Probing the high density behavior of the symmetry energy by using the neutron-proton differential flow

Based on the isospin- and momentum-dependent transport model IBUU04, we investigated the neutron-proton differential flow in the (132) Sn + (124) Sn mid-central collisions at beam energies of 400MeV/A, 600MeV/A and 800MeV/A by adopting two different symmetry energies. It was found that the neutron-proton differential flow as a function of rapidity is very sensitive to the density dependence of symmetry energy, especially at incident energies around 400MeV/A

Flipped symmetry potential in heavy-ion collisions

Within the IBUU transport model, flipping of the symmetry potential in heavy-ion collisions is studied. It is found that there exist flipping of the symmetry potential in the isospin fractionation, the single neutron to proton ratio, the double neutron to proton ratio and the neutron-proton differential flow from lower to higher incident energies. The flipping of the symmetry potential results from the change of the relative magnitude of the hard and soft symmetry energies at lower and higher densities. Future observations of the flipped symmetry potential in experiment will help the study of the density-dependent symmetry energy.

Properties of proto-neutron star and effect of three-body forces

Within the Brueckner-Hartree-Fock framework, the equation of state and the properties of newborn neutron stars are investigated by adopting a realistic nucleon-nucleon interaction AV(18) supplemented with a microscopic three-body force or a phenomenological three-body force. The maximum mass of newborn neutron star and the proton fraction in the newborn beta-stable neutron-star matter are calculated. The neutrino-trapping and the three-body force effects are discussed, and the interplay between the effects of the trapped neutrino and the three-body force are especially explored. It is shown that neutrino trapping considerably affects the proton abundance and the equation of state of the newborn neutron star in both cases with and without the three-body forces. The effect of neutrino trapping remarkably enhances the proton abundance, and the contribution of the three-body force makes the equation of state of the newborn neutron star much stiffer at high densities and consequently increases the proton abundance strongly. The trapped neutrinos significantly reduce the influence of the three-body force on the proton abundance in newborn neutron stars.

DBHF approach and thermodynamic consistency for nuclear matter calculations

Within the framework of Dirac Brueckner-Hartree-Fock (DBHF) approach, we calculate the energy per nucleon, the pressure, the nucleon self-energy, and the single-nucleon energy in the nuclear matter by adopting two different covariant representations for T-matrix. We mainly investigate the influence of different covariant representations on the satisfiable extent of the Hugenholtz-Van Hove (HVH) theorem in the nuclear medium in the framework of DBHF. By adopting the two different covariant representations of T-matrix, the predicted nucleon self-energy shows a quite different momentum and density dependence. Different covariant representations affect remarkably the satisfiable extent of the HVH theorem. By adopting the complete pseudo-vector representation of the T-matrix, HVH theorem is largely violated, which is in agreement with the result in the non-relativistic Brueckner-Hartree-Fock approach and reflects the importance of ground state correlations for single nucleon properties in nuclear medium, whereas by using the pseudoscalar representation, the ground state correlation cannot be shown. It indicates that the complete pseudo-vector presentation is more feasible than the pseudo-scalar one.

Probing density-dependent symmetry energy by using the double n/p ratio

Based on a transport model IBUU04, the double n/p ratio is studied. It is found that the double n/p ratio has almost the same sensitivity to the density dependence of nuclear symmetry energy as the single n/p ratio does. Because the double n/p ratio of nucleon emissions taken from two reaction systems can reduce systemic errors effectively, it is thus more useful for constraining the density-dependent symmetry energy further.

Single and double pi(-)/pi(+) ratios in heavy-ion reactions as probes of the high-density behavior of the nuclear symmetry energy

Based on the isospin- and momentum-dependent hadronic transport model IBUU04, effects of the nuclear symmetry energy on the single and double pi(-)/pi(+) ratios in central reactions of Sn-132+Sn-124 and Sn-112+Sn-112 at a beam energy of 400 MeV/nucleon are studied. It is found that around the Coulomb peak of the single pi(-)/pi(+) ratio the double pi(-)/pi(+) ratio taken from the two isotopic reactions retains about the same sensitivity to the density dependence of nuclear symmetry energy. Because the double pi(-)/pi(+) ratio can significantly reduce the systematic errors, it is thus a more effective probe for the high-density behavior of the nuclear symmetry energy.

Double neutron/proton ratio of nucleon emissions in isotopic reaction systems as a robust probe of nuclear symmetry energy

The double neutron/proton ratio of nucleon emissions taken from two reaction systems using four isotopes of the same element, namely, the neutron/proton ratio in the neutron-rich system over that in the more symmetric system, has the advantage of reducing systematically the influence of the Coulomb force and the normally poor efficiencies of detecting low energy neutrons. The double ratio thus suffers less systematic errors. Within the IBUU04 transport model the double neutron/proton ratio is shown to have about the same sensitivity to the density dependence of nuclear symmetry energy as the single neutron/proton ratio in the neutron-rich system involved. The double neutron/proton ratio is therefore more useful for further constraining the symmetry energy of neutron-rich matter.

Single nucleon potential and effective mass with ground state correlations in hot nuclear matter

In the framework of the finite temperature Brueckner-Hartree-Fock approach including the contribution of the microscopic three-body force, the single nuclear potential and the nucleon effective mass in hot nuclear matter at various temperatures and densities have been calculated by using the hole-line expansion for mass operator, and the effects of the three-body forces and the ground state correlations on the single nucleon potential have been investigated. It is shown that both the ground state correlations and the three-body force affect considerably the density and temperature dependence of the single nucleon potential. The rearrangement correction in the single nucleon potential is repulsive and it reduces remarkably the attraction of the single nucleon potential in the low-momentum region. The rearrangement contribution due to the ground state correlations becomes smaller as the temperature rises up and becomes larger as the density increases. The effect of the three-body force on the ground state correlations is to reduce the contribution of rearrangement. At high densities, the single nucleon potential containing both the rearrangement correction and the contribution of the three-body force becomes more repulsive as the temperature increases.

System size and beam energy effects on probing the high-density behavior of nuclear symmetry energy with pion ratio

Based on the isospin-and momentum-dependent hadronic transport model IBUU04, we have investigated the pi(-)/pi(+) ratio in the following three reactions: Ca-48+Ca-48, Sn-124 +Sn-124 and Au-197+Au-197 with nearly the same isospin asymmetry but different masses, at the bombarding energies from 0.25 to 0.6 A GeV. It is shown that the sensitivity of probing the E-sym (rho) with pi(-)/pi(+) increases with increasing the system size or decreasing the beam energy, showing a correlation to the degree of isospin fractionation. Therefore, with a given isospin asymmetry, heavier system at energies near the pion threshold is preferential to study the behavior Of nuclear symmetry energy at supra-saturation densities.

Recent Progress in Constraining the Equation of State of Dense Neutron-Rich Nuclear Matter with Heavy-Ion Reactions

The nuclear symmetry energy E-sym(rho) is the most uncertain part of the Equation of State (EOS) of dense neutron-rich nuclear matter. In this talk, we discuss the underlying physics responsible for the uncertain E-sym(rho) especially at supra-saturation densities, the circumstantial evidence for a super-soft E-sym(rho) from analyzing pi(-)/pi(+) ratio in relativistic heavy-ion collisions and its impacts on astrophysics and cosmology.

Effects of elastic and inelastic NN scattering cross sections on pi(-)/pi(+) ratios in heavy-ion collisions at intermediate energies

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model and the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross sections on pi(-)/pi(+) in the neutron-rich reaction of Ca-48 + Ca-48 at a beam energy of 400 MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect Delta(1232), pi(-) and pi(+) production, as well as the value of pi(-)/pi(+).

Can the nuclear symmetry potential at supra-saturation densities be negative?

In the framework of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, for the central Au-197 + Au-197 reaction at an incident beam energy of 400 MeV/nucleon, the effect of nuclear symmetry potential at supra-saturation densities on the preequilibrium clusters emission is studied. It is found that for the positive symmetry potential at supra-saturation densities the neutron-to-proton ratio of lighter clusters with mass number A less than or similar to 3 [(n/p)(A less than or similar to 3)] is larger than that of the heavier clusters with mass number A > 3 [(n/p)(A>3)], whereas for the negative symmetry potential at supra-saturation densities the (n/p)(A less than or similar to 3) is smaller than the (n/p)(A>3). This may be considered as a probe of the negative symmetry potential at supra-saturation densities.

Medium effects on pi(-)/pi(+) in heavy-ion collisions at intermediate energies

Based on the isospin-dependent transport model IBUU and on the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross-sections on pi(-)/pi(+) in the neutron-rich reaction Ca-48 + Ca-48 at a beam energy of 400MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect Delta(1232), pi(-) and pi(+) productions as well as the value of pi(-)/pi(+).

TRITON-(HE)-H-3 RELATIVE AND DIFFERENTIAL FLOWS AND THE HIGH DENSITY BEHAVIOR OF NUCLEAR SYMMETRY ENERGY

Using a transport model coupled with a phase-space coalescence after-burner we study the triton-He-3 relative and differential transverse flows in semi-central Sn-132 + Sn-124 reactions at a beam energy of 400 MeV/nucleon. We find that the triton-He-3 pairs carry interesting information about the density dependence of the nuclear symmetry energy. The t-He-3 relative flow can be used as a particularly powerful probe of the high-density behavior of the nuclear symmetry energy.

仿生物膜的电化学研究

本文简要介绍了生物膜的组成、结构和一些基本性质，详细描述了支撑类脂双层膜、非支撑类脂双层膜的成膜方法和各种制备方法的特点。概要总结了仿生膜的各个领域的研究情况，着重评述了仿生膜在电化学、生物传感器、膜片钳领域的发展过程及研究现状，展望仿生膜在电化学的发展前景。采用电化学方法对磷脂浇铸膜(Cast lipid film)、支撑双层磷脂膜（s-BLM）、杂化双磷脂膜（HBM）等不同的模拟生物膜体系进行了研究。主要结果如下：1、通过浇铸二茂铁和DMPC 氯仿溶液的办法，在玻碳（GC）电极表面制备了磷脂浇铸膜。固定在此仿生膜内的二茂铁有一对不可逆的循环伏安峰，阳极峰的电位是+340mV(Ag/AgCl)。在扫速150mV/以下，阳极峰电流与发速的平方根成线性关系，说明二茂铁在浇铸膜内的扩散进程是控制步骤。此电极对抗击环血酸具有很好的身体催化活性，我们研究了溶液pH值对催化效果的影响，发现在pH6.64时催化效果最好。与此同时我们也研究了浇铸膜 厚度和尿酸的干扰。在等摩尔尿酸存在的条件下，此电极仍然可以测定抗坏血酸。在1 * 10~(-4)至5 * 10~(-3)的范围内，抗坏血酸深度与催化电流成正比。2、我们在玻碳电极表面上浇铸（DPPC）磷脂多层膜，二茂铁稳定地固定资产在膜内并以多巴胺显示出良好的催化氧化能力，其阳极电流得到显著增加，并且使多巴胺氧化过电位降低了约80mV。二茂铁在膜内体现了受扩散控制的行为。我们发现溶液的pH值显著地影响催化效果，较高pH对催化有利。与此同明我们还研究磷脂极性基团所带电荷对催化的影响，发现带负电荷的磷脂有利于此电化学催化，而带正电的磷脂对多巴胺的催化不利。造反适当的条件可以分别测定多巴胺和抗坏血酸，在抗坏务酸存在的情况下，我们用此电极测定多巴胺，测定范围是1 * 10~(-4)至3 * 10~(-3) mol/L。3、在铂电极表面制备了卵磷脂和胆固醇支撑双层膜 ，采用循环伏安和交流阻抗方法，研究了支撑双层膜与杂多酸K_7Fe~(3+)P_2V_(17)O_(62)H_2之间的相互作用。发现该种杂多酸能够在双层膜 上产生一些“通道”，探针Ru(NH_3)_6~(3-)和Fe(CN)_6~(3-/4-)可经过这些通道达到电极表面，与此同时通道降低了膜 电阻，增加了膜电容。我们研究了杂多酸浓度和时间对孔洞形成的影响。我们推测K_7Fe~(3+)P_2V_(17)O_(62)H_2与卵磷脂的极度性关作用，减小卵磷脂之间、卵磷脂与胆固醇之间的作用使得双层膜 结构松散形成孔洞。4、利用涂抹-冷冻法制备了硫醇-磷脂杂化双层膜，采用循环伏安和交流阻抗方法，研究了硫醇-磷脂杂化双层膜 与杂多酸K_7Fe~(3+)P_2V_(17)O_(62)H_2作用前后通透性的变化。发现该种杂多酸能够诱导硫醇-磷脂杂化双层膜产生一些孔洞，降低了膜电阻，增加了膜电容，也啬了探针Fe(CN)63-/4-与电极的电子传递。同时对产生该现象的机理进行了初步的探讨。