Complex nonlinear aspects of aeroelastic phenomena include unsteady nonlinear aerodynamic loads, structural nonlinearities, as well as nonlinear couplings between the flow and the structural response. Nonlinearities in aerodynamic loads originate from unsteady shocks and/or flow separation. Structural nonlinearities are geometric, or a result of free play. Nonlinear fluid structure couplings result from nonlinear resonance between the aerodynamic load and structural modes. Under different conditions, one or a combination of these aspects could yield flutter or Limit Cycle Oscillations (LCO). The overall goal of this work is to develop the capabilities to quantify the role that these different nonlinear mechanisms could play in observed flutter and LCO. The realization of such a goal would help in providing a benchmark for the detection of nonlinear aeroelastic instabilities and possibly effective means for obtaining improved performance and reduced uncertainties through operation beyond conventional boundaries that are based on linear analysis. Additionally, this effort will provide a benchmark for the validation of computational methodologies. In this thesis, wavelet-based higher order spectra are applied to identify different nonlinear aeroelastic phenomena as encountered in two experiments. First, the analysis is applied to a set of experiments involving a flexible semispan model (FSM) of a High Speed Civil Transport (HSCT) wing configuration conducted by Silva et al. (Experimental Steady and Unsteady Aerodynamic and Flutter Results for HSCT Semispan Models; AIAA/ASME/ASCE/AHS/ASC 41st Structures, Structural Dynamics, and Materials Conference, 2000). The interest is in the identification of nonlinear aeroelastic phenomena associated with a high dynamic response region which was measured over a large range of dynamic pressures around Mach number 0.98. At the top of this region is a ``hard'' flutter point that resulted in the loss of the model. The results show that ``hard'' flutter is related to intermittent nonlinear coupling between the shock motion and large amplitude structural motions. Second, the analysis is applied to identify nonlinear aspects of LCO encountered during test flights of an F-16 aircraft. The results show quadratic and cubic couplings in the acceleration signals of the under-wing launchers and high quadratic coupling levels between flaperon motions and wing oscillations. The implications of applying these techniques in the capacity of a ``flutterometer'' are also discussed. / Ph. D.

An innovative implementation of the Herschel-Quincke tubes concept for the reduction of noise from turbofan engines is proposed here. The approach consists of installing circumferential arrays of Herschel-Quincke (HQ) tubes or waveguides in the inlet of the turbofan engine. An analytical technique was developed to predict the effects of HQ tubes applied to circular inlets. The modeling technique involves modeling the tubes-inlet interfaces as finite piston sources that couple the acoustic field inside the inlet with the acoustic field within the HQ tubes. An optimization technique based on genetic algorithms was also developed to be able to design and optimize the system parameters. The accuracy of the model was validated with experimental data obtained from two types of turbofan engines. Analytical predictions are shown to correlate well with experimental data. The analytical model is then used to provide insight into the noise control mechanisms involved in the system. It is shown that the energy in an incident mode is in part reflected back to the fan and that some energy is also scattered into other higher-order modes. Thus, the suppression of a particular mode is due to the combination of the scattered contributions from the various incident modes. The effects of the system parameters were analyzed and parametric studies were conducted. Different configurations for the arrays of HQ tubes such as helical patterns or tubes at an angle with respect to the inlet axis were also investigated. The results show the great potential of the HQ tubes system to reduce noise from turbofan engines. / Master of Science

A fundamental study of the Herschel-Quincke (HQ) tube concept for the reduction of noise in circular ducts is presented here. Recent testing of the Herschel-Quincke tube concept on the Pratt-Whitney JT15D and AlliedSignal TFE731-60 engines showed the potential for the practical application of this approach. A model of the HQ-system has been developed to aid in the design of the system tested. The model has revealed new noise control mechanisms associated to the implementation of multiple HQ-waveguides in a duct in the presence of higher order modes. However, the practical nature of these engine facilities results in limitations with regard to the fundamental research knowledge that could be gained from testing in a more controlled laboratory environment. A series of experiments was conducted at the NASA Langley Research Center 0.30 m ducted fan test facility where detailed modal measurements were performed. The main goals of this research endeavor were to evaluate the accuracy of the previously developed theoretical model and provide insight into the noise control mechanisms. Experiments were performed with different disturbance mode structures, number of HQ tubes and arrays, and axial positions. The modes in the duct were generated with an array of acoustic drivers (no flow case) and measured with logarithmically spaced circumferential and helical microphone arrays located on the duct wall. The modal amplitudes of the incident, transmitted, and reflected modes in the duct were determined from the microphone measurements. This allowed for the comparison of analytical and experimental modal amplitudes, modal powers, total power, and reductions. The results of this study provide insight into the three noise control mechanisms associated with this approach: reflection, circumferential scattering, and radial scattering. Comparison with the experimental results shows that the model accurately predicts the sound power attenuation except near the cut-off frequency of the modes where it tends to overestimate the attenuation. The effect of the number of tubes in the array and its axial position was also evaluated. Overall, the results of this study validate the general modeling approach for the HQ tube concept. / Master of Science

External and internal stakeholders in higher education are asking for accountability about what takes place in the classroom (Alexander, Clinton, and Kean, 1986; Hart Research Associates, 2010; Spellings, 2006). They want to be assured that the learning institutions claim is occurring on campus is in fact happening (Alexander, 2000). In response, academic leaders have produced information about active learning strategies in classrooms (Seifert, Pascarella, Wolniak, and Cruce, 2006; Tsui, 2002; Umbach and Wawrzynski, 2005), student approaches to learning (Biggs, Kember, and Leung, 2001), and faculty-student interaction that lead to increased use of higher order thinking skills (Kuh, 1995; Pascarella and Terenzini, 1991; Reason, Terenzini and Domingo, 2007). Although there is extensive literature on learning that occurs in academic settings on college campuses, data on whether students are engaging in higher order thinking skills in non-academic settings are less prevalent. This study sought to understand whether students' higher order thinking skills (HOTs) are influenced by their involvement in non-academic activities (NAIs). I analyzed data from college seniors who completed the 2010 National Survey of Student Engagement (NSSE) to address two questions. First, I explored what factors emerged from the items about non-academic involvement (NAI) on the NSSE. Second, multiple regression models were employed to determine the extent to which variance in HOTs could be explained by these NAI factors. There were 14 items on the 2010 NSSE that, based on literature, measured frequency with which students engaged in NAIs. Exploratory factor analysis revealed two independent factors consisting of 7 items: Relationships (3 items) and Diverse Perspectives (4 items). These two factors explained 21% of variance in students' higher order thinking skills. Students who are exposed to diversity and develop close relationships use HOT skills more frequently. This suggests implications for those who work in admissions, student affairs, and human resources, among others. The findings also inform policies related to promotion and tenure as well as student involvement. / Ph. D.

Neural networks play an important role in the execution of goal-oriented paradigms. They offer flexibility, adaptability and versatility, so that a variety of approaches may be used to meet a specific goal, depending upon the circumstances and the requirements of the design specifications. Development of higher-order neural units with higher-order synaptic operations will open a new window for some complex problems such as control of aerospace vehicles, pattern recognition, and image processing. The neural models described in this thesis consider the behavior of a single neuron as the basic computing unit in neural information processing operations. Each computing unit in the network is based on the concept of an idealized neuron in the central nervous system (CNS). Most recent mathematical models and their architectures for neuro-control systems have generated many theoretical and industrial interests. Recent advances in static and dynamic neural networks have created a profound impact in the field of neuro-control. Neural networks consisting of several layers of neurons, with linear synaptic operation, have been extensively used in different applications such as pattern recognition, system identification and control of complex systems such as flexible structures, and intelligent robotic systems. The conventional linear neural models are highly simplified models of the biological neuron. Using this model, many neural morphologies, usually referred to as multilayer feedforward neural networks (MFNNs), have been reported in the literature. The performance of the neurons is greatly affected when a layer of neurons are implemented for system identification, pattern recognition and control problems. Through simulation studies of the XOR logic it was concluded that the neurons with linear synaptic operation are limited to only linearly separable forms of pattern distribution. However, they perform a variety of complex mathematical operations when they are implemented in the form of a network structure. These networks suffer from various limitations such as computational efficiency and learning capabilities and moreover, these models ignore many salient features of the biological neurons such as time delays, cross and self correlations, and feedback paths which are otherwise very important in the neural activity. In this thesis an effort is made to develop new mathematical models of neurons that belong to the class of higher-order neural units (HONUs) with higher-order synaptic operations such as quadratic and cubic synaptic operations. The advantage of using this type of neural unit is associated with performance of the neurons but the performance comes at the cost of exponential increase in parameters that hinders the speed of the training process. In this context, a novel method of representation of weight parameters without sacrificing the neural performance has been introduced. A generalised representation of the higher-order synaptic operation for these neural structures was proposed. It was shown that many existing neural structures can be derived from this generalized representation of the higher-order synaptic operation. In the late 1960s, McCulloch and Pitts modeled the stimulation-response of the primitive neuron using the threshold logic. Since then, it has become a practice to implement the logic circuits using neural structures. In this research, realization of the logic circuits such as OR, AND, and XOR were implemented using the proposed neural structures. These neural structures were also implemented as neuro-controllers for the control problems such as satellite attitude control and model reference adaptive control. A comparative study of the performance of these neural structures compared to that of the conventional linear controllers has been presented. The simulation results obtained in this research were applicable only for the simplified model presented in the simulation studies.

Neural networks play an important role in the execution of goal-oriented paradigms. They offer flexibility, adaptability and versatility, so that a variety of approaches may be used to meet a specific goal, depending upon the circumstances and the requirements of the design specifications. Development of higher-order neural units with higher-order synaptic operations will open a new window for some complex problems such as control of aerospace vehicles, pattern recognition, and image processing. The neural models described in this thesis consider the behavior of a single neuron as the basic computing unit in neural information processing operations. Each computing unit in the network is based on the concept of an idealized neuron in the central nervous system (CNS). Most recent mathematical models and their architectures for neuro-control systems have generated many theoretical and industrial interests. Recent advances in static and dynamic neural networks have created a profound impact in the field of neuro-control. Neural networks consisting of several layers of neurons, with linear synaptic operation, have been extensively used in different applications such as pattern recognition, system identification and control of complex systems such as flexible structures, and intelligent robotic systems. The conventional linear neural models are highly simplified models of the biological neuron. Using this model, many neural morphologies, usually referred to as multilayer feedforward neural networks (MFNNs), have been reported in the literature. The performance of the neurons is greatly affected when a layer of neurons are implemented for system identification, pattern recognition and control problems. Through simulation studies of the XOR logic it was concluded that the neurons with linear synaptic operation are limited to only linearly separable forms of pattern distribution. However, they perform a variety of complex mathematical operations when they are implemented in the form of a network structure. These networks suffer from various limitations such as computational efficiency and learning capabilities and moreover, these models ignore many salient features of the biological neurons such as time delays, cross and self correlations, and feedback paths which are otherwise very important in the neural activity. In this thesis an effort is made to develop new mathematical models of neurons that belong to the class of higher-order neural units (HONUs) with higher-order synaptic operations such as quadratic and cubic synaptic operations. The advantage of using this type of neural unit is associated with performance of the neurons but the performance comes at the cost of exponential increase in parameters that hinders the speed of the training process. In this context, a novel method of representation of weight parameters without sacrificing the neural performance has been introduced. A generalised representation of the higher-order synaptic operation for these neural structures was proposed. It was shown that many existing neural structures can be derived from this generalized representation of the higher-order synaptic operation. In the late 1960s, McCulloch and Pitts modeled the stimulation-response of the primitive neuron using the threshold logic. Since then, it has become a practice to implement the logic circuits using neural structures. In this research, realization of the logic circuits such as OR, AND, and XOR were implemented using the proposed neural structures. These neural structures were also implemented as neuro-controllers for the control problems such as satellite attitude control and model reference adaptive control. A comparative study of the performance of these neural structures compared to that of the conventional linear controllers has been presented. The simulation results obtained in this research were applicable only for the simplified model presented in the simulation studies.

With the introduction of outcomes-based education (OBE) in South Africa the role of teachers and learners in the teaching and learning process had to change. Teachers had to adopt a facilitation role and learners had to focus on active learning and the mastering of outcomes. With the focus of OBE on outcomes, teachers in the teachinglearning process are continuously pressurised not only to focus on the teaching of theoretical subject matter, but also the development of higher-order cognitive skills (HOCS). Since 2006 the development of learners' HOCS in South African Schools have been emphasized in the Further Education and Training Phase (grades 10-12) through the National Curriculum Statements. Teachers in Business Studies (the new subject that replaced Business Economics as secondary school subject in 2006) have doubts in their ability to develop learners' HOCS because they doubt their own ability to demonstrate HOCS. This study indicates that the teacher training of Business Studies students should focus on the development of their HOCS, because they won't be able to develop their learners' HOCS if they can't demonstrate it themselves. The purpose of this study was to develop a teaching model for the development of education students in Business Studies' HOCS. Lecturers can use the teaching model during teacher training, to develop education students' knowledge of HOeS in Business studies, their ability to demonstrate HOCS and their critical and creative thinking skills. This study was approached from a pragmatic research paradigm. A literature study was conducted to motivate the rationale for the development of education students' HOCS, to investigate the meaning of HOCS and to determine the way in which HOCS can be learned, taught and assessed. The proposed teaching model that was developed, is based on the literature study. From the literature study a workable definition of HOCS was developed for the aim of this study. The literature study also showed that HOCS can best be learned and taught in a social constructivist learning environment, where lecturers enable students to construct their own knowledge and skills, with a combination of inductive teaching, cooperative learning and problem/activity based learning. During the empirical component of this study the teaching model for development of HOCS was applied to education students in Business Studies. Data was gathered over a period of four months by means of a mixed methods research design. This research design acted as a purposeful research framework wherein quantitative and qualitative methods were used to solve the research problem. Findings from the results of the empirical study indicated the extent to which the teaching model led to the development of the education students' HOCS, the experience of the education students and the way in which the model was executed. The contribution of this research is viewed as a clarification of the concept HOCS, the rationale for the development of HOCS and the proposed teaching model. / Thesis (PhD (Education))--North-West University, Potchefstroom Campus, 2010

With the introduction of outcomes-based education (OBE) in South Africa the role of teachers and learners in the teaching and learning process had to change. Teachers had to adopt a facilitation role and learners had to focus on active learning and the mastering of outcomes. With the focus of OBE on outcomes, teachers in the teachinglearning process are continuously pressurised not only to focus on the teaching of theoretical subject matter, but also the development of higher-order cognitive skills (HOCS). Since 2006 the development of learners' HOCS in South African Schools have been emphasized in the Further Education and Training Phase (grades 10-12) through the National Curriculum Statements. Teachers in Business Studies (the new subject that replaced Business Economics as secondary school subject in 2006) have doubts in their ability to develop learners' HOCS because they doubt their own ability to demonstrate HOCS. This study indicates that the teacher training of Business Studies students should focus on the development of their HOCS, because they won't be able to develop their learners' HOCS if they can't demonstrate it themselves. The purpose of this study was to develop a teaching model for the development of education students in Business Studies' HOCS. Lecturers can use the teaching model during teacher training, to develop education students' knowledge of HOeS in Business studies, their ability to demonstrate HOCS and their critical and creative thinking skills. This study was approached from a pragmatic research paradigm. A literature study was conducted to motivate the rationale for the development of education students' HOCS, to investigate the meaning of HOCS and to determine the way in which HOCS can be learned, taught and assessed. The proposed teaching model that was developed, is based on the literature study. From the literature study a workable definition of HOCS was developed for the aim of this study. The literature study also showed that HOCS can best be learned and taught in a social constructivist learning environment, where lecturers enable students to construct their own knowledge and skills, with a combination of inductive teaching, cooperative learning and problem/activity based learning. During the empirical component of this study the teaching model for development of HOCS was applied to education students in Business Studies. Data was gathered over a period of four months by means of a mixed methods research design. This research design acted as a purposeful research framework wherein quantitative and qualitative methods were used to solve the research problem. Findings from the results of the empirical study indicated the extent to which the teaching model led to the development of the education students' HOCS, the experience of the education students and the way in which the model was executed. The contribution of this research is viewed as a clarification of the concept HOCS, the rationale for the development of HOCS and the proposed teaching model. / Thesis (PhD (Education))--North-West University, Potchefstroom Campus, 2010

L'objectif de cette thèse est l'optimisation de la qualité perçue de la reproduction sonore par un système audio multicanal, dans un contexte de salle d'écoute domestique. Les travaux de recherche présentés s'articulent selon deux axes. Le premier concerne l'effet de salle, et plus particulièrement les aspects physiques et perceptifs liés aux premières réflexions d'une salle. Ces éléments sont décrits spécifiquement, et une expérience psychoacoustique a été menée afin d'étendre les données disponibles quant à leur perceptibilité, c'est à dire leur capacité à modifier la perception du son direct, que ce soit en termes de timbre ou de localisation. Les résultats mettent en évidence la dépendance du seuil en fonction du type de stimulus, ainsi que son évolution en fonction de la configuration spatiale de l'onde directe et de la réflexion. Pour une condition donnée, le seuil de perceptibilité est décrit comme une fonction de directivité dépendant de l'incidence de la réflexion.Le deuxième axe de travail concerne les méthodes de correction de l'effet de la salle de reproduction. Les méthodes numériques classiques sont d'abord étudiées. Leur principale lacune réside dans l'absence de prise en compte du rôle spécifique des propriétés temporelles et spatiales des première réflexions. Le travail de thèse se termine par la proposition d'une nouvelle méthode de correction utilisant un algorithme itératif de type FISTA modifié afin de prendre en compte la perceptibilité des réflexions. Le traitement est implémenté dans une représentation où l'information spatiale est analysée sur la base des harmoniques sphériques. / The goal of this Ph. D. thesis is to optimize the perceived quality of multichannel sound reproduction systems, in the context of a domestic listening room. The presented research work have been pursued in two different directions.The first deals with room effet, and more particularly with physical and perceptual aspects of first reflections within a room. These reflections are specifically described, and a psychoacoustical experiment have been carried out in order to extend the available data on their perceptibility, i.e. their potency in altering the perception of the direct sound, whether in its timbral or spatial features. Results exhibit the variation of the threshold depending on the type of stimulus, as well as on the spatial configuration of the direct sound and the reflection. For a given condition, the perceptibility threshold is given as a directivity function depending on the direction of incidence of the reflection.The second topic deals with room correction methods. Firstly, state-of-the art digital methods are investigated. Their main drawback is that they don't consider the specific impact of the temporal and spatial attributes of first reflections. A new correction method is therefore proposed. It uses an iterative algorithm, derivated from the FISTA method, in order to take into account the perceptibility of the reflections. All the processing is carried out in a spatial sound representation, where the spatial properties of the sound are analysed thanks to spherical harmonics.

We present a series of improvements to the Hybrid system, a formal theory implemented in Isabelle/HOL to support specifying and reasoning about formal systems using higher-order abstract syntax (HOAS). We modify Hybrid's type of terms, which is built definitionally in terms of de Bruijn indices, to exclude at the type level terms with `dangling' indices. We strengthen the injectivity property for Hybrid's variable-binding operator, and develop rules for compositional proof of its side condition, avoiding conversion from HOAS to de Bruijn indices. We prove representational adequacy of Hybrid (with these improvements) for a lambda-calculus-like subset of Isabelle/HOL syntax, at the level of set-theoretic semantics and without unfolding Hybrid's definition in terms of de Bruijn indices. In further work, we prove an induction principle that maintains some of the benefits of HOAS even for open terms. We also present a case study of the formalization in Hybrid of a small programming language, Mini-ML with mutable references, including its operational semantics and a type-safety property. This is the largest case study in Hybrid to date, and the first to formalize a language with mutable references. We compare four variants of this formalization based on the two-level approach adopted by Felty and Momigliano in other recent work on Hybrid, with various specification logics (SLs), including substructural logics, formalized in Isabelle/HOL and used in turn to encode judgments of the object language. We also compare these with a variant that does not use an intermediate SL layer. In the course of the case study, we explore and develop new proof techniques, particularly in connection with context invariants and induction on SL statements.