Volume 6, Issue 1, January 2005
Index of content:
6(2005); http://dx.doi.org/10.1121/1.1809151View Description Hide Description
Calibrated echo-sounder surveys were conducted on the backscatter from turbulent microstructure within internal lee-waves at a sill in Knight Inlet, B.C. Volumetric scatter strengths in the range to were observed within narrow (1 to 10 m thick) layers at three frequencies (38, 120, and 200 kHz). The observed acoustic scattering levels were in reasonable agreement with published models for microstructure scattering. A new volumetric multi-beam sonar was used to image the spatial structure of the turbulent billows.
6(2005); http://dx.doi.org/10.1121/1.1809152View Description Hide Description
Recently, a new paradigm for processing sounds for cochlear implants has been described that aims to normalize loudness for complex signals, relative to normal acoustic loudness perception [McDermott et al., J. Acoust. Soc. Am. 114, 2190–2197 (2003)]. A first implementation of a sound processor based on this paradigm, called SpeL, has been evaluated with speech perception tests conducted in quiet and in noise. For the five participating subjects, the average scores from these tests for SpeL were very close to those for the conventional ACE scheme. However, audibility was improved by about 5 dB for SpeL compared with ACE.
6(2005); http://dx.doi.org/10.1121/1.1815253View Description Hide Description
Vortex shedding that occurs in ducts with baffles in the presence of mean flow often leads to excitation of acoustic modes. Resulting flow oscillations may feed back to the process of vortex formation. A simple model is proposed for describing this complex interaction using the hypotheses for a quasi-steadiness of vortex shedding and for a short-period acoustic perturbation at the moment of vortex collision with a downstream baffle. The model is capable of predicting typical real-system phenomena, such as the lock-in of a dominant frequency of the vortex-acoustic instability in some ranges of the mean flowvelocity.
6(2005); http://dx.doi.org/10.1121/1.1815040View Description Hide Description
The AQUAmark 200® device is used to reduce the incidental by-catch of small cetaceans in fishing gear. Little information is known about the signal features of this system despite the fact that such knowledge is important to evaluate its efficiency. The AQUAmark 200 device emits eight different signals composed of one fundamental and several others harmonics with energy in the 5-160 kHz band. The mathematical equation of the temporal evolution of the frequency of each signal has been determined by the authors, and the resulting function has been used to build the six nonconstant evolutions.
6(2005); http://dx.doi.org/10.1121/1.1815039View Description Hide Description
Substantial enhancement of recombinant tissue plasminogen activator (rt-PA) thrombolysis can be achieved with ultrasound, suggesting its use as an adjunctive treatment in thrombolytic therapy for stroke. A microscopic visualization method was used to measure the lysis of human whole-blood clots treated with human fresh frozen plasma (HFFP), rt-PA, and 120-kHz ultrasound for 30 min at The clot–plasma interface was imaged using an inverted optical microscope and the thrombolytic front analyzed as a function of time. Ultrasoundtreatment significantly enhanced the mean lytic rate from 0.5 to 3.4 μm/min (a 580% change) compared with rt-PA treatment alone.
6(2005); http://dx.doi.org/10.1121/1.1815252View Description Hide Description
Holography is potentially the most powerful method for high spatial resolution real time 3D ultrasound imaging and diagnostics. Although versions of ultrasoundholography have existed since the 1970s, they use laser reconstruction, thus losing 3-D resolution. By using transmissive ultrasound with a scanning needle hydrophone, full 3D holographicimaging is proved to be possible, if both amplitude and time delay phase information can be obtained.
Similarity of spectral resolvability in chinchillas and human listeners based on phase discrimination6(2005); http://dx.doi.org/10.1121/1.1815251View Description Hide Description
Phase discrimination was measured in a “go/no-go” behavioral task for chinchillas and human listeners in order to compare spectral resolvability between the two groups. Tone complexes comprised a 250-Hz fundamental frequency with consecutive higher harmonics, and subjects discriminated the cosine-phase complex from a random-phase complex. Values of increased as increased and were similar between chinchillas and human listeners. Values of the criterion for each condition were also similar between chinchillas and humans. The results suggest that spectral resolvability is likely to be similar for the two groups.
6(2005); http://dx.doi.org/10.1121/1.1815244View Description Hide Description
This paper proposes a scheme for transmitting or storing a wideband version of voice (up to 7 kHz) in a narrowband channel or medium (up to 3.4 kHz) with a low resolution data format. The scheme is fully backward compatible; a conventional receiver, without any decoding mechanism, can still access a narrowband version of the wideband voice. The proposed scheme can be applied where a high quality wideband voice is needed but the physical capacity is limited. Examples are voice-over-IP, digital private branch exchange, as well as storage and playback. An audio demonstration is given in the paper.
6(2005); http://dx.doi.org/10.1121/1.1827811View Description Hide Description
The emission of light flashes from sound driven bubbles in ethylene glycol at 20–23 °C has been temporally stabilized. The intensity of the light flashes is approximately twice that of SBSL in degassed water at 20 °C. The time jitter is less than 100 ns and the flashes spatially jitter less than 2 mm around stable positions near the pressure antinode of the second harmonic. The light flashes trace out periodic, continuous orbits within this small region. Sonoluminescence in ethylene glycol is relatively stable with temporally stabilized SBSL bubbles lasting up to 60 min.
6(2005); http://dx.doi.org/10.1121/1.1815074View Description Hide Description
In medical and other important applications, it is desirable to achieve transmissive ultrasonic3D imaging in “real time.” Until now, transmissive ultrasonicimages have been possible, but either in real time 2D or relatively slow 3D. By using an ultrasonic stereo camera and a real time viewing system, live and interactive 3D transmissive ultrasonicimages have been produced. Fast transmissive ultrasoundtomography has been achieved by using a single ultrasoniccamera. Some advantages and applications are discussed.
6(2005); http://dx.doi.org/10.1121/1.1828106View Description Hide Description
A new method of measuring the adhesion strength of thin films to their substrates is reported. The method is based on an analogy with the common tensile test of materials. This is an acoustic method that uses acoustic microcavitation to bring about controlled erosion of the thin film. Based on the insonification pressure and the time to complete erosion the adhesion strength is assessed. The measurements correctly rank order a set of thin film samples of known adhesion strengths.