257,850 research outputs found
The Luminosity Function of Omega Centauri
Deep HST-WFPC2 observations of the stellar population in the globular cluster
Omega Cen (NGC 5139) have been used to measure the luminosity function of main
sequence stars at the low-mass end. Two fields have been investigated, located
respectively ~4.6' and ~7' away from the cluster center, or near the half-light
radius of this cluster (~4.8'). The color-magnitude diagrams derived from these
data show the cluster main sequence extending to the detection limit at I ~ 24.
Information on both color and magnitude is used to build the luminosity
functions of main sequence stars in these fields and the two independent
determinations are found to agree very well with each other within the
observational uncertainty. Both functions show a peak in the stellar
distribution around M_I ~ 9 followed by a drop at fainter magnitudes well
before photometric incompleteness becomes significant, as is typical of other
globular clusters observed with the HST. This result is at variance with
previous claims that the luminosity function of Omega Cen stays flat at low
masses, but is in excellent agreement with recent near-IR NICMOS observations
of the same cluster.Comment: To appear in The Astronomical Journal. Contains 7 pages, 4 figures,
prepared with the AAS LaTeX macr
Coherence and incoherence in extended broad band triplet interaction
In the present analysis we study the transition from coherent to incoherent
dynamics in a nonlinear triplet of broad band combs of waves. Expanding the
analysis of previous works, this paper investigates what happens when the band
of available modes is much larger than that of the initial narrower combs
within which the nonlinear interaction is not subjected to selection rules
involving wave momenta. Here selection rules are present and active, and we
examine how and when coherence can be defined.Comment: 6 pages, 2 figure
Series studies of the Potts model. I: The simple cubic Ising model
The finite lattice method of series expansion is generalised to the -state
Potts model on the simple cubic lattice.
It is found that the computational effort grows exponentially with the square
of the number of series terms obtained, unlike two-dimensional lattices where
the computational requirements grow exponentially with the number of terms. For
the Ising () case we have extended low-temperature series for the
partition functions, magnetisation and zero-field susceptibility to
from . The high-temperature series for the zero-field partition
function is extended from to . Subsequent analysis gives
critical exponents in agreement with those from field theory.Comment: submitted to J. Phys. A: Math. Gen. Uses preprint.sty: included. 24
page
Casimir forces in modulated systems
For the first time we present analytical results for the contribution of
electromagnetic fluctuations into thermodynamic properties of modulated
systems, like cholesteric or smectic liquid crystalline films. In the case of
small dielectric anisotropy we have derived explicit analytical expressions for
the chemical potential of such systems. Two limiting cases were specifically
considered: (i) the Van der Waals (VdW) limit, i.e., in the case when the
retardation of the electromagnetic interactions can be neglected; and (ii) the
Casimir limit, i.e. when the effects of retardation becomes considerable. It
was shown that in the Casimir limit, the film chemical potential oscillates
with the thickness of the film. This non-monotonic dependence of the chemical
potential on the film thickness can lead to step-wise wetting phenomena,
surface anchoring reorientation and other important effects. Applications of
the results may concern the various systems in soft matter or condensed matter
physics with multilayer or modulated structures.Comment: 13 page
Renormalization Ambiguities and Conformal Anomaly in Metric-Scalar Backgrounds
We analyze the problem of the existing ambiguities in the conformal anomaly
in theories with external scalar field in curved backgrounds. In particular, we
consider the anomaly of self-interacting massive scalar field theory and of
Yukawa model in the massless conformal limit. In all cases the ambiguities are
related to finite renormalizations of a local non-minimal terms in the
effective action. We point out the generic nature of this phenomenon and
provide a general method to identify the theories where such an ambiguity can
arise.Comment: RevTeX, 10 pages, no figures. Small comment and two references added.
Accepted for publication in Physical Review
Exotic looped trajectories via quantum marking
We provide an analytical and theoretical study of exotic looped trajectories
(ELTs) in a double-slit interferometer with quantum marking. We use an excited
Rydberg-like atom and which-way detectors such as superconducting cavities,
just as in the Scully-Englert-Walther interferometer. We indicate appropriate
conditions on the atomic beam or superconducting cavities so that we determine
an interference pattern and fringe visibility exclusive from the ELTs. We
quantitatively describe our results for Rubidium atoms and propose this
framework as an alternative scheme to the double-slit experiment modified to
interfere only these exotic trajectories.Comment: 10 pages, 5 figure
Nuclear re-interaction effects in quasi-elastic neutrino nucleus scattering
The quasi-elastic neutrino-nucleus cross section has been calculated by using
a Fermi gas model corrected to consider the re-scattering between the emitted
nucleon and the rest nucleus. As an example of the relevance of this effect we
show results for the muon production cross section on 16O target.Comment: 7 pages, 4 Postscript figures, Contribution to NuInt01 Workshop, KEK,
Tsukuba, Japa
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