| |
|
Biodiversity of standing floodplain waters and processes of its formation and preservation
Pithart, David
Water chemistry and planktic communities in the naturally eutrophic alluvial waters in the Lužnice floodplain have been studied. The floofplain waters are naturally eutrophic, with strong vertical physico-chemical gradients and oxygen depletions at the botom. Small pools and backwaters of this type have unique phytoplankton structure. Prevailing dominance of flegellates, namely Cryptophyceae, and low proportion of green chlorococcal algae and Diatoms, and almost absence of Cyanophyceae are very unusual for such eutrophic waters. Flagellate dominate thanks their ability to keep the vertical position in a permanently light limited conditions (resulted from poorly mixed water columns and intensive shading of water surface by vegetation). Floodplain geodiversity play crucial role, determining morphology and location of pools and backwaters, their exposition to flooding and inflows of underground water. Terrestial vegetation effects light exposition, leaf litter.
|
|
Initial stages of fatigue failure of polycrystalline materials
Man, Jiří ; Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav
Geometry of persistent slip markings (PSMs) formed during cyclic loading of polycrystalline stainless steels and superalloy was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM-FEG). Internal dislocation structure was investigated using transmission electron microscopy (TEM). Persistent slip bands with dislocation structure corresponding to the cyclic strain localization were identified and correlated with PSMs observed on the specimen surface.
|
|
Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
|
|
Analysis of Iron-Phosphorus Reaction Products Formation During Heat Treatment Processes
Skoumalová, Zuzana ; Jan, Vít (referee) ; Doležal, Pavel (advisor)
During high pressure pulsation tests repeated cracks of CP3. housings occur. High pressure pump CP3 is part of injection system Common Rail. Cracks can be caused by segregation of phosphorous from a washing medium on grain boundaries during subsequent heat treatment process. The present master´s thesis focuses on analysis of phosphorous compounds on specimen surface made from steel 20MnCr5, which were soaked in solutions with different concentration of phosphorous. Master’s thesis is also focused on potencial influence of phosphorous on structure and properties of this material. The first part of the thesis provides a summary of current knowledge in the studied field, experimental results can be found in the second part. The surface analysis XPS, the light microscopy, the scanning electron microscopy equipped by energy dispersive chemical analysis, the glow discharge optical emission spectroscopy, the methods of the phase analysis by means of the X-ray diffraction and impact test were used.
|
|
Dynamism and Codification
Šipková, Milena
The author attempts a typology of the language variants. She stresses that as far as codification is concerned, apart from the langue changes of the social and territorial character especially the processes of structural character are important; within them it is necessary to distinguish especially the progressive phenomena.
|
| |
| |
|
Realization of the device for measurement of electromagnetic waves scattering from structure of solar cells
Brilla, Pavol ; Březina, Tomáš (referee) ; Ohlídal, Miloslav (advisor)
The master thesis discusses the principles, design and realization of the original device for measuring of the electromagnetic radiation scattering in the structure of solar cells. It follows the results of a previous project "Analýza optických vlastností solárných článku" (ev.n.FT-TA3/142) and as well as knowledge gained from Ing. Vladimir Grundling’s master thesis, which has been done under this project. The subject of this thesis was to make a device for measuring of the electromagnetic radiation scattering in the visible spectrum. The aim of this work is an innovation of the previous device, so that the electromagnetic radiation scattering in the near infrared spectrum can be studied. This makes the possibility to qualify the influence of the rear surface of an active part of solar cell on electromagnetic radiation scattering, i.e., on the conversion efficiency of solar energy into electric. For this reasons it was necessary to modify the device, so that we can change the radiation source and detector because of the transparency of silicon wafers for the near infrared area. The work is supported by the project „Barevné solární články s vysokou účinností pro architektonické aplikace“ (FRTI1/168) in cooperation with Solartec s.r.o.
|
|
Computational modelling of noise inside cabin of aircraft VUT 100 Cobra
Prnka, Jiří ; Houfek, Lubomír (referee) ; Švancara, Pavel (advisor)
This master’s thesis deals with the computational simulation of low-frequency noise inside the cabin of small commercial airplane VUT 100 Cobra. For this low-frequncy range deterministic methods: Final Element Method (FEM) and Boundary Element Method (BEM) are used for simulation of the dynamic behaviour of the object. FEM has been used to compute eigenmodes and eigenfrequences of the structure of the aeroplane cabin and of the acoustic space inside cabin. Then response to harmonic excitation of engine represented by unit forces in place of contact has been computed. Obtained velocities on the surface of the cabin are then used as the basis for the noise calculation inside the cabin using BEM. After that effect of some construction modifications on sound level inside cabin are evaluated by computational modelling.
|
guest ::
