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Evaporation of thin films using intense laser light observed operando in a scanning electron microscope
Boleloucká, Eliška ; Ukropcová, Iveta (referee) ; Nováček, Zdeněk (advisor)
This work focuses on the modification of the sample surface using intense laser light. This is one of the desired features of the new generation of multifunctional SPM probes, which are under development. In the first chapter is introduced the SPM probe itself, which allows correlative measurements. Following section contains the implementation of the intense laser light into the electron microscope chamber, together with the modification made to the detection branch of the microscope. The COMSOL Multiphysics software environment is used to simulate the interaction of the laser light with the sample surface. The results of the simulations of the temperature field in the sample are then compared with the results of the direct interaction of the sample surface with the laser light in the electron microscope chamber.
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Single column multiple electron beam imaging
Podstránský, Jáchym ; Jánský, Pavel (referee) ; Zlámal, Jakub (advisor)
Tato práce je zaměřena na měření emise elektronů z více katod tvořených n-dopovaným křemíkem a zobrazování elektronových svazků fokusovaných čočkou typu einzel na kameru CMOS. Experimentální výsledky jsou porovnány s počítačovou simulací, aby bylo možné pochopit emisi elektronů z polovodičové katody a pozorované nedokonalosti zobrazení. Na závěr jsou navrženy úpravy experimentálního uspořádání, které by měly vést ke zlepšení extrakčního proudu a velikosti stop fokusovaných elektronových svazků a také k lepšímu pochopení procesů probíhajících v experimentu.
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Počítačové modelování tepelného namáhání skleněné tabule při gravírování laserem
ZOUBEK, Tomáš
Computer modelling is often used to understand the nature or behaviour of physical phenomena. In this work, a three-dimensional computer model was created from a 25x30x4 mm (width x height x thickness) glass plate on which twenty dots with a radius of 371.54 ?m were burned using a laser engraving process. The distance between the dots was 1.25 mm. A computer simulation of the thermal stress of the laser engraving process was carried out on this model. The input parameters used were the laser travel time between points (0,5 s^(-1)), the duration of the laser discharge (0,5 s^(-1)), the laser power (30 W), the laser intensity and the laser density over a given area (given by equation 11), the heat flux coefficient of the glass sheet (5,7 Wm^(-2)K^(-1)) and the function controlling the firing of the laser beam at specific points and times (equations 5.4 and 5.5). The simulation was carried out for two variants that differed in the order of the fired points. For the first variant, the points were fired chronologically from left to right in rows, whereas for the second variant the points were fired in the order 1, 3, 5, 11, 13, 15, 7, 9, 17, 19, 2, 4, 12, 14, 6, 8, 10, 16 and 20. The second variant proved to be more optimal for the geometry and material studied. It resulted in less thermal stress, as lower temperatures were achieved with a defined laser beam, and at the same time there was a greater time delay between processes stressing the same locations.
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Computer modeling of diffusional transport in hydrogel
Koláček, Jakub ; Sedláček, Petr (referee) ; Pekař, Miloslav (advisor)
This thesis focuses on the design of models applicable to the simulation of particle motion in a viscoelastic environment in COMSOL Multiphysics. Two approaches have been chosen for the design of these models: the first is the design of a geometry representing the porous structure of hydrogels and the second is the implementation of viscoelasticity using the mathematical concept of a continuous environment. Two elementary geometrical models are presented in this work – a three-dimensional periodic lattice and a spherical volume model. Furthermore, the possibilities of implementing the generalized Langevin equation in COMSOL Multiphysics are explored by using the interface for custom partial differential equations, by adding an auxiliary dependent variable, or by defining a custom external function written in the C language. The proposed geometric models did not prove to be suitable for the simulation of viscoelastic environment. An implementation using an external function seems to be the most promising, as it offers the most customization possibilities, and its implementation reflects the theoretical foundations. The thesis also includes a custom add-in written for COMSOL Multiphysics to facilitate the evaluation of simulation data and a modified Python script to calculate the complex shear modulus from MSD data.
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The water flow simulation in the cesspit
Šrámková, Dagmar ; Hyánková, Eva (referee) ; Kriška-Dunajský, Michal (advisor)
This diploma thesis consists of two parts, part research and part attachments. The first section describes the literary problems of today's way of cleaning wastewater from small producers and characteristics of wastewater. The work is focused on the aspect of nature and all of these methods are directed towards this direction. The literary section is devoted to anaerobic environment, which is just one of the natural ways of treatment of waste water, in our case in a septic tank. The second part of the thesis deals with modeling of flow and behavior of sludge and water mixture in the cesspit septic tank sludge with variable densities and flow speeds. Modeling and calculations are made using COMSOL Multhiphysics. The conclusion is then summarized findings from the flow cesspit septic tank with the results and the assessment of whether a septic tank still has its place among the modern methods of wastewater treatment.
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Microrheology modeling with COMSOL Multiphysics package
Koláček, Jakub ; Sedláček, Petr (referee) ; Pekař, Miloslav (advisor)
This bachelor thesis focuses on modeling Brownian motion using the COMSOL Multiphysics package and its Particle Tracing module. The aim of the work is to design and create elementary models that will be able to suitably simulate the movement of microparticles in viscous and viscoelastic environments, which can later be used for modeling passive microrheology. Within this work, Matlab scripts were created for the calculation of MSD from the simulation results, validation of the viscous model was performed on experimental data and elementary models for the simulation of the viscoelastic environment were also designed. Two different approaches were chosen for the design of these models, namely the use of rigid obstacles under the assumption of a discrete environment and a mathematical model assuming continuous environment. Data from the viscous model showed good agreement with the experimental results. The results of viscoelastic simulations are presented, and further possible development of these models is discussed. The continuous mathematical model is considered closest to modeling viscoelastic behavior because of a characteristic curvature that was observed in the evaluation of MSD.
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Multiband magnetic antenna
Ryšánek, Martin ; Hertl, Ivo (referee) ; Raida, Zbyněk (advisor)
The thesis deals with a parametric analysis of a magnetic multiband antenna and explains the principle of its operation. In the thesis, an optimization of the antenna by the particle swarm optimization is performed in order to meet impedance matching in prescribed frequency bands.
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Computer modeling of laser beam
Mittner, Ondřej ; Wilfert, Otakar (referee) ; Raida, Zbyněk (advisor)
This bachelor’s thesis theoretically describes Gaussian beam, its characteristics and its passing through optical elements. The main attention is focused on creating of computer models of Gaussian beam in COMSOL Multiphysics application, detailed description of these models, presentation of achieved results and comparing these results with theoretic presumptions.
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Elektromagnetic field mapping in tissue
Port, Martin ; Čížek, Martin (referee) ; Rozman, Jiří (advisor)
This thesis is an introduction to the modeling of electromagnetic fields in the tissue and is focused on the knowledge of electromagnetic field theory. Maxwell's equations and their solutions are described the spread of plane waves in the environment. It also discusses the exposure limit values of specific absorbed power and hygienic limits based on the standards in force in the Czech Republic on health protection against nonionizing radiation in accordance with Government Regulation No. 106/2010 Coll. It also deals with the software interface in COMSOL Multiphysics 4.2 for solving physical modeling and simulation. There is mention of the RF module, which is used for modeling. Work mentions in detail about the menu of the program and the most important part - the Model Builder.
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Modelling of organic electrochemical transistors
Truksa, Jan ; Omasta, Lukáš (referee) ; Salyk, Ota (advisor)
The topic of this work is the making of a virtual model of a circular organic electrochemical transistor (OECT) and its electric field, and comparison of the computed results to a real system of rotationally symmetrical electrodes. The electric potential field in the transistor was modelled using the finite element method and the electric field and current field were determined using the results. Later, the electric potential field was mapped in a real system of aluminium electrodes, submerged in water. The electric field model of an unusually configured circular OECT is presented in this work. Due to insufficient computing capacity, the model had to be significantly simplified. The computed results agree with the experimentally determined potential field despite the simplification. The deviations of the model output characteristic from real OECT characteristic were caused by simplifying the model in respect to reality.
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