Fluid mixing that is induced by hydrodynamic instability is ubiquitous in nature; the material interface between two fluids when perturbed even slightly, changes shape under the influence of hydrodynamic forces, and an additional zone called the mixing layer where the two fluids mix, develops and grows in size. This dissertation reports a study on the role of thermal fluctuations in fluid mixing at the interface separating two perfectly miscible fluids of different densities. Mixing under the influence of two types of instabilities is studied; the Rayleigh-Taylor (RTI) and Richtmyer-Meshkov (RMI) instabilities. The study was conducted using numerical simulations after verification of the simulation methodology. Specifically, fluctuating hydrodynamic simulations were used; the fluctuating compressible Navier-Stokes equations were the physical model of the system, and they were solved using numerical methods that were developed and implemented in-house. Our results indicate that thermal fluctuations can trigger the onset of RTI at an initially unperturbed fluid-fluid interface, which subsequently leads to mixing of multi-mode character. In addition we find that for both RMI and RTI, whether or not thermal fluctuations quantitatively affect the mixing behavior, depends on the magnitude of the dimensionless Boltzmann number of the hydrodynamic system in question, and not solely on its size. When the Boltzmann number is much smaller than unity, the quantitative effect of thermal fluctuations on the mixing behavior is negligible. Under this circumstance, we show that mixing behavior is the average of the outcome from several stochastic instances, with the ensemble of stochastic instances providing the bounds on mixing-related metrics such as the mixing width. Most macroscopic hydrodynamic systems fall in this category. However, when the system is such that the Boltzmann number is of order unity, we show that thermal fluctuations can significantly affect the mixing behavior; the ensemble-averaged solution shows a departure from the deterministic solution. We conclude that for such systems, it is important to account for thermal fluctuations in order to correctly capture their physical behavior.

Recently, experimental observations have shown that radar echoes from the irregularity<br />source region associated with mesospheric dusty space plasmas may be modulated by radio wave heating with ground-based ionospheric heating facilities. These experiments show great promise as a diagnostic for the associated dusty plasma in the Near-Earth Space Environment which is believed to have links to global change. This provides an alternative to more complicated and costly space-based observational approaches to investigating these layers. This dissertation seeks to develop new analytical and computational models to investigate fundamental physics of the associated dusty plasmas as well as utilize experimental observations during High Frequency HF ground-based heating experiments to develop practical techniques for diagnosing these dusty plasma layers.<br />The dependency of the backscattered signal strength (i.e. Polar Mesospheric Summer Echoes PMSEs) after the turn-on and turn-off of the radio wave heating on the radar frequency is an unique phenomenon that can shed light on the unresolved issues associated with the basic physics of the natural charged mesospheric dust layer. The physical process after turn-on and turn-off of radio wave heating is explained by competing ambipolar diffusion and dust charging processes. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during radiowave heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius<br />on the temporal evolution of electron irregularities associated with PMSE is investigated.<br />The possibility of observing the turn-on overshoot (enhancement of radar echoes after the<br />radiowave turn-on) in the high frequency HF radar band is discussed based on typical mesospheric<br />parameters. It has been shown that predicted enhancement of electron irregularity<br />amplitude after heater turn-on at HF band is the direct manifestation of the dust charging<br />process in the space. Therefore further active experiments of PMSEs should be pursued<br />at HF band to illuminate the fundamental charging physics in the space environment to<br />provide more insight on this unique medium. Preliminary observation results of HF PMSE<br />heating experiment with the new 7.9 MHz radar at the European Incoherent Scatter EISCAT<br />facility appear promising for the existence of PMSE turn-on overshoot. Therefore, future<br />experimental campaigns are planned to validate these predictions.<br />Computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930MHz corresponding to existing ionospheric heating facilities. Data from a 2009 very high frequency VHF (224 MHz) experiment at EISCAT<br />is compared with the computational model to obtain dust parameters in the PMSE. The<br />estimated dust parameters as a result of these comparison show very reasonable agreement to dust radius and density at PMSE altitudes measured during a recent rocket experiment providing validation to the computational model.<br /><br />The first comprehensive analytical model for the temporal evolution of PMSE after heater<br />turn-on is developed and compared to a more accurate computational model as a reference.<br />It is shown that active PMSE heating experiments involving multiple observing frequencies<br />at 7.9 (HF), 56, and 224 MHz (VHF) may contribute further diagnostic capabilities since<br />the temporal evolution of radar echoes is substantially different for these frequency ranges.<br />It is shown that conducting PMSE active experiments at HF and VHF band simultaneously<br />may allow estimation of the dust density altitude profile, dust charge state variation during<br />the heating cycle, and ratio of electron temperature enhancement in the irregularity source<br />region. These theoretical and computational models are extended to study basic physics of the evolution of relevant dusty plasma instabilities thought to play an important role in irregularity production in mesospheric dust layers. A key focus is the boundary layer of these charged dust clouds. Several aspects of the cloud\'s structure (thickness of boundary layer, average particle size and density, collisional processes, and cloud expansion speed) and the ambient plasma are varied to determine the effect of these quantities on the resulting irregularities.<br />It was shown that for high collision frequencies, the waves may be very weakly excited (or<br />even quenched) and confined to the boundary layer. The excited dust acoustic waves inside<br />the dust cloud with frequency range of 7-15Hz and in the presence of electron bite-outs is<br />consistent with measured low frequency waves near 10 Hz by sounding rocket experiments<br />over the past decade. The observed radar echoes associated with the artificially created dust<br />clouds at higher altitudes in the ionosphere including space shuttle exhaust and upcoming<br />active space experiments in which localized dust layers will be created by sounding rockets<br />could be related to the excited acoustic waves predicted.<br />Finally, variation of spatial structures of plasma and dust (ice) irregularities in the PMSE<br />source region in the presence of positively charged dust particles is investigated. The correlation and anti-correlation of fluctuations in the electron and ion densities in the background plasma are studied considering the presence of positive dust particle formation. Recent rocket payloads have studied the properties of aerosol particles within the ambient plasma environment in the polar mesopause region and measured the signature of the positively charged particles with number densities of (2000 cm"3) for particles of 0.5-1 nm in radius.<br />The measurement of significant numbers of positively charged aerosol particles is unexpected from the standard theory of aerosol charging in plasma. Nucleation on the cluster ions is one of the most probable hypotheses for the positive charge on the smallest particles. The utility being that it may provide a test for determining the presence of positive dust particles.<br />The results of the model described show good agreement with observed rocket data. As an<br />application, the model is also applied to investigate the electron irregularity behavior during<br />radiowave heating assuming the presence of positive dust particles. It is shown that the<br />positive dust produces important changes in the behavior during Polar Mesospheric Summer Echo PMSE heating experiments that can be described by the fluctuation correlation and anti-correlation properties.<br />The second part of this dissertation is dedicated to Stimulated Electromagnetic Emissions SEEs produced by interaction of high power electromagnetic waves in the ionosphere. Nearearth ionospheric plasma presets a neutral laboratory for investigation of nonlinear wave phenomena in plasma which can not be studied in the laboratory environment due to the effect of physical boundary conditions. This process has been of great interest due to the<br />important diagnostic possibilities involving ability to determine mass of constitutive ions in<br />the interaction region through measurements of various gyro-frequencies. Objectives include<br />the consideration of the variation of the spectral behavior under pump power, proximity to<br />the gyro-harmonic frequency, and beam angle. Also, the relationship between such spectral<br />features and electron acceleration and creation of plasma irregularities was an important<br />focus.<br />Secondary electromagnetic waves excited by high power electromagnetic waves transmitted<br />into the ionosphere, commonly know as Stimulated Electromagnetic Emissions SEEs,<br />produced through Magnetized Stimulated Brillouin Scatter MSBS are investigated. Data<br />from two recent research campaigns at the High Frequency Active Auroral Research Program<br />facility HAARP is presented in this work. These experiments have provided additional<br />quantitative interpretation of the SEE spectrum produced by MSBS to yield diagnostic measurements of the electron temperature in the heated ionosphere. SEE spectral emission lines corresponding to ion acoustic IA and electrostatic ion cyclotron EIC modes were observed with a shift in frequency up to a few tens of Hz from radio waves transmitted near the third harmonic of the electron gyro-frequency 3fce. The threshold of each emission line has been measured by changing the pump wave amplitude. The experimental results aimed to show the threshold for transmitter power to excite IA waves propagating along the magnetic field lines as well as for EIC waves excited at oblique angles relative to the background magnetic field. A full wave solution has been used to estimate the amplitude of the electric field at the interaction altitude. The estimated growth rate using the theoretical model is compared with the threshold of MSBS lines in the experiment and possible diagnostic information for the background ionospheric plasmas is discussed. Simultaneous formation of artificial field aligned irregularities FAIs and suppression of the MSBS process is investigated. Recently, there has been significant interest in ion gyro-harmonic structuring the Stimulated Electromagnetic Emission SEE spectrum due to the potential for new diagnostic information available about the heated volume and ancillary processes such as creation of artificial ionization layers. These relatively recently discovered emission lines have almost exclusively been studied for second electron gyro-harmonic heating. The first extensive systematic investigations of the possibility of these spectral features for third electron gyro-harmonic heating are provided here. Discrete spectral features shifted from the transmit frequency ordered by harmonics of the ion gyro-frequency were observed for third electron gyro-harmonic heating for the first time at a recent campaign at a High Frequency Active Auroral Research Program Facility HAARP. These features were also closely correlated with a broader band feature at a larger frequency shift from the transmit frequency known as the Downshifted Peak DP. The power threshold of these spectral features was measured, as well as their behavior with heater<br />beam angle, and proximity of the transmit frequency to the third electron gyro-harmonic frequency. Comparisons were also made with similar spectral features observed during 2nd<br />electron gyro-harmonic heating during the same campaign. A theoretical model is provided<br />that interprets these spectral features as resulting from parametric decay instabilities in<br />which the pump field ultimately decays into high frequency upper hybrid/electron Bernstein<br />and low frequency neutralized ion Bernstein IB and/or obliquely propagating ion acoustic<br />waves at the upper hybrid interaction altitude. Coordinated optical and SEE observations<br />were carried out in order to provide a better understanding of electron acceleration and precipitation<br />processes. Optical emissions were observed associated with SEE gyro-harmonic<br />features for pump heating near the second electron gyro-harmonic during the campaign. The<br />observations affirm strong correlation between the gyro-structures and the airglow. / Ph. D.

Fibre reinforced polymer matrix composites are used frequently in aerospace applications. Manufacturers of aerospace components favour composites over traditional metallic alloys due to their light weight, high modulus, corrosion resistance and fatigue resistance. Advantages of composites for non-structural interior components over metallic include: ease of manufacturing for single parts of complex geometry as opposed to assemblies, cheaper manufacturing of a limited series of parts and composites greatly reduced noise, vibration and harshness. However, manufacturing interior composite components requires critical attention to detail during the preforming stages and handling of dry fabric textiles. Since these components are handmade they often yield lower profits and therefore efficient preforming is critical. Designing draping strategies for industrial liquid composite moulding processes requires a significant amount of time and testing, in simulation and also working on physical moulds. Mould and part surfaces are often defined by a number of geometric features, labelled base surfaces in the context of this thesis, which can be used to quickly probe multiple draping strategies and identify the best one. Traditionally, trial and error work is performed over a full mould surface until a working or acceptable draping strategy is found, rarely identifying the best strategy. The work in this thesis presents the initial development stages for a draping predictive tool aimed at quickly probing multiple draping scenarios in simulation prior to receiving moulds and identifying the best draping strategy for industrial non-structural aerospace composites. A multi-parameter remodelling tool – the conical frustum – was developed for uniformly identifying base surfaces through 12 geometric parameters linked into a database of in-plane shear and yarn orientations results. The development of the database is discussed, detailing Taguchi methods of experimental design used for developing linear functions from the database results, which allow interpolation of results on base surfaces that do not directly exist within the database. This thesis also includes major developments for the core draping algorithm used for linking individual base surface results together when probing draping strategies. Further investigations were performed on unique elements of in-plane shear behaviour that are encountered during draping, so that these could ultimately be considered during the development of this version of the draping algorithm whilst others may be included in future developments.

The aim of this qualitative case study was to investigate the process of the enactment of a project-based learning method in an Advanced Placement American Government and Politics course and the effects of contextual factors, the beliefs of the teacher, and environmental factors had on the planning and implementation of PBL-aligned tasks. This study also investigates the experiences and perceptions of students in an Advanced Placement American Government and Politics course that enacted project-based learning. The study was conducted to add to the literature on project-based learning. Research on the steps a teacher takes to enact project-based learning can enhance understanding of the method and provide an increased understanding of implementation. This was a qualitative case study. The research was gathered using narrative inquiry, examination of documents, and observations to investigate teacher enactment of a project-based learning task. Semi-structured video-elicitation interviews, document analysis, and observations were conducted to investigate the experiences and perceptions of students who used project-based learning tasks in an Advanced Placement American Government and Politics class. The research of a teacher enacting project-based learning resulted in the identification of teacher’s beliefs as the foundational element for constructing pedagogy. Through the enactment of project-based learning, three themes emerged: the need for communication, alignment of tasks to key concepts, and flexibility. The perceptions of students in an Advanced Placement American Government and Politics course confirmed the importance of student choice, the value of collaborative and social learning experiences, and the desire to discuss controversial issues.

It is impossible to determine the amount of money that is spent every replacing products damaged from wear, but it is safe to assume that it is in the millions of dollars. With metallic materials, liquid lubricants are often used to prevent wear from materials rubbing against one another. However, with polymeric materials, liquid lubricants cause swelling, creating an increase in friction and therefore increasing the wear. Therefore, a different method or methods to mitigate wear in polymers should be developed. For better understanding of the phenomenon of wear, scratch resistance testing can be used. For this project, classic molecular dynamics is used to study the mechanics of nanometer scale scratching on amorphous polymeric materials. As a first approach, a model was created for polyethylene, considering intramolecular and intermolecular interactions as well as mass and volume of the CH2 monomers in a polymer chain. The obtained results include analysis of penetration depth and recovery percentage related to indenter force and size.

Rail wear can result in extensive costs for the track owner if it is not predicted and preventedin an efficient way. To limit these costs, one measure is to predict rail wear through wear simulations. The purpose with this work is to perform simulations of successive rail wear on the Swedish light rail line Tvärbanan in Stockholm, by means of the track-vehicle dynamics software GENSYS in combination with a wear calculation program developed in MATLAB. The simulation procedure is based on a methodology with a simulation set design, where the simulations to be performed are selected through a parametric study. The simulations include track-vehicle simulations, where the wheel-rail contact is modelled according to the Hertzian contact theory together with Kalker’s simplified theory (including the numerical algorithm FASTSIM). The results from the track-vehicle simulations serve as input to the wear calculations. When modelling rail wear Archard’s wear model has been used, including wear coefficients based on laboratory measurements. The measurements have been performed under dry conditions, so the wear coefficients under lubricated conditions (both natural and deliberate lubrication) are reduced by factors estimated by field observations. After the wear depth calculations the wear distribution is smoothed and the rail profile is updated. The simulation procedure continues with a new wear step as long as the desired tonnage is not attained. Four curves of Tvärbanan with different curve radii, ranging from 85 to 410 m, have beenstudied in this work. On three of the curves the high rail is deliberately lubricated, whereas no lubrication has been applied in the widest curve. The vehicle operating the light rail line is an articulated tram with two motor end bogies and one intermediate trailer bogie. The line was opened in August 1999 and extended in one direction one year later. Rail profile measurements have been carried out by SL since March 2002. The traffic tonnage at the selected sites from the opening of the line to the last measurement occasion (September2004) is at most 8.9 mega gross ton per track. The results of the rail wear prediction tool are evaluated by comparing worn-off area of the simulated rail profiles with that of the measured rail profiles. Simulated and measured resultsdo not agree too well, since the simulated rail wear is more extensive than the measured one, especially on the outer rail. However, the shapes of the simulated worn rail profiles are comparable to those of the measured rail profiles. / QC 20101123

No description available.

The intermetallic compound TiAl possesses a unique complex of properties that include sufficiently low material density, high values of the strength-to-ductility ratio, high elastic moduli, high oxidation resistance, low creep rate, and improved fatigue characteristics. These properties make TiAl alloys very attractive, particularly for structural applications for aerospace and aeronautic industries, where, at certain temperatures, they might be capable of replacing heavy nickel-based superalloys. However, so far applications of TiAl alloys have been limited by their poor ductility. Many of the recent studies have focused on the source of this limited ductility and on methods to improve this property. It has been found out experimentally that the strength and ductility of $gamma$-TiAl alloys can be affected by many different parameters, including alloy stoichiometry, heat treatment, deformation temperature, impurity content, grain size, and ternary element additions. In this thesis we present the results of our computer simulations of deformation and fracture in TiAl. In contrast to many previous studies our simulations include the interaction of the crack with point defects in the lattice. We use the molecular statics technique with atomic interactions described in terms of the embedded atom method. We simulate the crack propagation along (100), (001), (110) and (111) planes in TiAl. The cleavage along (100) and (001) planes shows purely brittle behavior, whereas the cleavage along (110) and (111) planes is accompanied by extensive dislocation emission. Our studies of the crack interaction with point defects reveal that vacancies and antisites near the crack tip can influence the amount of plastic deformation. Another important observation is that the antisite formation energy near the crack tip is generally lower than in the perfect lattice. This observation suggests the formation of relatively disordered zones near the crack tip at high temperatures, and leads us to a formulation of a new mechanism of a brittle-to-ductile transition in TiAl. / Ph. D.

Distance education (DE) can address barriers to training nutrition professionals by offering a convenient, flexible and efficient way of learning. One particularly valuable teaching tool in DE is the use of computer-based simulations (CBS). CBS stimulates confidence building, acquisition of new knowledge, exposure to new and challenging patient cases in a safe learning environment, development of communication and critical thinking skills, and the cultivation of sensitivity towards patient needs. Despite the benefits, there is a lack of research examining dietetic educator’s perceptions of and experience with CBS. Goals of this study were to determine: 1) whether dietetic program educators were open to the idea of using CBS and how these responses varied in relation to different factors, and 2) dietetic program educators’ perceptions of the benefits and barriers of using CBS. Secondary data analyses were conducted on a15-item survey developed by the American Dietetic Association (ADA). Surveys contained two qualitative questions and 13 quantitative questions related to CBS. Surveys were e-mailed via the ADA listserv to 535 program directors, including Dietetic Internship Programs (DI), Coordinated Programs in Dietetics (CP), Didactic Programs in Dietetics (DPD), and the Dietetic Technician Programs (DT). A total of 165 individuals responded to the survey. The majority of respondents were open to the use of CBS (n=117) and a small number were not open (n=24). Respondents open to CBS were more likely to 1) not prefer face-to-face communication with their students and colleagues 2) currently be using online case studies and simulations 3) be using standardized patients in supervised practice 4) believe that dietetics education needs alternatives to traditional supervised practice such as CBS 5) believe that they have IT and financial support from their administration 6) have medical simulation laboratories available for dietetics students 7) believe that they had the technological skills needed to use CBS. Educators commented on the potential for CBS to address the shortage of preceptors and facilities available for supervised practice, in addition to enhancing and expediting learning in various settings. Perceived barriers, included the idea that technology impedes learning and a concern about the resources needed to implement CBS. Understanding the perspectives and practices of education program directors is a crucial component of furthering the process of incorporating CBS into nutrition education. This is exciting new terrain for nutrition education and moving forward with research in both distance education and CBS will be beneficial to enhancing nutrition and dietetics education in DE, traditional classroom settings and in supervised practice.

No description available.