A practical implementation of acoustic reflectometry for determining airway areas in routine clinical use is described. Advances over previous systems include portability, free breathing during measurements. no need to equilibrate with helium/6xygen, and real-time display of airway areas. Validation of the reflectometer with an airway model gave accuracies and reproducibilities (coefficient of variation (cv)) in the range 5-10%. With human volunteers, the within-mn cv was typically IO%, and the day-today c v was 20%. The eKect of breathing pattem on airway areas is demonstrated.In ten normal volunteers, acoustic and magnetic resonance imaging (MRI) methods of assessing pharyngeal and glottal areas were compared. The results (meaniSD) for the oropharynx were l.0+0.3cm2 acoustically and 0.9+0.5cm1 by MRI (p=O.77]. The corresponding figures for glottal areas were 1.3*0.3 cm'and 1.1+0.4cm2 (p=O.O9).

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The contact charging of insulators is usually attributed to electron states which are characteristic of the material, for example the pendant groups of polymers. However, most materials normally encountered will have been charged by contact with other materials, if only during manufacture. Such charge is eventually neutralised by atmospheric ions (or by conduction in the case of poor insulators) but it is not at all certain that a 'neutralised' surface is equivalent in electronicstructure to a freshly created surface of the material. We report experiments to determine whether the contact charging of insulators is indeed influenced by previous contact and 'neutralisation' or whether it is, on the contrary, an invariant property governed solely by the chemical constitution of the material. We find that charge transfer is influenced by prior charging. Usually the charge transfer is decreased by prior contacts but in a few cases it is increased. Repeated cycles of contact and discharge have a cumulative but diminishing effect on charge transfer; typically about one third of the initial charge transfer is retained even after a large number of such cycles, and this accounts for the fact that even old and much-rubbed samples of a material retain their approximate position in the triboelectric series.

Research and development of pulsed-repetitively slab RF-excited CO2 laser is presented. The experiments were carried out for two modes operation: meander mode (duty factor 50%) and pulse repetition mode at S = 12.5%. The range of 240 ÷ 4000 Hz of pulse repetition frequency was used. Pulse power about 400 W for meander mode and up to 700 W for the second mode have been obtained. Input power, radiation pulse shape and output beam divergence were measured.