10,874 research outputs found
Propeller propulsion integration, phase 1
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
Dusty Cometary Globules in W5
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
We aim to directly determine the kinetic temperature and spatial density with
formaldehyde for the 100 brightest ATLASGAL-selected clumps at 870 m
representing various evolutionary stages of high-mass star formation. Ten
transitions ( = 3-2 and 4-3) of ortho- and para-HCO 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-HCO 3-2/3-2,
4-3/4-3, and 4-3/3-2
ratios. The gas kinetic temperatures derived from the p-HCO
3-2/3-2 and 4-3/4-3
line ratios are high, ranging from 43 to 300 K with an unweighted average of
91 4 K. Deduced values from the = 3-2 and 4-3
transitions are similar. Spatial densities of the gas derived from the
p-HCO 4-3/3-2 line ratios yield 0.6-8.3
10 cm with an unweighted average of 1.5 (0.1)
10 cm. A comparison of kinetic temperatures derived from p-HCO,
NH, and the dust emission indicates that p-HCO traces a distinctly
higher temperature than the NH (2,2)/(1,1) transitions and the dust,
tracing heated gas more directly associated with the star formation process.
The HCO 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 HCO do not vary
significantly with the evolutionary stage of the clumps. However, averaged gas
kinetic temperatures derived from HCO increase with time through the
evolution of the clumps.Comment: Accepted for publication in A&
On the correllation effect in Peierls-Hubbard chains
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
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
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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