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Optimization of process of preparing graphite electrodes with a layer of lead dioxide
Doros, Stanislav ; Vomáčková, Alena (referee) ; Pilátová, Ivana (advisor)
My study is focused on describing of complex electrochemical methods of preparing of graphite substrate lead dioxide anodes. The theoretical part is devoted to characterization of different parameters which influence the quality (morphology and composition) of the coating. In the experimental part are described the procedures of preparing of the graphite anodes with the lead dioxide coating. In the results are specified the best parameters for which permits the anode to resist high current densities. The whole process consists of substrate treatment, adjustment of current density, period of electroplating and the optimal thickness of plating, control of pH and temperature of solution, additives, rotation of electrode. The lifetime was tested by electrolysis of a potassium chloride water solution for 5 hours by applying 18 A/dm2, the mass of electrode after drying remained constant.
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High-Torque Motors for Battery Operated Material Handling Trucks
Höll, Jan ; Kurka,, Otakar (referee) ; Voženílek, Petr (referee) ; Kuchyňková, Hana (advisor)
he recent development of the power electronic and high-energy permanent magnets enables developing synchronous machines excited by permanent magnets, that are able to meet very gradual and exact control demands. Due to high torque density, that permanent magnet machines reach, the synchronous motors may be used even in direct (gearless) drives. One of the branches, in which direct drives can be used, is material handling. The most propelling drives in this branch consist of induction motor, simple gearbox with invariable gear ratio mounted to the drive wheel. Main aim of this thesis is designing the direct drive motor for low-lift truck. Motor is built-in the driven wheel, therefore outer rotor design appears to be more suitable. Two types of motors – permanent magnet synchronous motor and transverse flux motor have been chosen on the basis of technical paper study, many years lasting experience and verification computations. Both motor types are described in great details in this thesis. Both synchronous motor with PM and transverse flux motor have been designed for direct drive of the given low-lift truck. The proposals of both motors have been optimized by means of finite element method. Based on these design optimizing computations, both motors have been designed, produced and design accuracy has been verified by laboratory testing. Synchronous motor with PM achieves better electromagnetic parameters and its production is also simpler, therefore this motor is more suitable for this application. The solution with transverse flux motor may save substantial amount of active materials. Results of the detailed optimization and comparison of both motor types are the main benefits of this thesis.
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Ionizing Radiation Measurement
Podolský, Ondřej ; Pikula, Stanislav (referee) ; Beneš, Petr (advisor)
The bachelor’s thesis deals with measuring of ionizing radiation. The aim is to verify the measurement methods for measuring statistical parameters of ionizing radiation sources and verification of attenuation coefficient depending on density. The first contains characteristic of ionizing radiation, shielding, detection and interaction with the environment. The thesis also focuses on the description and testing of selected statistical distributions. In conclusion deals with the practical verifications of measuring methods which may be used as a laboratory exercises in the future.
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FATIGUE CHARACTERISTICS OF MODIFIED MAGNESIUM ALLOYS AFTER CORROSION DEGRADATION
Němcová, Aneta ; Očenášek, Vladivoj (referee) ; Hadzima, Branislav (referee) ; Pacal, Bohumil (advisor)
This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.
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Preparation and properties of ferroelectric ceramic materials
Vykoukalová, Tereza ; Maca, Karel (referee) ; Částková, Klára (advisor)
The aim of the work was a processing of ceramic material based on BST for ferroelectric application. Wet chemical techniques based on precipitations and sol-gel methods with ultrasound, hydrothermal or mechanochemical treatment supporting deaglomeration and reducing particle growth were used for BST ceramic powder synthesis. Suitable powders were selected by the evaluation of particle morphology, size and agglomeration, from these powders BST bulk ceramic with defined phase composition and morphology applicable for ferroelectric applications was prepared. It was found, that the most suitable method for preparation of phase pure and nanosized BST powder was sol-gel synthesis with solvothermal treatment (200 °C/48 h). Ceramic with relative density of 85 % TD and with the average grain size of about 1, 22 µm was prepared by pressing and sintering of the powder synthesized by the sol-gel method.
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Fluid flow analysis in the open cylindrical container with the free surface vortex
Illík, Jakub ; Klas, Roman (referee) ; Štigler, Jaroslav (advisor)
This master's thesis analyses fluid flow in an open cylindrical tank with vortex using numerical simulation. The theoretical part introduces a set of equations governing fluid flow and relations used to describe vortex motion. A general overview of terms used in computational fluid dynamics is presented. The experimental section consists of three parts. The vortex modelling is performed using ANSYS Fluent software. Data are consequently analysed within ANSYS CFD-Post software tool. Special focus is put on the vortex shape that is fitted with a curve corresponding to a probability density function of the Cauchy distribution. Results are then plotted in MATLAB software.
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Analýza tahové-tlakové asymetrie u koeficientů příčné deformace pomocí metody korelace digitálního obrazu
Zadina, Jan
This thesis deals with the analysis of tensile-compressive asymmetry in the coefficients of transverse deformation (Poisson's ratios) of spruce wood (Picea abies L. Karst) in all three principal directions of growth, i.e. for the complete set of 6 Poisson's ratios. Tensile and compressive stress within one direction was applied to the same test specimen, and the digital image correlation (DIC) method was used to analyze surface deformations. For this purpose, the surface of the test specimens in two adjacent planes was recorded by cameras during mechanical loading, and the deformations were fully evaluated from the digital images, from which the Poisson's ratios were subsequently calculated. The evaluation of Poisson's ratios was performed using statistical tests. Statistical t-tests were performed to test the equality of means to compare the tensile and compressive Poisson's ratios, which showed differences between the compressive and tensile Poisson's ratios only in some cases. A one-way ANOVA and Scheffé's test were also performed to compare the different directions with each other, which showed a distribution of large and small Poisson's ratios mainly in tension. A regression analysis was also performed to determine the degree of correlation between the tensile and compressive Poisson's ratios, and correlation was demonstrated in the radial and tangential directions. Regression analysis was also performed to examine the relationship with wood density, which showed a slight correlation with some of the Poisson's ratios.
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Účinky rostlinných produktů na růst, stravitelnost, složení těla, imunitní a stresovou reakci u ryb
ZARE, Mahyar
The plant powders and extracts contain bioactive compounds, including phenolic compounds, proteins, vitamins, and minerals. These compounds have been shown to possess antistress, antiviral, antibacterial, and antifungal effects on fish. Nettle has been extensively studied in mammalian medicine, but its effects on aquaculture species have not been well documented. Recent studies have demonstrated the positive impact of nettle on the growth performance, hematology, blood biochemistry, immune system, and pathogens resistance of fish species. Nettle leaf powder at a rate of 30 g/kg feed, improved the final body weight (FBW), weight gain (WG), weight gain percent% (WG%), specific growth rate (SGR%), and increased whole-body proximate protein and ash content while reducing whole-body proximate fat rainbow trout (Oncorhynchus mykiss) fingerlings. Tarragon leaf powder at a rate of 30 g/kg feed, significantly increased the haematocrit% (Hct%) and leukocyte count. The combination of 10 g/kg feed nettle leaf powder and 10 g/kg feed tarragon leaf powder resulted in the highest levels of erythrocyte count and haemoglobin (Hb). Nettle leaf powder at 30 g/kg feed, tarragon leaf powder at 30 g/kg feed, and a combination of 10 g/kg feed nettle leaf powder and 10 g/kg feed tarragon leaf powder significantly increased albumin levels in blood serum. Tarragon leaf powder at 10 g/kg feed showed the highest blood serum lysozyme enzyme activity compared to the control. Blood serum total immunoglobulin and total protein levels were significantly associated with nettle leaf powder at 30 g/kg feed. The study confirms the positive effects of these additives on growth performance, whole body proximate composition, immunological, haematological, and selected blood serum biochemical factors. Different levels of garlic powder did not significantly affect growth performance and somatic indices in European perch (Perca fluviatilis). However, adding 30 g/kg feed garlic powder resulted in a significantly higher level of whole-body proximate protein. Both 10 g/kg feed and 30 g/kg feed garlic powder showed significantly higher fat digestibility than the control and 20 g/kg feed garlic powder groups. The 20 g/kg feed garlic powder diet resulted in significantly higher erythrocyte and leukocyte count. Furthermore, all garlic groups had significantly lower blood serum cholesterol levels compared to the control. Garlic powder at level 30 g/kg feed improved European perch's resistance against high density and net handling stress, as well as their haematological and immunological parameters. Immediately after stress, the level of cortisol in all garlic-fed groups was significantly higher than in the control group, and there was no significant difference in glucose levels among the groups. However, after 24 hours, the levels of both cortisol and glucose were lower in all garlic-fed groups compared to the control group significantly. Garlic powder at a level of 10 g/kg feed improved apparent fat digestibility, whole body proximate protein, hematological parameters, immunological parameters, and increased resistance in high density and net handling stress. Overall, garlic powder could be considered as a potential dietary supplement for managing stress in European perch, however, further research is needed to determine the optimal dosage and long-term effects. Results of present thesis suggest that the use of natural feed phyto-additives could be a potential solution to address health issues in aquaculture, leading to more sustainable and efficient food production.
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Interaction of water vapor with epitaxial layers of cerium dioxide
Morvai, Orsolya ; Šmíd, Břetislav (advisor) ; López-Roso Redondo, Jesús Rubén (referee)
This thesis investigates the interaction between water and cerium oxide, which, due to its oxygen storage activity, could be widely used in nanomedicine, catalysis, and environmental applications. Despite extensive research, a fundamental understanding of how water interacts with cerium oxide under ambient conditions has been lacking. The study utilizes scanning tunneling microscopy, near-ambient pressure X-ray photoelectron spectroscopy, and the study of water dissociation on stoichiometric CeO2(111)/Pt(111) thin films with controlled step density. The results demonstrate the identification of three adsorption species and reveal that the dissociation kinetics depend on step density. These findings provide new insights into the role of water in cerium oxide interactions under operando conditions.
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Impact loading of lattice structures produced by Selective Laser Melting technology from magnesium alloy WE43
Foltán, Tomáš ; Červinek, Ondřej (referee) ; Jaroš, Jan (advisor)
Strut-based lattice structures manufactured with magnesium alloy WE43, due to their high strength-to-weight ratio, seem like an ideal solution for biomedical and aerospace industries. Previous research has focused mainly on the behaviour of these structures under quasi-static stress conditions. Dynamic stressing of these structures has not been deeply researched. Therefore, this work deals with impact testing of strut-based lattice structures manufactured by SLM. Low-velocity impact tests were performed on a set of cell topologies with different strut diameters. Absorbed energy, stress-strain curve, and deformation mechanism of each sample were studied. Clear effect of cell topology on the amount of absorbed energy was observed, where structures of similar relative densities displayed considerably different values. Highest specific absorbed energy was achieved with the FCCZ cell. In comparison with other materials (e.g., steel) magnesium proved to be far less efficient. This was most probably caused by its brittle fracture failure mode. Conducted tests give insight into mechanical behaviour of magnesium alloy structures under dynamic compression and their ability to absorb energy. Collected data may prove useful for biomedical applications e.g., in designing bone implants.
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