Volume 118, Issue 1, July 2005
Index of content:
- BIOACOUSTICS 
Measurements of the anisotropy of ultrasonic velocity in freshly excised and formalin-fixed myocardial tissue118(2005); http://dx.doi.org/10.1121/1.1925947View Description Hide Description
The objective of this study was to quantify the anisotropy of ultrasonic velocity in freshly excised myocardial tissue and to examine the effects of formalin-fixation. Through-transmission radio-frequency-based measurements were performed on ovine and bovine myocardial specimens from 24 different hearts. A total of 81 specimens were obtained from specific locations within each heart to investigate the possibility of regional differences in anisotropy of velocity in the left ventricular wall and septum. No regional differences were observed for either lamb or cow myocardial specimens. In addition, no specific species-dependent differences were observed between ovine and bovine myocardium. Average values of velocity at room temperature for perpendicular and parallel insonification were and ( error), respectively, for bovine myocardium and and for ovine myocardium . Immediately after measurements of freshly excised myocardium, ovine specimens were fixed in formalin for at least one month and then measurements were repeated. Formalin-fixation appears to increase the overall velocity at all angles of insonification and to increase the magnitude of anisotropy of velocity.
Characterizing noise in nonhuman vocalizations: Acoustic analysis and human perception of barks by coyotes and dogs118(2005); http://dx.doi.org/10.1121/1.1928748View Description Hide Description
Measuringnoise as a component of mammalian vocalizations is of interest because of its potential relevance to the communicative function. However, methods for characterizing and quantifying noise are less well established than methods applicable to harmonically structured aspects of signals. Using barks of coyotes and domestic dogs, we compared six acoustic measures and studied how they are related to human perception of noisiness. Measures of harmonic-to-noise-ratio (HNR), percent voicing, and shimmer were found to be the best predictors of perceptual rating by human listeners. Both acoustics and perception indicated that noisiness was similar across coyote and dog barks, but within each species there was significant variation among the individual vocalizers. The advantages and disadvantages of the various measures are discussed.
118(2005); http://dx.doi.org/10.1121/1.1937283View Description Hide Description
Analysis of the usual click rates of sperm whales (Physeter macrocephalus) at Kaikoura, New Zealand, confirms the potential for assessing abundance via “click counting.” Usual click rates over three dive cycles each of three photographically identified whales showed that averages of usual click rate did not differ significantly within dives, among dives of the same whale or among whales. Over the nine dives ( clicks) mean usual click rate was (95% ). On average, individual sperm whales at Kaikoura spent 60% of their time usual clicking in winter and in summer. There was no evidence that whale identity or stage of the dive recorded affects significantly the percentage of time spent usual clicking. Differences in vocal behavior among sperm whale populations worldwide indicate that estimates of abundance that are based on click rates need to based on data from the population of interest, rather than from another population or some global average.
118(2005); http://dx.doi.org/10.1121/1.1932227View Description Hide Description
Many insects produce sounds during flight. These acoustic emissions result from the oscillation of the wings in air. To date, most studies have measured the frequency characteristics of flight sounds, leaving other acoustic characteristics—and their possible biological functions—unexplored. Here, using close-range acoustic recording, we describe both the directional radiation pattern and the detailed frequency composition of the sound produced by a tethered flying (Lucilia sericata). The flapping wings produce a sound wave consisting of a series of harmonics, the first harmonic occurring around . In the horizontal plane of the fly, the first harmonic shows a dipolelike amplitude distribution whereas the second harmonic shows a monopolelike radiation pattern. The first frequency component is dominant in front of the fly while the second harmonic is dominant at the sides. Sound with a broad frequency content, typical of that produced by wind, is also recorded at the back of the fly. This sound qualifies as pseudo-sound and results from the vortices generated during wing kinematics. Frequency and amplitude features may be used by flies in different behavioral contexts such as sexual communication, competitive communication, or navigation within the environment.
Characterization of ultrasound contrast microbubbles using in vitro experiments and viscous and viscoelastic interface models for encapsulation118(2005); http://dx.doi.org/10.1121/1.1923367View Description Hide Description
Zero-thickness interface models are developed to describe the encapsulation of microbubble contrast agents. Two different rheological models of the interface, Newtonian (viscous) and viscoelastic, with rheological parameters such as surface tension,surface dilatational viscosity, and surface dilatational elasticity are presented to characterize the encapsulation. The models are applied to characterize a widely used microbubble based ultrasound contrast agent. Attenuation of ultrasound passing through a solution of contrast agent is measured. The model parameters for the contrast agent are determined by matching the linearized modeldynamics with measured attenuation data. The models are investigated for its ability to match with other experiments. Specifically, model predictions are compared with scattered fundamental and subharmonic responses. Experiments and model prediction results are discussed along with those obtained using an existing model [Church, J. Acoust. Soc. Am.97, 1510 (1995) and Hoff et al., J. Acoust. Soc. Am.107, 2272 (2000)] of contrast agents.