Volume 6, Issue 2, April 2005
6(2005); http://dx.doi.org/10.1121/1.1855351View Description Hide Description
Micrometeorite hits can create air leaks in manned spacecraft. Leak-generated-guided ultrasonic waves can be monitored within the platelike spacecraft skin to detect and locate leaks. Cross-correlation techniques allow measurement of the deterministic behavior of the leak-generated noise. Measured leak-into-vacuum cross-correlations of noise signals from two adjacent transducers are recorded as the transducer pair is rotated to determine the relative phase delay as a function of rotation angle. The direction to the leak is found from the variation of phase with angle or from synthetic aperture analysis. The leak is then located through triangulation from two or more sensor-pair locations.
6(2005); http://dx.doi.org/10.1121/1.1839611View Description Hide Description
Simultaneous measurements of the surface gravity wave field and the generated acoustic spectra were made in a sandy beached wave tank. A video camera captured the evolution of the breaking waves.Generated acoustic power levels as a function of the wave crest slope and frequency are presented. An empirical model relating the acoustic energy to the measuredwave crest slope for different surface wave frequencies is developed based on a linear regression. It is determined that the wave crest slope is a good predictor of generated acoustic energies. [Work supported by ONR base funding at NRL.]
Visualizing acoustic displacements of capacitive micromachined transducers using an interferometric microscope6(2005); http://dx.doi.org/10.1121/1.1851391View Description Hide Description
The modification of a commercial Wyko optical profilometer to operate stroboscopically has been demonstrated. This has then been applied to the characterization of a micro-mechanical device subjected to high frequency periodic excitation. It is demonstrated that displacement amplitudes can be mapped across the surface of a micromachined transducer at ultrasonic frequencies.
6(2005); http://dx.doi.org/10.1121/1.1850952View Description Hide Description
Functional data analysis is used to examine articulatory variability across repetitions in normal speech, under different movement constraints. A temporal normalization technique is applied to align trajectories of lips, jaw, and tongue in vowel-consonant-vowel sequences. Next, an index of amplitude variability is computed, defined as the mean standard deviation between peak velocities of the consonantal closure by the active articulator, in each VCV sequence. The results show that articulatory variability varies as a function of both the phonetic requirements of the consonant and the biomechanicalcharacteristics of the articulatory structures involved.
6(2005); http://dx.doi.org/10.1121/1.1850951View Description Hide Description
When Hurricane Juan made landfall in Nova Scotia, Canada in September 2003, meteorological and acoustical measurements were made independently. The meteorological data yielded surface wind speeds and directions while wind gust frequencies and noise from damage events were extracted from the acoustical data. By establishing a timeline for damage-related noise using acoustics, greater insight into when and how damage occurred near the audio recording site became possible. Examples of wind-induced damage to local maple and spruce trees are used to illustrate the value of acoustics in high-wind storm events like hurricanes.
Use of acoustic prior information for confidence measure in ASR (automatic speech recognition) applications6(2005); http://dx.doi.org/10.1121/1.1843171View Description Hide Description
In this paper, a new acoustic confidence measure of automatic speech recognition hypothesis is proposed and it is compared to approaches proposed in the literature. This approach takes into account prior information on the acoustic model performance specific to each phoneme. The new method is tested on two types of recognition errors: the out-of-vocabulary words and the errors due to additive noise. An efficient way to interpret the raw confidence measure as a correctness prior probability is also proposed in the paper.
6(2005); http://dx.doi.org/10.1121/1.1861092View Description Hide Description
The theory of wave propagation and scattering in cracked media is applied to study the wave attenuations in an isotropic solid medium containing perfectly aligned penny-shaped microcracks. The unit normals of all cracks are assumed parallel to a given direction. The wave scattering model is formulated using an anisotropic Green’s dyadic approach. Explicit expressions are derived for attenuations of the three wave modes in terms of the microcrack density. Numerical results are presented and discussed. In particular, comparisons of the attenuation results presented in this letter with previous results for the Rayleigh limit are given.