47 research outputs found
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
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
XMM-Newton observations of ultraluminous X-ray sources in nearby galaxies
An XMM-Newton study of ultraluminous X-ray sources (ULX) has been performed
in a sample of 10 nearby Seyfert galaxies. Eighteen ULX have been found with
positional uncertainty of about 4". The large collecting area of XMM-Newton
makes the statistics sufficient to perform spectral fitting with simple models
in 8 cases. The main results of the present minisurvey strengthen the theory
that the ULX could be accreting black holes in hard or soft state. In some
cases, the contribution of the ULX to the overall X-ray flux appears to be
dominant with respect to that of the active nucleus. In addition, 6 ULX present
probable counterparts at other wavelengths (optical/infrared, radio). A
multiwavelength observing strategy is required to better assess the nature of
these sources.Comment: 10 pages, 11 figures. Accepted for publication by Astronomy and
Astrophysics. If you want figures at full resolution, please send an email to
Foschin
Phenomenological Lambda-Nuclear Interactions
Variational Monte Carlo calculations for (ground and
excited states) and are performed to decipher information on
-nuclear interactions. Appropriate operatorial nuclear and
-nuclear correlations have been incorporated to minimize the
expectation values of the energies. We use the Argonne two-body
NN along with the Urbana IX three-body NNN interactions. The study demonstrates
that a large part of the splitting energy in () is
due to the three-body NN forces. hypernucleus is
analyzed using the {\it s}-shell results. binding to nuclear matter
is calculated within the variational framework using the
Fermi-Hypernetted-Chain technique. There is a need to correctly incorporate the
three-body NN correlations for binding to nuclear matter.Comment: 18 pages (TeX), 2 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.
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.
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
Optical Spectroscopy of Type Ia Supernovae
We present 432 low-dispersion optical spectra of 32 Type Ia supernovae (SNe
Ia) that also have well-calibrated light curves. The coverage ranges from 6
epochs to 36 epochs of spectroscopy. Most of the data were obtained with the
1.5m Tillinghast telescope at the F. L. Whipple Observatory with typical
wavelength coverage of 3700-7400A and a resolution of ~7A. The earliest spectra
are thirteen days before B-band maximum; two-thirds of the SNe were observed
before maximum brightness. Coverage for some SNe continues almost to the
nebular phase. The consistency of the method of observation and the technique
of reduction makes this an ideal data set for studying the spectroscopic
diversity of SNe Ia.Comment: Accepted for publication in the Astronomical Journal, 109 pages
(including data table), 44 figures, full resolution figures at
http://www.noao.edu/noao/staff/matheson/Iaspec.ps.g
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
Type of Disability, Gender, and Age Affect School Satisfaction:Findings from the UK Millennium Cohort Study
Background Self‐reported school satisfaction is an important indicator of child and adolescent well‐being. Few studies have examined how disability, gender, and age affect school satisfaction. Aim We sought to determine whether the interaction between disability and gender with regard to self‐reported school satisfaction might be specific to particular types of disability and particular ages. Methods We undertook secondary analysis of Waves 5 and 6 of the UK’s Millennium Cohort Study (MCS), a nationally representative sample of children born 2000–2002. MCS is the fourth in the series of British birth cohort studies. Result At 11 years of age (n = 12,207), school satisfaction was significantly higher for girls and those without disabilities. By contrast, at 14 (n = 10,933), school satisfaction was significantly higher for boys and those without disabilities. Subsequent analyses of gender moderation of the association between disability and school satisfaction revealed a significant interaction between gender and disabilities associated with mental health and with dexterity, respectively, at 14 years but not at age 11. Conclusion These findings will inform future research endeavours, policy, and practice in psychology, education, and other areas associated with child development and disability