Radial and azimuthal dynamics of the io plasma torus

Thesis (M.S.) University of Alaska Fairbanks, 2015The moon Io orbits Jupiter emitting neutral particles from its volcanic surface. This emission is ionized and forms the Io plasma torus around Jupiter. The variation of conditions at Io and Jupiter lead to variations in the content of the plasma in the torus. Volcanoes on Io's surface erupt and change the rate of neutral input. Hot electrons (30-100 eV), whose abundances vary in azimuth, create highly ionized species. Radial variation in subcorotation velocities, velocities less than than that of the motion of the dipole magnetic field, creates shears while maintaining coherent radial structure in the torus. Poorly understood changes in plasma density circulate through the torus creating the anomalous System IV behavior that has a period slightly longer than the rotation of Jupiter's magnetic field. This thesis summarizes the research that has produced a two-dimensional physical chemistry model, tested several existing theories about subcorotation velocities, System IV variation, and hot electrons, and adopted new methods of Io plasma torus analysis. In an attempt to understand important dynamics, the thesis modeled differing scenarios such as an initialized two-peak structure, a subcorotation profile dictated by mass loading and ionospheric conductivity, and a critical combination of two populations of hot electrons that accurately mimics the observed System IV phenomenon. This model was also used to solve the inverse problem of determining the best fit for the model parameters, neutral source input rate and radial transport rate, using observations of density, temperature, and composition. In addition the thesis shows the need for multi-dimensional modeling and the results from its groundbreaking two-dimensional model

Dynamic Response Analysis of an Icosahedron Shaped Lighter Than Air Vehicle

The creation of a lighter than air vehicle using an inner vacuum instead of a lifting gas is considered. Specifically, the icosahedron shape is investigated as a design that will enable the structure to achieve positive buoyancy while resisting collapse from the atmospheric pressure applied. This research analyzes the dynamic response characteristics of the design, and examines the accuracy of the finite element model used in previous research by conducting experimental testing. The techniques incorporated in the finite element model are confirmed based on the experimental results using a modal analysis. The experimental setup designed will allow future research on the interaction between the frame and skin of icosahedron like structures using various combinations of materials and construction methods. Additionally, a snapback behavior observed in previous static response analysis is further investigated to determine nonlinear instability issues with the design. Dynamic analysis of the structure reveals chaotic motion is present in the frame of the icosahedron under certain loads and boundary conditions. These findings provide information critical to the design of an icosahedron shaped lighter than air vehicle using an inner vacuum

Aortic dissection simulation models for clinical support: fluid-structure interaction vs. rigid wall models

BACKGROUND: The management and prognosis of aortic dissection (AD) is often challenging and the use of personalised computational models is being explored as a tool to improve clinical outcome. Including vessel wall motion in such simulations can provide more realistic and potentially accurate results, but requires significant additional computational resources, as well as expertise. With clinical translation as the final aim, trade-offs between complexity, speed and accuracy are inevitable. The present study explores whether modelling wall motion is worth the additional expense in the case of AD, by carrying out fluid-structure interaction (FSI) simulations based on a sample patient case. METHODS: Patient-specific anatomical details were extracted from computed tomography images to provide the fluid domain, from which the vessel wall was extrapolated. Two-way fluid-structure interaction simulations were performed, with coupled Windkessel boundary conditions and hyperelastic wall properties. The blood was modelled using the Carreau-Yasuda viscosity model and turbulence was accounted for via a shear stress transport model. A simulation without wall motion (rigid wall) was carried out for comparison purposes. RESULTS: The displacement of the vessel wall was comparable to reports from imaging studies in terms of intimal flap motion and contraction of the true lumen. Analysis of the haemodynamics around the proximal and distal false lumen in the FSI model showed complex flow structures caused by the expansion and contraction of the vessel wall. These flow patterns led to significantly different predictions of wall shear stress, particularly its oscillatory component, which were not captured by the rigid wall model. CONCLUSIONS: Through comparison with imaging data, the results of the present study indicate that the fluid-structure interaction methodology employed herein is appropriate for simulations of aortic dissection. Regions of high wall shear stress were not significantly altered by the wall motion, however, certain collocated regions of low and oscillatory wall shear stress which may be critical for disease progression were only identified in the FSI simulation. We conclude that, if patient-tailored simulations of aortic dissection are to be used as an interventional planning tool, then the additional complexity, expertise and computational expense required to model wall motion is indeed justified

Identification of dynamic characteristics of linear systems.

Structures, built in active earthquake zones, can be subjected to damaging dynamic loading. The health monitoring process for these structures is essential. When a structure is submitted to repetitive moderate earthquake events, it is expected to accumulate certain damage. The variation of the dynamic characteristics can be an indicator of the damage extension in a structure. The procedure of evaluating the dynamic characteristics of a structure is referred to as system identification. This investigation focuses on the analysis of different techniques for identifying linear structures with available recorded responses during earthquake events. These approaches are: (i) Fourier transform approach; (ii) Discrete-time filter method with Least Squares solver; and (iii) Discrete-time filter method with Instrumental Variables solver. A critical assessment of these methods is presented. The analysis of these methods was conducted considering four examples: (i) water tower subjected to blast loading; (ii) cantilever steel beam subjected to earthquake (1995 Kobe, Japan); (iii) ten-story residential reinforced-concrete building; and (iv) six-story commercial steel building. The dynamic responses of the first two examples are obtained numerically and therefore they are free of noise. For the real building examples the acceleration response recoded during the 1994 Northridge earthquake is used to identify the dynamic characteristics. The vibration data of the two buildings are obtained from the California Strong Motion Instrumentation Program (CSMIP).Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2003 .R345. Source: Masters Abstracts International, Volume: 42-03, page: 1001. Adviser: Faouzi Ghrib. Thesis (M.A.Sc.)--University of Windsor (Canada), 2003

Quantitative Analysis by 3D Graphics of Thoraco-Abdominal Surface Shape and Breathing Motion

Chest wall motion can provide information on respiratory muscles' action and on critical vital signs, like respiration and cardiac activity. The chest wall is a structure with three compartments that are independent to each other and can move paradoxically according to the pathophysiology of the disease. Opto-electronic plethysmography (OEP) allows for non-invasively 3D tracking of body movements. We aimed to extend the characteristics of OEP analysis to local analyses of thoraco-abdominal surface geometry and kinematics during respiration. Starting from the OEP output file, the 3D markers’ coordinates were combined with a triangulation matrix. A smoothing procedure (an automatic and iterative interpolation process to increase the number of vertices from 93 to 548) was applied to allow for precise local analysis of the thoraco-abdominal surface. A series of measurements can be performed to characterize the geometry of the trunk and its three compartments, in terms of volumes, height, diameters, perimeters, and area. Some shape factors, such as surface-to-volume ratio or height-to-perimeter ratio, can be also computed. It was also possible to build the vector field associated with the breathing motion of all the vertices, in terms of magnitude and motion direction. The vector field data were analyzed and displayed through two graphic tools: a 3D heatmap, in which the magnitude of motion was associated to different colors, and a 3D arrow plot, that allowed us to visualize both the magnitude and the direction of motion with color-coded arrows. The methods were applied to 10 healthy subjects (5 females) and also applied to two cases: a pregnant woman at each trimester of gestation and a patient before and after a demolition thoracic surgery. The results proved to be coherent with the physiology of healthy subjects and the physiopathology of the cases. We developed a new non-invasive method for respiratory analysis that allowed for the creation of realistic 3D models of the local and global trunk surface during respiration. The proposed representation constituted a very intuitive method to visualize and compare thoraco-abdominal surface movements within and between subjects, therefore enforcing the potential clinical translational value of the method

Three-dimensional flow instability in a lid-driven isosceles triangular cavity

Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed

The role of human ventral visual cortex in motion perception.

Visual motion perception is fundamental to many aspects of visual perception. Visual motion perception has long been associated with the dorsal (parietal) pathway and the involvement of the ventral 'form' (temporal) visual pathway has not been considered critical for normal motion perception. Here, we evaluated this view by examining whether circumscribed damage to ventral visual cortex impaired motion perception. The perception of motion in basic, non-form tasks (motion coherence and motion detection) and complex structure-from-motion, for a wide range of motion speeds, all centrally displayed, was assessed in five patients with a circumscribed lesion to either the right or left ventral visual pathway. Patients with a right, but not with a left, ventral visual lesion displayed widespread impairments in central motion perception even for non-form motion, for both slow and for fast speeds, and this held true independent of the integrity of areas MT/V5, V3A or parietal regions. In contrast with the traditional view in which only the dorsal visual stream is critical for motion perception, these novel findings implicate a more distributed circuit in which the integrity of the right ventral visual pathway is also necessary even for the perception of non-form motion

The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches

Any search effort for gravitational waves (GW) using interferometric detectors like LIGO needs to be able to identify if and when noise is coupling into the detector's output signal. The Critical Coupling Likelihood (CCL) method has been developed to characterize potential noise coupling and in the future aid GW search efforts. By testing two hypotheses about pairs of channels, CCL is able to identify undesirable coupled instrumental noise from potential GW candidates. Our preliminary results show that CCL can associate up to $\sim 80$ of observed artifacts with $SNR \geq 8$, to local noise sources, while reducing the duty cycle of the instrument by $\lesssim 15$. An approach like CCL will become increasingly important as GW research moves into the Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ

Multi-step self-guided pathways for shape-changing metamaterials

Multi-step pathways, constituted of a sequence of reconfigurations, are central to a wide variety of natural and man-made systems. Such pathways autonomously execute in self-guided processes such as protein folding and self-assembly, but require external control in macroscopic mechanical systems, provided by, e.g., actuators in robotics or manual folding in origami. Here we introduce shape-changing mechanical metamaterials, that exhibit self-guided multi-step pathways in response to global uniform compression. Their design combines strongly nonlinear mechanical elements with a multimodal architecture that allows for a sequence of topological reconfigurations, i.e., modifications of the topology caused by the formation of internal self-contacts. We realized such metamaterials by digital manufacturing, and show that the pathway and final configuration can be controlled by rational design of the nonlinear mechanical elements. We furthermore demonstrate that self-contacts suppress pathway errors. Finally, we demonstrate how hierarchical architectures allow to extend the number of distinct reconfiguration steps. Our work establishes general principles for designing mechanical pathways, opening new avenues for self-folding media, pluripotent materials, and pliable devices in, e.g., stretchable electronics and soft robotics.Comment: 16 pages, 3 main figures, 10 extended data figures. See https://youtu.be/8m1QfkMFL0I for an explanatory vide