7,979 research outputs found

    High index top layer for multimaterial coatings

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    For application in future cryogenically cooled gravitational wave detectors, the thermal noise of low absorbing mirror coatings has to be reduced. The development of low mechanical and optical loss materials is challenging, but thermal noise reduction can be significantly supported by using a multimaterial coating design. We analyze the possible improvement of the total (optical and mechanical) loss of a three-material based coating obtained by optimizing the properties of the top layer of the coating stack. A top-layer material with sufficiently high refractive index could have a significantly higher optical and mechanical loss than currently used tantala, while still enabling reduction of the total coating loss. Restrictions on possible top-layer material properties are made, and the option of a crystalline top layer is discussed

    Why is Long-Horizon Equity Less Risky? A Duration-Based Explanation of the Value Premium

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    This paper proposes a dynamic risk-based model that captures the high expected returns on value stocks relative to growth stocks, and the failure of the capital asset pricing model to explain these expected returns. To model the difference between value and growth stocks, we introduce a cross-section of long-lived firms distinguished by the timing of their cash flows. Firms with cash flows weighted more to the future have high price ratios, while firms with cash flows weighted more to the present have low price ratios. We model how investors perceive the risks of these cash flows by specifying a stochastic discount factor for the economy. The stochastic discount factor implies that shocks to aggregate dividends are priced, but that shocks to the time-varying price of risk are not. As long-horizon equity, growth stocks covary more with this time-varying price of risk than value stocks, which covary more with shocks to cash flows. When the model is calibrated to explain aggregate stock market behavior, we find that it can also account for the observed value premium, the high Sharpe ratios on value stocks relative to growth stocks, and the outperformance of value (and underperformance of growth) relative to the CAPM.

    The Measure of Poverty: A Boston Indicators Project Special Report

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    Examines Boston's poverty rate by race/ethnicity, family structure, education, and geography; income inequality; demand for safety-net programs; and how the high cost of living and budget cuts affect vulnerable households and those below the poverty line

    Fast solution of Cahn-Hilliard variational inequalities using implicit time discretization and finite elements

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    We consider the e�cient solution of the Cahn-Hilliard variational inequality using an implicit time discretization, which is formulated as an optimal control problem with pointwise constraints on the control. By applying a semi-smooth Newton method combined with a Moreau-Yosida regularization technique for handling the control constraints we show superlinear convergence in function space. At the heart of this method lies the solution of large and sparse linear systems for which we propose the use of preconditioned Krylov subspace solvers using an e�ective Schur complement approximation. Numerical results illustrate the competitiveness of this approach

    City of Ideas: Reinventing Boston's Innovation Economy: The Boston Indicators Report 2012

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    Analyzes indicators of the city's economic, social, and technological progress; potential for creating innovative solutions to global and national challenges; and complexities, disparities, and weaknesses in the indicators and innovation economy paradigm

    Beyond Chandra - the X-ray Surveyor

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    Over the past 16 years, NASA's Chandra X-ray Observatory has provided an unparalleled means for exploring the universe with its half-arcsecond angular resolution. Chandra studies have deepened our understanding of galaxy clusters, active galactic nuclei, galaxies, supernova remnants, planets, and solar system objects addressing almost all areas of current interest in astronomy and astrophysics. As we look beyond Chandra, it is clear that comparable or even better angular resolution with greatly increased photon throughput is essential to address even more demanding science questions, such as the formation and subsequent growth of black hole seeds at very high redshift; the emergence of the first galaxy groups; and details of feedback over a large range of scales from galaxies to galaxy clusters. Recently, NASA Marshall Space Flight Center, together with the Smithsonian Astrophysical Observatory, has initiated a concept study for such a mission named the X-ray Surveyor. This study starts with a baseline payload consisting of a high resolution X-ray telescope and an instrument set which may include an X-ray calorimeter, a wide-field imager and a dispersive grating spectrometer and readout. The telescope would consist of highly nested thin shells, for which a number of technical approaches are currently under development, including adjustable X-ray optics, differential deposition, and modern polishing techniques applied to a variety of substrates. In many areas, the mission requirements would be no more stringent than those of Chandra, and the study takes advantage of similar studies for other large area missions carried out over the past two decades. Initial assessments indicate that such an X-ray mission is scientifically compelling, technically feasible, and worthy of a high rioritization by the next American National Academy of Sciences Decadal Survey for Astronomy and Astrophysics.Comment: 6 pages, 6 figures, paper 9510-01 presented at SPIE Europe, Prague, April 201

    Fast Solvers for Cahn-Hilliard Inpainting

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    We consider the efficient solution of the modified Cahn-Hilliard equation for binary image inpainting using convexity splitting, which allows an unconditionally gradient stable time-discretization scheme. We look at a double-well as well as a double obstacle potential. For the latter we get a nonlinear system for which we apply a semi-smooth Newton method combined with a Moreau-Yosida regularization technique. At the heart of both methods lies the solution of large and sparse linear systems. We introduce and study block-triangular preconditioners using an efficient and easy to apply Schur complement approximation. Numerical results indicate that our preconditioners work very well for both problems and show that qualitatively better results can be obtained using the double obstacle potential

    Victims and Aggressors: Black and Jewish Interethnic Relationships in Contemporary American Literature

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    Though blacks and Jews are often portrayed together in African-American and Jewish-American writing, the reasons for the juxtapositions are curious. Contemporary authors have created a close relationship between blacks and Jews that, perhaps with the exception of their cooperation during the Civil Rights movement, historically did not exist. But, the relationship between these two groups in literature offers a unique perspective on American racial and ethnic social structures because both blacks and Jews are considered minority groups, yet they also maintain a hierarchical relationship with one another. By employing black and Jewish characters, American writers, especially Jewish-American writers, create a platform from which to speak about racial and ethnic binaries and the construction of interethnic relationships within American culture. I explore these binaries using the themes of guilt, sexuality and Democracy. The novels discussed in this thesis look at the confrontation between the white power structure and ethnic minorities as well as between the minority ethnic groups themselves to explain the difficulties in this articulation because of the deeply entrenched nature of binary ethnic relationships within American culture. This thesis intervenes in the discourse concerning the representations of blacks and Jews in literature and helps to illuminate interethnic relationships within American culture. Authors Saul Bellow, Alice Walker, Lore Segal and Philip Roth employ binary systems in their novels in order to illustrate how Jewish characters operate in an undefined position between blacks and whites and the consequences of their liminality. Though binaries characterize much of the relationship between races and ethnicities, the Jewish characters destabilize these hierarchical social structures, if only temporarily, opening up the possibility for interethnic relationships to exist outside of a hierarchical system
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