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Magic Angle Spinning
In solid-state NMR spectroscopy, magic-angle spinning (MAS) is a technique routinely used to produce better resolution NMR spectra. MAS NMR consists in spinning the sample (usually at a frequency of 1 to 130 kHz) at the magic angle θm (ca. 54.74°, where cos2θm=1/3) with respect to the direction of the magnetic field. Three main interactions responsible in solid state NMR (dipolar, chemical shift anisotropy, quadrupolar) often lead to very broad and featureless NMR lines. However, these three interactions in solids are orientation-dependent and can be averaged to some extent by MAS: * The nuclear dipolar interaction has a 3\cos^2\theta - 1 dependence, where \theta is the angle between the internuclear axis and the main magnetic field. As a result, the dipolar interaction vanish at the magic angle θm and the interaction contributing to the line broadening is removed. Even though all internuclear vectors cannot be all set to the magic angle, rotating the sample around t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silicon Nitride
Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable and commercially important of the silicon nitrides, and the term "silicon nitride" commonly refers to this specific composition. It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot . It is very hard (8.5 on the mohs scale). It has a high thermal stability with strong optical nonlinearities for all-optical applications. Production Silicon nitride is prepared by heating powdered silicon between 1300 °C and 1400 °C in a nitrogen atmosphere: :3 Si + 2 → The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen. Without an iron catalyst, the reaction is complete after several hours (~7), when no further weight increase due to nitrogen absorption (per gram of silicon) is detected. In addition to , several other silicon nitride phases (with chemica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Edward Raymond Andrew
Edward Raymond Andrew FRS FRSE (27 June 1921 – 27 May 2001) was a 20th-century British scientist who was a pioneer of nuclear magnetic resonance. He was a primary figure in the development and creation of the world's first MRI scanner. Life He was born in Boston, Lincolnshire on 27 June 1921 the only child of English parents of Scots descent. He was educated at Wellingborough School where he was head boy. He then won a place at Christ's College, Cambridge on a Natural Science Tripos from 1939 to 1942 under C. P. Snow, Lawrence Bragg, Norman Feather and David Shoenberg.Independent (newspaper) obituary 26 July 2001 From 1942 to 1945, during the Second World War he was Scientific Officer at the Air Defence Research and Development Establishment in Malvern studying the effects of gunflashes on radar. In 1945 he returned to Cambridge as a research student at Pembroke College and at the Cavendish Laboratory. Here he worked with David Shoenberg on superconductors, gainin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boron Nitride
Boron nitride is a thermally and chemically resistant refractory compound of boron and nitrogen with the chemical formula BN. It exists in various crystalline forms that are isoelectronic to a similarly structured carbon lattice. The hexagonal form corresponding to graphite is the most stable and soft among BN polymorphs, and is therefore used as a lubricant and an additive to cosmetic products. The cubic ( zincblende aka sphalerite structure) variety analogous to diamond is called c-BN; it is softer than diamond, but its thermal and chemical stability is superior. The rare wurtzite BN modification is similar to lonsdaleite but slightly softer than the cubic form. Because of excellent thermal and chemical stability, boron nitride ceramics are used in high-temperature equipment and metal casting. Boron nitride has potential use in nanotechnology. Structure Boron nitride exists in multiple forms that differ in the arrangement of the boron and nitrogen atoms, giving rise to var ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zirconium Dioxide
Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant. Production, chemical properties, occurrence Zirconia is produced by calcining zirconium compounds, exploiting its high thermostability.Ralph Nielsen "Zirconium and Zirconium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. Structure Three phases are known: monoclinic below 1170 °C, tetragonal between 1170 °C and 2370 °C, and cubic above 2370 °C. The trend is for higher symmetry at higher temperatures, as is usually the case. A small percentage of the oxides of calcium or yttrium stabilize in the cubic phase. The very rare mineral tazheranite, , ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vespel
Vespel is the trademark of a range of durable high-performance polyimide-based plastics made by DuPont. The one shown in the structure on the right was the first to be commercialized. Characteristics and applications Vespel is mostly used in aerospace, semiconductor, and transportation technology. It combines heat resistance, lubricity, dimensional stability, chemical resistance, and creep resistance, and can be used in hostile and extreme environmental conditions. Unlike most plastics, it does not produce significant outgassing even at high temperatures, which makes it useful for lightweight heat shields and crucible support. It also performs well in vacuum applications, down to extremely low cryogenic temperatures. However, Vespel tends to absorb a small amount of water, resulting in longer pump time while placed in a vacuum. Although there are polymers surpassing polyimide in each of these properties, the combination of them is the main advantage of Vespel. Thermophysic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polychlorotrifluoroethylene
Polychlorotrifluoroethylene (PCTFE or PTFCE) is a thermoplastic chlorofluoropolymer with the molecular formula , where ''n'' is the number of monomer units in the polymer molecule. It is similar to polytetrafluoroethene (PTFE), except that it is a homopolymer of the monomer chlorotrifluoroethylene (CTFE) instead of tetrafluoroethene. It has the lowest water vapor transmission rate of any plastic. History It was discovered in 1934 by Fritz Schloffer and Otto Scherer who worked at IG Farben Company, Germany. Trade names After World War II, PCTFE was commercialized under the trade name of Kel-F 81 by M. W. Kellogg Company in early 1950s. The name "Kel-F" was derived from "Kellogg" and "fluoropolymer", which also represents other fluoropolymers like the copolymer poly(chlorotrifluoroethylene-co-vinylidene fluoride) (Kel-F 800). These were acquired by 3M Company in 1957. But 3M discontinued manufacturing of Kel-F by 1996. PCTFE resin is now manufactured in different trade ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polyoxymethylene
Polyoxymethylene (POM), also known as acetal, polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Kocetal, Ultraform, Celcon, Ramtal, Duracon, Kepital, Polypenco, Tenac and Hostaform. POM is characterized by its high strength, hardness and rigidity to −40 °C. POM is intrinsically opaque white because of its high crystalline composition but can be produced in a variety of colors. POM has a density of 1.410–1.420g/cm3. Typical applications for injection-molded POM include high-performance engineering components such as small gear wheels, eyeglass frames, ball bearings, ski bindings, fasteners, gun parts, knife handles, and lock systems. The material is widely used in the automotive and consumer elec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Poly(methyl Methacrylate)
Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite, Astariglas, Lucite, Perclax, and Perspex, among several others ( see below). This plastic is often used in sheet form as a lightweight or shatter-resistant alternative to glass. It can also be used as a casting resin, in inks and coatings, and for many other purposes. Although not a type of familiar silica-based glass, the substance, like many thermoplastics, is often technically classified as a type of glass, in that it is a non-crystalline vitreous substance—hence its occasional historic designation as ''acrylic glass''. Chemically, it is the synthetic polymer of methyl methacrylate. It was developed in 1928 in several different laboratories by many chemists, such as William Chalmers, Otto Röhm, and Walter Bauer, and first brough ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Turbine
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator.Munson, Bruce Roy, T. H. Okiishi, and Wade W. Huebsch. "Turbomachines." Fundamentals of Fluid Mechanics. 6th ed. Hoboken, NJ: J. Wiley & Sons, 2009. Print. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels. Gas, steam, and water turbines have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to Anglo-Irish engineer Sir Charles Parsons (1854–1931) for invention of the reaction turbine, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid-state NMR
Solid-state NMR (ssNMR) spectroscopy is a technique for characterizing atomic level structure in solid materials e.g. powders, single crystals and amorphous samples and tissues using nuclear magnetic resonance (NMR) spectroscopy. The anisotropic part of many spin interactions are present in solid-state NMR, unlike in solution-state NMR where rapid tumbling motion averages out many of the spin interactions. As a result, solid-state NMR spectra are characterised by larger linewidths than in solution state NMR, which can be utilized to give quantitative information on the molecular structure, conformation and dynamics of the material. Solid-state NMR is often combined with magic angle spinning to remove anisotropic interactions and improve the resolution as well as the sensitivity of the technique. Nuclear spin interactions The resonance frequency of a nuclear spin depends on the strength of the magnetic field at the nucleus, which can be modified by isotropic (e.g. chemical shift, is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MAS Rotors
Mas, Más or MAS may refer to: Film and TV * Más y Menos, fictional superhero characters, from the Teen Titans animated television series * "Más" (''Breaking Bad''), a season three episode of ''Breaking Bad'' Songs * ''Más'' (album), by Spanish singer Alejandro Sanz * "Más", by José José from the 1985 album ''Promesas'' * "Más", by Kinky from their 2002 album '' Kinky'' * "Más" (Nelly Furtado song), from her 2009 album ''Mi Plan'' * "Más" (Ricky Martin song), from his 2011 album ''Música + Alma + Sexo'' * "Más", by Selena Gómez from her 2014 album '' For You'' * "+" (song), Aitana and Cali y El Dandee from her 2019 album ''11 Razones'' Computing * MAS 90, Sage accounting software * Motu Audio System, now Digital Performer, audio sequencer software * Multi-agent system, built of multiple interacting agents * Malware Analysis System by FireEye Education * Master of Advanced Studies, an academic degree * Master of Advanced Study, a professional degree * Master of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
