Abstract: An interface unit for coupling an international-type pay-telephone to a land-based or cellular telephone system. The interfacing unit of the invention has a microcomputer, and an associated EPROM in which is stored the exchanges of the telephone numbers that are accessible by that local payphone-terminal, which EPROM also stores a table indicative of the tariffing rates associated with the respective exchanges called. The invention also includes the tone-detectors for detecting the dialed DTMF digits of the pay-telephone, for the conversion thereof for storage in the microcomputer for the determination of a valid telephone number dialed in order to determine the associated tariffing rates. The tone detectors also detect the tone-signals received from the telephone system. The invention also includes "isolating" switching circuitry for isolating the coin-operated pay terminal from its couplement to the telephone system until the telephone call has been connected.

Abstract: The invention relates to a method of improving the heat transfer properties in boiling liquids of tubes and other surfaces by applying a very porous reticulated organic foam layer which has been precoated with graphite in contact with the tube surface, and then plating a thin metal coating on the foam substrate. Preferably, the tube is copper and the plating consists of an electroplated layer of copper which is applied over the conductive graphite coated foam. the foam is preferably in the form of a thin tape which is spirally wound about the tube. Pyrolyzation of the foam after plating improves the heat transfer performance of the tube. A method for applying the graphite to the foam is also disclosed.