[institut] Seminar Katedre za astronomiju - 24. oktobar 2017.

[Katedra za astronomiju]

                Seminar iz astronomije i astrofizike

                         Lucio Crivellari

               (INAF - Osservatorio Astronomico di Trieste &
 		Instituto de Astrofisica de Canarias)

       "Alternative representations of the radiant energy transport"

        utorak, 24. oktobar 2017. godine, u 18 sati, u ucionici 809.



NAPOMENA: Bice odrzana dva predavanja u trajanju od po 45 minuta sa 
kratkom pauzom izmedju.


Abstract:
 	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.



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