4,260 research outputs found
The stellar host in star-forming low-mass galaxies: Evidence for two classes
The morphological evolution of star-forming galaxies provides important clues
to understand their physical properties, as well as the triggering and
quenching mechanisms of star formation. We aim at connecting morphology and
star-formation properties of low-mass galaxies (median stellar mass
10 M) at low redshift ().
We use a sample of medium-band selected star-forming galaxies from the
GOODS-North field. H images for the sample are created combining both
spectral energy distribution fits and HST data. Using them, we mask the star
forming regions to obtain an unbiased two-dimensional model of the light
distribution of the host galaxies. For this purpose we use , a
new Bayesian photometric decomposition code. We apply it independently to 7 HST
bands assuming a S\'ersic surface brightness model.
Star-forming galaxy hosts show low S\'ersic index (with median
0.9), as well as small sizes (median 1.6 kpc), and negligible
change of the parameters with wavelength (except for the axis ratio, which
grows with wavelength). Using a clustering algorithm, we find two different
classes of star-forming galaxies: A more compact, redder, and high- (class
A) and a more extended, bluer and lower- one (class B). We also find
evidence that the first class is more spheroidal-like. In addition, we find
that 48% of the analyzed galaxies present negative color gradients (only 5% are
positive).
The host component of low-mass star-forming galaxies at separates
into two different classes, similar to what has been found for their higher
mass counterparts. The results are consistent with an evolution from class B to
class A. Several mechanisms from the literature, like minor and major mergers,
and violent disk instability, can explain the physical process behind the
likely transition between the classes. [abridged]Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 11
figure
Low energy universality and scaling of Van der Waals forces
At long distances interactions between neutral ground state atoms can be
described by the Van der Waals potential V(r) =-C6/r^6-C8/r^8 - ... . In the
ultra-cold regime atom-atom scattering is dominated by s-waves phase shifts
given by an effective range expansion p cot d0 (p) = -1/a0 + r0 p^2/2 + ... in
terms of the scattering length a0 and the effective range r0. We show that
while for these potentials the scattering length cannot be predicted, the
effective range is given by the universal low energy theorem r0 = A + B/a0+
C/a0^2 where A,B and C depend on the dispersion coefficients Cn and the reduced
di-atom mass. We confront this formula to about a hundred determinations of r0
and a0 and show why the result is dominated by the leading dispersion
coefficient C6. Universality and scaling extends much beyond naive dimensional
analysis estimates.Comment: 4 pages, 3 figure
Service level agreement framework for differentiated survivability in GMPLS-based IP-over-optical networks
In the next generation optical internet, GMPLS based IP-over-optical networks, ISPs will be required to support a wide variety of applications each having their own requirements. These requirements are contracted by means of the SLA. This paper describes a recovery framework that may be included in the SLA contract between ISP and customers in order to provide the required level of survivability. A key concern with such a recovery framework is how to present the different survivability alternatives including recovery techniques, failure scenario and layered integration into a transparent manner for customers. In this paper, two issues are investigated. First, the performance of the recovery framework when applying a proposed mapping procedure as an admission control mechanism in the edge router considering a smart-edge simple-core GMPLS-based IP/WDM network is considered. The second issue pertains to the performance of a pre-allocated restoration and its ability to provide protected connections under different failure scenarios
RECODIS : Resilient communication services protecting end-user applications from disaster-based failures
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