23,898 research outputs found
Solving Dirac equations on a 3D lattice with inverse Hamiltonian and spectral methods
A new method to solve the Dirac equation on a 3D lattice is proposed, in
which the variational collapse problem is avoided by the inverse Hamiltonian
method and the fermion doubling problem is avoided by performing spatial
derivatives in momentum space with the help of the discrete Fourier transform,
i.e., the spectral method. This method is demonstrated in solving the Dirac
equation for a given spherical potential in 3D lattice space. In comparison
with the results obtained by the shooting method, the differences in single
particle energy are smaller than ~MeV, and the densities are almost
identical, which demonstrates the high accuracy of the present method. The
results obtained by applying this method without any modification to solve the
Dirac equations for an axial deformed, non-axial deformed, and octupole
deformed potential are provided and discussed.Comment: 18 pages, 6 figure
Relativistic description of magnetic moments in nuclei with doubly closed shells plus or minus one nucleon
Using the relativistic point-coupling model with density functional PC-PK1,
the magnetic moments of the nuclei Pb, Pb, Tl and
Bi with a closed-shell core Pb are studied on the basis of
relativistic mean field (RMF) theory. The corresponding time-odd fields, the
one-pion exchange currents, and the first- and second-order corrections are
taken into account. The present relativistic results reproduce the data well.
The relative deviation between theory and experiment for these four nuclei is
6.1% for the relativistic calculations and somewhat smaller than the value of
13.2% found in earlier non-relativistic investigations. It turns out that the
meson is important for the description of magnetic moments, first by
means of one-pion exchange currents and second by the residual interaction
provided by the exchange.Comment: 11 pages, 7 figure
Low-lying states in Mg: a beyond relativistic mean-field investigation
The recently developed model of three-dimensional angular momentum projection
plus generator coordinate method on top of triaxial relativistic mean-field
states has been applied to study the low-lying states of Mg. The effects
of triaxiality on the low-energy spectra and E0 and E2 transitions are
examined.Comment: 6 pages, 3 figures, 1 table, talk presented at the 17th nuclear
physics conference "Marie and Pierre Curie" Kazimierz Dolny, 22-26th
September 2010, Polan
Covariant description of shape evolution and shape coexistence in neutron-rich nuclei at N\approx60
The shape evolution and shape coexistence phenomena in neutron-rich nuclei at
, including Kr, Sr, Zr, and Mo isotopes, are studied in the
covariant density functional theory (DFT) with the new parameter set PC-PK1.
Pairing correlations are treated using the BCS approximation with a separable
pairing force. Sharp rising in the charge radii of Sr and Zr isotopes at N=60
is observed and shown to be related to the rapid changing in nuclear shapes.
The shape evolution is moderate in neighboring Kr and Mo isotopes. Similar as
the results of previous Hartree-Fock-Bogogliubov (HFB) calculations with the
Gogny force, triaxiality is observed in Mo isotopes and shown to be essential
to reproduce quantitatively the corresponding charge radii. In addition, the
coexistence of prolate and oblate shapes is found in both Sr and
Zr. The observed oblate and prolate minima are related to the low
single-particle energy level density around the Fermi surfaces of neutron and
proton respectively. Furthermore, the 5-dimensional (5D) collective Hamiltonian
determined by the calculations of the PC-PK1 energy functional is solved for
Sr and Zr. The resultant excitation energy of state and
E0 transition strength are in rather good
agreement with the data. It is found that the lower barrier height separating
the two competing minima along the deformation in Zr gives
rise to the larger than that in Sr.Comment: 1 table, 11 figures, 23 page
Octet baryon masses in next-to-next-to-next-to-leading order covariant baryon chiral perturbation theory
We study the ground-state octet baryon masses and sigma terms using the
covariant baryon chiral perturbation theory (ChPT) with the
extended-on-mass-shell (EOMS) renormalization scheme up to
next-to-next-to-next-to-leading order (NLO). By adjusting the available 19
low-energy constants (LECs), a reasonable fit of the lattice quantum
chromodynamics (LQCD) results from the PACS-CS, LHPC, HSC, QCDSF-UKQCD and
NPLQCD collaborations is achieved. Finite-volume corrections to the lattice
data are calculated self-consistently. Our study shows that NLO BChPT
describes better the light quark mass evolution of the lattice data than the
NNLO BChPT does and the various lattice simulations seem to be consistent with
each other. We also predict the pion and strangeness sigma terms of the octet
baryons using the LECs determined in the fit of their masses. The predicted
pion- and strangeness-nucleon sigma terms are MeV and
MeV, respectively.Comment: 28 pages, 6 figures, minor revisions, typos corrected, version to
appear in JHE
Enhanced spin-orbit torques in MnAl/Ta films with improving chemical ordering
We report the enhancement of spin-orbit torques in MnAl/Ta films with
improving chemical ordering through annealing. The switching current density is
increased due to enhanced saturation magnetization MS and effective anisotropy
field HK after annealing. Both damplinglike effective field HD and fieldlike
effective field HF have been increased in the temperature range of 50 to 300 K.
HD varies inversely with MS in both of the films, while the HF becomes liner
dependent on 1/MS in the annealed film. We infer that the improved chemical
ordering has enhanced the interfacial spin transparency and the transmitting of
the spin current in MnAl layer
Micromachined membrane particle filters
We report here several particle membrane filters (8 x 8 mm^2) with circular, hexagonal and rectangular through holes. By varying hole dimensions from 6 to 12 pm, opening factors from 4 to 45 % are achieved. In order to improve the filter robustness, a composite silicon nitride/Parylene membrane technology is developed. More importantly, fluid dynamic performance of the filters is also studied by both experiments and numerical simulations. It is found that the gaseous flow through the filters depends strongly on opening factors, and the measured pressure drops are much lower than that from numerical simulation using the Navier-Stokes equation. Interestingly, surface velocity slip can only account for a minor part of the discrepancy. This suggests that a very interesting topic for micro fluid mechanics research is identified
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