Air Force Institute of Technology Research Report 2012

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems and Engineering Management, Operational Sciences, Mathematics, Statistics and Engineering Physics

Computational Models of Perceptual Organization and Bottom-up Attention in Visual and Audio-Visual Environments

Figure Ground Organization (FGO) - inferring spatial depth ordering of objects in a visual scene - involves determining which side of an occlusion boundary (OB) is figure (closer to the observer) and which is ground (further away from the observer). Attention, the process that governs how only some part of sensory information is selected for further analysis based on behavioral relevance, can be exogenous, driven by stimulus properties such as an abrupt sound or a bright flash, the processing of which is purely bottom-up; or endogenous (goal-driven or voluntary), where top-down factors such as familiarity, aesthetic quality, etc., determine attentional selection. The two main objectives of this thesis are developing computational models of: (i) FGO in visual environments; (ii) bottom-up attention in audio-visual environments. In the visual domain, we first identify Spectral Anisotropy (SA), characterized by anisotropic distribution of oriented high frequency spectral power on the figure side and lack of it on the ground side, as a novel FGO cue, that can determine Figure/Ground (FG) relations at an OB with an accuracy exceeding 60%. Next, we show a non-linear Support Vector Machine based classifier trained on the SA features achieves an accuracy close to 70% in determining FG relations, the highest for a stand-alone local cue. We then show SA can be computed in a biologically plausible manner by pooling the Complex cell responses of different scales in a specific orientation, which also achieves an accuracy greater than or equal to 60% in determining FG relations. Next, we present a biologically motivated, feed forward model of FGO incorporating convexity, surroundedness, parallelism as global cues and SA, T-junctions as local cues, where SA is computed in a biologically plausible manner. Each local cue, when added alone, gives statistically significant improvement in the model's performance. The model with both local cues achieves higher accuracy than those of models with individual cues in determining FG relations, indicating SA and T-Junctions are not mutually contradictory. Compared to the model with no local cues, the model with both local cues achieves greater than or equal to 8.78% improvement in determining FG relations at every border location of images in the BSDS dataset. In the audio-visual domain, first we build a simple computational model to explain how visual search can be aided by providing concurrent, co-spatial auditory cues. Our model shows that adding a co-spatial, concurrent auditory cue can enhance the saliency of a weakly visible target among prominent visual distractors, the behavioral effect of which could be faster reaction time and/or better search accuracy. Lastly, a bottom-up, feed-forward, proto-object based audiovisual saliency map (AVSM) for the analysis of dynamic natural scenes is presented. We demonstrate that the performance of proto-object based AVSM in detecting and localizing salient objects/events is in agreement with human judgment. In addition, we show the AVSM computed as a linear combination of visual and auditory feature conspicuity maps captures a higher number of valid salient events compared to unisensory saliency maps

Sparse Representations & Compressed Sensing with application to the problem of Direction-of-Arrival estimation.

PhDThe significance of sparse representations has been highlighted in numerous signal processing applications ranging from denoising to source separation and the emerging field of compressed sensing has provided new theoretical insights into the problem of inverse systems with sparsity constraints. In this thesis, these advances are exploited in order to tackle the problem of direction-of-arrival (DOA) estimation in sensor arrays. Assuming spatial sparsity e.g. few sources impinging on the array, the problem of DOA estimation is formulated as a sparse representation problem in an overcomplete basis. The resulting inverse problem can be solved using typical sparse recovery methods based on convex optimization i.e. `1 minimization. However, in this work a suite of novel sparse recovery algorithms is initially developed, which reduce the computational cost and yield approximate solutions. Moreover, the proposed algorithms of Polytope Faces Pursuits (PFP) allow for the induction of structured sparsity models on the signal of interest, which can be quite beneficial when dealing with multi-channel data acquired by sensor arrays, as it further reduces the complexity and provides performance gain under certain conditions. Regarding the DOA estimation problem, experimental results demonstrate that the proposed methods outperform popular subspace based methods such as the multiple signal classification (MUSIC) algorithm in the case of rank-deficient data (e.g. presence of highly correlated sources or limited amount of data) for both narrowband and wideband sources. In the wideband scenario, they can also suppress the undesirable effects of spatial aliasing. However, DOA estimation with sparsity constraints has its limitations. The compressed sensing requirement of incoherent dictionaries for robust recovery sets limits to the resolution capabilities of the proposed method. On the other hand, the unknown parameters are continuous and therefore if the true DOAs do not belong to the predefined discrete set of potential locations the algorithms' performance will degrade due to errors caused by mismatches. To overcome this limitation, an iterative alternating descent algorithm for the problem of off-grid DOA estimation is proposed that alternates between sparse recovery and dictionary update estimates. Simulations clearly illustrate the performance gain of the algorithm over the conventional sparsity approach and other existing off-grid DOA estimation algorithms.EPSRC Leadership Fellowship EP/G007144/1; EU FET-Open Project FP7-ICT-225913

The Evolution of China’s Nuclear Weapons Program and Doctrine and Its Implications for International Security

The Evolution of China’s Nuclear Weapons Program and Doctrine and Its Implications for International Securit

Six Decades of Flight Research: An Annotated Bibliography of Technical Publications of NASA Dryden Flight Research Center, 1946-2006

Titles, authors, report numbers, and abstracts are given for nearly 2900 unclassified and unrestricted technical reports and papers published from September 1946 to December 2006 by the NASA Dryden Flight Research Center and its predecessor organizations. These technical reports and papers describe and give the results of 60 years of flight research performed by the NACA and NASA, from the X-1 and other early X-airplanes, to the X-15, Space Shuttle, X-29 Forward Swept Wing, X-31, and X-43 aircraft. Some of the other research airplanes tested were the D-558, phase 1 and 2; M-2, HL-10 and X-24 lifting bodies; Digital Fly-By-Wire and Supercritical Wing F-8; XB-70; YF-12; AFTI F-111 TACT and MAW; F-15 HiDEC; F-18 High Alpha Research Vehicle, F-18 Systems Research Aircraft and the NASA Landing Systems Research aircraft. The citations of reports and papers are listed in chronological order, with author and aircraft indices. In addition, in the appendices, citations of 270 contractor reports, more than 200 UCLA Flight System Research Center reports, nearly 200 Tech Briefs, 30 Dryden Historical Publications, and over 30 videotapes are included