1,181 research outputs found

    The Relationship between Cost Analysis and Program Management

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    Cost analysis if often viewed as applying basic principles and cost methodologies to determine total system cost. These finished estimates then flow into a decision making process and the cost estimator leaves the stage. Reality shows that the cost estimator is actually one of the main contributors to the decision making process. Our introduction to this special issue explores the areas where cost estimating plays a major role in program management in areas beyond the normal program estimate. We have included articles that show the key role estimators can play in source selection strategies and evaluation; cost of delay analysis for management decisions, earned value management methods to predict program costs; decision criteria to rank competing projects that complement traditional cost-based methods; and a new methodology for determining research and development budget profiles

    Metal nanofilm in strong ultrafast optical fields

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    We predict that a metal nanofilm subjected to an ultrashort (single oscillation) optical pulse of a high field amplitude ∌3V/A˚\sim 3 \mathrm{V/\AA} at normal incidence undergoes an ultrafast (at subcycle times â‰Č1fs\lesssim 1 \mathrm{fs}) transition to a state resembling semimetal. Its reflectivity is greatly reduced, while the transmissivity and the optical field inside the metal are greatly increased. The temporal profiles of the optical fields are predicted to exhibit pronounced subcycle oscillations, which are attributed to the Bloch oscillations and formation of the Wannier-Stark ladder of electronic states. The reflected, transmitted, and inside-the-metal pulses have non-zero areas approaching half-cycle pulses. The effects predicted are promising for applications to nanoplasmonic modulators and field-effect transistors with petahertz bandwidth

    The Three Dimensional Structure of EUV Accretion Regions in AM Herculis Stars: Modeling of EUV Photometric and Spectroscopic Observations

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    We have developed a model of the high-energy accretion region for magnetic cataclysmic variables and applied it to {\it Extreme Ultraviolet Explorer} observations of 10 AM Herculis type systems. The major features of the EUV light curves are well described by the model. The light curves exhibit a large variety of features such as eclipses of the accretion region by the secondary star and the accretion stream, and dips caused by material very close to the accretion region. While all the observed features of the light curves are highly dependent on viewing geometry, none of the light curves are consistent with a flat, circular accretion spot whose lightcurve would vary solely from projection effects. The accretion region immediately above the WD surface is a source of EUV radiation caused by either a vertical extent to the accretion spot, or Compton scattering off electrons in the accretion column, or, very likely, both. Our model yields spot sizes averaging 0.06 RWD_{WD}, or f∌1×10−3f \sim 1 \times 10^{-3} the WD surface area, and average spot heights of 0.023 RWD_{WD}. Spectra extracted during broad dip phases are softer than spectra during the out-of-dip phases. This spectral ratio measurement leads to the conclusion that Compton scattering, some absorption by a warm absorber, geometric effects, an asymmetric temperature structure in the accretion region and an asymmetric density structure of the accretion columnare all important components needed to fully explain the data. Spectra extracted at phases where the accretion spot is hidden behind the limb of the WD, but with the accretion column immediately above the spot still visible, show no evidence of emission features characteristic of a hot plasma.Comment: 30 Pages, 11 Figure

    Substance Use Disorders, Violence, Mental Health, and HIV: Differentiating a Syndemic Factor by Gender and Sexuality

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    This paper measures syndemic substance use disorder, violence, and mental health and compares the syndemic among HIV-infected heterosexual men, heterosexual women, and men who have sex with men (MSM). Data were from a sample of high needs substance-using, HIV-infected people in South Florida between 2010 and 2012 (n = 481). We used confirmatory factor analysis to measure a syndemic latent variable and applied measurement invariance models to identify group differences in the data structure of syndemic co-morbidities among heterosexual men, heterosexual women, and MSM. We found that variables used to measure the syndemic fit each sub-group, supporting that substance use disorder, violence, and mental health coincide in HIV-infected individuals. Heterosexual men and MSM demonstrated similar syndemic latent variable factor loadings, but significantly different item intercepts, indicating that heterosexual men had larger mean values on substance use disorder, anxiety, and depression than MSM. Heterosexual men and heterosexual women demonstrated significantly different syndemic variable factor loadings, indicating that anxiety and depression contribute more (and substance use contributes less) to the syndemic in heterosexual men compared to heterosexual women. MSM and heterosexual women demonstrated similar syndemic latent variable factor loadings and intercepts, but had significantly different factor residual variances indicating more variance in violent victimization and depression for MSM and more variance in stress for heterosexual women than what is captured by the observed syndemic indicators. Furthermore, heterosexual women had a larger syndemic factor mean than MSM, indicating that the syndemic burden is greater among heterosexual women than MSM. Our findings support that measurement invariance can elucidate differences in the syndemic to tailor interventions to sub-group needs

    Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840

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    We present simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840. We model the polarisation data using the Stokes imaging technique of Potter et al. We find that the data are best modelled using a relatively high binary inclination and a small angle between the magnetic and spin axes. We find that for all spin-orbit beat phases, a significant proportion of the accretion flow is directed onto the lower hemisphere of the white dwarf, producing negative circular polarisation. Only for a small fraction of the beat cycle is a proportion of the flow directed onto the upper hemisphere. However, the accretion flow never occurs near the upper magnetic pole, whatever the orientation of the magnetic poles. This indicates the presence of a non-dipole field with the field strength at the upper pole significantly higher. We find that the brightest parts of the hard X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200

    Mesoscopic Cooperative Emission From a Disordered System

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    We study theoretically the cooperative light emission from a system of N≫1N\gg 1 classical oscillators confined within a volume with spatial scale, LL, much smaller than the radiation wavelength, λ0=2πc/ω0\lambda_0=2\pi c/\omega_0. We assume that the oscillators frequencies are randomly distributed around a central frequency, ω0\omega_0, with some characteristic width, Ωâ‰Șω0\Omega\ll\omega_0. In the absence of disorder, that is Ω=0\Omega=0, the cooperative emission spectrum is composed of a narrow subradiant peak superimposed on a wide superradiant band. When Ω≠0\Omega\neq 0, we demonstrate that if NN is large enough, the subradiant peak is not simply broadened by the disorder but rather splits into a system of random narrow peaks. We estimate the spectral width of these peaks as a function of N,L,ΩN, L, \Omega, and λ0\lambda_0. We also estimate the amplitude of this mesoscopic structure in the emission spectrum.Comment: 25 pages including 6 figure
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