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Using periodic boundary conditions in the reductive perturbation method for ion acoustic cnoidal waves in a collisionless, unmagnetized plasma consisting of warm ions and hot isothermal electrons, evolution equations for the first order and second order potential are derived. Determining the nonsecular solution of these coupled equations, expressions for wave phase velocity and averaged nonlinear ion flux are obtained. Variations of wave phase velocity and averaged nonlinear ion flux are examined for different values of wave frequency and ion to electron temperature ratio (Ti∕Te). It is found that wave phase velocity increases with an increase in wave amplitude for a given value of frequency and temperature ratio. But for a given wave amplitude, the wave phase velocity increases as the temperature ratio increases or wave frequency decreases. The averaged nonlinear ion flux associated with the propagation of large amplitude cnoidal waves in plasma is found to be negative, which corresponds to back flow of ions. The magnitude of the ion flux increases with increase in wave amplitude as temperature ratio or wave frequency increases.

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Background:The use of central venous catheters (CVCs) has greatly improved the quality-of-care in cancer patients, yet these catheters may cause serious infectious and thrombotic complications. The aim of this retrospective study was to study the various types of CVCs and their complications.Materials and Methods:We studied retrospectively 213 cases of CVCs in our institute with their indications, type and complications from August 2010 to July 2011.Results:A total of 213 CVCs were inserted in patients with hematological (62%) and solid organ malignancies (38%). Ninety-eight patients (46%) had peripheral inserted central catheter (PICC), 90 (42%) patients had Hickman catheters and 25 (12%) had a port. The median duration of retention of Hickman catheters was 104 days (3-365 days), for the peripherally inserted central catheters was 59 days (3-100 days) and for the port it was 280 days (45-365 days). Non-infective complications were more than infective (12% vs. 7%). The most common complication was non-infective occlusion and thrombophlebitis. In one patient with PICC thrombosis occurred in the cephalic, radial and ulnar vein and in one patient with port thrombosis occurred in the superior vena cava. Organisms were isolated in 60% (12 out of 20) of cultures. Common organisms isolated were Pseudomonas aeruginosa in 5 (42%), Staphylococcus aureus in 2 (16%), Escherichia coli in 2 (16%) and Aspergillus in 3 (25%) patients. 7 out of 12 infected patients had negative blood cultures within 7 days of antibiotic treatment, 5 patients remained positive for more than 7 days with antibiotics. In 155 patients (73%), the desired treatment protocol was completed and at present there are still 28 patients (13%) with catheters. 5 patients (2.3%) died of febrile neutropenia and septicemia with multi-organ failure. In 5 patients (2.3%), the catheters (1 Port, 1 Hickman and 3 PICC) were prematurely removed because of thrombosis.Conclusion:CVCs are better options to facilitate the long-term vascular access provided infection is prevented with meticulous care and treated promptly with proper antibiotics. Most CVCs is acceptable to patients.

Small bore pigtail catheters are safe, comfortable, cost effective and have few complications especially in loculated pleural effusions.