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1
Pearson, Charlie. "Vertical axis wind turbine acoustics." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245256.
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Increasing awareness of the issues of climate change and sustainable energy use has led to growing levels of interest in small-scale, decentralised power generation. Small-scale wind power has seen significant growth in the last ten years, partly due to the political support for renewable energy and the introduction of Feed In Tariffs, which pay home owners for generating their own electricity. Due to their ability to respond quickly to changing wind conditions, small-scale vertical axis wind turbines (VAWTs) have been proposed as an efficient solution for deployment in built up areas, where the wind is more gusty in nature. If VAWTs are erected in built up areas they will be inherently close to people; consequently, public acceptance of the turbines is essential. One common obstacle to the installation of wind turbines is noise annoyance, so it is important to make the VAWT rotors as quiet as possible. To date, very little work has been undertaken to investigate the sources of noise on VAWTs. The primary aim of this study was therefore to gather experimental data of the noise from various VAWT rotor configurations, for a range of operating conditions. Experimental measurements were carried out using the phased acoustic array in the closed section Markham wind tunnel at Cambridge University Engineering Department. Beamforming was used in conjunction with analysis of the measured sound spectra in order to locate and identify the noise sources on the VAWT rotors. Initial comparisons of the spectra from the model rotor and a full-scale rotor showed good qualitative agreement, suggesting that the conclusions from the experiments would be transferable to real VAWT rotors. One clear feature observed in both sets of spectra was a broadband peak around 1-2kHz, which spectral scaling methods demonstrated was due to laminar boundary layer tonal noise. Application of boundary layer trips to the inner surfaces of the blades on the model rotor was found to eliminate this noise source, and reduced the amplitude of the spectra by up to 10dB in the region of the broadband peak. This method could easily be applied to a full-scale rotor and should result in measurable noise reductions. At low tip speed ratios (TSR) the blades on a VAWT experience dynamic stall and it was found that this led to significant noise radiation from the upstream half of the rotor. As the TSR was increased the dominant source was seen to move to the downstream half of the rotor; this noise was thought to be due to the interaction of the blades in the downstream half of the rotor with the wake from the blades in the upstream half. It was suggested that blade wake interaction is the dominant noise source in the typical range of peak performance for the full-scale QR5 rotor. Different solidity rotors were investigated by using 2-, 3- and 4-bladed rotors and it was found that increasing the solidity had a similar effect to increasing the TSR. This is due to the fact that the induction factor, which governs the deflection of the flow through the rotor, is a function of both the rotor solidity and the TSR. With a large body of experimental data for validation, it was possible to investigate computational noise prediction methods. A harmonic model was developed that aimed to predict the sound radiated by periodic fluctuations in the blade loads. This model was shown to agree with similar models derived by other authors, but to make accurate predictions very high resolution input data was required. Since such high resolution blade loading data is unlikely to be available, and due to the dominance of stochastic sources, the harmonic model was not an especially useful predictive tool. However, it was used to investigate the importance of the near-field components of the sound radiated by the wind tunnel model to the acoustic array. It was shown that the near-field terms were significant over a wide range of frequencies, and the total spectrum was always greater than that of the far-field component. This implied that the noise levels measured by the acoustic array represented an upper bound on the sound radiated to the far-field, and hence that the latter would also be dominated by stochastic components. An alternative application of the harmonic model, which attempted to determine the blade loading harmonics from the harmonics in the sound field was proposed. This inversion method utilised a novel convex optimisation technique that was found to generate good solutions in the simulated test cases, even in the presence of significant random noise. The method was found to be insensitive at low frequencies, which made it ineffective for inverting the real microphone data, although this was shown to be at least partly due to the limitations imposed by the array size. In addition to the harmonic models, an empirical noise prediction method using the spectral scaling laws derived by \citet*{Brooks_1989} was trialled, and was found to be capable of making predictions that were in agreement with the measured data. The model was shown to be sensitive to the exact choice of turbulence parameters used and was also found to require good quality aerodynamic data to make accurate noise predictions. If such data were available however, it is expected that this empirical model would be able to make useful predictions of the noise radiated by a VAWT rotor.
2
Crocker, Steven Edward Miller James H. "Time domain modal beamforming for a near vertical acoustic array /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School; Available from the National Technical Information Service, 1991. http://handle.dtic.mil/100.2/ADA245272.
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Crocker, Steven Edward. "Time domain modal beamforming for a near vertical acoustic array." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/24239.
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Li, Lin. "Computer modeling of a vertical array in a stratified ocean." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/54393.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.GRSN 698569
Includes bibliographical references (leaves 76-78).
by Lin Li.
M.S.
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Li, Lin. "Computer modeling of a vertical array in a stratified ocean /." Online version of thesis as technical report, 1995. http://hdl.handle.net/1912/477.
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Tas, Gerard. "Transient localization in shallow water environments with a vertical line array." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA381469.
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Thesis (M.S. in Engineering Acoustics) Naval Postgraduate School, June 2000.Thesis advisor(s): Smith, Kevin B. "June 2000." Includes bibliographical references (p. 77-78). Also available in print.
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Feng, Wanjie, and Ben K. Sternberg. "Field Tests of the Vertical-Array Differential Target Antenna Coupling (DTAC) System." ENVIRONMENTAL ENGINEERING GEOPHYSICAL SOC, 2017. http://hdl.handle.net/10150/626249.
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We have tested the Vertical-Array Differential Target Antenna Coupling (DTAC) system over a variety of well-characterized, buried targets. The DTAC system produces a primary field in the frequency range of 10 Hz to 10 kHz and records secondary magnetic fields from subsurface targets, relative to a reference frequency. The current DTAC system has higher power, compared with our earlier tests, and this system is suitable for either ground or airborne mapping of a wide variety of near-surface targets, which might be encountered in civil engineering, water resources, environmental characterization, mining, and other natural-resource exploration. Profiles over three well-characterized targets show a close agreement between the measured DTAC response and model simulations. Conventional field measurements using induced magnetic fields are also displayed and they do not show nearly as effective mapping of the targets. Another profile shows that the DTAC method has greatly reduced sensitivity to surface clutter, compared to conventional measurements.
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Omans, Glenn A. "Broadband modal beamforming of acoustic tomography signals acquired by a vertical array." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23827.
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Sperry, Brian J. "Modal analysis of vertical array receptions for the Heard Island Feasibility Test." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38352.
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Maj, Tomasz. "Interconnection of a 2D vertical-cavity surface-emitting laser array to a receiver array via a fiber image guide." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0034/MQ64236.pdf.
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Maj, Tomasz. "Interconnection of a 2D vertical-cavity surface-emitting laser array to a receiver array via a fiber image guide." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30260.
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Parallel Optical Data Links (PODLs) have the potential to solve interconnection bottlenecks which are currently being experienced in high-speed communication and information processing systems. Such links often require a large number of channels and two-dimensional arrays of active optoelectronic devices are being developed. In order to interconnect these devices, fiber image guide technology consisting of a bundle of several thousand equally spaced optical fibers is being proposed to alleviate the need for dedicated fibers.This thesis examines the implementation of a two-dimensional parallel optical interconnect consisting of an array of Vertical-Cavity Surface-Emitting Lasers (VCSELs), a 1.35m Fiber Image Guide (FIG) and a Metal-Semiconductor-Metal (MSM) receiver array. Coupling issues associated with image guides are analysed and discussed as well as general image guide properties and transmission characteristics. The design, construction and integration aspects of the data link, including optics, electronics and optomechanics are summarised. Characterization results are presented and a transmission rate of 250 Mbit/s per channel is demonstrated with an optical crosstalk of less than -27 dB and a total optical loss of -3dB.
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Syring, James D. "Mixed and forced convection from an array of discrete heat sources in a vertical channel." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23961.
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Approved for public release; distribution is unlimitedMixed and forced convection liquid cooling of discrete heat sources in a vertical channel was investigated. Ten heat sources were flush mounted to one of the plexiglass channel walls, while the opposite wall was insulated. Measurements of heater surface temperatures were made for a channel Reynolds number rage of 500-7300 and heat flux range of 510-2700 W/m(2). Temperature patterns on the heated surface were visualized using liquid crystals. Effects of flow pulsations on heat transfer were also investigated in the 0-1.25 Hz range.
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Yu, Xiaoju, Min Liang, and Corey Shemelya. "3D Printable Multilayer RF Integrated System." International Foundation for Telemetering, 2015. http://hdl.handle.net/10150/596450.
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ITC/USA 2015 Conference Proceedings / The Fifty-First Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2015 / Bally's Hotel & Convention Center, Las Vegas, NVIn this work, a 3D-printable multilayer phased array system is designed to demonstrate the applicability of additive manufacturing technique combining dielectric and conductor processes at room temperature for RF systems. Phased array systems normally include feeding networks, antennas, and active components such as switches, phase shifters and amplifiers. To make the integrated system compact, the array system here uses multilayer structure that can fully utilize the 3D space. The vertical interconnections between layers are carefully designed to reduce the loss between layers. Simulated results show good impedance matching and high-directive scanning beam. This multilayer phased array will finally be 3D printed by integrating thermal / ultrasound wire mesh embedding method (for metal) and fused-deposition-modeling technique (for dielectric).
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Marburger, John M. "Estimation of geoacoustic properties in the South China Sea shelf using a towed source and vertical line hydrophone array." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Dec%5FMarburger.pdf.
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Thesis (M.S. in Physical Oceanography and Meteorology)--Naval Postgraduate School, Dec. 2004.Thesis Advisor(s): Ching-Sang Chiu. Includes bibliographical references (p. 33). Also available online.
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Anderson, Arthur D. III (Arthur Douglas). "The effect of towed array orientation on the 3D acoustic picture for sound sources and the vertical ambient noise profile." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100116.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 157-159).
The three dimensional (3D) acoustic arrival structure of the undersea ambient noise field is important for many reasons, and can give us significant insights into the Arctic environment. For example, the anthropomorphic sound of the ice cracking along the ice edge could be used to track the location of the ice edge as it advances and retracts throughout the seasons. The noise sources could also be used as a noise source to acoustically map the bathymetry of the largely unexplored Arctic seabed. In addition, vertical arrival structure of the ambient noise field could give hints and clues that allow for improvements in both acoustic communications and target tracking. In this research, we will examine the ability of an autonomous underwater vehicle (AUV) equipped with a towed array in a virtual environment to develop an accurate 3D acoustic picture of the undersea environment. While prior towed array experiments are generally limited to the arrays being towed in a horizontal manner, here a "yoyo" maneuver is introduced. In a yoyo maneuver, the vehicle moves up and down in the water column as it traverses in order to break up the ambiguity of the measured vertical arrival structure. This thesis presents a method to measure the "verticalness" introduced into the towed array by this maneuver, and quantifies how this improves the quality of the 3D arrival structure. The results conclude that within the vehicle maneuvering limits of a Bluefin-21 AUV, a fully pitched yoyo pattern vs. a constant depth pattern results in a relative increase in the maximum beam response of a source by approximately 6.5 dB, and also decreases the 3-dB down bandwidth in the vertical direction by approximately 12°. This is done without any significant losses for the bandwidth in the horizontal direction. When using a towed array to characterize a horizontally isotropic noise field, we find that within the AUV's maneuvering limits, the 3D beam response patterns are not sufficient to produce an accurate acoustic picture. To measure these fields, a vertical array is the most appropriate.
by Arthur Anderson.
Ph. D.
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Macelloni, Leonardo. "La sismica ad alta risoluzione digitale a mare: vincoli teorici, elaborazione numerica, nuovi sviluppi (High-resolution marine digital seismic method: theoretical constrains, digital processing, new developments )." Doctoral thesis, La Sapienza, 2005. http://hdl.handle.net/11573/917387.
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Möllerström, Erik. "Noise, eigenfrequencies and turbulence behavior of a 200 kW H-rotor vertical axis wind turbine." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-316385.
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Vertical-axis wind turbines (VAWTs) have with time been outrivaled by the today more common and economically feasible horizontal-axis wind turbines (HAWTs). However, VAWTs have several advantages which still make them interesting, for example, the VAWTs can have the drive train at ground level and it has been argued that they have lower noise emission. Other proposed advantages are suitability for both up-scaling and floating offshore platforms. The work within this thesis is made in collaboration between Halmstad University and Uppsala University. A 200-kW semi-guy-wired VAWT H-rotor, owned by Uppsala University but situated in Falkenberg close to Halmstad, has been the main subject of the research although most results can be generalized to suit a typical H-rotor. This thesis has three main topics regarding VAWTs: (1) how the wind energy extraction is influenced by turbulence, (2) aerodynamical noise generation and (3) eigenfrequencies of the semi-guy-wired tower. The influence from turbulence on the wind energy extraction is studied by evaluating logged operational data and examining how the power curve and the tip-speed ratio for maximum Cp is impacted by turbulence. The work has showed that the T1-turbine has a good ability to extract wind energy at turbulent conditions, indicating an advantage in energy extraction at turbulent sites for VAWTs compared to HAWTs.The noise characteristics are studied experimentally, and models of the two most likely aerodynamic noise mechanisms are applied. Here, inflow-turbulence noise is deemed as the prevailing noise source rather than turbulent-boundary-layer trailing-edge noise (TBL-TE) which is the most important noise mechanism for HAWTs. The overall noise emission has also been measured and proven low compared to similar sized HAWTs. The eigenfrequencies of a semi-guy-wired tower are also studied. Analytical expressions describing the first-mode eigenfrequency of both tower and guy wire has been derived and verified by experiments and simulations.
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Miller, Christopher W. "Estimating the acoustic modal arrivals using signals transmitted from two sound sources to a vertical line hydrophone array in the 1996 Shelfbreak PRIMER experiment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA350762.
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Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, June 1998.Thesis advisors, Ching-Sang Chiu, Charles W. Therrien. Includes bibliographical references (p. 31-33). Also available online.
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Mercier, Guillaume. "Modélisation de parcs d'hydroliennes à flux transverse avec une méthode d'équivalence." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI061/document.
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L'exploitation de l'énergie cinétique des courants marins ou fluviaux est une source d'énergie prometteuse et renouvelable. Les performances hydrodynamiques des hydroliennes sont à ce jour bien connues et l'attention se porte sur la compréhension des phénomènes de parc et l'interaction entre machines. Ce document présente la construction d'un modèle simplifié (ou méthode d'équivalence) pour les turbines à axe de rotation vertical. Une étape préliminaire consiste à valider l'utilisation de la méthode de maillage rotatif proposée par Code_Saturne (solveur CFD open source). La simulation de la turbine Darrieus/Achard A10 en 2D met en évidence une bonne concordance des mesures expérimentales (PIV). Cet outil sert dans une seconde étape à mettre au point un modèle simplifié de ces mêmes turbines. Celui-ci consiste à représenter la turbine dans l'écoulement par son équivalent en termes sources de quantité de mouvement sur la base d'une paramétrisation efficace des données empiriques. La méthode est validée pour une large plage de vitesses de rotation et de confinements, et sur plusieurs machines. La représentation du sillage par par les deux méthode de simulation est ensuite étudiée en détail. Des mesures par la technique de LDV dans le sillage proche d'un modèle réduit sont effectuées et établissent une référence expérimentale nécessaire pour ce type de machine. La dépendance forte des deux méthodes de simulation aux paramètres et aux modèles de turbulence est constatée. Deux phénomènes principaux sont relevés : la diffusion turbulente et les instabilités à grandes échelles. Des calculs de rendement sur des dispositions de machines variables illustrent l'applicabilité du modèle. Ils mettent notamment en avant l'effet positif de l'intensité turbulente ambiante sur le rendement dans un parcHarnessing kinetic energy from oceans or rivers is a promising source of renewable energy. The hydrodynamical performance of water turbines is well known and the focus is now on array optimization and turbine interaction. The present document aims to introduce a new modeling solution for vertical axis water current turbine of Darrieus/Achard type and its construction methodology. A preliminary stage consists in the validation of the new sliding mesh method available in Code_Saturne, EDF CFD open source solver. The good results obtained by comparison with PIV measurements on the Achard type turbine allow the use of this method as a reference tool. The second stage sees the construction of an equivalence model for the Darrieus turbine using momentum source terms. These terms are calculated thanks to an efficient parametrization of empirical data. The comparison of the model with full geometry calculation shows a good agreement in terms of power for a wide range of rotational velocity and blocking ratio. LDV measurements in the near wake of a small scale Achard turbine give a necessary reference set of data. The wake given by both simulations is strongly dependent of turbulence parameters or models, with the cohabitation of two main phenomena : momentum turbulent diffusion, and large scale fluctuations. To conclude, a calculation of the power output for several turbine distributions in an array illustrates the model capability
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Chandra, Johanes. "Analyses expérimentales de la réponse sismique non-linéaire du système sol-structure." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU023/document.
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La concentration de plus en plus importante de la population dans les milieux urbains exposés à une forte sismicité peut générer de plus en plus de dommages et de pertes. La réponse sismique en milieu urbain dépend des effets du site (direct amplification et non-linéarité du sol) et du couplage entre le sol et les structures (interaction sol-structure et site-ville). Par conséquent, la compréhension de la sismologie urbaine, c'est-à-dire le mouvement du sol intégrant l'environnement urbain, est critique pour réduire les dommages. Cela passe par la prédiction du mouvement du sol dans le milieu urbain, ingrédient fondamental à l'évaluation de l'aléa sismique. La prise en compte de l'amplification provoquée par la présence de sédiments est largement étudiée. Au contraire, la réponse non-linéarité du sol et du couplage entre le sol et la structure est rarement intégrée à la prédiction du mouvement du sol. A cause de leur complexité, ces problèmes ont toujours été abordés séparément. Dans ce contexte, cette thèse analyse la réponse non-linéaire du système sol-structure en intégrant la non-linéarité du sol et de l'interaction sol-structure. Deux travaux expérimentaux ont été conduits, avec comme but de proposer un proxy, rendant compte de la non-linéarité du sol. Le premier est l'essai en centrifugeuse qui reproduit à échelle réduite la réponse du sol et des structures. L'état de contrainte et de déformation est conservé en appliquant une accélération artificielle au modèle. Cet essai a été effectué à IFSTTAR Nantes dans le cadre de l'ANR ARVISE. Différentes configurations ont été testées, avec et sans bâtiments, sous différents niveaux de sollicitation, pour analyser la réponse du sol et des structures. Le deuxième utilise les enregistrements des réseaux accélérométriques verticaux de deux sites tests californiens : Garner Valley Downhole Arrat (GVDA) et Wildlife Liquefaction Array (WLA), gérés tout deux par l'Université de Californie, Santa Barbara (UCSB), Etats-Unis. La réponse in-situ est importante car elle décrit le comportement réel du site. Plusieurs informations décrivant les conditions de sites sont disponibles et les séismes enregistrés ont permis de tester plusieurs niveaux de déformations pour reconstruire la réponse globale de chaque site. De plus, le site GVDA est équipé d'une structure Soil-Foundation-Structure-Interaction (SFSI) qui a comme objectif d'étudier les problèmes d'interaction sol-structure. Dans les deux expériences, grace au réseau accélérométrique vertical dans le sol et la structure, on peut appliquer la méthode de propagation d'ondes 1D pour extraire la réponse de ces systèmes. Les ondes sont considérées comme des ondes SH qui se propage horizontalement dans une couche 1D. La méthode interférométrie sismique par déconvolution est appliquée pour extraire l'Impulse Response Function (IRF) du système 1D. On analyse ainsi la variation de Vs en fonction de la solliictation et à différente position dans le sol ainsi que la variation des éléments expliquant la réponse dynamique du système sol-structure. On propose au final un proxy de déformation permettant de rendre compte mais aussi de prédire la nonlinéarité des sols en fonction des niveaux sismiques subitsThe concentration of population in urban areas in seismic-prone regions can generate more and more damages and losses. Seismic response in urban areas depends on site effects (direct amplification and nonlinearity of the soil) and the coupling between the soil and structures (soil-structure and site-city interaction). Therefore, the understanding of urban seismology, that is the ground motion incorporating the urban environment, is critical to reduce the damage. This requires the prediction of ground motion in urban areas, a fundamental element in the evaluation of the seismic hazard. Taking into account the amplification caused by the presence of sediment has been widely studied. However, the non-linearity of the soil and the coupling between the ground and the structure is seldom integrated to the prediction of the ground motion. Because of their complexity, these problems have been addressed separately. In this context, this dissertation analyzes the non-linear response of the soil-structure by integrating the non-linearity of the soil and the soil-structure interaction. Two experimental studies were performed, with the aim of providing a proxy that reflects the non-linearity of the soil. The first is the centrifuge test that reproduces the response of soil and structures at reduced scale. The state of stress and strain is conserved by applying an artificial acceleration model. This test was performed at IFSTTAR Nantes in the framework of the ANR ARVISE. Different configurations were tested with and without buildings, under different stress levels, to analyze the response of the soil and structures. The second uses the vertical accelerometric networks of two sites in California: Garner Valley Downhole (GVDA) and the Wildlife Liquefaction Array (WLA), both managed by the University of California, Santa Barbara (UCSB), USA. In-situ response is important since it describes the actual behavior of the site. Information describing the conditions of sites is widely available and the earthquakes recorded were used to test several levels of shaking to reconstruct the overall response of each site. In addition, the GVDA site is equipped with a Soil-Foundation-Structure-Interaction structure (SFSI) which aims to study the problems of soil-structure interaction. In both experiments, thanks to the vertical accelerometer network in the ground and the structure we are able to apply the 1D wave propagation method to extract the response of these systems. The waves are considered as an SH wave which propagates in a 1D horizontal layer. Seismic interferometry by deconvolution method is applied to extract the Impulse Response Function (IRF) of the 1D system. Thus the analysis of the variation in function of elastic properties of the soil and the structure is done under several magnitude of shaking, including variation in depth and the elements of the total response of the structure including the soil-structure interaction. At the end, a deformation proxy to evaluate and also to predict the nonlinear response of the soil, the structure and the soil-structure interaction is proposed
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Zhao, Hangbo. "Vertical silicon nanowire arrays for gas sensing." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/87971.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, February 2014.Cataloged from PDF version of thesis. "February 2014."
Includes bibliographical references (pages 92-97).
The goal of this research was to fabricate and characterize vertically aligned silicon nanowire gas sensors. Silicon nanowires are very attractive for gas sensing applications and vertically aligned silicon nanowires are preferred over horizontal nanowires for gas sensing due to the high density of nanowire arrays and the increased nanowire surface area per substrate area. However, the development of such devices has been limited by a number of challenges. Two of the key challenges in fabricating vertical silicon nanowire sensors are the difficulty of making electrical contact to the tops of the wires and the large serial resistance of the substrate. In this thesis, highly ordered, dense arrays of vertically aligned silicon nanowires in patterned areas have been fabricated utilizing metal assisted chemical etching (MACE) in combination with interference lithography. In addition, we report a novel and simple approach for making reliable top electrical contacts by using tilted electron beam evaporation with a custom-built rotation plate. A suspended metal top contact layer was formed on vertically aligned silicon nanowires using this approach. We have also systematically investigated the contact behavior between silicon nanowires and metal electrodes with different nanowire doping and contact materials. Ohmic contact was formed between the suspended top metal layer and the tips of silicon nanowires. We have also solved the serial resistance problem by using lightly doped epitaxial silicon films (needed for the sensors) on heavily doped substrates. Based on these techniques and design considerations, we have successfully fabricated vertically aligned silicon nanowire field effect gas sensors. Finally, we have demonstrated highly sensitive detection of hydrogen, oxygen, 10 ppm (parts-per-million, 10-⁶) ammonia and nitrogen dioxide gases using the fabricated sensor devices at room temperature. The sensors have exhibited the highest sensitivity per unit chip area for hydrogen, oxygen and 10 ppm NH₃ gases at room temperature, among other vertically aligned silicon nanowire based gas sensors reported. Further improvements of the current sensor devices can be made to accelerate response and recovery of gas sensing.
by Hangbo Zhao.
S.M.
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Tastavridis, Konstantinos. "Dynamics of vertical cavity surface emitting laser arrays." Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268777.
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Sargent, Laurence John. "Performance enhancement in vertical-cavity surface-emitting lasers using focused ion beam etching." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269231.
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Yu, Feng [Verfasser]. "Vertical Field-Effect Transistors Based on 3D GaN Nanowire Arrays / Feng Yu." München : Verlag Dr. Hut, 2018. http://d-nb.info/1168535069/34.
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Greenberg, Kathryn J. "Thermal coupling and lensing in arrays of vertical cavity surface emitting lasers /." Connect to online version, 2009. http://ada.mtholyoke.edu/setr/websrc/pdfs/www/2009/370.pdf.
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Boyle, John K. "Performance Metrics for Depth-based Signal Separation Using Deep Vertical Line Arrays." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2198.
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Vertical line arrays (VLAs) deployed below the critical depth in the deep ocean can exploit reliable acoustic path (RAP) propagation, which provides low transmission loss (TL) for targets at moderate ranges, and increased TL for distant interferers. However, sound from nearby surface interferers also undergoes RAP propagation, and without horizontal aperture, a VLA cannot separate these interferers from submerged targets. A recent publication by McCargar and Zurk (2013) addressed this issue, presenting a transform-based method for passive, depth-based separation of signals received on deep VLAs based on the depth-dependent modulation caused by the interference between the direct and surface-reflected acoustic arrivals. This thesis expands on that work by quantifying the transform-based depth estimation method performance in terms of the resolution and ambiguity in the depth estimate. Then, the depth discrimination performance is quantified in terms of the number of VLA elements.
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Butler, Timothy Patrick. "The interaction of light with vertically aligned arrays of carbon nanotubes." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708152.
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Chang, Kai-Han. "Achromatic Liquid Crystal Electro-Optical Devices Based On a Twisted Vertical Alignment Configuration." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1523807996464507.
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Joseph, Johnson. "Numerical Modeling and Characterization of Vertically Aligned Carbon Nanotube Arrays." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/28.
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Since their discoveries, carbon nanotubes have been widely studied, but mostly in the forms of 1D individual carbon nanotube (CNT). From practical application point of view, it is highly desirable to produce carbon nanotubes in large scales. This has resulted in a new class of carbon nanotube material, called the vertically aligned carbon nanotube arrays (VA-CNTs). To date, our ability to design and model this complex material is still limited. The classical molecular mechanics methods used to model individual CNTs are not applicable to the modeling of VA-CNT structures due to the significant computational efforts required. This research is to develop efficient structural mechanics approaches to design, model and characterize the mechanical responses of the VA-CNTs. The structural beam and shell mechanics are generally applicable to the well aligned VA-CNTs prepared by template synthesis while the structural solid elements are more applicable to much complex, super-long VA-CNTs from template-free synthesis. VA-CNTs are also highly “tunable” from the structure standpoint. The architectures and geometric parameters of the VA-CNTs have been thoroughly examined, including tube configuration, tube diameter, tube height, nanotube array density, tube distribution pattern, among many other factors. Overall, the structural mechanics approaches are simple and robust methods for design and characterization of these novel carbon nanomaterials
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Su, Haiqiao. "Gas Detection Applications of Vertically Aligned Metal Oxide Nanowire Arrays." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1947.
Full textAbstract:
To build novel electronic noses for mimicking biological olfactory systems that consist of olfactory receptor arrays with large surface area and massively-diversified chemical reactivity, three dimensional (3D) vertical aligned ZnO nanowire arrays were employed as active materials for gas detection. ZnO nanowire arrays share 3D structures similar to mammalian olfactory receptor arrays, with thousands of vertical nanowires providing a high reception area which can significantly enhance the sensors’ sensitivity. Meanwhile, with different material decorations (such as SnO2, In2O3, WO3 and polymers), each array of nanowires can produce a distinguishable response for each separate analyte, which would provide a promising way to improve the selectivity. Both patterned grown well-aligned and wafer size random-distributed 3D nanowire array sensing devices are investigated. Several different types of gas sensors have been investigated in this dissertation. Metal oxide semiconductor gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have detected NO2 and H2S down to ppb level, and five gases of NO2, H2S, H2, NH3, and CO have been discriminated. Active self-powered gas sensors based on 3D metal oxides/ZnO vertical nanowire arrays have been successfully fabricated and worked well for H2S and NO2 detection. With the decoration by mixture of PEDOT polymer with metal oxide nanoparticles, ZnO vertical nanowire array gas sensors have fast response and recovery time as well as good sensitivity to volatile organic gases of acetone, methanol and ethanol. A novel ionization sensor also has been built by ZnO vertical nannowire arrays, and this device could be able to ionize air under safety operation voltage.
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Luongo, Stephanie A. "Design, modeling, and testing of microstrip parch antenna arrays for vertical takeoff & landing aircraft." abstract and full text PDF (UNR users only), 2009. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1472964.
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Ladan, Muhammad Bello. "Application of vertically aligned arrays of metal-oxide nanowires in heterojunction photovoltaics." University of the Western Cape, 2020. http://hdl.handle.net/11394/7915.
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Philosophiae Doctor - PhDThe commercial need to improve the performance of low-cost organic solar cells has led to the idea for this research. The study discusses the synthesis of one dimensional TiO2 and ZnO nanowire arrays synthesised using a hydrothermal autoclave method and their application in bulk heterojunction inverted organic solar cells. Previous literature has shown that the precise manipulation, positioning and assembly of 1D nanostructures remain one of the greatest challenges in the field of nanotechnology, with much of the difficulty arising primarily from the lack of size and scale of the materials as well as the inability to visualise the nanostructures. In particular, one dimensional metal-oxides such as TiO2, ZnO and Fe2O3 have emerged as attractive alternatives to traditional semiconductor structures such as Si and GaAs as they are simple and inexpensive to manufacture, with research showing that application of ZnO nano-cones yield efficiencies of 8.4%, which is very attractive given the scope that exists in optimising the metal-oxide architecture. Much is still to be learned from the precise structural features of these materials and their influence on device performance. In this regard, this work largely focuses on this aspect of metal-oxide nanowires prior their application in organic solar cells.
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Wick, Michael [Verfasser], and Helmut [Akademischer Betreuer] Seidel. "Mikrothermopaare mit vertikal freistehender Geometrie als Basis zum Aufbau von hochauflösenden Mikrothermoelement-Array-Detektoren / Michael Wick ; Betreuer: Helmut Seidel." Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1202039820/34.
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Gu, Wentian. "Increase the packing density of vertically aligned carbon nanotube array for the application of thermal interface materials." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41049.
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To fulfill the potential of carbon nanotube (CNT) as thermal interface material (TIM), the packing density of CNT array needs improvement. In this work, two potential ways to increase the packing density of CNT array are tested. They are liquid precursor(LP)CVD and cycled catalyst deposition method. Although LP-CVD turned out to be no help for packing density increase, it is proved to enhance the CNT growth rate. The packing density of CNT array indeed increases with the cycle number. The thermal conductivity of the CNT array increases with the packing density. This work is believed to be a step closer to the real life application of CNT in electronic packaging industry.
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Chen, Liang-Yu 1979. "Double-gated isolated vertically aligned carbon nanofiber field emission and field ionization arrays." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40492.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 161-168).
Electron impact ionization (ElI) is used extensively in mass spectrometry for gas-phase analytes. Due to the significant amount of fragmentation generated by ElI, the spectrum is usually very noisy. In addition, the thermionic emission electron source used in ElI has a slow response time and consumes large amount of power. To address these two issues, double-gated vertically aligned carbon nanofiber (VACNF) field emission and field ionization arrays have been developed. These arrays were characterized as field ionizers, which could produce molecular ions without severe fragmentation; and as field emitters, which act as an electron source with a fast response time and consume less power than using thermionic emission. Self-aligned double-gated isolated VACNF arrays, which were fabricated using a photoresist-based planarization process, are reported. These arrays were designed such that the tip electric field is maximized and the shielding effect from the neighboring tips is minimized while the device is capable of handling large voltages during field emission and field ionization. Two types of arrays were fabricated: (1) CNFs with tips in-plane with the gate and (2) CNFs with tips 0.9tm below the gate.
(cont.) These arrays were characterized as a field emitter and a low field emission turn-on voltage of 24V is reported. These arrays were used as electron sources for ElI at pressures ranging from 5x10-6 to lx10-3 Torr. The ion current is linearly related to the product of the electron current and the ambient pressure. Thus, the device could be used as a gas pressure sensor in vacuum. Field ionization experiments were also conducted with double-gated VACNF arrays. The field ionization turn-on voltage was reduced from about 10kV, typical of ungated ionizers, to 350V.
by Laing-Yu Chen.
Ph.D.
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Yuan, Guangbi. "Synthesis and Applications of Vertically Aligned Silicon Nanowire Arrays for Solar Energy Conversion." Thesis, Boston College, 2012. http://hdl.handle.net/2345/3738.
Full textAbstract:
Thesis advisor: Dunwei WangSolar energy, the most abundant and free renewable energy, holds great promise for humanity's sustainable development. How to efficiently and inexpensively capture, covert solar energy and store it for off peak usages constitutes a grand challenge for the scientific community. Photovoltaic devices are promising candidates but are too costly to be implemented in large scales. On a fundamental level, this is due to the dilemma that the length scales of the optical pathways and electrical pathways often do not match within the photovoltaic device materials. Consider traditional Si solar cell as an example, effective light absorption requires up to hundreds of microns material while the photogenerated charge carries can only diffuse less than a few microns or even shorter before recombination. Such a problem may be solved by using Si nanowires (SiNWs) because vertically aligned nanowires can orthogonalize the light absorption and charge carrier collection pathways, thereby enabling the use of low-cost materials for practically appealing solar energy conversion devices. The objective of this thesis work is to explore low-cost synthesis of vertically aligned SiNW arrays and study their performance in both solar energy conversion and storage devices. We developed a method to synthesize vertically aligned SiNW arrays in a hot-wall chemical vapor deposition system with tunable length, doping level, and diameter for systematical studies. Empowered by the synthetic control, various types of vertical SiNW arrays were characterized by both steady-state (photoelectrochemical measurement) and transient (electrochemical impedance spectroscopy) techniques in a photoelectrochemical cell platform. Additionally, SiNWs were demonstrated to be a promising candidate for photoelectrochemical aromatic ketone reduction and CO₂ fixation. The reactions studied in this thesis are in close resemblance to natural photosynthesis and the resulted product molecules are precursors to nonsteroidal anti-inflammatory drugs, ibuprofen and naproxen. Lastly, vertical transparent conductive oxide nanotubes were prepared from vertical SiNW array templates. Ultrathin hematite (Fe₂O₃) film was coated on the nanotube scaffold by atomic layer deposition to form a heteronanostructure photoelectrode for efficient solar water oxidation. Our results highlight the potential of vertically aligned SiNW arrays in solar cell, solar water splitting and artificial photosynthesis applications
Thesis (PhD) — Boston College, 2012
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Jayanty, Vivi. "Miniaturized electron-impact-ionization pumps using double-gated isolated vertically aligned carbon nanotube arrays." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75659.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 67-71).
There is a need for microscale vacuum pumps that can be readily integrated with other MEMS and electronic components at the chip-scale level. Miniaturized ion pumps exhibit favorable scaling down because they are surface-limited and miniaturization increases the ratio between the active surface and the chamber volume, resulting in enhanced ionization and pump rates. Therefore, scaled-down ion pumps are a promising choice for a variety of applications including portable mass spectrometers and sub-mm wavelength vacuum amplifiers. Our micropump architecture consist of a field-emission electron source that is an array of double-gated isolated vertically aligned carbon nanotubes (VA-CNTs), an electronimpact- ionization region, and a non-evaporative ion-implantation getter. Single-gated VA-CNT FEAs were tested as field emitters in high vacuum (10-9 Torr). The current density of the tested device is ~0.5A/cm2 (total current of 0.4mA) and a field enhancement factor of 1.41 x106 V/cm was measured, which is comparable to the simulation results by COMSOL. Two ways to fabricate double-gated VA-CNT FEAs were reported: one has the focus gate in plane with the extractor gate and the other has the focus gate above the extractor gate. Due to problems on fabrication process of double-gated VA-CNTs (short circuit between emitters, extractor gate, and focus gate), we were not able to collect four-terminal measurement, electron-impact-ionization, and pump data. However, procedure on how to collect and analyze field emission data with two gates to find [beta]G and [beta]F was described. In addition, procedures on how to collect and analyze data on electron impact ionization pump were also presented.
by Vivi Jayanty.
S.M.
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Chen, Jiajun. "Highly Sensitive and Selective Gas Sensors Based on Vertically Aligned Metal Oxide Nanowire Arrays." ScholarWorks@UNO, 2010. http://scholarworks.uno.edu/td/106.
Full textAbstract:
Mimicking the biological olfactory systems that consist of olfactory receptor arrays with large surface area and massively-diversified chemical reactivity, three dimensional (3D) metal oxide nanowire arrays were used as the active materials for gas detection. Metal oxide nanowire arrays share similar 3D structures as the array of mammal's olfactory receptors and the chemical reactivity of nanowire array can be modified by surface coatings. In this dissertation, two standalone gas sensors based on metal oxide nanowire arrays prepared by microfabrication and in-situ micromanipulation, respectively, have been demonstrated. The sensors based on WO3 nanowire arrays can detect 50 ppb NO2 with a fast response; well-aligned CuO nanowire array present a new detection mechanism, which can identify H2S at a concentration of 500 ppb. To expand the material library of 3D metal oxide nanowire arrays for gas sensing, a general route to polycrystalline metal oxide nanowire array has been introduced by using ZnO nanowire arrays as structural templates. The effectiveness of this method for high performance gas sensing was first investigated by single-nanowire devices. The polycrystalline metal oxide coatings showed high performance for gas detection and their sensitivity can be further enhanced by catalytic noble metal decorations. To form electronic nose systems, different metal oxide coatings and catalytic decorations were employed to diversify the chemical reactivity of the sensors. The systems can detect low concentrated H2S and NO2 at room temperature down to part-per-billion level. The system with different catalytic metal coatings is also capable of discriminiating five different gases (H2S, NO2, NH3, H2 and CO).
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Brownlee, Benjamin James. "Electrochemical Sensors Enhanced by Convection and by 3D Arrays of Vertically Aligned Carbon Nanotubes." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9197.
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Early and accessible diagnostics are important elements to reducing the negative side-effects of untreated disease. One key advancement in diagnostic monitoring is through the development of highly sensitive sensors that have the capability to detect lower concentrations, while still remaining accessible for point-of-care use. This dissertation characterizes electrochemical sensing platforms that are enhanced by convection and by 3D electrodes made from high surface area, vertically aligned carbon nanotubes (VACNTs). Free-standing VACNTs were patterned into microchannel arrays for flow-through amperometric sensing. Convective mass transfer enhancement was shown to improve sensor performance in amperometric sensing through the use of high surface area to fluid volume structures and concentration boundary layer confinement. Through-flow sensing of hydrogen peroxide produced drastically higher signals than stirred sensing, with over 90% of the hydrogen peroxide being oxidized as it passed through the channels. Non-enzymatic sensing of glucose was achieved by chemical reaction of glucose with methyl viologen to produce on average 3.4 electrons per glucose molecule, significantly higher than that obtained with enzymatic sensing with glucose oxidase. A scaled down sensor enabled detection from 200 μL of glucose by flow injection analysis with a limit of detection of 360 nM and a linear sensing range up to at least 150 μM glucose. Such sensing range offers the potential to measure glucose levels found in saliva. This work demonstrates the utility of high aspect ratio electrodes made of VACNTs. Convection and surface area are shown to enhance the sensitivity of flow-through VACNT amperometric sensors by effectively utilizing the available analyte to increase the measured current density. Advances in nanomaterials, combined with electrochemical impedance spectroscopy, have allowed impedimetric biosensors to have high sensitivity while remaining label-free, pushing towards enabling portable diagnosis at the point-of-care. Porous, 3D VACNT electrodes for impedance-based biosensing were fabricated with different electrode height, gap width, and configuration. Sensitivity was characterized by functionalizing the representative protein streptavidin onto VACNT electrodes for detection of biotin. Tall, closely-spaced VACNT interdigitated electrodes are shown to have the highest electroactive surface area (15x the 2D geometric area) and the highest sensitivity, allowing for a 1 ng/mL limit of detection. Aspect ratio and surface area are shown to be important factors in determining the sensitivity of 3D VACNT interdigitated electrodes for impedimetric sensing of biomolecules bound to electrode surfaces. Although this biosensing platform is shown with streptavidin and biotin, it could be extended to other proteins, antibodies, viruses, and bacteria.
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Cheng, Yajuan. "Synthesis of well arrayed structures with assistance of statistical experimental design." Doctoral thesis, KTH, Materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172938.
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During the synthesis of well arrayed nano/micro structures through wet chemical methods, plenty of parameters are usually involved. Consequently, it is extremely time- and cost-consuming to find out the optimized synthesis conditions by using the conventional "changing one separate factor at a time" (COST) strategy. Instead, the "statistical experimental design" method has been proven in a few works to be an efficient method for experiments involving many parameters. With this method, the responses could be optimized efficiently by using only a few experiments. Besides, several responses can be optimized simultaneously. Also, models could be built up and the changing tendency can be plotted to predict the required experimental settings for specific tasks. Two types of well arrayed structures including monolayer arrays of silica spheres and vertically aligned ZnO rod arrays were investigated in this work. Monolayer arrays of silica spheres were synthesized by using a dual-speed spin coating method. With assistance of statistical experimental design, the accelerating rate, the second rotation speed and time of the dual-speed spin coating system were found as non-significant parameters to the ordering degree of the obtained monolayer, and thus they can be fixed. This finding could remarkably increase the feasibility of optimizing the practical process. On the other hand, the relative humidity, the first rotation speed and the suspension concentration are identified as the significant parameters to the structures of the monolayer. Moreover, the optimal values for these three parameters were identified: 23% for the relative humidity, 1000 rpm for the first rotation speed and 30 wt.% for the suspension concentration. With these optimized parameters, the area of the obtained silica sphere monolayers reached over 1 cm2 and the defect-free domain size reached over 4000 μm2. These values are considerably higher compared to the previously reported values. Vertically aligned ZnO rod arrays were fabricated by chemical bath deposition. Parameters including precursor concentration, pH value, reaction temperature, reaction time and addition of capping agent were optimized by using statistical experimental design to improve and optimize the growth quality of ZnO rod arrays. Through several stages of optimization, the growth quality of the obtained structures was remarkably enhanced from sparse or clustered ZnO rods to upright and dense ZnO rods. The boundary conditions to achieve vertically aligned ZnO rods, such as a neutral solution and a precursor concentration over 0.02M, were determined. The changing tendency of the texture coefficient and aspect ratio with the factors was also plotted to predict the required experimental settings for specific requests. The points or regions to achieve the optimal properties were identified as well. For instance, the concentration should be as close as to 0.1 M, while the reaction temperature should be limited to 80-90 ◦C, to achieve the ideal preferential growth. With the optimized parameters, the texture coefficient reached almost the perfect value 1, and the aspect ratio was elevated to 21. Moreover, to obtain a dense ZnO thin film, tri-sodium citrate was added to the reaction system. The diameter was systematically controlled through varying the parameters. When both the diameter and the texture coefficient reached the optimal values, the rods were merged together to form a dense ZnO thin film. Furthermore, comments on the statistical experimental method are proposed, and both the advantages and disadvantages are presented according to the present thesis work. This might help the researchers to avoid the disadvantages and thus to employ this method more efficiently in the future.QC 20150903
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Klankowski, Steven Arnold. "Hybrid core-shell nanowire electrodes utilizing vertically aligned carbon nanofiber arrays for high-performance energy storage." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/27651.
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Doctor of PhilosophyDepartment of Chemistry
Jun Li
Nanostructured electrode materials for electrochemical energy storage systems have been shown to improve both rate performance and capacity retention, while allowing considerably longer cycling lifetime. The nano-architectures provide enhanced kinetics by means of larger surface area, higher porosity, better material interconnectivity, shorter diffusion lengths, and overall mechanical stability. Meanwhile, active materials that once were excluded from use due to bulk property issues are now being examined in new nanoarchitecture. Silicon was such a material, desired for its large lithium-ion storage capacity of 4,200 mAh g[superscript]-1 and low redox potential of 0.4 V vs. Li/Li[superscript]+; however, a ~300% volume expansion and increased resistivity upon lithiation limited its broader applications. In the first study, the silicon-coated vertically aligned carbon nanofiber (VACNF) array presents a unique core-shell nanowire (NW) architecture that demonstrates both good capacity and high rate performance. In follow-up, the Si-VACNFs NW electrode demonstrates enhanced power rate capabilities as it shows excellent storage capacity at high rates, attributed to the unique nanoneedle structure that high vacuum sputtering produces on the three-dimensional array. Following silicon’s success, titanium dioxide has been explored as an alternative highrate electrode material by utilizing the dual storage mechanisms of Li+ insertion and pseudocapacitance. The TiO[subscript]2-coated VACNFs shows improved electrochemical activity that delivers near theoretical capacity at larger currents due to shorter Li[superscript]+ diffusion lengths and highly effective electron transport. A unique cell is formed with the Si-coated and TiO[subscript]2-coated electrodes place counter to one another, creating the hybrid of lithium ion battery-pseudocapacitor that demonstrated both high power and high energy densities. The hybrid cell operates like a battery at lower current rates, achieving larger discharge capacity, while retaining one-third of that capacity as the current is raised by 100-fold. This showcases the VACNF arrays as a solid platform capable of assisting lithium active compounds to achieve high capacity at very high rates, comparable to modern supercapacitors. Lastly, manganese oxide is explored to demonstrate the high power rate performance that the VACNF array can provide by creating a supercapacitor that is highly effective in cycling at various high current rates, maintaining high-capacity and good cycling performance for thousands of cycles.
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Coskun, Nart. "A comparison of configutration arrays for the resistivity and induced polarisation methods and a direct interpretation technique for vertical profiling field data." Thesis, University of York, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261078.
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Arata, Frank A. "Nucleate boiling heat transfer study of direct immersion cooling of a 3x3 array of vertically orientated electronic components in a dielectric fluid." Thesis, Monterey, California : Naval Postgraduate School, 1992. http://handle.dtic.mil/100.2/ADA257558.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1992.Thesis Advisor: Kelleher, M. D. "September 1992." Description based on title screen as viewed on April 16, 2009. Includes bibliographical references (p. 92). Also available in print.
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Rivai, Kathryn. "Data analysis of experimental test results of a wave energy converter for the WECfarm project." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
There are different technologies to exploit marine energy, one of these is wave energy converters (WEC), that use the energy of the waves to produce electricity. To maximize the power production, the WECs are placed in arrays with specific geometric configurations, therefore it is important to study the interaction between the WECs (near-field interactions) and the effects of the WEC array on the waves behind the array (far-field effects).
A single ‘Master WEC’ is being developed, tested and fine-tuned prior to the array layout tests. The aim is to investigate and improve the behavior of the new WEC design, through tests in different waves conditions. The new shape of the WEC has been designed using a numerical study in order to improve the behavior of the WEC, reducing the surge force and increasing its radiation. The objective of this master dissertation is to study the behavior of the scale model (scale factor 0.525) of the hydrodynamic part of the WEC. Several tests were performed in the wave flume in the laboratory of Ghent University, and the obtained database was subsequently analyzed.
First a free decay test was performed to determine the natural period and the damping factor of the buoy.
Then the results from regular waves tests were analyzed to determine the interaction between two buoys using regular waves with different wave periods.
Several tests were conducted to quantify the horizontal and vertical forces acting on the buoy unit, with differing dispositions of the load cells and differing wave heights and periods.
All the tests were performed with a water depth of 0.65 m.
The data obtained from the measuring devices in the tests was processed with MATLAB to check the repeatability of the tests, to obtain graphs, averaged values of the forces and the acceleration acting on the buoy unit, amplitude and phase of the oscillatory motion of the buoy.
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Kiaei, Kimia. "Hierarchical carbon structures with vertically- aligned nanotube carpets for oil-water separation under different conditions." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1567700408926846.
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Matthews, Scott T. "Natural convection immersion cooling of an array of vertically oriented heated protrusions in an enclosure filled with a dielectric liquid : effects of enclosure width, Prandtl number and component orientation." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/28388.
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Hawatmeh, Derar Fayez. "Three Dimensional Direct Print Additively Manufactured High-Q Microwave Filters and Embedded Antennas." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7165.
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The need for miniaturized, and high performance microwave devices has focused significant attention onto new fabrication technologies that can simultaneously achieve high performance and low manufacturing complexity. Additive manufacturing (AM) has proven its capability in fabricating high performance, compact and light weight microwave circuits and antennas, as well as the ability to achieve designs that are complicated to fabricate using other manufacturing approaches. Direct print additive manufacturing (DPAM) is an emerging AM process that combines the fused deposition modeling (FDM) of thermoplastics with micro-dispensing of conductive and insulating pastes. DPAM has the potential to jointly combine high performance and low manufacturing complexity, along with the possibility of real-time tuning.
This dissertation aims to leverage the powerful capabilities of DPAM to come-up with new designs and solutions that meet the requirements of rapidly evolving wireless systems and applications. Furthermore, the work in this dissertation provides new techniques and approaches to alleviate the drawbacks and limitations of DPAM fabrication technology. Firstly, the development of 3D packaged antenna, and antenna array are presented along with an analysis of the inherent roughness of 3D printed structures to provide a deeper understanding of the antenna RF performance. The single element presents a new volumetric approach to realizing a 3D half-wave dipole in a packaged format, where it provides the ability to keep a signal distribution network in close proximity to the ground plane, facilitating the implementation of ground connections (e.g. for an active device), mitigating potential surface wave losses, as well as achieving a modest (10.6%) length reduction. In addition, a new approach of implementing conformal antennas using DPAM is presented by printing thin and flexible substrate that can be adhered to 3D structures to facilitate the fabrication and reduce the surface roughness. The array design leverages direct digital manufacturing (DDM) technology to realize a shaped substrate structure that is used to control the array beamwidth. The non-planar substrate allows the element spacing to be changed without affecting the length of the feed network or the distance to the underlying ground plane.
The second part describes the first high-Q capacitively-loaded cavity resonator and filter that is compatible with direct print additive manufacturing. The presented design is a compromise between quality factor, cost and manufacturing complexity and to the best of our knowledge is the highest Q-factor resonator demonstrated to date using DPAM compatible materials and processes. The final version of the single resonator achieves a measured unloaded quality factor of 200-325 over the frequency range from 2.0 to 6.5 GHz. The two pole filter is designed using a coupled-resonator approach to operate at 2.44 GHz with 1.9% fractional bandwidth. The presented design approach simplifies evanescent-mode filter fabrication, eliminating the need for micromachining and vias, and achieving a total weight of 1.97 g. The design is fabricated to provide a proof-of-principle for the high-Q resonator and filter that compromises between performance, cost, size, and complexity. A stacked version of the two-pole filter is presented to provide a novel design for multi-layer embedded applications.
The fabrication is performed using an nScrypt Tabletop 3Dn printer. Acrylonitrile Butadiene Styrene (ABS) (relative permittivity of 2.7 and loss tangent of 0.008) is deposited using fused deposition modeling to form the antenna, array, resonator, and filter structures, and Dupont CB028 silver paste is used to form the conductive traces conductive regions (the paste is dried at 90 °C for 60 minutes, achieving a bulk DC conductivity of 1.5×106 S/m.). A 1064 nm pulsed picosecond Nd:YAG laser is used to laser machine the resonator and filter input and output feedlines.
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Chan, Tsung Hsiang, and 詹倧祥. "Large Area Vertical Transistor Array." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/ky3k3a.
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Su, Ying-Chuan, and 蘇映全. "Vertical Organic Transistor Array Prepared by Photolithography." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7zy68f.
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碩士國立交通大學
物理研究所
106
This thesis is focus on the vertical organic transistor array prepared by photolithography process. Consider the scale of the pixel in displays, we not merely scale down the active region of the transistor from millimeters to micrometers but also try to form a transistor array on the substrate. In scaling down, the alignment in the photolithography process can be used to define the accurate active region. We successfully realize 24 Space-Charge Limited Transistors(SCLT) whose active area is 80 μm×80 μm on the 3 cm×4 cm glass substrate. We often choose blade coating to coat the organic transporting layer due to low cost of coating solution and being suitable in the fabrication of large area films. However, this coating method causes the low number of transistors having the ability to switch on/off in the array. We will discuss the reason later in this thesis. To solve this problem, we choose spin coating instead to coat the organic transporting layer. The number of transistors which is capable of switching on/off in the array also increases.
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Sun, Way-Chuang, and 孫維政. "Seismic Response of Soil at Hualien Vertical Array." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/01821672297173993235.
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碩士國立臺灣大學
土木工程學系
85
ABSTRATE The main purpose of this work is to identify the shear velocity and damping ratio of soil system basedon the earthquake record of Hualien vertical array andto certify the ground response under excitation. Shear stress and strain reations at various depth arederived from the earthquake record of vertical array inHualien site. Then the equivalent shear velocity and damping ratio can be identified from hystretic loop ofsoil. Subsequently the shear velocity and damping ratioby the method of system identification are compared withthose deduced by PS logging. The predictions of deconvolution analysis by the methodproposed here in agree better with the observations thanby PS logging.