2,254 research outputs found
Reworking the Tucson-Melbourne Three-Nucleon Potential
We introduce new values of the strength constants (i.e., , , , and
coefficients) of the Tucson-Melbourne (TM) 2 exchange three nucleon
potential. The new values come from contemporary dispersion relation analyses
of meson factory N scattering data. We make variational Monte Carlo
calculations of the triton with the original and updated three-body forces to
study the effects of this update. We remove a short-range -- -range part
of the potential due to the coefficient and discuss the effect on the
triton binding energy.Comment: 12 pages, to appear in Few-Body System
A Theoretical Examination of Double Jeopardy: Using Theory as a Guide to Concept Analysis
This article is a theoretical examination of the validity of the double jeopardy hypothesis from a number of social psychological perspectives. After a general review of the literature on double jeopardy, section two sets forth some alternative views on minority aging. In section three, four social psychological theories areexplicated in order to ascertain whether they would predict a double jeopardy outcome. In no case does the prediction suggest double jeopardy. Finally, a caveat is noted regarding how researchers define double jeopardy
Benchmark calculations for polarization observables in 3N scattering
High precision benchmark calculations for phase-shifts and mixing parameters
as well as observables in elastic neutron-deuteron scattering below the
deuteron breakup threshold are presented using a realistic nucleon-nucleon
potential. Two totally different methods, one using a variational principle in
configuration space and the other solving the Faddeev equations in momentum
space are used and compared to each other. The agreement achieved in
phase-shifts and mixing parameters as well as in the polarization observables
is excellent. The extreme sensitivity of the vector analyzing power Ay to small
changes of the phase shifts and mixing parameters is pointed out.Comment: 22 pages, 5 postscript figure
Momentum and Coordinate Space Three-nucleon Potentials
In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to and meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the TM force: the
, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon
request
Analysis of three-nucleon forces effects in the system
Using modern nucleon-nucleon interactions in the description of the
nuclear systems the per datum results to be much bigger than one. In
particular it is not possible to reproduce the three- and four-nucleon binding
energies and the scattering length simultaneously. This is one
manifestation of the necessity of including a three-nucleon force in the
nuclear Hamiltonian. In this paper we perform an analysis of some, widely used,
three-nucleon force models. We analyze their capability to describe the
aforementioned quantities and, to improve their description, we propose
modifications in the parametrization of the models. The effects of these new
parametrization are studied in some polarization observables at low energies.Comment: 10 pages, to be published in Few-Body Systems. Presented at the
workshop on "Relativistic Description of Two- and Three-body Systems in
Nuclear Physics" ECT* Trento, 19 - 23 October 200
A New Treatment of 2N and 3N Bound States in Three Dimensions
The direct treatment of the Faddeev equation for the three-boson system in 3
dimensions is generalized to nucleons. The one Faddeev equation for identical
bosons is replaced by a strictly finite set of coupled equations for scalar
functions which depend only on 3 variables. The spin-momentum dependence
occurring as scalar products in 2N and 3N forces accompanied by scalar
functions is supplemented by a corresponding expansion of the Faddeev
amplitudes. After removing the spin degrees of freedom by suitable operations
only scalar expressions depending on momenta remain. The corresponding steps
are performed for the deuteron leading to two coupled equations.Comment: 19 page
The Effects of Limiting Punitive Damage Awards
In response to concerns that jury awards in tort cases are excessive and unpredictable, nearly every state legislature has enacted some version of tort reform that is intended to curb extravagant damage awards. One of the most important and controversial reforms involves capping (or limiting) the maximum punitive damage award. We conducted a jury analogue study to assess the impact of this reform. In particular, we examined the possibility that capping punitive awards would cause jurors to inflate their compensatory awards to satisfy their desires to punish the defendant, particularly in situations where the defendant’s conduct was highly reprehensible. Relative to a condition in which punitive damages were unlimited, caps on punitive damages did not result in inflation of compensatory awards. However, jurors who had no option to award punitive damages assessed compensatory damages at a significantly higher level than did jurors who had the opportunity to do so. We discuss the policy implications of these findings
Cost-Effectiveness of Complementary Therapies in the United Kingdom—A Systematic Review(†)
Objectives: The aim of this review is to systematically summarize and assess all prospective, controlled, cost-effectiveness studies of complementary therapies carried out in the UK. Data sources: Medline (via PubMed), Embase, CINAHL, Amed (Alternative and Allied Medicine Database, British Library Medical Information Centre), The Cochrane Library, National Health Service Economic Evaluation Database (via Cochrane) and Health Technology Assessments up to October 2005. Review methods: Articles describing prospective, controlled, cost-effectiveness studies of any type of complementary therapy for any medical condition carried out in the UK were included. Data extracted included the main outcomes for health benefit and cost. These data were extracted independently by two authors, described narratively and also presented as a table. Results: Six cost-effectiveness studies of complementary medicine in the UK were identified: four different types of spinal manipulation for back pain, one type of acupuncture for chronic headache and one type of acupuncture for chronic back pain. Four of the six studies compared the complementary therapy with usual conventional treatment in pragmatic, randomized clinical trials without sham or placebo arms. Main outcome measures of effectiveness favored the complementary therapies but in the case of spinal manipulation (four studies) and acupuncture (one study) for back pain, effect sizes were small and of uncertain clinical relevance. The same four studies included a cost-utility analyses in which the incremental cost per quality adjusted life year (QALY) was less than £10 000. The complementary therapy represented an additional health care cost in five of the six studies. Conclusions: Prospective, controlled, cost-effectiveness studies of complementary therapies have been carried out in the UK only for spinal manipulation (four studies) and acupuncture (two studies). The limited data available indicate that the use of these therapies usually represents an additional cost to conventional treatment. Estimates of the incremental cost of achieving improvements in quality of life compare favorably with other treatments approved for use in the National Health Service. Because the specific efficacy of the complementary therapies for these indications remains uncertain, and the studies did not include sham controls, the estimates obtained may represent the cost-effectiveness non-specific effects associated with the complementary therapies
Modern nuclear force predictions for the neutron-deuteron scattering lengths
The nd doublet and quartet scattering lengths have been calculated based on
the modern NN and 3N interactions. We also studied the effect of the
electromagnetic interactions in the form introduced in AV18. Switching them off
for the various nuclear force models leads to shifts of up to +0.04 fm for
doublet scattering length, which is significant for present day standards. The
electromagnetic effects have also a noticeable effect on quartet scattering
length, which otherwise is extremely stable under the exchange of the nuclear
forces. For the current nuclear force models there is a strong scatter of the
3H binding energy and the doublet scattering length values around an averaged
straight line (Phillips line). This allows to use doublet scattering length and
the 3H binding energy as independent low energy observables.Comment: 16 pages, 1 table, 4 ps figure
Triton calculations with and exchange three-nucleon forces
The Faddeev equations are solved in momentum space for the trinucleon bound
state with the new Tucson-Melbourne and exchange three-nucleon
potentials. The three-nucleon potentials are combined with a variety of
realistic two-nucleon potentials. The dependence of the triton binding energy
on the cut-off parameter in the three-nucleon potentials is studied
and found to be reduced compared to the case with pure exchange. The
exchange parts of the three-nucleon potential yield an overall repulsive
effect. When the recommended parameters are employed, the calculated triton
binding energy turns out to be very close to its experimental value.
Expectation values of various components of the three-nucleon potential are
given to illustrate their significance for binding.Comment: 17 pages Revtex 3.0, 4 figures. Accepted for publication in Phys.
Rev.
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