Vietnamese speakers' mispronunciations of Japanese singleton and geminate stops were identified using the category boundary of the stops pronounced by native Japanese speakers. To clarify the characteristics of the Vietnamese speakers' mispronunciations, their speech segment durations were analyzed. In comparison with native Japanese speakers' correct pronunciations, Vietnamese speakers mispronounced a singleton stop with a longer closure and a shorter preceding consonant-vowel segment, whereas they mispronounced a geminate stop with a shorter closure and a longer following consonant-vowel segment. These results were consistent with the findings of Korean, Taiwanese Mandarin, and Thai speakers in previous studies, suggesting that non-native speakers may have a common tendency to have inadequate durations of closure and anteroposterior consonant-vowel segments in mispronunciations of Japanese singleton and geminate stops.

Inorganic fiber-based porous materials, such as glass and rock wool, are cost-effective, light weight, and currently make up the most commonly used sound-absorbing materials. However, the performance of these materials degrades owing to moisture, weather, and gravity. Porous materials have difficulty absorbing low-frequency sounds. In these cases, resonator-type sound-absorbers are used, but the target frequency is narrow. Thus, a novel sound-absorbing material that solves these issues is desired. Recently, the advancement of additive manufacturing enabled the realization of complex structures, and artificial acoustic materials have attracted significant attention. This study conducted numerical, theoretical, and experimental investigations to develop novel sound-absorbing materials with desired sound absorption properties based on a flexible situation. These materials also address aforementioned problems in conventional inorganic porous materials and resonators. Results suggest that the periodic structures based on resonators and their combination are good sound-absorbers for low- and middle-frequency ranges, exploiting the properties of each structure.

The integrity evaluation of the rotor wedges of turbine generators is discussed by observing the mechanical resonant frequency shift originating from cracks. We propose a simple method of obtaining the frequency response of the inspection target using point contact piezoelectric sensors and a network analyzer. Eigenmodes are identified in both experiments and finite element analysis, and frequency responses are compared. Several resonant frequencies shift to the lower side owing to the stiffness decrease caused by the crack, and the validity and effectiveness of the method are discussed. From both measurements and finite element analysis (FEA), the modes where the crack is located in the high-stress region have a more significant shift than the mode that does not. The shift was correlated between the FEA and measurement throughout most of the modes.

Intense ultrasonic beams suffer progressive waveform distortion due to the nonlinearity of the air, causing numerous harmonics to be generated in the beam. Since these harmonic pressures can be theoretically predicted with sufficient accuracy by the Khokhlov-Zabolotskaya-Kuznetsov model, it is possible to obtain the pressure sensitivity of a microphone at high frequencies. To generate intense ultrasonic waves, a planar aperture source of 118 mm in diameter and with resonant frequencies of 40 and 63 kHz was used. A specialized microphone developed and tested for receiving high-frequency ultrasonic waves was fabricated from a single cellular polypropylene (CPP) sheet of 50 μm in thickness and of a sensing area approximately 13 mm². Using at least the first nine harmonics, i.e., those in the range of 40 to 567 kHz, it was demonstrated in this study that the frequency response of the CPP microphone has a sensitivity of −70 to −80 dB re. 1 V/Pa at frequencies below 400 kHz.