National Repository of Grey Literature 123 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Influence of deformation on precipitation processes in commercial Al-based alloys with Sc,Zr-addition
Leibner, Michal ; Vlach, Martin (advisor) ; Cieslar, Miroslav (referee)
1 Abstract: Mechanical and thermal properties of Al-5.4wt.%Zn-3.1wt.%Mg-1.5wt.%Cu (AA- 7075), Al-5.2wt.%Zn-3.0wt.%Mg-1.4wt.%Cu-0.2wt.%Sc-0.1wt.%Zr (AA-7075-ScZr) and Al-2.93wt.%Mg-0.34wt.%Mn-0.33wt.%Si-0.22wt.%Fe-0.19wt.%Cr-0.24wt.%Sc-0.06wt.%Zr (AA-5754-ScZr) alloys in as-cast and cold-rolled states were studied by differential scanning calorimetry and microhardness measurements. The initial values of microhardness reflect an effect of cold-rolling. The Sc,Zr-addition caused a pronounced hardening during annealing above ~ 300 řC. An easier diffusion of Zn, Mg, Cu and Mn atoms along dislocations led to a precipitation of Zn,Mg,Cu-containing and Mn-containing particles at lower temperatures in comparison with the AA-7075(-ScZr) and AA-5754-ScZr alloy in the as-cast state, respectively. The Sc,Zr-addition does not significantly influence precipitation of the particles form the Al-Zn-Mg-Cu system.
Study of intermetallic phases in cast duplex steel
Ponížil, Ondřej ; Foret, Rudolf (referee) ; Pacal, Bohumil (advisor)
This thesis deals with the study of intermetallic phases in cast duplex stainless steel ASTM A890 Grade 4A considering degradation of mechanical properties in the result of isothermal aging in the temperature of 700 °C and 595 °C. The period of aging in the temperature of 700 °C was ranging from 1 to 160 hours and in the temperature of 595 °C it was ranging from 24 to 245 hours. The study of microstructure after aging in the temperature of 700 °C has proved that the -phases, Laves phases, chromium carbides and chromium nitrides were excluded. The phase was observed after four hours of aging in the temperature of 700 °C in / interface for the first time. The transformation was performed by eutectoid mechanism according to the equation + 2. The Laves phase has been observed after 10 hours of aging in / interphase and later in the ferrite grain as well. Chromium carbides and nitrides have created a continuous contour along to the / and /2 interface. After the temperature of 595°C there have been observed a large amount of small precipitates in the structure. The precipitates have been extracted from some selected samples to carbon replica. Following analysis has confirmed the presence of chromium carbides, -phases and Laves phases. The deterioration of mechanical properties, caused by the influence of secondary phase exclusion, has been confirmed by the Vickers hardness test and impact test including fractography analysis of the fracture surface. The hardness has an increasing tendency while the impact strength has been significantly reduced.
"Optimizing the Al casting heat treatment"
Ostrézí, Barbora ; Cileček, Jarmil (referee) ; Horáček, Milan (advisor)
This master’s thesis focuses on the heat treatment of the aluminium alloy AlSi7Mg0,6 and also investigates the effects of different coolants usage on its mechanical properties. First part is dedicated to the description of aluminium alloys, their chemical composition, behaviour and mechanical properties with particular attention to the Al-Si-Mg alloys. This part was followed by the summary of commonly used heat treatment of aluminium alloys. The third part is dedicated to the experiment. Castings and test specimens were wax casted at Alucast, s.r.o. company. After annealing, the samples were quickly cooled down in four different coolants and underwent tensile testing. Their mechanical properties (tensile strength, yield point and ductility) were evaluated as well as microstructure. In the last part, the achieved results are presented.
Recent changes of sea surface temperature in the North Atlantic
Kodetová, Tereza ; Pokorná, Lucie (advisor) ; Křížová, Milada (referee)
Sea surface temperatures (SST) have been changing in all world's oceans in the last decades; these changes have an impact on the continental climate. This bachelor thesis focuses on the recent changes of SST in the North Atlantic and their influence on the climate change in Europe. The first part of the thesis describes the physical-geographical characteristics of the North Atlantic. It consists of its divisions, bottom and coastal characteristics, spatial distributions of the water temperature and a water salinity. It also includes a description of the atmospheric circulation that occurs over the North Atlantic and the circulation inside of the North Atlantic. The second part of the bachelor thesis focuses on the SST and its measurement, Atlantic Multidecadal Oscillation (AMO) and a long-term changes which occur, and furthermore on the impact of these changes on the climate change in Europe. The results of the studies have shown that the biggest impact of SST changes in the North Atlantic is visible during summer months. These are the times of the greatest anomalies in the temperatures and precipitation, either on the positive or negative scale, depending on the phase of AMO or North Atlantic Oscillation. Key words: air temperature, Europe, Noth Atlantic, precipitation, sea surface temperature
Phenology of mangroves
Hradečný, Jakub ; Koubek, Tomáš (advisor) ; Sklenář, Petr (referee)
The mangroves are a globally important ecosystem with an important value for many organisms, humans included. Many of the organisms are addicted to leaf production, as a part of their diet. These foliovorous organisms are directly affected by mangrove phenology, which presents differences on the global scale. It seems possible that the phenology is influenced mainly by annual temperature oscillations and its changes mark the start and the end of phenological periods. The phenology of mangroves can be influenced by another climatic factor too, as for instance rainfall or salinity. In the latitudes of 20ř, the phenological phases show unimodal mode with the long duration of phenology periods, usually longer than one year. Closer to the equator, the phenology of the plants becomes to change into a bimodal mode, with more than one peak of phenological event per year. In the area of the equator, the phenology of the plants changes into a multimodal mode, without differences during the whole year. This ideal model can be changed by local climatic extremes changing the mangrove phenology into a different mode.
Runoff development in selected catchments in the Kyrgyz Range, Tian-Shan
Jedličková, Šárka ; Šobr, Miroslav (advisor) ; Janský, Bohumír (referee)
The main objective of this paper was to investigate runoff changes in the catchment Ala-Arca, Alamaedin and Kara-Balta in Kyrgyzstan, as well as change in climate conditions from available stations in the area. The runoff, precipitation, and temperature series were subjected to monthly, seasonal and annual analyses based on available data. Both absolute and relative data homogeneity were verified using statistical tests such as the Mann-Whitney-Pettit test, the SNHT test, and the WiIlcoxon's two- sample test for absolute homogeneity, and the Alexandersson's test for relative homogeneity. The Mann-Kendall test was used to determine the trend in each serie. There were inhomogeneities found in a number of runoff data. In most cases, the changes of rivers Ala-Arca and Kara-Balta were recorded in 1987. Compare to Ala-Arca and Kara-Balta, the changes of river Alamedin were recorded 3 years later, in 1990. There was a positive trend development by the rivers with the glacial-snow regime. However, there was no statistically significant trend for the entire time series. Key words: runoff change, precipitation, temperature, glacial-snow regime, snow-glacial regime, homogenization, Mann-Whitney-Pettit test, trend, Mann-Kendall test, glaciation, Kyrgyzstan, Tien- Shan
Examination of the polymorphism of the gene ApoE
Alzheimer´s disease (AD) belongs to the most frequent cause of dementia in the world. It is determined that it is about 65-75 % of all the dementias (Preiss, Přikryková Kučerová, 2006). The term Alzheimer Dementia, as well as Pre-senile Form (AD) is used with the patients at the age up to 65 years (Seidl, 2015). After the age of 65 years we use the term Senile Dementia of the Alzheimer Type. (SDAT). Up to the age of 45 this desease is rare (Seidl, Obenberger, 2004). Causal treatment of this disease does not exist, because etiopathogenesis of the disease is not entirely clarified (Seidl, 2015). The aim of this bachelor´s work was to write a professional search to the given topic. In this theoretical part there is summed up the information about neurodegenerative disease, about dementia and (AD). Most importantly there are described the symptoms, the causes, phase, treatment, diagnostics and genetic disposition of AD. The description of polymerase chain reaction (PCR) and reverse hybridization on strips is also an important part of this theoretical part. In the practical part, the main goal was to master molecular biological methods. To achieve the goals and to get the best results, I chose two methods. In addition to optimizing the PCR ARMS method, reverse hybridization was used on strips. The above-mentioned second method was performed using the commercially available ApoE StripAssay? kit from ViennaLab. In this part of the paper are described all the procedures by which I achieved the results. Molecular biological methods were performed in a laboratory at the Health and Social Faculty of the University of South Bohemia in České Budějovice.
Precipitation nowcasting for the warm part of the year
Mejsnar, Jan ; Sokol, Zbyněk (advisor) ; Jaňour, Zbyněk (referee) ; Žák, Michal (referee)
Current precipitation nowcasting systems primarily use the extrapolation of observed radar reflectivity. I used the extrapolation and studied limits of the forecast using the concept of the decorrelation time (DCT). I used data from two radars covering the territory of the Czech Republic from warm parts of four years and calculated DCT in dependence on several selected conditions describing the state of the atmosphere. I found that the mean DCT for the extrapolation is 45.4 minutes. On average the increase of the DCT in comparison when the persistence forecast is employed is 13.4 minutes. However, in dependence on current conditions the DCT may increase or decrease in more than 40 %. I also explored time evolution of the DCT during two storm events. I found that the DCT may significantly change in time, which is the consequence of changing character of the atmosphere during the storm development.
Influence of heat treatment on deformation behaviour of wrought Mg-Zn-based alloys
Olejňák, Juraj ; Drozdenko, Daria (advisor) ; Mathis, Kristián (referee)
Title: Influence of heat treatment on deformation behaviour of wrought Mg-Zn alloys Author: Juraj Olejňák Department: Department of Physics of Materials Supervisor: RNDr. Mgr. Daria Drozdenko, Ph.D. Abstract: The aim of the present thesis is to understand an influence of heat treatment on microstructure and mechanical properties of extruded Mg-Zn based alloys containing an addition of Ca and Nd. Microstructural analysis provided by electron microscopy gave us information about homogeneity and distribution of precipitates in investigated Mg alloys after extrusion and a subsequent heat treatment. Microhardness and compression test along the extrusion direction have been performed to determine optimal aging conditions for achieving better mechanical properties, such as hardness and strength. The acoustic emmision technique was used to follow active deformation mechanisms during plastic deformation. Application of the acquired knowledge in material research can contribute to design novel Mg alloys with enhanced mechanical properties for specific applications. Keywords: magnesium alloys, isothermal aging, precipitation, mechanical properties
Mechanical properties of pre-compressed Mg-Zn-Ca alloy
Hegedüs, Marius ; Dobroň, Patrik (advisor) ; Lukáč, Pavel (referee)
In wrought Mg alloys, their hexagonal closed packed structure together with a pronounced basal texture lead to anisotropy of mechanical properties. This bachelor thesis is focused on understanding the influence of previous deformation with further relaxation and/or additional heat treatment on deformation behaviour of the extruded Mg-Zn-Ca alloy. The significant influence of twins formed after pre-compression on mechanical properties was investigated. Evolution of microstructure, especially a formation of twins, is observed by light and scanning electron microscopy. The acoustic emission technique is used to determine active deformation mechanisms: dislocation slip and twinning. The results can be used for developing Mg alloys with enhanced properties.

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