<p> For homogenous systems with periodic coefficients, the existence of a quadratic Lyapunov function has been studied, and the Floquet theory has been applied to provide the necessary and sufficient condition for the stability of the system. However, determining the transformation that reduces a nonautonomous linear periodic system to an autonomous linear system (having constant coefficients) is in general a difficult problem which requires series methods and the theory of special functions. In this thesis, I analyze the stability of the system through linear matrix inequalities by restricting Lyapunov function to a piecewise linear function. This method does not distinguish the values of the system parameters with one discretization interval. However, it is possible to provide more information of the system in order to increase the accuracy of the result without finer discretization of the Lyapunov function. I also discretized the linear periodic system with delay and reformulate the criteria of the stability in the form of linear matrix inequalities.</p>

Analytical and experimental comparisons are presented for two control laws used in a laboratory structure designed to simulate large space structures. The proposed control laws are based on minimizing the amount of energy imparted to the flexible modes during the maneuver. Structure modeling and various control techniques are discussed. In the proposed modeling procedure, the finite element method is used to describe the equations of motion for a given structure. The main objective of the analysis is to determine optimal actuator locations and the command forces to the actuators such that the structure will follow a desired trajectory while minimizing the internal energy to the flexible modes. The numerical simulations are verified experimentally using a digital implementation of the control laws. Critical issues related to experimental implementation are discussed. A closed-loop control system design which will take care of nonlinearities and uncertain inputs is included in this dissertation.

Present study concentrates primarily on radial crack propagation by the explosive gas pressure and the associated fracture formation, and on estimating the effects of natural discontinuities on rock fragmentation in bench blasting. Boundary element and finite element methods coupled with fracture mechanics theories are used to study the crack propagation. Fractal geometry principles are used to study the effect of natural discontinuities. Predicted stresses from conventional bench blasting model without any radial crack differ little from those around a pressurized hole in an infinite medium. Contrary to field observations, the radially symmetric stress field predicts a thin failed zone concentric with the hole. A loading rate dependent model, developed considering microflaws, suggest only long micro fractures become the radial cracks. The biaxial compression zone at the side of a radial crack suppresses smaller cracks. Other cracks can grow beyond this zone. Some die as the cracks become pressurized. Tensile σ₃ outside this zone peaks near the crack tip. A biaxial tension zone forms ahead of the crack tip. A multicrack model of bench blasting is developed. Biaxial compression zone forms near the hole. σ₃ is tensile outside this zone and peaks near the crack tips. Numerous tensile fractures form in these regions. Tensile fractures continue to form with radial crack growth and existing fractures grow in sliding. Stress redistribution around the fractures produces second and lower order fractures. These fractures break rock between the radial cracks. Pressurization of radial cracks is essential to propagate them for longer distances and to form associated fractures for further breakage of burden. The beam bending model produces unrealistically large burden displacement. The equivalent cavity hypothesis correctly estimates the stresses beyond the radial cracks but ignores the radial crack propagation and the associated breakage. It predicts a failed region concentric with the hole. The effect of natural discontinuities on fragmentation is determined by comparing the Schuhmann size distribution curves of the blasted fragments and the in-situ blocks. In-situ block and after blast fragments sizes, measured from photographs, are fractal which is analogous to Schuhmann Distribution. Exploiting the fractal characteristics eliminates the problems associated with size determination. Automated data reduction processes can make this method very powerful for routine monitoring and design optimization of blasts. Discontinuity pattern, fracture density, block density, fault structure, and microcracks in laboratory specimens are also fractal. Fractal behavior at microscale (10⁻⁶ m) to megascale (10⁵ m) implies Self-similar rock fracture formation. The fractal dimension may be related to the applied stress field.

University technology transfer is of critical importance to the U.S. innovation economy. Understanding the drivers of technology transfer efficiency will shed light on University research portfolio management. In this dissertation, survey data from The Association of University Technology Managers is analyzed in various aspects to offer a overall understanding of the technology transfer industry, which include University research fund composition, technology transfer office staffing, licenses executed to start-ups, small companies, and large companies, license income composition, legal fee expenditures, new patents applications, provisional patents, utility patents, and non USA patents, invention disclosures, U.S. patents issued, start-ups initiated, and annual averages of U.S. University technology transfer offices. Then, a two-stage technology transfer model based on Data Envelopment Analysis is proposed to address the limitation of the single-stage model. The two-stage model provides the capacity to evaluate the efficiencies of university research and technology transfer office separately and also as a whole, offering better insights for university technology transfer management. Year to year productivity changes are also measured using Malmquist Index. It is found the productivity growth has stemmed primarily from a growth in commercialization by all universities rather than a catching up by the inefficient universities. Finally, technology transfer efficiency and academic reputation is studied for the first time. Counter intuitively, they are not correlated. To further understand University research portfolio management, Modern Portfolio Theory is applied for the first time in this field. University disciplines are categorized into three major disciplines: engineering, physical and mathematical sciences, and biological and life sciences. The risk and return of technology transfer are defined and research portfolio risk-return curve are solved. Then correlation between portfolio balance and technology transfer efficiency are studied. It is found that a balanced portfolio is correlated to technology transfer efficiency, which means Universities can structure its research portfolio to increase technology transfer efficiency. / Engineering and Applied Sciences

Many applications, such as search and rescue missions, hazardous environment exploration, and surveillance, call for miniature robots capable of agile locomotion in a variety of unpredictable environments. Recent advances in meso-scale fabrication techniques and an understanding of biological insect locomotion have enabled the creation of multiple miniature legged robots to meet this demand. Nearly all insect-scale legged robots take inspiration from rigid-body hexapods; however, another unique body morphology found in nature is that of the centipede, characterized by its many legs and flexible body. These characteristics are expected to offer performance benefits in terms of agility, stability, robustness, and adaptability. / Engineering and Applied Sciences

The nitrogen-vacancy (NV) center is a point defect in diamond and has been championed as a promising solid-state "artificial atom." NV center properties such as its bright luminescence, room-temperature optical readout of spin states, and long spin decoherence lifetime make it an excellent system for applications in quantum information processing, high sensitivity magnetometry, and biotagging. In all applications, near-surface NVs are desirable. However, it has been found that the favorable properties of the NV center are significantly diminished as the NV center nears the surface. This dissertation presents efforts in understanding the effect of the surface on the luminescence of NV centers less than a wavelength of light from the surface. We use plasma assisted etching to, independently, change the surface termination and bring the NV closer to the surface. We find that treating the surface with CF4 plasma results in a deposited polymerous fluorocarbon which helps stabilize nearby NVs. We propose using a downstream etcher to bring NVs closer to the surface, while minimizing damage and maintaining NV luminescence. Finally, we enhance emission of these near-surface NVs by coupling them into a hybrid diamond plasmonic cavity. The fabricated devices result in a measured Q of 170, higher than other previously fabricated diamond plasmonic devices. / Engineering and Applied Sciences

A Micro-electro-mechanical system (MEMS) gas turbine generator is currently under development. This device uses electrodeposited NisoFezo (thin film) as a structural material in the high speed rotating micro-generator used to convert mechanical energy to electrical energy. For structural applications, the materials' mechanical properties are vital for the design. However, for electrodeposited NisoFezo, currently, there is not any published data regarding its mechanical Properties. Therefore, the goal of this research is to model the mechanical properties of electrodeposited Ni80Fe20 as a function of three critical electrolytes variables: agitation, current density, and temperature. In achieving this goal, a typical off-the- shelf nickel iron electroplating solution was used to fabricate the Ni80Fe2~ test specimens. A 2k Factorial Analysis and Design of Experiments was used to identify the critical variables and boundary conditions, and a new Micro/Nano Testing System was designed and developed to measure the mechanical properties. Finally, a linear regression analysis was conducted to model Young's Modulus and Ultimate Strength as a function of the three critical electrolytes variables.

The work presented in this dissertation is the result of "application-driven" research, with the need to solve complex large-scale engineering problems of significance and relevance to the Army and NASA using state-of-the-art high performance computing (HPC) platforms as its primary motivation. Currently, a majority of commercially available computational fluid dynamics (CFD) simulation algorithms in use by Army and NASA researchers and scientists solve the Navier-Stokes equations using a finite volume method (FVM) framework. Although these codes are extremely mature and take advantage of the numerical schemes complimentary to FVM, many do lack in computational performance for second-order accurate time integration schemes, due to the resulting nonlinear system of equations for large-scale applications, and exhibit poor scalability on a number of supercomputing platforms. Therefore, the purpose of this work is the development of a fully implicit, finite volume solver for large-scale transient compressible viscous flows, optimized for implementation on parallel, vector, and multi-streaming architectures. Optimization will include reduction in memory requirements, increasing computation speed, and obtaining near-linear code scalability. This is accomplished through implementation of innovative Jacobian-free/matrix-free iterative algorithms and code parallelization and vectorization. The Jacobian-free Generalized Minimal RESidual (GMRES) method is used to solve the resulting linear system inside each nonlinear Newton-Raphson iteration. Furthermore, the matrix-free Lower-Upper Symmetric Gauss Seidel (LU-SGS) method is employed as a preconditioning technique to the GMRES solver. Massively parallel implicit computations of both 2-dimensional and 3-dimensional aerodynamic applications using vector/multi-streaming and cluster supercomputers are presented to demonstrate the performance of the present solver in several aspects. These applications show the current implementation to be highly robust and accurate for problems of all flow regimes, subsonic, transonic, and supersonic. Though not originally intended for subsonic flows within the incompressible limit, i.e. flows with Mach numbers of 0.3 or less, results are presented which show that the solution accuracy of this solver is maintained for this class of problem. However, additional cases would need to be studied to determine the full scope of application to subsonic flows. The scalability of the current implementation is shown to be near-linear and super-linear across multiple supercomputing platforms.

<p> Advanced analytical and computational capabilities are allowing researchers to enhance the model complexity of bicycles and motorcycles in order to understand handling, stability and dynamic behavior. These models allow designers to investigate new frame layouts, alternative materials and different architectures. The structural stiffness of a frame plays a critical role in the handling behavior of a bike. However, the influence of structural stiffness has received limited attention in the existing literature. This study attempts to fill the gap by presenting analytical results that investigate the influence of structural stiffness in conjunction with rider positions on three distinct bicycle layouts. The analytical model consists of four rigid bodies: rear frame, front frame (front fork and handle bar assembly), front wheel and rear wheel. The overall model exhibits three degrees-of-freedom: the roll angle of the frame, the steering of the front frame and the rotation of the rear wheel with respect to the frame. The rear frame is divided into two parts, the rider and the bicycle frame, that are assumed to be rigidly connected. This is done in order to allow the model to account for varying rider positions. The influence of frame flexibility is studied by coupling the structural stiffness of the frame to the governing equations of motion. The governing equations of motion from a benchmark bike in the existing literature have been used, and then modified to accommodate rider positions and frame stiffness. Layouts from the benchmark bicycle, a commercially manufactured bicycle, and a cargo bicycle are used for this study in conjunction with rider positions ranging from a no hands position to a small aero tuck. The results are analyzed and compared with some proven analytical and experimental results in the existing literature. Results indicate that some of the rider positions can play a significant role in influencing the dynamic characteristics of a bike. Structural stiffness is seen to significantly affect the weave mode when the stiffness is reduced substantially. It is observed that the forward and lower rider positions are generally associated with a faster speed for onset of self-stability, that additionally last for a longer range of speeds. Furthermore, addition of a large luggage load to the cargo bike is seen to have a stabilizing effect as well as increase instability sensitivity to stiffness. Overall, it is observed that the inclusion of frame stiffness and an assessment of the distribution of a rider&rsquo;s mass are important factors that govern the dynamic behavior of a bike, and should therefore be carefully evaluated.</p>

The axial velocity profiles (local velocity versus time or position) of single bubbles in the absence and presence of flotation reagents such as frother were measuredin a water-jacketed transparent Plexiglas square (10 x 10 cm) column over a distance of 400 cm. The test liquid temperature was maintained uniform and constant at 30 °Cby water circulation in the jacket. Single bubbles, covering a size range of interest in flotation, were studied. A bubble generation frequency was selected such that velocitywas independent of frequency. To follow the bubble during its rise, a video camera supported on a track and capable of moving vertically at adjustable speeds was employed. / Dans une colonne de flottation carree (10 x 10 cm) a chemise d'eau faite de plexiglas transparent, on a mesurd, sur une distance de 400 cm, les profils de velocite axiale (velocite locale versus temps ou position) de bulles simples avec ou sans la presence de reactifs de flottation tel le moussant. En circulant de l'eau dans la chemise, la temperature du liquide a l'interieur de la colonne fut maintenue a une temperature constante de 30°C. On a etudie des bulles simples ayant des diametres d'intdret pour la flottation. Une frequence de Ondration des bulles fut choisie afm que la velocite soit independante de la frequence. Pour suivre la bulle lors de son ascension, on a utilisë une camera video montee sur rail et pouvant se placer verticalement a des vitesses variables. fr