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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.
1

Acoustic source separation based on target equalization-cancellation

Mi, Jing 20 February 2018 (has links)
Normal-hearing listeners are good at focusing on the target talker while ignoring the interferers in a multi-talker environment. Therefore, efforts have been devoted to build psychoacoustic models to understand binaural processing in multi-talker environments and to develop bio-inspired source separation algorithms for hearing-assistive devices. This thesis presents a target-Equalization-Cancellation (target-EC) approach to the source separation problem. The idea of the target-EC approach is to use the energy change before and after cancelling the target to estimate a time-frequency (T-F) mask in which each entry estimates the strength of target signal in the original mixture. Once the mask is calculated, it is applied to the original mixture to preserve the target-dominant T-F units and to suppress the interferer-dominant T-F units. On the psychoacoustic modeling side, when the output of the target-EC approach is evaluated with the Coherence-based Speech Intelligibility Index (CSII), the predicted binaural advantage closely matches the pattern of the measured data. On the application side, the performance of the target-EC source separation algorithm was evaluated by psychoacoustic measurements using both a closed-set speech corpus and an open-set speech corpus, and it was shown that the target-EC cue is a better cue for source separation than the interaural difference cues.
2

Acoustically driven control of mobile robots for source localization in complex ocean environments

Bogdan, Caitlin 03 July 2018 (has links)
Ocean based robotic systems are an opportunity to combine the power of acoustic sensing in the water with sophisticated control schemes. Together these bodies of knowledge could create autonomous systems for mapping acoustic fields and localizing underwater sources. However, existing control schemes have often been designed for land and air robots. This creates challenges for applying these algorithms to complex ocean environments. Acoustic fields are strongly frequency dependent, can rarely be realistically modeled analytically, have complex contours where the feature of interest is not always located at the peak pressure, and include many sources of background noise. This work addresses these challenges for control schemes from three categories: feedback and observer control, gradient ascent control and optimal control. In each case the challenges of applying the control scheme to an acoustic field are enumerated and addressed to create a suite of acoustically driven control schemes. For many of these algorithms, the largest issue is the processing and collection of acoustic data, particularly in the face of noise. Two new methods are developed to solve this issue. The first is the use of Principal Component Analysis as a noise filter for acoustic signals, which is shown to address particularly high levels of noise, while providing the frequency dependent sound pressure levels necessary for subsequent processing. The second method addresses the challenge that an analytical expression of the pressure field is often lacking, due to uncertainties and complexities in the environmental parameters. Basis functions are used to address this. Several candidates are considered, but Legendre polynomials are selected for their low error and reasonable processing time. Additionally, a method of intermediate points is used to approximate high frequency pressure fields with low numbers of collected data points. Following this work, the individual control schemes are explored. A method of observer feedback control is proposed to localize sources by linearizing the acoustic fields. A gradient ascent method for localizing sources in real time is proposed which uses Matched Field Processing and Bayesian filters. These modifications allow the gradient ascent algorithm to be compatible with complex acoustic fields. Finally, an optimal control method is proposed using Pontryagin's Maximum Principle to derive trajectories in real time that balance information gain with control energy. This method is shown to efficiently map an acoustic field, either for optimal sensor placement or to localize sources. The contribution of this work is a new collection of control schemes that use acoustic data to localize acoustically complex sources in a realistic noisy environment, and an understanding of the tradeoffs inherent in applying each of these to the acoustic domain.
3

Measurement of Dispersion and Attenuation in Granular Media using a Filter-Correlation Method

O'Connor, Caleb S. 26 August 2015 (has links)
<p> A wideband technique for measuring sound dispersion and frequency-dependent attenuation in granular media is presented. The measurements were done on a mono-disperse medium of 2-cm solid polypropylene balls, over the frequency range of 500 Hz-20 kHz, enough to cover both weak and strong scattering regimes. A horn driver was used to launch sound into a foam-lined bucket containing the granular medium. The latter was mechanically isolated from the driver so as to minimize direct-contact coupling. The foam isolation was not enough, especially at resonances of the bucket-granular system. In the effort to simulate a free-granular medium, the bucket was replaced with a mesh bag hanging in free space. The frequency-dependent wavenumber of the granular is obtained by a filter-correlation method. After successive bandpass filtering, the phase speed and attenuation are obtained within each band, respectively, by signal alignment and amplitude log ratio. The attenuation coefficient yielded reasonable results, illustrating the transition from ``piston-like" dynamics to the strong scattering regime, as the frequency increased. The phase speed results where more sporadic, qualitatively there is a decrease in sound speed as the frequency increases.</p>
4

A non-contact, small volume method for light transmission aggregometry in biological fluids

January 2021 (has links)
archives@tulane.edu / Primary hemostasis is a process in which platelet plugs form to stop bleeding immediately following injury to the vascular wall. Platelet activation and aggregation work hand-in-hand to form these platelet plugs, and the study of these processes is crucial for diagnosing coagulopathies. Light transmission aggregometry is a primary in-vitro test clinicians use for evaluating platelets' ability to form aggregates in response to stimulation by a soluble agonist. However, these tests often employ large volumes of blood. This study aims to create a system for small-volume, non-contact light transmission aggregometry using acoustic levitation, and additionally aims to test such a system on platelet aggregation models using polystyrene microspheres, and then, platelet-rich plasma itself. / 1 / Jeremy Chinwe Orie
5

Acoustoopic Diffraction and Deflection in Tellurium for the Carbon Dioxide Laser

Souilhac, Dominique Jacques 01 1900 (has links)
No description available.
6

Four research topics on new acoustic liner concepts and modal propagation measurement

Matsumura, Yuya January 2008 (has links)
No description available.
7

The Determination of Failure Mechanisms in the Fatigue of Unidirectional Composites by the Use of Acoustic Emissions

Horstemeyer, Mark January 1987 (has links)
No description available.
8

Nonlinear Assessment of Material and Interface Imperfections Based on Non-Collinear Shear Wave Mixing

Zhang, Ziyin 28 June 2016 (has links)
No description available.
9

Characterization of targeted microbubbles for adhesiolysis

Doheny, Victoria Valeria 18 January 2024 (has links)
Peritoneal adhesions are bands of fibrous tissue that can bind adjacent tissue together and have a high probability of occurrence after a patient undergoes abdominal surgery. The development of adhesions can be detrimental as they can cause intestinal constriction or obstruction, organ displacement, infertility, chronic pain, and in severe cases, even death. Currently, there is no way of detecting adhesions in the body using clinically approved imaging modalities and the standard of care is to perform a controversial second surgery to treat adhesions that can cause more adhesions to form. Therefore, there is a critical need to find new ways of detecting and treating adhesions non-invasively. The larger, overarching project that this thesis is part of aims to fabricate a targeted microbubble that acts as a theranostic agent, which can detect and treat nascent adhesions when exposed to ultrasound.Towards this aim the goals of this thesis are to: 1) characterize the mechanical properties (shell stiffness and shell viscosity) of the microbubble targeting shell that contribute to the microbubble’s response to ultrasound; 2) determine the inertial cavitation threshold, since inertial response will likely be needed in order to break up early-stage adhesions, 3) provide feedback to the larger project to optimize microbubble design and fabrication. The objective of providing feedback is to find a balance between microbubble response to ultrasound and stability under storage and deployment that enables in vivo application. These three goals were achieved by a combination of in vitro experiments and computational modeling of bubble dynamics using the modified linearized Rayleigh- Plesset equation that can predict the dynamics of bubbles with a viscoelastic shell. The results show that inference of shell properties from acoustic transmission experiments shows a strong sensitivity to the microbubble size distribution. If the size distribution is sufficiently well known, then the results indicate that candidate lipid- shelled bubbles possess moderate (∼ 1.4 MPa) shell stiffness and moderate (∼ 0.05 Pa-s) shell viscosity, yielding only modestly resonant bubbles. Counter-intuitively, the results show that even non-resonant bubbles can exhibit a peaked transmission/attenuation frequency response. The inertial cavitation threshold for candidate lipid- shelled bubbles at 1.1 MHz was approximately 2 MPa for low-duty-cycle tone bursts. The results indicate that the candidate lipid shell fabrication technique will produce bubbles that are both sufficiently responsive to provide contrast imaging under diagnostic ultrasound while also requiring a relatively low therapeutic pressure for inertial cavitation lysis. Perhaps the most important feedback to the bubble design and fabrication is the requirement of independent and well-resolved microbubble size distributions. / 2026-01-17T00:00:00Z
10

Signal processing techniques on an underwater acoustic projector

Walden, Alan Keith 05 1900 (has links)
No description available.

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