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Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel
Král, Petr ; Dvořák, Jiří ; Sklenička, Václav ; Horita, Z. ; Tokizawa, Y. ; Tang, Y. ; Kunčická, Lenka ; Kuchařová, Květa ; Kvapilová, Marie ; Svobodová, M.
The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. The as-received P92 steel was deformed by high-pressure torsion (HTP), high-pressure sliding (HPS) and rotary swaging (RS) at room temperature prior creep testing. These SPD methods imposed significantly different equivalent plastic strain in the range from 1 up to 20. Constant load creep tests in tension were performed in an argon atmosphere at 873 K and applied stress ranging from 50 to 200 MPa. The microstructure and phase composition of P92 steel were studied using a scanning electron microscope Tescan Lyra 3 and a transmission electron microscope Jeol 2100F. The results show that under the same creep loading conditions the HPT and HPS-processed P92 steel exhibited significantly faster minimum creep rates, creep fracture strain and the decrease in the value of the stress exponent of the creep rate in comparison with as-received P92 steel. However, it was revealed that the RS-processed specimens exhibited one order of magnitude lower minimum creep rate and lower ductility compared to commercial P92 steel. The creep curves for the HPT and HPS-processed states exhibited a pronounced minimum of strain rate. The pronounced minimum of strain rate disappeared when these states were annealed at 923K/500h before application of creep loading. The microstructure changes occurring during creep and different creep behaviour between as-received and deformed states are discussed.
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Nonparametric estimation of the intensity function of a point process depending on covariates
Vlková, Eliška ; Dvořák, Jiří (advisor) ; Karafiátová, Iva (referee)
Point processes describe random point patterns in space. One of their most important characteristics is the intensity function. Furthermore, additional information about the surveyed area, so-called covariates, is often available for point processes. We derive a key formula for the function that describes the relation between the intensity function of the point process and the covariate. Based on this formula, we find its kernel estimate and formulate relations for the mean and variance of the estimate. We use simulation experiments to verify the accuracy of the kernel estimate. 1
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Truncated marked processes
Hrbáčová, Daniela ; Pešta, Michal (advisor) ; Dvořák, Jiří (referee)
This thesis explores the use of marked stochastic processes in the context of delayed reporting of claims in non-life insurance. The focus is on estimating the intensity of the claim occurrence process using the ν-transform of the claim reporting process. The first part provides the theoretical background, including the introduction of the Poisson process and the concept of marking. The ν-transform is defined and a special case of the ν-transform is applied in an example. As well as there is presented an approach how to handle with truncated data. The second chapter applies these theoretical concepts to real-world data from Motor Third Party Liability insurance. The result is a formula for estimating the intensity of the occurrence process based on the estimated intensity of the claim reporting process and the estimated truncated conditional density of delays given reporting times. While the approach is computationally intense, it has practical applica- tions in estimating claim reserves for insurance companies. Future work could expand on this approach by considering more complex cases, such as time-varying conditional dis- tribution of delays or including on input nonhomogeneous Poisson, or even more complex processes. Finishing the claim reserve calculation would be also beneficial. Overall, this thesis...
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Pólya-Lundberg process
Böhm, Igor ; Pawlas, Zbyněk (advisor) ; Dvořák, Jiří (referee)
The main subject of the Bachelor's thesis is the P'olya-Lundberg process. It is a non-homogenous Markov chain that represents a generalization of the Poisson process. The main aim of the thesis is to depict some of its important features, to prove them and to put them into context. The thesis is sectioned into four chapters where the first chapter introduces basic concepts and objects that are crucial for understanding of this text. In the second chapter we define the P'olya-Lundberg process and we derive some of its main characteristics. The third chapter is devoted to the relationship between the P'olya-Lundberg process and the mixed Poisson process. Lastly, the final chapter discusses the so-called urn models, especially its generalization for which there is shown that if several conditions are fulfilled the generalized urn model converges to the P'olya-Lundberg process at a fixed time.
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Point processes on linear networks and analysis of traffic accidents
Zemčík, Jan ; Dvořák, Jiří (advisor) ; Beneš, Viktor (referee)
In this thesis we shall study point processes on linear networks. We introduce the definition of first-order intensity function, which represents the intensity of occurrence of points of the point process in individual points of the linear net- work. We require the first-order intensity function estimate utilising a smooth- ing kernel to preserve mass on the linear network. We define the KD (u|x) function, which represents the smoothing kernel. Our next objective is to state theorems which show us, when the integral of the function KD (u|x) evaluates to 1. The first will be stated for linear networks without cycles of length smaller than the width of the kernel and the second for linear networks which may con- tain cycles. We believe that the relevant literature on the subject contains an erroneous statement of the latter version of the theorem. We present detailed proofs for both versions of the theorem. At the end of the thesis we present two analyses based on real data (traffic accidents on D1 highway and Chicago Crime Data). 1
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Suboptimal methods for path planning
Rybníček, Patrik ; Dvořák, Jiří (referee) ; Šoustek, Petr (advisor)
This thesis focuses on methods for path planning, specifically suboptimal methods. These may not find the optimal route, which is balanced by lower memory and time requirements. The theoretical part of the thesis deals with the problem of path finding and describes the properties of each method. The practical part implements a set of suboptimal methods in a simulation environment developed in Python. It then compares these methods and evaluates their effectiveness.
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Any-angle path planning
Polák, Robert ; Šoustek, Petr (referee) ; Dvořák, Jiří (advisor)
The final thesis deals with the issue of any-angle path planning. The theoretical part of the thesis is focused on the description of the general issue of path planning, on the description of existing methods of its search, and above all on the characteristics of any-angle planning methods. In addition to the assignment, a new algorithm for any-angle search was created. In the practical part, selected algorithms were implemented and then comparative experiments were performed.
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THE CONTROL OF CHAOS: METHODS AND APPLICATIONS
Kořenek, Miroslav ; Dvořák, Jiří (referee) ; Matoušek, Radomil (advisor)
This thesis deals with methods of stabilizing deterministic chaos. The first part provides a brief overview of the problem of deterministic chaos, including the framework used to describe and analyze chaotic systems. Furthermore, the most well-known chaotic systems are described in detail, with the logistic map and the Hénon map selected for experimental stabilization. The description of conventional methods for chaos stabilization, namely TDAS and ETDAS, follows. The principle of their optimization is also explained. Next chapter is dedicated to describing genetic programming and its potential use in chaos stabilization. In the practical part of the thesis, conventional methods and various implementations of genetic programming were applied to stabilize the selected systems. The utilization and experimentation with genetic programming to find stabilizing sequences are the most significant contributions of this work.
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Graph Colouring, Graph Clique, Algorithms and Applications
Valachová, Alžbeta ; Dvořák, Jiří (referee) ; Šeda, Miloš (advisor)
This thesis deals with the problem of graph coloring and finding cliques in a graph, with a focus on the description of algorithms and their applications. Graph coloring is the process of assigning colors to individual vertices of a graph so that adjacent vertices have different colors. This issue is important for solving various optimization problems. The work also focuses on finding cliques in a graph, which is an important problem in social network analysis or image recognition. The aim of this thesis is to provide a complex overview of graph coloring, finding cliques in a graph, introduce and analyze existing algorithms and show their applications in practice.
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Bidirectional path planning
Semeniuk, Andrii ; Nevoral, Tomáš (referee) ; Dvořák, Jiří (advisor)
This bachelor thesis deals with path planning of a mobile robot using artificial intelligence algorithms. The theoretical part describes different approaches to path planning with a focus on their bidirectional modifications. Furthermore, attention is paid to selected algorithms. In the practical part of the thesis, the emphasis is on the comparison of the selected algorithms by carrying out experiments in a self-developed simulation environment.
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