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Comparison of fitting approaches for cochlear implants
Fabíková, Veronika ; Čmiel, Vratislav (referee) ; Odstrčilík, Jan (advisor)
This bachelor’s thesis deals with topic of cochlear implantations (CI), especially with fitting of audio processors. Two hearing thresholds are usually determined during fitting of audio processors – Hearing Threshold (HT) and Maximum Comfortable Level threshold (MCL). In this work, a common subjective approach together with three objective methods for CI fitting is described. Individual approaches are then compared to each other. The second half of the thesis is devoted to description of methodology for XML files processing in MATLAB programming software, treatment of available data by a created program and statistical evaluation of acquired results. In the last chapter, there is a recommendation for audiologists stated, based on the results of the work.
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Physical properties of ultrafine-grained polycrystals of magnesium based alloys
Vrátná, Jitka
The objective of the thesis is the study of microstructure evolution, mechanical properties, defect structure and corrosion resistance of ultra-fine grained magnesium alloy AZ31 prepared by a combined two-step process: the extrusion and the equal-channel angular pressing (ECAP). The microstructure development was studied using light and transmission electron microscopy and electron backscatter diffraction (EBSD). Mechanical properties were studied by microhardness measurement and tensile tests and the defect structure by positron annihilation spectroscopy (PAS). The results of tensile tests indicates that the characteristic stress σ0.2 increases slightly with increasing number of ECAP passes only to the second pass and then decreases significantly with additional ECAP straining. This behaviour is in accordance with the results of PAS. EBSD measurements show that the microstructure of extruded and ECAPed material has a bimodal distribution of grain sizes. The bimodal distribution becomes homogeneous with increasing number of ECAP passes and no remaining large grains are observed after 8 passes. The average grain size in the specimen after 8 passes is in the submicrometer range and the fraction of high-angle grain boundary (HAGB) is approximately 80%. The extruded specimens after 8 ECAP passes show...
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Study of properties of Titanium prepared by SPD methods
Zháňal, Pavel ; Harcuba, Petr (advisor) ; Král, Robert (referee)
In present work the properties of comercially pure titanium fouth grade processed by equal channel angular pressing (ECAP) were studied. Experimental techniques such as Vickers microhardness, measurement of electrical resistivity, light and electron microscopy were used in this research. The dependence of the degree of the strain imposed by ECAP on microhardness of the material was measured. Microhardness measurement was used to indirectly investigate thermal stability of the prepared material, which is essential for ultra fine grained (UFG) materials. That was also the reason for establishing dependence of the electrical resistivity on the temperature. This method allows to detect changes in the material microstructure. Using scanning electron microscopy (SEM) the results obtained by previous methods were confirmed. It was found that the UFG titanium processed by ECAP is thermally stable aproximatelly up to 450řC. At this temperature begins recovery of the material which results in a decrease of the microhardness values and electrical resitivity. For the temperatures higher than 520řC material recrystalization begins.
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Physical properties of ultrafine-grained polycrystals of magnesium based alloys
Vrátná, Jitka
The objective of the thesis is the study of microstructure evolution, mechanical properties, defect structure and corrosion resistance of ultra-fine grained magnesium alloy AZ31 prepared by a combined two-step process: the extrusion and the equal-channel angular pressing (ECAP). The microstructure development was studied using light and transmission electron microscopy and electron backscatter diffraction (EBSD). Mechanical properties were studied by microhardness measurement and tensile tests and the defect structure by positron annihilation spectroscopy (PAS). The results of tensile tests indicates that the characteristic stress σ0.2 increases slightly with increasing number of ECAP passes only to the second pass and then decreases significantly with additional ECAP straining. This behaviour is in accordance with the results of PAS. EBSD measurements show that the microstructure of extruded and ECAPed material has a bimodal distribution of grain sizes. The bimodal distribution becomes homogeneous with increasing number of ECAP passes and no remaining large grains are observed after 8 passes. The average grain size in the specimen after 8 passes is in the submicrometer range and the fraction of high-angle grain boundary (HAGB) is approximately 80%. The extruded specimens after 8 ECAP passes show...
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Comparison of fitting approaches for cochlear implants
Fabíková, Veronika ; Čmiel, Vratislav (referee) ; Odstrčilík, Jan (advisor)
This bachelor’s thesis deals with topic of cochlear implantations (CI), especially with fitting of audio processors. Two hearing thresholds are usually determined during fitting of audio processors – Hearing Threshold (HT) and Maximum Comfortable Level threshold (MCL). In this work, a common subjective approach together with three objective methods for CI fitting is described. Individual approaches are then compared to each other. The second half of the thesis is devoted to description of methodology for XML files processing in MATLAB programming software, treatment of available data by a created program and statistical evaluation of acquired results. In the last chapter, there is a recommendation for audiologists stated, based on the results of the work.
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