Thesis (M.Sc.)--Memorial University of Newfoundland, 2006. / Bibliography: leaves 115-116. Also available online.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 126-133).

Une turbulence inhomogène est étudiée expérimentalement dans un contexte lagrangien. La mesure des trajectoires de traceurs lagrangiens et de particules inertielles a été effectuée dans un canal plan turbulent et a été utilisée pour obtenir des statistiques lagrangiennes conditionnées à leur distance initiale par rapport à la paroi. Ces mesures à haute résolution en temps et en espace fournissent les trois composantes de la position, la vitesse et l'accélération le long de la trajectoire d'une particule individuelle depuis des distances très proches de la paroi (~10 unités de paroi) jusqu'au centre du canal. Les corrélations temporelles lagrangiennes ont permis la mesure directe des échelles de temps de la vitesse et l'accélération dans chacune des trois directions. Ces échelles caractérisent l'inhomogénéité et l'anisotropie du canal turbulent dans une perspective lagrangienne. Une anisotropie à petite échelle, quantifiée par la "skewness", et les corrélations entre composantes de l'accélération sont observées dans tout le canal. Une séparation d'échelle significative entre les composantes de l'accélération et son amplitude a été mesurée au travers du canal notamment dans la zone proche de la paroi. Deux classes de particules inertielles ont été étudiées permettant ainsi la comparaison directe entre statistiques des traceurs et des non-traceurs dans la zone de fort cisaillement et de forte anisotropie proche de la paroi jusqu'à la région plus homogène du centre. Les propriétés statistiques des particules inertielles dans le canal turbulent sont significativement différentes de celles observées en turbulence homogène isotrope. Ces statistiques sont les ingrédients nécessaires à la construction de modèles stochastiques lagrangiens pour la prédiction de la dispersion et du mélange en turbulence inhomogène. / Inhomogeneous turbulence is experimentally investigated in a Lagrangian framework. Measurements of tracer and non-tracer particles in a turbulent channel were made, and were used to extract Lagrangian statistics conditioned on their initial distance to the channel wall. Highly resolved in time and space, these measurements provide the three components of position, velocity, and acceleration along a particle trajectory from very close to the channel wall ($y^+approx 10$) to the channel center. Lagrangian time correlations allow the direct measurement of velocity and acceleration timescales in each direction, and characterize the inhomogeneity and anisotropy of the turbulent channel from the Lagrangian perspective. Small scale-anisotropy, characterized by the skewness and the correlation of the components of the acceleration, was found to be significant throughout the channel. Significant scale separation between the magnitude and components of acceleration was found across the channel, even in the near-wall region. Two classes of non-tracer particle trajectories were also measured, allowing direct comparison of tracer and non-tracer statistics from the highly-sheared anisotropic zone near the channel wall to the more homogeneous outer layer. Non-tracer acceleration statistics in the turbulent channel were found to be significantly different from similar results in homogeneous, isotropic turbulence. These statistics are necessary components of advanced Lagrangian stochastic models to predict dispersion and mixing in inhomogeneous turbulence.

No description available.

In this thesis, the effect of inhomogeneous pre-stress on elastic wave propagation and scattering in nonlinear elastic materials is investigated. Four main problems are considered: 1. torsional wave propagation in a pre-stressed annular cylinder, 2. the scattering of horizontally polarised shear waves from a cylindrical cavity in a pre-stressed, infinite, nonlinear elastic material, 3. the use of pre-stress to cloak cylindrical cavities from incoming horizontally polarised shear waves, and 4. the scattering of shear waves from a spherical cavity in a pre-stressed, infinite, nonlinear elastic material.It is observed that waves in a hyperelastic material are significantly affected by pre-stress, and different results are obtained from those which would be obtained if the underlying stress was neglected and only geometrical changes were considered. In Chapter 3 we show that the dispersion curves for torsional waves propagating in an annular cylinder are strongly dependent on the pre-stress applied. A greater pressure on the inner surface than the outer causes the roots of the dispersion curves to be spaced further apart, whereas a greater pressure on the outer surface than the inner causes them to be spaced closer together. We also show that a longitudinal stretch causes the cut-on frequencies to move closer together and decreases the gradient of the dispersion curves, whilst a longitudinal compression causes the cut-on frequencies to move further apart and increases the gradient of the dispersion curves. In Chapter 4 we observe that pre-stress affects the scattering coefficients for shear waves scattered from a cylindrical cavity. It is shown that, for certain parameter values, the scattering coefficients obtained in a pre-stressed medium are closer to those that would be obtained in the undeformed configuration than those that would be obtained in the deformed configuration if the pre-stress were neglected. This result is utilised in Chapter 5 where the cloaking of a cylindrical cavity from horizontally polarised shear waves is examined. It is shown that neo-Hookean materials are optimal for this type of cloaking. A stonger dependence of the strain energy function on the second strain invariant leads to a less efficient cloak.We observe that, for a Mooney-Rivlin material, as S1 tends from 1 towards 0 (in other words, as a material becomes less dependent on the first strain invariant, and more dependent on the second strain invariant), there is more scattering from the cloaking region. For materials which are strongly dependent on the second strain invariant the pre-stress actually increases the scattering cross-section relative to the scattering cross-section for an unstressed material, hence these materials are unsuitable for pre-stress cloaking.Finally, in Chapter 6 we study the effect of pressure applied to the inner surface of a spherical cavity and at infinity on the propagation and scattering of shear waves in an unbounded medium. It is shown that the scattering coefficients and cross-sections for this problem are strongly dependent on the pre-stress considered. We observe that a region of inhomogeneous pre-stress can lead to some counterintuitive relationships between cavity size and scattering cross-sections and coefficients.

No description available.

Es erfolgt eine Darstellung der theoretischen Grundlagen, die für die Berechnung von inhomogenen optimalen Vektoren nötig sind. Diese Vektoren maximieren die Reaktion auf ein vorgegebenes Antriebsfeld und besitzen nach Ablauf der Optimierungszeit die größtmögliche kinetische Energie. Die inhomogenen optimalen Vektoren sind eng mit den Nullstellen der Nebenbedingung der Optimierungsaufgabe verknüpft, die die Gestalt eines Polynoms besitzt. Der Grad dieses Polynoms ist von der verwendeten Modellauflösung abhängig. Anhand eines barotropen Modells, welches um einen klimatologischen 300 hPa Grundstrom linearisiert ist, wird die Sensitivität der Störungen in Abhängigkeit von der Stärke des Antriebes untersucht. Das für die Berechnung der inhomogenen optimalen Vektoren benötigte Antriebsfeld ist die optimal korrelierte Stromfunktionstendenz im Falle eines blockierenden Hochs über dem Atlantik. Die Gestalt und Position der resultierenden Störungen besitzt Ähnlichkeiten mit beobachteten Blocking-Dipolen. / For linear inhomogeneous problems, a method is developed to maximize the response of a perturbation with fixed initial kinetic energy to a prescribed forcing field. These perturbations can be described as optimal, in the sense that they maximize linear disturbance growth (with respect to the kinetic energy) over a chosen integration period. The inhomogeneous optimal perturbations are found by calculating the roots of a polynomial, which represents the auxiliary condition of the optimization problem. The degree of this polynomial depends on the model truncation. For the numerical experiments a barotropic model triangularly truncated with global domain is used. The model is linearized about a 300 hPa climatological flow. The sensitivity of the inhomogeneous perturbations with respect to the strength of the forcing is investigated. The forcing needed for the calculation of the inhomogeneous optimal perturbations is the optimally correlated tendency field for the case of Atlantic blocking. The structure and position of the resulting perturbations are similar to observed blocking dipoles.

A new method, called chemical potential perturbation (CPP), has been developed to predict the chemical potential as a function of composition in molecular simulations. The CPP method applies a spatially varying external potential to the simulation, causing the composition to depend upon position in the simulation cell. Following equilibration, the homogeneous chemical potential as a function of composition can be determined relative to some reference state after correcting for the effects of the inhomogeneity of the system. The CPP method allows one to predict chemical potential for a wide range of composition points using a single simulation and works for dense fluids where other prediction methods become inefficient. For pure-component systems, three different methods of approximating the inhomogeneous correction are compared. The first method uses the van der Waals density gradient theory, the second method uses the local pressure tensor, and the third method uses the Triezenberg-Zwanzig definition of surface tension. If desired, the binodal and spinodal densities of a two-phase fluid region can also be predicted by the new method. The CPP method is tested for pure-component systems using a Lennard-Jones (LJ) fluid at supercritical and subcritical conditions. The CPP method is also compared to Widom's method. In particular, the new method works well for dense fluids where Widom's method starts to fail.The CPP method is also extended to an Ewald lattice sum treatment of intermolecular potentials. When computing the inhomogeneous correction term, one can use the Irving-Kirkwood (IK) or Harasima (H) contours of distributing the pressure. We show that the chemical potential can be approximated with the CPP method using either contour, though with the lattice sum method the H contour has much greater computational efficiency. Results are shown for the LJ fluid and extended simple point-charge (SPC/E) water. We also show preliminary results for solid systems and for a new LJ lattice sum method, which is more efficient than a full lattice sum when the average density varies only in one direction. The CPP method is also extended to activity coefficient prediction of multi-component fluids. For multi-component systems, a separate external potential is applied to each species, and constant normal component pressure is maintained by adjusting the external field of one of the species. Preliminary results are presented for five different binary LJ mixtures. Results from the CPP method show the correct trend but some CPP results show a systematic bias, and we discuss a few possible ways to improve the method.

We propose the use of depth-information to protect privacy in person-aware visual systems while preserving important foreground subjects and scene structures. We aim to preserve the identity of foreground subjects while hiding superfluous details in the background that may contain sensitive information. We achieve this goal by using depth information and relevant human detection mechanisms provided by the Kinect sensor. In particular, for an input color and depth image pair, we first create a sensitivity map which favors background regions (where privacy should be preserved) and low depth-gradient pixels (which often relates a lot to scene structure but little to identity). We then combine this per-pixel sensitivity map with an inhomogeneous image obscuration process for privacy protection. We tested the proposed method using data involving different scenarios including various illumination conditions, various number of subjects, different context, etc. The experiments demonstrate the quality of preserving the identity of humans and edges obtained from the depth information while obscuring privacy intrusive information in the background. / Computer and Information Science

<p>The propagation of light beams originating from synthetic ‘Type Ia’ supernovae, through an inhomogeneous universe with simplified dynamics, is simulated using a Monte-Carlo Ray-Tracing method. The accumulated statistical (redshift-magnitude) distribution for these synthetic supernovae observations, which is illustrated in the form of a Hubble diagram, produces a luminosity profile similar to the form predicted for a Dark-Energy dominated universe. Further, the amount of mimicked Dark-Energy is found to increase along with the variance in the matter distribution in the universe, converging at a value of Ω_X ≈ 0.7.</p><p>It can be thus postulated that at least under the assumption of simplified dynamics, it is possible to replicate the observed supernovae data in a universe with inhomogeneous matter distribution. This also implies that it is demonstrably not possible to make a direct correspondence between the observed luminosity and redshift with the distance of a cosmological source and the expansion rate of the universe, respectively, at a particular epoch in an inhomogeneous universe. Such a correspondences feigns an apparent variation in dynamics, which creates the illusion of Dark-Energy.</p>