2,720 research outputs found

    Parts and materials application review for space systems

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    Parts and materials application review for project management of space systems engineerin

    CVD Fiber Coatings for Al2O3/NiAl Composites

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    While sapphire-fiber-reinforced nickel aluminide (Al2O3/NiAl) composites are an attractive candidate for high-temperature structures, the significant difference in the coefficient of thermal expansion between the NiAl matrix and the sapphire fiber creates substantial residual stresses in the composite. This study seeks to produce two fiber-coating systems with the potential to reduce the residual stresses in the sapphire/NiAl composite system. Chemical vapor deposition (CVD) was used to produce both the compensating and compliant-fiber coatings for use in sapphire/NiAl composites. A special reactor was designed and built to produce the FGM and to handle the toxic nickel precursors. This process was successfully used to produce 500-foot lengths of fiber with coating thicknesses of approximately 3 microns, 5 microns, and 10 microns

    "Caring for Insiderness": Phenomenologically informed insights that can guide practice.

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    Understanding the ‘‘insider’’ perspective has been a pivotal strength of qualitative research. Further than this, within the more applied fields in which the human activity of ‘‘caring’’ takes place, such understanding of ‘‘what it is like’’ for people from within their lifeworlds has also been acknowledged as the foundational starting point in order for ‘‘care’’ to be caring. But we believe that more attention needs to be paid to this foundational generic phenomenon: what it means to understand the ‘‘insiderness’’ of another, but more importantly, how to act on this in caring ways. We call this human phenomenon ‘‘caring for insiderness.’’ Drawing on existing phenomenological studies of marginal caring situations at the limits of caring capability, and through a process of phenomenologically oriented reflection, we interrogated some existential themes implicit in these publications that could lead to deeper insights for both theoretical and applied purposes. The paper provides direction for practices of caring by highlighting some dangers as well as some remedies along this path

    Initiating solar system formation through stellar shock waves

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    Isotopic anomalies in presolar grains and other meteoritical components require nucleosynthesis in stellar interiors, condensation into dust grains in stellar envelopes, transport of the grains through the interstellar medium by stellar outflows, and finally injection of the grains into the presolar nebula. The proximity of the presolar cloud to these energetic stellar events suggests that a shock wave from a stellar outflow might have initiated the collapse of an otherwise stable presolar cloud. We have begun to study the interactions of stellar shock waves with thermally supported, dense molecular cloud cores, using a three spatial dimension (3D) radiative hydrodynamics code. Supernova shock waves have been shown by others to destroy quiescent clouds, so we are trying to determine if the much smaller shock speeds found in, e.g., asymptotic giant branch (AGB) star winds, are strong enough to initiate collapse in an otherwise stable, rotating, solar-mass cloud core, without leading to destruction of the cloud

    Mastoparan-Induced Intracellular Ca2+ Fluxes May Regulate Cell-to-Cell Communication in Plants

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    Autonomous, High-resolution Observations of Particle Flux in the Oligotrophic Ocean

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    Observational gaps limit our understanding of particle flux attenuation through the upper mesopelagic because available measurements (sediment traps and radiochemical tracers) have limited temporal resolution, are labor-intensive, and require ship support. Here, we conceptually evaluate an autonomous, optical proxy-based method for high-resolution observations of particle flux. We present four continuous records of particle flux collected with autonomous profiling floats in the western Sargasso Sea and the subtropical North Pacific, as well as one shorter record of depth-resolved particle flux near the Bermuda Atlantic Time-series Study (BATS) and Oceanic Flux Program (OFP) sites. These observations illustrate strong variability in particle flux over very short (~1-day) timescales, but at longer timescales they reflect patterns of variability previously recorded during sediment trap time series. While particle flux attenuation at BATS/OFP agreed with the canonical power-law model when observations were averaged over a month, flux attenuation was highly variable on timescales of 1–3 days. Particle fluxes at different depths were decoupled from one another and from particle concentrations and chlorophyll fluorescence in the immediately overlying surface water, consistent with horizontal advection of settling particles. We finally present an approach for calibrating this optical proxy in units of carbon flux, discuss in detail the related, inherent physical and optical assumptions, and look forward toward the requirements for the quantitative application of this method in highly time-resolved studies of particle export and flux attenuation

    Bedrock Geology and Sea-Level History of Fayetteville Quadrangle, Washington County, Arkansas

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    A digital map depicting the detailed bedrock geology of Fayetteville Quadrangle, Washington County, Arkansas was produced at 1:24,000 scale. This map was developed utilizing state-of-the-art Geographic Information Systems technology and represents the most detailed map of the geology of Fayetteville Quadrangle that has been produced. In addition, the stratigraphy was interpreted to develop a regional sea-level history for the quadrangle. The bedrock geology of Fayetteville Quadrangle consists of sedimentary rocks of the Mississippian and Pennsylvanian systems. The Mississippian System is represented by (in ascending order) the Boone, Batesville, Fayetteville, and Pitkin Formations. The Pennsylvanian System is represented by (in ascending order) the Hale, Bloyd, and Atoka Formations. Each of these formations has members that were mapped at 1:24,000 scale, with the exception of the Hindsville Member of the Batesville Formation. Depositional environments represented by Fayetteville Quadrangle strata range from shallow marine to terrestrial and were interpreted to reflect the interplay of tectonics and eustasy during the Mississippian-Pennsylvanian Periods. Analysis of the apparent tempo and amplitude of sea-level variations suggests tectonic processes dominated over eustatic processes during these times. Within Fayetteville Quadrangle there are also several geologic structures that deserve further investigation. These structures include faults, fractures, domes, and so-called collapse or subsidence structures

    Bedrock Geology of West Fork Quadrangle, Washington County, Arkansas

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    A digital geologic map of West Fork quadrangle was produced at 1:24,000 scale using the geographic information system (GIS) software Maplnfo. Data regarding stratigraphic relations observed in the field were digitized onto the United States Geological Survey (USGS) digital raster graphic (DRG) of West Fork quadrangle. The geology of West Fork quadrangle consists of sedimentary rocks of the Mississippian and Pennsylvanian systems. The Fayetteville Shale and Pitkin Formation represent the Mississippian system. The Hale, Bloyd, and Atoka Formations represent the Pennsylvanian System. Each of these formations consists of members that were mapped at 1:24,000 scale, and this mapping effort represents the first time stratigraphic members were mapped utilizing digital technologies at this scale in West Fork quadrangle. The Hale Formation consists of the Cane Hill Member and the Prairie Grove Member. The Bloyd Formation consists of the Brentwood Member, the Woolsey Member, the Dye Member, and the Kessler Member. The Atoka Formation in West Fork quadrangle includes the Trace Creek Member at its base. The overlying units of the Atoka Formation occur as unnamed alternating sandstone and shale units. The most prominent geologic structure in West Fork quadrangle is the Fayetteville Fault, which crosses the northwest quarter of the quadrangle. Several additional faults are associated with a fault zone surrounding the Fayetteville Fault. Another prominent normal fault was mapped striking east-west (downthrown to the south) in the southern part of the quadrangle
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