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Thin accretion disks with magnetic advective term
Vavřička, Radek ; Bursa, Michal (advisor) ; Horák, Jiří (referee)
Accretion disks around black holes with gas radiating out parts of its gravitational potential energy have long served as objects of both theoretical and observational studies. By solving the structure equations of the disk it is possible to predict the outgoing radia- tive flux and the observed spectrum of the disk and test the validity of the theory against direct observations. The standard thin disk model (Shakura-Sunyaev, Novikov-Thorne) shows, however, a still unexplained non-negligible deviance in the observed spectrum at higher mass accretion rates. To amend to the set of proposed explanations, in this thesis we examine the effect of the magnetic pressure on the trapping of some of the internal energy generated by viscous dissipation processes in the disk and advecting this energy to the black hole. A phenomenological description of heat advection mediated by a highly heterogenous magnetic field will be given, as well as its effect on the spectrum and observed effective temperature. 1
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Application of boundary element method for calculation of electric field in a radiofrequency ion trap
Vavřička, Radek ; Roučka, Štěpán (advisor) ; Hromádka, Jakub (referee)
In this thesis we explore numerical methods that could be used to solve La- place's equation. We compare the boundary element method (BEM), implemen- ted in Bempp library, and the finite element method (FEM), implemented in FEniCS library, by using them to solve Laplace's equation in the cases of a mul- tipole and a rf ion trap, which we create a model of through the use of Gmsh. In order to gauge effectiveness of a method, we measure the time of evaluation, me- mory usage and the squared deviation from theoretical values (if we know them) summed over the points of evaluation. In the end, we use the known values of electric field to simulate a charged particle moving within the trap, comparing evolution of its position and velocity for BEM and FEM. 1 2
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