12,340 research outputs found
A Cost-Benefit Study of Doing Astrophysics On The Cloud: Production of Image Mosaics
Utility grids such as the Amazon EC2 and Amazon S3 clouds offer computational and storage resources that can be used on-demand for a fee by compute- and data-intensive applications. The cost of running an application on such a cloud depends on the compute, storage and communication resources it will provision and consume. Different execution plans of the same application may result in significantly different costs. We studied via simulation the cost performance trade-offs of different execution and resource provisioning plans by creating, under the Amazon cloud fee structure, mosaics with the Montage image mosaic engine, a widely used data- and compute-intensive application. Specifically, we studied the cost of building mosaics of 2MASS data that have sizes of 1, 2 and 4 square degrees, and a 2MASS all-sky mosaic. These are examples of mosaics commonly generated by astronomers. We also study these trade-offs in the context of the storage and communication fees of Amazon S3 when used for long-term application data archiving. Our results show that by provisioning the right amount of storage and compute resources cost can be significantly reduced with no significant impact on application performance
Close range mini Uavs photogrammetry for architecture survey
The survey of historical façades contains several bottlenecks, mainly related to the geometrical structure, the decorative framework, the presence of natural or artificial obstacles, the environment limitations. Urban context presents additional restrictions, binding by ground acquisition activity and leading to building data loss. The integration of TLS and close-range photogrammetry allows to go over such stuff, not overcoming the shadows effect due to the ground point of view. In the last year the massive use of UAVs in survey activity has permitted to enlarge survey capabilities, reaching a deeper knowledge in the architecture analysis. In the meanwhile, several behaviour rules have been introduced in different countries, regulating the UAVs use in different field, strongly restricting their application in urban areas. Recently very small and light platforms have been presented, which can partially overcome these rules restrictions, opening to very interesting future scenarios. This article presents the application of one of these very small RPAS (less than 300 g), equipped with a low-cost camera, in a close range photogrammetric survey of an historical building façade in Bologna (Italy). The suggested analysis tries to point out the system accuracy and details acquisition capacity. The final aim of the paper is to validate the application of this new platform in an architectonic survey pipeline, widening the future application of close-range photogrammetry in the architecture acquisition process
Evidence for dust evolution within the Taurus Complex from Spitzer images
We present Spitzer images of the Taurus Complex (TC) and take advantage of
the sensitivity and spatial resolution of the observations to characterize the
diffuse IR emission across the cloud. This work highlights evidence of dust
evolution within the translucent sections of the archetype reference for
studies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100
um observations to produce a dust temperature map and a far-IR dust opacity map
at 5' resolution. The average dust temperature is about 14.5K with a dispersion
of +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger than
the average value for the diffuse ISM. This opacity increase and the
attenuation of the radiation field (RF) both contribute to account for the
lower emission temperature of the large grains. The structure of the TC
significantly changes in the mid-IR images that trace emission from PAHs and
VSGs. We focus our analysis of the mid-IR emission to a range of ecliptic
latitudes where the zodiacal light residuals are small. Within this cloud area,
there are no 8 and 24 um counterparts to the brightest 160 um emission
features. Conversely, the 8 and 24 um images reveal filamentary structure that
is strikingly inconspicuous in the 160 um and extinction maps. The IR colors
vary over sub-parsec distances across this filamentary structure. We compare
the observed colors with model calculations quantifying the impact of the RF
intensity and the abundance of stochastically heated particles on the dust SED.
To match the range of observed colors, we have to invoke variations by a factor
of a few of both the interstellar RF and the abundance of PAHs and VSGs. We
conclude that within this filamentary structure a significant fraction of the
dust mass cycles in and out the small size end of the dust size distribution.Comment: 43 pages, 13 figures, accepted for publication in Ap
New Constraints on Mass-Dependent Disruption of Star Clusters in M51
We use UBVI,Ha images of the Whirlpool galaxy, M51, taken with the ACS and
WFPC2 cameras on the Hubble Space Telescope (HST) to select star clusters, and
to estimate their masses and ages by comparing their observed colors with
predictions from population synthesis models. We construct the mass function of
intermediate age (1-4x10^8 yr) clusters, and find that it is well described by
a power law, psi(M) propto M^beta, with beta=-2.1 +/- 0.2, for clusters more
massive than approximately 6x10^3 Msun. This extends the mass function of
intermediate age clusters in M51 to masses lower by nearly a factor of five
over previous determinations. The mass function does not show evidence for
curvature at either the high or low mass end. This shape indicates that there
is no evidence for the earlier disruption of lower mass clusters compared with
their higher mass counterparts (i.e., no mass-dependent disruption) over the
observed range of masses and ages, or for a physical upper mass limit Mc with
which clusters in M51 can form. These conclusions differ from previous
suggestions based on poorer-quality HST observations. We discuss their
implications for the formation and disruption of the clusters. Ages of clusters
in two "feathers," stellar features extending from the outer portion of a
spiral arm, show that the feather with a larger pitch angle formed earlier, and
over a longer period, than the other.Comment: 24 pages, 7 figures; to be published in ApJ, 727, 8
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