Presents the historical development of perceptions and applications of the exponential law, tracing it from its ancient origins until the year 1900. Shows that many concepts such as mean life and half life and their relationships to differential equations were known long before their application to nuclear radioactivity. (GA)

Discusses the reduction of the one- and three-dimensional diffusion equation to the difference equation and its stability, convergence, and heat-flow applications under different boundary conditions. Indicates the usefulness of this presentation for beginning students of physics and engineering as well as college teachers. (CC)

Topological ideas can be used to predict a variety of textures and defects in condensed matter systems under certain conditions. This article describes one means of creating and observing textures in liquid crystals which exhibit a rich variety of such textures. The results of these observations are presented. (Author/SK)