Quantitative volume-scattering measurements were compared to the distribution of euphausiids in Saanich Inlet, British Columbia. Scattering was recorded at 42, 107, and 200 kHz from the depths of high euphausiid concentrations, and volume-scattering coefficients were determined. No scattering from euphausiids was recorded by a 11 kHz echo-sounder. Daily variations in the volume-scattering coefficients, m(Δz), generally compared well with variations in the concentration of euphausiids. The daily behaviour of the high-frequency scattering layer., and therefore m(Δz) and the concentration of euphausiids, was influenced by moonlight and weather conditions as well as the presence or absence of an oxycline in the inlet. In the absence of an oxycline conditions would have been closer to conditions in the open ocean. Under these circumstances euphausiid concentrations and m(Δz) were low in the mornings and gradually increased throughout the day; the high-frequency scattering layer consolidated. During the evening migration, the layer became more diffuse, and the number of euphausiids per cubic metre decreased. The scattering cross-section, σ (cm²), of a euphausiid was found to increase with the average dry weight and length, and with increased frequency. For each cruise σ was approximately one order of magnitude apart at the three frequencies. The values of σ (in cm²) ranged from 4.81 x 10⁻⁵ to 5.21 x 10⁻³(200 kHz), 5.49 x 10⁻⁶ to 3.99 x 10⁻⁴ (107 kHz), and 2.30 x 10⁻⁷ to 3.67 x 10⁻⁵ (42 kHz). / Science, Faculty of / Zoology, Department of / Graduate

No description available.

This thesis details the experimental development of a pneumatic infrasound generator, the purpose of which is for calibration, testing, and research. The source was an assembly of an air reservoir, a motor, and a rotor/stator pair, in the context of a siren. A rotating ball valve acted as the rotor/stator and modulated the compressed air from the reservoir as it vented into the atmosphere. The ball valve cross sectional area as a function of time varied as a triangular waveform, which in practice caused the infrasonic waveforms to be effectively sinusoidal. This thesis opens with a brief motivation for the creation of the source, in addition to previously developed infrasound generators and an overview of wind noise. The apparatus construction is then described. A theory is developed that describes the acoustic radiation from the infrasound generator as the superposition of a monopole and a dipole. Flow visualization, propagation, frequency response, reservoir volume, directivity, and jet velocity experimental setups and results are described next. The outcomes of the research are subsequently discussed, including a brief overview of a scaled up model of the infrasound generator. / text

<p>This thesis concerns a study undertaken on a railway vehicle cooling fan system. Several design modifications were proposed and tested in the laboratory in order to evaluate different noise control measures. The most effective noise control measure involving combining lots of different measures gave 7 dB(A) noise reduction. Furthermore a modification by replacing the axial fan by a radial fan can even reduce the radiated sound power by 10 dB(A). The transfer functions were also examined for a dipole source to acoustic pressure in the far field to evaluate the acoustic loading created by the cooling fan enclosure. One fan was taken out from the complete unit and mounted between two acoustic test chambers to measure the effect of various parameters on the acoustic source strength (power) under controlled conditions. To predict accurate data of radiated sound power for comparison with the experimental work, two models have been developed: one model using the Farassat formula for a rotating dipole and the other model based on a 3D acoustic-vortex model. The heat exchangers in the cooling unit can have a significant effect on sound emitted from a cooling fan. An acoustic model based on so called equivalent fluid model for an anisotropic medium was derived to evaluate the sound transmission and the absorption through a parallel plate type of heat exchanger.</p>

No description available.

<p>The collision threshold pressure (CTP), i.e. the smallest amount of subglottal pressure needed for vocal fold collision, has been explored as a possible complement or alternative to the now commonly used phonation threshold pressure (PTP), i.e. the smallest amount of subglottal pressure needed to initiate and sustain vocal fold oscillation. In addition, the effects of vocal warm-up (Paper 1) and vocal loading (Paper 2) on the CTP and the PTP have been investigated. Results confirm previous findings that PTP increases with an increase in fundamental frequency (F0) of phonation and this is true also for CTP, which on average is about 4 cm H₂O higher than the PTP. Statistically significant increases of the CTP and PTP after vocal loading were confirmed and after the vocal warm-up, the threshold pressures were generally lowered although these results were significant only for the females. The vocal loading effect was minor for the two singer subjects who participated in the experiment of Paper 2.</p><p>In Paper 3, the now commonly used audio spectral tilt (AST) is measured on the vowels of a large database (5277 sentences) containing speech of one male Swedish actor. Moreover, the new measure electroglottographic spectral tilt (EST) is calculated from the derivatives of the electroglottographic signals (DEGG) of the same database. Both AST and EST were checked for vowel dependency and the results show that while AST is vowel dependent, EST is not.</p><p>Paper 4 reports the findings from a perception experiment on Swedish accents performed on 47 Swedish native speakers from the three main parts of Sweden. Speech consisting of one sentence chosen for its prosodically interesting properties and spoken by 72 speakers was played in headphones. The subjects would then try to locate the origin of every speaker on a map of Sweden. Results showed for example that the accents of the capital of Sweden (Stockholm), Gotland and southern Sweden were the ones placed correctly to the highest degree.</p> / QC 20100915

Presented is an analysis of the performance of a matched field and matched beam processor in localization of a shallow water source using a 63-element bottom-moored planar array. Two scenarios are considered: in the first, a stationary, submerged CW source is localized in a high SNR environment; in the second, the source is being towed in the presence of multiple ship-generated directional noise sources. Array element localization is carried out using regularized linear inversion on transients from light bulb implosions around the array. The method provides the simplest array shape solution while still fitting the data and initial hydrophone position estimates to a statistically appropriate level. Estimation of geoacoustic parameters is accomplished using a hybrid inversion algorithm producing a robust geoacoustic model which is subsequently used to produce replica acoustic fields for the full field localization methods. Localization proved highly successful for the first scenario, while increased noise and geometrical limitations led to moderate performance in the second scenario.

The propagation of ultrasonic waves has been studied in single crystals of undoped and doped bismuth germanium oxide (Bi₁₂GeO₂₀) and undoped bismuth silicon oxide(Bi₁₂SiO₂₀). These crystals are piezoelectric (Cubic Space Group I23) and direct excitation of ultrasound was used wherever possible. Attenuation measurements were made from 10 to 190 MHz over the temperature range 4.2 to 260 K. A large attenuation peak was observed in the undoped crystals between 35 and 50 K for only those ultrasonic modes whose velocity depends on the elastic modulus C₄₄ This peak is shown to be a single anelastic relaxation peak and is interpreted as due to point defects. Using the selection rules for anelastic relaxation in cubic crystals, it is deduced that these defects must have trigonal symmetry. The magnitude of the attenuation peak in doped BGO samples is strongly dependent on the presence of dopants. Doping with Al, Ga, Pb, P + Ga, Ga+Cr, all removed the attenuation peak, while Cr increased it and Zn reduced it. A strong correlation was observed between the attenuation peak, the colour of the crystals and the optical absorption just below the band gap measured in these samples by other workers. These results indicate that the same defect centre is responsible for both the optical and the ultrasonic absorption. Possible defects are discussed taking the optical absorption, X-ray diffraction, EPR and other available measurements into consideration. The ultrasonic attenuation was measured before and after annealing at 450&deg;C in vacuo or in pure oxygen. No change was observed for an undoped sample. However, for the Cr doped sample the attenuation was reduced by vacuum annealing and restored by oxygen annealing. This seems to be closely related to previous observations of photo-chromic behaviour in BSO doped with Cr. Measurements were also made to study the effects of gamma irradiation on the attenuation in undoped BSO.

A set of high-order spatial and temporal finite difference stencils is developed. They are derived using an optimization procedure designed to ensure that the numerical derivatives preserve the wave number and angular frequency of the partial differential equations being discretized. In doing so, they guarantee that the numerical scheme preserves the dispersion relation of the analytic equations when the wave modes are in the long wave range. Consequently, the acoustic, entropy and vorticity waves propagate with the correct wave speeds and exhibit their appropriate properties. Waves that are short compared to the grid mesh size (waves with wavelength less than 5 mesh spacings) generally have totally different wave propagation characteristics. These waves are contaminants of the numerical solution. A method designed to eliminate such waves without significantly affecting the long waves is developed. A set of radiation and outflow boundary conditions is also constructed. These conditions are derived from the asymptotic solutions of the linearized Euler equations. A numerical simulation designed to test the effectiveness of the finite difference schemes and the boundary conditions is performed. The computed solutions agree very favorably with the exact solutions. These methods are applied then to a simulation of a 2-D supersonic Mach 1.7 jet. Initial conditions and a mapping based upon empirical data are derived. The mapping concentrates grid points in the mixing layer of the jet. In this region, very small time steps are required. A method which allows different regions of the grid to have different time steps is developed. This greatly improves the efficiency of the code. The steady state solution is computed. / Source: Dissertation Abstracts International, Volume: 54-07, Section: B, page: 3667. / Major Professor: Christopher K. W. Tam. / Thesis (Ph.D.)--The Florida State University, 1993.

<p> Audio has the capacity to display geospatial data. As auditory display design grapples with the challenge of aligning the spatial dimensions of the data with the dimensions of the display, this dissertation investigates the role of time in auditory geographic maps. Three auditory map types translate geospatial data into collections of musical notes, and arrangement of those notes in time vary across three map types: <i>sequential, augmented-sequential </i>, and <i>concurrent</i>. Behavioral and neuroimaging methods assess the auditory symbology. A behavioral task establishes geographic context, and neuroimaging provides a quantitative measure of brain responses to the behavioral task under <i>recall</i> and <i>active listening </i> response conditions. </p><p> In both behavioral and neuroimaging data, two paired contrasts measure differences between the sequential and augmented-sequential map types, and between the augmented- sequential and concurrent map types. Behavioral data reveal differences in both response time and accuracy. Response times for the augmented-sequential map type are substantially longer in both contrasts under the active response condition. Accuracy is lower for concurrent maps than for augmented-sequential maps; response condition influences direction of differences in accuracy between the sequential and augmented-sequential map types. Neuroimaging data from functional magnetic resonance imaging (fMRI) show significant differences in blood-oxygenation level dependent (BOLD) response during map listening. The BOLD response is significantly stronger in the left auditory cortex and planum temporale for the concurrent map type in contrast to the augmented- sequential map type. And the response in the right auditory cortex and bilaterally in the visual cortex is significantly stronger for augmented-sequential maps in contrast to sequential maps. Results from this research provide empirical evidence to inform choices in the design of auditory cartographic displays, enriching the diversity of geographic map artifacts. </p><p>