United States Naval Research Laboratory

About: United States Naval Research Laboratory is a facility organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Laser & Electron. The organization has 17395 authors who have published 45424 publications receiving 1583174 citations. The organization is also known as: NRL & Naval Research Laboratory.

Exploiting manifold geometry in hyperspectral imagery

Abstract: A new algorithm for exploiting the nonlinear structure of hyperspectral imagery is developed and compared against the de facto standard of linear mixing. This new approach seeks a manifold coordinate system that preserves geodesic distances in the high-dimensional hyperspectral data space. Algorithms for deriving manifold coordinates, such as isometric mapping (ISOMAP), have been developed for other applications. ISOMAP guarantees a globally optimal solution, but is computationally practical only for small datasets because of computational and memory requirements. Here, we develop a hybrid technique to circumvent ISOMAP's computational cost. We divide the scene into a set of smaller tiles. The manifolds derived from the individual tiles are then aligned and stitched together to recomplete the scene. Several alignment methods are discussed. This hybrid approach exploits the fact that ISOMAP guarantees a globally optimal solution for each tile and the presumed similarity of the manifold structures derived from different tiles. Using land-cover classification of hyperspectral imagery in the Virginia Coast Reserve as a test case, we show that the new manifold representation provides better separation of spectrally similar classes than one of the standard linear mixing models. Additionally, we demonstrate that this technique provides a natural data compression scheme, which dramatically reduces the number of components needed to model hyperspectral data when compared with traditional methods such as the minimum noise fraction transform.

Preparing to resume an interrupted task: effects of prospective goal encoding and retrospective rehearsal

Abstract: We examine people's strategic cognitive responses to being interrupted while performing a task. Based on memory theory, we propose that resumption of a task after interruption is facilitated by preparation during the interruption lag, or the interval between an alert to a pending interruption (e.g. the phone ringing) and the interruption proper (the ensuing conversation). To test this proposal, we conducted an experiment in which participants in a Warning condition received an 8-s interruption lag, and participants in an Immediate condition received no interruption lag. Participants in the Warning condition prepared more than participants in the Immediate condition, as measured by verbal reports, and resumed the interrupted task more quickly. However, Immediate participants resumed faster with practice, suggesting that people adapt to particularly disruptive forms of interruption. The results support our task analysis of interruption and our model of memory for goals, and suggest further means for studying operator performance in dynamic task environments.

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

Abstract: The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy1. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ∼4000J/m2 (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryc) in that was a maximum when bond thickness was equal to 2 ryc. At bond thicknesses less than 2 ryc, there was a restraint on the development of the plastic zone resulting in lower values.

Temperature Variation of the Elastic Constants of Cubic Elements. I. Copper

Abstract: The ultrasonic pulse technique has been used in conjunction with a specially devised cryogenic technique to measure the velocities of 10-Mc/sec acoustic waves in copper single crystals in the range from 4.2\ifmmode^\circ\else\textdegree\fi{}K to 300\ifmmode^\circ\else\textdegree\fi{}K. The values and the temperature variations of the elastic constants have been determined. The room temperature elastic constants were found to agree well with those of other experimental works. Fuchs' theoretical ${c}_{44}$ at 0\ifmmode^\circ\else\textdegree\fi{}K is 10 percent larger than our observed value but his theoretical ${c}_{11}$, ${c}_{12}$, $K$ and (${c}_{11}\ensuremath{-}{c}_{12}$) agree well with the observations. The isotropy, $\frac{({c}_{11}\ensuremath{-}{c}_{12})}{2{c}_{44}}$, was observed to remain practically constant from 4.2\ifmmode^\circ\else\textdegree\fi{}K to 180\ifmmode^\circ\else\textdegree\fi{}K, then to diminish gradually at higher temperatures. Some general features of the temperature variations of elastic constants are discussed.