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Design and optimalization switched power source controlled by microcontroller
Smejkal, Vít ; Bartušek, Karel (referee) ; Roubal, Zdeněk (advisor)
This thesis deals with an introduction to the theory of switching power supplies and with properties of magnetic materials. Special attention is paid to nanocrystalline materials. It also discusses the issues of simulating the behavior of ferromagnets. The properties of commonly used ferrite material and nanocrystalline materials was measured. Using the created program for the design of forward converter is designed a switching power supply to verify its proposal. Design optimization is based on using a nanocrystalline core, which allows to reduce the operating frequency.
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Design and optimalization switched power source controlled by microcontroller
Smejkal, Vít ; Bartušek, Karel (referee) ; Roubal, Zdeněk (advisor)
This thesis deals with an introduction to the theory of switching power supplies and with properties of magnetic materials. Special attention is paid to nanocrystalline materials. It also discusses the issues of simulating the behavior of ferromagnets. The properties of commonly used ferrite material and nanocrystalline materials was measured. Using the created program for the design of forward converter is designed a switching power supply to verify its proposal. Design optimization is based on using a nanocrystalline core, which allows to reduce the operating frequency.
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Photothermal and photocurrent spectroscopy of wide band gap nanocrystalline semiconductors
Remeš, Zdeněk ; Babchenko, Oleg ; Neykova, Neda ; Varga, Marián
Optical spectroscopy belongs to the most important methods applied to characterize thin films. Photothermal deflection spectroscopy (PDS) as well as the dual beam photocurrent (DBP) spectroscopy in near ultraviolet (200-400 nm), visible (400-700 nm) and near infrared regions (700-2000 nm) are particularly useful for study of the wide band gap semiconductors deposited as thin layers on glass substrates. In our laboratory we focus on optically transparent thin films such as nanocrystalline diamond (NCD) or ZnO nanostructures with size too small to be visualized in optical microscope and the optical absorption edge in the ultraviolet region. In this contribution we summarize how to evaluate the optical absorption edge and the defects in the band gap of these wide band gap nanocrystalline semiconductors.
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Nanokrystalické částice oxidů železa, karbidů železa a alfa-Fe připravené z ferihydritu
Schneeweiss, Oldřich ; Grygar, Tomáš ; David, Bohumil ; Pizúrová, Naděžda ; Žák, Tomáš ; Zbořil, R. ; Mašláň, M.
Preparation of nanocrystalline iron oxides (hematite alpha-Fe2O3, magnetite Fe3O4), Haag carbide (Fe5C2), and alpha-Fe by thermal treatment of ferrihydrite in various atmospheres is reported. The phase composition and size of nanoparticles was controlled using the annealing temperature and atmosphere (vacuum, hydrogen, or ethylene).
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Difúze 99Mo ve teplně zpracované slitině Fe76Mo8Cu1B15
Čermák, Jiří ; Stloukal, Ivo
Ion beam sputtering by Ar+ ions was used to investigate 99Mo tracer diffusion in Fe76Mo8Cu1B15 alloy in the temperature range 548 – 648 K. The experimental samples were prepared from ribbons of Fe76Mo8Cu1B15 alloy in as quenched state q, and after pre-annealing at 683 K for 1 h (state a1) and at 743 K for 1 h (state a2). The penetration profiles were obtained using serial sectioning method and consist of two parts suggesting that two different diffusion paths are operating. The Mo short-circuit diffusivity P was evaluated using both LeClaire’s analysis and Divinski’s theory derived for transition type-A/B regime in coarse-grained materials.
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Difúzní studie Fe a Mo ve slitině Fe76Mo8B15Cu1
Čermák, Jiří ; Stloukal, Ivo
59Fe and 99Mo tracer diffusion in Fe76Mo8B15Cu1 alloy was studied using serial sectioning method in the temperature range 527 – 649 K. The ribbon-like samples were annealed at 695 K for 1 and 5 hours before the diffusion experiments; the volume fraction of crystalline phase was checked by the Mössbauer spectroscopy. Concentration profiles obtained by sputtering by Ar+ ions in a glow discharge show two distinct branches suggesting that two diffusion paths are operating.
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Preparation and properties of nanocomposites based on Zr-Fe
Roupcová, Pavla ; Schneeweiss, Oldřich ; Bezdička, Petr
The spark erosion of the pure Zr and Fe electrodes in hydrogen yielded nanocrystalline powder consisting of the mixture of Zr-rich (Zr3FeH7, ZrO2, and Zr(Fe)) and Fe-rich phases with the mean chemical composition Zr-3.2wt.%Fe. Heat treatment in hydrogen atmosphere at 973K induced phase decomposition and transitions with the final composition of bcc Fe, Zr3Fe, ZrH2 and dominating ZrO2 phases. The result indicates that formation of Fe-rich phase (bcc Fe) embedded in ZrO2 could be possible using an appropriate heat treatment of the as-prepared powder.
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