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Concurrent tandem catalysis Lactones are good synthetic starting points for many natural products and are prevalent structures in biology therefore they are widely utilized in pharmaceuticals. One of the most studied and commercially important transition metal catalyzed reactions is alkene hydroformylation. This type of catalysis allows for the functionalization of simple alkenes into aldehydes and gives a remarkably useful handle to generate other functional groups. This transformation can be carried out using a cobalt or rhodium catalyst in a hydrogen/carbon monoxide atmosphere and consists of four stages: metal insertion, migratory insertion, heterolytic cleavage, and ligand exchange. Breit et al. generated extended alkane functionality by hydroformylation, olefination, and then hydrogenation. Orthogonal tandem catalysis is a "one-pot reaction in which sequential catalytic processes occur through two or more functionally distinct, and preferably non-interfering, catalytic cycles". This technique has been deployed in tandem alkane-dehydrogenation-olefin-metathesis catalysis | https://en.wikipedia.org/wiki?curid=22686225 |
Moving particle semi-implicit method The moving particle semi-implicit (MPS) method is a computational method for the simulation of incompressible free surface flows. It is a macroscopic, deterministic particle method (Lagrangian mesh-free method) developed by Koshizuka and Oka (1996). The MPS method is used to solve the Navier-Stokes equations in a Lagrangian framework. A fractional step method is applied which consists of splitting each time step in two steps of prediction and correction. The fluid is represented with particles, and the motion of each particle is calculated based on the interactions with the neighboring particles by means of a kernel function . The MPS method is similar to the SPH (smoothed-particle hydrodynamics) method (Gingold and Monaghan, 1977; Lucy, 1977) in that both methods provide approximations to the strong form of the partial differential equations (PDEs) on the basis of integral interpolants. However, the MPS method applies simplified differential operator models solely based on a local weighted averaging process without taking the gradient of a kernel function. In addition, the solution process of MPS method differs to that of the original SPH method as the solutions to the PDEs are obtained through a semi-implicit prediction-correction process rather than the fully explicit one in original SPH method. Through the past years, the MPS method has been applied in a wide range of engineering applications including Nuclear Engineering (e.g. Koshizuka et al., 1999; Koshizuka and Oka, 2001; Xie et al | https://en.wikipedia.org/wiki?curid=22690116 |
Moving particle semi-implicit method , 2005), Coastal Engineering (e.g. Gotoh et al., 2005; Gotoh and Sakai, 2006), Environmental Hydraulics (e.g. Shakibaeina and Jin, 2009; Nabian and Farhadi, 2016), Ocean Engineering (Shibata and Koshizuka, 2007; Sueyoshi et al., 2008), Structural Engineering (e.g. Chikazawa et al., 2001), Mechanical Engineering (e.g. Heo et al., 2002; Sun et al., 2009), Bioengineering (e.g. Tsubota et al., 2006) and Chemical Engineering (e.g. Sun et al., 2009). Improved versions of MPS method have been proposed for enhancement of numerical stability (e.g. Koshizuka et al., 1998; Zhang et al., 2005; Ataie-Ashtiani and Farhadi, 2006;Shakibaeina and Jin, 2009 ), momentum conservation (e.g. Hamiltonian MPS by Suzuki et al., 2007; Corrected MPS by Khayyer and Gotoh, 2008), mechanical energy conservation (e.g. Hamiltonian MPS by Suzuki et al., 2007), pressure calculation (e.g. Khayyer and Gotoh, 2009, Kondo and Koshizuka, 2010, Khayyer and Gotoh, 2010), and for simulation of multiphase and granular flows (Nabian and Farhadi 2016). | https://en.wikipedia.org/wiki?curid=22690116 |
Ionic partition diagram Similar to Pourbaix's diagram for the speciation of redox species as a function of the redox potential and the pH, ionic partition diagrams indicate in which an acid or a base are predominantly present in a biphasic system as a function of the Galvani potential difference between the two phases and the pH of the aqueous solution of an hydrophilic acid AH in a biphasic water/organic solvent system. At a high aqueous pH, the acid is in the anionic form and can exist in both phases according to the Galvani potential difference. The Nernst equation for the distribution of the anion, ignoring the activity coefficients is written. Thus, the separation limit between the anionic form in water and the organic solvent () is a horizontal straight line. As in Pourbaix diagrams, the separation limit between the acid and basic forms in water is a vertical line given by . The line separating the neutral acid in water and the anion Ao– in the organic phase is given by considering the aqueous acidity constant to give As in the Pourbaix diagrams, we obtain a delimiting line that depends on the pH as shown below. | https://en.wikipedia.org/wiki?curid=22691887 |
Pentachloronitrobenzene Pentachloronitrobenzene, typically abbreviated PCNB, is a registered fungicide formally derived from nitrobenzene. It is either an off-white or yellow solid, depending on its purity, with a musty odor. PCNB was originally synthesized in the laboratory in 1868. It was introduced to the agricultural world in the 1930s in Germany by Bayer AG as a substitute to mercurial pesticides. PCNB is prepared by chlorination of nitrobenzene at 60–70 °C in chlorosulfuric acid, with iodine as a catalyst. It can also be produced by the nitration of chlorinated benzenes. A side product of the synthesis of PCNB is hexachlorobenzene (HCB), which is considered as hazardous as PCNB. Reaction with ethanol and potassium hydroxide yields pentachlorophenetole, indicating its high reactivity: Although PCNB has a long shelflife, it is labile in soil, with a half life of 1.8 days. It degrades to other metabolites, mainly reducing to pentachloroaniline (PCA), but also to pentachlorophenol (PCP) through hydrolysis and pentachlorothioanisole (PCTA). Another metabolite is methyl pentachlorophenyl sulfide (MPCPS). Little information is available about the degradation mechanisms. PCNB is used as a fungicide to suppress the growth of fungi in various crops, such as cotton, rice, and seed grains. It is also used to prevent the formation of slime in industrial waters. Residual amounts of the compound and its metabolites can be found in crops. The degradation products, PCA and PCTA have been found in farming soils and in river sediments | https://en.wikipedia.org/wiki?curid=22695228 |
Pentachloronitrobenzene In April 1993, PCNB was declared a hazardous air pollutant in the U.S. PCNB was reexamined for re-registration eligibility by the U.S. EPA in 2006 as part of the 1996 Food Protection Quality Act (FPQA) and as a result, use on a number of crops were ended or limited. In August 2010, in response to the discovery of a potentially toxic metabolite in technical grade PCNB to be used in fungicide formulations, the sale of PCNB was halted by the U.S. EPA until the issue could be resolved. In November 2011, the EPA approved certain registrations for PCNB, allowing it back on the market for golf course turf, potato, cotton, ornamental bulb and cole crop uses in the United States. PCNB is used widely as a fungicide in other countries, such as China and Japan. | https://en.wikipedia.org/wiki?curid=22695228 |
Offshore Technology Conference (OTC) is a series of conferences and exhibitions, focused on the exchanging technical knowledge relevant to the development of offshore energy resources, primarily oil and natural gas. It was founded in 1969 . There are four events organized by OTC. The flagship is held annually during early May in Houston, Texas, USA since 1969. In 2011, OTC organized OTC Brasil and the Arctic Technology Conference to offer a version of the event focused on the development in the Brasil and Arctic regions. In 2014, OTC Asia was created. OTC Brasil and OTC Asia are held every other year. OTC is sponsored by 13 industry associations, who work cooperatively to develop the technical program each year. Sponsoring organizations include the American Association of Petroleum Geologists, the American Institute of Chemical Engineers, the American Society of Civil Engineers, the ASME International Petroleum Technology Institute, the Institute of Electrical and Electronics Engineers, the Marine Technology Society, the Society of Exploration Geophysicists, the Society for Mining, Metallurgy, and Exploration, the Society of Naval Architects and Marine Engineers, the Society of Petroleum Engineers, and the Minerals, Metals and Materials Society. OTC uses proceeds from the events to reinvest into the oil and gas industry through the 13 sponsoring organizations. All technical papers presented at events are available on OnePetro.org | https://en.wikipedia.org/wiki?curid=22695542 |
Offshore Technology Conference Offshore Technology Conference, the flagship OTC event, is the largest oil and gas sector trade show in the world. The first OTC was held in Houston, Texas in 1969. In 2017, OTC was ranked the 25th event on the Trade Show News Network 2017 Top US Trade Shows List. In 2018, the 50th edition of OTC was held and many outlets reflected on the impact of OTC on Houston and the industry over the years. To celebrate the 50th edition of the event, OTC created a special sign and commissioned Houstonian artist Mario E. Figueroa, Jr., also known as GONZO247, to create a one of a kind plexi glasscube painted live at OTC. The 2019 OTC is the 50th anniversary of OTC. It ranks among the largest 200 tradeshows held annually in the United States and is among the 10 largest meetings in terms of attendance. Attendance consistently exceeds 50,000, and more than 2,000 companies participate in the exhibition. OTC includes attendees from around the globe, with more than 120 countries represented at recent conferences. In 2009, 2,500 companies from 38 countries participated and 66,820 attendance, an 8.5% drop from previous year's 75,092, was reported despite a global economic recession and initial concerns about swine flu. Attendance in 2014 reached a 46-year high of 108,300, the highest in show history and up 3.3% from the previous year. The cost to attend the event is generally lower than prices for other oil and gas conferences | https://en.wikipedia.org/wiki?curid=22695542 |
Offshore Technology Conference In 2018, to attend the full conference as a professional who was a member of one of the 13 sponsoring organizations the registration fee was $180 which included full access to the technical sessions and massive exhibition. The annual Spotlight on New Technology Awards showcases the latest and most advanced hardware and software technologies that are leading the industry into the future. Technologies are awarded based on the following criteria: new and innovative, proven, broad interest for the industry and significant impact beyond existing technologies. OTC Brasil has been held in 2011, 2013, and 2017. In 2017, OTC Brasil was held in Rio de Janeiro and 150 technical papers were presented in 29 technical sessions. OTC Asia was held in 2014, 2016, and 2018. The 2018 OTC Asia was held in March in Kuala Lumpur. More than 290 technical papers were presented at OTC Asia in 2018. The Arctic Technology Conference has been held in 2011, 2012, 2014, 2015, 2016, and will be held in fall 2018. In 2011-2012 and 2014, the conference was held in Houston. The 2015 edition was held in Copenhagen, Denmark. The 2016th edition was held in St. John's, Canada and 135 technical papers were presented. The 2018th edition will be the first time the show returns to Houston in a couple years. The Arctic Technology Conference is an OTC event that covers the technical challenges that come along with exploration and production of petroleum and natural gas in the arctic | https://en.wikipedia.org/wiki?curid=22695542 |
Offshore Technology Conference The conference technical program will discuss the logistical and technical aspects involved with recovery oil and gas in the harsh icy arctic environment as well as the environmental and regulatory requirements in the unique arctic environment. | https://en.wikipedia.org/wiki?curid=22695542 |
Mill scale Mill scale, often shortened to just scale, is the flaky surface of hot rolled steel, consisting of the mixed iron oxides iron(II) oxide (FeO), iron(III) oxide (FeO), and iron(II,III) oxide (FeO, magnetite). is formed on the outer surfaces of plates, sheets or profiles when they are being produced by rolling red hot iron or steel billets in rolling mills. is bluish-black in color. It is usually less than thick, and initially adheres to the steel surface and protects it from atmospheric corrosion provided no break occurs in this coating. Because it is electrochemically cathodic to steel, any break in the mill scale coating will cause accelerated corrosion of steel exposed at the break. is thus a boon for a while until its coating breaks due to handling of the steel product or due to any other mechanical cause. becomes a nuisance when the steel is to be processed. Any paint applied over it is wasted, since it will come off with the scale as moisture-laden air gets under it. Thus mill scale can be removed from steel surfaces by flame cleaning, pickling, or abrasive blasting, which are all tedious operations that consume energy. This is why shipbuilders and steel fixers used to leave steel and rebar delivered freshly rolled from mills out in the open to allow it to 'weather' until most of the scale fell off due to atmospheric action. Nowadays, most steel mills can supply their product with mill scale removed and steel coated with shop primers over which welding or painting can be done safely | https://en.wikipedia.org/wiki?curid=22696307 |
Mill scale generated in rolling mills will be collected and sent to a sinter plant for recycling. is sought after by select abstract expressionist artists as its effect on steel can cause unpredicted and seemingly random abstract organic visual effects. Although the majority of mill scale is removed during its passage through scale breaker rolls during manufacturing, smaller structurally inconsequential residue can be visible. Leveraging this processing vestige by accelerating its corrosive effects through the metallurgical use of phosphoric acid or in conjunction with selenium dioxide can create a high contrast visual substrate onto which other compositional elements can be added. can be used as a raw material in granular refractory. When this refractory is cast and preheated, these scales provide escape routes for the evaporating water vapor, thus preventing cracks and resulting in a strong, monolithic structure. | https://en.wikipedia.org/wiki?curid=22696307 |
Flash smelting () is a smelting process for sulfur-containing ores including chalcopyrite. The process was developed by Outokumpu in Finland and first applied at the Harjavalta plant in 1949 for smelting copper ore. It has also been adapted for nickel and lead production. A second flash smelting system was developed by the International Nickel Company ('INCO') and has a different concentrate feed design compared to the Outokumpu flash furnace. The Inco flash furnace has end-wall concentrate injection burners and a central waste gas off-take, while the Outokumpu flash furnace has a water-cooled reaction shaft at one end of the vessel and a waste gas off-take at the other end. While the INCO flash furnace at Sudbury was the first commercial use of oxygen flash smelting, fewer smelters use the INCO flash furnace than the Outokumpu flash furnace. with oxygen-enriched air (the 'reaction gas') makes use of the energy contained in the concentrate to supply most of the energy required by the furnaces. The concentrate must be dried before it is injected into the furnaces and, in the case of the Outokumpu process, some of the furnaces use an optional heater to warm the reaction gas typically to 100–450 °C. The reactions in the flash smelting furnaces produce copper matte, iron oxides and sulfur dioxide. The reacted particles fall into a bath at the bottom of the furnace, where the iron oxides react with fluxes, such as silica and limestone, to form a slag | https://en.wikipedia.org/wiki?curid=22701233 |
Flash smelting In most cases, the slag can be discarded, perhaps after some cleaning, and the matte is further treated in converters to produce blister copper. In some cases where the flash furnaces are fed with concentrate containing a sufficiently high copper content, the concentrate is converted directly to blister in a single Outokumpu furnace and further converting is unnecessary. The sulfur dioxide produced by flash smelting is typically captured in a sulfuric acid plant, removing the major environmental effect of smelting. Outotec, formerly the technology division of Outokumpu, now holds Outokumpu's patents to the technology and licenses it worldwide. INCO was acquired by Brazil's Vale in 2006. | https://en.wikipedia.org/wiki?curid=22701233 |
Diphenylcyanoarsine Diphenylcyanoarsine, also called Clark 2 (Chlor-Arsen-Kampfstoff 2, being the successor of Clark 1) by the Germans, was discovered in 1918 by Sturniolo and Bellinzoni and shortly thereafter used like the related Clark 1 gas by the Germans for chemical warfare in the First World War. The substance causes nausea, vomiting and headaches. It can subsequently lead to e.g. pulmonary edema (fluid in the lungs). | https://en.wikipedia.org/wiki?curid=22706309 |
Gaseous detection device The gaseous detection device-GDD is a method and apparatus for the detection of signals in the gaseous environment of an environmental scanning electron microscope (ESEM) and all scanned beam type of instruments that allow a minimum gas pressure for the detector to operate. In the course of development of the ESEM, the detectors previously employed in the vacuum of a scanning electron microscope (SEM) had to be adapted for operation in gaseous conditions. The backscattered electron (BSE) detector was adapted by an appropriate geometry in accordance with the requirements for optimum electron beam transmission, BSE distribution and light guide transmission. However, the corresponding secondary electron (SE) detector (Everhart-Thornley detector) could not be adapted, because the high potential required would cause a catastrophic breakdown even with moderate increase of pressure, such as low vacuum. Danilatos (1983) overcame this problem by using the environmental gas itself as the detector, by virtue of the ionizing action of various signals. With appropriate control of electrode configuration and bias, detection of SE was achieved. A comprehensive survey dealing with the theory and operation of GDD has been published, from which the majority of the material presented below has been used. The GDD is in principle an adaptation of techniques for particle detection used in nuclear physics and astronomy | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device The adaptation involves the parameters required for the formation of images in the conditions of an electron microscope and in the presence of gas inside the specimen chamber. The signals emanating from the beam specimen-interaction, in turn, interact with the surrounding gas in the form of gaseous ionization and excitation. The type, intensity and distribution of signal-gas interactions vary. It is fortunate that generally the time-constant of these interactions is compatible with the time-constant required for the formation of images in the ESEM. The establishment of this compatibility constitutes the basis of the invention of GDD and the leap from particle physics to electron microscopy. The dominant signal-gas interactions are those by the BSE and SE, as they are outlined below. In its simplest form, the GDD involves one or more electrodes biased with a generally low voltage (e.g. up to 20 V), which is sufficient to collect the ionization current created by whatever sources. This is much the same as an ionization chamber in particle physics. The size and location of these electrodes determine the detection volume in the gas and hence the type of signal detected. The energetic BSE traverse a long distance, whereas the SE travel a much shorter lateral distance mainly by way of diffusion in the gas. Correspondingly, an electrode placed further away from the beam axis will have a predominantly BSE component in comparison to the predominant SE component collected by an electrode placed close to the axis | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device The precise proportion of signal mix and intensity depends on the additional parameters of gas nature and pressure in conjunction with electrode configurations and bias, bearing in mind that there is no abrupt physical distinction between SE and BSE, apart from the conventional definition of the 50 eV boundary between them. In another form, the GDD involves one or more electrodes as above but biased with a generally high voltage (e.g. 20–500 V). The processes involved are the same as in the low voltage case with the addition of an amplification of signal along the principle of a proportional amplifier as used in particle physics. That is, all slow electrons in the gas emanating either from the ionizing BSE or directly from the specimen (i.e. the SE) are multiplied in an avalanche form. The energy imparted on the traveling slow electrons by the external electrode field is sufficient to ionize the gas molecules through successive (cascade) collisions. The discharge is controlled in proportion by the applied electrode bias below the breakdown point. This form of detection is referred as ionization-GDD. Parallel to the ionization, there is also excitation of the gas in both cases above. The gaseous photons are produced both by BSE and SE both directly and by cascade avalanche with the ionization electrons. These photons are detected by appropriate means, like photo-multipliers | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device By positioning Light tubes strategically, using filters and other light optics means, the SE can again be separated from the BSE and corresponding images formed. This form of detection is referred as scintillation-GDD. The principles outlined above are best described by considering plane electrodes biased to form a uniform electric field, such as shown in the accompanying . The electron beam striking the specimen at the cathode effectively creates a point source of SE and BSE. The distribution of slow electrons emitted from a point source inside a gas acted upon by a uniform field is given from the equations (low field): formula_1 with formula_2 where R is the fraction of SE that arrives at the anode inside radius r, V the potential difference between the electrodes placed at distance d, k is Boltzmann’s constant, T the absolute gas temperature, e the electron charge and ε is the ratio of the thermal (agitation and kinetic) energy of the electrons divided by the thermal energy of the host gas; I is the corresponding current collected by the anode inside r, δ is the SE yield coefficient and I the incident electron beam current. This provides the spatial distribution of the initial electrons SE as they are acted upon by the uniform electric field that moves them from the cathode to the anode, while the electrons also diffuse away due to thermal collisions with the gas molecules. Plots are provided in the accompanying , for a set of operating conditions of pressure p and distance d | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device We note that a 100% collection efficiency is fast approached within a small radius even at moderate field strength. At high bias, a nearly complete collection is achieved within a very small radius, a fact that has favorable design implications. The above radial distribution is valid also in the presence of formation of electron avalanches at high electric field, but it must be multiplied by an appropriate gain factor. In its simplest form for parallel electrodes, the gain factor is the exponential in the current equation: formula_3 where α is the first Townsend coefficient. This gives the total signal amplification due to both electrons and ions. The spatial charge distribution and gain factor varies with electrode configuration and geometry and by additional discharge processes described in the referenced theory of the GDD. The BSE usually have energies in the kV range so that the much lower electrode bias has only a secondary effect on their trajectory. For the same reason, the finite number of collisions with the gas also results in a second order deflection from their trajectory they would have in vacuum. Therefore, their distribution is practically the same as has been worked out by SEM workers, the variation of which depends on the specimen surface properties (geometry and material composition). For a polished specimen surface the BSE distribution assumes a nearly cosine function but for a rough surface we may take it to be spherical (i.e. uniform in all directions) | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device For brevity, the equations of the second case only are given below. In vacuum, the current distribution from BSE on the electrode is given by formula_4 where η is the BSE yield coefficient. In the presence of gas at low electric field the corresponding equations become: formula_5 where S is the ionization coefficient of the gas and p its pressure Finally, for a high electric field we get formula_6 For practical purposes, the BSE predominantly fall outside the volume acted upon by predominantly the SE, while there is an intermediate volume of comparable fraction of the two signals. The interplay of the various parameters involved has been studied in the main, but it also constitutes a new field for further research and development, especially as we move outside the plane electrode geometry. Prior to practical implementations, it is helpful to consider a more esoteric aspect (principle), namely, the fundamental physical process taking place in the GDD. The signal in the external circuit is a displacement current i created by induction of charge on the electrodes by a moving charge e with velocity υ in the space between them: formula_7 At the point in time when the charge arrives at the electrode, there is no current flowing in the circuit since υ=0, only when the charge is in motion between the electrodes do we have a signal current. This is important in the case, for example, when a new electron-ion pair is generated at any point in the space between anode-cathode, say at x distance from the anode | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device Then, only a fraction ex/d of charge is induced by the electron during its transit to the anode, whilst the remainder fraction of e(d–x)/d charge is induced by the ion during its transit to the cathode. Addition of those two fractions gives a charge equal to the charge of one electron. Thus by counting the electrons arriving at the anode or the ions at the cathode we derive the same figure in current measurement. However, since the electrons have a drift velocity about three orders of magnitude greater (in nanosecond range) than the ions, the induced signal may be separated in two components of different significance when the ion transit time may become greater than the pixel time on the scanned image. The GDD has thus two inherent time-constants, a very short one due to the electrons and a longer one due to the ions. When the ion transit time is greater than the pixel dwell time, the useful signal intensity decreases together with an increase of signal background noise or smearing of image edges due to the ions lagging behind. As a consequence, the above derivations, which include the total electron and ion contributions must be modified accordingly with new equations for the case of fast scanning rates. The electrode geometry can be altered with a view to decrease the ion transit time as can be done with a needle or cylindrical geometry. This fundamental approach helps also understand the so-called “specimen absorbed current” mode of detection in the vacuum SEM, which is limited only to conductive specimens | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device Image formation of non-conductive specimens now possible in the ESEM, can be understood in terms of an induced displacement current in the external circuit via a capacitor-like action with the specimen being the dielectric between its surface and the underlying electrode. Therefore, the (misnomer) "specimen absorbed current" per se plays no part in any useful image formation except to dissipate the charge (in conductors), without which insulators cannot be generally imaged in vacuum (except in the rare case when the incident beam current equals the total emitted current). By use of a derivation for the Townsend coefficient given by von Engel, the gain factor G, in the case of SE with total current collection I (i.e. for R=1), is found by: formula_8 where A and B are tabulated constants for various gases. In the diagram supplied, we plot the for nitrogen with A=9.0 and B=256.5 valid in the range 75–450 V/(Pa·m) for the ratio E/p. We should note that in ESEM work the product pd<3 Pa·m, since at higher values no useful beam is transmitted through the gas layer to the specimen surface. The gray-shaded area shows the region of GDD operation provided also that the γ processes are very low and do not trigger a breakdown of the proportional amplification. This area contains the maxima of the gain curves, which further re-enforces the successful application of this technology to ESEM | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device The curves outside the shaded area can be used with beam energy greater than 30 kV, and in future development of environmental or atmospheric transmission scanning electron microscopes employing very high beam energy. The diagram showing the constitutes a versatile implementation that includes not only the SE mode but also the BSE and a combination of these. Even if only the SE signal is desirable to use alone, at least one additional concentric electrode is recommended to employ in order to help in the separation from interference of BSE and also from other noise sources such as the skirt electrons scattered out of the primary beam by the gas. This addition may act as a “guard” electrode, and by varying its bias independently from the SE electrode, the image contrast can be controlled purposefully. Alternative control electrodes are used such as a mesh between anode and cathode. A multipurpose array of electrodes below and above the specimen and above the pressure limiting aperture of the ESEM has also been described elsewhere. The development of this detector has required devoted electronics circuitry, especially when the signal is picked up by the anode at high bias, because the floating current amplified must be coupled at full bandwidth to the ground amplifier and video display circuits (developed by ElectroScan). An alternative is to bias the cathode with a negative potential and pickup the signal from the anode at floating ground without the need for coupling between amplifier stages | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device However, this would require extra precaution to protect users from exposure to a high potential at the specimen stage. A further alternative that has been implemented at the laboratory stage is by the application of a high bias at the anode but by pickup of the signals from the cathode at floating ground, as shown in the . Concentric electrodes (E2, E3, E4) are made on a copper-coated fiberglass printed circuit board (PCB) and a copper wire (E1) is added at the center of the disk. The anode is made again from the same PCB with a conical hole (400 micrometres) to act as a pressure limiting aperture in the ESEM. The exposed fiberglass material inside the aperture cone together with its surface above are coated with silver paint in continuity with the copper material of the anode electrode (E0), which is held at high potential. The cathode electrodes are independently connected to ground amplifiers, which, in fact, can be biased with low voltage directly from the amplifier power supplies in the range of ±15 volts without any further coupling required. On account of the induction mechanism operating behind the GDD, this configuration is equivalent to the previous diagram, except for the inverted signal that is electronically restored. While electrode E0 is held at 250 V, meaningful imaging is done as shown by a with composition of signals from various electrodes at two pressures of supplied air | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device All images show part of the central copper wire (E1), exposed fiber-glass (FG, middle), and copper (part of E2) with some silver paint used to attach the wire. The close resemblance of (a) with (b) at low pressure and (c) with (d) at high pressure is a manifestation of the principle of equivalence by induction. The purest SE image is (e) and the purest BSE is (h). Image (f) has prevailing SE characteristics, whilst (g) has a comparable contribution of both SE and BSE. Images (a) and (b) are dominated by SE with some BSE contribution, whilst (c) and (d) have comparable contribution by both SE and BSE. The very bright areas on the FG material result from genuine high specimen signal yield and not from erratic charging or other artifacts familiar with plastics in vacuum SEM. High yield of edges, oblique incidence, etc. can for the first time be studied from the true surfaces without obstruction in ESEM. Mild charging, if present, may produce stable contrast characteristic of material properties and can be used as a means for studies of the physics of the surfaces. The images presented in this series are reproductions from photographic paper with limited bandwidth, on which attempting to bring up detail in dark areas results in saturating the bright areas and vice versa, whilst a lot more information is usually contained on the negative film. Electronic manipulation of the signal together with modern computer graphics can overcome some old imaging limitations | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device An example of the GDD operating at low voltage is shown with of view of a polished mineral containing aluminum, iron, silicon and some unknown surface impurities. The anode electrode is a single thin wire placed on the side and below the specimen surface, several mm away from it. Image (a) shows predominantly SE contrast at low pressure, whilst (b) shows BSE material contrast at higher pressure. Image (c) shows cathodoluminescence (CL) from the specimen surface by use of water vapor (which does not scintillate), whilst (d) shows additional photon signal by changing the gas to air which scintillates by signal electrons originating from the specimen. The latter appears to be a mixture of CL with SE, but it may also contain additional information from the surface contaminant charging to a varying degree with gas pressure. The GDD at high voltage has clear advantages over the low voltage mode, but the latter may be used easily with special applications such as at very high pressures where the BSE produce a high ionization gain from their own high energy, or in cases when the electric field requires shaping to purposeful ends. In general, the detector should be designed to operate at both high and low bias levels including variable negative (electron retarding) bias with important contrast generation. Further improvements have been envisaged, such as the use of special electrode materials, gas composition and shaping the trajectory of detection electrons by special electric and magnetic fields (page 91) | https://en.wikipedia.org/wiki?curid=22712749 |
Gaseous detection device The first commercial implementation of the GDD was carried out by ElectroScan Corporation employing the acronym ESD for “environmental secondary detector”, which was followed by an improved version termed “gaseous secondary electron detector” (GSED). The use of the magnetic field of the objective lens of the microscope has been incorporated in another commercial patent. LEO company (now Carl Zeiss SMT) has used the scintillation mode and the ionization (needle) mode of the GDD on its environmental SEMs at low and also extended pressure range. | https://en.wikipedia.org/wiki?curid=22712749 |
C8H9NO2 The molecular formula CHNO may refer to: | https://en.wikipedia.org/wiki?curid=22712949 |
Journal of Biological Inorganic Chemistry is a peer-reviewed scientific journal. It is an official publication of the Society of Biological Inorganic Chemistry and published by Springer Science+Business Media. Areas of research covered in the journal include: advances in the understanding of systems involving one or more metal ions set in a biological matrix - particularly metalloproteins and metal-nucleic acid complexes - in order to understand biological function at the molecular level. Synthetic analogues mimicking function, structure and spectroscopy of naturally occurring biological molecules are also covered. Original articles, mini-reviews and commentaries on debated issues are being published. The journal is abstracted/indexed in Chemical Abstracts Service, Current Contents/Life Sciences, PubMed/MEDLINE, and the Science Citation Index. Indexed by ISI received an impact factor of 2.538 as reported in the 2014 Journal Citation Reports by Thomson Reuters, ranking it 157 out of 289 journals in the category "Biochemistry & Molecular Biology" and ranking it 9th out of 44 journals in the category "Chemistry, Inorganic & Nuclear". The current editor in chief is Lawrence Que (University of Minnesota) and Ivano Bertini was the founding editor. | https://en.wikipedia.org/wiki?curid=22714156 |
Magnet-assisted transfection is a transfection method which uses magnetic interactions to deliver DNA into target cells. Nucleic acids are associated with magnetic nanoparticles, and magnetic fields drive the nucleic acid-particle complexes into target cells, where the nucleic acids are released. Nanoparticles used as carriers for nucleic acids are mostly iron oxides. These iron oxides can be generated by precipitation from acidic iron-salt solutions upon addition of appropriate bases. The magnetic nanoparticles have an approximate size of 100 nm and are additionally coated with biological polymers to allow loading of nucleic acids. Particles and nucleic acids form complexes by ionic interaction of the negatively charged nucleic acid and the positively charged surface of the magnetic nanoparticle. The binding of the negatively charged nucleic acids to the positively charged iron particles occurs relatively fast. After complex formation, the loaded particles are incubated together with the target cells on a magnetic plate. The magnetic field causes the iron particles to be rapidly drawn towards the surface of the cell membrane. Cellular uptake occurs by either endocytosis or pinocytosis. Once delivered to the target cells, the DNA is released into the cytoplasm. The magnetic particles are accumulated in endosomes and/or vacuoles. Over time, the nanoparticles are degraded and the iron enters the normal iron metabolism. Influence of cellular functions by iron particles has not been reported yet | https://en.wikipedia.org/wiki?curid=22714697 |
Magnet-assisted transfection In most cases the increased iron concentration in culture media does not lead to cytotoxic effects. is a relatively new and time-saving method to introduce nucleic acids into a target cell with increased efficiency. In particular, adherent mammalian cell lines and primary cell cultures show very high transfection rates. Suspension cells and cells from other organisms can also be successfully transfected. A major advantage of the method is the mild treatment of the cells in comparison to liposome-based transfection reagents (lipofection) and electroporation, which may result in the death of 20-50% of cells. In addition, the transfection efficiency is increased in numerous cases by the directed transport in a magnetic field, especially for low amounts of nucleic acids. In contrast, methods like lipofection offer only statistical hits between cargo and cells, because of the three-dimensional motion of cells and transfection aggregates in a liquid suspension. can also be performed in the presence of serum, which is a further benefit. Currently, there are over 150 cells known to be successfully transfected. Additionally, synergistic effects in transfection efficiency can arise from the possible combination of lipofection and magnet-assisted transfection. In future, this technology might be also an alternative strategy to the currently used viral and non-viral vectors in gene-therapy and gene transfer. | https://en.wikipedia.org/wiki?curid=22714697 |
Taylor microscale The Taylor microscale, which is sometimes called the turbulence length scale, is a length scale used to characterize a turbulent fluid flow. This microscale is named after Geoffrey Ingram Taylor. The is the intermediate length scale at which fluid viscosity significantly affects the dynamics of turbulent eddies in the flow. This length scale is traditionally applied to turbulent flow which can be characterized by a Kolmogorov spectrum of velocity fluctuations. In such a flow, length scales which are larger than the are not strongly affected by viscosity. These larger length scales in the flow are generally referred to as the inertial range. Below the the turbulent motions are subject to strong viscous forces and kinetic energy is dissipated into heat. These shorter length scale motions are generally termed the dissipation range. Calculation of the is not entirely straightforward, requiring formation of certain flow correlation function(s), then expanding in a Taylor series and using the first non-zero term to characterize an osculating parabola. The is proportional to formula_1, while the Kolmogorov microscales is proportional to formula_2, where formula_3 is the integral scale Reynolds number. A turbulence Reynolds number calculated based on the formula_4 is given by formula_5 where formula_6 is the root mean square of the velocity fluctuations. The is given as formula_7 where formula_8 is the kinematic viscosity, and formula_9 is the rate of energy dissipation | https://en.wikipedia.org/wiki?curid=22720110 |
Taylor microscale A relation with turbulence kinetic energy can be derived as formula_10 The gives a convenient estimation for the fluctuating strain rate field formula_11 The falls in between the large scale eddies and the small scale eddies, which can be seen by calculating the ratios between formula_4 and the Kolmogorov microscale formula_13. Given the lengthscale of the larger eddies formula_14, and the turbulence Reynolds number formula_15 referred to these eddies, the following relations can be obtained: formula_16 formula_17 formula_18 formula_19 | https://en.wikipedia.org/wiki?curid=22720110 |
Heat number A heat number is an identification coupon number that is stamped on a material plate after it is removed from the ladle and rolled at a steel mill. Industry quality standards require materials to be tested at the manufacturer and the results of these tests be submitted through a report, also called a Mill Sheet, Mill Certificate or Mill Test Certificate (MTC). The only way to trace a steel plate back to its Mill Sheet is the Heat Number. A heat number is similar to a lot number, which is used to identify production runs of any other product for quality control purposes. Usually, but not universally, the numbers indicate: | https://en.wikipedia.org/wiki?curid=22728536 |
Nanoarchitectures for lithium-ion batteries are attempts to employ nanotechnology to improve the design of lithium-ion batteries. Research in lithium-ion batteries focuses on improving energy density, power density, safety, durability and cost. Increased energy density requires inserting/extracting more ions from the electrodes. Electrode capacities are compared through three different measures: capacity per unit of mass (known as "specific energy" or "gravimetric capacity"), capacity per unit volume ("volumetric capacity"), and area-normalized specific capacity ("areal capacity"). Separate efforts focus on improving power density (rate of charge/discharge). Power density is based upon mass and charge transport, electronic and ionic conductivity, and electron-transfer kinetics; easy transport through shorter distance and greater surface area improve the rates. Carbon anodes are traditionally used because of lithium's ability to intercalate without unacceptable volumetric expansion. The latter damages the battery and reduces the amount of lithium available for charging. Reduced intercalation limits capacity. Carbon based anodes have a gravimetric capacity of 372 mAh/g for LiC The specific capacity of silicon is approximately ten times greater than carbon. The atomic radius of Si is 1.46 angstroms, while the atomic radius of Li is 2.05 angstroms. The formation of LiSi causes significant volumetric expansion, progressively destroying the anode | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries Reducing the anode architecture to the nanoscale offers advantages, including improved cycle life and reduced crack propagation and failure. Nanoscale particles are below the critical flaw size within a conductive binder film. Reducing transport lengths(the distance between the anode and cathode) reduces ohmic losses (resistance). Nanostructuring increases the surface area to volume ratio, which improves both energy and power density due to an increase in the electrochemically active area and a reduction in transport lengths. However, the increase also increases side reactions between the electrode and the electrolyte, causing higher self-discharge, reduced charge/discharge cycles and lower calendar life. Some recent work focused on developing materials that are electrochemically active within the range where electrolyte decomposition or electrolyte/electrode reactions do not occur. A research concept has been proposed, in which the major parts of lithium-ion batteries, that is, anode, electrolyte and cathode are combined in one functional molecule. A layer of such functional molecules aligned by the use of Langmuir-Blodgett method than placed in between two current collectors. The feasibility is not confirmed yet. A significant majority of battery designs are two–dimensional and rely on layered construction. Recent research has taken the electrodes into three-dimensions | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries This allows for significant improvements in battery capacity; a significant increase in areal capacity occurs between a 2d thick film electrode and a 3d array electrode. Solid state batteries employ geometry most similar to traditional thin-film batteries. Three-dimensional thin-films use the third dimension to increase the electrochemically active area. Thin film two dimensional batteries are restricted to between 2-5 micrometres, limiting areal capacity to significantly less than that of three-dimensional geometries. Dimensionality is increased by using a perforated substrate. One way to create perforations is through inductive coupled plasma etching on silicon. Another approached used highly anisotropic etching of a silicon substrate through electrochemical or reactive ion etching to create deep trenches. The requisite layers, an anode, separator, and cathode, for a battery were then added by low-pressure chemical vapor deposition. The battery consists of a thin active silicon layer separated from a thin cathodic layer by a solid-state electrolyte. The electrochemically active area consists of 50 nm nanoparticles, smaller than the critical size for crack propagation. Another architecture is a periodic grouping of anodic and cathodic poles. For this design power and energy density is maximized by minimizing electrode separation. An innate non-uniform current density occurs and lowers cell efficiencies, reduces stability and produces non-uniform heating within the cell | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries Relative to a two dimensional battery the length (L) over which transport must occur is decreased by two-thirds, which improves kinetics and reduces ohmic loses. Optimization of L can lead to significant improvement in areal capacity; an L on the size scale of 500 micrometres results in a 350% increase in capacity over a comparable two dimensional battery. However, ohmic losses increase with L, eventually offsetting the enhancement achieved through increasing L. For this geometry, four main designs were proposed: rows of anodes and cathodes, alternating anodes and cathodes, hexagonally packed 1:2 anodes:cathodes, and alternating anodic and cathodic triangular poles where the nearest neighbors in the row are rotated 180 degrees. The row design has a large, non-uniform current distribution. The alternating design exhibits better uniformity, given a high number of electrodes of opposite polarity. For systems with an anode or cathode that is sensitive to non-uniform current density, non-equal numbers of cathodes and anodes can be used; the 2:1 hexagonal design allows for a uniform current density at the anode but a non-uniform current distribution at the cathode. Performance can be increased through changing the shape of the poles. The triangular design improves cell capacity and power by sacrificing current uniformity. A similar system uses interdigitated plates instead of poles. In 2013 researchers used additive manufacturing to create stacked, interdigitated electrodes | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries The battery was no larger than a grain of sand. The process placed anodes and cathodes closer to each other than before. The ink for the anode was nanoparticles of one lithium metal oxide compound, and the ink for the cathode from nanoparticles of another. The printer deposited the inks onto the teeth of two gold combs, forming an interlaced stack of anodes and cathodes. The concentric cylinder design is similar to interdigitated poles. Instead of discrete anode and cathode poles, the anode or cathode is kept as a pole that is coated by electrolyte. The other electrode serves as the continuous phase in which the anode/cathode resides. The main advantage is that the amount of electrolyte is reduced, increasing energy density. This design maintains a short transport distance like the interdigitated system and thus has a similar benefit to charge and mass transport, while minimizing ohmic loses. A version of the concentric cylinder packed particles or close-packed polymer to create a three-dimensionally ordered macroporous (3DOM) carbon anode. This system is fabricated by using colloidal crystal templating, electrochemical thin-film growth, and soft sol–gel chemistry. 3DOM materials have a unique structure of nanometer thick walls that surround interconnected and closed-packed sub-micrometer voids. The 3DOM structure is coated with a thin polymer layer and then filled with second conducting phase | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries This method leads to a battery with short transport lengths, high ionic conductivity and reasonable electrical conductivity. It removes the need for additives that do not contribute to electrochemical performance. Performance can be improved by coating with tin oxide nanoparticles to enhance the initial capacity. The coating infiltrates the network formed by the 3DOM structure to produce uniform thickness. Nanowire and nanotubes have been integrated with various battery components. The reason for this interest is because of shortened transport lengths, resistance to degradation and storage. For carbon nanotubes (CNT), lithium-ions can be stored on the exterior surface, in the interstitial sites between the nanotubes and on the tube's interior. Nanowires have been incorporated into the anode/cathode matrix to provide a builtin conductive charge collector and enhancing capacity. The nanowires were incorporated through a solution-based method that allows the active material to be printed on a substrate. Another approach uses a CNT-cellulose composite. CNTs were grown on a silicon substrate by thermal-CVD and then embedded in cellulose. Finally a lithium electrode is added on top of the cellulose across from the CNTs. In 2007 Si nanowires were fabricated on a steel substrate by a vapor-liquid solid growth method. These nanowires exhibited close to the theoretical value for silicon and showed only minimal fading after a 20% drop between the first to second cycles | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries This performance is attributed to the facile strain relaxation that allows for accommodations of large strains, while maintaining good contact with the current collector and efficient 1D electron transport along the nanowire. Periodic structures lead to non-uniform current densities that lower efficiency and decrease stability. The aperiodic structure is typically made of either aerogels or somewhat more dense ambigels that forms a porous aperiodic sponge. Aerogels and ambigels are formed from wet gels; aerogels are formed when wet gels are dried such that no capillary forces are established, while ambigels are wet gels dried under conditions that minimize capillary forces. Aerogels and ambigels are unique in that 75-99% of the material is ‘open’ but interpenetrated by a solid that is on the order of 10 nm, resulting in pores on the order of 10 to 100 nm. The solid is covalently networked and resistant to agglomeration and sintering. Beyond aperiodicity, these structures are used because the porous structure allows for rapid diffusion throughout the material, and the porous structure provides a large reaction surface. Fabrication is through coating the ambigel with a polymer electrolyte and then filling the void space with RuO colloids that act as an anode. Most designs were half-cell experiments; testing only the anode or cathode. As geometries become more complex, non-line-of-sight methods to in-fill the design with electrolyte materials supply the oppositely charged electrode is essential | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries These batteries can be coated with various materials to improve their performance and stability. However, chemical and physical heterogeneity leaves molecular-level control a significant challenge, especially since the electrochemistry for energy storage is not defect-tolerant. LbL approaches are used to coat 3d nanoarchitecture. Electrostatically binding a charged polymer to an oppositely charged surface coats the surface with polymer. Repeated steps of oppositely charged polymer build up a well-controlled thick layer. Polyelectrolyte films and ultrathin (less than 5 nm) of electroactive polymers have been deposited on planar substrates using this method. However, problems exist with the deposition of polymers within complex geometries, e.g. pores, on the size scale of 50-300 nm, resulting in defective coatings. One potential solution is to use self-limiting approaches. Another approach to coating is ALD which coats the substrate layer-by-layer with atomic precision. The precision is because reactions are confined to the surface containing an active chemical moiety that reacts with a precursor; this limits thickness to one monolayer. This self-limiting growth is essential for complete coatings since deposition does not inhibit the access by other polymeric units to non-coated sites. Thicker samples can be produced by cycling gases in a similar manner to alternating with oppositely charged polymers in LbL | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries In practice ALD may require a few cycles in order to achieve the desired coverage and can result in varied morphologies such as islands, isolated crystallites, or nanoparticles. Morphology can alter electrochemical behavior and therefore must be carefully controlled. ALD was also used to deposit iron oxide on 3DOM carbon to enhance reactivity between lithium and oxygen. The iron was then coatedwith palladium nanoparticles, which effectively reduced carbon's destructive reaction with oxygen and improved the discharge cycle. Wang said the findings show 3DOm carbon can meet new performance standards when it is stabilized. Electropolymerization supplies a thin polymer film, 10 to 100 nm. The electropolymerization of an insulating polymer results in self-limiting deposition as the active moiety is protected; the deposition can also be self-limiting if the polymer can block the solubilized monomer and prohibit continued growth. Through the control of electrochemical variables, polyaniline and polythiophene can be deposited in a controlled manner. Styrene, methyl methacrylate, phenols and other electrically insulating polymers have been deposited on the electrodes to act as a separator that allows ionic transport, but inhibits electrical transport to prevent shorts. Mesoporous manganese dioxide ambigels have been protected by 7-9 nm films of polymer such that dissolution of the manganese dioxide in aqueous acid was avoided | https://en.wikipedia.org/wiki?curid=22730221 |
Nanoarchitectures for lithium-ion batteries Uniform coatings require the architecture to be wetted by the monomer solution; this can be achieved through a solution that displays a similar surface energy to that of the porous solid. As the scale continuous to decrease and transport through the solid becomes more difficult, pre-equilibration is needed to ensure coating uniformity. | https://en.wikipedia.org/wiki?curid=22730221 |
Conductivity (electrolytic) Conductivity (or specific conductance) of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is Siemens per meter (S/m). Conductivity measurements are used routinely in many industrial and environmental applications as a fast, inexpensive and reliable way of measuring the ionic content in a solution. For example, the measurement of product conductivity is a typical way to monitor and continuously trend the performance of water purification systems. In many cases, conductivity is linked directly to the total dissolved solids (T.D.S.). High quality deionized water has a conductivity of about 5.5 μS/m at 25 °C, typical drinking water in the range of 5–50 mS/m, while sea water about 5 S/m (or 5,000,000 μS/m). Conductivity is traditionally determined by connecting the electrolyte in a Wheatstone bridge. Dilute solutions follow Kohlrausch's Laws of concentration dependence and additivity of ionic contributions. Lars Onsager gave a theoretical explanation of Kohlrausch's law by extending Debye–Hückel theory. The SI unit of conductivity is S/m and, unless otherwise qualified, it refers to 25 °C. Often encountered in industry is the traditional unit of μS/cm. The commonly used standard cell has a width of 1 cm, and thus for very pure water in equilibrium with air would have a resistance of about 10 ohm, known as a megohm. Ultra-pure water could achieve 18 megohms or more. Thus in the past, megohm-cm was used, sometimes abbreviated to "megohm" | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) Sometimes, conductivity is given in "microsiemens" (omitting the distance term in the unit). While this is an error, it can often be assumed to be equal to the traditional μS/cm. The conversion of conductivity to the total dissolved solids depends on the chemical composition of the sample and can vary between 0.54 and 0.96. Typically, the conversion is done assuming that the solid is sodium chloride, i.e., 1 μS/cm is then equivalent to about 0.64 mg of NaCl per kg of water. Molar conductivity has the SI unit S m mol. Older publications use the unit Ω cm mol. The electrical conductivity of a solution of an electrolyte is measured by determining the resistance of the solution between two flat or cylindrical electrodes separated by a fixed distance. An alternating voltage is used in order to avoid electrolysis. The resistance is measured by a conductivity meter. Typical frequencies used are in the range 1–3 kHz. The dependence on the frequency is usually small, but may become appreciable at very high frequencies, an effect known as the Debye–Falkenhagen effect. A wide variety of instrumentation is commercially available. There are two types of cell, the classical type with flat or cylindrical electrodes and a second type based on induction. Many commercial systems offer automatic temperature correction. Tables of reference conductivities are available for many common solutions | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) Resistance, "R", is proportional to the distance, "l", between the electrodes and is inversely proportional to the cross-sectional area of the sample, "A" (noted "S" on the Figure above). Writing ρ (rho) for the specific resistance (or resistivity), In practice the conductivity cell is calibrated by using solutions of known specific resistance, ρ, so the quantities "l" and "A" need not be known precisely. If the resistance of the calibration solution is "R", a cell-constant, "C", is derived. The specific conductance (conductivity), κ (kappa) is the reciprocal of the specific resistance. Conductivity is also temperature-dependent. Sometimes the ratio of "l" and "A" is called as the cell constant, denoted as G, and conductance is denoted as G. Then the specific conductance κ (kappa), can be more conveniently written as The specific conductance of a solution containing one electrolyte depends on the concentration of the electrolyte. Therefore, it is convenient to divide the specific conductance by concentration. This quotient, termed molar conductivity, is denoted by Λ Strong electrolytes are hypothesized to dissociate completely in solution. The conductivity of a solution of a strong electrolyte at low concentration follows Kohlrausch's Law where formula_7 is known as the limiting molar conductivity, "K" is an empirical constant and "c" is the electrolyte concentration. (Limiting here means "at the limit of the infinite dilution" | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) ) In effect, the observed conductivity of a strong electrolyte becomes directly proportional to concentration, at sufficiently low concentrations i.e. when As the concentration is increased however, the conductivity no longer rises in proportion. Moreover, Kohlrausch also found that the limiting conductivity of an electrolyte; The following table gives values for the limiting molar conductivities for selected ions. An interpretation of these results was based on the theory of Debye and Hückel, yielding the Debye-Hückel-Onsager theory: where "A" and "B" are constants that depend only on known quantities such as temperature, the charges on the ions and the dielectric constant and viscosity of the solvent. As the name suggests, this is an extension of the Debye–Hückel theory, due to Onsager. It is very successful for solutions at low concentration. A weak electrolyte is one that is never fully dissociated (i.e. there are a mixture of ions and complete molecules in equilibrium). In this case there is no limit of dilution below which the relationship between conductivity and concentration becomes linear. Instead, the solution becomes ever more fully dissociated at weaker concentrations, and for low concentrations of "well behaved" weak electrolytes, the degree of dissociation of the weak electrolyte becomes proportional to the inverse square root of the concentration. Typical weak electrolytes are weak acids and weak bases | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) The concentration of ions in a solution of a weak electrolyte is less than the concentration of the electrolyte itself. For acids and bases the concentrations can be calculated when the value(s) of the acid dissociation constant(s) is (are) known. For a monoprotic acid, HA, obeying the inverse square root law, with a dissociation constant "K", an explicit expression for the conductivity as a function of concentration, "c", known as Ostwald's dilution law, can be obtained. Various solvents exhibit the same dissociation if the ratio of relative permittivities equals the ratio cubic roots of concentrations of the electrolytes (Walden's rule). Both Kohlrausch's law and the Debye-Hückel-Onsager equation break down as the concentration of the electrolyte increases above a certain value. The reason for this is that as concentration increases the average distance between cation and anion decreases, so that there is more inter-ionic interaction. Whether this constitutes ion association is a moot point. However, it has often been assumed that cation and anion interact to form an ion pair. Thus the electrolyte is treated as if it were like a weak acid and a constant, "K", can be derived for the equilibrium Davies describes the results of such calculations in great detail, but states that "K" should not necessarily be thought of as a true equilibrium constant, rather, the inclusion of an "ion-association" term is useful in extending the range of good agreement between theory and experimental conductivity data | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) Various attempts have been made to extend Onsager's treatment to more concentrated solutions. The existence of a so-called "conductance minimum" in solvents having the relative permittivity under 60 has proved to be a controversial subject as regards interpretation. Fuoss and Kraus suggested that it is caused by the formation of ion triplets, and this suggestion has received some support recently. Other developments on this topic have been done by Theodore Shedlovsky, E. Pitts, R. M. Fuoss, Fuoss and Shedlovsky, Fuoss and Onsager. The limiting equivalent conductivity of solutions based on mixed solvents like water alcohol has minima depending on the nature of alcohol. For methanol the minimum is at 15 molar % water, and for the ethanol at 6 molar % water. Generally the conductivity of a solution increases with temperature, as the mobility of the ions increases. For comparison purposes reference values are reported at an agreed temperature, usually 298 K (≈ 25 °C), although occasionally 20 °C is used. So called 'compensated' measurements are made at a convenient temperature but the value reported is a calculated value of the expected value of conductivity of the solution, as if it had been measured at the reference temperature. Basic compensation is normally done by assuming a linear increase of conductivity versus temperature of typically 2% per Kelvin. This value is broadly applicable for most salts at room temperature | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) Determination of the precise temperature coefficient for a specific solution is simple and instruments are typically capable of applying the derived coefficient (i.e. other than 2%). The change in conductivity due to the isotope effect for deuterated electrolytes is sizable. Notwithstanding the difficulty of theoretical interpretation, measured conductivity is a good indicator of the presence or absence of conductive ions in solution, and measurements are used extensively in many industries. For example, conductivity measurements are used to monitor quality in public water supplies, in hospitals, in boiler water and industries which depend on water quality such as brewing. This type of measurement is not ion-specific; it can sometimes be used to determine the amount of total dissolved solids (T.D.S.) if the composition of the solution and its conductivity behavior are known. Conductivity measurements made to determine water purity will not respond to non conductive contaminants (many organic compounds fall into this category), therefore additional purity tests may be required depending on application. Sometimes, conductivity measurements are linked with other methods to increase the sensitivity of detection of specific types of ions. For example, in the boiler water technology, the boiler blowdown is continuously monitored for "cation conductivity", which is the conductivity of the water after it has been passed through a cation exchange resin | https://en.wikipedia.org/wiki?curid=22738815 |
Conductivity (electrolytic) This is a sensitive method of monitoring anion impurities in the boiler water in the presence of excess cations (those of the alkalizing agent usually used for water treatment). The sensitivity of this method relies on the high mobility of H in comparison with the mobility of other cations or anions. Beyond cation conductivity, there are analytical instruments designed to measure Degas conductivity, where conductivity is measured after dissolved carbon dioxide has been removed from the sample, either through reboiling or dynamic degassing. Conductivity detectors are commonly used with ion chromatography. | https://en.wikipedia.org/wiki?curid=22738815 |
Frank Newman Speller Award The is an annual award for significant contributions to corrosion engineering and is administered by NACE International. (The organization was previously known as the National Association of Corrosion Engineers.) The award is named in honor of Frank Newman Speller, a Canadian-born American metallurgical engineer notable for his pioneering text on corrosion. Source: NACE International | https://en.wikipedia.org/wiki?curid=22751916 |
Alpha-Hexachlorocyclohexane α-Hexachlorocyclohexane (α-HCH) is an organochloride which is one of the isomers of hexachlorocyclohexane (HCH). It is a byproduct of the production of the insecticide lindane (γ-HCH) and it is typically still contained in commercial grade lindane used as insecticide. Lindane, however, has not been produced or used in the United States for more than 20 years. At ambient temperatures it is a stable, white, powdery solid substance. As of 2009, the Stockholm Convention on Persistent Organic Pollutants classified (α-HCH) and (β-HCH) as persistent organic pollutants (POPs), due to the chemical's ability to persistence in the environment, bioaccumulative, biomagnifying, and long-range transport capacity. | https://en.wikipedia.org/wiki?curid=22758158 |
Micromirror device Micromirror devices are devices based on microscopically small mirrors. The mirrors are Microelectromechanical systems (MEMS), which means that their states are controlled by applying a voltage between the two electrodes around the mirror arrays. Digital micromirror devices are used in video projectors and optics and micromirror devices for light deflection and control. "→ See main article digital micromirror device" Digital Micromirror Devices (DMD) were invented by Texas Instruments in 1987 and are the core of the DLP technology used for video projection. The mirrors are arranged in a matrix and have two states, "on" or "off" (digital). In the on state, light from the projector bulb is reflected into the lens making the pixel appear bright on the screen. In the off state, the light is directed elsewhere (usually onto a heatsink), making the pixel appear dark. Colours could be produced by various technologies like different light sources or gratings. The mirrors could not only be switched between two states, their rotation is in fact continuous. This could be used for controlling the intensity and direction of incident light. One future application is controlling the light in buildings, based on micromirrors between the two panes of Insulated glazing. The power and direction of the incident light is determined by the mirrors state, which itself is controlled electrostatically. A MEMS scanning micromirror consists of a silicon device with a millimeter-scale mirror at the center | https://en.wikipedia.org/wiki?curid=22763312 |
Micromirror device The mirror is typically connected to flexures that allow it to oscillate on a single axis or biaxially, to project or capture light. | https://en.wikipedia.org/wiki?curid=22763312 |
Multi-mission radioisotope thermoelectric generator The multi-mission radioisotope thermoelectric generator (MMRTG) is a type of radioisotope thermoelectric generator developed for NASA space missions such as the Mars Science Laboratory (MSL), under the jurisdiction of the United States Department of Energy's Office of Space and Defense Power Systems within the Office of Nuclear Energy. The MMRTG was developed by an industry team of Aerojet Rocketdyne and Teledyne Energy Systems. Space exploration missions require safe, reliable, long-lived power systems to provide electricity and heat to spacecraft and their science instruments. A uniquely capable source of power is the radioisotope thermoelectric generator (RTG) – essentially a nuclear battery that reliably converts heat into electricity. Radioisotope power has been used on eight Earth orbiting missions, eight missions travelling to each of the outer planets as well as each of Apollo missions following 11 to Earth's moon. Some of the outer Solar System missions are the Pioneer, Voyager, Ulysses, "Galileo", "Cassini" and "New Horizons" missions. The RTGs on "Voyager 1" and "Voyager 2" have been operating since 1977. Similarly, Radioisotope Heat Units (RHUs) were used to provide heat to critical components on Apollo 11 as well as the first two generations of Mars rovers. In total, over the last four decades, 26 missions and 45 RTGs have been launched by the United States. RTGs convert the heat from the natural decay of a radioisotope into electricity. The MMRTG's heat source is plutonium-238 dioxide | https://en.wikipedia.org/wiki?curid=22774009 |
Multi-mission radioisotope thermoelectric generator Solid-state thermoelectric couples convert the heat to electricity. Unlike solar arrays, the RTGs are not dependent upon the Sun, so they can be used for deep space missions. In June 2003, the Department of Energy (DOE) awarded the MMRTG contract to a team led by Aerojet Rocketdyne. Aerojet Rocketdyne and Teledyne Energy Systems collaborated on an MMRTG design concept based on a previous thermoelectric converter design, SNAP-19, developed by Teledyne for previous space exploration missions. SNAP-19s powered "Pioneer 10" and "Pioneer 11" missions as well as the Viking 1 and Viking 2 landers. The MMRTG is powered by eight Pu-238 dioxide general-purpose heat source (GPHS) modules, provided by the Department of Energy. Initially, these eight GPHS modules generate about 2 kW thermal power. The MMRTG design incorporates PbTe/TAGS thermoelectric couples (from Teledyne Energy Systems), where the TAGS material is a material incorporating Tellurium (Te), Silver (Ag), Germanium (Ge) and Antimony (Sb). The MMRTG is designed to produce 125 W electrical power at the start of mission, falling to about 100 W after 14 years. With a mass of 45 kg the MMRTG provides about 2.8 W/kg of electrical power at beginning of life. The MMRTG design is capable of operating both in the vacuum of space and in planetary atmospheres, such as on the surface of Mars. Design goals for the MMRTG included ensuring a high degree of safety, optimizing power levels over a minimum lifetime of 14 years, and minimizing weight | https://en.wikipedia.org/wiki?curid=22774009 |
Multi-mission radioisotope thermoelectric generator "Curiosity", the MSL rover that was successfully landed in Gale Crater on August 6, 2012, uses one MMRTG to supply heat and electricity for its components and science instruments. Reliable power from the MMRTG will allow it to operate for several years. In February 20, 2015, a NASA official reported that there is enough plutonium available to NASA to fuel three more MMRTG like the one used by the "Curiosity" rover. One is already committed to the Mars 2020 rover. The other two have not been assigned to any specific mission or program, and could be available by late 2021. | https://en.wikipedia.org/wiki?curid=22774009 |
Latex beads are the polymeric particles suspended in a latex. They are used in applications as contrast agents for fluorescent imaging, as particles for flow tracking, or as biological carriers. | https://en.wikipedia.org/wiki?curid=22774082 |
Graham Richards (William) (born 1 October 1939; Hoylake, Cheshire, United Kingdom) is a chemist and Emeritus Fellow of Brasenose College, Oxford. He served as head of the department of chemistry at the University of Oxford from 1997 to 2006. Richards is a pioneer in the field of computer-aided molecular design, in particular its application to the pharmaceuticals industry. He was the founding scientist of Oxford Molecular Ltd., and introduced a novel model for the funding of research at Oxford University, which has been copied elsewhere. Richards has published more than 300 scientific papers, including 15 books. was born 1 October 1939 in Hoylake, England, to Percy and Gwendoline Julia (Evans) Richards. Both parents were of Welsh extraction. Richards was educated at Birkenhead School. Richards won a scholarship to Brasenose College, Oxford, starting his studies there in 1958. Richards received his bachelor's degree in Chemistry with first class honors from the University of Oxford in 1961. Richards then studied the electronic spectroscopy of diatomic molecules with Richard F. Barrow, earning his Master of Arts and Doctor of Philosophy degrees from the University of Oxford in 1964. After his PhD, he continued his spectroscopic work with fellowships in Oxford (ICI Research Fellowship, Junior Research Fellowship at Balliol College) and Paris, France (Centre de Mécanique Ondulatoire Appliquée). soon returned to Oxford as a research fellow at Balliol College, Oxford (1964-1966) | https://en.wikipedia.org/wiki?curid=22775177 |
Graham Richards He was promoted to a lecturer at Oxford University (1966-1994), to reader (1994-1996), and to professor (1996-2007). He served as chairman of the chemistry department from 1997-2006. Richards celebrated his formal retirement from the University of Oxford on 18 May 2007. He is now an Emeritus fellow of Brasenose College. In the fourth year of his degree course Richard's research project led him to using Oxford's Ferranti Mercury computer to solve integrals. During a fellowship year in France at Centre de Mécanique Ondulatoire Appliquée, he was able to use more powerful computers. Returning to Oxford, he worked on "ab initio" computations and applied computational techniques to solving quantum mechanical problems in theoretical chemistry, in particular studying spin-orbit coupling. His influential paper "Third age of quantum chemistry" (1979) marked the development of computational techniques for theoretical analysis whose precision equaled or surpassed experimental results. Richards saw the potential to apply computer techniques for examining the structure and properties of compounds in the area of pharmaceutical applications. He became a pioneer in the field of computer-aided molecular design. He was the first to produce coloured images modelling molecular structure graphically, and introduced many of the techniques now widely used in academia and industry. In 1982, Richards became a founding member of the Molecular Graphics Society (now the Molecular Graphics and Modelling Society, MGMS) | https://en.wikipedia.org/wiki?curid=22775177 |
Graham Richards The society started the "Journal of Molecular Graphics" in 1983. Richards served as the editor-in-chief of the journal from 1984 to 1996. The journal's name changed to "Journal of Molecular Graphics and Modelling" in 1997. In 1989 Richards was the scientific co-founder (with Tony Marchington, David Ricketts, James Hiddleston, and Anthony Rees) of Oxford Molecular Limited. The company developed software for modelling of small molecules and proteins, and drug design. The company was possible in part because of economic and legal changes under the government of Margaret Thatcher that enabled British universities to become involved with venture capital and technology transfer. As Oxford Molecular Group, Ltd. (OMG) the company was floated on the London Stock Exchange in 1992, making the university £10 million. The company was worth £450 million at its peak but was eventually sold for £70 million. It was one of several companies that combined to form Accelrys in 2001. Richards was instrumental in raising £64 million to fund a new laboratory for Oxford University through an innovative funding approach. £20 million worth of funding began with an "unusual collaboration" between Graham and David Norwood. Norwood then arranged for Beeson-Gregory to provide £20 million in exchange for half the University's equity share of any spin-out companies emanating from the Chemistry Department for 15 years | https://en.wikipedia.org/wiki?curid=22775177 |
Graham Richards In 2003, Beeson-Gregory and Evolution Group merged, later creating a subsidiary, IP2IPO ("Intellectual property to initial public offering". became a Non-executive Director of IP2IPO in 2001, and Non-executive Chairman of IP2IPO in 2004. Through this arrangement the Chemistry Department has contributed over £100 million to the University of Oxford. Richards served as a director of ISIS Innovation Ltd., the University of Oxford's technology transfer company. It became Oxford University Innovation as of June 2016. It has brought around 60 spin-out companies into existence. The "Financial Times" has described the approach as "the way universities should be financed in the future". Richards also introduced the use of distributed computing in pharmaceutical design. Started in 2000, his Screensaver Lifesaver project exploited idle time on more than 3.5 million personal computers in over 200 countries, whose owners agreed to be involved and downloaded the project's screensaver. Using idle time from these computers, the project's software created a virtual supercomputer that screened billions of compounds against protein targets, searching for possible drug treatments for cancer, anthrax and smallpox. The project involved collaboration between Intel, United Devices, and the Centre for Computational Drug Discovery at the University of Oxford, headed by Richards and funded by the National Foundation for Cancer Research (NFCR). Graham formed the spin-out company InhibOx Ltd. in 2001 | https://en.wikipedia.org/wiki?curid=22775177 |
Graham Richards InhibOx applied cloud computing techniques to computational chemistry and drug discovery, and developed a searchable database of small-molecules called Scopius. In 2002, Richards donated his shares, twenty-five percent of the company, to the National Foundation for Cancer Research. In 2017, InhibOx relaunched as Oxford Drug Design Ltd., with a new focus on antibiotic discovery. Richards is a non-executive director of IP Group plc, having also served as its chairman. Richards is a council member of the Royal Society of Chemistry and of The Royal Institution, a Fellow of the Royal Society, and was appointed Commander of the Order of the British Empire (CBE). The "Times Higher Education Supplement" (2006) considered Richards to be one of twelve academic "super-earners" in the United Kingdom. "Times" magazine's first "Eureka" issue (2010) included Richards in its list of the top 100 British scientists. Richards' work has been acknowledged through a number of more formal awards and honours, including the following: Richards was married to his first wife, Jessamy Kershaw on 12 December 1970. She died of cancer in November 1988. As of 5 October 1996, Richards married Mary Elizabeth Phillips, director of research planning at University College London. He has two sons and three stepchildren. | https://en.wikipedia.org/wiki?curid=22775177 |
Liquid rheostat A liquid rheostat or water rheostat or salt water rheostat is a type of variable resistor. This may be used as a dummy load or as a starting resistor for large slip ring motors. In the simplest form it consists of a tank containing brine or other electrolyte solution, in which electrodes are submerged to create an electrical load. The electrodes may be raised or lowered into the liquid to respectively decrease or increase the electrical resistance of the load. To stabilize the load, the mixture must not be allowed to boil. Modern designs use stainless steel electrodes, and sodium carbonate, or other salts, and do not use the container as one electrode. In some designs the electrodes are fixed and the liquid is raised and lowered by an external cylinder or pump. Motor start systems used for frequent and rapid starts and re-starts, thus a high heat load to the rheostats, may include water circulation to external heat exchangers. In such cases anti-freeze and anti-corrosion additives must be carefully chosen to not change the resistance or support the growth of algae or bacteria. The salt water rheostat operates at unity power factor and presents a resistance with negligible series inductance compared to a wire wound equivalent, and was widely used by generator assemblers, until 20 years ago, as a matter of course. They are still sometimes constructed on-site for the commissioning of large diesel generators in remote places, where discarded oil drums and scaffold tubes may form an improvised tank and electrodes | https://en.wikipedia.org/wiki?curid=22775557 |
Liquid rheostat Typically a traditional liquid rheostat consists of a steel cylinder (the negative), about in size, standing on insulators, in which was suspended a hollow steel cylinder. This acted as the positive electrode and was supported by a steel rope and insulator from an adjustable pulley. The water pipe connection included an insulated section. The tank contained salt water, but not at the concentration that could be described as “brine”. The whole device was fenced off for safety. Operation was very simple, as adding more salt, more water or varying the height of the centre electrode would vary the load. The load proved to be quite stable, varying only slightly as the water heated up. It never came to the boil. Power dissipation was about 1 megawatt, at a potential of about 700 volts and current of about 1,500 amperes. Modern designs use stainless steel electrodes, and sodium carbonate, or other salts, and do not use the container as one electrode. Systems with frequent starting may include water circulation to external heat exchangers. In such cases anti-freeze and anti-corrosion additives must be carefully chosen to not change the resistance or support the growth of algae or bacteria. An advantage is silent operation, with none of the fan noise of current resistive grid designs. Disadvantages include: Railways commonly used salt water load banks in the 1950s to test the output power of diesel-electric locomotives. They were subsequently replaced by specially designed resistive load banks | https://en.wikipedia.org/wiki?curid=22775557 |
Liquid rheostat These later designs, rated for , currently cost in the region of 100,000 to 180,000 euro. Hence, it is economically advantageous for railways to build their own salt-water type. Some electric locomotives also used liquid rheostats, in particular in Italy for early three-phase AC types such as the FS Class E550. Some direct current designs also used them as starting resistors. Liquid rheostats were sometimes used in large (thousands of kilowatts/horsepower) wound rotor motor drives, to control the rotor circuit resistance and so the speed of the motor. Electrode position could be adjusted with a small electrically operated winch or a pneumatic cylinder. A cooling pump and heat exchanger were provided to allow slip energy to be dissipated into process water or other water system. High voltage distribution networks use fixed electrolyte resistors to ground the neutral, to provide a current limiting action, so that the voltage across the ground during fault is kept to a safe level. Unlike a solid resistor, the liquid resistor is self healing in the event of overload. Normally the resistance is set up during commissioning, and then left fixed. Modern motor starters are totally enclosed and the electrode movement is servo motor controlled. Typically a 1 tonne tank will start a 1 megawatt slip ring type motor, but there is considerable variation in start time depending on application. The fully salt-water load bank dates from an earlier, less regulated and litigious era | https://en.wikipedia.org/wiki?curid=22775557 |
Liquid rheostat To pass current safety legislation requires more enclosed designs. They are no more dangerous than electrode heaters, which work on the same principle, but with plain water, or electrical immersion heaters, provided the correct precautions are used. This requires connecting the container to both ground and neutral and breaking all poles with a linked over-current circuit breaker. If in the open, safety barriers are required. | https://en.wikipedia.org/wiki?curid=22775557 |
3,4-Dihydroxyphenylacetaldehyde (DOPAL) is an important metabolite of the major brain neurotransmitter dopamine. All of the enzymatic metabolism of dopamine in neurons passes through DOPAL. According to the "catecholaldehyde hypothesis," DOPAL plays a role in the pathogenesis of Parkinson's disease. DOPAL has been chemically synthesized. DOPAL is detoxified mainly by aldehyde dehydrogenase. | https://en.wikipedia.org/wiki?curid=22778967 |
Dioxetane A dioxetane or dioxacyclobutane is an organic compound with formula COH, whose backbone is a four-membered ring of two oxygen atoms and two carbon atoms. There are two isomers: | https://en.wikipedia.org/wiki?curid=22785075 |
Double diffusive convection is a fluid dynamics phenomenon that describes a form of convection driven by two different density gradients, which have different rates of diffusion. Convection in fluids is driven by density variations within them under the influence of gravity. These density variations may be caused by gradients in the composition of the fluid, or by differences in temperature (through thermal expansion). Thermal and compositional gradients can often diffuse with time, reducing their ability to drive the convection, and requiring that gradients in other regions of the flow exist in order for convection to continue. A common example of double diffusive convection is in oceanography, where heat and salt concentrations exist with different gradients and diffuse at differing rates. An effect that affects both of these variables is the input of cold freshwater from an iceberg. is important in understanding the evolution of a number of systems that have multiple causes for density variations. These include convection in the Earth's oceans (as mentioned above), in magma chambers, and in the sun (where heat and helium diffuse at differing rates). Sediment can also be thought as having a slow Brownian diffusion rate compared to salt or heat, so double diffusive convection is thought to be important below sediment laden rivers in lakes and the ocean | https://en.wikipedia.org/wiki?curid=22786313 |
Double diffusive convection Two quite different types of fluid motion exist—and therefore are classified accordingly—depending on whether the stable stratification is provided by the density-affecting component with the lowest or the highest molecular diffusivity. If the stratification is provided by the component with the lower molecular diffusivity (for example in case of a stable salt-stratified ocean perturbed by a thermal gradient due to an iceberg—a density ratio between 0 and 1), the stratification is called to be of "diffusive" type (see external link below), otherwise it is of "finger" type, occurring frequently in oceanographic studies as salt-fingers. These long fingers of rising and sinking water occur when hot saline water lies over cold fresh water of a higher density. A perturbation to the surface of hot salty water results in an element of hot salty water surrounded by cold fresh water. This element loses its heat more rapidly than its salinity because the diffusion of heat is faster than of salt; this is analogous to the way in which just unstirred coffee goes cold before the sugar has diffused to the top. Because the water becomes cooler but remains salty, it becomes denser than the fluid layer beneath it. This makes the perturbation grow and causes the downward extension of a salt finger. As this finger grows, additional thermal diffusion accelerates this effect. Double diffusion convection plays a significant role in upwelling of nutrients and vertical transport of heat and salt in oceans | https://en.wikipedia.org/wiki?curid=22786313 |
Double diffusive convection Salt fingering contributes to vertical mixing in the oceans. Such mixing helps regulate the gradual overturning circulation of the ocean, which control the climate of the earth. Apart from playing an important role in controlling the climate, fingers are responsible for upwelling of nutrients which supports flora and fauna. The most significant aspect of finger convection is that they transport the fluxes of heat and salt vertically, which has been studied extensively during the last five decades. The conservation equations for vertical momentum, heat and salinity equations (under Boussinesq’s approximation) have following form for double diffusive salt fingers: Where, U and W are velocity components in horizontal (x axis) and vertical (z axis) direction; k is the unit vector in the Z-direction, k is molecular diffusivity of heat, k is molecular diffusivity of salt, α is coefficient of thermal expansion at constant pressure and salinity and β is the coefficient of saline expansion at constant pressure and temperature. The above set of conservation equations governing the two-dimensional finger-convection system is non-dimensionalised using the following scaling: the depth of the total layer height H is chosen as the characteristic length, velocity (U, W), salinity (S), temperature (T) and time (t) are non-dimensionalised as Where, (T, S) and (T, S) are the temperature and concentration of the top and bottom layers respectively | https://en.wikipedia.org/wiki?curid=22786313 |
Double diffusive convection On introducing the above non-dimensional variables, the above governing equations reduce to the following form: Where, R is the density stability ratio, Ra is the thermal Rayleigh number, Pr is the Prandtl number, Sc is the Schmidt number which are defined as Figure 1(a-d) shows the evolution of salt fingers in heat-salt system for different Rayleigh numbers at a fixed R. It can be noticed that thin and thick fingers form at different Ra. Fingers flux ratio, growth rate, kinetic energy, evolution pattern, finger width etc. are found to be the function of Rayleigh numbers and R.Where, flux ratio is another important non-dimensional parameter. It is the ratio of heat and salinity fluxes, defined as, holds importance in natural processes and engineering applications. The effect of double diffusive convection is not limited to oceanography, also occurring in geology, astrophysics, and metallurgy. | https://en.wikipedia.org/wiki?curid=22786313 |
Chemotactic drug-targeting A special, reversal form of drug delivery where modulation of active migratory behaviour of the target cells is used to achieve targeted effects. The general components of the conjugates are designed as follows: (i) carrier – regularly possessing promoter effect also on internalization into the cell; (ii) chemotactically active ligands acting on the target cells; (iii) drug to be delivered in a selective way and (iv) spacer sequence which joins drug molecule to the carrier and due to it enzyme labile moiety makes possible the intracellular compartment specific release of the drug. Careful selection of chemotactic component of the ligand not only the chemoattractant character could be expended, however, chemorepellent ligands are also valuable as they are useful to keep away cell populations degrading the conjugate containing the drug. This mechanism of drug delivery is currently being studied. | https://en.wikipedia.org/wiki?curid=22787622 |
Chris Dobson Sir Christopher Martin Dobson (8 October 1949 – 8 September 2019) was a British chemist, who was the John Humphrey Plummer Professor of Chemical and Structural Biology in the Department of Chemistry at the University of Cambridge, and Master of St John's College, Cambridge. Dobson was born on 8 October 1949 in Rinteln, Germany, where his father, Arthur Dobson was commissioned as an officer. Both Arthur Dobson and Christopher Dobson's mother, Mabel Dobson (née Pollard), were originally from Bradford in Yorkshire and had left school at age 14. Dobson had two older siblings, Graham and Gillian. Due to his father's postings, Dobson also lived in Lagos, Nigeria. Christopher Dobson was educated at Hereford Cathedral Junior School, and then Abingdon School from 1960 until 1967. He completed a Master of Arts and Doctor of Philosophy at the University of Oxford, where he was a student of Keble College, Oxford and Merton College, Oxford. Dobson's research largely focused on protein folding and protein misfolding, and its association with medical disorders particularly Alzheimer's disease and Parkinson's disease. By applying chemical and biophysical techniques, Dobson investigated links between protein structure, function, and disease. He is well known for his serendipitous discovery that ordinary proteins can misfold and aggregate to form amyloid structures. Dobson authored and co-authored over 800 papers and review articles, including 38 in "Nature", "Science" and Cell, which have been cited over 100,000 times | https://en.wikipedia.org/wiki?curid=22790978 |
Chris Dobson his H-index is 153. Dobson held research fellowships at Merton College, Oxford and then Linacre College, Oxford before working at Harvard University. He returned to Oxford in 1980 as a Fellow of Lady Margaret Hall, Oxford and as a University Lecturer in Chemistry, later receiving promotions to Reader, then Professor of Chemistry in 1996. Dobson moved to the University of Cambridge in 2001 as the John Humphrey Plummer Professor of Chemical and Structural Biology. In 2007, he became the Master of St John's College, Cambridge, a post which he held until his death in September 2019. In 2012, Dobson founded the Cambridge Centre for Misfolding Diseases, which is currently based in the Chemistry of Health building at the Department of Chemistry at the University of Cambridge. In 2016, co-founded Wren Therapeutics, a biotechnology start-up company whose mission is to find new therapeutics for Alzheimer's disease. Dobson was knighted in the 2018 Queen's Birthday Honours for his contributions to science and higher education. In 2009, Dobson was awarded the Royal Medal by the Royal Society "for his outstanding contributions to the understanding of the mechanisms of protein folding and mis-folding, and the implications for disease", and in 2014 he received both the Heineken Prize for Biochemistry and Biophysics and the Feltrinelli International Prize for Medicine. Dobson was elected a Fellow of the Royal Society (FRS) in 1996 | https://en.wikipedia.org/wiki?curid=22790978 |
Chris Dobson His nomination reads: Dobson's other accolades include: Dobson mentored and supervised many notable PhD students and post-doctoral researchers, many of whom became renowned experts in their own field. These include: Dobson met his wife, Dr Mary Dobson (née Schove) at Merton College at the University of Oxford. They had two sons, Richard and William. He died on 8 September 2019, from cancer, at Royal Marsden Hospital in Sutton, near Surrey. | https://en.wikipedia.org/wiki?curid=22790978 |
Mole map (chemistry) In chemistry, the mole map is a graphical representation of an algorithm that compares molar mass, number of particles / mole, and factors from balanced equations or other formulae. | https://en.wikipedia.org/wiki?curid=22792377 |
Carpanone is a naturally occurring lignan-type natural product most widely known for the remarkably complex way nature prepares it, and the similarly remarkable success that an early chemistry group, that of Orville L. Chapman, had at mimicking nature's pathway. is an organic compound first isolated from the carpano trees ("Cinnamomum sp.") of Bougainville Island by Brophy and coworkers, trees from which the natural product derives its name. The hexacyclic lignan is one of a class of related diastereomers isolated from carpano bark as mixtures of equal proportion of the "handedness" of its components (i.e., racemic mixtures), and is notable in its stereochemical complexity, because it contains five contiguous stereogenic centers. The route by which this complex structure is achieved through biosynthesis involves a series of reactions that, almost instantly, take a molecule with little three-dimensionality to the complex final structure. Notably, Brophy and coworkers isolated the simpler carpacin, a phenylpropanoid with a 9-carbon framework, recognized its substructure as being dimerized within the complex carpanone structure, and proposed a hypothesis of how carpacin was converted to carpanone in plant cells: Remarkably, within two years, Chapman and coworkers were able to chemically design a route to mimic this proposed biosynthetic route, and achieved the synthesis of carpanone from carpacin in a single "pot", in about 50% yield | https://en.wikipedia.org/wiki?curid=22792515 |
Carpanone itself is limited in its pharmacologic and biologic activities, but related analogs arrived at by variations of the Brophy-Chapman approach have shown activities as tool compounds relevant to mammalian exocytosis and vesicular traffic, and provided therapeutic "hits" in antiinfective, antihypertensive, and hepatoprotective areas. The original Chapman design and synthesis is considered a classic in total synthesis, and one that highlights the power of biomimetic synthesis. The first total synthesis of carpanone was the biomimetic approach published by Chapman "et al." in 1971. The required desmethylcarpacin (2-allylsesamol), shown below as the starting molecule in the scheme, is acquired in two high-yield steps involving three transformations: This procedure is one of several that gives the required desmethylcarpacin (carpacin with the methyl of its methoxy group removed). Though oxidative dimerizations of phenols normally used a 1-electron oxidant, Chapman then followed a precedent involving a 2-electron oxidant and treated desmethylcarpacin with PdCl in the presence of sodium acetate (e.g., dissolved in a mixture of methanol and water); the reaction was perceived to proceed via a complexation of a pair of carpacins to the Pd(II) metal via their phenolic anions (as shown in scheme, below right), followed by a classic 8-8' (β-β') oxidative phenolic coupling of the two olefin tails—shown crossing in the image—to give a dimeric "trans"-"ortho"-quinone methide-type of lignan intermediate | https://en.wikipedia.org/wiki?curid=22792515 |
Carpanone A particular conformation of this dimer then places a 4-electron enone of one ring over the 2-electron enol of the other (shown adjacent in image for clarity), setting the state for a variant of the Diels-Alder reaction termed an inverse demand Diels-Alder reaction (see curved arrows in image), which closes the 2 new rings and generates the 5 contiguous stereocenters. The carpanone is produced in yields of ≈50% by the original method, and in yields >90% in modern variants (see below). The synthesis of a single diastereomer was confirmed in the original Chapman work, using X-ray crystallography. For the elegance of its "one-pot construction of a tetracyclic scaffold with complete stereocontrol of five contiguous stereo centers", the original Chapman design and synthesis is "[n]ow considered a classic in total synthesis" that "highlights the power of biomimetic synthesis". The Chapman approach has been applied in a variety of ways since its original report, varying substrates, oxidants, and other aspects (and so synthesis of carpanone has subsequently been achieved by "quite a few research groups"); the actual mechanism of Pd(II) action is likely more complex than the original conjecture, and there is evidence that the mechanism, broadly speaking, depends on actual conditions (specific substrate, oxidant, etc.). Various groups, including the laboratories of Steve Ley, Craig Lindley, and Matthew Shair, have succeeded in extending the Chapman method to "solid-supported synthesis", i.e | https://en.wikipedia.org/wiki?curid=22792515 |
Carpanone , phenolic starting materials on polymeric supports, thus allowing the generation of libraries of carpanone analogs. A hetero-8-8' oxidative coupling system akin to the Chapman approach has been developed that uses IPh(OAC), and that allows for preparation of more electron rich homodimers, and for hetero-tetracyclic analogs of carpanone. | https://en.wikipedia.org/wiki?curid=22792515 |
Cucurbitacin is any of a class of biochemical compounds that some plants — notably members of the family Cucurbitaceae, which includes the common pumpkins and gourds — produce and which function as a defence against herbivores. Cucurbitacins are chemically classified as triterpenes, formally derived from cucurbitane, a triterpene hydrocarbon—specifically, from the unsaturated variant cucurbita-5-ene, or 19-(10→9β)-abeo-10α-lanost-5-ene. They often occur as glycosides. They and their derivatives have been found in many plant families (including Brassicaceae, Cucurbitaceae, Scrophulariaceae, Begoniaceae, Elaeocarpaceae, Datiscaceae, Desfontainiaceae, Polemoniaceae, Primulaceae, Rubiaceae, Sterculiaceae, Rosaceae, and Thymelaeaceae), in some mushrooms (including Russula and Hebeloma) and even in some marine mollusks. Cucurbitacins may be a taste deterrent in plants foraged by some animals and in some edible plants preferred by humans, like cucumbers. In laboratory research, cucurbitacins have cytotoxic properties and are under study for their potential biological activities. The biosynthesis of cucurbitacin C has been described. Zhang et al. (2014) identified nine cucumber genes in the pathway for biosynthesis of cucurbitacin C and elucidated four catalytic steps. These authors also discovered the transcription factors "Bl" (Bitter leaf) and "Bt" (Bitter fruit) that regulate this pathway in leaves and fruits, respectively | https://en.wikipedia.org/wiki?curid=22800366 |
Cucurbitacin The Bi gene confers bitterness to the entire plant and is genetically associated with an operon-like gene cluster, similar to the gene cluster involved in thalianol biosynthesis in "Arabidopsis". Fruit bitterness requires both Bi and the dominant Bt (Bitter fruit) gene. Nonbitterness of cultivated cucumber fruit is conferred by bt, an allele selected during domestication. Bi is a member of the oxidosqualene cyclase (OSC) gene family. Phylogenetic analysis showed that Bi is the ortholog of cucurbitadienol synthase gene CPQ in squash ("Cucurbita pepo") The cucurbitacins include: There are several substances that can be seen as derving from cucurbita-5-ene skeleton by loss of one of the methyl groups (28 or 29) attached to carbon 4; often with the adjacent ring (ring A) becoming aromatic. Several other cucurbitacins have been found in plants. Constituents of the colocynth fruit and leaves ("Citrullus colocynthis") include cucurbitacins. The 2-O-β-D-glucopyranosides of cucurbitacins K and L can be extracted with ethanol from fruits of "Cucurbita pepo" cv "dayangua". Pentanorcucurbitacins A and B can be extracted with methanol from the stems of "Momordica charantia". Cucurbitacins B and I, and derivatives of cucurbitacins B, D and E, can be extracted with methanol from dried tubers of "Hemsleya endecaphylla". Cucurbitacins impart a bitter taste in plant foods such as cucumber, zucchini, melon and pumpkin | https://en.wikipedia.org/wiki?curid=22800366 |
Cucurbitacin Cucurbitacins are under basic research for their biological properties, including toxicity and potential pharmacological uses in development of drugs for inflammation, cancer, cardiovascular diseases, and diabetes, among others. The toxicity associated with consumption of foods high in cucurbatincs is sometimes referred to as "toxic squash syndrome". In France in 2018, two women who ate soup made from bitter pumpkins became sick, involving nausea, vomiting, and diarrhea, and had hair loss weeks later. Another French study of poisoning from bitter squash consumption found similar acute illnesses and no deaths. The high concentration of toxin in the plants could result from cross-pollination with wild cucurbitaceae species, or from plant growth stress due to high temperature and drought. Research on antitumor activity of cucurbitacin focuses on four main variants of this molecule. Cucurbitacins with the most prominent antitumor activity are B, D, E and I. Of these, cucurbitacin B and D are the most common in plants. The mechanisms by which it affects cancer cells are mainly inhibition of STAT3 signaling pathway, induction of apoptosis and cell cycle arrest. It also affects function of proteasome and inflammasome. Pathologists found cucurbitacin in the stomach of a 79-year-old man who died in Baden-Württemberg, Germany, shortly after eating a casserole containing zucchini he had received from a neighbor. | https://en.wikipedia.org/wiki?curid=22800366 |
Biexciton In condensed matter physics, biexcitons are created from two free excitons. In quantum information and computation, it is essential to construct coherent combinations of quantum states. The basic quantum operations can be performed on a sequence of pairs of physically distinguishable quantum bits and, therefore, can be illustrated by a simple four-level system. In an optically driven system where the formula_1 and formula_2 states can be directly excited, direct excitation of the upper formula_3 level from the ground state formula_4 is usually forbidden and the most efficient alternative is coherent nondegenerate two-photon excitation, using formula_1 or formula_2 as an intermediate state. Three possibilities of observing biexcitons exist: (a) excitation from the one-exciton band to the biexciton band (pump-probe experiments); (b) two-photon absorption of light from the ground state to the biexciton state; (c) luminescence from a biexciton state made up from two free excitons in a dense exciton system. The biexciton is a quasi-particle formed from two excitons, and its energy is expressed as where formula_8 is the biexciton energy, formula_9 is the exciton energy, and formula_10 is the biexciton binding energy. When a biexciton is annihilated, it disintegrates into a free exciton and a photon. The energy of the photon is smaller than that of the biexciton by the biexciton binding energy, so the biexciton luminescence peak appears on the low-energy side of the exciton peak | https://en.wikipedia.org/wiki?curid=22802888 |
Biexciton The biexciton binding energy in semiconductor quantum dots has been the subject of extensive theoretical study. Because a biexciton is a composite of two electrons and two holes, we must solve a four-body problem under spatially restricted conditions. The biexciton binding energies for CuCl quantum dots, as measured by the site selective luminescence method, increased with decreasing quantum dot size. The data were well fitted by the function where formula_12 is biexciton binding energy, formula_13 is the radius of the quantum dots, formula_14 is the binding energy of bulk crystal, and formula_15 and formula_16 are fitting parameters. In the effective-mass approximation, the Hamiltonian of the system consisting of two electrons (1, 2) and two holes (a, b) is given by where formula_18 and formula_19 are the effective masses of electrons and holes, respectively, and where formula_21 denotes the Coulomb interaction between the charged particles formula_22 and formula_23 (formula_24 denote the two electrons and two holes in the biexciton) given by where formula_26 is the dielectric constant of the material. Denoting formula_27 and formula_28 are the c.m. coordinate and the relative coordinate of the biexciton, respectively, and formula_29 is the effective mass of the exciton, the Hamiltonian becomes where formula_31; formula_32 and formula_33 are the Laplacians with respect to relative coordinates between electron and hole, respectively. And formula_34 is that with respect to relative coordinate between the c. m | https://en.wikipedia.org/wiki?curid=22802888 |
Biexciton of excitons, and formula_35 is that with respect to the c. m. coordinate formula_27 of the system. In the units of the exciton Rydberg and Bohr radius, the Hamiltonian can be written in dimensionless form where formula_38 with neglecting kinetic energy operator of c. m. motion. And formula_39 can be written as To solve the problem of the bound states of the biexciton complex, it is required to find the wave functions formula_41 satisfying the wave equation If the eigenvalue formula_8 can be obtained, the binding energy of the biexciton can be also acquired where formula_10 is the binding energy of the biexciton and formula_9 is the energy of exciton. The diffusion Monte Carlo (DMC) method provides a straightforward means of calculating the binding energies of biexcitons within the effective mass approximation. For a biexciton composed of four distinguishable particles (e.g., a spin-up electron, a spin-down electron, a spin-up hole and a spin-down hole), the ground-state wave function is nodeless and hence the DMC method is exact. DMC calculations have been used to calculate the binding energies of biexcitons in which the charge carriers interact via the Coulomb interaction in two and three dimensions, indirect biexcitons in coupled quantum wells, and biexcitons in monolayer transition metal dichalcogenide semiconductors. Biexcitons with bound complexes formed by two excitons are predicted to be surprisingly stable for carbon nanotube in a wide diameter range | https://en.wikipedia.org/wiki?curid=22802888 |
Biexciton Thus, a biexciton binding energy exceeding the inhomogeneous exciton line width is predicted for a wide range of nanotubes. The biexciton binding energy in carbon nanotube is quite accurately approximated by an inverse dependence on formula_47, except perhaps for the smallest values of formula_47. The actual biexciton binding energy is inversely proportional to the physical nanotube radius. Experimental evidence of biexcitons in carbon nanotubes was found in 2012. The binding energy of biexcitons increase with the decrease in their size and its size dependence and bulk value are well represented by the expression | https://en.wikipedia.org/wiki?curid=22802888 |
Lilleby smelteverk was a smeltmill located in Lilleby, Trondheim, Sør-Trøndelag county, Norway, next to City Lade. It is well known for having produced the world's cleanest ferrosilicon (an alloy that contains iron and silicon) for NASA. Professor Harald Christian Pederson founded the A/S Ila and melting facilities in the 1920s. He worked with a chemical process which later has been called the Pederson-2 process. It consists of melting ironmalm which gives ferrosilicon as a by-product. Lilleby closed on the same day Norway was attacked by Nazi Germany, but it did not remain closed for long. The Norwegian aluminium industry was of great strategic importance for the German government, which requested that Lilleby resume operation right away. Birger Solberg was placed in charge, because professor Pedersen had left with his family to Sweden. Solberg was dismissed the day that Pederson returned, undoubtedly related to his views on the occupation, which differed from Professor Pedersen's views: Pedersen was a supporter of Nazi Germany and wanted to collaborate with the occupation. During the war, the plant was geared mostly towards aluminium, which was more important for the German war effort; however, many employees sabotaged the work in order to keep productivity low. After the war, Birger Solberg resumed control, but the economics and equipment of the facility had become unfavorable | https://en.wikipedia.org/wiki?curid=22803616 |
Lilleby smelteverk Feeling empathy for the former workers, he devised a new business plan based on collecting German plane wrecks and other debris in middle-Norway and re-melting them. The facility was closed on December 20, 2002 and production moved to Mo i Rana. | https://en.wikipedia.org/wiki?curid=22803616 |
Ferrocene-containing dendrimers are dendrimers that contain ferrocene substituents. Some ferrocene-containing dendrimers feature ferrocene cores and others do not. All feature with peripheral ferrocene groups. can be synthesized by both convergent and divergent methods. Some of the first dendrimers of this type, were made by attaching ferrocene units to small silicon containing dendrimers. Dendrimers with peripheral ferrocene groups are usually synthesized by attaching ferrocene to the core by either olefin metathesis or by hydrosilylation. As an example, tetraallylsilane undergoes Pt-catalyzed hydrosilylation to form the core. This core was then reacted with ferrocenyllithium to form 1. Convergent approaches can also be used to make dendrimers with peripheral ferrocene. As an example, figure 1 shows a 54-ferrocene dendrimer which was synthesized by a fast convergent approach. Dendrimers with ferrocene cores have been synthesized by decorating suitably functionalized ferrocenes, e.g., decaallylferrocene. synthesis can be synthesized by convergence and diffusion methods. By linking ferrocene units to small silicon-containing dendrimers, some of these first-type dendrimers can be made. [3] Dendritic macromolecules with peripheral ferrocene groups are usually synthesized by linking ferrocene to the core through olefin metathesis or hydrosilylation [1]. For example, tetraallyl silane undergoes Pt-catalyzed hydrosilylation to form a core. The core is then reacted with ferrocenyl lithium to form 1. [4] | https://en.wikipedia.org/wiki?curid=22808473 |
Ferrocene-containing dendrimers The convergence method can also be used to make dendrimers with peripheral ferrocene. en.china.cn is a good place to supply polymer resin No applications have been identified for ferrocene-containing dendrimers. They exhibit multielectron redox indicating that the ferrocenyl moieties are essentially noninteracting redox centers. | https://en.wikipedia.org/wiki?curid=22808473 |
Sterically induced reduction In chemistry, a sterically induced reduction happens when an oxidized metal behaves as, and exhibits similar reducing properties to, the more reduced form of the metal. This effect is mainly caused by the surrounding ligands that are complexed to the metal and it is the ligands that are involved in the reduction chemistry instead of the metal due to electronic destabilization by being significantly distanced from the metal. Sterically induced reductions commonly involve metals found in the lanthanoid and actinoid series. Divalents Lanthanides are extremely reducing (can reduce alkali cations) compounds. Of these divalent lanthanides, Samarium(II) iodide, SmI, is a common reducing agent that is used in a variety of synthetic applications, mainly because all other divalent lanthanides are unstable. Complexes of Sm(II) have also been investigated and used in similar applications. However, even though Sm(II) complexes and compounds have had tremendous success when used in conjunction with a variety of substrates. There have been instances where chemistry of certain materials cannot be performed due to unclean reactions in which products are not easily isolated from reaction mixtures when Sm(II) compounds are used to perform the desired reduction. In these cases, adjusting the size of the metal (which is commonly and easily done for the trivalent lanthanide compounds) may fine tune the nature of a specific reaction, which should produce desired and clean products | https://en.wikipedia.org/wiki?curid=22809644 |
Sterically induced reduction One drawback to this notion is that Sm(II) is uniquely stable compared to other divalent lanthanides, where the other metals in the series tend to exist freely in the trivalent state. The discovery and application of sterically induced reductions allows the unique reducing properties and chemistry to be applicable to all of the lanthanide metals while remaining in their more stable trivalent state. When Sm(III) is complexed with (pentamethylcyclopentadiene) to give the compound , this trivalent species has been shown to have the same reducing reactivity of the Sm(II) derivative. The top reaction is the Sm(III) derivative and the bottom involves the Sm(II) derivative. Notice that the oxidation state of the metal in the top reaction does not change, while the oxidation state changes in the bottom one. If the metal was involved in the reduction the oxidation states should have changed (+3 to +4). For the trivalent compound this is not the case, thus the ligands themselves must be involved in the reduction process via the following redox reaction: But ligand induced reductions are not new and have been known to happen with a variety of lanthanide complexes. However, steric factors must also be considered on the reactivity of the Sm(III) complex as less crowded structures do not have any reductive activity. For years, it was thought that (CMe)Sm was not a possible compound due to the huge strain of cone angles greater than 120 degrees | https://en.wikipedia.org/wiki?curid=22809644 |
Sterically induced reduction However, this compound is formed from the Sm(II) complex, and X-Ray structures of the Sm(II) complex have shown that there was enough room for a third spot. Also, X-ray structures of (CMe)Sm show that the CMes are 0.1 Angstroms farther from the metal than normally predicted and expected. This increased distance, forced by sterics, makes the ligands have less electronic stability and may be a possible reason for the observed redox reaction of the ligands instead of the metal. Sm is a typical and well studied metal due to its unusual stability in a divalent and trivalent state. With the discovery of sterically induced reductions other lanthanide metals can now be studied in their more stable trivalent state, which can allow for more control of reduction reactions by tuning the reaction based on the metal size and electronics. | https://en.wikipedia.org/wiki?curid=22809644 |
Strep-tag The Strep-tag® system is a method which allows the purification and detection of proteins by affinity chromatography. The II is a synthetic peptide consisting of eight amino acids (Trp-Ser-His-Pro-Gln-Phe-Glu-Lys). This peptide sequence exhibits intrinsic affinity towards Strep-Tactin®, a specifically engineered streptavidin, and can be N- or C- terminally fused to recombinant proteins. By exploiting the highly specific interaction, "Strep"-tagged proteins can be isolated in one step from crude cell lysates. Because the "Strep"-tag elutes under gentle, physiological conditions it is especially suited for generation of functional proteins. Streptavidin is a tetrameric protein expressed in "Streptomyces avidinii". Because of its high affinity for the vitamin h-biotin, Streptavidin is commonly used in the fields of molecular biology and biotechnology. The was originally selected from a genetic library to specifically bind to a proteolytically truncated "core" version of streptavidin. Over the years, the was systemically optimized, to permit a greater flexibility in the choice of attachment site. Further, its interaction partner, Streptavidin, was also optimized to increase peptide-binding capacity, which resulted in the development of Strep-Tactin. The binding affinity of to Strep-Tactin is nearly 100 times higher than to Streptavidin. The so-called system, consisting of and Strep-Tactin, has proven particularly useful for the functional isolation and analysis of protein complexes in proteome research | https://en.wikipedia.org/wiki?curid=22810498 |
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