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Magnetic shape memory alloys - ab initio approach
Heczko, Martin ; Šesták, Petr (referee) ; Zelený, Martin (advisor)
This Bachelor’s thesis is focused on theoretical study of magnetic shape memory alloys based on Ni2MnGa using ab initio calculations of electronic structure within the projector augmented wave method. In particular, the effect of increasing concertation of manganese instead of gallium was studied on total-energy and magnetic moment profiles along the tetragonal deformation path between austenite phase with cubic L21 structure and phase of nonmodulated martensite. Further, the effect of manganese atoms distribution within the gallium sublattice was studied as well as changes of this distribution under applied tetragonal deformation. At last but not at least, the elastic constants for austenitic and martensitic structures of studied alloys were calculated. The results show that the non-modulated martensite stabilized with increasing concentration of manganese, because its total energy decreased. The energetic barrier between austenitic and martensitic structures also decreased, which means the metastable austenite will change to unstable.
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Ab initio calculations of the phase stability in Ni-Mn-Ga alloys
Pongrácz, Jakub ; Šesták, Petr (referee) ; Zelený, Martin (advisor)
This thesis deals with theoretical study of magnetic shape memory alloy based on Ni2MnGa with help of ab initio calculations of electronic structure within the projector augmented wave method. In particular the effect of Co- and Cu-doping is studied on total-energy profile along the tetragonal deformation path between austenite phase with cubic L21 structure and phase of nonmodulated martensite. Obtained results are used for estimation of doping influence on martensitic transformation temperature. Transformation temperature increases in the alloy doped by 3.125 at. % of copper instead of gallium whereas transformation temperature decreases in the alloy doped by 3.125 at. % of cobalt instead of nickel. If both type of doping are used the transformation temperature increases slightly because the effect of copper is stronger. Comparison of results from this work with available results obtained with help of the coherent potential approximation shows that a local lattice distortion around doping atom has negligible effect on studied properties.
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First-principles study of stability of solid crystals
Pleskot, Ondřej ; Šesták, Petr (referee) ; Černý, Miroslav (advisor)
This work deals with a modeling of an electronic structure of solid crystals. Specifically, densities of valence electrons, and the density of states are calculated using first-principles code VASP for three crystals representing three different types of bonding. These are the metal bonding in a crystal of aluminum, the covalent bonding in a diamond crystal, and an ionic bonding in the crystal of rock salt. From calculated values of stress and crystal energy are then determined some macroscopic parameters of crystals, such as the equilibrium lattice parameter, the bulk modulus and the theoretical strength under isotropic tension.
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Electronic structure and mechanical properties of interfaces in solids
Češka, Jakub ; Šesták, Petr (referee) ; Černý, Miroslav (advisor)
In this work I focus on a theoretical study of the properties of transition metal nitrides (TiN, AlN and VN in the rock-salt structure). In addition to the nitrides themselves, I focus on the interface in systems of multilayers consisting of pairs of these nitrides. For nitrides, I predict the lattice parameter and cleavage energy using ab initio calculations. For the interface, the main goal is to predict the cleavage energy of the interface and to predict the influence that an atom substituted in one of layers on the interface has on the value of cleavage energy. According to the calculations performed, an oxygen atom substituted in the interface has a significant influence on the value of cleavage energy. The value of cleavage energy for the interface with an oxygen atom differs significantly from that for the pure interface. Whether there was a decrease or an increase depended on which of the layers at the interface the oxygen atom was substituted in.
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Memory Materials
Josiek, Robert ; Šesták, Petr (referee) ; Molliková, Eva (advisor)
Currently, shape memory materials are very popular, especially intermetallic compounds NiTi. This alloy is very stable and corrosion resistant, but its production is very difficult because of the high reactivity of titanium. Shape memory effect in this material is dependent on many parameters, such as chemical composition or heat treatment. This bachelor’s thesis explains one-way and two-way memory effect. Another one phenomenon associated with the martensitic transformation, superelasticity, is mentioned, too. The applications of these materials are described in separate chapter of this bachelor’s thesis.
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Assemblies for ambient microphone techniques
Šesták, Petr ; Schimmel, Jiří (referee) ; Jirásek, Ondřej (advisor)
For proper understanding of a function of individual ambient microphone techniques, the presented bachelor’s thesis first describes, among other things, the principles of the behaving of microphones and selected pair techniques. Furthermore, the work describes the process of design and then manufacture of two constructions for ambient microphone techniques. It focuses on their properties, function and differences between them, for example in applications. It contains the marking of the directionality of individual ambient techniques.
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The mechanisms of pollen incompatibility in the Brassicaceae family
Šesták, Petr ; Fíla, Jan (advisor) ; Vosolsobě, Stanislav (referee)
Sporophytic incompatibility (SI) represents one of the systems by which angiosperms prevent pollination by their own pollen or by the pollen from a genetically related plant. It is mostly studied in the Brassicaceae family, mainly due to its agricultural importance. Another reason is that the model plant Arabidopsis thaliana belongs to this family. In the last three decades, advances in molecular biological methods enabled the characterization of a large part of the signalling cascade that leads to the rejection of incompatible pollen. Then, the functions of various cellular components (e.g. cytoskeleton, exocyst or proteasome) involved in the incompatible response to pollination are studied mainly by live cell microscopy. Last but not least, the function of SI under various abiotic stresses was described to reveal their influence on SI mechanisms. The aim of this bachelor thesis is to summarize the new discoveries characterizing the molecular mechanisms of SI in the Brassicaceae family, to describe the processes leading to the germination of compatible pollen grain and to characterize the newly described proteins involved in cellular signalling leading to the rejection of incompatible pollen.
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Short story or an autobiographical complaint? Characteristics of Czech Contemporary Short Stoires
Šesták, Petr ; Mocná, Dagmar (referee)
Based on the interpretation of selected texts, this work aims at describing some significant phenomenons of the contemporary Czech short story written by young and middle-age authors and at searching a short story-specific depiction of their conception of nowadays life. Its partial purpose is to figure out in which way the texts follow - or not - and influence - or not - the conventions of the genre. This analysis is founded on several Czech and foreign theoretical concepts of the short story; the studied materials being the texts of three authors of distinct poetics, namely Kateřina Rudčenková, Jan Balabán and Emil Hakl. Interpretations of these diverse texts reveal some common symptomatic aspects and coherences between the rejection of certain conventions of the short story genre and the testimony of contemporary life. The interdisciplinary-concepted closing chapter explores the possible relations between this specific literary message about the human being and his world and the sociological or philosophical reflections on postmodern times.
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