Investigation of Ionospheric Plasma Flow Effects on Current Collection to Parallel Wires Using Self-Consistent Steady-State Kinetic Simulations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77393/1/AIAA-2005-4293-799.pd

Enhancement of electrodynamic tether electron current collection using radio frequency power: numerical modeling and measurements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77143/1/AIAA-2001-3339-153.pd

Applications of electrodynamic tethers utilizing their transmission-line characteristics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76490/1/AIAA-2000-3868-231.pd

A Comparison of Laboratory Experimental and Theoretical Results for Electrodynamic Tether Electron Collection Performance for Some Bare Tether Geometries

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76910/1/AIAA-2009-6659-508.pd

Measurement of Cross-Section Geometry Effects on Electron Collection to Long Probes in Mesosonic Flowing Plasmas

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77060/1/AIAA-2003-4950-410.pd

Current Collection to Electrodynamic Tether Systems in Space

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77109/1/AIAA-2004-5670-600.pd

Ground simulations of electron current to wide probes for electrodynamic tethers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76486/1/AIAA-2001-3337-341.pd

Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water

Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but these transitions are more poorly understood. We use computed tomography to study changes in the inner ear vestibular system, involved in sensing balance and equilibrium, as one of these groups, extinct crocodile relatives called thalattosuchians, transitioned from terrestrial ancestors into pelagic (open ocean) swimmers. We find that the morphology of the vestibular system corresponds to habitat, with pelagic thalattosuchians exhibiting a more compact labyrinth with wider semicircular canal diameters and an enlarged vestibule, reminiscent of modified and miniaturized labyrinths of other marine reptiles and cetaceans. Pelagic thalattosuchians with modified inner ears were the culmination of an evolutionary trend with a long semiaquatic phase, and their pelagic vestibular systems appeared after the first changes to the postcranial skeleton that enhanced their ability to swim. This is strikingly different from cetaceans, which miniaturized their labyrinths soon after entering the water, without a prolonged semiaquatic stage. Thus, thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition.Facultad de Ciencias Naturales y Muse

Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water

© 2020 National Academy of Sciences. All rights reserved. Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but these transitions are more poorly understood. We use computed tomography to study changes in the inner ear vestibular system, involved in sensing balance and equilibrium, as one of these groups, extinct crocodile relatives called thalattosuchians, transitioned from terrestrial ancestors into pelagic (open ocean) swimmers. We find that the morphology of the vestibular system corresponds to habitat, with pelagic thalattosuchians exhibiting a more compact labyrinth with wider semicircular canal diameters and an enlarged vestibule, reminiscent of modified and miniaturized labyrinths of other marine reptiles and cetaceans. Pelagic thalattosuchians with modified inner ears were the culmination of an evolutionary trend with a long semiaquatic phase, and their pelagic vestibular systems appeared after the first changes to the postcranial skeleton that enhanced their ability to swim. This is strikingly different from cetaceans, which miniaturized their labyrinths soon after entering the water, without a prolonged semiaquatic stage. Thus, thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition

Theory and experimental evaluation of a consistent steady-state kinetic model for two-dimensional conductive structures in ionospheric plasmas with application to bare electrodynamic tethers in space.

A steady-state kinetic computational model is developed, allowing for self-consistent simulations of collisionless, unmagnetized flowing plasmas in a vast region surrounding any two-dimensional conductive object. An optimization approach is devised based on a stable, noise-robust Tikhonov-regularized Newton method. Dynamic, adaptive, unstructured meshing allows arbitrary geometries and adequate resolution of plasma sheath features. A 1-D cylindrical solver (KiPS-1D) and a full 2-D solver (KiPS-2D) were developed, the latter using coarse-grained parallelism. This technique is applied to investigate various applications of special and fundamental importance, principally for space plasmas, although not limited as such. This thesis addresses new simulations and experiments relevant to space borne electrodynamic tethers for propellantless propulsion and for the remediation of radiation belts through charge precipitation, as well as to Langmuir probes for plasma diagnostic in flowing plasmas. Here, the existing set of plasma sheath profiles and current collection characteristics for round cylinders in stationary plasmas is extended to large bias potentials. Interference effects between two parallel cylinders are shown to exist for spacings upward of 20 times the single-cylinder sheath radius, and an optimal spacing equal to the single-cylinder sheath radius maximizes the sheath area, a finding qualitatively supported by our new experimental data on electron-collecting thin slotted tapes. Also, a thin conductive solid tape is shown to have an equal-capacitance circular radius of about 0.29 times its width. Its predicted collected current characteristic as a function of width approximately agrees with experimental measurements. Further, it has a lower current collection capability than the equal-capacitance circular cylinder. For ion-attracting cylinders, ionospheric plasma representative of an altitude of 1500 km with a flow energy on the order of the thermal energy is shown to cause significant sheath asymmetries, reducing the sheath radius and current collection by about 30%. For electron-attracting cylinders, a mesosonic flow is experimentally shown to significantly enhance electron collection. This cannot be predicted by a collisionless model and may be due to an elongation of the ram-side pre-sheath into a collisional zone for electrons.Ph.D.Aerospace engineeringApplied SciencesElectrical engineeringPlasma physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124722/2/3150248.pd