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Study of thermal stability of Mg-alloys strengthened by quasicrystalline phase
Vlasák, Tomáš ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
This bachelor thesis deals with thermal stability of icosahedral phase in Mg-Zn-Y alloys. To study this phenomenon, samples of Mg-3.5Y-35Zn alloy were prepared and equal channel angular pressing method (ECAP) performed at two different temperatures was used to refine their microstructure. Phases in the samples were characterised by scanning electron microscopy and energy-dispersive X- ray spectroscopy. Strengthening effect of icosahedral phase (I-phase) with quasicrystalline structure was examined by measuring Vickers hardness of the samples. Temperatures at which precipitation and dissolution of various phases occur were studied by differential scanning calorimetry. Finally, defect recovery with increasing temperature was investigated by means of positron annihilation lifetime measurement. To identify chemical elements surrounding dislocations coincidence measurements of Doppler broadening of annihilation peak were conducted. Obtained results are as follows. Icosahedral dendritic structures are stable in Mg-3.5Y-35Zn alloy at temperatures up to 350 řC, at higher temperatures they are dissolved in the matrix. Recovery of dislocations takes place in the temperature range from 140 řC to 260 řC and leads to decrease in strength of the alloy processed by ECAP. Concentrations of zinc and yttrium are not enhanced...
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Studies of Drell-Yan process with polarized target at COMPASS
Pešková, Markéta ; Finger, Michael (advisor) ; Procházka, Ivan (referee)
Title: Studies of Drell-Yan process with polarized target at COMPASS Author: Markéta Pešková Department / Institute: Department of Low Temperature Physics Supervisor of the bachelor thesis: M.Sc. Michael Finger, CSc. Abstract: The presented thesis intends to give an introduction into the studies of the spin structure of a nucleon. The knowledge about the structure of nucleon has grown in the last few decades; however, its spin structure is still a mystery. One of the concepts that might help solving this spin puzzle is the polarized Drell-Yan process. This process can give us the access to the spin-dependent structure functions of a nucleon via measuring spin asymmetries. In the following text, an outline of the theoretical background of the semi- inclusive Deep Inelastic Scattering and the Drell-Yan is given. The Parton Distribution Functions (PDFs) and the transverse-momentum-dependent PDFs (TMDs) are discussed. And the way of accessing the TMDs via polarized Drell-Yan process is briefly described. This is the goal of the Drell-Yan program at COMPASS experiment, using the transversely polarized target and pion beam in 2014-15. The description of experimental apparatus is given and the system of collecting and processing data is outlined. The data-taking conditions of the 2009 DY beam test and the 2014 DY...
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Studies of Drell-Yan process at Compass experiment
Matoušek, Jan ; Finger, Miroslav (advisor) ; Procházka, Ivan (referee)
Hadron structure is not fully understood yet. While the spin-averaged Parton Dis- tribution Functions (PDFs) and the helicity-dependent PDFs are well determined, little is known about the transverzity and some other transverse-momentum de- pendent PDFs (TMDs). The COMPASS experiment at CERN is preparing for studying the TMDs using a Drell-Yan process on transversely polarized target hit by pion beam in 2014-2015. An outline of the parton model of hadrons and of the TMDs is given. The COMPASS spectrometer is described, with emphasis on the modifications for the Drell-Yan program, and its capabilities to measure the TMDs is briefly discussed. A special attention is paid to the polarized target. The dilution refrigerator, the DNP system for polarizing the nuclei and the NMR for polarization measurement are described. The new monitoring system of the refrigerator is described, including the author's contribution to it. Issues of the new NMR coils design are discussed. 1
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Hyperfine interactions in hexagonal ferrites
Cvešperová, Kateřina ; Štěpánková, Helena (advisor) ; Procházka, Ivan (referee)
Nuclear magnetic resonance is a method, which provides information about the magnitude of hyperfine field present on izotope's nuclei with non-zero spin. The hyperfine field is sensitive to the local ordering of atoms surrounding the nuclei. The hyperfine field changes can be observed in response to changes in surroundings caused by substitution. The NMR spektra of 57Fe nuclei in the hexagonal ferrites with magnetoplumbit structure which contain cation substitution of trivalent cations Nd, Pr in crystallographic position of divalent cations Sr are measured and interpreted in this work. All experiment are measured at 4.2 K and we investigate the influence of the cation substituion on hyperfine field in thr measured oxides.
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Studium mikrostruktury ultrajemnozrnných kovových materiálů metodou pozitronové anihilace
Barnovská, Zuzana ; Čížek, Jakub (advisor) ; Procházka, Ivan (referee)
In the presented thesis we study the changes in distribution of the size of vacancy clusters in metals processed by severe plastic deformation, so called ul- tra fine grained materials. We use a modern non-destructive method of positron annihilation spectroscopy, which is one of the few methods that allow us to inves- tigate point defects like vacancies with sizes of a few ˚A. The obtained spectra of positrons annihilating in the samples enable us to determine changes of vacancy cluster sizes depending on temperature or severity of the deformation applied on the samples. 1
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Hyperfine interactions in maghemite and magnetite particles
Křišťan, Petr ; Štěpánková, Helena (advisor) ; Procházka, Ivan (referee)
Thesis is aimed at studying of magnetic iron oxide particles of submicron and nanoscale dimensions by means of nuclear magnetic resonance (NMR). 57 Fe NMR inves- tigations were carried out in composite bentonite/maghemite with respect to tempera- ture of calcination (Tcalc) during the sample preparation and in magnetite submicron powders with respect to various range of the particles size. One of the main findings is that increasing Tcalc improves resolution in the NMR spectra, which is most likely connected with higher degree of atomic ordering in the spinel structure. Evaluating the integral intensities of NMR spectra allowed us to determine the relative content of maghemite phase in particular samples of the series: the content rapidly grows for Tcalc up to ∼420 deg. An approach to distinguish signal from tetrahedral and octahedral irons was developed and tested on pure maghemite sample. Analysis based on vacancy- distribution models was performed in the spinel structure and the results were compared to the experiment. 57 Fe NMR spectra in submicron magnetite samples were found to differ markedly from spectrum of a single crystal. It was concluded that the investigated powders possess high amount of defects in the crystal structure or contain additional phase (probably closely related to the maghemite phase).
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Comparison of ORM frameworks for PHP
Procházka, Ivan ; Pavlíčková, Jarmila (advisor) ; Schrotter, Michal (referee)
This study deals with a comparison of object relational mapping frameworks for PHP program language. On theoretical review, it describes the possibilities of mapping and available design patterns for mapping are presented. Basic principles of object oriented programming and relational databases are surveyed. For a comparison of tools, a model case of a library is suggested and implemented in chosen tools. Based on specified criteria, a comparison of selected frameworks is given. The main goal is to evaluate features of chosen frameworks, demonstrate their usage on the model case of a library and summarize the possibilities of object relational mapping on PHP platform.
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