3,672 research outputs found
Measured unsteady transonic aerodynamic characteristics of an elastic supercritical wing with an oscillating control surface
Transonic steady and unsteady aerodynamic data were measured on a large elastic wing in the NASA Langley Transonic Dynamics Tunnel. The wing had a supercritical airfoil shape and a leading-edge sweepback of 28.8 deg. The wing was heavily instrumented to measure both static and dynamic pressures and deflections. A hydraulically driven outboard control surface was oscillated to generate unsteady airloads on the wing. Representative results from the wind tunnel tests are presented and discussed, and the unexpected occurrence of an unusual dynamic wing instability, which was sensitive to angle of attack, is reported
The JCMT Gould Belt Survey: the effect of molecular contamination in SCUBA-2 observations of Orion A
Thermal emission from cold dust grains in giant molecular clouds can be used
to probe the physical properties, such as density, temperature and emissivity
in star-forming regions. We present the SCUBA-2 shared-risk observations at 450
m and 850 m of the Orion A molecular cloud complex taken at the James
Clerk Maxwell Telescope (JCMT). Previous studies showed that molecular emission
lines can contribute significantly to the measured fluxes in those continuum
bands. We use the HARP CO J=3-2 integrated intensity map for Orion A in
order to evaluate the molecular line contamination and its effects on the
SCUBA-2 maps. With the corrected fluxes, we have obtained a new spectral index
map for the thermal emission of dust in the well-known integral-shaped
filament. Furthermore, we compare a sample of 33 sources, selected over the
Orion A molecular cloud complex for their high CO J=3-2 line
contamination, to 27 previously identified clumps in OMC-4. This allows us to
quantify the effect of line contamination on the ratio of 850 m to 450
m flux densities and how it modifies the deduced spectral index of
emissivity for the dust grains. We also show that at least one
Spitzer-identified protostellar core in OMC-5 has a CO J=3-2
contamination level of 16 %. Furthermore, we find the strongest contamination
level (44 %) towards a young star with disk near OMC-2. This work is part of
the JCMT Gould Belt Legacy Survey.Comment: 13 pages, 6 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
SANEPIC: A Map-Making Method for Timestream Data From Large Arrays
We describe a map-making method which we have developed for the Balloon-borne
Large Aperture Submillimeter Telescope (BLAST) experiment, but which should
have general application to data from other submillimeter arrays. Our method
uses a Maximum Likelihood based approach, with several approximations, which
allows images to be constructed using large amounts of data with fairly modest
computer memory and processing requirements. This new approach, Signal And
Noise Estimation Procedure Including Correlations (SANEPIC), builds upon
several previous methods, but focuses specifically on the regime where there is
a large number of detectors sampling the same map of the sky, and explicitly
allowing for the the possibility of strong correlations between the detector
timestreams. We provide real and simulated examples of how well this method
performs compared with more simplistic map-makers based on filtering. We
discuss two separate implementations of SANEPIC: a brute-force approach, in
which the inverse pixel-pixel covariance matrix is computed; and an iterative
approach, which is much more efficient for large maps. SANEPIC has been
successfully used to produce maps using data from the 2005 BLAST flight.Comment: 27 Pages, 15 figures; Submitted to the Astrophysical Journal; related
results available at http://blastexperiment.info/ [the BLAST Webpage
A Monte Carlo Approach to Evolution of the Far-Infrared Luminosity Function with BLAST
We constrain the evolution of the rest-frame far-infrared (FIR) luminosity
function out to high redshift, by combining several pieces of complementary
information provided by the deep Balloon-borne Large-Aperture Submillimeter
Telescope surveys at 250, 350 and 500 micron, as well as other FIR and
millimetre data. Unlike most other phenomenological models, we characterise the
uncertainties in our fitted parameters using Monte Carlo Markov Chains. We use
a bivariate local luminosity function that depends only on FIR luminosity and
60-to-100 micron colour, along with a single library of galaxy spectral energy
distributions indexed by colour, and apply simple luminosity and density
evolution. We use the surface density of sources, Cosmic Infrared Background
(CIB) measurements and redshift distributions of bright sources, for which
identifications have been made, to constrain this model. The precise evolution
of the FIR luminosity function across this crucial range has eluded studies at
longer wavelengths (e.g., using SCUBA and MAMBO) and at shorter wavelengths
(e.g., Spitzer), and should provide a key piece of information required for the
study of galaxy evolution. Our adoption of Monte Carlo methods enables us not
only to find the best-fit evolution model, but also to explore correlations
between the fitted parameters. Our model-fitting approach allows us to focus on
sources of tension coming from the combination of data-sets. We specifically
find that our choice of parameterisation has difficulty fitting the combination
of CIB measurements and redshift distribution of sources near 1 mm. Existing
and future data sets will be able to dramatically improve the fits, as well as
break strong degeneracies among the models. [abridged]Comment: 20 pages, 14 figures, accepted to MNRA
Changing Daily Wind Speeds on Alaska’s North Slope: Implications for Rural Hunting Opportunities
Because of their reliance on the harvest of fish and game, Alaskan rural communities have experienced a variety of impacts from climate change, the effects of which are amplified at high latitudes. We collaborated with hunters from the coastal community of Wainwright, Alaska, to document their observations of environmental change (e.g., sea ice, wind, temperature) and the implications of those changes for opportunities to hunt bowhead whale (Balaena mysticetus) during spring and caribou (Rangifer tarandus) during summer. We integrated hunter observations on wind with statistical analysis of daily wind speed data collected in the nearby community of Barrow, Alaska, between 1971 and 2010 to characterize changes in the number of days with suitable hunting conditions. Hunters in Wainwright currently observe fewer days than in previous decades with wind conditions suitable for safely hunting bowhead whales and caribou. The statistical analysis of wind speed data supported these conclusions and suggested that the annual windows of opportunity for hunting each species have decreased by up to seven days since 1971. This study demonstrates the potential power of collaboration between local communities and researchers to characterize the societal impacts of climate change. Continued collaborative research with residents of rural northern Alaskan communities could produce knowledge and develop tools to help rural Alaskans adapt to novel social-ecological conditions.Les collectivités rurales de l’Alaska dépendent de la récolte du poisson et du gibier et à ce titre, elles sont assujetties à une panoplie d’incidences découlant du changement climatique, dont les effets sont amplifiés en haute altitude. Grâce à l’aide des chasseurs de la collectivité côtière de Wainwright, en Alaska, nous avons consigné les observations de ces chasseurs relativement à l’évolution de l’environnement (en ce qui a trait, par exemple, à la glace de mer, au vent et aux températures) de même que les incidences de cette évolution sur les possibilités de chasse de la baleine boréale (Balaena mysticetus) au printemps, et du caribou (Rangifer tarandus) à l’été. Nous avons intégré les observations des chasseurs au sujet du vent à l’analyse statistique des données de la vitesse quotidienne du vent, données recueillies dans la localité avoisinante de Barrow, en Alaska, entre 1971 et 2010, afin de caractériser les changements quant au nombre de jours où les conditions de chasse sont convenables. Comparativement aux décennies précédentes, les chasseurs de Wainwright observent un moins grand nombre de jours, à l’heure actuelle, qu’au cours des décennies précédentes pendant lesquels le régime des vents se prête à la chasse sécuritaire de la baleine boréale et du caribou. L’analyse statistique des données de la vitesse du vent permet de soutenir ces conclusions et suggère qu’annuellement, la période pendant laquelle chacune de ces espèces peut faire l’objet de la chasse a diminué dans une mesure allant jusqu’à sept jours depuis 1971. Cette étude témoigne du pouvoir de collaboration qui pourrait exister entre les collectivités de la région et les chercheurs dans le but de caractériser les incidences du changement climatique sur la société. Les travaux de recherche en collaboration continue avec les habitants des collectivités rurales du nord de l’Alaska pourraient permettre de produire des connaissances et d’élaborer des outils qui aideraient les Alaskiens à s’adapter aux nouvelles conditions socioécologiques
Measuring star formation in high-z massive galaxies: A mid-infrared to submillimeter study of the GOODS NICMOS Survey sample
We present measurements of the mean mid-infrared-to-submillimeter flux
densities of massive (M\ast \approx 2 \times 10^11 Msun) galaxies at redshifts
1.7 < z < 2.9, obtained by stacking positions of known objects taken from the
GOODS NICMOS Survey (GNS) catalog on maps: at 24 {\mu}m (Spitzer/MIPS); 70,
100, and 160{\mu}m (Herschel/PACS); 250, 350, 500{\mu}m (BLAST); and 870{\mu}m
(LABOCA). A modified blackbody spectrum fit to the stacked flux densities
indicates a median [interquartile] star-formation rate of SFR = 63 [48, 81]
Msun yr^-1 . We note that not properly accounting for correlations between
bands when fitting stacked data can significantly bias the result. The galaxies
are divided into two groups, disk-like and spheroid-like, according to their
Sersic indices, n. We find evidence that most of the star formation is
occurring in n \leq 2 (disk-like) galaxies, with median [interquartile] SFR =
122 [100,150] Msun yr^-1, while there are indications that the n > 2
(spheroid-like) population may be forming stars at a median [interquartile] SFR
= 14 [9,20] Msun yr^-1, if at all. Finally, we show that star formation is a
plausible mechanism for size evolution in this population as a whole, but find
only marginal evidence that it is what drives the expansion of the
spheroid-like galaxies.Comment: Accepted by MNRAS. 10 pages, 3 figures, 3 table
BLAST05: Power Spectra of Bright Galactic Cirrus at Submillimeter Wavelengths
We report multi-wavelength power spectra of diffuse Galactic dust emission
from BLAST observations at 250, 350, and 500 microns in Galactic Plane fields
in Cygnus X and Aquila. These submillimeter power spectra statistically
quantify the self-similar structure observable over a broad range of scales and
can be used to assess the cirrus noise which limits the detection of faint
point sources. The advent of submillimeter surveys with the Herschel Space
Observatory makes the wavelength dependence a matter of interest. We show that
the observed relative amplitudes of the power spectra can be related through a
spectral energy distribution (SED). Fitting a simple modified black body to
this SED, we find the dust temperature in Cygnus X to be 19.9 +/- 1.3 K and in
the Aquila region 16.9 +/- 0.7 K. Our empirical estimates provide important new
insight into the substantial cirrus noise that will be encountered in
forthcoming observations.Comment: Submitted to the Astrophysical Journal. Maps and other data are
available at http://blastexperiment.info
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