3,713 research outputs found
Understanding star formation in molecular clouds I. Effects of line-of-sight contamination on the column density structure
Column-density maps of molecular clouds are one of the most important
observables in the context of molecular cloud- and star-formation (SF) studies.
With the Herschel satellite it is now possible to determine the column density
from dust emission. We use observations and simulations to demonstrate how LOS
contamination affects the column density probability distribution function
(PDF). We apply a first-order approximation (removing a constant level) to the
molecular clouds of Auriga, Maddalena, Carina and NGC3603. In perfect agreement
with the simulations, we find that the PDFs become broader, the peak shifts to
lower column densities, and the power-law tail of the PDF flattens after
correction. All PDFs have a lognormal part for low column densities with a peak
at Av~2, a deviation point (DP) from the lognormal at Av(DP)~4-5, and a
power-law tail for higher column densities. Assuming a density distribution
rho~r^-alpha, the slopes of the power-law tails correspond to alpha(PDF)=1.8,
1.75, and 2.5 for Auriga, Carina, and NGC3603 (alpha~1.5-2 is consistent
gravitational collapse). We find that low-mass and high-mass SF clouds display
differences in the overall column density structure. Massive clouds assemble
more gas in smaller cloud volumes than low-mass SF ones. However, for both
cloud types, the transition of the PDF from lognormal shape into power-law tail
is found at the same column density (at Av~4-5 mag). Low-mass and high-mass SF
clouds then have the same low column density distribution, most likely
dominated by supersonic turbulence. At higher column densities, collapse and
external pressure can form the power-law tail. The relative importance of the
two processes can vary between clouds and thus lead to the observed differences
in PDF and column density structure.Comment: A&A accepted, 15.12. 201
Geobase Information System Impacts on Space Image Formats
As Geobase Information Systems increase in number, size and complexity, the format compatability of satellite remote sensing data becomes increasingly more important. Because of the vast and continually increasing quantity of data available from remote sensing systems the utility of these data is increasingly dependent on the degree to which their formats facilitate, or hinder, their incorporation into Geobase Information Systems. To merge satellite data into a geobase system requires that they both have a compatible geographic referencing system. Greater acceptance of satellite data by the user community will be facilitated if the data are in a form which most readily corresponds to existing geobase data structures. The conference addressed a number of specific topics and made recommendations
3D video coding and transmission
The capture, transmission, and display of
3D content has gained a lot of attention in the last few
years. 3D multimedia content is no longer con fined to
cinema theatres but is being transmitted using stereoscopic
video over satellite, shared on Blu-RayTMdisks,
or sent over Internet technologies. Stereoscopic displays
are needed at the receiving end and the viewer needs to
wear special glasses to present the two versions of the
video to the human vision system that then generates
the 3D illusion. To be more e ffective and improve the
immersive experience, more views are acquired from a
larger number of cameras and presented on di fferent displays,
such as autostereoscopic and light field displays.
These multiple views, combined with depth data, also
allow enhanced user experiences and new forms of interaction
with the 3D content from virtual viewpoints.
This type of audiovisual information is represented by a
huge amount of data that needs to be compressed and
transmitted over bandwidth-limited channels. Part of
the COST Action IC1105 \3D Content Creation, Coding
and Transmission over Future Media Networks" (3DConTourNet)
focuses on this research challenge.peer-reviewe
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