Transport demand planning in South Africa is a neglected field of study, using obsolete methods to model an extremely complex, dynamic system composed of an eclectic mix of First and Third World transport technologies, infrastructure and economic participants. We identify agent-based simulation as a viable modelling paradigm capable of capturing the effects emerging from the complex interactions within the South African transport system, and proceed to implement the Multi-Agent Transport Simulation Toolkit (MATSim) for South Africa's economically important Gauteng province. This report describes the procedure followed to transform household travel survey, census and Geographic Information System (GIS) data into an activity-based transport demand description, executed on network graphs derived from GIS shape files. We investigate the influence of network resolution on solution quality and simulation time, by preparing a full network representation and a small version, containing no street-level links. Then we compare the accuracy of our data-derived transport demand with a lower bound solution. Finally the simulation is tested for repeatability and convergence. Comparisons of simulated versus actual traffic counts on important road network links during the morning and afternoon rush hour peaks show a minimum mean relative error of less than 40%. Using the same metric, the small network differs from the full representation by a maximum of 2% during the morning peak hour, but the full network requires three times as much memory to execute, and takes 5.2 times longer to perform a single iteration. Our census- and travel survey-derived demand performs significantly better than uniformly distributed random pairings of home- and work locations, which we took to be analogous to a lower bound solution. The smallest difference in corresponding mean relative error between the two cases comes to more than 50%. We introduce a new counts ratio error metric that removes the bias present in traditional counts comparison error metrics. The new metric shows that the spread (standard deviation) of counts comparison values for the random demand is twice to three times as large as that of our reference case. The simulation proves highly repeatable for different seed values of the pseudo-random number generator. An extended simulation run reveals that full systematic relaxation requires 400 iterations. Departure time histograms show how agents 'learn' to gradually load the network while still complying with activity constraints. The initial implementation has already sparked further research. Current priorities are improving activity assignment, incorporating commercial traffic and public transport, and the development and implementation of the minibus taxi para-transit mode. Copyright / Dissertation (MEng)--University of Pretoria, 2009. / Industrial and Systems Engineering / unrestricted

<div>With the transistor dimensions scaling down to a few atoms, quantum phenomena - like quantum tunneling and entanglement - will dictate the operation and performance of the next generation of electronic devices, post-CMOS era. While quantum tunneling limits the scaling of the conventional transistor, Tunneling Field Effect Transistor (TFET) employs band-to-band tunneling for the device operation. This mechanism can reduce the sub-threshold swing (S.S.) beyond the Boltzmann's limit, which is fundamentally limited to 60 mV/dec in a conventional Si-based metal-oxide-semiconductor field-effect transistor (MOSFET). A smaller S.S. ensures TFET operation at a lower supply voltage and, therefore, at lesser power compared to the conventional Si-based MOSFET.</div><div><br></div><div>However, the low transmission probability of the band-to-band tunneling mechanism limits the ON-current of a TFET. This can be improved by reducing the body thickness of the devices i.e., using 2-Dimensional (2D) materials or by utilizing heterojunction designs. In this thesis, two promising methods are proposed to increase the ON-current; one for the 2D material TFETs, and another for the III-V heterojunction TFETs.</div><div><br></div><div>Maximizing the ON-current in a 2D material TFET by determining an optimum channel thickness, using compact models, is presented. A compact model is derived from rigorous atomistic quantum transport simulations. A new doping profile is proposed for the III-V triple heterojunction TFET to achieve a high ON-current. The optimized ON-current is 325 uA/um at a supply voltage of 0.3 V. The device design is optimized by atomistic quantum transport simulations for a body thickness of 12 nm, which is experimentally feasible.</div><div> </div><div>However, increasing the device's body thickness increases the atomistic quantum transport simulation time. The simulation of a device with a body thickness of over 12 nm is computationally intensive. Therefore, approximate methods like the mode-space approach are employed to reduce the simulation time. In this thesis, the development of the mode-space approximation in modeling the triple heterojunction TFET is also documented.</div><div><br></div><div>In addition to the TFETs, quantum computing is an emerging field that utilizes quantum phenomena to facilitate information processing. An extra chapter is devoted to the electronic structure calculations of the Si:P delta-doped layer, using the empirical tight-binding method. The calculations agree with angle-resolved photoemission spectroscopy (ARPES) measurements. The Si:P delta-doped layer is extensively used as contacts in the Phosphorus donor-based quantum computing systems. Understanding its electronic structure paves the way towards the scaling of Phosphorus donor-based quantum computing devices in the future.</div>

Photorealistic rendering has a wide variety of applications, and so there are many rendering algorithms and their variations tailored for specific use cases. Even though practically all of them do physically-based simulations of light transport, their results on the same scene are often different - sometimes because of the nature of a given algorithm or in a worse case because of bugs in their implementation. It is difficult to compare these algorithms, especially across different rendering frameworks, because there is not any standardized testing software or dataset available. Therefore, the only way to get an unbiased comparison of algorithms is to create and use your dataset or reimplement the algorithms in one rendering framework of choice, but both solutions can be difficult and time-consuming. We address these problems with our test suite based on a rigorously defined methodology of evaluation of light transport algorithms. We present a scripting framework for automated testing and fast comparison of rendering results and provide a documented set of non-volumetric test scenes for most popular research-oriented render- ing frameworks. Our test suite is easily extensible to support additional renderers and scenes. 1

Autonomous and integrated passenger and freight transport (APFIT) is a promising approach to tackle both, traffic and last-mile-related issues such as environmental emissions, social and spatial conflicts or operational inefficiencies. By conducting an agent-based simulation, we shed light on this widely unexplored research topic and provide first indications regarding influential target figures of such a system in the rural area of Sarstedt, Germany. Our results show that larger fleets entail inefficiencies due to suboptimal utilization of monetary and material resources and increase traffic volume while higher amounts of unused vehicles may exacerbate spatial conflicts. Nevertheless, to fit the given demand within our study area, a comparatively large fleet of about 25 vehicles is necessary to provide reliable service, assuming maximum passenger waiting times of six minutes to the expense of higher standby times, rebalancing effort, and higher costs for vehicle acquisition and maintenance.

Ce mémoire décrit un cadre pour l'élaboration et l'évaluation de politiques de pilotage des réseaux de création de valeur de l'industrie des produits forestiers. Il permet de déterminer la combinaison optimale de politiques de niveau tactique (production et distribution) et de politiques au niveau de l'exécution. Le cadre s’appuie, d’abord, sur le logiciel LogiLab qui permet de modéliser le réseau de l'industrie des produits forestiers et d'effectuer une optimisation mathématique afin de proposer un plan agrégé de production et de distribution. À partir de ce plan, on extrait des politiques de gestion des flux de production et de transport qui guideront au jour le jour les opérations au niveau opérationnel. Ensuite, les décideurs pourront proposer des politiques d'exécution (par exemple: règles à utiliser pour le chargement des camions). La combinaison de ces politiques est évaluée en utilisant un modèle de simulation à événements discrets, en utilisant le logiciel de simulation SIMIO, qui permet d'évaluer dans le détail ce que serait l'impact de la mise en œuvre de ces politiques.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta dissertação propomos a utilização do método espectro-nodal SGF, cf. spectral Greens function, para transporte SN de partículas neutras, para determinarmos os fluxos angulares nas interfaces das regiões homogêneas do domínio espacial heterogêneo, com espalhamento linearmente anisotrópico usando preferencialmente altas ordens de quadraturas angulares. As reconstruções espaciais analíticas dos fluxos angulares são feitas no interior das regiões homogêneas, determinando as constantes arbitrárias da solução analítica local das equações SN no interior dos nodos espaciais da grade de dicretização. A seguir, utilizando essas constantes, determinamos as expressões do fluxo escalar e da corrente de nêutrons, que são substituídas na equação de transporte unidimensional em geometria retangular Cartesiana no termo de fonte por espalhamento linearmente anisotrópico. Resolvemos analiticamente a equação de transporte com os termos do fluxo escalar e corrente de nêutrons assim aproximados para estimarmos o perfil do fluxo angular de nêutrons no domínio. Esta reconstrução analítica aproximada da solução da equação de transporte de partículas neutras em geometria unidimensional Cartesiana constitui um problema inverso, na medida em que a partir da solução nodal de malha grossa fazemos primeiramente uma reconstrução analítica espacial do fluxo angular nas direções das ordenadas discretas, para em seguida procedermos à reconstrução analítica aproximada do fluxo no domínio angular. / We describe the application of the spectral Greens function SN nodal method for one-speed neutral particle transport calculations to determine the angular fluxes at the homogeneized regions within heterogeneous domains, for linearly anisotropic scattering, using preferably high-order angular quadratures. The reconstruction scheme in the space variable of the angular flux is carried out within the homogenized regions using uniform spatial grid. We determine the arbitrary constants of the analytical SN general solution inside each spatial node. Then, we determine the SN expression for the scalar flux and total current that we substitute into the analytical slab-geometry transport equation, precisely into its linearly anisotropic scattering source term. Further, we solve analytically the slab-geometry transport equation, so approximated, to obtain the flux profile within the space and angular domains. This approximate analytical reconstruction scheme of the solution of the neutral particle transport equation in slab geometry is an inverse problem, in the sense that we use accurate coarse-mesh SN numerical solution, to recover the SN analytical solution in the space variable, and then reconstruct the solution approximately in the angular domain.

Nesta tese mostraremos uma aplicação do método SGF, cf., spectral Greens function, para gerar fluxos angulares nas interfaces dos nodos na formulação de ordenadas discretas (SN) para equação de transporte de partículas neutras em geometria cartesiana unidimensional e a uma velocidade, usando quadraturas de alta ordem. Utilizando o método de malha grossa SGF, primeiramente determinamos as constantes arbitrárias da solução geral analítica das equações SN em cada nodo espacial. Então usamos a fórmula de quadratura angular para estimar uma expressão para o fluxo escalar de nêutrons e substituímos no termo de fonte de espalhamento isotrópico na equação de transporte. Resolvemos analiticamente a equação unidimensional de transporte de nêutrons com a fonte de espalhamento aproximada desta maneira e geramos os valores para o fluxo angular no interior de cada nodo espacial. Como o método SGF gera soluções numéricas de malha grossa completamente livres de erro de truncamento espacial, esperamos que o esquema de reconstrução analítica proposto tenha alta precisão para os fluxos angulares, considerando as condições de continuidade nas interfaces dos nodos do domínio espacial. Esta técnica caracteriza um problema inverso, pois a partir da solução de malha grossa do método SGF, podemos reconstruir o fluxo angular de nêutrons em qualquer ponto do domínio. / We offer in this work an application of the SGF method, cf., spectral Greens function, to generate the angular fluxes at the region interfaces of multilayer slabs, using high-order angular quadrature sets in the one-speed discrete ordinates (SN) formulation of the neutral particle transport equation. Using the SGF coarse-mesh numerical solution, we first determine the arbitrary constants of the analytical general solution of the SN equations within each spatial node. Then, we use the angular quadrature formula to estimate the expression of the scalar flux distribution, that we substitute into the isotropic scattering source term of the transport equation. We solve analytically the slab-geometry transport equation, with the scattering source so approximated, in order to generate the angular flux profile within each spatial node. As the SGF method generates coarse-mesh numerical solution, which is completely free from spatial truncation errors, we expect that the offered approximate analytical reconstruction scheme be accurate enough for the localized angular flux distribution, considering the node interface continuity conditions within the domain. This technique is thought of as an inverse problem since from the SGF coarse-mesh nodal solution we are able to reconstruct the angular flux profile at any point inside the domain.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta dissertação propomos a utilização do método espectro-nodal SGF, cf. spectral Greens function, para transporte SN de partículas neutras, para determinarmos os fluxos angulares nas interfaces das regiões homogêneas do domínio espacial heterogêneo, com espalhamento linearmente anisotrópico usando preferencialmente altas ordens de quadraturas angulares. As reconstruções espaciais analíticas dos fluxos angulares são feitas no interior das regiões homogêneas, determinando as constantes arbitrárias da solução analítica local das equações SN no interior dos nodos espaciais da grade de dicretização. A seguir, utilizando essas constantes, determinamos as expressões do fluxo escalar e da corrente de nêutrons, que são substituídas na equação de transporte unidimensional em geometria retangular Cartesiana no termo de fonte por espalhamento linearmente anisotrópico. Resolvemos analiticamente a equação de transporte com os termos do fluxo escalar e corrente de nêutrons assim aproximados para estimarmos o perfil do fluxo angular de nêutrons no domínio. Esta reconstrução analítica aproximada da solução da equação de transporte de partículas neutras em geometria unidimensional Cartesiana constitui um problema inverso, na medida em que a partir da solução nodal de malha grossa fazemos primeiramente uma reconstrução analítica espacial do fluxo angular nas direções das ordenadas discretas, para em seguida procedermos à reconstrução analítica aproximada do fluxo no domínio angular. / We describe the application of the spectral Greens function SN nodal method for one-speed neutral particle transport calculations to determine the angular fluxes at the homogeneized regions within heterogeneous domains, for linearly anisotropic scattering, using preferably high-order angular quadratures. The reconstruction scheme in the space variable of the angular flux is carried out within the homogenized regions using uniform spatial grid. We determine the arbitrary constants of the analytical SN general solution inside each spatial node. Then, we determine the SN expression for the scalar flux and total current that we substitute into the analytical slab-geometry transport equation, precisely into its linearly anisotropic scattering source term. Further, we solve analytically the slab-geometry transport equation, so approximated, to obtain the flux profile within the space and angular domains. This approximate analytical reconstruction scheme of the solution of the neutral particle transport equation in slab geometry is an inverse problem, in the sense that we use accurate coarse-mesh SN numerical solution, to recover the SN analytical solution in the space variable, and then reconstruct the solution approximately in the angular domain.

Nesta tese mostraremos uma aplicação do método SGF, cf., spectral Greens function, para gerar fluxos angulares nas interfaces dos nodos na formulação de ordenadas discretas (SN) para equação de transporte de partículas neutras em geometria cartesiana unidimensional e a uma velocidade, usando quadraturas de alta ordem. Utilizando o método de malha grossa SGF, primeiramente determinamos as constantes arbitrárias da solução geral analítica das equações SN em cada nodo espacial. Então usamos a fórmula de quadratura angular para estimar uma expressão para o fluxo escalar de nêutrons e substituímos no termo de fonte de espalhamento isotrópico na equação de transporte. Resolvemos analiticamente a equação unidimensional de transporte de nêutrons com a fonte de espalhamento aproximada desta maneira e geramos os valores para o fluxo angular no interior de cada nodo espacial. Como o método SGF gera soluções numéricas de malha grossa completamente livres de erro de truncamento espacial, esperamos que o esquema de reconstrução analítica proposto tenha alta precisão para os fluxos angulares, considerando as condições de continuidade nas interfaces dos nodos do domínio espacial. Esta técnica caracteriza um problema inverso, pois a partir da solução de malha grossa do método SGF, podemos reconstruir o fluxo angular de nêutrons em qualquer ponto do domínio. / We offer in this work an application of the SGF method, cf., spectral Greens function, to generate the angular fluxes at the region interfaces of multilayer slabs, using high-order angular quadrature sets in the one-speed discrete ordinates (SN) formulation of the neutral particle transport equation. Using the SGF coarse-mesh numerical solution, we first determine the arbitrary constants of the analytical general solution of the SN equations within each spatial node. Then, we use the angular quadrature formula to estimate the expression of the scalar flux distribution, that we substitute into the isotropic scattering source term of the transport equation. We solve analytically the slab-geometry transport equation, with the scattering source so approximated, in order to generate the angular flux profile within each spatial node. As the SGF method generates coarse-mesh numerical solution, which is completely free from spatial truncation errors, we expect that the offered approximate analytical reconstruction scheme be accurate enough for the localized angular flux distribution, considering the node interface continuity conditions within the domain. This technique is thought of as an inverse problem since from the SGF coarse-mesh nodal solution we are able to reconstruct the angular flux profile at any point inside the domain.

Das Simulationsprogramm Delphin ermöglicht die Berechnung des gekoppelten Wärme-, Feuchte-, Luft- und Stofftransports in kapillarporösen Materialien. Die Simulation verwendet ein numerisches Lösungsverfahren für die Differentialgleichungen welche die Transportprozesse beschreiben. Zur Kontrolle der numerischen Fehler sowie der korrekten Implementierung der physikalischen Gleichungen werden Validierungsrechnungen durchgeführt. Dafür werden vordefinierte Testfälle eingegeben, gerechnet und mit Referenzlösungen bzw. den Ergebnissen anderer Simulationsprogramme verglichen. In diesem Artikel werden die Ergebnisse der Validierung der Delphin Versionen 5.6, 5.8, 6.0 und 6.1 zusammengefasst. Es wurden folgende Testfälle gerechnet: HAMSTAD Benchmarks 1 bis 5, DIN EN ISO 10211 Fall 1 und 2, DIN EN 15026 und der Aufsaug-Trocknungs-Test. Die Validierung von Delphin erfolgte hinsichtlich des Wärme-, Feuchte- und Lufttransports bei ein- und zweidimensionalen Problemstellungen. Alle Programmversionen erfüllen die Anforderungen aller Testfälle.