Семинар из астрономије и астрофизике, 24. октобар 2017.

• 23. Октобар, 2017
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Наредни састанак Семинара биће одржан у уторак, 24. октобра 2017, у сали 809 Математичког факултета са почетком у 18 часова.

Предавач: Lucio Crivellari, INAF - Osservatorio Astronomico di Trieste and Instituto de Astrofisica de Canarias

Наслов предавања: ALTERNATIVE REPRESENTATIONS OF THE RADIANT ENERGY TRANSPORT

Апстракт: In alternative to the representation of the electromagnetic field through the Maxwell`s equation and its propagation in terms of the corresponding wave equations, in this seminar we will consider a description based on the corpuscular theory of light. Such an approach leads to a picture analogous to that employed in fluid dynamics: the radiation field is assumed to consist of rays (photon beams) characterized by their energy and direction of propagation. The energy carried on by a ray is the fundamental observable of the transport process. Its quantitative representation by means of a suitable macroscopic quantity, namely the specific intensity of the radiation field, makes it possible to go beyond the ray picture and paves the way to a much more convenient mathematical formulation of radiative transfer (RT), widely used by astrophysicists.

The propagation of the radiation field through a material medium, for which we will adopt a semi-classical model based on the hypotheses of Planck, Bohr and Einstein, will be formulated as a kinetic (Boltzmann) equation that allows for the space-time evolution of the specific intensity of the radiation field. All the physical information, described at microscopic level by proper photon distribution functions, will be merged into a few macroscopic coefficients that characterized any specific RT equation.

Eventually, we will compare the description of the localization, energy balance and transport of radiant energy, as formulated in the Maxwell`s theory, with the macroscopic representation in terms of the specific intensity of the radiation field.