The feasibility of nonvolatile spin-based memory device concepts is explored. The first memory device concept utilizes the electrically controlled paramagnetic-ferromagnetic transition in a diluted magnetic semiconductor layer (quantum well or dot) when the ferromagnetism in the diluted magnetic semiconductor is mediated by itinerant holes. The specific structure under consideration consists of a diluted magnetic semiconductor quantum well (or quantum dot) and a nonmagnetic quantum well, which acts as a hole reservoir, separated by a permeable barrier. The quantitative analysis is done by calculating the free energy of the system. Formation of two stable states at the same external conditions, i.e., bistability, is found feasible at temperatures below the Curie temperature with proper band engineering. The effects of scaling the magnetic quantum well to quantum dot on bistability are analyzed. The bit retention time, i.e., lifetime, with respect to spontaneous leaps between the two stable states is calculated. The write/erase and read operations are discussed as well as the dissipation energy. Also, potential logic operations are proposed. In the second memory concept, the active region is a semiconductor quantum dot sharing an interface with a dielectric magnetic layer. The operating principle of the device is based on the spontaneous magnetic symmetry breaking due to exchange interaction between the magnetic ions in the magnetic layer and the spins of the itinerant holes in the quantum dot. Room temperature operation is possible given the availability of insulating ferromagnetic or antiferromagnetic materials whose Curie temperature is above room temperature. The specific range of material parameters where bistability is achieved is found. Analysis is extended to different quantum dot and magnetic dielectric materials and designs. Influence of material choice and design on the memory robustness, i.e., lifetime, is discussed.

Faults, if remained undetected lead to huge financial losses. Troubleshooting faults requires analytical skills and knowledge of the system. Elementary skills help in solving common faults but faults that are infrequent or those which cannot be debugged by a consumer or even a field technician due to lack of in-depth knowledge of the system requires an expert?s intervention. Experts are not always available in the field and lack of knowledge on the field technician?s part may lead to huge financial losses and inconvenience on the part of the consumer. To avoid such situations an approach to make available expert?s knowledge and capability to the field technicians is demonstrated through this research. A qualitative modeling approach to develop a knowledge representation is outlined here. A qualitative knowledge of the system from expert?s point of view is modeled for a Bosch dishwasher for whom knowledge is extracted to generate a rule base, which reasons the characteristics of the system like an expert. Further it has been explored that using the rule base one can develop a questionnaire using the concept of model based diagnosis for troubleshooting. A qualitative model is useful for this kind of system because it resembles the analytical thinking capability of an expert and in general for any human being making it easier to communicate and interpret. Thus providing such a system to the field technician or even the consumer will simplify the troubleshooting process and will help in reducing downtime and financial losses.

Multiple input multiple output (MIMO) systems using multiple transmit and receive antennas are widely considered as the vital breakthrough that will allow future wireless systems to achieve higher date rates and link reliability with limited bandwidth and power resources. In this dissertation, we address four interesting topics in the wireless MIMO systems, in both point-to-point and multiuser environments. First, in a point-to-point MIMO spatial diversity system, usually the probability distribution function (PDF) of the received SNR is rather involved, which leads to the difficulty in analyzing the average symbol error rate (SER). We provide a succinct result at the high SNR region. Second, in point-to-point wireless MIMO communications, in order to protect the transmitted data against random channel impairment, we consider the problem of link adaptation, including rate adaptation and power control to improve the system performance and guarantee certain quality of service. Third, in a multiuser MIMO wireless network, there is another form of diversity called multiuser diversity which can be exploited to increase the system throughput. By analyzing the scheduling gain (defined as the rate difference between the opportunistic scheduling and round-robin scheduling scheme), we provide a complete analysis on the interaction between the spatial diversity and multiuser diversity. Fourth, in a multiuser MIMO wireless network, we propose a crosslayer-based scheduling scheme that exploits Tomlinson-Harashima Precoding (THP) at the physical (PHY) layer to reduce the multiuser scheduling burden at the medium access control (MAC) layer. Compared with some existing scheduling schemes, the proposed scheme greatly reduces the scheduling complexity while simultaneously improves overall system performance.

Magnetic Resonance Imaging (MRI) is one of the most widely used clinical diagnostic procedures. Evaluation of safety due to Radio Frequency (RF) energy deposition and tissue heating in patients during MRI, especially in the presence of implantable prosthetic devices is significant for MR safety. The work presented in this thesis aims to characterize the interactions between the pulsed RF fields during MRI and biological tissues of a patient with a Retinal Prosthesis (RP) implant, in terms of Specific Absorption Rate (SAR) and temperature elevation. A logarithmically expanding grid Finite-Difference Time-Domain (FDTD) is used for computational modeling of the MR environment at 64, 128 and 256 MHz. Unlike traditional methods, expanding grid FDTD facilitates in accurate modeling of the region of the implant where a finer grid with cell sizes of the order of micrometers is used. Also, this technique greatly helps to reduce the constraints on computational memory and time. It was found that, while the RF magnetic field, B1, homogeneity decreases with frequency; power deposition in the tissues increases slightly. However, thermal elevation resulting from the SAR distribution as well as the induced currents in the RP implant, evaluated using the bio-heat equation, is observed to be minimal at these frequencies. These results provide useful information for RF safety guidelines during MRI at high fields.

This dissertation presents an assessment of the worst case stresses produced in an induction motor when the motor is allowed to ride through a power supply voltage disturbance. Results from laboratory experiments and computer simulations are shown. The experimental results are obtained from tests conducted on three squirrel cage induction motors, sized 10 hp, 50 hp, and 75 hp. Each motor is tested with three different load inertias, various motor loadings, and numerous interruption durations. The computer simulation results are obtained using a non-linear motor-load model, whose parameters are derived from a non-linear least squares parameter estimation technique. Experimental data acquired in the lab is used for the parameter estimation data and for the validation data. Deficiencies in the standard motor-load model are presented and addressed. Good agreement between the experimental data and the non-linear motor-load model data is achieved. Results show significant current and torque transients, but caused no significant damage to the motors or loads used for testing.

As the complexity of SoC design grows, the traditional register transfer level (RTL) centric design flow cannot meet the time to market. In that case, a higher modeling level of abstraction is need for designer to explore the design space at system level. Transaction-level model (TLM) is such an approach since it could run much faster than RTL model and also have enough accuracy. There are different modeling styles of TLM for different applications. In this thesis, we develop a hybrid-TLM of Network-on-chip (NoC) based on OSCI TLM-2.0 standard. We use a simplified version of the AMBA AXI protocol for the bus. This model contains a cycle-accurate AXI router and other periphery modules with approximately-timed coding style, which achieve fast simulation speed and accurate result. This model keeps good interoperability since it entirely based on TLM-2.0 standard. And the designer could build complex NoCs by making use of this model.

This thesis develops an algorithm for shape representation and matching. The algorithm is an object centered, boundary based method for shape recognition. Global features of the shape are utilized to define a frame of reference relative to which local shape features are characterized. The curvature of the boundary at a point is the local feature used. Curvature is computed by the Digital Straight Segments algorithm. Matching is done using the process of evidence accumulation similar in approach to the Generalized Hough Transform. The algorithm is tested for invariance to similarity transforms. Its robustness to noise and blurring is also tested. A multi-layer, feed-forward neural network architecture that implements the algorithm is proposed.

This dissertation develops novel methods to reconstruct a three-dimensional surface together with a characterization of the surface composition given one or more images obtained from the same viewing direction. First, a vector space method to reconstruct a surface given a gradient field is developed using the linear relationship between a surface and its gradient field in discrete surface domains. The developed gradient field representation is generalized to alleviate the common assumption of uniform integrability in gradient fields to partial integrability, allowing adequate reconstruction of surfaces with non-integrable gradient fields. In addition, the developed technique is further explored for gradient field noise reduction, by embedding multiscale properties providing sparse gradient field representations. Next, the ambiguity in possible surface gradients obtained by a two-image photometric stereo analysis is resolved using a cyclic projections algorithm based on the set of possible gradient fields and the previously developed gradient field representation. An algorithm that provides accurate surface reconstructions and surface type characterizations given two images of an unknown composite surface is established. We then apply this algorithm to Scanning Electron Microscopy (SEM) images to extract specimen surface topography and material type information from a pair of Secondary Electron (SE) and Back-scattered Electron (BSE) images. We then use a similar cyclic projections algorithm to reconstruct a surface from a single image. The simulation results indicate that the developed algorithm solves this classical shape-from-shading problem in a robust and accurate manner for varying illumination conditions. Finally, we establish a unified surface reconstruction framework using previously developed techniques on a photometric stereo image triplet containing shadows. We categorize the surface pixels as those illuminated in all three images, only two images and only one image. We then establish through simulation results that the developed method uses the surface gradient information obtained from the brightness images efficiently and effectively, and provides an accurate surface reconstruction.

As various wireless networks evolves into the next generation to provide better services, a key technology, mobile ad hoc networks (MANETs), has emerged recently. The dynamic topology, multi-hop transmission, and the nature of wireless channels create many challenging research topics in the area of MANETs. Recently, there has been work on determining the capacity of MANETs. The effects of some factors, such as node mobility, number of nodes, and transmission range, on the capacity of MANETs have been considered. In this work, we define and investigate the capacity of MANETs, considering the effects of medium access control (MAC). Since all the nodes in MANETs use a single or multiple channels to communicate, MAC plays an important role in coordinating channel access among nodes so that information gets through from one node to another. The MAC affects the capacity of MANETs in two aspects: collisions and spatial reuse. Three basic mechanisms are adopted to eliminate the incidence of collisions and maximize spatial reuse, i.e., carrier sense, handshake, and back-off. We define and use persistent probability, sensing range and back-off time to represent the effect of these mechanisms. The characteristics of MAC are thoroughly examined and an analytical solution for capacity evaluation is proposed. Numerical results are presented to demonstrate the effects of MAC, including carrier sense, handshake and back-off mechanism on the capacity of MANETs in terms of persistent probability, sensing range, and back-off time.

Recent experimental and physical modeling studies demonstrate that, as opposed to systems with smaller bandwidth, the Ultra-Wideband (UWB) channel exhibits frequency-dependent distortion of individual multipath components. This per-path distortion is particularly significant in outdoor UWB applications, where line-of-sight (LOS) or non-distorted reflected signals might not be available at the receiver (for example, in a canyon-like street). In these cases, the dominant propagation mechanisms involve shadowing (diffraction) and reflection by small objects (e.g. signs or lamp-posts). In this dissertation, a physical model is developed to investigate the position-dependent distortion of the UWB pulse. The results indicate that both the shadowed pulse and the reflected pulse (by small objects with dimensions bounded by the wavelengths present in the signal) are distorted. Design of optimal and suboptimal templates for the correlation receiver are investigated. The UWB pulses that accommodate robust template choice given by the transmit pulse shape for all propagation conditions and satisfy the FCC spectral mask for outdoor channels are identified. Finally, we analyze the frequency-dependent propagation gain of the UWB channels in various outdoor conditions. This knowledge quantifies the potential benefits of adapting the transmitted signal to the dominant propagation mechanism.