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Astrophysical processes near a galactic centre
Hamerský, Jaroslav ; Karas, Vladimír (advisor) ; Kulhánek, Petr (referee) ; Janiuk, Agnieszka (referee)
An accretion torus is an important astrophysical phenomenon which is be- lieved to account for various features of mass inflow and release of radiation on diverse scales near stellar-mass as well as supermassive black holes. When the stationary torus is perturbed it starts to oscillate and once some part of the torus overflows the closed equipotential surface, defined by the stationary solution, this material is accreted or ejected. These oscillations reveal both spacetime properties and the intrinsic characteristics of the torus model. We study the oscillation and accretion properties of geometrically thick accretion tori using general relativistic magnetohydrodynamic simulations. Assuming axial symmetry these simulations are restricted to 2-D approximation. We discuss the impact of the presence of the large scale magnetic field and the profile of the specific angular momentum on the oscillation properties and on the accretion flow motion. 1
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Transition from regular to chaotic motion in black hole magnetospheres
Kopáček, Ondřej ; Karas, Vladimír (advisor) ; Kulhánek, Petr (referee) ; Rezzolla, Luciano (referee)
Cosmic black holes can act as agents of particle acceleration. We study properties of a system consisting of a rotating black hole immersed in a large-scale organized magnetic field. Electrically charged particles in the immediate neighborhood of the horizon are influenced by strong gravity acting together with magnetic and induced electric components. We relax several constraints which were often imposed in previous works: the magnetic field does not have to share a common symmetry axis with the spin of the black hole but they can be inclined with respect to each other, thus violating the axial symmetry. Also, the black hole does not have to remain at rest but it can instead perform fast translational motion together with rotation. We demonstrate that the generalization brings new effects. Starting from uniform electro-vacuum fields in the curved spacetime, we find separatrices and identify magnetic neutral points forming in certain circumstances. We suggest that these structures can represent signatures of magnetic reconnection triggered by frame-dragging effects in the ergosphere. We further investigate the motion of charged particles in these black hole magnetospheres. We concentrate on the transition from the regular motion to chaos, and in this context we explore the characteristics of chaos in...
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Shell-like structures in the ISM: Observation versus simulations
Sidorin, Vojtěch ; Palouš, Jan (advisor) ; Kulhánek, Petr (referee) ; Recchi, Simone (referee)
Title: Shell-like structures in the ISM: Observation versus simulations Author: Vojtěch Sidorin (vojtech.sidorin@gmail.com)1 Department: Astronomical Institute of Charles University2 Supervisor: Prof. RNDr. Jan Palouš, DrSc. (palous@asu.cas.cz), Astronomical Institute of the Czech Academy of Sciences3 Abstract: Shell-like structures are objects found in large numbers in the inter- stellar medium (ISM). They usually appear as bubbles or segments of bubbles and are believed to result from the deposition of mass and energy into the ISM by stars, gamma-ray bursts, or high-velocity clouds. Interstellar turbulence may play a role in their creation too. These structures influence the dynamics of the ISM and are also linked to star formation. In this thesis, I review our current knowledge of the ISM, interstellar turbulence, and shell-like structures in the ISM. Then I present the research into the GLIMPSE bubble N107 conducted in collaboration with my colleagues. N107 is a dusty shell-like structure found in our Galaxy. We explored its atomic, molecular, and radio-continuum components; derived its distance (3.6 kpc), size (radius of 12 pc), and expansion velocity (8 km s−1 ); and identified 49 associated molecular clumps. Using numerical simulations, we estimated the conditions under which N107 formed and concluded...
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Role of Magnetosheath Parameters on Magnetopause Processes
Tkachenko, Oksana ; Šafránková, Jana (advisor) ; Kulhánek, Petr (referee) ; Šimůnek, Jiří (referee)
Title: Role of magnetosheath parameters on magnetopause processes Author: Oksana Tkachenko Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc. e-mail address: Jana.Safrankova@mff.cuni.cz Abstract: The thesis addresses of two regions significant for the solar wind- magnetosphere coupling: the cusp in high geomagnetic latitudes and the low-latitude (LLBL) subsolar magnetopause. A penetration of plasma of a solar origin into the magnetosphere could be realized directly through magnetospheric cusps. The region adjacent to the magnetopause in the cusp vicinity is highly turbulent, occupied by the heated magnetosheath- -like plasma with a low drift velocity for which occurrence of vortices is a very common feature. In the first part of the thesis, we present a de- tailed analysis of a vortex-like structure created by a turbulent plasma flow around the magnetopause indentation above the cusp and using the data from Interball-1 and Magion-4; we find necessary conditions and a possible mechanisms to creation of such structures. The second part concerns the low-latitude boundary layer formation, its spatial structure and temporal changes based on THEMIS multipoint observations. In spite of its cru- cial role in transfer of mass, momentum, and energy from the...
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Magnetopause: location,shape and structure
Dušík, Štefan ; Šafránková, Jana (advisor) ; Kulhánek, Petr (referee) ; Šimůnek, Jiří (referee)
For studies of the solar wind-magnetosphere interaction, the magnetopause is a key region. Prediction of its location and knowledge of its structure in a broad range of upstream parameters are important for further progress on this eld. The present thesis deals with statistical investigations of the magnetopause location as well as case studies of the magnetopause and LLBL structure. Based on simultaneous Themis, Geotail, Interball and Magion measurements, we prepared a study of possible sources of the deviations from magnetopause models including low and high latitudes. We found a signicant deformation of the magnetopause surface in the cusp region at high latitudes and the dependence of the subsolar magnetopause position on the IMF cone angle. The analysis of several events using so called n-T plots brings new results connected with mechanisms of the LLBL formation. We found that during the northward pointing interplanetary magnetic eld, reconnection tailward of the cusp creates the outer part of the LLBL, whereas this sublayer is missing through southward magnetic eld.
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Photocontrolled Biomolecules
Planer, Jakub ; Bartošík, Miroslav (referee) ; Vácha,, Robert (referee) ; Kulhánek, Petr (advisor)
This work is focused on molecular dynamics simulations of artificial photosensitive ion channel and AFM probe. To assemble this ion channel, DFT methods were employed for reparametrization of the GAFF force field describing the bridged azobenzene, which was used as a light controlled molecular switch. We proved by molecular dynamics simulations that newly developed parameters correctly describe behavior of assembled model of ion channel in a lipid bilayer. We also constructed a model of AFM probe and observed formation of water meniscus between the AFM probe and surface, both made of -quartz, by employing molecular dynamics simulations. A contribution of this work is the set of new parameters extending GAFF force field for description of the bridged azobenzene. We also verified functionality of ion channel model and model of AFM probe, which can be used for the further water meniscus studies.
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Transparent public administration - Using IT to reduce corruption and increase efficiency
Kulhánek, Petr ; Střížová, Vlasta (advisor) ; Ptáček, Jaroslav (referee)
The thesis present usage of information technologies in public sector and is focused on e-procurement. The aim is to inform about possible solutions which increase transparency and efficiency of public tenders. It begins with theoretic aspects of public sector, corrupt conduct, assumptions and barriers of implementing information technologies in the public sector. E-procurement is mentioned together with the European and national approach and both are compared. Furthermore, special tools and systems, which are available in the Czech Republic at all levels of public administration, are described. Finally, the closing part illustrates the usage of e-procurement tools in the environment of particular public authority.
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E-learning at primary and secondary schools
Kulhánek, Petr ; Šedivá, Zuzana (advisor) ; Jaša, Milan (referee)
This thesis is focused on use of e-learning at primary and secondary schools in the Czech Republic. The aim is to inform about the possibilities of implementation, explain the basic idea of how e-learning works, what are the possibilities to choose from, with its advantages and disadvantages. Furthermore, information about special needs for the e-learning solutions at this level of education with the options of state and EU financial support are included. The thesis also contains a few examples of concrete e-learning solutions at primary and secondary schools and my own research showing the actual measure of usage at primary and secondary schools.
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