|
Zerodur
Zerodur (notation of the manufacturer: ZERODUR®), registered trademarkof Schott AG, is a lithium-aluminosilicate glass-ceramic produced by Schott AG since 1968. It has been used for a number of very large telescope mirrors including GTC, Keck I, Keck II, and SOFIA, as well as some smaller telescopes (such as the GREGOR Solar Telescope). With its very low coefficient of thermal expansion (CTE) it can be used to produce mirrors that retain acceptable figures in extremely cold environments such as deep space. Although it has advantages for applications requiring a coefficient of thermal expansion less than that of borosilicate glass, it remains very expensive as compared to borosilicate. The tight tolerance on CTE, ±0.007 K−1, allows for its use in high-precision applications. Applications # Optics # Microlithography # Measurement technology Properties Zerodur has both an amorphous (vitreous) component and a crystalline component. Its most important properties are: * Particul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schott AG
Schott AG is a German multinational glass company specializing in the manufacture of glass and glass-ceramics. Headquartered in Mainz, Germany, it is owned by the Carl Zeiss Foundation. The company's founder and namesake, Otto Schott, is credited with the invention of borosilicate glass. History Founding In 1884, Otto Schott, Ernst Abbe, Carl Zeiss and his son Roderich Zeiss founded the ''Glastechnische Laboratorium Schott & Genossen'' (Glass Technical Laboratory Schott & Associates) in Jena, which initially produced optical glasses for microscopes and telescopes. In 1891, the Carl Zeiss Foundation founded two years earlier by Ernst Abbe became a partner in the glass laboratory. Jena glass, an early borosilicate glass, was one of its early manufactured products. The invention of borosilicate glass, resistant to chemicals, heat and temperature change, paved the way for new technical glasses for thermometers, laboratory equipment and gas lamps. The company experience ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glass-ceramic
Glass-ceramics are polycrystalline materials produced through controlled crystallization of base glass, producing a fine uniform dispersion of crystals throughout the bulk material. Crystallization is accomplished by subjecting suitable glasses to a carefully regulated heat treatment schedule, resulting in the nucleation and growth of crystal phases. In many cases, the crystallization process can proceed to near completion, but in a small proportion of processes, the residual glass phase often remains. Glass-ceramic materials share many properties with both glasses and ceramics. Glass-ceramics have an amorphous phase and one or more crystalline phases and are produced by a so-called "controlled crystallization" in contrast to a spontaneous crystallization, which is usually not wanted in glass manufacturing. Glass-ceramics have the fabrication advantage of glass, as well as special properties of ceramics. When used for sealing, some glass-ceramics do not require brazing but can withs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gran Telescopio Canarias
The Gran Telescopio Canarias (GranTeCan or GTC) is a reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain. It is the world's largest single-aperture optical telescope. Construction of the telescope took seven years and cost €130 million. Its installation was hampered by weather conditions and the logistical difficulties of transporting equipment to such a remote location. First light was achieved in 2007 and scientific observations began in 2009. The GTC Project is a partnership formed by several institutions from Spain and Mexico, the University of Florida, the National Autonomous University of Mexico, and the Instituto de Astrofísica de Canarias (IAC). Planning for the construction of the telescope, which started in 1987, involved more than 1,000 people from 100 companies. The division of telescope time reflects the structure of its financing: 90% Spain, 5% Mexico and 5% the University of Florida. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keck I
The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when completed in 1993 (Keck 1) and 1996 (Keck 2) were the largest astronomical telescopes in the world. They are currently the 3rd and 4th largest. Overview With a concept first proposed in 1977, telescope designers at the University of California, Berkeley (Terry Mast) and Lawrence Berkeley Laboratory ( Jerry Nelson) had been developing the technology necessary to build a large, ground-based telescope. With a design in hand, a search for the funding began. In 1985, Howard B. Keck of the W. M. Keck Foundation gave $70 million to fund the construction of the Keck I telescope, which began in September 1985, with first light occurring on 24 November 1990 using nine of the eventual 36 segments. With construction of the first telescope well ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coefficient Of Thermal Expansion
Thermal expansion is the tendency of matter to change its shape A shape or figure is a graphics, graphical representation of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other properties such as color, Surface texture, texture, or material type. A pl ..., area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain (mechanics), strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coefficient Of Thermal Expansion
Thermal expansion is the tendency of matter to change its shape A shape or figure is a graphics, graphical representation of an object or its external boundary, outline, or external Surface (mathematics), surface, as opposed to other properties such as color, Surface texture, texture, or material type. A pl ..., area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain (mechanics), strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ELT Secondary Mirror Blank Successfully Cast
ELT may refer to: Education * English language teaching * Expanded learning time, an American education strategy * Kolb's experiential learning theory Mathematics and science * Ending lamination theorem * Extremely large telescope, a type of telescope * Extremely Large Telescope, an astronomical observatory under construction in Chile * Effective lifetime temperature, used in rehydroxylation dating Medicine * Endovenous laser treatment * Euglobulin lysis time * Excimer laser trabeculostomy Music * Every Little Thing (band), a Japanese J-Pop band * "ELT", a song by the band Wilco from their 1999 album '' Summerteeth'' Technology * Emergency locator transmitter * Extract, load, transform, a data processing concept * End-of-life tyre Transport * East London Transit, a British public transport system * El Tor Airport, in Egypt * Elizabethtown station, Pennsylvania Other uses * Electrical lighting technician, a stage-lighting technician * Electronic lien and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically, density is defined as mass divided by volume: : \rho = \frac where ''ρ'' is the density, ''m'' is the mass, and ''V'' is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure. To simplify comparisons of density across different s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sintered
Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plastics, and other materials. The atoms in the materials diffuse across the boundaries of the particles, fusing the particles together and creating one solid piece. Because the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points such as tungsten and molybdenum. The study of sintering in metallurgical powder-related processes is known as powder metallurgy. An example of sintering can be observed when ice cubes in a glass of water adhere to each other, which is driven by the temperature difference between the water and the ice. Examples of pressure-driven sintering are the compact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fracture Toughness
In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value which is a material property. The critical value of stress intensity factor in mode I loading measured under plane strain conditions is known as the plane strain fracture toughness, denoted K_\text. When a test fails to meet the thickness and other test requirements that are in place to ensure plane strain conditions, the fracture toughness value produced is given the designation K_\text. Fracture toughness is a quantitative way of expressing a material's resistance to crack propagation and standard values for a given material are generally available. Slow self-sust ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dispersion (optics)
In optics, and by analogy other branches of physics dealing with wave propagation, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency; sometimes the term chromatic dispersion is used for specificity to optics in particular. A medium having this common property may be termed a dispersive medium (plural ''dispersive media''). Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, and in gravity waves (ocean waves). Within optics, dispersion is a property of telecommunication signals along transmission lines (such as microwaves in coaxial cable) or the pulses of light in optical fiber. Physically, dispersion translates in a loss of kinetic energy through absorption. In optics, one important and familiar consequence of dispersion is the change in the angle of refra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Poisson's Ratio
In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Poisson's ratio is the negative of the ratio of transverse strain to axial strain. For small values of these changes, \nu is the amount of transversal elongation divided by the amount of axial compression. Most materials have Poisson's ratio values ranging between 0.0 and 0.5. For soft materials, such as rubber, where the bulk modulus is much higher than the shear modulus, Poisson's ratio is near 0.5. For open-cell polymer foams, Poisson's ratio is near zero, since the cells tend to collapse in compression. Many typical solids have Poisson's ratios in the range of 0.2–0.3. The ratio is named after the French mathematician and physicist Siméon Poisson. Origin Poisson's ratio is a measure of the Poisson effect, the phenomenon in which a ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
