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The safe decommissioning as well as decontamination of the radioactive waste resulting from the nuclear accident in Fukushima Daiichi represents a huge task for the next decade. At present, research and development on long-term safe storage containers has become an urgent task with international cooperation in Japan. One challenge is the generation of hydrogen and oxygen in significant amounts by means of radiolysis inside the containers, as the nuclear waste contains a large portion of sea water. The generation of radiolysis gases may lead to a significant pressure build-up inside the containers and to the formation of flammable gases with the risk of ignition and the loss of integrity. In the framework of the project “R&D on technology for reducing concentration of flammable gases generated in long-term waste storage containers” funded by the Japanese Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), the potential application of catalytic recombiner devices inside the storage containers is investigated. In this context, a suitable catalyst based on the so-called intelligent automotive catalyst for use in a recombiner is under consideration. The catalyst is originally developed and mass-produced for automotive exhaust gas purification, and is characterized by having a self-healing function of precious metals (Pd, Pt and Rh) dissolved as a solid solution in the perovskite type oxides. The basic features of this catalyst have been tested in an experimental program. The test series in the REKO-4 facility has revealed the basic characteristics of the catalyst required for designing the recombiner system.

Copper is expected to have many applications due to its virus inactivation properties, but it has been difficult to produce a thin layer with high bonding strength. A multi-beam blue diode laser installed laser metal deposition (B-LMD) system was newly developed with a laser intensity of 4.7 × 105 W/cm2, which is improved about five times higher than that of conventional systems. Using this system, we demonstrated the high-speed formation of a pure copper layer on a stainless steel type 304 (SS304) circular tube. A pure copper powder and the blue diode lasers were simultaneously supplied to a SS304 circular tube, and the powder was melted and solidified to form a pure copper layer on it. As the result, the laser intensity was increased with increasing layer formation efficiency, and at the laser intensity of 4.7 × 105 W/cm2, the maximum value of layer formation efficiency was obtained at the peripheral speed of 400 mm/s. Moreover, it was revealed that the dilution length was decreased with increasing peripheral speed, the minimum value of 3 μm at the peripheral speed of 400 mm/s was obtained.

Selective laser melting (SLM), which is an additive manufacturing technology, is attractive due to its ability to freely form shapes. SLM forms a 3D material by building it layer-by-layer from a metal powder. However, some issues have yet to be resolved, including dimensional accuracy, surface finish, processing time, and mechanical properties such as surface roughness, hardness, and crystal orientation. We demonstrate that pure titanium (Ti), which is clinically used for artificial bone and hard tissue implants because it is lightweight and biocompatible, can be fabricated by the SLM process in vacuum to develop a spatter-less process. The amount of spatter was dependent on the laser scanning rate; at 10 mm/s and an output power of 200 W, the spatter was minimized so that the surface roughness was reduced to 4.2 µm from 50 µm with a laser scanning rate of 50 mm/s. Defects such as pores, voids and delamination were found to be caused with an increase in the amount of spatter.

A welding of a pure copper wire was conducted with a hybrid laser system, which combines a blue laser and an infrared (IR) laser to achieve a highly efficient and spatterless laser welding of pure copper. In the experiment, a blue-IR hybrid laser was irradiated onto a 3 × 3 × 20 mm3 pure copper wire, and the intensity of the blue laser was varied to clarify the effect of the combining of the blue diode laser. While irradiating the laser, the sample was observed by using a high-speed video camera, and the temperature of the processing point was measured by using a thermal camera. After laser irradiation, a molten volume and welding efficiency was evaluated. It was clarified that the welding efficiency of the pure copper wire increased as the intensity of the blue laser increased. At the maximum, the welding efficiency with a 6.31 × 107 W/cm2 IR laser became 1.88 times higher by combining a 9.98 × 105 W/cm2 blue laser. This finding can contribute to a further increase in the welding efficiency of pure copper wires, leading to high production efficiency in the pure copper welding process.

The authors developed a galvano selective laser melting (SLM) system equipped with a blue diode laser and clarified that the volume of the fabricated pure copper part has an influence on the relative density. SLM is a 3D printing technology. Blue diode laser is anticipated to effectively form pure copper parts because the absorptance of 450 nm light on pure copper is higher than that of conventional 1 μm light. In our previous study, the authors reported a newly developed blue diode laser whose wavelength was 450 nm. Laser power and fiber core diameter were 200 W and 100 μm, respectively. In this study, the height and width of the copper part were changed, and their influence on the density of the parts was investigated. As a result, it was found that the larger the volume of the fabricated copper part, the lower the density. In addition, the diluted layer of pure copper and the stainless steel baseplate in the copper part were measured. By controlling the amount of laser heat input between the diluted layer and the undiluted layer, it was possible to form a pure copper part with a high density of 99.6%.

A multimaterial car body design, using light materials in combination with steel, has become widespread in recent years in order to reduce a vehicle's weight. The joining of dissimilar materials is one of the most critical issues in this area. In our previous research, we reported on a new dissimilar laser lap joining method, using a cold-spray process. In that procedure, a steel coating was first sprayed onto an aluminum surface, after which a steel sheet, together with the coating, was laser welded. However, it was found that porosity occurred in the weld metal due to melting of the coating. In this study, we investigated the effects of welding parameters on porosity formation in this joining process as well as the behavior patterns of the flow and bubbles in a molten pool. The porosity increased as the laser input energy decreased. It was also discovered that the porosity could be reduced drastically by the melting of the aluminum substrate, together with the steel sheet and coating, even at lower input energy. Electron probe microanalyzer results showed that both the solidification rate, related to the input energy, and aluminum's melting were strongly associated with the generation of flow from the bottom to the surface of the molten pool. This was captured by means of an x-ray in situ observation, using tungsten tracers, behind the keyhole. The bubbles, moving upward and reaching the surface of the pool, were also observed there in the welding conditions, where only a little porosity occurred. These results demonstrated that this flow helped the bubbles move up and go outside the molten pool and, hence, prevented porosity formation.

The suppression of ablation rate on a titanium surface irradiated by a double-pulse beam with a two-color laser was experimentally investigated with time delays of Δt = 0–700 ps. The double pulse beam consists of 800 nm with 150 fs pulse and 400 nm with >150 fs pulse. The fundamental-pulse fluence F800 is kept below the ablation threshold (F800th = 0.108 J/cm2), while the second harmonic pulse fluence F400 is above the ablation threshold (F400th = 0.090 J/cm2). The ablation rate of titanium is clearly suppressed to 2.39 nm per pair with a time delay of Δt = 200 ps. This ablation rate corresponds to one-third of the 7.3 nm/pulse for only the first pulse beam, but it corresponds to about one-half of the one-color double-pulse irradiation. Ablation suppression with a two-color double-pulse beam is more pronounced compared to that for a one-color double pulse beam, which may be due to the shorter optical penetration length of the first pulse.

The Perpendicular Period and Phase Scanning (P3S) method can evaluate the uniformity of a laser-induced periodic surface structure (LIPSS). P3S assesses the uniformity of LIPSS using the standard deviation of the peak period and the average of the phase difference in the direction perpendicular to LIPSS. The P3S method demonstrates that LIPSS formed by two-color double-pulse irradiation is reduced to a quarter of the period dispersion, and the average phase difference of LIPSS is also reduced compared to the single-pulse irradiation. In addition, a 3D electromagnetic particle-in-cell simulation was performed to evaluate the possibility of an improved uniformity of LIPSS. The results confirm that the two-color double-pulse irradiation produces a uniform LIPSS and validates the effectiveness of the P3S method to assess the uniformity of LIPSS.

Highly efficient welding of pure copper was achieved using a hybrid laser system, which combined a blue diode laser and a single-mode fiber laser. Pure copper is used as a motor coil for electric vehicles (EVs). However, the processing efficiency of laser welding for pure copper is low since it has a low light absorption rate for the wavelength of the fiber laser. In this study, a hybrid laser system, which combined coaxially with a blue diode laser and a high-power single-mode fiber laser, was developed to realize highly efficient laser welding for pure copper. The beam profile of hybrid laser was alimented to set a stair-shape beam at the processing point. To investigate the effect of the beam profile, the hybrid laser was irradiated onto a 3 × 3 × 20 mm3 copper wire for welding, and the molten volume of copper wire was evaluated. As a result, it was found that the molten volume with a blue diode laser became 1.8 times larger than that without it. Moreover, the welding efficiency of the hybrid laser was 1.45 times higher than that of the fiber laser only.

A 100 W blue diode laser with an optical fiber having a core diameter of 100 μm was developed and installed into a blue diode laser metal deposition system (B-LMD), achieving a laser intensity of 7.58 × 104 W/cm2, four times higher than that of the previous B-LMD system. The increase in laser intensity is expected to enable faster and more efficient 3D processing of pure copper. The authors conducted the rod formation experiment by varying the processing speed. The rod formation process is observed with a high-speed video camera to clarify the mechanism of copper rod formation. As a result of rod formation as a 3D modeling of pure copper, a 30 mm rod was formed in 1.5 s under the following conditions: a laser intensity of 1.27×106W/cm2, a powder feed rate of 220 mg/s, and a processing speed of 20 mm/s. It was found that the mode of rod forming changed depending on the processing speed. When the processing speed is high, the mode becomes molten layer type and the energy efficiency becomes high. In addition, the processing point became closer to the focal point at high speed, and the cross-sectional shape of the formed rod was closer to the circular ones.

Laser metal deposition (LMD), which is one of the additive manufacturing technologies, is suitable for making 3D objects with complex shapes. In this method, a blue diode laser is used to explore the formation of pure copper parts because of the high light absorption of pure copper in blue light. Inspired by this method, in this study, we developed a high-power blue diode laser with a wavelength of 450 nm. This laser had an output power of 100 W and a fiber core diameter of 100 μm. We also developed a multibeam LMD system with the blue diode laser in which metal powder was supplied perpendicularly to the processing point and multiple lasers were irradiated from the surroundings for additively manufactured pure copper. We investigated the differences in copper layer formation that are dependent on the properties of substrates. Upon using the multibeam LMD system, a pure copper layer formed on pure aluminum and stainless-steel substrates. The interaction of pure copper powder and the substrates was observed using a high-speed video camera. After laser irradiation, copper cladding samples were observed with an optical microscope and scanning electron microscope and energy dispersive x-ray spectroscopy to evaluate the cross-sectional area of the pure copper layer and the dilution zone. As a result, a pure copper layer formed on the aluminum surface under the laser irradiation condition under which the aluminum substrate was not subjected to melting by heating with the blue laser. It was suggested that the pure copper powder heated by the laser melted the aluminum and formed a copper layer on the aluminum substrate.

Poly(methyl methacrylate) (PMMA) is widely used as a biomaterial. The formation of periodic nanostructures on the surface is necessary to improve the biocompatibility. A method was proposed and developed to form periodic nanostructures on a PMMA surface. A PMMA plate was placed on titanium (Ti) plate, and then the Ti plate was irradiated with a laser through the PMMA plate. We try to effectively produce periodic nanostructures on PMMA with a femtosecond laser at a fundamental wavelength by increasing the contact pressure and using titanium (Ti) plate. The contact pressure between PMMA and Ti required to form a periodic nanostructure is 300 kPa, and for a contact pressure of 2400 kPa, periodic nanostructures are formed in 62% of the laser-irradiated area on the PMMA surface. These results suggest that the formation efficiency of the periodic nanostructure depends on the laser conditions and the contact pressure.

Poly-methyl methacrylate (PMMA) has been widely used as biomaterial. In order to add a new function to PMMA, we developed a method to form periodic nanostructures on PMMA surface by femtosecond laser irradiation with a wavelength of 800 nm. Since PMMA had a low absorbance of light in the near-infrared wavelength region, it was difficult to form the structures by femtosecond laser irradiation on PMMA surface. We proposed a method that the femtosecond laser was focused on a titanium (Ti) plate surface through a polymer plate. As a result, the depth of the periodic nanostructures was about 70 nm, and the period of it was about 410 nm. A cell cultivation test was carried out on PMMA plate with and without periodic nanostructures. Consequently, although cells (MG-63) on the non-irradiated PMMA plate were spread in a random direction, cell spreading on the PMMA plate with periodic nanostructures occurs along the grooves.

Liquid benzoquinone and naphthoquinone having diethylene glycol monomethyl ether groups are designed and synthesized as redox active materials that dissolve supporting electrolytes. The Li-ion batteries based on the liquid quinones using LiBF4 /PC show good performance in terms of voltage, capacity, energy efficiency, and cyclability in both static and flow modes. A battery is constructed without using intentionally added organic solvent, and its high energy density (264 W h L-1 ) demonstrates the potential of solvent-free organic redox flow batteries using liquid active materials.

Aphasia is an acquired communication disorder marked by difficulties in understanding the language or expressing oneself using language. In order to support communication of a person with aphasia, a concept of supported communication has been proposed, wherein a conversation partner assists a person with aphasia in communicating. We are designing a conversation partner agent, a software agent that embodies the functions of a conversation partner. In this paper, we focus on the function of assisting a person with aphasia who has difficulty retrieving words. More specifically, multiple choice questions are generated using a domain ontology and presented in appropriate order to a person with aphasia. Through this question and answer process, the system infers the word that a person with aphasia wants to express.

Background: In order to facilitate conversation for people with moderate‐to‐severe aphasia, a conversation‐support system has been developed. This system consists of three electronic resources: a vocabulary data file, an encyclopaedia, and homepages on the Internet. The vocabulary data file we created contains approximately 50,000 words, mostly consisting of various proper names, which are classified into 10 categories. These words function as keywords in conversation. Kazuhiro Kuwabara is currently with Ritsumeikan University. Tamotsu Kasyo, Toshikazu Kubo, Chotaro Sindo, and Kazuo Herai entered words into the vocabulary data file. i Kobo Inc. converted the text data files into HTML files. Minoru Uchida uploaded the files to the Internet. We are also indebted to the following people for their assistance: Kazuyoshi Niizumi, Wakako Suzuki, Jyunichi Oura, Akiko Iwamoto, Rie Ishida, Kaname Tate, Midori Abe, Motoshi Uchimura, Tetsuo Nakamura, and Yoshihiro Sakon. We wish to express special thanks to Bobbie Be...

The redox flow battery has received significant research interest as a large scale energy storage system for renewable-energy sources. Although the all-vanadium aqueous redox flow battery has been most developed, its energy density is not sufficient mainly because of narrow electrochemical stability window of water. Therefore, recent efforts have shifted to developing nonaqueous redox flow batteries because they can achieve higher voltage due to wider electrochemical stability window of nonaqueous electrolytes. However, nonaqueous redox flow batteries generally suffer from insufficient energy densities because of low solubility of organic active materials in nonaqueous electrolytes. In this study, we designed and synthesized two highly soluble organic active materials, benzoquinone 1 and naphthoquinone 2 having diethylene glycol mono methyl ether groups. Both 1 and 2 were highly soluble in propylene carbonate (PC). Charge-discharge properties of the batteries using 1 and 2 as organic active materials were measured in LiBF4/PC using a cell equipped with a carbon fiber anode, a lithium-metal anode, and a glass filter separator. The charge-discharge measurements showed that 1 and 2 exhibited high voltages of ca. 3 V and good charge-discharge properties. Notably, 2 showed a higher energy density than conventional all-vanadium aqueous redox flow batteries.

This paper describes a system for supporting remote conversation for people with aphasia. We have constructed an initial prototype using Skype for video chat and the RemoteX plug-in for screen sharing over a network. Preliminary experiments conducted using the prototype have revealed that simply providing video chat and screen-sharing functions is not sufficient for supporting remote conversation with people with aphasia. We propose various simple communication tools to facilitate questioning and answering in the remote conversation, where a person with aphasia can reply by marking an appropriate portion of a window provided by the tool. Their effectiveness is demonstrated through experiments.