Abstract: Semiconductor apparatus comprises a split-gate semiconductor device (1) which has a first layer (3) of a first undoped semiconductor material (e.g. GaAs) and a second layer (4) of a second semiconductor material (e.g. AlGaAs) which is doped through at least part of its thickness. The second material has a higher energy band gap than the first material, and the layers form a heterojunction so that electrons from the second layer collect in the first layer to form a two-dimensional electron gas. Drain and source contacts (7,6) are provided on the second layers, and a gate electrode (8) is so configured that on application of a sufficiently large negative bias to the gate electrode a constriction is formed in the first layer through which only a one-dimensional electron gas can pass between the source and drain contacts. The apparatus also includes a bias supply (17) for applying a bias voltage between the source and drain contacts. The source/drain bias is made equal to or greater than E.sub.f /e where E.sub.

Abstract: An electrostatic precipitator comprises an upright cylindrical vessel (10) containing a number of vertically spaced precipitator stages (12). Ducting (18) provides a path for gas flow from an inlet (14) to an outlet (15) passing successively through each of the precipitator stages (12).

Abstract: A fume extraction assembly comprises an elevated canopy adapted to collect fume; and elongated outlet means offset from an apex of the canopy and having gas flow characteristics compensating for a tendency to uncontrolled extraction rates along said outlet means.

Abstract: A process for preparing tubercidin in a more acceptable form for injection consisting of mixing whole blood with a saline solution of tubercidin.