National Repository of Grey Literature 15 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Multilevel methods
Vacek, Petr ; Strakoš, Zdeněk (advisor)
The analysis of the convergence behavior of the multilevel methods is in the literature typically carried out under the assumption that the problem on the coarsest level is solved exactly. The aim of this thesis is to present a description of the multilevel methods which allows inexact solve on the coarsest level and to revisit selected results presented in literature using these weaker assumptions. In particular, we focus on the derivation of the uniform bound on the rate of convergence. Moreover, we discuss the possible dependence of the convergence behavior on the mesh size of the initial triangulation. 41
Factors Influencing the Radicality of Resection During Endoscopic Endonasal Transsphenoidal Potuitary Surgery.Intraoperative Magnetic Resonace Imaging in a Traditional Imaging Suite During Endonasal Pituitary Adenoma Resection.
Vacek, Petr ; Přibáň, Vladimír (advisor) ; Brichtová, Eva (referee) ; Lipina, Radim (referee)
Objective: Our primary goal was to evaluate our experience with performing intraoperative magnetic resonance imaging (iMRI) in a traditional MRI suite during endoscopic endonasal pituitary adenoma resection. Methods: From March 2008 to February 2013 a single department performed endoscopic endonasal pituitary adenoma resection on 50 patients. Surgical outcomes were compared between the first 25 patients (no iMRI) and the second 25 patients with whom iMRI was used. We evaluated not only the number of total resections in both groups, but also the prolongation of the time of the surgery in the second group. We also evaluated the progression of ophthalmic and endocrinological symptoms in both groups and the rate of complications. Results: The average length of the surgery was prolonged from 205 to 238 minutes (marginally statistically insignificant). We achieved total adenoma resection in seven cases (28%) in the first group and in 16 cases (64%) in the second group (a statistically significant difference). iMRI was successfully performed on all the patients in the second group without any complications related to patient transport or the execution of the imaging. There were no statistically significant differences in diabetes insipidus occurrence, postoperative visual field improvement, or...
Extended defects in Ga and Al nitrides
Vacek, Petr ; Holec, David (referee) ; Hospodková,, Alice (referee) ; Gröger, Roman (advisor)
III-nitridy běžně krystalizují v hexagonální (wurtzitové) struktuře, zatímco kubická (sfaleritová) struktura je metastabilní a má pouze mírně vyšší energii. Jejich fyzikální vlastnosti jsou silně ovlivněny přítomností rozsáhlých defektů, které jsou v těchto dvou strukturách od sebe odlišné. U wurtzitových nitridů se jedná primárně o vláknové dislokace. Některé vláknové dislokace tvoří hluboké energetické stavy v zakázaném pásu, kterými ovlivňují elektrické a optoelektronické vlastnosti těchto materiálů. Oproti tomu, kubické nitridy obsahují množství vrstevných chyb, které představují lokální transformace do stabilnější wurtzitové struktury. Cílem této práce je charakterizovat rozsáhlé defekty v obou krystalových strukturách pomocí elektronové mikroskopie, mikroskopie atomárních sil a rentgenové difrakce. Prokázali jsme, že vzorky GaN/AlN a AlN s orientací (0001) rostlé na substrátu Si (111) pomocí epitaxe z organokovových sloučenin obsahují velkou hustotu vláknových dislokací. Nejčastější jsou dislokace s Burgersovým vektorem s komponentou ve směru a wurtzitové struktury, následované dislokacemi s Burgersovým vektorem s komponentou ve směru a+c, zatímco dislokace s Burgersovým vektorem s c komponentou jsou relativně vzácné. Pravděpodobný původ vláknových dislokací je diskutován v souvislosti s různými mechanismy růstu těchto vrstev. Prizmatické vrstevné chyby byly nalezeny v tenkých nukleačních vrstvách AlN, ale v tlustších vrstvách již nebyly přítomny. Na rozhraní AlN / Si byla nalezena amorfní vrstva složená ze SiNx a částečně taky z AlN. Navrhujeme, že by tato amorfní vrstva mohla hrát významnou roli při relaxaci misfitového napětí. Analýza elektrické aktivity rozsáhlých defektů v AlN byla provedena pomocí měření proudu indukovaného elektronovým svazkem. Zjistili jsme, že vláknové dislokace způsobují slabý pokles indukovaného proudu. Díky jejich vysoké hustotě a rovnoměrnému rozložení však mají větší vliv na elektrické vlastnosti, než mají V-defekty a jejich shluky. Topografické a krystalografické defekty byly studovány na nežíhaných a žíhaných nukleačních vrstvách kubického GaN deponovaných na 3C-SiC (001) / Si (001) substrátu. Velikost ostrůvků na nežíhaných vzorcích se zvyšuje s tloušťkou nukleační vrstvy a po žíhání se dále zvětšuje. Po žíhání se snižuje pokrytí substrátu u nejtenčích nukleačních vrstev v důsledku difúze a desorpce (nebo leptání atmosférou reaktoru). Vrstevné chyby nalezené ve vrstvách GaN, poblíž rozhraní se SiC, byly většinou identifikovány jako intrinsické a byly ohraničené Shockleyho parciálními dislokacemi. Jejich původ byl diskutován, jako i vliv parciálních dislokací na relaxaci misfitového napětí. Díky velkému množství vrstevných chyb byly podrobněji studovány jejich interakce. Na základě našich zjištění jsme vyvinuli teoretický model popisující anihilaci vrstevných chyb v kubických vrstvách GaN. Tento model dokáže předpovědět pokles hustoty vrstevných chyb se zvyšující se tloušťkou vrstvy.
Primary Architecture / School for Third World
Vepřková, Adéla ; Vacek, Petr (referee) ; Ponešová, Barbora (advisor)
Unrest has been going on in the eastern part of the Democratic Republic of Congo for several years. People live in refugee camps or temporary shelters, and children do not attend school for several years. Now it seems that the situation is calming down, so there could be an opportunity for change. The aim of the work is to design a school for Buleosa village in a cooperation with the local ranger Alain Hamisi Mitondo, with whom I have been communicated during the course. The school project is supported by Buleosa‘s management and locals. Everyone in the community should be involved in the construction, because above all they should benefit from the school. I know that it is not possible to build a European-type building here, but rather to combine knowledge of these two worlds with the use of local materials. The simplicity of such a project is fundamental, because it will involve more different people, even without the slightest experience.
Multilevel methods
Vacek, Petr ; Strakoš, Zdeněk (advisor) ; Pultarová, Ivana (referee)
The analysis of the convergence behavior of the multilevel methods is in the literature typically carried out under the assumption that the problem on the coarsest level is solved exactly. The aim of this thesis is to present a description of the multilevel methods which allows inexact solve on the coarsest level and to revisit selected results presented in literature using these weaker assumptions. In particular, we focus on the derivation of the uniform bound on the rate of convergence. Moreover, we discuss the possible dependence of the convergence behavior on the mesh size of the initial triangulation. 41
Green Roofs Using Hydrophilic Mineral Wool
Vacek, Petr ; Moudrý, Ivan (referee) ; Šrámek,, František (referee) ; Matějka, Libor (advisor)
The thesis deals with the use of hydrophilic mineral wool in green roof structures. In the first part of the thesis, based on current legislation, there are summarized relevant technical properties of the hydrophilic wool. Specific demands on the green roof parts were classified and the work was consequently updated by the research of available products from the national market. A large part of the thesis consists of the extended documentation of technical properties of new products and also the changes that are associated with ageing after the material incorporation into the structure. Not only the laboratory properties of the material itself, but also properties of the material embedded in green roof structure were measured, for example an acoustic capabilities. Water accumulation properties of the mineral wool were documented on the real roof models too. Various impacts were observed by using mineral wool in comparison with substrate assemblies. Additional experiments were applied on using different types of mineral wool for an assessment of specific green roof vegetation adaptation. The environmental product declarations for each mineral wool product were calculated with the specific software using LCA methodology. In this way, the environmental impacts of mineral wool could be compared with other materials, such as artificial substrates, foils, etc. As a conclusion of the research results were summarized and reported demands for the hydrophilic mineral wool use in the green roof structures.
Multilevel methods and adaptivity
Vacek, Petr ; Strakoš, Zdeněk (advisor) ; Tichý, Petr (referee)
After introduction of the model problem we derive its weak formulation, show the existence and the uniqueness of the solution, and present the Galerkin finite element method. Then we briefly describe some of the stationary iterative methods and their smoothing property. We present the most common multigrid schemes, i.e. two-grid correction scheme, V-cycle scheme, and the full multigrid algorithm. Then we perform numerical experiment showing the differences between the use of the direct and iterative coarsest grid solver in V-cycle scheme and experiment considering a perturbation of the correction vector simulating a fault of a computational device. Powered by TCPDF (www.tcpdf.org)
Modification of HVOF and cold spray deposited coatings via electron beam technology
Vacek, Petr ; Šiška, Filip (referee) ; Čížek, Jan (advisor)
The aim of this thesis was to modify microstructure and coating-substrate interface of CoNiCrAlY coatings deposited by HVOF and cold spray on Inconel 718 substrates. Electron beam remelting and annealing in a protective atmosphere were used to modify the coatings. Microstructure, chemical and phase composition were analyzed. The effect of beam current, transversal velocity and beam defocus on remelted depth was evaluated. As-sprayed microstructure and chemical composition of coatings were analyzed and compared with remelted samples. The effect of annealing of the as-sprayed and remelted samples was evaluated. Remelted layers exhibited dendritic structure. Chemical composition changed only after remelting of interface and part of a substrate. When only the coating was remelted, chemical composition remained the same. Phases coarsened after the annealing. Chemical composition changed after annealing due to the diffusion.
Sol-gel synthesis and properties of piezoceramic nanoparticles on the base of (BaxCa1-x)(TiyZr1-y)O3
Vacek, Petr ; Matoušek, Aleš (referee) ; Cihlář, Jaroslav (advisor)
The aim of the work was sol-gel synthesis of piezoceramic nanoparticles on the base of BaxCa1-xTiyZr1-yO3 (BCTZ), preparation of sintered samples and analysis of their structure and properties. Theoretical part includes information about piezoelectricity, piezoelectric materials and preparation of ceramics. Experimental part describes sol-gel synthesis of BCTZ nanoparticles and achieved phase composition and particle size. The next topic of experimental part was preparation of sintered BCTZ samples and analysis of their properties.

National Repository of Grey Literature : 15 records found   1 - 10next  jump to record:
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6 Vacek, Pavel
2 Vacek, Přemysl
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