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Dimensional measurements from a limited set of X-ray projections
Iser, Tomáš ; Horáček, Jan (advisor) ; Křivánek, Jaroslav (referee)
Modern non-destructive approaches for quality control in manufacturing often rely on X-ray computed tomography to measure even difficult-to-reach features. Unfortunately, such measurements require hundreds or thousands of calibrated X-ray projections, which is a time-consuming process and may cause bottlenecks. In the recent state-of-the-art research, tens and hundreds of projections are still required. In this thesis, we examine the radiography physics, technologies, and ex- isting solutions, and we propose a novel approach for non-destructive dimensional measurements from a limited number of projections. Instead of relying on com- puted tomography, we formulate the measurements as a minimization problem in which we compare our parametric model to reference radiographs. We propose the whole dimensional measurements pipeline, including object parametrizations, material calibrations, simulations, and hierarchical optimizations. We fully im- plemented the method and evaluated its accuracy and repeatability using real radiographs of real physical objects. We achieved accuracy in the range of tens or hundreds of micrometers, which is almost comparable to industrial computed tomography, but we only used two or three reference radiographs. These results are significant for industrial quality control. Acquiring...
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Plasma Heat Flux to Solid Structures in Tokamaks
Vondráček, Petr ; Horáček, Jan (advisor) ; Gunn, James P. (referee) ; Svoboda, Vojtěch (referee)
Plasma Heat Flux to Solid Structures in Tokamaks Petr Vondráček Energy and particle exhaust is the key issue for future fusion reactors based on magnetic plasma confinement, namely for tokamaks. Good understanding of processes controlling plasma heat fluxes impinging the first wall of tokamaks is of a main concern for fusion research. This doctoral thesis is focused on experimental investigation of plasma heat fluxes in different locations of the COMPASS tokamak. A new infrared thermography system was built for this purpose as a part of this PhD research. There are four main topics studied using the system. First of all, a narrow near-SOL heat flux channel with a very steep radial profile is characterised in HFS limited discharges. It is shown that the near-SOL heat flux decay length is consistent with the drift-based model of the SOL heat transport. Secondly, heat loading of leading edges of misaligned limiters is broadly studied. The optical approximation of the heat flux distribution around a poloidal leading edge is confirmed as a valid approach. Heat loading of a magnetically shadowed side of a toroidal limiter gap is observed experimentally for the first time confirming predictions of particle-in-cell code simulations. Thirdly, localised hot-spots caused by the impact of runaway electrons as well as...
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Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub ; Jiráková, Kateřina ; Adámek, Jiří ; Grover, Ondřej ; Horáček, Jan ; Hron, Martin ; Vondráček, Petr
We have identified two distinct types of turbulent fluctuations in COMPASS plasmas, the high-frequency edge oscillations and low-frequency SOL blobs. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of isat fluctuations is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL. This supports, together with turbulence spreading rate being positive in the near SOL but negative in the edge, the picture presented in [3] that most of the fluctuations that form a positive skewness in the edge region disappear around LCFS and new blobs are formed in the near SOL. Further, we cannot confirm the assumption that the blobs are generated randomly according to a Poisson process. Oscillations of all measured quantities, incl. radial particle flux, in the near SOL are peaked around ∼13 kHz. This seems to correspond to a poloidally rotating structure with a rather large poloidal wave-length ∼ 15 − 20 cm, that at least partly modulates blob generation. Nevertheless, we note that time separation of blobs becomes more random further in the SOL, possibly due to differences in their individual propagation. These observations hold for diverted plasmas, but the situation may be different in limited low-elongation plasmas where the radius of zero skewness was observed to be shifted significantly (several cm) inwards, compared to diverted configuration, and Gamma-like PDF is detected even inside the LCFS. Study of these plasmas is ongoing.
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Fluctuations in the scrape-off layer and edge plasma of the COMPASS tokamak
Seidl, Jakub ; Jiráková, Kateřina ; Adámek, Jiří ; Grover, Ondřej ; Horáček, Jan ; Hron, Martin ; Vondráček, Petr
In this work we study properties of turbulent structures in the scrape-off layer (SOL) and edge plasma of the COMPASS tokamak. Two distinct types of coherent oscillations are observed: a) broadband high frequency branch rotating in the electron diamagnetic direction, appearing mainly in the confined region but protruding also to the SOL b) low-frequency blobs rotating in an opposite poloidal direction, formed in the vicinity of the radius of zero electric field. The transition region is localized in the near SOL, where both types spatially overlap and interact and the radial particle transport gradually transfers from high to low frequencies. Even though skewness of fluctuations of the ion saturation current is positive even inside LCFS, distinguishable Gamma-distributed PDF, formed by the low-frequency fluctuations, arises in the near SOL and most of the fluctuations that form a positive skewness in the edge region disappear around LCFS.
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Local sharpness prediction and image segmentation
Kopál, Jakub ; Šikudová, Elena (advisor) ; Horáček, Jan (referee)
The problem of automatic segmentation turned out to be complicated andtothisday, notcompletelysolved.Sinceitisacomplexproblem,thispaperis not- tryingtosolveitinitsmostgeneralform. Instead,itisfocusedonautomatic, bina- rypicturesegmentation,withtheoptiontochooseattributes, basedonwhich the seg- mentation should operate. Among these attributes are the focus and color of the picture. The results of the segmentation based on the assumption "focused object, blurry background" turned out to be very similar to the groundtruth in pictures, which fulfill this assumption. 1
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Hybrid renderer
Goliaš, Matúš ; Pelikán, Josef (advisor) ; Horáček, Jan (referee)
Title: Hybrid renderer Author: Matúš Goliaš Department: Department of Software and Computer Science Education Supervisor: RNDr. Josef Pelikán, KSVI Abstract: In medical applications, there are often used both volume data and objects defined by their surface. However, rendering these two types of data together is rather dif- ficult. This thesis provides the description of ray marching algorithm for volume rendering. We base the algorithm on the emission-absorption model of light trans- fer through a gaseous material. Moreover, we discuss the problems of adding meshes to the volume with respect to the algorithm. Next, we propose an ex- tension of ray marching which takes all meshes into account and renders them with the volume correctly. In addition, we compare the individual approaches for solving steps of the algorithm. Finally, we implement our solution in an ap- plication for volume viewing. We develop this renderer using OpenGL and we discuss our options of implementation. Furthermore, we extend our application by allowing the camera inside the volume, clipping the scene and interactive edit- ing of transfer functions which define the colour representation of volume data. Subsequently, we describe every feature and discuss its possible implementations. Keywords: volume data, ray marching, translucent...
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Big data visualization
Lehončák, Michal ; Pelikán, Josef (advisor) ; Horáček, Jan (referee)
Nowadays, data are an integral part of our lives. Their volume is growing every day, and it often prevents us from understanding what these data means. The object of this thesis is to develop an application for large dataset analysis and visualization. Thesis also explores statistical methods used to reduce volume and dimensionality of data and implements selected algorithms from this field. Another goal is to explore the possibilities of modern graphics cards, as their performance increases every year. The visualization should use a graphics processor with data are shown as points in point- cloud in 3D space and user should be able to browse this data interactively.
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Volumetric data processing for CT enterography
Horáček, Jan ; Pelikán, Josef (advisor) ; Czanner, Silvester (referee) ; Schier, Jan (referee)
Title: Volumetric data processing for CT enterography Author: Jan Horáček Department: Department of Software and Computer Science Education Supervisor: RNDr. Josef Pelikán, Department of Software and Computer Sci- ence Education Abstract: The overall goal of our work is to develop algorithms for efficient processing, segmentation and tracking of the small intestine in CT enterography scans. The small intestine is a complex organ, the shape of which can vary con- siderably between patients: and in addition to this, its location and shape can change significantly between subsequent scans of the same person. The CT en- terography process uses contrast agents to improve the visibility of the intestine, so that various potentially problematic features, such as inflammations, obstruc- tions and so on, can be properly seen. However, due to the convoluted shape of the organ, manual diagnosis of raw CT enterography data is still a difficult and time-consuming task, and is prone to diagnostic errors. We have prepared a set of methods for automatic preprocessing, segmentation and tracking of such data that aims at providing a much clearer data visualization: such tools can greatly improve the diagnostic process. Our first contribution is to make a high quality denoising method for volumet- ric data practically usable: so...
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Software-based eye tracking
Dominec, Adam ; Zitová, Barbara (advisor) ; Horáček, Jan (referee)
Abstract. This thesis presents a software library for eye gaze tracking. The typical use case is a person watching their computer screen. All data is obtained from a single video camera and is processed in real time. The resulting software is freely available including its source code.
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Real-Time Light Transport in Analytically Integrable Participating Media
Iser, Tomáš ; Elek, Oskár (advisor) ; Horáček, Jan (referee)
The focus of this thesis is the real-time rendering of participating media, such as fog. This is an important problem, because such media significantly influence the appearance of the rendered scene. It is also a challenging one, because its physically correct solution involves a costly simulation of a very large number of light-particle interactions, especially when considering multiple scattering. The existing real-time approaches are mostly based on empirical or single-scattering approximations, or only consider homogeneous media. This work briefly examines the existing solutions and then presents an improved method for real-time multi- ple scattering in quasi-heterogeneous media. We use analytically integrable den- sity functions and efficient MIP map filtering with several techniques to minimize the inherent visual artifacts. The solution has been implemented and evaluated in a combined CPU/GPU prototype application. The resulting highly-parallel method achieves good visual fidelity and has a stable computation time of only a few milliseconds per frame.
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