11,838 research outputs found
Star-formation in the central kpc of the starburst/LINER galaxy NGC1614
A high angular resolution, multi-wavelength study of the LINER galaxy NGC1614
has been carried out. OVRO CO 1-0 observations are presented together with
extensive multi-frequency radio continuum and HI absorption observations with
the VLA and MERLIN. Toward the center of NGC1614, we have detected a ring of
radio continuum emission with a radius of 300 pc. This ring is coincident with
previous radio and Paschen-alpha observations. The dynamical mass of the ring
based on HI absorption is 3.1 x 10E9 Msun. The peak of the integrated CO 1-0
emission is shifted by 1" to the north-west of the ring center and a
significant fraction of the CO emission is associated with a crossing dust
lane. An upper limit to the molecular gas mass in the ring region is 1.7 x 10E9
Msun. Inside the ring, there is a north to south elongated 1.4GHz radio
continuum feature with a nuclear peak. This peak is also seen in the 5GHz radio
continuum and in the CO. We suggest that the R=300 pc star forming ring
represents the radius of a dynamical resonance - as an alternative to the
scenario that the starburst is propagating outwards from the center into a
molecular ring. The ring-like appearance probably part of a spiral structure.
Substantial amounts of molecular gas have passed the radius of the ring and
reached the nuclear region. The nuclear peak seen in 5GHz radio continuum and
CO is likely related to previous star formation, where all molecular gas was
not consumed. The LINER-like optical spectrum observed in NGC1614 may be due to
nuclear starburst activity, and not to an Active Galactic Nucleus (AGN).
Although the presence of an AGN cannot be excluded.Comment: Accepted by Astronomy and Astrophysics, 12 pages, 10 figure
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
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The Physio-Chemical Properties for the Interior of Enceladus
We have reviewed the current physical and chemical conditions of the Enceladus sub-surface environment, including the composition, temperature, pH and pressure. Here we have defined some of these parameters and, through the aid of modelling, will define and refine the remaining parameters needed for our experimental work. Simulations of the chemical reactions occurring within Enceladus can then be carried
out to advance our understanding of the internal environment of Enceladus and help evaluate its potential habitability. Once a better understanding of the chemical reactions occurring at the rock-water interface has been carried out, then potential analogues on Earth can be evaluated and known microbial life can be tested to see if it could survive the conditions of Enceladus
In Search of the Vortex Loop Blowout Transition for a type-II Superconductor in a Finite Magnetic Field
The 3D uniformly frustrated XY model is simulated to search for a predicted
"vortex loop blowout" transition within the vortex line liquid phase of a
strongly type-II superconductor in an applied magnetic field. Results are shown
to strongly depend on the precise scheme used to trace out vortex line paths.
While we find evidence for a transverse vortex path percolation transition, no
signal of this transition is found in the specific heat.Comment: 11 pages, 17 figure
Semi-leptonic B decays into higher charmed resonances
We apply HQET to semi-leptonic meson decays into a variety of excited
charm states. Using three realistic meson models with fermionic light degrees
of freedom, we examine the extent that the sum of exclusive single charmed
states account for the inclusive semi-leptonic decay rate. The consistency
of form factors with the Bjorken and Voloshin sum rules is also investigated.Comment: Latex, 27 pages. A few references and errors corrected, to appear in
Phys. Rev.
From scalar to string confinement
We outline a connection between scalar quark confinement, a
phenomenologically successful concept heretofore lacking fundamental
justification, and QCD. Although scalar confinement does not follow from QCD,
there is an interesting and close relationship between them. We develop a
simple model intermediate between scalar confinement and the QCD string for
illustrative purposes. Finally, we find the bound state masses of scalar,
time-component vector, and string confinement analytically through
semi-classical quantization.Comment: ReVTeX, 9 pages, 5 figure
Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic
system as grown by the flux-feeding floating zone technique. A supercurrent
flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances
that are far beyond those expected in a conventional proximity scenario. The
current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted
from the eutectic, exhibit signatures of superconductivity in the bilayered
ruthenate. Detailed microstructural, morphological and compositional analyses
address issues on the concentration and the size of Sr2RuO4 inclusions within
the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous
superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the
Sr2RuO4 inclusions.Comment: Pages 4, figures 3, submitted to Phys. Rev. Let
Instantaneous Bethe-Salpeter equation: utmost analytic approach
The Bethe-Salpeter formalism in the instantaneous approximation for the
interaction kernel entering into the Bethe-Salpeter equation represents a
reasonable framework for the description of bound states within relativistic
quantum field theory. In contrast to its further simplifications (like, for
instance, the so-called reduced Salpeter equation), it allows also the
consideration of bound states composed of "light" constituents. Every
eigenvalue equation with solutions in some linear space may be (approximately)
solved by conversion into an equivalent matrix eigenvalue problem. We
demonstrate that the matrices arising in these representations of the
instantaneous Bethe-Salpeter equation may be found, at least for a wide class
of interactions, in an entirely algebraic manner. The advantages of having the
involved matrices explicitly, i.e., not "contaminated" by errors induced by
numerical computations, at one's disposal are obvious: problems like, for
instance, questions of the stability of eigenvalues may be analyzed more
rigorously; furthermore, for small matrix sizes the eigenvalues may even be
calculated analytically.Comment: LaTeX, 23 pages, 2 figures, version to appear in Phys. Rev.
Soluble `Supersymmetric' Quantum XY Model
We present a `supersymmetric' modification of the -dimensional quantum
rotor model whose ground state is exactly soluble. The model undergoes a
vortex-binding transition from insulator to metal as the rotor coupling is
varied. The Hamiltonian contains three-site terms which are relevant: they
change the universality class of the transition from that of the ()--- to
the -dimensional classical XY model. The metallic phase has algebraic ODLRO
but the superfluid density is identically zero. Variational wave functions for
single-particle and collective excitations are presented.Comment: 12 pages, REVTEX 3.0, IUCM93-00
On the validity of the reduced Salpeter equation
We adapt a general method to solve both the full and reduced Salpeter
equations and systematically explore the conditions under which these two
equations give equivalent results in meson dynamics. The effects of constituent
mass, angular momentum state, type of interaction, and the nature of
confinement are all considered in an effort to clearly delineate the range of
validity of the reduced Salpeter approximations. We find that for
the solutions are strikingly similar for all
constituent masses. For zero angular momentum states the full and reduced
Salpeter equations give different results for small quark mass especially with
a large additive constant coordinate space potential. We also show that
corrections to heavy-light energy levels can be accurately
computed with the reduced equation.Comment: Latex (uses epsf macro), 24 pages of text, 12 postscript figures
included. Slightly revised version, to appear in Phys. Rev.
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