460 research outputs found

    The Economic and Cultural Impacts of Veterans on Rural America: The Case of Iowa

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    Rural America has long been a crucial supplier of recruits and civilian personnel to the U.S. military. Rural America is also an essential source of cultural and political support for military activity. After their tours of duty have ended, many veterans return to rural communities where they continue to carry the values of their military experiences and extend military traditions into rural culture. Far away from the Pentagon, and other corridors of military power, live millions of geographically-dispersed rural veterans whose Veterans Administration benefits (cash payments, loans, medical care) and retirement pensions flow into, and become a crucial economic support of, rural communities. Using the state of Iowa as an illustrative case, we map the geographical concentration of veterans in rural communities. We then map the economic impacts of veterans on rural communities, tracing the labyrinth of ongoing financial transactions, medical services, and other benefits so important to the vitality of rural communities. We also map indicators of the cultural importance of veterans to rural communities and the role that veteran service organizations play in the maintenance of a rural culture that honors military service. Linkages between military service and the enduring values of patriotism are continually reinforced through a variety of community celebrations, events, and traditions that serve to make rural places fertile recruiting grounds for the armed services

    Advances in Feature Selection with Mutual Information

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    The selection of features that are relevant for a prediction or classification problem is an important problem in many domains involving high-dimensional data. Selecting features helps fighting the curse of dimensionality, improving the performances of prediction or classification methods, and interpreting the application. In a nonlinear context, the mutual information is widely used as relevance criterion for features and sets of features. Nevertheless, it suffers from at least three major limitations: mutual information estimators depend on smoothing parameters, there is no theoretically justified stopping criterion in the feature selection greedy procedure, and the estimation itself suffers from the curse of dimensionality. This chapter shows how to deal with these problems. The two first ones are addressed by using resampling techniques that provide a statistical basis to select the estimator parameters and to stop the search procedure. The third one is addressed by modifying the mutual information criterion into a measure of how features are complementary (and not only informative) for the problem at hand

    Evaluation of the two-photon absorption characteristics of GaSb/GaAs quantum rings

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    The optical parameters describing the sub-bandgap response of GaSb/GaAs quantum rings solar cells have been obtained from photocurrent measurements using a modulated pseudomonochromatic light source in combination with a second, continuous photo-filling source. By controlling the charge state of the quantum rings, the photoemission cross-sections describing the two-photon sub-bandgap transitions could be determined independently. Temperature dependent photo-response measurements also revealed that the barrier for thermal hole emission from the quantum rings is significantly below the quantum ring localisation energy. The temperature dependence of the sub-bandgap photo-response of the solar cell is also described in terms of the photo-and thermal-emission characteristics of the quantum rings. (C) 2014 AIP Publishing LLC

    Simulation of the enhanced infrared photoresponse of type-II GaSb/GaAs quantum ring solar cells

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    The extended photo-response of solar cells containing ten periods of GaSb/GaAs quantum rings imbedded in the p-i-n junction has been described using a single-band representation of the type-II quantum ring structure. By fitting the experimental data, the authors were able to deduce that the quantum rings are well represented by a Gaussian height distribution and a large valence band discontinuity. The simulated band of states is shown to be well matched to the photoluminescence analysis of the structure, with the inhomogeneous size distribution resulting in a band of hole states roughly 390 meV above the valence band

    H-tailored surface conductivity in narrow band gap In(AsN)

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    We show that the n-type conductivity of the narrow band gap In(AsN) alloy can be increased within a thin (similar to 100 nm) channel below the surface by the controlled incorporation of H-atoms. This channel has a large electron sheet density of similar to 10(18) m(-2) and a high electron mobility (mu > 0.1 m(2)V(-1)s(-1) at low and room temperature). For a fixed dose of impinging H-atoms, its width decreases with the increase in concentration of N-atoms that act as H-traps thus forming N-H donor complexes near the surface. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License

    Highly-mismatched InAs/InSe heterojunction diodes

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    We report on heterojunction diodes prepared by exfoliation and direct mechanical transfer of a p-type InSe thin film onto an n-type InAs epilayer. We show that despite the different crystal structures and large lattice mismatch (34%) of the component layers, the junctions exhibit rectification behaviour with rectification ratios of 10[superscript]4 at room temperature and broad-band photoresponse in the near infrared and visible spectral ranges

    Photoluminescence studies of individual and few GaSb/GaAs quantum rings

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    We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at half maximum of 200 µeV. The detail provided by these measurements allows the characteristic type-II blueshift, observed with increasing excitation power, to be studied at the level of individual nanostructures. These findings are in agreement with hole-charging being the origin of the observed blueshif
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