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Rovnice vedení tepla ve fyzice planetek a meteoroidů
Pohl, Leoš ; Brož, Miroslav (advisor) ; Vokrouhlický, David (referee)
Non-gravitational forces caused by thermal emission of photons can significantly change orbits and spin states of asteroids in the long term. A solution of the Heat Conduction Equation (HCE) in an asteroid is necessary to evaluate the forces. Finite Difference Methods (FDMs) are implemented in a Fortran numerical HCE solver to calculate a temperature distribution within a system of 1-dimensional slabs which approximate the asteroid. We compare the methods w.r.t. convergence, accuracy and computational efficiency. The numerical results are compared with a simplified steady-state analytical solution. We calculate the non-gravitational accelerations and resulting semimajor axis drift from the numerical results. The implemented FDMs are shown to be convergent with denser grids and the best method has been selected. The analytical solution provides a good first-guess estimate of the temperature amplitude. The drift in semimajor axis of the tested asteroids, which is due to the non-gravitational forces, is in order-of-magnitude agreement with more accurate models and observational data.
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Dynamical processes in Jupiter's and Saturn's ring systems
Řehák, Matyáš ; Brož, Miroslav (advisor) ; Hanuš, Josef (referee)
The main subject of this thesis is a review of dynamical processes acting in Jupiter's and Saturn's rings. The thesis is divided into three chapters. Observed orbital and physical characteristics of the rings are described in the first one. In Chapter 2, we discuss physical processes forming the rings. Tidal disruptions, mutual collisions of ring particles, meteoroid bombardment and ballistic transport are among them. Various electromagnetic effects are analyzed too - e.g. the Poynting-Robertson effect, the Lorentz resonaces, plasma drag and radiation pressure. Yet another types of phenomena are resonant gravitational influence of satellites, shepherding moons and also collective dynamics of ring particles which results in formation of spiral waves. Finally, there is a review of theories concerning the origin of Saturn's rings in Chapter 3. We can distinguish three types of models - a disruption of a moon, a disruption of an external body and a formation from protolunar matter. At present, a tidal disruption of large differentiated moon seems to be the most probable theory.
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The evolution of stars with various masses
Cibulková, Helena ; Brož, Miroslav (advisor) ; Zasche, Petr (referee)
In the present work we study changes of the structure of a star that occur during stellar evolution and the dependence of these changes on the initial mass of the star. Internal changes affect also characteristics of the star which are observable from the outside like the effective tempe- rature or luminosity. At first we briefly derive basic equations of the stellar structure which describe the most important processes inside the star. We assume the star is nonrotating and spherically symmetric. For a detailed description of the stellar evolution, we plot individual quantities for different initial masses (from 0,1 to 100 M⊙). We use the program EZ2 for numerical calculations which enables to model the stellar evolution as long as the condition of the hydrostatistic equilib- rium is satisfied. Finally, we use the theory of the stellar evolution to determine the ages of two open clusters NGC 188 and M 45 using the method of isochrones. Keywords: stellar evolution, Hertzsprung-Russell diagram, equations of stellar structure, pro- gram EZ2 1
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Statistical analysis of the gamma-ray bursts satellite data
Bystřický, Pavel ; Mészáros, Attila (advisor) ; Brož, Miroslav (referee)
In this thesis the Gamma-Ray Bursts (GRBs) are studied, the brightest explosions in the universe. GRBs have been observed since year 1967, but there are several unsolved problems. In the first chapter there is an introduction to the issue of GRBs, and the history of observations are briefly described. The Fermi satellite, the latest satellite devoted to gamma-ray burst observations is described in chapter two. Characteristics of the Fermi instruments are also described. The observed data of GRBs are characterized in the third chapter. The distribution of GRB durations, distances, and spectral hardnesses are described. The characteristics of long and short GRBs (distance, isotropy of distribution, metalicity dependence, isotropic energy) are described. A chance of the appearance of a GRB in the Milky Way is discussed. New Fermi observations are described too. Fourth chapter is about models of GRBs. The fireball and canonball models are described. Fifth chapter is focused on the exposure function of CGRO-BATSE, Fermi-GBM, Swift. I have created the exposure function for GBM on Fermi satellite. It is quite difficult, and I have assumed some simplified hypotheses. Information of the satellite's position, position of detectors on the Fermi satellite, have been found on the Fermi web pages and in the article...
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Simulation of the astrolabe of the Prague astronomical clock for PC
Makara, Tomáš ; Šolc, Martin (advisor) ; Brož, Miroslav (referee)
In this work we create a computer simulation of the astrolabe of the Prague astronomical clock. The result of this work will by a didactic instrument which will help users discover and understand the astronomical clock. The task is to create a realistic three-dimensional computer model of the astronomical clock and also to implement all movement of the clock. The application will offer three-dimensional realistic visualization of the astronomical clock, description of the clock's parts, and projection of the celestial sphere on the astronomical dial and information which can be read from the dial. The application will provide a possibility to see animation of the astronomical clock and also to set the clock to an arbitrary time during the year.
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