The overarching goal of this dissertation research is to realize a virtual collaboratory for the investigation of large-scale scientific computing applications which generally experience different execution phases at runtime and each phase has different computational, communication and storage requirements as well as different physical characteristics. Consequently, an optimal solution or numerical scheme for one execution phase might not be appropriate for the next phase of the application execution. Choosing the ideal numerical algorithms and solutions for all application runtime phases remains an active research area. In this dissertation, we present Physics Aware Programming (PAP) paradigm that enables programmers to identify the appropriate solution methods to exploit the heterogeneity and the dynamism of the application execution states. We implement a Physics Aware Runtime Manager (PARM) to exploit the PAP paradigm. PARM periodically monitors and analyzes the runtime characteristics of the application to identify its current execution phase (state). For each change in the application execution phase, PARM will adaptively exploit the spatial and temporal attributes of the application in the current state to identify the ideal numerical algorithms/solvers that optimize its performance. We have evaluated our approach using a real world application (Variable Saturated Aquifer Flow and Transport (VSAFT2D)) commonly used in subsurface modeling, diffusion problem kernel and seismic problem kernel. We evaluated the performance gain of the PAP paradigm with up to 2,000,000 nodes in the computation domain implemented on 32 processors. Our experimental results show that by exploiting the application physics characteristics at runtime and applying the appropriate numerical scheme with adapted spatial and temporal attributes, a significant speedup can be achieved (around 80%) and the overhead injected by PAP is negligible (less than 2%). We also show that the results using PAP is as accurate as the numerical solutions that use fine grid resolution.

No description available.

Existing research shows that plants produce less root when growing alone than when growing in competition with other plants. When plants under root competition over-allocate resources to roots at the cost of reproduction, it represents a Tragedy of the Commons. I constructed simulation models to determine the circumstances likely to give rise to a Tragedy of the Commons, and explore mechanisms by which plants may solve it. I grew plants in nutrient-rich transparent gel, allowing me to quantify root growth and development without destructive sampling. My plants responded positively to additional space and the presence of a competitor at full nutrient treatment levels, and negatively to those same conditions between low phosphorus treatment levels, demonstrating nutrient mediation of the direction of plant response to an added competitor with additional space. This effect may feature self / non-self recognition by roots. Since the hard barrier in these studies blocks nutrients, roots, and root signaling compounds from passing between the plants in the barrier treatment level, existing studies cannot tease apart the effects on plant development of these individual factors. I add a semi-permeable membrane treatment level, which allows nutrients and signaling compounds to pass while preventing root growth between sides.

Le photovoltaïque nécessite de nouveaux matériaux pour diminuer ces coûts et améliorer les rendements. Ces travaux de thèse ont concerné le développement de nouvelles phases d'oxyde de titane pour l'électronique transparente et la conversion de photon appliquée au PV silicium. L'ablation laser pulsé est une méthode de croissance particulièrement adaptée pour la prospection de matériaux aux propriétés innovantes. Le contrôle des phases anatase, rutile et d'une phase de composition TiO1.45 épitaxié en fonction de la pression partielle d'oxygène a permis de réaliser des films aux propriétés électriques, optiques innovantes. Un film biphasé anatase/rutile dopé niobium (TNO1.80) présente ainsi une transition métal-semi-conducteur aux alentours de 68K. Par ailleurs, le film de composition TiO1.45 épitaxié s'est révélé être un oxyde transparent conducteur de type p. La découverte de ce nouveau p-TCOs a été valorisée et validée par l'élaboration d'une homojonction p - n transparente. Les matrices d'oxyde de titane rutile et anatase ont également été utilisées pour accueillir des ions terres rares Ln3+ afin de convertir les photons ultra-violet du spectre solaire incident vers le proche infrarouge (800 > λ > 1100 nm). Le transfert d'énergie des matrices TiO2 vers les dopants Ln3+ a été étudié en fonction de la structure, de la quantité de dopant ainsi que la qualité de la microstructure des films dopés Ln3+ (Ln3+=Pr3+,Tm3+,Eu3+,Yb3+,Nd3+).

The focus of this thesis is on the optimization and fabrication of p-i-n amorphous silicon (a-Si:H) solar cells both on glass and transparent plastic substrates. These solar cells are specifically fabricated on transparent substrates to facilitate the integration of thin film batteries with these solar cells. To comply with plastic substrates, different silicon layers are optimized at the low processing temperature of 135 C. In the first part of the optimization process, the structural, electronic, and optical properties of boron- and phosphorous-doped, hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at the substrate temperature of 135 C are elaborated. Additionally, in this part, the deposition of protocrystalline silicon (pc-Si) films on glass substrates are investigated. In the device integration and fabrication part of this thesis, the optimization process is continued by fabricating single junction devices with different hydrogen dilution ratios for the cell absorber layer. The optimum device performance is achieved with an absorber layer right at the transition from amorphous to microcrystalline silicon. To further improve the performance of the fabricated solar cells, amorphous silicon carbide buffer layers are introduced between the nc-Si p-layer and the undoped pc-Si absorber layer. Single junction p-p'-i-n solar cells are fabricated and characterized both on glass and plastic substrates. Our measurements show conversion efficiencies of 7.0% and 6.07% for the cells fabricated on glass and plastic substrates, respectively. In the last part of this research, the light trapping enhancement in amorphous silicon solar cells using Distributed Bragg Reflectors (DBRs) are experimentally demonstrated. Reflectance characteristics of DBR test structures, consisting of amorphous silicon (a-Si) / amorphous silicon nitride (SiN) film stacks are analysed and compared with those of conventional ZnO/Al back reflectors. DBR optical measurements show that the average total reflectance over the wavelength region of 600-800 nm is improved by 28% for DBR back structures. Accordingly, single junction amorphous silicon solar cells with DBR and Al back reflectors are fabricated both on glass and plastic substrates. Our results show that the short-circuit current density and consequently the conversion efficiency is enhanced by 10% for the cells fabricated on textured transparent conductive oxide substrates. In addition, these DBR back structures are designed and employed to improve the efficiency of semi-transparent solar cells. In this application, the optimized DBR structures are designed to be optically transparent for the part of the visible range and highly reflective for the red and infra-red part of the spectrum. Using these DBR structures, the efficiency of the optimum semi-transparent solar cell is enhanced by 5%.

Die vorliegenden Arbeit befasst sich mit der Herstellung und Charakterisierung von transparenten Metall-Halbleiter- Feldeffekttransistoren. Dazu werden im ersten Kapitel transparente gleichrichtende Kontakte, basierend auf dem Konzept von Metalloxidkontakten, hergestellt und im Hinblick auf chemische Zusammensetzung des Kontaktmaterials, Barriereninhomogenität und Kompatibilität mit amorphen Halbleitern untersucht. Außerdem wird die Anwendbarkeit der Kontakte als UV-Sensor studiert. Im zweiten Kapitel werden transparente leitfähige Oxide vorgestellt und insbesondere deren optische und elektrische Eigenschaften in Abhängigkeit von den Herstellungsbedingungen studiert. Das dritte Kapitel beinhaltet Untersuchungen zu transparenten Feldeffektransistoren, die auf den im ersten Kapitel untersuchten transparenten gleichrichtenden Kontakten basieren (TMESFETs). Insbesondere die elektrischen Stabilität der Bauelemente hinsichtlich Beleuchtung, erhöhten Temperaturen und Spannungsstress wird untersucht. Auch die Langzeitstabilität, Reproduzierbarkeit und der Effekt gepulster Spannungen wird betrachtet. Weiterhin wird die Verwendung amorpher Halbleiter im Kanal und damit auch die Herstellung flexibler Transistoren auf Folie demonstriert. Zuletzt werden die TMESFETs integriert und als Inverterschaltkreise aufgebaut und untersucht. Außerdem wird die Eignung der Transistoren zur Messung von Aktionspotentialen von Nervenzellen studiert.

The use of gold-based nanoparticles and thin films is very promising when it comes to improving several green nanotechnologies. Therefore, in order to further their use in applications such as electrochromic devices, photovoltaics, light-emitting diodes and photocatalysis, the aim of this work was to study the growth of gold-based nanoparticles and thin films. All depositions were made using DC magnetron sputtering, and optical, structural, electrochemical, electrical and photocatalytic studies of the films and particles were performed. The various applications yield a variety of substrate properties, and how these substrate properties affect gold coalescence was studied by depositing gold on glass slides and on SnO2:In, ITO and TiO2 base layers. Temperature also affects the gold coalescence. Therefore, gold was deposited on heated and non-heated substrates, where the latter were also post-heated, with a temperature range between 25ºC and 140ºC in both cases. Various temperatures were also used for manufacturing gold nanoparticles, and their effect as photocatalytic improvers was tested on WO3 films. The optical properties of Au films on glass were determined by ellipsometry in the 0.25 – 2 µm range, and then a spectral density analysis was performed of the effective dielectric permittivity. This work showed that thin gold films are excellent replacements for oxide-based transparent conductors in electrochromic devices. It was also shown that thin homogeneous gold films were better conductors when they were deposited on glass, compared to when they were deposited on oxide base layers, regardless of the optical, electrical and structural properties, or the doping concentration of the base layers. The results also showed that thin gold films were durable at 76ºC, and hence hold for a typical window temperature of ~70ºC. For higher temperatures, gold deposition on heated and non-heated substrates resulted in a distinct difference in growth, and there was also a distinct difference between post-heated gold films produced at 25ºC, compared to when the films were deposited on heated substrates. In the latter case, an island structure was obtained at 140ºC. Spectral density analysis gave spectral densities of similar shape for nanoparticles and continuous gold films, which is useful information for further investigations.

Techn. Univ., Diss.--Braunschweig, 2007.

Zugl.: Erlangen, Nürnberg, Univ., Diss., 2009

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references. Also available on the World Wide Web.