Momentum dependence of the symmetry potential and nuclear reactions induced by neutron-rich nuclei at RIA

Effects of the momentum-dependence of the symmetry potential in nuclear reactions induced by neutron-rich nuclei at RIA energies are studied using an isospin- and momentum-dependent transport model. It is found that symmetry potentials with and without the momentum-dependence but corresponding to the same density-dependent symmetry energy $E_{sym}(\rho)$ lead to significantly different predictions on several $E_{sym}(\rho)$-sensitive experimental observables. The momentum-dependence of the symmetry potential is thus critically important for investigating accurately the equation of state (${\rm EOS}$) and novel properties of dense neutron-rich matter at RIA.Comment: Rapid Communication, Phys. Rev. C in pres

On the choice of colliding beams to study deformation effects in relativistic heavy ion collisions

It has been suggested that collisions between deformed shapes will lead to interesting effects on various observables such as K production and elliptic flow. Simple formulae can be written down which show how to choose the colliding beams which will maximise the effects of deformation.Comment: 2 pages, this version supersedes the previous on

A Transport Model for Nuclear Reactions Induced by Radioactive Beams

Major ingredients of an isospin and momentum dependent transport model for nuclear reactions induced by radioactive beams are outlined. Within the IBUU04 version of this model we study several experimental probes of the equation of state of neutron-rich matter, especially the density dependence of the nuclear symmetry energy. Comparing with the recent experimental data from NSCL/MSU on isospin diffusion, we found a nuclear symmetry energy of $)\approx 31.6(\rho /\rho_{0})^{1.05}$ at subnormal densities. Predictions on several observables sensitive to the density dependence of the symmetry energy at supranormal densities accessible at GSI and the planned Rare Isotope Accelerator (RIA) are also made.Comment: 10 pages. Talk given at the 2nd Argonne/MSU/JINA/INT RIA Workshop at MSU, March 9-12, 2005 to be published in the Proceedings by the American Institute of Physic

Effects of momentum-dependent symmetry potential on heavy-ion collisions induced by neutron-rich nuclei

Using an isospin- and momentum-dependent transport model we study effects of the momentum-dependent symmetry potential on heavy-ion collisions induced by neutron-rich nuclei. It is found that symmetry potentials with and without the momentum-dependence but corresponding to the same density-dependent symmetry energy $E_{sym}(\rho)$ lead to significantly different predictions on several $E_{sym}(\rho)$-sensitive experimental observables especially for energetic nucleons. The momentum- and density-dependence of the symmetry potential have to be determined simultaneously in order to extract the $E_{sym}(\rho)$ accurately. The isospin asymmetry of midrapidity nucleons at high transverse momenta is particularly sensitive to the momentum-dependence of the symmetry potential. It is thus very useful for investigating accurately the equation of state of dense neutron-rich matter.Comment: The version to appear in Nucl. Phys. A. A paragraph and a figure on neutron and proton effective masses in neutron-rich matter are adde

Regional astrocyte IFN signaling restricts pathogenesis during neurotropic viral infection

Type I IFNs promote cellular responses to viruses, and IFN receptor (IFNAR) signaling regulates the responses of endothelial cells of the blood-brain barrier (BBB) during neurotropic viral infection. However, the role of astrocytes in innate immune responses of the BBB during viral infection of the CNS remains to be fully elucidated. Here, we have demonstrated that type I IFNAR signaling in astrocytes regulates BBB permeability and protects the cerebellum from infection and immunopathology. Mice with astrocyte-specific loss of IFNAR signaling showed decreased survival after West Nile virus infection. Accelerated mortality was not due to expanded viral tropism or increased replication. Rather, viral entry increased specifically in the hindbrain of IFNAR-deficient mice, suggesting that IFNAR signaling critically regulates BBB permeability in this brain region. Pattern recognition receptors and IFN-stimulated genes had higher basal and IFN-induced expression in human and mouse cerebellar astrocytes than did cerebral cortical astrocytes, suggesting that IFNAR signaling has brain region–specific roles in CNS immune responses. Taken together, our data identify cerebellar astrocytes as key responders to viral infection and highlight the existence of distinct innate immune programs in astrocytes from evolutionarily disparate regions of the CNS

Effects of isospin and momentum dependent interactions on liquid-gas phase transition in hot asymmetric nuclear matter

The liquid-gas phase transition in hot neutron-rich nuclear matter is investigated within a self-consistent thermal model using an isospin and momentum dependent interaction (MDI) constrained by the isospin diffusion data in heavy-ion collisions, a momentum-independent interaction (MID), and an isoscalar momentum-dependent interaction (eMDYI). The boundary of the phase-coexistence region is shown to be sensitive to the density dependence of the nuclear symmetry energy with a softer symmetry energy giving a higher critical pressure and a larger area of phase-coexistence region. Compared with the momentum-independent MID interaction, the isospin and momentum-dependent MDI interaction is found to increase the critical pressure and enlarge the area of phase-coexistence region. For the isoscalar momentum-dependent eMDYI interaction, a limiting pressure above which the liquid-gas phase transition cannot take place has been found and it is shown to be sensitive to the stiffness of the symmetry energy.Comment: 6 pages, 4 figures, revised version, to appear in PL

First molecular phylogenetic insights into the evolution of Eriocaulon (Eriocaulaceae, Poales)

Eriocaulon is a genus of c. 470 aquatic and wetland species of the monocot plant family Eriocaulaceae. It is widely distributed in Africa, Asia and America, with centres of species richness in the tropics. Most species of Eriocaulon grow in wetlands although some inhabit shallow rivers and streams with an apparent adaptive morphology of elongated submerged stems. In a previous molecular phylogenetic hypothesis, Eriocaulon was recovered as sister of the African endemic genus Mesanthemum. Several regional infrageneric classifications have been proposed for Eriocaulon. This study aims to critically assess the existing infrageneric classifications through phylogenetic reconstruction of infrageneric relationships, based on DNA sequence data of four chloroplast markers and one nuclear marker. There is little congruence between our molecular results and previous morphology-based infrageneric classifications. However, some similarities can be found, including Fyson’s sect. Leucantherae and Zhang’s sect. Apoda. Further phylogenetic studies, particularly focusing on less well sampled regions such as the Neotropics, will help provide a more global overview of the relationships in Eriocaulon and may enable suggesting the first global infrageneric classification

Excitation functions in central Au+Au collisions from SIS/GSI to AGS/Brookhaven

Using the relativistic transport model (ART), we predict the energy dependence of the stopping power, maximum baryon and energy densities, the population of resonance matter as well as the strength of the transverse and radial flow for central Au+Au reactions at beam momentum from 2 to 12 GeV/c available at Brookhaven's AGS. The maximum baryon and energy densities are further compared to the predictions of relativistic hydrodynamics assuming the formation of shock waves. We also discuss the Fermi-Landau scaling of the pion multiplicity in these reactions.Comment: 20 pages, latex, 10 figures available upon request from the authors, Nucl. Phys. A in pres

Near-threshold K+K^{+} Production in Heavy-ion Collisions

Within a hadronic transport model we study in detail contributions to kaon yields and momentum spectra from various baryon (resonance)-baryon (resonance) and $\pi N$ interactions in heavy-ion collisions at beam energies near the free-space kaon production threshold. It is found that the finite lifetime of baryon resonances affects significantly the shape of kaon spectra, and the high energy parts of the kaon spectra are dominated by kaons from $\pi N\rightarrow \Lambda K^{+}$ processes. $N^{*}(1440)$ resonances are found to contribute about 10\% to the kaon yield. Effects of boosting the Fermi momentum distributions of the two colliding nuclei into their center of mass frame, centrality of the reaction as well as the nuclear equation of state on kaon yields and spectra are also discussed. Model calculations on $K^{+}$, $\pi^{+}$ and $\pi^{-}$ spectra for the reaction of Au+Au at $E_{beam}/A= 1.0$ GeV are compared with the experimental data from the KaoS collaboration.Comment: 18 pages, 11 figures available upon request. TAMU preprint #940403

Constraining the Radii of Neutron Stars with Terrestrial Nuclear Laboratory Data

Neutron star radii are primarily determined by the pressure of isospin asymmetric matter which is proportional to the slope of the nuclear symmetry energy. Available terrestrial laboratory data on the isospin diffusion in heavy-ion reactions at intermediate energies constrain the slope of the symmetry energy. Using this constraint, we show that the radius (radiation radius) of a 1.4 solar mass neutron star is between 11.5 (14.4) and 13.6 (16.3) km.Comment: 11 pages, 3 figures; version to be published in Phys. Lett.