In a recent paper [1] it was shown in examples that the covariant retarded Green's functions in particular gauges for electromagnetism and linearized gravity can be used to reproduce field configurations correctly in spite of the spacelike nature of past infinity in de Sitter spacetime. In this paper we extend the work of Ref.[1] concerning the electromagnetic field and show that the covariant retarded Green's function with an arbitrary value of the gauge parameter reproduces the electromagnetic field from two opposite charges at antipodal points of de Sitter spacetime.

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A portable, passive, non‐destructive, non‐intrusive instrument is currently in use by the U.S. Navy to detect fluid leakage through shipboard steam, water, hydraulic, and high‐pressure air valves. The Acoustic Valve Leak Detector (AVLD) was developed by the David W. Taylor Naval Ship RID Center (DTNSRDC) under the financial sponsorship and technical direction of the Nuclear Powered Fleet Ballistic Missile Submarine (SSBN) Ship Systems Maintenance Monitoring and Support Office (SMMSO) of the Naval Ship Engineering Center. The instrument is used to identify more precisely internal leakage points which may require opening and visual inspection of Submarine piping system. “Open‐and‐inspect” routines generate both risk of system damage and high man‐hour expenditure. The degree to which such procedures are necessary to achieve confidence in the material condition of systems is dependent on the availability and performance of non‐intrusive test equipment which can detect and assess the nature and degree of malfunctions. The development, design, operations, limitations, and successful applications of the existing AVLD are described. The AVLD is currently being used for troubleshooting, for overhaul planning, and in a systematic preventive maintenance program for seawater valves. Plans for future development and progress achieved in current work are described. The AVLD listens for the ultrasonic acoustic emissions characteristic of internal valve leakage and uses transducers attached temporarily to the valve or adjacent piping. The background spectra of structureborne noise can be subtracted automatically by the AVLD when a second transducer is attached to the piping system at a point far enough away from the valve in question that it picks up no leakage noise. Since the transducers are attached to the outside of the valves, the time and expense of dismantling the valves or of removing them from the systems are avoided.