National Repository of Grey Literature 23 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Structure and evolution of stars deformed by a nearby companion
Vokrouhlický, David ; Pejcha, Ondřej (advisor) ; Krtička, Jiří (referee)
The tidal field from a nearby binary companion affects the structure and evolution of stars. We successfully applied the Kippenhahn averaging formalism to the Roche potential and used the method to formulate approximate models of tidally deformed primaries in close binary systems. We considered both the detached and the contact configurations and neglected chemical composition evolution. These tidally deformed models are thermally stable. We explored the parametric dependence of the results on three quantities: mass ratio q in the binary, surface equipotential C of the primary or the fill-out factor F(C), and mass M1 of the primary. We found that the depth of the surface convective layer of low mass primaries in- creased due to tidal deformation. All models decreased their effective temperature when compared to their spherical counterparts. Our results also predict a positive correlation between the effective temperature and the fill-out factor for contact systems. Further- more, the temperature negatively correlates with the mass ratio of the deformed system. Finally, when isolating the tidal deformation effects, a jump in temperatures was found around 1.2 M⊙ for most fill-out factors. These findings could help to explain the observa- tionally reported dichotomy of contact binary systems at the temperature...
Recent asteroid breakups and accretion of interplanetary dust on the Earth
Pokorný, Petr ; Vokrouhlický, David (advisor) ; Šolc, Martin (referee)
The major aim of the thesis is an analysis of an accretion of dust originating from breakup events of Emilkowalski and YC2 asterodial families. Using a numerical integrator we follow orbits of individual dust particles, some of which will result in an impact onto one of the planets in the Solar system. Employing some non-trivial transformation we compare recorded impacts onto the Earth to available dust measurements values acquired in antarctic ice-cores. We also analyse the dynamical e ffects of Poynting-Robertson e ffect and their influence on the dust particles of variable sizes.
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.
Inner belt asteroids in the spin-orbital resonance
Vraštil, Jan ; Vokrouhlický, David (advisor)
Context: Slivan (2002) determined spin state of ten asteroids in the Koronis family. Surprisingly, all four asteroids with prograde sense of rotation were shown to have spin axes nearly parallel in the inertial space. All asteroids with retrograde sense of rotation had large obliquities and rotation periods either short or long. It was shown that Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect can explain all these peculiar facts. In particular, it drives spin axes of the prograde rotators to be captured in a secular spin-orbital resonance known as Cassini state 2. Vokrouhlický et al. (2002) dubbed these configurations "Slivan states". Aims: A question arises whether Slivan states could exist also in other regions of the main asteroid belt, in particular its inner part, where observations are most easily obtained. Here, however, dynamical difficulties arise due to convergence of the proper frequency s and the planetary frequency s6. We investigate possibilities of a long-term stable capture in the Slivan state in the inner part of the main belt. Method: We used SWIFT integrator to determine orbital evolution of selected asteroids in the inner part of the main belt. In the case of 20 Massalia, we observed the asteroid in 2011, and used these new data to help better solve the rotation state using the...
Short-lived Delocalization and Absorption by Light
Vokrouhlický, David ; Mančal, Tomáš (advisor) ; Veis, Libor (referee)
Coherent exciton delocalization improves the light harvesting function of photosyn- thetic antennae by creating conditions for very fast excitation transfer in space. This thesis focuses on two different effects creating coherence - short-lived excitation by light and weak coupling between pigments that is present in the system on longer timescales. The evolution and relaxation of simple systems - the dimer and trimer - are calculated. The core of this thesis are newly developed numerical methods for distinguishing and quantifying the effect of the two types of coherence throughout evolution, which are applied to the aforementioned systems. 1

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