Situation awareness (SA) is a measure of an individual's knowledge and understanding of the current and expected future states of a situation. While there are numerous options for SA measurement, none are currently suitable in dynamic, uncontrolled environments. The current research explored the relationship between direct measures of SA and eye tracking measures as a first step in the development of an unobtrusive measure to be used in environments not suited for existing SA measurement methods. Results showed that the more individuals fixated on an important aircraft in an air traffic control task, the higher their SA for that aircraft. The study also provided evidence that the way operators allocate attention (i.e., distributed widely or narrowly) affects their SA, as well as their task performance. The results indicate that eye tracking may be a viable option for measuring SA in environments not conducive to current direct SA measurement techniques.

Judgments of passability help to quantify differences in perception between DLS and TO. These results will be useful in the design of training regimes for TO tasks. Increasing operator understanding of performance differences under varying conditions will lead them to be more accurate when making critical decisions in remote environments.

We consider a forced nonlinear wave equation on a bounded domain which, under certain physical assumptions, models the torsional oscillation of the main span of a suspension bridge. We use Leray-Schauder degree theory to prove that, under small periodic external forcing, the undamped equation has multiple periodic solutions. To establish this multiplicity theorem, we prove an abstract degree theoretic result that can be used to prove multiplicity of solutions for more general operators and nonlinearities. Using physical constants from the engineers' reports of the collapse of the Tacoma Narrows Bridge, we solve the damped equation numerically and observe that multiple periodic solutions exist and that whether the span oscillates with small or large amplitude depends only on its initial displacement and velocity. Moreover, we observe that the qualitative properties of our computed solutions are consistent with the behavior observed at Tacoma Narrows on the day of its collapse.

We study two systems of nonlinearly coupled ordinary di erential equations that govern the vertical and torsional motions of a cross section of a suspension bridge. We observe n umerically that the structure of the set of periodic solutions changes considerably when we smooth the nonlinear terms. The smoothed nonlinearities describe the force that we wish to model more realistically and the resulting periodic solutions more accurately replicate the phenomena observed at the Tacoma Narrows Bridge on the day of its collapse. The main conclusion is that purely vertical periodic forcing can result in subharmonic primarily torsional motion.

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