• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 223
  • 65
  • 48
  • 33
  • 18
  • 15
  • 9
  • 4
  • 4
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 484
  • 103
  • 87
  • 64
  • 59
  • 44
  • 43
  • 37
  • 37
  • 37
  • 36
  • 33
  • 33
  • 32
  • 32
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
171

Towards two dimensional optical beam steering with silicon nanomembrane-based optical phased arrays

Kwong, David Nien 18 October 2013 (has links)
Silicon based on-chip optical phased arrays are an enabling technology to achieving agile and compact large angle beam steering. In this work, a single layer array is presented, and approaches to multilayer 3D photonic integration for achieving a 2D array are also discussed. Finally, two dimensional optical beam steering is achieved using both thermo-optic and wavelength tuning. Various structures are considered as an alternative to the conventionally used shallow etched surface gratings to achieve narrow beam widths in the far field along with low switching power. The corrugated waveguide interspersed with 2D photonic crystal for crosstalk suppression is presented as a novel structure for coupling to free space that can provide lithographically defined index contrast in a single fabrication step, along with the smallest beam widths presented to date, at 0.25°. In addition, a polysilicon overlay with an oxide etch stop layer on top of a silicon waveguide is also presented as a grating coupler that achieves narrow far field beam widths. With this structure, two dimensional steering of 20° X 15° is demonstrated with a 16 element optical phased array, with a beam width of 1.2° X 0.4° and maximum power consumption of 20mW per channel. / text
172

A quasi Yagi antenna with end fire radiation over a metal ground

Melais, Sergio E 01 June 2009 (has links)
This dissertation presents a detailed investigation on the development of a quasi Yagi antenna with end fire radiation at 2.4 GHz (ISM band) over a metal reflector. Realization of an end fire radiator on top of a metal ground is very difficult because the reflected waves and image currents from the ground degrade the frequency bandwidth and steer the radiation pattern in the broadside direction. This destructive interference is reduced in this research through two quasi Yagi-ground configurations. The first arrangement utilizes a substrate of suitable thickness (7.5mm-0.19 ?g) to displace the ground away from the antenna. The second design implements a high impedance surface (HIS) as ground plane for the antenna. The preferred HIS is the Jerusalem Cross Frequency Selective Surface (JC-FSS) because of its compact size, numerous parameters for tuning and frequency stability in the operating band for a large angular spectrum of TE and TM polarized incident waves. In this work a new parameter is added to the model used for the derivation of the JC-FSS which accounts for the substrate of the antenna lying on top of the FSS, this addition allows for a smaller cell grid. The results for the quasi Yagi antenna over the 7.5mm grounded slab presented an operational bandwidth of 190 MHz with 40°; of beam steering in the end fire direction while the quasi Yagi over the JC-FSS offered 260 MHz of functional bandwidth and 54° of beam steering towards the end fire direction. In addition, the quasi Yagi design over the JC-FSS decreases the combined profile (antenna/backing structure) by 33% in relation to the 7.5mm grounded slab. This dissertation combines for the first time a quasi Yagi antenna with a JC-FSS to achieve end fire radiation in the presence of a ground metal.
173

IEEE 802.11b wireless LAN sensor system and antenna design

Guerra, Leonard 01 June 2006 (has links)
A novel approach to miniaturizing an 802.11b WLAN card using folded-flex ultra-thin substrates is presented. A 73 percent reduction in size was realized using hybrid circuits on FR4 and polyimide. There is even more potential for further reduction if more copper layers are used. The miniaturized 802.11b WLAN cards were used to design 802.11b wireless sensor nodes. A research test-bed was setup to study how 802.11b networked sensor nodes could operate in the field. There are many applications for such sensor networks like habitat monitoring, object tracking, seismic detection, military surveillance, or fire detection to name a few. This investigation focuses on the requirements, design, and performance of a miniaturized 802.11b wireless LAN sensor node that is reliable, can be deployed in large-scale, and has the endurance long-lived for surveillance applications. An aperture coupled microstrip antenna is investigated for 2.44 GHz wireless local area networks (WLAN) which has the advantages of being low-profile and compact. The most important parameters for antenna optimization have been determined through extensive simulation using Ansoft's HFSS and experimental verification. As a result, an omnidirectional antenna with a size of 36.2 mm x 32 mm x 4.75 mm has been realized using Rogers 5880 duroid (permittivity = 2.20 ; loss tangent = 0.0004) with 4.4 dBi of gain, > 80 MHz, and a return loss > -32 dB. These types of performance characteristics make the antenna highly desirable for both 802.11b and Bluetooth applications.
174

Silicon nanomembranes for optical phased array (OPA) applications

Hosseini, Amir 04 November 2011 (has links)
Theory, design, fabrication and characterization of on-chip optical beam steering systems are presented in this dissertation. Silicon photonics is being considered for integration with conventional CMOS technology for large-band width and low loss on and off-chip communications. We choose silicon nanomembrane, or silicon-on-insulator (SOI) substrates for implementation of large-angle and agile beam steeres. While working on the targeted device, we contributed to the theory, modeling, engineering and implementation of different building blocks. Multimode-interference couplers (MMIs) constitute important parts of this dissertation. These devices are commonly used as on-chip beam splitters, optical switches and on-chip static phase shifters. The MMIs’ principles of operation are suited in more details and design rules are derived for the first time. MMI based beam splitters with number of outputs as large as 12 are fabricated and tested on SOI wafers. Traditionally, MMIs devices were designed by means of computationally expensive numerical simulations. Numerically and experimentally, we show that our analytical design rules make design of MMIs with low insertion loss and highly uniform outputs possible without additional optimization processes. Optical phased arrays include phase shifter blocks. In the first prototype, we use micro-heaters for tuning the optical phase. The bread-loafing effect, which is generally considered an undeniable phenomenon in the silicon industry, is engineered to realize a mechanical structure to efficiently direct heat toward the silicon waveguides. We also investigate slow light photonic crystal based delay lines to be used as phase shifters. An important drawback of such devices is the low coupling efficiency between slow-light photonic crystal waveguides and fast light strip waveguides. We numerically and experimentally investigate the coupling efficiency, and show for the first time that a few-period long fast-light photonic crystal waveguide without any group index tapering suffices for efficient coupling. The prototype is fabricated, packaged and tested and optical beam steering angle over ±30degrees is demonstrated. Finally, preliminary investigations for 3D implementation of the beam steerer system are presented to clarify the approaches to take for future works. / text
175

Evaluating Swiftpoint as a Mobile Device for Direct Manipulation Input

Amer, Taher January 2006 (has links)
Swiftpoint is a promising new computer pointing device that is designed primarily for mobile computer users in constrained space. Swiftpoint has many advantages over current pointing devices: it is small, ergonomic, has a digital ink mode, and can be used over a flat keyboard. This thesis aids the development of Swiftpoint by formally evaluating it against two of the most common pointing devices with today's mobile computers: the touchpad, and mouse. Two laws commonly used with pointing devices evaluations, Fitts' Law and the Steering Law, were used to evaluate Swiftpoint. Results showed that Swiftpoint was faster and more accurate than the touchpad. The performance of the mouse was however, superior to both the touchpad and Swiftpoint. Experimental results were reflected in participants' choice for the mouse as their preferred pointing device. However, some participants indicated that their choice was based on their familiarity with the mouse. None of the participants chose the touchpad as their preferred device.
176

An examination of the utility of the concept of governance in relation to the sports of swimming, football and cricket

Hindley, David January 2002 (has links)
Much has been written in recent years about governance in the areas of political science, public policy, local government, and international relations. However, social scientific usage of the governance concept has been eclectic, diverse and at times contradictory (Jessop, 1998: 29) as well as confusing and sometimes misleading. In addition, despite the burgeoning literature on governance, little research effort has to date been devoted to examining the term in relation to the organisation, administration and management of sports organisations. This thesis is concerned with reviewing the range of applications of the concept, and in particular evaluating the utility of governance in understanding aspects of the management and policy process of sport. For the purpose of this study a case study approached is adopted, focusing on three sports: cricket, association football and swimming, and within these the pattern of interrelationships between the government and related agencies, the media and broadcasters, athlete-representative groups and supporter organisations, as well as focusing on issues relating to gender. The study concludes by arguing that governance broadens our conceptual repertoire, introduces greater sensitivity and subtlety into policy analysis, and highlights problems of coordination both in government and across a range of agencies, organisations and policy actors.
177

Optimierung der Hupkraftverteilung eines airbagintegrierten Automobillenkrades mit Hilfe einer Parameterstudie / Horn force optimization of a airbag integrated automotive steering wheel with a parameter analysis

Pietsch, Karsten 12 May 2011 (has links) (PDF)
Die Hupkraftverteilung eines airbagintegrierten Automobillenkrades wird mit Hilfe einer Parameterstudie in MathCAD so optimiert, das an jeder Krafteinleitungsposition die Hupe mit einer geforderten Mindestkraft betätigt werden kann. Nach der Modellierung in MathCAD der zugehörigen Geometrie und der Dimensionierung der Federlagerung ist das zugehörige mechanische Ersatzmodell mit Hilfe einer Parameterstudie verändert worden, so dass die Hupkraftforderung erfüllt wird.
178

Perspectives on capacity strengthening and co-learning in communities: Experiences of an Aboriginal community-based research steering committee

Stringer, Heather 05 January 2016 (has links)
Community-university partnerships have become more prevalent to support community-based research, especially as a collaborative approach to research with Aboriginal Peoples in Canada. One practice is the activation of a community-based research steering committee to initiate, govern, and review research pertaining to their local community. Within literature related to community-based research, perspectives on capacity strengthening and co-learning from the members of a community-based research steering committee are under-represented. A qualitative case study approach was used to explore the research question: What are the experiences of the Alexander Research Committee (ARC) members in defining and operationalizing capacity strengthening and co-learning across multi-sectoral research projects? Nine current and past members of the ARC participated in individual semi-structured interviews and five of these ARC members also participated in a subsequent focus-group discussion. Analysis of these qualitative data indicated that foundational relationships and a conducive learning environment are key factors for a community-based research committee to experience co-constructed knowledge and learning. The findings of this study highlight the importance of an operational foundation of trusting relationships in order to establish and sustain a working environment where a community-based research committee can learn together and from each other. This study also yielded insights about how this community-based research committee predicated capacity strengthening from the understanding that ‘we are all learners’, with each member bringing forward unique strengths, questions and growth to the research processes. / Graduate
179

Hållbar utveckling i F-3 : En kvalitativ studie om styrdokumentens och lärarnas beskrivningar av undervisning för hållbar utveckling / Teaching for sustainable development in primary school : A qualitative study of steering documents and teachers' descriptions of education for sustainable development

Tavio Viera, Natalie January 2015 (has links)
Previous research has shown that sustainable development is a complex concept that can be difficult to apply in a teaching context. The purpose of this study is to investigate how the concept of sustainable development and education for sustainable development are formulated in school policy documents related to the five teachers' descriptions of how they practice it in reality. I have, based on the purpose of this study issued following questions: What are projected on sustainable development and education for sustainable development in the school curriculum as well as other documents that support school activities? What is included? What is not included? How does the teachers interpret the concept of sustainable development? How does the teachers say that they work with sustainable development in the subjects of social science? What difficulties does the teachers experience with education for sustainable development?  This study is made through a qualitative method based on a contextual analysis and interviews with five teachers. The results show that neither the documents nor the teachers' descriptions of education for sustainable development seem to indicate that sustainable development is seen as a political issue. Rather, the descriptions indicate that sustainable development is seen as a matter of ethics. In both the documents and the teachers' descriptions all levels of sustainable development i.e. local, national and international level are mentioned. Therefore, it is also described as a collective responsibility rather than an individual responsibility. In the teachers' descriptions of sustainable development the environmental dimension is mainly mentioned. The documents on the other hand emphasize all dimensions i.e. the social, economic and environmental. According to the documents these three should be balanced in order for sustainable development to be possible to achieve. Teachers' descriptions of how they work with sustainable development show a more clear vision of education for sustainable development as value mediation compared to what is written out in the documents. The steering documents also emphasize that knowledge of sustainable development is required to enable sustainable development. The difficulties that the teachers’ describe on education for sustainable development is mostly related to the complexity of the concept.  One conclusion of this study is that the documents and the teachers' descriptions of sustainable development and education for sustainable development are quite similar. This despite the few differences mentioned above and the fact that one teacher believes that the directives of the curriculum syllabus is a bit unclear in terms of sustainable development.
180

Behaviour Modelling and System Control with Human in the Loop / Modélisation du comportement et commande avec l'humain dans la boucle

Onyango, Stevine Obura 13 February 2017 (has links)
Malgré le progrès en recherche et développement dans le domaine de système autonome, de tels systèmes nécessitent l’intervention humaine pour résoudre les problèmes imprévus durant l’exécution des tâches par l’utilisateur.Il est donc nécessaire, malgré cette autonomie, de tenir compte du comportement du conducteur et il est difficile d’ignorer l’effet de l’intervention humaine dans le cadre de l’évolution continue de l’environnement et des préférences de l’utilisateur. Afin d’exécuter les opérations selon les attentes de l’opérateur, il est nécessaire d’incorporer dans la commande les besoins de l’utilisateur.Dans les travaux présentés dans cette thèse un modèle comportemental de l’utilisateur est développé et intégré dans la boucle de commande afin d’adapter la commande à l’utilisateur. Ceci est appliqué à la commande des fauteuils électrique et assiste dans la navigation du fauteuil dans un milieu encombré.Le développement du modèle comportemental est basé sur la méthode de potentielles orientées et la détection des obstacles et le comportement du conducteur vs de ces obstacles par l’adaptation duL’étude contribue également au développement d’un modèle dynamique du fauteuil utilisable dans des situations normales et exceptionnelles telle que le dérapage. Ce modèle est développé pour un le cas le plus courant des fauteuil avec roues arrière conductrices utilisant le formalisme Euler Lagrange avec les forces gravitationnelles et sur des surfaces inclinées.Dans la formulation de la commande, le modèle du conducteur est introduit dans la boucle de commande. L’optimalité de la performance est assurée par l’utilisation du commande prédictif généralisé pour le système en temps continue. Les résultats de la simulation démontrent l’efficacité de l’approche proposée pour l’adaptation de la commande au comportement du conducteur / Although the progressive research and development of autonomous systems is fairly evident, such systems still require human interventions to solve the unforeseen complexities, and clear the uncertainties encountered in the execution of user-tasks. Thus, in spite of the system's autonomy, it may not be possible to absolutely disregard the operator's role. Human intervention, particularly in the control of auto-mobiles, may as well be hard to ignore because of the constantly changing operational context and the evolving nature of the drivers' needs and preferences. In order to execute the autonomous operations in conformity with the operator's expectations, it may be necessary to incorporate the advancing needs and behaviour of the operator in the design. This thesis formulates an operator behaviour model, and integrates the model in the control loop to adapt the functionality of a human-machine system to the operator's behaviour. The study focuses on a powered wheelchair, and contributes to the advancement of steering performance, through background assistance by modelling, empirical estimation and incorporation of the driver's steering behaviour into the control system. The formulation of the steering behaviour model is based on two fundamentals: the general empirical knowledge of wheelchair steering, and the experimental steering data captured by a standard powered wheelchair, on both virtual and real environments. The study considers a reactive directed potential field (DPF) method in the modelling of drivers' risk detection and avoidance behaviour, and applies the ordinary least square procedure in the identification of best-fitting driver parameters. The study also contributes to the development of a dynamic model of the wheelchair, usable under normal and non-normal conditions, by taking into consideration the conventional differential drive wheelchair structure with two front castor wheels. Derivation of the dynamic model, based on the Euler Lagrange formalism, is carried out in two folds: initially by considering the gravitational forces subjected to the wheelchair on inclined configurations with no slipping situations, and finally by incorporating slipping parameters into the model. Determination of the slipping parameters is approached from the geometric perspective, by considering the non-holonomic motions of the wheelchair in the Euclidean space. In the closed-loop model, the input-output feedback controller is proposed for the tracking of user inputs by torque compensation. The optimality of the resulting minimum-phase closed-loop system is then ensured through the performance index of the non-linear continuous-time generalised predictive control (GPC). Simulation results demonstrate the expected behaviour of the wheelchair dynamic model, the steering behaviour model and the assistive capability of the closed-loop system

Page generated in 0.0159 seconds