6,612 research outputs found
Nuclear /EC decays in covariant density functional theory and the impact of isoscalar proton-neutron pairing
Self-consistent proton-neutron quasiparticle random phase approximation based
on the spherical nonlinear point-coupling relativistic Hartree-Bogoliubov
theory is established and used to investigate the /EC-decay half-lives
of neutron-deficient Ar, Ca, Ti, Fe, Ni, Zn, Cd, and Sn isotopes. The isoscalar
proton-neutron pairing is found to play an important role in reducing the decay
half-lives, which is consistent with the same mechanism in the decays
of neutron-rich nuclei. The experimental /EC-decay half-lives can be
well reproduced by a universal isoscalar proton-neutron pairing strength.Comment: 12 pages, 4 figure
Self-similarity under inflation and level statistics: a study in two dimensions
Energy level spacing statistics are discussed for a two dimensional
quasiperiodic tiling. The property of self-similarity under inflation is used
to write a recursion relation for the level spacing distributions defined on
square approximants to the perfect quasiperiodic structure.
New distribution functions are defined and determined by a combination of
numerical and analytical calculations.Comment: Latex, 13 pages including 6 EPS figures, paper submitted to PR
Pumping in an interacting quantum wire
We study charge and spin pumping in an interacting one-dimensional wire. We
show that a spatially periodic potential modulated in space and time acts as a
quantum pump inducing a dc-current component at zero bias. The current
generated by the pump is strongly affected by the interactions. It has a power
law dependence on the frequency or temperature with the exponent determined by
the interaction in the wire, while the coupling to the pump affects the
amplitudes only. We also show that pure spin-pumping can be achieved, without
the presence of a magnetic field.Comment: 13 pages,2 figure
Effect of circular motion exercise on bone modeling and bone mass in young rats: An animal model of isometric exercise
The aims of the study are to develop a non-invasive animal model of circular motion exercise and to evaluate the effect of this type of exercise on bone turnover in young rats. The circular motion exercise simulates isometric exercise using an orbital shaker that oscillates at a frequency of 50 Hz and is capable of speeds from 0-400 rpm. A cage is fixed on top of the shaker and the animals are placed inside. When the shaker is turned on, the oscillatory movement should encourage the animals to hold on to the cage and use various muscle forces to stabilize themselves. Rats at 8 weeks of age were trained on the shaker for 6 weeks and static and dynamic histomorphometric analyses were performed for the proximal tibial metaphysis and the tibial shaft. The exercise resulted in no significant effect on animal body weight, gastrocnemius muscle weight and femoral weight. Although the bone formation rate of cancellous and cortical periosteum was increased by the exercise, trabecular bone volume was decreased. The exercise increased periosteal and marrow perimeters and the cross-sectional diameter of cortical bone from medial to lateral without a significant increase in the cortical bone area. These results suggest that circular motion exercise under force without movement or additional weight loading will cause bone-modeling drift with an increase in bone turnover to reconstruct bone shape in adaptation to the demand in strength. Since there is no additional weight loading during circular motion exercise, the net mass of bone is not increased. The bone mass lost in trabecular bone could possibly be due to a re-distribution of mineral to the cortical bone
The X-ray variation of M81* resolved by Chandra and NuSTAR
Despite advances in our understanding of low luminosity active galactic
nuclei (LLAGNs), the fundamental details about the mechanisms of radiation and
flare/outburst in hot accretion flow are still largely missing. We have
systematically analyzed the archival Chandra and NuSTAR X-ray data of the
nearby LLAGN M81*, whose . Through a
detailed study of X-ray light curve and spectral properties, we find that the
X-ray continuum emission of the power-law shape more likely originates from
inverse Compton scattering within the hot accretion flow. In contrast to Sgr
A*, flares are rare in M81*. Low-amplitude variation can only be observed in
soft X-ray band (amplitude usually ). Several simple models are
tested, including sinusoidal-like and quasi-periodical. Based on a comparison
of the dramatic differences of flare properties among Sgr A*, M31* and M81*, we
find that, when the differences in both the accretion rate and the black hole
mass are considered, the flares in LLAGNs can be understood universally in a
magneto-hydrodynamical model.Comment: 11 pages, 8 figures, and 4 tables. Accepted to MNRA
- …