The diploma thesis Radiocaesium in agricultural uncultivated soils is focused on creation literary review, collection soil samples and then preparation of samples for gamaspectrometric analysis to determine content of the radionuclide (137Cs). In the first part of literature review radiocaesium and its sources in the environment are characterised. Radiocaesium transport in atmosphere, the 137Cs deposition on soil and its influence on human is included. In the next part, soil parameters, behaviour of radiocaesium in soil, following countermeasures, differences between soils in agroecosystems and agricultural uncultivated soils, contamination of soils with radiocaesium in Czech Republic are described. Materials, methodology and description of chosen locations are followed. The main part of the thesis is focused on determination of radiocaesium content in uncultivated soils. In 2013, soil samples (57 samples of 5-cm-top A organic profiles and 57 samples of deeper B mineral profiles from 5-12-cm of depth) were taken from four selected locations: Valašské Meziříčí-Juřinka, Velké Karlovice, Loukov, Prostřední Bečva. Soil samples were always collected in three specific areas: meadow, deciduous forest (mixed forest) and coniferous forest. The lowest values of 137Cs activity in soils were observed in Juřinka (average value in profiles A 16.9 +- 4.29 Bq.kg-1 and B 11.6 +- 2.53 Bq.kg-1), then in Loukov (average value in profiles A 38.8 +- 30.22 Bq.kg-1 and B 18.6 +- 12.60 Bq.kg-1). The highest values 137Cs in Velké Karlovice (in profiles A 64.7 +- 44.11 Bq.kg-1 and B 30.1 +- 21.50 Bq.kg-1), lower values in Prostřední Bečva (in profiles A 46.6 +- 30.01 Bq.kg-1 and B 24.9 +- 28.50 Bq.kg-1) were measured. Significant differences between 137Cs activity in top A soil profile and deeper B profile in all four locations were found (T-test, P less then 0.05). In all locations, the highest average values radiocaesium activities were observed in coniferous forest (average values in profiles A 65.7 +- 41.91 Bq.kg-1 and B 35.03 +- 28.94 Bq.kg-1), then in deciduous forest (average values in profiles A 33.8 +- 17.27 Bq.kg-1 and B 20.1 +- 7.51 Bq.kg-1) and the lowest in meadows (average values in profiles A 14.9 +- 4.53 Bq.kg-1 and B 10.7 +- 3.63 Bq.kg-1), (P less then 0.05). The 137Cs activities in soil profiles were converted from the radiocaesium activity concentration (Bq kg-1) to the 137Cs depositional density (kBq m-2), and the densities ranged from 0.93 to 12.94 kBq m-2. Results were processed to tables, graphs and map. In the closing part of thesis, our results were discussed and compared with published data and ecological importance of radiocaesium activity in agricultural uncultivated soils was also assessed.

CO2 efflux from soil at three different ecosystems (spruce forest, beech forest, wetland) and from the whole ecosystem at one site (grassland) was measured during campaigns of manual measurements or automated continuous measurements during growing seasons 2008 -- 2012. There were determined factors driving spatial variability and temporal dynamics of CO2 efflux. Soil temperature was mostly the driving factor responsible for temporal dynamics and soil water content contributed to both temporal dynamic and spatial variability. Also the amount of grass or litter affected the variability. We also determined that time of the day when the measurements of soil CO2 efflux are done can influence estimation of seasonal sum of released carbon from soil. Finally, it was determined that changing precipitation pattern with simulated drought in the first half of the growing season has both immediate and long-term impact on CO2 efflux from the grassland ecosystem.

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Rod bundle is a typical constitutive element of a very wide range of nuclear reactor designs. This thesis describes the investigation of such geometry with wall-resolved Large Eddy Simulation (LES). In order to alleviate the mesh constraint, imposed by the near wall resolution, the usage of embedded refinements and polyhedral meshes is analysed firstly with a inviscid laminar case (Taylor Green vortices) and secondly with a fully turbulent case (channel flow only with embedded refinement). The inviscid test case shows that the addition of embedded refinements decreases the conservation properties of the code. Indeed the accuracy decreases from second order in a structured conformal mesh, to something in between first and second order depending on the quality of the unstructured mesh. Better results are obtained when the interface between refined and coarse areas presents a more regular and structured pattern, reducing the generation of skewed and stretched cells. The channel flow simulation shows that the Reynolds stresses, of some embedded refined meshes, are affected by spurious oscillations. Surprisingly this effect is present in the unstructured meshes with the best orthogonal properties. Indeed analysis of Reynolds stress budgets shows that terms, where the gradient in the wall normal direction is dominant, have a largely oscillatory behaviour. The cause of the problem is attributed to the convective term and in particular in the method used for the gradient reconstruction. As a consequence of these contradictory signs between the inviscid and the fully turbulent cases, the rod bundle test case is analysed using a conventional body fitted multiblock mesh. Two different Reynolds numbers are investigated reporting Reynolds stresses and budgets. The flow is characterised by an energetic and almost periodic azimuthal flow pulsation in the gap region between adjacent sub-channels, which makes turbulent quantities largely different from those in plane channel and pipes and enhances mixing. Experiments found that a constant Strouhal number, with the variation of the Reynolds number, characterises the phenomenon. The frequency analysis finds that present simulations are distinguished by three dominant frequencies, the first in agreement with the experimental value and two higher ones, which might be due to the correlation of the azimuthal velocity in the streamwise direction. Several passive temperature fields are added at the simulations in order to study the effects of the variation of the Prandtl number and the change in boundary conditions (Neumann and Dirichlet). A simplified case where an imbalance of the scalar between adjacent sub-channels is also investigated in order to evaluate the variation of the heat fluxes with respect to the homogeneous case. An alternative solution, to reduce the mesh constraint imposed by the wall, is to hybridize LES with RANS. The main achievement of this work is to integrate the heat transfer modelling to the already existing model for the dynamic part. Further investigations of the blending function, used to merge the two velocity fields, are carried out in conjunction with a study of the model dependency on the mesh resolution. The validation is performed on a fully developed channel flow at different Reynolds numbers and with constant wall heat flux. On coarse meshes the model shows an improvement of the results for both thermal and hydraulic parts with respect to a standard LES. On refined meshes, suitable for wall-resolved LES, the model suffers from a problem of double counting of modelled Reynolds stresses and heat fluxes because the RANS contribution does not naturally disappear as the mesh resolution increases.

L'objectif de cette thèse est l'étude de la dispersion de pesticides à partir de parcelles de vigneet l'influence de l'aménagement de parcelles sur la dispersion. Pour atteindre cet objectif, nous avons utilisé la méthode de simulation des grandes échelles (LES) et l'approche lagrangienne combinées avec des expérimentations. Pour l'étude de la dynamique du vent dans les couverts en rangs, une expérimentation a été conduite sur une parcelle de vigne. Le modèle Atmosphérique ARPS a été utilisé pour la modélisation de l'écoulement atmosphérique dans les couverts en rangs. Pour la validation du modèle, les différentes statistiques mesurées ont été comparées à celles simulées. L'accord entre les mesures et les prédictions du modèle était encourageant. L'expérimentation et la modélisation ont montré que l'écoulement dans les couverts en rangs se comporte différemment selon la direction du vent en termes d'organisation et de paramètres aérodynamiques. De plus, les structures cohérentes turbulentes dans les couverts en rangs sont quasi-indépendantes de la direction du vent et partagent les mêmes propriétés que dans les couverts homogènes horizontalement. Pour l'étude de la dispersion de pesticide à partir de la vigne, une expérimentation sur vigne artificielle a été menée. En parallèle, un modèle numérique de dispersion, qui repose sur le modèle de vigne validé, a été développé. Il est ressortit de la modélisation et de l'expérimentation que, à temps court, la dispersion de pesticides à l'échelle de quelques rangs de vigne est dominée par les jets d'air du sprayer. Les comparaisons qualitative et quantitative de la progression du nuage émis par le sprayer, des pertes verticales et des dépôts obtenus par simulation et expérimentation étaient assez satisfaisantes. Les résultats de l'expérimentation sur la dispersion sur vigne artificielle ont été combinés avec la modélisation numérique pour l'étude de la dispersion à l'échelle de la parcelle et l'analyse de l'influence des aménagements de parcelles sur la dispersion. L'analyse comparative des scénarios a montré que le maximum d'exposition des individus vivant à proximité de parcelle viticoles est observé quand les rangs de vigne sont parallèles à la direction moyenne du vent et que les haies d'arbre constituent une alternative pour réduire les niveaux d'exposition. / The aim of this work is to study pesticide dispersal from vineyards and the effect of the layingout of the vineyards on pesticide dispersal. For this purpose, we have used the Large Eddy Simulation (LES) method and the lagrangian approach combined with the experiments. To examine the wind dynamic in row vegetable canopy, an experiment was achieved on a natural vineyard. The atmospheric model ARPS was used to model the atmospheric wind flow above and within row vegetable canopy. For validating the model, the measured wind flow statistics were compared to the simulated ones. The agreement between the measurement and the prediction of the model was encouraging. In addition, experiment and modeling have shown that the wind flow in the row vegetable canopy behave following the wind direction in term of the flow organization and aerodynamic parameters. Moreover, the turbulent coherent structures in row vegetable canopy are independent on the wind direction and share the same properties as in the horizontally homogeneous canopy. To study the pesticide dispersal from vineyard, an experiment on artificial vineyard was accomplished. In parallel, a numerical model lying on the validated row vegetable canopy model was developed. From both experiment and modeling, it appears that the short term pesticide dispersal at the scale of the few vine rows is dominated by the air jet sprayer. The qualitative and quantitative comparisons of the measured and simulated cloud spreading, upward loss and deposit were promising. The experimental results on pesticide dispersal from the artificial vineyard were combined with numerical modeling in order to analyze the pesticide dispersal at the scale of the vineyard and the effect of the vineyard laying out on the exposure level of the bystanders. Comparative analysis of the scenarios has shown that the maximum level of exposure is reached when the vine rows are parallel to the dominant wind direction and it can be reduced by using tree-wall.

In the last century, many coppice forests were transformed into high forests. Nowadays we can see the increase of interest in coppice forests and their management for wood production and nature conservation. The aim of this thesis was to provide the data from the experimental plot TARMAG Hády where the high forest was transformed into the coppice and coppice with standards. The goal was to study the sprouting capacity of different woody species and the production of biomass in those species. It was studying the dependence of biomass production on wood species. It was also surveyed if the number of standards affected the production of biomass. The research plot was measured twice, in 2014 and 2016. Biomass for each stump with sprouts in 2016 was found. The results of the experiment show that the woody biomass was affected by stand basal area previous forest stand. The biomass production was affected by the number of standards. The biggest production of biomass per individual was found in Tilia sp. Implementation of selective thinning is not necessary.

Le résumé en français n'a pas été communiqué par l'auteur. / Le résumé en anglais n'a pas été communiqué par l'auteur.

The present research investigates the details of mixture preparation and combustion in a two-stroke, small-scale research engine with a numerical methodology based on large eddy simulation (LES) technique. A major motivation to study such small-scale engines is their potential use in applications requiring portable power sources with high power density. The investigated research engine has a rectangular planform with a thickness very close to quenching limits of typical hydrocarbon fuels. As such, the combustor has a high aspect ratio (defined as the ratio of surface area to volume) that makes it different than the conventional engines which typically have small aspect ratios to avoid intense heat losses from the combustor in the bulk flame propagation period. In most other aspects, this engine involves all the main characteristics of traditional reciprocating engines. A previous experimental work has identified some major design problems and demonstrated the feasibility of cyclic combustion in the high aspect ratio combustor. Because of the difficulty of carrying out experimental studies in such small devices, resolving all flow structures and completely characterizing the flame propagation have been an enormously challenging task. The numerical methodology developed in this work attempts to complement these previous studies by providing a complete evolution of flow variables. Results of the present study demonstrated strengths of the proposed methodology in revealing physical processes occurring in a typical operation of the high aspect ratio combustor. For example, in the scavenging phase, the dominant flow structure is a tumble vortex that forms due to the high velocity reactant jet (premixed) interacting with the walls of the combustor. LES gives the complete evolution of this flow structure, from its beginning to its eventual decay after the scavenging period is over. In addition, LES is able to predict the interaction between the bulk flow at top dead center (TDC) and the turbulent flame propagation. The success of this depends on the ability of the model in predicting turbulent flow structure including its length and velocity scales.

Texte remanié de: Habilitationsschrift--Philosophische Fakultät I--Universität Zürich, 1995. / Bibliogr. p. 557-599.

Texte remanié de: Thèse de doctorat--Droit--Sfax (Tunisie)--Faculté de droit, 2006. / Bibliogr. p. 445-465. Index. Résumé en anglais.