Recently, the need for high power, high frequency devices continues to grow with the increase in wireless communication, radar systems, HDTV, digital communication, and other military application of the RF spectrum. Traditionally when higher power is needed, one needs to either combine the output power of multiple devices or use vacuum tubes, which are still uncontested at very high power levels, capable of up to a few hundred kilowatts at 5 GHz [11]. But wide band gap semiconductor devices capable of competing in this application. Moreover, the static induction transistor (SIT) in silicon carbide can provide very high total power at microwave frequency. This is due to the vertical structure of the SIT which consists of a vertical channel that is defined by a mesa with gate electrodes of the Schottky type to control the current between a top side source contact and a drain contact on the backside of the wafer. This thesis demonstrates that through careful modeling by means of simulations and inclusion of all significant device physics, good agreement is reached between theoretical prediction and simulation results. It is shown in particular that by careful choice of the device critical parameters, such as mesa width, gate length, and contact resistance, SIT should be able to obtain cut-off frequency up to 42 GHz and shown temperature simulation results of SIT.

C++ and Microsoft's Component Object Model (COM) are examples of a high- level lan- guage and development framework that were built on top of the lower-level, primitive lan- guage, C. C was never designed to support concepts like object orientation, type enforcement, and language independence. Further, these languages and frameworks are designed to com- pile and run directly on the processor where these concepts are also not supported. Other high-level languages that do support these concepts make use of a runtime or virtual machine to create a computing model to suit their needs. By forcing these high-level concepts into a primitive computing model, many security issues have been introduced. Existing binary- level security analysis tools and runtime enforcement frameworks operate at the lowest level of context. As such, they struggle to detect and remedy higher-level security issues. In this dissertation, a framework for elevating the context of binary code is presented. By bringing the context for analysis closer to where these security issues are introduced, this framework allows for higher-level analyses and enforcement frameworks to be developed.

Published Article / This article reviews research on learning with external representations and provides a theoretical background on how to optimize learning from external representations. General factors, such as the type of material to be learned, learner characteristics and the testing method, are some of the variables that can determine if graphic medium can increase a subject's comprehension and if such comprehension can be accurately measured. These factors are discussed and represented by a model to suggest how external representations can be effectively used in a learning environment. Two key conclusions are drawn from the observation made in these studies. Firstly, the proper design of a particular external representation and supporting text can promote relevant activities that ultimately contribute to fuller understanding of the content. Secondly, external representations must be developed to address the size complexity and variety of the content that must be analysed in order to extract knowledge for scientific discovery.

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This study investigated the variability of response associated with various perimetric techniques, with the aim of improving the clinical interpretation of automated static threshold perirnetry. Evaluation of a third generation of perimetric threshold algorithms (SITA) demonstrated a reduction in test duration by approximately 50% both in normal subjects and in glaucoma patients. SITA produced a slightly higher, but clinically insignificant, Mean Sensitivity than with the previous generations of algorithms. This was associated with a decreased between-subject variability in sensitivity and hence, lower confidence intervals for normality. In glaucoma, the SITA algorithms gave rise to more statistically significant visual field defects and a similar between-visit repeatability to the Full Threshold and FASTPAC algorithms. The higher estimated sensitivity observed with SITA compared to Full Threshold and FASTPAC were not attributed to a reduction in the fatigue effect. The investigation of a novel method of maintaining patient fixation, a roving fixation target which paused immediately prior lo the stimulus presentation, revealed a greater degree of fixational instability with the roving fixation target compared to the conventional static fixation target. Previous experience with traditional white-white perimetry did not eradicate the learning effect in short-wavelength automated perimetry (SWAP) in a group of ocular hypertensive patients. The learning effect was smaller in an experienced group of patients compared to a naive group of patients, but was still at a significant level to require that patients should undertake a series of at least three familiarisation tests with SWAP.

The individual soft tissues in the human body, such as liver, prostate, thyroid and breast, can each be characterized by a set of mechanical properties. Among these properties, the stiffness, or Young’s modulus, is of particular interest, as disease processes or abnormal growths introduce changes in the tissue stiffness. For example, cirrhosis is associated with an increase in stiffness in the affected region(s) of the liver, and the severity has a strong positive correlation with the measured liver tissue stiffness. Although the conventional ultrasound image is produced by changes in acoustic properties, most notably acoustic impedance (equal to density times sound speed), it is in fact possible to measure tissue strain ultrasonically, by performing ultrasound imaging while the tissue region of interest is mechanically perturbed. Although in principle incorrect, such strain imaging methods are commonly referred to as ultrasound elastography imaging. While tissue strain can reveal the presence of stiffness changes, its diagnostic value is limited due to the inability to reveal the magnitude of the stiffness change. Still, strain imaging is a feature on several commercial scanners. There does in fact exist an elegant, but complex and quite expensive, quantitative ultrasound method of imaging the elasticity of soft tissues, called Supersonic Shear imaging (SSI). However, a much lower cost method of quantitatively imaging tissue elasticity would be useful, especially if the method can be implemented with only minor modifications to existing ultrasound scanner design. This dissertation research deals with an attempt of designing and testing such a method. Ultrasound elastography encompasses a number of diverse techniques, roughly categorized by the mechanical perturbation method into two main groups: quasi-static and dynamic methods. Dynamic elastography requires a vibrating source, either separate or integrated with a transducer, making the imaging system cumbersome, especially for the portable systems. Quasi-static elastography only requires conventional ultrasound hardware, however current techniques remain qualitative with unknown stress distribution. This dissertation focuses on the investigation of free hand quantitative quasi-static elastography, aiming to real time assessment. Our proposed low cost real-time ultrasound elastography system is based on determining an axial strain and an axial stress over a region of interest, i.e., an axial strain image and an axial stress image are required. By taking the axial stress/axial strain ratio for each pixel in the image, an actual elasticity image is established. To achieve this goal, our system needs to ultrasonically measure the mechanical strain fast and accurately over a specified image plane; likewise, the system needs to be able to calculate the mechanical stress over the same image plane in real time. Now, the stress imaging will require us to apply a quasi-static force function and also to be able to quantify this force function. There are two major research efforts we have made to implement a low cost real-time ultrasound elastography system. The first important topic of this dissertation involves the development of a novel displacement and strain estimator based on analytical phase tracking (APT), which has been demonstrated to give better performance in terms of accuracy, resolution and computational efficiency (approximately 40 times faster than the standard time domain cross correlation method). The second important topic is the stress field reconstruction, with efforts in: 1) integrate force sensors into a single linear array transducer probe, with the goal of quantifying the applied force function; 2) propose a superposition method based on Love’s analytical equation to calculate the stress distribution, where this solution is computationally fast enough to allow real time stress field estimation; 3) analyze the accuracy of the proposed stress method using finite element analysis as a reference on different simulated phantoms. The final objective is to combine the strain and stress information together for quantitative elastography. Correspondingly, we have implemented experiments to evaluate the method on homogeneous and inhomogeneous phantoms of various types. Results show that this method is able to distinguish medium with different stiffness. We have conducted experiments to study the feasibility and improve the accuracy of this estimation technique based on phantoms with known elasticity. In principle, such a technique could be used to image the distribution of Young’s modulus under quasi-static compression, with specific applications to medical imaging.

In this thesis we shall investigate the numerical solutions to several important practical static and dynamic optimization problems in engineering and physics. The thesis is organized as follows.In Chapter 1 a general literature review is presented, including motivation and development of the problems, and existing results. Furthermore, some existing computational methods for optimal control problems are also discussed.In Chapter 2 the design of a semiconductor device is posed as an optimization problem: given an ideal voltage-current (V - I) characteristic, find one or more physical and geometrical parameters so that the V-I characteristic of the device matches the ideal one optimally with respect to a prescribed performance criterion. The voltage-current characteristic of a semiconductor device is governed by a set of nonlinear partial differential equations (PDE), and thus a black-box approach is taken for the numerical solution to the PDEs. Various existing numerical methods are proposed for the solution of the nonlinear optimization problem. The Jacobian of the cost function is ill-conditioned and a scaling technique is thus proposed to stabilize the resulting linear system. Numerical experiments, performed to show the usefulness of this approach, demonstrate that the approach always gives optimal or near-optimal solutions to the test problems in both two and three dimensions.In Chapter 3 we propose an efficient approach to numerical integration in one and two dimensions, where a grid set with a fixed number of vertices is to be chosen so that the error between the numerical integral and the exact integral is minimized. For one dimensional problem two schemes are developed for sufficiently smooth functions based on the mid-point rectangular quadrature rule and the trapezoidal rule respectively, and another method is also developed for integrands which are not ++ / sufficiently smooth. For two dimensional problems two schemes are first developed for sufficiently smooth functions. One is based on the barycenter rule on a rectangular partition, while the other is on a triangular partition. A scheme for insufficiently smooth functions is also developed. For illustration, several examples are solved using the proposed schemes, and the numerical results show the effectiveness of the approach.Chapter 4 deals with optimal recharge and driving plans for a battery-powered electric vehicle. A major problem facing battery-powered electric vehicles is in their batteries: weight and charge capacity. Thus a battery-powered electric vehicle only has a short driving range. To travel for a longer distance, the batteries are required to be recharged frequently. In this chapter we construct a model for a battery-powered electric vehicle, in which driving strategy is to be obtained so that the total traveling time between two locations is minimized. The problem is formulated as an unconventional optimization problem. However, by using the control parameterization enhancing transformation (CPET) (see [100]) it is shown that this unconventional optimization is equivalent to a conventional optimal parameter selection problem. Numerical examples are solved using the proposed method.In Chapter 5 we consider the numerical solution to a class of optimal control problems involving variable time points in their cost functions. The CPET is first used to convert the optimal control problem with variable time points into an equivalent optimal control problem with fixed multiple characteristic times (MCT). Using the control parameterization technique, the time horizon is partitioned into several subintervals. Let the partition points also be taken as decision variables. The control functions are approximated by piecewise constant or piecewise linear functions ++ / in accordance with these variable partition points. We thus obtain a finite dimensional optimization problem. The CPET transform is again used to convert approximate optimal control problems with variable partition points into equivalent standard optimal control problems with MCT, where the control functions are piecewise constant or piecewise linear functions with pre-fixed partition points. The transformed problems are essentially optimal parameter selection problems with MCT. The gradient formulae are obtained for the objective function as well as the constraint functions with respect to relevant decision variables. Numerical examples are solved using the proposed method.A numerical approach is proposed in Chapter 6 for constructing an approximate optimal feedback control law of a class of nonlinear optimal control problems. In this approach, the state space is partitioned into subdivisions, and the controllers are approximated by a linear combination of the 3rd order B-spline basis functions. Furthermore, the partition points are also taken as decision variables in this formulation. To show the effectiveness of the proposed approach, a two dimensional and a three dimensional examples are solved by the approach. The numerical results demonstrate that the method is superior to the existing methods with fixed partition points.

Static Whirling Rods: Past researchers suggested that “static instabilities” exist at certain rotational speeds of whirling rods. This thesis shows these instabilities are an artefact of the material constitutive laws that are being used well outside their range of applicability. An alternative approach is developed where strains due to rotation are separated from the superimposed vibration. This enables the generally predicted lowering of longitudinal natural frequencies with rotational speed shown to be simply a result of the bulk changes in the geometry of whirling rods. Steady state equations of whirling rods are formulated in Lagrangian coordinates. Due to the non-linear nature of the governing equations, an original numerical method is applied to solve the problem. Numerical results are compared with analytical results obtained from the linearized uniaxial model. There is a close agreement between these two models at low angular velocities. However, at high angular velocities, discrepancies between them arise, confirming that the nonlinear strain-displacement relationship has significant effect on the results and the inferred “static instabilities”. This approach first solves the “static” problem of the deformed geometry of a highly strained whirling rod before longitudinal natural modes are determined by classical methods. Furthermore, conditions for existence and uniqueness of solutions are derived. Dynamic Rotating Annuli: In-plane modes of vibration of annular plates are investigated. Two different models of equations one from Bhuta and Jones and the other from Biezeno and Grammel that govern the rotational motions of annuli will be studied. Since Biezeno and Grammel’s model was originally derived in Eulrian coordinates, their model will be transformed to the Lagrangian coordinates for the purpose of comparison with Bhuta and Jones’ model. / The solutions of the equations assume small oscillations of vibration being superimposed on the steady state of the annulus while it is in rotation. Exact and approximate solutions are obtained for the Bhuta and Jones’ model, where the approximate solutions on in-plane displacements and natural frequencies are acquired by ignoring the Coriolis effect. A proposed numerical scheme is implemented to solve the governing equations coupled with radial and circumferential displacements. Uniqueness of solutions will be mentioned although it will not be rigorously derived because it is out of the scope of this thesis. Approximate analytical results show that both radial and circumferential natural frequencies are decreasing when the rotational speed of an annulus is increasing. The exact and numerical results on both models that take the Coriolis effect into account show that radial natural frequencies are increasing and circumferential natural frequencies are decreasing when the rotational speed of an annulus is increasing.

This experiment was designed to examine aspects of human visual perception during approaches to a runway. The runway width illusion has commonly been reported to contribute to the dangerous tendency of pilots to fly low approaches to runways that are wide and high approaches to runways that are narrow. Attempts to prevent the runway width illusion have not attempted to identify the ideal location for an indicator of altitude. Thus the present experiment examined the effect of varying runway width and manipulated scenes in order to determine whether the runway width illusion was present and where participants were focusing their attention in the scenes. Thirty-two non-pilot participants and 3 pilots took part in the experiment and viewed static and dynamic scenes of runways that were narrow (30.48m), medium (60.96m) or wide (91.44m) at one of three viewing heights low (30.48m), medium (45.72m) or high (60.96m). After viewing scenes, participants were required to estimate their altitude and aim-point. The results of this experiment revealed that participants were fairly inaccurate at estimating altitude and were inclined to overestimate aim-point, however the data also indicated that there was a robust runway width illusion that was present across static and dynamic trials and in both altitude and aim-point data. The standard marking on the runway in an attempt to prevent the runway width illusion was not effective at preventing incorrect altitude estimations but did assist participants to estimate aim-point. It was also found that the objects that participants' most commonly reported using to estimate altitude in the visual scene were located in the lower segment of the scenes.