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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Development of a dilatant damage zone along a thrust relay in a low-porosity quartz arenite

Cook, Jennie E., January 2005 (has links) (PDF)
Thesis (M.S.) -- University of Tennessee, Knoxville, 2005. / Title from title page screen (viewed on Feb. 6, 2006). Thesis advisor: William M. Dunne. Vita. Includes bibliographical references.
32

Can growth strata identify individual paleoearthquakes and characterize fold kinematics? : a case study from the La Laja fault system, Sierra de Villicum, Argentina /

Schultz, Emily S. January 1900 (has links)
Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 67-71). Also available on the World Wide Web.
33

Quasi-optimal steady state and transient maneuvers with and without thrust vectoring

Dwyer, Michael E. 29 September 2009 (has links)
Steady state and transient maneuver problems for a high performance fighter aircraft with and without thrust vectoring are investigated. The steady state aspect of these studies determines control combinations with and without thrust vectoring which optimize selected level-flight point performance criteria including minimum speed, maximum instantaneous range, and maximum sustained turn rate. The transient maneuvers are initiated from straight and level flight and include a longitudinal pitch-up to a desired fuselage pointing angle and a lateral-directional transition (wind-up) to a desired steady level turn rate. For the transient maneuvers, a full six-degree-of-freedom model of the aircraft is used with three conventional aerodynamic controls, throttle control and pitch and yaw thrust vectoring control. Each of the control time histories are parameterized so as to include both the rate and range limits of the controls. A nonlinear programming algorithm is used to determine the control parameter values which yield the minimum time to execute the prescribed maneuvers. Results indicate that thrust vectoring does not significantly change the steady state behavior in the scenarios investigated. However, flight times for the transient maneuvers are found to be reduced by up to 28%. The greatest effect of thrust vectoring occurs at low Mach number. / Master of Science
34

Flow Properties of Moine Thrust Zone Mylonites in Northern Assynt, NW Scotland

Roth, Benjamin Louis 11 January 2011 (has links)
Quartz-rich mylonites present along the Moine Thrust Zone are well suited for the application of various analytical techniques designed for investigating the flow processes by which rock deformation occurred. These analytical techniques were applied to a suite of samples from the footwall and hangingwall of the Moine thrust exposed along the Allt Pol aâ Mhadaich stream located in the northern part of the Assynt window. Vorticity analyses were performed to determine the relative contributions of pure and simple shear deformation within the penetratively deforming thrust sheets. Integration of vorticity data with 3D strain analyses demonstrated that sub-vertical shortening perpendicular to the flow plane, accompanied by thrust transport parallel extension, occurred during mylonitization, and was driven by emplacement of the overlying Moine nappe. Quartz c-axis fabrics in the mylonites are characterized by well-defined asymmetric Type-1 cross girdles in which internal and external skeletal asymmetries are indicative of a top-to-the-WNW shear sense, compatible with regional thrusting. These c-axis fabrics were also used to estimate deformation temperatures. Differential flow stresses associated with mylonitization were estimated from the grain size of dynamically recrystallized quartz. Deformation temperature and flow stress data were then incorporated into a dislocation creep flow law for quartz to estimate strain rates. Finally, along strike variation in these flow properties at the base of the Moine nappe to the north and south of the APM section were investigated and results from the APM section compared with previously published studies of mylonites exposed in eastern Assynt that occupy similar structural positions. / Master of Science
35

Neuromuscular factors related to varus thrust during walking in knee osteoarthritis

Espinosa Marazita, Sofia Elizabeth 14 June 2019 (has links)
BACKGROUND: Up to 37% of people with knee osteoarthritis (OA) present with varus thrust, an abrupt and dynamic worsening of varus alignment during the load-bearing stages of gait. Varus thrust is associated with up to 4-fold increased odds of medial knee OA progression as well as worsening clinical outcomes. While the implications of varus thrust have been well studied, the neuromuscular factors related to varus thrust are still not well understood and many studies report contradictory findings. Additionally, many potential factors remain unstudied. This warrants further efforts to determine associations between neuromuscular factors and varus thrust. The purpose of this study is to investigate knee muscle strength and muscle activation during walking in relation to biomechanical measures of varus thrust. METHODS: Analyses of existing data from participants with and without knee OA recruited at three institutions were used for this study. All participants underwent gait analyses at their self-selected pace while kinematics, kinetics, and surface EMG data were collected. Quadriceps and hamstrings strength was measured using isokinetic dynamometry. Gait data were used to calculate adduction excursion and peak knee adduction velocity as measures of varus thrust. A custom MATLAB code was used to calculate the rate of force development of the quadriceps, and a muscular co-contraction equation was used to calculate co-contraction values for four antagonist muscle pairs (VL-LH, VM-MH, VL-LG, and VM-MG) from surface EMG data during walking. Correlational analyses were performed to assess associations of strength, rate of force development, and muscle co-contraction variables with measures of varus thrust. RESULTS: A total of 183 participants were enrolled, however, a varying number of participants were used for different analyses based on available data. Peak isokinetic quadriceps strength at 60 degrees/second and peak hamstrings strength at both 60 and 120 degrees/second were negatively correlated with knee adduction velocity in people with knee OA. This association was not observed for people without knee OA. VLLH and VMMH co-contraction indices during preactivation were positively correlated with knee adduction excursion. VLLG co-contraction during midstance was positively correlated with peak knee adduction velocity. Association between rate of force development and varus thrust variables was not significant. CONCLUSIONS: Lower isokinetic thigh muscle strength and greater preactivation during walking are related to greater magnitude of varus thrust measured using motion capture. These results advance our understanding of neuromuscular factors related to varus thrust and could inform future interventions to reduce thrust and prevent further progression of OA. / 2020-06-14T00:00:00Z
36

Vorticity of Flow, Deformation Temperatures, and Strain Symmetry of the Moine Thrust Zone, NW Scotland: Constraining the Kinematic and Thermal Evolution of a Collisional Orogenic System

Thigpen, James Ryan 16 July 2009 (has links)
Examination of deformation temperature, flow vorticity, and strain symmetry in the Loch Eriboll, Loch More, and Assynt regions of the Moine thrust zone (MTZ) in northwest Scotland allows quantitative kinematic and thermal characterization of a crustal-scale shear zone at the base of the Scandian (435-425 Ma) orogenic wedge. Quartz crystal fabrics, kinematic vorticity (Wm), and strain estimates from the ductile thrust sheets in this region are used to determine how pure and simple shear components of deformation are partitioned, and indicate that these processes may be thermally, structurally, and lithologically dependent. Vorticity analysis of samples collected along strike in the MTZ and overlying Moine nappe indicate that Scandian thrusting and deformation involved a considerable pure shear component. Integrated strain and vorticity estimates indicate that significant sub-vertical foliation normal shortening has occurred as nappe stacking progressed. Along strike Wm variation could not be directly correlated with changes in footwall structural architecture, lithology, deformation temperatures, or structural depth and are thus interpreted to reflect local variability driven by a complex interplay of these and possibly other factors. Quartz c- and a-axis fabrics indicate that deformation in the footwall of the Moine thrust involved plane strain to general flattening strain with only a minor rotational (non-coaxial) component. In contrast, deformation in the Moine nappe was strongly non-coaxial, as indicated by asymmetric single girdle c-axis fabrics. Quartz c-axis opening angles and microstructures suggest that deformation temperatures increase from north to south and from structurally lower to structurally higher levels in the footwall to the Moine thrust. Vertical ductile thinning must be accommodated by either volume loss or extrusion of material towards the synorogenic topographic surface. Extrusion towards the synorogenic topographic surface implies a causal link between upper and lower crustal processes, with significant implications for the kinematic, geometric, and kinetic (deformation rates) evolution of the Scandian orogenic wedge. New thermobarometric and deformation temperature estimates are combined with structural and kinematic investigations to characterize the thermal structure of the Moine, Ben Hope, and related nappes. At the leading edge of the Moine thrust, subhedral garnets with prograde compositional growth zoning yield peak temperatures (grt-bio) of 440-492 °C at 4.5-6.0 kbars from Creagan Meall Horn to northern Assynt. Three samples collected at similar structural positions along the leading edge of the Moine nappe yield deformation temperatures of 420-460 °C, as determined from quartz c-axis opening angles. At the structurally highest position in the Moine nappe, garnet prograde compositional zoning profiles are preserved and samples yields P-T estimates of 565-571 °C (grt-bio) and 4.5-5.1 kbar (GRAIL barometer, minimum pressure due to absence of Al2SiO5 phase). Quartz c-axis fabrics of samples collected at similar structural positions yield deformation temperature estimates of 490-565 °C. In the structurally higher Ben Hope nappe, two phases of prograde compositional growth zoning are preserved in garnet bearing amphibolite near Portvasgo. The later outer garnet rim records P-T conditions of 655-672 °C at 3.9-5.1 kbars. The inverted metamorphic sequence from the Moine to the Naver thrust is mostly intact and is interpreted to be Scandian (435-420 Ma) in age. It is likely that the formation of this inverted sequence is due to a combination of progressive accretion of successively lower grade thrust sheets onto the base of the Scandian wedge and heating of the Moine and Ben Hope nappes from above by the relatively higher temperature migmatites of the Naver thrust. Vertical ductile thinning, in conjunction with erosion and normal faulting, likely led to rapid exhumation of the Scandian nappe pile and in turn preserved the inverted metamorphic sequence. / Ph. D.
37

Continuous Low-Thrust Trajectory Optimization: Techniques and Applications

Kim, Mischa 25 April 2005 (has links)
Trajectory optimization is a powerful technique to analyze mission feasibility during mission design. High-thrust trajectory optimization problems are typically formulated as discrete optimization problems and are numerically well-behaved. Low-thrust systems, on the other hand, operate for significant periods of the mission time. As a result, the solution approach requires continuous optimization; the associated optimal control problems are in general numerically ill-conditioned. In addition, case studies comparing the performance of low-thrust technologies for space travel have not received adequate attention in the literature and are in most instances incomplete. The objective of this dissertation is therefore to design an efficient optimal control algorithm and to apply it to the minimum-time transfer problem of low-thrust spacecraft. We devise a cascaded computational scheme based on numerical and analytical methods. Whereas other conventional optimization packages rely on numerical solution approaches, we employ analytical and semi-analytical techniques such as symmetry and homotopy methods to assist in the solution-finding process. The first objective is to obtain a single optimized trajectory that satisfies some given boundary conditions. The initialization phase for this first trajectory includes a global, stochastic search based on Adaptive Simulated Annealing; the fine tuning of optimization parameters — the local search — is accomplished by Quasi-Newton and Newton methods. Once an optimized trajectory has been obtained, we use system symmetry and homotopy techniques to generate additional optimal control solutions efficiently. We obtain optimal trajectories for several interrelated problem families that are described as Multi-Point Boundary Value Problems. We present and prove two theorems describing system symmetries for solar sail spacecraft and discuss symmetry properties and symmetry breaking for electric spacecraft systems models. We demonstrate how these symmetry properties can be used to significantly simplify the solution-finding process. / Ph. D.
38

Determining the Geometry and Former Extent of the North Mountain Thrust from Fluid Inclusion and Microstructural Analysis

Castles, Megan Erin 17 May 2010 (has links)
No description available.
39

Thrust-Cushion Vehicles, A Preliminary Analysis

Cocksedge, Graham George 09 1900 (has links)
<p> Air-cushion vehicles (ACV) are defined as surface vehicles that utilize air pressure for partial-or total support over the operational surface. An outline of the history of the five widely known ACV concepts and an analysis of the mode of operation of each is given, with their advantages and disadvantages.</p> <p> A sixth type, called the thrust-cushion vehicle (TCV), is a promising but unknown concept which, as yet, has not received much study or recognition. A preliminary theoretical analysis for design purposes is made, and the test results of a static model and a model running on a radial tether are given to establish a research and design basis for future work.</p> / Thesis / Master of Engineering (MEngr)
40

Method and Simulation of On-Orbit Sub-microthrust Evaluation

Hood, Jonathan 01 June 2022 (has links) (PDF)
With the advent of smaller satellites, along with the need for less than 0.1 μN precision attitude control for interferometry and imaging missions, finer micro- to sub-micro- thrusters have become an area of high interest. As thrusters are developed and ground-tested, it is necessary to evaluate their thrust performance on-orbit. On-orbit measurements offer actual thrust performance in mission conditions, free from ground facility vibrations and miniaturization restraints, and allow a thruster system to achieve a NASA Technology Readiness Level (TRL) of 7-8. A review is conducted of existing and proposed ground and on-orbit thrust measurement techniques. Experimental gaps and complementary methods are examined along with the current thrust resolution limits. A novel fusion technique combining attitude determination, torsional balance, and filtering techniques is proposed to increase resolution beyond current on-orbit minimums, 4μN, via a dedicated sub-μN on-orbit thrust measurement mission. A simulated case study in the application of this measurement technique to a theoretical Casimir-thruster-equipped, 10-7-10-13 N, smallsat mission is explored. A detailed error analysis is conducted, and the technique is found to be analytically viable for greater than or equal to 10-7 N on a 1U nanosat equipped with sun sensor and three-axis gyroscope, as well as physically viable at a TRL 7-9 level. Recommended next steps are modification of the post-processing technique to decrease gyroscope noise and mass restrictions or exploration of suggested alternate methods, including orbit estimation, direct force sensing, and formation flying.

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