You searched for +publisher:"Virginia Tech" +contributor:("Scales, Wayne A.").
Showing records 1 – 30 of
89 total matches.
◁ [1] [2] [3] ▶
Virginia Tech
1.
Glesner, Colin Christopher.
Development of Magnetic Nozzle Simulations for Space Propulsion Applications.
Degree: MS, Aerospace and Ocean Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/74947 
► A means of space propulsion using the channeling of plasma by a divergent magnetic field, referred to as a magnetic nozzle has been explored by…
(more)
▼ A means of space propulsion using the channeling of plasma by a divergent magnetic field, referred to as a magnetic nozzle has been explored by a number of research groups. This research develops the capability to apply the high order accurate Runge-Kutta discontinuous Galerkin numerical method to the simulation of magnetic nozzles. The resistive magnetohydrodynamic model of plasma behavior is developed for these simulations. To facilitate this work, several modeling capabilities are developed, including the implementation of appropriate inflow and far-field boundary conditions, the application of a technique for correcting errors that develop in the divergence of the magnetic field, and a split formulation for the magnetic field between the applied and the perturbed component. This model is then applied to perform a scaling study of the performance of magnetic nozzles over a range of Bk and Rm. In addition, the effect of the choice of simulation domain size is
investigated. Finally, recommendations for future work are made.
Advisors/Committee Members: Srinivasan, Bhuvana (committeechair), Scales, Wayne A. (committeechair), Adams, Colin (committee member).
Subjects/Keywords: Plasma; Simulation
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Glesner, C. C. (2017). Development of Magnetic Nozzle Simulations for Space Propulsion Applications. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/74947
Chicago Manual of Style (16th Edition):
Glesner, Colin Christopher. “Development of Magnetic Nozzle Simulations for Space Propulsion Applications.” 2017. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/74947.
MLA Handbook (7th Edition):
Glesner, Colin Christopher. “Development of Magnetic Nozzle Simulations for Space Propulsion Applications.” 2017. Web. 06 Dec 2019.
Vancouver:
Glesner CC. Development of Magnetic Nozzle Simulations for Space Propulsion Applications. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/74947.
Council of Science Editors:
Glesner CC. Development of Magnetic Nozzle Simulations for Space Propulsion Applications. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/74947
Virginia Tech
2.
Thirukoveluri, Padma Latha.
Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.
Degree: MS, Electrical and Computer Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/32969
► The objective of this thesis was to select a star for observation and determine the error in the retrieval technique for a rocket experiment to…
(more)
▼ The objective of this thesis was to select a star for observation and determine the error in the retrieval technique for a rocket experiment to measure lower thermospheric Nitric Oxide in the polar night using stellar occultation technique. These objectives are accomplished by planning the geometry, determining the requirements for observations, window for launch and discussing the retrieval technique. The planning is carried out using an approximated (no drag) and simulated rocket trajectory (provided by NSROC: NASA Rocket Operations Contract). The simulation for the retrievals is done using data from Student Nitric Oxide Explorer. Stars were taken from a catalogue called TD1. Launch times were obtained from the geometry planned resulting from selecting a zenith angle after choosing a maximum occultation height and determining rocket apogee. Window for observing Spica was found to be 20 minutes. The retrieval technique and simulations showed that column densities and volume densities should be retrievable to less than 5% and 20% respectively observing occultation heights 90-120km. The study suggests that choosing a star positioned north w.r.t the observation location gives us more poleward latitudes and larger launch window. Future research can be carried out applying the stellar occultation and retrieval technique to a satellite.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Scales, Wayne A. (committee member), Henderson, Troy A. (committee member).
Subjects/Keywords: launch time selection; star selection; rocket experiment; rocket experiment simulation; density retrieval techniques; stellar occultation technique; rocket geometry planning; rocket observation planning
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Thirukoveluri, P. L. (2011). Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/32969
Chicago Manual of Style (16th Edition):
Thirukoveluri, Padma Latha. “Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.” 2011. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/32969.
MLA Handbook (7th Edition):
Thirukoveluri, Padma Latha. “Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation.” 2011. Web. 06 Dec 2019.
Vancouver:
Thirukoveluri PL. Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/32969.
Council of Science Editors:
Thirukoveluri PL. Planning and Simulating Observations for a Sounding Rocket Experiment to Measure Polar Night Nitric Oxide in the Lower Thermosphere by Stellar Occultation. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/32969
Virginia Tech
3.
Kim, Alexander.
Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.
Degree: MS, Electrical and Computer Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/34568
► The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of…
(more)
▼ The ultimate goal for power electronics is to convert one form of raw electrical energy into a usable power source with the lowest amount of loss. A considerable portion of these losses are due to the use of switching devices themselves. Device losses can be apportioned to conduction loss and switching loss. It is commonly known and practiced that conduction loss can be reduced by driving MOSFETs and IGBTs harder with gate voltages closer to the maximum rating. This lowers the voltage across the device in the path of the amplified current and ultimately reduces power dissipated by the device. However, switching losses of these devices are not as easily characterized or intuitive for power electronics designers. This is mainly due to the fact that the parasitic reactive elements are nonlinear and not as readily documented as I-V characteristics of a given power device. For example, non-linear parasitic capacitances in the device are given for a fixed frequency across a voltage sweep. Parasitic inductance is typically not even mentioned in the datasheet. The switching losses of these devices depend on these mysterious reactances. A functional way to obtain estimates
of switching loss is to test the device under the conditions the device will be used. However, this task must be approached carefully in order to accurately measure the voltage and current of the device. Measurement devices also have parasitic impedances of their own that can add or subtract to switching energy during turn on or turn off and create misleading results. Preliminary testing was performed on multiple devices. After preliminary testing and deliberation, a device-measurement printed circuit board was made to easily replace switching devices of the same package.
This thesis presents switching loss measurements of medium-power capable devices in the tens of kW range. It also aims to attribute characteristics of switching voltage and current waveforms to the internal structure of the devices. The device tester designed is versatile since the output buffer of the gate drive is comprised of D-PAK totem pole BJTs. This is able to drive both current and voltage driven devices, i.e. SiC J-FETs (current-driven) and other voltage-driven devices (i.e. MOSFETs and IGBTs). It also allows for TO-220 and TO-247 packaged power diodes.
Advisors/Committee Members: Lai, Jih-Sheng Jason (committeechair), Meehan, Kathleen (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: SupreMOS; CoolMOS; Switching Loss; Z-FET; Device Testing; MDMesh
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Kim, A. (2011). Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/34568
Chicago Manual of Style (16th Edition):
Kim, Alexander. “Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.” 2011. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/34568.
MLA Handbook (7th Edition):
Kim, Alexander. “Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems.” 2011. Web. 06 Dec 2019.
Vancouver:
Kim A. Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/34568.
Council of Science Editors:
Kim A. Switching-Loss Measurement of Current and Advanced Switching Devices for Medium-Power Systems. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/34568
Virginia Tech
4.
Peng, Senlin.
Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals.
Degree: MS, Electrical and Computer Engineering, 2010, Virginia Tech
URL: http://hdl.handle.net/10919/40873
► A 12 channel real-time GPS L1 C/A-code software receiver has been implemented on a Desktop with 1.84GHz Intel CPU. The software receiver has the…
(more)
▼ A 12 channel real-time GPS L1 C/A-code software receiver has been implemented on a
Desktop with 1.84GHz Intel CPU. The software receiver has the capability to acquire new
satellites coming in, keep tracking of satellites in view and give a user solution accuracy of
30 meters. This study also explores a real-time correlator for the GLONASS L1 signals.
This software receiver is going to be used for scientiï¬ c research and education. This work
is a part of the ongoing effort to develop a low-cost, ï¬ exible, and capable GNSS receiver
for use as a scientiï¬ c instrument and for GNSS receiver technology development.
The software receiver developed here makes use of a reconï¬ gurable RF front end called
the Universal Software Radio Peripheral (USRP) with a maximum real sampling frequency
of 8MHz of complex samples. The USRP uses interchangeable daughter boards to down-
convert and digitize RF signals in the range of DC to 2.9GHz, where each daughterboard
covers an overlapping subset of this range. This RF front end was chosen for its ï¬ exibility
and ease of use. The output of the RF front end is 8-bit complex I/Q samples output via a
USB cable.
The software receiver processing of the RF front-end outputs is accomplished by using
bit-wise parallelism, as described in References [1] and [2]. In order to process the incom-
ing RF data in this manner, the 8-bit complex I/Q samples are quantized to two bits. This is
performed in the software receiver prior to signal correlation. In-phase and quadrature ac-
cumulations are computed using bit-wise parallel techniques, and these accumulations are
used to drive code tracking delay-lock loops (DLLs) and carrier tracking phase-lock loops(PLLs). The computation of accumulations and the implementation of DLLs and PLLs for
the GNSS ranging signals are detailed in the thesis.
The software receiver is developed by C++. It consists of two parts: the software
receiver core program and a simple interface. The current software receiver runs under
Ubuntu Linux systems, but it is convenient to implement on other Linux systems. The
software prerequisites for the software receiver are GNUradio and QT4.0. GNUradio is an
open source program which provides the driver for the USRP board. The current version
used by the software receiver is GNUradio-3.1.3. The user interface program is developed
by using the classes provided by QT4.0. The hardware of the whole system consists of
computer with intel 1.84 GHz CPU and 2GHz RAM, GPS and GLONASS antenna, USRP,
and analogue signal generator. One problem with the USRP is that its on-board oscillator
is not particularly stable in terms of frequency and phase. One solution to this problem is to
use a high-quality external oscillator. An Agilent N5181A MXG Analog Signal Generator
conï¬ gured to output a 64MHz signal has been used as an external input clock to the USRP.
This oscillator has a stated frequency error of 1 ppm/yr, has decent short-term frequency
stability, and has a reasonably low phase noise at 64MHz. The outputs of the…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Bailey, Scott M. (committee member), Reed, Jeffrey Hugh (committee member).
Subjects/Keywords: GPS GLONASS Software Receiver
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Peng, S. (2010). Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/40873
Chicago Manual of Style (16th Edition):
Peng, Senlin. “Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals.” 2010. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/40873.
MLA Handbook (7th Edition):
Peng, Senlin. “Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals.” 2010. Web. 06 Dec 2019.
Vancouver:
Peng S. Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals. [Internet] [Masters thesis]. Virginia Tech; 2010. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/40873.
Council of Science Editors:
Peng S. Implementation of Real-Time Software Receiver for Gps or Glonass L1 Signals. [Masters Thesis]. Virginia Tech; 2010. Available from: http://hdl.handle.net/10919/40873
Virginia Tech
5.
Harris Jr, Frederick Bernard.
GNSS Hardware-In-The-Loop Formation and Tracking Control.
Degree: MS, Electrical and Computer Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/71380
► Formation and tracking control are critical for of today's vehicle applications in and this will be true for future vehicle technologies as well. Although the…
(more)
▼ Formation and tracking control are critical for of today's vehicle applications in and this will be true for future vehicle technologies as well. Although the general function of these controls is for data collection and military applications, formation and tracking control may be applied to automobiles, drones, submarines, and spacecraft. The primary application here is the investigation of formation keeping and tracking solutions for realistic, real-time, and multi-vehicle simulations. This research explores the creation of a predictive navigation and control algorithm for formation keeping and tracking, raw measurement data collection, and building a real-time GNSS closed HWIL testbed for simulations of different vehicles. The L1 frequency band of the Global Positioning System (GPS) constellation is used to observe and generate raw measurement data that encompasses range, pseudo-range, and Doppler frequency. The closed HWIL simulations are implemented using Spirent's Communication Global Navigation Satellite system (GNSS) 6560 and 8000 hardware simulators along with Ashtech, G-12 and DG-14, and Novetel OEM 628 receivers. The predictive navigation control is similar to other vision-based tracking techniques, but relies mainly on vector projections that are controlled by acceleration, velocity magnitude, and direction constraints to generate realistic motion.
The current state of the testbed is capable of handling one or more vehicle applications. The testbed can model simulations up to 24 hours. The vehicle performance during simulations can be customized for any required precision by setting a variety of vehicle parameters. The testbed is built from basic principles and is easily upgradable for future expansions or upgrades.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Baker, Joseph Benjamin (committee member), Ellingson, Steven W. (committee member).
Subjects/Keywords: Hardware-In-The-Loop; Formation Flying; Formation Travel; Tracking Control; Linear Navigation; Ashtech G-12; Spirent; GNSS 8000; GNSS 6560; Real-Time; Predictive Navigation Algorithm; GPS; Global Positioning System
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Harris Jr, F. B. (2016). GNSS Hardware-In-The-Loop Formation and Tracking Control. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/71380
Chicago Manual of Style (16th Edition):
Harris Jr, Frederick Bernard. “GNSS Hardware-In-The-Loop Formation and Tracking Control.” 2016. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/71380.
MLA Handbook (7th Edition):
Harris Jr, Frederick Bernard. “GNSS Hardware-In-The-Loop Formation and Tracking Control.” 2016. Web. 06 Dec 2019.
Vancouver:
Harris Jr FB. GNSS Hardware-In-The-Loop Formation and Tracking Control. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/71380.
Council of Science Editors:
Harris Jr FB. GNSS Hardware-In-The-Loop Formation and Tracking Control. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/71380
Virginia Tech
6.
Jean, Marc Henri.
Multi-Constellation GNSS Scintillation at Mid-Latitudes.
Degree: MS, Electrical and Computer Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/73704
► Scintillation of Global Positioning Systems (GPS) signals have been extensively studied at low and high latitude regions of the Earth. It has been shown in…
(more)
▼ Scintillation of Global Positioning Systems (GPS) signals have been extensively studied
at low and high latitude regions of the Earth. It has been shown in past studies that amplitude
scintillation is severe at low latitudes and phase scintillation is severe at high latitudes. Unlike
low and high latitude regions, mid-latitude scintillation has not been extensively studied. Further, it has been suggested that mid-latitude scintillation is negligible. The purpose of this research is to challenge this belief.
A multi-constellation and multi-frequency receiver, that tracks American, Russian, and
European satellites, was used to monitor scintillation activity at the
Virginia Tech Space Center.
Analysis was performed on collected data from various days and compared to past research done at high, mid, and low latitudes. The results are discussed in this thesis.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Bailey, Scott M. (committee member), Sweeney, Dennis G. (committee member).
Subjects/Keywords: Mid-Latitude scintillation; amplitude scintillation; phase scintillation; Novatel GP6-Station receiver; Novatel Connect; spectral index; histogram distribution; GPS L1; GPS L2; GPS L5; GLONASS G1; GLONASS G2; Galileo E1; Galileo E5A; Galileo E5B; SP
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Jean, M. H. (2016). Multi-Constellation GNSS Scintillation at Mid-Latitudes. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/73704
Chicago Manual of Style (16th Edition):
Jean, Marc Henri. “Multi-Constellation GNSS Scintillation at Mid-Latitudes.” 2016. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/73704.
MLA Handbook (7th Edition):
Jean, Marc Henri. “Multi-Constellation GNSS Scintillation at Mid-Latitudes.” 2016. Web. 06 Dec 2019.
Vancouver:
Jean MH. Multi-Constellation GNSS Scintillation at Mid-Latitudes. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/73704.
Council of Science Editors:
Jean MH. Multi-Constellation GNSS Scintillation at Mid-Latitudes. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/73704
Virginia Tech
7.
Roback, Vincent Eric.
Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.
Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/76845
► Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized and flight tested under the Autonomous Landing and…
(more)
▼ Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized and flight tested under the Autonomous Landing and Hazard Avoidance (ALHAT) project (in its fourth development and field test cycle) which is seeking to develop a guidance, navigation, and control (GNC) and sensing system based on lidar technology capable of enabling safe, precise human-crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The flash lidars incorporate pioneering 3-D imaging cameras based on Indium-Gallium-Arsenide Avalanche Photo Diode (InGaAs APD) and novel micro-electronic technology for a 128 x 128 pixel array operating at 30 Hz, high pulse-energy 1.06 ?m Nd:YAG lasers, and high performance transmitter and receiver fixed and zoom optics. The two flash lidars are characterized on the NASA-Langley Research Center (LaRC) Sensor Test Range, integrated with other portions of the ALHAT GNC system from around the country into an instrument pod at NASA-JPL, integrated onto an Erickson Aircrane Helicopter at NASA-Dryden, and flight tested at the Edwards AFB Rogers dry lakebed over a field of human-made geometric hazards. Results show that the maximum operational range goal of 1000m is met and exceeded up to a value of 1200m, that the range precision goal of 8 cm is marginally met, and that the transmitter zoom optics divergence needs to be extended another eight degrees to meet the zoom goal 6° to 24°. Several hazards are imaged at medium ranges to provide three-dimensional Digital Elevation Map (DEM) information.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Scales, Wayne A. (committee member), Henderson, Troy A. (committee member).
Subjects/Keywords: Precision Landing; Safe Landing; 3-D Imaging; Flash Lidar; Laser Remote Sensing; Hazard Detection; ALHAT; Flight Test; Planetary Landing; Lunar Landing
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Roback, V. E. (2012). Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/76845
Chicago Manual of Style (16th Edition):
Roback, Vincent Eric. “Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.” 2012. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/76845.
MLA Handbook (7th Edition):
Roback, Vincent Eric. “Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing.” 2012. Web. 06 Dec 2019.
Vancouver:
Roback VE. Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/76845.
Council of Science Editors:
Roback VE. Characterization and Helicopter Flight Test of 3-D Imaging Flash LIDAR Technology for Safe, Autonomous, and Precise Planetary Landing. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/76845
Virginia Tech
8.
Williams, Jon A.
Enabling Validation of a CubeSat Compatible Wind Sensor.
Degree: MS, Electrical and Computer Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78711
► The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures neutral wind characteristics in the upper atmosphere. Neutral gas interactions…
(more)
▼ The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures neutral wind characteristics in the upper atmosphere. Neutral gas interactions with plasma in the ionosphere/thermosphere are responsible for spacecraft drag, radio frequency disturbances such as scintillation, and other geophysical phenomena. REDD is designed to collect in-situ measurements within this region of the atmosphere where in-flight data collection using spacecraft has proven particularly challenging due to both the atmospheric density and the dominating presence of highly reactive atomic oxygen (AO). NASA Marshall Space Flight Center has a unique AO Facility (AOF) capable of simulating the conditions the sensor will encounter on orbit by creating a supersonic neutral beam of AO. Collimating the beam requires an intense magnetic field that creates significant interference for sensitive electronic devices. REDD is undergoing the final stages of validation testing in the AOF. In this presentation, we describe the LabVIEW-automated system design, the measured geometry and magnitude of the field and the specially designed mount and passive shielding that are utilized to mitigate the effects of the magnetic interference.
Advisors/Committee Members: Earle, Gregory D. (committeechair), Scales, Wayne A. (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: CubeSat; Retarding Potential Analyzer; Microchannel Plate Detector; Atomic Oxygen; Validation
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Williams, J. A. (2017). Enabling Validation of a CubeSat Compatible Wind Sensor. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78711
Chicago Manual of Style (16th Edition):
Williams, Jon A. “Enabling Validation of a CubeSat Compatible Wind Sensor.” 2017. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/78711.
MLA Handbook (7th Edition):
Williams, Jon A. “Enabling Validation of a CubeSat Compatible Wind Sensor.” 2017. Web. 06 Dec 2019.
Vancouver:
Williams JA. Enabling Validation of a CubeSat Compatible Wind Sensor. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/78711.
Council of Science Editors:
Williams JA. Enabling Validation of a CubeSat Compatible Wind Sensor. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78711
Virginia Tech
9.
Peng, Yuxiang.
GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.
Degree: MS, Electrical and Computer Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/79594
► The Global Navigation Satellite System (GNSS) is significantly advantageous to absolute and relative navigation for spacecraft formation flying. Ionospheric remote sensing, such as Total Electron…
(more)
▼ The Global Navigation Satellite System (GNSS) is significantly advantageous to absolute and relative navigation for spacecraft formation flying. Ionospheric remote sensing, such as Total Electron Content (TEC) measurements or ionospheric irregularity studies are important potential Low Earth Orbit (LEO) applications. A GNSS-based Hardware-in-the-loop (HIL) simulation testbed for LEO spacecraft formation flying has been developed and evaluated. The testbed infrastructure is composed of GNSS simulators, multi-constellation GNSS receiver(s), the Navigation & Control system and the Systems Tool Kit (STK) visualization system. A reference scenario of two LEO spacecraft is simulated with the initial in-track separation of 1000-m and targeted leader-follower configuration of 100-m along-track offset. Therefore, the feasibility and performance of the testbed have been demonstrated by benchmarking the simulation results with past work.
For ionospheric remote sensing, multi-constellation multi-frequency GNSS receivers are used to develop the GNSS TEC measurement and model evaluation system. GPS, GLONASS, Galileo and Beidou constellations are considered in this work. Multi-constellation GNSS TEC measurements and the GNSS-based HIL simulation testbed were integrated and applied to design a LEO satellite formation flying mission for ionospheric remote sensing. A scenario of observing sporadic E is illustrated and adopted to demonstrate how to apply GNSS-based spacecraft formation flying to study the ionospheric irregularities using the HIL simulation testbed. The entire infrastructure of GNSS-based spacecraft formation flying simulation and ionospheric remote sensing developed at
Virginia Tech is capable of supporting future ionospheric remote sensing mission design and validation.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Sweeney, Dennis G. (committee member), Black, Jonathan T. (committee member).
Subjects/Keywords: HIL Simulation; Remote Sensing; Spacecraft Formation Flying; GPS; GNSS; TEC; Ionospheric Irregularity; Scintillation
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Peng, Y. (2017). GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/79594
Chicago Manual of Style (16th Edition):
Peng, Yuxiang. “GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.” 2017. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/79594.
MLA Handbook (7th Edition):
Peng, Yuxiang. “GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications.” 2017. Web. 06 Dec 2019.
Vancouver:
Peng Y. GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/79594.
Council of Science Editors:
Peng Y. GNSS-based Spacecraft Formation Flying Simulation and Ionospheric Remote Sensing Applications. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/79594
Virginia Tech
10.
Cagas, Petr.
Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.
Degree: PhD, Aerospace and Ocean Engineering, 2018, Virginia Tech
URL: http://hdl.handle.net/10919/84979
► A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters,…
(more)
▼ A careful study of plasma-material interactions is essential to understand and improve the operation of devices where plasma contacts a wall such as plasma thrusters, fusion devices, spacecraft-environment interactions, to name a few. This work aims to advance our understanding of fundamental plasma processes pertaining to plasma-material interactions, sheath physics, and kinetic instabilities through theory and novel numerical simulations. Key contributions of this work include (i) novel continuum kinetic algorithms with novel boundary conditions that directly discretize the Vlasov/Boltzmann equation using the discontinuous Galerkin method, (ii) fundamental studies of plasma sheath physics with collisions, ionization, and physics-based wall emission, and (iii) theoretical and numerical studies of the linear growth and nonlinear saturation of the kinetic Weibel instability, including its role in plasma sheaths.
The continuum kinetic algorithm has been shown to compare well with theoretical predictions of Landau damping of Langmuir waves and the two-stream instability. Benchmarks are also performed using the electromagnetic Weibel instability and excellent agreement is found between theory and simulation. The role of the electric field is significant during nonlinear saturation of the Weibel instability, something that was not noted in previous studies of the Weibel instability. For some plasma parameters, the electric field energy can approach magnitudes of the magnetic field energy during the nonlinear phase of the Weibel instability.
A significant focus is put on understanding plasma sheath physics which is essential for studying plasma-material interactions. Initial simulations are performed using a baseline collisionless kinetic model to match classical sheath theory and the Bohm criterion. Following this, a collision operator and volumetric physics-based source terms are introduced and effects of heat flux are briefly discussed. Novel boundary conditions are developed and included in a general manner with the continuum kinetic algorithm for bounded plasma simulations. A physics-based wall emission model based on first principles from quantum mechanics is self-consistently implemented and demonstrated to significantly impact sheath physics. These are the first continuum kinetic simulations using self-consistent, wall emission boundary conditions with broad applicability across a variety of regimes.
Advisors/Committee Members: Srinivasan, Bhuvana (committeechair), Adams, Colin (committee member), Scales, Wayne A. (committee member), Warburton, Timothy (committee member).
Subjects/Keywords: plasma sheath; discontinuous Galerkin; continuum kinetic method; plasma instabilities; plasma-material interactions
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Cagas, P. (2018). Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/84979
Chicago Manual of Style (16th Edition):
Cagas, Petr. “Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.” 2018. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/84979.
MLA Handbook (7th Edition):
Cagas, Petr. “Continuum Kinetic Simulations of Plasma Sheaths and Instabilities.” 2018. Web. 06 Dec 2019.
Vancouver:
Cagas P. Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. [Internet] [Doctoral dissertation]. Virginia Tech; 2018. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/84979.
Council of Science Editors:
Cagas P. Continuum Kinetic Simulations of Plasma Sheaths and Instabilities. [Doctoral Dissertation]. Virginia Tech; 2018. Available from: http://hdl.handle.net/10919/84979
Virginia Tech
11.
Venkataramani, Karthik.
Simulating Nitric Oxide in the lower thermosphere using a 3D model.
Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/46171
► Nitric oxide (NO), despite being a minor species, influences the chemistry, composition and energy balance of the earth's atmosphere above 90 kilometers. Variations in its…
(more)
▼ Nitric oxide (NO), despite being a minor species, influences the chemistry, composition and energy balance of the earth's atmosphere above 90 kilometers. Variations in its density have been shown to strongly correlate with solar x-ray irradiance at lower latitudes and precipitating energetic particles at higher latitudes. Though the broad variations in NO densities with altitude and latitude are well known, there are still uncertainties associated with its chemistry. It is important to accurately model NO and its associated chemistry in an atmospheric model in order to obtain an accurate representation of the thermosphere.
The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) is a three dimensional first principles based model which includes a self consistent aeronomic scheme that solves for winds, temperatures and densities of various neutral and charged species in the earth's upper atmosphere. Using a combination of the solar irradiance spectrum and solar indices as inputs, the model computes these outputs at every time step.
The ability of the TIEGCM to predict NO densities in the thermosphere is examined by comparing results from the model with data obtained from the Student Nitric Oxide Explorer (SNOE). The comparisons are made for the year 1999 at 110 km and 150 km at the equator. Changes are made to the NO chemistry present in the model to reflect recent results obtained from laboratory data. Paricularly, the reaction of atomic oxygen with the first excited electronic state of nitrogen, N
2 (A) has been shown to play an important role in the production of NO. These changes are introduced to the model and their effect on NO densities is studied.
Overall, it is seen that the updated chemistry scheme reduces the model agreement with the SNOE data at 110 km while slightly improving the agreement at a 150 km. The loss of agreement at 110 km is attributed to the fact that the neutral temperatures and atomic oxygen densities calculated by the TIEGCM are in sharp disagreement to the temperatures predicted by the NRL-MSIS at a 110 km, on which the new chemistry scheme is based.
While the chemistry scheme used in this thesis is a step in the right direction for modelling NO using the TIEGCM, the parameters used were determined from the best fit obtained from the 1-D NO model. In the light of the differences between the NRL-MSIS and TIEGCM, it is necessary to return to the laboratory data and modify the parameters used here to achieve a better agreement with the data.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Earle, Gregory D. (committee member), Scales, Wayne A. (committeecochair).
Subjects/Keywords: Simulating NO; Thermospheric Modelling; N2(A); TIEGCM; Nitric Oxide
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Venkataramani, K. (2012). Simulating Nitric Oxide in the lower thermosphere using a 3D model. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/46171
Chicago Manual of Style (16th Edition):
Venkataramani, Karthik. “Simulating Nitric Oxide in the lower thermosphere using a 3D model.” 2012. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/46171.
MLA Handbook (7th Edition):
Venkataramani, Karthik. “Simulating Nitric Oxide in the lower thermosphere using a 3D model.” 2012. Web. 06 Dec 2019.
Vancouver:
Venkataramani K. Simulating Nitric Oxide in the lower thermosphere using a 3D model. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/46171.
Council of Science Editors:
Venkataramani K. Simulating Nitric Oxide in the lower thermosphere using a 3D model. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/46171
Virginia Tech
12.
Nikrant, Alex Warner.
Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.
Degree: MS, Aerospace Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/93959
► In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is…
(more)
▼ In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is the spacecraft’s propulsion system, which allows the vehicle to achieve and maintain its desired orbit or trajectory through space. One class of propulsion systems known as “electric propulsion” uses electrical power to accelerate the fuel of the spacecraft. These types of propulsion systems are far more efficient than traditional propulsion systems, which use chemical reactions to create thrust. One of the main components of certain types of electric propulsion systems is the hollow cathode, which initiates and sustains the thruster operation. In this research, a hollow cathode with several non-conventional characteristics is developed and tested. First of all, standard hollow cathodes use a heater to bring the cathode up to operational temperature, but this design is heaterless which offers several benefits to the cathode and electrical power system designs. Secondly, the cathode uses a non-conventional choice of material for the “emitter”, which emits electrons when heated and allows the cathode to operate. Lastly, while typical electric propulsion systems use xenon for fuel, this cathode uses argon which has several benefits over xenon including cost. An overview of electric propulsion is presented, as well as a new physics-based model of this type of cathode that allows useful calculations based on simple measurements. The design and test results of the cathode are discussed in detail, with several interesting and insightful behaviors that were noted during testing. Heaterless cathodes have the potential to improve the efficiency, cost, and weight of electric propulsion systems, and this research therefore contributes to an important field for the future of space exploration.
Advisors/Committee Members: Adams, Colin (committeechair), Scales, Wayne A. (committee member), Srinivasan, Bhuvana (committee member).
Subjects/Keywords: heaterless hollow cathode; electric propulsion; plasma dynamics; plume mode
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Nikrant, A. W. (2019). Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/93959
Chicago Manual of Style (16th Edition):
Nikrant, Alex Warner. “Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.” 2019. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/93959.
MLA Handbook (7th Edition):
Nikrant, Alex Warner. “Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode.” 2019. Web. 06 Dec 2019.
Vancouver:
Nikrant AW. Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. [Internet] [Masters thesis]. Virginia Tech; 2019. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/93959.
Council of Science Editors:
Nikrant AW. Development and Modelling of a Low Current LaB6 Heaterless Hollow Cathode. [Masters Thesis]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/93959
Virginia Tech
13.
Peng, Senlin.
A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.
Degree: PhD, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/28605
► Ionospheric scintillations can cause significant amplitude and/or phase fluctuations of GNSS signals. This work presents analysis results of scintillation effects on the new GPS L5…
(more)
▼ Ionospheric scintillations can cause significant amplitude and/or phase fluctuations of GNSS signals. This work presents analysis results of scintillation effects on the new GPS L5 signal based on data collected using a real-time scintillation monitoring and data collection system at HAARP, Alaska. The data collection setup includes a custom narrow band front end that collects GPS L1, L2 IF samples and two reconfigurable USRP2 based RF front ends to collect wideband GPS L5 and GLONASS L1 and L2 signals. The results confirm that scintillation has a stronger impact on GPS L2 and L5 signals than on the L1 signal. Our preliminary results also show that carrier phase and amplitude scintillations on each signal are highly correlated. The amplitude and carrier phase scintillation are also correlated among the three signals.
In this study, a multi-constellation multi-band GNSS software receiver has been developed based on USRP2, a general purpose radio platform. The C++ class-based software receiver were developed to process the IF data for GPS L1, L2C, and L5 and GLONASS L1 and L2 signals collected by the USRP2 front end. The front end performance is evaluated against the outputs of a high end custom front end driven by the same local oscillator and two commercial receivers, all using the same real signal sources. These results demonstrate that the USRP2 is a suitable front end for applications, such as ionosphere scintillation studies.
Another major contribution of this work is the implementation of a Vector tracking loop (VTL) for robust carrier tracking. The VTL is developed based on the extended Kalman filter (EKF) with adaptive covariance matrices. Both scalar tracking loop (STL) and VTL are implemented. Once an error in the scalar loop is detected, the results from the VTL are used to assist the STL. The performance of the VTL is compared with the traditional STL with three different data sets: raw GPS RF data with short signal outages, RF data with strong scintillation impacts collected during the last solar maximum, and high dynamic data with long interval signal outages from a GPS simulator. The results confirm the performance improvement of the VTL over scintillation impacts and show that the VTL can maintain signal lock during long intervals of signal outage if the satellite ephemerides are available and the pseudorange estimation is within one code chip accuracy. The dynamic performance improvement of the VTL is verified as well. The results show the potential of robust tracking based on VTL during scintillation and interference.
Advisors/Committee Members: Scales, Wayne A. (committeechair), Farhood, Mazen (committee member), Bose, Tamal (committee member), Reed, Jeffrey Hugh (committee member), Morton, Jade Yu (committee member).
Subjects/Keywords: GNSS; Ionosphere scintillation; Software receiver; Vector tracking loop
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Peng, S. (2012). A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28605
Chicago Manual of Style (16th Edition):
Peng, Senlin. “A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.” 2012. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/28605.
MLA Handbook (7th Edition):
Peng, Senlin. “A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies.” 2012. Web. 06 Dec 2019.
Vancouver:
Peng S. A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. [Internet] [Doctoral dissertation]. Virginia Tech; 2012. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/28605.
Council of Science Editors:
Peng S. A Multi-Constellation Multi-Frequency GNSS Software Receiver Design for Ionosphere Scintillation Studies. [Doctoral Dissertation]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/28605
Virginia Tech
14.
Ravindran Varrier, Nitya.
Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model.
Degree: MS, Electrical and Computer Engineering, 2010, Virginia Tech
URL: http://hdl.handle.net/10919/33998
► The Super Dual Auroral Radar Network (SuperDARN) is an international network of high frequency (HF) coherent scatter radars, employed to detect backscatter from magnetic field…
(more)
▼ The Super Dual Auroral Radar Network (SuperDARN) is an international network of high frequency (HF) coherent scatter radars, employed to detect backscatter from magnetic field aligned plasma irregularities in the ionosphere and to study the near- Earth space weather. Space weather impacts many technological systems including HF communications, Global Positioning System (GPS), and surveillance radars. Variations in the pattern of the backscatter from the ground (â ground scatterâ ) observed by the SuperDARN radars give information regarding the state of the ionosphere. In this thesis, ray tracing simulation of the observed ground scatter pattern for the mid-latitude SuperDARN radar at Blackstone,
Virginia is implemented. An existing ray tracing code was modified, to incorporate the IRI-2007 model for electron density. This ray tracing code was used to simulate the ground scatter pattern observed at Blackstone in the year 2009. Simulations were compared with the observed ground scatter to assess our understanding of the ionospheric conditions. The IRI-2007 model is found to be adequate to predict the average ground scatter pattern observed through the year, including the winter anomaly. However, one deficiency with the IRI-2007 model is its inability to predict the sporadic E layer formation in summer and an anomalous evening enhancement in backscatter power observed in some months of the year, described here for the first time. Finally some suggestions are presented for the further improvement of the simulation methods for backscatter prediction.
Advisors/Committee Members: Ellingson, Steven W. (committee member), Scales, Wayne A. (committee member), Baker, Joseph (committeecochair), Ruohoniemi, J. Michael (committeecochair).
Subjects/Keywords: Propagation Analysis; IRI-2007; HF radar; Ray Tracing; SuperDARN
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Ravindran Varrier, N. (2010). Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/33998
Chicago Manual of Style (16th Edition):
Ravindran Varrier, Nitya. “Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model.” 2010. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/33998.
MLA Handbook (7th Edition):
Ravindran Varrier, Nitya. “Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model.” 2010. Web. 06 Dec 2019.
Vancouver:
Ravindran Varrier N. Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model. [Internet] [Masters thesis]. Virginia Tech; 2010. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/33998.
Council of Science Editors:
Ravindran Varrier N. Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model. [Masters Thesis]. Virginia Tech; 2010. Available from: http://hdl.handle.net/10919/33998
Virginia Tech
15.
Malhotra, Garima.
HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.
Degree: MS, Electrical and Computer Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/78084
► The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling…
(more)
▼ The equatorial Quasi Biennial Oscillation (QBO) is known to be an important source of inter-annual variability at mid and high latitudes in both hemispheres. Coupling between QBO and the polar vortex has been extensively studied over the past few decades, however, less is known about QBO influences in the mid-latitude mesosphere. One reason for this is the relative lack of instrumentation available to study mesospheric dynamics at mid-latitudes. In this study, we have used the mid-latitude SuperDARN HF radar at Saskatoon (52.16 N, -106.53 E) to study inter-annual variation in mesospheric winds. The specific aim was to determine whether or not a Quasi Biennial signature could be identified in the Saskatoon mesosphere, and if so, to understand its relationship with the equatorial stratospheric QBO. To achieve this goal, a technique has been developed which extracts meteor echoes from SuperDARN near-range gates and then applies least-squares fitting across all radar beam directions to calculate hourly averages of the zonal and meridional components of the mesospheric neutral wind. Subsequent analysis of 13 years (2002-2014) of zonal wind data produced using this technique indicates that there is indeed a significant QBO signature present in Saskatoon mesospheric winds during late winter (Jan-Feb). This mesospheric QBO signature is in opposite phase with the equatorial stratospheric QBO, such that when QBO (at 50 hPa) is in its easterly (westerly) phase, the late winter winds in Saskatoon mesosphere become more (less) westerly. To further examine the source of the signature, we also analyzed winds in the Saskatoon stratosphere between 5 hPa and 70 hPa using the ECMWF ERA-Interim reanalysis data set, and found that the late winter stratospheric winds become less (more) westerly when QBO is easterly (westerly). This QBO signature in the mid-latitude stratospheric winds is essentially the same as that observed for the polar vortex in previous studies but it is opposite in phase to the mid-latitude mesospheric QBO. We therefore conclude that filtering of gravity waves through QBO-modulated stratospheric winds plays a major role in generating the mesospheric QBO signature we have identified in the Saskatoon HF radar data. When the Saskatoon stratospheric winds are anomalously westward during easterly QBO, the gravity waves having westward momentum might be filtered out, depositing a net eastward momentum in the mesosphere as they propagate upwards. This would result in increased westerly mesospheric winds at Saskatoon. The opposite would happen when the equatorial QBO is westerly.
Advisors/Committee Members: Scales, Wayne A. (committee member), Clauer, Robert C. (committee member), Baker, Joseph B. H. (committeecochair), Ruohoniemi, J. Michael (committeecochair).
Subjects/Keywords: HF Radar Meteor echoes; SuperDARN radar; Gravity wave filtering; Mesospheric QBO; Mid-Latitude QBO; Holton Tan; SuperDARN Radar Mesospheric winds
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Malhotra, G. (2016). HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78084
Chicago Manual of Style (16th Edition):
Malhotra, Garima. “HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.” 2016. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/78084.
MLA Handbook (7th Edition):
Malhotra, Garima. “HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds.” 2016. Web. 06 Dec 2019.
Vancouver:
Malhotra G. HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. [Internet] [Masters thesis]. Virginia Tech; 2016. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/78084.
Council of Science Editors:
Malhotra G. HF Radar Observations of Inter-Annual variations in Mid-Latitude Mesospheric Winds. [Masters Thesis]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/78084
Virginia Tech
16.
Brosie, Kayla Nicole.
Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.
Degree: MS, Electrical and Computer Engineering, 2017, Virginia Tech
URL: http://hdl.handle.net/10919/78710
► A full solar eclipse is going to be visible from a range of states in the contiguous United States on August 21, 2017. Since the…
(more)
▼ A full solar eclipse is going to be visible from a range of states in the contiguous United States on August 21, 2017. Since the atmosphere of the Earth is charged by the sun, the blocking of the sunlight by the moon may cause short term changes to the atmosphere, such as density and temperature alterations. There are many ways to measure these changes, one of these being ionospheric scintillation. Ionospheric scintillation is rapid amplitude and phase fluctuations of signals passing through the ionosphere caused by electron density irregularities in the ionosphere. At mid-latitudes, scintillation is not as common of an occurrence as it is in equatorial or high-altitude regions. One of the theories that this paper looks into is the possibility of the solar eclipse producing an instability in the ionosphere that will cause the mid-latitude region to experience scintillations that would not normally be present. Instabilities that could produce scintillation are reviewed and altered further to model similar conditions to those that might occur during the solar eclipse. From this, the satellites that are being used are discuses, as is hardware and software tools were developed to record the scintillation measurements. Although this work was accomplished before the eclipse occurred, measurement tools were developed and verified along with generating a model that predicted if the solar eclipse will produce an instability large enough to cause scintillation for high frequency satellite downlinks.
Advisors/Committee Members: McGwier, Robert W. (committeechair), Earle, Gregory D. (committeechair), Buehrer, Richard Michael (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: ionospheric scintillation; solar eclipse; temperature gradient instability; ionospheric instabilities
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Brosie, K. N. (2017). Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/78710
Chicago Manual of Style (16th Edition):
Brosie, Kayla Nicole. “Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.” 2017. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/78710.
MLA Handbook (7th Edition):
Brosie, Kayla Nicole. “Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse.” 2017. Web. 06 Dec 2019.
Vancouver:
Brosie KN. Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. [Internet] [Masters thesis]. Virginia Tech; 2017. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/78710.
Council of Science Editors:
Brosie KN. Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse. [Masters Thesis]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/78710
Virginia Tech
17.
Thomas, Evan Grier.
Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.
Degree: MS, Electrical and Computer Engineering, 2012, Virginia Tech
URL: http://hdl.handle.net/10919/19207
► Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network…
(more)
▼ Total electron content (TEC) data measured from ground-based GPS receivers is compared to HF backscatter from ionospheric irregularities obtained by Super Dual Auroral Radar Network (SuperDARN) radars. We present the first observations of a recurrent region of anomalous enhanced TEC at mid-latitudes over North America and attempt to characterize its frequency of occurrence. Next, we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization (TOI) from mid-latitude plumes of storm enhanced density (SED) during a geomagnetic storm on 26 September 2011. A channel of high density F region plasma was transported from the dayside ionosphere and into the polar cap by enhanced convection electric fields extending to mid-latitudes. After the solar wind IMF conditions quieted and the dayside convection electric fields retreated to higher latitudes, an SED was observed extending to, but not entering, the dayside cusp region. The source mechanism (enhanced electric fields) previously drawing the plasma from mid-latitudes and into the polar cap was no longer active, resulting in a fossil feature which persisted for several hours as it elongated in magnetic local time. Finally, we discuss ground surface effects on the HF backscatter observed by four SuperDARN radars. Monthly ground scatter occurrence rates are calculated for comparison with Arctic sea ice boundaries derived from satellite observations, showing reduced backscatter from regions covered by ice.
Advisors/Committee Members: Ruohoniemi, John Michael (committeechair), Baker, Joseph Benjamin (committeechair), Scales, Wayne A. (committee member), Pratt, Timothy (committee member).
Subjects/Keywords: SuperDARN; GPS; mid-latitude; ionosphere
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Thomas, E. G. (2012). Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19207
Chicago Manual of Style (16th Edition):
Thomas, Evan Grier. “Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.” 2012. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/19207.
MLA Handbook (7th Edition):
Thomas, Evan Grier. “Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars.” 2012. Web. 06 Dec 2019.
Vancouver:
Thomas EG. Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. [Internet] [Masters thesis]. Virginia Tech; 2012. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/19207.
Council of Science Editors:
Thomas EG. Dynamics of the geomagnetically disturbed ionosphere as measured by GPS receivers and SuperDARN HF radars. [Masters Thesis]. Virginia Tech; 2012. Available from: http://hdl.handle.net/10919/19207
Virginia Tech
18.
Pramodkumar, Neeraj.
Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.
Degree: MS, Electrical and Computer Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23845
► The Sub-Auroral Polarization Stream (SAPS) is a narrow, intense and persistent westward (sunward) ionospheric convection flow channel observed equatorward of the auroral electron precipitation boundary,…
(more)
▼ The Sub-Auroral Polarization Stream (SAPS) is a narrow, intense and persistent westward (sunward) ionospheric convection flow channel observed equatorward of the auroral electron precipitation boundary, predominantly on the nightside. Previous studies have identified disturbed-time SAPS to be a geomagnetic activity dependent phenomenon, which exhibits average pre-midnight and post-midnight velocities of 1000 m/s and 400 m/s respectively. Numerous studies have reported even narrower and more intense westward plasma flows called SAIDs to be embedded within SAPS channels, especially during substorm recovery phases. Quiet-time SAPS studies, although relatively few, have shown these SAPS to be associated with much weaker velocities and to be influenced by substorm intensifications. However, these studies have been limited in their ability to make simultaneous measurements of SAPS flow velocities over many hours of MLT. The recent expansion of SuperDARN radars to middle latitudes facilitates unprecedented large-scale observations of SAPS over 10 hours of MLT with high temporal and spatial resolution. In this thesis, we first examine the spatial and temporal dynamics of one quiet-time SAPS event, using the mid-latitude SuperDARN radars. The SAPS was identified as elevated flows lying equatorward of the auroral electron precipitation boundary specified by the NOAA POES satellites. We demonstrate the L-shell fitting technique to analyze the dynamics in the strength and direction of the two-dimensional SAPS flow velocities at three separate magnetic longitudes. The quiet-time SAPS event thus examined lasted for over 4 hours in UT and extended over 10 hours of MLT, as is commonly observed for disturbed-time SAPS.
However, the decrease in SAPS peak latitudes and peak velocities with MLT and MLon respectively, observed for disturbed-time SAPS, was not observed for this event. We also find the dynamics of the enhancements in the quiet-time SAPS peak velocities, to correlate well with that of substorm intensifications identified using the CARISMA magnetometers. We then identify numerous such conjunctions between quiet-time SAPS and substorms to infer that quiettime SAPS were almost always associated with substorms and their durations were well bounded by that of the substorms for most cases. Next, we extend this analysis over to a statistical study of quiet-time and disturbed-time SAPS events identified over two years. From this study, we find quiet-time SAPS to occur between the relatively narrow nightside MLT range of [18, 4] whereas disturbed-time SAPS was found to occur between the broader nightside MLT range of [15, 5]. We also find the occurrence percentage of quiet-time SAPS to be at its highest between the narrow latitude range of 60-66⁰, while disturbed-time SAPS was observed to occur within a much broader latitude range of 55-66⁰. Finally, the calibration and validation of a control card used in the SuperDARN radar transmitters, is discussed.
Advisors/Committee Members: Ruohoniemi, John Michael (committeechair), Baker, Joseph Benjamin (committeechair), Pratt, Timothy (committee member), Scales, Wayne A. (committee member).
Subjects/Keywords: SuperDARN; SAPS; mid-latitude; substorm; ionosphere
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Pramodkumar, N. (2013). Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23845
Chicago Manual of Style (16th Edition):
Pramodkumar, Neeraj. “Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.” 2013. Masters Thesis, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/23845.
MLA Handbook (7th Edition):
Pramodkumar, Neeraj. “Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars.” 2013. Web. 06 Dec 2019.
Vancouver:
Pramodkumar N. Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. [Internet] [Masters thesis]. Virginia Tech; 2013. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/23845.
Council of Science Editors:
Pramodkumar N. Large-scale observations of the spatial and temporal dynamics of quiet-time Sub-auroral Polarization Streams using SuperDARN HF Radars. [Masters Thesis]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23845
Virginia Tech
19.
Mahmoudian, Alireza.
New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.
Degree: PhD, Electrical and Computer Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/19239
► Recently, experimental observations have shown that radar echoes from the irregularity source region associated with mesospheric dusty space plasmas may be modulated by radio wave…
(more)
▼ Recently, experimental observations have shown that radar echoes from the irregularity source region associated with mesospheric dusty space plasmas may be modulated by radio wave heating with ground-based ionospheric heating facilities. These experiments show great promise as a diagnostic for the associated dusty plasma in the Near-Earth Space Environment which is believed to have links to global change. This provides an alternative to more complicated and costly space-based observational approaches to investigating these layers. This dissertation seeks to develop new analytical and computational models to investigate fundamental physics of the associated dusty plasmas as well as utilize experimental observations during High Frequency HF ground-based heating experiments to develop practical techniques for diagnosing these dusty plasma layers. The dependency of the backscattered signal strength (i.e. Polar Mesospheric Summer Echoes PMSEs) after the turn-on and turn-off of the radio wave heating on the radar frequency is an unique phenomenon that can shed light on the unresolved issues associated with the basic physics of the natural charged mesospheric dust layer. The physical process after turn-on and turn-off of radio wave heating is explained by competing ambipolar diffusion and dust charging processes. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during radiowave heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius on the temporal evolution of electron irregularities associated with PMSE is investigated. The possibility of observing the turn-on overshoot (enhancement of radar echoes after the radiowave turn-on) in the high frequency HF radar band is discussed based on typical mesospheric parameters. It has been shown that predicted enhancement of electron irregularity amplitude after heater turn-on at HF band is the direct manifestation of the dust charging process in the space. Therefore further active experiments of PMSEs should be pursued at HF band to illuminate the fundamental charging physics in the space environment to provide more insight on this unique medium. Preliminary observation results of HF PMSE heating experiment with the new 7.9 MHz radar at the European Incoherent Scatter EISCAT facility appear promising for the existence of PMSE turn-on overshoot. Therefore, future experimental campaigns are planned to validate these predictions. Computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930MHz corresponding to existing ionospheric heating facilities. Data from a 2009 very high frequency VHF (224 MHz) experiment at EISCAT is compared with the computational model to obtain dust parameters in…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Pratt, Timothy (committee member), Earle, Gregory D. (committee member), Roy, Christopher John (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: Ionospheric Modification; Plasma; Numerical Simulations; Analytical model
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Mahmoudian, A. (2013). New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/19239
Chicago Manual of Style (16th Edition):
Mahmoudian, Alireza. “New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.” 2013. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/19239.
MLA Handbook (7th Edition):
Mahmoudian, Alireza. “New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities.” 2013. Web. 06 Dec 2019.
Vancouver:
Mahmoudian A. New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/19239.
Council of Science Editors:
Mahmoudian A. New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/19239
Virginia Tech
20.
Esmond, Micah Jeshurun.
Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.
Degree: PhD, Mechanical Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/81447
► A two-dimensional, time-dependent model and code have been developed to model electrothermal (ET) plasma discharges. ET plasma discharges are capillary discharges that draw tens of…
(more)
▼ A two-dimensional, time-dependent model and code have been developed to model electrothermal (ET) plasma discharges. ET plasma discharges are capillary discharges that draw tens of kA of electric current. The current heats the plasma, and the plasma radiates energy to the capillary walls. The capillary walls ablate by melting and vaporizing and by sublimation. The newly developed model and code is called the Three-fluid, 2D Electrothermal Plasma Flow Simulator (THOR). THOR simulates the electron, ion, and neutral species as separate fluids coupled through interaction terms. The two-dimensional modeling capabilities made available in this new code represent a tool for the exploration and analysis of the physics involved in ET plasma discharges that has never before been available.
Previous simulation models of ET plasma discharges have relied primarily on a 1D description of the plasma. These models have often had to include a tunable correction factor to account for the vapor shield layer - a layer of cold ablated vapor separating the plasma core from the ablating surface and limiting the radiation heat flux to the capillary wall. Some studies have incorporated a 2D description of the plasma boundary layer and shown that the effects of a vapor shield layer can be modeled using this 2D description. However, these 2D modeling abilities have not been extended to the simulation of pulsed ET plasma discharges. The development of a fully-2D and time-dependent simulation model of an entire ET plasma source has enabled the investigation of the 2D development of the vapor shield layer and direct comparison with experiments. In addition, this model has provided novel insight into the inherently 2D nature of the internal flow characteristics involved within the plasma channel in an ET plasma discharge. The model is also able to capture the effects of inter-species interactions.
This work focuses on the development of the THOR model. The model has been implemented using C++ and takes advantage of modern supercomputing resources. The THOR model couples the 2D hydrodynamics and the interactions of the plasma species through joule heating, ionization, recombination, and elastic collisions. The analysis of simulation results focuses on emergent internal flow characteristics, direct simulation of the vapor shield layer, and the investigation of source geometry effects on simulated plasma parameters. The effect of elastic collisions between electrons and heavy species are shown to affect internal flow characteristics and cause the development of back-flow inside the ET plasma source. The development of the vapor shield layer has been captured using the diffusion approximation for radiation heat transfer within the ET plasma source with simulated results matching experimental measurements. The relationship between source radius and peak current density inside ET plasma discharges has also been explored, and the transition away from the ablation-controlled operation of ET plasma discharges has been observed.
Advisors/Committee Members: Battaglia, Francine (committeechair), Winfrey, Leigh (committeechair), Scales, Wayne A. (committee member), Liu, Yang (committee member), Vick, Brian (committee member).
Subjects/Keywords: Electrothermal plasma; capillary discharge; plasma simulation
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Esmond, M. J. (2016). Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/81447
Chicago Manual of Style (16th Edition):
Esmond, Micah Jeshurun. “Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.” 2016. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/81447.
MLA Handbook (7th Edition):
Esmond, Micah Jeshurun. “Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges.” 2016. Web. 06 Dec 2019.
Vancouver:
Esmond MJ. Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/81447.
Council of Science Editors:
Esmond MJ. Two-dimensional, Hydrodynamic Modeling of Electrothermal Plasma Discharges. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/81447
Virginia Tech
21.
Zheng, Yi.
Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.
Degree: PhD, Electrical and Computer Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/48892
► Fast and accurate diagnosis is always in demand by modern medical professionals and in the area of national defense. At present, limitations of testing speed,…
(more)
▼ Fast and accurate diagnosis is always in demand by modern medical professionals and in the area of national defense. At present, limitations of testing speed, sample conditions, and levels of precision exist under current technologies, which are usually slow and involve testing the specimen under laboratory conditions. Typically, these methods also involve several biochemical processing steps and subsequent detection of low energy luminescence or electrical changes, all of which reduce the speed of the test as well as limit the precision. In order to solve these problems and improve the sensing performance, this project proposes an innovative CMOS magnetic biological sensor system for rapidly testing the presence of potential pathogens and bioterrorism agents (zoonotic microorganisms) both in specimens and especially in the environment. The sensor uses an electromagnetic detection mechanism to measure changes in the number of microorganisms – tagged by iron nanoparticles – that are placed on the surface of an integrated circuit (IC) chip. Measured magnetic effects are transformed into electronic signals that count the number and type of organisms present. This biosensor introduces a novel design of a conical-shaped inductor, which achieves ultra-accuracy of sensing biological pathogens. The whole system is integrated on a single chip based on the fabrication process of IBM 180 nm (CMOS_IBM_7RF), which makes the sensor small-sized, portable, high speed, and low cost. The results of designing, simulating, and fabricating the sensor are reported in this dissertation.
Advisors/Committee Members: Tront, Joseph G. (committeechair), Scales, Wayne A. (committee member), Ha, Dong S. (committee member), Sriranganathan, Nammalwar (committee member), Schaumont, Patrick Robert (committee member).
Subjects/Keywords: Biohazard; Antibody and antigen; Pathogen; Iron nanoparticle; CMOS; Integrated circuit; Conical-shaped inductor; Uniform magnetic field; Magnetic sensor; LC oscillator; Frequency counter; Prototype; Antenna effect
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Zheng, Y. (2014). Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/48892
Chicago Manual of Style (16th Edition):
Zheng, Yi. “Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.” 2014. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/48892.
MLA Handbook (7th Edition):
Zheng, Yi. “Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System.” 2014. Web. 06 Dec 2019.
Vancouver:
Zheng Y. Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/48892.
Council of Science Editors:
Zheng Y. Biological Agent Sensing Integrated Circuit (BASIC): A New Complementary Metal-oxide-semiconductor (CMOS) Magnetic Biosensor System. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/48892
Virginia Tech
22.
Samimi, Alireza.
Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.
Degree: PhD, Electrical and Computer Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/51833
► Stimulated Electromagnetic Emissions SEEs may provide important diagnostic information about space plasma composition, energetics, and dynamics during active experiments in which ground-based high powered radio…
(more)
▼ Stimulated Electromagnetic Emissions SEEs may provide important diagnostic information about space plasma composition, energetics, and dynamics during active experiments in which ground-based high powered radio waves are transmitted into the ionosphere. The nonlinear plasma processes producing this secondary radiation are not well understood particularly for some recent observations where the transmitter (pump) frequency is near the second harmonic of the electron gyro-frequency. New, more comprehensive, experimental observations of spectral features within 1kHz of the pump wave frequency are reported here in order to begin more careful comparisons of the experimental observations and a possible theoretical underpinning which is also provided. The experimental observations typically show two distinct types of secondary radiation spectra which are a) discrete narrowband harmonic spectral structures ordered by the ion gyro-frequency, so-called stimulated ion Bernstein Scatter (SIBS) and, b) broadband spectral structure with center frequency near 500 Hz and similar spectral bandwidth named ion acoustic parametric decay (IAPD). A theoretical model is provided that interprets these spectral features as resulting from parametric decay instabilities in which the pump field ultimately decays into high frequency upper hybrid/electron Bernstein and low frequency neutralized ion Bernstein and/or obliquely propagating ion acoustic waves at the upper hybrid interaction altitude. Detailed calculations of the threshold level, growth rate, unstable wavenumber and frequency bandwidth of the instabilities are provided for comparisons with experimental observations. An assessment of the effect of the critical instability parameters are provided including pump electric field strength, proximity of the pump frequency to the electron gyro-frequency and pump electric field geometry. The model shows quite reasonable agreement with the experimental observations.
Next, a two dimensional Particle-In-Cell Monte-Carlo Collision computational model (PIC-MCC) is employed in order to consider nonlinear aspects such as 1) electron acceleration through wave-particle heating, 2) more complex nonlinear wave-wave processes and 3) temporal evolution of electron irregularities through nonlinear saturation. The simulation results show that the IB associated parametric decay is primarily associated with electron acceleration perpendicular to the geomagnetic field. More gyro-harmonic lines are typically associated with more intense heating. Heating is reduced when the pump frequency is sufficiently close to 2fce. The IA associated parametric decay instability is primarily associated with electron tail heating along the magnetic field and heating is reduced when the pump frequency is sufficiently close to 2fce. Characteristics of caviton collapse behavior become prevalent in this case. Results are discussed within the context of some recent experimental observations. Further discussions are provided of connections with past observed SEE spectral features…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Ruohoniemi, John Michael (committee member), Sharpe, Eric R. (committee member), Bailey, Scott M. (committee member), Pratt, Timothy (committee member).
Subjects/Keywords: Stimulated Electromagnetic Emission (SEE); Parametric decay instability (PDI); Oscillating two stream instability (OTSI)
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Samimi, A. (2013). Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/51833
Chicago Manual of Style (16th Edition):
Samimi, Alireza. “Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.” 2013. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/51833.
MLA Handbook (7th Edition):
Samimi, Alireza. “Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating.” 2013. Web. 06 Dec 2019.
Vancouver:
Samimi A. Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/51833.
Council of Science Editors:
Samimi A. Study of Narrow-Band Spectral Characteristics of Stimulated Electromagnetic Emission (SEE) During Second Electron Gyro-Harmonic Heating. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/51833
Virginia Tech
23.
Wang, Pu.
Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas.
Degree: PhD, Aerospace and Ocean Engineering, 2010, Virginia Tech
URL: http://hdl.handle.net/10919/37368
► Surface charging is a fundamental interaction process in space plasma engineering. A three-dimensional Immersed Finite Element Particle-In-Cell (IFE-PIC) method is developed to model surface charging…
(more)
▼ Surface charging is a fundamental interaction process in space plasma engineering. A three-dimensional Immersed Finite Element Particle-In-Cell (IFE-PIC) method is developed to model surface charging involving complex boundary conditions. This method extends the previous IFE-PIC algorithm to explicitly include charge deposition on a dielectric surface for charging calculations. Three simulation studies are carried out using the new algorithm to model current collection and charging in both the orbital motion limited (OML) and space charge limited regime. The first one is a full particle simulation of the charging process of single small sphere and clusters of multiple small spheres in plasma. We find that while single sphere charging agrees well with the predictions of the OML theory, the charging of a sphere in a cluster is significantly, indicating that the often used OML charging model is not an accurate one to model charging in dusty plasma. The second one concerns a secondary electron emission experiment. The simulation includes detailed experimental setup in a vacuum chamber and the results are compared against experimental data. The simulation is used to determine the facility error in experiments. The third one is a full particle simulation of charging on lunar surface. The simulation concerns both flat and non-flat surface, and spacecraft on lunar surface, in the lunar polar region. The surface sees a mesothermal solar wind plasma flow and the emission of photoelectrons and secondary electrons. At a small sun elevation angle, the surface landscape generates a complex plasma flow field and local differential charging on surface. The results will be useful for further study of charging and levitation of lunar dust.
Advisors/Committee Members: Wang, Joseph J. (committeechair), Scales, Wayne A. (committee member), Lin, Tao (committee member), Roy, Christopher J. (committeecochair).
Subjects/Keywords: Charging; Particle-In-Cell; Immersed Finite Element
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Wang, P. (2010). Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/37368
Chicago Manual of Style (16th Edition):
Wang, Pu. “Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas.” 2010. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/37368.
MLA Handbook (7th Edition):
Wang, Pu. “Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas.” 2010. Web. 06 Dec 2019.
Vancouver:
Wang P. Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas. [Internet] [Doctoral dissertation]. Virginia Tech; 2010. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/37368.
Council of Science Editors:
Wang P. Immersed Finite Element Particle-In-Cell Modeling of Surface Charging in Rarefied Plasmas. [Doctoral Dissertation]. Virginia Tech; 2010. Available from: http://hdl.handle.net/10919/37368
Virginia Tech
24.
Bordikar, Maitrayee Ranade.
Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment.
Degree: PhD, Electrical and Computer Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23206
► This work focuses on the analysis of plasma irregularities generated during two active space experiments: the injection of an artificial dust layer, and high-power radio…
(more)
▼ This work focuses on the analysis of plasma irregularities generated during two active space experiments: the injection of an artificial dust layer, and high-power radio waves. The objective of the "first experiment is to examine the effects of arti"ficially created dust layers on the scatter of radars from plasma irregularities embedded in dusty plasma in space. This is an alternate approach for understanding the mechanisms of enhanced radar scatter from plasma irregularities embedded in Noctilucent Clouds and Polar Mesospheric Summer Echoes. The second experiment involves a transmission of high power electromagnetic waves into the ionospheric plasma from the ground, which can excite stimulated electromagnetic emissions off"set from the transmitter frequency. These stimulated electromagnetic emissions provide diagnostic information of the ionosphere and thus can be used to investigate fundamental physical principles which govern the earth\'s ionosphere, so that present and future transmission technologies may take into account the complexities of the ionosphere. The interaction altitude of the artificial dust layer and high power radio waves is approximately 250 km and 160 km respectively, thus dealing with uniquely different regions of the ionosphere. Each experiment is discussed separately using theoretical, observational and advanced computational methodologies. The study fi"rst investigates plasma turbulence associated with the creation of an artificial dust layer in the earth\'s ionosphere. Two scenarios are considered for plasma irregularity generation as dust is injected at an oblique angle across the geomagnetic "field. The "first is a shear-driven plasma instability due to inhomogeneities in the boundary layer between the injected charged dust layer and the background plasma. This begins to appear at very early times once the dust is released into the space plasma, which is of the order or less than the dust charging time period. The second mechanism is free streaming of the charged dust relative to the background plasma. This produces irregularities at times much longer than the dust charging period and also longer than the dust plasma period. Although both mechanisms are shown to produce turbulence in the lower hybrid frequency range, the resulting irregularities have important differences in their physical characteristics. A comparison between the processes is made to determine the consequences for upcoming observations. Both processes are shown to have the possibility of generating turbulence after the release of dust for the regimes of upcoming space experiments over a range of timescales. This work also presents the fi"rst observations of unique narrowband emissions ordered near the Hydrogen ion (H+) gyro-frequency (fcH) in the Stimulated Electromagnetic Emission (SEE) spectrum when the transmitter is tuned near the second electron gyro-harmonic frequency (2fce), during ionospheric…
Advisors/Committee Members: Scales, Wayne A. (committeechair), Clauer, C Robert (committee member), Davis, William A. (committee member), Pratt, Timothy (committee member), Tafti, Danesh K. (committee member).
Subjects/Keywords: Dusty Plasma; Particle-in-Cell Code; Hybrid Code; Numerical Simulation; SEE; Ion-Ion Hybrid Structuring; Three-wave Parametric Decay Instability
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bordikar, M. R. (2013). Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23206
Chicago Manual of Style (16th Edition):
Bordikar, Maitrayee Ranade. “Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment.” 2013. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/23206.
MLA Handbook (7th Edition):
Bordikar, Maitrayee Ranade. “Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment.” 2013. Web. 06 Dec 2019.
Vancouver:
Bordikar MR. Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/23206.
Council of Science Editors:
Bordikar MR. Analysis of Plasma Wave Irregularities Generated during Active Experiments in Near-Earth Space Environment. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23206
Virginia Tech
25.
Janeski, John.
Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.
Degree: PhD, Aerospace and Ocean Engineering, 2013, Virginia Tech
URL: http://hdl.handle.net/10919/23922
► Electrodynamic tethers have a wide range of proposed applications in the fields of satellite propulsion and space plasma research. The fundamental purpose of this dissertation…
(more)
▼ Electrodynamic tethers have a wide range of proposed applications in the fields of satellite propulsion and space plasma research. The fundamental purpose of this dissertation is to improve the understanding of the behavior of an electrodynamic tether (EDT) system in Earth's ionosphere. An electrodynamic tether system consists of two satellites connected by a long tether that generates current to produce either power or thrust via the system's electromagnetic interaction with the space environment. Previous electrodynamic tether investigations decouple the interaction between the tether and the constantly changing plasma environment. The limiting factor inhibiting the development of a full system model that has an accurate characterization of the tether/plasma interaction is that the understanding of that interaction is not well developed over a wide range of system parameters. The EDT system model developed in this study uses a high fidelity dynamics model that includes a tether current described by an analytical current collection model whose plasma parameters are determine by the International Reference Ionosphere. It is first shown that new instabilities are induced in the system dynamics under a basic analytical current model versus a constant current model.
A 2-D3v Particle-in-Cell (PIC) code has been developed to study the plasma dynamics near a positively charged EDT system end-body and their impact on the current collected. Simulations are run over a range of system parameters that occur throughout a LEO orbit. The azimuthal current structures observed during the TSS-1R mission are found to enhance the current collected by the satellite when the magnetic field is slightly off of perpendicular to the orbital velocity. When the in-plane component of the magnetic field becomes large, the electrons are not able to easily cross the field lines causing plasma lobes form above and below the satellite. The lobes limit the current arriving to the satellite and also cause an enhanced wake to develop. A high satellite bias causes a stable bow-shock structure to form in the ram region of the satellite, which limits the number of electrons entering the sheath region and thus limiting the current collected. Electron-neutral collisions are found to destabilize the bow-shock structure and remove its current limiting effects. Additionally, as the magnetization of the plasma is increased, the current becomes limited by the charged particle's inability to cross magnetic field lines. Analytical curve fits based on the simulation results are presented that characterize the dependence of the average current collected on the local magnetic field orientations, space plasma magnetization and satellite potential.
The results from the PIC simulations characterizing the magnetic field's influence on the tether's current are incorporated into the system dynamics model to study the behavior of the EDT system over a range of inclinations. The magnetic field is found to limit the diurnal variations in the current collected by the…
Advisors/Committee Members: Hall, Christopher D. (committeechair), Scales, Wayne A. (committeechair), Woolsey, Craig A. (committee member), Earle, Gregory D. (committee member).
Subjects/Keywords: Electrodynamic Tether; Current Collection; Spacecraft Charging; Particle-In-Cell Simulations
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Janeski, J. (2013). Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/23922
Chicago Manual of Style (16th Edition):
Janeski, John. “Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.” 2013. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/23922.
MLA Handbook (7th Edition):
Janeski, John. “Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment.” 2013. Web. 06 Dec 2019.
Vancouver:
Janeski J. Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. [Internet] [Doctoral dissertation]. Virginia Tech; 2013. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/23922.
Council of Science Editors:
Janeski J. Dynamics of an Electrodynamic Tether System in a Varying Space-Plasma Environment. [Doctoral Dissertation]. Virginia Tech; 2013. Available from: http://hdl.handle.net/10919/23922
Virginia Tech
26.
Robertson, Ellen Faith.
Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.
Degree: PhD, Electrical Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/94631
► Prior to launch, space craft instruments need to be tested in a relevant environment to prove operational functionality. Thus, we have developed an ion source…
(more)
▼ Prior to launch, space craft instruments need to be tested in a relevant environment to
prove operational functionality. Thus, we have developed an ion source to stimulate thermal
plasma instruments in a vacuum chamber. This dissertation presents the mechanical design
of the source, simulations of the potentials and charged particle trajectories in and around
the source, and vacuum chamber measurements of the emitted ion beam. Once the ion
source is understood, it is successfully used to test a typical ion instrument. Further aspects
of the ion source, efficiency, thermionic filament emission, and collision frequencies are also
discussed.
Advisors/Committee Members: Earle, Gregory D. (committeechair), Tront, Joseph G. (committee member), Srinivasan, Bhuvana (committee member), Scales, Wayne A. (committee member), Bailey, Scott M. (committee member).
Subjects/Keywords: Space Science; Ion source; Simulations; Plasma; Vacuum Testing; Satellite Instrumentation
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Robertson, E. F. (2019). Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/94631
Chicago Manual of Style (16th Edition):
Robertson, Ellen Faith. “Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.” 2019. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/94631.
MLA Handbook (7th Edition):
Robertson, Ellen Faith. “Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments.” 2019. Web. 06 Dec 2019.
Vancouver:
Robertson EF. Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/94631.
Council of Science Editors:
Robertson EF. Validation and Characterization of a Laboratory Ion Source for Testing Thermal Space-Plasma Instruments. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/94631
Virginia Tech
27.
Debchoudhury, Shantanab.
Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise.
Degree: PhD, Electrical Engineering, 2019, Virginia Tech
URL: http://hdl.handle.net/10919/88466
► The plasma environment in Earth’s upper atmosphere is dynamic and diverse. Of particular interest is the ionosphere - a region of dense ionized gases that…
(more)
▼ The plasma environment in Earth’s upper atmosphere is dynamic and diverse. Of particular interest is the ionosphere - a region of dense ionized gases that directly affects the variability in weather in space and the communication of radio wave signals across Earth. Retarding potential analyzers (RPA) are instruments that can directly measure the characteristics of this environment in flight. With the growing popularity of small satellites, these probes need to be studied in greater detail to exploit their ability to understand how ions - the positively charged particles- behave in this region. In this dissertation, we aim to understand how the RPA measurements, obtained as current-voltage relationships, are affected by electronic noise. We propose a methodology to understand the associated uncertainties in the estimated parameters through a simulation study. The results show that a statistics based algorithm can help to interpret RPA data in the presence of noise, and can make autonomous, robust and more accurate measurements compared to a traditional non-linear curve-fitting routine. The dissertation presents the challenges in analyzing RPA data that is affected by noise and proposes a new method to better interpret measurements in the ionosphere that can enable further scientific progress in the space physics community.
Advisors/Committee Members: Earle, Gregory D. (committeechair), Sengupta, Srijan (committee member), Scales, Wayne A. (committee member), Abbott, Amos L. (committee member), Davidson, Ryan (committee member).
Subjects/Keywords: Retarding Potential Analyzers; in-situ data in terrestrial ionosphere; impact of noise; uncertainty in the presence of noise; statistics guided resampling
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Debchoudhury, S. (2019). Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/88466
Chicago Manual of Style (16th Edition):
Debchoudhury, Shantanab. “Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise.” 2019. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/88466.
MLA Handbook (7th Edition):
Debchoudhury, Shantanab. “Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise.” 2019. Web. 06 Dec 2019.
Vancouver:
Debchoudhury S. Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise. [Internet] [Doctoral dissertation]. Virginia Tech; 2019. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/88466.
Council of Science Editors:
Debchoudhury S. Parameter Estimation from Retarding Potential Analyzers in the Presence of Realistic Noise. [Doctoral Dissertation]. Virginia Tech; 2019. Available from: http://hdl.handle.net/10919/88466
Virginia Tech
28.
Thurber, Andrew.
Investigations of Hypervelocity Impact Physics.
Degree: PhD, Mechanical Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/95298
► Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm…
(more)
▼ Spacecraft and satellites in orbit are under an increasing threat of impact from orbital debris and naturally occurring meteoroids. While objects larger than 10 cm are routinely tracked and avoided, collisions inevitably occur with smaller objects at relative velocities exceeding 10 km/s. Such hypervelocity impacts (HVI) create immense shock pressures and can melt or vaporize aerospace materials, even inducing brief plasmas at higher speeds. Sacrificial shields have been developed to protect critical components from damage under these conditions, but the response of many materials in such an extreme event is still poorly understood.
This work presents the summary of computational analysis methods to quantify the relevant physical mechanisms at play in a hypervelocity impact. Strain rate-dependent behavior was investigated using several models, and fluid material descriptions were used to draw parallels under high shear rate loading. The production and expansion of impact plasmas were modeled and compared to experimental evidence. Additionally, a parametric study was performed on a multitude of possible material candidates for sacrificial shield design, and new shielding configurations were proposed.
A comparison of material models indicated that the Johnson-Cook and Steinberg-Cochran-Guinan-Lund metallic formulations yielded the most consistent results with the lowest deviation from experimental measures in the strain rate regime of interest. Both meshless Lagrangian and quasi-Eulerian meshed schemes approximated the qualitative and quantitative characteristics of HVI debris clouds with average measurable errors under 5%. While the meshless methods showed better resolution of interfaces and small details, the meshed methods were shown to converge faster under several metrics with fewer regions of spurious instability.
Additionally, a new technique was introduced using hypothetical viscous fluids to approximate debris cloud behavior, which showed good correlation to experimental results when such models were constructed using the shear rates seen in hypervelocity impacts. Formulations using non-Newtonian fluids showed additional capability in approximating solid behavior, both quantitatively and qualitatively. Such fluid models are significant, in that they reproduced the qualitative and quantitative characteristics of evolving debris clouds with better fidelity than purely hydrodynamic models using inviscid fluids. This indicates that while inertial effects can dominate overdriven shock phenomena, neglecting shear forces invariably introduces errors; such forces can instead be simplistically approximated via viscous models. The viscous approximation also allowed for a successful scaling analysis using dimensionless Pi terms, which was unfeasible using solid constitutive relations.
Attempts to model plasma dynamics saw success in the simulation of a laser ablation-driven flyer plate by using a hot gas with solid initial conditions; similar strategies were used to analyze plasma production in hypervelocity impacts…
Advisors/Committee Members: Bayandor, Javid (committeechair), Battaglia, Francine (committee member), O'Brien, Walter F (committee member), Scales, Wayne A (committee member), Samareh, Jamshid A. (committee member).
Subjects/Keywords: impact; orbital debris; finite element; shock physics
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Thurber, A. (2014). Investigations of Hypervelocity Impact Physics. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/95298
Chicago Manual of Style (16th Edition):
Thurber, Andrew. “Investigations of Hypervelocity Impact Physics.” 2014. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/95298.
MLA Handbook (7th Edition):
Thurber, Andrew. “Investigations of Hypervelocity Impact Physics.” 2014. Web. 06 Dec 2019.
Vancouver:
Thurber A. Investigations of Hypervelocity Impact Physics. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/95298.
Council of Science Editors:
Thurber A. Investigations of Hypervelocity Impact Physics. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/95298
29.
Thomas, Evan Grier.
Morphology and dynamics of storm-time ionospheric density structures.
Degree: PhD, Electrical and Computer Engineering, 2016, Virginia Tech
URL: http://hdl.handle.net/10919/64905
► Accurate knowledge of the electron density structure of the Earth's upper atmosphere is crucial to forecasting the performance of transionospheric radio signals. For this research,…
(more)
▼ Accurate knowledge of the electron density structure of the Earth's upper atmosphere is crucial to forecasting the performance of transionospheric radio signals. For this research, we focus on storm-time structuring in the mid- to high latitude ionosphere where large gradients in electron density can cause severe degradation of communication and navigation signals. We begin in Chapter 2 with a review of the primary data sets and methods used to accomplish the collaborative, multi-instrument studies described in this dissertation. In Chapter 3, we compare observational techniques for tracking polar cap patches during a moderate geomagnetic storm interval. For the first time, we monitor the transportation of patches with high spatial and temporal resolution across the polar cap for 1 – 2~h using a combination of GPS TEC, all-sky airglow imagers (ASIs), and Super Dual Auroral Radar Network (SuperDARN) HF radar backscatter. Simultaneous measurements from these data sets allow for continuous tracking of patch location, horizontal extent, and velocity even under adverse observational conditions for one or more of the techniques. A focus is placed on the structuring of patches, particularly on the nightside ionosphere as they become wider in the dawn-dusk direction and develop narrow finger-like structures. In Chapter 4, we perform a superposed epoch analysis to characterize the average response of GPS TEC in the North American sector during more than 100 geomagnetic storms over a 13-year interval. For the first time a rigorous approach is used to fully separate storm-time, local time, longitudinal, and seasonal effects at midlatitudes where dense ground receiver coverage is available. The rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer-lasting negative phase across all latitudes and local times. Our results show clear seasonal variations in the storm-time TEC, such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects. A prominent magnetic declination effect is identified and examined in terms of thermospheric zonal winds pushing plasma upward/downward along magnetic field lines of opposite declination. Finally in Chapter 5 we summarize several co-authored studies which examined various storm-time phenomena utilizing GPS TEC mapping tools developed for this dissertation research, with topics including subauroral polarization stream (SAPS), storm enhanced density (SED), tongue of ionization (TOI), and polar cap patches.
Advisors/Committee Members: Baker, Joseph Benjamin (committeechair), Ruohoniemi, John Michael (committeechair), McGwier, Robert W. (committee member), Bailey, Scott M. (committee member), Scales, Wayne A. (committee member), Shinpaugh, Kevin A. (committee member).
Subjects/Keywords: SuperDARN; GPS TEC; Polar Cap Patch; Ionospheric Storm
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Thomas, E. G. (2016). Morphology and dynamics of storm-time ionospheric density structures. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/64905
Chicago Manual of Style (16th Edition):
Thomas, Evan Grier. “Morphology and dynamics of storm-time ionospheric density structures.” 2016. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/64905.
MLA Handbook (7th Edition):
Thomas, Evan Grier. “Morphology and dynamics of storm-time ionospheric density structures.” 2016. Web. 06 Dec 2019.
Vancouver:
Thomas EG. Morphology and dynamics of storm-time ionospheric density structures. [Internet] [Doctoral dissertation]. Virginia Tech; 2016. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/64905.
Council of Science Editors:
Thomas EG. Morphology and dynamics of storm-time ionospheric density structures. [Doctoral Dissertation]. Virginia Tech; 2016. Available from: http://hdl.handle.net/10919/64905
Virginia Tech
30.
Lin, Ying-Tsen.
Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.
Degree: PhD, Electrical and Computer Engineering, 2014, Virginia Tech
URL: http://hdl.handle.net/10919/64980
► On-board the International Space Station (ISS), the Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of limb-scanning monitors taking measurements from the extreme…
(more)
▼ On-board the International Space Station (ISS), the Remote Atmospheric and Ionospheric Detection System (RAIDS) is a suite of limb-scanning monitors taking measurements from the extreme ultraviolet (EUV) to the near infrared (NIR). A single-scattering Rayleigh model is developed to eliminate the scattered brightness below 90 km and an inversion technique is applied on limb-scanned radiance profiles at 236.5 nm, NO (0,1) gamma band. The ISS orbit allows observations from 7:00 to 16:00 local hours over a one-month period from mid-June to mid-July of 2010 and observation of the local-time variation of NO abundance in the lower thermosphere is derived. The uniquely stable solar activity during 2010 allows the local time variation of NO to be observed with limited influence of solar variability. The comparison with a 1D model shows good agreement at altitude above 120 km, suggesting that most of the local time variation of NO is due to solar illumination, radiation, chemistry, and vertical diffusion.
Solar soft X-ray is the major driver of the variability observed in the ionospheric and thermospheric constituents at the equatorial region. Over the years measurements in these wavelengths are scarce and discrepancies lie among the existing data. The Solar Aspect Monitor (SAM) is a pinhole camera on the Extreme-ultraviolet Variability Experiment (EVE) flying on the Solar Dynamics Observatory (SDO). Every 10 seconds SAM projects the solar disk onto the CCD through a metallic filter designed to allow only solar photons shortward of 7 nm to pass. Contamination from energetic particles and out-of-band irradiance is, however, present. The broadband (BB) technique is developed for isolating the 0.1 to 7 nm integrated irradiance to produce broadband irradiance. The results agree with the zeroth-order product from the EUV SpectroPhotometer (ESP) with 25% regardless of solar activity level. Active regions in the solar atmosphere are tracked by the Apertural Progression Procedure for Light Estimate (APPLE). The photon event detection (PED) algorithm takes both BB and APPLE results as prior information to extract in-band photons. Applications of the PED products, including solar feature studies and spectral resolved irradiance, are demonstrated.
Advisors/Committee Members: Bailey, Scott M. (committeechair), Minschwaner, Kenneth R. (committee member), Hsiao, Michael S. (committee member), Scales, Wayne A. (committee member), Earle, Gregory D. (committee member).
Subjects/Keywords: solar irradiance; soft X-ray; image processing; nitric oxide; thermosphere
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Lin, Y. (2014). Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/64980
Chicago Manual of Style (16th Edition):
Lin, Ying-Tsen. “Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.” 2014. Doctoral Dissertation, Virginia Tech. Accessed December 06, 2019.
http://hdl.handle.net/10919/64980.
MLA Handbook (7th Edition):
Lin, Ying-Tsen. “Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor.” 2014. Web. 06 Dec 2019.
Vancouver:
Lin Y. Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. [Internet] [Doctoral dissertation]. Virginia Tech; 2014. [cited 2019 Dec 06].
Available from: http://hdl.handle.net/10919/64980.
Council of Science Editors:
Lin Y. Comparison and Investigation of Solar Spectral Irradiance with Solar Aspect Monitor. [Doctoral Dissertation]. Virginia Tech; 2014. Available from: http://hdl.handle.net/10919/64980
◁ [1] [2] [3] ▶
. 
Open Access Theses and Dissertations
