<p> This dissertation describes experiments in spherical Couette devices, using both gas and liquid sodium. The experimental geometry is motivated by the Earth's outer core, the seat of the geodynamo, and consists of an outer spherical shell and an inner sphere, both of which can be rotated independently to drive a shear flow in the fluid lying between them. In the case of experiments with liquid sodium, we apply DC axial magnetic fields, with a dominant dipole or quadrupole component, to the system. We measure the magnetic field induced by the flow of liquid sodium using an external array of Hall effect magnetic field probes, as well as two probes inserted into the fluid volume. This gives information about possible velocity patterns present, and we extend previous work categorizing flow states, noting further information that can be extracted from the induced field measurements. The limitations due to a lack of direct velocity measurements prompted us to work on developing the technique of using acoustic modes to measure zonal flows. Using gas as the working fluid in our 60 cm diameter spherical Couette experiment, we identified acoustic modes of the container, and obtained excellent agreement with theoretical predictions. For the case of uniform rotation of the system, we compared the acoustic mode frequency splittings with theoretical predictions for solid body flow, and obtained excellent agreement. This gave us confidence in extending this work to the case of differential rotation, with a turbulent flow state. Using the measured splittings for this case, our colleagues performed an inversion to infer the pattern of zonal velocities within the flow, the first such inversion in a rotating laboratory experiment. This technique holds promise for use in liquid sodium experiments, for which zonal flow measurements have historically been challenging.</p>

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A method for calculating the acoustic radiation generated by the large scale instabilities of axisymmetric jets is developed. The characteristics of the flow instabilities are obtained from the linearized, inviscid, compressible equations of motion in terms of an asymptotic expansion. This asymptotic expansion is not uniformly valid far away from the jet flow. To obtain a solution valid far away from the jet, the method of matched asymptotic expansions is used. The matching of inner and outer solutions provide two very important results. First, a new interpretation of the eigenvalue problem of classical instability theory is given. Secondly, matching provides a method for determining the slow varying wave amplitude of the instability wave allowing for a complete spatial description of the instability wave to order unity. Calculations of the instability wave characteristics, near- and far-field pressure fluctuations for an unheated, ideally expanded, moderate Reynolds number jet with jet exit Mach number of 2.1 are performed at several frequencies and for the axisymmetric and helical instabilities. The numerical results of this model are then compared with experiments and good agreement is found in both the jet flow and near-field. / Source: Dissertation Abstracts International, Volume: 42-10, Section: B, page: 4099. / Thesis (Ph.D.)--The Florida State University, 1981.

acase@tulane.edu

Musical expression is largely dependent upon accentuation, yet there have been few attempts to study the perception of dynamic accent in music or to relate the results of psychoacoustical research in intensity to realistic musical situations. The purpose of the experiment was to estimate the relationships among (a) the intensity increment in dB(A) required to meet an 80% correct criterion in the perception of one accented tone embedded within a seven-tone isochronous series of identical 87 dB(A) snare drum timbre stimuli of 333 ms onsets (accent level, or AL), (b) the different limen (DL) for intensity increase to meet a 75% correct criterion in a 2AFC task for pairs for the stimuli, and (c) the age of the subjects, all of whom have normal audiograms. / The 51 subjects (N = 51) were female nonmusicians ranging in age from 9 to 33 years (M = 17.98, SD = 5.21). The response tasks involved saying whether the second tone of each pair was louder or softer and circling the accented note in notated quarter notes. The stimuli production, the headphone calibration process, and their rationales were detailed. The global regression model was significant (F(2, 48) = 5.505, p =.007, $R\sp2$ =.187), and the relationship between AL and DL was not significant (F(1, 48) = 5.505, p =.197, $R\sp2$ change =.029), the relationship between AL and age was significant (F(1, 48) = 5.732, p =.021, $R\sp2$ change =.098) at an alpha level of.05 and power calculated at.66 for a medium ES. / It was concluded that accented sounds are easier to perceive in tone pairs than they are in a musical setting and that subject maturation improves performance of intensity judgement tasks. Suggestions for further research include shortening the length of the experimental session for younger subjects and increasing the number of intensity increments as well as using smaller increments to accommodate individual differences in perception. / Source: Dissertation Abstracts International, Volume: 53-03, Section: A, page: 0662. / Major Professor: Jack A. Taylor. / Thesis (Ph.D.)--The Florida State University, 1992.

Experimental investigations of two ultrasonic lenses are presented, a graded acoustic index lens and a cylindrical lens. The first lens is a short rod which has a graded acoustic velocity profile in the radial direction giving it the ability to focus acoustic waves. Electron probe microanalyses, optical refractive index measurements and acoustic velocity measurements are used to characterize the lens. The ray acoustics approach is used for the theoretical interpretation and the focussing behavior is visualized with a Schlieren system. Potential applications of the lens are discussed. / The cylindrical lens consists of a lead zirconate titanate (PZT) coated wire or optical fibre. The fabrication and evaluation of the lens is described. Ultrasonic measurements of miniature transducers and electronically controllable deflection are demonstrated. A novel laser ablation patterning technique is used to make an interdigital transducer with a 20$ mu$m resolution on the outer electrode of the lens for special applications. Finally, possible applications of the cylindrical lens are outlined.

In this paper, we present a software tool for the computation of eigenvalues of starlike domains defined by polar boundary functions. We also offer and numerically test a conjecture on the monotonicity of the fundamental eigenvalues of the members of a family of starlike domains.

Differential semblance measures the deviation from flatness or focus of image gathers. The differential semblance objective function posed on the sub-surface offset domain responds smoothly to velocity changes. Therefore gradient descent methods are uniquely attractive for velocity updating by differential semblance optimization. Because of their kinematic fidelity, wave equation (depth extrapolation) migration methods are natural platforms for velocity analysis in complex structures. The gradient of the objective function with respect to velocity is fomulated through the adjoint of differential migration. Limited memory BFGS algorithm is used for the velocity optimization. The method for wave equation velocity analysis developed in this thesis study is applied to both synthetic and real data examples.