National Repository of Grey Literature 52 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Fatigue Crack Propagation under Combined Load in Selected Polymer and Metal Materials
Slávik, Ondrej ; Klusák, Jan (referee) ; Padovec,, Zdeněk (referee) ; Náhlík, Luboš (advisor)
Material fatigue plays key role in terms of lifetimes of many service parts. Study of fatigue behavior of materials is ongoing from the previous century. To a large degree, the focus is put on studies of fatigue crack growth under uniaxial loading, or the so-called opening mode crack growth. However, in practice there are multiple cases of multiaxially loaded service parts, in which cracks loaded under mixed-mode loading conditions may be present. There is currently not enough knowledge with regards to this topic. This thesis is focused on some of the aspects of fatigue crack growth under combined loading. The aim is to find appropriate experimental specimens for studies regarding these issues and with their help to acquire necessary experimental data. Obtained results were used for simplification of residual fatigue lifetime estimation of parts made of polymer and metal materials. In the thesis it is also noticed about the differences in fatigue fractures between polymer and metal materials loaded by combination of tension and shear loading. These results contribute to better understanding of the processes of fatigue fractures of parts loaded by combined loading. Therefore, the submitted thesis is focused on the studies of fatigue behavior of metal and polymer materials under multiaxial loading.
Trophic structure of fish communities in anthropogenically impacted rivers
Dostál, David ; Horká, Petra (advisor) ; Slavík, Ondřej (referee)
The aim of this work was to describe trophic relationships in fish communities in an anthropogenically influenced environment. In them, non-specialized, so-called eurytopic fish species predominate over rheophilic fish, which have a more complex life cycle, greater demands on habitat, food resources, or spawning substrate. They are less able to adapt to human-induced changes. On the other hand, eurytopic species have very little requirements, so they are able to adapt to environmental changes without major problems. With this work, I wanted to verify the assumption that eurytopic fish species will have a wider trophic niche and a better trophic position in such an environment than rheophilic species. All this using the analysis of stable isotopes 15 N and 13 C with the contribution of the SIBER and tRophic position computing program. Key words: stable isotopes, trophic niche and position, riverine systems, freshwater fish
Seasonal variation of activity and pathogen prevalence in populations of the spiny-cheek crayfish
Matasová, Klára ; Petrusek, Adam (advisor) ; Slavík, Ondřej (referee)
The most widespread of invasive crayfish in the Czech Republic is the spiny-cheek crayfish (Orconectes limosus). It is a major disease carrier of crayfish plague, caused by the pathogen Aphanomyces astaci. The infection is lethal to European native species of crayfish. Transmission of this disease is usually associated with the spread of crayfish, which is dependent on their movement. The main aim of this work was to evaluate the differences in crayfish migratory activity in the Pšovka brook among seasons, and assess the factors that may affect it, by the use of radiotelemetry and trapping. We tested the hypothesis that crayfish use brook in the period from spring to autumn and then return back into a pond to overwinter. Furthermore, we evaluated how far from the pond crayfish migrate, and whether there is any relationship between migration and the season or water temperature. The results demonstrate that the activity varies among seasons (being strongly affected by breeding season) but in most studied periods did not significantly depend on water temperature. According to our monitoring, the spiny-cheek crayfish does not spread substantially to upstream parts of the Pšovka. Seasonal migration between the pond and the brook was monitored using two-way flow-through traps installed at the mouth of...
Spatial distribution of the European catfish Silurus glanis influenced by familiarity
Fořt, Martin ; Slavík, Ondřej (advisor) ; Kozák, Pavel (referee)
One of the key elements of animal social behaviour is the recognition of individuals on the basis of previous experience. This relationship is called familiarity and affects individual's behaviour. We know many examples of familiarity-based behaviour among fish. Many results show that familiarity is advantageous. Familiar individuals are less aggressive, forage more, make more cohesive shoals and grow faster. We tested the influence of the familiarity on the spatial distribution of juvenile wels catfish Silurus glanis from two unfamiliar groups, which were held in separate tanks. In a laboratory experiment was the spatial distribution of individuals monitored in the artificial stream by using passive integrated transponders. Shelters, which were occupied by individuals, were placed in the stream. Two groups of fish were subsequently added into the experiment under conditions of limited or unlimited shelters. These groups came from the same tank (so they were familiar) or from different tanks (so they were unfamiliar). 1080 individuals were used in this experiment and over three million individual fish positions were recorded. We discovered changing levels of activity under different conditions. When we compared activity of original and additional individuals, we measured higher level of activity in...
Within-group fish behaviour: effect of common experience
Fořt, Martin ; Slavík, Ondřej (advisor) ; Frouzová, Jaroslava (referee)
Recently, behavioral studies focusing on social relationships of fish in groups became popular. Fish are able individually recognize conspecifics or even heterospecifics. This ability allows distinguishing among individuals in and between groups and shows that fish prefer associating with familiar or kin individuals. An interaction with kin individuals is called condition-dependent recognition, whilst relationship based on previous experience is called condition independent recognition or familiarity. Both of these interactions can bring the participants some advantages, such as better protection from predators, foraging benefits, lower aggression levels, etc.
Age structure and growth of wild brown trout in relation to population density and habitat quality
Závorka, Libor ; Slavík, Ondřej (advisor) ; Matěna, Josef (referee) ; Reichard, Martin (referee)
Brown trout Salmo trutta L. is a fish species with high socio-economic value, which is favourable among anglers and a successful invader worldwide. The aim of this thesis is to explore environmental factors affecting body growth and survival of brown trout with emphasis on density dependent selection in juvenile life stages. This thesis is specifically focused on: (1) effect of population density on growth and survival with respect to a dynamic of a local group of individuals (papers I and II); (2) effect of inter-individual differences in behaviour on the relationship between individuals life-history traits and available resources (papers III and IV); (3) link between demo-genetic structure of population and growth and mortality rates of individuals (papers V, VI and VII). Datasets for this thesis were collected during a long-term mark-recapture study on wild brown trout population (2005-2011) in the catchment of the Otava River in Šumava National Park (Czech Republic) and a set of field and laboratory studies conducted on wild populations in streams on west coast of Sweden. In accordance with some previous studies, this thesis showed that growth of juvenile brown trout is negatively affected by population density. Nonetheless, this thesis reveals that the negative effect of density dependent...
A behaviour of the European catfish Silurus glanis in the mating season and for rest of the year with focus on social interactions among individuals
Lüftner, Radek ; Slavík, Ondřej (advisor) ; Randák, Tomáš (referee)
Reproduction ability is the key factor for survival and dispersal of every species. There is, however, only limited information about reproduction of large-bodied fish. Males of European catfish, our biggest native fish, build nests in vegetation and mate there later with females. After succesful mating male guards the nest and takes care of eggs and fry. According to literature, the act of reproduction should take place at nights with water temperature from 18 to 24 řC. However, available records about reproductive behaviour are outdated, fragmentary or come from aquacultures. Thus, a study was designed to evaluate behaviour of European catfish in their natural environment in the Berounka river using radiotelemetry, the results of which I processed in this thesis. Spatial distribution of catfish was followed during the whole year, with special attention on separating mating season from the rest of the year. The goal was to determine conditions characteristic for the mating period and to verify that catfish in the field indeed reproduce in pairs. For this purpose, 10 adults were tracked for two-year period (2002-2004) in the Berounka river by radiotelemetry. Exact positions of all individuals were followed in fourteen-day cycles. In every tracking episode, the position of an individual fish was...
Trophic structure of fish communities in the tributaries upstream of the Lipno Reservoir
Kofentová, Nikola ; Horká, Petra (advisor) ; Slavík, Ondřej (referee)
River obstacles, especially dams, are known to alter the natural environment in streams, which significantly impacts fish communities. The cyprinid species migrate from the reservoirs upstream to the reservoir's tributaries, where they may cause changes in the trophic structure of native fish communities. The aim of this study was to evaluate the trophic structure of the fish community composed mainly of cyprinid and salmonid species throughout seven localities in the Vltava River upstream of the Lipno reservoir. Stable isotope analysis was used to identify trophic positions, trophic niche width and trophic niche overlap between species. Trophic relationships of individual species were then evaluated to assess the potential for food competition. The trophic niche width of the salmonid species was significantly higher than that of the cyprinid species. Trophic niche overlap between salmonids and cyprinids was observed, with the most significant overlap being with both common dace Leuciscus Leuciscus and common roach Rutilus rutilus, suggesting a potential competition for food. The effect of the presence of cyprinids on the trophic niche width of salmonids was shown not to be statistically significant. From the perspective of protecting native salmonid species, there should be special attention paid...

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