Noninvasive viscoelasticity imaging, or “dynamic elastography”, methods have recently been developed to objectively quantify the local viscoelastic properties of soft tissues by measuring the local propagation velocity of mechanical shear vibrations (e.g. faster velocity indicates stiffer material). But, the existing elastography technologies require a potentially uncomfortable external mechanical stimulation (e.g. vibrations probe) to induce muscle vibrations; and sophisticated and expensive imaging equipments (such as MRI and ultrafast ultrasound elastography), involving complex signal processing, to record and analyze these muscle vibrations. The work in this dissertation lays the foundation for the development of a low cost, passive, non-invasive elastography by analyzing and processing Surface Mechanomyograms (S-MMGs) measured with one dimensional accelerometers from the biceps brachii muscle. Aim 1 of this dissertation focused on the 3-dimensional aspect of vibrations measured by accelerometers on the skin surface above the biceps brachii. While Aim 2 focused on using one-dimensional accelerometers to determine the propagation direction of the propagating S-MMG waves. Using this newly developed knowledge on S-MMG Aim 3 was accomplished, a method to analyze the propagating wave and develop a metric that can track the changes in the muscle was developed, namely, the coherence length. The coherence length was found to significantly increase with increased contraction levels for all seven of the subjects. Overall the results of this study show that the propagation features of S-MMG vibrations reflect the architecture and contraction level of the biceps brachii muscle. Hence S-MMG could potentially be used for monitoring physiological changes of skeletal muscles.

Ultra-wideband (UWB) wireless systems rely on signals spanning very wide bandwidths, typically several gigahertz, for information transmission. The distinguishing feature of UWB communications technology is the unrivalled data-rates it provides, with other benefits such as fade resistance and spectral reusability. These characteristics render UWB the technology of choice for a gamut of modern wireless communications applications, including multimedia transmission, personal- and body-area networks, imaging devices, and sensor networks. The use of wide bandwidth signals, however, leads to many complications that necessitate specialised design considerations. The propagation channel and system components acquire frequency-selective characteristics, and their nonlinear and dispersive nature, usually innocuous in a conventional setting, causes signal distortion and erroneous detection. This thesis analyses various aspects of the indoor channel and the distortion to a UWB signal propagating through it. The performance of transmitter and receiver sub-systems is evaluated, with an emphasis on the challenges posed by the large operating bandwidth. The significance of incorporating this knowledge into the system design process is demonstrated, and a novel framework for optimising the performance-complexity tradeoff is presented. • The following are the contributions of this thesis to the state of the art in UWB communications. • Experimental characterisation of the indoor UWB channel spanning the FCC band (3.1-10.6 GHz) • Demonstration of the variability of propagation characteristics in the spectral sub-bands • Assessment of frequency-dependent pathless and the consequent signal waveform distortion • Polarimetric analysis of the temporal, spectral and angular channel evolution • Evaluation of rake receiver performance and its dependence on various channel conditions • Investigation of the effect of antenna angular-spectral distortion on signal propagation • A technique for the normalisation of UWB link aberration due to antennas • Performance evaluation of diversity and spatial multiplexing with multiple-antenna systems • Design of gigabit wireless links for high data-rate applications or high user density scenarios • A novel holistic framework for the design of an optimal UWB communications system.

This thesis centers on the development and analysis of numerical multiscale methods for multiscale problems arising in steady heat conduction, heat transfer and wave propagation in heterogeneous media. In a multiscale problem several scales interact with each other to form a system which has variations over a wide range of scales. A direct numerical simulation of such problems requires resolving the small scales over a computational domain, typically much larger than the microscopic scales. This demands a tremendous computational cost. We develop and analyse multiscale methods based on the heterogeneous multiscale methods (HMM) framework, which captures the macroscopic variations in the solution at a cost much lower than traditional numerical recipes. HMM assumes that there is a macro and a micro model which describes the problem. The micro model is accurate but computationally expensive to solve. The macro model is inexpensive but incomplete as it lacks certain parameter values. These are upscaled by solving the micro model locally in small parts of the domain. The accuracy of the method is then linked to how accurately this upscaling procedure captures the right macroscopic effects. In this thesis we analyse the upscaling error of existing multiscale methods and also propose a micro model which significantly reduces the upscaling error invarious settings. In papers I and IV we give an analysis of a finite difference HMM (FD-HMM) for approximating the effective solutions of multiscale wave equations over long time scales. In particular, we consider time scales T^ε = O(ε−k ), k =1, 2, where ε represents the size of the microstructures in the medium. In this setting, waves exhibit non-trivial behaviour which do not appear over short time scales. We use new analytical tools to prove that the FD-HMM accurately captures the long time effects. We first, in Paper I, consider T^ε =O(ε−2 ) and analyze the accuracy of FD-HMM in a one-dimensional periodicsetting. The core analytical ideas are quasi-polynomial solutions of periodic problems and local time averages of solutions of periodic wave equations.The analysis naturally reveals the role of consistency in HMM for high order approximation of effective quantities over long time scales. Next, in paperIV, we consider T^ε = O(ε−1 ) and use the tools in a multi-dimensional settingto analyze the accuracy of the FD-HMM in locally-periodic media where fast and slow variations are allowed at the same time. Moreover, in papers II and III we propose new multiscale methods which substantially improve the upscaling error in multiscale elliptic, parabolic and hyperbolic partial differential equations. In paper II we first propose a FD-HMM for solving elliptic homogenization problems. The strategy is to use the wave equation as the micro model even if the macro problem is of elliptic type. Next in paper III, we use this idea in a finite element HMM setting and generalize the approach to parabolic and hyperbolic problems. In a spatially fully discrete a priori error analysis we prove that the upscaling error can be made arbitrarily small for periodic media, even if we do not know the exact period of the oscillations in the media. / <p>QC 20150216</p> / Multiscale methods for wave propagation

Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references. / vi, 62 leaves, bound ill. 29 cm

v, 137 p. : ill., plates ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1974

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1974.

Thesis (Ph. D.)--Ohio University, August, 1999. / Title from PDF t.p.

Thesis (M.Sc.)--University of Adelaide, Dept. of Physics, 1969. / Candidate's reply (16 leaves) in pocket.

Thesis (PhD) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2007. / Submitted for the degree of Doctor of Philosophy at the Industrial Research Institute Swinburne (IRIS), Swinburne University of Technology - 2007. Typescript. "August 2007". Includes bibliographical references (p. 256-270).

Thesis (Ph. D.)--Carleton University, 2001. / Includes bibliographical references (p. 182-195). Also available in electronic format on the Internet.