Volume 107, Issue 5, May 2000
Index of content:
- BIOACOUSTICS 
Optimization of a low-frequency ultrasonic technique to monitor the change in physical states in viscoelastic media: Gelation process107(2000); http://dx.doi.org/10.1121/1.428659View Description Hide Description
A new low-frequency ultrasonic device (50–100 kHz) in highly sharpened end sensors that behave as point sources were examined. The application of this new ultrasonic technique with two sensors coupled in the near field is to explore the relations between the physical properties measured through the evolution of the wavetime of flight and structural changes during gel formation which is related to two factors: the ambient temperature and the mechanical resistance of the medium. The network evolution was interpreted by an approach based on the Flory model. The physical significance of this model was shown through a series of experiments using a low-frequency ultrasonic technique. Response curves demonstrate the different stages during gel formation.
107(2000); http://dx.doi.org/10.1121/1.428660View Description Hide Description
Previous attempts at localizing cetaceans have generally used multiple hydrophone arrays and multichannel recording systems. In this paper, a low-budget localization technique using only one hydrophone is described. The time delays of the signals traveling via the surface and bottom reflection paths to the hydrophone, relative to the direct signal, are used to calculate the distance and the depth of a phonating animal. Only two additional measures, the depth of the bottom and hydrophone, have to be taken. The method requires relatively shallow waters and a flat bottom surface. Echolocating and burst pulsing Hawaiian spinner dolphins (Stenella longirostris) at the Waianae coast of Oahu, Hawaii, were localized over different bottom substrates. A tracking range of up to 100 m was achieved. The accuracy of the method is estimated by the total error differential technique. The relative distance estimation error is below 35% and the absolute depth error below 0.7 m, so that the location method is sufficiently precise for examining source levels in our study area. Because of its simplicity, the method ideally complements sound recordings and visual sightings of marine mammals and could lead to a better understanding of the nature and use of click trains by dolphins.
Classification of electronically generated phantom targets by an Atlantic bottlenose dolphin (Tursiops truncatus)107(2000); http://dx.doi.org/10.1121/1.428661View Description Hide Description
Animal behavior experiments require not only stimulus control of the animal’s behavior, but also precise control of the stimulus itself. In discrimination experiments with real target presentation, the complex interdependence between the physical dimensions and the backscattering process of an object make it difficult to extract and control relevant echo parameters separately. In other phantom-echo experiments, the echoes were relatively simple and could only simulate certain properties of targets. The echo-simulation method utilized in this paper can be used to transform any animal echolocation sound into phantom echoes of high fidelity and complexity. The developed 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. In this experiment, the capability of a dolphin to discriminate between acoustically simulated phantom replicas of targets and their real equivalents was tested. Phantom replicas were presented in a probe technique during a materials discrimination experiment. The animal accepted the phantom echoes and classified them in the same manner as it classified real targets.