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Echoes from Providence
the cooler was studied in order to determine its effects on the cooling power and to minimize its effects by modifying the cooler geometry. The streaming effect deals with acoustical- ly stimulated gas flow within the cooler which transfers heat to its cold parts; this is due to acoustically stimulated viscous losses with the cooler walls and with the stack which causes forced connection .
As a result of this study dealing with higher acoustic intensity levels we show that an optimized high frequency thermoacoustic cooler can reach cooling power density levels of a few hundred watts per square centimeter, with applica- tions to laser cooling, electronic cooling, and other applica- tions needing thermal management.
This work is funded by The Office of Naval Research.
This article is based on paper 4pPA11 presented at the 151st ASA meeting in Providence.
Husam El-Gendy, Laurence Lyard, and Orest Symko.
CLASSIFYING KILLER WHALE VOCALIZATION USING TIME WARPING
Judith C. Brown
Physics Department, Wellesley College Wellesley, Massachusetts 02481 and
Media Laboratory, Massachusetts Institute of Technology Cambridge Massachusetts 02139
Patrick J. O. Miller
Sea Mammal Research Unit, University of St. Andrews St. Andrews, Fife KY16 9QQ, UK
frequency tracking” in the speech literature. This measure gives rise to a pitch contour which is equivalent to the melodic line of a song (see Fig. 2).
Killer whales produce a number of highly stereo-
Fig. 1 Recording killer whale sounds.
Introduction and background
Marine mammals produce a wide range of vocaliza- tions; therefore an improved ability to classify recorded sounds could aid in species identification as well as in tracking movements of animal groups. Killer whales pro- duce three forms of vocalizations: clicks, whistles, and pulsed calls. Clicks consist of an impulse train (series of broadband pulses); whistles consist, for the most part, of a single sinusoid with varying frequency; and pulsed calls are more complex sounds with many harmonics. The rep- etition rate is a measure of the periodicity of the signal, and its measurement is called “pitch tracking” or “fundamental
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Fig. 2. Spectrogram showing pitch contours of the low frequency and high fre- quency sources in one killer whale pulsed call. Note there is noise before and after the onset of the calls.
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