In this paper the author describes a high sensitivity Doppler ultrasound system based on the principle of ensemble mean processing utilizing automatic gain optimization through system parameters. This technique allows a reduction of the physical size of the hardware and simplifies gain adjustment by reducing the gain range substantially. Such a system is not subject to Doppler ultrasound system artifacts such as the mirror effect and quantization.
In this paper, a method of calculating transient responses in a three-dimensional (3-D) sound field with constant geometry along the longitudinal direction is described. In the presented method, two-dimensional (2-D) solutions obtained from the finite-difference time-domain method are applied to the efficient calculation procedure to transform the 2-D solution into the 3-D solution proposed by Duhamel. In order to confirm the validity of the presented calculation method, the insertion loss of two types of barriers is analyzed and the calculation results are compared with experimental results obtained from a scale-model experiment.
Changes in vocal tract size vary the formant frequencies, even when the shape of vocal tracts is the same and the spoken vowels are categorized to be the same. Several studies have demonstrated that the normalization of vocal tract size can be achieved in a bottom-up manner. To investigate how fast this process works, the identification of vowel sequences was examined under conditions where the size was sinusoidally modulated with several frequencies (0.24–62.50 Hz). The performance level changed slightly, but significantly depending on the modulation frequency, and the dependence was not monotonic. The performance dropped for modulation around 4 Hz. The nonmonotonic function could not be predicted by a simple assumption of usage of a single size-estimator that requires a certain processing time. Mismatches were prominent for high frequencies: a deterioration was predicted because of the limited processing time, while the actual performance showed a recovery. This indicates that a switching of the process mode for modulation occurs at around 4 Hz. Below 4 Hz, the auditory system can successfully normalize the size change. Above 4 Hz, the auditory system segregates the sounds using the size cue and the recognition of each vowel is not critically affected.
There are several factors that affect human speaker recognition. In this study, two experiments were conducted in order to see the effects that the stimulus contents and the familiarity to the speakers give to the perception of the speakers. The results showed that: a) stimuli including a nasal were effective for accurate speaker identification; b) coronal nasals were more effective than the labial nasal, and c) the familiarity to the speakers gives a great influence on the performance. The tendencies a) and b) were observed both in familiar and unknown speaker identifications. The results of the acoustical analyses also showed that there were correspondences between the perception of the speaker identity and the cepstral distances among the speakers. The inter-speaker cepstral distances were greater in vowel intervals than in the consonant intervals; especially, notably they were greater in nasals than in orals in the consonant intervals.
A method for in situ estimation of the acoustic impedance of surfaces in interiors is introduced in this paper. The key difference with traditional in situ measurement techniques is the use of an inverse acoustic boundary framework which allows us to overcome some geometry constraints from previous methods (such as the planar-surface requirement and placement of microphone arrays). Furthermore, estimation of the acoustic impedance of not only one but all the surfaces is possible provided that local reaction is the predominant effect, and the following parameters are known: geometry of the surfaces, sound pressure at a number of arbitrary points in the interior field and the strength of the sound source. The estimation of the acoustic impedance at each surface is achieved by the solution of an optimization problem formulated from the linear equations of the boundary element method (BEM) applied to the discretized interior boundaries of an interior space. Previous work on similar methods have reported examples with numerical simulations. The work in this paper goes further and numerical examples together with results obtained with experimental data are presented.
A questionnaire survey and interviews were conducted among victims of the Mid-Niigata Earthquake from Yamakoshi village to elucidate the problems related to the living environment and the stressful experiences encountered by them in the temporary shelters. In this study we aim to clarify the relationships between environmental problems, including acoustic environment problems, and stressful experiences encountered in the temporary shelters, and we examine the impact of the acoustic environment of the temporary shelters on evacuee stress. Among the environmental problems (living space, temperature, illumination, acoustic environment, odor, and problems related to the shelter facilities and to maintaining privacy), the acoustic environment was the fifth most frequently cited environmental problem. However, a higher proportion of the participants who complained about the acoustic environment of the temporary shelters had stressful experiences than those who did not complain about the acoustic environment. These relationships were shown to be statistically significant by chi-square tests. It was found by logistic regression analyses that among the living environment problems, the acoustic environment was the most important factor in determining whether refugees found living conditions unpleasant and/or experienced stress. These results suggest that improvements to the acoustic environment of temporary shelters should lead to the mitigation of some evacuee stress.
Various tissue displacement vector measurement methods have been proposed by us, i.e., the multidimensional cross-spectrum phase gradient method (MCSPGM), the multidimensional autocorrelation method (MAM) and the multidimensional Doppler method (MDM). In this paper, actual measurement results obtained by MAM and MDM are reported. Specifically, for a compressed agar-graphite phantom (infinitesimally compressed, ≈0.07%; largely compressed, ≈0.7%), the measurement results for axial strain using MAM and MDM are shown and compared with those using MCSPGM, the conventional one-dimensional (1D) AM and the direct strain measurement method based on 1D AM (DSMM). Although DSMM was also developed by us in 1993, the method and the actual measurement results have not been reported elsewhere. Because the multidimensional methods can provide more accurate axial displacement measurements in real time and enable displacement vector measurement, 1D AM and DSMM might now be ineffective for practical applications.
Two-dimensional (2D) shear modulus reconstructions are performed on an agar phantom using our previously developed ultrasound lateral Gaussian envelope cosine modulation method (LGECMM) together with multidimensional displacement vector measurement methods, i.e., the multidimensional cross-spectrum phase gradient method (MCSPGM), the multidimensional autocorrelation method (MAM) and the multidimensional Doppler method (MDM). The accuracies of the obtained 2D reconstructions are compared with each other in addition to those of 1D reconstructions obtained from the respective ratios of lateral and axial strains.