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Influence of changes in concrerte pore structure on actually durability of reinforced and pre-stressed structures.
Kovalčíková, Hana ; Adámek, Jiří (advisor)
This master thesis deals with a durability of concrete, which has become the centre of the interests of international scientific insitutes during the last years. The resistence of reinforced concrete depends on the covercrete which the aggresive liquids and gases penetrate through from the environment to reinforcement. According to the ability of the covercrete to penetrate degradative species is possible to tell the durability of concrete constructions. In experimental part we look for the actual state of covercrete, ordinary and high strength, by combination of various experiments. We can find here the test´s results of water and gas permeability and absorbability and sorption of concrete which complete the permeability tests. In final part the impact of different concrete types on durability of reinforced concrete is discussed.
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Simulations of synthetic diffusion MRI data based on Brownian motion
Valla, Radek ; Mikl, Michal (referee) ; Labounek, René (advisor)
This master thesis focuses on dMRI (diffusion magnetic resonance imaging) and its dependance on diffusion in human brain tissue. It is described how to retrieve an image from gained data and its properties, advantages and disadvantages. It mentions problem in detecting kissing fibres due to its similarity with crossing fibres. Design of mathematical models of axons is decribed and suggested measurement to detect difference in signals for kissing and crossing fibres. It describes new simulator of diffusion-weighted MRI (dMRI) data which is able to generate it based on random walk algorithm with geometrical constraints not only for crossing fiber geometry, but also as o novelty for bending and kissing fiber geometries. This study contains results of simulations and disscusion about their usefulness with suggestions for simulator improvement. Simulated dMRI data shows significant difference in certain gradients. Data reconstruction shows, that these reults cannot be reconstructed into the same geometry as it was simulated for.
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Measurement of selected samples relaxations by use of NMR
Kovalčík, Tomáš ; Gescheidtová, Eva (referee) ; Bartušek, Karel (advisor)
The work deals with nuclear magnetic resonance and principles of relaxation measurement and diffusion constants. Magnetic resonance is phenomenon, when energy in the form of RF pulse with Larmor frequency is added to this material in the magnetic field B0, the elements will be excited to a higher energy level. When you measure FID up to 90° RF pulse, from the absorption line, you will acquire . Further we can, for measurement of the transverse relaxation time T2, use the Spin echo method, that makes use of the 90° RF pulse and the series of 180° RF pulses. From measured values, the T2 relaxation time is directly acquired (inhomogeneity will prevent existence).
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Computer modeling of MOSFET transistor
Major, Jan ; Harwot, Ondřej (referee) ; Pokorný, Michal (advisor)
Work is focused on computer modeling of PN junction and MOSFET transistor in the program COMSOL Multiphysics and in program TiberCAD. The text is discussed on the drift and diffusion in semiconductors. Also shown is a method of modeling the PN junction and MOSFET transistor in the programs and compare models.
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Effect of humic acids on mobility of ionic compounds
Herzog, Milan ; Weidlich,, Tomáš (referee) ; Sedláček, Petr (advisor)
The content of this diploma thesis is study of interactions between humic acids and model probes (such as organic dyes and ions of heavy metals) by the simple diffusion experiments in diffusion cell. The main aim was to desctibe the influence of charge of different diffusion sonds (solved substances) on interactions with humic acids imobilized in model gel phase. As a appropriete model probe was chosen copper ions (as a representation of heavy metals) and organic dyes (methylene blue, rhodamine, fluorescein and chicago blue). Experimental results could be used to improve knowledge based on natural barier properties of humic acids and to inovate simple diffusion laboratory techniques for characterization of reaktivity of biopolymers in general.
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Study on the transport of humic acids through the plant cuticles
Smilková, Marcela ; Záhora, Jaroslav (referee) ; Sedláček, Petr (advisor)
This diploma thesis is focused on foliar fertilization. It is nowadays one of the most widespread types of application of commercial fertilizers. Concern of this thesis is the study of plant cuticles as a thin layer on the leaves. These thin membranes are responsible for regulation of water transport and nutrients. Further function of plant cuticles is the mechanical protection of the outer part of the plant. Plant cuticles were characterized by fluorescence spectroscopy, classical optical microscopy and profilometry. The main aim of this thesis is the optimization and verification of experimental methodology aimed to the transport of commercial humic product through plant cuticles by simple diffusion techniques. The results obtained by presented diffusion techniques of humic product through plant cuticles were correlated with the same diffusion experiments through synthetic membranes with defined pore size and density. The study on transport of commercial humic product was realized in hydrogel medium by two different diffusion methods – non-stationary diffusion technique and diffusion couple. The important part of this diploma thesis is the characterization of supported hydrogel matrix by rheology tests, mercury intrusion porosimetry and scanned electron microscopy. Conclusions of this diploma thesis could be used for improving of efficiency of foliar fertilization.
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Diffusion of cupric ions in humic hydrogels
Grunt, Jakub ; Pabst, Willi (referee) ; Klučáková, Martina (advisor)
Presented diploma thesis focuses on the study of diffusion of cupric ions in humic acid hydrogels. A total of eight different hydrogels were prepared by dissolving the humic acids with sodium hydroxide and sodium triphosphate. For the purpose of precipitation and cross linking, hydrochloric acid and chlorides of magnesium, calcium and iron were used during a modified preparation of gels. Different gel-forming interactions were achieved by modifying the preparation of hydrogel systems. The aim of the thesis was to assess the effect of gel preparation procedure on the transport properties of the gels. Therefore, diffusion coeficients were determined for all samples. Two different methods - constant-source diffusion and instantaneous planar source diffusion - were used to assign the diffusion coefficients. Methods differ in source concentrations of cupric ions and are suitable for assessing the impact of the concentration on the diffusion coefficient. Both these methods were based on monitoring temporal evolution of diffusion profiles of cupric ions and on assigning the overall diffusion flow. Copper ions were elected as diffusing medium because of their high affinity and strong binding to humic acids. Measurements show that gels prepared using polyphosphate allow slightly faster diffusion of cupric ions and that the constant-source method provides higher diffusion coefficients in comparison to instantaneous planar source method.
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