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Study of Properties of Metallic Thin Films and Nanostructures Using Scanning Probe Microscopy
Doupal, Antonín ; Fejfar, Antonín (referee) ; Kalousek, Radek (advisor)
This diploma thesis is focused on investigation of metallic thin films and nanostructures using scanning probe microscopy. Magnetic properties of these objects are studied by magnetic force microscopy, which is modification of scanning probe microscopy. In the theoretical part basic principles of scanning probe microscopy and magnetic force microscopy are summarized, and also principle of creation of magnetic domains and some special properties of ferromagnetic and antiferromagnetic materials. Further, two techniques of fabricating nanostructures are described. Experimental part is focused on imaging and simulating of magnetic domains. Further, exchange bias is revealed. This phenomenon is present in systems composed from ferromagnetic and antiferromagnetic materials. One part of this diploma thesis is also focused on discussion of problems with magnetic force microscopy.
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Enterohepatic circulation of bilirubin
Zelenka, Jaroslav ; Vítek, Libor (advisor) ; Entlicher, Gustav (referee) ; Červinková, Zuzana (referee)
Bilirubin is a main physiological product of heme degradation possessing important antioxidant and antiinflammatory properties. On the other hand, it could be neurotoxic during severe unconjugated hyperbilirubinemia combined with insufficiency of blood-brain barrier (neonatal jaundice). It is secreted from the body via bile and is further metabolized in the intestine. Part of the substance is reduced to urobilinoids, part is adsorbed to the intestinal content and some part could be reabsorbed back to the systemic circulation. This enterohepatically and enterosystemically circulating fraction varies in size depending on the rate of bilirubin secretion, solubility in the intestine and intensity of its intestinal metabolism. Under specific circumstances, EHC and ESC may significantly increase serum and bile bilirubin levels and influence physiological as well as pathological processes occuring in the body. Among the most important is the protective elevation of UCB levels in Gilbert syndrome subjects and dangerous increase in severity of neonatal jaundice. In the presented thesis, the mechanisms affecting EHC and ESC of bilirubin and tools for further research in BP metabolism were investigated. The solubility of intestinal UCB is strongly decreased by addition of divalent cations. However, such approach to...
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Fatigue failure mechanism of nickel-based superalloy Inconel 713LC under 800°C
Smékalová, Jana ; Juliš, Martin (referee) ; Hutařová, Simona (advisor)
Nickel superalloys are used for high-temperature application in energetic and aerospace industry. They are exposed to aggressive environment at high temperatures with the interactions between fatigue and creep processes, high-temperature oxidation, corrosion and erosion. Lifetime extension of such strained parts while increasing the performance of particular machine is possible by applying protective surface coatings. The subject of this work is to investigate the fatigue failure mechanisms of superalloy Inconel 713LC at 800 °C and to compare these mechanisms between material with a protective coating based on Al-Si and material without coating. The location of initiation fatigue cracks, their propagation and the fatigue crack propagation rate in some areas were analyzed by optical microscopy, scanning electron microscopy and confocal laser scanning microscopy. Based on previous research it was found that the application of the coating AlSi has a positive effect on lifetime of alloy Inconel 713LC. These results were confirmed and estimated in the diploma thesis.
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Costs reduction in production of Al-alloy castings
Nováková, Lucie ; Lána, Ivo (referee) ; Roučka, Jaromír (advisor)
This thesis deals with solving the most serious internal defects in castings made of aluminum alloys which are cast in sand molds in Slévárna a modelárna Nové Ransko Ltd. The problem solving contains a description of the problematic castings with the investigation of the structure and phases and subsequent detailed analysis of their production. The Author of this thesis also examines the influence of Fe and Mn on a possible formation of the internal porosity with the help of test meltings with the evaluation of the internal structural change. The Author’s design solution is a close checking of chemical composition with regard to the ratio Mn / Fe present in the alloy, the purchase of Foundry Degassing Unit to reduce gassiness of melted metals and better control of gassiness with the help of the appropriate equipment for the density Dichte index.
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Changes in structure and phase composition in the surface of tram rail
Švábenská, Eva ; Roupcová, Pavla ; Schneeweiss, Oldřich
We have investigated structure and phase composition of surface layer of tram rails after long time running and the results were compared with those obtained on the original part of material. Changes due to effects of severe plastic deformation together with thermal shocks by friction process were expected. The information about structure and phase composition was obtained by optical and scanning electron microscopy, X-Ray Powder Diffraction, Mössbauer Spectroscopy and Glow Discharge Emission Spectroscopy (GDOES) and this was completed by microhardness measurements. The results show that the surface layer in comparison with the original material exhibits important changes in grain structure, an increase in microhardness and high content of iron oxide and hydrooxides. According to the depth profile of the chemical composition measured by GDOES there is an increase in carbon content in the surface layer which can be effect of up-hill diffusion.
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HYDROGEN ABSORPTION IN A-Co30Fe55B15
Čermák, Jiří ; Král, Lubomír ; Roupcová, Pavla
Hydrogen solved in amorphous alloys (AAs) influences their magnetic characteristics. AAs are also perspective\nas additives that can improve hydrogen storage kinetic in certain types of ball-milled hydrogen storage\nmaterials (HSMs). Therefore, knowledge of hydrogen solubility and hydrogen sorption kinetics in AAs are of a\ngreat importance for aimed design both AAs with optimal magnetic parameters and HSMs with desired sorption\ncharacteristics. In the present paper, amorphous alloy Co30Fe55B15 (an example of the type a-TM1xTM2y Bz ;\nTM - transition metal) was investigated. Hydrogen concentration c H was measured by Sieverts method in\ntemperature interval from T = 150 °C to T = 350 °C under hydrogen pressure p up to 6 MPa. It was found that\nc H was an increasing function of p and its maximum value was typically 0.5 wt.% H2 at 350 °C and 6 MPa.\nHowever, when the alloy was preliminary hydrogen charged (PHC), the pressure dependence of total c Htot in\nthe first absorption cycle(s) is non-monotonous in dependence on PHC conditions. For the sake of comparison,\nthe same absorption characteristics were measured also in Mg2Ni intermetallic that is a common constituent\nin Mg-based HSMs. Comparing Co30Fe55B15 and Mg2Ni, it was concluded that Co30Fe55B15 shows lower\nhydrogen solubility, but much better absorption kinetics.
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Measurement of transverse relaxation using spin echo methods
Škoch, Antonín ; Tošner, Zdeněk (advisor) ; Hanyková, Lenka (referee)
Title: Measurement of transverse relaxation using spin echo methods Author: MUDr. Antonin Skoch, Ph.D. Department: Department of Low Temperature Physics Supervisor: RNDr. Zdenek ToSner, Ph.D. NMR laboratory, of Faculty of science, Charles University in Prague Supervisor's e-mail address: tosner(o)karlov.mff.cuni.cz Abstract: The study of TI relaxation in systems with homonuclear J-coupling is complicated by modulation in the relaxation curve. This J-modulation can be removed when CPMG sequence is used and the period of repetition of refocusing pulse Tfulfils a condition r « * ( 1 ) Ai' where Av is the frequency difference of coupled nuclei. However, the condition (I) cannot be in practice always fulfilled. The aim of this work was to investigate J-modulation and relaxation behaviour of homonuclear J-coupled system in various parameters of CPMG sequence. Simulations based on numerical solution of Liouville-von Neumann equation and Redfield theory were performed. Relaxation curves of Chh group of citrate were measured on high-resolution NMR spectrometer. It was found that the suppression of J-modulation can be achieved also for T longer than required by the condition (1) providing that the refocusing angle in CPMG for both J-coupling partners 9^180ř. The simulations yielded conditions for T when J-modulation...
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Application of Friction Stir Welding in Aircraft Structures
Šrubař, Martin ; Urík, Tomáš (referee) ; Klement, Josef (advisor)
Slitiny hliníku řad 2XXX a 7XXX nejsou shledávány jako svařitelné s použitím tradičních metod svařování. Jsou však široce používány v leteckých a kosmických konstrukcích. Obvyklý způsob jejich spojování je pomocí nýtování. Nově vznikající technologie lineárního svařování třením rotujícím nástrojem (Friction Stir Welding - FSW) již ukázala slibné výsledky při svařování těchto slitin. V této práci jsme prozkoumali aplikace technologie FSW v leteckých konstrukcích zejména jako náhradu nýtování na panelech vyztužených stringery. Sestavili jsme výrobní postup pro daný panel a navrhli další kroky k jeho optimalizaci. Dále jsme sestavili znalostní bázi základních svařovacích parametrů a porovnali jsme nýtování a FSW na jednoduchém modelu využitím metody konečných prvků a s cílem identifikovat rozdíly v charakteru rozložení napětí v těchto vzorcích.
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Anthropological conceptualisations of sexual categories
Prokopík, Petr ; Vrhel, František (advisor) ; Uherek, Zdeněk (referee) ; Skupnik, Jaroslav (referee)
The thesis inquires into the possibilities which anthropological study has in attempting to conceptualise the rich manifestations of human sexuality. It discusses the problems of biological determination and normativity in the study of sexuality as well as its problems in cross-cultural applications. In examples of interpretation of well known phenomena such as "hijra", "two-spirit" and "ritual homosexuality" it demonstrates theoretical concepts of "third sex", "third gender", and "sexual lifeways" as possible tools of cross-cultural categorization. It presents an original field research investigating the formation of a specific new alternative sexual category within gay communities in three language contexts - Czech, English and German. Offering a situational analysis which concerns not only a description of cultural meanings and symbols known by actors, and an analyses of historical development, but also offers an interpretation of actors subjectivity displayed in individual motivations, desires and meanings created and used by actors. It endeavours to give a reflection of relations between sexual category and individual motivations during the process of accepting sexual identity and forming an alternative sexual category.
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Solidification of castings by pouring into shell moulds in vakuum furnaces
Odložil, Jan ; Ňuksa, Petr (referee) ; Roučka, Jaromír (advisor)
Heat transfer during metal pouring and its solidification in the vacuum furnace have been investigated by experiments using model set of castings of different diameters and insulations. The pouring metal was Inconel 713LC alloy based on nickel. The found data have been used for optimization of the numerical simulation of the thermal regime during the both pouring and solidification phases of the process in vacuum. Numerical simulation of the alloy structure in individual castings has been made by the CAFE module of the ProCast software and obtained results compared with the real structure. The optimized boundary conditions can be used for simulation of real castings.
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