Thesis (Ph. D.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

Thesis (M. S.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

Thesis (M. S.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

Thesis (M. S.)--Oklahoma State University, 2007. / Vita. Includes bibliographical references.

<p> Numerical investigations of an optimized thin airfoil with a passive and an active flow control device (riblets and rotary cylinder) have been performed. The objectives of the thesis were to investigate the tip vortices reduction using riblets and decrease in flow separation, using a rotary cylinder for improved lift-to-drag ratio. The investigations has application potentials in improving performances of Micro Air Vehicles (MAVs). The airfoil has a chord length of 19.66 cm and a span of 25 cm. with the free stream mean velocity was set at 20 m/s. The Reynolds number was calculated as 3 &times; 10⁴. Investigations with base model of the airfoil have shown flow separation at approximately 85% chord length at an angle of attack of 17 degrees. For investigation using passive flow control device, i.e. riblets, investigations were performed for different radial sizes but at a fixed location. It was found that with 1 mm radial size riblet, the tip vortices were reduced by approximately 95%, as compared to the baseline model. Although negligible lift-to-drag improvement was seen, a faster dissipation rate in turbulent kinetic energy was observed. Furthermore, investigations were carried out using the active flow control device. The rotary cylinder with a 0.51 cm in diameter was placed slightly downstream of the location of flow separation, i.e. at x/c = 0.848. Investigations were performed at different cylinder's rotations, corresponding to different tangential velocities of being higher than, equal to and less than the free stream mean velocity. Results have shown approximately 10% improvement in lift to drag ratio when the tangential velocity is near the free stream mean velocity. Further investigation may include usage of the riblets and the rotary cylinder combined, to increase the stability as well as the lift-to-drag ratio of the MAVs.</p>

<p> The purpose of this research was to investigate the cybersecurity controls needed to protect Unmanned Aircraft Systems (UAS) to ensure the safe integration of this technology into the National Airspace System (NAS) and society. This research presents the current vulnerabilities present in UAS technology today along with proposed countermeasures, a description of national and international rules, standards, and activities pertaining to UAS and cybersecurity, and a minimum set of safety operational requirements which are recommended to be implemented by manufacturers of small UAS and mandated by governing agencies. UAS attacks are defined in three categories: hardware attack, wireless attack, and sensor spoofing. The future influx of small and hobby oriented UAS should consider a minimum set of regulated cyber safety standards right out of the box, such as Geofencing technology and isolated auto safety measures. The commonality between national and international cyber related activities point to several operational requirements, hardware limitations, and heightened UAS vulnerabilities. These include type of radio frequency spectrum that is used during operation, methods for detect and avoid, safety measures, lost link procedures, and corrupted data communications.</p>

<p> The goal of this work is to assess the feasibility of using a two-CubeSat constellation to make continuous solar science measurements from low Earth orbit. There is a growing interest in using CubeSats for scientific missions since they are relatively inexpensive, can be manufactured quickly, and they have a standard form factor. CubeSats have increased access to space, and there is a growing interest in the solar science community to be able to conduct remote sensing solar science missions from a CubeSat platform. By using a constellation separated by differential drag, this mission concept enables continuous measurements of the sun, allowing scientists to have a complete record despite the spacecraft's eclipse periods. In this thesis, I have developed a two-body propagator that takes various inputs for starting altitude, density model, attitude, and spacecraft configuration to enable investigation over a large trade space. Following the model development, I ran a series of simulations to explore the feasibility of this concept, finding that there are many combinations of parameters that produce a feasible mission design. I show that the model is validated by altitude decay data from the MinXSS CubeSat, I will discuss areas of the design that require further study, and I explore the logical next steps for future development of this concept.</p><p>

<p> Future nuclear arms-control agreements may call for reductions of the total number of nuclear weapons and warheads in the world arsenals. Such agreements would require new trusted verification mechanisms to confirm that items presented to inspectors are nuclear warheads and not spoofs. Proliferation and national security concerns require, however, that inspectors gain no warhead design information through this process. To address this paradox, considerable efforts have been directed towards the development of "information barriers." These barriers consist of automated measurement systems that process sensitive information but only display the results of internal analysis in a binary valid/invalid manner. These systems are, by their nature, at risk of electronic tampering and snooping &ndash; and their trusted implementation has so far proved extremely difficult to realize. </p><p> This thesis takes radically different directions to address this challenge. It demonstrates new approaches to information protection and trusted instruments for nuclear warhead verification that are based on the cryptographic concepts of zero-knowledge proofs and physically unclonable functions. </p><p> To the author's knowledge, this thesis provides the first demonstration of a zero-knowledge physical measurement technique. Using fast neutron differential radiography and superheated emulsion detectors, such a technique can show two objects have identical geometry and opacity to 14-MeV neutrons without revealing what these properties are. This zero-knowledge feature no longer holds when the objects compared are significantly different. Such a technique could form the basis of a template-matching verification system that could confirm the authenticity of nuclear weapons without sharing any secret design information. </p><p> The thesis then introduces and demonstrates key elements of an optical physical unclonable function sensitive to neutrons and based on superheated emulsions. Such sensors are unique objects that cannot be cloned or simulated. The data they produce are a function of both their internal disordered structure and the physical quantity they measure. Due to their sensitivity against any structural variation, including through neutron irradiation, it is possible to show that they &ndash; or the data they have recorded -- have not been tampered with. Such sensors could be used by adversarial parties in sensitive facilities without the risk of being compromised.</p><p>