In this thesis examples of translationally invariant one-dimensional (1D) Vlasov-Maxwell (VM) equilibria are investigated. The 1D VM equilibrium equations are equivalent to the motion of a pseudoparticle in a conservative pseudopotential, with the pseudopotential being proportional to one of the diagonal components of the plasma pressure tensor. A necessary condition on the pseudopotential (plasma pressure) to allow for force-free 1D VM equilibria is formulated. It is shown that linear force-free 1D VM solutions correspond to the case where the pseudopotential is an attractive central potential. The pseudopotential for the force-free Harris sheet is found and a Fourier transform method is used to find the corresponding distribution function. The solution is extended to include a family of equilibria that describe the transition between the Harris sheet and the force-free Harris sheet. These equilibria are used in 2.5D particle-in-cell simulations of magnetic reconnection. The structure of the diffusion region is compared for simulations starting from anti-parallel magnetic field configurations with different strengths of guide field and self-consistent linear and non-linear force-free magnetic fields. It is shown that gradients of off-diagonal components of the electron pressure tensor are the dominant terms that give rise to the reconnection electric field. The typical scale length of the electron pressure tensor components in the weak guide field case is of the order of the electron bounce widths in a field reversal. In the strong guide field case the scale length reduces to the electron Larmor radius in the guide magnetic field.

Pražské metro jako prostor pro realizaci geologických exkurzí Abstract: The aim of this diploma thesis is to evaluate and explore the potential of the tiling materials used in the Prague metro and to create guidelines suitable for organizing geological excursions. Ysdfvwavweefawfbaljehbrrkvjasdhbflavjsdhbf alskdjfbalksjdfnaůksjdnaůkjsdfnaůksjsa Sdfasdfasdfasfavsdfvaskedjfnalksjdfnca weuifhmacskdjfmcapisdjfcaksdjnfcamůskdjfnmacsdkjfnmacůskjdfmnacůs kdjfmnaclskdjfnmacůskdjfnacf askdjfaůksjdf nasdkfjn askdjfn aůksjdnf aůskjdfn aůkjsdf akjsdn fakůjsd fnaůksjdfnaůksrjng adg

The aim of this research work is to study the inter-relationship, under controlled industrial conditions, among skin pass reductions, surface topography characterized by 2D and 3D roughness parameters, stampability and painted surface finish quality for automotive steel sheet stampings. Different surface textures obtained from cold rolling finishing have been evaluated in terms of paint appearance (rating and spectral curve) and tentatively related to roughness parameters (2D and 3D) obtained from the cold finished sheets. Some relevant tendencies have been established amongst these parameters. The results presented here are in accordance with other recently published research showing that there is a clear relationship between these parameters, and that further detailed studies are needed. / O foco do presente trabalho é o estudo, em condições industriais, da inter-relação entre grau de redução do passe de acabamento, topografia superficial caracterizada pelos parâmetros de rugosidade 2D e 3D, estampabilidade e aparência de pintura de chapas de aço para painéis automotivos. Diferentes texturas superficiais de chapas de aço foram analisadas em termos de aparência de pintura (rating e curvas espectrais) e tentativamente relacionadas com os parâmetros de rugosidades (2D e 3D) obtidos na chapa antes de estampar. Algumas tendências relevantes foram estabelecidas entre estes parâmetros. Os resultados presentes aqui estão de acordo com publicações recentes mostrando uma clara relação entre estes parâmetros e que trabalhos futuros ainda são necessários.

A família Rubiaceae se caracteriza por produzir uma grande variedade de metabólitos secundários. Alcalóides, triterpenos iridóides e antraquinonas destacam-se entre os produtos naturais de maior ocorrência nas rubiaceas. Espécies desta família ocorrem com frequência no cerrado brasileiro, sendo que o gênero Alibertia, não havia sido estudado até recentemente. O presente trabalho, que é o primeiro com a espécie Alibertia edulis A. Rich, descreve o isolamento, identificação e determinação estrutural de triterpenos presentes nas folhas de um espécimen coletado nas proximidades de Campo Grande, Mato Grosso do Sul. O estudo da fração clorofórmica do extrato etanólico mostrou a ocorrência predominante de triterpenos. Foram isolados através dos métodos cromatográficos usuais (coluna e placa preparativa), os pares oleanano-ursano urs-12-en-3β,28-diol e olean-12-en-3β,28-diol; 3β-hidroxiurs-12-en-28-óico e 3β-hidroxiolean-12-en-28-óico; 3β,23-diidroxiurs-12-en-28-óico e 3β,23-diidroxiolean-12-en-28-óico, que foram identificados através dos espectros de RMN de 13C e 1H. A mistura dos ésteres metílicos dos ácidos 3β, 19α,23,24-tetraidroxiurs-12-en-28-óico e 3β, 19α,23,24-tetraidroxiolean-12-en-28-óico também foi isolada desta mesma fração. Após ser acetilada, esta mistura foi submetida à cromatografia líquida de alta eficiência, o que possibilitou a separação dos seus componentes. Destes, o triterpeno com esqueleto tipo ursano foi identificado pelos seus espectros de RMN de 13C e 1H. Como não foi encontrado registro na literatura do triterpeno com esqueleto oleanano, a determinação estrutural deste foi feita por comparação com os dados de RMN do éster metílico do ácido 3β,19α,23,24-tetraidroxiur-12-en-28-óico, associado a uma análise do espectro bidimensional 1H-1H (COSY). Do extrato hexânico de A. edulis também foi isolada uma mistura, constituída por α e β-amirina, além de fitol. / The Rubiaceae family affords as secondary metabolites, mainly alkaloids, triterpenes and iridoids. Species of this family are spread in the region of Brazilian \"cerrado\". The genus Alibertia has not been studied until recently. This work, the first one with the specie Alibertia. edulis A. Rich, reports the isolation, identification and structural determination of the triterpenes that occurred in the leaves of a specimen colleted in Campo Grande, Mato Grosso do Sul, Brazil. The chloroform fraction of the ethanolic extract shows the predominance of triterpene compounds. From this fraction, we isolate, by means of chromatographic procedures, the ursane-oleanane pairs: 3β,28-dihydroxy-urs-12-en and 3β,28-dihydroxy-olean-12-en; 3β-hydroxyurs-12-en-28-oic and 3β-hydroxyolean-12-en-28-oic; 3β,23-dihydroxyurs-12-en-28-oic and 3β,23-dihydroxyolean-12-en-28-oic; 3β,19α,23,24-tetrahydroxyurs-12-en-28-oic and 3β,19α,23,24-tetrahydroxyolean-12-en-28-oic. The last compound is a new natural product and its structure was determined based on methyl-triacetylated derivative. From the hexanic extract we isolated α and β-amyrin and phytol.

O objetivo do trabalho é analisar e compreender os efeitos das características do fibrocimento reforçado com fibras sintéticas na retração por secagem deste compósito. A importância social do fibrocimento como material de construção, justifica a realização do presente trabalho, de modo a expor como acontece a retração por secagem neste compósito, e desta forma auxiliar o meio técnico na mitigação das manifestações patológicas relacionadas à retração e contribuindo para a redução do importante problema da indústria produtora de fibrocimento, que é a fissuração de borda nas telhas onduladas. Para tal buscou-se demostrar o efeito da porosidade e distribuição de tamanho de poros na retração por secagem. Além disso, foram realizados experimentos onde se variou o tipo de cimento utilizado, as quantidades de todas as matérias-primas envolvidas, além da aplicação de tratamentos modificadores da movimentação higroscópica, manipulando diretamente a tensão capilar causadora da retração. Concluiu-se que a porosidade elevada do fibrocimento faz com que a retração por secagem deste compósito seja fortemente influenciada pela porosidade total do mesmo, com correlação direta com a quantidade de mesoporos. Além disso, no estudo de caso realizado concluiu-se que a redução da retração devido à redução da tensão superficial da água do poro, se refletiu em menor fissuração de borda nas telhas onduladas. / The objective is to analyze and comprehend the effects of properties of cement based composite reinforced with synthetic fibers, on drying shrinkage of such composite. The social importance of fiber cement as construction material justifies the execution of the present work, in order to expose how drying shrinkage occurs on this composite and by those means to assist the technical community on mitigating pathological manifestations related to shrinkage, thus contributing for the reduction of an important problem on fiber cement industry, the edge cracking on corrugated sheets. In order to achieve this goal, it was sought to demonstrate the effect of porosity and pore size distribution on drying shrinkage. Moreover, experiments were performed, varying the type of cement used and the quantities of all materials involved, in addition to the application of treatments that modify hygroscopic movement, directly manipulating the capillary tension which causes shrinkage. It was concluded that the elevated porosity of the fiber cement causes drying shrinkage of this composite to be strongly influenced by its total porosity, directly correlated to the quantity of mesopores. Furthermore, in the case study performed it was concluded that shrinkage reduction due to the reduction of pore water surface tension was reflected into minor edge cracking on corrugated sheets.

The influence of several hardwoods and softwoods pulp fibre on the free shrinkage of isotropic paper sheets was investigated. The effect of properties such as density, grammage, Fractional Contact Area (FCA), Water Retention Value (WRV), fines content and fibre morphology were also investigated on the free shrinkage of isotropic paper sheets. Further, the influence of Lyocell fibre and glycerol on the free shrinkage of isotropic paper sheets is reported. Experimental results showed that in general the free shrinkage of hardwood pulps is a few percent higher than that of softwood pulps at the same density. It was found that although free shrinkage increases with fines content, a high fines content does not imply high shrinkage, and some pulp samples with higher amount of fines, exhibited lower free shrinkage. For all pulps at low densities there is little influence of grammage on free shrinkage, though as density increases a significant dependence is observed. The results showed that the free shrinkage of isotropic paper sheets formed from hardwood pulps is more sensitive to grammage compared to that of softwood pulps. Interestingly, it was shown that some pulp samples with the same intrinsic density, WRV and FCA exhibited different free shrinkage over the range of grammages. In addition, some pulp samples with stiffer fibres but higher amount of fines exhibited higher free shrinkage. Experimental results showed that longitudinal shrinkage of a fibre is an important parameter and pulp samples with higher microfibril angle (MFA) exhibited higher longitudinal shrinkage. Finally, the free shrinkage of isotropic paper sheets was reduced by applying Lyocell fibre and glycerol. Interestingly, by adding a small amount of Lyocell fibre, 2%, an increase in tensile index, tensile energy absorption (TEA) and modulus is observed, while the free shrinkage reduced up to 2%. In addition, adding glycerol to the pulp samples not only reduced the free shrinkage of isotropic paper sheets up to 1.5%, but also mechanical properties, such as tensile index and stretch slightly improved.

No description available.

The West Antarctic Ice Sheet is drained primarily by five major ice streams, which together control the volume of ice discharged into the ocean across the grounding line. The grounding line of Kamb Ice Stream (KIS) is unusual because the ice stream upstream of it is stagnant. Here, a set of surface features--shore-parallel, long wavelength, low amplitude undulations--found only at that grounding line are examined and found to be "pinch and swell" features formed by an instability in the viscous deformation of the ice. When a relatively competent layer is surrounded by lower strength materials, particular wavelength features within the layer may be amplified under certain layer thickness and strain rate conditions. The undulations at KIS grounding line are possible due to the relatively large strain rates and particular ice thickness at that location. Several data sets are used to characterize the surface features. High resolution surface profiles are created using kinematic GPS carried on board a sled that was used to tow ice penetrating radar equipment. The radar data are used to examine the relationship between surface shape and basal crevasses. Additional surface profiles are created using ICESat laser altimeter observations. Repeat GPS surveys of a strain grid across the grounding line yields strain rate information. Analysis of repeat observations over tidal cycles and multi-day intervals shows that the features are not standing or traveling waves. Together, these observations are then used to evaluate the contributions of elastic and viscous deformation of the ice in creating the grounding line undulations.

<p>Currently, our world is getting more and more connected: information flows are everywhere at anytime. We are only at the beginning of the communication era. However, few want to know how those data are delivered as long as they are well delivered. Which paths they take, using optical fibres or regular copper cables, such questions do not matter for end-customers.</p><p>As a part of a telecommunication company, these questions do really matter. As networks become increasingly complex, it is significant to keep them under control and make them reliable to deliver high-quality services to users.</p><p>One of our main problems is how to get a representation of this network. More precisely how to get a relevant image of elements that compose this huge web and what points are significant in order to increase the quality of offered services. This thesis will try to answer these questions.</p>

This thesis aims at studying the breakup of swirling liquid sheets discharging from the outer orifice of gas centered swirl coaxial atomizers. Such atomizers are considered as propellant injection systems for semi-cryogenic liquid rocket engines. A gas centered swirl coaxial type atomizer discharges an annular swirling liquid sheet which is atomized by a gaseous jet issuing from the central orifice of the atomizer. The primary objectives of this work were to understand the fluid dynamic interaction process between the outer liquid sheet and the central gas jet and its role on the breakup process of the liquid sheet. Cold flow experiments were carried out by constructing custom made gas centered swirl coaxial atomizers. Two different atomizer configurations with varying swirl effect were studied. The jets were injected into ambient atmospheric air medium with tap water and air as experimental fluids. The flow conditions were described in terms of Weber number (Wel) and Reynolds number (Reg) for liquid sheet and the air jet respectively. Spray images were captured by employing an image acquisition system comprising a high resolution digital camera and a strobe lamp. The captured spray images at different combinations of Wel and Reg were analyzed to extract quantitative measurements of breakup length (Lb), spray cone angle (θs), spray width (SW) and two-dimensional surface profile of liquid sheets. Quantitative analysis of the variation of Lb with Reg with different values of Wel suggested that low inertia liquid sheets undergo an efficient breakup process. High inertia liquid sheets ignore the presence of central air jet at lower values of Reg however undergo air jet breakup at higher values of Reg. Qualitative analysis of experimental observations revealed that the entrainment process, established between the inner surface of the liquid sheet and the boundary of central jet, triggers the air assisted sheet breakup by drawing the liquid sheet closer to the spray axis. The entrainment process may be developing corrugations on the surface of liquid sheet which promotes the production of thick liquid ligaments from the sheet surface. The level of surface corrugations on the liquid sheet, quantified by means of tortuosity of liquid sheet profile, increases with increasing Reg. Limited studies on the effect of variation swirl intensity on the air assisted breakup process of liquid sheets did not show any significant influence for the atomizers examined in the present work.