Yoshiaki Fukuda

Loudspeaker diaphragm made of a molded, sintered ceramic body

A loudspeaker diaphragm comprising a molded, sintered ceramic body is described. The body is made of ceramic crystalline particles whose maximum size is below 1/5 time a thickness of the body which is in the form of a dome or cone. The dome- or cone-shaped diaphragm may have a flange along an opening side thereof in order to prevent deformation as may occur during firing.

Diving Behavior of Sei Whales Balaenoptera borealis Relative to the Vertical Distribution of Their Potential Prey

Abstract. In this study, we investigated the diving behavior of sei whales relative to the vertical distribution of their potential prey in the western North Pacific during the summer of 2013. Acoustic time-depth transmitters were attached to two sei whales for 10.2 and 32.0 h, respectively. The vertical distribution and density (expressed as the volume backscattering strength, SV) of their potential prey were recorded by an echosounder. Diving behavior was classified into two shapes: U-shaped and V-shaped. For both individuals, U-shaped diving was associated with higher SV values than V-shaped diving and the frequency of U-shaped diving increased from late afternoon until sunset. During the daytime, dense scattering layers (presumably zooplankton) were distributed at approximately 40 m and they then migrated toward the surface around sunset. The diving depth of the whales followed the diel migration of the scattering layers and the diving was concentrated in these layers when the density became high. The results of this study indicate that sei whales change their diving depth and shapes in response to the diel vertical migration of their potential prey.

Comparison of zooplankton density estimated by acoustic inversion method and net sampling

A multi-frequency acoustic zooplankton fish profiler (AZFP, ASL Environmental Sciences) with temperature-salinity and depth sensor was moored at 10 m from the bottom (ca. 30 m) at the mouth of Yamada Bay in Iwate Prefecture, Japan, from 14 January to 16 June 2015 in order to measure volume backscattering strength profiles from the transducer surface to the water surface at four frequencies (125, 200, 455, and 769 kHz). Zooplankton density by size was estimated from the measured volume backscattering strength at four frequencies by the inversion method. Monitoring period was selected to cover the period when juvenile salmon stay in the bay before leaving for oceans. Zooplankton sampling was conducted periodically (once a week or two weeks, day and night) using a Kitahara Net (30 cm dia., 335 µm mesh) and a Norpac Net (45 cm dia., 335 µm mesh) at near the moored position. These observations revealed that large zooplankton, which juvenile salmon prefers, arrived with the Oyashio Current, and the zooplankton ...