Most dune sand is transported close to the surface by saltation and reptation of grains. The shearing action of the wind is resisted by grain size and shape, bed slope, moisture content, and surface roughness elements (especially the presence of vegetation). The relations between sand flux, particle size, aerodynamic roughness, slope, and wind shear velocity are complex, especially on dune surfaces, and may depart significantly from estimates derived from transport equations. The formation of wind ripples is intimately associated with the transport of sand by saltation and reptation, but the relationships between grain transport processes and the formation and development of ripples are complex, leading to a self-organizing pattern that responds rapidly to changes in sand flux and wind speed.

This chapter presents salient concepts to understand a vast literature on dynamics of charged macromolecules. Starting from a description of hydrodynamic interaction, dynamics of folded proteins, colloids, flexible polyelectrolytes, DNA are described. For flexible macromolecules, the models of Rouse, Zimm, reptation, and entropic barrier are developed in increasing order of complexity. Using this groundwork, the phenomena of ordinary-extraordinary transition, electrophoretic mobility, and topologically frustrated dynamical state are explained.