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Lin Z.,Shanghai University | Zhang J.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Key Laboratory for Astrophysics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

In this paper, we investigate systematically the Mott-insulator-superfluid quantum phase transitions for ultracold scalar bosons in triangular, hexagonal, and Kagomé optical lattices. With the help of the field-theoretical effective potential, by treating the hopping term in the Bose-Hubbard model as perturbation, we calculate the phase boundaries analytically for different integer filling factors. Our analytical results are in good agreement with recent numerical results. © 2012 American Physical Society.


Lin Z.,Shanghai University | Zhang J.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Key Laboratory for Astrophysics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

In this paper, by treating the hopping parameter in the Bose-Hubbard model as a perturbation, with the help of the resummed Green's function method and cumulant expansion, the momentum distribution function of an ultracold Bose system in a triangular optical lattice is calculated analytically. By its use, the time-of-flight absorption picture is plotted and the corresponding visibility is determined. A comparison between our analytical results and the experimental data of Becker exhibits a qualitative agreement. © 2012 American Physical Society.


Zhang J.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Shanghai Key Laboratory of High Temperature Superconductors | Jiang Y.,Key Laboratory for Astrophysics
Laser Physics | Year: 2016

By treating the hopping parameter as a perturbation, with the help of cumulant expansion and the re-summing technique, the one-particle Green's function of a spin-1 Bose system in a honeycomb optical lattice is calculated analytically. By the use of the re-summed Green's function, the quantum phase diagrams of the system in ferromagnetic cases as well as in antiferromagnetic cases are determined. It is found that in antiferromagnetic cases the Mott insulating states with even filling factor are more robust against the hopping parameter than that with odd filling factor, in agreement with results via other different approaches. Moreover, in order to illustrate the effectiveness of the re-summed Green's function method in calculating time-of-flight pictures, the momentum distribution function of a honeycomb lattice spin-1 Bose system in the antiferromagnetic case is also calculated analytically and the corresponding time-of-flight absorption pictures are plotted. © 2016 Astro Ltd.


Zhu Y.,Shanghai University | Jiang Y.,Shanghai University | Jiang Y.,Key Laboratory for Astrophysics
General Relativity and Gravitation | Year: 2011

Dislocation condensation in (2+1)-dimensional World crystal can lead to an emerging linearized gravitation. In this note, we extend the (2+1)D world crystal model to 4-dimensional. By defining the density tensors of defect surfaces in 4-dimensional crystals, we establish the defect field theory of 4D crystal. We present that the proliferation of dislocation surfaces in the 4D world crystal also results in the emergence of linearized gravitation. © 2011 Springer Science+Business Media, LLC.


Shen S.,Chinese Academy of Sciences | Shen S.,Key Laboratory for Astrophysics | Yang X.,Chinese Academy of Sciences | Yang X.,Shanghai JiaoTong University | And 3 more authors.
Astrophysical Journal | Year: 2014

We examine the statistical properties of the brightest group galaxies (BGGs) by using a complete spectroscopic sample of groups/clusters of galaxies selected from the Data Release 7 of the Sloan Digital Sky Survey. We test whether BGGs and other bright members of groups are consistent with an ordered population among the total population of group galaxies. We find that the luminosity distributions of BGGs do not follow the predictions from the order statistics (OS). The average luminosities of BGGs are systematically brighter than OS predictions. On the other hand, by properly taking into account the brightening effect of the BGGs, the luminosity distributions of the second brightest galaxies are in excellent agreement with the expectations of OS. The brightening of BGGs relative to the OS expectation is consistent with a scenario that the BGGs on average have overgrown about 20% masses relative to the other member galaxies. The growth (ΔM) is not stochastic but correlated with the magnitude gap (G 1, 2) between the brightest and the second brightest galaxy. The growth (ΔM) is larger for the groups having more prominent BGGs (larger G 1, 2) and averagely contributes about 30% of the final G 1, 2 of the groups of galaxies. © 2014. The American Astronomical Society. All rights reserved..


Yang Y.-G.,Huaibei Normal University | Shao Z.-Y.,Chinese Academy of Sciences | Shao Z.-Y.,Key Laboratory for Astrophysics | Pan H.-J.,Chinese Academy of Sciences | Yin X.-G.,Huaibei Normal University
Publications of the Astronomical Society of the Pacific | Year: 2011

New CCD photometry for the eclipsing binary EH Cnc was made from 2009 to 2011, and five new eclipsing times are presented. Through using the updated Wilson-Devinney code, we first deduced the photometric solution at Χ2 = 0.9906. The results show that EH Cnc is aW-type contact binary, whose mass ratio and overcontact degree are q = 2.51 (±0.02) and f = 27.7% (±3.4%), respectively. By analyzing the O - C curve of EH Cnc, it is found that there exists a secular-period decrease with a cyclic variation. The period and semiamplitude are P3 = 16.6 (±0.4) yr and A = 0.0032 days (±0.0003 days), respectively. This kind of cyclic variation may probably be attributed to the light-time effect via the presence of an unseen third body, because the values of ΔQ1,2 are much smaller than the typical one for close binaries. The orbital period of EH Cnc continuously decreases at a rate of dP/dt = -1:01 (±0.05) × 10-7 days yr-1. This kind of secular period decrease may result from mass transfer from the primary to the secondary, accompanied by mass and angular momentum loss from the system. With the orbital period decreasing, the inner and outer Roche lobes will shrink, causing the contact degree to increase. Finally, binaries with decreasing periods, such as EH Cnc, will evolve into deep-contact configurations. © 2011.


Chang R.X.,Chinese Academy of Sciences | Shen S.Y.,Chinese Academy of Sciences | Shen S.Y.,Key Laboratory for Astrophysics | Hou J.L.,Chinese Academy of Sciences
Astrophysical Journal Letters | Year: 2012

The disk galaxy UGC8802 has high neutral gas content and a flat profile of star formation rate compared to other disk galaxies with similar stellar mass. It also shows a steep metallicity gradient. We construct a chemical evolution model to explore its growth history by assuming its disk grows gradually from continuous gas infall, which is shaped by a free parameter - the infall-peak time. By adopting the recently observed molecular surface density related star formation law, we show that a late infall-peak time can naturally explain the observed high neutral gas content, while an inside-out disk formation scenario can fairly reproduce the steep oxygen abundance gradient. Our results show that most of the observed features of UGC8802 can be well reproduced by simply "turning the knob" on gas inflow with one single parameter, which implies that the observed properties of gas-rich galaxies could also be modeled in a similar way. © 2012. The American Astronomical Society. All rights reserved..


Shen S.,Chinese Academy of Sciences | Shen S.,Key Laboratory for Astrophysics | Shao Z.,Chinese Academy of Sciences | Shao Z.,Key Laboratory for Astrophysics | And 2 more authors.
Astrophysical Journal Letters | Year: 2010

We examine the distribution of axis ratios of a large sample of disk galaxies hosting type 2 active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey and compare it with a well-defined control sample of non-active galaxies. We find them significantly different, where the type 2 AGNs show both an excess of edge-on objects and deficit of round objects. This systematical bias cannot be explained by a nuclear obscurer oriented randomly with respect to the stellar disk. However, a nuclear obscurer coplanar with the stellar disk also does not fit the data very well. By assuming that the nuclear obscurer having an opening angle of ∼60°, we find that the observed axis ratio distribution can be nicely reproduced by a mean tilt angle of ∼30° between the nuclear obscurer and the stellar disk. © 2010 The American Astronomical Society. All rights reserved.


Gao X.-H.,Chinese Academy of Sciences | Gao X.-H.,University of Chinese Academy of Sciences | Gao X.-H.,Key Laboratory for Astrophysics | Chen L.,Chinese Academy of Sciences | Chen L.,Key Laboratory for Astrophysics
Research in Astronomy and Astrophysics | Year: 2010

We present metallicities and radial velocities for five old open clusters (NGC 6791, NGC 2420, NGC 2682, NGC 2158, and NGC 7789) using data from the seventh public data release of the Sloan Digital Sky Survey (SDSS), which includes the directed stellar program SEGUE: Sloan Extension For Galactic Understanding and Exploration. The radial velocities are used to calculate cluster membership probabilities for stars in each cluster region. NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are found to have mean metallicities [Fe/H]= +0.08 ± 0.09, -0.38 ± 0.11, -0.08 ± 0.05, -0.41 ± 0.13 and -0.19 ± 0.13 dex (s.d.), respectively. The mean radial velocities for NGC 6791, NGC 2420, NGC 2682, NGC 2158 and NGC 7789 are V r = -45.9 ± 0.2, +76.1 ± 0.2, +35.0 ± 0.2, +26.9 ± 0.2 and -48.2 ± 0.2 km s-1(s.e.m.), respectively. We have compared our results with the values from literatures, and found that our metallicity of NGC 6791 is significantly underestimated (by about 0.3 dex) and our radial velocities of the open clusters agree well with the values derived using high-resolution spectroscopy.


Xie X.,Chinese Academy of Sciences | Xie X.,University of Chinese Academy of Sciences | Shen S.,Chinese Academy of Sciences | Shen S.,Key Laboratory for Astrophysics | And 3 more authors.
Astrophysical Journal Letters | Year: 2015

We investigate the luminosity and redshift dependence of the quasar continuum by means of the composite spectrum using a large non-BAL radio-quiet quasar sample drawn from the Sloan Digital Sky Survey. Quasar continuum slopes in the UV-Opt band are measured at two different wavelength ranges, i.e., αν12 (1000 - 2000 Å) and αν24 (2000 - 4000 Å) derived from a power-law fitting. Generally, the UV spectra slope becomes harder (higher αν) toward higher bolometric luminosity. On the other hand, when quasars are further grouped into luminosity bins, we find that both αν12 and αν24 show significant anti-correlations with redshift (i.e., the quasar continuum becomes redder toward higher redshift). We suggest that the cosmic dust extinction is very likely the cause of this observed αν - z relation. We build a simple cosmic dust extinction model to quantify the observed reddening tendency and find an effective dust density nσν ∼ 10-5h Mpc-1 at z < 1.5. The other possibilities that could produce such a reddening effect have also been discussed. © 2015. The American Astronomical Society. All rights reserved.

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