14,593 research outputs found
Has Blending Compromised Cepheid-Based Determinations of the Extragalactic Distance Scale?
We examine the suggestion that half of the HST Key Project- and
Sandage/Saha-observed galaxies have had their distances systematically
underestimated, by 0.1-0.3 mag in the distance modulus, due to the
underappreciated influence of stellar profile blending on the WFC chips. The
signature of such an effect would be a systematic trend in (i) the Type Ia
supernovae corrected peak luminosity and (ii) the Tully-Fisher residuals, with
increasing calibrator distance, and (iii) a differential offset between PC and
WFC distance moduli, within the same galaxy. The absence of a trend would be
expected if blending were negligible (as has been inherently assumed in the
analyses of the aforementioned teams). We adopt a functional form for the
predicted influence of blending that is consistent with the models of Mochejska
et al. and Stanek & Udalski, and demonstrate that the expected correlation with
distance predicted by these studies is not supported by the data. We conclude
that the Cepheid-based extragalactic distance scale has not been severely
compromised by the neglect of blending.Comment: 14 pages, 2 figures, 1 table, LaTeX, accepted for publication in
Astrophysical Journal Letters, also available at
http://casa.colorado.edu/~bgibson/publications.htm
Peculiar Velocities of Nonlinear Structure: Voids in McVittie Spacetime
As a study of peculiar velocities of nonlinear structure, we analyze the
model of a relativistic thin-shell void in the expanding universe. (1) Adopting
McVittie (MV) spacetime as a background universe, we investigate the dynamics
of an uncompensated void with negative MV mass. Although the motion itself is
quite different from that of a compensated void, as shown by Haines & Harris
(1993), the present peculiar velocities are not affected by MV mass. (2) We
discuss how precisely the formula in the linear perturbation theory applies to
nonlinear relativistic voids, using the results in (1) as well as the previous
results for the homogeneous background (Sakai, Maeda, & Sato 1993). (3) We
re-examine the effect of the cosmic microwave background radiation. Contrary to
the results of Pim & Lake (1986, 1988), we find that the effect is negligible.
We show that their results are due to inappropriate initial conditions. Our
results (1)-(3) suggest that the formula in the linear perturbation theory is
approximately valid even for nonlinear voids.Comment: 12 pages, aastex, 4 ps figures separate, Fig.2 added, to appear in
Ap
Charge Exchange Spin-Dipole Excitations of 90Zr and 208Pb and Neutron Matter Equation of State
Charge exchange spin-dipole (SD) excitations of Zr and Pb are
studied by using a Skyrme
Hartree-Fock(HF) + Random Phase approximation (RPA). The calculated
spin-dipole strength distributions are compared with experimental data obtained
by Zr (p,n) Nb and Zr (n,p) Nb reactions. The
model-independent SD sum rule values of various Skyrme interactions are studied
in comparison with the experimental values in order to determine the neutron
skin thickness of Zr. The pressure of the neutron matter equation of
state (EOS) and the nuclear matter symmetry energy are discussed in terms of
the neutron skin thickness and peak energies of SD strength distributions.Comment: 26pages, 10figure
Metamagnetism of antiferromagnetic XXZ quantum spin chains
The magnetization process of the one-dimensional antiferromagnetic Heisenberg
model with the Ising-like anisotropic exchange interaction is studied by the
exact diagonalization technique. It results in the evidence of the first-order
spin flop transition with a finite magnetization jump in the N\'eel ordered
phase for . It implies that the S=1/2 chain is an exceptional case
where the metamagnetic transition becomes second-order due to large quantum
fluctuations.Comment: 4 pages, Revtex, with 6 eps figure
Critical exponent in the magnetization curve of quantum spin chains
The ground state magnetization curve around the critical magnetic field
of quantum spin chains with the spin gap is investigated. We propose a size
scaling method to estimate the critical exponent defined as from finite cluster calculation. The applications of the
method to the S=1 antiferromagnetic chain and S=1/2 bond alternating chain lead
to a common conclusion . The same result is derived for both edges
of the magnetization plateau of the S=3/2 antiferromagnetic chain with the
single ion anisotropy.Comment: 4 pages, Revtex, with 4 eps figure
The thermal conductivity of alternating spin chains
We study a class of integrable alternating (S1,S2) quantum spin chains with
critical ground state properties. Our main result is the description of the
thermal Drude weight of the one-dimensional alternating spin chain as a
function of temperature. We have identified the thermal current of the model
with alternating spins as one of the conserved currents underlying the
integrability. This allows for the derivation of a finite set of non-linear
integral equations for the thermal conductivity. Numerical solutions to the
integral equations are presented for specific cases of the spins S1 and S2. In
the low-temperature limit a universal picture evolves where the thermal Drude
weight is proportional to temperature T and central charge c.Comment: 15 pages, 1 figur
Fe-doping-induced evolution of charge-orbital ordering in a bicritical-state manganite
Impurity effects on the stability of a ferromagnetic metallic state in a
bicritical-state manganite, (La0.7Pr0.3)0.65Ca0.35MnO3, on the verge of
metal-insulator transition have been investigated by substituting a variety of
transition-metal atoms for Mn ones. Among them, Fe doping exhibits the
exceptional ability to dramatically decrease the ferromagnetic transition
temperature. Systematic studies on the magnetotransport properties and x-ray
diffraction for the Fe-doped crystals have revealed that charge-orbital
ordering evolves down to low temperatures, which strongly suppresses the
ferromagnetic metallic state. The observed glassy magnetic and transport
properties as well as diffuse phase transition can be attributed to the
phase-separated state where short-range charge-orbital-ordered clusters are
embedded in the ferromagnetic metallic matrix. Such a behavior in the Fe-doped
manganites form a marked contrast to the Cr-doping effects on
charge-orbital-ordered manganites known as impurity-induced collapse of
charge-orbital ordering.Comment: 8 pages, 7 figure
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