Calculations of the Exclusive Processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn) within a Generalized Glauber Approach

The exclusive processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn), have been analyzed using realistic few-body wave functions and treating the final state interaction (FSI) within a Generalized Eikonal Approximation (GEA), based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon with the nucleons of the A-1 system. The approach represents an improvement of the conventional Glauber approach (GA), in that it allows one to take into account the effects of the nuclear excitation of the $A-1$ system on the rescattering of the struck nucleon. Using realistic three-body wave functions corresponding to the AV18 interaction, the results of our parameter free calculations are compared with available experimental data. It is found that in some kinematical conditions FSI effects represent small corrections, whereas in other kinematics conditions they are very large and absolutely necessary to provide a satisfactory agreement between theoretical calculations and experimental data. It is shown that in the kinematics of the experimental data which have been considered, covering the region of missing momentum and energy with p_m < 0.6 GeV/c and E_m < 100 MeV in the perpendicular kinematics, the GA and GEA predictions differ only by less than 3-4 %.Comment: Typos detected and removed while Proof reading. Physical Review C. in Pres

Short-Distance Structure of Nuclei

One of Jefferson Lab's original missions was to further our understanding of the short-distance structure of nuclei. In particular, to understand what happens when two or more nucleons within a nucleus have strongly overlapping wave-functions; a phenomena commonly referred to as short-range correlations. Herein, we review the results of the (e,e'), (e,e'p) and (e,e'pN) reactions that have been used at Jefferson Lab to probe this short-distance structure as well as provide an outlook for future experiments.Comment: 16 pages, 8 figures, for publication in Journal of Physics

Adolescent drug use escalation and de-escalation: a 3-year follow-up study [Abstract]

This study aims to assess adolescents drug use with a longitudinal perspective in order to identify factors interacting with drug use onset and course. Supported by the Swiss Federal Office of Public Health, the study was initiated in 1999 with a follow-up in 2001 and 2002. The first objective was to measure risk factors for substance use initiation. The second objective was to analyse the co-variation of substance use with environmental, social, relational, medical and psychological factors. A total of 102 adolescents, aged 14-19 years, were recruited for the study in the French-speaking part of Switzerland. Results clearly show that substance use is not a disorder per se in adolescence, but that it is part of a multidimensional complex of problems that some adolescents may encounter: increase and decrease in substance use is paralleled with an increase or decrease in the other areas. This implies that prevention of substance use should not be focused mainly on substances but should consider the adolescent's environment and significant life area

Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold

The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.Comment: 19 pages, 7 figure

Multipole analysis of spin observables in vector meson photoproduction

A multipole analysis of vector meson photoproduction is formulated as a generalization of the pseudoscalar meson case. Expansion of spin observables in the multipole basis and behavior of these observables near threshold and resonances are examined.Comment: 15 pages, latex, 2 figure

Quasifree Pion Electroproduction from Nuclei in the Δ\Delta Region

We present calculations of the reaction $A(e,e^\prime \pi N)B$ in the distorted wave impulse approximation. The reaction allows for the study of the production process in the nuclear medium without being obscured by the details of nuclear transition densities. First, a pion electroproduction operator suitable for nuclear calculations is obtained by extending the Blomqvist-Laget photoproduction operator to the virtual photon case. The operator is gauge invariant, unitary, reference frame independent, and describes the existing data reasonably well. Then it is applied in nuclei to predict nuclear cross sections under a variety of kinematic arrangements. Issues such as the effects of gauge-fixing, the interference of the $\Delta$ resonance with the background, sensitivities to the quadrupole component of the $\Delta$ excitation and to the electromagnetic form factors, the role of final-state interactions, are studied in detail. Methods on how to experimentally separate the various pieces in the coincidence cross section are suggested. Finally, the model is compared to a recent SLAC experiment.Comment: 27 pages in REVTEX, plus 22 PS figures embedded using psfig.sty (included), uuencode

The pd→3HΛK+pd\to ^3H_\Lambda K^+ reaction cross section

The one- and two-step mechanisms of the $pd\to ^3H_\Lambda K^+$ reaction in the range of incident proton kinetic energy 1.13-3.0 GeV have been investigated. A remarkable peculiarity of the two-step mechanism which incorporates subprocesses $pp\to d\pi ^+$ and $\pi^+n\to K^+\Lambda$ is the so called velocity matching providing the presence of all intermediate particles nearly to the on-mass-shell. The differential cross section has been calculated using a realistic model for the hypertritium $^3H_\Lambda$ wave function. The maximum value of the cross section is estimated as $\sim$1nb/sr. The contribution of the one-step mechanism with the elementary process $pN\to NK\Lambda$ into the cross section has been found to be two - three orders of magnitude smaller in comparison with the two-step mechanism.Comment: 10 pages, Latex, 3 Postscript figure

Évolution des comportements et des représentations sociales liés à la consommation de cannabis chez les adolescents. Résumé

La recherche, dont les résultats principaux sont décrits dans ce résumé, visait trois objectifs différents: a) mieux comprendre l'évolution de la consommation de substances durant l'adolescence; b) mesurer les représentations sociales, par rapport à la consommation, dans une population de consommateurs comparée à une population «tout-venant»; c) valider un instrument de dépistage de la consommation. L'échantillon, sur lequel porte l'observation du suivi, est représentatif d'une population de consommateurs de substances. Le suivi a été réalisé sur une période de quatre ans, l'âge des sujets variant entre 15 et 20 ans au moment du premier entretien. Pour l'évaluation des représentations sociales, une population «tout-venant» a été recrutée, afin de pouvoir comparer les attitudes et opinions des adolescents en relation avec la consommation. Enfin, pour la validation de l'instrument de screening, les deux populations, suivi et «tout-venant», ont été réunies

Photoproduction of the Eta-Prime Mesons as a New Tool to Probe Baryon Resonances

We examine eta prime photoproduction, as a novel tool to study baryon resonances around 2 GeV, of particular interest to the quark shell model, which predicts a number of them. We find important roles of the form factors at the strong vertices, and show that the N^*(2080) can be probed efficiently by this reaction.Comment: Will be published in Phys. Rev.

Attenuation and modification of the ballast water microbial community during voyages into the Canadian Arctic

Aim: Ballast water is a major vector of non-indigenous species introductions world-wide. Our understanding of population dynamics of organisms entrained in ballast is largely limited to studies of zooplankton and phytoplankton. Bacteria are more numerous and diverse than zooplankton or phytoplankton, yet remain comparatively understudied. We apply a metagenomics approach to characterize changes in the microbial ballast water community over the course of three voyages on one ship, and assess the effects of ballast water exchange (BWE), spring/summer sampling month and time since voyage start. Location: Quebec City and Deception Bay, Quebec, and the coastal marine region offshore of eastern Canada. Methods: We used universal primers to Ion Torrent sequence a fragment of the bacterial 16S ribosomal DNA for samples collected over three voyages of one ship between Quebec City and Deception Bay in June, July and August 2015. We compared richness (total number of species in the community) and diversity (accounts for both species abundance and evenness) using linear mixed-effects analysis and compared community composition using non-metric multidimensional scaling and permutational multivariate analysis of variance. Initial comparisons were between months. Subsequent analyses focused on each month separately. Results: Ion Torrent sequencing returned c. 2.9 million reads and revealed monthly differences in diversity and richness, and in community structure in ballast water. June had higher richness and diversity than either July or August, and showed most clearly the effect of BWE on the microbial community. Main conclusions: Our results suggest that environmental conditions associated with different spring/summer sampling months drive differences in microbial diversity in ballast water. This study showed that BWE removes some components of the freshwater starting microbial community and replaces them with other taxa. BWE also changed proportional representation of some microbes without removing them completely. It appears that some taxa are resident in ballast tanks and are not removed by BWE. © 2017 John Wiley & Sons Lt