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Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System
Čapek, David
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System Abstract of the Ph.D. thesis \s David Capek It has been shown, that the thermal effects are very important in the dynamics of small Solar System bodies. A phenomenon which is known as the Yarkovsky effect is able to secularly change the semimajor axis of an orbit, while the YORP effect affects the rotation state of a body. The Yarkovsky effect and the YORP effect were previously calculated with many constraining assumptions like spherical shapes of asteroids, circular orbits, small variations of the surface temperature, principal axis rotation, constant thermal parameters, etc. We developed a sophisticated numerical model of the Yarkovsky/YORP effect without such simplifications. With this model, we have been able to describe the shape, the orbit, the rotation and the thermal behaviour of an asteroid in a very precise way. The YORP effect was studied on a sample of artificially generated shapes, roughly resembling Main Belt asteroids, and also on several shapes of real asteroids. The depen- dence of YORP on the obliquity and the thermal parameters of the surface were studied (Vokrouhlicky and Capek, 2002; Capek and Vokrouhlicky, 2004). A wide variety of pos- sible YORP evolution paths of the spin state was found. The possibility of...
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Yarkovsky and YORP Effects in Dynamics of Small Bodies of the Solar System
Žižka, Jindřich ; Vokrouhlický, David (advisor) ; Čapek, David (referee) ; Neslušan, Luboš (referee)
In this thesis, we study the influence of non-gravitational perturbations induced by the Yarkovsky/YORP effect and solar radiation pressure (SRP) on the orbital evolution of selected asteroids, asteroid families and pairs. These perturbations are of great importance if one wants to perform precise and long-term propagation of meter-sized and kilometer-sized bodies. Although they have found many applications in the Solar System, here, we particularly investigated how they influence the orbit of near-Earth asteroid (99942) Apophis and what is their role in the age determination of asteroid families and pairs. Our numerical simulations showed that the perturbations of Apophis' orbit caused by the SRP are orders of magnitude smaller than those produced by the Yarkovsky effect. The age determination of asteroid families and pairs was another pillar of this work. Over the past decade it turned out that the Yarkovsky effect must be taken into account for backward propagation of pair/family members. We modified the current method for estimating the age of asteroid pairs to be suitable for weakly convergent cases and discovered 7 young pairs with similar-sized components, which is in contradiction with the current theory of pair formation. In addition, we focused on an interesting pair of asteroids -...
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Modern trends crime prevention
ČAPEK, David
The bachelor thesis deals with a characterization of crime prevention, focusing on selected prevention programs and new modern trends in crime prevention. The thesis addresses basic concepts, typologies of crime prevention, kinds and structure. It points out to the development of crime prevention in the Czech Republic and selected programs. A part of the thesis specifies some modern trends in crime prevention that are used in the Czech Republic. This work can serve students as an overview of crime prevention programs as well as it can be of information benefit to the general public
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YORP effect on asteroids with heterogeneous distribution of surface thermophysical properties
Chrbolková, Kateřina ; Čapek, David (advisor) ; Ďurech, Josef (referee)
In this thesis, we study the influence of heterogeneous distribution of optical and thermal properties on asteroid surfaces onto the YORP effect. Modelling of the surface heterogeneities is done in three ways. In the first one, we create an impact crater with higher albedo regolith on a regolith-covered asteroid. In the second way, we suppose presence of higher albedo regolith on steep slopes (slope angle > 35◦ ) and in the third one, we state properties of bare rock (with different thermal parameters) in these areas. Then we evaluate the influence of torques caused by scattered or thermally emitted radiation on 200 asteroids based on different distribution of described parameters by means of statistics. We have found that the presence of heterogeneities caused by landslides on asteroid surfaces does not significantly affect the YORP effect with two exceptions: a slight inclination to decelerate the rotation in the case of landslides uncovering bare rock due to critical rotation and significant preference for deceleration in the configurations with uncovered higher albedo regolith on steep slopes. Our data suggest that the influence of heterogeneous distribution of optical properties caused by landslides on the value of typical acceleration time, so-called doubling time td, is 2 % and it does not exceed 5 % in the case...
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Modern numerical models of the YORP effect
Chrbolková, Kateřina ; Čapek, David (advisor) ; Ďurech, Josef (referee)
This thesis deals with the study of an non-gravitational effect called the YORP effect which affects the rotational state of irregularly shaped asteroids. In its first part, there is discussed the very physical nature of this phenomenon and further it demonstrates an effect similar to the YORP: the Yarkovsky effect. Second part analyzes several outstanding numerical models, which describe the YORP effect. It focuses on some aspects that no other models took in account and it also points out what approximations these models make. We have used two different nume- rical models on an asteroid shape of our own and we present it in the last part of this bachelor thesis. At the end of this paper, we compare our outputs with the findings of appropriate models. Our results agree with the cited articles in the majority of cases. We tried to analyze how the YORP effect depends on the chan- ging conductivity of the asteroids and we also found out that better resolution of shapes of asteroids leads to the convergence of the values of the YORP effect.
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Heat diffusion equation and thermophysical modelling of asteroids
Pohl, Leoš ; Ďurech, Josef (advisor) ; Čapek, David (referee)
Light curve inversion is a standard method to determine shapes, rotation periods and spin axis orientations of asteroids. This method can be extended to determine the size, albedo, thermal inertia and surface roughness parameters of an asteroid by including observations in thermal infrared. A solution of the Heat Conduction Equation (HCE) is necessary to model infrared flux from the asteroid. We analyse the accuracy requirements of the extended method for numerical solution of the HCE. We show that current implementation leads to errors in flux that are substantial. We recommend changes in the current implementation of the HCE solving approach to address the accuracy issues. We discuss uniqueness and stability of the solutions produced by the extended method as well as the accuracy of the determined parameters and their stability. Shapes of asteroids are produced and their physical attributes are determined based on light curve and infrared data.
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Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System
Čapek, David
Thermal Effects in Physics and Dynamics of Small Bodies of the Solar System Abstract of the Ph.D. thesis \s David Capek It has been shown, that the thermal effects are very important in the dynamics of small Solar System bodies. A phenomenon which is known as the Yarkovsky effect is able to secularly change the semimajor axis of an orbit, while the YORP effect affects the rotation state of a body. The Yarkovsky effect and the YORP effect were previously calculated with many constraining assumptions like spherical shapes of asteroids, circular orbits, small variations of the surface temperature, principal axis rotation, constant thermal parameters, etc. We developed a sophisticated numerical model of the Yarkovsky/YORP effect without such simplifications. With this model, we have been able to describe the shape, the orbit, the rotation and the thermal behaviour of an asteroid in a very precise way. The YORP effect was studied on a sample of artificially generated shapes, roughly resembling Main Belt asteroids, and also on several shapes of real asteroids. The depen- dence of YORP on the obliquity and the thermal parameters of the surface were studied (Vokrouhlicky and Capek, 2002; Capek and Vokrouhlicky, 2004). A wide variety of pos- sible YORP evolution paths of the spin state was found. The possibility of...
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