The maintenance of species diversity occurs at the regional scale but depends on interacting processes at the full range of lower scales. Although there is a long history of study of regional diversity as an emergent property, analyses of fully multiscale dynamics are rare. Here, we use scale transition theory for a quantitative analysis of multiscale diversity maintenance with continuous scales of dispersal and environmental variation in space and time. We develop our analysis with a model of a linear habitat, applicable to streams or coastlines, to provide a theoretical foundation for the long-standing interest in environmental variation and dispersal, including downstream drift. We find that the strength of regional coexistence is strongest when local densities and local environmental conditions are strongly correlated. Increasing dispersal and shortening environmental correlations weaken the strength of coexistence regionally and shift the dominant coexistence mechanism from fitness-density covariance to the spatial storage effect, while increasing local diversity. Analysis of the physical and biological determinants of these mechanisms improves understanding of traditional concepts of environmental filters, mass effects, and species sorting. Our results highlight the limitations of the binary distinction between local communities and a species pool and emphasize species coexistence as a problem of multiple scales in space and time.

This research is concerned with inheritance as used in object-oriented database. More specifically, partial bi-directional inheritance among classes is examined. In partial inheritance, a class can inherit a proper subset of instance variables from another class. Two subclasses of the same superclass do not need to inherit the same proper subset of instance variables from their superclass. Bi-directional partial inheritance allows a class to inherit instance variables from its subclass. The prototype of an object-oriented database that supports both full and partial bi-directional inheritance among classes was developed on top of an existing relational database management system. The prototype was tested with two database applications. One database application needs full and partial inheritance. The second database application required bi-directional inheritance. The result of this testing suggests both advantages and disadvantages of partial bi-directional inheritance. Future areas of research are also suggested.

With the rapid development of the modern technology, radio frequency and microwave systems are playing more and more important roles. Since the time the first microwave device was invented, they have been leading not only the military but also our daily life to a new era. In order to make the devices have more practical applications, more and more strict requirements have been imposed. For example, good adaptability, reduced cost and shrank size are highly required. In this thesis, three devices are designed based on this requirement. At first, a symmetric four-port microwave varactor based 90-degree directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. Then, a novel reconfigurable 3-dB directional coupler is presented. Varactors and inductors are loaded to the device to realize the reconfigurable performance. By adjusting the voltage applied to the varactors, the proposed coupler can be reconfigured from a branch-line coupler (90-degree coupler) to a rat-race coupler (180 degree coupler) and vice versa. At last, two types (Type-I and Type-II) of microwave baluns with generalized structures are presented. Different from the conventional transmission-line-based baluns where λ/2 transmission lines or λ/4 coupled lines are used, the proposed baluns are constructed by transmission lines with arbitrary electrical lengths.

Additive manufacturing (AM) offers a way to manufacture highly complex designs with potentially enhanced performance as it is free from many of the constraints associated with traditional manufacturing. However, current design and optimisation tools, which were developed much earlier than AM, do not allow efficient exploration of AM's design space. Among these tools are a set of numerical methods/algorithms often used in the field of structural optimisation called topology optimisation (TO). These powerful techniques emerged in the 1980s and have since been used to achieve structural solutions with superior performance to those of other types of structural optimisation. However, such solutions are often constrained during optimisation to minimise structural complexities, thereby, ensuring that solutions can be manufactured via traditional manufacturing methods. With the advent of AM, it is necessary to restructure these techniques to maximise AM's capabilities. Such restructuring should involve identification and relaxation of the optimisation constraints within the TO algorithms that restrict design for AM. These constraints include the initial design, optimisation parameters and mesh characteristics of the optimisation problem being solved. A typical TO with certain mesh characteristics would involve the movement of an assumed initial design to another with improved structural performance. It was anticipated that the complexity and performance of a solution would be affected by the optimisation constraints. This work restructured a TO algorithm called the bidirectional evolutionary structural optimisation (BESO) for AM. MATLAB and MSC Nastran were coupled to study and investigate BESO for both two and three dimensional problems. It was observed that certain parametric values promote the realization of complex structures and this could be further enhanced by including an adaptive meshing strategy (AMS) in the TO. Such a strategy reduced the degrees of freedom initially required for this solution quality without the AMS.

This doctoral thesis is comprised of five parts. The first three parts concern signal processing and electromagnetic modelling of multiport antennas. The last two parts concern signal processing and transmission line theory applied to wave splitting on transmission lines. In Part I, the spherical vector wave expansion of the electromagnetic field is used to completely characterize a multiport antenna. A general framework for modelling an antenna configuration based on measurement data and numerical computation is obtained. The generic electromagnetic model for arbitrary multiport antennas or vector sensors is applied in direction of arrival (DOA) estimation. Next, in Part II using the generic electromagnetic model (from Part I), we obtain the Cramér–Rao bound (CRB) for DOA and polarization estimation using arbitrary multiport antennas. In the Gaussian case, the CRB is given in terms of the transmission matrix, the spherical vector harmonics and its spatial derivatives. Numerical examples using an ideal Tripole antenna array and a non-ideal Tetrahedron antenna array are included. In Part III, the theory of optimal experiments is applied to a cylindrical antenna near-field measurement setup. The D-optimal (determinant) formulation using the Fisher information matrix of the multipole coefficients in the spherical wave expansion of the electrical field result in the optimal measurement positions. The estimation of the multipole coefficients and corresponding electric field using the optimal measurement points is studied using numerical examples and singular value analysis. Further, Part IV describes a Digital Directional Coupler (DDC), a device for wave splitting on a transmission line. The DDC is a frequency domain digital wave splitter based on two independent wide-band measurements of the voltage and the current. A calibration of the digital processor is included to account for the particular transmission line and the sensors that are employed. Properties of the DDC are analyzed using the CRB and an experiment where wave splitting was conducted on a coaxial–cable is accounted for. Finally, in Part V the DDC has been designed and implemented for wave splitting on a medium voltage power cable in a power distribution station using low cost wide–band sensors. Partial discharge measurements are conducted on cross–linked polyethylene insulated power cables. The directional separation capabilities of the DDC are visualized and utilized to separate multiple reflections from partial discharges based on the direction of travel.

This research was designed to investigate the fundamental nature in which blind people utilize audible cues to attend to their surroundings. Knowledge on how blind people respond to external spatial stimuli is expected to assist in development of better tools for helping people with visual disabilities navigate their environment. There was also interest in determining how blind people compare to sighted people in auditory localization tasks. The ability of sighted individuals, blindfolded individuals, and blind individuals in localizing spatial auditory targets was assessed. An acoustic display board allowed the researcher to provide multiple sound presentations to the subjects. The subjects’ responses in localization tasks were measured using a combination of kinematic head tracking and eye tracking hardware. Data was collected and analyzed to determine the ability of the groups in localizing spatial auditory targets. Significant differences were found among the three groups in spatial localization error and temporal patterns.

Détection d’hétérogénéités linéaires dans les textures directionnelles – application à la détection de failles en sismique de réflexion: les méthodes développées concernent la classe particulière de textures directionnelles. Dans un premier chapitre, nous rappelons la notion de texture, le concept de contour et le contexte applicatif concernant l’imagerie sismique. Le deuxième chapitre a pour objet l’analyse des différentes contributions que l’on peut trouver dans la littérature concernant la détection de contours dans le contexte des images texturées: les approches qui relèvent du domaine de la géophysique et les méthodes proposées par la communauté des traiteurs d’image pour la détection de contours. Le troisième chapitre regroupe nos propositions: une approche basée sur une un critère géométrique, une variante récursive robuste et une extension alliant mesure 2D et diffusion 3D. Ces propositions sont validées par une analyse quantitative par rapport aux méthodes existantes. / Linear disparity detection in directional textures – application to fault detection in seismic images: the developed approaches deal with the particular family of directional textures. In the first chapter the notion of texture and the concept of contour are introduced. Also, a detailed presentation of the application concerning seismic imagery is presented in the first chapter. The object of the second chapter is the analysis of the different contributions concerning edge and contour detection in textured images found in the literature: the approaches used in the field of geophysics and the approaches proposed by the image processing community. The third chapter regroups our contributions: a geometric criterion based approach, a recursive robust extension of the geometric approach and a 3D recursive robust extension combining a 2D measure and a 3D diffusion technique. Apart the qualitative comparisons, these contributions are validated by a quantitative analysis in comparison with the existing methods.

Cette thèse, de nature expérimentale, porte sur l'étude du couplage fluide / interface de croissance en solidification dirigée en lames minces. En solidification naturelle, les écoulements de nature convective ou solutale engendrent un transport de soluté devant le front et modifient la dynamique des microstructures. Ils sont modélisés ici en lames minces par un écoulement de Poiseuille induit par un thermosiphon. Au-delà des effets d'inclinaison de microstructures et d'asymétrie du développement des branchements, un nouveau phénomène est mis en évidence : des ondes progressives interfaciales modifiant fortement les microstructures. Trois types d'ondes sont observés. Leur diagramme d'existence est déterminé en fonction des vitesses de solidification et d'écoulement, et leurs caractéristiques principales en vitesse de phase, amplitude et asymétrie sont identifiées. Elles apparaissent quasi-insensibles à l'épaisseur de l'échantillon et à la longueur thermique. La cohérence de leur mécanisme de propagation est explicitée en tenant compte de la concentration et de la vitesse de l'interface, ainsi que de la forme des microstructures et de leur rejet de soluté. Ces ondes interfaciales créent des modulations de concentration, dont l'échelle caractéristique ne dépend pas de la nature des ondes ou du gradient thermique, mais seulement du rapport entre vitesse de l'écoulement et vitesse de solidification. La microségrégation et donc les propriétés résultantes des matériaux en sont alors directement influencées. / This thesis addresses the experimental study of the coupling between a flow and a growth interface in directional solidification in a thin sample. In natural solidification, the convective or solutal flows both generate a transport of solute along the front and modify the microstructure dynamics. They are modelled here in a thin sample by a Poiseuille flow induced by a thermosiphon. Beyond the effects of microstructure inclination and of asymmetry of sidebranch development, a new phenomenon is evidenced : the existence of the interfacial travelling waves that strongly affect microstructures. Three kinds of waves are observed. Their diagram of existence is determined as a function of both the pulling velocity and the flow velocity, and their main characteristics in phase velocity, amplitude and asymmetry are identified. They appear almost insensitive to the thickness of the sample and to the thermal length. The coherence of their propagation mechanism is made explicit when involving the concentration and the velocity of interface together with the form and the solute rejection of microstructures. These interfacial waves create concentration modulations whose characteristic scale does not depend on the wave type or the thermal gradient, but on the ratio of flow velocity to solidification velocity only. They then directly influence the microsegregation and thus, the resulting material properties.

Approved for public release, distribution is unlimited / Rip current spacings are compared with wave energetics and directional spreading in the Southern Monterey Bay. Southern Monterey Bay affords a unique environment to study rip currents owing to their prevalence created by near-normally incident waves on a sandy shoreline. It is hypothesized that rip current spacing is a function of wave directional spreading and energy flux, based on the morphodynamic modeling by Reniers et al. 2003. A gradient of wave energy flux exists due to headlands and refraction over Monterey Canyon. Rip currents are shown to occur between cusps in the shoreline, allowing cusp spacing to be a surrogate for rip spacing. Rip current spacing was inferred from beach morphology surveys, LIDAR imagery, and Argus cameras, and found to be O(150m) at Sand City and O(300m) at Marina, separated by 6km . Measured waves during a two month period using wave-rider buoys, show a gradient of across-shore energy flux between Sand City, 2 28000( / ) F Jm x . , and Marina, 2 33000( / ) F Jm x . . The two sites have the same peak directional spreading of energy value, 14 peak ̤= o , and slightly different bulk values for Sand City, 18 bulk ̤= o , and Marina, 20 bulk ̤= o . Therefore, the variations in rip current spacing could not be attributed to directional spreading but appear related to variations in energy flux. / Ensign, United States Naval Reserve

Median filtering is a non-linear filtering technique which is effective in removing impulsive noise from data. In this thesis, directional median filtering has been implemented using cumulative histogram of samples in several directions. Different methods to implement directional median filtering have been proposed. The filtered images are smoothed along the direction of the filtering window. All implementations aimed to generate outputs in the least amount of time, while reducing the resource utilization on hardware. The implementation methods were designed for Xilinx Virtex 5 FPGA devices but were also attempted on Spartan 3E. The proposed methods used less than 30% of the resources on Virtex 5 FPGA but the resource utilization on Spartan 3E exceeded the number of available resources. After an initial delay, methods 1 and 2 generate a new output for every 5 clock cycles while method 3 generates an output for every 1.5 clock cycles.