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Raghavan R.S.,Air Force Research Lab
IEEE Transactions on Signal Processing | Year: 2013

Maximal invariants for adaptive detection of a signal in unknown interference from multiple observations is derived. Given coherent samples from P sets of observations, it is shown that a maximal invariant statistic for the detection problem is a 2P × 1-dimensional vector comprising the eigenvalues of two Hermitian positive definite matrices obtained from the data set. Two invariant detectors, well known for P=1, are generalized for the case of multiple observations and closed form expressions for the probability of detection and probability of false alarm are derived along with the distributions of the signal-to-interference-plus-noise loss factors. Several novel invariant detectors are constructed from the maximal invariants and the receiver operating characteristics of the detectors compared. © 1991-2012 IEEE. Source

Miracle D.B.,Air Force Research Lab
Acta Materialia | Year: 2013

The present work develops a physical model of metallic glass structure that gives a reasonable estimate of density. The efficient cluster-packing model is used as a starting point, and is refined by a high-fidelity estimate of the size of structure-forming clusters and cluster-cluster separations. These are predicted as continuous functions of composition and relative atom radii. Predicted densities are all are within ±10% of measured densities for 200 binary metallic glasses, representing a precision in cluster-cluster separations of ±3%. New structural insights from this work include the importance of acknowledging the unique cluster topologies to estimate cluster-cluster separations; an improved ability to estimate the higher packing efficiency of unlike atoms in the first coordination shell of atomic clusters; and an improved estimate of metalloid-metalloid separations. The unusual, bilinear influence of composition on density in Fe-B glasses is explained by considering the sizes of β and γ sites in different metallic glass structures. Global atom packing fractions derived from measured densities range from about 0.62 to 0.76, and the most stable binary glasses all have packing fractions in excess of 0.70, supporting the idea that atom packing efficiency influences glass stability. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Selesnick R.S.,Air Force Research Lab
Journal of Geophysical Research: Space Physics | Year: 2012

The dynamics of inner radiation belt electrons are governed by competing source, loss, and transport processes. However, during the recent extended solar minimum period the source was inactive and electron intensity was characterized by steady decay. This provided an opportunity to determine contributions to the decay rate of losses by precipitation into the atmosphere and of diffusive radial transport. To this end, a stochastic simulation of inner radiation belt electron transport is compared to data taken by the IDP instrument on the DEMETER satellite during 2009. For quasi-trapped, 200keV electrons at L = 1.3, observed in the drift loss cone (DLC), results are consistent with electron precipitation losses by atmospheric scattering alone, provided account is taken of non-diffusive wide-angle scattering. Such scattering is included in the stochastic simulation using a Markov jump process. Diffusive small-angle atmospheric scattering, while causing most of the precipitation losses, is too slow relative to azimuthal drift to contribute significantly to DLC intensity. Similarly there is no contribution from scattering by VLF plasma waves. Energy loss, energy diffusion, and azimuthal drift are also included in the model. Even so, observed decay rates of stably-trapped electrons with L < 1.5 are slower than predicted by scattering losses alone, requiring radial diffusion with coefficient DLL ∼ 3 × 10-10 s-1 to replenish electrons lost to the atmosphere at low L values. © 2012 by the American Geophysical Union. Source

Organophosphates are some of the most acutely toxic compounds synthesized on an industrial scale, and organophosphorus hydrolase (OPH) has the ability to hydrolyze and inactivate a number of these chemicals. However, OPH activity is vulnerable to harsh environmental conditions that would accompany its practical utility in the field; a limitation that can also be extended to conditions required for incorporation of OPH into useful materials. Here we present evidence that entrapment of OPH in silk fibroin leads to stabilization of OPH activity under a variety of conditions that would otherwise reduce free enzyme activity, such as elevated temperature, UV light exposure and the presence of detergent. Silk fibroin entrapment of OPH also allowed for its dispersal into a polyurethane-based coating that retained organophosphate hydrolysis activity after formulation, application and drying. Together, the data presented here demonstrate the utility of silk fibroin entrapment for the protection of OPH activity under a variety of environmental conditions. Source

Perlovsky L.,Air Force Research Lab
Physics of Life Reviews | Year: 2010

Theories of music origins and the role of musical emotions in the mind are reviewed. Most existing theories contradict each other, and cannot explain mechanisms or roles of musical emotions in workings of the mind, nor evolutionary reasons for music origins. Music seems to be an enigma. Nevertheless, a synthesis of cognitive science and mathematical models of the mind has been proposed describing a fundamental role of music in the functioning and evolution of the mind, consciousness, and cultures. The review considers ancient theories of music as well as contemporary theories advanced by leading authors in this field. It addresses one hypothesis that promises to unify the field and proposes a theory of musical origin based on a fundamental role of music in cognition and evolution of consciousness and culture. We consider a split in the vocalizations of proto-humans into two types: one less emotional and more concretely-semantic, evolving into language, and the other preserving emotional connections along with semantic ambiguity, evolving into music. The proposed hypothesis departs from other theories in considering specific mechanisms of the mind-brain, which required the evolution of music parallel with the evolution of cultures and languages. Arguments are reviewed that the evolution of language toward becoming the semantically powerful tool of today required emancipation from emotional encumbrances. The opposite, no less powerful mechanisms required a compensatory evolution of music toward more differentiated and refined emotionality. The need for refined music in the process of cultural evolution is grounded in fundamental mechanisms of the mind. This is why today's human mind and cultures cannot exist without today's music. The reviewed hypothesis gives a basis for future analysis of why different evolutionary paths of languages were paralleled by different evolutionary paths of music. Approaches toward experimental verification of this hypothesis in psychological and neuroimaging research are reviewed. Source

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