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Comparison of different approaches in ab initio modeling of mechanical and magnetic properties of materials
Čavojec, Martin ; Řehák, Petr (referee) ; Zelený, Martin (advisor)
Tato diplomová práce se zabývá zkoumáním vlivu kvantově-mechanického popisu mezi-atomárních interakcí na výsledky ab initio výpočtů magnetických a mechanických vlastností Fe, -TiAl a Ni2MnGa. Zkoumány byly dvě metody pro popis interakcí, jmenovitě metoda projektovaných přidružených vln a metoda lineární kombinace atomových orbitalů, které jsou implementovány v ab initio softwarech VASP a SIESTA. Hodnoty magnetických momentů v závislosti na objemových a tetragonálních deformačních drahách poukazují na relativní srovnatelnost napříč těmito metodami. Avšak výsledky elastických konstant poukazují na nevhodnost ab initio softwaru SIESTA pro výpočet elastických konstant metodou napětí-deformace (stress-strain metoda). Součástí praktické části této diplomové práce je vytvoření skriptu pro výpočet elastických konstant v programovacím jazyku Python.
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FIRST PRINCIPLES ANALYSIS OF MECHANICAL STABILITY OF SOLID CRYSTALS
Řehák, Petr ; Buršík, Jiří (referee) ; Šob, Mojmír (referee) ; Černý, Miroslav (advisor)
The aim of the author’s research in the period of his PhD study was the analysis of mechanical stability of cubic crystals under external loading. This work demonstrates several methods used for a study of mechanical stability of fcc crystals (C, Al, Ir, Pt, Au) during isotropic (hydrostatic) tensile loading. Ab initio methods were used for this purpose. Studied crystals were subjected to simulated isotropic tensile deformation and an analysis of elastic stability was performed. This analysis shows that first elastic instability in Al, Pt and Au crystals corresponds to vanishing of the trigonal shear modulus and diamond, Ir remains stable up to the state of maximum isotropic stress. According to the calculated band structure diamond crystal preserves his insulating character up to the onset of instability. Consequently, phonon spectra of all crystals were calculated using the linear response method and their dynamic stability was assessed. Obtained results reveal soft phonon modes in Al, Pt and Ir before an occurrence of elastic instability. Selected short-wavelength instabilities are confirmed using models of microscopic deformation and also using dispersion curves obtained by a supercell method. The observed instabilities lower critical strains related to the volumetric instability up to 40 % whereas the reduction of critical stress is by 20 % at the most.
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Stability of crystalline solids from first principles
Řehák, Petr ; Šob, Mojmír (referee) ; Černý, Miroslav (advisor)
This work deals with study of stability of solid crystals under isotropic loading. Ab initio methods were used for this purpose. Crystals of four fcc metals (Al, Cu, Ir, Au) and diamond were subjected to simulated isotropic tensile deformation and maximum value of isotropic stress was evaluated for them. Consequently, phonon spectra were calculated for several strain values in order to assess crystal stability. Phonon instabilities in dispersion curves of diamond, Al, Ir and Au appeared at strains lower than those corresponding to their decohesion. This appearance of instability determinates the value of ideal strength. However, significant reduction (by about 20%) was found only in the cases of Au and Ir.
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Study of the influence of separator modification on the properties of Li-S batteries
Řehák, Petr ; Jaššo, Kamil (referee) ; Kazda, Tomáš (advisor)
This thesis deals with the development and current issues of Li-ion and Li-S accumulators, especially the separators. In the theoretical part is described history of Li-ion batteries, their properties and materials for the positive electrode. Li-S batteries and their problems are also described in this diploma thesis. In the practical part, electrochemical methods were described, and several separator samples with various modifications were created. These samples were then photographed using an SEM electron microscope and evaluated using electrochemical methods.
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Comparison of different approaches in ab initio modeling of mechanical and magnetic properties of materials
Čavojec, Martin ; Řehák, Petr (referee) ; Zelený, Martin (advisor)
Tato diplomová práce se zabývá zkoumáním vlivu kvantově-mechanického popisu mezi-atomárních interakcí na výsledky ab initio výpočtů magnetických a mechanických vlastností Fe, -TiAl a Ni2MnGa. Zkoumány byly dvě metody pro popis interakcí, jmenovitě metoda projektovaných přidružených vln a metoda lineární kombinace atomových orbitalů, které jsou implementovány v ab initio softwarech VASP a SIESTA. Hodnoty magnetických momentů v závislosti na objemových a tetragonálních deformačních drahách poukazují na relativní srovnatelnost napříč těmito metodami. Avšak výsledky elastických konstant poukazují na nevhodnost ab initio softwaru SIESTA pro výpočet elastických konstant metodou napětí-deformace (stress-strain metoda). Součástí praktické části této diplomové práce je vytvoření skriptu pro výpočet elastických konstant v programovacím jazyku Python.
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Rationalising religious discrepancies
Poruba, Lukáš ; Štampach, Ivan Odilo (advisor) ; Řehák, Petr (referee)
In this thesis I discuss a religious phenomenon which I consider in-sufficiently researched in available Czech literature. This phenomenon constitutes of situations where a religious group or an individual reacts to conflicting meanings of their belief by an interpretation in such a way that these so far conflicting meanings become consistent. In the first section of the thesis I look at the examples of such a phenomenon that can be found in official scriptures and texts of selected religions. In the next section of the thesis I investigate the phenomenon by the use of the psychology. I focus on the theory of cognitive dissonance, especially then the reduction of the cognitive dissonance by adding new cognitive elements. In the practical section of the thesis I then research the phenomenon in real life settings. I assume that this phenomenon can be also found outside the framework given by the official religious doctrines and thereafter I try to find out if and how this phenomenon occurs in the personal life of any religious (nebo spis believing) person. Keywords Religion, religious discrepancy, religious viewpoint, cognitive dissonance, cognitive consonance, reduction of cognitive dissonance, adding new cognitive element.
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Sathya Sai Baba and his movement
Marčík, Pavel ; Štampach, Ivan Odilo (advisor) ; Řehák, Petr (referee)
Sathya Sai Baba is the most popular spiritual leader in India. He has about fifty million disciples, usually they are from India, but he has also some disciples from european and north american countries. Sathya Sai Baba proclaims about himself he is second incarnation of actual avatar, he also proclaims the first incarnation was Sai Baba from Shirdi, who is very popular indian saint. Sathya Sai Baba's cult is popular especially for Sathya Sai Baba's acts like is for example healing of his disciples, materialization etc. These acts interpretate his disciples like a miracles. Sathya Sai Baba accents in his teaching, which is based on traditional Hindu texts, ethic dimension of religions. Sathya Sai Baba also created his official organization. This organization focus her activities especially to adoration of Sathya Sai Baba, to study his texts, to service and education. Organization has also branch in Czech republic. Czech branch counts about thirty people. Sathya Sai Baba is criticised from suspects in cheating, sexual abuses of his disciples and from political scheming. Criticism often appears from his exdisciples. Keywords Sathya Sai Baba - new religious movement - cult - followers - official organization - criticism.
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Study of the influence of separator modification on the properties of Li-S batteries
Řehák, Petr ; Jaššo, Kamil (referee) ; Kazda, Tomáš (advisor)
This thesis deals with the development and current issues of Li-ion and Li-S accumulators, especially the separators. In the theoretical part is described history of Li-ion batteries, their properties and materials for the positive electrode. Li-S batteries and their problems are also described in this diploma thesis. In the practical part, electrochemical methods were described, and several separator samples with various modifications were created. These samples were then photographed using an SEM electron microscope and evaluated using electrochemical methods.
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