8,887 research outputs found
Coulomb effects in nucleon-deuteron polarization-transfer coefficients
Coulomb effects in the neutron-deuteron and proton-deuteron
polarization-transfer coefficients , ,
and are studied at energies above the deuteron breakup threshold.
Theoretical predictions for these observables are evaluated in the framework of
the Kohn Variational Principle using correlated basis functions to expand the
three-nucleon scattering wave function. The two-nucleon Argonne and
the three-nucleon Urbana IX potentials are considered. In the proton-deuteron
case, the Coulomb interaction between the two protons is included explicitly
and the results are compared to the experimental data available at
MeV. In the neutron-deuteron case, a comparison to a
recent measurement of by Hempen {\sl et al.} at MeV
evidences a contribution of the calculated Coulomb effects opposite to those
extracted from the experiment.Comment: 7 pages, 3 figure
Bayesian analysis of the multivariate dependence of three transition water ecosystem classifications
The Water Framework Directive (WFD) recognizes benthic macroinvertebrates as a good biological quality element for transitional waters as they are the most exposed to natural variability patterns characteristic of these ecosystems, due to their life cycles and space-use behavior. Here, we address the ecological status classification issue for three lagoons in Apulia, using benthic macroinvertebrates and three proposed multimetric indices (namely M-AMBI, BITS and ISS), likely to respond differently to different sources of stress and natural variability. Lagoon classification is based on discretization by standard classification boundaries with only partial consideration of the natural variability of ecosystem properties and possible inaccuracies of the classification procedures. In order to investigate the possible contrasting behavior of the three classifications, we propose Bayesian hierarchical models in which the multimetric indices and their discrete counterparts are jointly modeled as function of abiotic covariates, external anthropogenic pressures indicators and spatio-temporal effects
Use of balloon catheter dilation vs. traditional endoscopic sinus surgery in management of light and severe chronic rhinosinusitis of the frontal sinus: a multicenter prospective randomized study
OBJECTIVE: Chronic rhinosinusitis (CRS) of the frontal sinus is a complex pathological condition and many surgical techniques were described to treat this area endoscopically, like traditional endoscopic sinus surgery (ESS) and balloon catheter dilation (BCD).
PATIENTS AND METHODS: We designed a multicenter prospective randomized study to assess the validity and safety of BCD vs. ESS in symptomatological chronic rhinosinusitis of the frontal sinus enrolling a population of 102 adult patients (64 men and 38 women; overall 148 frontal sinuses studied) with non-polypoid CRS. For a better evaluation of the disease, in our study we decided to analyze both radiological (Lund-McKay CT scoring modified by Zinreich) and symptomatological results (SNOT-20 questionnaire). We divided the population affected in two groups, one with light/mild frontal CRS and the other with moderate/severe frontal CRS, basing on radiological findings at Lund-MacKay modified by Zinreich score. Every group was divided in two subgroups, in one we used BCD and in the other we used traditional ESS.
RESULTS: The current literature does not support the suggestion that indications for BCD and ESS are identical, and additional research is needed to determine the role for BCD in specific patient populations. The results showed a not statistically significative difference between BCD and conventional ESS of the frontal sinus in patients with light/mild CRS and in patients with moderate/severe CRS at Lund-Mackay modified by Zinreich score. The same not statistically significative difference was observed comparing the results of SNOT-20 questionnaire in the group of light/mild frontal chronic rhinosinusitis. However, we noticed a statistically significant better outcome of SNOT-20 score in patients with moderate/severe chronic rhinosinusitis that underwent BCD of frontal sinus compared to ESS.
CONCLUSIONS: BCD and ESS are two alternative weapons in the baggage of every endoscopic surgeon, even because they present similar outcomes, safeness and effectiveness both in light/mild and moderate/severe chronic rhinosinusitis of the frontal sinus. An interesting result of our study was the statistically significant better outcome of SNOT-20 score in patients that underwent BCD of frontal sinus for a moderate/severe CRS, compared to those that underwent a traditional ESS
When chickens graze in olive orchards, the environmental impact of both chicken rearing and olive growing decreases
info:eu-repo/semantics/publishedVersio
Electromagnetic transitions for A=3 nuclear systems
Recent advances in the study of pd radiative capture in a wide range of
center-of-mass energy below and above deuteron breakup threshold are presented
and discussed.Comment: Invited lead talk at the 19th European Conference on Few-Body
Problems in Physics, Groningen, The Netherlands, 8/23 - 8/27 2004, 5 pages, 4
figure
Chiral effective field theory predictions for muon capture on deuteron and 3He
The muon-capture reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are
studied with nuclear strong-interaction potentials and charge-changing weak
currents, derived in chiral effective field theory. The low-energy constants
(LEC's) c_D and c_E, present in the three-nucleon potential and (c_D)
axial-vector current, are constrained to reproduce the A=3 binding energies and
the triton Gamow-Teller matrix element. The vector weak current is related to
the isovector component of the electromagnetic current via the
conserved-vector-current constraint, and the two LEC's entering the contact
terms in the latter are constrained to reproduce the A=3 magnetic moments. The
muon capture rates on deuteron and 3He are predicted to be 399(3) sec^{-1} and
1494 (21) sec^{-1}, respectively, where the spread accounts for the cutoff
sensitivity as well as uncertainties in the LEC's and electroweak radiative
corrections. By comparing the calculated and precisely measured rates on 3He, a
value for the induced pseudoscalar form factor is obtained in good agreement
with the chiral perturbation theory prediction.Comment: 4 pages, 2 figures, revisited version accepted for publication on
Phys. Rev. Let
Electromagnetic structure of A=2 and 3 nuclei and the nuclear current operator
Different models for conserved two- and three-body electromagnetic currents
are constructed from two- and three-nucleon interactions, using either
meson-exchange mechanisms or minimal substitution in the momentum dependence of
these interactions. The connection between these two different schemes is
elucidated. A number of low-energy electronuclear observables, including (i)
radiative capture at thermal neutron energies and deuteron
photodisintegration at low energies, (ii) and radiative capture
reactions, and (iii) isoscalar and isovector magnetic form factors of H and
He, are calculated in order to make a comparative study of these models for
the current operator. The realistic Argonne two-nucleon and Urbana IX
or Tucson-Melbourne three-nucleon interactions are taken as a case study. For
=3 processes, the bound and continuum wave functions, both below and above
deuteron breakup threshold, are obtained with the correlated
hyperspherical-harmonics method. Three-body currents give small but significant
contributions to some of the polarization observables in the
H()He process and the H()H cross section at
thermal neutron energies. It is shown that the use of a current which did not
exactly satisfy current conservation with the two- and three-nucleon
interactions in the Hamiltonian was responsible for some of the discrepancies
reported in previous studies between the experimental and theoretical
polarization observables in radiative capture.Comment: 48 pages, 25 figures, 4 tables, revtex4. Submitted to Phys. Rev.
Electrodisintegration of He below and above deuteron breakup threshold
Recent advances in the study of electrodisintegration of 3He are presented
and discussed. The pair-correlated hyperspherical harmonics method is used to
calculate the initial and final state wave functions, with a realistic
Hamiltonian consisting of the Argonne v18 two-nucleon and Urbana IX
three-nucleon interactions. The model for the nuclear current and charge
operators retains one- and many-body contributions. Particular attention is
made in the construction of the two-body current operators arising from the
momentum-dependent part of the two-nucleon interaction. Three-body current
operators are also included so that the full current operator is strictly
conserved. The present model for the nuclear current operator is tested
comparing theoretical predictions and experimental data of pd radiative capture
cross section and spin observables.Comment: 5 pages, 5 figures, submitted to Eur. Phys. J.
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