Hiroshi Yoshida

Valuable seabed mineral resources such as rare earth elements are deposited 2–3 meters into the deep sea floor, and sampling and analyzing the seafloor is necessary to clarify how they are generated and distributed. The current general sampling method based on vertical drilling effectively acquires the geological profile in the vertical direction. However, it is inefficient for investigating deposits widely distributed in the horizontal direction because the sampling range is limited to the diameter of the pipe. We are developing a seafloor robotic explorer that can excavate horizontally and collect samples of rare earth elements, which may enable wide-area exploration as multiple robots could be simultaneously implemented to autonomously search beneath the seabed. The excavation depth of our previously reported underwater drilling robot SEAVO II was limited to 430 mm; the discharging outlet became buried in the ground, making it difficult to discharge the drilled soil and ultimately limiting the excavation depth. In this work, we introduce a discharging mechanism that implements water jetting to improve the excavation depth.

We report a novel approach to slow the translocation of single-stranded DNA (ssDNA) by employing polyethylene oxide (PEO) filled nano-cylindrical domains as transportation channels. DNA strands were demonstrated to electrophoretically translocate through PEO filled cylindrical domains with diameters of 2 and 9 nm, which were self-assembled by amphiphilic liquid crystalline block copolymers. The average translocation rate of ssDNA strands was effectively reduced to an order of 10 μs per nucleotide, which was 1–2 orders slower than that attained by utilizing conventional solid-state nanopore devices.

An underwater laser ranging system to capture microscopic fluctuations in relative plate motion around subduction zone has been developed since 2010. We believe that direct detection of the fluctuations resulted from plate motion suggests the degree of interplate mechanical instability for long-term prediction of oceanic intraplate earthquake. In April 2011, sea trial using the first prototype was carried out in shallow water zone in Okinawa. Distance measurements could be performed in the distance of 10 meters but results included large error variation of 0–10 cm. To improve measurement resolution and accuracy of the sub-millimeter fluctuations, we have developed the second prototype of laser ranging system based on the first one. The main part of the system consists of a transmitting unit (Tx) and a receiving unit (Rx). One of the units is composed of a transparent acrylic cylindrical pressure hull (PH), a main PH, a battery pack, and sensors, which are installed on an aluminum alloy frame. The transparent PH of Tx is equipped with a 1 Watt semiconductor blue laser, a modulator and a driver which are set on a horizontal turntable with elevation adjustment. Its Rx has an avalanche photo diode as detector and a demodulator on a same type turntable. A controller and an optical communication device are installed in each main PH. The Tx is connected with the Rx via thin optical glass fiber to transmit reference signal. We carried out a sea-trial in Okinawa by the second prototype in February 2014. We received optical signal at distance between the Tx and the Rx of up to 20 meters. The ranging was performed at 10 meters and measurement raw data errors were within a range of millimeters. On the other hand, automatic optical alignment at 20 meters was completely failed. These results show that measurement accuracy is closer to a goal but system completion is away from the goal. We need review not only the algorithm but also optical hardware of the alignment.

Japan Agency for Marine – Earth Science and Technology (JAMSTEC) has been recently advanced the development of several underwater vehicles for the survey of mineral resources buried under Japan’s territorial sea. One of them is Yumeiruka. It has characteristic canard wings and rudders which are attached on its fore and rear parts. Since they cause good maneuverability, good survey results using acoustic observation devices can be obtained. And it has a high performance compact inertial navigation system which was developed as Japan’s first INS for an underwater vehicle by the cooperation between JAMSTEC and a Japanese manufacture. Yumeiruka has now conducted sea trials in order to improve its performance and functionality.

Chemical epitaxy with a density multiplication process was applied to the perpendicularly oriented hexagonal cylinder nanostructure of liquid crystalline block copolymer (PEO-b-PMA(Az)) thin film through thermally induced microphase separation by using a newly designed PMA(Az)₂₄ brush. The hexagonal lattice orientation with 1.9 tera-cylinders per inch² was laterally controlled for long-range-ordered direct self-assembly. Furthermore, the direct pattern-transfer of the assembled structure to an Au nanodot array was demonstrated by doping of HAuCl₄ selectively into the PEO cylindrical microdomains and then vacuum ultraviolet light irradiation to cause polymer etching and reduction of the Au ions.