14,634 research outputs found
Bose-Einstein condensation in linear sigma model at Hartree and large N approximation
The BEC of charged pions is investigated in the framework of O(4) linear
sigma model. By using Cornwall-Jackiw-Tomboulis formalism, we have derived the
gap equations for the effective masses of the mesons at finite temperature and
finite isospin density. The BEC is discussed in chiral limit and non-chiral
limit at Hartree approximation and also at large N approximation.Comment: 11 pages, 9 figure
Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A
Magnetic fields are believed to play a crucial role in the process of star
formation. We compare high-angular resolution observations of the submillimeter
polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a
low-mass protostar, with models of the collapse of magnetized molecular cloud
cores. Assuming a uniform dust alignment efficiency, we computed the Stokes
parameters and synthetic polarization maps from the model density and magnetic
field distribution by integrations along the line-of-sight and convolution with
the interferometric response. The synthetic maps are in good agreement with the
data. The best-fitting models were obtained for a protostellar mass of 0.8
solar masses, of age 9e4 yr, formed in a cloud with an initial mass-to-flux
ratio ~2 times the critical value. The magnetic field morphology in NGC 1333
IRAS 4A is consistent with the standard theoretical scenario for the formation
of solar-type stars, where well-ordered, large-scale, rather than turbulent,
magnetic fields control the evolution and collapse of the molecular cloud cores
from which stars form.Comment: 4 pages, 5 figures. Accepted by Astronomy and Astrophysic
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
Simple generic method for predicting the effect of strain on surface diffusion
Journal ArticleWe show, by first-principles calculations, that the effect of external strain on surface diffusion is inherently correlated with the intrinsic surface stress induced by the adatom along its diffusion pathways. We demonstrate a simple generic method for a priori predicting quantitatively how an external strain will change surface diffusion on any given surface, based on calculations of surface-stress tensors of the unstrained surface
The CJT calculation in studying nuclear matter beyond mean field approximation
We have introduced a CJT calculation in studying nuclear matter beyond mean
field approximation. Based on the CJT formalism and using Walecka model, we
have derived a set of coupled Dyson equations of nucleons and mesons.
Neglecting the medium effects of the mesons, the usual MFT results could be
reproduced. The beyond MFT calculations have been performed by thermodynamic
consistently determining the meson effective masses and solving the coupled gap
equations for nucleons and mesons. The numerical results for the nucleon and
meson effective masses at finite temperature and chemical potential in nuclear
matter are discussed.Comment: 8 pages, 8 figure
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