The major problems associated with implementing synthetic apertures in sonar may be overcome by applying the technique to sub-bottom imaging. The use of a low frequency aids both penetration of the sediment and the attainment of long coherent apertures. The implementation of synthetic apertures realises a narrow fan beam. By directing this beam out sideways, a more rapid survey rate is possible than that achieved by the normal echo-sounding mode used in sub-bottom profiling. The synthetic aperture technique appears to offer significant advantages over that of parametric arrays, for high resolution sub-bottom imaging. Synthetic apertures have been implemented in a laboratory tank, under controlled conditions at a fresh water reservoir, and under realistic operational conditions at sea. Encouraging results have been obtained.

Using analytical formula to estimate a complex problem of cavity based on a transmission line approach is called the ETL (Equivalent Transmission Line) method . Operating frequency of dominant mode of standard case is several hundreds of megahertz that is lower than frequency of CPU, higher-order mode must be considered . Several papers always discuss a single aperture that does not correspond to practical array of apertures of case .Array of apertures can be estimated using analytical formula and higher-order mode can be considered in this paper .Usually array of apertures is not placed at the center of metallic plate, we can modify the analytical formula to get ETL of shifted array of apertures. To consider industrial design and esthetics, many possible shape of array of apertures are discussed by adapting to the ETL method .The problem of how to improve the shielding effectiveness of array of apertures is treated in the latter half of this thesis. The FDTD (Finite-Difference Time Domain) method is a full-wave analytical algorithm and is not efficient for analyzing cavity. Advantage of ETL is that it is faster than full-wave analytical algorithm .However, traditional ETL can not get accurate level of shielding effectiveness without higher-order modes. Thus improved ways are introduced in the paper to simulate practical array of apertures to reach the result of good agreement and short computing time.

Thesis (M.E.)--University of Canterbury, 2006. / Typescript (photocopy). "December 2006." Includes bibliographical references (p. 99-103). Also available via the World Wide Web.

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Chez les organismes pluricellulaires, la diversité morphologique observée à tous les niveaux est frappante, que ce soit au niveau de la taille, des couleurs, ou de la forme des individus, et des différentes parties qui les composent. La sélection naturelle, ainsi que les contraintes développementales, influencent l’évolution de ces différents attributs, sur le court terme comme sur le long terme. Le modèle choisi ici pour étudier l’évolution des formes est le grain de pollen des plantes à fleurs, qui présente une très grande diversité morphologique. Nous nous sommes focalisés sur un caractère morphologique, les apertures, qui sont des structures de la paroi du grain de pollen impliquées dans la survie et la reproduction. Nous avons étudié l’évolution des apertures à grande échelle taxonomique chez les angiospermes, et nous montrons que s’il existe de nombreuses variations, deux types principaux dominent : un pollen à une aperture chez les Monocotylédones et les angiospermes divergeant à la base, et un pollen à trois apertures chez les Eudicotylédones. En étudiant la dominance du pollen à trois apertures, nous avons pu montrer que la stase chez les Eudicotylédones était vraisemblablement due à une sélection stabilisante plutôt qu’à des contraintes développementales. Nous avons également montré, grâce à l’utilisation de mutants de la plante modèle Arabidopsis thaliana, qu’un nombre d’apertures élevé est défavorable face à un stress osmotique, ce qui pourrait suggérer que les pollens triaperturés représentent un bon compromis entre survie et germination. Enfin, nous nous sommes intéressés à un type particulier de pollen possédant de nombreuses apertures, dont nous avons étudié la distribution chez les angiospermes. L’apparition de ce type de pollen est récurrente, mais il n’est que rarement fixé à grande échelle taxonomique, suggérant l’existence d’un mécanisme de sélection interphylétique éliminant ce type de pollen sur le long terme. / Multicellular organisms are morphologically very diverse at every scale, regarding size, color, and shape of individuals and of their different parts. Natural selection and developmental constraints influence evolution of these characteristics, on the short term as well as on the long term. The model chosen here to study form evolution is the pollen grain of flowering plants, which is very diversified morphologically. We focused on specific features called apertures, which are structures of the pollen wall involved in survival and reproduction. We studied aperture evolution at large taxonomic scale in angiosperms, and we showed that in spite of variations, two main pollen types dominate: a pollen with one aperture in Monocots and early diverging angiosperms, and a pollen with three apertures in Eudicots. The study of this pattern showed that the stasis of triaperturate pollen in Eudicots is likely due to stabilizing selection rather than developmental constraints. Experiments on Arabidopsis thaliana mutants also revealed that an increase in aperture number was associated with lower resistance to osmotic stress. This result could suggest that triaperturate pollen grains represent a good trade-off between survival and germination. Moreover, we focused on a particular pollen type with many apertures, to determine its distribution in angiosperms. This type of pollen has many origins, however it is seldom fixed at large taxonomical scale, suggesting the intervention of lineage selection, eliminating this pollen type in the long run.

Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). "January 2007." Includes bibliographical references (p. [209]-223). Also available via the World Wide Web.

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "June 2006." Includes bibliographical references (p. [169]-182) and index. Also available via the World Wide Web.

Synthetic Aperture Sonar (SAS) provides the best opportunity for side-looking sonar mounted on underwater platforms to achieve high-resolution images. However, SAS processing requires strict constraints on resolvable platform motion. The most common approach to estimate this motion is to use the Redundant Phase Center (RPC) technique. Here the ping interval is set, such that a portion of the sonar array overlaps as the sensor moves forward. The time delay between the pings received on these overlapping elements is estimated using cross-correlation. These time delays are then used to infer the pingto-ping vehicle motion. Given the stochastic nature of the operational environment, some level of decorrelation between these two signals is likely. In this research, two iterative signal decomposition methods well suited for nonlinear and non-stationary signals, are investigated for their potential to improve the Time Delay Estimation (TDE). The first of this type, the Empirical Mode Decomposition (EMD) was introduced by Huang in the seminal paper, The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis and is the foundation for the algorithms used in this research. This method decomposes a signal into a finite sequence of simple components termed Intrinsic Mode Functions (IMFs). The Iterative Filter (IF) approach, developed by Lin, Wang and Zhou, builds on the EMD framework. The sonar signals considered in this research are complex baseband signals. Both the IF and EMD algorithms were designed to decompose real signals. However, the IF variant, the Multivariate Fast Iterative Filtering (MFIF) Algorithm, developed by Cicone, and the EMD variant, the Fast and Adaptive Multivariate Empirical Mode Decomposition (FAMVEMD) algorithm, developed by Thirumalaisamy and Ansell, preserve both the magnitude and phase in the decomposition and hence were chosen for this analysis. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "August 2006." Includes bibliographical references (p. [167]-179) and index. Also available via the World Wide Web.

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