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AN INTERPLAY BETWEEN HEAT TREATMENT CONDITIONS AND B2 <-> B19 ' TRANSFORMATION IN Ni-Ti SHAPE MEMORY ALLOYS
Kuběnová, Monika ; Zálešák, Jakub ; Čermák, Jiří ; Dlouhý, Antonín
This study investigates the influence of a heat treatment atmosphere on multistage martensitic transformations in a Ti-50.9at% Ni shape memory alloy. Evacuated quartz tubes were filled with hydrogen while the hydrogen partial pressure was carefully controlled in each experiment. The encapsulated specimens were subjected to heat treatments consisting of annealing and aging. After the heat treatment, the path of martensitic transformation was investigated using differential scanning calorimetry (DSC). On cooling, martensite initial temperatures decrease with the increasing partial pressure of hydrogen applied during the heat treatment. Moreover, the formation of martensite phase may not take place for partial pressures that exceed a certain limit. On the other hand, two-and multiple-step B2/R/B19' martensitic transformations are observed in specimens heat treated at lower hydrogen pressures. Results obtained using transmission electron microscopy (TEM) clearly show that the size of Ni4Ti3 precipitates becomes smaller in alloys that were heat treated at higher hydrogen pressures. The results are discussed in terms of a chain of events. It is suggested that diffusion of hydrogen into the specimen during the annealing step first influences the nucleation of the Ni4Ti3 phase. The sizes and distribution of the Ni4Ti3 precipitates than control the characteristics of B2/B19' transformation.
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Comparison of TEM sample preparation methods for immunogold labeling
GRECHHAMER, Christian
The tracking of antigens in biological samples can be achieved by labeling them with gold-gonjugated antibodies (immunogold labeling). This thesis gives an overview of several sample preparation methods for TEM and investigates their effects on the binding efficiency of antibodies to certain antigens. For this reason, protein samples were processed according to four different protocols, cut into ultra-thin sections and labeled with primary and secondary antibodies. The micrographs, taken during observation with a TEM, were analysed quantitatively and the obtained data was statistically evaluated.
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Preparation and characterization of nanoparticles for in vitro cell studies
Hladík, Martin ; Černoch, Peter (advisor) ; Pilař, Jan (referee)
This thesis deals with the preparation, characterization methods and in vitro imaging of nanoparticles with great potential for medical diagnostics. A key role in this work occupy nanoparticles comprising a core of calcium tungstate, CaWO4, covered by a natural polysaccharide together serve as a suitable model contrast agent for cell imaging techniques. CaWO4 natural properties such as the absorption of X-rays, natural fluorescence capabilities and capacities for doping fluorescently active lanthanides, makes from nanoparticles suitable candidates for the position of contrast agents for imaging in the diagnosis of oncological diseases. Moreover, by coverage of the inorganic core by natural polysaccharide nanoparticles reach the desired size and the possibility of active targeting to specific or nonspecific interactions with the cell membrane, which are key factors in in vitro cell studies. It was found the most suitable synthesis both doped and undoped core of this model reaching the formation of spherical particles of colloidal dimensions. Doping was realized by red fluorescent trivalent europium, Eu3+ , and green fluorescent trivalent terbium, Tb3+ , and neither of these dopants affected the original crystalline structure CaWO4. In the next stage, these fluorescent nuclei successfully dispersed...
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Electron microscopy study of nanostructured thin film catalysts for micro-fuel cell application
Lavková, Jaroslava ; Matolínová, Iva (advisor) ; Ruterana, Pierre (referee) ; Šubrt, Jan (referee)
Present doctoral thesis is focused on electron microscopy and spectroscopy investigation of novel metal-oxide anode catalyst for fuel cell application. Catalyst based on Pt- doped cerium oxide in form of thin layers prepared by simultaneous magnetron sputtering deposition on intermediate carbonaceous films grown on silicon substrate has been studied. The influence of catalyst support composition (a-C and CNx films), deposition time of CeOx layer and other deposition parameters, as deposition rate, composition of working atmosphere and Pt concentration on the morphology of Pt-CeOx layers has been investigated mainly by Transmission Electron Microscopy (TEM). The obtained results have shown that by suitable preparation conditions combination we are able to tune final morphology and composition of catalyst. Composition of carbonaceous films and Pt-CeOx layers was examined by complementary spectroscopy techniques - Energy Dispersive X-ray Spectroscopy (EDX), Electron Energy Loss Spectroscopy (EELS) and X-ray Photoelectron Spectroscopy (XPS). Such prepared porous structures of Pt-CeOx are of promising as anode catalytic material for real fuel cell application. Keywords: cerium oxide, platinum, fuel cell, magnetron sputtering, Transmission Electron Microscopy
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Electron cryo-microscopy techniques in biological research and nanotechnologies
Mistríková, Veronika ; Bednár, Jan (advisor) ; Nebesářová, Jana (referee) ; Benada, Oldřich (referee)
Preparation of biological samples for transmission electron microscopy is not a trivial task. The samples must withstand a vacuum environment present inside a microscope, and it is often necessary to use non-physiological procedures for their processing. These procedures usually involve aldehyde-based fixation, replacing water with alcohol (i.e. dehydration/substitution), and embedding into a resin, which creates support for the subsequent preparation of thin sections that can be placed into the microscope. In the last decade, the method of cryo-fixation (vitrification) using ultra-fast high-pressure freezing followed by freeze substitution and low-temperature resin embedding gained a dominant position in the cell biology research. In this way, a range of biological samples with a thicknesses up to several hundreds of micrometers was successfully vitrified to a state that was closely related to their in vivo structures. The cryo-fixation of isolated biological objects (with a limited thickness up to several micrometers) is possible in a thin layer of vitrified water by plunge freezing at ambient pressure. In combination with electron cryo-microscopy, this method has become the most effective and fundamental principle for the high-resolution studies and image analysis of fully hydrated samples...
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Contributions to Volatile Compound Generation of Arsenic, Silver and Gold by Tetrahydroborate Reaction for Atomic Absorption Spectrometry
Musil, Stanislav ; Rychlovský, Petr (advisor) ; Kanický, Viktor (referee) ; Spěváčková, Věra (referee)
(EN) The presented dissertation thesis summarizes the results contained in five original research papers that were published in prestigious international scientific journals in the field of analytical chemistry and atomic spectrometry. It is devoted to the method of generation of volatile compounds using a tetrahydroborate reaction and detection in a quartz multiatomizer by atomic absorption spectrometry. The thesis can be divided into two thematic parts - speciation analysis of arsenic based on hydride generation technique with collection and separation in a cryogenic trap and generation of volatile species of transition metals. In the first thematic part pre-reduction of pentavalent inorganic and methylated arsenicals has been studied. A simple setup for on-line pre-reduction employing thioglycolic acid as a fast pre-reductant has been developed, connected with a current hydride generator and applied/verified to oxidation state specific arsenic speciation analysis of human urine samples. In the same method the possibility of drying the gaseous phase from water vapor has been investigated to avoid incidental blocking the cryogenic trap by frozen water and to decrease fluctuations of signal baseline. Pronounced losses of methylated species have been discovered on Nafion tube dryer currently used in...
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Comicellization of polystyrene-block-poly(acrylic acid) with low-molar-mass surfactants
Paloncýová, Markéta ; Matějíček, Pavel (referee) ; Štěpánek, Miroslav (advisor)
This B.Sc. thesis deals with the study of the effect of low-molar-mass ionic surfactants sodium dodecyl sulfate (SDS) and hexydecyltrimethylammonium bromide (HTAB) on association behavior of the block copolymer polystyrene-b-polyacrylic acid (PS-b-PAA) in alkaline aqueous solutions. Prepared polymeric nanoparticles were characterized by static and dynamic light scattering, transmission electron microscopy and 1 H NMR spectroscopy. It was found that both surfactants interact only with PAA blocks and their presence in the system leads to worsening of the copolymer solubility which manifests itself in the formation of large micellar aggregates and in precipitation of the copolymer-surfactant complexes.
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Segmentation of carbon nanocones in TEM images using generalized Hough transform
Sladký, Vladimír ; Odstrčilík, Jan (referee) ; Walek, Petr (advisor)
Bachelor thesis deals with automatic detection of carbon nanostructures in TEM images using generalized Hough transform. There is described the theory of Hough transform in order to detect analytic as well as general structures in images. According to the characteristics of carbon nanostructures TEM images synthetic test images, that are preprocessed by morphological operations and thresholding with global threshold, are created. Hough transform algorithm that detects nanocones in synthetic images of carbon nanocone structures is created. Success and accuracy of detection is tested changing the parameters of artificial images or level of preprocessing.
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Comparison of microscopic diagnostic methods
Veselý, Jakub ; Tihlaříková, Eva (referee) ; Čudek, Pavel (advisor)
This thesis deals with the description and comparison of diagnostic methods, transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The introduction is a description of diagnostic methods. The following experimental section dealing with the diagnosis of ferritic chromium steel sample methods of scanning electron microscopy, atomic force microscopy, transmission electron microscopy and the evaluation and interpretation of measured results. The conclusion provides a comparison, the advantages and disadvantages of diagnostic methods.
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Changes in dislocation substructure of S235JR steel during fatigue loading
Jandová, D. ; Gajdoš, Lubomír ; Šperl, Martin ; Kaiser, J.
Changes in dislocation substructure were studied in normalized and annealed S235JR steel in relation to the number of symmetrical reversed stress cycles with the amplitude σa = 242 MPa and corresponding mean life Nf = 17,950 cycles. The microstructure of the steel consisted of ferrite with a small amount of pearlite. The substructure was observed in as received condition and after application of various relative numbers of cycles n/Nf, these being 0.25, 0.50 and 0.75. An irregular dislocation net occurred in the virgin specimen, however, during cyclic loading the dislocations started to accumulate gradually in slip bands and to form a cell substructure in grains of favourable crystallographic orientations. Total dislocation density, dislocation density in slip bands and inter-band distance were measured using transmission electron microscopy (TEM). The total dislocation density was found to slightly decrease and the density in slip bands to increase with increasing number of cycles. The results concerning the dislocation density were compared with changes in the microplastic limit (MPL) which were determined by the measurement of the inductance of the “specimen - coil” system. They consisted in a rapid initial decrease at the first stage of the fatigue process and in a gradual increase during the major part of the life. These changes can be interpreted on the basis of changes in dislocation density as was verified independently by X-ray diffraction and nanoindentation tests. On the basis of the measurement of dislocation density by TEM it appears that changes in MPL can be connected with the dislocation density in slip bands rather than with the total dislocation density.
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