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Articles 121 - 134 of 134
Full-Text Articles in Engineering
Leveraging Human Insights By Combining Multi-Objective Optimization With Interactive Evolution, Joshua R. Christman
Leveraging Human Insights By Combining Multi-Objective Optimization With Interactive Evolution, Joshua R. Christman
Theses and Dissertations
Deceptive fitness landscapes are a growing concern for evolutionary computation. Recent work has shown that combining human insights with short-term evolution has a synergistic effect that accelerates the discovery of solutions. While humans provide rich insights, they fatigue easily. Previous work reduced the number of human evaluations by evolving a diverse set of candidates via intermittent searches for novelty. While successful at evolving solutions for a deceptive maze domain, this approach lacks the ability to measure what the human evaluator identifies as important. The key insight here is that multi-objective evolutionary algorithms foster diversity, serving as a surrogate for novelty, …
The Theory And Application Of Privacy-Preserving Computation, Michael R. Clark
The Theory And Application Of Privacy-Preserving Computation, Michael R. Clark
Theses and Dissertations
Privacy is a growing concern in the digital world as more information becomes digital every day. Often the implications of how this information could be exploited for nefarious purposes are not explored until after the fact. The public is becoming more concerned about this. This dissertation introduces a new paradigm for tackling the problem, namely, transferable multiparty computation (T-MPC). T-MPC builds upon existing multiparty computation work yet allows some additional flexibility in the set of participants. T-MPC is orders of magnitude more efficient for certain applications. This greatly increases the scalability of the sizes of networks supported for privacy-preserving computation.
Computational Electromagnetic Studies For Low-Frequency Compensation Of The Reflector Impulse-Radiating Antenna, Casey E. Fillmore
Computational Electromagnetic Studies For Low-Frequency Compensation Of The Reflector Impulse-Radiating Antenna, Casey E. Fillmore
Theses and Dissertations
The reflector impulse-radiating antenna (IRA) is considered to meet the requirement for a wideband, directional antenna with short temporal response and small electrical footprint. Standard reflector IRA designs are modeled and performance is simulated using full-wave computational electromagnetic (CEM) software. Characterization of the standard designs reveals the possible existence of wide, frequency-independent backlobes containing nearly 40% of the radiated power at high frequencies. These undesirable backlobes have never been hypothesized, predicted or measured, likely due in part to their alignment outside the primary measurement planes. At the lowest operating frequencies, the reflector IRA is unaffected by backlobes, but is characterized …
Improving The Performance Of The Space Surveillance Telescope As A Function Of Seeing Parameter, Jae H. Jeon
Improving The Performance Of The Space Surveillance Telescope As A Function Of Seeing Parameter, Jae H. Jeon
Theses and Dissertations
This research paper investigates ways to improve the detection capability and predict the performance of the Space Surveillance Telescope (SST) system when it's relocated to Exmouth, Australia. The dataset collected by the SST observing the Geosynchronous Earth Orbit (GEO) satellite, ANIK-F1, entering the earth's eclipse is used to test the performance of the three existing and one new detection algorithm. The three existing algorithms are the point detection (Binary Hypothesis Test (BHT)), correlation detection (CD-BHT), and Multi-hypothesis Test using ten hypotheses (MHT10), and the new detection algorithm is the Multi-hypothesis Test using six hypotheses (MHT6). To improve the accuracy and …
Modeling Navigation System Performance Of A Satellite-Observing Star Tracker Tightly Integrated With An Inertial Measurement Unit, Scott J. Pierce
Modeling Navigation System Performance Of A Satellite-Observing Star Tracker Tightly Integrated With An Inertial Measurement Unit, Scott J. Pierce
Theses and Dissertations
This dissertation evaluates a navigation system using satellite observations from a star tracker tightly-integrated with an inertial measurement unit (IMU) and a barometric altimeter using an extended Kalman filter. The star tracker measurement accuracy of a satellite is derived. Several system configurations are simulated comparing the performance of the estimate with respect to system parameters of the IMU, and star tracker, as well as comparing performance when providing a remote sensor satellite ephemeris error correction. Experimental observations are used to evaluate the model performance. Additionally, power requirements were calculated for a satellite signal operating in imaging bands, such that a …
Precision Relative Positioning For Automated Aerial Refueling From A Stereo Imaging System, Kyle P. Werner
Precision Relative Positioning For Automated Aerial Refueling From A Stereo Imaging System, Kyle P. Werner
Theses and Dissertations
The United States Air Force relies upon aerial refueling to fulfill its missions. Unmanned aerial systems (UAS) and remotely piloted aircraft (RPA) do not currently have access to this capability due to the lack of an on-board pilot to safely maintain a refueling position. This research examines stereo vision for precision relative navigation in order to accomplish the Automated Aerial Refueling (AAR) task. Previous work toward an AAR solution has involved the use of Differential Global Positioning (DGPS), Light Detection and Ranging (LiDAR), and monocular vision. This research aims to leverage organic systems in future aircraft to compliment these solutions. …
On The Integration Of Medium Wave Infrared Cameras For Vision-Based Navigation, Justin S. Tharp
On The Integration Of Medium Wave Infrared Cameras For Vision-Based Navigation, Justin S. Tharp
Theses and Dissertations
The ubiquitous nature of GPS has fostered its widespread integration of navigation into a variety of applications, both civilian and military. One alternative to ensure continued flight operations in GPS-denied environments is vision-aided navigation, an approach that combines visual cues from a camera with an inertial measurement unit (IMU) to estimate the navigation states of a moving body. The majority of vision-based navigation research has been conducted in the electro-optical (EO) spectrum, which experiences limited operation in certain environments. The aim of this work is to explore how such approaches extend to infrared imaging sensors. In particular, it examines the …
Expected Position Error For An Onboard Satellite Gps Receiver, Anthony S. Williams
Expected Position Error For An Onboard Satellite Gps Receiver, Anthony S. Williams
Theses and Dissertations
The Global Positioning System (GPS) constellation provides ranging information that delivers inexpensive, high precision positioning for terrestrial users. Satellites in Low Earth Orbit (LEO) can use an onboard GPS receiver resulting in meter-level navigation solution accuracy. There are limitations to using GPS for positioning for satellites above LEO. The number of GPS satellites who's signal can be received decreases as the receivers altitude approaches that of the GPS constellation. Above the GPS constellation, the available GPS signals for ranging will originate from satellites on the opposite side of Earth. This research calculates the available GPS signals to the receiver and …
Surface Geometry And Chemistry Of Hydrothermally Synthesized Single Crystal Thorium Dioxide, Scott W. Key
Surface Geometry And Chemistry Of Hydrothermally Synthesized Single Crystal Thorium Dioxide, Scott W. Key
Theses and Dissertations
The surface chemistry and geometry of hydrothermally grown, single crystal ThO2 was studied using X-ray Photoemission Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The crystal was studied before and after sputter etching with Ar+, heating up to 675 K, and dehydration with dry nitrogen. The hydrothermal growth technique incorporated Cs and F into the near surface bulk. Heating to 675 K drove off the F, but did not the Cs. Sputtering with Ar+ at 75° cleaned the crystal and created a more uniform surface geometry. The Th 4f peak resolution, as measured by XPS improved by …
The Brazilian Air Force Uniform Distribution Process: Using Lean Thinking, Statistical Process Control And Theory Of Constraints To Address Improvement Opportunities, Luciano A. Dos Santos
The Brazilian Air Force Uniform Distribution Process: Using Lean Thinking, Statistical Process Control And Theory Of Constraints To Address Improvement Opportunities, Luciano A. Dos Santos
Theses and Dissertations
In the Brazilian Air Force, all enlisted Soldiers and Corporals (corresponding to USAF ranks from Airman Basic to Senior Airman) are entitled to receive their uniforms from their assigned, respective organizations, free of charge. An important portion of the uniform s distribution process is accomplished by the Brazilian Air Force Intendancy Central Depot (ICD). This organization carries the uniform inventory and performs the selection and distribution activities, following the guidance of the Sub-directorate of Supply. ICD process performance data for the peak distribution seasons of 2012 and 2013 was collected and analyzed. Several indications of inefficiencies became apparent, exemplified by …
The Cognition Of Multiaircraft Control (Mac): Cognitive Ability Predictors, Working Memory, Interference, And Attention Control In Radio Communication, Kelly M. Amaddio
The Cognition Of Multiaircraft Control (Mac): Cognitive Ability Predictors, Working Memory, Interference, And Attention Control In Radio Communication, Kelly M. Amaddio
Theses and Dissertations
As the number of U.S. Air Force missions requiring UAVs has rapidly increased without commensurate increases in manpower, systems which permit a single operator to supervise and control multiple, highly-automated aircraft are being considered. The operator of such a system may be required to monitor and respond to voice communications for multiple UAVs, each of which can have aircraft specific call signs. The need to monitor this array of call signs may impose excessive requirements on constrained operator attention, working memory, and cognitive processing. The current research investigates the cognitive load (number of aircraft call signs) an individual can handle …
Detection And Characterization Of Malathion Adherence To Piping Materials Used In Water Distribution Systems, William D. Flemings
Detection And Characterization Of Malathion Adherence To Piping Materials Used In Water Distribution Systems, William D. Flemings
Theses and Dissertations
Protection of the public water supply is a national security priority, and as such, it is important to better understand the fate of a chemical weapons agent injection into a public water distribution system. This study investigated the adherence of malathion to pipe materials that are used in public water distribution systems, with malathion serving as a chemical representative of the organophosphorus nerve agent VX. Copper and iron specimen were exposed to malathion solutions for periods of 4, 8, and 24 hours and then tested for evidence of chemical adherence to the metal surfaces. Nonlinear desiccation profiles revealed total mass …
Using Earned Value Data To Forecast The Duration Of Department Of Defense (Dod) Space Acquisition Programs, Shedrick M. Bridgeforth
Using Earned Value Data To Forecast The Duration Of Department Of Defense (Dod) Space Acquisition Programs, Shedrick M. Bridgeforth
Theses and Dissertations
The accuracy of cost estimates is vital during this era of budget constraints. A key component of this accuracy is regularly updating the cost estimate at completion (EAC). A 2014 study by the Air Force Cost Analysis Agency (AFCAA) improved the accuracy of the cost estimate at completion (EAC) for space system contracts. The study found schedule duration to be a cost driver, but assumed the underlying duration estimate was accurate. This research attempts to improve the accuracy of the duration estimate from the AFCAA study; accuracy is evaluated with the Mean Absolute Percent Error (MAPE). The methods researched here …
Electrical And Physical Property Characterization Of Single Walled Carbon Nanotube Ink For Flexible Printed Electronics, Kristian E. Warner Jr.
Electrical And Physical Property Characterization Of Single Walled Carbon Nanotube Ink For Flexible Printed Electronics, Kristian E. Warner Jr.
Theses and Dissertations
This research presents a method of characterizing single-walled carbon nanotube (SWCNT) ink. This research also examines the results of our characterization efforts. First, the process of ink jet printing SWCNT ink onto organic and inorganic substrates is discussed. Next, the tests for measuring sheet resistance, conductance, inductance, adherence, thickness, roll-off, and S-parameters of the ink are described. Results and findings of the research are presented. The SWCNT ink created by Brewer Science © is shown to be an effective material for additive manufacturing using an aerosol jet printer, but not an inkjet printer. The ink is shown to have a …