Laboratory realization of relativistic pair-plasma beams.

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behavior differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. We present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN's Super Proton Synchrotron (SPS) accelerator. Monte Carlo simulations agree well with the experimental data and show that the characteristic scales necessary for collective plasma behavior, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations.

[Percutaneous closure of patent ductus arteriosus: results and costs compared to surgical closure]. / Fermeture du canal artériel par voie percutanée: comparaison des résultats et des coûts avec la fermeture chirurgicale.

The comparison of the clinical results and costs of the two methods of closure of patient ductus arteriosus was undertaken in two comparable groups of 40 patients treated in the same period in the same hospital. After transcatheter closure there was a 9% residual shunt rate at 3 years, the 2 patients with a residual continuous murmur being operated secondarily. The only complication was severe haemolysis which regressed after transcatheter ablation of the prosthesis. After surgical closure, there were no residual shunt. Some postoperative complications were observed in 20% of cases, usually benign (ventilatory problems, dysphonia or urinary infection), but occasionally more serious (peroperative lesion of the pulmonary artery). Morbidity, inherent to the technique of closure, was very different and much less in catheter closure. The average cost (daily cost x average length of hospital stay) was much less with transcatheter closure 38,558 francs versus 11,240 francs. On the other hand, the direct cost of transcatheter closure was greater than that of surgery: 32,798 francs versus 20,903 francs, the difference being related to the actual price of the prosthesis. The authors conclude that the 3 year results of transcatheter closure of patent ductus arterious make this technique a reasonable therapeutic alternative to surgery. From the safety point of view, the two techniques are comparable bu patient confort is greater with transcatheter closure for an increase in cost of the initial procedure which should decrease in relation to the types and prices of the prosthesis used.