Glossary - D

defect

Imperfection in a lattice resulting in a less symmetrical lattice (e.g. dislocations in a crystalline lattice).

dimension

One of the the least number of independent coordinates required to specify uniquely a point in a space or space-time. For example, the position of a dot on a piece of paper can be uniquely specified by giving two coordinates, conventionally called x and y. The point is specified by giving its coordinates in the x and y dimensions.

dimensional

Of so many dimensions. For example: a line is a one-dimensional object; a plane, like a sheet of paper with no thickness, is a two dimensional object; and ordinary objects such as tea cups are three-dimensional. Time is often considered as a fourth dimension giving rise to the phrase `four dimensional space-time'. Physicists and mathematicians also consider objects and spaces with more dimensions which may or may not include time.

discrete

Divided into a finite number sections or levels. An example would be an approximation to a smooth curve draw with a set of straight lines. Triangulations are discrete models of surfaces.

dislocation

A type of defect found in crystal lattices. For a triangular lattice - a pair of vertices with coordination number five and seven respectively (recollect that a normal vertex on a triangular lattice has a coordination number of six.)