<p> The underlying goal of this dissertation is to understand how the amygdala, a brain region involved in establishing the emotional significance of sensory input, contributes to the processing of complex sounds. The general hypothesis is that communication calls of big brown bats (<i>Eptesicus fuscus</i>) transmit relevant information about social context that is reflected in the activity of amygdalar neurons. </p><p> The first specific aim analyzed social vocalizations emitted under a variety of behavioral contexts, and related vocalizations to an objective measure of internal physiological state by monitoring the heart rate of vocalizing bats. These experiments revealed a complex acoustic communication system among big brown bats in which acoustic cues and call structure signal the emotional state of a sender. </p><p> The second specific aim characterized the responsiveness of single neurons in the basolateral amygdala to a range of social syllables. Neurons typically respond to the majority of tested syllables, but effectively discriminate among vocalizations by varying the response duration. This novel coding strategy underscores the importance of persistent firing in the general functioning of the amygdala. </p><p> The third specific aim examined the influence of acoustic context by characterizing both the behavioral and neurophysiological responses to natural vocal sequences. Vocal sequences differentially modify the internal affective state of a listening bat, with lower aggression vocalizations evoking the greatest change in heart rate. Amygdalar neurons employ two different coding strategies: low background neurons respond selectively to very few stimuli, whereas high background neurons respond broadly to stimuli but demonstrate variation in response magnitude and timing. Neurons appear to discriminate the valence of stimuli, with aggression sequences evoking robust population-level responses across all sound levels. Further, vocal sequences show improved discrimination among stimuli compared to isolated syllables, and this improved discrimination is expressed in part by the timing of action potentials. </p><p> Taken together, these data support the hypothesis that big brown bat social vocalizations transmit relevant information about the social context that is encoded within the discharge pattern of amygdalar neurons ultimately responsible for coordinating appropriate social behaviors. I further propose that vocalization-evoked amygdalar activity will have significant impact on subsequent sensory processing and plasticity.</p>

Master of Science / Department of Architectural Engineering and Construction Science / Julia A. Keen / Throughout recent years, to minimize the cost of construction, a large number of multipurpose spaces have been built using lightweight, less expensive materials without considering or designing for noise control to mitigate any sound that is loud, unpleasant, unexpected, or undesired yet after construction is completed, noise issues are often evident within the space and, if severe enough, may render the intended function of the structure useless. To address this problem, this report is intended to introduce Owners and Facility Managers to some of the common solutions to resolve noise issues in multipurpose rooms. The report focuses on solutions for existing projects primarily, but it is also sensitive to budget constraints and the impact of renovation. Typical multipurpose rooms researched have a volume of 50,000-150,000 cubic feet and are expected to be used for speech activities, small music functions, and some physical sports activities. Therefore, this report will introduce the fundamentals of sound and room acoustics including interior surface materials and construction. Also included are typical noise issues from interior sources, solutions that can be taken within the building to attenuate noise, and the trade-offs associated with each solution.

Motivated by previous relevant research on phononics including both active and passive phononics, the interest of faster turnability and more functions of the active phononics of further study led to this proposing research topic: magnetic field tunable active functional phononics. The first design of magnetic field tunable reciprocal--non-reciprocal transmission acoustic device was established, material was characterized, and numerical simulation has been performed. The simulation results show clear T-symmetric breaking non-reciprocity due to energy level splitting effect with Doppler effect – an acoustic Zeeman effect. Inspired by this preliminary work, further experiments were planned to demonstrate this effective Zeeman effect in phononics and effectively charged phonons in water based ferro-fluid. The objectives of this work as the next series of tasks were to illustrate acoustic Zeeman effect and acoustic Landau levels in various strength of magnetic field to investigate a design non-reciprocal sound device with magnetic field switching, which could be controlled on the amount of non-reciprocity with the strength of magnetic field. Once this new field first discovered by the proposed study tasks, more active tunable magnetic field phononics devices could be designed and exemplified in terms of both simulations and experiments. Faster and more controllable active phononic devices could be designed and made based on this study. The experimental maximum non-reciprocity was measured as 22 dB difference and the amount of the non-reciprocity can be further controlled by adjusting the strength of the external magnetic field. The remote pumping system in the device worked as expected and did not introduce any impact of the cavity properties.

No description available.

Acoustic properties of periodic elastic structures have been a subject of active research for more than a century. Here, I derived and analyzed the dispersion equation for sound waves propagating in a periodic layered heterogeneous structure containing at least one viscous fluid as a constituent. The derivation of the dispersion equation is based on the Navier-Stokes equation for sound wave and the boundary conditions of continuity of fluid displacement and stresses at the interfaces with Bloch periodic boundary condition. The obtained dispersion equation is very general, it is valid for different combinations of elastic layers, any direction of propagation, and frequency of sound. In the case of superlattice consisting of narrow layers with high viscosity fluid and layers of ideal fluid, an acoustic analog of the Borrmann effect is predicted. In the other part of my dissertation, I study the nonreciprocal wave propagation in phononic crystals induced by viscosity. Using Fourier-transformed wave equation, I proved analytically that for an infinite phononic crystal with broken PT-symmetry dispersion relation remains the same switching the direction of the wave propagation, while Fourier components of velocity are nonreciprocal. I optimized shape of the scatterer to reach the highest value of the nonreciprocity in a two-dimensional finite phononic crystal. Sound propagation through crystals with various unit cells is numerically simulated with COMSOL Multiphysics to create a dataset of transmission values. For each introduced parameter the optimized scatterer's geometries are obtained utilizing machine learning techniques. I found parameters of the crystal, which may serve as a linear non-resonant passive acoustic diode.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Liang-Wu Cai / A computational system is built for conducting deterministic simulations of three-dimensional multiple scattering of elastic waves by spherical inclusions. Based on expansion expression of elastic wave fields in terms of scalar and vector spherical harmonics, analytically exact solutions of single scattering and multiple scattering are obtained, implemented and verified. The verification is done by using continuities of displacement and surface traction at the interface between an inclusion and host medium, energy conservation and published results. The scatterer polymerization methodology is extended to three-dimensional multiple scattering solution. By using this methodology, an assemblage of actual scatterers can be treated as an abstract scatterer. This methodology is verified by using different approaches, with or without scatterer polymerization, to solve a physically the same multiple scattering problem. As an application example, band gap formation process for elastic wave propagation in cubic lattice arrangements of spherical scatterers is observed through a series of numerical simulations. Along the direction of the incident wave, scatterer arrangements are viewed as comprising layers of scatterers, within which scatterers form a square grid. Starting from one layer and by increasing the number of layers, near-field forward wave propagation spectra are computed as the number of layers increases. These simulations also demonstrates that the computational system has the capability to simulate multiple scattering solutions of elastic waves in three-dimension.

The noise (unwanted sound) from fans of all sizes, operating in close proximity to people, can be a design constraint due to annoyance or, in the worse cases, health damage. Of the total noise, aeroacoustic noise - produced by unsteadiness in the air - often represents a significant source and is intrinsically linked to the aerodynamic features of the flow field. In this work, the aeroacoustics of low-speed fans are investigated using a compact mixed-flow fan as a test case. The low-speed regime is less developed compared to large-scale, high-speed machines and is increasingly relevant to applications such as micro air vehicles, small wind turbines, and other environmental comfort technologies found in buildings or vehicles. The test case fan Reynolds number is of the order of 104 which is a couple of orders lower than those generally found in gas turbines. Its main sources are therefore best identified experimentally in the absence of proven alternative methods. In order to do this, a way of quantifying fan noise is developed in tandem with control of the aerodynamic operating point. Following a study of sources of the significant broadband and tonal noise, a low-order noise prediction scheme is developed and applied to predict tonal noise with reference to Reynolds number effects. The new, duct-based rig and method has several advantages over the existing sound power measurement rig built to the ISO 5136 standard at Dyson. The approach, which makes no assumptions about the relative power of different modes, has resulted in a rig that is much shorter. Unlike the ISO rig, it is capable of accurate narrow-band tone measurements with sources which excite strong non-plane-wave duct modes (as the modal structure of the sound is determined) for the frequencies of interest. Tests have been carried out at different operating points with a range of geometry modifications produced with 3D printing techniques. In terms of tonal sources which particularly impact sound quality, the mixed-flow impeller alone produces tones due to very high sensitivity to inflow distortion of the mean flow (giving unsteady blade loading). This means that the product inlet must be designed very carefully to optimally condition the flow. Periodicity in the impeller outlet flow produces rotor-stator interaction tones even with a number of guide vanes chosen to satisfy the Tyler-Sofrin theory cut-off criteria. This is thought to be due to abrupt radius change after the guide vanes in the rig (while the theory assumes constant radius). In the product, abrupt radius change also occurs. The sensitivity of the broadband level to inflow turbulence was confirmed to be low in the rig, although the in-product inflow appears much less ideal. The main broadband noise source in rig tests is suggested to be impeller self-noise as only small reductions in rotor-stator interaction noise are achieved with far fewer vanes. The low-order modelling scheme to understand the fundamental unsteady loading noise mechanism compares well to experiments for sample rotor-stator interaction tones. The velocity fluctuations which induce this noise, measured experimentally with a 2D hotwire, are shown to increase in intensity as Reynolds number is reduced towards 104. This is due to a higher importance of viscosity which can give boundary layers that are thicker and liable to laminar separation. Surface treatments such as boundary layer trips could be used to prevent such separation and potentially reduce noise. Based on the thesis findings, further tests, simulations and possible design modifications are suggested to understand and reduce the important noise sources.

Various anomalous effects that emerge when the interfaces between media are involved in sound-matter or light-matter interactions are studied. The three specific systems examined are a fluid channel between elastic metal plates, a linear chain of metallic perforated cylindrical shells in air, and a metal-dielectric slab with the interfaces treated as finite regions of smoothly changing material properties. The scattering of acoustic signals on the first two is predicted to be accompanied by the effects of redirection and splitting of sound. In the third system, which supports the propagation of surface plasmons, it is discovered that the transition region introduces a nonradiative decay mechanism which adds to the plasmon dissipation. The analytical results are supported with numerical simulations. The outlined phenomena provide the ideas and implications for applications involving manipulation of sound or excitation of surface plasmons.

Mémoire en recherche-création ; Aide financière octroyée : CIRMMT Student Award / Les conditions d'utilisation de théories scientifiques au cours du processus de composition musicale et plus généralement pour l'élaboration de théories esthétiques musicales sont au coeur du travail proposé. Une position critique est tout d'abord avancée relativement aux nombreux écueils historiques relevés. Elle permet d'en dégager quelques pistes d'exploration pour les processus compositionnels que je me suis proposé de suivre au fur et à mesure des pièces électroacoustiques et mixtes présentées. En particulier, des spécificités empruntées aux mécanismes vibratoires non-linéaires, aux modèles sociologiques déterministes ou prédictifs sont injectés au sein même des processus de création des mes oeuvres. Cinq pièces sont présentées. Les thématiques et les contraintes occasionnées par les modèles empruntés sont décrits ainsi que les réalisations techniques qui leur ont servi de support. Chaque pièce présente donc une démarche et des outils technologiques et informatiques particuliers. Ces pistes exploratoires feront intervenir contrainte formelle, limitation du contrôle du compositeur, improvisation, traitement et spatialisation en temps réel et développements originaux implémentés en Max/MSP et en Python. Par ailleurs, un outil d'aide à la composition spatiale proposant une perspective inédite de visualisation du champs de pression produit par les trajectoires et par le système de reproduction virtuel, et développé pendant ma maîtrise est présenté. / The use of science theories during the compositionnal process, especially in a purpose of esthetical properties abstraction is questionned. First, a criticist point-of-vue is adressed, on the basis of several historical examples. A personnal method dedicated to the development of original compositionnal process were deduced. In particular, the specific mecanisms related to nonlinear vibrations and deterministic sociological model could be inserted into the creative processes. Five electroacoustic and contemporay music pieces are presented. Themes and constraints provoked by the model insertion are detailed. They gather form-contraints, control limitations, improvisation, real-time processing and real-time spatialization implemented in Max/MSP and Python. Moreover, a refined sound-field rendering tool dedicated to computer-assisted composition is introduced.