National Repository of Grey Literature 88 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Segmentation and density estimation in femur
Horáček, Jan ; Maršálek, Lukáš (advisor)
Title: Segmentation and Density Estimation in Femur Author: Jan Horáček Department: Department of Software and Computer Science Education Supervisor: Mgr. Lukáš Maršálek Supervisor's e-mail address: lukas.marsalek@mff.cuni.cz Abstract: There are two basic ways of surgical treatment of femoral neck frac- ture - total endoprosthesis or a special metal screw in the bone. In case of a dense enough bone the screws are preferred. But for a too sparse bone, the screw may cut through the femoral head, which results in further surgical operations. We present a novel method for femoral head density measurement, which serves as another hint for the doctor's decision, whether to apply a screw or total endo- prosthesis. Our approach is based on semi-automatical femoral head segmenta- tion from CT dataset based on finding optimal path through polar coordinates on axial slices. The cost function is based on a combination of corticallis proper- ties, mostly the directional behavior of 3D gradients and their size in 2D slices, where they form typical "channels". The final volume is computed using filling and morphological algorithms and its properties are further measured. The final implementation was experimentally validated on RTG clinic of Bulovka hospital and allows radiologists to intuitively and accurately estimate...
Automation of nuclear fuel visual inspection
Knotek, Jaroslav ; Blažek, Jan (advisor) ; Horáček, Jan (referee)
The safety and performance of nuclear plant relies, among others, on the quality of nuclear fuel. The quality fulfilling designed criteria of the fuel in use is inspected and reported on periodically. Visual inspection focuses on the condition of the fuel based on its visual properties. During the inspection, the fuel is being recorded and analysed by the inspector. The current state of the fuel assemblies is compared to the historical statistics which helps do decide whether this particular assembly remains or gets replaced. This thesis describe a project initiated by Centrum Výzkumu Řež focusing on digital image processing methods application to visual inspection process. The result of the project is a tool that accelerates the process of report making. Firstly, it transforms the inspection video into one image overview and highlight a significant part (more than 95%) of possible defects to the inspector. 1
Virtual Reality Lens Image Distortion Correction
Procházka, Tomáš ; Wilkie, Alexander (advisor) ; Horáček, Jan (referee)
Lenses in virtual reality headsets make it possible to put displays close to users' eyes and they provide users with wider field of view. However, they also distort the displayed image. Providing we know the lens distortion properties, it is possible to compensate for the distortion by displaying an image that is distorted in the opposite way. This thesis focuses on measurement of the distortion for an arbitrarily complex lens, while also considering chromatic aberration. A system capable of measuring of the distortion using just a camera attached to the virtual reality headset is designed and implemented. It is based on pattern detection and comparison of relative positions of points on the display and their correspondences in the distorted image. The result is a 2D distortion map that can be used to transform images such that they appear undistorted to the virtual reality headset users.
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...
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...
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.
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.
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
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...
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.

National Repository of Grey Literature : 88 records found   1 - 10nextend  jump to record:
See also: similar author names
6 HORÁČEK, Jakub
1 Horáček, J.
6 Horáček, Jakub
67 Horáček, Jaromír
9 Horáček, Jaroslav
23 Horáček, Jiří
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