Absorbing particles interaction with medium

Interactions with the surrounding transparent medium include the heating of the medium through conduction fi-om the absorbing particle, and the generation of fluid motions through stirring and convection currents. 

The medium that interacts with radiation may contain particles and gases which absorb and scatter the radiant energy. In combustion chambers, for example, soot, char, fly-ash, coal particles and spray droplets affect the propagation of radiant energy. Among various gases, carbon dioxide and water vapor are the major participants to radiative transfer, both in combustion chambers and in the atmosphere. 

The idea that two species (solid,-solid2> should interact with each other, so that their mutual potential energy can be represented by some function of the distance between them, has been described in the literature (Israelachvili, 2011). Furthermore, colloidal particles frequently adsorb (and even absorb) ions from their dispersing medium (such as in ground water treatment and purification). Sorption that is much stronger than what would be expected from dispersion forces is called chemisorption, a process that is of both chmical and physical interest. 

Here P(ra,t), Eq. (14), is the polarization at point ra at time t and P+ is the hermitian conjugate of P. The angular brackets denote averaging over the thermal bath with which the absorbers interact. Equation (25) reflects the fact that the 4WM signal results from a coherent parametric emission, involving many particles emitting in phase. Usually, different particles in the nonlinear medium are not correlated, so that the two-body average can be factorized in the form... 

---