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Modelling of flow over a backward-facing step in streams with various turbulence level
Příhoda, Jaromír ; Sedlář, M.
Turbulent flow over a backward-facing step in streams with a various turbulence level was numerically simulated using software ANSYS CFX-5. Numerical solution carried on with the two-equation SST model and/or with a k-omega based Reynolds stress model was compared with experimental data obtained for three different values of free-stream turbulence level. The predicted length of the recirculation region corresponds well with experimental data but the dependence of the ratio xr/h on free-stream turbulence level is smaller.
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Clustering and regression analysis of micro panel data
Sobíšek, Lukáš ; Pecáková, Iva (advisor) ; Komárek, Arnošt (referee) ; Brabec, Marek (referee)
The main purpose of panel studies is to analyze changes in values of studied variables over time. In micro panel research, a large number of elements are periodically observed within the relatively short time period of just a few years. Moreover, the number of repeated measurements is small. This dissertation deals with contemporary approaches to the regression and the clustering analysis of micro panel data. One of the approaches to the micro panel analysis is to use multivariate statistical models originally designed for crosssectional data and modify them in order to take into account the within-subject correlation. The thesis summarizes available tools for the regression analysis of micro panel data. The known and currently used linear mixed effects models for a normally distributed dependent variable are recapitulated. Besides that, new approaches for analysis of a response variable with other than normal distribution are presented. These approaches include the generalized marginal linear model, the generalized linear mixed effects model and the Bayesian modelling approach. In addition to describing the aforementioned models, the paper also includes a brief overview of their implementation in the R software. The difficulty with the regression models adjusted for micro panel data is the ambiguity of their parameters estimation. This thesis proposes a way to improve the estimations through the cluster analysis. For this reason, the thesis also contains a description of methods of the cluster analysis of micro panel data. Because supply of the methods is limited, the main goal of this paper is to devise its own two-step approach for clustering micro panel data. In the first step, the panel data are transformed into a static form using a set of proposed characteristics of dynamics. These characteristics represent different features of time course of the observed variables. In the second step, the elements are clustered by conventional spatial clustering techniques (agglomerative clustering and the C-means partitioning). The clustering is based on a dissimilarity matrix of the values of clustering variables calculated in the first step. Another goal of this paper is to find out whether the suggested procedure leads to an improvement in quality of the regression models for this type of data. By means of a simulation study, the procedure drafted herein is compared to the procedure applied in the kml package of the R software, as well as to the clustering characteristics proposed by Urso (2004). The simulation study demonstrated better results of the proposed combination of clustering variables as compared to the other combinations currently used. A corresponding script written in the R-language represents another benefit of this paper. It is available on the attached CD and it can be used for analyses of readers own micro panel data.
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The stability of biologically active compounds in elderberry (Sambucus nigra L.) inflorescence during processing
SUCHÁ, Renata
This thesis examines the stability of rutin in the inflorescences of the elder during processing. Elder (Sambucus nigra L.) is a medicinal plant that was used for medical purposes as early as in the Middle Ages. Both flowers (Flos Sambuci) and fruit (Fructus Sambuci) of the elder are on the list of official medicinal products of the State Institute for Drug Control. The main active phenolic substance is flavonoid rutin. Flavonoids are phenolic substances of plant origin. Among the best known properties of these substances is their antioxidant activity. They protect the low density blood lipoproteins from the oxidation modifications that cause the development of arteriosclerosis and hypertension. As a medical plant, the elder is used especially for the preparation of a medicinal drink. It is also commonly used as a material for the preparation of syrup. This product serves as a basis for a refreshing and tasty drink and lately is has also started to be sold in shops. For comparison, five single-flower syrups from the elderflower by different producers were bought. A method of preparation of the elderflower syrup was devised, based in one case on frozen elder inflorescences and in the other on dried inflorescences. The plant material came from wildly growing shrubs and it was collected in June 2013. Altogether, 8 syrups were prepared in the laboratory, 4 of them from fresh material and 4 from dried material. Two different methods were used. The first one was based on extraction using sugar solution, the second one on extraction using water solution where sugar was added afterwards. Another added substance was ethanol. The method for measuring the amount of rutin in the samples was a combination of two extraction steps. The first step was the usual exraction using aqueous methanol and the second step was extraction using a solid sorbent (SPE). The analysis of fresh and dried material concluded that dried elderflowers contain many times more rutin than fresh elder. Among the commercially produced syrups, the "Kitl Syrob Bezový" contained most rutin; a little less rutin was found in "Hamé Bylinný sirup Bezový květ". The concentration of rutin in the syrups prepared in the laboratory was much higher than in the commercial products. By using different methods of syrup preparation and their subsequent analysis, it was found that the syrups prepared from the dried inflorescences contained a higher amount of rutin than the syrups produced in the same way, but from frozen material. Addition of a small amount of ethanol had no effect on extraction of rutin from inflorescences. Free quercetin, which indicate a decomposition of rutin, wasn´t found in any of produced syrups. The produced syrups were used for the preparation of a drink and then underwent sensory analysis. The paired two-sided preference test included pairs of drinks consisting of a fresh elder drink and dried elder drink. The results showed that the evaluators preferred syrups from dried elderflowers in two of the cases, while in the other two evaluated pairs, the results were not statistically significant. In all cases, the evaluators most often found small and middle differences. The gained results show that the best method of syrup preparation uses dried plant material and sucrose solution as the extraction agent. The syrup prepared in this way contained most rutin and at the same time showed the smallest losses of this substance, which is beneficial to human health. Furthermore, it also tasted better in comparison with syrup prepared in the same way, but from fresh material.
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Two-step sintering of advanced ceramic materials with various crystal structures
Žalud, Pavel ; Trunec, Martin (referee) ; Maca, Karel (advisor)
The influence of Two-Step Sintering (TSS) process on the final microstructure of oxide ceramics materials with two different crystal structures was studied. Tetragonal zirconia (stabilized with 3mol%Y2O3, particle size 90nm and 140nm ) and cubic zirconia (8mol%Y2O3, 70nm) powders were cold isostatically pressed and pressure less sintered with different heating schedules. The microstructures achieved with TSS method were compared with microstructures achieved with conventional Single-Step Sintering schedule (SSS). The results showed that the efficiency of the TSS of these oxide ceramics was more dependent on their crystal structure than on their particle size and green body microstructure. The method of TSS brought only negligible improvement of the microstructure of tetragonal zirconia ceramics. On the other hand, TSS was successful in the sintering of cubic zirconia ceramics; it led to a decrease in grain size by a factor of 2.
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Optimization Models for Strategical Decision Making
Ulverová, Michaela ; Škapa, Stanislav (referee) ; Popela, Pavel (advisor)
The thesis deals with possibilities of mathematical modeling for public university budgets. Firstly, external conditions of public university financial inflows are discussed and~illustrated by using particular data. The related basic legislature is introduced. In~the~next part, internal financial flows are described the help of a general scheme. Step-by-step, a mathematical model of the university budget was built with using analysis of existing data, rules and formulas. The proposed model represents nonlinear multi–stage scenario-based stochastic programme, involving linear and network-flow like constraints. It allows to take into account more objective functions and related parametric analysis. The model was implemented in the algebraic modeling system GAMS with~interface to MS Excel. The aim of the presented mathematical model was not to offer a tool that would be used for automatic distribution of financial resources of the university, but to give flexible possibilities to its user to realize computational experiments and in this way to achieve a deeper insight into the modeled problem.
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Stability and convergence of numerical computations
Sehnalová, Pavla ; Dalík, Josef (referee) ; Horová, Ivana (referee) ; Kunovský, Jiří (advisor)
Tato disertační práce se zabývá analýzou stability a konvergence klasických numerických metod pro řešení obyčejných diferenciálních rovnic. Jsou představeny klasické jednokrokové metody, jako je Eulerova metoda, Runge-Kuttovy metody a nepříliš známá, ale rychlá a přesná metoda Taylorovy řady. V práci uvažujeme zobecnění jednokrokových metod do vícekrokových metod, jako jsou Adamsovy metody, a jejich implementaci ve dvojicích prediktor-korektor. Dále uvádíme generalizaci do vícekrokových metod vyšších derivací, jako jsou např. Obreshkovovy metody. Dvojice prediktor-korektor jsou často implementovány v kombinacích modů, v práci uvažujeme tzv. módy PEC a PECE. Hlavním cílem a přínosem této práce je nová metoda čtvrtého řádu, která se skládá z dvoukrokového prediktoru a jednokrokového korektoru, jejichž formule využívají druhých derivací. V práci je diskutována Nordsieckova reprezentace, algoritmus pro výběr proměnlivého integračního kroku nebo odhad lokálních a globálních chyb. Navržený přístup je vhodně upraven pro použití proměnlivého integračního kroku s přístupe vyšších derivací. Uvádíme srovnání s klasickými metodami a provedené experimenty pro lineární a nelineární problémy.
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Virtual environment by Xen software
Kulíř, Tomáš ; Kouřil, Jiří (referee) ; Jelínek, Mojmír (advisor)
This bachelor thesis, which is called the virtual environment by Xen software, deals with the operating system GNU / Linux and its distributions. It also deals with the virtualization on the server or desktop computer, in particular, describes in detail the Xen environment, including all of its options and the most forgotten server services. In the first chapter is analyzed the concept of GNU / Linux. First, there is documented history. Another section deals with a brief overview of the most commonly occurring distributions. The main part of this chapter is primarily devoted to a specific distribution Debian. There is described not only the history and development of this distribution, but also more packaging system is analyzed there. The last part of this chapter is devoted to the installation options with a detailed description of the whole process step by step. Second and the most important chapter is devoted to virtual environments. Once again, there is first described their history, the possibility of practical use and the types of virtualization are also indicated there. Reader will find there a brief analysis of the most commonly used virtualization systems. The third chapter detailed deals with the Xen technology. There is not only explained the principle on which the virtualization is built, but the main part of this chapter focuses on the practical use and a summary of basic functions. The next section describes the installation and administration of hypervisor including previous preparation. A very important point is also creation of the virtual machines and their control, their migration to another physical hardware or a description of the installation of other operating systems than Linux. Fourth, shorter chapter deals with a listing and a brief description of server services. The final chapter consists of a summary of problems or complications, which in the course of this work occurred.
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The development of e-shop for WordPress
Štencek, Jiří ; Kunstová, Renáta (advisor) ; Šubrta, Václav (referee)
The thesis focuses on developing e-shop with CMS WordPress and plugin eShop. Its aim is to write a methodology by which it would be possible to create e-shop step by step. The work outlines the advantages and possible disadvantages of this solution. Outcome of this work are also additional scripts that optimizes functionality of eShop plugin and extensions for linking e-shop with Czech e-commerce services. Czech localization for plugin eShop is also part of this thesis. Writing methodology precedes the preparation of the technical background documents WordPress and the selected extension called eShop. The first chapter defines the objective of the thesis and are defined substrates. The following is research that confirms the absence of similar methodologies or guidelines in both Czech and foreign language. The third chapter presents the used solution and reveals the technical basics of WordPress and plugins. The main part - the fourth chapter contains the very methodology of creating e shop. It takes the reader through the process from installation to launch the e-shop. Includes introduction of making templates, analysis appropriate plugins and show how to edit them. This part also presents how to manage products and orders, create Czech localization, links to e-commerce services and additional programming required functions in e-shop. Chapter contains recommendations for the operation and maintenance of the e shop and subchapter about user testing describes method by Steve Krug, use it as a practical demonstrations and evaluating conclusions. Contribution of this thesis is the know-how in terms of methodology, expanding the knowledge base of the community, the additional scripts for e-shop and written recommendations for the process of operation e-shop by WordPress.
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