2,471 research outputs found

    Analytical modeling of intumescent coating thermal protection system in a JP-5 fuel fire environment

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    The thermochemical response of Coating 313 when exposed to a fuel fire environment was studied to provide a tool for predicting the reaction time. The existing Aerotherm Charring Material Thermal Response and Ablation (CMA) computer program was modified to treat swelling materials. The modified code is now designated Aerotherm Transient Response of Intumescing Materials (TRIM) code. In addition, thermophysical property data for Coating 313 were analyzed and reduced for use in the TRIM code. An input data sensitivity study was performed, and performance tests of Coating 313/steel substrate models were carried out. The end product is a reliable computational model, the TRIM code, which was thoroughly validated for Coating 313. The tasks reported include: generation of input data, development of swell model and implementation in TRIM code, sensitivity study, acquisition of experimental data, comparisons of predictions with data, and predictions with intermediate insulation

    A comparative analysis of rawinsonde and NIMBUS 6 and TIROS N satellite profile data

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    Comparisons are made between rawinsonde and satellite profiles in seven areas for a wide range of surface and weather conditions. Variables considered include temperature, dewpoint temperature, thickness, precipitable water, lapse rate of temperature, stability, geopotential height, mixing ratio, wind direction, wind speed, and kinematic parameters, including vorticity and the advection of vorticity and temperature. In addition, comparisons are made in the form of cross sections and synoptic fields for selected variables. Sounding data from the NIMBUS 6 and TIROS N satellites were used. Geostrophic wind computed from smoothed geopotential heights provided large scale flow patterns that agreed well with the rawinsonde wind fields. Surface wind patterns as well as magnitudes computed by use of the log law to extrapolate wind to a height of 10 m agreed with observations. Results of this study demonstrate rather conclusively that satellite profile data can be used to determine characteristics of large scale systems but that small scale features, such as frontal zones, cannot yet be resolved

    Acoustic Remote-Sensing of Reef Benthos in Broward County, Florida (USA)

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    Benthic assemblages of variable density cover three progressively deeper ridges that parallel the Broward County, Florida, coast. An acoustic bottom classification survey using QTCView5 with a 50 kHz transducer showed different acoustic classes on the shallow reef-ridge and the two deeper reef-lines, which both showed the same acoustic signature. Ground-truthing showed that the differences in acoustic signature corresponded to different benthic assemblages: nearshore hardgrounds had low live cover and were dominated by algae covering substrate, the two deeper reef-ridges had the same acoustic signature and similar benthic assemblages (dominated by sponges and gorgonians). The QTCView5 was also able to differentiate between stable sands covered by a thin red algae turf and more mobile sand without turf cover. Acoustic remote-sensing methods can be used to differentiate benthic assemblages, as long as enough differences exist in the growth-form characteristics of the dominant species to provide for a different acoustic roughness

    A Tale of Germs, Storms, and Bombs: Geomorphology and Coral Assemblage Structure at Vieques (Puerto Rico) Compared to St. Croix (U.S. Virgin Islands)

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    The former U.S. Navy range at Vieques Island (Puerto Rico, United States) is now the largest national wildlife refuge in the Caribbean. We investigated the geomorphology and benthic assemblage structure to understand the status of the coral reefs. Coral assemblages were quantified at 24 sites at Vieques and at 6 sites at St. Croix, U.S. Virgin Islands. These sites were chosen to represent the major zones of reef geomorphology. Sites consisted of two or three 21-m-long photo-quadrate belt transects. The results revealed surprisingly little differentiation in the coral assemblages within and between reefs of comparable geomorphological and oceanographic setting at Vieques and St. Croix. At Vieques, the Acropora palmata zone was almost completely lost, and it was severely reduced at St. Croix, presumably primarily due to diseases and hurricane impacts since the 1970s. Subtle, but nonsignificant, differences with respect to the nature of the shelf margin (north adjacent to the bank, south adjacent to the open sea) and depth zone were observed at Vieques. At St. Croix, benthic assemblages differed more between depth zones but not between north and south. Effects of natural disturbances were severe at Vieques, outweighing impacts of past military activity— which were present but not quantitatively discernible at our scale of sampling. Germs and storms, rather than bombs (and associated naval activities), primarily seem to have taken the worst toll on corals at both Vieques and St. Croix

    A Statistics-Based Material Property Analysis to Support Ablation Simulation UQ Efforts

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    Accurate characterization of entry capsule heat shield material properties is a critical component in modeling and simulating Thermal Protection System (TPS) response in a prescribed aerothermal environment. The thermal decomposition of the TPS material during the pyrolysis and charring processes is typically poorly characterized and results in large uncertainties in material properties as inputs for ablation models. These material property uncertainties contribute to large design margins on flight systems and cloud re-construction efforts for data collected during flight and ground testing, making revision to existing models for entry systems more challenging. This work focuses on the following areas of interest to the ablation modeling community: a proper characterization of input probability density functions for material properties, an uncertainty propagation to identify how the uncertainties affect quantities of interest, a sensitivity and uncertainty contributor breakdown, and an analysis of how errors in input characterization contribute to errors in output distributions

    Stability and electronic structure of the complex K2_2PtCl6_6 structure-type hydrides

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    The stability and bonding of the ternary complex K2_2PtCl6_6 structure hydrides is discussed using first principles density functional calculations. The cohesion is dominated by ionic contributions, but ligand field effects are important, and are responsible for the 18-electron rule. Similarities to oxides are discussed in terms of the electronic structure. However, phonon calculations for Sr2_2RuH6_6 also show differences, particularly in the polarizability of the RuH6_6 octahedra. Nevertheless, the yet to be made compounds Pb2_2RuH6_6 and Be2_2FeH6_6 are possible ferroelectrics. The electronic structure and magnetic properties of the decomposition product, FeBe2_2 are reported. Implications of the results for H storage are discussed

    Rodent Habitat On ISS: Spaceflight Effects On Mouse Behavior

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    The NASA Decadal Survey (2011), Recapturing a Future for Space Exploration: Life and Physical Sciences Research for a New Era, emphasized the importance of expanding NASA life sciences research to long duration, rodent experiments on the International Space Station (ISS). To accomplish this objective, flight hardware, operations, and science capabilities supporting mouse studies in space were developed at NASA Ames Research Center. The first flight experiment carrying mice, Rodent Research Hardware and Operations Validation (Rodent Research-1), was launched on Sept 21, 2014 in an unmanned Dragon Capsule, SpaceX4, exposing the mice to a total of 37 days in space. Ground control groups were maintained in environmental chambers at Kennedy Space Center. Mouse health and behavior were monitored for the duration of the experiment via video streaming. Here we present behavioral analysis of two groups of five C57BL/6 female adult mice viewed via fixed camera views compared with identically housed Ground Controls. Flight (Flt) and Ground Control (GC) mice exhibited the same range of behaviors, including eating, drinking, exploratory behavior, self- and allo-grooming, and social interactions at similar or greater levels of occurrence. Mice propelled themselves freely and actively throughout the Habitat using their forelimbs to push off or by floating from one cage area to another, and they quickly learned to anchor themselves using tails and/or paws. Overall activity was greater in Flt as compared to GC mice, with spontaneous ambulatory behavior including the development of organized circling or race-tracking behavior that emerged within the first few days of flight and encompassed the primary dark cycle activity for the remainder of the experiment. We quantified the bout frequency, duration and rate of circling with respect to characteristic behaviors observed in the varying stages of the progressive development of circling: flipping utilizing two sides of the habitat, circling, multi-lap circling and group-circling. Once begun, mice did not regress to flipping behavior or other previous behavioral milestones for the remainder of flight. An overall upward trend in circling frequency, rate, duration, participation, and organization was observed over the course of the 37-day spaceflight experiment. In this presentation, we will summarize qualitative observations and quantitative comparisons of mice in microgravity and 1g conditions. Behavioral analyses provide important insights into the overall health and adaptation of mice to the space environment, and identify unique behaviors and social interactions to guide future habitat development and research on rodents in space
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