Thermal force exact results

This survey begins with a summary of exact results for the thermal-force problem. Then approximate developments will be discussed in the light of available data. Finally, some developments for the thermal force in dense gases and liquids as well as new effects in dilute host gas will be described. 

Exact results for the thermal force for a highly viscous, stable particle in dilute, monatomic host gas are available in the limits Kn. oo, Kn 0. The particle is in... 

Section IV is devoted to excitons in a disordered lattice. In the first subsection, restricted to the 2D radiant exciton, we study how the coherent emission is hampered by such disorder as thermal fluctuation, static disorder, or surface annihilation by surface-molecule photodimerization. A sharp transition is shown to take place between coherent emission at low temperature (or weak extended disorder) and incoherent emission of small excitonic coherence domains at high temperature (strong extended disorder). Whereas a mean-field theory correctly deals with the long-range forces involved in emission, these approximations are reviewed and tested on a simple model case the nondipolar triplet naphthalene exciton. The very strong disorder then makes the inclusion of aggregates in the theory compulsory. From all this study, our conclusion is that an effective-medium theory needs an effective interaction as well as an effective potential, as shown by the comparison of our theoretical results with exact numerical calculations, with very satisfactory agreement at all concentrations. Lastly, the 3D case of a dipolar exciton with disorder is discussed qualitatively. 

Surface charge on a particle results in an unequal distribution of ions in the polar medium in the vicinity of the surface. Ions of opposite charge (counterions) are attracted to the surface, and ions of like charges (coions) are repelled away from the surface. This unequal distribution gives rise to a potential across the interface. The exact distribution of the counterions in the solution surrounding the charged surface is very important, since it determines the potential decay into the bulk from the charged surface. Electrostatic attraction, thermal motion and forces other than electrostatic (specific adsorption) influence the counterions in the vicinity of the surface. 

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