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Study of mechanical properties of magnesium-based composites
Farkas, Gergely ; Mathis, Kristián (advisor) ; Drozd, Zdeněk (referee)
In the present work, the mechanical properties of AJ51 magnesium alloy and composite is studied. Compression tests in the temperature range of 20řC-300řC have been preformed. The microstructure of the specimen was studied by means of light optical microscopy. The work is focused on the elucidation of the micromechanisms acting during plastic deformation of the composite specimens. Further a comparison between the mechanical properties of alloy and the composite is presented.
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Interaction of ultrashort laser pulses with semiconductor nanostructures
Preclíková, Jana ; Malý, Petr (advisor) ; Potůček, Zdeněk (referee) ; Oswald, Jiří (referee)
The thesis is devoted to the optical spectroscopy (photoluminescence, transmission, ultrafast photoluminescence) of nanocrystalline diamond films and silver nanoparticles in titanium dioxide matrix. We studied the influence of the laser irradiation on optical properties of both materials under various conditions. Nanocrystalline diamond exhibits strong subpicosecond and picosecond photoluminescence parameters of which (intensity and decay rate) change with the laser irradiation and ambient air pressure. The effects are accompanied by a change in optical thicknesses of the nanocrystalline diamond films. We assigned the phenomena to light induced adsorption processes which influence the subgap states originating from surface and grainboundaries atoms. We implemented and optimized the preparation technique of the nanocomposite Ag-TiO2films exhibiting the multicolour photochromic effect. The analysis of the initial stages of the photochromic transformation revealed that during the laser irradiation the plasmon frequency of the resonating silver nanoparticles was blue shifted. The photoluminescence spectroscopy confirmed an increase in number of the Ag+ ions during the photochromic transformation. The photoluminescnece of the nanocrystalline TiO2 is due to the two types of radiative transitions: the...
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ecovery processes in dispersion and precipitation hardened Al alloys
Uhlíř, Jaromír
In this thesis the analysis of second phase particles influence on recovery and recrystallization processes in twin-roll cast sheets of AA 8011 aluminium alloy based on Al-Fe-Si is studied. The role of arrangement of impurity atoms and the type of thermomechanical treatment is investigated. Unbalanced crystallization of solid solution, which occurs during twin-roll casting, results in the creation of complicated structure of second phases, which isn't as a rule homogenously distributed in the volume. Therefore these materials exhibit poor mechanical properties in comparison with conventionally cast alloys. Important question the materials science deals with in the last years, is to find such a thermomechanical treatment, which results in balanced phase composition and optimal mechanical properties, comparable with properties of products produced by conventional methods. Such properties are especially high formability combined with sufficient strengths. To study physical properties of the alloy the resistometric measurement during linear heating, thermo-electric measurement and hardness measurement were used. Evolution of structure and microstructure in the alloy during heat treatment was studied by means of optical microscopy and transmission and scanning electron microscopy.
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Studies of nanocrystalline silicon colloidal suspensions
Fučíková, Anna ; Valenta, Jan (advisor) ; Chaloupka, Roman (referee)
This diploma thesis deals with optical and biophysical properties of colloidal suspensions of porous nanocrystalline silicon (por-Si) in different media, conditions necessary to create por-Si with different luminescence peaks and their optical characterization (emission and excitation spectra). The lifetime excited state = (28,6±0,9) us on emission wavelength 600 nm for orange emitting por-Si is measured by the time resolved fluorescence. The behaviour of por-Si and grinded silicon (crystals of size about 1um) in biological environment (L929 mouse fibroblast) is studied with optical transmission microscopy, time-lapse microphotography of cell culture evolution, fluorescent microscopy, and scanning electron microscopy (SEM). Transmission pictures prove an aggregation in presence of por-Si in media. This aggregates are going to internal environment of cells. At high concentration of grinded silicon we see meronecrosis. Por-Si has had also mildly negative effect on evolution of cell culture at very high concentrations, but cells are viable and cell division proceeds normally - next cell generation shows normal behaviour. Fluorescence microscopy used on orange emitting por-Si shows that por-Si is concentrated probably on cell membranes and its presence in internal cell environment is also proved. SEM proved...
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Porovnanie rôznych prístupov k stanoveniu indexu listovej plochy
Haninec, Pavel
Leaf area index (LAI) is one of the most important characteristics of forest stand affecting fundamentals of tree physiological processes, biomass production or mechanical stability. The aim of this thesis was to compare three different methods (gravimetrical, optical -- LAI 2000 plant canopy analyzer - and needle method) for estimation of LAI. Additionally, the seasonal development of LAI was measured using the LAI 2000 method. Research was conducted in three European beech (Fagus sylvatica L.) and one sycamore maple (Acer pseudoplatanus L.) stands. The age of forest stands was from 13 to 77 years. Seasonal development of LAI followed general pattern typical for broadleaf stands in central Europe, with fastest rate of leaf growth in the first month following budbreak. Maximal LAI was observed in mid-June and July and it was 4.52 -- 5.08 m2m-2 in beech and 4 m2m-2 in maple stand. LAI 2000 underestimated the gravimetrically measured LAI on average by 15.1 % in beech stands and by 5.8 % in maple stand (these differences were not statistically significant). Needle method underestimated gravimetrical LAI in beech on average by 22 % and in a maple stand by 40 % (this difference was significant in three out of four stands). Overall, gravimetrical method is most laborious but provides most accurate results. LAI 2000 slightly underestimates results (albeit not significantly in broadleaf species) but enables multiple measurements of LAI in the course of growing season. Needle method is inexpensive and easy to use but it significantly underestimates LAI. Its use for comparison of multiple species will always require calibration.
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Universal timer for sport activity
Janůš, Tomáš ; Klíma, Martin (referee) ; Macháň, Ladislav (advisor)
This bachelor thesis deals with a proposal and implementation of wireless electronic time measurement. In the thesis a proposal and implementation of simple wireless time measurement is described. Its part is also a proposal and creating of the optical barrier. The theoretical part further contains description and usage of various sensors. All sensors are wirelessly interconnected with the main device. The time measurement is being processed in the computer by means of a created programme which enables to control the time measurement and to save measured times as well.
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Optical fibre sensors
Gallo, Martin ; Šifta, Radim (referee) ; Münster, Petr (advisor)
The aim of this thesis is to examine in detail the possibility of fiber as optical sensor. This work deals with optical fiber sensors, their distribution and use. Describes the most renowned types, their advantages and disadvantages. At the beginning of this thesis there is an introduction to optical fibers, description of well-known linear and nonlinear phenomena occurring in them, development of optical sensors. Sensors are cleraly divided by usage and common attributes. The paper focuses on distributed optical fiber sensors and includes two different designs of these sensors there are also basic principles in designing distributed sensors. At the end of the work, the sensor using Brillouin scattering measuring vibration is simulated in the simulation program. Viewed transmitted signal spectra are shown and conclusions of results are drawn.
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Nonlinear optical properties of semiconductor nanostructures
Kořínek, Miroslav
Title: Nonlinear optical properties of semiconductor nanostructures Abstract: Laser ablation of solid state wafer in liquids is a simple and reliable method for creation of nanocrystals of almost any kind of metals and semiconductors. We performed pulsed laser ablation of a silicon wafer in deionized water to prepare colloidal silicon nanocrystals. The samples were prepared by femtosecond laser ablation using Ti: sapphire laser (wavelength 800 nm, pulse duration 100 fs, pulse energy 0.06 mJ - 0.7 mJ, repetition rate 1 kHz) and characterised by time-integrated photoluminescence spectroscopy, extinction measurements, transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD) and time-resolved measurements of photoluminescence. The time-integrated photoluminescence spectrum demonstrated a blue emission. In addition, we observed that aging of nanocrystals in deionized water for several weeks improved the photoluminescence intensity. It is generally accepted that the unique properties of Si nanocrystals result from both quantum confinement size effect and surface states. Modification and oxide passivation of surface states and defects in oxide layer can effectively increase the photoluminescence intensity. Using extinction measurement it was found that absorption of nanocrystals is...
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