4,409 research outputs found
Complex Lagrangian embeddings of moduli spaces of vector bundles
By means of a Fourier-Mukai transform we embed moduli spaces of stable
bundles on an algebraic curve C as isotropic subvarieties of moduli spaces of
mu-stable bundles on the Jacobian variety J(C). When g(C)=2 this provides new
examples of special Lagrangian submanifolds.Comment: 9 pages, no figures, to appear in Diff. Geom. App
Monte Carlo study of Si(111) homoepitaxy
An attempt is made to simulate the homoepitaxial growth of a Si(111) surface
by the kinetic Monte Carlo method in which the standard Solid-on-Solid model
and the planar model of the (7x7) surface reconstruction are used in
combination.
By taking account of surface reconstructions as well as atomic deposition and
migrations, it is shown that the effect of a coorparative stacking
transformation is necessary for a layer growth.Comment: 4 pages, 5 figures. For Fig.1 of this article, please see Fig.2 of
Phys.Rev. B56, 3583 (1997). To appear in Phys.Rev.B. (June 1998
Pseudo-gap behavior in dynamical properties of high-Tc cuprates
Dynamical properties of 2D antiferromagnets with hole doping are investigated
to see the effects of short range local magnetic order on the temperature
dependence of the dynamical magnetic susceptibility. We show the pseudo-gap
like behavior of the temperature dependence of the NMR relaxation rate. We also
discuss implications of the results in relations to the observed spin gap like
behavior of low-doped copper oxide high- superconductors.Comment: 3 pages, Revtex, with 2 eps figures, to appear in J.Phys.Soc.Jpn.
Vol.67 No.
Enhancement of Resonant Thermonuclear Reaction Rates in Extremely Dense Stellar Plasmas
The enhancement factor of the resonant thermonuclear reaction rates is
calculated for the extremely dense stellar plasmas in the liquid phase. In
order to calculate the enhancement factor we use the screening potential which
is deduced from the numerical experiment of the classical one-component plasma.
It is found that the enhancement is tremendous for white dwarf densities if the
^{12}C + ^{12}C fusion cross sections show resonant behavior in the
astrophysical energy range. We summarize our numerical results by accurate
analytic fitting formulae.Comment: 13 pages, 3 figures, accepted for publication in ApJ, replaced with
revised versio
Magneto--thermal evolution of neutron stars
We study the mutual influence of thermal and magnetic evolution in a neutron
star's crust in axial symmetry. Taking into account realistic microphysical
inputs, we find the heat released by Joule effect consistent with the
circulation of currents in the crust, and we incorporate its effects in 2D
cooling calculations. We solve the induction equation numerically using a
hybrid method (spectral in angles, but a finite--differences scheme in the
radial direction), coupled to the thermal diffusion equation. We present the
first long term 2D simulations of the coupled magneto-thermal evolution of
neutron stars. This substantially improves previous works in which a very crude
approximation in at least one of the parts (thermal or magnetic diffusion) has
been adopted. Our results show that the feedback between Joule heating and
magnetic diffusion is strong, resulting in a faster dissipation of the stronger
fields during the first million years of a NS's life. As a consequence, all
neutron stars born with fields larger than a critical value (about 5 10^13 G)
reach similar field strengths (approximately 2-3 10^{13} G) at late times.
Irrespectively of the initial magnetic field strength, after years the
temperature becomes so low that the magnetic diffusion timescale becomes longer
than the typical ages of radio--pulsars, thus resulting in apparently no
dissipation of the field in old NS. We also confirm the strong correlation
between the magnetic field and the surface temperature of relatively young NSs
discussed in preliminary works. The effective temperature of models with strong
internal toroidal components are systematically higher than those of models
with purely poloidal fields, due to the additional energy reservoir stored in
the toroidal field that is gradually released as the field dissipates.Comment: 10 pages, 5 figures, accepted for publication in A&
The effect of the neutron star crust on the evolution of a core magnetic field
We consider the expulsion of the magnetic field from the super-conducting
core of a neutron star and its subsequent decay in the crust. Particular
attention is paid to a strong feedback of the distortion of magnetic field
lines in the crust on the expulsion of the flux from the core. This causes a
considerable delay of the core flux expulsion if the initial field strength is
larger than 10^{11} G. It is shown that the hypothesis on the magnetic field
expulsion induced by the neutron star spin-down is adequate only for a
relatively weak initial magnetic field G. The expulsion
time-scale depends not only on the conductivity of the crust, but also on the
initial magnetic field strength itself. Our model of the field evolution
naturally explains the existence of the residual magnetic field of neutron
stars. Its strength is correlated with the impurity concentration in neutron
star crusts and anti-correlated with the initial field strengths.Comment: 15 pages, 6 figures, accepted to MNRA
- âŠ