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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.
1

Investigating ionospheric scintillation mechanisms via theory and experimentation

Burston, Robert January 2009 (has links)
This thesis aims to answer the question, “What physical process dominates the formation of plasma irregularities, capable of directly or indirectly causing GPS L1 band scintillation, in polar cap plasma patches during magnetic storm conditions?.” A novel modelling technique utilising an ionospheric imaging algorithm is developed and used to elucidate the relative importance of the two most commonly discussed processes. These are the Gradient Drift Instability (GDI) and turbulence induced by electric field mapping to the ionosphere from the magnetosphere. The results show that in magnetic storm conditions, at times the GDI process is dominant, but that at other times turbulence may be as significant as the GDI in determining how the plasma within a polar cap patch behaves, possibly more so. This in turn suggests that further study of the turbulence process is necessary in order to fully understand how big a role it plays in causing GPS L1 band scintillation in the polar cap. The success of the modelling technique developed here shows the utility of ionospheric imaging as a tool for understanding physical problems of the ionosphere; efforts to improve it and to apply it in other contexts would be worthwhile.
2

Liquid fuel spray characteristics

Savic, Sasha January 2000 (has links)
No description available.
3

Ist-Analyse des Geoinformationswesens im Freistaat Sachsen

Müller, Andre 07 September 2007 (has links) (PDF)
Der Wandel der Industriegesellschaften von gestern hin zu Informationsgesellschaften ist allgemein bekannt. Die Anwendung moderner Kommunikationsmittel und neuer Technologien gehören bereits zum Alltag. Die Wichtigkeit von Geoinformationen als Wirtschaftsgut und Informationsressource ist in Politik und Gesellschaft ebenfalls angekommen. Das Geoinformationswesens stellt einen wachsenden Markt dar, der die Zukunft von Arbeit und Wohlstand zukünftig mit sichern kann. Der Aufbau der Geodateninfrastruktur im Freistaat Sachsen befindet sich noch am Anfang. Trotzdem sind bereits viele Aktivitäten im IT-Bereich durch eGovernment Projekte erfolgreich umgesetzt worden. Auch eine Vielzahl an Bestrebungen auf kommunaler Ebene haben den Prozess weiter voran gebracht. Durch die Gründung der gdi.initiative.sachsen ist eine weitere positive Entwicklung beim Aufbau der Geodateninfrastruktur in Sachsen möglich. Dem Hauptziel des einfachen Zugangs zu Geodaten und einem transparenten Geoinformationswesen kommt man schrittweise näher. Die Diplomarbeit gibt einen Überblick über das Geoinformationswesen und die vorhandenen Aktivitäten in Sachsen. Eine so umfassende Betrachtung des gesamten Bereiches lag bisher noch nicht vor. Die in der Aufgabenstellung geforderte detaillierte Datenerhebung konnte aufgrund des begrenzten, zeitlichen Umfangs nicht durchgeführt werden. Für diese ausstehende umfangreiche Ist-Erhebung beschreibt die Arbeit anzuwendende Methoden und nutzbare Datenquellen. Die Erstellung eines Portals des Geoinformationswesens in Sachsen und die Einbindung vorhandener Komponenten als Grundlage für eine umfassende Analyse sollte dabei Ziel sein. Die Diplomarbeit stellt somit die Diskussionsgrundlage für die weiteren Aktivitäten dar. Ein besonderes Augenmerk wurde auch auf vergleichbare Erhebungen anderer Bundesländer gelegt. Aus den Ergebnissen lassen sich Ziele und Thesen für die Untersuchungen im Freistaat Sachsen ableiten. Da eine detaillierte Ist-Analyse eine enge Kommunikation aller Akteure erfordert, würde automatisch der Aufbau einer Geodateninfrastruktur in Sachsen beflügelt. Darüber hinaus könnte die viel geforderte Transparenz des Geoinformationswesens und der Verwaltung Wirklichkeit werden. Die technischen und organisatorischen Voraussetzungen sind weitestgehend geschaffen, sodass dem erfolgreichen Aufbau einer Geodateninfrastruktur im Prinzip nichts entgegensteht.
4

Exhaust Temperature Modeling and Optimal Control of Catalytic Converter Heating

Petersson, Victor January 2019 (has links)
After reaching its light-off temperature, the catalytic aftertreatment system plays a major part in maintaining emissions at low levels for vehicles equipped with combustion engines. In this thesis, modelling of the exhaust gas temperature is investigated along with optimal control strategy for variable ignition and exhaust valve opening angles for optimal catalytic converter heating. Models for exhaust gas temperature and mass flow are presented and validated against measurement data. According to the model validation, the proposed models capture variations in ignition and exhaust valve opening angles well. Optimal control strategy for the ignition and exhaust valve opening angles to heat the catalytic converter to a predetermined temperature in the most fuel and time optimal ways are investigated by implementation of the validated models. Optimal control analysis indicates that with open wastegate, the heating time for the catalytic converter can be reduced by up to 16.4 % and the accumulated fuel to reach the desired temperature can be reduced by up to 4.6 %, compared to the case with ignition and exhaust valve opening angles fixed at nominal values. With closed wastegate the corresponding figures are 16.4 % and 4.7 %. By also including control of the variable λ-value, the heating time can be further reduced by up to 19.8 %, and the accumulated fuel consumption by up to 9.5 % with open wastegate. With closed wastegate the corresponding figures are 20.1 % decrease in heating time, and 9.8 % decrease in accumulated fuel consumption.
5

Numerical studies of gasoline direct injection engine processes

Beavis, Nicholas J. January 2017 (has links)
The GDI engine has a number of practical advantages over the more traditional port-fuel injection strategy, however a number of challenges remain the subject of continued research in an attempt to fully exploit the advantages of the GDI engine. These include complex in-cylinder flow fields and fuel-air mixing strategies, and significant temporal variation, both through an engine cycle and on a cycle-by-cycle basis. Despite advances in experimental techniques, the relative difficulty and cost of taking detailed measurements remains high, thus computational techniques are an integral part of research activities. The research work presented in this thesis has focused on the use of detailed 3D-CFD techniques for investigating physical phenomena of the in-cylinder flow field and fuel injection process in a single cylinder GDI engine with early injection event. A detailed validation of the numerical predictions of the in-cylinder flow field using both the RANS RNG k-ε turbulence model and the Smagorinsky LES SGS turbulence model was completed with both models showing good agreement against available experimental results. A detailed validation of the numerical predictions of the fuel injection process using a Lagrangian DDM and both RANS RNG k-ε turbulence model and Smagorinsky LES SGS turbulence model was completed with both models showing excellent agreement against experimental data. The model was then used to investigate the in-cylinder flow field and fuel injection process including research into: the three dimensional nature of the flow field; intake valve jet flapping, characterisation, causality and CCV, and whether it could account for CCV of the mixture field at spark timing; the anisotropic characteristics of the flow field using both the fluctuating velocity and turbulence intensity, including the increase in anisotropy due to the fuel injection event; the use of POD for quantitatively analysing the in-cylinder flow field; investigations into the intake valve, cylinder liner and piston crown spray plume impingement processes, including the use of a multi-component fuel surrogate and CCV of the formed liquid film; characterisation and CCV of the mixture field though the intake and compression strokes up to spark timing. Finally, the predicted turbulence characteristics were used to evaluate the resultant premixed turbulent combustion event using combustion regime diagrams.
6

dotNet som multimediaplattform / dotNet as a multimediaplatform

Johansson, Glenn January 2008 (has links)
<p>As the speed and complexity of computers have increased so have software and the expectations of users. Software development follows a straightforward evolution where complicated tasks are made easier by better tools; this repeats itself as those tasks in turn are automated.</p><p>Software mechanics that were seen as revolutionary a decade ago are seen as obvious requirements that no multimedia application can be without.</p><p>dotNet is the next step in line and makes it easier and faster to build software.</p><p>This report focuses on the development of a multimedia platform developed in dotNet. It does this by developing the tools and framework from which a complete game can be built.</p><p>A game is selected because it combines the most aspects of multimedia development, such as interaction, graphics, sound & music. The report goes further by describing why the game looks like it does as well as the mechanics of the game and the benefits of the dotNet platform.</p> / <p>Allteftersom hastigheten och komplexiteten hos datorer har ökat så har också användarens förväntningar ökat. Mjukvaruutveckling följer en klar linje där problem görs enklare genom bättre verktyg och automatisering. Denna cykel repeterar sig själv, vilket i sin tur för nivån uppåt som programmerare arbetar på.</p><p>Attribut som för ett årtionde sedan var revolutionerande är idag en självklarhet som ingen multimediaplattform skulle klara sig utan. dotNet är nästa steg av verktyg och lösningar som gör det snabbare och enklare att utveckla mjukvara.</p><p>Denna rapport fokuserar på utvecklingen av en multimediaplattform gjord med dotNet och vad för attribut som gör en sådan plattform bra eller dålig. Rapporten åstadkommer detta genom att följa utvecklingen av ett ramverk som kan användas för att skapa ett komplett spel.</p><p>Utvecklingen av ett spel väljs på grund av de många multimedia-aspekter som går att återfinna, exempelvis interaktion, grafik, ljud & musik. Rapporten utvecklar på detta genom att beskriva de attribut som gör ett bra spel samt interaktion och fördelarna dotNet fört med sig.</p>
7

dotNet som multimediaplattform / dotNet as a multimediaplatform

Johansson, Glenn January 2008 (has links)
As the speed and complexity of computers have increased so have software and the expectations of users. Software development follows a straightforward evolution where complicated tasks are made easier by better tools; this repeats itself as those tasks in turn are automated. Software mechanics that were seen as revolutionary a decade ago are seen as obvious requirements that no multimedia application can be without. dotNet is the next step in line and makes it easier and faster to build software. This report focuses on the development of a multimedia platform developed in dotNet. It does this by developing the tools and framework from which a complete game can be built. A game is selected because it combines the most aspects of multimedia development, such as interaction, graphics, sound &amp; music. The report goes further by describing why the game looks like it does as well as the mechanics of the game and the benefits of the dotNet platform. / Allteftersom hastigheten och komplexiteten hos datorer har ökat så har också användarens förväntningar ökat. Mjukvaruutveckling följer en klar linje där problem görs enklare genom bättre verktyg och automatisering. Denna cykel repeterar sig själv, vilket i sin tur för nivån uppåt som programmerare arbetar på. Attribut som för ett årtionde sedan var revolutionerande är idag en självklarhet som ingen multimediaplattform skulle klara sig utan. dotNet är nästa steg av verktyg och lösningar som gör det snabbare och enklare att utveckla mjukvara. Denna rapport fokuserar på utvecklingen av en multimediaplattform gjord med dotNet och vad för attribut som gör en sådan plattform bra eller dålig. Rapporten åstadkommer detta genom att följa utvecklingen av ett ramverk som kan användas för att skapa ett komplett spel. Utvecklingen av ett spel väljs på grund av de många multimedia-aspekter som går att återfinna, exempelvis interaktion, grafik, ljud &amp; musik. Rapporten utvecklar på detta genom att beskriva de attribut som gör ett bra spel samt interaktion och fördelarna dotNet fört med sig.
8

Ist-Analyse des Geoinformationswesens im Freistaat Sachsen

Müller, Andre 28 August 2007 (has links)
Der Wandel der Industriegesellschaften von gestern hin zu Informationsgesellschaften ist allgemein bekannt. Die Anwendung moderner Kommunikationsmittel und neuer Technologien gehören bereits zum Alltag. Die Wichtigkeit von Geoinformationen als Wirtschaftsgut und Informationsressource ist in Politik und Gesellschaft ebenfalls angekommen. Das Geoinformationswesens stellt einen wachsenden Markt dar, der die Zukunft von Arbeit und Wohlstand zukünftig mit sichern kann. Der Aufbau der Geodateninfrastruktur im Freistaat Sachsen befindet sich noch am Anfang. Trotzdem sind bereits viele Aktivitäten im IT-Bereich durch eGovernment Projekte erfolgreich umgesetzt worden. Auch eine Vielzahl an Bestrebungen auf kommunaler Ebene haben den Prozess weiter voran gebracht. Durch die Gründung der gdi.initiative.sachsen ist eine weitere positive Entwicklung beim Aufbau der Geodateninfrastruktur in Sachsen möglich. Dem Hauptziel des einfachen Zugangs zu Geodaten und einem transparenten Geoinformationswesen kommt man schrittweise näher. Die Diplomarbeit gibt einen Überblick über das Geoinformationswesen und die vorhandenen Aktivitäten in Sachsen. Eine so umfassende Betrachtung des gesamten Bereiches lag bisher noch nicht vor. Die in der Aufgabenstellung geforderte detaillierte Datenerhebung konnte aufgrund des begrenzten, zeitlichen Umfangs nicht durchgeführt werden. Für diese ausstehende umfangreiche Ist-Erhebung beschreibt die Arbeit anzuwendende Methoden und nutzbare Datenquellen. Die Erstellung eines Portals des Geoinformationswesens in Sachsen und die Einbindung vorhandener Komponenten als Grundlage für eine umfassende Analyse sollte dabei Ziel sein. Die Diplomarbeit stellt somit die Diskussionsgrundlage für die weiteren Aktivitäten dar. Ein besonderes Augenmerk wurde auch auf vergleichbare Erhebungen anderer Bundesländer gelegt. Aus den Ergebnissen lassen sich Ziele und Thesen für die Untersuchungen im Freistaat Sachsen ableiten. Da eine detaillierte Ist-Analyse eine enge Kommunikation aller Akteure erfordert, würde automatisch der Aufbau einer Geodateninfrastruktur in Sachsen beflügelt. Darüber hinaus könnte die viel geforderte Transparenz des Geoinformationswesens und der Verwaltung Wirklichkeit werden. Die technischen und organisatorischen Voraussetzungen sind weitestgehend geschaffen, sodass dem erfolgreichen Aufbau einer Geodateninfrastruktur im Prinzip nichts entgegensteht.
9

Negative Feedback and Competition in the Yeast Polarity Establishment Circuit

Wu, Chi-Fang January 2013 (has links)
<p>Many cells spontaneously establish a polarity axis even in the absence of directional cues, a process called symmetry breaking. A central question concerns how cells polarize towards one, and only one, randomly oriented "front". The conserved Rhotype GTPase Cdc42p is an essential factor for both directed and spontaneous polarization in various organisms, whose local activation is thought to define the cell's front. We previously proposed that in yeast cells, a small stochastic cluster of GTP-Cdc42p at a random site on the cortex can grow into a large, dominating cluster via a positive feedback loop involving the scaffold protein Bem1p. As stochastic Cdc42p clusters could presumably arise at many sites, why does only one site become the dominating "front"? We speculated that competition between growing clusters for limiting factors would lead to growth of a single winning "front" at the expense of the others. Utilizing time-lapse imaging with high spatiotemporal resolution, we now document initiation of multiple polarized clusters that competed rapidly to resolve a winning cluster. Such multicluster intermediates are observed in wild-type yeast cells with functional directional cues, but the locations where they are initiated are biased by the spatial cues. In addition, we detected an unexpected oscillatory polarization in a majority of the cells breaking symmetry, in which polarity factors initially concentrated very brightly and then dimmed in an oscillatory manner, dampening down to a final intermediate level after 2-3 peaks. Dampened oscillation suggests that the polarity circuit contains an in-built negative feedback loop. Mathematical modeling predicts that negative feedback would confer robustness to the polarity circuit and make the kinetics of competition between polarity factor clusters relatively insensitive to polarity factor concentration.</p><p>We are trying to understand how competition between clusters occurs. We find that the yeast guanine-nucleotide dissociation inhibitor (GDI), Rdi1p, is needed for rapid competition between clusters. In the absence of Rdi1p the initial clustering of polarity</p><p>factors is slowed, and competition is also much slower: in some cases cells still have two clusters at the time of bud emergence and they form two buds. We suggest that in the absence of Rdi1p, the clusters compete for a limiting pool of Cdc42p, and that slow</p><p>exchange of Cdc42p on and off the membrane in the absence of Rdi1p leads to slow competition.</p> / Dissertation
10

Gender Inequality, GDP per capita and Economic Growth

Jonsson, Sara January 2011 (has links)
The purpose of this thesis is to investigate the effects of gender inequality on GDP and GDP per capita. A cross sectional analysis of 177 countries over the time period 1998 to 2008 is undertaken with the use of linear regressions. There are several different factors that contribute to the gender inequality within a country and several ways to measure that disparity. The most well known measurement is the Gender-related Development Index and the components within this composite index have been studied thoroughly, although the index as a whole has not. This thesis then contributes with an overall view of how the gender inequality is important for the GDP and GDP per capita. The findings illustrate how significant equality between the genders is for the economy, irrespective of the human development level within the countries. The implication of this is that gender equality is important for the GDP and GDP per capita, which is in accordance with the theories. One large issue is that there is no way of confirming the way of causality between gender equality and GDP or GDP per capita.

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