Index of content:
Volume 104, Issue 3, September 1998
- SELECTED RESEARCH ARTICLES 
104(1998); http://dx.doi.org/10.1121/1.424323View Description Hide Description
An analytical investigation is made of the compression wave generated when a high-speed train enters a long tunnel with distributed venting. The compression wave amplitude is determined by train speed and the area ratio of the train and tunnel, but its rise time depends principally on the geometry of the tunnel entrance. Vented tunnel entrance “hoods” are frequently used to increase the rise time, in order to reduce the impact of the micro-pressure pulse radiated from the tunnel exit when the compression wave arrives at the far end of the tunnel. Approximate calculations are performed to determine the initial rise time for a tunnel of rectangular cross section with a continuously variable vented roof near the entrance, for train Mach numbers less than about 0.2 (∼150 mph). The distribution of venting apertures can be optimized to maximize rise time, and a sixfold increase is shown to be possible when the aperture distribution decreases exponentially with distance into the tunnel. The method of this paper is applicable also to more general tunnel entrance geometries, and for higher train Mach numbers.
104(1998); http://dx.doi.org/10.1121/1.424324View Description Hide Description
In behavioral experiments where real targets are used to investigate dolphin echolocation, it is often very difficult to extract the relevant echo parameters that the animals use to discriminate or classify. The complex relationship between the physical dimensions and the reflection characteristic of real targets prevents separate control of various echo parameters of the stimuli presented in an echolocation experiment. A new echo simulation method presented in this paper avoids this problem. Dolphin echolocation sounds are transformed with the target impulse response into artificial echoes, which are played back to the animal. The phantom echo system is implemented on a digital signal processing board and gives an experimenter fully programmable control over the echo generating process and the echo structure itself. Echoes of several underwater targets were simulated to evaluate the quality of the method. A comparison of simulated echoes with the original echoes demonstrated very good agreement independent of the incident signal (cross-correlation coefficient ). The method has tremendous potential for investigating animal echolocation and understanding biosonarsignal processing.