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Nuclear magnetic resonance in magnetic systems
Křišťan, Petr ; Štěpánková, Helena (advisor) ; Mašláň, Miroslav (referee) ; Schneeweiss, Oldřich (referee)
Title: NMR in magnetic systems Author: Petr Křišťan Department: Department of Low Temperature Physics Supervisor: prof. RNDr. Helena Štěpánková, CSc. Abstract: Magnetically ordered iron oxides, namely magnetite, maghemite, hexagonal ferrite M or system Fe-B, with nano or submicron dimensions of particles are the main subject of study of the presented thesis. The materials were investigated mainly by 57 Fe nuclear magnetic resonance (NMR). The results were thoroughly analyzed and compared with the results obtained by other methods (Mössbauer spectroscopy, ZFC/FC magnetic measurement, X-ray diffraction or TEM). In case of the maghemite nanoparticles a regular distribution of vacancies in octahedral positions was verified by the help of NMR in external magnetic fields and at various temperatures. The experi- mental results were also compared with ab-initio calculations. In thin layers of barium M type hexaferrite, effects of reduced particle size on 57 Fe NMR spectra were observed. The NMR methods were also successfully applied to investigation of system FeMoCuB of amorphous and nanocrystalline ribbons, where 57 Fe NMR was able to resolve formation of different phases in depen- dence on the process of preparation. Due to different NMR excitation condi- tions of signal from strontium M type hexaferrite and maghemite,...
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MR spectroscopy in patients with diabetes mellitus
Šedivý, Petr ; Štěpánková, Helena (advisor) ; Roztočil, Karel (referee)
This thesis deals with in vivo MR spectroscopy. Measurements in this thesis were performed on whole-body MR tomograph at the Institute for Clinical and Experimental Medicine in Prague. The objective of the thesis was to study differences in the biochemical processes and energy metabolism in the muscle tissue under physical workload between the groups of healthy subjects and patients with type 1 diabetes mellitus (DM1). We used phosphorous spectroscopy in combination with ergometer. The thesis is divided into five chapters. The first chapter describes theoretical introduction to in vivo 1 H and 31 P MR spectroscopy and muscle metabolism, the second chapter deals with the description of the experimental equipment and measurement, results of the thesis are reported in the third chapter and the fourth chapter is a discussion of results. Main result of this work is summarized in conclusion; we found differences between the metabolism of patients with DM1 and healthy volunteers.
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Local structure of hexagonal ferrites studied by NMR
Kouřil, Karel ; Štěpánková, Helena (advisor) ; Pištora, Jaromír (referee) ; Schneeweiss, Oldřich (referee)
Title: Local structure of hexagonal ferrites studied by NMR Author: Karel Kouřil Department/Institute: Department of Low Temperature Physics Supervisor of the doctoral thesis: prof. RNDr. Helena Štěpánková, CSc. Abstract: Hexagonal ferrites of M, W, X and Y structure types were studied by means of NMR, electronic structure calculations and magnetoelectric experi- ments. Presented results deal with cation distribution, localization of ferrous ions, interpretation of NMR spectra of studied materials and effects of size reduction. In oriented layers M type strontium ferrite and submicron particles of M type barium ferrite pronounced effects of reduced size were observed on 57 Fe NMR spectra. Performance of magnetoelectric barium-strontium Y type hexaferrites with divalent zinc cations improved upon thermal treatment of samples while distribution of zinc was not significantly altered. In Sc sub- stituted BaM, Sc content was found to be uniform throughout TSSG grown crystal. In LaSrM systems electron localization in 2a sublattice was observed, co-substitution with La+Zn, La+Co and La+Cu was found to lead to partial charge compensation. In strontium ferrites of type W and X localization of ferrous ions in octahedral sites in SS block pair was observed. Keywords: NMR, hexagonal ferrites, structure,...
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Theory of cleavages and development of Party System. Comparison of Czech Republic, Slovakia and Poland
Štěpánková, Helena ; Novák, Miroslav (advisor) ; Mlejnek, Josef (referee)
This diploma thesis deals with a development of the socioeconomic cleavage in the party systems of the Czech Republic, Slovakia and Poland in 2006 - 2012. At the beginning the theory of cleavages by S. Rokkan and S. M. Lipset and the enlargement to post-communist countries of Klaus von Beyme, are presented. There are also mentioned concepts of other authors. The thesis tries to answer a few questions. Firstly, what form did this line have in the monitored period (transformation line vs. classical socioeconomic line). Secondly, how big was an impact on the political right-left orientation of the political parties, and thirdly, how significant was this line for the party-political system of selected countries in this period. There is also a brief development of the party system after 1989 as well as the ideological profiles of parliamentary parties given in each chapter focused on particular country. One part of it deals also with the economic and social climate in the monitored period. Then the work is based mainly on the analysis of party's agenda, with an emphasis on the socioeconomic line.
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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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The Study of Dynamic Behaviour and Interactions During the Temperature-Induced Phase Separation in Polymer Solutions
Kouřilová, Hana ; Hanyková, Lenka (advisor) ; Štěpánková, Helena (referee) ; Dušková - Smrčková, Miroslava (referee)
Title: The Study of Dynamic Behaviour and Interactions During the Tempera- ture-Induced Phase Separation in Polymer Solutions Author: Hana Kouřilová Department / Institute: Charles University in Prague, Faculty of Mathemat- ics and Physics, Department of Macromolecular Physics Supervisor of the doctoral thesis: doc. RNDr. Lenka Hanyková, Dr. Abstract: 1 H and 13 C high-resolution NMR spectroscopies were used for the phase separation investigation in three types of polymer solutions: i) poly(N -isopropylmethacrylamide)/D2O/ethanol with or without negatively charged comonomer sodium methacrylate, ii) random copolymers poly(N -isopro- pylmethacrylamide-co-acrylamide) in D2O, D2O/ethanol and D2O/acetone and iii) D2O solutions of polymer mixtures poly(N -isopropylmethacrylamide)/poly(N - vinylcaprolactam). For i) cononsolvency effect and influence of temperature on the phase separation was studied. Differences between mesoglobules formed as a consequence of cononsolvency effect and of temperature were found. While inside the cononsolvency-induced mesoglobules no bound ethanol molecules were detect- ed, in the mesoglobules formed by the effect of temperature ethanol molecules were present. The charge introduced into the polymer chains strenghtens polymer- solvent interactions. For ii) mesoglobules were found to be...
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Spin-lattice and spin-spin NMR relaxation of 1H nuclei in deuterated etanol and butanol doped by TEMPO radical
Matoušek, Jan ; Englich, Jiří (advisor) ; Štěpánková, Helena (referee)
The thesis deals with study of deuterated ethanol and butanol (ethyl-D5 alcohol, butyl-D9 alcohol) with a small amount (0 to 1.5% weight) of dissolved stable free radical TEMPO by methods of NMR. This system is used in polarized targets for high energy experiments. The linear dependence of spin-lattice and spin-spin relaxation rate of hydrogen nuclei from OH group of an alcohol on the radical concentration and dependence of the relaxation rates decreasing with temperature (in range from 250 to 298K) were obtained. The T1/T2 ratio from 1.3 to 2.0 was calculated. This was interpreted as an effect of a contact interaction via hydrogen bond between alcohol and radical molecules. The linear dependence of the resonance frequency of hydrogen nuclei from OH group on the radical concentration was obtained. The slope of the dependence line didn't change with temperature. Using this dependence the hyperfine constant of the interaction between hydrogen nucleus and the free electron of the radical was estimated approximately 8·10-28 J. It was found out that the lifetime of the hydrogen bonds between alcohol and radical molecules are about 10-11 s or longer.
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Nuclear magnetic resonance in yttrium-iron garnets with cobalt and germanium substitutions
Schimm, Petr ; Štěpánková, Helena (advisor) ; Rotter, Miloš (referee)
Title: Nuclear Magnetic Resonance of Yttrium Iron Garnets with Substitutions of Cobalt and Germanium Author: Petr Schimm Department: Department of Low Temperature Physics Supervisor: prof. RNDr. Helena Štěpánková, CSc., Department of Low Temperature Physics Abstract: The work is devoted to investigation of thin films of nominally pure yttrium iron garnet and garnets containing cationic substitutions of Co, Ca and Ge. The examined samples were prepared by epitaxial growth from barium flux BaO/Ba2O3/BaF2. The aim was to find whether and how the substitutions, especially cobalt, influence the spectra of 57 Fe nuclear magnetic resonance (NMR). The 57 Fe NMR spectra (in zero external magnetic field and at a temperature of 4.2K) were measured and a good resolution and high signal-to-noise ratio were reached. The weak satellite lines induced by defects, impurities and aimed substitutions were detected. The primary analysis of the spectra and their comparison were performed. Keywords: NMR, yttrium iron garnet, defects, substitution of Co, Ge, Ca
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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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