Exact categoryIn mathematics, an exact category is a concept of due to Daniel Quillen which is designed to encapsulate the properties of short exact sequences in without requiring that morphisms actually possess , which is necessary for the usual definition of such a sequence. An exact category E is an possessing a class E of "short exact sequences": triples of objects connected by arrows satisfying the following axioms inspired by the properties of short exact sequences in an : E is closed under isomorphisms and contains the canonical ("split exact") sequences: Suppose occurs as the second arrow of a sequence in E (it is an admissible epimorphism) and is any arrow in E.
Pre-abelian categoryIn mathematics, specifically in , a pre-abelian category is an that has all and . Spelled out in more detail, this means that a category C is pre-abelian if: C is , that is over the of abelian groups (equivalently, all hom-sets in C are abelian groups and composition of morphisms is bilinear); C has all finite (equivalently, all finite coproducts); note that because C is also preadditive, finite products are the same as finite coproducts, making them biproducts; given any morphism f: A → B in C, the equaliser of f and the zero morphism from A to B exists (this is by definition the kernel of f), as does the coequaliser (this is by definition the cokernel of f).
Thermal radiationThermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is converted to electromagnetic radiation. All matter with a temperature greater than absolute zero emits thermal radiation. At room temperature, most of the emission is in the infrared (IR) spectrum. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation.
Color temperatureColor temperature is a parameter describing the color of a visible light source by comparing it to the color of light emitted by an idealized opaque, non-reflective body. The temperature of the ideal emitter that matches the color most closely is defined as the color temperature of the original visible light source. Color temperature is usually measured in kelvins. The color temperature scale describes only the color of light emitted by a light source, which may actually be at a different (and often much lower) temperature.
Sugar alcoholSugar alcohols (also called polyhydric alcohols, polyalcohols, alditols or glycitols) are organic compounds, typically derived from sugars, containing one hydroxyl group (–OH) attached to each carbon atom. They are white, water-soluble solids that can occur naturally or be produced industrially by hydrogenating sugars. Since they contain multiple –OH groups, they are classified as polyols. Sugar alcohols are used widely in the food industry as thickeners and sweeteners.
Digital compositingDigital compositing is the process of digitally assembling multiple to make a final image, typically for print, motion pictures or screen display. It is the digital analogue of optical film compositing. The basic operation used in digital compositing is known as alpha blending, where an opacity value, 'α', is used to control the proportions of two input pixel values that end up a single output pixel. As a simple example, suppose two images of the same size are available and they are to be composited.
Polylactic acidPolylactic acid, also known as poly(lactic acid) or polylactide (PLA), is a thermoplastic polyester with backbone formula (C3H4O2)n or [–C(CH3)HC(=O)O–]n, formally obtained by condensation of lactic acid C(CH3)(OH)HCOOH with loss of water (hence its name). It can also be prepared by ring-opening polymerization of lactide [–C(CH3)HC(=O)O–]2, the cyclic dimer of the basic repeating unit. PLA has become a popular material due to it being economically produced from renewable resources.
Thermal insulationThermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials. Heat flow is an inevitable consequence of contact between objects of different temperature.
Oil wellAn oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may be termed a gas well. Wells are created by drilling down into an oil or gas reserve that is then mounted with an extraction device such as a pumpjack which allows extraction from the reserve.
Oil refineryAn oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, liquefied petroleum gas and petroleum naphtha. Petrochemical feedstock like ethylene and propylene can also be produced directly by cracking crude oil without the need of using refined products of crude oil such as naphtha. The crude oil feedstock has typically been processed by an oil production plant.
