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J. Sheikh

Publications and source records attributed to J. Sheikh.

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Computing Heavy Elements

Reliable calculations of the structure of heavy elements are crucial to address fundamental science questions such as the origin of the elements in the universe. Applications relevant for energy production, medicine, or national security also rely on theoretical predictions of basic properties of atomic nuclei. Heavy elements are best described within the nuclear density functional theory (DFT) and its various extensions. While relatively mature, DFT has never been implemented in its full power, as it relies on a very large number (~ 10^9-10^12) of expensive calculations (~ day). The advent of leadership-class computers, as well as dedicated large-scale collaborative efforts such as the SciDAC 2 UNEDF project, have dramatically changed the field. This article gives an overview of the various computational challenges related to the nuclear DFT, as well as some of the recent achievements.

nucl-th

Temperature-induced pair correlations in clusters and nuclei

The pair correlations in mesoscopic systems such as $nm$-size superconducting clusters and nuclei are studied at finite temperature for the canonical ensemble of fermions in model spaces with a fixed particle number: i) a degenerate spherical shell (strong coupling limit), ii) an equidistantly spaced deformed shell (weak coupling limit). It is shown that after the destruction of the pair correlations at T=0 by a strong magnetic field or rapid rotation, heating can bring them back. This phenomenon is a consequence of the fixed number of fermions in the canonical ensemble.

physics.atm-clus

Electron Capture in Early Gravitational Collapse -- Nuclear Equation of State

We present the spectra of pre trapping neutrinos emitted from a core collapse supernova (having main sequence masses 15 and 25 $M_{\sun}$) within 1 kpc which can be detected by terrestrial detectors. The neutrino spectrum depends on the abundance of nuclei and free protons which undergo electron capture which in turn is determined by nuclear properties of the stellar core. The ambient temperature in the early pre-trapping phase is not so high as to wipe out shell and pairing effects. We present results from Relativistic Mean Field (RMF) calculations, which we use to predict properties of the neutron rich nuclei which dominate the stellar composition at this stage of stellar collapse and compare the RMF results with the Baron et al (BCK) equation of state.

astro-ph