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Study of precipitation effects in Mg-Y and Mg-Y-Nd systems
Heteš, Michal ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
The aim of this bachelor's thesis was to investigate the precipitation processes in the binary system Mg-Y and the ternary alloy Mg-Y-Nd using positron annihilation spect- roscopy and hardness testing, where we measured 2 samples with 3% and 6% by weight representation of Yttrium impurity atoms and 3 sample with 4% by weight representation of yttrium atoms and 3% by weight representation of neodymium atoms. The develop- ment of the hardness of the alloys was measured by the Vickers method of hardness measurement. Together with the hardness measurement, the characterization of crystal lattice disorders of the cloudy alloy samples was carried out using positron annihilation spectroscopy. It was measured that at higher temperatures hardening of the studied sys- tems occurs. Hardening was caused by the formation of GP zone precipitates and the β′ phase by Y, Nd and Mg atoms. 1
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Microstructural investigations of novel high entropy alloys
Vlasák, Tomáš ; Čížek, Jakub (advisor) ; Nový, František (referee) ; Moreira, Afonso (referee)
High entropy alloys constitute a novel approach in materials research. In this thesis, four novel alloys (namely NbTaTiZr, HfNbTaTiZr, HfNbTiVZr and HfNbTaTiVZr) are investigated. Their microstructure and mechanical properties are studied both in the as-cast and the annealed state. It is shown that their strengthening is caused by lattice distortions, which are the result of random filling of lattice sites by atoms of various elements with different atomic radii. Furthermore, positron annihilation investigations revealed that positrons actively search for open volumes in interstitial regions associated with lattice distortions, and therefore lattice distortions can be characterised by positron lifetimes.
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Copyright aspects of radio broadcast
Čížek, Jakub ; Žikovská, Petra (advisor) ; Wünschová Pujmanová, Alexandra (referee)
1 RESUMÉ This dissertation focuses on selected aspects of copyright and rights related to copyright in connection with radio broadcasting. It specializes in use of authors' works, artistic performances of performers and phonograms of phonogram producers in the way of radio broadcasting and on internet connected to radio broadcasting according to the current legislation in Czech Republic. In the first part it concentrates on items of copyright protection, their use in radio broadcasting, on broadcasters as users in the view of copyright law, on licence agreement, term of protection and radio broadcasting itself. As far as the broadcasting is concerned the dissertation approaches it in the view of administrative law focusing on its content. In the second part it deals exclusively with collective rights management as with the key institute for broadcasters to get appropriate copyright licences to use the protected items. It concerns the compulsory and voluntary collective rights management, the cumulative agreements and royalties, and collecting societies operating in Czech Republic. With regard to the present trends this dissertation, in its third part, aims at broadcasters' activities on internet and further platforms. The last part is devoted to several nowadays issues in copyright, such as extension of...
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Hydrogen-induced defects in titanium
Knapp, Jan ; Čížek, Jakub (advisor) ; Vlach, Martin (referee)
Titanium is a very important industrial material with quite a versatile use. This thesis examines the influence of hydrogen absorbed in metal lattice of titanium on defects inside the lattice. In this work titanium samples were loaded with hydrogen using two different methods: electrochemical charging, where titanium sample was immersed in solution of H3PO4 and glycerin as a cathode. The anode was be made of platinum and constant electrical current in order of miliampers was run throw the solution. The H+ cations went to the cathode and were neutralized to a hydrogen atom there. The hydrogen atoms subsequently penetrated into the titanium lattice by diffusion. Gas loading was used as the second method of hydrogen doping. Titanium samples were put into hydrogen atmosphere with defined pressure and kept at constant temperature. Hydrogen loaded samples were examined by positron lifetime spectroscopy which represents a non-destructive technique for studying defects in materials. Analysis of phase composition was performed by X- ray diffraction. Developments of mechanical properties of hydrogen loaded samples were monitored by Vickers micro-hardness testing. Differential Scanning calorimetry was employed for investigation of thermal stability of absorbed hydrogen.
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Studium defektů v tenkých kovových vrstvách
Hruška, Petr ; Čížek, Jakub (advisor) ; Bulíř, Jiří (referee)
In the present work Mg films prepared by RF magnetron sputtering were studied. Variable energy positron annihilation spectroscopy (VEPAS) was employed for investigation of defects in the Mg films. VEPAS characterization was combined with scanning electron microscopy and X-ray diffraction in order to determine grain size, phase composition and texture. The effect of different deposition rate and deposition temperature, annealing, various substrates and film thickness on the structure and amount of defects present in the Mg films was examined. Defect studies by VEPAS showed that positrons in studied Mg films are trapped at misfit dislocations and at vacancy-like defects in grain boundaries and their density can be reduced by the deposition at elevated temperature. 1
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Study of hydrogen interaction with defects in thin metallic films
Hruška, Petr ; Čížek, Jakub (advisor) ; Krsjak, Vladimír (referee) ; Mathis, Kristián (referee)
Thin metallic films are particularly interesting as potential hydrogen storage materials as well as hydrogen sensitive optical sensors. Thin films with various microstructure from nanocrystalline to epitaxial can be relatively easily prepared by varying the deposition parameters. Deposition of multi-layers enables preparation of thin films with arbitrary composition. Defects structure plays a key role in hydrogen absorption. Hydrogen atoms segregated at open volume defects reduce their formation energy leading to enhan- ced concentration of hydrogen-induced defects in the material. Moreover hydrogen diffusion along dislocations and grain boundaries facilitates hydrogen absorption in the metal lattice. Thin films clamped to the stiff substrate undergo anisotropic volume expansion during the hydrogen loading. As a consequence high stresses are induced in the film and can result in detachment of the film from the substrate. In this work hydrogen absorption in Gd and Pd films and Pd-Mg multi-layers was studied. Development of the defect structure of hydrogen-loaded films was investigated by means of variable energy positron annihilation spectroscopy com- bined with X-ray diffraction, atomic force microscopy and optical transmittance measurement. Complementary studies of interaction of hydrogen with defects in...
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Study of free volumes in Nafion using positronium
Košinová, Lucie ; Čížek, Jakub (advisor) ; Vlach, Martin (referee)
Title: Study of free volumes in Nafion using positronium Author: Lucie Košinová Department: Department of Low-Temperature Physics Supervisor: doc. Mgr. Jakub Čížek, Ph.D., Department of Low-Temperature Physics Abstract: The object of this thesis is investigation of the absorption of water in Nafion and the influence of temperature on the absorption and desorption kinetics. Study of the absorption and desorption of water was carried out either measurement of changes in the macroscopic physical properties of Nafion (weighing, differential scanning calorimetry) either by microscopic characterization of the size distribution of free volume that arises as a consequence of an imperfect arrangement of polymer chains. For this purpose I used a non- destructive method used positron annihilation spectroscopy, which is currently the only technique capable of determination of the size distribution of free volumes having the free volume distribution by size of a few Å. The development of the size distribution and the concentration free volumes in the sample were determined on the based on the measurement of lifetime spectra of positrons annihilating in the sample of Nafion. The results obtained in this thesis can be further used in research of Nafion, which is widely used as a semipermeable membrane during industrial...
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