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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

Choosing a Rendering Framework : A Comparative Evaluation of Modern JavaScript Rendering Frameworks

Wernersson, Denni, Sjölund, Viktor January 2023 (has links)
This bachelor thesis explores the rapidly evolving landscape of JavaScript rendering frameworks, comparing and evaluating Next.js, SvelteKit, and Astro. The motivation behind this investigation is to help determine the most suitable rendering framework for contemporary web developers. To address this problem, a two-pronged methodology was employed: firstly, a survey was conducted to gather insights into web developers' usage of rendering frameworks and their opinions on different aspects of the frameworks; secondly, a controlled experiment was carried out by building web applications using the three frameworks to gather data on their performance, capabilities, and developer experience. The results of the study indicate that all three evaluated frameworks are strong options, but each offers unique advantages and drawbacks that must be considered when motivating a decision between them.
182

Dry Stacked Surface Bonded Masonry - Structural Testing and Evaluation

Murray, Eric B. 03 December 2007 (has links) (PDF)
The ENDURA block system is a dry-stack surface-bonded masonry system. Typical masonry construction uses thin-set mortar in the bed joints to provide a bearing surface for the blocks while the ENDURA system typically relies on shims and a surface bonding coat to ensure that the wall is level and plumb and to provide stability. Typical ENDURA block walls are built with the reinforcement placed eccentrically in the walls. Testing was performed on ten walls in order to determine axial capacity. The walls were ten feet high by eight feet wide. Each of the walls was built using a different configuration of block type, reinforcement spacing, and amount of grout. A steel frame with two hydraulic jacks was used to apply vertical load to the top of the walls. Three conclusions were drawn from the axial testing performed. First, typical ENDURA block walls built without thin set mortar in the bed joints have similar axial capacity to walls built with the thin set mortar. Second, walls built with un-reinforced cells grouted resisted significantly more load than walls built with only the reinforced cells grouted. Third, more research is required in order to establish a control and to determine whether the eccentrically placed rebar has a significant effect on the axial capacity of the walls.
183

Carbon dioxide separation by disc stack centrifuge at low CO2 concentration / Koldioxid separaring via staplad disk centrifug vid låg CO2 halt

Correa Zapisotski, David January 2022 (has links)
Medan världen undergår en klimatkris, nya sätt för att mildra den har undersökts till det korta och långa loppet. Koldioxid är ett ämne som uppmärksammats då stora mängder av den släpps ut till atmosfären på grund av förbränningsprocesser. Då detta sker, ett sätt för att mildra klimatomställningen är genom ”Carbon Capture and Storage”, CCS. Det finns redan metoder för att fånga och separera CO2, genom exempelvis roterande packade säng eller vattnade vägg kolumner. Dock har staplade disk centrifug inte undersökts. Denna rapport har undersökt och använt en staplad disk centrifug för just koldioxid separering, genom användning av vatten och NaOH-lösning som absorbenter. Några parametrar har varierats såsom koncentrationen på NaOH-lösningen, luftflödeshastighet och koldioxid koncentration. Resultaten visade att användning av en staplad disk centrifug separerade inte märkvärdiga mängder av CO2. Det hittades däremot förklaringar till detta och det var att den låga halten CO2, de begränsade mätinstrumenten och det experimentella uppställningen som ej gav tid för absorption att ske. / As the world is going through a climate crisis, ways to mitigate it in the short and long term have been investigated. Carbon dioxide is a molecule of importance due to the amounts that are freely emitted into the atmosphere because of combustion processes. Due to this, one way of many, to mitigate climate change is Carbon capture and storage, CCS. There are also consequently several ways to capture and separate CO2 in post combustion processes, such as the use of rotating packed beds or wetted wall columns, however the use of disc stack centrifuges has not been investigated for this application. This paper has investigated and used a disc stack centrifuge for this purpose, by using water and NaOH solution as aerosol absorbents. Some parameters have been varied such as NaOH concentration, air flow speed and carbon dioxide concentration.  Results had shown that the use of a disc stack centrifuge did not yield considerable CO2 separation, however, an explanation for this was found to be due to low CO2 concentration and limited measuring instruments as well as a setup that did not make it possible for absorbent and CO2 to fully react and be efficiently separated.
184

Electrostatic Self-Assembly of Linear and Nonlinear Optical Thin Films

Cooper, Kristie Lenahan 06 May 1999 (has links)
This dissertation demonstrates the feasibility of using novel electrostatic self-assembly (ESA) methods to fabricate linear and nonlinear optical thin films and components. The ESA process involves the layer-by-layer alternate adsorption of anionic and cationic complexes from aqueous solutions. Selection of the molecules in each layer, their orientation at the molecular level, and the order in which the layers are assembled determine the film's bulk optical, electronic, magnetic, thermal, mechanical and other properties. In this work, the capability of nanoscale control over film optical properties allowed the fabrication of complicated refractive index profiles required for linear optical interference filters. The inherent ordered nature of ESA films yielded extremely stable noncentrosymmetric thin films for second-order nonlinear optical applications. The ESA technique offers numerous advantages over conventional thin film fabrication methods and offers great potential in commercial applications such as reflectance and AR filters, EO waveguides and modulators and other optoelectronic devices. The structure of each monolayer in ESA films is dependent on the processing parameters, producing subsequent variations in bulk film properties both intentionally and incidentally. As this method is still in its infancy, variations in ESA processing methods, including process automation, are considered first in this document. These results allowed carefully controlled refractive index experiments and the synthesis of both step and graded index structures, several microns thick. Dielectric stack, Rugate, and antireflection optical interference filters were designed, synthesized and demonstrated. c(2) films of both commercially available polymer dyes and novel polymers designed specifically for the ESA process were demonstrated using second harmonic generation. UV/vis spectroscopy, ellipsometry and atomic force microscopy analysis are presented. / Ph. D.
185

Comparing network coding implementations on different OSI layers / Jacobus Leendert van Wyk

Van Wyk, Jacobus Leendert January 2010 (has links)
Network coding is a technique used to increase the capacity of a network by combining messages sent over the network. The combined messages could be separated by using sufficient original messages which were used to combine the messages. Network coding can be implemented in different layers of the 051 stack, but to date a complete comparison between different implementations of network coding has not been done. The goal of this dissertation is to implement a wireless node model with network coding in the MAC layer and evaluate the performance characteristics of reference networks that implement the new node model. This will serve as the first step of a greater goal, namely finding the most favourable position in the 051 stack to implement network coding. The characteristics of the different implementations of network coding are presented in this dissertation. Simulations were done in OPNET® to find further attributes concerning the implementation of network coding in the MAC layer. The simulation process used is presented and explained, and the results from the simulations are analysed. Network coding in the simulations was implemented opportunistically. The results show that the more often different nodes send frames to the coding node, the better network coding performs. The work contributes to finding the best layer for implementing network coding for its increased throughput. A benchmark network was created so that network coding could be implemented in all the layers of the 051 stack, and then be compared to each other. An implementation of network coding in the MAC layer was simulated and analyzed. We conclude that, because there are so many different purposes for which networks are used, a single instance of network coding is unlikely to be similarly beneficial to all purposes. There still remains work to find the most favourable position for network coding in the 051 stack for all the different types of network coding. / Thesis (M. Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011
186

[en] A SPECIFICATION FOR A JAVA REGISTER-BASED MACHINE / [pt] UMA ESPECIFICAÇÃO DE MÁQUINA DE REGISTRADORES PARA JAVA

GUILHERME CAMPOS HAZAN 21 May 2007 (has links)
[pt] A linguagem Java foi definida tendo como foco a portabilidade. O código gerado pela compilação é interpretado por uma máquina virtual, e não diretamente pelo processador destino, como um programa em C. Este código intermediário, também conhecido como bytecode, é a chave da portabilidade de Java. Os Bytecodes Java usam uma pilha para manipular os operandos das instruções. O uso de pilha tem suas vantagens e desvantagens. Dentre as vantagens, podemos citar a simplicidade da implementação do compilador e da máquina virtual. A principal desvantagem é a redução na velocidade de execução dos programas, devido à necessidade de se mover os operandos para a pilha e retirar dela o resultado, gerando um aumento no número de instruções que devem ser processadas. Diversos estudos indicam que máquinas virtuais baseadas em registradores podem ser mais rápidas que as baseadas em pilha. Decidimos criar uma nova especificação de bytecodes, específicos para máquinas virtuais baseadas em registradores. Esperamos com isso obter um aumento no desempenho das aplicações. / [en] The Java language was created with a focus on portability. The code generated by the compiler is interpreted by a virtual machine, and not directly by the target processor, like programs written in C. This intermediate code, also known as bytecode, is the key to Java's portability. The Java Bytecodes use a stack to manipulate the instruction operands. The use of stack has its their pros and cons. Among the advantages, we can cite the simplicity of implementation of the compiler and virtual machine. On the other hand, there is a speed reduction in the program's execution, due to the need to move the operands to and from the stack, and retrieve results from it, increasing the number of instructions that are processed. Much study has been done that indicating that register-based virtual machines can be faster than the ones based on stacks. Based on this, we decided to create a new bytecode specification, proper for a virtual machine based on registers. By doing this, we hope to obtain an increase in an application's performance.
187

Manufacturing and characterization of single cell intermediate-temperature solid oxide fuel cells for APU in transportation application / Synthèse et caractérisation de cellules pour pile à combustible de type IT-SOFC utilisée en tant que système APU dans les transports

Sivasankaran, Visweshwar 09 July 2014 (has links)
La fabrication de cellules de piles à combustible IT-SOFC de large dimension par un nouveau procédé simple et peu coûteux est présentée dans ce manuscrit. L’optimisation de ce nouveau procédé en regard de l’utilisation d’agents de porosité, d’épaisseur de couches et de température de frittage a été réalisée. Les résultats des tests électrochimiques sur des cellules de surface active 10 cm2 réalisés dans le dispositif Fiaxell semi-ouvert ont été détaillés pour différentes cellules. Des tests de performance de longue durée ont également été menés sur le dispositif Fiaxell, présentés et discutés. La préparation et la réalisation d’un nouveau banc de test de stack a également été mené et présenté dans ces travaux. / The fabrications of large area IT-SOFC planar cell by new simple and cost effective process were explained. The optimization of the new process with respect to pore formers, thickness of layers, sintering temperature were performed. The electrochemical results of 10cm2 performed in Fiaxell open flange set up were detailed with respect to different configuration. Long term ageing performance tests of single cells were conducted in Fiaxell device and results are discussed. Preparation of new test bench and stacking process performed till now were briefed.
188

Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells

Price, Robert January 2018 (has links)
Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
189

Analyse et simulation de mouvements d'atteinte contraints en position et orientation pour un humanoïde de synthèse / Analysis and simulation of human reaching motion with position and rotation constraints for humanoid synthesis

Datas, Adrien 09 July 2013 (has links)
La simulation du geste humain est une thématique de recherche importante et trouve notamment une application dans l'analyse ergonomique pour l'aide à la conception de postes de travail. Le sujet de cette thèse concerne la génération automatique de tâches d'atteinte dans le plan horizontal pour un humanoïde. Ces dernières, à partir d'un objectif exprimé dans l'espace de la tâche, requièrent une coordination de l'ensemble des liaisons. L'une des principales difficultés rencontrées lors de la simulation de gestes réalistes est liée à la redondance naturelle de l'humain. Notre démarche est focalisée principalement sur deux aspects : - le mouvement de la main dans l'espace opérationnel (trajectoire spatiale et profil temporel), - la coordination des différentes sous-chaînes cinématiques. Afin de caractériser le mouvement humain, nous avons mené une campagne de capture de mouvements pour des gestes d'atteinte contraignant la position et l'orientation de la main dans le plan horizontal. Ces acquisitions nous ont permis de connaître l'évolution spatiale et temporelle de la main dans l'espace de la tâche, en translation et en rotation. Ces données acquises couplées à une méthode de rejeu ont également permis d'analyser les relations intrinsèques qui lient l'espace de la tâche à l'espace articulaire du mannequin. Le schéma de génération automatique de mouvements réalistes est basé sur une pile de tâche avec une approche cinématique. L'hypothèse retenue pour simuler le geste est de suivre le chemin le plus court dans l'espace de la tâche tout en bornant le coût dans l'espace articulaire. Un ensemble de paramètres permet de régler le schéma. Il en résulte une cartographie de réglages qui permet de simuler une classe de mouvements réalistes. Enfin, ce schéma de génération automatique de mouvements réalistes est validé par une comparaison quantitative et qualitative entre la simulation et le geste humain. / The simulation of human movement is an active theme of research, particularly in ergonomic analysis to aid in the design of workstations. The aim of this thesis concerns the automatic generation of reaching tasks in the horizontal plane for a virtual humanoid. An objective expressed in the task space, requires coordination of all joints of the mannequin. The main difficulties encountered in the simulation of realistic movements is related to the natural redundancy of the human. Our approach is focused mainly on two aspects: - Motion of the hand's operator in the task space (spatial and temporal aspect), - Coordination of all kinematic chains. To characterize human movement, we conducted a set of motion capture with position and orientation constraints of the hand in the horizontal plane. These acquisitions allowed to know the spatial and temporal evolution of the hand in the task space, for translation and rotation aspects. These acquired data were coupled with a playback method to analyze the intrinsic relations that link the task space to joint space of the model. The automatic generation scheme of realistic motion is based on a stack of task with a kinematic approach. The assumption used to simulate the action is to follow the shortest path in the task space while limiting the cost in the joint space. The scheme is characterized by a set of parameters. A global map of parameter adjustment enables the simulation of a class of realistic movements. Finally, this scheme is validated quantitatively and qualitatively with comparison between the simulation and the human gesture.
190

A Portable Generator Incorporating Mini-Tubular Solid Oxide Fuel Cells

Hyde, Andrew Justin January 2008 (has links)
Modern society has become reliant on battery powered electronic devices such as cell phones and laptop computers. The standard way of recharging these devices is by connecting to a reticulated electricity supply. In situations with no electricity supply some other recharging method is required. Such a possibility is a small, portable, generator based on fuel cell technology, specifically mini-tubular solid oxide fuel cells (MT-SOFC). MT-SOFCs have been developed since the 1990s but there is limited analysis, discussion or research on developing and constructing a portable generator based on MT-SOFC technology. Such a generator, running on a portable gas supply, requires combining the key aspects of cell performance, a heating and fuel reforming system, and cell manifolds. Cell design, fuel type, fuel flow rate, current-collection method and operating temperature all greatly affected MT-SOFCs performance. Segmenting the cathode significantly increased the power output. Maximum power density from an electrolyte supported MT-SOFC was 140 mW/cm2. The partial oxidation reactor (POR) developed provided the required heat to maintain the MT-SOFCs at an operating temperature suitable for generating electricity. The exhaust gas from the POR was a suitable fuel for MT-SOFCs, having sufficient carbon monoxide and hydrogen to generate electricity. Various manifold materials were evaluated including solid metal blocks and folded sheet metal. It was found that manifolds made from easily worked alumina fibre board decreased the thermal stresses and therefore the fracture rate of the MT-SOFCs. The final prototype developed comprised a partial oxidation reactor and MT-SOFCs mounted in alumina fibre board manifolds within a well-insulated enclosure, which could be run on LPG. Calculated efficiency of the final prototype was 4%. If all the carbon monoxide and hydrogen produced by the partial oxidation reactor were converted to electrical energy, efficiency would increase to 39%. Under ideal conditions, efficiency would be 78%. Efficiency of the prototype can be improved by increasing the fuel and oxygen utilisation ratios, ensuring heat from the exhaust gases is transferred to the incoming gases, and improving the methods for collecting current at both the anode and cathode.

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