The present master thesis deals with the design of wheel disk for passenger car. The review part of this thesis summaries the history and development of the wheel; this is followed by a description of individual construction types of wheel disk for passenger car presently used. The construction part of this thesis provides a design of disk of given parameters based on the analysis of forces acting on the car wheel. For the purposes of design, the stress and fatigue analyses are performed.

The presented text deals with designing of a multilingual application and its following implementation in the C++ language. The application encrypts disk volumes with Microsoft Windows system using symmetric cryptography and password authentication, where the password security strength is verified. Securing the sensitive data is one of the important security goals in area of information technology. The symmetric cryptography uses the same key for both the encryption and the decryption and due to its speed it is suitable for the data storage encryption. For the higher security it is possible to encrypt a whole disk volume with sensitive data.

This thesis was aimed developing a fundamental understanding of the boundary layer response to arbitrary motion. In this context arbitrary motion was defined as the unsteady translation and rotation of an object. Research objectives were developed from the gaps in knowledge as defined during the literature survey. The objectives were divided into three main activities; mathematical formulations for non-inertial bulk flow and boundary layer equations, implementation of said formulations in a numerical solver and simulations for various applications in arbitrary motion. Mathematical formulations were developed for the bulk flow and boundary layer equations in arbitrary motion. It was shown that the conservation of momentum and energy equations remains invariant in the non-inertial forms. The conservations of momentum equation can at most have six fictitious terms for unsteady arbitrary motion. The origin of the terms were found to be from transformation of the material derivative to the non-inertial frame. All fictitious terms were found to be present in the boundary layer equations, none could be eliminated during an order of magnitude analysis. The vector form of the non-inertial equations were implemented in a novel OpenFOAM solver. The non-inertial solver requires prescribed motion input and operate on a stationary mesh. Validation of the solver was done using analytical solutions of a steady, laminar flat plate and rotating disk respectively. Numerical simulation were done for laminar flow on a translating plate, rotating disk and rotating cone in axial flow. A test matrix was executed to investigated various cases of acceleration and deceleration over a range of 70 g to 700 000g. The boundary layer profiles, boundary layer parameters and skin friction coefficients were reported. Three types of boundary layer responses to arbitrary motion were defined. Response Type I is viscous dominant and mimics the steady state velocity profile. In Response Type II certain regions of the boundary layer are dominated by viscosity and others by momentum. Response Type III is dominated by momentum. In acceleration the near-wall velocity gradient increases with increasing acceleration. In deceleration separation occurs at a result of momentum changes in the flow. The mechanism that causes these responses have been identified using the developed boundary layer equations. In acceleration the relative frame fictitious terms become a momentum source which results in an increase in velocity gradient at the wall. In deceleration the relative frame fictitious terms become a momentum sink that induced an adverse pressure gradient and subsequently laminar separation. / Hierdie tesis is gerig op die ontwikkeling van 'n fundamentele begrip aangaande die grenslaag reaksie op arbitrêre beweging. In hierdie konteks word arbitrêre beweging gedefinieer as die ongestadigde translasie en rotasie van 'n voorwerp. Navorsingsdoelwitte is ontwikkel uit die gapings soos omskryf in die literatuuroorsig. Die doelwitte is verdeel in drie hoof aktiwiteite; wiskundige formulerings vir ongestadigde vloei en grenslaag vergelykings, implementering van hierdie formulerings in 'n numeriese kode en simulasies vir verskeie gevalle van arbitrêre beweging. Wiskundige formulerings is ontwikkel vir die vloei en grenslaag vergelykings in arbitrêre beweging. Daar is bewys dat die behoud van massa en energie vergelykings onveranderd in die nie-inertiële vorms bly. Die behoud van momentum vergelyking kan hoogstens ses fiktiewe terme vir ongestadigde, arbitrêre beweging hê. Die oorsprong van die terme is vanuit die transformasie van die ongestadigde en adveksie terme (aan die linker kant van die momentum vergelyking) na die nie-inertiële raam. Alle fiktiewe terme is teenwoordig in die grenslaag vergelykings. Die vektor vorm van die nie-inertiële vergelykings is in 'n nuwe OpenFOAM oplosser geïmplementeer. Die nie-inertiële oplosser vereis voorgeskrewe beweging insette en werk op 'n stilstaande rooster. Die oplosser is getoets teen analitiese oplossings van 'n gestadigde, laminêre plaat plaat en 'n roterende skyf, onderskeidelik. Numeriese simulasies is gedoen vir laminêre vloei op 'n translerende plaat, roterende skyf en roterende konus in aksiale vloei. 'n Toets matriks is gebruik om ondersoek in te stel na gevalle van versnelling en vertraging oor 'n verskeidenheid van 70 g tot 700 000 g. Die grenslaag profiele, grenslaag parameters en oppervlak wrywingskoëffisiënte is aangemeld nie. Drie tipes grenslaag reaksies op arbitrêre beweging is gedefinieer. Reaksie Tipe I is viskeus dominant en boots die bestendige snelheidsprofiel na. In reaksie Tipe II sekere dele van die grenslaag is oorheers deur viskositeit en ander deur momentum. Reaksie Tipe III word in totaliteit oorheers deur momentum. In versnelling die snelheid helling teen die objek neem toe met toenemende versnelling. In vertraging is 'n negatiewe snelheidsprofiel waargeneem as gevolg van momentum veranderinge in die vloei. Die meganisme wat hierdie reaksies veroorsaak is geïdentifiseer deur die grenslaag vergelykings. In versnelling word die fiktiewe terme 'n bron van momentum. Dit lei tot 'n toename in snelheid helling op die objek. In vertraging word die fiktiewe terme 'n momentum gebruiker wat 'n negatiewe drukgradiënt veroorsaak en gevolglik laminêre vloei wegbreking veroorsaak. / Thesis (PhD)--University of Pretoria, 2016. / Mechanical and Aeronautical Engineering / PhD / Unrestricted

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Depuis les années 1970, le développement des sources lasers de puissance fonctionnant autour de 2 µm basées sur des cristaux dopés Thulium Tm3+ et/ou Holmium Ho3+est un domaine de recherche actif du fait de ses multiples applications. L’émission autour de 1.9 µm correspond à une transition du niveau excité 3F4 vers le niveau fondamental 3H6 dans un ion trivalent Tm3+, alors que l’émission à 2 µm et au-delà correspond à la transition entre le niveau 5I7 et le niveau fondamental 5I8 de l’ion Ho3+. Ces transitions laser font aujourd’hui l’objet de nombreuses applications dans domaines très variés. nous avons étudié les propriétés spectroscopiques de cristaux de fluorures dopés terres rares en vue d’une émission autour de 2 µm. À partir des spectres d’absorption obtenus, l’analyse de Judd-Ofelt a permis de calculer les durées de vie radiatives ainsi que les rapports de branchement dans les ions Tm3+ et Ho3+. En comparaison avec d’autres cristaux tels que les oxydes, les durées de vie des niveau 3F4(Tm3+) et 5I7(Ho3+) dans les cristaux de fluorures sont plus longues ce qui favorise un fonctionnement laser en régime impulsionnel. Une étude sur la dynamique de fluorescence a été réalisée afin de caractériser l’émission autour de 1.9µm de l’ion Tm3+ et celle autour de 2µm de l’ion Ho3+. Les spectres d’émission obtenus offrent de larges bandes, assez structurées dans la matrice LiYF4 et plus larges et moins structurées dans la matrice CaF2. Dans un second temps, en mesurant les durées de vie du niveau émetteur 3F4 pour différentes concentrations en ions Tm3+, nous avons calculé les paramètres de transferts. Les résultats obtenus ont montré que le processus de relaxation croisée est beaucoup plus efficace dans le cristal CaF2 que dans le LiYF4. Nous avons calculé également les coefficients de transfert et de transfert inverse entre les ions Tm3+ et Ho3+ suite à une excitation de l’ion Tm3+. Nous avons montré que la matrice LiYF4 offre une meilleure efficacité de transfert en vue d’une émission autour de 2µm. Le fonctionnement laser de couches minces en configuration « disque mince » a été étudié. Une première démonstration d’un laser en disque mince LiYF4 : Tm émettant à 1.9 µm réalisé à partir d’une couche épitaxiée par LPE a été faite. En simple passge, une puissance de sortie de 306 mW et une efficacité laser de 36% en puissance absorbée sont atteintes pour une couche de 240 μm d'épaisseur.nous avons étudié un oscillateur laser en guide d’onde LiYF4 :Tm en géométrie planaire et linéaire. Ces guides sont caractérisés par de faibles pertes de propagation grâce à la qualité du procédé de fabrication. Une puissance maximale de 470 mW et un rendement de 14% en puissance incidente ont été obtenus. Une modélisation numérique de l’amplification optique montre que le guidage des faisceaux pompe et sonde permet d’atteindre des gains importants. Le modèle est ensuite adapté pour le régime de saturation afin de calculer le rendement d’extraction et de déterminer le potentiel des guides LiYF4 :Tm3+ en tant comme amplificateur autour de 1.9 µm / Since the 1970s, the development of power laser sources operating around 2 μm based on Thulium Tm3 + and / or Holmium Ho3 + doped crystals is an active field of research because of its multiple applications. The emission around 1.9 μm corresponds to a transition from the excited level 3F4 to the fundamental level 3H6 in a trivalent ion Tm3 +, whereas the emission at 2 μm and beyond corresponds to the transition between the level 5I7 and the fundamental level 5I8 of the Ho3 + ion. These laser transitions are today the subject of many applications in a wide variety of fields. We have studied the spectroscopic properties of rare earth doped fluoride crystals for emission around 2 μm. From the absorption spectra obtained, the Judd-Ofelt analysis made it possible to calculate the radiative lifetimes as well as the branching ratios in the Tm3 + and Ho3 + ions. In comparison with other crystals such as oxides, the lifetimes of the 3F4 (Tm3 +) and 5I7 (Ho3 +) levels in the fluoride crystals are longer, which favors pulse-mode laser operation. A study on fluorescence dynamics was carried out in order to characterize the emission around 1.9 μm of the Tm3 + ion and that around 2 μm of the Ho3 + ion. The emission spectra obtained have broad bands, fairly structured in the LiYF4 matrix and wider and less structured in the CaF2 matrix. In a second step, by measuring the lifetimes of the 3F4 emitter level for different Tm3 + ion concentrations, we calculated the transfer parameters. The results obtained showed that the process of cross relaxation is much more efficient in the CaF2 crystal than in LiYF4. We also calculated the transfer and inverse transfer coefficients between Tm3 + and Ho3 + ions following excitation of the Tm3 + ion. We have shown that the LiYF4 matrix offers a better transfer efficiency with a view to emission around 2 μm. The laser operation of thin layers in "thin disc" configuration has been studied. A first demonstration of a thin-film LiYF4: Tm laser emitting at 1.9 μm made from an epitaxial layer with LPE was made. In single passge, an output power of 306 mW and a laser efficiency of 36% in absorbed power are reached for a 240 μm thick layer. We have studied a laser oscillator in LiYF4: Tm waveguide in planar geometry. and linear. These guides are characterized by low propagation losses thanks to the quality of the manufacturing process. A maximum power of 470 mW and a yield of 14% in incident power were obtained. A numerical modeling of the optical amplification shows that the guidance of the pump and probe beams makes it possible to achieve significant gains. The model is then adapted for the saturation regime in order to calculate the extraction efficiency and to determine the potential of the LiYF4: Tm3 + guides as an amplifier around 1.9 μm

Multimedia im Wohnzimmer - Dank Linux kann man sich zurücklehnen! Welche Funktionen können Wohnzimmerrechner übernehmen? Welche Anforderungen stellen sie an die Umgebung? Und welche Rolle spielt Linux dabei?

In shared-disk database systems, disk access has to be scheduled properly to avoid unnecessary contention between processors. The first part of this report studies the allocation of intermediate results of join queries (buckets) on disk and derives heuristics to determine the number of processing nodes and disks to employ. Using an analytical model, we show that declustering should be applied even for single buckets to ensure optimal performance. In the second part, we consider the order of reading the buckets and demonstrate the necessity of highly dynamic load balancing to prevent excessive disk contention, especially under skew conditions.

Shared-disk database systems offer a high degree of freedom in the allocation of workload compared to shared-nothing architectures. This creates a great potential for load balancing but also introduces additional complexity into the process of query scheduling. This report surveys the problems and opportunities faced in scan processing in a shared-disk environment. We list the parameters to tune and the decisions to make, as well as some known solutions and commonsense considerations, in order to identify the most promising areas of future research.

An accretion torus is an important astrophysical phenomenon which is be- lieved to account for various features of mass inflow and release of radiation on diverse scales near stellar-mass as well as supermassive black holes. When the stationary torus is perturbed it starts to oscillate and once some part of the torus overflows the closed equipotential surface, defined by the stationary solution, this material is accreted or ejected. These oscillations reveal both spacetime properties and the intrinsic characteristics of the torus model. We study the oscillation and accretion properties of geometrically thick accretion tori using general relativistic magnetohydrodynamic simulations. Assuming axial symmetry these simulations are restricted to 2-D approximation. We discuss the impact of the presence of the large scale magnetic field and the profile of the specific angular momentum on the oscillation properties and on the accretion flow motion. 1

In der folgenden Arbeit soll ein Überblick über den aktuellen Stand der Technik bei 3D-Druckern gegeben werden. Der Fokus liegt dabei auf dem Druck von Softwarevisualisierungen. Hierfür beginnt diese Arbeit mit der Ersteinrichtung eines Druckers und dabei entstehenden Problemen und endet mit einer Werkzeugkette, welche den einfachen Druck der Visualisierungen erlaubt. Die Arbeit zielt darauf ab, die am Lehrstuhl „Softwareentwicklung“ der Universität Leipzig eingesetzten Modelle zu erklären und für den Druck nötige Anpassungen durchzuführen. Die Wahl der verwendeten Software wird jeweils erläutert. Es wird betrachtet, welche Modelle mit welchen Veränderungen druckbar sind. So soll ein Überblick über die Möglichkeiten des 3D-Drucks von Softwaremodellen gegeben werden und die Erstellung, Anpassung und der Druck solcher Modelle in Zukunft vereinfacht werden.