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Marshall and his co-workers used their asymmetric allenylmetal-homoaldol tactic to construct polypropionate frameworks of (+)-discodermolide. The novelty of the Marshall approach is that the three stereotriad subunits are assembled through addition of non-racemic allenylmetal reagents to (S)-3-silyloxy-2-methylpropanal to generate both syn/syn and syn/anti adducts. The central feature for the synthesis of the alkyl iodide fragment was the treatment of aldehyde to allenyltributylstannane in the presence of BF3-etherate to get the syn/syn isomer. Syn/anti methyl-hydroxyl-methyl stereotriads were obtained through the reaction between aldehyde and homochiral allenylzinc reagent.
In the Marshall synthesis, the coupling between the alkyne fragment to the aldehyde fragment proceeded in 92% yield, with 85:15 diastereoselectivity. The condensation of aldehyde with iodoethylidene triphenylphosphorane was the most challenging step, which produce 40% yield and an 85:15 inseparable mixture of (Z) and (E) isomers. The last coupling was performed via a Suzuki union of vinyl iodide with the boronate derived of alkyl iodide. The Marshall synthesis of (+)-discodermolide has an overall yield of 1.3% with a longest linear sequence of 30 steps and 48 total steps. | 0 | Theoretical and Fundamental Chemistry |
Despite the fact that the process of chemosynthesis has been known for more than a hundred years, its significance and importance are still relevant today in the transformation of chemical elements in biogeochemical cycles. Today, the vital processes of nitrifying bacteria, which lead to the oxidation of ammonia to nitric acid, require scientific substantiation and additional research. The ability of bacteria to convert inorganic substances into organic ones suggests that chemosynthetics can accumulate valuable resources for human needs.
Chemosynthetic communities in different environments are important biological systems in terms of their ecology, evolution and biogeography, as well as their potential as indicators of the availability of permanent hydrocarbon- based energy sources. In the process of chemosynthesis, bacteria produce organic matter where photosynthesis is impossible. Isolation of thermophilic sulfate-reducing bacteria Thermodesulfovibrio yellowstonii and other types of chemosynthetics provides prospects for further research. Thus, the importance of chemosynthesis remains relevant for use in innovative technologies, conservation of ecosystems, human life in general. The role of Sergey Winogradsky in discovering the phenomenon of chemosynthesis is underestimated and needs further research and popularization. | 1 | Applied and Interdisciplinary Chemistry |
Consider a plane wall located at in the cylindrical coordinates , moving with a constant velocity towards the left. Consider another plane wall(scraper), at an inclined position, making an angle from the positive direction and let the point of intersection be at . This description is equivalent to moving the scraper towards right with velocity . The problem is singular at because at the origin, the velocities are discontinuous, thus the velocity gradient is infinite there.
Taylor noticed that the inertial terms are negligible as long as the region of interest is within ( or, equivalently Reynolds number ), thus within the region the flow is essentially a Stokes flow. For example, George Batchelor gives a typical value for lubricating oil with velocity as . Then for two-dimensional planar problem, the equation is
where is the velocity field and is the stream function. The boundary conditions are | 1 | Applied and Interdisciplinary Chemistry |
The mechanism involves the addition of amine to dichlorocarbene, a reactive intermediate generated by the dehydrohalogenation of chloroform. Two successive base-mediated dehydrochlorination steps result in formation of the isocyanide. | 0 | Theoretical and Fundamental Chemistry |
Before the Great Oxygenation Event, copper was not readily available for living organisms. Most early copper was Cu and Cu. This oxidation state of copper is not very soluble in water. One billion years ago, after the great oxidation event the oxygen pressure rose sufficiently to oxidise Cu to Cu, increasing its solubility in water. As a result, the copper became much more available for living organisms.
Most copper-containing proteins and enzymes can be found in eukaryotes. Only a handful of prokaryotes such as aerobic bacteria and cyanobacteria contain copper enzymes or proteins. Copper can be found in both prokaryotes and eukaryotes superoxide dismutase (SOD) enzyme. There are three distinct types of SOD, containing Mn, Fe and Cu respectively. Mn-SOD and Fe-SOD are found in most prokaryotes and mitochondria of the eukaryotic cell. Cu-SOD can be found in the cytoplasmic fraction of the eukaryotic cells. The three elements, copper, iron and manganese, can all catalyze superoxide to ordinary molecular oxygen or hydrogen peroxide. However, Cu-SOD is more efficient than Fe-SOD and Mn-SOD. Most prokaryotes only utilize Fe-SOD or Mn-SOD due to the lack of copper in the environment. Some organisms did not develop Cu-SOD due to the lack of a gene pool for the Cu-SOD adoption. | 0 | Theoretical and Fundamental Chemistry |
Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often have distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Several fluorocarbons and their derivatives are commercial polymers, refrigerants, drugs, and anesthetics. | 1 | Applied and Interdisciplinary Chemistry |
In environmental chemistry, air sparging is an in situ remediation technique that removes volatile pollutants from contaminated groundwater and soil. | 1 | Applied and Interdisciplinary Chemistry |
Exposure limits for UV, particularly the germicidal UV-C range, have evolved over time due to scientific research and changing technology. The American Conference of Governmental Industrial Hygienists (ACGIH) and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) have set exposure limits to safeguard against both immediate and long-term effects of UV exposure. These limits, also referred to as Threshold Limit Values (TLVs), form the basis for emission limits in product safety standards.
The UV-C photobiological spectral band is defined as 100–280 nm, with limits currently applying only from 180 to 280 nm. This reflects concerns about acute damage such as erythema and photokeratitis as well as long-term delayed effects like photocarcinogenesis. However, with the increased safety evidence surrounding UV-C for germicidal applications, the existing ACGIH TLVs were revised in 2022.
The TLVs for the 222 nm UV-C wavelength (peak emissions from KrCl excimer lamps), following the 2022 revision, are now 161 mJ/cm for eye exposure and 479 mJ/cm for skin exposure over an eight-hour period. For the 254 nm UV wavelength, the updated exposure limit is now set at 6 mJ/cm for eyes and 10 mJ/cm for skin. | 0 | Theoretical and Fundamental Chemistry |
A solvent (from the Latin solvō, "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar molecules, and the most common solvent used by living things; all the ions and proteins in a cell are dissolved in water within the cell.
Major uses of solvents are in paints, paint removers, inks, and dry cleaning. Specific uses for organic solvents are in dry cleaning (e.g. tetrachloroethylene); as paint thinners (toluene, turpentine); as nail polish removers and solvents of glue (acetone, methyl acetate, ethyl acetate); in spot removers (hexane, petrol ether); in detergents (citrus terpenes); and in perfumes (ethanol). Solvents find various applications in chemical, pharmaceutical, oil, and gas industries, including in chemical syntheses and purification processes. | 1 | Applied and Interdisciplinary Chemistry |
Se-79, half-life of 327k years, is one of the long-lived fission products. Given the stability of its next lighter and heavier isotopes and the high cross section those isotopes exhibit for various neutron reactions, it is likely that the relatively low yield is due to Se-79 being destroyed in the reactor to an appreciable extent. | 0 | Theoretical and Fundamental Chemistry |
Ernest Rutherford was born on 30 August 1871 in Brightwater, a town near Nelson, New Zealand. He was the fourth of twelve children of James Rutherford, an immigrant farmer and mechanic from Perth, Scotland, and his wife Martha Thompson, a schoolteacher from Hornchurch, England. Rutherfords birth certificate was mistakenly written as Earnest'. He was known by his family as Ern.
When Rutherford was five he moved to Foxhill and attended Foxhill School. At age 11 in 1883, the Rutherford family moved to Havelock, a town in the Marlborough Sounds. The move was made to be closer to the a flax mill the father was operating near the Ruapaka Stream. Ernest studied at Havelock School.
In 1887, on his second attempt, he won a scholarship to study at Nelson College. On his first examination attempt, he received 75 out of 130 marks for geography, 76 out of 130 for history, 101 out of 140 for English, and 200 out of 200 for arithmetic, totalling 452 out of 600 marks. With these marks, he had the highest of anyone from Nelson. When he was awarded the scholarship, he had received 580 out of 600 possible marks. After being awarded the scholarship, Havelock School presented him with a five-volume set of books titled The Peoples of the World. He studied at Nelson College between 1887 and 1889, and was head boy in 1889. He also played in the school's rugby team. He was offered a cadetship in government service, but he declined as he still had 15 months of college remaining.
In 1889, after his second attempt, he won a scholarship to study at Canterbury College, University of New Zealand, between 1890 and 1894. He participated in its debating society and the Science Society. At Canterbury, he was awarded a complex BA in Latin, English, and Maths in 1892, a MA in Mathematics and Physical Science in 1893, and a BSc in Chemistry and Geology in 1894.
Thereafter, he invented a new form of radio receiver, and in 1895 Rutherford was awarded an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851, to travel to England for postgraduate study at the Cavendish Laboratory, University of Cambridge. In 1897, he was awarded a BA Research Degree and the Coutts-Trotter Studentship from Trinity College, Cambridge. | 1 | Applied and Interdisciplinary Chemistry |
The low cost ($200/ton) and high cycle rate (2,000 ×) of synthetic zeolites such as Linde 13X with water adsorbate has garnered much academic and commercial interest recently for use for thermal energy storage (TES), specifically of low-grade solar and waste heat. Several pilot projects have been funded in the EU from 2000 to the present (2020). The basic concept is to store solar thermal energy as chemical latent energy in the zeolite. Typically, hot dry air from flat plate solar collectors is made to flow through a bed of zeolite such that any water adsorbate present is driven off. Storage can be diurnal, weekly, monthly, or even seasonal depending on the volume of the zeolite and the area of the solar thermal panels. When heat is called for during the night, or sunless hours, or winter, humidified air flows through the zeolite. As the humidity is adsorbed by the zeolite, heat is released to the air and subsequently to the building space. This form of TES, with specific use of zeolites, was first taught by John Guerra in 1978. | 0 | Theoretical and Fundamental Chemistry |
John Gaddum (1900–1965) held the Chair of Pharmacology from 1935 to 1938.
Like A.J. Clark, he had a profound interest in quantitative methods.
He extended A.J. Clark's work on competitive antagonism, and applied the law of mass action to describe the relationship (the Gaddum equation) between receptor occupancy and the concentrations of an agonist and a competitive antagonist at equilibrium with the receptors in a tissue. The theory for two or more competing ligands had been known since Michaelis & Menten (1914), but Gaddum was the first to apply it in a pharmacological context). Like Clark before him, Gaddum failed to spot how to use the theory to estimate equilibrium constants.
Gaddum was also a master of bioassay which was then the preferred, and usually the only, way to determine the concentrations of biologically active molecules such as labile neurotransmitters and the neuropeptides. | 1 | Applied and Interdisciplinary Chemistry |
NV centers emit bright red light (E→A transitions), if excited off-resonantly by visible green light (A →E transitions). This can be done with convenient light sources such as argon or krypton lasers, frequency doubled Nd:YAG lasers, dye lasers, or He-Ne lasers. Excitation can also be achieved at energies below that of zero phonon emission.
As the relaxation time from the excited state is small (~10 ns), the emission happens almost instantly after the excitation. At room temperature the NV center's optical spectrum exhibits no sharp peaks due to thermal broadening. However, cooling the NV centers with liquid nitrogen or liquid helium dramatically narrows the lines down to a width of a few MHz. At low temperature it also becomes possible to specifically address the zero-phonon line (ZPL).
An important property of the luminescence from individual NV centers is its high temporal stability. Whereas many single-molecular emitters bleach (i.e. change their charge state and become dark) after emission of 10–10 photons, bleaching is unlikely for NV centers at room temperature. Strong laser illumination, however, may also convert some NV into NV centers.
Because of these properties, the ideal technique to address the NV centers is confocal microscopy, both at room temperature and at low temperature. | 0 | Theoretical and Fundamental Chemistry |
In 2007 a quantum model was proposed by Graham Fleming and his co-workers which includes the possibility that photosynthetic energy transfer might involve quantum oscillations, explaining its unusually high efficiency.
According to Fleming there is direct evidence that remarkably long-lived wavelike electronic quantum coherence plays an important part in energy transfer processes during photosynthesis, which can explain the extreme efficiency of the energy transfer because it enables the system to sample all the potential energy pathways, with low loss, and choose the most efficient one. This claim has, however, since been proven wrong in several publications.
This approach has been further investigated by Gregory Scholes and his team at the University of Toronto, which in early 2010 published research results that indicate that some marine algae make use of quantum-coherent electronic energy transfer (EET) to enhance the efficiency of their energy harnessing. | 0 | Theoretical and Fundamental Chemistry |
Almost all coal-fired power stations, petroleum, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as all natural gas power stations are thermal. Natural gas is frequently burned in gas turbines as well as boilers. The waste heat from a gas turbine, in the form of hot exhaust gas, can be used to raise steam by passing this gas through a heat recovery steam generator (HRSG). The steam is then used to drive a steam turbine in a combined cycle plant that improves overall efficiency. Power stations burning coal, fuel oil, or natural gas are often called fossil fuel power stations. Some biomass-fueled thermal power stations have appeared also. Non-nuclear thermal power stations, particularly fossil-fueled plants, which do not use cogeneration are sometimes referred to as conventional power stations.
Commercial electric utility power stations are usually constructed on a large scale and designed for continuous operation. Virtually all electric power stations use three-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz. Large companies or institutions may have their own power stations to supply heating or electricity to their facilities, especially if steam is created anyway for other purposes. Steam-driven power stations have been used to drive most ships in most of the 20th century. Shipboard power stations usually directly couple the turbine to the ship's propellers through gearboxes. Power stations in such ships also provide steam to smaller turbines driving electric generators to supply electricity. Nuclear marine propulsion is, with few exceptions, used only in naval vessels. There have been many turbo-electric ships in which a steam-driven turbine drives an electric generator which powers an electric motor for propulsion.
Cogeneration plants, often called combined heat and power (CHP) facilities, produce both electric power and heat for process heat or space heating, such as steam and hot water. | 1 | Applied and Interdisciplinary Chemistry |
In Ancient Greece, there existed a separation between physician and herbalist. The duties of the herbalist was to supply physicians with raw materials, including plants, to make medicines. According to Edward Kremers and Glenn Sonnedecker, "before, during and after the time of Hippocrates there was a group of experts in medicinal plants. Probably the most important representative of these rhizotomoi was Diocles of Carystus (4th century BC). He is considered to be the source for all Greek pharmacotherapeutic treatises between the time of Theophrastus and Dioscorides."
Between 60 and 78 AD, the Greek physician Pedanius Dioscorides wrote a five-volume book, De materia medica, covering over 600 plants and coining the term materia medica. It formed the basis for many medieval texts, and was built upon by many Middle Eastern scientists during the Islamic Golden Age. | 1 | Applied and Interdisciplinary Chemistry |
The human trace amines include:
While not trace amines themselves, the classical monoamines norepinephrine, serotonin, and histamine are all partial agonists at the human TAAR1 receptor; dopamine is a high-affinity agonist at human TAAR1. and are endogenous amines in humans, however, their human TAAR1 binding has not been determined | 1 | Applied and Interdisciplinary Chemistry |
Spin echo small angle neutron scattering (SESANS) measures structures from around 20 to 2000 nm in size. The information is presented as a real-space (similar to g(r)) as opposed to a reciprocal space (q(r)) mapping. This can simplify the interpretation for some systems.
SESANS is useful for studying processes that occur over relatively long time scales, as data collection is often slow, but large length scales. Aggregation of colloids, block copolymer micelles, Stöber silica particles being a prime examples.
The technique offers some advantages over SANS but there are fewer SESANS instruments available than SANS instruments. Facilities for SESANS exist at TUDelft (Netherlands) and Rutherford Appleton Laboratory (UK). | 0 | Theoretical and Fundamental Chemistry |
As tissue replacements, nanocomposite hydrogels need to interact with cells and form functional tissues. With the incorporated nanoparticles and nanomaterials, these hydrogels can mimic the physical, chemical, electrical, and biological properties of most native tissue. Each type of nanocomposite hydrogels has its own unique properties that let it mimic certain types of animal tissue. | 0 | Theoretical and Fundamental Chemistry |
Laser spray ionization refers to one of several methods for creating ions using a laser interacting with a spray of neutral particles or ablating material to create a plume of charged particles. The ions thus formed can be separated by m/z with mass spectrometry. Laser spray is one of several ion sources that can be coupled with liquid chromatography-mass spectrometry for the detection of larger molecules. | 0 | Theoretical and Fundamental Chemistry |
In 2000, EPA drafted plans to phase out the use of MTBE nationwide over four years.. Some states enacted MTBE prohibitions without waiting for federal restrictions. California banned MTBE as a gasoline additive in 2002. The State of New York banned the use of MTBE as a "fuel additive", effective in 2004. MTBE use is still legal in the state for other industrial uses.
The federal Energy Policy Act of 2005 removed the oxygenate requirement for reformulated gasoline and established a renewable fuel standard. The lack of MTBE liability protection in the law also prompted refiners to substitute ethanol for MTBE as a gasoline additive. | 1 | Applied and Interdisciplinary Chemistry |
Magnetometers are used in directional drilling for oil or gas to detect the azimuth of the drilling tools near the drill. They are most often paired with accelerometers in drilling tools so that both the inclination and azimuth of the drill can be found. | 0 | Theoretical and Fundamental Chemistry |
A polar organic chemical integrative sampler (POCIS) is a passive sampling device which allows for the in situ collection of a time-integrated average of hydrophilic organic contaminants developed by researchers with the United States Geological Survey in Columbia, Missouri. POCIS provides a means for estimating the toxicological significance of waterborne contaminants. The POCIS sampler mimics the respiratory exposure of organisms living in the aquatic environment and can provide an understanding of bioavailable contaminants present in the system. POCIS can be deployed in a wide range of aquatic environments and is commonly used to assist in environmental monitoring studies.
__TOC__ | 0 | Theoretical and Fundamental Chemistry |
Bawendi was one of the most cited chemists of the decade from 2000 to 2010. He is a leading figure in the research and development of quantum dots. Quantum dots are tiny semiconducting crystals whose nanoscale size gives them unique optical and electronic properties.
A major challenge in quantum dot research was to find ways to create high quality quantum dots that are stable and uniform. Bawendi is recognized for his work in developing standardized methods for quantum dot synthesis. In 1993, Bawendi, and his PhD students David J. Norris and Christopher B. Murray, reported on a hot-injection synthesis method for producing reproducible quantum dots with well-defined size and with high optical quality.
This breakthrough in chemical production methods made it possible to “tune” quantum dots according to size, and achieve predictable properties as a result. It gave scientists much greater control over the material, and made it possible to achieve precise and reproducible results.
The method opened the door to the development of large-scale technological applications of quantum dots in a wide range of areas. Quantum dots are now used in light-emitting diodes (LEDs), photovoltaics (solar cells), photodetectors, photoconductors, lasers, biomedical imaging, biosensing and other applications. | 0 | Theoretical and Fundamental Chemistry |
The petition was addressed to the President and Council of the Chemical Society. It highlighted that in the previous thirty years that there were "about 150 women" who had appeared as authors on some 300 papers published by the Society. It listed the number of papers in the Journal of the Chemical Society in the periods 1873 - 1882 (20 papers), 1883 - 1892 (33 papers), 1893 - 1902 (142 papers), and 1903 to August 1904 (50 papers). They continue that as the Society deemed it fit to publish the work completed by female chemists, that they should help support this work by enabling "free access to chemical literature and by the right to attend the meetings of the Society". | 1 | Applied and Interdisciplinary Chemistry |
Transition metal phosphate complexes are coordination complexes with one or more phosphate ligands. Phosphate binds to metals through one, two, three, or all four oxygen atoms. The bidentate coordination mode is common. The second and third pK's of phosphoric acid, pK and pK, are 7.2 and 12.37, respectively. It follows that are sufficiently basic to serve as ligands. The examples below confirm this expectation. Molecular metal phosphate complexes have no or few applications. | 0 | Theoretical and Fundamental Chemistry |
The rate of hormone biosynthesis and secretion is often regulated by a homeostatic negative feedback control mechanism. Such a mechanism depends on factors that influence the metabolism and excretion of hormones. Thus, higher hormone concentration alone cannot trigger the negative feedback mechanism. Negative feedback must be triggered by overproduction of an "effect" of the hormone.
Hormone secretion can be stimulated and inhibited by:
* Other hormones (stimulating- or releasing -hormones)
* Plasma concentrations of ions or nutrients, as well as binding globulins
* Neurons and mental activity
* Environmental changes, e.g., of light or temperature
One special group of hormones is the tropic hormones that stimulate the hormone production of other endocrine glands. For example, thyroid-stimulating hormone (TSH) causes growth and increased activity of another endocrine gland, the thyroid, which increases output of thyroid hormones.
To release active hormones quickly into the circulation, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre- or prohormones. These can then be quickly converted into their active hormone form in response to a particular stimulus.
Eicosanoids are considered to act as local hormones. They are considered to be "local" because they possess specific effects on target cells close to their site of formation. They also have a rapid degradation cycle, making sure they do not reach distant sites within the body.
Hormones are also regulated by receptor agonists. Hormones are ligands, which are any kinds of molecules that produce a signal by binding to a receptor site on a protein. Hormone effects can be inhibited, thus regulated, by competing ligands that bind to the same target receptor as the hormone in question. When a competing ligand is bound to the receptor site, the hormone is unable to bind to that site and is unable to elicit a response from the target cell. These competing ligands are called antagonists of the hormone. | 1 | Applied and Interdisciplinary Chemistry |
The field of Cu isotope biogeochemistry is still in a relatively early stage, so the Cu isotope compositions of materials in the environment are not well-documented. However, based on a compilation of measurements already made, it appears that Cu isotope ratios vary somewhat widely within and between environmental materials (e.g., plants, minerals, seawater, etc.), though as a whole, these ratios do not vary by more than ±10‰. | 0 | Theoretical and Fundamental Chemistry |
Constrained geometry complexes are related to ansa-metallocenes except that one ligand is not Cp-related. | 0 | Theoretical and Fundamental Chemistry |
Robert Goulston Gilbert (born 1946) is a polymer chemist whose most significant contributions have been in the field of emulsion polymerisation. In 1970, he gained his PhD from the Australian National University, and worked at the University of Sydney from then until 2006. In 1982, he was elected a fellow of the Royal Australian Chemical Institute; in 1994, he was elected a fellow of the Australian Academy of Science. In 1992, he was appointed full professor, and in 1999 he started the Key Centre for Polymer Colloids, funded by the Australian Research Council, the University and industry. He has served in leadership roles in the International Union of Pure and Applied Chemistry (IUPAC), the world ‘governing body’ of chemistry. He was founding chair (1987–98) of the IUPAC Working Party on the Modelling of Kinetics Processes of Polymerisation, of which he remains a member, and is a member of the IUPAC scientific task groups on starch molecular weight measurements, and terminology. He was vice-president (1996–97) and president (1998–2001) of the IUPAC Macromolecular Division, and secretary of the International Polymer Colloids Group (1997–2001). As of 2007, he is Research Professor at the Centre of Nutrition and Food Science, University of Queensland, where his research program concentrates on the relations between starch structure and nutrition.
His scientific advances have been based on developing novel theoretical and experimental methods to isolate individual processes in very complex systems. By revealing the mechanistic bases of these individual processes through a combination of theory and experiment, he has significantly deepened, and in some cases revolutionised, the understanding of whole systems in small (gas-phase) and giant (polymer) reaction dynamics. | 0 | Theoretical and Fundamental Chemistry |
Similarly to bond angles, the hybridisation of an atom can be related to the lengths of the bonds it forms. As bonding orbitals increase in s character, the σ bond length decreases.
By adding electronegative substituents and changing the hybridisation of the central atoms, bond lengths can be manipulated. If a molecule contains a structure X-A--Y, replacement of the substituent X by a more electronegative atom changes the hybridization of central atom A and shortens the adjacent A--Y bond.
Bonds between elements of disparate electronegativities will be polar and the electron density in such bonds will be shifted towards the more electronegative element. Applying this idea to the molecule fluoromethane illustrates the power of Bent's rule. Because carbon is more electronegative than hydrogen, the electron density in a C-H bond will be shortened and the C-F bond will be elongated.
The same trend also holds for the chlorinated analogs of methane, although the effect is less dramatic because chlorine is less electronegative than fluorine.
The above cases seem to demonstrate that the size of the chlorine is less important than its electronegativity. A prediction based on sterics alone would lead to the opposite trend, as the large chlorine substituents would be more favorable far apart. As the steric explanation contradicts the experimental result, Bent's rule is likely playing a primary role in structure determination. | 0 | Theoretical and Fundamental Chemistry |
Time-of-flight Lorentz force velocimetry, is intended for contactless determination of flow rate in conductive fluids. It can be successfully used even in case when such material properties as electrical conductivity or density are not precisely known under specific outer conditions. The last reason makes time-of-flight LFV especially important for industry application. According to time-of-flight LFV (Fig. 9) two coherent measurement systems are mounted on a channel one by one. The measurement is based on getting of cross-correlating function of signals, which are registered by two magnetic measurement's system. Every system consists of permanent magnet and force sensor, so inducing of Lorentz force and measurement of the reaction force are made simultaneously. Any cross-correlation function is useful only in case of qualitative difference between signals and for creating the difference in this case turbulent fluctuations are used. Before reaching of measurement zone of a channel liquid passes artificial vortex generator that induces strong disturbances in it. And when such fluctuation-vortex reaches magnetic field of measurement system we can observe a peak on its force-time characteristic while second system still measures stable flow. Then according to the time between peaks and the distance between measurement system observer can estimate mean velocity and, hence, flow rate of the liquid by equation:
<div class="center"> <math>
Q_{flow} = k \frac{D}{\tau}
where is the distance between magnet system, the time delay between recorded peaks, and is obtained experimentally for every specific liquid, as shown in figure 9. | 1 | Applied and Interdisciplinary Chemistry |
Dissimilatory nitrate reduction to ammonium (DNRA), or nitrate/nitrite ammonification, is an anaerobic respiration process. Microbes which undertake DNRA oxidise organic matter and use nitrate as an electron acceptor, reducing it to nitrite, then ammonium (). Both denitrifying and nitrate ammonification bacteria will be competing for nitrate in the environment, although DNRA acts to conserve bioavailable nitrogen as soluble ammonium rather than producing dinitrogen gas. | 1 | Applied and Interdisciplinary Chemistry |
The molecule malabaricane and its derivatives, the malabaricanes, are triterpene and triterpenoid compounds found in various organisms. They are named after the rain forest tree Ailanthus malabarica (Ailanthus triphysa), from which they were first isolated in 1967 by scientists at the National Chemical Laboratory in Pune, India. Later, great varieties of malabaricanes were discovered in other organisms, mostly in marine sponges such as Rhabdastrella globostellata.
Isomalabaricanes are malabaricanes in which the three carbon rings of the molecule are connected in trans−syn−trans conformation, as opposed to other malabaricanes, where the rings are connected in trans−anti−trans conformation. They are of particular research interest because many of them have been reported to show anti-tumour activity in cell culture. | 1 | Applied and Interdisciplinary Chemistry |
Under severe stress conditions the bacteria Escherichia coli protects its DNA from damage by sequestering it within a crystalline structure. This process is mediated by the stress response protein Dps and allows the bacteria to survive varied assaults such as oxidative stress, heat shock, ultraviolet light, gamma radiation and extremes of pH. | 1 | Applied and Interdisciplinary Chemistry |
The level sets of the PRA are objective in two dimensions but not in three dimensions. An additional shortcoming of the polar rotation tensor is its dynamical inconsistency: polar rotations computed over adjacent sub-intervals of a total deformation do not sum up to the rotation computed for the full-time interval of the same deformation. Therefore, while is the closest rotation tensor to in the norm over a fixed time interval , these piecewise best fits do not form a family of rigid-body rotations as and are varied. For this reason, rotations predicted by the polar rotation tensor over varying time intervals divert from the experimentally observed mean material rotation of fluid elements.
An alternative to the classic polar decomposition provides a resolution to both the non-objectivity and the dynamic inconsistency issue. Specifically, the Dynamic Polar Decomposition (DPD) of the deformation gradient is also of the form
where the proper orthogonal tensor is the dynamic rotation tensor and the non-singular tensors are the left dynamic stretch tensor and right dynamic stretch tensor, respectively. Just as the classic polar decomposition, the DPD is valid in any finite dimension. Unlike the classic polar decomposition, however, the dynamic rotation and stretch tensors are obtained from solving linear differential equations, rather than from matrix manipulations. In particular, is the deformation gradient of the purely rotational flow
and is the deformation gradient of the purely straining flow
The dynamic rotation tensor can further be factorized into two deformation gradients: one for a spatially uniform (rigid-body) rotation, and one that deviates from this uniform rotation:
As a spatially independent rigid-body rotation, the proper orthogonal relative rotation tensor is dynamically consistent, serving as the deformation gradient of the relative rotation flow
In contrast, the proper orthogonal mean rotation tensor is the deformation gradient of the mean-rotation flow
The dynamic consistency of implies that the total angle swept by around its own axis of rotation is dynamically consistent. This intrinsic rotation angle is also objective, and turns out to equal to one half of the Lagrangian-averaged vorticity deviation (LAVD). The LAVD is defined as the trajectory-averaged magnitude of the deviation of the vorticity from its spatial mean. With the vorticity and its spatial mean
the LAVD over a time interval therefore takes the form
with denoting the (possibly time-varying) domain of definition of the velocity field . This result applies both in two- and three dimensions, and enables the computation of a well-defined, objective and dynamically consistent material rotation angle along any trajectory.
Outermost complex tubular level curves of the LAVD define initial positions of rotationally coherent material vortex boundaries in two-dimensional unsteady flows (see Fig. 11a). By construction, these boundaries may exhibit transverse filamentation, but any developing filament keeps rotating with the boundary, without global transverse departure form the material vortex. (Exceptions are inviscid flows where such a global departure of LAVD level surfaces from a vortex is possible as fluid elements preserve their material rotation rate for all times). Remarkably, centers of rotationally coherent vortices (defined by local maxima of the LAVD field) can be proven to be the observed centers of attraction or repulsion for finite-size (inertial) particle motion in geophysical flows (see Fig. 11b). In three-dimensional flows, tubular level surfaces of the LAVD define initial positions of two-dimensional eddy boundary surfaces (see Fig. 11c) that remain rotationally coherent over a time intcenter|erval (see Fig. 11d). | 1 | Applied and Interdisciplinary Chemistry |
The school was founded in 1929. In 1932, constructivist building was built for the school (architect: A. I. Bobrov). | 1 | Applied and Interdisciplinary Chemistry |
In the case of concrete, curing entails the formation of silicate crosslinks. The process is not induced by additives.
In many cases, the resin is provided as a solution or mixture with a thermally-activated catalyst, which induces crosslinking but only upon heating. For example, some acrylate-based resins are formulated with dibenzoyl peroxide. Upon heating the mixture, the peroxide converts to a free radical, which adds to an acrylate, initiating crosslinking.
Some organic resins are cured with heat. As heat is applied, the viscosity of the resin drops before the onset of crosslinking, whereupon it increases as the constituent oligomers interconnect. This process continues until a tridimensional network of oligomer chains is created – this stage is termed gelation. In terms of processability of the resin this marks an important stage: before gelation the system is relatively mobile, after it the mobility is very limited, the micro-structure of the resin and the composite material is fixed and severe diffusion limitations to further cure are created. Thus, in order to achieve vitrification in the resin, it is usually necessary to increase the process temperature after gelation.
When catalysts are activated by ultraviolet radiation, the process is called UV cure. | 0 | Theoretical and Fundamental Chemistry |
Optical lens design is the process of designing a lens to meet a set of performance requirements and constraints, including cost and manufacturing limitations. Parameters include surface profile types (spherical, aspheric, holographic, diffractive, etc.), as well as radius of curvature, distance to the next surface, material type and optionally tilt and decenter. The process is computationally intensive, using ray tracing or other techniques to model how the lens affects light that passes through it. | 0 | Theoretical and Fundamental Chemistry |
Conventional chain-growth polymerization involves at least two phases; initiation and propagation, while and in some cases termination and chain transfer phases also occur. Chain-growth supramolecular polymerization in a broad sense involves two distinct phases; a less favored nucleation and a favored propagation. In this mechanism, after the formation of a nucleus of a certain size, the association constant is increased, and further monomer addition becomes more favored, at which point the polymer growth is initiated. Long polymer chains will form only above a minimum concentration of monomer and below a certain temperature. However, to realize a covalent analogue of chain-growth supramolecular polymerization, a challenging prerequisite is the design of appropriate monomers that can polymerize only by the action of initiators. Recently one example of chain-growth supramolecular polymerization with "living" characteristics is demonstrated. In this case, a bowl-shaped monomer with amide-appended side chains form a kinetically favored intramolecular hydrogen bonding network and does not spontaneously undergo supramolecular polymerization at ambient temperatures. However, an N-methylated version of the monomer serves as an initiator by opening the intramolecular hydrogen bonding network for the supramolecular polymerization, just like ring-opening covalent polymerization. The chain end in this case remains active for further extension of supramolecular polymer and hence chain-growth mechanism allows for the precise control of supramolecular polymer materials. | 0 | Theoretical and Fundamental Chemistry |
Many diphenylamine derivatives are used as redox indicators that are particularly useful in alkaline redox titrations. The diphenylaminesulfonic acid is a simple prototype redox indicator, owing to its improved aqueous solubility compared with diphenylamine. Attempts have been made to explain the color changes associated with the oxidation of diphenylamine.
In a related application, diphenylamine is oxidized by nitrate to give a similar blue coloration in the diphenylamine test for nitrates. | 0 | Theoretical and Fundamental Chemistry |
The Ycf4 protein domain found on the thylakoid membrane is vital to photosystem I. This thylakoid transmembrane protein helps assemble the components of photosystem I. Without it, photosynthesis would be inefficient. | 0 | Theoretical and Fundamental Chemistry |
Tritium has leaked from 48 of 65 nuclear sites in the US. In one case, leaking water contained of tritium per liter, which is 375 times the current EPA limit for drinking water, and 28 times the World Health Organization's recommended limit. This is equivalent to or roughly 0.8 parts per trillion.
The US Nuclear Regulatory Commission states that in normal operation in 2003, 56 pressurized water reactors released of tritium (maximum: ; minimum: ; average: ) and 24 boiling water reactors released (maximum: ; minimum: 0 Ci; average: ), in liquid effluents. 40,600 Curie of tritium are approximately equivalent to
According to the U.S. Environmental Protection Agency, self-illuminating exit signs improperly disposed in municipal landfills have been found to contaminate waterways. | 0 | Theoretical and Fundamental Chemistry |
The main types of steps in chain reaction are of the following types.
* Initiation (formation of active particles or chain carriers, often free radicals, in either a thermal or a photochemical step)
* Propagation (may comprise several elementary steps in a cycle, where the active particle through reaction forms another active particle which continues the reaction chain by entering the next elementary step). In effect the active particle serves as a catalyst for the overall reaction of the propagation cycle. Particular cases are:
** chain branching (a propagation step where one active particle enters the step and two or more are formed);
** chain transfer (a propagation step in which the active particle is a growing polymer chain which reacts to form an inactive polymer whose growth is terminated and an active small particle (such as a radical), which may then react to form a new polymer chain).
* Termination (elementary step in which the active particle loses its activity; e. g. by recombination of two free radicals).
The chain length is defined as the average number of times the propagation cycle is repeated, and equals the overall reaction rate divided by the initiation rate.
Some chain reactions have complex rate equations with fractional order or mixed order kinetics. | 0 | Theoretical and Fundamental Chemistry |
In the early part of the 20th century, most engineering schools had a department of metallurgy and perhaps of ceramics as well. Much effort was expended on consideration of the austenite - martensite - cementite phases found in the iron - carbon phase diagram that underlies steel production. The fundamental understanding of other materials was not sufficiently advanced for them to be considered as academic subjects. In the post WWII era, the systematic study of polymers advanced particularly rapidly. Rather than create new polymer science departments in engineering schools, administrators and scientists began to conceive of materials science as a new interdisciplinary field in its own right, one that considered all substances of engineering importance from a unified point of view. Northwestern University instituted the first materials science department in 1955.
Richard E. Tressler was an international leader in the development of high temperature materials. He pioneered high temperature fiber testing and use, advanced instrumentation and test methodologies for thermostructural materials, and design and performance verification of ceramics and composites in high temperature aerospace, industrial and energy applications. He was founding director of the Center for Advanced Materials (CAM), which supported many faculty and students from the College of Earth and Mineral Science, the Eberly College of Science, the College of Engineering, the Materials Research Laboratory and the Applied Research Laboratories at Penn State on high temperature materials. His vision for interdisciplinary research played a key role in the creation of the Materials Research Institute. Tressler's contribution to materials science is celebrated with a Penn State lecture named in his honor.
The Materials Research Society (MRS) has been instrumental in creating an identity and cohesion for this young field. MRS was the brainchild of researchers at Penn State University and grew out of discussions initiated by Prof. Rustum Roy in 1970. The first meeting of MRS was held in 1973. As of 2006 , MRS has grown into an international society that sponsors a large number of annual meetings and has over 13,000 members. MRS sponsors meetings that are subdivided into symposia on a large variety of topics as opposed to the more focused meetings typically sponsored by organizations like the American Physical Society or the IEEE. The fundamentally interdisciplinary nature of MRS meetings has had a strong influence on the direction of science, particularly in the popularity of the study of soft materials, which are in the nexus of biology, chemistry, physics and mechanical and electrical engineering. Because of the existence of integrative textbooks, materials research societies and university chairs in all parts of the world, BA, MA and PhD programs and other indicators of discipline formation, it is fair to call materials science (and engineering) a discipline. | 1 | Applied and Interdisciplinary Chemistry |
Bioorganic chemistry is a scientific discipline that combines organic chemistry and biochemistry. It is that branch of life science that deals with the study of biological processes using chemical methods. Protein and enzyme function are examples of these processes.
Sometimes biochemistry is used interchangeably for bioorganic chemistry; the distinction being that bioorganic chemistry is organic chemistry that is focused on the biological aspects. While biochemistry aims at understanding biological processes using chemistry, bioorganic chemistry attempts to expand organic-chemical researches (that is, structures, synthesis, and kinetics) toward biology. When investigating metalloenzymes and cofactors, bioorganic chemistry overlaps bioinorganic chemistry. | 1 | Applied and Interdisciplinary Chemistry |
Coal plies and particles have different relative densities, determined by vitrinite content, rank, ash value/mineral content and porosity. Coal is usually washed by passing it over a bath of liquid of known density. This removes high-ash value particle and increases the saleability of the coal as well as its energy content per unit volume. Thus, coals must be subjected to a float-sink test in the laboratory, which will determine the optimum particle size for washing, the density of the wash liquid required to remove the maximum ash value with the minimum work.
Float-Sink testing is achieved on crushed and pulverised coal in a process similar to metallurgical testing on metallic ore. | 0 | Theoretical and Fundamental Chemistry |
If an electron in a two level atomic system is excited by narrow line width coherent electro-magnetic radiation, like a laser, that is on resonance with the two level transition, the electron will Rabi flop. During Rabi flopping the electron oscillates between the ground and excited states and can be described by a continuous rotation around the Bloch sphere.
For a perfectly isolated system the Rabi oscillation will continue indefinitely and will undergo no phase change, making it a "coherent state". In physical systems interactions between the system and the environment introduce an unknown phase in the Rabi oscillation between the two levels with respect to the Rabi oscillation in the perfectly isolated system causing "decoherence".
If instead of a single two-level system an ensemble of identical two level systems (such as a chain of identical atoms in an ion trap) is prepared and continuously addressed with a laser, all the atoms may begin to simultaneously Rabi flop. At the beginning all two level systems will have a defined relative phase relation (they will all be in phase) and the system will be coherent.
As atoms begin to undergo random spontaneous emission their Rabi oscillations will accumulate a random relative phase with respect to each other and become decoherent. In actual experiments ambient magnetic field noise and thermal heating from collisions between atoms cause decoherence faster than random spontaneous emission and are the dominant uncertainties when running atomic clocks or trapped ion quantum computers. Atomic coherence can also apply to multi-level systems which require more than a single laser.
Atomic coherence is essential in research on several effects, such as electromagnetically induced transparency (EIT), lasing without inversion (LWI), stimulated raman adiabatic passage (STIRAP) and nonlinear optical interaction with enhanced efficiency.
Atomic systems demonstrating continuous superradiance exhibit long coherence time, a property shared with lasers. | 0 | Theoretical and Fundamental Chemistry |
DEHPA is used in the solvent extraction of uranium salts from solutions containing the sulfate, chloride, or perchlorate anions. This extraction is known as the “Dapex procedure” (dialkyl phosphoric extraction). Reminiscent of the behaviours of carboxylic acids, DEHPA generally exists as a hydrogen-bonded dimer in the non-polar organic solvents. For practical applications, the solvent, often called a diluent, is typically kerosene. A complex is formed from two equivalents of the conjugate base of DEHPA and one uranyl ion. Complexes of the formula (UO)[(OP(OR)] also form, and at high concentrations of uranium, polymeric complexes may form.
The extractability of Fe is similar to that of uranium, so it must be reduced to Fe before the extraction. | 0 | Theoretical and Fundamental Chemistry |
Marc Delafontaine (March 31, 1837/1838, Céligny, Switzerland–1911) was a Swiss chemist and spectroscopist who was involved in discovering and investigating some of the rare earth elements. | 1 | Applied and Interdisciplinary Chemistry |
Molecularity in chemistry is the number of colliding molecular entities that are involved in a single reaction step.
* A reaction step involving one molecular entity is called unimolecular.
* A reaction step involving two molecular entities is called bimolecular.
* A reaction step involving three molecular entities is called trimolecular or termolecular.
In general, reaction steps involving more than three molecular entities do not occur, because is statistically improbable in terms of Maxwell distribution to find such a transition state. | 0 | Theoretical and Fundamental Chemistry |
A buoyant sediment-laden river plume can induce a secondary turbidity current on the ocean floor by the process of convective sedimentation. Sediment in the initially buoyant hypopycnal flow accumulates at the base of the surface flow, so that the dense lower boundary become unstable. The resulting convective sedimentation leads to a rapid vertical transfer of material to the sloping lake or ocean bed, potentially forming a secondary turbidity current. The vertical speed of the convective plumes can be much greater than the Stokes settling velocity of an individual particle of sediment. Most examples of this process have been made in the laboratory, but possible observational evidence of a secondary turbidity current was made in Howe Sound, British Columbia, where a turbidity current was periodically observed on the delta of the Squamish River. As the vast majority of sediment laden rivers are less dense than the ocean, rivers cannot readily form plunging hyperpycnal flows. Hence convective sedimentation is an important possible initiation mechanism for turbidity currents. | 1 | Applied and Interdisciplinary Chemistry |
S has been positively correlated with the magnitude of carbon isotope fractionation (represented by ΔC), with larger values of S corresponding with a larger values of ΔC. It has been theorized that because increasing S means the transition state is more like the product, the OC---C-2 bond will be shorter, resulting in a higher overall potential energy & vibrational energy. This creates a higher energy transition state, which makes it even harder for CO (lower in the potential energy well than CO) to overcome the required activation energy. The RuBisCOs used by varying photosynthetic organisms vary slightly in their enzyme structure, and this enzyme structure results in varying transition states. This diversity in enzyme structure is reflected in the resulting ΔC values measured from different photosynthetic organisms. However, overlap exists between the ΔC values of different groups because the carbon isotope values measured are generally of the entire organism, and not just its RuBisCO enzyme. Many other factors, including growth rate and the isotopic composition of the starting substrate, can affect the carbon isotope values of whole organism and cause the spread seen in C isotope measurements. | 0 | Theoretical and Fundamental Chemistry |
Tomlin was a student of mathematics and of the history of science and philosophy of science at the University of Leeds, where she earned a combined bachelors degree in those topics in 1987. She continued at Leeds as a graduate student in physical chemistry, completing her dissertation Bifurcation analysis for non-linear chemical kinetics' in 1990.
After earning her doctorate, and performing post-doctoral research at Leeds and Princeton University, she returned to Leeds as a lecturer in the Department of Fuel and Energy in 1994. | 0 | Theoretical and Fundamental Chemistry |
There are many fish oil dietary supplements on the market. Evidence suggests that marine based omega-3 dietary supplements are able to reduce cardiovascular disease, and premature death. These effects may not carry over in other populations such as people who have diabetes. The ingredients of dietary supplements are not as carefully controlled as prescription products and have not been fixed and tested in clinical trials, as prescription drugs have, and the prescription forms are more concentrated, requiring fewer capsules to be taken and increasing the likelihood of compliance. | 1 | Applied and Interdisciplinary Chemistry |
Isotropic formulations are thermodynamically stable microemulsions possessing lyotropic liquid crystal properties. They inhabit a state of matter and physical behaviour somewhere between conventional liquids and that of solid crystals. Isotropic formulations are amphiphillic, exhibiting selective synchronicity with both the water and lipid phases of the substrate to which they are applied. Most recently, isotropic formulations have been used extensively in dermatology for drug delivery. | 0 | Theoretical and Fundamental Chemistry |
For the bacteria to use quorum sensing constitutively, they must possess three abilities: secretion of a signaling molecule, secretion of an autoinducer (to detect the change in concentration of signaling molecules), and regulation of gene transcription as a response. This process is highly dependent on the diffusion mechanism of the signaling molecules. QS signaling molecules are usually secreted at a low level by individual bacteria. At low cell density, the molecules may just diffuse away. At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expression. | 1 | Applied and Interdisciplinary Chemistry |
There are also electrostatic confinement fusion devices. These devices confine ions using electrostatic fields. The best known is the fusor. This device has a cathode inside an anode wire cage. Positive ions fly towards the negative inner cage, and are heated by the electric field in the process. If they miss the inner cage they can collide and fuse. Ions typically hit the cathode, however, creating prohibitory high conduction losses. Also, fusion rates in fusors are very low due to competing physical effects, such as energy loss in the form of light radiation. Designs have been proposed to avoid the problems associated with the cage, by generating the field using a non-neutral cloud. These include a plasma oscillating device, a Penning trap and the polywell. The technology is relatively immature, however, and many scientific and engineering questions remain.
The most well known Inertial electrostatic confinement approach is the fusor. Starting in 1999, a number of amateurs have been able to do amateur fusion using these homemade devices. Other IEC devices include: the Polywell, MIX POPS and Marble concepts. | 0 | Theoretical and Fundamental Chemistry |
* PEX1
* PEX2
* PEX3
* PEX5
* PEX6
* PEX7
* PEX10
* PEX11A, PEX11B, PEX11G
* PEX12
* PEX13
* PEX14
* PEX16
* PEX19
* PEX26 | 1 | Applied and Interdisciplinary Chemistry |
Agglomerins are bacterial natural products, identified as metabolites of Pantoea agglomerans which was isolated in 1989 from river water in Kobe, Japan. They belong to the class of tetronate antibiotics, which include tetronomycin, tetronasin, and abyssomicin C. The members of the agglomerins differ only in the composition of the acyl chain attached to the tetronate ring. They possess antibiotic activity against anaerobic bacteria and weak activity against aerobic bacteria in vitro. The structures were solved in 1990. Agglomerin A is the major component (38%), followed by agglomerin B (30%), agglomerin C (24%), and agglomerin D (8%). | 1 | Applied and Interdisciplinary Chemistry |
Pullulan bioconjugate systems can be formed to respond to many different stimuli to enhance the release of the drug to the target tissue. These stimuli include pH, temperature, photothermal, electrical, ultrasonic, magnetic, and enzymatic. The pH is often used to target tumor tissues, as the extracellular pH of tumors is more acidic than the normal cells.
A pullulan and polydopamine hydrogel loaded with crystal violet demonstrated pH responsive behavior due to the protonation of the polydopamine, which increased the release of the crystal violet in the acidic environment. The study showed that at a pH of a normal cell's extracellular environment, 7.4, about 60% of the crystal violet was released compared to the 87% release when in a pH of 5.0. The use of pH responsive systems for the treatment of cancer may aid in the ability to overcome resistance of the drug as well as prevent excess damage to healthy tissue.
Another pH responsive pullulan system was formed with pullulan and doxorubicin where the doxorubicin is attached to the pullulan by hydrazone bonds. The drug release of the doxorubicin was tested at two pHs, 7.4 and 5, where the hydrazine is stable at 7.4 and cleaves in acidic environments. The results from this study supported the results from the pullulan and polydopamine study, as doxorubicin was released faster in the acidic environment than the pH that reflected a normal cell's extracellular environment.
Temperature can also be used as a trigger to control the drug release from pullulan systems. Thermal responsive pullulan systems can be used in conjunction with thermal generating treatments for cancer in order to improve the treatment. Nanoparticles composed of periodate oxidized carboxymethyl pullulan crosslinked with two Jeffamines were synthesized and demonstrated that the nanoparticle size could be decreased with increased temperature. The nanoparticles decrease in size with increasing temperature due to the increased temperature promoting the hydrophobic interactions of the structure. Altering the temperature can induce heating or cooling dynamics that are reversible, which allows for unique properties in terms of drug release. Pullulan can be altered with photosensitizers in order to provide a controlled thermal reaction in a target area. Spiropyrane can be added to pullulan in order to act as a photosensitizer.
Electrical stimuli can be used to alter the delivery of drugs through pullulan constructs. A copolymer polyacrylamide-graft-pullulan was synthesized and used for transdermal delivery of rivastigmine tartarate. In this study, the use of electric stimuli demonstrated the ability to increase the diffusion rate and in a way acted as a controllable switch to control diffusion rate. Pullulan systems can be used to enhance ultrasound imaging, as pullulan-graft-poly(carboxybetaine methacrylate) demonstrated the ability to generate carbon dioxide in response to ultrasound, which enhanced the contrast. Superparamagnetic iron oxide nanoparticles (SPIONs) have been generated which have magnetic properties, which showed to improve uptake and also decrease the cytotoxicity. Enzymes can also be used to trigger drug release mechanisms, such as how esterase has been used to cleave photosensitizers from pullulan in order to increase the photodynamic reaction.
As demonstrated in the last example, these stimuli response mechanisms do not have to be independent. They can be used in combinations in order to improve the efficacy of the drug delivery. | 1 | Applied and Interdisciplinary Chemistry |
First-row metal complexes tend to undergo reductive elimination faster than second-row metal complexes, which tend to be faster than third-row metal complexes. This is due to bond strength, with metal-ligand bonds in first-row complexes being weaker than metal-ligand bonds in third-row complexes. Additionally, electron-poor metal centers undergo reductive elimination faster than electron-rich metal centers since the resulting metal would gain electron density upon reductive elimination. | 0 | Theoretical and Fundamental Chemistry |
GAI or Gibberellic-Acid Insensitive is a gene in Arabidopsis thaliana which is involved in regulation of plant growth. GAI represses the pathway of gibberellin-sensitive plant growth. It does this by way of its conserved DELLA motif. | 1 | Applied and Interdisciplinary Chemistry |
In order to maintain the solution electroneutrality inside the pit populated by cations released by oxidation in the anodic zone (e.g., in case of steel), anions need to migrate inside the narrow pit. It is worth to notice that the electromobilities of thiosulfate () and chloride () anions are the highest after these of and ions in aqueous solution. Moreover, the molar conductivity of thiosulfate ions is even higher than that of chloride ions because they are twice negatively charged (weak base reluctant to accept a proton). In capillary electrophoresis, thiosulfate moves faster than chloride and eluates before this latter. The high electromobility of both anions could also be one of the many factors explaining their harmful impact for pitting corrosion when compared with other much less damaging ion species such as and . | 1 | Applied and Interdisciplinary Chemistry |
In fluid mechanics (specifically rheology), rheoscopic fluids are fluids whose internal currents are visible as it flows. Such fluids are effective in visualizing dynamic currents, such as convection and laminar flow. They are microscopic crystalline platelets such as mica, metallic flakes, or fish scales in suspension in a fluid such as water or glycol stearate.
When the fluid is put in motion, the suspended particles orient themselves in localized, preferential alignment, larger parts of the fluid moving sheer parallel to other parts of the fluid. With appropriate illumination, the particle-filled fluid will reflect differing intensities of light.
A Kalliroscope is an art device/technique based on rheoscopic fluids (using crystalline guanine as the indicator particles) invented by artist Paul Matisse. | 1 | Applied and Interdisciplinary Chemistry |
The saprobic index is only regarded as a valid estimate if the sum of the abundance classes is at least 20. For example, if a survey only found a total of 500 individuals of any species, the sample would still be valid if the survey found four species with 125 individuals each (abundance class 5).
Likewise, a single water body has to be surveyed several times in different months in order to account for fluctuations.
During its history, several correcting factors have been introduced. For example, they deal with the flow rate of the river (fast-flowing water bodies are inherently better oxygenated, thus speeding up organic matter degradation), water acidification, and human-made changes to the water body. Likewise, corrections must be applied for the altitude of the ecosystem (lowland rivers naturally carry more organic matter than mountainous ones, where biomass production is lower), and for the different size of catchment areas.
The saprobic system was never designed to accurately indicate water quality if only a selection of organisms is surveyed. Deviations can be sizeable if a survey only studies ciliates and members of the macrozoobenthos (benthos animals larger than 1 millimeter), as the latter's abundance can be easily influenced by oxygen levels and not by the availability of organic matter. | 1 | Applied and Interdisciplinary Chemistry |
An atom interferometer creates coherent atomic beams, where the coherence is with respect to the phase of the atom's de Broglie wave. | 0 | Theoretical and Fundamental Chemistry |
Acid chlorides can be used as a chloride source. Thus acetyl chloride can be distilled from a mixture of benzoyl chloride and acetic acid:
Other methods that do not form HCl include the Appel reaction:
Another is the use of cyanuric chloride: | 0 | Theoretical and Fundamental Chemistry |
As for pure liquids, the viscosity of a blend of liquids is difficult to predict from molecular principles. One method is to extend the molecular "cage" theory presented above for a pure liquid. This can be done with varying levels of sophistication. One expression resulting from such an analysis is the Lederer–Roegiers equation for a binary mixture:
where is an empirical parameter, and and are the respective mole fractions and viscosities of the component liquids.
Since blending is an important process in the lubricating and oil industries, a variety of empirical and propriety equations exist for predicting the viscosity of a blend. | 1 | Applied and Interdisciplinary Chemistry |
Charge referencing is needed when a sample suffers a charge induced shift of experimental binding energies to obtain meaningful binding energies from both wide-scan, high sensitivity (low energy resolution) survey spectra (0-1100 eV), and also narrow-scan, chemical state (high energy resolution) spectra. Charge induced shifting is normally due to a modest excess of low voltage (-1 to -20 eV) electrons attached to the surface, or a modest shortage of electrons (+1 to +15 eV) within the top 1-12 nm of the sample caused by the loss of photo-emitted electrons. If, by chance, the charging of the surface is excessively positive, then the spectrum might appear as a series of rolling hills, not sharp peaks as shown in the example spectrum.
Charge referencing is performed by adding a Charge Correction Factor to each of the experimentally measured peaks. Since various hydrocarbon species appear on all air-exposed surfaces, the binding energy of the hydrocarbon C (1s) XPS peak is used to charge correct all energies obtained from non-conductive samples or conductors that have been deliberately insulated from the sample mount. The peak is normally found between 284.5 eV and 285.5 eV. The 284.8 eV binding energy is routinely used as the reference binding energy for charge referencing insulators, so that the charge correction factor is the difference between 284.8 eV and the experimentally measured C (1s) peak position.
Conductive materials and most native oxides of conductors should never need charge referencing. Conductive materials should never be charge referenced unless the topmost layer of the sample has a thick non-conductive film. The charging effect, if needed, can also be compensated by providing suitable low energy charges to the surface by the use of low-voltage (1-20 eV) electron beam from an electron flood gun, UV lights, low-voltage argon ion beam with low-voltage electron beam (1-10 eV), aperture masks, mesh screen with low-voltage electron beams, etc. | 0 | Theoretical and Fundamental Chemistry |
Leakage current increases significantly in bipolar transistors (especially germanium-based bipolar transistors) as they increase in temperature. Depending on the design of the circuit, this increase in leakage current can increase the current flowing through a transistor and thus the power dissipation, causing a further increase in collector-to-emitter leakage current. This is frequently seen in a push–pull stage of a class AB amplifier. If the pull-up and pull-down transistors are biased to have minimal crossover distortion at room temperature, and the biasing is not temperature-compensated, then as the temperature rises both transistors will be increasingly biased on, causing current and power to further increase, and eventually destroying one or both devices.
One rule of thumb to avoid thermal runaway is to keep the operating point of a BJT so that V ≤ 1/2V
Another practice is to mount a thermal feedback sensing transistor or other device on the heat sink, to control the crossover bias voltage. As the output transistors heat up, so does the thermal feedback transistor. This in turn causes the thermal feedback transistor to turn on at a slightly lower voltage, reducing the crossover bias voltage, and so reducing the heat dissipated by the output transistors.
If multiple BJT transistors are connected in parallel (which is typical in high current applications), a current hogging problem can occur. Special measures must be taken to control this characteristic vulnerability of BJTs.
In power transistors (which effectively consist of many small transistors in parallel), current hogging can occur between different parts of the transistor itself, with one part of the transistor becoming more hot than the others. This is called second breakdown, and can result in destruction of the transistor even when the average junction temperature seems to be at a safe level. | 1 | Applied and Interdisciplinary Chemistry |
Tang was educated at Northeastern University (China), where he received his BSc degree in chemistry in 1995. Then he attended the Institute of Metal Research in China and was awarded a MSc degree in inorganic materials in 1998. In 2001, Tang was awarded a PhD in physical chemistry with research on heterogeneous catalytic conversion of NO to N, supervised by Tao Zhang at Dalian Institute of Chemical Physics (DICP), China | 0 | Theoretical and Fundamental Chemistry |
The G-less cassette is a reporter gene that encodes a transcript lacking guanine nucleotides in the sense strand of the DNA (hence "G-less"). A plasmid containing such a gene is located downstream of a MCS. After the promoter is inserted into the MCS, transcription proceeds with the addition of radiolabeled UTP, CTP, and ATP (as well as non-radiolabeled/cold nucleotides) and continues until the end of the G-less cassette is reached and guanine residues are once again apparent in the sense strand of the DNA. The absence of GTP in vitro results in transcription being prematurely terminated at the first guanine residue in the sense strand following the cassette. Gel electrophoresis is performed on the transcription products and the amount of radioactivity is quantified by autoradiography or phosphorimaging to determine the strength of the promoter of interest. | 1 | Applied and Interdisciplinary Chemistry |
Pregnant leach solution or pregnant liquor solution (PLS) is acidic metal-laden water generated from stockpile leaching and heap leaching. Pregnant leach solution is used in the solvent extraction and electrowinning (SX/EW) process.
The portion of an original liquid that remains after other components have been dissolved by a solvent is called raffinate. | 1 | Applied and Interdisciplinary Chemistry |
P. rubens is the principal source of a class of antibiotics, penicillins. The species produces three such compounds, benzylpenicillin (G), phenoxymethylpenicillin (V) and octanoylpenicillin (K). Penicillin G is the first naturally occurring compound isolated and used as an antibiotic. It is also the source of cephalosporins. | 1 | Applied and Interdisciplinary Chemistry |
The viral epitranscriptome includes all modifications to viral transcripts, studied by viral epitranscriptomics. Like the more general epitranscriptome, these modifications do not affect the sequence of the transcript, but rather have consequences on subsequent structures and functions. | 1 | Applied and Interdisciplinary Chemistry |
Sustained load cracking, or SLC, is a metallurgical phenomenon that occasionally develops in pressure vessels and structural components under stress for sustained periods of time.
It is particularly noted in aluminium pressure vessels such as diving cylinders.
Sustained load cracking is not a manufacturing defect; it is a phenomenon associated with certain alloys and service conditions:
*6351 aluminum alloy
*Overstressing due to excessive filling pressure
*Abuse and mechanical damage | 1 | Applied and Interdisciplinary Chemistry |
Type K (chromel–alumel) is the most common general-purpose thermocouple with a sensitivity of approximately 41 μV/°C. It is inexpensive, and a wide variety of probes are available in its −200 °C to +1350 °C (−330 °F to +2460 °F) range. Type K was specified at a time when metallurgy was less advanced than it is today, and consequently characteristics may vary considerably between samples. One of the constituent metals, nickel, is magnetic; a characteristic of thermocouples made with magnetic material is that they undergo a deviation in output when the material reaches its Curie point, which occurs for type K thermocouples at around 185 °C.
They operate very well in oxidizing atmospheres. If, however, a mostly reducing atmosphere (such as hydrogen with a small amount of oxygen) comes into contact with the wires, the chromium in the chromel alloy oxidizes. This reduces the emf output, and the thermocouple reads low. This phenomenon is known as green rot, due to the color of the affected alloy. Although not always distinctively green, the chromel wire will develop a mottled silvery skin and become magnetic. An easy way to check for this problem is to see whether the two wires are magnetic (normally, chromel is non-magnetic).
Hydrogen in the atmosphere is the usual cause of green rot. At high temperatures, it can diffuse through solid metals or an intact metal thermowell. Even a sheath of magnesium oxide insulating the thermocouple will not keep the hydrogen out.
Green rot does not occur in atmospheres sufficiently rich in oxygen, or oxygen-free. A sealed thermowell can be filled with inert gas, or an oxygen scavenger (e.g. a sacrificial titanium wire) can be added. Alternatively, additional oxygen can be introduced into the thermowell. Another option is using a different thermocouple type for the low-oxygen atmospheres where green rot can occur; a type N thermocouple is a suitable alternative. | 1 | Applied and Interdisciplinary Chemistry |
Double ionization is a process of formation of doubly charged ions when laser radiation is exerted on neutral atoms or molecules. Double ionization is usually less probable than single-electron ionization. Two types of double ionization are distinguished: sequential and non-sequential. | 0 | Theoretical and Fundamental Chemistry |
There has been a growing interest in the application of IC in the analysis of pharmaceutical drugs. IC is used in different aspects of product development and quality control testing. For example, IC is used to improve stabilities and solubility properties of pharmaceutical active drugs molecules as well as used to detect systems that have higher tolerance for organic solvents. IC has been used for the determination of analytes as a part of a dissolution test. For instance, calcium dissolution tests have shown that other ions present in the medium can be well resolved among themselves and also from the calcium ion. Therefore, IC has been employed in drugs in the form of tablets and capsules in order to determine the amount of drug dissolve with time. IC is also widely used for detection and quantification of excipients or inactive ingredients used in pharmaceutical formulations. Detection of sugar and sugar alcohol in such formulations through IC has been done due to these polar groups getting resolved in ion column. IC methodology also established in analysis of impurities in drug substances and products. Impurities or any components that are not part of the drug chemical entity are evaluated and they give insights about the maximum and minimum amounts of drug that should be administered in a patient per day. | 0 | Theoretical and Fundamental Chemistry |
(a) Capturing of the magnetic beads.<br>
During this suction process,
when the magnetic field are applied to the separation region of piper tip, from outside of pipette tip, by the magnet arranged on the outside of the pipette tip,
as liquid containing magnetic beads passes through a separation region of the pipette tip,
the magnetic particles are attracted to and arrested to the inner wall of tile separation region of pipette tip.
Subsequently, when that solution are discharged under the conditions of has been kept the magnetic field,
magnetic particles only are left in the inside of pipette tip.
In this way magnetic particles are separated from liquid.
In accordance with Tajima,
the preferable suction height of the mixture liquid is such that
:the bottom level of the liquid is higher than the lower end of the separation region of the liquid passage (That means bottom level of the liquid is higher than the lower end of the magnet.),
::when all the mixture liquid is drawn up,
::so as to ensure that the aspirated magnetic particles can be completely arrested.
At this time, because the magnetic particles are wet, they stay attached to the inner surface of the
separation region of the liquid passage of the pipette tip. If the pipette tip P is moved or
transported, the magnetic particles will not come off easily.
(b) Re-suspension of the captured magnetic beads.<br>
After the magnetic particles are arrested by above mentioned manner (a),
::so the mixture liquid removed of the magnetic particles is discharged into the liquid accommodating portion (Vessel) and drained out, with only the magnetic particles remaining in the pipette tip,
we can do the re-suspension process.
Re-suspension of the captured magnetic beads are in detail, consists of the following steps.
Of cause, we consider that, the state in which that magnetic material has been captured
by above mention way.
*Aspirate liquid such as washing buffer into the tip
*Quit the application of a magnetic field
::By "Quit the application of a magnetic field" the magnetic particles are suspended in the liquid.
*Discharging the liquid (such as washing buffer) from pipette tip to vessel (in the condition of magnetic force generated by the magnet body is cut off.). | 1 | Applied and Interdisciplinary Chemistry |
Snail shell is an aragonite-protein composite, with a hierarchical groove structure. The regular roughness of the structure creates a hydrophilic structure, a thin layer of water trapped on the surface, that doesn’t allow oil to attach to the snail shell, thereby keeping the shell clean. These surface properties of snail shell have inspired the use of similar surface patterns on ceramic tiles and ceramic structures by the INAX corporation, which applies these techniques to kitchens and bathrooms. | 0 | Theoretical and Fundamental Chemistry |
()() had the highest quantum yield in visible light for visible light-based photocatalysts that do not utilize sacrificial reagents as of October 2008. The photocatalyst featured a quantum yield of 5.9% and a water splitting rate of 0.4 mmol/h. Tuning the catalyst was done by increasing calcination temperatures for the final step in synthesizing the catalyst. Temperatures up to 600 °C helped to reduce the number of defects, while temperatures above 700 °C destroyed the local structure around zinc atoms and were thus undesirable. The treatment ultimately reduced the amount of surface Zn and O defects, which normally function as recombination sites, thus limiting photocatalytic activity. The catalyst was then loaded with at a rate of 2.5 wt% Rh and 2 wt% Cr for better performance. | 0 | Theoretical and Fundamental Chemistry |
It is indicated for intraocular pressure reduction in patients with open-angle glaucoma or ocular hypertension. | 0 | Theoretical and Fundamental Chemistry |
ATP can also be synthesized through several so-called "replenishment" reactions catalyzed by the enzyme families of nucleoside diphosphate kinases (NDKs), which use other nucleoside triphosphates as a high-energy phosphate donor, and the ATP:guanido-phosphotransferase family. | 1 | Applied and Interdisciplinary Chemistry |
Levorphanol acts predominantly as an agonist of the μ-opioid receptor (MOR), but is also an agonist of the δ-opioid receptor (DOR), κ-opioid receptor (KOR), and the nociceptin receptor (NOP), as well as an NMDA receptor antagonist and a serotonin-norepinephrine reuptake inhibitor (SNRI). Levorphanol, similarly to certain other opioids, also acts as a glycine receptor antagonist and GABA receptor antagonist at very high concentrations. As per the World Health Organization, levorphanol is a step 3 opioid and is considered eight times more potent than morphine at the MOR (2 mg levorphanol is equivalent to 15 mg morphine).
Relative to morphine, levorphanol lacks complete cross-tolerance and possesses greater intrinsic activity at the MOR. The duration of action is generally long compared to other comparable analgesics and varies from 4 hours to as much as 15 hours. For this reason levorphanol is useful in palliation of chronic pain and similar conditions. Levorphanol has an oral to parenteral effectiveness ratio of 2:1, one of the most favorable of the strong narcotics. Its antagonism of the NMDA receptor, similar to those of the phenylheptylamine open-chain opioids such as methadone or the phenylpiperidine ketobemidone, make levorphanol useful for types of pain that other analgesics may not be as effective against, such as neuropathic pain. Levorphanol's exceptionally high analgesic efficacy in the treatment of neuropathic pain is also conferred by its action on serotonin and norepinephrine transporters, similar to the opioids tramadol and tapentadol, and mutually complements the analgesic effect of its NMDA receptor antagonism.
Levorphanol shows a high rate of psychotomimetic side effects such as hallucinations and delirium, which have been attributed to its binding to and activation of the KOR. At the same time however, activation of this receptor as well as of the DOR have been determined to contribute to its analgesic effects. | 0 | Theoretical and Fundamental Chemistry |
The effective fragment potential (EFP) method is a computational approach designed to describe intermolecular interactions and environmental effects. It is a computationally inexpensive means to describe interactions in non-bonded systems. It was originally formulated to describe the solvent effects in complex chemical systems. But it has undergone vast improvements in the past two decades, and is currently used to represent intermolecular interactions (represented as rigid fragments), and in molecular dynamics (MD) simulations as well. | 0 | Theoretical and Fundamental Chemistry |
To illustrate how choices of coordinate systems for calculations of chemical bonds can immensely affect the results and consequently engender ill-defined descriptors of the bonds, sample calculations for n-butane and cyclobutane are shown in this section. Note that it is known that the all the four equivalent C-C bonds in cyclobutane are weaker than any of the two distinct C-C bonds in n-butane; therefore, juxtaposition and evaluation of the strength of the C-C bonds in this C4 system can exemplify how force constants fail and how compliance constants do not. The tables immediately below are results that are calculated at MP2/aug-cc-pvtz level of theory based on typical force constants calculation.
Tables 1 and 2 display a force constant in N/cm between each pair of carbon atoms (diagonal) as well as the coupling (off-diagonal). Considering natural internal coordinates on the left, the results make chemical sense. Firstly, the C-C bonds are n-butane are generally stronger than those in cyclobutane, which is in line with what is expected. Secondly, the C-C bonds in cyclobutane are equivalent with the force constant values of 4.173 N/cm. Lastly, there is little coupling between the force constants as seen as the small compliance coupling constants in the off-diagonal terms.
However, when z-matrix coordinates are used, the results are different from those obtained from natural internal coordinates and become erroneous. The four C-C bonds all have distinct values in cyclobutane, and the coupling becomes much more pronounced. Significantly, the force constants of the C-C bonds in cyclobutane here are also larger than those of n-butane, which is in conflict with chemical intuition. Clearly for cyclobutane—and numerous other molecules, using force constants therefore gives rise to inaccurate bond descriptors due to its dependence on coordinate systems. | 0 | Theoretical and Fundamental Chemistry |
Defective function of the survival of motor neuron (SMN) protein in snRNP biogenesis, caused by a genetic defect in the SMN1 gene which codes for SMN, may account for the motor neuron pathology observed in the genetic disorder spinal muscular atrophy. | 1 | Applied and Interdisciplinary Chemistry |
The surface tension (γ) of a material is directly related to its intramolecular and intermolecular forces. The stronger the force, the greater the surface tension. This can be modeled by an equation:
Where ΔU is the energy of vaporization, N is the Avogadro constant, and a is the surface area per molecule. This equation also implies that the energy of vaporization affects surface tension. It is known that the stronger the force, the higher the energy of vaporization. Surface tension can then be used to calculate surface energy (u). An equation describing this property is:
Where T is temperature and the system is at constant pressure and area. Specifically for hydrogels, the free surface energy can be predicted using the Flory–Huggins free energy function for the hydrogels.
For hydrogels, surface tension plays a role in several additional characteristics including swelling ratio and stabilization. | 0 | Theoretical and Fundamental Chemistry |
There are numerous applications for quantitative polymerase chain reaction in the laboratory. It is commonly used for both diagnostic and basic research. Uses of the technique in industry include the quantification of microbial load in foods or on vegetable matter, the detection of GMOs (genetically modified organisms) and the quantification and genotyping of human viral pathogens. | 1 | Applied and Interdisciplinary Chemistry |
The typical composition of commercial HTS catalyst has been reported as 74.2% FeO, 10.0% CrO, 0.2% MgO (remaining percentage attributed to volatile components). The chromium acts to stabilize the iron oxide and prevents sintering. The operation of HTS catalysts occurs within the temperature range of 310 °C to 450 °C. The temperature increases along the length of the reactor due to the exothermic nature of the reaction. As such, the inlet temperature is maintained at 350 °C to prevent the exit temperature from exceeding 550 °C. Industrial reactors operate at a range from atmospheric pressure to 8375 kPa (82.7 atm). The search for high performance HT WGS catalysts remains an intensive topic of research in fields of chemistry and materials science. Activation energy is a key criteria for the assessment of catalytic performance in WGS reactions. To date, some of the lowest activation energy values have been found for catalysts consisting of copper nanoparticles on ceria support materials, with values as low as Ea = 34 kJ/mol reported relative to hydrogen generation. | 0 | Theoretical and Fundamental Chemistry |
The repair of the MAT locus after cutting by the HO endonuclease almost always results in a mating type switch. When an a cell cuts the MATa allele present at the MAT locus, the cut at MAT will almost always be repaired by copying the information present at HML. This results in MAT being repaired to the MATα allele, switching the mating type of the cell from a to α. Similarly, an α cell which has its MATα allele cut by the HO endonuclease will almost always repair the damage using the information present at HMR, copying the MATa gene to the MAT locus and switching the mating type of α cell to a.
This is the result of the action of a recombination enhancer (RE) located on the left arm of chromosome III. Deletion of this region causes a cells to incorrectly repair using HMR. In a cells, Mcm1 binds to the RE and promotes recombination of the HML region. In α cells, the α2 factor binds at the RE and establishes a repressive domain over RE such that recombination is unlikely to occur. An innate bias means that the default behaviour is repair from HMR. The exact mechanisms of these interactions are still under investigation. | 1 | Applied and Interdisciplinary Chemistry |
The history of thermodynamics as a scientific discipline generally begins with Otto von Guericke who, in 1650, built and designed the worlds first vacuum pump and demonstrated a vacuum using his Magdeburg hemispheres. Guericke was driven to make a vacuum in order to disprove Aristotles long-held supposition that nature abhors a vacuum. Shortly after Guericke, the Anglo-Irish physicist and chemist Robert Boyle had learned of Guerickes designs and, in 1656, in coordination with English scientist Robert Hooke, built an air pump. Using this pump, Boyle and Hooke noticed a correlation between pressure, temperature, and volume. In time, Boyles Law was formulated, which states that pressure and volume are inversely proportional. Then, in 1679, based on these concepts, an associate of Boyle's named Denis Papin built a steam digester, which was a closed vessel with a tightly fitting lid that confined steam until a high pressure was generated.
Later designs implemented a steam release valve that kept the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and a cylinder engine. He did not, however, follow through with his design. Nevertheless, in 1697, based on Papin's designs, engineer Thomas Savery built the first engine, followed by Thomas Newcomen in 1712. Although these early engines were crude and inefficient, they attracted the attention of the leading scientists of the time.
The fundamental concepts of heat capacity and latent heat, which were necessary for the development of thermodynamics, were developed by Professor Joseph Black at the University of Glasgow, where James Watt was employed as an instrument maker. Black and Watt performed experiments together, but it was Watt who conceived the idea of the external condenser which resulted in a large increase in steam engine efficiency. Drawing on all the previous work led Sadi Carnot, the "father of thermodynamics", to publish Reflections on the Motive Power of Fire (1824), a discourse on heat, power, energy and engine efficiency. The book outlined the basic energetic relations between the Carnot engine, the Carnot cycle, and motive power. It marked the start of thermodynamics as a modern science.
The first thermodynamic textbook was written in 1859 by William Rankine, originally trained as a physicist and a civil and mechanical engineering professor at the University of Glasgow. The first and second laws of thermodynamics emerged simultaneously in the 1850s, primarily out of the works of William Rankine, Rudolf Clausius, and William Thomson (Lord Kelvin).
The foundations of statistical thermodynamics were set out by physicists such as James Clerk Maxwell, Ludwig Boltzmann, Max Planck, Rudolf Clausius and J. Willard Gibbs.
Clausius, who first stated the basic ideas of the second law in his paper "On the Moving Force of Heat", published in 1850, and is called "one of the founding fathers of thermodynamics", introduced the concept of entropy in 1865.
During the years 1873–76 the American mathematical physicist Josiah Willard Gibbs published a series of three papers, the most famous being On the Equilibrium of Heterogeneous Substances, in which he showed how thermodynamic processes, including chemical reactions, could be graphically analyzed, by studying the energy, entropy, volume, temperature and pressure of the thermodynamic system in such a manner, one can determine if a process would occur spontaneously. Also Pierre Duhem in the 19th century wrote about chemical thermodynamics. During the early 20th century, chemists such as Gilbert N. Lewis, Merle Randall, and E. A. Guggenheim applied the mathematical methods of Gibbs to the analysis of chemical processes. | 0 | Theoretical and Fundamental Chemistry |
Source:
Fixed air, or fixible air, is an ancient term for carbon dioxide
Joseph Priestley credited Joseph Black for discovering and coining "fixed air", which was thought to exist in a fixed state in alkaline salts, chalk, and other calcareous substances. Black considered substances containing fixed air to be "mild", and upon expulsion of the gas by heating the resulting state is "caustic" by corroding or burning plants and animals (e.g. released by chalk upon decomposition to calcium oxide). In other words, the fixed air (also known as fixible air) was thought to be fixated within a corrosive molecule.
Priestley likewise credited the discovery of fixed air to contributions from several scientists including: David Macbride, John Pringle, William Brownrigg (regarded carbonated water to have an acidulous taste), Stephen Hales, and many others.
Henry Cavendish provided a definition: "By fixed air, I mean that particular species of factitious air, which is separated from alkaline substances by solution in acids or by calcination". Cavendish essentially defined potassium oxide or calcium oxide as a base, which can contain a fixated air within its composition, setting the stage for the historical definition of carbonate. | 1 | Applied and Interdisciplinary Chemistry |
During transcription, RNA polymerase unwinds a short section of the DNA double helix near the start of the gene (the transcription start site). This unwound section is known as the transcription bubble. The RNA polymerase, and with it the transcription bubble, travels along the noncoding strand in the opposite, 3 to 5, direction, as well as polymerizing a newly synthesized strand in 5 to 3 or downstream direction. The DNA double helix is rewound by RNA polymerase at the rear of the transcription bubble. Like how two adjacent zippers work, when pulled together, they unzip and rezip as they proceed in a particular direction. Various factors can cause double-stranded DNA to break; thus, reorder genes or cause cell death. | 1 | Applied and Interdisciplinary Chemistry |
Among his awards are the Boris Pregel Award for Research in Chemical Physics (New York Academy of Sciences) in 1971 and election in 1981 as a Fellow of the American Association for the Advancement of Science for "pioneering work in transition metal organometallic chemistry and synthetic oxygen carriers". | 0 | Theoretical and Fundamental Chemistry |
In medicine, the term "labile" means susceptible to alteration or destruction. For example, a heat-labile protein is one that can be changed or destroyed at high temperatures.
The opposite of labile in this context is "stable". | 1 | Applied and Interdisciplinary Chemistry |
As Reynolds number increases ( becomes larger), the flow tends to become uniform(thus approaching potential flow solution), except for boundary layers near the walls. Since is large and is given, it is clear from the solution that must be large, therefore . But when , , the solution becomes
It is clear that everywhere except in the boundary layer of thickness . The volume flux is so that and the boundary layers have classical thickness . | 1 | Applied and Interdisciplinary Chemistry |
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