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Synthesis of ceramic powder materials in the presence of the ultrasound field
Kočicová, Pavla ; Bartoníčková, Eva (referee) ; Částková, Klára (advisor)
The thesis concerns the synthesis Ceric Oxide, Samarium Oxide and Samarium doped Cerium Oxide. The theoretical part is focused on the characteristics, applications and possibilities of the Cerium Oxide synthesis. The experimental part describes the precipitation of the Cerium Oxide powder. The synthesis of the powders were proceeded in the normal conditions or in the presence of ultrasonic field. For the purposes of description of the ready powders the x-ray diffraction (XRD) and the raster electron microscopy (SEM) were used. The ceramics were made of the selected powders where the structure was described by SEM, the density by Archimedes´Method and the grain size by grid-line intersect method. Using the precipitation synthesis, the pure powders of Ceric Oxide, Samarium Oxide and Samarium doped Cerium Oxide were prepared. The powder morphology was strongly involved by the pH level and by ageing time. The ultrasound was accelerating the ageing. At the values of pH > 11 the rodlike particles were created. The ageing time and the ultrasound supported the creation of the rodlike particles. The ceramics made of the powder with the presence of the rodlike morphology showed the density up to 97,14% of the theoretical density.
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Automated area measurement of precipitation intensity via a network of microwave links
Bubniak, Milan ; Pospíšil, Ondřej (referee) ; Musil, Petr (advisor)
Point-to-point microwave links can be utilized as a large sensor network to measure rainfall. This work deals with the application of this procedure in practice. The first part of the thesis deals with atmospheric precipitation in general and standard methods of their measurement; and the propagation of the microwave signal and various causes of its attenuation, focusing on the attenuation caused by rain and the recommendation ITU-R P.838. This is followed by a state of the art summarization of the measurement of rainfall by microwave links. In the second part of the work, a manual procedure for calculating rainfall from microwave link data is performed, taking wet antenna attenuation into account. Then the creation of a support tool in the C# language is being described, which supply the data to the functions of the RAINLINK rainfall calculation library. Several rainfall calculations that are validated by physical rain gauges are performed. Furthermore, the own Telcorain application for rainfall calculation is created in the Python language, based on the pycomlink library. It has a graphical user interface created in PyQt. Several rainfall calculations validated by rain gauges are performed again, and the results are compared with the RAINLINK library.
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"Optimizing the Al casting heat treatment"
Ostrézí, Barbora ; Cileček, Jarmil (referee) ; Horáček, Milan (advisor)
This master’s thesis focuses on the heat treatment of the aluminium alloy AlSi7Mg0,6 and also investigates the effects of different coolants usage on its mechanical properties. First part is dedicated to the description of aluminium alloys, their chemical composition, behaviour and mechanical properties with particular attention to the Al-Si-Mg alloys. This part was followed by the summary of commonly used heat treatment of aluminium alloys. The third part is dedicated to the experiment. Castings and test specimens were wax casted at Alucast, s.r.o. company. After annealing, the samples were quickly cooled down in four different coolants and underwent tensile testing. Their mechanical properties (tensile strength, yield point and ductility) were evaluated as well as microstructure. In the last part, the achieved results are presented.
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Structure and properties of electron beam penetration produced in steel AMS 5659
Říčan, Daniel ; Foret, Rudolf (referee) ; Kouřil, Miloslav (advisor)
This master thesis deals with the electron beam welding of the AMS 5659 steel used in industry for special hydraulic cylinders (Fig. 1). A theoretical analysis of electron beam welding and analysis of the influence of selected welding parameters on penetration characteristics are in the first part of the thesis. The second part contains an evaluation of the implemented experimental penetrations on samples of the steel in the hardened condition H1025 and after solution heat. It was also done a properties assessment of the same samples that were been hardened again. The light microscopy (SM), the scanning electron microscopy (SEM) and the measurement method of hardness according to Vickers were used for evaluation and comparison of the steel properties in the region of penetration and the heat affected zones properties.
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Synthesis of bioceramic materials based on hydroxyapatite
Kočicová, Pavla ; Králová, Marcela (referee) ; Částková, Klára (advisor)
The thesis deals with the precipitation synthesis of nanoparticle hydroxyapatite with goal to study the influence of reaction conditions on the morphology of the particles. The theoretical part is focused on biomaterials, bioceramics and phosphates characterization. Further the work is focused on hydroxyapatite, its characteristics and possible synthesis in particular. The synthesis of hydroxyapatite precipitation is described in the experimental part. Syntheses were performed at a reaction temperature of 0-80 °C at pH = 8-11, at the aging time of 0-24 h, in the presence of surfactant and the chelating agent and with the post-precipitation hydrothermal or ultrasonic treatment. For characterization of the prepared powders, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), laser diffraction (LD) and the analysis of the specific surface area (BET) were used. Pure hydroxyapatite powders or a mixture of hydroxyapatite and tricalcium phosphate were prepared by precipitation syntheses. HA particle morphology was strongly affected by the reaction temperature – with increasing temperature the larger particles with a clearer morphology were formed, mostly in the rod shape. Postprecipitation hydrothermal treatment had a significant influence on the morphology of HA particles – it caused the formation of spherical or slightly elongated particles. The reaction medium of water/ethanol significantly affected the particle morphology – it inhibited the particle growth.
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Hydration Process of Magnesium Oxide from Partly Calcined Dolomite
Tišnovský, Michal ; Bartoníčková, Eva (referee) ; Ptáček, Petr (advisor)
This bachelor thesis deals with the study of half-burnt dolomite, it‘s thermal decomposition (calcination) and preparation of a mixture of magnesium hydroxide and calcium carbonate by precipitation. At the beginning of the experimental part, the dolomite material sample is characterized. It‘s moisture content, double magnesium carbonate content and other carbonates are found. The second part deals with the study of the burning process in which a suitable interval of thermal treatment temperature was found. The investigation of the dissolution of dolomite in hydrochloric acid revealed the reaction kinetics. For precipitation, a method based on boiling a dolomite suspension in a hydrochloric acid solution under reflux, was used. The precipitation product in this case was magnesium carbonate in the modification of aragonite.
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Measuring of winter precipitation and derivation of precipitation time series using snow water equivalent at selected stations in the Sumava Mts.
Valešová, Petra ; Jeníček, Michal (advisor) ; Míka, Dominik (referee)
The measurement of winter precipitation is an important part of many scientific fields, but the same time there are many uncertainties in the measurement that can arise from inaccuracy or poor calibration of sensors, rain gauges and the influence of environmental factors. Measurement inaccuracies can be caused by the influence of wind, evaporation from heated rain gauges or clogging of the rain gauge. The aim of this work is to process data measured by a heated tipping bucket rain gauge, a classical rain gauge and snow water equivalent sensors from selected stations in the Sumava Mountains. These measured data are subsequently processed and, in case of failures, supplemented with data from other stations according to the given principles. Cumulative precipitation series for the hydrological years 2016 to 2022 are then compiled from the data thus supplemented. Key words: precipitation, snow water equivalent, snow depth, measuring of precipitation
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Change in precipitation distribution as temperature rises expressed in diagnostic and prognostic data
Sokol, Zbyněk ; Řezáčová, Daniela
We summarize the main results that show how the distribution of precipitation changes with increasing temperature. Hourly rainfall totals from 97 rain gauge stations in the Czech Republic for the years 1997 to 2019 are used for the evaluation. Ground temperature, ground dew point temperature and temperature at the lifting condensation level are used to express the temperature change. The results show how an increase in temperature and a corresponding increase in saturation humidity (CC scaling) affects the distribution of precipitation in the study area. In general, the increase in precipitation as a function of observed temperature is clearly evident for the upper quantile values, but only for certain temperature intervals. It confirms the findings of other studies. In this paper, data from reanalyses performed by the ALADIN-CLIMAT/CZ model are treated similarly to the measured data.\n
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Stochastic Weather Generators and Regional Climate Models: Rivals or Allies?
Dubrovský, Martin ; Štěpánek, Petr ; Meitner, Jan ; Zahradníček, Pavel
The paper demonstrates 'collaboration' between the stochastic weather generator SPAGETTA (WG) and Regional Climate Models (RCM) in analysing impacts of Climate Change (CC). In the first part of the paper, the generator is compared with the ensemble of 19 RCMs in terms of their ability to reproduce 11 spatial temperature and precipitation indices in eight European regions: the indices are based on registering days and spells exhibiting spatially significant occurrence of dry, wet, hot or cold weather, or possible combination of dryor-wet and hot-or-cold conditions. The obtained results indicate that both methodologies provide weather series of comparable quality. In the second part of the paper (which was done only for the Central Europe region), the WG parameters are modified using the RCM-based CC scenarios and the synthetic weather series representing the future climate are produced. This experiment is based on a set of CC scenarios, which consist of changes in selected combinations of following characteristics: (1) mean temperature, (2) temperature variability, (3) daily average precipitation (considering only wet days), (4) probability of wet day occurrence, (5) spatial lag-0 and lag-1day correlations of temperature and precipitation series. The synthetic series generated for each version of the CC scenario are analysed in terms the above mentioned spatial validation indices, the stress was put on effect of each of the five component of the CC scenario on individual validation indices. The results of the experiment indicate that the changes in temperature means is the main contributor to the changes in the validation obviously, except for the purely precipitation-based indices. Positive changes in the lag-0 and lag-1day correlations of both temperature and precipitation are the second most significant contributor to the changes in the validation indices.
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Precipitation by PERUN
Zacharov, Petr, jr. ; Brožková, R. ; Řezáčová, Daniela
Weather reanalyses are a powerful tool for studying historical weather both at individual points and especially over an area. The detailed reanalysis produced by the PERUN project thus makes it possible to reveal various aspects of the atmosphere to a degree that we are unable to achieve with measurements. Since it is still a model approximation, it is of course necessary to detect systematic biases by verification before its use. Climate model runs, on the other hand, can uncover the future evolution of the atmosphere. Since these calculations cannot yet be verified, it is necessary to validate a historical run of the same model and subtract the revealed systematic errors from the future projections. In the PERUN project, both the historical run and two climate runs up to 2100 have been calculated. In this work, we present a basic verification and validation of the precipitation forecasts and an evaluation of the separation of precipitation into stratiform and convective precipitation and, in addition, into\nliquid and solid precipitation.
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