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Diffuse ultrasonic waves for structural health monitoring offer the advantages of simplicity of signal generation and reception, sensitivity to damage, and large area coverage; however, there are the serious disadvantages of no accepted methodology for analyzing the complex recorded signals and sensitivity to environmental changes such as temperature and(More)
The level of post-subtraction noise due to benign structural features limits the sensitivity that guided wave structural health monitoring systems can achieve. Subtraction of reference signals without compensation leads to unacceptably high post-subtraction noise in the presence of modest environmental changes, and in particular temperature. Hence some form(More)
Matching pursuit has typically been applied to ultrasonic signal analysis for the purpose of identifying or estimating discrete echoes. In this paper, a specific numerical implementation of matching pursuit designed for ultrasonic signal decomposition is proposed, consisting of the selection of a coarse set of basis functions, the search method for finding(More)
—Strongly reverberating diffuse-like ultrasonic waves can interrogate large areas of complex structures that do not support more easily interpreted guided waves. However, sensitivity to environmental changes such as temperature and surface wetting can degrade the performance of a structural health monitoring system using these types of waves. Surface(More)
Matching pursuit is an iterative method whereby a signal is decomposed into a linear combination of functions that are selected from a redundant dictionary. In the original paper by Mallat and Zhang [1], a dictionary of Gabor functions is proposed. Each Gabor function is the product of a Gaussian function with a complex sinusoid, and is specified by time,(More)
To my wife, I-Wen for her patience, support, and unending love iii ACKNOWLEDGEMENTS I would like to earnestly thank my advisor, Dr. Jennifer Michaels, for her excellent guidance and patience, and for providing me with an excellent atmosphere for doing research. Throughout my doctoral work, Dr. Michaels always gave me the freedom to pursue my own interests(More)
Benign environmental effects, including temperature and surface condition changes, can adversely affect the performance of an ultrasonic structural health monitoring system because ultrasonic waves are sensitive to such changes as well as to damage. Compared to temperature, the problem of surface condition changes is more difficult to formalize because of(More)
Changes in diffuse ultrasonic signals recorded from permanently mounted sensors can be correlated to initiation and growth of structural damage, offering hope that sparse sensor arrays can be utilized for monitoring large areas. It is well-known that benign environmental changes also have significant effects on diffuse ultrasonic signals that are of(More)
Diffuse ultrasonic waves for structural health monitoring offer the advantages of simplicity of signal generation and reception, sensitivity to damage, and large area coverage. However, one of the difficulties associated with these complex signals is extraction of robust features that can be related to progression of damage. This paper investigates feature(More)
IN THE TITLE COMPOUND [SYSTEMATIC NAME: 1(2),1(5)-dibromo-5(2),5(5)-dimethoxy-2,7-dithia-1,5(1,4)-dibenzenaoctaphane], C(18)H(18)Br(2)O(2)S(2), the dihedral angle between the aromatic rings is 0.6 (2)° and their centroid separation is 3.251 (2) Å, indicating that a trans-annular π-π interaction occurs. The dimeth-oxy and dibromo substituents are located at(More)
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