberinfrastructure component of the OOI links marine infrastructure to scientists and users. The OOI Cyberinfrastructure manages and integrates data from all the different OOI sensors. It will provide a common operating infrastructure, the Integrated Observatory Network (ION), connecting and coordinating the operations of the marine components (global, regional, and coastal scale arrays). It will also provide resource management, observatory mission command and control, product production, data management and distribution (including strong data provenance), and centrally available collaboration tools.
The Integrated Observatory Network (ION) connects and coordinates the operations of the OOI marine components with the scientific and educational pursuits of oceanographic research communities. The cyberinfrastructure is being designed and constructed by the University of California, San Diego. | 0 | Theoretical and Fundamental Chemistry |
PDE3 inhibitors:
*antagonize platelet aggregation
*block oocyte maturation
*increase contractility of the heart
*enhance vascular smooth muscle relaxation
*enhance airway smooth muscle relaxation
It has been demonstrated that PDE3A inhibition prevents oocyte maturation in vitro and in vivo. For example, when mice are made completely deficient of PDE3A, they become infertile.
Aggregation of platelets is highly regulated by cyclic nucleotides. PDE3A is a regulator of this process, and PDE3 inhibitors effectively prevent aggregation of platelets. Cilostazol is approved for treatment of intermittent claudication and is thought to involve inhibition of platelet aggregation and also inhibition of smooth muscle proliferation and vasodilation.
The most studied roles of PDE3B have been in the areas of insulin, IGF1, and leptin signaling. When PDE3B is overexpressed in β-cells in mice, it causes impaired insulin secretion and glucose intolerance. | 1 | Applied and Interdisciplinary Chemistry |
Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through chemical reaction, metabolic pathway, or a biological cell. The reactant is labeled by replacing one or more specific atoms with their isotopes. The reactant is then allowed to undergo the reaction. The position of the isotopes in the products is measured to determine the sequence the isotopic atom followed in the reaction or the cell's metabolic pathway. The nuclides used in isotopic labeling may be stable nuclides or radionuclides. In the latter case, the labeling is called radiolabeling.
In isotopic labeling, there are multiple ways to detect the presence of labeling isotopes; through their mass, vibrational mode, or radioactive decay. Mass spectrometry detects the difference in an isotopes mass, while infrared spectroscopy detects the difference in the isotopes vibrational modes. Nuclear magnetic resonance detects atoms with different gyromagnetic ratios. The radioactive decay can be detected through an ionization chamber or autoradiographs of gels.
An example of the use of isotopic labeling is the study of phenol (CHOH) in water by replacing common hydrogen (protium) with deuterium (deuterium labeling). Upon adding phenol to deuterated water (water containing DO in addition to the usual HO), the substitution of deuterium for the hydrogen is observed in phenol's hydroxyl group (resulting in CHOD), indicating that phenol readily undergoes hydrogen-exchange reactions with water. Only the hydroxyl group is affected, indicating that the other 5 hydrogen atoms do not participate in the exchange reactions. | 0 | Theoretical and Fundamental Chemistry |
Friedel's salt is a layered double hydroxide (LDH) of general formula:
or more explicitly for a positively-charged LDH mineral:
or by directly incorporating water molecules into the Ca,Al hydroxide layer:
where chloride and hydroxide anions occupy the interlayer to compensate the excess of positive charges.
In the cement chemist notation (CCN), considering that
and doubling all the stoichiometry, it could also be written in CCN as follows:
A simplified chemical composition with only Cl in the interlayer, and without OH, as:
can be also written in cement chemist notation as:
Friedels salt is formed in cements initially rich in tri-calcium aluminate (CA). Free-chloride ions directly bind with the AFm hydrates (CAH and its derivatives) to form Friedels salt. | 0 | Theoretical and Fundamental Chemistry |
Henri Pitot discovered that the velocity of a fluid was proportional to the square root of its head in the early 18th century. It takes energy to push a fluid through a pipe, and Antoine de Chézy discovered that the hydraulic head loss was proportional to the velocity squared. Consequently, the Chézy formula relates hydraulic slope S (head loss per unit length) to the fluid velocity V and hydraulic radius R:
The variable C expresses the proportionality, but the value of C is not a constant. In 1838 and 1839, Gotthilf Hagen and Jean Léonard Marie Poiseuille independently determined a head loss equation for laminar flow, the Hagen–Poiseuille equation. Around 1845, Julius Weisbach and Henry Darcy developed the Darcy–Weisbach equation.
The Darcy-Weisbach equation was difficult to use because the friction factor was difficult to estimate. In 1906, Hazen and Williams provided an empirical formula that was easy to use. The general form of the equation relates the mean velocity of water in a pipe with the geometric properties of the pipe and slope of the energy line.
where:
* V is velocity (in ft/s for US customary units, in m/s for SI units)
* k is a conversion factor for the unit system (k = 1.318 for US customary units, k = 0.849 for SI units)
* C is a roughness coefficient
* R is the hydraulic radius (in ft for US customary units, in m for SI units)
* S is the slope of the energy line (head loss per length of pipe or h/L)
The equation is similar to the Chézy formula but the exponents have been adjusted to better fit data from typical engineering situations. A result of adjusting the exponents is that the value of C appears more like a constant over a wide range of the other parameters.
The conversion factor k was chosen so that the values for C were the same as in the Chézy formula for the typical hydraulic slope of S=0.001. The value of k is 0.001.
Typical C factors used in design, which take into account some increase in roughness as pipe ages are as follows: | 1 | Applied and Interdisciplinary Chemistry |
Some unstable isotopes which occur naturally (such as , , and ) are not primordial, as they must be constantly regenerated. This occurs by cosmic radiation (in the case of cosmogenic nuclides such as and ), or (rarely) by such processes as geonuclear transmutation (neutron capture of uranium in the case of and ). Other examples of common naturally occurring but non-primordial nuclides are isotopes of radon, polonium, and radium, which are all radiogenic nuclide daughters of uranium decay and are found in uranium ores. The stable argon isotope Ar is actually more common as a radiogenic nuclide than as a primordial nuclide, forming almost 1% of the Earths atmosphere, which is regenerated by the beta decay of the extremely long-lived radioactive primordial isotope K, whose half-life is on the order of a billion years and thus has been generating argon since early in the Earths existence. (Primordial argon was dominated by the alpha process nuclide Ar, which is significantly rarer than Ar on Earth.)
A similar radiogenic series is derived from the long-lived radioactive primordial nuclide Th. These nuclides are described as geogenic, meaning that they are decay or fission products of uranium or other actinides in subsurface rocks. All such nuclides have shorter half-lives than their parent radioactive primordial nuclides. Some other geogenic nuclides do not occur in the decay chains of Th, U, or U but can still fleetingly occur naturally as products of the spontaneous fission of one of these three long-lived nuclides, such as Sn, which makes up about 10 of all natural tin. Another, Tc, has also been detected. There are five other long-lived fission products known. | 0 | Theoretical and Fundamental Chemistry |
The Kröhnke pyridine synthesis is reaction in organic synthesis between α-pyridinium methyl ketone salts and α, β-unsaturated carbonyl compounds used to generate highly functionalized pyridines. Pyridines occur widely in natural and synthetic products, so there is wide interest in routes for their synthesis. The method is named after Fritz Kröhnke. | 0 | Theoretical and Fundamental Chemistry |
The direct dipole-dipole coupling is very useful for molecular structural studies, since it depends only on known physical constants and the inverse cube of internuclear distance. Estimation of this coupling provides a direct spectroscopic route to the distance between nuclei and hence the geometrical form of the molecule, or additionally also on intermolecular distances in the solid state leading to NMR crystallography notably in amorphous materials.
For example, in water, NMR spectra of hydrogen atoms of water molecules are narrow lines because dipole coupling is averaged due to chaotic molecular motion. In solids, where water molecules are fixed in their positions and do not participate in the diffusion mobility, the corresponding NMR spectra have the form of the Pake doublet. In solids with vacant positions, dipole coupling is averaged partially due to water diffusion which proceeds according to the symmetry of the solids and the probability distribution of molecules between the vacancies.
Although internuclear magnetic dipole couplings contain a great deal of structural information, in isotropic solution, they average to zero as a result of diffusion. However, their effect on nuclear spin relaxation results in measurable nuclear Overhauser effects (NOEs).
The residual dipolar coupling (RDC) occurs if the molecules in solution exhibit a partial alignment leading to an incomplete averaging of spatially anisotropic magnetic interactions i.e. dipolar couplings. RDC measurement provides information on the global folding of the protein-long distance structural information. It also provides information about "slow" dynamics in molecules. | 0 | Theoretical and Fundamental Chemistry |
Lichens are pioneer species, among the first living things to grow on bare rock or areas denuded of life by a disaster. Lichens may have to compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing. Lichens are often the first to settle in places lacking soil, constituting the sole vegetation in some extreme environments such as those found at high mountain elevations and at high latitudes. Some survive in the tough conditions of deserts, and others on frozen soil of the Arctic regions.
A major ecophysiological advantage of lichens is that they are poikilohydric (poikilo- variable, hydric- relating to water), meaning that though they have little control over the status of their hydration, they can tolerate irregular and extended periods of severe desiccation. Like some mosses, liverworts, ferns and a few resurrection plants, upon desiccation, lichens enter a metabolic suspension or stasis (known as cryptobiosis) in which the cells of the lichen symbionts are dehydrated to a degree that halts most biochemical activity. In this cryptobiotic state, lichens can survive wider extremes of temperature, radiation and drought in the harsh environments they often inhabit.
Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants, thus they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs, and monuments. Many lichens also grow as epiphytes (epi- on the surface, phyte- plant) on plants, particularly on the trunks and branches of trees. When growing on plants, lichens are not parasites; they do not consume any part of the plant nor poison it. Lichens produce allelopathic chemicals that inhibit the growth of mosses. Some ground-dwelling lichens, such as members of the subgenus Cladina (reindeer lichens), produce allelopathic chemicals that leach into the soil and inhibit the germination of seeds, spruce and other plants. Stability (that is, longevity) of their substrate is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand. In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, vascular (higher) plant seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water.
Lichens may be eaten by some animals, such as reindeer, living in arctic regions. The larvae of a number of Lepidoptera species feed exclusively on lichens. These include common footman and marbled beauty. They are very low in protein and high in carbohydrates, making them unsuitable for some animals. The Northern flying squirrel uses it for nesting, food and winter water. | 1 | Applied and Interdisciplinary Chemistry |
Although the drugs omeprazole, lansoprazole, pantoprazole, and rabeprazole share common structure and mode of action, each differs somewhat in its clinical pharmacology.
Differing pyridine and benzimidazole substituents result in small, but potentially significant different physical and chemical properties.
Direct comparison of pantoprazole sodium with other anti-secretory drugs showed that it was significantly more effective than H-receptor antagonists and either equivalent or better than other clinically used PPIs. Another study states rabeprazole undergoes activation over a greater pH range than omeprazole, lansoprazole, and pantoprazole, and converts to the sulphenamide form more rapidly than any of these three drugs.
Most oral PPI preparations are enteric-coated, due to the rapid degradation of the drugs in the acidic conditions of the stomach. For example omeprazole is unstable in acid with a half-life of 2 min at pH 1–3, but is significantly more stable at pH 7 (half-life ca. 20 h).
The acid protective coating prevents conversion to the active principle in the lumen of the stomach, which then will react with any available sulfhydryl group in food and will not penetrate to the lumen of the secretory canaliculus
The oral bioavailability of PPIs is high; 77% for pantoprazole, 80–90% for lansoprazole and 89% for esomeprazole. All the PPIs except tenatoprazole are rapidly metabolized in the liver by CYP enzymes, mostly by CYP2C19 and CYP3A4. PPIs are sensitive to CYP enzymes and have different pharmacokinetic profiles. Studies comparing the efficacy of PPIs indicate that esomeprazole and tenatoprazole have stronger acid suppression, with a longer period of intragastric pH (pH > 4).
Studies of the effect of tenatoprazole on acid secretion in in vivo animal models, such as pylorus-ligated rats and acute gastric fistula rats, demonstrated a 2- to 4-fold more potent inhibitory activity compared with omeprazole. A more potent inhibitory activity was also shown in several models of induced gastric lesions. In Asian as well as Caucasian healthy subjects, tenatoprazole exhibited a seven-fold longer half-life than the existing H/K ATPase inhibitors. It is thus hypothesized that a longer half-life results in a more prolonged inhibition of gastric acid secretion, especially during the night.
A strong relationship has been stated between the degree and duration of gastric acid inhibition, as measured by monitoring of the 24-hour intragastric pH in pharmacodynamic studies, and the rate of healing and symptom relief reported.
A clinical study showed that nocturnal acid breakthrough duration was significantly shorter for 40 mg of tenatoprazole than for 40 mg of esomeprazole, with the conclusion that tenatoprazole was significantly more potent than esomeprazole during the night. Although, the therapeutic relevance of this pharmacological advantage deserves further study.
PPIs have been used successfully in triple-therapy regiments with clarithromycin and amoxicillin for the eradication of Helicobacter pylori with no significant difference between different PPI-based regimens. | 1 | Applied and Interdisciplinary Chemistry |
Most knowledge about cys-loop receptors comes from inferences made while studying various members of the family. Research on the structures of [http://www.proteopedia.org/wiki/index.php/Acetylcholine_binding_protein acetylcholine binding proteins] (AChBP) determined that the binding sites consist of six loops, with the first three forming the principal face and the next three forming the complementary face. The last loop on the principal face wraps over the ligand in the active receptor. This site is also abundant in aromatic residues.
Recent literature indicates that the Trp residue on loop B is crucial for both agonist and antagonist binding. The neurotransmitter is taken into the binding site where it interacts (through hydrogen and cation-π bonding) with the amino acid resides in the aromatic box, located on the principal face of the binding site. Another essential interaction occurs between the agonist and a tyrosine on loop C. Upon interaction, the loop undergoes a conformational change and rotates down to cap the molecule in the binding site. | 1 | Applied and Interdisciplinary Chemistry |
Thermosynthesis is a theoretical mechanism proposed by Anthonie Muller for biological use of the free energy in a temperature gradient to drive energetically uphill anabolic reactions. It makes use of this thermal gradient, or the dissipative structure of convection in this gradient, to drive a microscopic heat engine that performs condensation reactions. Thus negative entropy is generated. The components of the biological thermosynthesis machinery concern progenitors of today's ATP synthase, which functions according to the binding change mechanism, driven by chemiosmosis. Resembling primitive free energy generating physico-chemical processes based on temperature-dependent adsorption to inorganic materials such as clay, this simple type of energy conversion is proposed to have sustained the origin of life, including the emergence of the RNA World. For this RNA World it gives a model that describes the stepwise acquisition of the set of transfer RNAs that sustains the Genetic code. The phylogenetic tree of extant transfer RNAs is consistent with the idea.
Thermosynthesis may still occur in some terrestrial
and extraterrestrial environments. However, no organisms are known at present that use thermosynthesis as a source of energy, although it is possible that it might occur in extraterrestrial environments where no light is available, such as on the subsurface ocean that may exist on the moon Europa. Thermosynthesis also permits a simple model for the origin of photosynthesis. It has moreover been used to explain the origin of animals by symbiogenesis of benthic sessile thermosynthesizers at hydrothermal vents during the Snowball Earths of the Precambrian. Preliminary experiments have started to attempt to isolate thermosynthetic organisms. | 1 | Applied and Interdisciplinary Chemistry |
The biosynthesis of neopterin occurs in two steps from guanosine triphosphate (GTP). The first being catalyzed by GTP cyclohydrolase, which opens the ribose group. Phosphatases next catalyze the hydrolysis of the phosphate ester group. | 1 | Applied and Interdisciplinary Chemistry |
Sir Isaac Newtons 1687 Principia' includes a computation of the speed of sound in air as . This is too low by about 15%. The discrepancy is due primarily to neglecting the (then unknown) effect of rapidly-fluctuating temperature in a sound wave (in modern terms, sound wave compression and expansion of air is an adiabatic process, not an isothermal process). This error was later rectified by Laplace.
During the 17th century there were several attempts to measure the speed of sound accurately, including attempts by Marin Mersenne in 1630 (1,380 Parisian feet per second), Pierre Gassendi in 1635 (1,473 Parisian feet per second) and Robert Boyle (1,125 Parisian feet per second). In 1709, the Reverend William Derham, Rector of Upminster, published a more accurate measure of the speed of sound, at 1,072 Parisian feet per second. (The Parisian foot was 325 mm. This is longer than the standard "international foot" in common use today, which was officially defined in 1959 as 304.8 mm, making the speed of sound at 1,055 Parisian feet per second).
Derham used a telescope from the tower of the church of St. Laurence, Upminster to observe the flash of a distant shotgun being fired, and then measured the time until he heard the gunshot with a half-second pendulum. Measurements were made of gunshots from a number of local landmarks, including North Ockendon church. The distance was known by triangulation, and thus the speed that the sound had travelled was calculated. | 1 | Applied and Interdisciplinary Chemistry |
Dally (division abnormally delayed) is the name of a gene that encodes a HS-modified-protein found in the fruit fly (Drosophila melanogaster). The protein has to be processed after being codified, and in its mature form it is composed by 626 amino acids, forming a proteoglycan rich in heparin sulfate which is anchored to the cell surface via covalent linkage to glycophosphatidylinositol (GPI), so we can define it as a glypican. For its normal biosynthesis it requires sugarless (sgl), a gene that encodes an enzyme which plays a critical role in the process of modification of dally. | 1 | Applied and Interdisciplinary Chemistry |
Living organisms typically consist of large quantities of water. Many anisotropic materials of interest are biological in nature and as such require hydration during spectroscopic measurements. While some limited novel techniques to measure properties of materials inside a hydrated sample chamber have been recently reports, the primary design requirement of ATM is that the material is accessible through a window that is transparent to THz light such as quartz. Similarly, samples requiring cryo-cooling or low pressure vacuum environment are readily interrogated in ATM using THz-transparent window materials. | 0 | Theoretical and Fundamental Chemistry |
For many years, alongside scientific research, he has carried out an intense dissemination activity, also on the relationship between science and society and between science and peace, with particular reference to energy and resource issues. He is convinced that scientists have a great responsibility that derives from their knowledge and therefore it is their duty to actively contribute to solving the problems of humanity, particularly those connected to the current energy-climate crisis. Every year he holds dozens of seminars in primary or secondary schools and public conferences to illustrate to students and citizens the problems created by the use of fossil fuels: climate change, ecological unsustainability and the social unease deriving from growing inequalities. He believes that three transitions are necessary: from fossil fuels to renewable energies, from the linear economy to the circular economy and from consumerism to sobriety. On these themes he is coauthor of books much appreciated by students and teachers of secondary schools: Chimica (2000); Energia oggi e domani: Prospettive, sfide, speranze (2004); Energia per lastronave Terra (2017), whose first edition (2007) won the Galileo award for scientific dissemination; Chimica! Leggere e scrivere il libro della natura (2012), english version: Chemistry! Reading and writing the book of Nature (2014); Energia, risorse, ambiente (2014); Le macchine molecolari' (2018), finalist in the National Award for Scientific Dissemination Giancarlo Dosi. | 0 | Theoretical and Fundamental Chemistry |
Arthur Derek Campbell (27 May 1925 – 20 December 2020) was a New Zealand analytical chemist. He was a faculty member in the Department of Chemistry at the University of Otago from 1948 to 1988, becoming a professor emeritus on his retirement. | 0 | Theoretical and Fundamental Chemistry |
Various clinical studies have shown that levamlodipine has more selectivity and better efficacy than (R)-amlodipine. In pooled data, from three comparative studies conducted in 200 patients with mild to moderate hypertension, 2.5 mg of levamlodipine was found to be equivalent in its blood pressure lowering efficacy to 5 mg of amlodipine. The average reduction in systolic BP was 19±3 vs 19±4, 20±2 vs 19±3 and 20±2 vs 19±3 mm of Hg recorded in standing, supine and sitting position respectively for levamlodipine compared to racemic amlodipine. The studies also reported a significant reduction in total cholesterol and triglyceride levels with levamlodipine, which was not seen with amlodipine.
Efficacy and safety of levamlodipine (2.5 mg, once daily) has been evaluated in the patients with isolated systolic hypertension (ISH). Levamlodipine effectively reduced the systolic BP (mean reduction 22±14 mm of Hg) in all grades of ISH. After 28 days of the treatment, overall responder rate was 73%. It significantly reduced the systolic and diastolic BP within 4 weeks with a responder rate of 96.5%.
Elderly hypertensives with diabetes mellitus exhibits higher response to levamlodipine therapy than non-diabetic patients. Levamlodipine is an effective switch-over option for the elderly patients who experience oedema and other adverse events with racemic amlodipine. | 0 | Theoretical and Fundamental Chemistry |
Random column packing is the practice of packing a distillation column with randomly fitting filtration material in order to optimize surface area over which reactants can interact while minimizing the complexity of construction of such columns. Random column packing is an alternative to structured column packing. | 1 | Applied and Interdisciplinary Chemistry |
Unlike sodium hydroxide, which is soluble, the hydroxides of most transition metals are insoluble, and therefore sodium hydroxide can be used to precipitate transition metal hydroxides. The following colours are observed:
* Copper - blue
* Iron(II) - green
* Iron(III) - yellow / brown
Zinc and lead salts dissolve in excess sodium hydroxide to give a clear solution of or .
Aluminium hydroxide is used as a gelatinous flocculant to filter out particulate matter in water treatment. Aluminium hydroxide is prepared at the treatment plant from aluminium sulfate by reacting it with sodium hydroxide or bicarbonate. | 0 | Theoretical and Fundamental Chemistry |
The first step in the sequence leading to the construction of a process plant and its use in the manufacture of a product is the conception of a process. The concept is embodied in the form of a "flow sheet". Process design then proceeds on the basis of the flow sheet chosen. Physical property data are the other component needed for process design apart from a flow sheet. The result of process design is a process flow diagram, PFD. Detailed engineering for the project and vessel specifications then begin. Process flowsheeting ends at the point of generation of a suitable PFD.
General purpose flowsheeting programs became usable and reliable around 1965-1970. | 1 | Applied and Interdisciplinary Chemistry |
Biotin hydrazide is a biotinyl derivative that can be used as a probe for the determination of protein carbonylation. It readily forms Schiff bases with carbonyl groups. | 1 | Applied and Interdisciplinary Chemistry |
Laves phases are intermetallic phases that have composition AB and are named for Fritz Laves who first described them. The phases are classified on the basis of geometry alone. While the problem of packing spheres of equal size has been well-studied since Gauss, Laves phases are the result of his investigations into packing spheres of two sizes. Laves phases fall into three Strukturbericht types: cubic MgCu (C15), hexagonal MgZn (C14), and hexagonal MgNi (C36). The latter two classes are unique forms of the hexagonal arrangement, but share the same basic structure. In general, the A atoms are ordered as in diamond, hexagonal diamond, or a related structure, and the B atoms form tetrahedra around the A atoms for the AB structure.
Laves phases are of particular interest in modern metallurgy research because of their abnormal physical and chemical properties. Many hypothetical or primitive applications have been developed. However, little practical knowledge has been elucidated from Laves phase study so far.
A characteristic feature is the almost perfect electrical conductivity, but they are not plastically deformable at room temperature.
In each of the three classes of Laves phase, if the two types of atoms were perfect spheres with a size ratio of , the structure would be topologically tetrahedrally close-packed. At this size ratio, the structure has an overall packing volume density of 0.710. Compounds found in Laves phases typically have an atomic size ratio between 1.05 and 1.67. Analogues of Laves phases can be formed by the self-assembly of a colloidal dispersion of two sizes of sphere.
Laves phases are instances of the more general Frank-Kasper phases. | 1 | Applied and Interdisciplinary Chemistry |
Pradeep Mathur, born on 17 August 1955 in Teheran to Damyanti and Amrit Dayal. Mathur and his older brother, renowned physicist at TIFR, Deepak Mathur (married to Helen Mathur) were both brought up and educated in London whilst their father Amrit Dayal worked as a senior diplomatic official at the Indian High Commission in London and Accra. Mathur continued to live in England till he moved to Yale. He gained an honours degree at the University of North London in 1976 and secured a PhD from Keele University in 1981 before moving onto Yale University as a post-doctoral researcher. Mathur chose to move to India and joined Indian Institute of Technology, Mumbai in 1984 as a member of the faculty of chemistry where he held several positions before reaching the position of a professor and the head of the National Single Crystal X-ray Diffraction Facility. When the Indian Institute of Technology, Indore was established in 2009, Mathur was appointed as its founder director. At the end of his first five-year term, his contract was extended for a second term and he continues to hold the position, simultaneously serving as a professor of the department of chemistry. He has been a visiting professor at University of Cambridge, University of Freiburg and University of Karlsruhe and has been associated with a number of scientific journals, viz. Organometallics, Journal of Organometallic Chemistry and Journal of Cluster Science as a member of their editorial boards.
Mathur is married to Vinita and the couple have two daughters, Nehika and Saloni. | 0 | Theoretical and Fundamental Chemistry |
In their 1959 publication, Yukawa and Tsuno attributed observed deviations from Hammett Plot linearity in electrophilic reactions to additional resonance effects occurring through the pi bonds of substituent groups in their compounds. This implied that the inductive component of the Hammett substituent constant remains constant in such reactions, while the resonance component, , does not. From this assumption, the two scientists defined a new resonance substituent constant, , that is mathematically represented as follows:
for a reaction in which positive charge is built up at the reactive center in the transition state. In order to quantify the extent of the observed enhanced resonance effects, Yukawa and Tsuno introduced an enhanced resonance parameter, , that quantifies the "demand for resonance" at the reactive center. Thus, the resultant Yukawa–Tsuno effective substituent constant is given by:
and the Yukawa–Tsuno equation (modified Hammett equation) takes the form:
Values of have been determined and catalogued for a number of substituents for quick application of the Yukawa–Tsuno equation. | 0 | Theoretical and Fundamental Chemistry |
Another use of the term occurs in industrial refrigeration, specifically vapor-compression refrigeration. Normally, the economizer concept is applied when a particular design or feature on the refrigeration cycle, allows a reduction either in the amount of energy used from the power grid, in the size of the components (basically the gas compressor's nominal capacity) used to produce refrigeration, or both.
For example, for a walk-in freezer that is kept at , the main refrigeration components would include: an evaporator coil (a dense arrangement of pipes containing refrigerant and thin metal fins used to remove heat from inside the freezer), fans to blow air over the coil and around the box, an air-cooled condensing unit sited outdoors, and valves and piping. The condensing unit would include a compressor and a coil and fans to exchange heat with the ambient air.
An economizer display takes advantage of the fact that refrigeration systems have increasing efficiencies at increasing pressures and temperatures. The power the gas compressor needs is strongly correlated to both the ratio and the difference, between the discharge and the suction pressures (as well as to other features like the refrigerants heat capacity and the type of compressor). Low temperature systems such as freezers move less fluid in same volumes. That means the compressors pumping is less efficient on low temperature systems. This phenomenon is notorious when taking in account that the evaporation temperature for a walk-in freezer at may be around .
Systems with economizers aim to produce part of the refrigeration work on high pressures, condition in which gas compressors are normally more efficient. Depending on the application, this technology either allows smaller compression capacities to be able to supply enough pressure and flow for a system that normally would require bigger compressors, increases the capacity of a system that without economizer would produce less refrigeration, or allows the system to produce the same amount of refrigeration using less power.
The economizer concept is linked to subcooling as the condensed liquid line temperature is usually higher than that on the evaporator, making it a good place to apply the notion of increasing efficiencies. Recalling the walk-in freezer example, the normal temperature of the liquid line in that system is around or even higher (it varies depending on the condensing temperature). That condition is by far less hostile to produce refrigeration, than the evaporator at . | 0 | Theoretical and Fundamental Chemistry |
Consider we have an inertial frame of reference and a rotating frame of reference which both are sharing common origin . Assume that frame is rotating around a fixed axis with angular velocity . Now assuming fluid velocity to be and fluid velocity relative to rotating frame of reference to be :
Rothalpy of a fluid point can be defined as
where and and is the stagnation enthalpy of fluid point relative to the rotating frame of reference , which is given by
and is known as relative stagnation enthalpy.
Rothalpy can also be defined in terms of absolute stagnation enthalpy:
where is tangential component of fluid velocity . | 1 | Applied and Interdisciplinary Chemistry |
It should first be noted that the first inelastic mechanism of these polymers is the mobility of the chains and the conformational rearrangement of the groups. Then the effect on semi-crystalline and amorphous polymers must be distinguished. In both cases, anchor points must be created that act as "triggers" for the effect. In the case of amorphous polymers, these will be the knots or "tangles" of the chains, and in the case of semi-crystalline polymers, the crystals themselves will form these anchor points.
By modifying the shape of the material under minimal critical stress, the chains slide and a metastable structure is created, which increases the organization and order of the chains (lower entropy), when the deformation load is eliminated, the anchor points provide a storage mechanism for macroscopic stresses in the form of small localized stresses and decreasing entropy.
In the glassy state the rotational motions of the molecules are frozen and impeded, as the temperature increases and the glassy state is reached, these motions thaw and rotations and relaxations occur, the molecules take the form that is entropically most favorable to them, the one with the lowest energy. These movements are called relaxation process and the formation of "random strings" to eliminate stresses is called shape-memory loss.
A polymer will exhibit the shape-memory effect if it is susceptible to being stabilized in a given state of deformation, preventing the molecules from slipping and regaining their higher entropy (lower energy) form. This can be achieved almost entirely by creating crosslinking or vulcanization, these new bonds act as anchors and prevent the relaxation of the chains, the anchor points can be physical or chemical. | 0 | Theoretical and Fundamental Chemistry |
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