Thesis (Ph. D.)--Texas A&M University, 2004. / "Major Subject: Interdisciplinary Engineering" Title from author supplied metadata (automated record created on Sep. 21, 2005.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Interdisciplinary Engineering" Title from author supplied metadata (automated record created on Apr. 14, 2006.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Interdisciplinary Engineering" Title from author supplied metadata (automated record created on Apr. 14, 2006.) Vita. Abstract. Includes bibliographical references.

This dissertation examines the fundamental physical properties and material processing methods required to design and fabricate the next generation of optical modulators based on the vanadium dioxide metal-insulator transition. All-optical devices capable of performing at GHz speeds, which are only limited by the laser pulse duration, were designed, fabricated and tested. Broad-band pump-probe experiments examined the femtosecond phase transition dynamics in vanadium dioxide when excited at a range of wavelengths from 400 nm to 1500 nm and indicate that THz modulation speeds could be achieved. In addition, fabrication methods and doping were explored as paths to tune the phase transition properties. The optical modulator design and material performance are discussed in the context of current state-of-the-art technology.

This opera is the composer’s fanciful speculation on the origin of the banshee, a character out of Irish legend whose keening is a herald of death. In three scenes, the opera tells the story of a witch whose quest for power leads her from one depravity to the next and ends with the destruction of her family. When the witch finally confronts the ruin she has caused, she wails with grief and transforms into the banshee. The work is scored for soprano, mezzo-soprano, baritone, dancer, and chamber orchestra, and it is approximately one hour in duration.

The integration of optical components with silicon complementary metalâoxideâsemiconductor (CMOS) technology may lead to the increase in information carrying capacity and reduction in power consumption necessary to continue the scaling the performance of microelectronic devices historically predicted by Mooreâs law. Silicon photonic structures that can guide light are well suited for such integration. However, the indirect band gap and relatively weak electro-optic responses of silicon provide challenges for chip-based lasing and modulation, two key functions necessary for an integrated photonic platform. For this reason, incorporation of materials possessing superior optical properties to silicon is actively being explored on silicon photonic platforms. The focus of this dissertation is to advance the scientific understanding and performance metrics of silicon-based optical modulators through hybridization with the actively tunable optical phase change material, vanadium dioxide (VO2). First, integration of VO2 onto a silicon ring resonator photonic platform and the subsequent electro-optic modulation of this hybrid structure are demonstrated. A tradeoff between extinction ratio and device response times is found when different VO2 patch lengths are utilized. Second, a platform in which VO2 is embedded within a silicon waveguide is realized. This embedded geometry increases interaction between the guided mode and VO2 in comparison to a geometry in which VO2 is placed on top of the silicon waveguide. Theoretical and experimental characterization through finite-difference time-domain analysis and temperature-dependent transmission measurements, respectively, demonstrates the tradeoff between extinction ratio and insertion loss as a function of VO2 patch length. Finally, the potential implementation of the hybrid silicon/VO2 embedded waveguide as an all-optical modulator with in-plane excitation is considered and its expected performance is compared to state-of-the-art all-optical modulators.

Zinc oxide is a wide band gap (3.37 eV) semiconductor with a high exciton binding energy (60 meV), of interest for optoelectronic applications due to both its ultraviolet (UV) and visible emissions. This dissertation shows four methods of tuning the UV band-edge emission of ZnO nanostructures. First, in a ZnO/MgO core-shell nanowire there exists a UV photoluminescence enhancement that varies with MgO thickness due to the formation of Fabry-Perot and whispering gallery optical cavity modes. Second, exciton-plasmon coupling in ZnO/MgO core-shell nanowires leads to enhanced emission of the UV luminescence. The combination of optical cavity formation and Ag plasmons leads to two enhancement mechanisms that depend on the MgO spacer thickness. Third, the structure of the MgO shell in the core-shell nanowires depends on the ZnO surface conditions. Changing the growth parameters of the ZnO nanowires tunes the ZnO m-plane surface conditions and thus the MgO shell structure. A smooth MgO shell supports enhanced UV photoluminescence through the formation of guided-wave optical modes, while a rough MgO shell supports neither the enhancement nor the guided modes. Fourth, temperature-dependent studies of exciton-phonon coupling elucidate that the vertically oriented nanowires, grown hydrothermally, have fewer defects and a sharper UV band-edge emission than the previously studied randomly oriented nanowires, further indicating that growth protocol has a critical influence on the UV optical properties of ZnO. Additionally, a novel structure, ZnO ânanopopcornâ showed strong exciton-phonon coupling, highlighting its high defect density. In summary, there is a range of mechanisms that can be used to enhance, modify, and control the UV band-edge emission in ZnO nanostructures, with vertically oriented ZnO nanowires having the most promise for enhanced UV emission optoelectronic and all-optical devices, from on-chip waveguides, lasers and LEDs, to scintillators and sensors.

Cette thèse avait pour but d’élargir le champ d’application des ultrasons en cardiologie, dans le domaine de l’imagerie et dans le domaine de la thérapie. Concernant l’imagerie, ce sont les capacités, les atouts et les limites des ultrasons à hautes cadences d’image (ultrafast echo) qui ont été explorés. Dans un premier temps, nous avons montré la possibilité et l’intérêt d’estimer la rigidité du myocarde par ultrason en pratique clinique, chez l’enfant et chez l’adulte. La technique de l’élastographie par onde de cisaillement, utilisant une nouvelle approche de l’imagerie par sommation cohérente harmonique ultrarapide (imagerie non-linéaire), a été appliquée pour la première fois chez l’humain en cardiologie. De plus, nous avons montré que la rigidité du foie, également estimée grâce à l’élastographie par onde de cisaillement, était directement corrélée aux pressions de remplissage du cœur droit, qui sont difficiles à évaluer de manière quantitative en pratique clinique. Dans un second temps, nous nous sommes intéressés à caractériser l’orientation des fibres myocardiques durant le cycle cardiaque en développant l’imagerie du tenseur de rétrodiffusion ultrasonore en trois dimensions. Le but était de réaliser la preuve de concept sur un cœur battant afin d’ouvrir sur les possibilités d’applications. Dans un troisième temps, le doppler de puissance en ultrafast echo nous a permis d’estimer les capacités des ultrasons à visualiser et analyser les flux (et donc les débits) intra coronariens. C’est à l’heure actuelle la seule technique d’imagerie clinique ayant une résolution spatiale (et temporelle) suffisante pour voir les flux dans des vaisseaux ayant un diamètre inférieur à 500 micromètres. Enfin, l’ultrafast echo nous a permis de visualiser les micro déplacements du myocarde, qui sont eux-mêmes initiés par l’activité électrique intra-myocardique, dans un intervalle de temps très réduit. Ceci est le couplage électromécanique, et y avoir accès par ultrason ouvrirait de multiples perspectives. Nous avons commencé à l’appliquer chez le fœtus humain et chez l’adulte en transthoracique. Concernant la thérapie, nous avons exclusivement utilisé les effets mécaniques des ultrasons focalisés à hautes intensités (phénomène de cavitation). Plusieurs équipes avaient déjà montré que cela était applicable en médecine cardiovasculaire, notamment pour perforer le septum inter-atrial (zone musculaire séparant les deux oreillettes cardiaques) ou pour détruire un thrombus intravasculaire. Nous avons décidé de montrer que le phénomène de cavitation peut avoir deux autres applications distinctes : 1) la section de cordage valvulaire mitral, qui est une technique utilisée actuellement en chirurgie (donc à cœur ouvert et en circulation extra-corporelle) visant à diminuer une fuite valvulaire à cause de cordage restrictif ; 2) l’assouplissement des feuillets valvulaires calcifiés, qui est une maladie représentant un enjeu de santé publique touchant des millions de personnes, et n’ayant à ce jour aucune stratégie non invasive disponible et applicable en pratique clinique. Pour ces deux applications, nous avons réalisé des preuves de concept in vitro puis in vivo à cœur battant, sur modèle animal (ovin). L’application humaine sera la prochaine étape. C’est donc la translation de nouvelles technologies ultrasonores vers des applications cliniques en cardiologie qui a motivé et guidé ce travail de thèse. / No abstract

The role of the hospice social worker is unclear and misunderstood by interdisciplinary team members due to role blurring, communication challenges, and poor collaboration efforts. This is important because these actions may result in decreased quality of patient care and decreased quality of life for the clinical hospice social workers. The purpose of this action research project was to explore communication, role blurring, professional activities and abilities, and cohesive goals among hospice clinical social workers. The theoretical foundation for this research was the model of interdisciplinary collaboration (MIC) which was used to describe both the concepts of interdisciplinary collaboration and the influences on that collaboration. The research question addressed the 5 concepts of the MIC to fully understand the collaboration challenges identified within hospice interdisciplinary teams. This action research study utilized the design and method of open-ended questions to gather the information using an online questionnaire. The data were coded by the action researcher to yield the key results of 3 main concepts of challenges for clinical hospice social workers (a) underutilization and misunderstanding of skillsets, (b) role blurring among the disciplines, and (c) working toward cohesive goals. A conclusion of this research was that hospice social workers are misunderstood, which presents a spectrum of challenges for the entire hospice interdisciplinary team. Implications for positive social change occurred through recommendations to reduce or eliminate these challenges, thus improving the quality of patient care and clinical hospice social workers' quality of life.

This study explores the factors that support the development of interdisciplinary research connections in a large public research university. Graduate students and faculty from 15 departments (n = 227) responded to an online survey focusing on an individual's openness toward interdisciplinary research, applied epistemological orientation, and potential interdisciplinary collaborations. The findings suggest that the formation of interdisciplinary connections is tied to two main determinants: interdisciplinary openness, which is supported by reporting a more applied epistemological orientation and being a graduate student. The diversity of interdisciplinary connections is influenced by the academic status, with tenured faculty exhibiting the most diversity in connections. Finally, research network analysis suggests that the patterns of interdisciplinary collaborations tend to orient toward collaborations between similar and familiar methodological partners, and not toward collaborations with partners that are wholly unfamiliar in terms of methodology or research focus. / Ph. D.