97,033 research outputs found
Microscopic study of induced fission dynamics of Th with covariant energy density functionals
Static and dynamic aspects of the fission process of Th are analyzed
in a self-consistent framework based on relativistic energy density
functionals. Constrained relativistic mean-field (RMF) calculations in the
collective space of axially symmetric quadrupole and octupole deformations,
based on the energy density functional PC-PK1 and a -force pairing, are
performed to determine the potential energy surface of the fissioning nucleus,
the scission line, the single-nucleon wave functions, energies and occupation
probabilities, as functions of deformation parameters. Induced fission dynamics
is described using the time-dependent generator coordinate method in the
Gaussian overlap approximation. A collective Schr\"odinger equation, determined
entirely by the microscopic single-nucleon degrees of freedom, propagates
adiabatically in time the initial wave packet built by boosting the
ground-state solution of the collective Hamiltonian for Th. The
position of the scission line and the microscopic input for the collective
Hamiltonian are analyzed as functions of the strength of the pairing
interaction. The effect of static pairing correlations on the pre-neutron
emission charge yields and total kinetic energy of fission fragments is
examined in comparison with available data, and the distribution of fission
fragments is analyzed for different values of the initial excitation energy.Comment: 25 pages, 14 figures, accepted for publication in Phys. Rev.
Accurate Modelling of Left-Handed Metamaterials Using Finite-Difference Time-Domain Method with Spatial Averaging at the Boundaries
The accuracy of finite-difference time-domain (FDTD) modelling of left-handed
metamaterials (LHMs) is dramatically improved by using an averaging technique
along the boundaries of LHM slabs. The material frequency dispersion of LHMs is
taken into account using auxiliary differential equation (ADE) based dispersive
FDTD methods. The dispersive FDTD method with averaged permittivity along the
material boundaries is implemented for a two-dimensional (2-D) transverse
electric (TE) case. A mismatch between analytical and numerical material
parameters (e.g. permittivity and permeability) introduced by the time
discretisation in FDTD is demonstrated. The expression of numerical
permittivity is formulated and it is suggested to use corrected permittivity in
FDTD simulations in order to model LHM slabs with their desired parameters. The
influence of switching time of source on the oscillation of field intensity is
analysed. It is shown that there exists an optimum value which leads to fast
convergence in simulations.Comment: 17 pages, 7 figures, submitted to Journal of Optics A Nanometa
special issu
Observation of a resonant four-body interaction in cold cesium Rydberg atoms
Cold Rydberg atoms subject to long-range dipole-dipole interactions represent
a particularly interesting system for exploring few-body interactions and
probing the transition from 2-body physics to the many-body regime. In this
work we report the direct observation of a resonant 4-body Rydberg interaction.
We exploit the occurrence of an accidental quasi-coincidence of a 2-body and a
4-body resonant Stark-tuned Forster process in cesium to observe a resonant
energy transfer requiring the simultaneous interaction of at least four
neighboring atoms. These results are relevant for the implementation of quantum
gates with Rydberg atoms and for further studies of many-body physics.Comment: 5 pages, 5 figure
Measurement of the Dynamical Structure Factor of a 1D Interacting Fermi Gas
We present measurements of the dynamical structure factor of an
interacting one-dimensional (1D) Fermi gas for small excitation energies. We
use the two lowest hyperfine levels of the Li atom to form a
pseudo-spin-1/2 system whose s-wave interactions are tunable via a Feshbach
resonance. The atoms are confined to 1D by a two-dimensional optical lattice.
Bragg spectroscopy is used to measure a response of the gas to density
("charge") mode excitations at a momentum and frequency . The
spectrum is obtained by varying , while the angle between two laser
beams determines , which is fixed to be less than the Fermi momentum
. The measurements agree well with Tomonaga-Luttinger theory
Anomalous Hall effect in non-collinear antiferromagnetic antiperovskite MnNiCuN
We report the anomalous Hall effect (AHE) in antiperovskite MnNiN with
substantial doping of Cu on the Ni site (i.e. MnNiCuN),
which stabilizes a noncollinear antiferromagnetic (AFM) order compatible with
the AHE. Observed on both sintered polycrystalline pieces and single
crystalline films, the AHE does not scale with the net magnetization, contrary
to the conventional ferromagnetic case. The existence of the AHE is explained
through symmetry analysis based on the AFM order in Cu doped
MnNiN. DFT calculations of the intrinsic contribution to the AHE reveal
the non-vanishing Berry curvature in momentum space due to the noncollinear
magnetic order. Combined with other attractive properties, antiperovskite
MnAN system offers great potential in AFM spintronics.Comment: Supplemental Materials not include
Chemical composition of 90 F and G disk dwarfs
High resolution, high S/N spectra have been obtained for a sample of 90 F and
G main-sequence disk stars covering the metallicity range -1.0 < [Fe/H] < +0.1,
and have been analysed in a parallel way to the work of Edvardsson et al.
(1993). Effective temperatures are based on the Alonso et al. (1996)
calibration of color indices and surface gravities are calculated from
Hipparcos parallaxes, which also allow more accurate ages to be calculated. In
addition, more reliable kinematical parameters are derived from Hipparcos
distances and proper motions. Finally, a larger spectral coverage, 5600 - 8800
A, makes it possible to improve the abundance accuracy by studying more lines
and to discuss several elements not included in the work of Edvardsson et al.
The present paper provides the data and discusses some general results of the
abundance survey. A group of stars in the metallicity range of -1.0 < [Fe/H] <
-0.6 having a small mean Galactocentric distance in the stellar orbits, Rm < 7
kpc, are shown to be older than the other disk stars and probably belong to the
thick disk. Excluding these stars, a slight decreasing trend of [Fe/H] with
increasing Rm and age is found, but a large scatter in [Fe/H] (up to 0.5 dex)
is present at a given age and Rm. The derived trends of O, Mg, Si, Ca, Ti, Ni
and Ba as a function of [Fe/H] agree rather well with those of Edvardsson et
al., but the overabundance of Na and Al for metal-poor stars found in their
work is not confirmed. Furthermore, the Galactic evolution of elements not
included in Edvardsson et al., K, V and Cr, is studied.Comment: 16 pages with 10 figures. Accepted for publication in A&A
Submillimeter Array multiline observations of the massive star-forming region IRAS 18089-1732
Submillimeter Array (SMA) observations of the high-mass star-forming region
IRAS 18089-1732 in the 1 mm and 850 m band with 1 GHz bandwidth reveal a
wealth of information. We present the observations of 34 lines from 16
different molecular species. Most molecular line maps show significant
contributions from the outflow, and only few molecules are confined to the
inner core. We present and discuss the molecular line observations and outline
the unique capabilities of the SMA for future imaging line surveys at high
spatial resolution.Comment: Accepted for ApJ Letters, SMA special volum
SMA outflow/disk studies in the massive star-forming region IRAS18089-1732
SMA observations of the massive star-forming region IRAS 18089-1732 in the
1mm and 850mu band reveal outflow and disk signatures in different molecular
lines. The SiO(5--4) data show a collimated outflow in the northern direction.
In contrast, the HCOOCH3(20--19) line, which traces high-density gas, is
confined to the very center of the region and shows a velocity gradient across
the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the
outflow axis but between an assumed disk plane and the outflow axis. We
interpret these HCOOCH3 features as originating from a rotating disk that is
influenced by the outflow and infall. Based on the (sub-)mm continuum emission,
the mass of the central core is estimated to be around 38M_sun. The dynamical
mass derived from the HCOOCH3 data is 22Msun, of about the same order as the
core mass. Thus, the mass of the protostar/disk/envelope system is dominated by
its disk and envelope. The two frequency continuum data of the core indicate a
low dust opacity index beta ~ 1.2 in the outer part, decreasing to beta ~ 0.5
on shorter spatial scales.Comment: 7 pages of text, 1 table, 3 figures, accepted for ApJ Letter
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