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The technique of ultrasonic flowrate measurement by multipath flowcells is presented and analysed. It is shown that the presence of flow asymmetry has an influence on the accuracy of quadrature integration as a basic tool for data processing in ultrasonic multipath spoolpieces. To obtain the metrological effectiveness of the multipath flowcells for the case of disturbed flows, full characterization and reconstruction of the flow velocity profile at each point of some cross-section of the transport channel is necessary. As the first stage, an implementation of Abel's transform is suggested.

A threshold model is described which permits one to determine the properties of limiters for high-powered laser light. It takes into account the threshold characteristics of the nonlinear optical interaction between the laser beam and the limiter working material. The traditional non-threshold model is a particular case of the threshold model when the limiting threshold is zero. The nonlinear characteristics of carbon nanotubes in liquid and solid media are obtained from experimental Z-scan data. Specifically, the nonlinear threshold effect was observed for aqueous dispersions of nanotubes, but not for nanotubes in solid polymethylmethacrylate. The threshold model fits the experimental Z-scan data better than the non-threshold model. Output characteristics were obtained that integrally describe the nonlinear properties of the optical limiters.

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