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In condensed matter physics and physical chemistry, the Lifshitz theory of van der Waals forces, sometimes called the macroscopic theory of van der Waals forces, is a method proposed by Evgeny Mikhailovich Lifshitz in 1954 for treating van der Waals forces between bodies which does not assume pairwise additivity of the individual intermolecular forces; that is to say, the theory takes into account the influence of neighboring molecules on the interaction between every pair of molecules located in the two bodies, rather than treating each pair independently. | 0 | Theoretical and Fundamental Chemistry |
The SECIS element is found in a wide variety of organisms from all three domains of life (including their viruses). | 1 | Applied and Interdisciplinary Chemistry |
Several commodity chemicals are produced by alkylation. Included are several fundamental benzene-based feedstocks such as ethylbenzene (precursor to styrene), cumene (precursor to phenol and acetone), linear alkylbenzene sulfonates (for detergents). | 0 | Theoretical and Fundamental Chemistry |
Pyrimidine biosynthesis creates derivatives —like orotate, thymine, cytosine, and uracil— de novo from carbamoyl phosphate and aspartate.
As is often the case with parent heterocyclic ring systems, the synthesis of pyrimidine is not that common and is usually performed by removing functional groups from derivatives. Primary syntheses in quantity involving formamide have been reported.
As a class, pyrimidines are typically synthesized by the principal synthesis involving cyclization of β-dicarbonyl compounds with N–C–N compounds. Reaction of the former with amidines to give 2-substituted pyrimidines, with urea to give 2-pyrimidinones, and guanidines to give 2-aminopyrimidines are typical.
Pyrimidines can be prepared via the Biginelli reaction and other multicomponent reactions. Many other methods rely on condensation of carbonyls with diamines for instance the synthesis of 2-thio-6-methyluracil from thiourea and ethyl acetoacetate or the synthesis of 4-methylpyrimidine with 4,4-dimethoxy-2-butanone and formamide.
A novel method is by reaction of N-vinyl and N-aryl amides with carbonitriles under electrophilic activation of the amide with 2-chloro-pyridine and trifluoromethanesulfonic anhydride: | 1 | Applied and Interdisciplinary Chemistry |
Simple N-heterocyclic carbene (NHC)-based ligands have proven impractical for asymmetrical hydrogenation.
Some C,N ligands combine an NHC with a chiral oxazoline to give a chelating ligand. NHC-based ligands of the first type have been generated as large libraries from the reaction of smaller libraries of individual NHCs and oxazolines. NHC-based catalysts featuring a bulky seven-membered metallocycle on iridium have been applied to the catalytic hydrogenation of unfunctionalized olefins and vinyl ether alcohols with conversions and ee's in the high 80s or 90s. The same system has been applied to the synthesis of a number of aldol, vicinal dimethyl and deoxypolyketide motifs, and to the deoxypolyketides themselves.
C-symmetric NHCs have shown themselves to be highly useful ligands for the asymmetric hydrogenation. | 0 | Theoretical and Fundamental Chemistry |
A 2009 study has shown additional benefits of HACs, namely their ability to stably contain extremely large genomic fragments. Researchers incorporated the 2.4Mb dystrophin gene, in which a mutation is a key causal element of Duchenne muscular dystrophy. The resulting HAC was mitotically stable, and correctly expressed dystrophin in chimeric mice. Previous attempts at correctly expressing dystrophin have failed. Due to its large size, it has never before been successfully integrated into a vector.
In 2010, a refined human artificial chromosome called 21HAC was reported. 21HAC is based on a stripped copy of human chromosome 21, producing a chromosome 5Mb in length. Truncation of chromosome 21 resulted in a human artificial chromosome that was mitotically stable. 21HAC was also able to be transferred into cells from a variety of species (mice, chickens, humans). Using 21HAC, researchers were able to insert a herpes simplex virus thymidine kinase coding gene into tumor cells. This "suicide gene" is required to activate many antiviral medications. These targeted tumor cells were successfully, and selectively, terminated by the antiviral drug ganciclovir in a population including healthy cells. This research opens a variety of opportunities for using HACs in gene therapy.
In 2011, researchers formed a human artificial chromosome by truncating chromosome 14. Genetic material was then introduced using the Cre-Lox recombination system. This particular study focused on changes in expression levels by leaving portions of the existing genomic DNA. By leaving existing telomeric and sub-telomeric sequences, researchers were able to amplify expression levels of genes coding for erythropoietin production over 1000-fold. This work also has large gene therapy implications, as erythropoietin controls red blood cell formation.
HACs have been used to create transgenic animals for use as animal models of human disease and for production of therapeutic products. | 1 | Applied and Interdisciplinary Chemistry |
Several additives, including polystyrene, cyclen, and polyamines, to the Stöber process allow the creation of shell-core silica particles. Two configurations of the shell-core morphology have been described. One is a silica core with an outer shell of an alternative material such as polystyrene. The second is a silica shell with a morphologically different core such as a polyamine.
The creation of the polystrene/silica core composite particles begins with creation of the silica cores via the one-step Stöber process. Once formed, the particles are treated with oleic acid, which is proposed to react with the surface silanol groups. Styrene is polymerized around the fatty-acid-modified silica cores. By virtue of size distribution of the silica cores, the styrene polymerizes around them evenly resulting composite particles are similarly sized.
The silica shell particles created with cyclen and other polyamine ligands are created in a much different fashion. The polyamines are added to the Stöber reaction in the initial steps along with the TEOS precursor. These ligands interact with the TEOS precursor, resulting in an increase in the speed of hydrolysis; however, as a result they get incorporated into the resulting silica colloids. The ligands have several nitrogen sites that contain lone pairs of electrons that interact with the hydrolyzed end groups of TEOS. Consequently, the silica condense around the ligands encapsulating them. Subsequently, the silica/ligand capsules stick together to create larger particles. Once all of the ligand has been consumed by the reaction the remaining TEOS aggregates around the outside of the silica/ligand nanoparticles, creating a solid silica outer shell. The resultant particle has a solid silica shell and an internal core of silica-wrapped ligands. The sizes of the particles cores and shells can be controlled through selection of the shape of the ligands along with the initial concentrations added to the reaction. | 0 | Theoretical and Fundamental Chemistry |
Each tissue returns to its equilibrium state after excitation by the independent relaxation processes of T1 (spin-lattice; that is, magnetization in the same direction as the static magnetic field) and T2 (spin-spin; transverse to the static magnetic field).
To create a T1-weighted image, magnetization is allowed to recover before measuring the MR signal by changing the repetition time (TR). This image weighting is useful for assessing the cerebral cortex, identifying fatty tissue, characterizing focal liver lesions, and in general, obtaining morphological information, as well as for post-contrast imaging.
To create a T2-weighted image, magnetization is allowed to decay before measuring the MR signal by changing the echo time (TE). This image weighting is useful for detecting edema and inflammation, revealing white matter lesions, and assessing zonal anatomy in the prostate and uterus.
The standard display of MRI images is to represent fluid characteristics in black and white images, where different tissues turn out as follows: | 0 | Theoretical and Fundamental Chemistry |
The intake of radioactive material can occur through four pathways: inhalation of airborne contaminants such as radon, ingestion of contaminated food or liquids, absorption of vapors such as tritium oxide through the skin, and injection of medical radioisotopes such as technetium-99m.
Some artificial radioisotopes such as iodine-131 are chemically identical to natural isotopes needed by the body, and may be more readily absorbed if the individual has a deficit of that element. For instance, potassium iodide (KI), administered orally immediately after exposure, may be used to protect the thyroid from ingested radioactive iodine in the event of an accident or attack at a nuclear power plant, or the detonation of a nuclear explosive which would release radioactive iodine.
Other radioisotopes have an affinity for particular tissues, such as plutonium into bone, and may be retained there for years in spite of their foreign nature.
Not all radiation is harmful. The radiation can be absorbed through multiple pathways, varying due to the circumstances of the situation. If the radioactive material is necessary, it can be ingested orally via stable isotopes of specific elements. This is only suggested to those that have a lack of these elements however, because radioactive material can go from healthy to harmful with very small amounts. The most harmful way to absorb radiation is that of ingestion absorption because it is almost impossible to control how much will enter the body. | 0 | Theoretical and Fundamental Chemistry |
The Boltzmann equation can be used to derive the fluid dynamic conservation laws for mass, charge, momentum, and energy. For a fluid consisting of only one kind of particle, the number density is given by
The average value of any function is
Since the conservation equations involve tensors, the Einstein summation convention will be used where repeated indices in a product indicate summation over those indices. Thus and , where is the particle velocity vector. Define as some function of momentum only, which is conserved in a collision. Assume also that the force is a function of position only, and that f is zero for . Multiplying the Boltzmann equation by A and integrating over momentum yields four terms, which, using integration by parts, can be expressed as
where the last term is zero, since is conserved in a collision. The values of correspond to moments of velocity (and momentum , as they are linearly dependent). | 1 | Applied and Interdisciplinary Chemistry |
The Blastocrithidia nuclear code (translation table 31) is a genetic code used by the nuclear genome of the trypanosomatid genus Blastocrithidia. This code, along with translation tables 27 and 28, is remarkable in that every one of the 64 possible codons can be a sense codon. | 1 | Applied and Interdisciplinary Chemistry |
The second part of the B ring synthesis (Scheme 5) was concerned with correct chemistry for the newly formed ethylene bridge connecting the A and C rings. After Scheme 4, this bridge contained an exocyclic methylene group, but in the ultimate taxol molecule this bridge is an α-acylketone. The required conversion was accomplished in the next 10 steps.
The tert-butylsilyl protecting group in diene 39 was not compatible in later reactions and was replaced by a triethylsilyl. Epoxidation of diene 40 with meta-chloroperoxybenzoic acid gave the oxirane ring. This served solely as a protecting group in preparation for modifications of the exocyclic alkene. In the next two steps, the benzyl protecting group in compound 41 was replaced by an acetyl group. Carbonate ester 43 was opened by reaction with phenyllithium to give alcohol 44. The cleavage of the exocyclic double bond was difficult and accomplished only with forcing conditions (19 equivalents of osmium tetroxide, 105 °C, 24 hours) by the putative osmate ester (45). Subsequent oxidative cleavage with lead tetraacetate gave ketone 46. The epoxide protecting group was removed with samarium (II) iodide to give α-ß-unsaturated ketone 47. The enolate was formed by the reaction of ketone 47 with potassium tert-butoxide, and subsequent reaction with phenylseleninic anhydride followed by acylation gave α-acylketone 49. | 0 | Theoretical and Fundamental Chemistry |
The company collaborates with the Budker Institute of Nuclear Physics. In 2020, Sibelektroterm completed several complicated orders for the research work of this scientific organization. In addition, in November 2020, the company won a tender for the supply of magnetic cores for the Siberian Ring Photon Source (SKIF), which has been under construction in Koltsovo since August 2021.
According to an article published in Kontinent Sibir Online in 2021, 80% of the customers of Sibelektroterm's products were Kazakhstan plants. | 1 | Applied and Interdisciplinary Chemistry |
Nanofluid-based direct solar collectors are solar thermal collectors where nanoparticles in a liquid medium can scatter and absorb solar radiation. They have recently received interest to efficiently distribute solar energy. Nanofluid-based solar collector have the potential to harness solar radiant energy more efficiently compared to conventional solar collectors.
Nanofluids have recently found relevance in applications requiring quick and effective heat transfer such as industrial applications, cooling of microchips, microscopic fluidic applications, etc. Moreover, in contrast to conventional heat transfer (for solar thermal applications) like water, ethylene glycol, and molten salts, nanofluids are not transparent to solar radiant energy; instead, they absorb and scatter significantly the solar irradiance passing through them.
Typical solar collectors use a black-surface absorber to collect the sun's heat energy which is then transferred to a fluid running in tubes embedded within. Various limitations have been discovered with these configuration and alternative concepts have been addressed. Among these, the use of nanoparticles suspended in a liquid is the subject of research. Nanoparticle materials including aluminium, copper, carbon nanotubes and carbon-nanohorns have been added to different base fluids and characterized in terms of their performance for improving heat transfer efficiency. | 0 | Theoretical and Fundamental Chemistry |
Currently there are four categories of membership: Member (including Student Member), Fellow, Honorary Fellow (the highest honour of the NZIC), and school member. A member of the New Zealand Institute of Chemistry is designated with the honorific affix "MNZIC". As the professional body for chemistry in New Zealand, the Institute can promote a member to Fellow of the institute ("FNZIC"). This requires a minimum of 5 years’ professional experience as a Member, and the candidate must have shown a substantial measure of ability or achievement in chemistry. | 1 | Applied and Interdisciplinary Chemistry |
The Tensorial Anisotropy Index A extends the Zener ratio for fully anisotropic materials and overcomes the limitation of the AU that is designed for materials exhibiting internal symmetries of elastic crystals, which is not always observed in multi-component composites. It takes into consideration all the 21 coefficients of the fully anisotropic stiffness tensor and covers the directional differences among the stiffness tensor groups.
It is composed of two major parts and , the former referring to components existing in cubic tensor and the latter in anisotropic tensor so that This first component includes the modified Zener ratio and additionally accounts for directional differences in the material, which exist in orthotropic material, for instance. The second component of this index covers the influence of stiffness coefficients that are nonzero only for non-cubic materials and remains zero otherwise.
where is the coefficient of variation for each stiffness group accounting for directional differences of material stiffness, i.e. In cubic materials each stiffness component in groups 1-3 has equal value and thus this expression reduces directly to Zener ratio for cubic materials.
The second component of this index <math>
A^A | 0 | Theoretical and Fundamental Chemistry |
Scheme 1 shows the synthesis of the oxetane D ring from the C ring starting from the (+) enantiomer of the Wieland-Miescher ketone (1). Reduction of this diketone with sodium borohydride provided unsaturated ketoalcohol 2, which was protected as an acetate. Formation of the ketal was accompanied by alkene rearrangement. The acetyl group was replaced by a tert-butyldimethylsilyl protecting group. Hydroboration followed by oxidation with hydrogen peroxide gave alcohol 5. The hydroxyl group was then oxidized to a carbonyl group giving ketone 6 by action of pyridinium dichromate. With all the sensitive functional groups protected, the methylene group required for the oxetane ring D was then provided by the Corey-Chaykovsky reagent, which converted the carbonyl group to an epoxide (7). Treatment of this epoxide with aluminium isopropoxide gave allylic alcohol 8. Two more hydroxyl groups were added by oxidation of the newly formed double bond with a catalytic amount of osmium tetroxide in the presence of N-methylmorpholine N-oxide. This reaction lacked stereospecificity and the yield of triol 9 with the correct stereochemistry was therefore reduced. The primary alcohol was protected as a silyl ether and the secondary alcohol was activated as a triflate (11). Heating this trimethylsilyl protected triflate in refluxing ethlyene glycol closed the ring to give oxetane 12. | 0 | Theoretical and Fundamental Chemistry |
The DNA in an organisms genome can be analyzed to diagnose vulnerabilities to inherited diseases, and can also be used to determine a childs paternity (genetic father) or a person's ancestry. Normally, every person carries two variations of every gene, one inherited from their mother, the other inherited from their father. The human genome is believed to contain around 20,000–25,000 genes. In addition to studying chromosomes to the level of individual genes, genetic testing in a broader sense includes biochemical tests for the possible presence of genetic diseases, or mutant forms of genes associated with increased risk of developing genetic disorders.
Genetic testing identifies changes in chromosomes, genes, or proteins. Usually, testing is used to find changes that are associated with inherited disorders. The results of a genetic test can confirm or rule out a suspected genetic condition or help determine a person's chance of developing or passing on a genetic disorder. Several hundred genetic tests are currently in use, and more are being developed. | 1 | Applied and Interdisciplinary Chemistry |
In mirror writing a text is deliberately displayed as its mirror image, in order to be read through a mirror. For example, emergency vehicles such as ambulances or fire engines use mirror images in order to be read from a vehicle's rear-view mirror. Some movie theaters also use mirror writing in a Rear Window Captioning System used to assist individuals with hearing impairments in watching films. | 0 | Theoretical and Fundamental Chemistry |
Chemi-excitation via oxidative stress by reactive oxygen species or catalysis by enzymes (i.e., peroxidase, lipoxygenase) is a common event in the biomolecular milieu. Such reactions can lead to the formation of triplet excited species, which release photons upon returning to a lower energy level in a process analogous to phosphorescence. That this process is a contributing factor to spontaneous biophoton emission has been indicated by studies demonstrating that biophoton emission can be increased by depleting assayed tissue of antioxidants or by addition of carbonyl derivatizing agents. Further support is provided by studies indicating that emission can be increased by addition of reactive oxygen species. | 1 | Applied and Interdisciplinary Chemistry |
Available evidence from geobiological studies of Archean (>2500 Ma) sedimentary rocks indicates that life existed 3500 Ma. Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old, consistent with recent studies of photosynthesis. Early photosynthetic systems, such as those from green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, using various molecules as electron donors. Green and purple sulfur bacteria are thought to have used hydrogen and hydrogen sulfide as electron and hydrogen donors. Green nonsulfur bacteria used various amino and other organic acids. Purple nonsulfur bacteria used a variety of nonspecific organic and inorganic molecules. It is suggested that photosynthesis likely originated at low-wavelength geothermal light from acidic hydrothermal vents, Zn-tetrapyrroles were the first photochemically active pigments, the photosynthetic organisms were anaerobic and relied on without relying on H emitted by alkaline hydrothermal vents. The divergence of anoxygenic photosynthetic organisms at the photic zone could have led to the ability to strip electrons from more efficiently under ultraviolet radiation. There is geochemical evidence that suggests that anaerobic photosynthesis emerged 3.3 to 3.5 billion years ago. The organisms later developed a Chlorophyll F synthase. They could have also stripped electrons from soluble metal ions although it is unknown.
The first oxygenic photosynthetic organisms are proposed to be -dependent. It is also suggested photosynthesis originated under sunlight, using emitted by volcanoes and hydrothermal vents which ended the need for scarce H emitted by alkaline hydrothermal vents. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen () in the photosynthetic reaction center. The biochemical capacity for oxygenic photosynthesis evolved in a common ancestor of extant cyanobacteria. The first appearance of free oxygen in the atmosphere is sometimes referred to as the oxygen catastrophe. The geological record indicates that this transforming event took place during the Paleoproterozoic era at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic Eon (2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation. Green algae joined blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic (251–65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. | 0 | Theoretical and Fundamental Chemistry |
The family of long non-coding RNAs includes a variety of different kinds of RNA, including, but not limited to, circular RNA (circRNA), nuclear lncRNA, long intergenic non-coding RNA, and enhancer RNA. The development of next-generation sequencing has made the study of lncRNA more accessible (because lncRNA is not very common in the cell relative to other types of RNA).
Editing and modifications to lncRNA have demonstrated to result in changes in RNA expression and rate of mutation. 5-methylcytosine (mC), N-methyladenosine (mA), and pseudouridine are the three most common and most studied modifications occurring in lncRNA. Modifications to the nucleotide structure are likely to impact the structure of lncRNAs and modulate their overall function. The study of the reversibility of these modifications is an active area of research. These modifications impact a variety of different qualities including the lncRNA's function and the initiation of translation. Modifications to lncRNAs have been demonstrated to impact where they localize within the cell and while complicated structures, such as the crucifix of tRNA, are not typically found in lncRNA, modifications may alter their structure and impact the overall function and pathway the lncRNA takes. | 1 | Applied and Interdisciplinary Chemistry |
Carbon-13 (C) is a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth. | 0 | Theoretical and Fundamental Chemistry |
While rich veins of tin are known to exist in Central and South Africa, whether these were exploited during ancient times is still debated . However, the Bantu culture of Zimbabwe are known to have actively mined, smelted and traded tin between the 11th and 15th centuries AD. | 1 | Applied and Interdisciplinary Chemistry |
*P. Grathwohl: Diffusion in natural porous media: Contaminant transport, sorption/desorption and dissolution kinetics. Kluwer Academic Publishers, 1998,
*R. K. M. Thambynayagam: The Diffusion Handbook: Applied Solutions for Engineers. McGraw-Hill, 2011,
*van Brakel, J., Heertjes, P. M. (1974): Analysis of diffusion in macroporous media in terms of a porosity, a tortuosity and a constrictivity factor. Int. J. Heat Mass Transfer, 17: 1093–1103 | 1 | Applied and Interdisciplinary Chemistry |
The principle of the Rietveld method is to minimize a function which analyzes the difference between a calculated profile and the observed data . Rietveld defined such an equation as:
where is the statistical weight and is an overall scale factor such that . | 0 | Theoretical and Fundamental Chemistry |
In Malaysia, sago plantations are mostly semi-wild, situated near rivers such as in Sarawak, although Malaysia also imports sago from Sumatra to make noodles. Peatlands are also used by the Jakun people in South East Pahang for hunting, gathering and fishing. | 1 | Applied and Interdisciplinary Chemistry |
The International Standard for making artificial seawater can be found at ASTM International. The current standard is named ASTM D1141-98 (The original standard was ASTM D1141-52) and describes the standard practice for the preparation of substitute ocean water.
The ASTM D1141-98 standard comes in a ready-made artificial seawater form or a "Sea Salt" mix that can be prepared by engineers and hobbyists. Generally, the ready-made artificial seawater comes in 1 gallon and 5 gallon containers, whereas the "Sea Salt" mix comes in 20lb pails (makes approximately 57 gallons) and 50lb pails (makes approximately 143 gallons). | 0 | Theoretical and Fundamental Chemistry |
The momentum conservation equation for this case is given as follows:
This is used in combination with the continuity equation.
The energy equation is also needed, which is:
The above equation, on solving, gives the temperature profile for the fluid region.
When solved as a scalar equation, it can be used to calculate the temperatures at the fin and cylinder surfaces, by reducing to:
Where:
q = internal heat generation = 0 (in this case).
Also dT/dt = 0 due to steady state assumption.
These flow and energy equations can be set up and solved in any simulation software, e.g. Fluent. In order to do so, all parameters of flow and thermal conditions like fluid velocity and temperature of body have to be specified according to the requirement. Also, the boundary conditions and assumptions if any must be specified.
This results in velocity profiles and temperature profiles for various surfaces and this knowledge can be used to design the fin. | 1 | Applied and Interdisciplinary Chemistry |
Hybrid difference scheme is a method used in the numerical solution for convection-diffusion problems. These problems play important roles in computational fluid dynamics. It can be described by the general partial equation as follows:
Where, is density, is the velocity vector, is the diffusion coefficient and is the source term. In this equation property, can be temperature, internal energy or component of velocity vector in x, y and z directions.
For one-dimensional analysis of convection-diffusion problem in steady state and without the source the equation reduces to,
With boundary conditions, and , where L is the length, and are the given values. | 1 | Applied and Interdisciplinary Chemistry |
Shortly after the invention of the laser by Theodore Maiman in 1960, it was quickly recognized that a laser could act as a point source to evaporate source material in a vacuum chamber for fabricating thin films. In 1965, Smith and Turner succeeded in depositing thin films using a ruby laser, after which Groh deposited thin films using a continuous-wave CO laser in 1968. Further work demonstrated that laser-induced evaporation is an effective way to deposit dielectric and semiconductor films. However, issues occurred with regard to stoichiometry and the uniformity of the deposited films, thus diminishing their quality compared to films deposited by other techniques. Experiments to investigate the deposition of thin films using a pulsed laser at high power densities laid the foundation for pulsed laser deposition, an extremely successful growth technique that is widely used today.
Experiments utilizing continuous-wave lasers continued to be performed throughout the latter half of the twentieth century, highlighting the many advantages of continuous-wave laser evaporation including low power densities, which can reduce surface damage to sensitive films. It proved challenging to achieve congruent evaporation from compound sources using continuous-wave lasers, and film deposition was typically limited to sources with high vapor pressures due to the low continuous wave power densities available.
In 2019, the evaporation of sources using continuous-wave lasers was rediscovered at the Max Planck Institute for Solid State Research and dubbed "thermal laser epitaxy". This new technique uses elemental sources illuminated by high-power continuous-wave lasers (typically with peak powers around 1 kW at a wavelength of 1000 nm), thus allowing the deposition of low-vapor-pressure materials such as carbon and tungsten while avoiding issues with congruent evaporation from compound sources. | 0 | Theoretical and Fundamental Chemistry |
PET is a functional imaging technique that produces a three-dimensional image of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. | 1 | Applied and Interdisciplinary Chemistry |
Greater-than-normal ceruloplasmin levels may indicate or be noticed in:
* copper toxicity / zinc deficiency
* pregnancy
* oral contraceptive pill use
* lymphoma
* acute and chronic inflammation (it is an acute-phase reactant)
* rheumatoid arthritis
* Angina
* Alzheimer's disease
* Schizophrenia
* Obsessive-compulsive disorder | 1 | Applied and Interdisciplinary Chemistry |
Another use of NMMO is in the dissolution of scleroprotein (found in animal tissue). This dissolution occurs in the crystal areas which are more homogeneous and contain glycine and alanine residues with a small number of other residues. How NMMO dissolves these proteins is scarcely studied. Other studies, however, have been done in similar amide systems (i.e. hexapeptide). The hydrogen bonds of the amides can be broken by NMMO. | 0 | Theoretical and Fundamental Chemistry |
Several computer applications attempt to relate the peaks in an electropherogram to specific bacteria in a database. Normally this type of analysis is done by simultaneously resolving several profiles of a single sample obtained with different restriction enzymes. The software then resolves the profile by attempting to maximize the matches between the peaks in the profiles and the entries in the database so that the number of peaks left without a matching sequence is minimal. The software withdraws from the database only those sequences which have their TRFs in all analyzed profiles. | 1 | Applied and Interdisciplinary Chemistry |
The Holton Taxol total synthesis, published by Robert A. Holton and his group at Florida State University in 1994, was the first total synthesis of Taxol (generic name: paclitaxel).
The Holton Taxol total synthesis is a good example of a linear synthesis. The synthesis starts from patchoulene oxide, a commercially available natural compound .
This epoxide can be obtained in two steps from the terpene patchoulol and also from borneol. The reaction sequence is also enantioselective, synthesizing (+)-Taxol from (−)-patchoulene oxide or (−)-Taxol from (−)-borneol with a reported specific rotation of +- 47° (c=0.19 / MeOH). The Holton sequence to Taxol is relatively short compared to that of the other groups (46 linear steps from patchoulene oxide). One of the reasons is that patchoulene oxide already contains 15 of the 20 carbon atoms required for the Taxol ABCD ring framework.
Other raw materials required for this synthesis include 4-pentenal, m-chloroperoxybenzoic acid, methyl magnesium bromide and phosgene. Two key chemical transformations in this sequence are a Chan rearrangement and a sulfonyloxaziridine enolate oxidation. | 0 | Theoretical and Fundamental Chemistry |
Etching is the immersion of the part into the chemical bath, and the action of the chemical on the part to be milled. The time spent immersed in the chemical bath determines the depth of the resulting etch; this time is calculated via the formula:
where E is the rate of etching (usually abbreviated to etch rate), s is the depth of the cut required, and t is the total immersion time. Etch rate varies based on factors such as the concentration and composition of the etchant, the material to be etched, and temperature conditions. Due to its inconstant nature, etch rate is often determined experimentally immediately prior to the etching process. A small sample of the material to be cut, of the same material specification, heat-treatment condition, and approximately the same thickness is etched for a certain time; after this time, the depth of the etch is measured and used with the time to calculate the etch rate. Aluminium is commonly etched at rates around , and magnesium about | 1 | Applied and Interdisciplinary Chemistry |
The bioprinting of biofilms utilizes the same methods as other bioprinting. Oftentimes, the biofilm begins with an extrusion of a polysaccharide to provide structure for biofilm growth. An example of one of these polysaccharides is alginate. The alginate structure can have microbes embedded within the structure. Hydrogels can also be used to assist in the formation of functional biofilms. Biofilms are difficult to analyze in a laboratory setting due to the complex structure and the time it takes for a functional biofilm to form. 3D bioprinting biofilms allows us to skip certain processes and makes it easier to analyze functional biofilms. Thickness of the biofilm being printed with change the functionality due to nutrient and oxygen diffusion. Thicker 3D printed biofilms will naturally select for anaerobes for example.
Biofilms are capable of remediation in the natural environment which suggests there is potential in regards to the use of 3D bioprinted biofilm use in environmental remediation. Microbes are able to degrade a large range of chemicals and metals and providing a structure for these microbes to flourish such as in biofilm structures is beneficial. Artificial biofilms protect the microbes from the dangers of the environment while promoting signaling and overall microbial interactions. 3D bioprinting allows functional microorganisms to be placed in structures that provide mechanical stability and protects them from environmental conditions. The larger contact area provided by 3D printed structures compared to normal environmental structures provides more efficient removal of pollutants. | 1 | Applied and Interdisciplinary Chemistry |
The Weyburn and Midale oil fields were discovered in 1954 near Midale, Saskatchewan.
The Weyburn Oilfield covers an area of some and has a current oil production rate of ~3,067 m3/day. Original oil-in-place is estimated to be . The oil is produced from a total of 963 active wells made up of 534 vertical wells, 138 horizontal wells, and 171 injection systems. There are also 146 enclosed wells. Current production consists primarily of medium-gravity crude oil with a low gas-to-oil ratio.
The Midale oil field is about in size, and has of oil-in-place. It began injecting CO in 2005.
Various enhanced oil recovery techniques were used in the Weyburn field prior to the introduction of CO, between the 1970s and 1990s. These include additional vertical drilling, the introduction of horizontal drilling, and the use of waterfloods to increase pressure in the reservoir. In October 2000, Cenovus (formerly Pan Canadian, Encana) began injecting significant amounts of carbon dioxide into the Weyburn field in order to boost oil production. Cenovus was the operator and held the largest share of the 37 current partners in the oilfield prior to the sale of local assets to Whitecap in 2017. | 1 | Applied and Interdisciplinary Chemistry |
Reverse transcription polymerase chain reaction (RT-PCR) is a laboratory technique combining reverse transcription of RNA into DNA (in this context called complementary DNA or cDNA) and amplification of specific DNA targets using polymerase chain reaction (PCR). It is primarily used to measure the amount of a specific RNA. This is achieved by monitoring the amplification reaction using fluorescence, a technique called real-time PCR or quantitative PCR (qPCR). Confusion can arise because some authors use the acronym RT-PCR to denote real-time PCR. In this article, RT-PCR will denote Reverse Transcription PCR. Combined RT-PCR and qPCR are routinely used for analysis of gene expression and quantification of viral RNA in research and clinical settings.
The close association between RT-PCR and qPCR has led to metonymic use of the term qPCR to mean RT-PCR. Such use may be confusing, as RT-PCR can be used without qPCR, for example to enable molecular cloning, sequencing or simple detection of RNA. Conversely, qPCR may be used without RT-PCR, for example to quantify the copy number of a specific piece of DNA. | 1 | Applied and Interdisciplinary Chemistry |
The symmetry-imposed barrier heights of group transfer reactions can also be analyzed using correlation diagrams. A model reaction is the transfer of a pair of hydrogen atoms from ethane to perdeuterioethylene shown to the right.
The only conserved symmetry element in this reaction is the mirror plane through the center of the molecules as shown to the left.
The molecular orbitals of the system are constructed as symmetric and antisymmetric combinations of σ and σ C–H bonds in ethane and π and π bonds in the deutero-substituted ethene. Thus the lowest energy MO is the symmetric sum of the two C–H σ-bond (σ), followed by the antisymmetric sum (σ). The two highest energy MOs are formed from linear combinations of the σ antibonds – highest is the antisymmetric σ, preceded by the symmetric σ at a slightly lower energy. In the middle of the energetic scale are the two remaining MOs that are the π and π of ethene.
The full molecular orbital correlation diagram is constructed in by matching pairs of symmetric and asymmetric MOs of increasing total energy, as explained above. As can be seen in the adjacent diagram, as the bonding orbitals of the reactants exactly correlate with the bonding orbitals of the products, this reaction is not predicted to have a high electronic symmetry-imposed barrier. | 0 | Theoretical and Fundamental Chemistry |
FG-7142 (ZK-31906) is a drug which acts as a partial inverse agonist at the benzodiazepine allosteric site of the GABA receptor. It has anorectic, anxiogenic and pro-convulsant effects. It also increases release of acetylcholine and noradrenaline, and improves memory retention in animal studies. | 1 | Applied and Interdisciplinary Chemistry |
Combinatorial chemistry was invented by Furka Á (from Eötvös Loránd University in Budapest, Hungary) who described the principle of it, the combinatorial synthesis and a deconvolution procedure in a document that was notarized in 1982. The principle of the combinatorial method is: synthesize a multi-component compound mixture (combinatorial library) in a single stepwise procedure and screen it to find drug candidates or other kinds of useful compounds also in a single process. The most important innovation of the combinatorial method is to use mixtures in the synthesis and screening that ensures the high productivity of the process. Motivations that led to the invention had been published in 2002. | 1 | Applied and Interdisciplinary Chemistry |
Lithium is recommended for the treatment of schizophrenic disorders only after other antipsychotics have failed; it has limited effectiveness when used alone. The results of different clinical studies of the efficacy of combining lithium with antipsychotic therapy for treating schizophrenic disorders have varied. | 1 | Applied and Interdisciplinary Chemistry |
As mentioned before, scientists Monika Suchanek, Anna Radzikowski, and Christoph Thiele wanted to study protein-protein interaction in their natural environment. Specifically, the membrane proteins (in a complex and are SCAP, Insig-1, and SREBP) that regulate cholesterol homeostasis so they wanted to know what their function was and the complex structure. What they had found was that using this photo-reactive amino acid was incorporated efficiently into the protein by mammalian cells, but did not need to use modified tRNAs (transfer RNAs) or AARSs (aminoacyl tRNA syntheses) which that allowed the specific cross-linking needed. This cross-linking could be determined by western blotting and they had discovered a direct interaction between Insig-1 and PGRMC1 (a progesterone-binding membrane protein). All four of the membrane proteins are found in the endoplasmic reticulum and the complex responds to low cholesterol levels. Cells (COS7) that had HA (hemagglutinin tagged PGRMC1) and Myc tagged Insig-1 were grown with and without photo-Met. In the presence of photo-Met, Insig-1 and SCAP had cross-linked with PGRMC1; specifically, Insig-1 cross-linked had a strong band. The cross-linking was detected by immunoprecipitating detergent-extracts with an antibody to HA then the precipitant was tested for Insig-1 using western blotting with the antibody for Myc. An identical band was found doing the reverse order of the detection; meaning Myc antibody was immunoprecipitated then followed by blotting with the HA antibody. So, the method had proven to work that photo-Met could cross-link proteins, but the physiological implications of this cross-linking has yet to be determined. | 0 | Theoretical and Fundamental Chemistry |
Photoelectron display thermophysical studies for simultaneous thermals are very important and critical in many relevant academic sciences. The heating capacity is closely related to the microstructure of the approved material and is important in monitoring the energy content of the system. Therefore, calorimetry plays an important role in the cataloging of physical systems, especially in the transition phase where energy fluctuations are very important. This paper summarizes the ability of photothermographic technology to study the variation of certain heat and other thermal parameters with temperature and is closely related to the transition. The working principle is applied to the theoretical basis, and the experimental structure and additional benefits of the technology compared with the traditional technology are described in detail. The integration in the calorimetric setting provides the possibility of performing calorimetric studies while also depicting the complementary nature of optical, structural and electrical properties. This paper reviews the high temperature resolution results for several phase transition parameters in different systems under various possible configurations. | 0 | Theoretical and Fundamental Chemistry |
Due to the electronegativity difference between carbon and oxygen / nitrogen, there will be a slight electron withdrawing effect through inductive effect (known as the –I effect). However, the other effect called resonance add electron density back to the ring (known as the +M effect) and dominate over that of inductive effect. Hence the result is that they are EDGs and ortho/para directors.
Phenol is an ortho/para director, but in a presence of base, the reaction is more rapid. It is due to the higher reactivity of phenolate anion. The negative oxygen was forced to give electron density to the carbons (because it has a negative charge, it has an extra +I effect). Even when cold and with neutral (and relatively weak) electrophiles, the reaction still occurs rapidly. | 0 | Theoretical and Fundamental Chemistry |
Scientists are capable of retrieving genetic information from hair, skin, blood, sperm, tissue, and saliva as long as the sample contains intact DNA. Nucleotide sequences between humans differ by only 0.1%. Even so, this 0.1% includes approximately three million bases. DNA can be analyzed through restriction fragment length polymorphism (RFLP) and Polymerase chain reactions (PCR). The RFLP process was introduced in 1988. Restriction enzymes digest portions of the DNA, leaving short fragments. These fragments are sorted through gel electrophoresis. The gel demonstrates the length of the fragments allowing specialists to determine whether the fragments came from the same person. PCR is more commonly used today because it more efficient and requires smaller samples of genetic samples. | 1 | Applied and Interdisciplinary Chemistry |
Dissociative pathways are characterized by a rate determining step that involves release of a ligand from the coordination sphere of the metal undergoing substitution. The concentration of the substituting nucleophile has no influence on this rate, and an intermediate of reduced coordination number can be detected. The reaction can be described with k, k and k, which are the rate constants of their corresponding intermediate reaction steps:
Normally the rate determining step is the dissociation of L from the complex, and [L'] does not affect the rate of reaction, leading to the simple rate equation:
However, in some cases, the back reaction (k) becomes important, and [L] can exert an effect on the overall rate of reaction. The backward reaction k therefore competes with the second forward reaction (k), thus the fraction of intermediate (denoted as "Int") that can react with L to form the product is given by the expression , which leads us to the overall rate equation:
When [L] is small and negligible, the above complex equation reduces to the simple rate equation that depends on k and [LM-L] only. | 0 | Theoretical and Fundamental Chemistry |
Single-drop microextraction (SDME) is a sample preparation technique in chemical test or analytical chemistry. SDME uses only a single drop of solvent to isolate and preconcentrate analytes from a sample matrix. The extremely low solvent use of SDME makes it cost-effective and less harmful to the environment, subscribing to the principles of green analytical chemistry.
In many chemical test procedures, sample preparation, often the time- and cost-determining step, is designed to isolate analytes from interferences and to provide (typically through enrichment) an analyte concentration suitable for detection. Liquid−liquid extraction (LLE) has long been a widely used technique for the preparation of aqueous samples. Numerous efforts have been made to improve upon the LLE technique for decades.
SDME using only one microdrop of organic solvent to perform LLE was first described in 1996 in Analytical Chemistry. [https://academictree.org/chemistry/peopleinfo.php?pid=844613 Liu] and Dasgupta described a microdrop LLE system with a drop (~1.3 microliter) of chloroform at the tip of a tube suspended in an aqueous drop to perform automatic drop-in-drop extraction and in situ optical detection. Jeannot and [https://academictree.org/chemistry/peopleinfo.php?pid=574033 Cantwell] introduced a method with a single drop (8 microliter) of n-octane at the end of a Teflon rod in a stirred aqueous sample solution to extract the analyte into the organic drop for GC analysis. Since its introduction, SDME has become a popular LLE technique because it is inexpensive, easy to operate, and uses only minuscule amount of solvent. | 0 | Theoretical and Fundamental Chemistry |
Disposal of expired radioactive sources presents similar challenges to the disposal of other nuclear waste, although to a lesser degree. Spent low level sources will sometimes be sufficiently inactive that they are suitable for disposal via normal waste disposal methods — usually landfill. Other disposal methods are similar to those for higher-level radioactive waste, using various depths of borehole depending on the activity of the waste.
A notorious incident of neglect in disposing of a high level source was the Goiânia accident, which resulted in several fatalities. The Tammiku radioactive material theft involved the accidental theft of caesium-137 material in Tammiku, Estonia, in 1994. | 0 | Theoretical and Fundamental Chemistry |
Tissue fixation is performed by chemical fixation using formalin. This prevents the postmortem degeneration of the tissue and hardens soft tissue. The tissue is dehydrated using ethanol and the alcohol is cleared using an organic solvent such as xylene. The tissue is embedded in paraffin which infiltrates the microscopic spaces present throughout the tissue. The embedded tissue is sliced using a microtome and subsequently stained to produce contrast needed to visualize the tissue. | 1 | Applied and Interdisciplinary Chemistry |
Cegelski's work has earned her several awards:
* Presidential Early Career Award for Scientists and Engineers (PECASE)
*Burroughs Wellcome Career Award at the Scientific Interface, for "Mapping the structural and functional landscape of the microbial extracellular matrix."
* 2010 NIH Director's New Innovator Award, for "Structure, Function, and Disruption of Microbial Amyloid Assembly and Biofilm Formation."
* National Science Foundation CAREER Award, for "Form and Function of Bacterial Amyloid Fibers." | 0 | Theoretical and Fundamental Chemistry |
A further method to synthesize Grignard reagents involves reaction of Mg with an organozinc compound. This method has been used to make adamantane-based Grignard reagents, which are, due to C-C coupling side reactions, difficult to make by the conventional method from the alkyl halide and Mg. The reductive transmetalation achieves:
:AdZnBr + Mg → AdMgBr + Zn | 0 | Theoretical and Fundamental Chemistry |
is a Japanese chemist. In 1974 he earned his doctorate in chemistry, in the group of Shun’ichi Yamada. He did a post doc with Elias J. Corey at Harvard. He returned to Japan and became a professor in 1977 at Teikyō University and moved to Hokkaidō University 1986. 1983–1986 Shibasaki was a research group leader at the Sagami chemical research center. From 1991 until 2010 he served as professor at Tokyo University. Since 2010 he is representative director of Microbial Chemistry Research Foundation (Chemistry), Tokyo. He is perhaps best known for developing a range of binol based heterobimetallic catalysts, which now bear his name. | 0 | Theoretical and Fundamental Chemistry |
In the 1879 paper the assumption that reaction rate was proportional to the product of concentrations was justified microscopically in terms of the frequency of independent collisions, as had been developed for gas kinetics by Boltzmann in 1872 (Boltzmann equation). It was also proposed that the original theory of the equilibrium condition could be generalised to apply to any arbitrary chemical equilibrium.
The exponents α, β etc. are explicitly identified for the first time as the stoichiometric coefficients for the reaction. | 0 | Theoretical and Fundamental Chemistry |
Epibiotech developed an autologous dermal papilla cell that was scheduled to enter clinical trials at the end of 2023. | 1 | Applied and Interdisciplinary Chemistry |
Malonyl-CoA, in a series of reactions, is further split into acetyl-CoA and glyoxylate. Glyoxylate is incorporated into beta-methylmalyl-coA which is then split, again through a series of reactions, to release pyruvate as well as acetate, which is used to replenish the cycle. | 1 | Applied and Interdisciplinary Chemistry |
The mechanism of carboboration depends highly on the substrate and reagents utilized in the reaction. Shown below are examples of two types of Pd-catalyzed alkene 1,2 carboborations, Heck-type and the Wacker-type. However, the Cu- and Ni-catalyzed reactions can proceed through similar mechanisms. These two mechanisms mainly differ in the oxidation state of the active catalyst and how the carbon group is delivered to the substrate: whether the C–C bond is formed via migratory insertion from the catalyst (inner sphere) or attack by an external nucleophile (outer sphere). Wacker-type carboborations, catalyzed by Pd, are much rarer than Heck-type. The first example of a Wacker-type 1,2 carboboration was reported by the Engle group in 2019.
Despite the common trend of utilizing transition metals, transition metal-free processes have also been developed, such as utilizing boronic acids or light-mediated radical initiation. These reactions usually lead to the boron substituent being at the terminus or less substituted side of the substrate, but anti-carborborations have also been developed which produce reverse regioselectivity. Much work has also been done to render 1,2 carboboration enantioselective using various ligands on transition metal catalysts. | 0 | Theoretical and Fundamental Chemistry |
Many natural building materials are hygroscopic, that is they can absorb (water condenses) and release water (water evaporates). The process is thus:
*Condensation (gas to liquid) ΔH<0; enthalpy decreases (exothermic process) gives off heat.
*Vaporization (liquid to gas) ΔH>0; enthalpy increases (endothermic process) absorbs heat (or cools).
While this process liberates a small quantity of energy, large surfaces area allows significant (1–2 °C) heating or cooling in buildings. The corresponding materials are wool insulation and earth/clay render finishes. | 0 | Theoretical and Fundamental Chemistry |
Activation energy asymptotics (AEA), also known as large activation energy asymptotics, is an asymptotic analysis used in the combustion field utilizing the fact that the reaction rate is extremely sensitive to temperature changes due to the large activation energy of the chemical reaction. | 1 | Applied and Interdisciplinary Chemistry |
Sodium trimethylsilylpropanesulfonate (DSS) is the organosilicon compound with the formula (CH)SiCHCHCHSONa. It is the sodium salt of trimethylsilylpropanesulfonic acid. A white, water-soluble solid, it is used as a chemical shift standard for proton NMR spectroscopy of aqueous solutions. The chemical shift, specifically the signal for the trimethylsilyl group, is relatively insensitive to pH.
The proton spectrum of DSS also exhibits resonances at 2.91 ppm (m), 1.75 ppm (m), and 0.63 ppm (m) at an intensity of 22% of the reference resonance at 0 ppm. | 0 | Theoretical and Fundamental Chemistry |
Epoxy and modified epoxy are standard coatings used to provide protective barriers to corrosion in ballast tanks. Exposed, unprotected steel will corrode much more rapidly than steel covered with this protective layer. Many ships also use sacrificial anodes or an impressed current for additional protection. Empty ballast tanks will corrode faster than areas fully immersed due to the thin - and electo conducting - moisture film covering them.
The main factors influencing the rate of corrosion are diffusion, temperature, Conductivity, type of ions, pH, and
electrochemical corrosion potential. | 1 | Applied and Interdisciplinary Chemistry |
With improvements in measuring techniques such as AFM, confocal microscopy and SEM, researchers were able to produce and image droplets at ever smaller scales. With the reduction in droplet size came new experimental observations of wetting. These observations confirm that the modified Young’s equation does not hold at the micro-nano scales. In addition the sign of the line tension is not maintained through the modified Young’s equation.
For a sessile droplet, the free energy of the three phase system can be expressed as:
At constant volume in thermodynamic equilibrium, this reduces to:
Usually, the VdP term has been neglected for large droplets, however, VdP work becomes significant at small scales. The variation in pressure at constant volume at the free liquid-vapor boundary is due to the Laplace pressure, which is proportional to the mean curvature of the droplet, and is non zero. Solving the above equation for both convex and concave surfaces yields:
Where the constant parameters A, B, and C are defined as:
:, and
This equation relates the contact angle , a geometric property of a sessile droplet to the bulk thermodynamics, the energy at the three phase contact boundary, and the curvature of the surface α. For the special case of a sessile droplet on a flat surface (α=0),
The first two terms are the modified Young’s equation, while the third term is due to the Laplace pressure. This nonlinear equation correctly predicts the sign and magnitude of κ, the flattening of the contact angle at very small scales, and contact angle hysteresis. | 0 | Theoretical and Fundamental Chemistry |
Pañcastikayasara (en: the essence of reality), is an ancient Jain text authored by Acharya Kundakunda. Kundakunda explains the Jain concepts of dravya (substance) and Ethics. The work serves as a brief version of the Jaina philosophy. There are total 180 verses written in Prakrit language. The text is about five (panch) āstikāya, substances that have both characteristics, viz. existence as well as body. | 1 | Applied and Interdisciplinary Chemistry |
Flutamide and hydroxyflutamide have been found in vitro to inhibit CYP17A1 (17α-hydroxylase/17,20-lyase), an enzyme which is required for the biosynthesis of androgens. In accordance, flutamide has been found to slightly but significantly lower androgen levels in GnRH analogue-treated male prostate cancer patients and women with polycystic ovary syndrome. In a directly comparative study of flutamide monotherapy (375mg once daily) versus bicalutamide monotherapy (80mg once daily) in Japanese men with prostate cancer, after 24weeks of treatment flutamide decreased dehydroepiandrosterone (DHEA) levels by about 44% while bicalutamide increased them by about 4%. As such, flutamide is a weak inhibitor of androgen biosynthesis. However, the clinical significance of this action may be limited when flutamide is given without a GnRH analogue to non-castrated men, as the medication markedly elevates testosterone levels into the high normal male range via prevention of AR activation-mediated negative feedback on the hypothalamic–pituitary–gonadal axis in this context. | 0 | Theoretical and Fundamental Chemistry |
Lamellar bodies are groups of lipids and protein that are structurally similar to tubular myelin, but are found inside instead of outside the type II pneumocytes. Similarly to its function in organizing tubular myelin, SP-B arranges lipids into the lamellar body structure. Basically, SP-B plays a role in the organogenesis (formation of structure) of lamellar bodies. The lamellar bodies are then secreted into the fluid lining the interior of alveoli, and become tubular myelin. This role is critical for making pulmonary surfactant (see below) | 0 | Theoretical and Fundamental Chemistry |
The effectiveness of a dispersant may be analyzed with the following equations. The Area refers to the area under the absorbance/wavelength curve, which is determined using the trapezoidal rule. The absorbances are measured at 340, 370, and 400 nm.
Area = 30(Abs + Abs)/2 + 30(Abs + Abs)/2 (1)
The dispersant effectiveness may then be calculated using the equation below.
Effectiveness (%) = Total oil dispersed x 100/(ρV)
* ρ = density of the test oil (g/L)
* V = volume of oil added to test flask (L)
* Total oil dispersed = mass of oil x 120mL/30mL
* Mass of oil = concentration oil x V
* V = final volume of DCM-extract of water sample (0.020 L)
* Concentration of oil = area determined by Equation (1) / slope of calibration curve | 1 | Applied and Interdisciplinary Chemistry |
There is direct evidence that the Romans mechanised at least part of the extraction processes. They used water power from water wheels for grinding grains and sawing timber or stone, for example. A set of sixteen such overshot wheels is still visible at Barbegal near Arles and dates from the 1st century AD or possibly earlier, the water being supplied by the main aqueduct to Arles. It is likely that the mills supplied flour for Arles and other towns locally. Multiple grain mills also existed on the Janiculum hill in Rome.
Ausonius attests the use of a water mill for sawing stone in his poem Mosella from the 4th century AD. They could easily have adapted the technology to crush ore using tilt hammers, and just such is mentioned by Pliny the Elder in his Naturalis Historia dating to about 75 AD, and there is evidence for the method from Dolaucothi in South Wales. The Roman gold mines developed from c. 75 AD. The methods survived into the medieval period, as described and illustrated by Georgius Agricola in his De re metallica.
They also used reverse overshot water-wheels for draining mines, the parts being prefabricated and numbered for ease of assembly. Multiple set of such wheels have been found in Spain at the Rio Tinto copper mines and a fragment of a wheel at Dolaucothi. An incomplete wheel from Spain is now on public show in the British Museum. | 1 | Applied and Interdisciplinary Chemistry |
At 4.2 light-years (1.3 parsecs, 40 trillion km, or 25 trillion miles) away from Earth, the closest potentially habitable exoplanet is Proxima Centauri b, which was discovered in 2016. This means it would take more than 18,100 years to get there if a vessel could consistently travel as fast as the Juno spacecraft (250,000 kilometers per hour or 150,000 miles per hour). It is currently not feasible to send humans or even probes to search for biosignatures outside of the Solar System. The only way to search for biosignatures outside of the Solar System is by observing exoplanets with telescopes.
There have been no plausible or confirmed biosignature detections outside of the Solar System. Despite this, it is a rapidly growing field of research due to the prospects of the next generation of telescopes. The James Webb Space Telescope, which launched in December 2021, will be a promising next step in the search for biosignatures. Although its wavelength range and resolution will not be compatible with some of the more important atmospheric biosignature gas bands like oxygen, it will still be able to detect some evidence for oxygen false positive mechanisms.
The new generation of ground-based 30-meter class telescopes (Thirty Meter Telescope and Extremely Large Telescope) will have the ability to take high-resolution spectra of exoplanet atmospheres at a variety of wavelengths. These telescopes will be capable of distinguishing some of the more difficult false positive mechanisms such as the abiotic buildup of oxygen via photolysis. In addition, their large collecting area will enable high angular resolution, making direct imaging studies more feasible. | 1 | Applied and Interdisciplinary Chemistry |
Biogeochemical cycling of elements is an essential component of lithotrophs within microbial environments. For example, in the carbon cycle, there are certain bacteria classified as photolithoautotrophs that generate organic carbon from atmospheric carbon dioxide. Certain chemolithoautotrophic bacteria can also produce organic carbon, some even in the absence of light. Similar to plants, these microbes provide a usable form of energy for organisms to consume. On the contrary, there are lithotrophs that have the ability to ferment, implying their ability to convert organic carbon into another usable form. Lithotrophs play an important role in the biological aspect of the iron cycle. These organisms can use iron as either an electron donor, Fe(II) --> Fe(III), or as an electron acceptor, Fe (III) --> Fe(II). Another example is the cycling of nitrogen. Many lithotrophic bacteria play a role in reducing inorganic nitrogen (nitrogen gas) to organic nitrogen (ammonium) in a process called nitrogen fixation. Likewise, there are many lithotrophic bacteria that also convert ammonium into nitrogen gas in a process called denitrification. Carbon and nitrogen are important nutrients, essential for metabolic processes, and can sometimes be the limiting factor that affects organismal growth and development. Thus, lithotrophs are key players in both providing and removing these important resource. | 1 | Applied and Interdisciplinary Chemistry |
“In situ” is a latin phrase whose literal translation is “on site.” It is a term that has been used in the English language since the mid-eighteenth century to describe something that is in its original place or position. In the context of muscle tissue engineering, in situ tissue engineering involves the introduction and implantation of an acellular scaffold into the site of injury or degenerated tissue. The goal of in situ muscle tissue engineering is to encourage host cell recruitment, natural scaffold formation, and proliferation and differentiation of host cells. The main idea which in situ muscle tissue engineering is based on is the self-healing, regenerative properties of the mammalian body. The primary method for in situ muscle tissue engineering is described in the following section:
As described in Biomaterials for In Situ Tissue Regeneration: A Review (Abdulghani & Mitchell, 2019), in situ muscle tissue engineering requires very specific biomaterials which have the capability to recruit stem cells or progenitor cells to the site of the muscle defect, thus allowing regeneration of tissue without implantation of seed cells. The key to a successful scaffold is the appropriate properties (i.e. biocompatibility, mechanical strength, elasticity, biodegradability) and the correct shape and volume for the specific muscle defect in which they are implanted. This scaffold should effectively mimic the cellular response of the host tissue, and Mann et al. have found that Polyethylene glycol-based hydrogels are very successful as in situ biomaterial scaffolds because they are chemically modified to be degraded by biological enzymes, thus encouraging cell migration and proliferation. Beyond Polyethylene glycol-based hydrogels, synthetic biomaterials such as PLA and PCL are successful in situ scaffolds as they can be fully customized to each specific patient. These materials stiffness, degradation, and porosity properties are tailored to the degenerated tissues topology, volume, and cell type so as to provide the optimal environment for host cell migration and proliferation.
In situ engineering promotes natural regeneration of damaged tissue by effectively mimicking the mammalian body's own wound healing response. The use of both biological and synthetic biomaterials as scaffolds promotes host cell migration and proliferation directly to the defect site, thus decreasing the amount of time required for muscle tissue regeneration. Furthermore, in situ engineering effectively bypasses the risk of implant rejection by the immune system due to the biodegradable qualities in each scaffold. | 1 | Applied and Interdisciplinary Chemistry |
Fellowship of the Royal Society of Chemistry (FRSC) is an award conferred by the Royal Society of Chemistry (RSC) in the United Kingdom. | 1 | Applied and Interdisciplinary Chemistry |
DABCO and related amines are quenchers of singlet oxygen and effective antioxidants, and can be used to improve the lifetime of dyes. This makes DABCO useful in dye lasers and in mounting samples for fluorescence microscopy (when used with glycerol and PBS). DABCO can also be used to demethylate quaternary ammonium salts by heating in dimethylformamide (DMF). | 0 | Theoretical and Fundamental Chemistry |
As an example of a thermodynamic process involving a photon gas, consider a cylinder with a movable piston. The interior walls of the cylinder are "black" in order that the temperature of the photons can be maintained at a particular temperature. This means that the space inside the cylinder will contain a blackbody-distributed photon gas. Unlike a massive gas, this gas will exist without the photons being introduced from the outside – the walls will provide the photons for the gas. Suppose the piston is pushed all the way into the cylinder so that there is an extremely small volume. The photon gas inside the volume will press against the piston, moving it outward, and in order for the transformation to be isothermic, a counter force of almost the same value will have to be applied to the piston so that the motion of the piston is very slow. This force will be equal to the pressure times the cross sectional area (A ) of the piston. This process can be continued at a constant temperature until the photon gas is at a volume V . Integrating the force over the distance (x ) traveled yields the total work done to create this photon gas at this volume
where the relationship V = Ax has been used. Defining
The pressure is
Integrating, the work done is just
The amount of heat that must be added in order to create the gas is
where H is the enthalpy at the end of the transformation. It is seen that the enthalpy is the amount of energy needed to create the photon gas. | 0 | Theoretical and Fundamental Chemistry |
Photoacids are molecules which become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid or the light causes photoassociation (such as a ring forming reaction) that leads to an increased acidity and dissociation of a proton.
There are two main types of molecules that release protons upon illumination: photoacid generators (PAGs) and photoacids (PAHs). PAGs undergo proton photodissociation irreversibly, while PAHs are molecules that undergo proton photodissociation and thermal reassociation. In this latter case, the excited state is strongly acidic, but reversible. | 0 | Theoretical and Fundamental Chemistry |
Although there were some studies that showed an inverse correlation between serum bilirubin level and prevalences of ischemic coronary artery disease, cancer mortality, or colorectal cancer in general population, the potential benefits of the chemopreventive function of bilirubin and their causative relations haven't been proved. | 1 | Applied and Interdisciplinary Chemistry |
Premelting (also surface melting) refers to a quasi-liquid film that can occur on the surface of a solid even below melting point (). The thickness of the film is temperature () dependent. This effect is common for all crystalline materials.
Premelting shows its effects in frost heave, and, taking grain boundary interfaces into account, maybe even in the movement of glaciers.
Considering a solid-vapour interface, complete and incomplete premelting can be distinguished. During a temperature rise from below to above , in the case of complete premelting, the solid melts homogeneously from the outside to the inside; in the case of incomplete premelting, the liquid film stays very thin during the beginning of the melting process, but droplets start to form on the interface. In either case, the solid always melts from the outside inwards, never from the inside. | 0 | Theoretical and Fundamental Chemistry |
Homolysis makes two new radicals from a spin-paired molecule by breaking a covalent bond, leaving each of the fragments with one of the electrons in the bond. Because breaking a chemical bond requires energy, homolysis occurs under the addition of heat or light. The bond dissociation energy associated with homolysis depends on the stability of a given compound, and some weak bonds are able to homolyze at relatively lower temperatures.
Some homolysis reactions are particularly important because they serve as an initiator for other radical reactions. One such example is the homolysis of halogens, which occurs under light and serves as the driving force for radical halogenation reactions.
Another notable reaction is the homolysis of dibenzoyl peroxide, which results in the formation of two benzoyloxy radicals and acts as an initiator for many radical reactions. | 1 | Applied and Interdisciplinary Chemistry |
A bubble column reactor is a chemical reactor that belongs to the general class of multiphase reactors, which consists of three main categories: trickle bed reactor (fixed or packed bed), fluidized bed reactor, and bubble column reactor. A bubble column reactor is a very simple device consisting of a vertical vessel filled with water with a gas distributor at the inlet. Due to the ease of design and operation, which does not involve moving parts, they are widely used in the chemical, biochemical, petrochemical, and pharmaceutical industries to generate and control gas-liquid chemical reactions.
Despite the simple column arrangement, the hydrodynamics of bubble columns is very complex due to the interactions between liquid and gas phases. In recent years, Computational Fluid Dynamics (CFD) has become a very popular tool to design and optimize bubble column reactors. | 1 | Applied and Interdisciplinary Chemistry |
In the United States, there are over 300 materials recovery facilities. The total market size is estimated at $6.6B as of 2019.
As of 2016, the top 75 were headed by Sims Municipal Recycling out of Brooklyn, New York. Waste Management operated 95 MRF facilities total, with 26 in the top 75. ReCommunity operated 6 in the top 75. Republic Services operated 6 in the top 75. Waste Connections operated 4 in the top 75. | 1 | Applied and Interdisciplinary Chemistry |
In the United States, the Environmental Protection Agency (EPA) is responsible for regulating pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Food Quality Protection Act (FQPA).
Studies must be conducted to establish the conditions in which the material is safe to use and the effectiveness against the intended pest(s). The EPA regulates pesticides to ensure that these products do not pose adverse effects to humans or the environment, with an emphasis on the health and safety of children. Pesticides produced before November 1984 continue to be reassessed in order to meet the current scientific and regulatory standards. All registered pesticides are reviewed every 15 years to ensure they meet the proper standards. During the registration process, a label is created. The label contains directions for proper use of the material in addition to safety restrictions. Based on acute toxicity, pesticides are assigned to a Toxicity Class. Pesticides are the most thoroughly tested chemicals after drugs in the United States; those used on food require more than 100 tests to determine a range of potential impacts.
Some pesticides are considered too hazardous for sale to the general public and are designated restricted use pesticides. Only certified applicators, who have passed an exam, may purchase or supervise the application of restricted use pesticides. Records of sales and use are required to be maintained and may be audited by government agencies charged with the enforcement of pesticide regulations. These records must be made available to employees and state or territorial environmental regulatory agencies.
In addition to the EPA, the United States Department of Agriculture (USDA) and the United States Food and Drug Administration (FDA) set standards for the level of pesticide residue that is allowed on or in crops. The EPA looks at what the potential human health and environmental effects might be associated with the use of the pesticide.
In addition, the U.S. EPA uses the National Research Council's four-step process for human health risk assessment: (1) Hazard Identification, (2) Dose-Response Assessment, (3) Exposure Assessment, and (4) Risk Characterization.
In 2013 Kauai County (Hawaii) passed Bill No. 2491 to add an article to Chapter 22 of the countys code relating to pesticides and GMOs. The bill strengthens protections of local communities in Kauai where many large pesticide companies test their products.
The first legislation providing federal authority for regulating pesticides was enacted in 1910. | 1 | Applied and Interdisciplinary Chemistry |
The total synthesis of galanthamine (Trost 2005) is described as follows: the sequence starts by bromination by electrophilic aromatic substitution of isovanillin 1 to bromophenol 2, then by synthesis of the second intermediate 5 by reacting dialdehyde 3 in a coupled aldol reaction and Horner–Wadsworth–Emmons reaction with trimethyl phosphonoacetate 4. The hydroxyl group is activated as a trichloroethyl carbonate leaving group to 6. Next an enantioselective Trost AAA reaction takes place between bromophenol 2 and carbonate 6 to the allyl ether 7. Next the aldehyde group is protected as an acetal in 8 and this step enables the organic reduction of the ester group to the alcohol 9 with DIBAH and subsequent homologation of this alcohol to a nitrile by Mitsunobu-type reaction using acetone cyanohydrine as the source of cyanide, to yield 10 followed by aldehyde deprotection to 11. The intramolecular Heck reaction to 12 forms the dihydrofuran ring. Allylic oxidation by selenium dioxide provides allylic alcohol 13 with the correct stereochemistry. The aldehyde reacts with methylamine to the imine 14 and reduction of the imine and nitrile by DIBAL-H leading to ring-closure to the aminal 15 (not isolated) followed by acid quenching gives the hemi-aminal 16. In the final step the hemiaminal is reduced to give Galanthamine 17 together with 6% of the epi isomer 18. | 0 | Theoretical and Fundamental Chemistry |
Liquid scintillation counting is the measurement of radioactive activity of a sample material which uses the technique of mixing the active material with a liquid scintillator (e.g. zinc sulfide), and counting the resultant photon emissions. The purpose is to allow more efficient counting due to the intimate contact of the activity with the scintillator. It is generally used for alpha particle or beta particle detection. | 0 | Theoretical and Fundamental Chemistry |
The only energy required is provided by compressed air. This air is usually compressed by a compressor or a blower. The air is injected in the lower part of a pipe that transports a liquid. By buoyancy the air, which has a lower density than the liquid, rises quickly. By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air. The calculation of the volume flow of the liquid is possible thanks to the physics of two-phase flow. | 1 | Applied and Interdisciplinary Chemistry |
Lisa Michelle Jones (born February 1977) is an associate professor of pharmaceutical sciences at the University of Maryland, Baltimore (UMB). Her research is in structural proteomics, using mass spectrometry together with fast photochemical oxidation of proteins (FPOP), allowing researchers to study the solvent accessibility of proteins experimentally. | 1 | Applied and Interdisciplinary Chemistry |
These responses require at least 1μmol/m to be initiated and become saturated at about 1000μmol/m. Unlike VLFRs, these responses are photoreversible. This was shown by exposing lettuce seed to a brief flash of red light causing germination. It was then shown if this red flash was followed by a flash of far red light, germination was again inhibited. LFRs also follow the law of reciprocity. Other examples of LFRs include leaf de-etiolation and enhancement of rate of chlorophyll production. | 0 | Theoretical and Fundamental Chemistry |
Aside from decorative dentistry which they wore in life and carried the grave with them, ranking datus were often buried with items of gold, either in the form of gold burial goods, or as specifically designed funerary art such as death masks.
Burial goods found in graves from early Philippine history includes various beads earrings rings pendants, combs, strips, and other ornaments.
Another gold feature commonly discovered in elite burials from early historic Philippines are death mask artifacts, meant to cover either part or all of the deceased's face in the grave
When this practice was discovered by the Spanish colonizers, they created a rule that a government representative should always be present whenever the Spanish settlers dug up a grave - so that the Spanish government could get its designated 1/5 of the dug up goods.
Burial goods are among the most common surviving gold artifacts in the Philippines because gold which was not buried was typically eventually reforged into other forms as the colonial period proceeded. | 1 | Applied and Interdisciplinary Chemistry |
The SFA has more recently been extended to perform dynamic measurements, thereby determining viscous and viscoelastic properties of fluids, frictional and tribological properties of surfaces, and the time-dependent interaction between biological structures. | 0 | Theoretical and Fundamental Chemistry |
*If reactions have to be reversed for their products to be equal, the sign of ΔH must also be reversed.
*If an agent has to be multiplied for it to equal another agent, all other agents and ΔH must also be multiplied by its coefficient.
*Generally, ΔH values given in tables are under 1 atm and 25 °C (298.15 K). | 0 | Theoretical and Fundamental Chemistry |
UbiD protein domain - ubiquitin—calmodulin ligase - UDP-3-O-N-acetylglucosamine deacetylase - UDP-4-amino-4,6-dideoxy-N-acetyl-alpha-D-glucosamine transaminase - undecaprenyl-phosphate 4-deoxy-4-formamido-L-arabinose transferase - untranslated RNA - upstream - upstream activator sequence - upstream DNA - upstream (transduction) - uracil - uracil/thymine dehydrogenase - ureidoglycolate hydrolase - | 1 | Applied and Interdisciplinary Chemistry |
The Cornforth reagent is a strong oxidizing agent which can convert primary alcohols to aldehydes and secondary alcohols to ketones, both as a solution or suspension. This application was first mentioned in 1969, but fully developed only in 1979 by E. J. Corey and G. Schmidt. They mentioned that reaction of saturated primary alcohols with PDC, using dimethylformamide as solvent, results in oxidation to carboxylic acids rather than aldehydes. However, no oxidation to carboxylic acids occurs on allylic and benzylic primary alcohols.
The oxidation is usually carried out at ambient conditions, in nearly neutral pH conditions, in dimethylformamide or dichloromethane or their mixture. The choice of solvent or their ratio affects the reaction rate; in particular, higher content of dimethylformamide results in stronger oxidation. The slow oxidation rate for some alcohols can be accelerated by the addition of molecular sieves, organic acids or acetic anhydride or of their combinations. The acceleration by molecular sieves works best when their pore diameter is about 0.3 nm, and it is apparently unrelated to their water absorption capability. Among organic acids, acetic acid, pyridinium trifluoroacetate or pyridinium tosylate can be added, the first one being most efficient and easiest to remove. The achieved acceleration is remarkable, but the reaction inevitably turns from neutral (pH) to acidic. Comparable acceleration is achieved with acetic anhydride, which is used in sugar and nucleoside chemistry. Reaction acceleration depends not only on the additives but also on their form, so all reagents are preferred dry and freshly prepared, and PDC and molecular sieves should be finely ground. The disadvantage of the accelerators is that they may simultaneously promote several oxidation routes thereby reducing the selectivity of the reaction.
In its chemical structure and functions, the Cornforth reagent is closely related to other pyridinium salts of hexavalent chromium oxide, such as pyridinium chlorochromate [PyH][CrOCl] and to pyridine complexes such as the Collins reagent, CrO·2Py in dichloromethane and the Sarret reagent, CrO·2Py in pyridine. | 0 | Theoretical and Fundamental Chemistry |
Oceanic anoxic events most commonly occurred during periods of very warm climate characterized by high levels of carbon dioxide (CO) and mean surface temperatures probably in excess of . The Quaternary levels, the current period, are just in comparison. Such rises in carbon dioxide may have been in response to a great outgassing of the highly flammable natural gas (methane) that some call an "oceanic burp". Vast quantities of methane are normally locked into the Earth's crust on the continental plateaus in one of the many deposits consisting of compounds of methane hydrate, a solid precipitated combination of methane and water much like ice. Because the methane hydrates are unstable, except at cool temperatures and high (deep) pressures, scientists have observed smaller outgassing events due to tectonic events. Studies suggest the huge release of natural gas could be a major climatological trigger, methane itself being a greenhouse gas many times more powerful than carbon dioxide. However, anoxia was also rife during the Hirnantian (late Ordovician) ice age.
Oceanic anoxic events have been recognized primarily from the already warm Cretaceous and Jurassic Periods, when numerous examples have been documented, but earlier examples have been suggested to have occurred in the late Triassic, Permian, Devonian (Kellwasser event), Ordovician and Cambrian.
The Paleocene–Eocene Thermal Maximum (PETM), which was characterized by a global rise in temperature and deposition of organic-rich shales in some shelf seas, shows many similarities to oceanic anoxic events.
Typically, oceanic anoxic events lasted for less than a million years, before a full recovery. | 0 | Theoretical and Fundamental Chemistry |
A sub-plot shows the variation of isentropic (i.e. adiabatic) efficiency with flow, at constant speed. Some maps use polytropic efficiency. Alternatively, for illustrative purposes, efficiency contours are sometimes cross-plotted onto the main map.
Note that the locus of peak efficiency exhibits a slight kink in its upward trend. This is due to the choking-up of the compressor as speed increases, with the variable stators closed-off. The trend line resumes once the variables start to move open. | 0 | Theoretical and Fundamental Chemistry |
At 12, Taube left his hometown and moved to Regina to attend Luther College where he completed high school. After graduating, Taube stayed at Luther College and worked as laboratory assistant for Paul Liefeld, allowing him to take first year university classes. Taube attended the University of Saskatchewan, receiving his BSc in 1935 and his MSc in 1937. His thesis advisor at the University of Saskatchewan was John Spinks. While at the University of Saskatchewan, Taube studied with Gerhard Herzberg, who would be awarded the 1971 Nobel Prize in Chemistry. He moved to University of California, Berkeley, where he completed his PhD studies in 1940. His PhD mentor was William C. Bray. Taube's graduate research focused on the photodecomposition of chlorine dioxide and hydrogen peroxide in solution. | 0 | Theoretical and Fundamental Chemistry |
Sodium trifluoromethanesulfinate (CFSONa) as a trifluoromethylation reagent was introduced by Langlois in 1991. The reaction requires t-butyl hydroperoxide and generally a metal and proceeds through a radical mechanism. The reagent has been applied with heterocyclic substrates | 0 | Theoretical and Fundamental Chemistry |
Magic numbers are typically obtained by empirical studies; if the form of the nuclear potential is known, then the Schrödinger equation can be solved for the motion of nucleons and energy levels determined. Nuclear shells are said to occur when the separation between energy levels is significantly greater than the local mean separation.
In the shell model for the nucleus, magic numbers are the numbers of nucleons at which a shell is filled. For instance, the magic number 8 occurs when the 1s, 1p, 1p energy levels are filled, as there is a large energy gap between the 1p and the next highest 1d energy levels.
The atomic analog to nuclear magic numbers are those numbers of electrons leading to discontinuities in the ionization energy. These occur for the noble gases helium, neon, argon, krypton, xenon, radon and oganesson. Hence, the "atomic magic numbers" are 2, 10, 18, 36, 54, 86 and 118. As with the nuclear magic numbers, these are expected to be changed in the superheavy region due to spin/orbit-coupling effects affecting subshell energy levels. Hence copernicium (112) and flerovium (114) are expected to be more inert than oganesson (118), and the next noble gas after these is expected to occur at element 172 rather than 168 (which would continue the pattern).
In 2010, an alternative explanation of magic numbers was given in terms of symmetry considerations. Based on the fractional extension of the standard rotation group, the ground state properties (including the magic numbers) for metallic clusters and nuclei were simultaneously determined analytically. A specific potential term is not necessary in this model. | 0 | Theoretical and Fundamental Chemistry |
Polymers were first classified according to polymerization method by Wallace Carothers in 1929, who introduced the terms addition polymer and condensation polymer to describe polymers made by addition reactions and condensation reactions respectively. However this classification is inadequate to describe a polymer which can be made by either type of reaction, for example nylon 6 which can be made either by addition of a cyclic monomer or by condensation of a linear monomer.
Flory revised the classification to chain-growth polymerization and step-growth polymerization, based on polymerization mechanisms rather than polymer structures. IUPAC now recommends that the names of step-growth polymerization and chain-growth polymerization be further simplified to polycondensation (or polyaddition if no low-molar-mass by-product is formed when a monomer is added) and chain polymerization.
Most polymerizations are either chain-growth or step-growth reactions. Chain-growth includes both initiation and propagation steps (at least), and the propagation of chain-growth polymers proceeds by the addition of monomers to a growing polymer with an active centre. In contrast step-growth polymerization involves only one type of step, and macromolecules can grow by reaction steps between any two molecular species: two monomers, a monomer and a growing chain, or two growing chains. In step growth, the monomers will initially form dimers, trimers, etc. which later react to form long chain polymers.
In chain-growth polymerization, a growing macromolecule increases in size rapidly once its growth is initiated. When a macromolecule stops growing it generally will add no more monomers. In step-growth polymerization on the other hand, a single polymer molecule can grow over the course of the whole reaction.
In chain-growth polymerization, long macromolecules with high molecular weight are formed when only a small fraction of monomer has reacted. Monomers are consumed steadily over the course of the whole reaction, but the degree of polymerization can increase very quickly after chain initiation. However in step-growth polymerization the monomer is consumed very quickly to dimer, trimer and oligomer. The degree of polymerization increases steadily during the whole polymerization process.
The type of polymerization of a given monomer usually depends on the functional groups present, and sometimes also on whether the monomer is linear or cyclic. Chain-growth polymers are usually addition polymers by Carothers' definition. They are typically formed by addition reactions of C=C bonds in the monomer backbone, which contains only carbon-carbon bonds. Another possibility is ring-opening polymerization, as for the chain-growth polymerization of tetrahydrofuran or of polycaprolactone (see Introduction above).
Step-growth polymers are typically condensation polymers in which an elimination product as such as HO are formed. Examples are polyamides, polycarbonates, polyesters, polyimides, polysiloxanes and polysulfones. If no elimination product is formed, then the polymer is an addition polymer, such as a polyurethane or a poly(phenylene oxide). Chain-growth polymerization with a low-molar-mass by-product during chain growth is described by IUPAC as "condensative chain polymerization".
Compared to step-growth polymerization, living chain-growth polymerization shows low molar mass dispersity (or PDI), predictable molar mass distribution and controllable conformation. Generally, polycondensation proceeds in a step-growth polymerization mode. | 0 | Theoretical and Fundamental Chemistry |
Leaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. When the leaf is shed, it leaves a leaf scar on the twig. In cold autumns, they sometimes change color, and turn yellow, bright-orange, or red, as various accessory pigments (carotenoids and xanthophylls) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production. Red anthocyanin pigments are now thought to be produced in the leaf as it dies, possibly to mask the yellow hue left when the chlorophyll is lost—yellow leaves appear to attract herbivores such as aphids. Optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves. | 0 | Theoretical and Fundamental Chemistry |
The thanator (Palulukan in Navi) is a large hexapodal land predator that is believed, by the RDA, to be the apex land predator. It is scientifically known as Bestiapanthera ferox. Cameron personally designed the creature. The thanator is first seen when Jake wanders off into the jungle and touches multiple helicoradian leaves, at which they retract to reveal a family of hammerhead titanotheres behind. The thanator frightens the titanotheres and pursues Jake. Jake later escapes the thanator by jumping off a cliff into pool below. It later appears during the climax where it assists Neytiri and later battles Quaritchs AMP Suit Beyond Glory, but is killed by the AMP suit's knife. The thanator is black with white fleshy skin under each hand. Its appearance is similar to a panther; Cameron describes the thanator as "the panther from hell". The thanator has ten sensory quills connected to six pads at the rear of the skull that flare up before it attacks the prey. The director explained how the thanator is the most fearsome creature on Pandora, "The thanator could eat a T-Rex and have the Alien for dessert." | 1 | Applied and Interdisciplinary Chemistry |
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