Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xiii, 195 p.; also includes graphics (some col.) Includes bibliographical references (p. 190-195). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 158-167).

Thesis (Ph.D.)--City University of Hong Kong, 2009. / "Submitted to Department of Manufacturing Engineering and Engineering Management in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [169]-205)

This thesis contains some results on the behavior of a delay differential equation (DDE) with two delays, at a Hopf bifurcation, for the nonzero equilibrium, using the growth rate, r, as bifurcation parameter. This DDE is a model for population growth, incorporating a maturation delay, and a second delay in the harvesting term. Considering a Taylor expansion of the non-dimensionalized model, we find a region of stability for the nonzero equilibrium, after which we find a pair of ODEs which help define the flow on the center manifold. We then find an expression for the first Lypapunov coefficient, which changes sign, so we also find the second Lyapunov coefficient, allowing us to predict multi-stability in the model. Numerical simulations provide examples of the behavior expected. For a similar model with one delay (PMC model), we prove the Hopf bifurcation at the nonzero equilibrium is always supercritical.

Performance and stability of bilateral teleoperation control systems are adversely affected by variations in environment dynamics and time delay in communication channel. Prior relevant research in the literature has mainly yielded control algorithms that sacrifice performance in order to guarantee robust stability. In contrast, this thesis proposes methods to deal with these two main problems in order to maintain the stability without compromising performance. To handle changes in environment dynamics, a multiple model controller for teleoperation is introduced. It is assumed that the dynamics of the environment are governed by a model from a finite set of environment models at any given time with Markov chain switching between these models. The first-order generalized pseudo-Bayesian (GPB1) multi-model estimation technique is used to identify the effective model at each time step given the sensory observations. The control action is a weighted sum of mode-based control laws that are designed for each mode of operation. The second major problem in teleoperation systems that this thesis deals with is communication channel time delay. The constant time-delay problem is solved using two different methods, i.e. discrete-time and continuous-time predictive type Linear Quadratic Gaussian (LQG) controllers. The treatment of the problem in the discrete-time domain allows for the development of a finite dimension state-space model that explicitly encompasses the time delay. The robustness of the controller with respect to uncertainty in the system parameters is examined via Nyquist analysis. In continuous-time, a modified state transformation is proposed to obtain delay-free dynamics based on the original dynamics with delayed inputs and outputs. The application of the continuous-time LQG control synthesis to these reduced dynamics yields a control law that guarantees closed-loop stability and performance. Mode-based controllers are designed for each phase of operation, i.e. free motion/soft contact and contact with rigid environments. Performance objectives such as position tracking and tool impedance shaping for free motion/soft contact, as well as position and force tracking for contact with rigid environments are incorporated into the LQG control design framework. Simulation and experimental results are presented for each of the proposed controllers in various scenarios. These results demonstrate the effectiveness of the proposed methods in providing a stable transparent interface for teleoperation in free motion and in contact with rigid environments. / Thesis / Master of Applied Science (MASc)

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / This paper will describe a test technique developed to measure the delays caused by the use of asynchronous multiplexers/demultiplexers. These devices are used for both signal transmission (microwave and fiber optic) and signal recording (especially helical scan digital recorders). The test technique involves the generation and decoding of asynchronous telemetry signals. The bit rates of the telemetry signals are variable. Relative time is embedded in the telemetry signal as a 32-bit data word. The paper will also present measured delays for two multiplexers/demultiplexers for different combinations of bit rates.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Approved for public release; distribution is unlimited / The estimation of time delay and Doppler difference of a signal arriving at two physically separated sensors is investigated in this thesis. Usually, modified cross power spectrum coupled with Doppler compensation is used to detect a common, passive signal received at two separated sensors. Another successful approach uses the cross coherence to achieve this goal. This thesis modifies these two techniques to model the Doppler difference via an autoregressive (AR) technique. Analytical results are derived and experimentally verified via a computer simulation. Performance at high and low signal to noise ratios (SNRs) is examined. / http://archive.org/details/armodelingofcohe00leej / Captain, Korea Air Force

Dans cette thèse, on s'intéresse au développement de nouvelles méthodes d'auscultation GPR pour déterminer la géométrie et la structure des chaussées. Cette thèse a deux objectifs principaux. Tout d'abord, elle a pour but d'améliorer la compréhension des mécanismes de diffusion à très large bande dans un milieu stratifié composé d'interfaces rugueuses. Avec l'augmentation des fréquences d'utilisation de différents systèmes, les interfaces de chaussée ne peuvent plus être considérées comme planes. Ainsi, la rugosité des interfaces doit être prise en compte dans la modélisation de la propagation. Donc, une analyse de l'influence de cette rugosité sur l'onde rétrodiffusée a été réalisée. Elle a permis de montrer que la rugosité induit une décroissance en fréquence de l'amplitude des échos. Cette décroissance a ensuite été introduite dans le modèle du signal. Dans un second temps, plusieurs méthodes de traitement de signal ont été proposées pour estimer conjointement les paramètres de rugosité et d'épaisseur. D'abord, des méthodes multidimensionnelles ont été proposées en prenant en compte l'influence de la rugosité. Ensuite, afin de réduire la charge de calcul, des méthodes monodimensionnelles ont été proposées. Ces méthodes ont été évaluées à partir de signaux simulés. Les résultats ont montré de bonnes performances pour l'estimation des temps de retard et des paramètres de rugosité des interfaces. Enfin, les méthodes de traitement proposées dans ce manuscrit ont été testées sur des données expérimentales, qui permettent de valider les résultats théoriques et de montrer la faisabilité de la mesure de couches minces de chaussée et du paramètre de rugosité. / In this thesis, we focus on the development of new GPR methods to estimate the pavement structure. This thesis has two main objectives. First, it aims to improve the understanding of the scattering mechanisms for large-band radars in a stratified medium composed of rough interfaces. With increasing frequencies, pavement interfaces can no longer be considered as flat. The interface roughness must be taken into account in the propagation modelling. Thus, the influence of the roughness has been analysed. It has been shown that the interface roughness provides a continuous frequency decay of the magnitude of the echoes. This continuous frequency decay has then been introduced into the signal model. Secondly, several signal processing methods have been proposed to jointly estimate the roughness and thickness of pavement. Thus, multidimensional methods have been proposed by taking into account the roughness.Then, in order to reduce the computational burden, one-dimensional methods have also been proposed. From simulations, it can be seen that the proposed algorithms provide a good performance in parameter estimations (time delay, permittivity, roughness and thickness). Finally, the proposed signal processing methods are tested on experimental data. The results confirm the theoretical prediction. They show the feasibility to estimate both the thickness of thin pavements and roughness parameter.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.