Doctor of Philosophy / Department of Chemistry / Jun Li / Developing new and rapid methods for pathogen detection with enhanced sensitivity and temporal resolution is critical for protecting general public health and implementing the food and water safety standards. In this research vertically aligned carbon nanofiber nanoelectrode arrays (VACNF NEAs) have been explored as a sample manipulation tool and coupled with fluorescence, surface enhanced Raman scattering (SERS) and impedance techniques for pathogen detection and identification. The key objective for employing a nanoelectrode array is that the nano-Dielectrophoresis (nano-DEP) at the tip of a carbon nanofiber (CNF) acts as a potential trap to capture pathogens. A microfluidic device was fabricated where nanofibers (~ 100 nm in diameter) were placed at the bottom of a fluidic channel to serve as a ‘point array’ while an indium tin oxide coated glass slide acted as a macroscale counter electrode. The electric field gradient was highly enhanced at the tips of the CNFs when an AC voltage was applied. The first study focused on the capture of the viral particles (Bacteriophage T4r) by employing a frequency of 10.0 kHz, a flow velocity of 0.73 mm/sec, and a voltage of 10.0 Vpp. A Lithenburg type of phenomenon was observed, that were drastically different from the isolated spots of bacteria captured on VACNF tips in previous study. At the lowest employed virus concentration (1 × 10[superscript]4 pfu/mL), a capture efficiency of 60% was observed with a fluorescence microscope. The motivation of the second study was to incorporate the SERS detection for specific pathogen identification. Gold-coated iron-oxide nanoovals labeled with Raman Tags (QSY 21), and antibodies that specifically bound with E.coli cells were utilized. The optimum capture was observed at a frequency of 100.0 kHz, a flow velocity of 0.40 mm/sec, and a voltage of 10.0 Vpp. The detection limit was ~210 CFU/mL for a portable Raman system with a capture time of 50 seconds. In the final study, a real-time impedance method was employed to detect Vaccinia virus (human virus) in the nano-DEP device at 1.0 kHz and 8.0 Vpp giving a detection limit of 2.51 × 10[superscript]3 pfu/mL.

Made available in DSpace on 2014-12-17T14:58:21Z (GMT). No. of bitstreams: 1 ElisangelaBNH_DISSERT.pdf: 5500408 bytes, checksum: 312e914c2b5560a38c07ef6f6b3c70be (MD5) Previous issue date: 2013-01-14 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The composites manufactured with long fibres aligned in a single direction, and overlay has been shown to have better performance than the short fibers randomly distributed. In particular, the lignocellulosic fibers extracted from the sisal leaves, used in conjunction with the epoxy resin has attracted the attention of many researchers because the final properties of the system formed. In this work composites based on epoxy resin reinforced with sisal fibers were manufactured. The sisal fibres were treated with an alkaline solution of 0.06 mol/l NaOH. The treated, and untreated fibres were subjected to tension x extension tests. The composites were manufactured in the "Lossy" mold with the specifications of the samples to be produced (300x20x4 mm). The tension tests were carried out in accordance with the ASTM standards 3039 (for the composite aligned in a single direction) and ASTM D5573 (for composites in overlay), three point bending tests were performed according to ASTM D790. Analyzing the results of the tests of tension and three point bending tests, it was observed that the composites with the configuration of overlapping had the better elastic module in both tests. As to the maximum resistance to tension, the best result was the composites aligned in a single direction. Tests of absorption of water and micrographs are in progress / Os comp?sitos fabricados com fibras longas alinhadas unidirecionalmente e em sobreposi??o tem demonstrado que possuem melhor desempenho do que as fibras cortadas aleatoriamente distribu?das. Em especial, as fibras lignocelul?sicas extra?das do sisal, utilizadas em conjunto com a resina ep?xi tem atra?do a aten??o de muitos pesquisadores devido ?s propriedades finais do sistema formado. No presente trabalho foram fabricados comp?sitos ? base de resina ep?xi refor?ado com fibras de sisal. As fibras de sisal foram submetidas ao tratamento alcalino com NaOH a 0,06 mol/l, em seguida submetidas ao ensaio de tra??o na fibra tratada e n?o tratada. Os comp?sitos foram fabricados no molde denominado de Lossy (molde com perdas) usinado de acordo com as especifica??es das amostras a serem produzidas (300x20x4 mm). Os ensaios de tra??o foram realizados de acordo com as normas ASTM 3039 (Para os comp?sitos alinhados unidirecionalmente) e ASTM D5573 (Para os comp?sitos em sobreposi??o), os ensaios de flex?o em tr?s pontos foram realizados de acordo com as normas ASTM D 790. Analisando os resultados dos ensaios de tra??o e flex?o em tr?s pontos, foram observados que os comp?sitos com a configura??o de sobreposi??o teve melhor m?dulo de elasticidade em ambos os ensaios. Quanto a resist?ncia m?xima a tra??o o melhor resultado foi do comp?sito alinhado unidirecionalmente. No ensaio de absor??o de ?gua foi observado que os comp?sitos possuem um n?vel muito baixo de absor??o e o comp?sito alinhado unidirecionalmente obteve percentual de satura??o de 1,97 %. Nas micrografias, se observa as regi?es de ruptura/trincas do comp?sito e seu comportamento (fibra/matriz)

Ce travail porte sur le développement et la vérification d’une nouvelle approche de coordonnées alignées FCI (Flux-Coordinate Independent), qui tire partie de l’anisotropie du transport dans un plasma immergé dans un fort champ magnétique. Sa prise en compte dans les codes numériques permet de réduire grandement le coût de calcul nécessaire pour une précision donnée. Une particularité de l’approche nouvellement développée dans ce manuscrit est en particulier sa capacité à traiter, pour la première fois, des configurations avec point X. Toutes ces analyses ont été conduites avec FENICIA, code modulaire entièrement développé dans le cadre de cette thèse, et permettant la résolution d’une classe de modèles génériques. En résumé, la méthode développée dans ce travail est validée. Elle peut s’avérer pertinente pour un large champ d’application dans le contexte de la fusion magnétique. Il est montré dans cette thèse que cette technique devrait pouvoir s’appliquer aussi bien aux modèles fluides que gyrocinétiques de turbulence, et qu’elle permet notamment de surmonter un des problèmes fondamentaux des techniques actuelles, qui peinent à traiter de manière précise la traversée de la séparatrice. / The primary thrust of this work is the development and implementation of a new approach to the problem of field-aligned coordinates in magnetized plasma turbulence simulations called the FCI approach (Flux-Coordinate Independent). The method exploits the elongated nature of micro-instability driven turbulence which typically has perpendicular scales on the order of a few ion gyro-radii, and parallel scales on the order of the machine size. Mathematically speaking, it relies on local transformations that align a suitable coordinate to the magnetic field to allow efficient computation of the parallel derivative. However, it does not rely on flux coordinates, which permits discretizing any given field on a regular grid in the natural coordinates such as (x, y, z) in the cylindrical limit. The new method has a number of advantages over methods constructed starting from flux coordinates, allowing for more flexible coding in a variety of situations including X-point configurations. In light of these findings, a plasma simulation code FENICIA has been developed based on the FCI approach with the ability to tackle a wide class of physical models. The code has been verified on several 3D test models. The accuracy of the approach is tested in particular with respect to the question of spurious radial transport. Tests on 3D models of the drift wave propagation and of the Ion Temperature Gradient (ITG) instability in cylindrical geometry in the linear regime demonstrate again the high quality of the numerical method. Finally, the FCI approach is shown to be able to deal with an X-point configuration such as one with a magnetic island with good convergence and conservation properties.

<p>Functional oxide-based thin films have attracted much attention owing to their broad applications in modern society. The multifunction tuning in oxide thin films is critical for obtaining enhanced properties. In this dissertation, four new nanocomposite thin film systems with highly textured growth have been fabricated by pulsed laser deposition technique. The functionalities including ferromagnetism, ferroelectricity, multiferroism, magnetoelectric coupling, low-field magnetoresistance, transmittance, optical bandgap and dielectric constants have been demonstrated. Besides, the tunability of the functionalities have been studied via different approaches.</p> <p>First, varies deposition frequencies have been used in vertically aligned nanocomposite BaTiO₃:YMnO₃ (BTO:YMO) and BaTiO₃:La_0.7Sr_0.3Mn₃(BTO:LSMO) thin films. In both systems, the strain coupling effect between the phases are affected by the density of grain boundaries. Increasing deposition frequency generates thinner columns in BTO:YMO thin films, which enhances the anisotropic ferromagnetic response in the thin films. In contrast, the columns in BTO:LSMO thin films become discontinuous as the deposition frequency increases, leading to the diminished anisotropic ferromagnetic response. Coupling with the ferroelectricity in BTO, the room temperature multiferroic properties have been obtained in these two systems.</p> <p> Second, the impact of the film composition has been demonstrated in La_0.7Ca_0.3MnO₃ (LCMO):CeO₂thin film system, which has an insulating CeO₂in ferromagnetic conducting LCMO matrix structure. As the atomic percentage of the CeO₂increases, enhanced low-field magnetoresistance and increased metal-to-insulator transition temperature are observed. The thin films also show enhanced anisotropic ferromagnetic response comparing with the pure LCMO film.</p> <p> Third, the transition metal element in Bi₃MoM_TO₉(M_T, transition metals of Mn, Fe, Co and Ni) thin films have been varied. The thin films have a multilayered structure with M_T-rich pillar-like domains embedded in Mo-rich matrix structure. The anisotropic magnetic easy axis and optical properties have been demonstrated. By the element variation, the optical bandgaps, dielectric constants as well as anisotropic ferromagnetic properties have been achieved. </p> <p> The studies in this dissertation demonstrate several examples of tuning the multifunctionalities in oxide-based nanocomposite thin films. These enhanced properties can broaden the applications of functional oxides for advanced nanoscale devices.</p><br>

<p>Understanding how light interacts with the matter is essential for developing future opto-electronic devices. Furthermore, tuning such light-matter interaction requires designing new material platforms that is essential for developing devices which are functional in different light wavelength regimes. Among these designs, particle-in-matrix, multilayer or nanowire morphology, consisting of metal and dielectric materials, have been demonstrated for achieving improved physical and optical properties, such as ferroelectricity, ferromagnetism and negative refraction. For example, Au-TiO₂ two phase nanocomposite has been explored in this dissertation as a way of achieving enhanced photocatalysis. However, due to the availability of a limited range of structures in terms of crystallinity and morphology in the two-phase nanocomposites, a greater design flexibility and structural complexity along with versatile growth techniques are needed for developing next generation integrated photonic and electronic devices. This can be achieved by incorporating a third phase through the three phase nanocomposite designs by judicious selection of materials and functionalities. </p> <p>In this dissertation, a new nanocomposite design having three different phases has been introduced: Au, BaTiO₃ and ZnO, which grow in a highly ordered ‘nanoman’-like structure. More interestingly, the three phases in the novel ‘nanoman’-like structure combine to give an emergent new property which are not found individually in the three phases. The ordered ‘nanoman’-like structures enable a high degree of tunability in their optical and electrical properties, including the hyperbolic dispersion in the visible and near infrared regime, in addition to the prominent ferroelectric/piezoelectric properties. Moreover, the growth kinetics and the thermal stability (using in-situ Transmission Electron Microscopy) of the ‘nanoman’ structures has also been studied. This study introduces a new growth paradigm of fabricating three-phase nanocomposite that will surely generate wide interests with potential applications to different systems. The ordered three-phase ‘nanoman’ structures present enormous opportunities for novel complex nanocomposite designs towards future optical, electrical and magnetic property tuning.</p>

Not all categories are created equal in object recognition. Fine-grained visual categorization (FGVC) is a branch of visual object recognition that aims to distinguish subordinate categories within a basic-level category. Examples include classifying an image of a bird into specific species like "Western Gull" or "California Gull". Such subordinate categories exhibit characteristics like small inter-category variation and large intra-class variation, making distinguishing them extremely difficult. To address such challenges, an algorithm should be able to focus on object parts and be invariant to object pose. Like many other computer vision tasks, FGVC has witnessed phenomenal advancement following the resurgence of deep neural networks. However, the proposed deep models are usually treated as black boxes. Network interpretation and understanding aims to unveil the features learned by neural networks and explain the reason behind network decisions. It is not only a necessary component for building trust between humans and algorithms, but also an essential step towards continuous improvement in this field. This dissertation is a collection of papers that contribute to FGVC and neural network interpretation and understanding. Our first contribution is an algorithm named Pose and Appearance Integration for Recognizing Subcategories (PAIRS) which performs pose estimation and generates a unified object representation as the concatenation of pose-aligned region features. As the second contribution, we propose the task of semantic network interpretation. For filter interpretation, we represent the concepts a filter detects using an attribute probability density function. We propose the task of semantic attribution using textual summarization that generates an explanatory sentence consisting of the most important visual attributes for decision-making, as found by a general Bayesian inference algorithm. Pooling has been a key component in convolutional neural networks and is of special interest in FGVC. Our third contribution is an empirical and experimental study towards a thorough yet intuitive understanding and extensive benchmark of popular pooling approaches. Our fourth contribution is a novel LMPNet for weakly-supervised keypoint discovery. A novel leaky max pooling layer is proposed to explicitly encourages sparse feature maps to be learned. A learnable clustering layer is proposed to group the keypoint proposals into final keypoint predictions. 2020 marks the 10th year since the beginning of fine-grained visual categorization. It is of great importance to summarize the representative works in this domain. Our last contribution is a comprehensive survey of FGVC containing nearly 200 relevant papers that cover 7 common themes.

<p>Devices that can process more information in reduced dimensions are essential for an increasingly information- and efficiency-driven future. To this end, nanocomposites are promising due to their inherent multifunctional properties and special behavior at the nanoscale. Vertically aligned nanocomposites (VANs) are particularly interesting because of their ability to self-assemble into anisotropic nanostructures and high density of heterointerfaces – characteristics which introduce unique functionalities and offer exciting new avenues for device applications. However, a vast majority of VAN systems are currently fabricated on single-crystal oxide substrates, which may be cost-prohibitive at large scales and are generally incompatible with the prevalent device fabrication techniques. Thus, integration of VAN thin films on silicon becomes a critical step toward implementing VANs in a well-established semiconductor manufacturing industry. </p> <p>In this dissertation, the viability of oxide-metal and nitride-metal VAN thin films integrated on silicon substrates has been demonstrated through a set of unique buffer layer designs. For the first three systems presented in this dissertation, namely, LaSrFeO₄-Fe, BaTiO₃-Au, and BaTiO₃-Fe, microstructural and physical property (i.e. electrical, magnetic, and optical) analyses confirm their successful epitaxial growth on silicon, with only minor differences compared to their counterparts grown on single-crystal oxide substrates. For the fourth system, a new and robust TiN-Fe VAN has been proposed and demonstrated. The new TiN-Fe VAN system on Si exhibits superior magnetic properties and unusual optical properties. With further growth optimization and/or patterning techniques, VAN thin film integration on silicon presents itself as a feasible and cost-effective approach to designing electronic, spintronic, photonic, and sensing devices.</p>

The bow shock is formed due to the abrupt deceleration of the supersonic solar wind in front of the terrestrial magnetic field. The solar wind plasma and the Interplanetary Magnetic Field (IMF) are both compressed across the shock, and according to Ampère's law a current thus flows on the bow shock at all times. The Bow Shock Current (BSC) is suggested to play an important role in solar wind-magnetosphere coupling, but there is still an open debate about its closure path. For predominantly east-west IMF, the BSC has been suggested to close to Earth's high latitude ionosphere as Field-Aligned Currents (FACs). Since the bow shock is magnetically connected to the solar wind, it must do so via open field lines through the magnetosheath. For southwards IMF with a significant east-west component, the R0 FAC flows into the ionosphere in one hemisphere, and out of it in the other. The R0 current flows on open field lines, and is thus a potential candidate to close the BSC. While a few studies have already found evidence in favour of this idea, the majority have been based on simulations. Additional observational evidence is required to confirm these findings. We used OMNI data for the IMF at the bow shock, and Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data for the FACs, to make simultaneous observations of the IMF at the bow shock and the northern hemisphere FACs, including the R0 current. We successfully identified 15 events of southwards but predominantly east-west IMF (Bz&lt;0, |By|&gt;|Bz|) at the bow shock, for which the northern hemisphere R0 current could be observed both in the AMPERE and DMSP data. In each of these events, the R0 current was of the correct polarity to connect to the BSC. Moreover, using Defense Meteorological Satellite Program (DMSP) and Super Dual Auroral Radar Network (SuperDARN) data, we were able to verify that part of the R0 current was flowing on open field lines. Collectively, the 15 events presented here constitute an argument in favour of at least a partial BSC closure to Earth's high latitude ionosphere as R0 FACs, for predominantly east-west IMF. Additional investigation is required to reveal the details of BSC closure.

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