National Repository of Grey Literature 33 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
A Logical Characteristic of Read-Once Branching Programs
Žák, Stanislav
We present a mathematical model of the intuitive notions such as the knowledge or the information arising at different stages of computations on branching programs (b.p.). The model has two appropriate properties: i) The ”knowledge” arising at a stage of computation in question is derivable from the ”knowledge” arising at the previous stage according to the rules of the model and according to the local arrangement of the b.p. ii) The model confirms the intuitively well-known fact that the knowledge arising at a node of a computation depends not only on it but in some cases also on a ”mystery” information. (I. e. different computations reaching the same node may have different knowledge(s) arisen at it.) We prove that with respect to our model no such information exists in read-once b.p.‘s but on the other hand in b. p.‘s which are not read-once such information must be present. The read-once property forms a frontier. More concretely, we may see the instances of our models as a systems S = (U,D) where U is a universe of knowledge and D are derivation rules. We say that a b.p. P is compatible with a system S iff along each computation in P S derives F (false) or T (true) at the end correctly according to the label of the reached sink. This key notion modifies the classic paradigm which takes the computational complexity with respect to different classes of restricted b.p.‘s (e.g. read-once b.p.‘s, k-b.p.‘s, b.p.‘s computing in limited time etc.). Now, the restriction is defined by a subset of systems and only these programs are taken into account which are compatible with at least one of the chosen systems. Further we understand the sets U of knowledge(s) as a sets of admissible logical formulae. It is clear that more rich sets U‘s imply the large restrictions on b.p.‘s and consequently the smaller complexities of Boolean functions are detected. More rich logical equipment implies stronger computational effectiveness. Another question arises: given a set of Boolean functions (e.g. codes of some graphs) what logical equipment is optimal from the point of complexity?
Deformation and stress fields at the front of shear cracks with complicated geometry
Žák, Stanislav ; Hutař,, Pavel (referee) ; Kunz,, Jiří (referee) ; Horníková, Jana (advisor)
Tato závěrečná práce je shrnutím výzkumu smykově zatěžovaných trhlin, který proběhl v průběhu čtyř let doktorského studia jejich autora Ing. Stanislava Žáka (Středoevropský technologický institut, Vysoké učení technické v Brně). Předložená práce je zaměřena na prohloubení znalostí v oblasti pokročilé lomové mechaniky, konkrétně pro smykové zatěžování trhlin kombinované s případy geometrických odchylek trhlin od běžně používaných modelů. To mimo jiné znamená návrh nových přístupů a modelů a popis součinitelů intenzity napětí pro geometricky komplikované trhliny. První část práce je věnována shrnutí současných přístupů v lomové mechanice a dále i popisu numerických metod, použitých v dalších výpočtech. Kromě klasických přístupů se tato část textu zabývá i novějším výzkumem zaměřeným na smykové zatěžování trhlin, speciálně pro dva typy zkušebních těles – válcový vzorek s obvodovým vrubem a trhlinou zatížený prostým smykem nebo krutem a CTS těleso umožňující zatížení trhliny v módech I, II a také v jejich kombinaci I+II. Další část textu je zaměřena na konkrétní výpočty lomových parametrů při použití nových modelů s komplikovaným čelem trhliny. Teoretické řešení lomových parametrů pro oba výše zmíněné modely je porovnáno s experimentálními výsledky, získanými v navazujících projektech. U modelu válcového vzorku je popsána možnost zjednodušení budoucích modelů těles s podobným typem komplikované trhliny a současně je na něm popsán lokální vliv zubatosti čela trhliny na indukci lokálního zatížení v módu II při globálním zatížení v módu III. Tyto výsledky jsou přímo propojeny s experimentální kvantifikací únavového šíření lomu při zatížení v módu III. CTS těleso je použito k popisu vlivu drsnosti trhliny na součinitele intenzity napětí. Na tomto modelu je pozorován jak globální pokles hodnoty KII při zvyšující se drsnosti trhliny, tak i lokální změny v namáhání trhliny podél jednotlivých nerovností. Výsledky potvrzují, i pro dosud málo zkoumané smykové zatěžování, že mikrostruktura lomových ploch a čela trhliny má vliv na lomové parametry. Rozšiřují tak současné znalosti v oboru lomové mechaniky popisem geometrického stínění čela trhliny pro zátěžné módy II a III.
Elasticity problems in Python language
Tichoň, Dušan ; Žák, Stanislav (referee) ; Profant, Tomáš (advisor)
This bachelor thesis deals with the programming language Python. Its aim is acquaintance of NumPy, SymPy and Matplotlib libraries and their later application. Also it shows the great computing potential of programming language in creating exercises which will be used and presented for educational purposes.
A study of the stress distribution near the sharp notch tip
Beňo, Tomáš ; Žák, Stanislav (referee) ; Profant, Tomáš (advisor)
This bachelor’s thesis is studying problems of stress distribution near the sharp notch tip. The theoretical part discloses the history of fracture mechanics and it’s basic principles. The practical part solves stress singularity exponents for geometry of particular notch.
Influence of a Notch on Stress-Strain States at the Front of Cracks Loaded by Shear Modes
Ščotka, Martin ; Žák, Stanislav (referee) ; Horníková, Jana (advisor)
This diploma thesis deals with influence of a notch on stress-strain states at the front of cracks by shear modes. Starting with fracture mechanics and its division, followed by stress intensity factor and calculate its by finite element method. Calculation is solved for two types of notches, U-notched and V-notched, both notches were modeled parametrically so their geometry was changeable and stress intensity factor were calculated for all configurations. Subsequently was solved next calculation of stress intensity factor but for shaft without notch. Finally, was evaluated influence of notch on stress intensity factor. Software for finite element method has been used ANSYS. Others calculation was provided in software MATLAB
Suicide as Search of Life
Žák, Stanislav ; Ventura, Václav (advisor) ; Hogenová, Anna (referee) ; Budil, Ivo (referee)
Searching for the primary causes of human suicidal behaviour, if any primary causes even exists, I put the following question: Is voluntary termination of life something abnormal that has its cause in health, psychical or social stress of the individual or does it not have to be so? If the cause of human suicidal behaviour is the result of any disturbance in the organism, why the suicide rate increases the most where health care is at the maximum possible level and where the suicide is, in terms of cultural history, considered to be a symptom of one of the worst health abnormalities or ethic aberrances of human life? Can the causes of human suicidal behaviour also consist in other things than in health, psychological or social breakdown of human organism? In my thesis, I seek the answer to this question. It is generally known that the human is a very complex being which needs not only good health and social conditions but also spiritual conditions for its life and survival. In my opinion, it is a tragedy of scientifically focused approach of the modern era, which at the same time rigorously restricts socially acknowledged boundaries of human knowledge, that it refuses to take into account the research of this fourth dimension of human existence. It was C. G. Jung who came to this opinion; as he says: "Where...
Stress and deformation analysis of railway bridge over the Svratka River
Kovář, Jaroslav ; Žák, Stanislav (referee) ; Fuis, Vladimír (advisor)
This thesis deals with stress and strain analysis of real truss bridge structure. This structure is modelled as plane bar system. The opening part dedicates to theory, which is further used for calculations. The calculation part dedicates to compare statically determinate and indeterminate variation of structure for load by own weight and passage of the train. Analytic calculations are numerically verified with program ANSYS. In thesis is assessed concentration of stress, when the rivet drops out of the structure. The next part of thesis dedicates the spatial model of bridge, which is compared witch plane model.
Assessment of characteristic of a helical conus-shaped spring under compression
Loveček, Libor ; Žák, Stanislav (referee) ; Burša, Jiří (advisor)
The presented bachelor thesis pursue the behaviour of coiled conical pressure spring while loaded. Thesis includes analytical calculation in accordace to the slighty curvatured rod theory. Calculation is designed for a specific coiled conical spring in a MAPLE environment. The results are compared with data acquired while experimenting with the spring.
Description of Stress and Strain States at the Front of Cracks Loaded by Shear Modes
Žák, Stanislav ; Majer, Zdeněk (referee) ; Horníková, Jana (advisor)
The main goal of this work is the comparison of the size of the plastic zone at the crack tip for two analysis methods: an analytical linear method and an elastic-plastic analysis employing the Finite Element method (ANSYS software). All calculations were made for a crack loaded under pure shear modes. These types of loading are not sufficiently described in the literature. The first part of this work introduces the problem with the crack tip plastic zone using both linear and nonlinear fracture parameters. The second part is dedicated to the construction of the Finite Element model in the ANSYS software. The geometry of the samples and the loading levels were chosen to match an existing experimental test of the impact of shear modes on the crack behavior. In the third part of this thesis, the plastic zone radii for pure shear modes II and III are estimated using several methods and the results are compared. In the last part of this work, the same procedure as in the previous part is applied on a mixed-mode II+III loading. A result of this thesis is the assessment of the application limits of the linear analysis method used to estimate the size of the plastic zone at the crack tip for a specific geometry and material model.
Elastic Analysis of Crack Stability under Shear Loading Modes
Žák, Stanislav ; Profant, Tomáš (referee) ; Horníková, Jana (advisor)
The main goal of this thesis is to create a numerical simulation of a real experiment for specifying the ultimate state of spread of fatigue crack in pure shear stress modes and to deal with results of simulations for different specimen geometries. The simulations emulate real conditions of the experiment within the frame of linear elastic fracture mechanics. The first part of this work discusses a number of approaches to describe the stability and behaviour of cracks. The second part of this thesis deals with several possibilities of calculating crack characteristics employing ANSYS software. The third and most comprehensive part of the thesis describes the experiment which served as the template for the calculations. In addition, the setup of the simulations and the post-processing of the results for different crack parameters are discussed.

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