Global properties of the Skyrme-force-induced nuclear symmetry energy

Large scale calculations are performed to establish the global mass dependence of the nuclear symmetry energy, $a_{sym}(A)$, which in turn depends on two basic ingredients: the mean-level spacing, $\epsilon(A)$, and the effective strength of the isovector mean-potential, $\kappa(A)$. Surprisingly, our results reveal that in modern parameterizations including SLy4, SkO, SkXc, and SkP these two basic ingredients of $a_{sym}$ are almost equal after rescaling them linearly by the isoscalar and the isovector effective masses, respectively. This result points toward a new fundamental property of the nuclear interaction that remains to be resolved. In addition, our analysis determines the ratio of the surface-to-volume contributions to $a_{sym}$ to be $\sim$1.6, consistent with hydrodynamical estimates for the static dipole polarizability as well as the neutron-skin.Comment: 4 pages, 2 figures, 1 tabl

Spin-orbit term and spin-fields: extension of Skyrme-force induced local energy density approach

A systematic study of terminating states in A$\sim$50 mass region using the self-consistent Skyrme-Hartree-Fock model is presented. The objective is to demonstrate that the terminating states, due to their intrinsic simplicity, offer unique and so far unexplored opportunities to study different aspects of the effective NN interaction or nuclear local energy density functional. In particular, we demonstrate that the agreement of the calculations to the data depend on the spin fields and the spin-orbit term which, in turn, allows to constrain the appropriate Landau parameters and the strength of the spin-orbit potential.Comment: 23 pages, 9 figures, submitted to PR

Microscopic structure of fundamental excitations in N=Z nuclei

Excitation energies of the $T$=1 states in even-even as well as $T$=0 and $T$=1 states in odd-odd $N$=$Z$ nuclei are calculated within the mean-field approach. It is shown that the underlying structure of these states can be determined in a consistent manner only when both isoscalar and isovector pairing collectivity as well as isospin projection, treated within the iso-cranking approximation, are taken into account. In particular, in odd-odd $N$=$Z$ nuclei, the interplay between quasiparticle excitations (relevant for the case of $T$=0 states) and iso-rotations (relevant for the case of $T$=1 states) explains the near-degeneracy of these fundamental excitations.Comment: 4 pages, 4 figure

Comments on the nuclear symmetry energy

According to standard textbooks, the nuclear symmetry energy originates from the {\it kinetic} energy and the {\it interaction} itself. We argue that this view requires certain modifications. We ascribe the physical origin of the {\it kinetic} term to the discreteness of fermionic levels of, in principle arbitrary binary fermionic systems, and relate its mean value directly to the average level density. Physically it connects this part also to the isoscalar part of the interaction which, at least in self-bound systems like atomic nuclei, decides upon the spatial dimensions of the system. For the general case of binary fermionic systems possible external confining potentials as well as specific boundary conditions will contribute to this part. The reliability of this concept is tested using self-consistent Skyrme Hartree-Fock calculations.Comment: 11 pages, 4 figure

Nuclear Symmetry Energy in Relativistic Mean Field Theory

The Physical origin of the nuclear symmetry energy is studied within the relativistic mean field (RMF) theory. Based on the nuclear binding energies calculated with and without mean isovector potential for several isobaric chains we conform earlier Skyrme-Hartree-Fock result that the nuclear symmetry energy strength depends on the mean level spacing $\epsilon (A)$ and an effective mean isovector potential strength $\kappa (A)$. A detaied analysis of isospin dependence of the two components contributing to the nuclear symmetry energy reveals a quadratic dependence due to the mean-isoscalar potential, $\sim\epsilon T^2$, and, completely unexpectedly, the presence of a strong linear component $\sim\kappa T(T+1+\epsilon/\kappa)$ in the isovector potential. The latter generates a nuclear symmetry energy in RMF theory that is proportional to $E_{sym}\sim T(T+1)$ at variance to the non-relativistic calculation. The origin of the linear term in RMF theory needs to be further explored.Comment: 14 pages and 6 figure

Isovector and isoscalar superfluid phases in rotating nuclei

The subtle interplay between the two nuclear superfluids, isovector T=1 and isoscalar T=0 phases, are investigated in an exactly soluble model. It is shown that T=1 and T=0 pair-modes decouple in the exact calculations with the T=1 pair-energy being independent of the T=0 pair-strength and vice-versa. In the rotating-field, the isoscalar correlations remain constant in contrast to the well known quenching of isovector pairing. An increase of the isoscalar (J=1, T=0) pair-field results in a delay of the bandcrossing frequency. This behaviour is shown to be present only near the N=Z line and its experimental confirmation would imply a strong signature for isoscalar pairing collectivity. The solutions of the exact model are also discussed in the Hartree-Fock-Bogoliubov approximation.Comment: 5 pages, 4 figures, submitted to PR

Astrocytes: biology and pathology

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions

A neurophysiological interpretation of the respiratory act

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47945/1/10254_2005_Article_BF02320667.pd