<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>

Real world perceptual environments are characterized by objects that often co-occur, occlude one another, and display time-variant behavior. In addition there may be variations in the signal-to-noise ratio. Successful object recognition depends on the extraction of adequate disambiguating features, which are neither easily identifiable nor stationary in such environments. In an effort to improve recognition accuracy and do so efficiently, Adaptive Perceptual Systems have emerged that re-configure their signal processing in response to variations in the signal to ensure extraction of adequate features. Key to adaptive signal processing is determining when and in what manner to modify signal processing. Symbolic object models play a pivotal role in this process by serving to interpret data, predict signal behavior and account for interference from objects simultaneously present. Unfortunately, symbolic object models are typically hand-crafted, a tedious error-prone task that constitutes a knowledge acquisition bottleneck, which limits object database size and impedes deployment for new and changing environments. This thesis explores the integration of feature extraction with model construction, viewing the two processes as driving one another until the goal of producing unambiguous symbolic object models is satisfied. The paradigm has been fielded to acquire acoustic-event models for a sound understanding system.

As polymers are utilized in new applications they encounter environments that push them to their limits. In response to this demand, materials are being engineered on the molecular, meso, and macro levels such that their properties match those required of properties is the incorporation of an inorganic heterogeneity. One of the most effective methods of modifying physical and mechanical properties is the incorporation of an inorganic heterogeneity. Recent advances in controlled SiO2 Sol-gel synthesis have made it possible to created unique heterogeneities of desired dimensions. A detailed investigation of the mechanism of the room temperature sol-gel synthesis of rectangular cross section silica tubes is presented. It is elucidated that tubes are formed by simultaneous template formation and coating with rapidly condensing SiO2. The templates are subsequently dissolved out from within the SiO2 coating yielding tubes whose size and geometry match those of the templates. Knowledge gained in examining the mechanism is utilized to create tubes of desired length and diameter. The process shows promise for fabricating hollow silica shapes of controlled dimension and geometry. The morphology and damage states of complex multicomponent polymeric materials and composites are extremely difficult to characterize by current methods. Traditionally, morphology is characterized via gross differences in electron density (via electron microscopy), chemical nature (staining enhanced electron microscopy) and optical density (via optical microscopy). Ultrasonic spectroscopy is a new technique that utilizes high frequency (10–100 MHz) transducers to transmit and receive sound waves through materials. Sound waves translate via successive perturbations of the medium and consequently the rate and manner in which they are transmitted is a function of the medium's physical and mechanical properties. Hence, morphology is imaged through density or modulus differences regardless of optical clarity. Ultrasonic spectroscopy was applied to the morphological analysis of model polymers containing phase separated spherical heterogeneities, characterization of model reacting systems, and the elucidation of residual strengths in graphite fiber reinforced epoxy laminates exposed to thermal loads. This research resulted in the development of analysis methods that successfully characterized morphology on several levels, monitored gelation and phase separation in situ, and detected thermally induced incipient damage in polymer matrix composites.

This study explores the acquisition of intonation by Spanish second language speakers while on a study abroad program in Valencia, Spain. The investigation consists of two groups: a control group and an instruction group. The instruction group participated in perception trainings while the control group did not. As this region of Spain is also bilingual, and there are no studies currently in the literature that describe the Spanish of Valencian speakers, this study also presents data from native speakers who completed the same task as the non-native speakers. / A Thesis submitted to the Department of Modern Languages and Linguistics in partial fulfillment of the requirements for the degree of Master of Arts. / Summer Semester 2015. / June 18, 2015. / Bilingualism, Intonation, Second Language Acquisition, Spanish, Study Abroad / Includes bibliographical references. / Carolina González, Professor Directing Thesis; Lara Reglero, Committee Member; Antje Muntendam, Committee Member; Anel Brandl, Committee Member.

Includes bibliographical references. / This thesis builds on research by Bolton and Gold, who developed the theory of using cepstral analysis to determine the absorption coefficient of elastic porous materials. Jongens, in his Masters thesis, applied this technique to determine the absorption coefficient of asphalt samples mounted in a sample holder at the end of a tube. Jongens and others identified numerous factors that introduced uncertainties into the measurement. These uncertainties fall into two main categories. The first deals with the influences that the links of the measurement chain have on the ability to separate the incident and reflected signal. The second deals with the influence of the air leakage between the tube and the surface under measurement in-situ. This thesis deals with the first category. The objectives of this project are to continue the work of Jongens, to produce an apparatus that can rapidly determine the sound power absorption coefficient by a non-skilled operator in a noisy environment. The results should correlate closely with the standardised impedance tube method, within 0.05 over the range 200 Hz to 2000 Hz. The constraint that the apparatus be usable by a non-skilled operator means that little or no calibration should be required, nor should the microphone need to be handled. This thesis presents a survey of related methods used to determine the sound power absorption coefficient. Theory of the cepstral technique is discussed, along with methods that could be used to improve the accuracy of the technique. Excitation signals that could be used with the cepstral method are put forward. The Inverse Repeat Sequence (IRS) was used to excite the system. It was chosen for its high noise immunity, as well as its complete odd-order non-linearity immunity. Sources of uncertainties from the links of the measurement chain are considered and methods to overcome them are presented. Issues that arise from liftering - cepstral equivalent of windowing - are then highlighted. The apparatus for the cepstral technique and method of standing wave ratios used to determine the absorption coefficient is given. The results obtained using the cepstral technique are correlated with the impedance tube results. It was found that the cepstral method correlates closely with the impedance tube over the range of 200 Hz to 2000 Hz for a wide variety of samples. The apparatus was developed to be used by a non-skilled operator, only requiring the press of a button to perform the measurement. With the high noise immunity of the IRS signal, the measurement could be carried out in a noisy environment.

This study aimed to investigate the possible means of mitigating noise disturbance in naturally ventilated classrooms that are exposed to road-traffic noise. Specifically, the efficacy of façade design, building orientation, distance from the road and noise barriers was tested to achieve a suitable ambient sound pressure level (SPL) in classrooms. The outcome is a heuristic framework to assist school infrastructure planners and architects in the early stages of a project to choose suitable acoustic interventions. The context was the urbanised province of Gauteng, South Africa, where many new schools are needed and where urbanisation has enveloped many previously suburban schools in traffic noise. Classrooms are typically naturally ventilated with open windows that allow noise in. This increases the classroom ambient noise level which has potentially negative effects on the occupants’ health, well-being and academic outcomes. A computer model of a typical classroom, based on data collected at four Gauteng schools, was used to experiment with various sound attenuation interventions. The modelled results showed that the façade construction material is acoustically inconsequential due to the compromising effect of large openings. A suitable classroom ambient noise level (40 dBA) was only achieved for a building modelled without a barrier at the maximum distance modelled, which was 136 m from the road, provided that the building was perpendicular to the road. Barriers of varying heights (1.5 m – 7 m) were inserted, either at the school boundary (12 m from the centre of the road) or 3 m from the classroom façade. With a barrier, the closest distance from the road at which the target SPL was achieved was at 42.5 m with a 5.5 m high barrier. As the distance from the road to the building increased, the height of the barrier required decreased. Considering a maximum practical barrier height of 3.5 m, the ideal SPL was only achieved for a classroom at least 51 m from the road. Barriers inserted 3 m from the façade were more effective than barriers at the school boundary. A significant SPL decrease (≥ 6 dB) was, however, achieved in classrooms as close as 17 m from the road with the insertion of a barrier (≥ 2 m high), and a suitable signal-to-noise ratio was achieved for a classroom 17 m from the road with a 2.5 m high barrier. These findings are particularly useful for application in existing schools with limited space. The findings provided a data set that was used to develop a heuristic framework as guidance for planners in the early stages of school infrastructure design. / Thesis (PhD (Architecture))--University of Pretoria, 2020. / CSIR / Architecture / PhD (Architecture) / Unrestricted

This account of the beginning of music might equally well be applied to man's discovery of sounds produced by the stretched string on his hunting-bow, or skins stretched across wooden frames. Pure fancy though it may be, the account serves to illustrate the dependence of music on the universal principles of science. Sound, the medium of expression, the vehicle, of music, is purely physical phenomenon. All aspects of its production, its transmission, and its ultimate reception are based invariable on physical laws. All musical instruments operate under these laws, as do the tones and combinations of tones which the instruments produce. Since that time when our prehistoric man made his discoveries, all musicians have had to depend upon scientific principles in producing the various sounds with which they work In order to deal most effectively with these tones, it is necessary that the musician understand some of the principles governing their production and their various relationships. It is with this necessity in mind that this thesis is being written. In the thesis an attempt is made to present those physical aspects of sound which will be of the most practical use to the musician and which will give him a better understanding of the materials with which he works. As often as it is possible and practical, direct illustration of the applications to the musician's work of the principles discussed are given. this thesis is not intended to be a study of sound. The subject is covered thoroughly in a number of text-books. lt is rather an attempt to show how the Science of Sound is related to the Art of Music, to demonstrate in what ways the latter is dependent upon the former, and to outline an approach to a study of the physical principles of sound for the musician.

The investigation covered various aspects of the effects of a single delayed echo on the intelligibility of speech and was extended to cover the case of multiple echoes which is more in line with practical conditions than a single echo. The application of the results obtained to architectural acoustics and speech reinforcement is discussed.

No description available.

No description available.