34 research outputs found
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 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
GRADIOMĂTRE GRAVIFIQUE Ă ATOMES FROIDS
La présente invention concerne un systÚme de gradiomÚtre 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 systÚme 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 patientsâ 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
Hellerâs esophagocardiomyotomy in the authorsâ institutions.
Methods: Between March 1993 and October 1998, the files of
all the children with achalasia who underwent laparoscopic
Hellerâs esophagocardiomyotomy in a community hospital in
Naples, Italy, and a private hospital in Paris, France, were
reviewed. A 5-port technique was used associating Hellerâs
esophagocardiomyotomy to an antireflux surgical mechanism
(Dorâs or Toupetâs) in all cases. Intra- and postoperative
complications, as well as the postoperative outcome, were
evaluated.
Results: Ten laparoscopic Hellerâs 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 Hellerâs
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
Hellerâs esophagocardiomyotomy in the authorsâ institutions.
Methods: Between March 1993 and October 1998, the files of
all the children with achalasia who underwent laparoscopic
Hellerâs esophagocardiomyotomy in a community hospital in
Naples, Italy, and a private hospital in Paris, France, were
reviewed. A 5-port technique was used associating Hellerâs
esophagocardiomyotomy to an antireflux surgical mechanism
(Dorâs or Toupetâs) in all cases. Intra- and postoperative
complications, as well as the postoperative outcome, were
evaluated.
Results: Ten laparoscopic Hellerâs 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 Hellerâs
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