2,006 research outputs found
Secondary Star Formation in a Population III Object
We explore the possibility of subsequent star formation after a first star
forms in a Pop III object, by focusing on the radiation hydrodynamic (RHD)
feedback brought by ionizing photons as well as H2 dissociating photons. For
the purpose, we perform three-dimensional RHD simulations, where the radiative
transfer of ionizing photons and H2 dissociating photons from a first star is
self-consistently coupled with hydrodynamics based on a smoothed particle
hydrodynamics method. As a result, it is shown that density peaks above a
threshold density can keep collapsing owing to the shielding of H2 dissociating
radiation by an H2 shell formed ahead of a D-type ionization front. But, below
the threshold density, an M-type ionization front accompanied by a shock
propagates, and density peaks are radiation hydrodynamically evaporated by the
shock. The threshold density is dependent on the distance from a source star,
which is for the source distance of 30pc. Taking into
consideration that the extent of a Pop III object is pc and
density peaks within it have the density of cm, it is
concluded that the secondary star formation is allowed in the broad regions in
a Pop III object.Comment: 4pages, 2 figures, submitted to Ap
Spin polarization in a T-shape conductor induced by strong Rashba spin-orbit coupling
We investigate numerically the spin polarization of the current in the
presence of Rashba spin-orbit interaction in a T-shaped conductor proposed by
A.A. Kiselev and K.W. Kim (Appl. Phys. Lett. {\bf 78} 775 (2001)). The
recursive Green function method is used to calculate the three terminal spin
dependent transmission probabilities. We focus on single-channel transport and
show that the spin polarization becomes nearly 100 % with a conductance close
to for sufficiently strong spin-orbit coupling. This is interpreted
by the fact that electrons with opposite spin states are deflected into an
opposite terminal by the spin dependent Lorentz force. The influence of the
disorder on the predicted effect is also discussed. Cases for multi-channel
transport are studied in connection with experiments
Presence of 3d Quadrupole Moment in LaTiO3 Studied by 47,49Ti NMR
Ti NMR spectra of LaTiO3 are reexamined and the orbital state of this
compound is discussed. The NMR spectra of LaTiO3 taken at 1.5 K under zero
external field indicate a large nuclear quadrupole splitting. This splitting is
ascribed to the presence of the rather large quadrupole moment of 3d electrons
at Ti sites, suggesting that the orbital liquid model proposed for LaTiO3 is
inappropriate. The NMR spectra are well explained by the orbital ordering model
expressed approximately as originating from
a crystal field effect. It is also shown that most of the orbital moment is
quenched.Comment: 4 pages, 3 fugures; to appear in Phys. Rev. Let
Surface-enhanced pair transfer in quadrupole states of neutron-rich Sn isotopes
We investigate the neutron pair transfer modes associated with the low-lying
quadrupole states in neutron-rich Sn isotopes by means of the quasiparticle
random phase approximation based on the Skyrme-Hartree-Fock-Bogoliubov mean
field model. The transition strength of the quadrupole pair-addition mode
feeding the state is enhanced in the Sn isotopes with . The
transition density of the pair-addition mode has a large spatial extension in
the exterior of nucleus, reaching far to fm. The quadrupole
pair-addition mode reflects sensitively a possible increase of the effective
pairing interaction strength in the surface and exterior regions of
neutron-rich nuclei.Comment: 14 page
Microscopic description of large-amplitude shape-mixing dynamics with inertial functions derived in local quasiparticle random-phase approximation
On the basis of the adiabatic self-consistent collective coordinate method,
we develop an efficient microscopic method of deriving the five-dimensional
quadrupole collective Hamiltonian and illustrate its usefulness by applying it
to the oblate-prolate shape coexistence/mixing phenomena in proton-rich
68,70,72Se. In this method, the vibrational and rotational collective masses
(inertial functions) are determined by local normal modes built on constrained
Hartree-Fock-Bogoliubov states. Numerical calculations are carried out using
the pairing-plus-quadrupole Hamiltonian including the quadrupole-pairing
interaction. It is shown that the time-odd components of the moving mean-field
significantly increase the vibrational and rotational collective masses in
comparison with the Inglis-Belyaev cranking masses. Solving the collective
Schroedinger equation, we evaluate excitation spectra, quadrupole transitions
and moments. Results of the numerical calculation are in excellent agreement
with recent experimental data and indicate that the low-lying states of these
nuclei are characterized as an intermediate situation between the
oblate-prolate shape coexistence and the so-called gamma unstable situation
where large-amplitude triaxial-shape fluctuations play a dominant role.Comment: 17 pages, 16 figures, Submitted to Phys. Rev.
Low-Mass Star Formation, Triggered by Supernova in Primordial Clouds
The evolution of a gas shell, swept by the supernova remnant of a massive
first generation star, is studied with H_2 and HD chemistry taken into account.
When a first-generation star explodes as a supernova, H_2 and HD molecules are
formed in the swept gas shell and effectively cool the gas shell to
temperatures of 32 K - 154 K. If the supernova remnant can sweep to gather the
ambient gas, the gas shell comes to be dominated by its self-gravity, and
hence, is expected to fragment. Our result shows that for a reasonable range of
temperatures (200 K - 1000 K) of interstellar gas, the formation of
second-generation stars can be triggered by a single supernova or hypernova.Comment: 38pages, 10 figures, The Astrophysical Journal, accepted 8 Dec. 200
Novel ordering of the pyrochlore Heisenberg antiferromagnet with the ferromagnetic next-nearest-neighbor interaction
The ordering property of the classical pyrochlore Heisenberg antiferromagnet
with the ferromagnetic next-nearest-neighbor interaction is investigated by
means of a Monte Carlo simulation. The model is found to exhibit a first-order
transition at a finite temperature into a peculiar ordered state. While the
spin structure factor, i.e., the thermal average of the squared Fourier
amplitude of the spin, exhibits a finite long-range order characterized by the
commensurate spin order of the period four, the thermal average of the spin
itself almost vanishes. It means that, although the amplitude of the spin
Fourier component is long-range ordered, the associated phase degree of freedom
remains to be fluctuating.Comment: Proceedings of the Highly Frustrated Magnetism (HFM2006) conference.
To appear in a special issue of J. Phys. Condens. Matte
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