14,945 research outputs found
Active plasmon injection scheme for subdiffraction imaging with imperfect negative index flat lens
We present an active physical implementation of the recently introduced
plasmon injection loss compensation scheme for Pendry's non-ideal negative
index flat lens in the presence of realistic material losses and
signal-dependent noise. In this active implementation, we propose to use a
physically convolved external auxiliary source for signal amplification and
suppression of the noise in the imaging system. In comparison with the previous
passive implementations of the plasmon injection scheme for sub-diffraction
limited imaging, where an inverse filter post-processing is used, the active
implementation proposed here allows for deeper subwavelength imaging far beyond
the passive post-processing scheme by extending the loss compensation to even
higher spatial frequencies.Comment: 13 pages, 15 figure
Re-analysis of the radio luminosity function of Galactic HII regions
We have re-analyzed continuum and recombination lines radio data available in
the literature in order to derive the luminosity function (LF) of Galactic HII
regions. The study is performed by considering the first and fourth Galactic
quadrants independently. We estimate the completeness level of the sample in
the fourth quadrant at 5 Jy, and the one in the first quadrant at 2 Jy. We show
that the two samples (fourth or first quadrant) include, as well as giant and
super-giant HII regions, a significant number of sub-giant sources. The LF is
obtained, in each Galactic quadrant, with a generalized Schmidt's estimator
using an effective volume derived from the observed spatial distribution of the
considered HII regions. The re-analysis also takes advantage of recently
published ancillary absorption data allowing to solve the distance ambiguity
for several objects. A single power-law fit to the LFs retrieves a slope equal
to -2.23+/-0.07 (fourth quadrant) and to -1.85+/-0.11 (first quadrant). We also
find marginal evidence of a luminosity break at L_knee = 10^23.45 erg s^(-1)
Hz^(-1) for the LF in the fourth quadrant. We convert radio luminosities into
equivalent H_alpha and Lyman continuum luminosities to facilitate comparisons
with extra-galactic studies. We obtain an average total HII regions Lyman
continuum luminosity of 0.89 +/- 0.23 * 10^(53) sec^(-1), corresponding to 30%
of the total ionizing luminosity of the Galaxy.Comment: accepted for publication in Ap
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