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High Power Matrix Converter for Wind Power Generation Applications
Jun Kang,Noriyuki Takada,Eiji Yamamoto,Eiji Watanabe 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
The matrix converter has many advantages in wind power system applications. Matrix converter is compact and highly efficient because it directly converts generated power from AC generator to AC grid without intermediate DC bus while conventional back-to-back converter systems requires many electrolytic capacitors in DC link bus which are bulky and have short life-time. Matrix converter has both motoring and regenerative power flows keeping low harmonics current in grid. It also can provide reactive power to the grid, which is important characteristic for wind farms to stabilize power system during and after grid failure. In this paper, high power matrix converter is introduced for wind power applications. Major technical features and advantages are described. Experimental results with a PM generator show good feasibility for the wind power applications.
Multi-step Internal Nitriding of Tungsten-titanium Alloys
Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
Internally nitrided dilute W-Ti alloy specimens having a heavily deformed surface microstructure were prepared by a multi-step internal nitriding at 1573-2073 K. Primary nitriding below their recrystallization temperature induced a precipitation of ultrafine TiN particles. After secondary and tertiary nitriding, those precipitates grew into rod-like TiN with a length of 20-60 nm. The recrystallization temperature after nitriding was elevated above 2073 K. The yield strength at 1773 K obtained from nitrided W-0.5 mass% Ti alloy was about 5 times as large as that of the recrystallized specimen. DBTT of the nitrided alloys was about 373 K.
Use Chains to Block DNS Attacks: A Trusty Blockchain-based Domain Name System
Wen-Bin Hsieh,Jenq-Shiou Leu,Jun-Ichi Takada 한국통신학회 2022 Journal of communications and networks Vol.24 No.3
The Internet has become one of the most importanttechnologies in the world, and hackers use various methods tolaunch cyber attacks to profit from it. Phishing is one of famoussocial engineering attacks, it is often used to steal user data,including login credentials and credit card numbers. Althoughthe Transport Layer Security certificate is used to verify the trustof websites, there are still a series of vulnerabilities. The demandfor trusted IP addresses has led a lot of research, including IPwhitelisting, DNS filtering and so on. However, these technologiesstill have many shortcomings. In view of this, we proposeda novel mechanism for verifying websites using blockchaintechnology. The URL and IP address of a permissioned websiteare recorded in blockchain through a specific smart contract. A DNS query is executed through a smart contract designedto avoid URL redirection attacks. With the help of immutablenature of blockchian, phishing websites can be detected. Themechanism will not add any load to users and provides tamperprooffunctions based on the characteristics of blockchain. Thecomparison of related works shows that the proposed mechanismis more secure. We also provided a reference implementationof the proposed mechanism on Ethereum Quorum simulationplatform, which proves the effectiveness and practicability of themechanism.
Carbon Monoxide Gas Carburization Behavior of Molybdenum Materials
Hieda Koji,Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
For pure Molybdenum carburized in mixed gases of argon and carbon monoxide, microstructural observations were carried out. X-ray diffraction analysis for carburized specimens revealed that brittle - layer hardly formed in the case of low carbon monoxide concentration. Fracture strength of the specimen carburized at 1673 K for 16 h is about 550 MPa higher than that of the un-carburized specimen. SEM observation revealed that with increasing carburizing temperature, the region demonstrating a transgranular fracture mode progressed towards the center of specimen. This result means that the grain boundaries were strengthened by the grain boundary diffusion of carbon and the strength of grain boundaries exceeded that of grain itself.
Toyosima Gouhei,Nagae Masahiro,Yoshio Tetsuo,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
TZM alloy having elongated coarse-grain structure was developed by three-step internal nitriding treatment at 1423 to 1873 K in and subsequent recrystallization treatment at 2173 K in vacuum. Some specimens were subjected to re-nitriding treatment at 1873 K for 16 h. After the recrystallization treatment, aspect ratio (L/W) of grains for rolling direction was about 50 at the maximum. Yield stress obtained at 1773 K after re-nitriding treatment was about 6 times as large as that of recrystallized specimen. Re-nitriding was very effective in the improvement in strength of TZM alloy having elongated coarse-grain structure.
Nakahara Takayuki,Okamoto Yoshihisa,Nagae Masahiro,Yoshio Tetsuo,Kurishita Hiroaki,Takada Jun,Hiraoka Yutaka,Takida Tomohiro 한국분말야금학회 2006 한국분말야금학회 학술대회논문집 Vol.2006 No.1
In order to overcome the recrystallization embrittlement and irradiation embrittlement of Mo, which are major problems for its fusion applications, internally nitrided Mo alloys were prepared by a novel multi-step internal nitriding. Neutron irradiation was performed in the Japan Material Testing Reactor (JMTR). After irradiation, nitrided Mo alloys exhibited ower ductile-brittle transition temperature than irradiated TZM. These results suggested that multi-step internal nitriding was effective to the improvement in the embrittlement by irradiation. Transmission electron microscope observation revealed that TiN particles precipitated by nitriding acted as a sink for irradiation-induced defects.