There is no evidence in the literature of biomechanical stability characteristics comparing conventional rectangular screw placement with that of an angled mono-cortical screw plating system where standard 2mm diameter screws are applied at angles more acute than conventional 90° screws, through plate holes machined (cut) for a definite specific screw angle placement P. Angled screws will have an obvious clinical advantage of direct line of vision insertion, through an intra-oral route without the disadvantage of trans-buccal (cutaneous) approach required for conventional 90° rectangular screw application. Angled screw application will result in the prevention of possible, less post-operative swelling, nerve fall out (motor and/or sensory), haematoma, false aneurysm and scarring as unwanted clinical complications associated with trans-buccal extra-oral surgical technique. Intra-oral angled screw application will result in definitive cost saving due to less operating time required. Post-treatment removal of angled screws is uncomplicated, requiring only intra-oral surgical approach, without trochar use or skin incisions for screwdriver application. By determining angle displacement values at certain clinical relevant force values for both compression/tension and torsion, preference can be established for ideal angle(s) of screw application in a plating system. An own unique, designed and manufactured, jig and inclined screw insertion (ISI) plates were implemented during the biomechanical evaluation of stability at different screw angle applications in a Zwick machine. For the purpose of this biomechanical comparative investigation an inclined screw insertion (ISI) plate was manufactured with 90°, 75°, 60° and 45° angled plate holes orientated in line with the long-axis (quadrant 3) of the distal section of the plates and diagonal across (quadrant 1) in the proximal section of the plates. Screws with an ISI angle of 30° in any quadrant application resulted in lifting the plate from the bone surface and caused cortical bone destruction during pilot drilling. The results for mono-cortical 7mm screw placement proved superior in biomechanical stability during tension/compression - forces for screw insertion angles of 60° and 45°, when compared to conventional 90° rectangular screw placement. Screws inserted at an angle of 75° demonstrated no improvement in compression/tension stability when compared with 90°.Torsion force stability for all of the 75°, 60° and 45° inclined screw insertion (ISI) systems proved more stable compared to conventional 90° screw angle plates. It is concluded that angled monocortical screw placement between angles 60° and 45° has clinical significance as far as stability, intra-oral surgical technique and time-cost factor is concerned. The results of this biomechanical behaviour investigation of ISI, evolved new terminology such as screw-tip shifting, screw-tip travel, lag potential and clinical significance for the range of screw angle placement. Angled orientation to the plate design and plate geometry is also defined in terms of tension line distribution in the anatomical region for application in the mandible. An unique quadrant description for ISI is described for future communication. An international patent, based on the ISI principle, has been registered for monocortical six-hole plates of firstly different geometric designs to conform to specific anatomical topographic sites in the mandible and secondly specific screw plate-holes angled at 60° in different orientation to the plate (Patent:PCT/EP 2006/006365), (Addendum 6). A specific L-shaped, mandibular angle plate with screw holes at a 60° angle where orientation shifts from in-line with the long-axis of the plate in the distal three plate holes to diagonal orientation in the proximal section of the plate, is designed and manufactured by Stryker/Leibinger as an example of such a patent plate. It is recommended that a smart-lock plate with plate holes at 55° angles be manufactured to allow screw angle placements of 65° - 45° in different angle orientations. Pilot hole drilling and ISI can be performed without the use of a drill-guide. / Thesis (PhD)--University of Pretoria, 2009. / Maxillo-Facial and Oral Surgery / unrestricted

A direct consequence of hierarchical galaxy formation is the existence of dual supermassive black holes, which may be preferentially triggered as active galactic nuclei (AGNs) during galaxy mergers. Despite decades of searching, however, dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 100 morphologically identified interacting galaxies or mergers that display red mid-infrared colors often associated in extragalactic sources with powerful AGNs. The vast majority of these advanced mergers are optically classified as star-forming galaxies, which suggests that they may represent an obscured population of AGNs that cannot be found through optical studies. In this work, we present Chandra/ACIS observations and near-infrared spectra with the Large Binocular Telescope of six advanced mergers with projected pair separations less than similar to 10 kpc. The combined X-ray, near-infrared, and mid-infrared properties of these mergers provide confirmation that four out of the six mergers host at least one AGN, with four of the mergers possibly hosting dual AGNs with projected separations less than similar to 10 kpc, despite showing no firm evidence for AGNs based on optical spectroscopic studies. Our results demonstrate that (1) optical studies miss a significant fraction of single and dual AGNs in advanced mergers, and (2) mid-infrared pre-selection is extremely effective in identifying dual AGN candidates in late-stage mergers. Our multi-wavelength observations suggest that the buried AGNs in these mergers are highly absorbed, with intrinsic column densities in excess of similar to N-H > 10(24) cm(-2), consistent with hydrodynamic simulations.

Ce travail de thèse se concentre sur l'approche non-perturbative canonique à la formulation d'une théorie quantique de la gravitation dans le cadre de la Gravitation quantique à boucles (LQG), répondant à deux problèmes majeurs. Dans la première partie, nous étudions la possible quantification, dans le cadre de la LQG, de la gravité en trois dimensions avec constante cosmologique et nous essayons de prendre contact avec autres approches de quantification déjà existantes dans la littérature. Dans la deuxième partie, nous nous concentrons sur une application très importante de la LQG: la définition et le comptage des états microscopiques d'un ensemble en mécanique statistique qui fournit une description de l'entropie des trous noirs. Notre analyse s'appuie fortement sur et s'étend à un traitement manifestement SU(2) invariant les travaux fondateurs de Ashtekar et al. / This thesis work concentrates on the non-perturbative canonical approach to the formulation of a quantum theory of gravity in the framework of Loop Quantum Gravity (LQG), addressing two major problems. In the first part, we investigate the possible quantization, in the context of LQG, of three dimensional gravity in the case of non-vanishing cosmological constant and try to make contact with alternative quantization approaches already existing in the literature. In the second part, we concentrate on a very important application of LQG: the definition and the counting of microstates of a statistical mechanical ensemble which provides a description and accounts for the black hole entropy. Our analysis strongly relies on and extends to a manifestly SU(2) invariant treatment the seminal work of Ashtekar et al.

Automated narrow-gap girth-butt welds are replacing conventional welding methods to join sections of austenitic stainless steel pipe in the primary circuit of Pressurised Water Reactors, to reduce manufacturing costs and improve quality. To ensure the safe operation of these systems, reliable structural integrity assessments have to be undertaken, requiring the mechanical properties of welded joints to be characterised alongside the weld residual stress magnitude and distribution.This research project characterised, for the first time, the weld residual stress field and the tensile and ductile fracture toughness properties of a 33 mm thick narrow-gap 304L stainless steel pipe weld. The residual stress was characterised using two complementary approaches: deep hole drilling and neutron diffraction. A novel neutron diffraction scanning technique was developed to characterise the residual stress field, without cutting an access window into the component, leaving the original weld residual stress field undisturbed. A modified deep hole drilling technique was developed to characterise the residual stress retained in fracture mechanics specimens extracted from the pipe weld in two orientations. The modified technique was shown to measure the original weld residual stress field more accurately than through conventional deep hole drilling. Residual stresses, exceeding 50% of the weld material proof strength, were retained in axially-orientated fracture mechanics specimens.Tensile tests showed that the weld was approximately 60% overmatched. It was demonstrated that neither retained residual stress, nor specimen orientation, had a discernible effect on the measured fracture toughness of the weld material. In less ductile materials, however, the level of retained residual stress may unduly influence the measurement of fracture toughness. At initiation, the fracture toughness properties of both the parent and weld materials were far in excess of the measuring capacity of the largest fracture mechanics specimens that could be machined from the weld.The influence of residual stress and fracture toughness on the performance of narrow-gap welded pipework was investigated. Full elastic-plastic finite element analyses were used to model the pipe weld, containing a postulated defect under combined primary and secondary loading. The results, applied within the framework of an R6 structural integrity assessment, compared different plasticity interaction parameters on the prediction of failure load; the conventional ρ-parameter approach was compared with the recently developed, more advanced, g-parameter. It was shown that the g-parameter significantly reduced the conservatism of the ρ-parameter approach. However, for this pipe weld, plastic collapse was predicted to precede failure by ductile initiation, suggesting that a plastic collapse solution may be an appropriate failure criterion to use in structural integrity assessments of similar component and defect combinations.

The random deployment of Wireless Sensor and Actuator Network (WSAN) nodes in areas often inaccessible, results in so-called coverage holes – i.e. areas in the network that are not adequately covered by nodes to suit the requirements of the network. Various coverage protocol algorithms have been designed to reduce or eliminate coverage holes within WSANs by indicating how to move the nodes. The effectiveness of such coverage protocols could be jeopardised by inaccuracy in the initial node location data that is broadcast by the respective nodes. This study examines the effects of location inaccuracies on five sensor deployment and reconfiguration algorithms – They include two algorithms which assume that mobile nodes are deployed (referred to as the VEC and VOR algorithms); two that assume static nodes are deployed (referred to as the CNPSS and OGDC algorithms); and a single algorithm (based on a bidding protocol) that assumes a hybrid scenario in which both static and mobile nodes are deployed. Two variations of this latter algorithm are studied. A location simulation tool was built using the GE Smallworld GIS application and the Magik programming language. The simulation results are based on three above-mentioned deployment scenarios; mobile, hybrid and static. The simulation results suggest the VOR algorithm is reasonably robust if the location inaccuracies are somewhat lower than the sensing distance and also if a high degree of inaccuracy is limited to a relatively small percentage of the nodes. The VEC algorithm is considerably less robust, but prevents nodes from drifting beyond the boundaries in the case of large inaccuracies. The bidding protocol used by the hybrid algorithm appears to be robust only when the static nodes are accurate and there is a low degree of inaccuracy within the mobile nodes. Finally the static algorithms are shown to be the most robust; the CPNSS algorithm appears to be immune to location inaccuracies whilst the OGDC algorithm was shown to reduce the number of active nodes in the network to a better extent than that of the CPNSS algorithm. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Computer Science / unrestricted

Para muitos componentes e estruturas de engenharia a determinação precisa do estado de tensões residuais presente é de fundamental importância para a avaliação de sua integridade estrutural. O método do furo cego (MFC) é um dos métodos mais difundidos para a medição de tensões residuais, no entanto, por se tratar de um ensaio relativamente complexo, a determinação da sua incerteza de medição apresenta uma série de dificuldades, as quais se refletem na inexistência de estudos na literatura que abordem esse assunto de forma completa. Este trabalho tem como objetivo a determinação da incerteza de medição do MFC englobando todas as fontes de incerteza em potencial do método. Para tanto, foi elaborado um procedimento envolvendo a determinação e caracterização das fontes de incerteza tanto na parte experimental como no tratamento matemático dos dados. A partir da caracterização das fontes de incerteza detectou-se como fator principal na determinação da incerteza o erro do operador, que foi possível através do desvio de repetitividade. A fonte de incerteza devido ao erro do operador foi a de determinação mais complexa e envolveu o projeto e a construção de uma máquina especialmente desenvolvida para a aplicação de um estado de tensões homogêneo e que permitisse medir com precisão as tensões residuais com o método do furo cego. Técnicas de medição de tensões residuais por difração de raios-X e monitoramento de tensão com extensometria de resistência elétrica foram utilizadas para a verificação da homogeneidade das tensões nas amostras. A metodologia se mostrou adequada, conduzindo a resultados que permitiram determinar com sucesso a incerteza de medição através de planilhas eletrônicas. / The characterization of the residual stress state of engineering components and structures is of fundamental importance for assessments of their structural integrity. The hole drilling method is one of the most commonly used methods; however, due to its relative complexity, quantifying its measurement uncertainties is not straightforward. It is a semi-destructive method, which means that multiple measurements cannot be repeated in a same location, and stress distributions mean that it is difficult to guarantee that a number of points in the same state will be available in a given volume. This study suggests a global uncertainty measurement which includes a study of repeatability related to the operator. This is thought to be novel in the existing literature. For this, a standard sample and a machine which guarantees a homogeneous stress distribution in the sample were developed. To ensure the homogeneity of the stresses, x-ray diffraction measurements were performed. The results obtained show good repeatability for different operators and good results for the uncertainty of measurements for the method.

Tesis para optar al grado de Magíster en Minería / La excavación de galerías subterráneas es una actividad fundamental en las minas explotadas por hundimiento, debido a que abre los frentes de trabajo para todas las actividades que se ejecutan posteriormente. Por tal razón, mejorar los tiempos de ejecución de esta tarea permitirá adelantar la entrada en producción de un proyecto de explotación de minería subterránea. Así mismo, la prefabricación de elementos de hormigón armado como solución a la construcción de infraestructura minera necesaria para la explotación de sectores en preparación, nace como una alternativa a la construcción de obras civiles convencionales. Este tipo de soluciones transforman la tarea de construcción in situ en una tarea de montaje, donde los elementos son fabricados en una planta por métodos de producción industrial quedando disponible para ser transportados a la obra y montados en el lugar definido. Sin embargo, su utilización en infraestructura minera aún es incipiente debido a la escasa información acerca de los beneficios, ventajas y mejoras en la productividad que se logran con este nuevo sistema. El presente trabajo de tesis tiene como objetivo principal reducir los costos y mejorar rendimientos de las actividades de Preparación Minera, estableciendo una metodología a través de la optimización de los procesos de Desarrollo y Construcción de infraestructura, con el fin de adelantar la disposición de mineral a la producción. Para llevar a cabo este estudio, del punto de vista técnico, se efectuó una revisión bibliográfica relacionada con la excavación de galerías subterráneas mediante la metodología Desarrollo Rápido (Rapid development) y la industrialización y prefabricación de elementos estructurales de hormigón, su aplicación en proyectos de infraestructura y tunelería civil. De la misma manera, desde el punto de vista de la gestión, se revisó detalladamente cómo se realiza funcionalmente la preparación minera a través del estudio en profundidad de la Dirección de Proyecto Preparación de Minas, entidad encargada de ejecutar los proyectos al interior de la División El Teniente. El diagnóstico integral de la preparación minera en la División El Teniente, donde se analiza cómo se ejecuta esta actividad del punto de vista de un proyecto operacional, permitió plantear una hipótesis sobre la optimización de los procesos de preparación minera basado en dos ámbitos: la gestión y las operaciones de desarrollo y construcción. En el ámbito de gestión se realizó un plan estratégico, basado en el plan de negocio divisional PND 2010, que entrega la cantidad de obra necesaria para sustentar la producción en el quinquenio 2011-2015, el que permitió establecer una mirada a mediano y largo plazo para la continuidad de esta actividad en la División El Teniente. En el ámbito de operaciones, se trabajó en las actividades más relevantes; por una parte la excavación de galerías o desarrollos horizontales y por otra dos tipos de obras civiles que representan la mayor inversión anual en la preparación minera, la construcción de puntos de extracción y muros de confinamiento. El resultado de este estudio, permite concluir que si bien es cierto, la aplicación de la metodología de desarrollo rápido es factible en el método de hundimiento por Block Caving de la mina El Teniente, ésta no es aplicable en su totalidad debido a las solicitaciones dinámicas asociadas a los eventuales estallidos de roca que impiden la eliminación de la malla como solución de fortificación y las interferencias que generan los distintos tipos de turnos y aislaciones por tronadura que se ejecutan en horarios definidos para las faenas de extracción de mineral, los que no son compatibles con los turnos de obras o preparación minera. En el caso de las obras civiles las pruebas se validaron con resultados superiores a las expectativas planteadas, es decir, ahorros de costos superiores al 20 % para los distintos elementos de infraestructura estudiados, donde además se obtuvieron mejoras intangibles como la descongestión de los portales de ingreso a la mina (ADIT) y la logística de abastecimiento de materiales.

As the technology underlying modern electronics advances, it is unlikely that previous rates of power use and computational speed improvement can be maintained. Devices using the spin of an electron or hole, "spintronic" systems, can begin to address these problems, creating new devices which can be used as a continuation and augmentation of existing electronic systems. In addition, spintronic devices could make special use of coherent quantum states, making it feasible to address certain problems which are computationally intractable using classical electronic components. Unlike higher-dimensional nanostructures such as quantum wires and wells, quantum dots allow a single electron or hole to be confined to the dot. Through the spin-orbit effect, the electron and hole g-tensor can be influenced by quantum dot shape and applied electric fields, leading to the possibility of gating a single quantum dot and using a single electron or hole spin for quantum information storage or manipulation. In this thesis, the spin of electrons and holes in isolated semiconductor quantum dots are investigated in the presence of electric and magnetic fields using realspace numerical 8-band strain-dependent k · p theory. The calculations of electron and hole g-tensors are then used to predict excitonic g-tensors as a function of electric field. These excitonic g-factors are then compared against existing experimental work, and show that in-plane excitonic g-factor dependence on electric field is dominated by the hole g-factor. The dependence of the electron and hole g-tensors on the applied electric field are then used to propose a class of novel quantum dot devices which manipulate the electron or hole spins in either a resonant or a non-resonant mode. Because of the highly parabolic dependence of some components of the hole g-tensor on the applied electric field, a shift in the Larmor frequency and an additional resonance are predicted, with additional shifts and resonances occurring for higher-order dependencies. Spin manipulation times down to 3.9ns for electrons and 180ps for holes are reported using these methods.

Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 119-126). / Developing accurate and computationally efficient models for ocean acoustics is inherently challenging due to several factors including the complex physical processes and the need to provide results on a large range of scales. Furthermore, the ocean itself is an inherently dynamic environment within the multiple scales. Even if we could measure the exact properties at a specific instant, the ocean will continue to change in the smallest temporal scales, ever increasing the uncertainty in the ocean prediction. In this work, we explore ocean acoustic prediction from the basics of the wave equation and its derivation. We then explain the deterministic implementations of the Parabolic Equation, Ray Theory, and Level Sets methods for ocean acoustic computation. We investigate methods for evolving stochastic fields using direct Monte Carlo, Empirical Orthogonal Functions, and adaptive Dynamically Orthogonal (DO) differential equations. / As we evaluate the potential of Reduced-Order Models for stochastic ocean acoustics prediction, for the first time, we derive and implement the stochastic DO differential equations for Ray Tracing (DO-Ray), starting from the differential equations of Ray theory. With a stochastic DO-Ray implementation, we can start from non-Gaussian environmental uncertainties and compute the stochastic acoustic ray fields in a reduced order fashion, all while preserving the complex statistics of the ocean environment and the nonlinear relations with stochastic ray tracing. We outline a deterministic Ray-Tracing model, validate our implementation, and perform Monte Carlo stochastic computation as a basis for comparison. We then present the stochastic DO-Ray methodology with detailed derivations. We develop varied algorithms and discuss implementation challenges and solutions, using again direct Monte Carlo for comparison. / We apply the stochastic DO-Ray methodology to three idealized cases of stochastic sound-speed profiles (SSPs): constant-gradients, uncertain deep-sound channel, and a varied sonic layer depth. Through this implementation with non-Gaussian examples, we observe the ability to represent the stochastic ray trace field in a reduced order fashion. / by Michael Jesus Humara. / S.M. / S.M. Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution)

Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), September, 2020 / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 97-102). / Robotic swarms are becoming increasingly complex on the surface and in air due to highspeed and reliable communication links, Global Positioning Satellites (GPS), and visual support to relative navigation. However, the limited propagation of these signals in the ocean has impacted similar advances in undersea robotics. Autonomous underwater vehicles (AUVs) often rely on acoustics to inform navigation solutions; however, this approach presents challenges for scalable robotic swarms. Acoustic navigation is a means to inform range and bearing to a target. Many methods for range and bearing estimation, including current low-cost solutions, rely on precision time synchronization or two-way communication to compute ranges as part of a full navigation solution. The high cost of reliable Chip-scale atomic clocks (CSACs) and acoustic modems relative to other vehicle components limits large-scale swarms due to the associated cost-per-vehicle and communications infrastructure. / We propose a single, high-cost vehicle with a reliable navigation solution as a "leader" for a scalable swarm of lower-cost vehicles that receive acoustic signals from a source onboard the lead vehicle using a single hydrophone. These lower-cost "followers" navigate relative to the leader according to the preferred behavioral pattern, but for simplicity, we will refer to a simple following behavior in this work. This thesis outlines a method to obtain range estimates to sound sources in which the signal content, including frequency and power at its origin, can be reasonably approximated. Total transmission loss is calculated based on empirical equations for the absorption of sound in seawater and combined with geometric spreading loss from environmental models to estimate range to a source based on the loss at differential frequencies. We refer to this calculation as the signal absorption-based range estimator (SABRE). / This method for obtaining range combines with Doppler-shift methods for target bearing based on the maximum frequency detected within a banded limit around a known source frequency. A primary objective for SABRE is to address techniques that support low-cost options for undersea swarming. This thesis's contributions include a novel method for range estimation onboard underwater autonomous vehicles that supports navigation relative to a known source when combined with Doppler-shift methods for target bearing. This thesis seeks to develop the theory, algorithms, and analytical tools required and apply those tools to real-world data sets to investigate the feasibility, sources of error, and accuracy of this new approach to range estimation for underwater swarms. / by Brendan O'Neill. / S.M. / S.M. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution)