國小學童網路化寫作學習社群的設計與建構

[[issue]]3

Delineating effects of tensor force on the density dependence of nuclear symmetry energy

In this talk, we report results of our recent studies to delineate effects of the tensor force on the density dependence of nuclear symmetry energy within phenomenological models. The tensor force active in the isosinglet neutron-proton interaction channel leads to appreciable depletion/population of nucleons below/above the Fermi surface in the single-nucleon momentum distribution in cold symmetric nuclear matter (SNM). We found that as a consequence of the high momentum tail in SNM the kinetic part of the symmetry energy $E^{kin}_{sym}(\rho)$ is significantly below the well-known Fermi gas model prediction of approximately $12.5 (\rho/\rho_0)^{2/3}$. With about 15% nucleons in the high momentum tail as indicated by the recent experiments at J-Lab by the CLAS Collaboration, the $E^{kin}_{sym}(\rho)$ is negligibly small. It even becomes negative when more nucleons are in the high momentum tail in SNM. These features have recently been confirmed by three independent studies based on the state-of-the-art microscopic nuclear many-body theories. In addition, we also estimate the second-order tensor force contribution to the potential part of the symmetry energy. Implications of these findings in extracting information about nuclear symmetry energy from nuclear reactions are discussed briefly.Comment: Talk given by Chang Xu at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

ADAPTIVE FEC WITH DYNAMICALLY BLOCK SIZE CONTROL FOR VIDEO STREAMING OVER WIRELESS NETWORK

[[conferencetype]]國際[[conferencedate]]20150718~20150718[[booktype]]電子版[[iscallforpapers]]Y[[conferencelocation]]日本/東

控股股东股权质押与企业创新投入

近年来,上市公司控股股东股权质押已经成为中国资本市场的一种普遍现象。与此同时,国家大力鼓励创新,企业创新已成为中国经济转型升级的必然选择。本文利用2011-2015年中国A股上市公司,实证分析了控股股东股权质押与企业创新投入之间的关系。研究发现:(1)控股股东股权质押会抑制企业创新投入,且这种作用在控股股东持股比例较低和两职合一的公司中会更加显著;(2)进一步研究发现,控股股东股权质押对企业创新投入的负面影响只有在股权质押率较高和距离平仓线越近时才会发挥作用。国家自然科学基金项目(71672157、71572165、71790601)和国家自然科学基金青年科学基金项目(71502150)的资

Too massive neutron stars: The role of dark matter?

The maximum mass of a neutron star is generally determined by the equation of state of the star material. In this study, we take into account dark matter particles, assumed to behave like fermions with a free parameter to account for the interaction strength among the particles, as a possible constituent of neutron stars. We find dark matter inside the star would soften the equation of state more strongly than that of hyperons, and reduce largely the maximum mass of the star. However, the neutron star maximum mass is sensitive to the particle mass of dark matter, and a very high neutron star mass larger than 2 times solar mass could be achieved when the particle mass is small enough. Such kind of dark-matter- admixed neutron stars could explain the recent measurement of the Shapiro delay in the radio pulsar PSR J1614-2230, which yielded a neutron star mass of 2 times solar mass that may be hardly reached when hyperons are considered only, as in the case of the microscopic Brueckner theory. Furthermore, in this particular case, we point out that the dark matter around a neutron star should also contribute to the mass measurement due to its pure gravitational effect. However, our numerically calculation illustrates that such contribution could be safely ignored because of the usual diluted dark matter environment assumed. We conclude that a very high mass measurement of about 2 times solar mass requires a really stiff equation of state in neutron stars, and find a strong upper limit (<= 0.64 GeV) for the particle mass of non-self- annihilating dark matter based on the present model.Comment: Astroparticle Physics (2012) in Pres

Extended quark mean-field model for neutron stars

We extend the quark mean-field (QMF) model to strangeness freedom to study the properties of hyperons ($\Lambda,\Sigma,\Xi$) in infinite baryon matter and neutron star properties. The baryon-scalar meson couplings in the QMF model are determined self-consistently from the quark level, where the quark confinement is taken into account in terms of a scalar-vector harmonic oscillator potential. The strength of such confinement potential for $u,d$ quarks is constrained by the properties of finite nuclei, while the one for $s$ quark is limited by the properties of nuclei with a $\Lambda$ hyperon. These two strengths are not same, which represents the SU(3) symmetry breaking effectively in the QMF model. Also, we use an enhanced $\Sigma$ coupling with the vector meson, and both $\Sigma$ and $\Xi$ hyperon potentials can be properly described in the model. The effects of the SU(3) symmetry breaking on the neutron star structures are then studied. We find that the SU(3) breaking shifts earlier the hyperon onset density and makes hyperons more abundant in the star, in comparisons with the results of the SU(3) symmetry case. However, it does not affect much the star's maximum mass. The maximum masses are found to be $1.62 M_{\odot}$ with hyperons and $1.88 M_{\odot}$ without hyperons. The present neutron star model is shown to have limitations on explaining the recently measured heavy pulsar.Comment: 7 pages, 7 figures, Phys. Rev. C (2014) accepte