A survey is given of the main mechanisms of dc electrical conductivity in disordered systems and of how the conductivity depends on temperature. If the localization length is large, metallic behaviour will be observed at high temperatures, at lower temperature the resistance will increase with a power of T-', and at very low temperatures, when variable range hopping occurs, the resistance will ...

R. D. Noble, a research profissor in chemical engineering at the Univ. of Colorado, specializes in the use of reversible chemical reactions in chemical gas and liquid separation processes, most notably the use of ion-exchange membranes as supports for complexing agents and the modeling and analysis of various facilitated transport systems. Refore joining the Univ, of Colorado, he served as an a...