63 research outputs found
The Lick Observatory Supernova Search
We report here the current status of the Lick Observatory Supernova Search
(LOSS) with the Katman Automatic Imaging Telescope (KAIT). The progress on both
the hardware and the software of the system is described, and we present a list
of recent discoveries. LOSS is the world' most successful search engine for
nearby supernovae.Comment: 4 pages, 1 figure, Submitted to the proceedings of the 10th Annual
October Astrophysics Conference in Maryland on Cosmic Explosion
Near-threshold measurement of the 4He(g,n) reaction
A near-threshold 4He(g,n) cross-section measurement has been performed at
MAX-lab. Tagged photons from 23 < Eg < 42 MeV were directed toward a liquid 4He
target, and neutrons were detected by time-of-flight in two liquid-scintillator
arrays. Seven-point angular distributions were measured for eight photon
energies. The results are compared to experimental data measured at comparable
energies and Recoil-Corrected Continuum Shell Model, Resonating Group Method,
and recent Hyperspherical-Harmonic Expansion calculations. The angle-integrated
cross-section data is peaked at a photon energy of about 28 MeV, in
disagreement with the value recommended by Calarco, Berman, and Donnelly in
1983.Comment: 10 pages, 3 figures, some revisions, submitted to Physics Letters
Spectroscopy with the (d,n) Reaction at 80 MeV
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
Novel Weak Decays in Doubly Strange Systems
The strangeness-changing () weak baryon-baryon interaction is
studied through the nonmesonic weak decay of double- hypernuclei.
Besides the usual nucleon-induced decay we discuss novel
hyperon-induced decay modes and . These reactions provide unique access to the exotic
K and K vertices which place new constraints
on Chiral Pertubation Theory (PT) in the weak SU(3) sector. Within a
meson-exchange framework, we use the pseudoscalar octet for the
long-range part while parametrizing the short-range part through the vector
mesons . Realistic baryon-baryon forces for the and
-2 sectors account for the strong interaction in the initial and final states.
For He the new hyperon-induced decay modes account for up
to 4% of the total nonmesonic decay rate. Predictions are made for all possible
nonmesonic decay modes.Comment: 19 pages, 2 ps figures, 9 table
Quasifree eta photoproduction from nuclei and medium modifications of resonances
We investigate the sensitivity of the differential cross section, recoil
nucleon polarization and the photon asymmetry to changes in the elementary
amplitude, medium modifications of the resonance masses, as
well as nuclear target effects. All calculations are performed within a
relativistic plane wave impulse approximation formalism resulting in analytical
expressions for all observables. The spin observables are shown to be unique
tools to study subtle effects that are not accessible by only looking at the
unpolarized differential cross section.Comment: 27 pages, 8 figures, Revtex, To be published in Phys. Rev.
Final State Interactions in Hypernuclear Decay
We present an update of the One-Meson-Exchange (OME) results for the weak
decay of s- and p-shell hypernuclei (Ref. Phys. Rev. C {\bf 56}, 339 (1997)),
paying special attention to the role played by final state interactions between
the emitted nucleons. The present study also corrects for a mistake in the
inclusion of the and exchange mechanisms, which substantially
increases the ratio of neutron-induced to proton-induced transitions,
. With the most up-to-date model ingredients, we find that
the OME approach is able to describe very satisfactorily most of the measured
observables, including the ratio .Comment: 20 pages, 2 eps figure
Light-year Scale Radio Cores in Four LINER Galaxies
The LINER galaxies NGC 2911, NGC 3079, NGC 3998, and NGC 6500 were observed
at 5 GHz with the European VLBI Network at a resolution of 5 milliarcsecond and
found to possess flat-spectrum, variable, high-brightness temperature ( K) radio cores. These radio characteristics reinforce the view that
these LINERs host central engines associated with active galactic nuclei.Comment: 6 page
On the Surface Structure of Strange Superheavy Nuclei
Bound, strange, neutral superheavy nuclei, stable against strong decay, may
exist. A model effective field theory calculation of the surface energy and
density of such systems is carried out assuming vector meson couplings to
conserved currents and scalar couplings fit to data where it exists. The
non-linear relativistic mean field equations are solved assuming local baryon
sources. The approach is calibrated through a successful calculation of the
known nuclear surface tension.Comment: 12 pages, 9 figure
New Discrete Basis for Nuclear Structure Studies
A complete discrete set of spherical single-particle wave functions for
studies of weakly-bound many-body systems is proposed. The new basis is
obtained by means of a local-scale point transformation of the spherical
harmonic oscillator wave functions. Unlike the harmonic oscillator states, the
new wave functions decay exponentially at large distances. Using the new basis,
characteristics of weakly-bound orbitals are analyzed and the ground state
properties of some spherical doubly-magic nuclei are studied. The basis of the
transformed harmonic oscillator is a significant improvement over the harmonic
oscillator basis, especially in studies of exotic nuclei where the coupling to
the particle continuum is important.Comment: 13 pages, RevTex, 6 p.s. figures, submitted to Phys. Rev.
Gamow Shell Model Description of Weakly Bound Nuclei and Unbound Nuclear States
We present the study of weakly bound, neutron-rich nuclei using the nuclear
shell model employing the complex Berggren ensemble representing the bound
single-particle states, unbound Gamow states, and the non-resonant continuum.
In the proposed Gamow Shell Model, the Hamiltonian consists of a one-body
finite depth (Woods-Saxon) potential and a residual two-body interaction. We
discuss the basic ingredients of the Gamow Shell Model. The formalism is
illustrated by calculations involving {\it several} valence neutrons outside
the double-magic core: He and O.Comment: 19 pages, 20 encapsulated PostScript figure
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