Two-dimensional shape discrimination by sighted people using simulated virtual echoes.

In this study, a new research method using psychoacoustic experiments and acoustic simulations is proposed for human echolocation research. A shape discrimination experiment was conducted for sighted people using pitch-converted virtual echoes from targets of dissimilar two-dimensional (2D) shapes. These echoes were simulated using a three-dimensional acoustic simulation based on a finite-difference time-domain method from Bossy, Talmat, and Laugier [(2004). J. Acoust. Soc. Am. 115, 2314-2324]. The experimental and simulation results suggest that the echo timbre and pitch determined based on the sound interference may be effective acoustic cues for 2D shape discrimination. The newly developed research method may lead to more efficient future studies of human echolocation.

Bat-inspired signal design for target discrimination in human echolocation.

Echolocating bats exhibit sophisticated sonar behaviors using ultrasounds with actively adjusted acoustic characteristics (e.g., frequency and time-frequency structure) depending on the situation. In this study, the utility of ultrasound in human echolocation was examined. By listening to ultrasonic echoes with a shifted pitch to be audible, the participants (i.e., sighted echolocation novices) could discriminate the three-dimensional (3D) roundness of edge contours. This finding suggests that sounds with suitable wavelengths (i.e., ultrasounds) can provide useful information about 3D shapes. In addition, the shape, texture, and material discrimination experiments were conducted using ultrasonic echoes binaurally measured with a 1/7 scaled miniature dummy head. The acoustic and statistical analyses showed that intensity and timbre cues were useful for shape and texture discriminations, respectively. Furthermore, in the discrimination of objects with various features (e.g., acrylic board and artificial grass), the perceptual distances between objects were more dispersed when frequency-modulated sweep signals were used than when a constant-frequency signal was used. These suggest that suitable signal design, i.e., echolocation sounds employed by bats, allowed echolocation novices to discriminate the 3D shape and texture. This top-down approach using human subjects may be able to efficiently help interpret the sensory perception, "seeing by sound," in bat biosonar.

Temperature Distribution and Thermal Conductivity Measurements of Chirality-Assigned Single-Walled Carbon Nanotubes by Photoluminescence Imaging Spectroscopy.

It is expected that single-walled carbon nanotubes (SWCNTs) have high thermal conductivity along the tube axis and that the thermal conductivities depend on their structure, such as length, diameter, chirality (n, m), and so forth. Although many experimental measurements of the thermal conductivity have been reported, the SWCNT structure was not characterized sufficiently. In particular, the chirality was not assigned, and it was not confirmed whether SWCNT was isolated or not (bundled with multiplicate SWCNTs). Therefore, measured values widely vary (101 to 104 W/(m·K)) so far. Here, we measured the thermal conductivity of chirality-assigned SWCNTs, which were individually suspended, by using photoluminescence (PL) imaging spectroscopy. The temperature distribution along the tube axis was obtained, and the temperature dependence of the thermal conductivity was measured in a wide-temperature range (from 350 to 1000 K). For (9, 8) SWCNTs with 10-12 µm in length, the thermal conductivity was 1166 ± 243 W/(m·K) at 400 K. The proposed PL imaging spectroscopy enables to measure the thermal conductivity of SWCNTs with high precision and without any contacts, and it is an effective method in the temperature distribution measurements of nanomaterials.