Mars is one of the most intriguing planets in the solar system. It is the fourth terrestrial planet and is differentiated into a core, mantle and crust. The crust of Mars is divided into the Southern highlands and the Northern lowlands. The largest volcano in the solar system, Olympus Mons is found on the crustal dichotomy boundary. The presence of isolated volcanism on the surface suggests the importance of internal activity on the planet. In addition to volcanism in the past, there has been evidence of present day volcanic activity. Convective upwelling, including decompression melting, has remained an important contributing factor in melting history of the planet. In this thesis, I investigate the production of melt in the mantle for a Newtonian rheology, and compare it with the melt needed to create Tharsis. In addition to the melt production, I analyze the 3D structure of the mantle for a stagnant lithosphere. I vary different parameters in the Martian mantle to understand the production of low or high degree structures early on to explain the crustal dichotomy. This isothermal structure in the mantle contributes to the geoid and topography on the planet. I also analyze how much of the internal density contributes to the surface topography and areoid of Mars. In contrast to Mars, Ceres is a dwarf planet in the Asteroid belt. Ceres is an icy body and it is unclear if it is differentiated into a core, mantle and crust yet. However, studies show that it is most likely a differentiated body and the mantle consists of ice and silicate. The presence of brucite and serpentine on the surface suggests the presence of internal activity. Being a massive body and also believed to have existed since the beginning of the solar system, studying Ceres will shed light on the conditions of the early solar system. Ceres has been of great interest in the scientific community and its importance has motivated NASA to launch a mission, Dawn, to study the planet. Dawn will collect data from the dwarf planet when it arrives in 2015. In my modeling studies, I implement a similar technique on Ceres, as followed on Mars, and focus on the mantle convection process and the geoid and topography. The silicate-ice mixture in the mantle gives rise to a non-Newtonian rheology that depends on the grain size of the ice particle. The geoid and topography observed for different differentiated scenarios in my modeling can be compared with the data from the Dawn mission when it arrives at Ceres in 2015. / Ph. D.

Recent interest in three-dimensional (3-D) stereoscopic displays has prompted the need to assess the efficacy of retinal disparity depth cues. Accordingly, this study analyzed performance on two 3-D tasks under three levels of signal-to-clutter ratio as participants viewed three display formats portrayed with or without retinal disparity depth cues. Display formats included a plan view and two types of perspective formats. The two tasks assessed viewer ability to compare inter-object distances and extrapolate object positions given a known vector within a 3-D volume. Results indicate that retinal disparity depth cues reduce the number and magnitude of errors within a course prediction task, but did not affect search times or ratings of viewer confidence. Display format affected search times as follows. In a relative distance task, search times for the perspective format are lower than for either the plan view or enhanced perspective formats. In a course prediction task, search times for the plan view and perspective formats are lower than for the enhanced perspective format. Display format does not affect error rate, error magnitude, or ratings of viewer confidence. No interaction between depth cues and display format was observed. The inclusion of retinal disparity depth cues in a visual display system are suggested when the viewer task involves predictions of object position in a 3-D volume and when reducing the number and magnitude of errors is important. Perspective display formats are suggested when fast search times are important. / Master of Science

With the development of fuel cell based power systems, the need for more advanced DC-DC power converters has become apparent. In such applications DC-DC converters provide an important link between low voltage fuel cell sources and inverter buses operating at significantly higher voltages. Advancements in converter efficiency, cost reduction, and size reduction are the most necessary. These challenges are formidable, even when considering the improvements made to conventional DC-DC topologies. However, it can be possible to achieve these criteria through the implementation of more advanced topologies. A recently developed efficient three-phase DC-DC topology offers benefits over standard designs. Passive component sizes and output ripple voltage were reduced as a result of an effective boost in switching frequency. Converter output voltage was reached more easily due to an increased transformer voltage boost ratio in addition to the turns ratio. For cost reduction, the converter was designed and built with discrete components instead of more expensive integrated modules. This thesis presents an overview of the three-phase converter, with a detailed focus on the design, implementation, and performance of the switching stage. The functionality of the three-phase topology is covered along with the selection of converter components. Simulation results are shown for both ideal and real converter models. Considerations for the switching device package with respect to circuit board and heat sinking configurations are discussed in support of the selection of an insulated metal substrate (IMS) circuit board. An effective circuit layout designed to minimize parasitic trace inductances as well as provide favorable component positioning is presented. Experimental converter test results are shown and the causes of undesired effects are identified. Switching stage modifications and their results are discussed along with the benefits of proposed future design enhancements. / Master of Science

Current-mode control architectures have been an indispensable technique in many applications, such as Voltage Regulator, Point-of-load converters, power factor correction, battery charger and LED driver. Since the inductor current ramp is used in the modulator in current-mode control without any low pass filter, high order harmonics play important role in the feedback control. This is the reason for the difficulty in obtaining the small-signal model for current-mode control in the frequency domain. A continuous time domain model was recently proposed as a successful model for current-mode control architectures. However, the model was derived by describing function method, which is very arithmetically complicated, not to mention time consuming. For the analysis and design of non-linear system, equivalent circuit model, which is user friendly and intuitive, is an effective tool. In this dissertation, the primary objective is to develop a unified three-terminal switch model for current-mode controls using the results of describing function derivation, which characterizes the small signal property of the common subcircuit of current mode controlled PWM converters. Its application is extended to average current mode control, V2 control and other proposed novel current mode control schemes. First, the existing model for current mode control is reviewed. The limitations of existing model for current-mode control are identified. Based on the universal small signal relationship between terminal currents and the results of describing function derivation, a unified three-terminal switch model for current mode control is proposed. A three-terminal equivalent circuit is developed to represent the small signal behavior of this common sub-circuit. The proposed model is applicable in both constant frequency and variable frequency modulation. After that, the modeling of digital predictive current mode control is presented. Predictive current mode control is one of the promising digital current mode control method featuring fast dynamic response and low sample rate requirement. Many implementations were presented in past ten years. To understand the benefit and the limitation of each implementation, help the engineer to choose the modulation scheme and design the control loop, a small signal Laplace-domain model for digital predictive current mode controls is proposed. The model is extended to the multi-sampled implementation. The modeling result is summarize as the small signal equivalent circuit mode, whose form is consistent with that of analog current mode controls. Based on S-domain model, digital predictive current mode controls are compared with analog implementation to demonstrate the advantages and limitation. Implementation selection guideline and compensation is discussed based on the modeling results. Then, using the proposed unified model is used in the analysis of average current mode control. Under proper design, the inductor current ripple passes through the current compensator and appears in PWM comparator. It significantly influence the high frequency small signal property of the converter. In chapter 3, the proportional feedback is separated from integral feedback so that the sideband frequency feedback effect can be taken into consideration. It extends the results obtained in peak-current model control to average current mode control. The proposed small signal model is accurate up to half switching frequency, predicting the sub-harmonic instability. Based on the proposed model, a new feedback design guideline is proposed. By designing the external ramp following the proposed design guideline, quality factor of the double poles at half of switching frequency in control-to-output transfer function can be precisely controlled. This helps the feedback design to achieve widest control bandwidth and proper damping. V2 control is a popular control scheme in Point-of-load converters due to the unique fast transient response. As the output voltage ripple is used as PWM modulation ramp, V2 control has close relationship with current mode control but this relationship was not addressed in the existing model. Chapter 4 utilizes the three-terminal switch model to build the equivalent circuit model for V2 control, which clearly shows that V2 control is a particular implementation of current mode control, with proportional capacitor voltage feedback and load current feedback embedded. The analysis presented in Chapter 3 provides a clear physical understanding of average current mode control. With constant frequency modulation, the control bandwidth is usually limited by the double pole at half of swithcing frequency, especially in the converters with wide duty cycle range. Chapter 5 proposed a novel I2 current mode control to improve the dynamic performance of average current mode control. In particular, constant on-time I2 control eliminates the need of external ramp while the current loop is inherently stable. Moreover, constant on-time modulation improves the light load efficiency. As a conclusion, this dissertation proposed a unified three-terminal switch model for current mode controls. The application of this equivalent circuit model is extended to average current mode control, V2 control and the novel I2 current mode control. The Laplace-domain model of predictive current mode control is also presented. All the modeling results are verified through simulation and experiments. / Ph. D.

The work seeks toward further developing a novel robotic platform capable of stable three legged locomotion. This will be accomplished by creating a robust and adaptable robotic platform capable of executing different walking strategies and taking multiple continuous steps. Previous iterations of this platform have been developed, all of which have used a single gait strategy. This study will seek to develop two new strategies. The first of which is a modification of the original strategy with theoretically improved gate robustness. A second strategy will seek to implement more advanced control techniques to create a fully stable balanced gait. / Master of Science

Inspired by writings on creativity and by Howard Gardner's theory of multiple intelligences, I conducted a series of ten "exercises" -- each of them a guided visualization followed by an opportunity to produce -- with nine- and ten-year-old students. The visualizations, which were designed to encourage the students to explore some of the many ways our minds have of knowing and learning, began with a simple relaxation exercise and proceeded to more challenging exercises involving, for instance, kinesthetic learning, sensory awareness, the logical and linguistic mind versus the spatial mind, and intra- and interpersonal intelligence. Following each visualization the students discussed what they had experienced (transcripts of the visualizations and the discussions are included in the thesis). The students responded in visual terms as well: after each visualization, each student created a two- or three-dimensional piece of art from materials such as matboard, construction and origami paper, glue, felt-tip pens, pipe cleaners, and plastic-coated wire. These visual responses have been photographed, described, and scored according to the number of materials used, the number of colors used, and the dimensionality of the piece (photos, descriptions, and scores are included in the "Gallery". I found, surprisingly, that the visualizations in which the students were the most imaginatively engaged did not always produce the most interesting art, and that girls were much less likely than boys to create three-dimensional pieces, although girls tended to use more colors and occasionally used relief on otherwise two-dimensional pieces. / Master of Architecture

According to the Federal Communications Commission's rules and recommendations set forth for the 3.5 GHz Citizens Broadband Radio Service, a three-tiered structure shall govern the newly established shared wireless band. The three tiers are comprised of three different levels of spectrum access; Incumbent Access, Priority Access and General Authorized Access. In accordance and fulfillment with this dynamic spectrum access framework, we present the inclusion of Priority Access tier into a two-tiered privacy-preserving ESC-based dynamic spectrum access system. / Master of Science / With the development of wireless communication technologies, the number of wireless communication reliant applications has been increasing. Most of these applications require dedicated spectrum frequencies as communication channels. As such, the radio frequency spectrum, utilized and allocated for these wireless applications, is depleting. This problem can be alleviated by adopting dynamic spectrum access schemes. The current static spectrum allocation scheme assigns designated spectrum frequencies to specific users. This static frequency management approach leads to inefficient frequency utilization as the occupation of frequency channels may vary depending upon time periods. Dynamic spectrum access schemes allow unlicensed users opportunistic access to vacant spectrum spaces. Thus, the adoption of these spectrum sharing schemes will increase the efficiency of spectrum utilization, and slow down the spectrum depletion. However, the design and implementation of these schemes face different challenges. These spectrum sharing systems need to guarantee the privacy of the involved parties while maintaining specific functionalities required and recommended by the Federal Communications Commission. In this thesis, we present the inclusion of a three-tiered frame, approved by the Federal Communications Commission, into a privacy-preserving dynamic spectrum system.

No / This study investigates the impact of LIFFE's introduction of individual equity futures contracts on the risk characteristics of the underlying stocks trading on the LSE. We employ the Fama and French three-factor model (TFM) to measure the change in the systematic risk of the underlying stocks which arises subsequent to the introduction of futures contracts. A GJR-GARCH(1,1) specification is used to test whether the futures contract listing affects the permanent and/or the transitory component of the residual variance of returns, and a control sample methodology isolates changes in the risk components that may be caused by factors other than futures contract innovation. The observed increase (decrease) in the impact of current (old) news on the residual variance implies that futures contract listing enhances stock market efficiency. There is no evidence that futures innovation impacts on either the systematic risk or the permanent component of the residual variance of returns.

Current-mode control architectures with different implementation approaches have been an indispensable technique in many applications, such as voltage regulator, power factor correction, battery charger and LED driver. Since the inductor current ramp, one of state variables influenced by the input voltage and the output voltage, is used in the modulator in current-mode control without any low pass filter, high order harmonics play important role in the feedback control. This is the reason for the difficulty in obtaining the small-signal model for current-mode control in the frequency domain. A continuous time domain model was recently proposed as a successful model for current-mode control architectures with different implementation. However, the model was derived by describing function method, which is very arithmatically complicated, not to mention time consuming. Although an equivalent circuit for a current mode control Buck converter was proposed to help designers to use the model without involving complicated math, the equivalent circuit is not a complete model. Moreover, no equivalent circuit for other topologies is available for designers. In this thesis, the primary objective is to develop a unified three-terminal switch model for current-mode control with different implementation methods, which are applicable in all the current mode control power converters. First, the existing model for current mode control is reviewed. The limitation of average models and the discrete time model for current-mode control is identified. The continuous time model and its equivalent circuit of Buck converter is introduced. The deficiency of the equivalent circuit is discussed. After that, a unified three-terminal switch model for current mode control is presented. Based on the observation, the PWM switch and the closed current loop is taken as an invariant sub-circuit which is common to different DC/DC converter topologies. A basic small signal relationship between terminal currents is studied and the result shows that the PWM switch with current feedback preserves the property of the PWM switch in power stage. A three-terminal equivalent circuit is developed to represent the small signal behavior of this common sub-circuit. The proposed model is a unified model, which is applicable in both constant frequency modulation and variable frequency modulation. The physical meaning of the three-terminal equivalent circuit model is discussed. The model is verified by SIMPLIS simulation in commonly used converters for both constant frequency modulation and variable frequency modulation. Then, based on the proposed unified model, a comparison between different current mode control implementations is presented. In different applications, different implementations have their unique benefit on extending control bandwidth. The properties of audio susceptibility and output impedance are discussed. It is found that, for adaptive voltage positioning design, constant on-time current mode control can simplifies the outer loop design. Next, since multiphase interleaving structure is widely used in PFC, voltage regulator and other high current applications, the model is extended to multiphase current mode control. Some design concerns are discussed based on the model. As a conclusion, a unified three-terminal switch model for current mode controls is investigated. The proposed model is quite general and not limited by implementation methods and topologies. All the modeling results are verified through simulation and experiments. / Master of Science

Considerable research has centered around the issue of whether stereoscopic (3D) viewing allows improved viewer performance for tasks that involve three-dimensional information. Taken as a whole, such previous research indicates that the potential stereoscopic advantage may be dependent on the nature of the task being examined. This task dependency makes it difficult to predict whether stereoscopic viewing will improve viewer performance for a given untested task. By measuring performance over a variety of component tasks, this research examined the potential task-dependent nature of the stereoscopic advantage. In addition, a method was proposed to employ such component-task data for predicting the stereoscopic advantage within future unknown tasks. A set of 12 component tasks (in six task groups, each with two representative tasks) was developed to represent the various task demands of processing 3D visual information. Participants performed each of the 12 component tasks in both a monoscopic (2D) and a stereoscopic (3D) viewing condition. Performance was measured in terms of viewing time, percent accuracy, and a generic mental effort rating. Results indicate that when certain display guidelines are not violated, stereoscopic display improves or at least maintains the overall level of viewer performance for most tasks. Furthermore, the results clearly indicate that the stereoscopic advantage is dependent on the nature of the task. Although further refinement to the set of component tasks is necessary before the precise nature of the task dependency can be determined, the component task method displays considerable promise for being able to predict the stereoscopic advantage for any number of complex 3D tasks. / Ph. D.