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  • 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.

Comparison of the Performance of Different Time Delay Estimation Techniques for Ultrasound Elastography

Sambasubramanian, Srinath 2010 August 1900 (has links)
Elastography is a non-invasive medical imaging modality that is used as a diagnostic tool for the early detection of several pathological changes in soft tissues. Elastography techniques provide the local strain distributions experienced by soft tissues due to compression. The resulting strain images are called “elastograms”. In elastography, the local tissue strains are usually estimated as the gradient of local tissue displacement. The local tissue displacements are estimated from the time delays between gated pre- and post-compression echo signals. The quality of the resulting elastograms is highly dependent on the accuracy of these local displacement estimates. While several time delay estimation (TDE) techniques have been proposed for elastography applications, there is a lack of systematic study that statistically compares the performance of these techniques. This information could prove to be of great importance to improve currently employed elastographic clinical methods. This study investigates the performance of selected time delay estimators for elastography applications. Time delay estimators based on Generalized Cross Correlation (GCC), Sum of Squared Differences (SSD) and Sum of Absolute Differences (SAD) are proposed and implemented. Within the class of GCC algorithms, we further consider: an FFT-based cross correlation algorithm (GCC-FFT), a hybrid time-domain and frequency domain cross correlation algorithm with prior estimates (GCC-PE) and an algorithm based on the use of fractional Fourier transform to compute the cross correlation (GCC -FRFT) . Image quality factors of the elastograms obtained using the different TDE techniques are analyzed and the results are compared using standard statistical tools. The results of this research suggests that correlation based techniques outperform SSD and SAD techniques in terms of SNRe, CNRe, dynamic range and robustness. The sensitivity of GCC-FFT and SSD were statistically similar and statistically higher than those of all other methods. Within the class of GCC methods, there is no statistically significant difference between SNRe of GCC-FFT, GCC-PE and GCC –FRFT for most of the strain values considered in this study. However, in terms of CNRe, GCC-FFT and GCC-FRFT were significantly better than other TDE algorithms. Based on these results, it is concluded that correlation-based algorithms are the most effective in obtaining high quality elastograms.

Developing and automating time delay system stability analysis of dynamic systems using the Matrix Lambert W (MLW) function method

Pietarila, Kristel M., Fales, Roger. January 2009 (has links)
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 16, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Roger Fales. Vita. Includes bibliographical references.

Stability analysis and controller synthesis of continous-time linear time-delay systems

Du, Baozhu., 杜宝珠. January 2010 (has links)
published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Identification and adaptive control of retarded systems - a continuous time approach

Rad, A. B. January 1988 (has links)
No description available.

Multi-microprocessor control of processes with pure time delay

Mitchell, Richard James January 1987 (has links)
No description available.

Delay-Dependent Robust Stability Analysis and Stabilization for Uncertain Systems with Time-Varying Delay

Chen, Jun-Shen 04 September 2010 (has links)
This thesis concerns delay-dependent robust stability analysis and stabilization for time-delay system with uncertainties. By choosing new Lyapunov-Krasovskii functional and using methods which can reduce conservativeness of stability condition in the literature, new delay-dependent sufficient stability conditions are obtained in terms of linear matrix inequality. It is shown that the new stability conditions can provide less conservative results than some existing ones. Furthermore, the new stability conditions are also used to design the state feedback controllers. Finally, numerical examples are given to show the derived results and compared with results in the literature.

Computational algorithms for stability analysis of linear systems with time-delay /

Kalavagunta, Sushma, January 2003 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 26-28). Also available on the Internet.

Computational algorithms for stability analysis of linear systems with time-delay

Kalavagunta, Sushma, January 2003 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 26-28). Also available on the Internet.

Model order reduction of time-delay systems with variational analysis

Wang, Xiang, 王翔 January 2011 (has links)
published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

Delay identification and model predictive control of time delayed systems

Lu, Mu-Chiao, January 1900 (has links)
Thesis (Ph.D.). / Written for the Dept. of Electrical and Computer Engineering. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

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