6,228 research outputs found
Investigation of a liquid-fed water resistojet plume
Measurements of mass flux and flow angle were taken throughout the forward flow region of the exhaust of a liquid-fed water resistojet using a quartz crystal microbalance (QCM). The resistojet operated at a mass flow rate of 0.1 g/s with a power input of 330 Watts. Measured values were compared to theoretical predictions obtained by employing a source flow approximation. Excellent agreement between predicted and measured mass flux values was attained; however, this agreement was highly dependent on knowledge of nozzle flow conditions. Measurements of the temperature at which the exhaust condensed on the QCM were obtained as a function of incident mass flux
Diffraction Analysis of 2-D Pupil Mapping for High-Contrast Imaging
Pupil-mapping is a technique whereby a uniformly-illuminated input pupil,
such as from starlight, can be mapped into a non-uniformly illuminated exit
pupil, such that the image formed from this pupil will have suppressed
sidelobes, many orders of magnitude weaker than classical Airy ring
intensities. Pupil mapping is therefore a candidate technique for coronagraphic
imaging of extrasolar planets around nearby stars. Unlike most other
high-contrast imaging techniques, pupil mapping is lossless and preserves the
full angular resolution of the collecting telescope. So, it could possibly give
the highest signal-to-noise ratio of any proposed single-telescope system for
detecting extrasolar planets. Prior analyses based on pupil-to-pupil
ray-tracing indicate that a planet fainter than 10^{-10} times its parent star,
and as close as about 2 lambda/D, should be detectable. In this paper, we
describe the results of careful diffraction analysis of pupil mapping systems.
These results reveal a serious unresolved issue. Namely, high-contrast pupil
mappings distribute light from very near the edge of the first pupil to a broad
area of the second pupil and this dramatically amplifies diffraction-based edge
effects resulting in a limiting attainable contrast of about 10^{-5}. We hope
that by identifying this problem others will provide a solution.Comment: 23 pages, 13 figures, also posted to
http://www.orfe.princeton.edu/~rvdb/tex/piaaFresnel/ms.pd
First Canadian Record of \u3ci\u3eHexacola Neoscatellae\u3c/i\u3e (Hymenoptera: Figitidae: Eucoilinae), A Parasitoid of the Shore Fly, \u3ci\u3eScatella Stagnalis\u3c/i\u3e
This paper documents the first occurrence of Hexacola neoscatellae, a shore fly parasitoid, in Canada. The discovery of H. neoscatellae is significant because currently there are no suitable biological control agents available for shore fly control to the floriculture industry
Space Trajectory Error Analysis Program (STEAP) for halo orbit missions. Volume 2: Programmer's manual
The six month effort was responsible for the development, test, conversion, and documentation of computer software for the mission analysis of missions to halo orbits about libration points in the earth-sun system. The software consisting of two programs called NOMNAL and ERRAN is part of the Space Trajectories Error Analysis Programs. The program NOMNAL targets a transfer trajectory from earth on a given launch date to a specified halo orbit on a required arrival date. Either impulsive or finite thrust insertion maneuvers into halo orbit are permitted by the program. The transfer trajectory is consistent with a realistic launch profile input by the user. The second program ERRAN conducts error analyses of the targeted transfer trajectory. Measurements including range, doppler, star-planet angles, and apparent planet diameter are processed in a Kalman-Schmidt filter to determine the trajectory knowledge uncertainty
Rotation and Macroturbulence in Metal-poor Field Red Giant and Red Horizontal Branch Stars
We report the results for rotational velocities, Vrot sin i, and
macroturbulence dispersion, zeta(RT), for 12 metal-poor field red giant branch
stars and 7 metal-poor field red horizontal branch stars. The results are based
on Fourier transform analyses of absorption line profiles from high-resolution
(R ~ 120,000), high-S/N (~ 215 per pixel) spectra obtained with the Gecko
spectrograph at CFHT. We find that the zeta(RT) values for the metal-poor RGB
stars are very similar to those for metal-rich disk giants studied earlier by
Gray and his collaborators. Six of the RGB stars have small rotational values,
less than 2.0 km/sec, while five show significant rotation, over 3 km/sec. The
fraction of rapidly rotating RHB stars is somewhat lower than found among BHB
stars. We devise two empirical methods to translate the line-broadening results
obtained by Carney et al. (2003, 2008) into Vrot sin i for all the RGB and RHB
stars they studied. Binning the RGB stars by luminosity, we find that most
metal-poor field RGB stars show no detectable sign, on average, of rotation.
However, the most luminous stars, with M(V) <= -1.5, do show net rotation, with
mean values of 2 to 4 km/sec, depending on the algorithm employed, and these
stars also show signs of radial velocity jitter and mass loss.Comment: accepted for publication in the Astronomical Journa
Elemental Abundance Ratios in Stars of the Outer Galactic Disk. IV. A New Sample of Open Clusters
We present radial velocities and chemical abundances for nine stars in the
old, distant open clusters Be 18, Be 21, Be 22, Be 32, and PWM 4. For Be 18 and
PWM 4, these are the first chemical abundance measurements. Combining our data
with literature results produces a compilation of some 68 chemical abundance
measurements in 49 unique clusters. For this combined sample, we study the
chemical abundances of open clusters as a function of distance, age, and
metallicity. We confirm that the metallicity gradient in the outer disk is
flatter than the gradient in the vicinity of the solar neighborhood. We also
confirm that the open clusters in the outer disk are metal-poor with
enhancements in the ratios [alpha/Fe] and perhaps [Eu/Fe]. All elements show
negligible or small trends between [X/Fe] and distance (< 0.02 dex/kpc), but
for some elements, there is a hint that the local (RGC < 13 kpc) and distant
(RGC > 13 kpc) samples may have different trends with distance. There is no
evidence for significant abundance trends versus age (< 0.04 dex/Gyr). We
measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find
that the scatter about the mean trend is comparable to the measurement
uncertainties. Comparison with solar neighborhood field giants shows that the
open clusters share similar abundance ratios [X/Fe] at a given metallicity.
While the flattening of the metallicity gradient and enhanced [alpha/Fe] ratios
in the outer disk suggest a different chemical enrichment history to the solar
neighborhood, we echo the sentiments expressed by Friel et al. that definitive
conclusions await homogeneous analyses of larger samples of stars in larger
numbers of clusters. Arguably, our understanding of the evolution of the outer
disk from open clusters is currently limited by systematic abundance
differences between various studies.Comment: Accepted for publication in A
Slow-growth approximation for near-wall patch representation of wall-bounded turbulence
Wall-bounded turbulent shear flows are known to exhibit universal small-scale
dynamics that are modulated by large-scale flow structures. Strong pressure
gradients complicate this characterization, however; they can cause significant
variation of the mean flow in the streamwise direction. For such situations, we
perform asymptotic analysis of the Navier-Stokes equations to inform a model
for the effect of mean flow growth on near-wall turbulence in a small domain
localized to the boundary. The asymptotics are valid whenever the viscous
length scale is small relative to the length scale over which the mean flow
varies. To ensure the correct momentum environment, a dynamic procedure is
introduced that accounts for the additional sources of mean momentum flux
through the upper domain boundary arising from the asymptotic terms.
Comparisons of the model's low-order, single-point statistics with those from
direct numerical simulation and well-resolved large eddy simulation of
adverse-pressure gradient turbulent boundary layers indicate the asymptotic
model successfully accounts for the effect of boundary layer growth on the
small-scale near-wall turbulence
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