Abstract: An improved scheduling system which normally schedules the operation of number of functions using a shared resource based on time considerations is modified so as to provide a means to predict when the system has a condition that may cause the system to operate below the level required to operate all the functions. When the warning condition is triggered, the scheduler shifts to value based system where critical systems are given priority based on their criticality to the survival of the system.

Abstract: An ultrasonic transducer is improved, particularly for use in perivascular blood flow measurement, by the provision of a coupling member made of a hydrogel. The hydrogel is suitably acrylic based; has a water content in the range from 75 to 90% by weight and preferably about 85%; and has acoustic attenuation of less than 2 dBcm.sup.-1 at 5 MHz, with longitudinal velocity of sound and acoustic impedance of similar order to those for tissue. The crystals of the transducer are preferably sealed from the coupling member by a water resistant coating, the member suitably has an exposed face of part cylindrical shape to accommodate a vascular vessel, and the member is preferably releasably mounted to allow size interchange for different vessels.