Servo-Stabilization of Low-Frequency Oscillations in a Liquid Bipropellant Rocket Motor

The recent work of H. S. Tsien concerning the servostabilization of rocket motors is extended to the liquid bipropellant rocket motor. It is shown that by use of a feedback system containing a device to sense the combustion chamber pressure, a suitably designed amplifier, and a servomechanism which governs the propellant How, the low-frequency oscillations which occur in the rocket configuration may be stabilized for any value of combustion time lag. A method is given for determining a transfer function of the feedback loop which will assure stable operation. The technique of the Satche diagram is employed in stability analysis

Current Trends and Future Outlook for Retiree Health Benefits

Documents the increasing costs of retiree benefits for large private sector employers and their retirees. Looks at the response of large employers to the Medicare prescription drug law and the subsidies it provides for maintaining retiree drug coverage

Technical Efficiency of the Danish Trawl fleet: Are the Industrial Vessels Better than Others?

Technical efficiency in the Danish trawl fishery in the North Sea is estimated for 1997 and 1998 by a stochastic production frontier model. This model allows noise when the frontier and the technical efficiency is found, which for fisheries is a reasonable assumption. The results show that the production frontier can be modelled by a translog function without time effects and a technical ineffi-ciency function. The type of fishery (industrial or consumption), size of vessel (greater or lesser than 60 GRT) and year give a good explanation for the ineffi-ciency in the fleet. The average technical efficiency is estimated to be 0.82. On average, industrial vessels have a higher technical efficiency than human con-sumption vessels, and smaller vessels have higher technical efficiency than lar-ger vessels. In sum, the analysis reveals that vessel larger than 60 GRT and fishing industrial species are the most efficient.Technical efficiency, stochastic production frontier, Danish trawl fishery