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Phase Transformations during Heat Treatment of Fe - C Materials
Škvarka, Jakub ; Pacal, Bohumil (referee) ; Molliková, Eva (advisor)
The goal of this thesis is a study of heat treatment of iron-carbon alloys from a physical angle. Characteristics of main components from this system and their modifications are described there. There is also described what is going on during heat treatment especially from an angle of thermodynamics and kinetics, thanks to available information from literature. The knowledge is applied on specific types of heat treatment of material and processes which can follow it.
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Ice nucleating particles in the atmosphere
Gaálová, Gabriela ; Zíková, Naděžda (advisor) ; Sedlák, Pavel (referee)
The production of clouds and precipitation in the atmosphere is greatly influenced by microscopic ice nucleating particles, acting in the process of heterogeneous ice nucleation as ice nuclei. Examining the properties and variations of ice nucleating particles concent- rations over time might help to better predict future changes to the climate. The aim of this thesis is to summarise the information about processes of homogeneous, but primarily heterogeneous ice nucleation where specific physical and chemical features of these particles are applied. In this thesis, the main aerosol sources of ice nucleating particles and their abilities to directly or indirectly influence the atmosphere and climate are described. The observational methods of the concentration of ice nucleating particles in the air are also pre- sented, while the structure of the cloud expansion chamber PINE, which was used to obtain data values representing the amount of ice nucleating particles in the Czech Republic, is also described in more detail. From the data set total average values and time dependen- cies, including daily and weekly cycle were calculated; the part of the data processing is the statistical evaluation and comparison of the results with other studies. Keywords: ice nucleating particles, nucleation, aerosol,...
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Chemical deposition of diamond thin films from gas vapors
Kromka, Alexander
The preparation of diamond layers and their (nano-) structures requires the optimization of several technological steps. In the first step of “diamond technology” it is important to activate the surface of the non-diamond substrate by a suitable process known as nucleation or nucleation. The second key step is the growth of the diamond layer itself by chemical vapor deposition (CVD) under low pressures (10 ÷ 10,000 Pa) and temperatures in the range of 250 ÷ 1000 °C, and from a gas mixture of methane and hydrogen commonly used in a hot filament or microwave plasma CVD systems. In this paper, both technological steps, nucleation and growth, are discussed in light of current trends and experimental activities taking place in the laboratories of the Institute of Physics of the Academy of Sciences of the Czech Republic (FZÚ).
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Nucleation in complex systems
Kulveit, Jan ; Demo, Pavel (advisor) ; Slanina, František (referee) ; Vlček, Jaroslav (referee)
Title: Nucleation in complex systems Author: Jan Kulveit Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: prof. Pavel Demo, Institute of Physics of the Czech Academy ofSciences, Department of Optical Materials Abstract: We studied nucleation in progressively more abstract contexts and systems, starting from classical nucleation theory and ending with nucleation in complex networks. The cases studied include impurity nucleation in a solid matrix on several alkali halide crystals, where we determined formation energies for clusters, treated as defects, starting from single impurity-vacancy dipole and small aggregates to possible configurations of larger clusters. In the next part, we turn to the study of heterogeneous nucleation. While in the usual treatment of heterogeneous nucleation the surface energy is assumed to be homogenous, we ask the question what happens if we consider the surface energy to be heteroge- neous.Utilizing umbrella sampling computer simulations we find the nucleation barrier can be significantly lowered in the presence of surface heterogeneity, even if the average surface energy is kept constant. In the last part we study influence of clustering coefficient on phase transitions in scale-free networks, using forward flux sampling (FFS). Keywords: nucleation,...
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Numerical model for the origin of magmatic textures and its application to the Fichtelgebirge/Smrčiny granite batholith
Špillar, Václav ; Dolejš, David (advisor) ; Ježek, Josef (referee) ; Žák, Jiří (referee)
Magmatic processes are major agents responsible for the formation and differentiation of the Earth's crust. In contrast to extensive efforts to improve understanding and utility of igneous geochemistry, physical processes of magma differentiation and solidification remain largely unclear. Large variability of igneous textures provides record of these processes and intensive parameters governing the crystallization. In this thesis, we develop quantitative methods, which allow us to better interpret igneous textures in the framework of physics of solidification. We have developed a new three-dimensional model of crystallization from one- component melt driven by homogeneous and heterogeneous nucleation and crystal growth. The predicted textures are quantitatively characterized by crystal size distributions, spatial distribution functions and parameters representing grain contact relationships. The model employs high resolution in a large volume simulation domain in order to produce statistically stable results. Our simulations, performed for various functional forms of nucleation and growth rates with respect to time, imply that (i) crystals are ordered (anti-clustered) on short length scales. This reflects that other crystals already have a finite size at the time of nucleation of younger crystal,...
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Mechanisms of Microtubules Dynamics and Nucleation in a Plant Cell
Mauerová, Zdeňka ; Schwarzerová, Kateřina (advisor) ; Žárský, Viktor (referee)
Nucleation of microtubules co-determines organization of this cytoskeleton component in cells and makes a significant contribution to shaping its dynamics. In plant cells, micro- tubules are mainly nucleated on preexisting ones and nucleation takes place in the cortex and also within the mitotic spindle and the fragmoplast. Recruiting the γTuRC, a pre- served universal nucleator, to the wall of microtubules is provided by augmin in cooperation with NEDD1/GCP-WD. The function of the γTuRC is at least in the case of nucleation in the spindle, but apparently in other situations as well further enhanced by XMAP215/MOR1, which raises efficiency of the γTuRC through its own polymerization activity, and TPX2, or its homologs, which for one thing, directly activates the complex and for another, locally increases concentration of tubulins by forming condensate with them, which also augments the probability of success of nucleation. Not much is known about regulatory pathways controlling this process, with the exception of the TTP complex, which is functional in the cortex. Overall, knowledge covering nucleation in plants is rather meager and information concerning the molecular mechanisms of functioning of mentioned factors comes mainly from research in animals. Keywords augmin, cytoskeleton, γTuRC,...
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Phase Transformations during Heat Treatment of Fe - C Materials
Škvarka, Jakub ; Pacal, Bohumil (referee) ; Molliková, Eva (advisor)
The goal of this thesis is a study of heat treatment of iron-carbon alloys from a physical angle. Characteristics of main components from this system and their modifications are described there. There is also described what is going on during heat treatment especially from an angle of thermodynamics and kinetics, thanks to available information from literature. The knowledge is applied on specific types of heat treatment of material and processes which can follow it.
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Nucleation in complex systems
Kulveit, Jan ; Demo, Pavel (advisor) ; Slanina, František (referee) ; Vlček, Jaroslav (referee)
Title: Nucleation in complex systems Author: Jan Kulveit Institute: Institute of Physics of the Czech Academy of Sciences Supervisor: prof. Pavel Demo, Institute of Physics of the Czech Academy ofSciences, Department of Optical Materials Abstract: We studied nucleation in progressively more abstract contexts and systems, starting from classical nucleation theory and ending with nucleation in complex networks. The cases studied include impurity nucleation in a solid matrix on several alkali halide crystals, where we determined formation energies for clusters, treated as defects, starting from single impurity-vacancy dipole and small aggregates to possible configurations of larger clusters. In the next part, we turn to the study of heterogeneous nucleation. While in the usual treatment of heterogeneous nucleation the surface energy is assumed to be homogenous, we ask the question what happens if we consider the surface energy to be heteroge- neous.Utilizing umbrella sampling computer simulations we find the nucleation barrier can be significantly lowered in the presence of surface heterogeneity, even if the average surface energy is kept constant. In the last part we study influence of clustering coefficient on phase transitions in scale-free networks, using forward flux sampling (FFS). Keywords: nucleation,...
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The Distinctive Changes of Particles' Numeric Concentrations, Are Caused by Electrostatic Flue Gases Cleaning.
Molchanov, O. ; Krpec, K. ; Horák, J. ; Hopan, F. ; Ždímal, Vladimír ; Schwarz, Jaroslav
A burning processes are always accompanied by emissions, and solid fuel combustion is believed to be the main source of dust releases. Solid fuels are predominant for using by boilers under 300 kW, which are mostly use for heating the domestic buildings and small premises in industrial and other use. It is well known, that using such boilers is inevitably involves the pollution releases, among which are emissions of oxides of carbon, nitrogen and sulfur oxides and particulate matters. After 2020 all boilers in European Union are have to be consistent with the list of ecological norms, and norm ECODESIGN is the one of them. This norm, inter alia, means that PM concentration could not exceed 40 mg/m3N. Such legislative measures are compelling the producers to make steps to decrease boiler´s pollutions. However, it is hard to achieve the desired results by optimization of burning processes only. That´s why arises a need to equip the boilers with the gas cleaning units. Within this context, precipitation particulate matter with electrostatic method is one of the most perspective. Within studies to optimize the constructional and high voltages parameters of ESP, it was appeared unusual phenomenon, which has describing below.\n
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