An Analytical Model for Closed Networks with a General Single Queue and an Infinite Server Station

In this paper we propose a new analytical model to solve a class of closed queuing networks with general servers and with a small number of customers. This model can be applied to analyze problems such as the machine-repairman problem and simultaneous resource possession. Our algorithm is based on exact mean value analysis and on two-moment approximations of GI/G/l queues. The model gives good results for a large range of the network parameters

Multi frequency evaporative cooling to BEC in a high magnetic field

We demonstrate a way to circumvent the interruption of evaporative cooling observed at high bias field for $^{87}$Rb atoms trapped in the (F=2, m=+2) ground state. Our scheme uses a 3-frequencies-RF-knife achieved by mixing two RF frequencies. This compensates part of the non linearity of the Zeeman effect, allowing us to achieve BEC where standard 1-frequency-RF-knife evaporation method did not work. We are able to get efficient evaporative cooling, provided that the residual detuning between the transition and the RF frequencies in our scheme is smaller than the power broadening of the RF transitions at the end of the evaporation ramp.Comment: 12 pages, 2 figure

Coherent matter wave inertial sensors for precision measurements in space

We analyze the advantages of using ultra-cold coherent sources of atoms for matter-wave interferometry in space. We present a proof-of-principle experiment that is based on an analysis of the results previously published in [Richard et al., Phys. Rev. Lett., 91, 010405 (2003)] from which we extract the ratio h/m for 87Rb. This measurement shows that a limitation in accuracy arises due to atomic interactions within the Bose-Einstein condensate

Double-well magnetic trap for Bose-Einstein condensates

We present a magnetic trapping scheme for neutral atoms based on a hybrid of Ioffe-Pritchard and Time-averaged Orbiting Potential traps. The resulting double-well magnetic potential has readily controllable barrier height and well separation. This offers a new tool for studying the behavior of Bose condensates in double-well potentials, including atom interferometry and Josephson tunneling. We formulate a description for the potential of this magnetic trap and discuss practical issues such as loading with atoms, evaporative cooling and manipulating the potential.Comment: 7 pages, 6 figures, Revtex

GRADIOMÈTRE GRAVIFIQUE À ATOMES FROIDS

La présente invention concerne un système de gradiomètre gravifique à atomes froids comprenant une source de laser qui produit un faisceau laser qui se propage le long d'une direction de propagation. Le système comprend en outre un réflecteur qui réfléchit une partie du faisceau laser et transmet une autre partie du faisceau laser (la partie transmise). Un second réflecteur spatialement séparé su premier réflecteur le long de la direction de propagation réfléchit la partie transmise du faisceau laser

Complications of laparoscopic antireflux surgery in childhood.

Background: The aim of this study was to assess the complications associated with the laparoscopic treatment of gastroesophageal reflux disease (GERD) in children. Methods: From March 1992 to March 1998, we used the laparoscopic approach to treat 289 children affected by gastroesophageal reflux disease. The patients’ ages ranged between 4 months and 17 years (median, 4.3 years), and their body weight ranged between 5 and 52 kg. In 148 children (51.3%), we adopted a Nissen-Rossetti procedure and in 141 (48.7%) a Toupet technique. Results: The duration of surgery ranged between 40 and 180 min (median, 70). There were no deaths and no anesthesiological complications in our series. We recorded 15 (5.1%) intraoperative complications: six pleural perforations, four lesions of the posterior vagus nerve, two esophageal perforations, two gastric perforations, and one pericardiac perforation. Conversion to open surgery was necessary in only four cases (1.3%). We recorded 10 (3.4%) postoperative complications: one peritonitis due to an esophageal perforation not detected during the intervention that required a reoperation, five cases of herniation of the epiploon through a trocar orifice, three cases of dysphagia that disappeared spontaneously after a few months, and one case of delayed gastric emptying that subsequently required a pyloroplasty. We had six recurrences of GERD (2.1%). In two cases, a new fundoplication was performed using the laparoscopic approach; in the other four, the GERD was controlled with medical therapy. Conclusion: Our results show that laparoscopic fundoplication is an adequate treatment for children with GERD that has a low rate of complications. When severe complications do occur, they can be treated effectively via the laparoscopic approach

Complications of laparoscopic treatment of esophageal achalasia in children

Background/Purpose: The aim of this study was to evaluate the incidence and management of the complications that occurred in some children who underwent laparoscopic Heller’s esophagocardiomyotomy in the authors’ institutions. Methods: Between March 1993 and October 1998, the files of all the children with achalasia who underwent laparoscopic Heller’s esophagocardiomyotomy in a community hospital in Naples, Italy, and a private hospital in Paris, France, were reviewed. A 5-port technique was used associating Heller’s esophagocardiomyotomy to an antireflux surgical mechanism (Dor’s or Toupet’s) in all cases. Intra- and postoperative complications, as well as the postoperative outcome, were evaluated. Results: Ten laparoscopic Heller’s esophagocardiomyotomies were performed in 5 girls and 5 boys with achalasia. Age ranged between 2 and 13 years. Mean operating time was 120 minutes. Hospital stay ranged between 3 and 41 days. Complications were recorded in 3 patients: in 2 an esophageal mucosal perforation and in 1 a prolonged dysphagia. Two of these complications occurred in the last patients operated on. Follow-up varied from 6 months to 6 years. All children were free of symptoms. Conclusions: The results show that laparoscopic Heller’s esophagocardiomyotomy in children is a feasible procedure. Assessment of mucosal integrity immediately after the myotomy must be performed. Complications can happen even if the operation is performed by expert laparoscopic surgeons

Complications of laparoscopic treatment of esophageal achalasia in children.

Background/Purpose: The aim of this study was to evaluate the incidence and management of the complications that occurred in some children who underwent laparoscopic Heller’s esophagocardiomyotomy in the authors’ institutions. Methods: Between March 1993 and October 1998, the files of all the children with achalasia who underwent laparoscopic Heller’s esophagocardiomyotomy in a community hospital in Naples, Italy, and a private hospital in Paris, France, were reviewed. A 5-port technique was used associating Heller’s esophagocardiomyotomy to an antireflux surgical mechanism (Dor’s or Toupet’s) in all cases. Intra- and postoperative complications, as well as the postoperative outcome, were evaluated. Results: Ten laparoscopic Heller’s esophagocardiomyotomies were performed in 5 girls and 5 boys with achalasia. Age ranged between 2 and 13 years. Mean operating time was 120 minutes. Hospital stay ranged between 3 and 41 days. Complications were recorded in 3 patients: in 2 an esophageal mucosal perforation and in 1 a prolonged dysphagia. Two of these complications occurred in the last patients operated on. Follow-up varied from 6 months to 6 years. All children were free of symptoms. Conclusions: The results show that laparoscopic Heller’s esophagocardiomyotomy in children is a feasible procedure. Assessment of mucosal integrity immediately after the myotomy must be performed. Complications can happen even if the operation is performed by expert laparoscopic surgeons