Thesis supervisor: Kyung K. Choi. Includes bibliographic references (p. 165-170).

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 212-228).

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 228-235). Available also in a digital version from Dissertation Abstracts.

Amorphous hydrogenated carbon (a-C:H), diamond & diamond-like (DLC) thin films are some of the many terms used when referring to the generic group of coatings based on hard carbon. They are an emerging technological area within the surface coating discipline and are being increasingly used to improve the efficiency of a wide range of engineering components. In addition, the unique and extreme characteristics of these films result in unequalled material properties, such that in many cases a wide range of new and superior performance devices have only recently begun to be realised. This study focuses on hydrogenated & non-hydrogenated diamond-like thin films deposited by various plasma based, hybrid and beam deposition techniques. The wear resistant and low friction properties of these films are of great importance in many of the potential application areas and has attracted particular interest in recent years. Therefore the major thrust of this research has been on the tribological aspect, particularly in relation to other advanced ceramic coatings, and to highlight the applicability of endurance wear tests used to evaluate diamond-like films. The main findings have been:- a} That carbon can be deposited by several techniques in a hard amorphous phase, the properties of which depend heavily upon the conditions, substrate choice and method of deposition. For a particular technique, material properties can be made to be repeatable by a good understanding of deposition process control. b} The use of plasma based hybrid PVD and beam methods have resulted in a considerably improved structural performance of the films over those produced by the direct evaporation of graphite. The introduction of a hydrocarbon gas into the plasma at the synthesis stage has also been shown to provide further improvements in the physical properties which has correspondingly led to an enhancement in the tribological behaviour. The levels of hydrogen, whether in an unbonded or bonded form, included in the film after deposition has been demonstrated to affect the mechanical and optical properties of the considerably. c) The wear resistant and frictional performance of these coatings has been shown to be variable, depending upon the method and conditions of deposition as well as test parameters such as humidity, surface roughness, film structure, adhesive strength and oxide/impurity formation. In some cases the tribological performance was found to be excellent. The presence of the diamond-like carbon coating has been shown to be beneficial in reducing wear between contacting bodies experiencing relative movement by encouraging the formation of a carbon transfer layer on the surface of the counterface material which acts as a zone of low shear and provides a physical barrier to tribo-chemical interactions. Under certain conditions, such tribo-chemical interactions can occur readily at the interface, facilitating the formation of strong interfacial bonding and increased wear. d) The inclusion of metallic elements into the carbon matrix has been shown to enhance the wear resistant properties of the film to only a small extent, although at the expense of a deterioration in the friction coefficient. The most beneficial effect of doping carbon films with metal species has been the improved resistance to thermal degradation. e) Thin intermediate layers of titanium nitride have also been shown to produce a remarkable improvement in both wear resistance and frictional performance of the diamond-like carbon films to an extent which appears to be related to the level of stoichiometry of the titanium nitride. The main mechanism behind this increased performance appears to be due largely to an enhancement in adhesive strength at the diamond-like carbon/titanium nitride junction, with an increase in load support being provided as a secondary benefit. f) A critical assessment of the available techniques and methodology available for testing hard carbon films has been made and in some cases methods have been found to be either entirely inappropriate or appropriate only when suitable precautionary measures have been taken. These difficulties largely stem from the exacting demands of thin, hard layers of diamond-like carbon due to its unique and extreme mechanical, electrical and optical properties.

Correlation techniques for the identification of nonlinear systems are discussed in Chapter 1. The Volterra series expansion of the response of a nonlinear system is described, together with its counterpart in the frequency domain. Qosscorrelation methods for identifying the kernel functions which occur in this expansion are reviewed, with particular emphasis on techniques or obtaining the linear approximant to a nonlinear system. A crosscorrelation method is also discussed which appears to be unrelated to the Volterra approach. This technique uses a 4-level test signal and is the subject of detailed analysis in later chapters. The 4-level test signal is discussed in detail in Chapter 2 and it is shown that the linear channel of a nonlinear system may be identified. The concept of the almost periodic function is presented and it is concluded that by means of almost periodic fi.ncti&ns it is possible to identify the linear portion of the nonlinear channel in the system. The technique is essentially based on destroying the ynchronisation of the two 2-level signals originally used to produce the 4-level signal. A generalised technique is developed to calculate the parameters of the 4-level aperiodic signal in order to apply the method to any single-valued nonlinearity, assuming that 'a priori' knowledge of the nonlinearity is available. The technique is extended to permit identification of the impulse response of the linear elements when the nonlinearity is single valued but contains only even components. This is achieved by modifying the nonlinear characteristic to provide an odd component. A further extension of the technique shows that identification of certain nonlinear channels containing elements with memory is possible. Several situations are analysed in detail. An extension is also considered where the nonlinear channel is composed of two linear transfer functions separated by a nonlinearity. Experimental results are included to show the accuracy of the techniques developed. In Chapter 4 the application of high frequency signals (dither) as a technique to be used in the identification of certain open and pl,osed loop nonlinear systems is discussed. It is shown that certin types of dither permit linearization or elimination of nonlinear channels in certain open and closed systems. It is therefore possible, under these conditions, to identify the linear portions by impulse response or frequency testing techniques, and experimental results show the accuracy achieved. The concept of the equivalent nonlinearity provides a simple interpretation of the action of the dither. Dither is next considered in its role as a means of stabilizing nonlinear control systems, and the particular case of a third order system containing a hysteresis type relay characteristic is analysed in detail. The concepts of equivalent nonlinearity and describing function are used to derive an expression for the minimum amplitude of dither required to quench limit cycle oscillations in the system. The system is shown to hAve an effective gain margin once oscillations have been quenched. A typical point in this region is investigated and the three dimensional domain of stability for the system is presented,together with typical trajectories. The system is also shown to exhibit subharmonic resonance apci jump phenomena. In chapter 6 the use of dither in adaptive control systems is discussed, and the specific case of dither adaptive control system proposed as the solution to a qonstant fuel-rate problem is analysed in detail. The dynamic analysis presented divides the system into two loops via an extension of the equivalent nonlinearity concept. The final chapter reviews the work described in the body of the thesis, and explores several avenues for future research.

Acoustic arrays have been widely studied and can be used for a variety of applications. Existing acoustic array systems have mainly utilised linear and planar geometries. Such geometries have limited scan angles and can suffer from beam broadening and large grating lobes. This thesis presents a new acoustic array topology, the random spherical volumetric array. The system developed consists of 64 omni-directional microphones arranged at pseudo random locations within a spherical volume. The spherical array geometry provides the potential for full elevation and azimuth scan coverage. The projected aperture of a spherical array is direction independent, with the beamwidth and gain of the direction response being constant for all scan angles. The non-periodic element arrangement eliminates the possibility of large grating lobes and results in an array pattern with an average sidelobe level that is inversely proportional to the number of array elements. These properties enable wide-angle beam steering over a very large frequency bandwidth. The potential of acoustic volumetric arrays is examined and the results of theoretical and experimental investigations are presented. Holographic techniques have been implemented on the experimental system to produce images of sound sources and of reflections in the test environment. The concept of a synthetic volumetric array is introduced in which original synthetic aperture and multiple frequency techniques can be successfully used to reduce the average sidelobe level of the random spherical volumetric array. Initially, the acoustic random spherical volumetric array was envisaged as an inexpensive test-bed for microwave and radar system algorithm development. Since that time it has been found that application areas for the random spherical volumetric array also include covert surveillance operations, acoustic imaging and auditorium characterisation. Development of the system could allow security forces to monitor large crowds and riot situations; help in the detection of sniper location; and assist designers to build better auditoriums by highlighting areas of high reflection and reverberation.

Concurrent engineering and virtual prototyping are two emerging techniques that are bringing considerable economical benefits to the manufacturing industry. This work proposes the use of virtual prototyping to produce quantitative measures of product lifecycle performances to facilitate the implementation of concurrent engineering. A multiobjective, virtual prototyping-based global optimization problem is formulated to close the open loop of present virtual prototyping methods and to allow concurrent engineering design to be carried out systematically and automatically. Virtual prototyping-based design optimization faces several technical challenges. First, virtual prototyping is usually computationally intensive; relations between design variables and product life-cycle performances are often implicit. Secondly, the optimization problem usually consists of multi-modal design (objective and constraint) functions. The complexity and multi-modal nature of the optimization problem preclude the direct use of conventional local and global optimization methods. In this work, a new and efficient search method for virtual prototyping-based global design optimization is introduced. The method, called Adaptive Response Surface Method (ARSM), carries out systematic “design experiments” through virtual prototyping to build second-order regression models to approximate the design functions. Through an iterative process, the regression models are improved and the global design optimum is obtained. The ARSM search scheme requires only a modest number of design function evaluations, making virtual prototyping-based global design optimization feasible. The proposed quantitative concurrent design method is then applied to the components, stack and system design of a transportation fuel cell. The approach led to an optimized multi-functional component, a reduction of the system cost, and an improvement of the system performance. The approach can be applied to the concurrent design and design optimization of other complex mechanical components, assemblies and systems. / Graduate

The work presented in this thesis is concerned with developing a greater understanding of piston ring lubrication and consists of both experimental and theoretical components. It begins with a review of piston ring and ring pack lubrication studies, describing how the understanding of the operation of piston rings has progressed since the late 19th Century. A well-established method of analysing the hydrodynamic lubrication of a single piston ring, utilizing coordinate data to describe the ring face profile, is then presented. Calculation of mixed/boundary friction, when the lubricant film thickness falls below a pre-determined level, is included. The predictions of this program are then compared to results obtained by other workers to validate its operation. This analysis is then developed to investigate the influence of the circumferential variation in piston ring face profile on the lateral motion of the piston ring centre. The complex relationship between variation in ring face profile, angular ring gap position and bore shape is then examined. These features are shown to have a significant effect on the calculation of ring centre locus, oil transport and lubricant film thicknesses. The model is then applied to predict the influence of the distorted bore shape of a cylinder from an experimental engine apparatus. Following this, the development, testing, calibration and performance of a capacitance based measurement system capable of recording piston ring face profiles on a single pass, is described. This system was used with twenty-one transducers, of novel design, to allow the axial and circumferential distribution of lubricant film thickness to be monitored on an engine liner. This liner was fitted in an engine apparatus which had the additional facility of being able to measure the instantaneous friction between the piston assembly and cylinder liner using a "floating liner" technique. Experimental measurements of instantaneous friction force and the circumferential distribution of lubricant film thickness are then compared to theoretical predictions for a range of operating conditions. The comparisons reveal a reasonable level of agreement between measurements with consistent overall trends. The effect of varying bore distortion is also examined theoretically. It is shown that an increase in the severity of bore distortion does not necessarily result in an increase in net oil transport.

No description available.

US competitiveness in the 21st century global economy depends on a workforce that is science, technology, engineering and mathematics (STEM) literate, and has knowledge and skills to tackle complex technological problems. In response to the need for a STEM literate workforce equipped with 21st century skills there is a push for K-12 educational reform. STEM literacy is the ability to use content knowledge and skills in science, technology, engineering and math in solving human problems in a collaborative manner (NRC, 2009, Wiggins and McTighe, 2005). Researchers have argued that the integrative STEM education (I-STEM ED) pedagogical approach (with its roots in technology education) promotes active learning through student discovery of using science and mathematics content and practices in novel situations, with active construction of understanding by doing (Cajas, 2001; Wells, 2010, 2016b) Critical thinking and problem solving (CT and PS) skills, collectively identified as 21st century skills by P21 (2005a), involved in solving authentic design problems are not assessed in traditional science and mathematics standardized testing or in Tech-ED classrooms in K-12 grades. Assessments in traditional classrooms, focus on the extent of correctness of the end-result, and rarely, if ever, on the reasoning or procedures leading to the result (Docktor and Heller, 2009; Shavelson, Ruiz-Primo, Li and Ayala, 2003; Steif and Dantzler, 2005). Furthermore, the content knowledge tested is directly related to what has been recently taught in the classroom, and eliminates the need for solvers' demonstration of metacognitive processes involved in CT and PS that require recalling/selecting the discipline specific content knowledge. Within traditional Tech-ED classrooms, students are assessed using competencies defined in the Career and Technical Education curriculum framework which do not focus on solving authentic problems. Herein lies the gap between what is needed for the 21st century worker and what is currently the focus of secondary education. The purpose of this study was to measure the extent to which students immersed in an I-STEM ED program were successful in solving an authentic design-based problem presented to them outside the context of the classroom where the content was learned. In addition, five specific student abilities (SAs) that contribute to authentic problem-solving were identified and a rubric to assess these SAs was developed and validated. A design-no-make challenge (DNMC) was developed and administered to these students. Analysis of their responses showed that students immersed in an integrative STEM education program performed significantly better in designing a solution to the DNMC when compared with a hypothesized mean for students in a traditional classroom. Furthermore, the specific SAs associated with selecting and utilizing the relevant science and math content and practices, and communicating logical reasoning in their design of a solution were found to be strongly correlated to students' successful problem-solving. / Ph. D.