3,247 research outputs found

    In-space fabrication of thin-film structures

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    A conceptual study of physical vapor-deposition processes for in-space fabrication of thin-film structures is presented. Potential advantages of in-space fabrication are improved structural integrity and surface reflectivity of free-standing ultra-thin films and coatings. Free-standing thin-film structures can find use as photon propulsion devices (solar sails). Other applications of the concept involve free-standing shadow shields, or thermal control coatings of spacecraft surfaces. Use of expendables (such as booster and interstage structures) as source material for the physical vapor deposition process is considered. The practicability of producing thin, textured, aluminum films by physical vapor deposition and subsequent separation from a revolving substrate is demonstrated by laboratory experiments. Heating power requirement for the evaporation process is estimated for a specific mission

    Fabrication of carbon film composites for high-strength structures

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    Physical and mechanical properties of fiber composite materials consisting of carbon films are described. Application of carbon film structural composites for constructing microwave filters or optical instruments is proposed. Applications in aerospace and architectural structures for high strength and low density properties are discussed

    Physical properties of thin films

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    Studies and experiments are presented on carbon, boron, aluminum oxide, zirconium silicate, aluminum, and titanium vapor-deposited on polyimide film substrates

    Searching for Meaning: A Personal and Historical Exploration of Progressive Education

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    In this study the author seeks to better understand the meaning of progressive education. This study does not attempt to answer the question What is progressive education?, but rather it seeks to bring the question to the forefront of the minds of fellow thoughtful, reflective, progressive educators who, like the author, struggle with the contradictions and discrepancies present among progressive educators, both historically and contemporarily. Utilizing Sara Lawrence-Lightfoot\u27s style of portraiture (1997, with J. H. Davis), the author writes in the narrative style, sharing with the reader three conversations with progressive educators whose work has informed her own educational philosophy. Themes of freedom, community, and social justice are woven throughout the portraits. A full review of relevant literature is also included, touching on these and additional themes, such as the importance of reflection, the individual versus the democratic group, and the teacher\u27s role in the progressive classroom. While a study of this nature does not seek to provide definitive conclusions, the author does share her newfound belief, as a result of this study, in the importance of being able to articulate one\u27s educational beliefs in an historical context, as well as to begin to reclaim or more clearly define some key terms used to describe one\u27s educational philosophy and practices

    Limits on Superconductivity-Related Magnetization in Sr2_2RuO4_4 and PrOs4_4Sb12_{12} from Scanning SQUID Microscopy

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    We present scanning SQUID microscopy data on the superconductors Sr2RuO4 (Tc = 1.5 K) and PrOs4_4Sb12_{12} (Tc = 1.8 K). In both of these materials, superconductivity-related time-reversal symmetry-breaking fields have been observed by muon spin rotation; our aim was to visualize the structure of these fields. However in neither Sr2_2RuO4_4 nor PrOs4_4Sb12_{12} do we observe spontaneous superconductivity-related magnetization. In Sr2_2RuO4_4, many experimental results have been interpreted on the basis of a px±ipypx \pm ipy superconducting order parameter. This order parameter is expected to give spontaneous magnetic induction at sample edges and order parameter domain walls. Supposing large domains, our data restrict domain wall and edge fields to no more than ~0.1% and ~0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to ~30 nm for random domains, or ~500 nm for periodic domains.Comment: 8 pages, 7 figures. Submitted to Phys. Rev.
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