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A system of three coupled, non-linear, singularly perturbed differential equations, which arise in the modelling of plasma sheaths, is studied. For one of the component equations theoretical results are given, which show that a numerical method based on a simple linearisation technique, a piecewise-uniform mesh of Shishkin type and a standard upwind finite difference operator generate parameter-uniform numerical approximations. Motivated by this, a numerical method for generating approximations to the solution of the full system of equations is constructed. Numerical results are presented, which indicate that this method is parameter uniform.

We present a method for the treatment of the boundary conditions and the particle loading in a self-consistent semi-infinite Particle-In-Cell simulation. We assume a nonionizing, collisional plasma in contact with an electrode. The simulation is planar and one-dimensional (1d-2v), and is driven by an rfand/or DC current source. The particle loading is done by appropriate drifting velocity distributions, both for ions and electrons. Limiting the simulation to the region immediately adjacent to the electrode dramatically improves run-times and diagnostic resolution and is ideal for studying the sheath and plasma-sheath interface independently from the rest of the plasma. The method can be generalized easily to model cylindrical and spherical geometries, and surface processes can also be included. The control parameters of the simulation are the values for the current drive (Irf, ωrf, IDC), the species temperatures in the bulk plasma Ts, and the values of the ion fluxes Γs.

An audit of patients with velopharyngeal incompetence treated by the Orticochea pharyngoplasty was undertaken. 54 patients who had been treated by a single surgeon over a 10-year period were identified. All patients had pre- and postoperative speech therapy and were followed up for an average of 6 months.49/54 patients had lessening of their nasal escape; in40/54 it was eliminated completely. Nasal resonance was assessed as normal in46/54 of patients postoperatively. The results are compared with those of other similar studies.