A theoretical analysis of the acoustic field around a sound source suggested that fish would be able to locate a sound source by detecting the associated near field displacements with their lateral line system. Blinded goldfish and Mexican blind cave characins were able to locate both stationary objects and sound sources. The lateral line system was implicated as the directionally sensitive organs involved. Blind cave fish were able to locate both stationary objects and a sound source against a background noise. The existence of a noise suppressing mechanism to the lateral line organs was suggested. An efferent nervous supply was shown to innervate anterior lateral line organs of goldfish, and the inhibitory nature of the efferent nerves was demonstrated. The efferent nerves were found to be insensitive to the stimulation of acoustically sensitive organs on the fish, but responded to changing states of muscular activity in the fish. Swimming goldfish changed hydrodynamically during respiration from bluff bodies, when their mouths were shut, to streamlined bodies, when their mouths were open. This change in configuration lead to the proposal that the anterior lateral line organs function both as velocity detectors and near field displacement detectors. A central location was suggested for a neuro-physiological noise attenuating system to the lateral line system, and the efferent nerves innervating the lateral line organs were suggested to form part of a mechanism reflexively controlling swimming velocity. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

The properties of all-optical nonlinear waveguide devices are investigated. In particular, the nonlinear directional coupler (NLDC) and nonlinear Mach-Zehnder interferometer (NLMZ) are analyzed using perturbation theory. The perturbation theory provides differential equations that describe the amplitude of the waveguide modes as a function of the propagation distance. To be practical, these waveguide devices require nonlinear phase shifts of π or more. Therefore, the theoretical investigation of these devices emphasizes their fabrication in bulk and multiple-quantum-well (MQW) gallium arsenide (GaAs). For the first time, absorption, carrier diffusion, and thermal effects are included in the theoretical investigation of the NLMZ and NLDC. The nonlinear dependence of the coupling terms, which has been neglected in all previous work, is shown to be significant for semiconductor based NLDC's. The effects of carrier diffusion on the nonlinear response of a GaAs waveguide is demonstrated using a self-consistent numerical method. The effects are heavily dependent on the waveguide geometry, and, therefore, should be included in the analysis of nonlinear semiconductor waveguide devices. However, if the diffusion length is large compared to the mode width, carrier diffusion simplifies the investigation since the nonlinear absorption and index change are uniform across the mode. This important conclusion is used in the models for the NLMZ and NLDC. The theoretical models predict the NLMZ and NLDC should work in bulk and MQW GaAs. To demonstrate that the required nonlinear phase shifts for the NLMZ and NLDC are indeed possible in bulk and MQW GaAs, the first experimental observation of electronic optical bistability in a MQW GaAs strip-loaded waveguide is recounted. This original research illustrated that phase shifts in excess of 2π are possible in MQW GaAs waveguides and, therefore, the future of all-optical waveguide devices in semiconductors is optimistic.

No description available.

Student Number : 0210528 - PhD thesis - School of Mining Engineering - Faculty of Engineering and the Built Environmnet / This thesis describes the development of a directional primer charge for use in blasting in mining operations. The directional primer charge is an explosive gun which takes the place of a standard primer charge in a blasthole. It is a shaped charge which directs the explosive energy forwards into the blasthole. Its effectiveness is enhanced by a metal liner which is located at a specified stand-off distance from the toe of the hole. The explosive energy of the column charge is converted into the kinetic energy of the metal liner which transforms into an ultrasonic slug. This in turn converts into the impact energy of the slug impacting on the rock. This rock is axially compressed to such a degree that a radial fracture is developed. This radial fracture is termed an umbrella crack. Prior to the development of the directional primer charge, the phenomenon of the umbrella crack had only been observed in experimental Perspex blasting models and its formation mechanism had never been satisfactorily explained. If the directional primer charge could cause an umbrella crack in hard rock mining at the end of blastholes, then more rock would be broken out per blast than is currently achieved in practice. This thesis records the historical development of the explosive shaped charge with particular reference to the development of the explosively-forged projectile. It describes the classical theories and models which apply in determining the theoretical prediction of the physical properties of the designed directional primer charge. It describes the experimental procedures and measurements using flash X-ray radiography and electronic shorting screens to freeze the flight of a metal slug traveling at speeds of over 2000 metres per second. Underground tests were undertaken under full mining production conditions to compare the rock breaking effects of various designs. The theoretical calculation of the extent of the movement of the rock at the toe of the blasthole indicates that umbrella cracks should be formed. The underground tests confirm their formation. It is concluded that the use of the directional primer charge in stoping operations can improve the blasting efficiency in South African hard rock mines by up to 15 %.

The reliability of structures subjected to time-invariant or time-variant random loads is considered herein. This is an important field of engineering, as it provides the framework for assessing whether newly designed or existing structural systems meet their design requirements in a given lifetime, or whether they experience what is termed “structural failure”. An important aspect of reliability analysis is the study of structures subjected to multiple time-varying loads. For this class of systems, it is well-known that by modelling the loads as (time-variant) random processes, the reliability may be evaluated by considering the outcrossing of a vector process out of a safe domain. However, due to the possibility that the loads may not be fully-dependent, all loads may not necessarily contribute to structural failure. To account for this the treatment of vector-outcrossings may need to allow for the possibility of outcrossings being caused by individual loads, as distinct from combinations of all loads. The procedure used to analyse combinations of loads depends on the stochastic process model used to represent the loads. Two well-known load models have been presented in the literature—they are referred to herein as the ‘on-off’ model and the ‘standard’ model. The ‘on-off’ model typically assumes loads are non-negative, and are either ‘on’ (eg their value is non-zero) or ‘off’ (eg their value is strictly zero). They can contribute to failure only when they are ‘on’. This model is represented by a somewhat artificial ‘composite’ probability distribution, obtained by modifying the original load probability density function (pdf) so that a ‘finite’ non-zero probability represents explicitly the possibility that the load is ‘off’. To implement this model in time-variant analysis, it is necessary to consider all possible combinations of loads being ‘on’ and ‘off’. In contrast, the ‘standard’ model (which is the more commonly used) typically allows loads to be negative; it is also typically represented solely by the original load pdf, and therefore effectively assumes each load is always ‘on’. To allow for the possibility of one or more loads not to cause failure, herein the value of such loads is held ‘constant’ at the time of failure, when the value of all loads actually causing failure is allowed to change. Use of the ‘standard’ model is examined herein. The “Directional Simulation in the Load Space (DS-LS)” approach is a tool used to perform reliability analysis. It is particularly suitable for time-variant analysis, as it allows loads to be represented as random processes, and to be modelled properly. DS-LS has so far been shown to work well for relatively simple structures subjected to one or more time-invariant random loads, and has been used to examine vector outcrossings in systems comprising either discrete or continuous loads. To enable the proper consideration of load combinations, and to provide some improvements in the formulation of the technique, a generalisation of the DS-LS approach is proposed herein. The generalisation is achieved in two stages. The first involves modifying the time-invariant and time-variant DS-LS formulation to allow for the possibility of positioning the origin of DS-LS not only in the ‘safe’ region of the load space (which the formulation currently requires) but in the ‘failure’ region, or even ‘exactly’ on the boundary separating the safe and failure regions. The modifications are necessary because for even simple structures, the ‘exact’ location of the safe and failure region is not always known explicitly ‘a priori’. The second involves developing the time-variant DS-LS formulation to consider explicitly outcrossings caused by combinations of one or more loads, during analysis of systems comprising stationary continuous gaussian loads. To do this, the direction of the load process vector is ‘fixed’ at each point of outcrossing, to physically represent the particular combination of loads causing the outcrossing. By considering each possible load combination, all loads not causing an outcrossing are then held constant during radial integration, thereby modelling those that do not contribute to each outcrossing. The proposed formulation differs from most load combination analysis techniques (which, evidently, simplify the analysis) as it is analytically ‘exact’, and it considers explicitly all possible combinations of loads. The concepts and formulations proposed herein may provide further understanding of reliability analysis performed by DS-LS (or other techniques) and may aid their future development. / PhD Doctorate

To establish the credibility of surface wave measurements from two phased-array WERA HF (High Frequency) radars, SEACOOS (SouthEast Atlantic Coastal Ocean Observing System) funded the Mini-Waves experiment from March to May, 2005. For this study, the surface wave parameter (significant wave height) and directional wave spectrum obtained from two WERA radars were compared with those obtained from two Tri-Axys buoys during the same period. The Wyatt (1990) method was used to obtain the directional wave spectra, and significant wave heights were obtained by integrating the directional wave spectra over all directions and the selected frequency band. The SWAN (Simulating WAve Nearshore) directional wave model was used to evaluate the comparison results between WERA radars and buoys. There was a good agreement between WERA radars and Tri-Axys buoys when the echo-Doppler spectrum had a high 2nd-order SNR (signal-to-noise) ratio. The measurements didn?t agree in low sea states when the echo-Doppler spectrum had a lower SNR. Also, strong horizontal current shear caused by Florida Current (FC) had an effect on wave propagation direction. To improve the quality of WERA radar wave measurements, a longer sampling interval (10-minute interval) and procedures to remove the effect of RFI are needed.

This dissertation describes the development of a new multi-directional direct simple shear testing device, the Texas A&M Multi-directional Direct Simple Shear (TAMU-MDSS), for testing marine soil samples under conditions, which simulate, at the element level, the state of stress acting within a submarine slope under dynamic loading. Prototype testing and an experimental program to characterize the response of marine clays to complex loading conditions are presented. The work is divided into four major components: 1) Equipment Development: Design and construction of a prototype multi-directional direct simple shear testing device (TAMU-MDSS) that addresses the limitations of previous devices. 2) Support systems: selection of control software, development of data acquisition system and design of back pressure systems for direct pore pressure measurements. 3) Prototype Testing: performance of the TAMU MDSS system and testing of strain-control and stress-control capabilities. 4) Experimental Testing: characterize the response of marine clays to monotonic, dynamic and random loads. The two-directional monotonic, cyclic, circular and figure-8 tests demonstrated the undrained shear strength increases with increasing initial shear stress, (i.e, slope), for shearing in the same direction (equivalent to downhill). The strength decreases for shearing in the direction opposite to the initial stress (shearing uphill). The response is as brittle for shearing in the same direction as the shear stress applied during consolidation initial shear stress and ductile for shearing opposite to initial shear stress. These findings have important implications for the stability of the slope, predicting that forces acting downward in the slope direction will need to mobilize less strain to reach peak strength and initiate failure. This information provides insight into the behavior of marine soils under complex loading conditions, and provides high quality laboratory data for use in constitutive and finite element model development for analysis of submarine slopes.

A navigation system developed for an omni-directional wheeled mobile robot, called the Omnibot, is presented. This system is developed to enable the Omnibot to autonomously navigate, in a collision-free manner, along predefined paths in indoor structured office or factory-like environments. The navigation system is composed of four integrated subsystems: localization, path- following, velocity control, and obstacle detection. The path-following subsystem is responsible for driving the Omnibot along a given path based on feedback about its location relative to its environment. A localization system that uses a combination of odometry and a novel indoor GPS-like system provides the necessary estimates of the Omnibot's position and orientation (i.e., pose). Using the pose updates from the localization subsystem, the path-following subsystem is able to compute motion commands to drive the Omnibot along the path. Execution of these motion commands is performed by the velocity control subsystem, which uses feedback control to regulate the angular velocities of the motors driving the Omnibot's wheels to produce the required motion of the robot. To ensure collision-free navigation, the Omnibot is equipped with an array of infrared distance sensors for detecting obstacles around its perimeter. Interaction between a human operator and the Omnibot is facilitated with a user-control interface running on a remote workstation. The interface allows the operator to visualize the Omnibot's location within a 3D model of its indoor workspace and provides a means to input commands. Testing of the developed system is performed, and the results confirm its e effectiveness at enabling the Omnibot to perform collision-free autonomous navigation in an indoor structured environment. / UOIT

Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.