24 research outputs found
Nuclear energy density functional from chiral pion-nucleon dynamics: Isovector spin-orbit terms
We extend a recent calculation of the nuclear energy density functional in
the systematic framework of chiral perturbation theory by computing the
isovector spin-orbit terms: . The calculation
includes the one-pion exchange Fock diagram and the iterated one-pion exchange
Hartree and Fock diagrams. From these few leading order contributions in the
small momentum expansion one obtains already a good equation of state of
isospin-symmetric nuclear matter. We find that the parameterfree results for
the (density-dependent) strength functions and agree
fairly well with that of phenomenological Skyrme forces for densities . At very low densities a strong variation of the strength functions
and with density sets in. This has to do with chiral
singularities and the presence of two competing small mass scales
and . The novel density dependencies of and
as predicted by our parameterfree (leading order) calculation should
be examined in nuclear structure calculations.Comment: 9 pages, 3 figure, published in: Physical Review C68, 014323 (2003
Mean-field description of ground-state properties of drip-line nuclei. (I) Shell-correction method
A shell-correction method is applied to nuclei far from the beta stability
line and its suitability to describe effects of the particle continuum is
discussed. The sensitivity of predicted locations of one- and two-particle drip
lines to details of the macroscopic-microscopic model is analyzed.Comment: 22 REVTeX pages, 13 uuencoded postscript figures available upon
reques
Nuclear isospin mixing and elastic parity-violating electron scattering
The influence of nuclear isospin mixing on parity-violating elastic electron
scattering is studied for the even-even, N=Z nuclei 12C, 24Mg, 28Si, and 32S.
Their ground-state wave functions have been obtained using a self-consistent
axially-symmetric mean-field approximation with density-dependent effective
two-body Skyrme interactions. Some differences from previous shell-model
calculations appear for the isovector Coulomb form factors which play a role in
determining the parity-violating asymmetry. To gain an understanding of how
these differences arise, the results have been expanded in a spherical harmonic
oscillator basis. Results are obtained not only within the plane-wave Born
approximation, but also using the distorted-wave Born approximation for
comparison with potential future experimental studies of parity-violating
electron scattering. To this end, for each nucleus the focus is placed on
kinematic ranges where the signal (isospin-mixing effects on the
parity-violating asymmetry) and the experimental figure-of-merit are maximized.
Strangeness contributions to the asymmetry are also briefly discussed, since
they and the isospin mixing contributions may play comparable roles for the
nuclei being studied at the low momentum transfers of interest in the present
work.Comment: 25 pages, 9 figure
Surface incompressibility of semi-infinite nuclear matter via constrained Hartree-Fock calculations
Glass transition and polymer dynamics in silver/poly(methyl methacrylate) nanocomposites
Dynamic mechanical-thermal analysis (DMTA), differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and, mainly, broadband dielectric relaxation spectroscopy (DRS) were employed to investigate in detail glass transition and polymer dynamics in silver/poly(methyl methacrylate) (Ag/PMMA) nanocomposites. The nanocomposites were prepared by radical polymerization of MMA in the presence of surface modified Ag nanoparticles with a mean diameter of 5.6 nm dispersed in chloroform. The fraction of Ag nanoparticles in the final materials was varied between 0 and 0.5 wt%, the latter corresponding to 0.055 vol%. The results show that the nanoparticles have practically no effect on the time scale of the secondary ß and ¿ relaxations, whereas the magnitude of both increases slightly but systematically with increasing filler content. The segmental ¿ relaxation, associated with the glass transition, becomes systematically faster and stronger in the nanocomposites. The glass transition temperature T g decreases with increasing filler content of the nanocomposites up to about 10 °C, in good correlation by the four techniques employed. Finally, the elastic modulus decreases slightly but systematically in the nanocomposites, both in the glassy and in the rubbery state. The results are explained in terms of plasticization of the PMMA matrix, due to constraints imposed to packing of the chains by the Ag nanoparticles, and at the same time, of the absence of strong polymer-filler interactions, due to the surface modification of the Ag nanoparticles by oleylamine at the stage of preparation. © 2011 Elsevier Ltd. All rights reserved.JLGR acknowledges the support of the Spanish Ministry of Science and Innovation through project No. EUI2008-00126 and funding in the Centro de Investigacion Principe Felipe in the field of Regenerative Medicine through the collaboration agreement from the Conselleria de Sanidad (Generalitat Valenciana), and the Instituto de Salud Carlos III (Ministry of Science and Innovation).Pandis, C.; Logakis, E.; Kyritsis, A.; Pissis, P.; Vodnik, VV.; Dzunuzovic, E.; Nedeljkovic, JM.... (2011). Glass transition and polymer dynamics in silver/poly(methyl methacrylate) nanocomposites. EUROPEAN POLYMER JOURNAL. 47(8):1514-1525. https://doi.org/10.1016/j.eurpolymj.2011.06.001S1514152547