In the mathematical field of representation theory, a Lie algebra representation or representation of a Lie algebra is a way of writing a Lie algebra as a set of matrices (or endomorphisms of a vector space) in such a way that the Lie bracket is given by the commutator. In the language of physics, one looks for a vector space together with a collection of operators on satisfying some fixed set of commutation relations, such as the relations satisfied by the angular momentum operators.
Relief is a sculptural method in which the sculpted pieces remain attached to a solid background of the same material. The term relief is from the Latin verb relevo, to raise. To create a sculpture in relief is to give the impression that the sculpted material has been raised above the background plane. When a relief is carved into a flat surface of stone (relief sculpture) or wood (relief carving), the field is actually lowered, leaving the unsculpted areas seeming higher.
A rock relief or rock-cut relief is a relief sculpture carved on solid or "living rock" such as a cliff, rather than a detached piece of stone. They are a category of rock art, and sometimes found as part of, or in conjunction with, rock-cut architecture. However, they tend to be omitted in most works on rock art, which concentrate on engravings and paintings by prehistoric peoples. A few such works exploit the natural contours of the rock and use them to define an image, but they do not amount to man-made reliefs.
A spatial database is a general-purpose database (usually a relational database) that has been enhanced to include spatial data that represents objects defined in a geometric space, along with tools for querying and analyzing such data. Most spatial databases allow the representation of simple geometric objects such as points, lines and polygons. Some spatial databases handle more complex structures such as 3D objects, topological coverages, linear networks, and triangulated irregular networks (TINs).
Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. When aggregate is mixed with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape.