121 research outputs found
Misfits in Skyrme-Hartree-Fock
We address very briefly five critical points in the context of the
Skyrme-Hartree-Fock (SHF) scheme: 1) the impossibility to consider it as an
interaction, 2) a possible inconsistency of correlation corrections as, e.g.,
the center-of-mass correction, 3) problems to describe the giant dipole
resonance (GDR) simultaneously in light and heavy nuclei, 4) deficiencies in
the extrapolation of binding energies to super-heavy elements (SHE), and 5) a
yet inappropriate trend in fission life-times when going to the heaviest SHE.
While the first two points have more a formal bias, the other three points have
practical implications and wait for solution.Comment: 9 pages, 4 figure
The Skyrme energy functional and low lying 2+ states in Sn, Cd and Te isotopes
We study the predictive power of Skyrme forces with respect to low lying
quadrupole spectra along the chains of Sn, Cd, and Te isotopes. Excitation
energies and B(E2) values for the lowest quadrupole states are computed from a
collective Schroedinger equation which as deduced through collective path
generated by constraint Skyrme-Hartree-Fock (SHF) plus self-consistent cranking
for the dynamical response. We compare the results from four different Skyrme
forces, all treated with two different pairing forces (volume versus
density-dependent pairing). The region around the neutron shell closure N=82 is
very sensitive to changes in the Skyrme while the mid-shell isotopes in the
region N<82 depend mainly on the adjustment of pairing. The neutron rich
isotopes are most sensitive and depend on both aspects
Optimization of relativistic mean field model for finite nuclei to neutron star matter
We have optimized the parameters of extended relativistic mean-field model
using a selected set of global observables which includes binding energies and
charge radii for nuclei along several isotopic and isotonic chains and the
iso-scalar giant monopole resonance energies for the Zr and Pb
nuclei. The model parameters are further constrained by the available
informations on the energy per neutron for the dilute neutron matter and bounds
on the equations of state of the symmetric and asymmetric nuclear matter at
supra-nuclear densities. Two new parameter sets BSP and IUFSU* are obtained,
later one being the variant of recently proposed IUFSU parameter set. The BSP
parametrization uses the contributions from the quartic order cross-coupling
between and mesons to model the high density behaviour of the
equation of state instead of the meson self-coupling as in the case of
IUFSU* or IUFSU. Our parameter sets yield appreciable improvements in the
binding energy systematics and the equation of state for the dilute neutron
matter. The importance of the quartic order cross coupling term
of the extended RMF model, as often ignored, is realized.Comment: 22 pages, 11 figures, Nucl. Phys. A (in press
Oxygenated compounds in aged biomass burning plumes over the Eastern Mediterranean: evidence for strong secondary production of methanol and acetone
International audienceAirborne measurements of acetone, methanol, PAN, acetonitrile (by Proton Transfer Reaction Mass Spectrometry), and CO (by Tunable Diode Laser Absorption Spectroscopy) have been performed during the Mediterranean Intensive Oxidants Study (MINOS August 2001). We have identified ten biomass burning plumes from strongly elevated acetonitrile mixing ratios. The characteristic biomass burning signatures obtained from these plumes reveal secondary production of acetone and methanol, while CO photochemically declines in the plumes. Mean excess mixing ratios - normalized to CO - of 1.8%, 0.20%, 3.8%, and 0.65% for acetone, acetonitrile, methanol, and PAN, respectively, were found. By scaling to an assumed global annual source of 663-807Tg CO, biomass burning emissions of 25-31 and 29-35 Tg/yr for acetone and methanol are estimated, respectively. Our measurements suggest that the present biomass burning contributions of acetone and methanol are significantly underestimated due to the neglect of secondary formation within the plume. Median acetonitrile mixing ratios throughout the troposphere were around 150pmol/mol, in accord with current biomass burning inventories and an atmospheric lifetime of ~6 months
Properties of odd nuclei and the impact of time-odd mean fields: A systematic Skyrme-Hartree-Fock analysis
We present a systematic analysis of the description of odd nuclei by the
Skyrme-Hartree-Fock approach augmented with pairing in BCS approximation and
blocking of the odd nucleon. Current and spin densities in the Skyrme
functional produce time-odd mean fields (TOMF) for odd nuclei. Their effect on
basic properties (binding energies, odd-even staggering, separation energies
and spectra) is investigated for the three Skyrme parameterizations SkI3, SLy6,
and SV-bas. About 1300 spherical and axially-deformed odd nuclei with 16 < Z <
92 are considered. The calculations demonstrate that the TOMF effect is
generally small, although not fully negligible. The influence of the Skyrme
parameterization and the consistency of the calculations are much more
important. With a proper choice of the parameterization, a good description of
binding energies and their differences is obtained, comparable to that for even
nuclei. The description of low-energy excitation spectra of odd nuclei is of
varying quality depending on the nucleus
The two-proton shell gap in Sn isotopes
We present an analysis of two-proton shell gaps in Sn isotopes. As the
theoretical tool we use self-consistent mean-field models, namely the
relativistic mean-field model and the Skyrme-Hartree-Fock approach, both with
two different pairing forces, a delta interaction (DI) model and a
density-dependent delta interaction (DDDI). We investigate the influence of
nuclear deformation as well as collective correlations and find that both
effects contribute significantly. Moreover, we find a further significant
dependence on the pairing force used. The inclusion of deformation plus
correlation effects and the use of DDDI pairing provides agreement with the
data.Comment: gzipped tar archiv containing LaTeX source, bibliography file
(*.bbl), all figures as *.eps, and the style file
Ozone production and trace gas correlations during the June 2000 MINATROC intensive measurement campaign at Mt. Cimone
An intensive measurement campaign was performed in June 2000 at the Mt. Cimone station (44°11' N-10°42' E, 2165 m asl, the highest mountain in the northern Italian Apennines) to study photochemical ozone production in the lower free troposphere. In general, average mixing ratios of important trace gases were not very high (121 ± 20 ppbv CO, 0.284 ± 0.220 ppbv NOx, 1.15 ± 0.8 ppbv NOy, 58 ± 9 ppbv O<sub>3</sub>), which indicates a small contribution by local pollution. Those trace gas levels are representative of continental background air, which is further supported by the analysis of VOCs (e.g.: C<sub>2</sub>H<sub>6</sub> = (905 ± 200) pptv, C<sub>3</sub>H<sub>8</sub> = (268 ±110) pptv, C<sub>2</sub>H<sub>2</sub> = (201 ± 102) pptv, C<sub>5</sub>H<sub>8</sub> = (111 ± 124) pptv, benzene = (65 ± 33) pptv). Furthermore, significant diurnal variations for a number of trace gases (O<sub>3</sub>, CO, NOx, NOy, HCHO) indicate the presence of free tropospheric airmasses at nighttime as a consequence of local catabatic winds. Average mid-day peroxy radical concentrations at Mt. Cimone are of the order of 30 pptv. At mean NO concentrations of the order of 40 pptv this gives rise to significant in situ net O<sub>3</sub> production of 0.1-0.3 ppbv/hr. The importance of O<sub>3 </sub>production is supported by correlations between O<sub>3</sub>, CO, NOz, and HCHO, and between HCHO, CO and NOy
Systematics of collective correlation energies from self-consistent mean-field calculations
The collective ground-state correlations stemming from low-lying quadrupole
excitations are computed microscopically. To that end, the self-consistent
mean-field model is employed on the basis of the Skyrme-Hartre-Fock (SHF)
functional augmented by BCS pairing. The microscopic-macroscopic mapping is
achieved by quadrupole-constrained mean-field calculations which are processed
further in the generator-coordinate method (GCM) at the level of the Gaussian
overlap approximation (GOA).
We study the correlation effects on energy, charge radii, and surface
thickness for a great variety of semi-magic nuclei. A key issue is to work out
the influence of variations of the SHF functional. We find that collective
ground-state correlations (GSC) are robust under change of nuclear bulk
properties (e.g., effective mass, symmetry energy) or of spin-orbit coupling.
Some dependence on the pairing strength is observed. This, however, does not
change the general conclusion that collective GSC obey a general pattern and
that their magnitudes are rather independent of the actual SHF parameters.Comment: 13 pages, 13 figure
- …