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Influence of chemical composition of steel on structure and properties of stainless steels
Valenta, Pavel ; Čech, Jan (referee) ; Záděra, Antonín (advisor)
The thesis is focused on high-alloy austenitic and austenitic-ferritic (duplex) steel. The theoretical part includes research about high-alloy steels and basic introduction to this issue. In the practical part of the test there were casted refractory austenitic steel 30CH3N17G2L, duplex stainless steel 1.4462, low carbon steel and high carbon steel. On the castings of austenitic steel were made mechanical and technological tests. There were evaluated the effects of different casting temperature and casting wall thickness to the microstructures and macrostructures of steel, tensile strength and charpy impact tests. The technological tests compared technological properties of these steels.
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Optimization of heavy steel castings manufacture
Procházka, Zdeněk ; Čech, Jan (referee) ; Šenberger, Jaroslav (advisor)
The Master’s thesis was conducted under the project FR-TI1/070 “Optimalization of heavy steel casting manufacture” in cooperation with ŽĎAS a. s. foundry. It evaluates rate of conchoidal fracture in samples extracted from experimental castings. The testing bar for the static tensile test were extracted from thermal axis of casting. The research part describes ways of deoxidating the liquid metal and usage of separate deoxidating chemical parts, followed by summary of research knowledge on conchoidal fractures. In the practical part, the process of sample evaluation is described. The conchoidal fracture, the surface of which was evaluated on the fracture surfaces, influences mechanical qualities of cast steel. Simultaneously, impacts of metallurgical factors on rate of conchoidal fracture were examined
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Precipitation of Intermetallic Phases in Austenitic-Ferritic Duplex Steels
Myška, Martin ; Foret, Rudolf (referee) ; Čech, Jan (referee) ; Záděra, Antonín (advisor)
This PhD thesis addresses the issue of precipitation of intermetallic phases in cast duplex stainless steel according to the ASTM A890 Gr4A standard. The aim of the thesis was to determine the amount of precipitated intermetallic phases depending on the temperature and holding time during isothermal annealing and under anisothermal conditions during cooling of the material in the temperature range from 1000 to 600 °C. The partial aim of the work was to determine the relationship between the amount of precipitated intermetallic phases and the mechanical properties of cast steel ASTM A890 Gr4A. As part of the work, the description and prediction of the kinetics of precipitation of intermetallic phases using the Johnson-Mehl-Avrami equation were verified. The relationship between the amount of precipitated intermetallic phases and the failure character of the material was determined by fractographic evaluation. The critical cooling rate of the casting was determined to ensure the minimum toughness of the steel that is desirable to reduce the risk of cracking during cooling of duplex stainless steel castings.
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Detection of changes in the image
Čech, Jan ; Zemčík, Tomáš (referee) ; Richter, Miloslav (advisor)
The aim of this thesis is finding changes in two similar pictures made in different periods. This task belongs to the field of computer vision. To solve this problem different methods of computer visions are used in several solution versions. Program is working with two scenes. In final version are objects from both scenes compared. The result is written into logging file.
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Study of the release of active substances from PHA-based particles
Čech, Jan ; Mikulíková, Renata (referee) ; Kovalčík, Adriána (advisor)
This bachelor thesis deals with the study of the release kinetics of caffeic acid and acetylsalicylic acid from polylactic acid, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and poly(3-hydroxybutyrate)-based microparticles. In the theoretical part, the mechanical and thermal properties of polyhydroxyalkanoates, their biological synthesis by microorganisms, their industrial extraction from biomass and applications are described. Furthermore, the properties of PHA microparticles, their use as carriers, the most common microparticle preparations and the release method of the loaded drug are described. In the experimental part, PLA, P(3HB) and P(3HB-co-4HB) based microparticles prepared by the solvent evaporation emulsion method were characterized by dynamic light scattering. Subsequently, caffeic acid or acetylsalicylic acid was incorporated into these microparticles, and the release kinetics of the active ingredient was observed spectrophotometrically for one week. Once measurement of the releasing kinetics ended, microparticles were again measured by DLS and compared with the characterized microparticles before releasing kinetics. Finally, the encapsulation efficiency and microparticle recovery were calculated.
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Porovnání pevnostních charakteristik filamentů ovlivněných prostředím
ČECH, Jan
The thesis aims to create models using 3D printing from different filament materials, then expose them to selected environmental influences and evaluate their characteristical strength. This thesis contains a concise summary of 3D printing methods and their parameters in the theoretical part. Furthermore, a description of the properties of the materials used in the work. Specifically, the materials are acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), Polylactic acid (PLA) and Copolyester (PETG). The practical part aims to create models using 3D printing and research the impact of the environment on these models. Experiments are conducted in room temperature, reduced temperature, elevated temperature, and UV radiation environments. Following these experiments, the models are subjected to a traction test and the results of this test are then compared. In the discussion part of the thesis, the results and some problems from the whole experiment are thereafter evaluated.
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Zjišťování pevnostních charakteristik výrobků u 3D tisku
ČECH, Jan
This work inquires into the 3D printing by means of FMD technology. There are compared PLA and Pet-G materials. Further, the horizontal and the vertical printing positions are compared. The results are influenced by the height of the layer as well. There are tested higher layer of 0.25mm and lower layer of 0.15mm. The results are acquired by tensile test.
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Detection of changes in the image
Čech, Jan ; Zemčík, Tomáš (referee) ; Richter, Miloslav (advisor)
The aim of this thesis is finding changes in two similar pictures made in different periods of time. This task belongs to the field of computer vision. To solve this problem different methods of computer vision are used. First the angle of scanning has to be found. Then pictures go through the proces of preprocessing, afterwards the segmentation and the determination of descriptors are carried out. Finally, the pictures are compared and the differences are pointed out.
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Rule-of-thumb consumers in the New Keynesian framework
Adam, Tomáš ; Baxa, Jaromír (advisor) ; Čech, Jan (referee)
iv Abstract This thesis investigates the effects of government spend- ing on aggregate economic variables in the Czech Republic. The standard RBC and New Keynesian models assume only forward-looking households despite the evidence of a sig- nificant fraction of non-optimizing households. These mod- els do not provide reasonable predictions for the response of consumption: both models predict its fall following a gov- ernment spending shock. Therefore, a variant of the New Keynesian model, where rule-of-thumb households coexist with optimizing households, is used for the analysis. We have found that fiscal policy has a positive impact on output, although government spending multiplier does not exceed one. Also, the impact on consumption is positive for several periods following a fiscal spending shock, which is consistent with the evidence. JEL Classification: C32, E32, E62 Keywords: fiscal policy, fiscal multipliers, fiscal VAR, rule- of-thumb consumers
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Three essays on Joseph Stiglitz and information asymmetry
Pospíšil, Martin ; Mertlík, Pavel (advisor) ; Čech, Jan (referee)
This thesis contains three essays related to the work of economist Joseph Stiglitz. The first essay describes the contribution of Stiglitz to economic theory by analysing problems of information asymmetry, new Keynesian and institutional economics, rationality, and market theories. Shortcomings of neoclassical economics are described and possible solutions are outlined. The last part of this is essay summarizes the main critique to Stiglitz. The second essay applies the topic of information asymmetry by discussing whether the current level of economic development leads to convergence or divergence in the technology and information levels. The conclusion is that even though globalisation affects the level of technology and information, we do not see convergence as predicted by several theoretical models and information asymmetry remains an important element in the economy. The last essay links the Stiglitz-Greenwald theory of credit rationing using recent Czech data from years 2008 and 2009. Data confirm that credit rationing increases, information asymmetry increases, and the transmission mechanism does not function well during economic decline. I conclude that Czech banks increase their screening of clients and consequently credit rationing in the times uncertainty leading to ambiguous development...
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