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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.
21

<p>Underwater acoustic imaging: Image reconstruction using speckle interferometry.</p>

Cheng, Yan Don January 1994 (has links)
No description available.
22

APPLICATION OF ACOUSTIC NUCLEAR MAGNETIC RESONANCE TO MEDICAL IMAGING

Hirsch, Thomas John, 1958- January 1986 (has links)
No description available.
23

Engineering of protein-based multifunctional nanoparticles with near-infrared absorption as photoacoustic contrast agents for biological applications

Gao, Du Yang January 2018 (has links)
University of Macau / Faculty of Health Sciences
24

Acoustic imaging of diel vertical migration of zooplankton on the Newfoundland shelf /

Record, Nicholas, January 2005 (has links)
Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Bibliography: leaves 174-183.
25

Magneto-photo-acoustic imaging

Qu, Min 25 June 2012 (has links)
Cancer is a major public health problem worldwide due to its poor prognosis. Detection of cancer in the earliest stages is crucial for the success of therapeutic strategies to truly cure the disease. Molecular imaging provides the potential to diagnose and image cancers at an asymptomatic stage. In molecular imaging, the nanoparticles are designed to target the cancer cells. Molecular imaging is capable of assessing the molecular processes within the tumors by detecting the accumulated or targeted nanoparticles. However, for most molecular imaging systems, the background signal is a common problem, obscuring signals from specific probes and limiting sensitive detection. A hybrid imaging technique, entitled magneto-photo-acoustic (MPA) imaging, was developed as a non-invasive imaging tool to detect nanoparticles, which are used to target pathologies, with high sensitivity and specificity. Based on dual-contrast of both optical absorption and magnetic susceptibility, MPA imaging can significantly improve the molecular contrast specificity as well as investigate the interaction of nanoparticles with cells. Studies were performed using tissue-mimicking phantoms, ex vivo tissue sample and in vivo animal models of cancer. The results indicate that, coupled with dual-contrast agent, the molecular MPA imaging will allow not only mapping the pathologies located in the body, but also sensing the molecular and physiological processes. / text
26

Ultrasonic imaging of the structure and elasticity of the carotid bifurcation

Jackson, Joel R. 05 1900 (has links)
No description available.
27

Applications of acoustic measurements in shale stability research /

Davidson, James Alexander, January 1999 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 169-173). Available also in a digital version from Dissertation Abstracts.
28

Application de la réfraction négative à l'imagerie acoustique à l'aide de cristaux phononiques bidimensionnels / Application of negative refraction to acoustic imaging with two dimensional phononic crystals

Manga, Etoungh Dimitri 28 September 2012 (has links)
La propagation des ondes ultrasonores à travers des cristaux phononiques CP à deux dimensions 2D constitués de diffuseurs solides dans des matrices solide et fluide est ici étudiée, ainsi que la caractérisation de ces milieux et leur application à l’imagerie acoustique. Les techniques expérimentales utilisées permettent une mesure complète des champs transmis à travers les cristaux. Les études sont menées dans des bandes fréquentielles autorisant les effets de réfraction négative indispensables à l’obtention d’une résolution inférieure à la limite de diffraction (super-résolution). De manière à compléter les analyses, différents outils théoriques sont exploités Décomposition en Ondes Planes et Eléments Finis, notamment.La première partie du document concerne la réalisation et la caractérisation de cristaux phononiques possédant des propriétés nécessaires à la réalisation de systèmes d’imagerie acoustique réfraction négative, contours équi-fréquences circulaires, accord d’indice, accord d’impédance. Cette première étude est menée sur un cristal à matrice solide, elle met en relief la possibilité de générer différents modes de Bloch au cours de la propagation. L’accord d’indice avec l’eau n’étant cependant pas obtenu, la seconde partie porte sur la réfraction négative et la focalisation des ondes à travers un CP à matrice fluide. Les propriétés du CP déterminées, le dernier chapitre s’attache à évaluer les performances des systèmes d’imagerie développés : dynamique et résolution. / This investigation deals with wave propagation in two dimensional phononic crystals (PC) made of solid scatterers embedded in solid or fluid matrices. After characterizing such composite materials, their application to acoustic imaging is brought to the forth. The ultrasonic techniques used in the experiments allow the complete measurement of the acoustic transmitted fields and the investigations concern frequency bandwidth able to exhibit negative refraction allowing Oie super-resolution effects. In order to complete the analysis, different theoretical tools are used: Plane Wave Expansion (PWE) and Finite Elements Method (FEM).The first part of this work deals with the realization and characterization of PC to be introduced into acoustic imaging devices (lenses) based on negative refraction. Special attention is given to characteristics such as circular equi-frequency contours, or index and impedance matching. However, during the acoustic wave propagation in a solid PC immersed in water, the presence of different Bloch modes contributing to the transmission of ultrasound is revealed and the index matching was not possible to obtain. Therefore the second part of the manuscript deals with negative refraction and waves focusing through a PC filled with a fluid. After determining the crystal properties, last chapter is devoted to the evaluation of the performances of acoustic imaging systems based on phononic lens.
29

An acoustic scatter-mapping imaging system

Mellema, Garfield Richard January 1990 (has links)
The development of improved models of seismic diffraction is assisted by the availability of accurate scattering data. An acoustic scatter-mapping system was developed for the purpose of providing such data rapidly and at low cost. This system uses a source-receiver pair suspended on a trolley over the structure to be mapped. Signal generation, acquisition, processing, and plotting are performed on an AT-compatible microcomputer and a laser printer. The entire process can be performed in an automated manner within five hours, generating scatter-mapping plots in a format familiar to the geophysical industry. The system hardware was similar to those of Hilterman [1] and others referenced by him, but used a controlled source transducer. The available processing power of a microcomputer allowed the use of a 1 to 15 KHz swept-frequency source signal, similar to that used in Vibroseis and Chirp Radar, which is later crosscorrelated with received signal to provide precise scatter-mapping data for the target structure. Several examples of theoretical and experimental acoustic scatter-mappings are provided for comparison. The novelty of this system lies in its use of a swept frequency source signal. While common in the fields of seismology and radar, swept frequency source signals are new to the area of acoustic scatter mapping. When compared to a similar system using a pulsed source signal, this system produces a better controlled source signal of greater energy, resulting in a more useful resultant signal and better mapping characteristics. The system was able to map scattering from features in the target structure smaller than one percent of the crosscorrelated source signal's 37 mm dominant wavelength. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate
30

Coding Strategies and Implementations of Compressive Sensing

Tsai, Tsung-Han January 2016 (has links)
<p>This dissertation studies the coding strategies of computational imaging to overcome the limitation of conventional sensing techniques. The information capacity of conventional sensing is limited by the physical properties of optics, such as aperture size, detector pixels, quantum efficiency, and sampling rate. These parameters determine the spatial, depth, spectral, temporal, and polarization sensitivity of each imager. To increase sensitivity in any dimension can significantly compromise the others. </p><p>This research implements various coding strategies subject to optical multidimensional imaging and acoustic sensing in order to extend their sensing abilities. The proposed coding strategies combine hardware modification and signal processing to exploiting bandwidth and sensitivity from conventional sensors. We discuss the hardware architecture, compression strategies, sensing process modeling, and reconstruction algorithm of each sensing system. </p><p>Optical multidimensional imaging measures three or more dimensional information of the optical signal. Traditional multidimensional imagers acquire extra dimensional information at the cost of degrading temporal or spatial resolution. Compressive multidimensional imaging multiplexes the transverse spatial, spectral, temporal, and polarization information on a two-dimensional (2D) detector. The corresponding spectral, temporal and polarization coding strategies adapt optics, electronic devices, and designed modulation techniques for multiplex measurement. This computational imaging technique provides multispectral, temporal super-resolution, and polarization imaging abilities with minimal loss in spatial resolution and noise level while maintaining or gaining higher temporal resolution. The experimental results prove that the appropriate coding strategies may improve hundreds times more sensing capacity. </p><p>Human auditory system has the astonishing ability in localizing, tracking, and filtering the selected sound sources or information from a noisy environment. Using engineering efforts to accomplish the same task usually requires multiple detectors, advanced computational algorithms, or artificial intelligence systems. Compressive acoustic sensing incorporates acoustic metamaterials in compressive sensing theory to emulate the abilities of sound localization and selective attention. This research investigates and optimizes the sensing capacity and the spatial sensitivity of the acoustic sensor. The well-modeled acoustic sensor allows localizing multiple speakers in both stationary and dynamic auditory scene; and distinguishing mixed conversations from independent sources with high audio recognition rate.</p> / Dissertation

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