Abstract: The specification describes an interferometric in-situ end point detection technique for plasma etching in which the end point is predicted before any overetching occurs. It is based on the recognition that the wavelength of the monitoring beam can be selected so that only a single interferometric fringe appears before clearing. Knowing there is only one fringe, detection is simplified and the etching process can be terminated while a finite but small thickness of the layer remains. This allows etching partial thicknesses of layers. It also allows a two step etch process wherein the etch chemistry can be changed to a highly selective etch to complete clearing of the layer.

Abstract: A method and apparatus for discriminating a valid return pulse from noise in a return signal received by an ultrasonic transducer in response to an interrogating pulse transmitted into a wall of a gas pipe by an ultrasonic transducer of a scan assembly. A discriminator is provided to compare the return signal with adjustable reference voltage thresholds which are continually adjusted by a discriminator computer in accordance with the noise characteristics of the return signal.

Abstract: An advance notification system (10) and method notifies passengers of impending arrival of a transportation vehicle (19), for example, a school bus, at a particular vehicle stop. The system (10) generally includes an on-board vehicle control unit (VCU) (12) for each vehicle (19) and a base station control unit (BSCU) (14) for making telephone calls to passengers in order to inform the passengers when the vehicle (19) is a certain predefined time period and/or distance away from the vehicle stop. The VCU (12) compares elapsed time and/or travelled distance to the programmed scheduled time and/or travelled distance to determine if the vehicle (19) is on schedule. If the vehicle (19) is behind or ahead of schedule, the VCU (12) calls the BSCU (14), which then adjusts its calling schedule accordingly.