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The effective length of a flag executing photogate transit varies from photogate to photogate. It also varies with the position in the gap where it crosses the beam, and with the speed of the flag. Measurements were made using 23 photogates (the PASCO model 9204 and its newly updated version, the model 9204A). The flags were 11.66-mm-diam cylinders. The effective length of these flags was found to vary from photogate to photogate by up to 20%; vary with gap position by up to 8%; decrease by about 0.2% per meter/second with flag speed. Measurements and analysis are presented along with suggestions for minimizing systematic errors when using photogates in the laboratory.

The time domain response of a reverberant structural network of connected 1-D wave bearing systems excited by a spatial/temporal impulse is calculated and displayed in a spatial/temporal format. The response of a sensor at an arbitrary point in the network will be a time series of events. A segment of this time series is recorded, reversed in time, and used as an input to the Green function model of the network at the point where it was recorded. The model then shows the constructive interference at the original source location; however, it is not possible to ‘‘run the movie backward’’ in any strict sense. Constructive interference occurs at other alias locations, and the ability to locate the source degrades with increased damping and complexity. The advantage of using structural intensity and nonphysical modeling ‘‘tricks’’ such as negative damping (do not try this experimentally) and altered reflection coefficients after the injection of the time-reversed pulse are demonstrated. This technique can be useful in locating impact points in structural networks.

The partial radiation efficiency from a line-driven panel was previously defined and investigated by the authors [‘‘Partial radiation efficiency of line-driven panels,’’ J. Sound Vib. 144, 71–86 (1991)]. In the present paper, the counterpart to the previous work is presented. It is shown that the radiation efficiency, like the partial radiation efficiency, is dependent on the mechanical damping in the panel; and again, the efficiency increases with increase in the mechanical loss factor in the panel. Also, the dependence of the radiation efficiency on fluid loading is analogous to that of the partial radiation efficiency described in the previous work. In this paper, in addition, the radiated power as a function of frequency is investigated. It is shown that the radiated power appropriately diminishes with an increase in the mechanical damping. This result, in contrast, shows the fallibility of the conclusion that ‘‘a higher radiation efficiency implies, without further qualifications, more radiated power.’’ The results of computer experiments are cited in support of the various aspects in the paper.