10,874 research outputs found

    Propeller propulsion integration, phase 1

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    A bibliography was compiled of all readily available sources of propeller analytical and experimental studies conducted during the 1930 through 1960 period. A propeller test stand was developed for the measurement of thrust and torque characteristics of full scale general aviation propellers and installed in the LaRC 30 x 60 foot full scale wind tunnel. A tunnel entry was made during the January through February 1980 period. Several propellers were tested, but unforseen difficulties with the shaft thrust torque balance severely degraded the data quality

    Homing in Pigeons with Impaired Vision

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    Dusty Cometary Globules in W5

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    We report the discovery of four dusty cometary tails around low mass stars in two young clusters belonging to the W5 star forming region. Fits to the observed emission profiles from 24 micron observations with the Spitzer Space Telescope give tail lifetimes < 30 Myr, but more likely < 5 Myr. This result suggests that the cometary phase is a short lived phenomenon, occurring after photoevaporation by a nearby O star has removed gas from the outer disk of a young low mass star (see also Balog et al. 2006; Balog et al. 2008).Comment: 11 pages, 3 figures. Accepted for publication to ApJ Letter

    ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde

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    We aim to directly determine the kinetic temperature and spatial density with formaldehyde for the ∼\sim100 brightest ATLASGAL-selected clumps at 870 μ\mum representing various evolutionary stages of high-mass star formation. Ten transitions (JJ = 3-2 and 4-3) of ortho- and para-H2_2CO near 211, 218, 225, and 291 GHz were observed with the APEX 12 m telescope. Using non-LTE models with RADEX, we derive the gas kinetic temperature and spatial density using the measured p-H2_2CO 321_{21}-220_{20}/303_{03}-202_{02}, 422_{22}-321_{21}/404_{04}-303_{03}, and 404_{04}-303_{03}/303_{03}-202_{02} ratios. The gas kinetic temperatures derived from the p-H2_2CO 321_{21}-220_{20}/303_{03}-202_{02} and 422_{22}-321_{21}/404_{04}-303_{03} line ratios are high, ranging from 43 to >>300 K with an unweighted average of 91 ±\pm 4 K. Deduced TkinT_{\rm kin} values from the JJ = 3-2 and 4-3 transitions are similar. Spatial densities of the gas derived from the p-H2_2CO 404_{04}-303_{03}/303_{03}-202_{02} line ratios yield 0.6-8.3 ×\times 106^6 cm−3^{-3} with an unweighted average of 1.5 (±\pm0.1) ×\times 106^6 cm−3^{-3}. A comparison of kinetic temperatures derived from p-H2_2CO, NH3_3, and the dust emission indicates that p-H2_2CO traces a distinctly higher temperature than the NH3_3 (2,2)/(1,1) transitions and the dust, tracing heated gas more directly associated with the star formation process. The H2_2CO linewidths are found to be correlated with bolometric luminosity and increase with the evolutionary stage of the clumps, which suggests that higher luminosities tend to be associated with a more turbulent molecular medium. It seems that the spatial densities measured with H2_2CO do not vary significantly with the evolutionary stage of the clumps. However, averaged gas kinetic temperatures derived from H2_2CO increase with time through the evolution of the clumps.Comment: Accepted for publication in A&

    On the correllation effect in Peierls-Hubbard chains

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    We reexamine the dimerization, the charge and the spin gaps of a half-filled Peierls-Hubbard chain by means of the incremental expansion technique. Our numerical findings are in significant quantitative conflict with recently obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002) 697] based on a bosonization and a renormalization group method, especially with respect to the charge gap. Their approach seems to be valid only in the weakly correlated case.Comment: 7pages,4figures(6eps-files

    Hydrological impacts of warmer and wetter climate in Troutlake and Sturgeon River basins in central Canada

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    The impact of climate change on water availability in two river basins located in central Canada is investigated. Several statistical downscaling methods are used to generate temperature and precipitation scenarios from the third-generation Canadian Coupled General Circulation Model, forced with different emission scenarios. The hydrological model SLURP is used to simulate runoff. All downscaling methods agree that temperature will increase with time and that precipitation will also increase, although there is considerably more uncertainty in the magnitude of precipitation change. The study concludes that the change in total annual precipitation does not necessarily translate into similar changes in runoff. The seasonal distribution of precipitation changes is important for runoff, as is the increase in evapotranspiration. The choice of downscaling method appears to have a greater impact on runoff projections than the choice of emission scenario. Therefore, it is important to consider several downscaling methods when evaluating the impact of climate change on runoff

    Investigating the Effectiveness of the Tutorials in Introductory Physics in Multiple Instructional Settings

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    This paper examines the educational impact of the implementation of "Changes in Energy and Momentum" from the Tutorials in Introductory Physics in five different instructional settings. These settings include (1) a completely computer-based learning environment and (2) use of cooperative learning groups with varying levels of instructor support. Pre- and post-tests provide evidence that a computer-based implementation falls significantly short of classroom implementations which involve both collaborative learning groups and interactions with a teaching assistance. Other findings provide insight into the importance of certain elements of instructor training and the appropriate use of the tutorial as an initial introduction to a new concept.Comment: 8 Pages, 3 figures, 4 table
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