Singing behavior of fin whales in the Davis Strait with implications for mating, migration and foraging

Most baleen whales undertake migrations between low-latitude breeding grounds and high-latitude feeding grounds. Though little is known about the timing of their migration from the Arctic, fin whales are assumed to undertake a similar migratory pattern. To address questions about habitat use and migrations, the acoustic activity of fin whales in Davis Strait, between Greenland and Canada, was monitored continuously for two years using three bottom-moored acoustic recorders. The acoustic power in the fin whale call frequencies peaked in November-December, showing that fin whales are present in Davis Strait much later in the year than previously expected. The closely timed peaks in song activity and conception time imply that not all fin whales migrate south to mate, but rather start mating at high latitudes rather than or before migrating. Singing activity was strongly linked to daylight hours, suggesting that fin whales might feed during the few daylight hours of the late fall and early Arctic winter. A negative correlation between the advancing sea ice front and power in fin whale frequencies indicates that future changes in sea ice conditions from global warming might change the distribution and migratory patterns of fin whales near the poles.     

Anisotropy of ultrasonic backscatter and attenuation from human calcaneus: implications for relative roles of absorption and scattering in determining attenuation

Although bone sonometry has been demonstrated to be useful in the diagnosis of osteoporosis, much remains to be learned about the processes governing the interactions between ultrasound and bone. In order to investigate these processes, ultrasonic attenuation and backscatter in two orientations were measured in 43 human calcaneal specimens in vitro at 500 kHz. In the mediolateral (ML) orientation, the ultrasound propagation direction is approximately perpendicular to the trabecular axes. In the anteroposterior (AP) orientation, a wide range of angles between the ultrasound propagation direction and trabecular axes is encountered. Average attenuation slope was 18% greater while average backscatter coefficient was 50% lower in the AP orientation compared with the ML orientation. Backscatter coefficient in both orientations approximately conformed to a cubic dependence on frequency, consistent with a previously reported model. These results support the idea that absorption is a greater component of attenuation than scattering in human calcaneal trabecular bone.     

A unified approach for predicting sound radiation from baffled rectangular plates with arbitrary boundary conditions

This paper discusses sound radiation from a baffled rectangular plate with each of its edges arbitrarily supported in the form of elastic restraints. The plate displacement function is universally expressed as a 2-D Fourier cosine series supplemented by several 1-D series. The unknown Fourier expansion coefficients are then determined by using the Rayleigh-Ritz procedure. Once the vibration field is solved, the displacement function is further simplified to a single standard 2-D Fourier cosine series in the subsequent acoustic analysis. Thus, the sound radiation from a rectangular plate can always be obtained from the radiation resistance matrix for an invariant set of cosine functions, regardless of its actual dimensions and boundary conditions. Further, this radiation resistance matrix, unlike the traditional ones for modal functions, only needs to be calculated once for all plates with the same aspect ratio. In order to determine the radiation resistance matrix effectively, an analytical formula is derived in the form of a power series of the non-dimensional acoustic wavenumber; the formula is mathematically valid and accurate for any wavenumber. Several numerical examples are presented to validate the formulations and show the effect of the boundary conditions on the radiation behavior of planar sources.     

Subjective loudness of simulated quarry blast waves, with implications for the transition from impulsive to continuous sound.

The tradeoff between amplitude and duration for equal loudness was explored for idealized quarry blast waves. An extended low-frequency response loudspeaker-driven simulation booth was employed with computer-generated imput test signals. In place of actual irregular blast waves, the simulated signatures were composed of sequences of identical shock-decay impulses of 25 ms duration and 0.2 ms rise time. Sequences of 1--16 impulses yielded overall durations of 25--400 ms. At the short durations the loudness was found to increase 2 dB for each doubling of duration; above 100 ms the increase was progressively lower, approaching as an asymptote the level for continuous sound. The results were compared with theoretical predictions: for this purpose the spectral method of Johnson and Robinson, well varified in our earlier studies of sonic boom impulses, was used. The shorter quarry blast judgments (T less than or equal to 100 ms) were found to be in very good agreement in terms of relative loudness levels. With an ad hoc--but physically plausible--modification (including adjustment of the critical integration time of the ear) the predictive method was extended to encompass the long duration signals as well. Thus the applicability of the method has been demonstrated for other types of transient sounds than the N wave; and the extension of the method tentatively appears to bridge the range between impulsive and continuous sounds of similar spectral content.