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A robust rendezvous controller design for multi-agent systems (MAS) is presented. The agents are modeled as Euler-Lagrange systems which exchange their position information on a packet-switched communication network, where the resulting communication delay is modeled in a distributed delay framework. A synthesis method for static position feedback controllers for these agents is proposed. It achieves rendezvous for uncertain communication delays with bounded average delay and for heterogeneous uncertain agent dynamics. The controllers only have to satisfy certain design conditions that relate sector bounds of the agent dynamics, Lipschitz bounds of the controllers, and the average communication delays of the network. A major advantage of the presented design condition is that the controller parameters depend only on the dynamics of the corresponding agent and the average communication delay to its neighbors, but not on the dynamics of the other agents or the delays in other parts of the network. This decentralized feature of the controller design is particularly useful for large and heterogeneous MAS. The performance of the controllers is illustrated by simulation.

Between January 1984 and December 1990, 56 patients with hydatid liver disease were treated surgically at our Department. Diagnosis was made by using clinical criteria, serology and imaging techniques. Most frequent clinical symptom was abdominal pain or local discomfort (38 patients, 68%). Plain X-ray of the abdomen was helpful in 20 patients (36%), liver ultrasound in 53 (93%) and computerised tumorgraphy in 56 patients, (100%). The immunoelectrophoresis test of "arc 5" was sensitive in 51 patients (91%). Thirty patients (53%) underwent partial resection and omentoplasty, 17 patients (30%) underwent external drainage, two cystic resection (3%), one left lateral lobectomy (2%) and six (11%) underwent omentoplasty and T-tube insertion. Fatal complications did not occur. Four patients developed hepatic abscess (7%), three wound infection (5%), one bowel obstruction (2%) and in five instances (8%) drainage was maintained for more than three months. Of the 49 patients available for follow-up (87%), three (6%) developed recurrent disease.