Stochastic Semi-Classical Description of Fusion at Near-Barrier Energies

Fusion reactions of heavy ions are investigated by employing a simple stochastic semi-classical model which includes the coupling between relative motion and low frequency collective surface modes of colliding ions similarly to the quantal coupled-channels description. The quantal effect enters into the calculation through the initial zero-point fluctuations of the surface vibrations. Good agreement with the result of coupled-channels calculations as well as data is obtained for the fusion cross sections of nickel isotopes. The internal excitations in non-fusing events as well as the fusion time are investigated.Comment: 8 pages, 8 figures, Published in Phys. Rev.

Measuring the Effectiveness of Research Grant Getting

To a very large extent, the national and international reputation of major research universities depends upon their research performance. That explains why competition is so fierce among them to get as much as they can from the three Canadian government major granting agencies. This study demonstrates how performance indicators were developed to measure the effectiveness of research grant getting among eleven Canadian universities. It shows how amount of money received, size of teaching staff, and disciplinary characteristics were standardized to yield objective disciplinary and institutional rankings.La réputation nationale et internationale des principales universités où il se fait beaucoup de recherche dépend dans une très large mesure de leur rendement dans ce domaine .C'est pourquoi ces institutions mènent une lutte serrée pour obtenir le maximum de subventions des trois principaux organismes subventionnaires du gouvernement canadien. L'article porte sur l'approche utilisée pour mesurer, à l'aide des indices de rendement, l'efficacité des subventions de recherche réparties entre onze universités canadiennes. Il montre que pour en arriver à un classement objectif des disciplines et des institutions, il a fallu standardiser les sommes versées, l'importance numérique du corps professoral et les caractéris-tiques disciplinaires

The XENON100 exclusion limit without considering Leff as a nuisance parameter

In 2011, the XENON100 experiment has set unprecedented constraints on dark matter-nucleon interactions, excluding dark matter candidates with masses down to 6 GeV if the corresponding cross section is larger than 10^{-39} cm^2. The dependence of the exclusion limit in terms of the scintillation efficiency (Leff) has been debated at length. To overcome possible criticisms XENON100 performed an analysis in which Leff was considered as a nuisance parameter and its uncertainties were profiled out by using a Gaussian likelihood in which the mean value corresponds to the best fit Leff value smoothly extrapolated to zero below 3 keVnr. Although such a method seems fairly robust, it does not account for more extreme types of extrapolation nor does it enable to anticipate on how much the exclusion limit would vary if new data were to support a flat behaviour for Leff below 3 keVnr, for example. Yet, such a question is crucial for light dark matter models which are close to the published XENON100 limit. To answer this issue, we use a maximum Likelihood ratio analysis, as done by the XENON100 collaboration, but do not consider Leff as a nuisance parameter. Instead, Leff is obtained directly from the fits to the data. This enables us to define frequentist confidence intervals by marginalising over Leff.Comment: 10 pages;, 9 figures; references adde

Bimodality as a signal of Liquid-Gas phase transition in nuclei?

We use the HIPSE (Heavy-Ion Phase-Space Exploration) Model to discuss the origin of the bimodality in charge asymmetry observed in nuclear reactions around the Fermi energy. We show that it may be related to the important angular momentum (spin) transferred into the quasi-projectile before secondary decay. As the spin overcomes the critical value, a sudden opening of decay channels is induced and leads to a bimodal distribution for the charge asymmetry. In the model, it is not assigned to a liquid-gas phase transition but to specific instabilities in nuclei with high spin. Therefore, we propose to use these reactions to study instabilities in rotating nuclear droplets.Comment: 4 pages, 4 figures Accepted to PR

Partial Disorder and Metal-Insulator Transition in the Periodic Anderson Model on a Triangular Lattice

Ground state of the periodic Anderson model on a triangular lattice is systematically investigated by the mean-field approximation. We found that the model exhibits two different types of partially disordered states: one is at half filling and the other is at other commensurate fillings. In the latter case, the kinetic energy is lowered by forming an extensive network involving both magnetic and nonmagnetic sites, in sharp contrast to the former case in which the nonmagnetic sites are rather isolated. This spatially extended nature of nonmagnetic sites yields a metallic partially-disordered state by hole doping. We discuss the mechanism of the metal-insulator transition by the change of electronic structure.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp

Stochastic mean-field dynamics for fermions in the weak coupling limit

Assuming that the effect of the residual interaction beyond mean-field is weak and has a short memory time, two approximate treatments of correlation in fermionic systems by means of Markovian quantum jump are presented. A simplified scenario for the introduction of fluctuations beyond mean-field is first presented. In this theory, part of the quantum correlations between the residual interaction and the one-body density matrix are neglected and jumps occur between many-body densities formed of pairs of states $D=| \Phi_a > < \Phi_b |/$ where $| \Phi_a >$ and $| \Phi_b >$ are antisymmetrized products of single-particle states. The underlying Stochastic Mean-Field (SMF) theory is discussed and applied to the monopole vibration of a spherical $^{40}$Ca nucleus under the influence of a statistical ensemble of two-body contact interaction. This framework is however too simplistic to account for both fluctuation and dissipation. In the second part of this work, an alternative quantum jump method is obtained without making the approximation on quantum correlations. Restricting to two particles-two holes residual interaction, the evolution of the one-body density matrix of a correlated system is transformed into a Lindblad equation. The associated dissipative dynamics can be simulated by quantum jumps between densities written as $D = | \Phi >$ is a normalized Slater determinant. The associated stochastic Schroedinger equation for single-particle wave-functions is given.Comment: Enlarged version, 10 pages, 2 figure

Les charges d'enseignement dans les universités québécoises : une réplique au Rapport Gobeil

This article responds to the recommendation in the "Gobeil Report" (Rapport Gobeil) which proposes an increase in teaching workload of 50% in all Quebec universities in order to conform to what "exists" elsewhere in Canada. After having undertaken a survey among 39 Canadian universities of all sizes, and after having analysed the number of students at the graduate and/or undergraduate levels as well as the amount of grant assistance provided to research, the authors conclude that it is necessary to distinguish between two types of university establishments: research universities and teaching universities. Results demonstrate clearly that course hours represent but one component of the teaching load and that it is also necessary to consider the graduate studies program of the institution as well as the research activities being undertaken by the university before drawing a conclusion as general as that presented in the Gobeil Report. The authors of this study conclude that there is a net difference in the teaching responsibilities in Canadian universities outside of Quebec — whether it be a research or a teaching university. In the francophone universities of Quebec, teaching loads are uniform no matter what the commitment to research or advanced studies happens to be. An indiscriminate increase in the teaching assignment would compromise graduate studies and the research carried out in research universities.Cet article répond à la recommandation du Rapport Gobeil qui propose indis- tinctement /'augmentation de 50% de la charge des professeurs dans toutes les universités québécoises pour se conformer à ce qui "existerait" ailleurs au Canada. Après avoir mené une enquête auprès de 39 universités canadiennes de toutes tailles, et après avoir analysé le nombre d'étudiants de tous cycles et le niveau de subventions de recherche, les auteurs concluent qu'il faut distinguer deux catégories d'universités: les universités de recherche et les universités d'enseignement. Les résultats démontrent clairement que les heures de cours ne représentent qu'une partie des charges d'enseignement et qu'il faut considérer l'encadrement d'étudiants avancés et les activités de recherche avant de tirer une conclusion aussi générale que celle présentée par le Rapport Gobeil. Les auteurs concluent qu'il y a une nette différence dans les charges de cours dans les universités canadiennes hors Québec selon qu'il s'agit d'une université de recherche ou d'enseignement. Dans les universités francophones du Québec, les charges d'enseignement sont uniformisées quel que soit l'engagement en recherche et dans les études avancées. Une augmentation indistincte des charges d'enseignement compromettrait fortement les études avancées et la recherche des universités de recherche

Effects of live-bait shrimp trawling on seagrass beds and fish bycatch in Tampa Bay, Florida

The use of live shrimp for bait in recreational fishing has resulted in a controversial fishery for shrimp in Florida. In this fishery, night collections are conducted over seagrass beds with roller beam trawls to capture live shrimp, primarily pink shrimp, Penaeus duorarum. These shrimp are culled from the catch on sorting tables and placed in onboard aerated “live” wells. Beds of turtlegrass, Thalassia testudinum, a species that has highest growth rates and biomass during summer and lowest during the winter (Fonseca et al., 1996) are predominant areas for live-bait shrimp trawling (Tabb and Kenny, 1969). Our study objectives were 1) to determine effects of a roller beam trawl on turtlegrass biomass and morphometrics during intensive (up to 18 trawls over a turtlegrass bed), short-term (3-hour duration) use and 2) to examine the mortality of bycatch finfish following capture by a trawl

Transfemoral treatment for iliac occlusive disease with endoluminal stent-grafts

Objectives:Percutaneous treatment of iliac artery occlusive disease has replaced open vascular reconstruction for several indications. A balloon angioplasty with or without stent is not an option in the presence of infrainguinal extension of the disease. The authors describe a technique that allows the construction of an aorto- or iliofemoral graft through a single groin incision, using a 4 mm PTFE graft, anchoring it proximally with a Palmaz stent and dilating both to the desired diameter.Design:Retrospective non-randomised study.Materials and Methods:Nineteen procedures were performed in 16 patients mainly because of ischaemic rest pain, often with trophic skin changes or minor gangrene. Three patients had a bilateral procedure. Twelve patients had one or more associated procedures: 10 distal bypasses, one thrombectomy, one reimplantation of a distal bypass on the iliofemoral graft, one contralateral profundaplasty and two stents of the contralateral common iliac artery.Results:Two patients died, one of small bowel ischaemia and the other of a myocardial infarction. During the mean follow-up of 8.8 months, two graft thromboses occurred. In another patient bilateral stenting of a residual stenosis was necessary.Conclusions:Our experience shows that the reported technique is feasible. Whether the procedure is truly “less invasive” and the long-term results acceptable remains to be shown

On nucleon exchange mechanism in heavy-ion collisions at near-barrier energies

Nucleon drift and diffusion mechanisms in central collisions of asymmetric heavy-ions at near-barrier energies are investigated in the framework of a stochastic mean-field approach. Expressions for diffusion and drift coefficients for nucleon transfer deduced from the stochastic mean-field approach in the semiclassical approximation have similar forms familiar from the phenomenological nucleon exchange model. The variance of fragment mass distribution agrees with the empirical formula $\sigma^2_{AA}(t)= N_{\rm exc}(t)$. The comparison with the time-dependent Hartree-Fock calculations shows that, below barrier energies, the drift coefficient in the semiclassical approximation underestimates the mean number of nucleon transfer obtained in the quantal framework. Motion of the window in the dinuclear system has a significant effect on the nucleon transfer in asymmetric collisions.Comment: 10 pages, 10 figures, submitted for publicatio