49,771 research outputs found
The Differences of Star Formation History Between Merging Galaxies and Field Galaxies in the EDR of the SDSS
Based on the catalog of merging galaxies in the Early Data Release (EDR) of
the Sloan Digital Sky Survey (SDSS), the differences of star formation history
between merging galaxies and field galaxies are studied statistically by means
of three spectroscopic indicators the 4000-\r{A} break strength, the Balmer
absorption-line index, and the specific star formation rate. It is found that
for early-type merging galaxies the interactions will not induce significant
enhancement of the star-formation activity because of its stability and lack of
cool gas. On the other hand, late-type merging galaxies always in general
display more active star formation than field galaxies on different timescales
within about 1Gyr. We also conclude that the mean stellar ages of late-type
merging galaxies are younger than those of late-type field galaxies.Comment: 9 pages, 4 figures, accepted for publication in PAS
Entering the Union : European accession and capacity-building priorities
The authors examine the impact of trade facilitation on bilateral trade flows. They examine trade facilitation and capacity-building priorities in 12 countries in the Europe and Central Asia region-eight of the current members of the European Union: Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia,and Slovenia, and three candidate members: Bulgaria, Romania, and Turkey. The results suggest that behind-the-border factors play an important role in determining bilateral trade flows (controlling for the effects of tariffs, development levels, distance, and regional characteristics of exporters and importers, among other factors). The development of new data sets to expand work related to trade facilitation, including strengthening the empirical work explored here, is a key priority without which intelligent policy and priorities cannot be made. The authors'analysis is based on data from the World Economic Forum, Global Competitiveness Report 2001-2002, World Competitiveness Yearbook 2000, and Kaufmann, Kraay, and Zoido-Lobaton (2002). The results indicate that more gains in exports than in imports are expected should the values of three out of the four indicators (port efficiency, regulatory regimes, and information technology infrastructure) of the new and candidate member countries improve halfway to the EU15 average. These countries would expect large trade gains as well as improvements in trade balances as their integration into the EU continues. For example, the greatest absolute trade gains-62 billion respectively-could be expected if their port efficiency and information technology infrastructure reach half the average level of the EU, and 70 percent of trade gains are associated with export expansion.Economic Theory&Research,Trade and Regional Integration,Trade Policy,Transport and Trade Logistics,Common Carriers Industry
Theoretical modeling of spatial and temperature dependent exciton energy in coupled quantum wells
Motivated by a recent experiment of spatial and temperature dependent average
exciton energy distribution in coupled quantum wells [S. Yang \textit{et al.},
Phys. Rev. B \textbf{75}, 033311 (2007)], we investigate the nature of the
interactions in indirect excitons. Based on the uncertainty principle, along
with a temperature and energy dependent distribution which includes both
population and recombination effects, we show that the interplay between an
attractive two-body interaction and a repulsive three-body interaction can lead
to a natural and good account for the nonmonotonic temperature dependence of
the average exciton energy. Moreover, exciton energy maxima are shown to locate
at the brightest regions, in agreement with the recent experiments. Our results
provide an alternative way for understanding the underlying physics of the
exciton dynamics in coupled quantum wells.Comment: 8 pages, 5 figure
Improved lattice QCD with quarks: the 2 dimensional case
QCD in two dimensions is investigated using the improved fermionic lattice
Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved
theory leads to a significant reduction of the finite lattice spacing errors.
The quark condensate and the mass of lightest quark and anti-quark bound state
in the strong coupling phase (different from t'Hooft phase) are computed. We
find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures
SED-inferred properties and morphology of Lyman-break galaxies at in the CDF-S
After carefully cross-identifying a previously discovered GALEX-selected
Lyman Break Galaxy (LBG) candidates one-to-one with their optical counterparts
in the field of the CDF-S, we re-estimate their photometric redshifts using
multi-wavelength data from UV, optical to NIR. We refine a new updated sample
of 383 LBGs at 0.7\la z \la 1.4.
Most LBGs are classified as starburst and irregular types. Ages spread from
several Myr to 1.5Gyr. Their dust-corrected star formation rates (SFRs) and
stellar masses () are from 4\my to 220\my and from 2.3\times 10^8
\msun to 4 \times 10^{11} \msun. The rest-frame FUV luminosity function of
LBGs are presented. LBGs of irregular types mainly distribute along the "main
sequence" of star forming galaxies while most LBGs of starburst types locate in
the starburst region. A "downsizing" effect is clearly found and LBGs
distribute in the "blue" cloud.
HST images in F606W ( band) and F850LP ( band) are taken from the GEMS
and GOODS-S surveys. SExtractor and GALFIT are applied to get their
morphological parameters. A morphological sample of 142 LBGs with reliable
results of \sersic and sizes in both bands is defined. We find that LBGs at
are dominated by disk-like galaxies. Correlations between
photometric and morphological properties of LBGs are investigated. Strong
correlations between their half-light radii and , i.e., size-stellar mass
relations, are found in both bands. Physical connections between correlations
and the "downsizing" effect are discussed.Comment: 26 pages, 30 figures, 6 tables, accepted by MNRA
Thermal 3D modelling
This paper presents the case of 3D reconstructing an object using infrared imagery. Conversely to previous solutions that used the RGB imagery to make the 3D reconstruction and later superimpose the infrared, this paper makes use of the infrared imagery directly. The results of the reconstruction are then compared to an accurate laser scan of the object which provides a ground-truth. The results show that although it is still inaccurate this is mainly due to the low resolution of thermal imagery rather than their direct application for reconstruction
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