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Ishii, Mamoru*; Shiota, Daiko*; Tao, Chihiro*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Ishii, Takako*; Ichimoto, Kiyoshi*; Kataoka, Ryuho*; Koga, Kiyokazu*; Kubo, Yuki*; et al.
Earth, Planets and Space (Internet), 73(1), p.108_1 - 108_20, 2021/12
Times Cited Count：8 Percentile：57.39(Geosciences, Multidisciplinary)We surveyed the relationship between the scale of space weather events and their occurrence rate in Japan and we discussed the social impact of these phenomena during the Project for Solar-Terrestrial Environment Prediction (PSTEP). The information was compiled for domestic users of space weather forecasts for appropriate preparedness against space weather disasters. This paper gives a comprehensive summary of the survey, focusing on the fields of electricity, satellite operations, communication and broadcasting, satellite positioning usage, aviation, human space activity, and daily life on the Earth's surface, using the cutting-edge knowledge of space weather. Quantitative estimations of the economic impact of space weather events on electricity and aviation are also given.
Kusano, Kanya*; Ichimoto, Kiyoshi*; Ishii, Mamoru*; Miyoshi, Yoshizumi*; Yoden, Shigeo*; Akiyoshi, Hideharu*; Asai, Ayumi*; Ebihara, Yusuke*; Fujiwara, Hitoshi*; Goto, Tadanori*; et al.
Earth, Planets and Space (Internet), 73(1), p.159_1 - 159_29, 2021/12
Times Cited Count：6 Percentile：51.19(Geosciences, Multidisciplinary)The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.
(3) sigma modelJimmenez, S.*; Oka, Makoto; Sasaki, Kiyoshi*
Physical Review D, 97(11), p.114506_1 - 114506_28, 2018/06
Times Cited Count：0 Percentile：0.01(Astronomy & Astrophysics)We nonperturbatively calculate the wave-function renormalization in the two-dimensional (3) sigma model. It is evaluated in a box with a finite spatial extent. We determine the anomalous dimension in the finite-volume scheme through an analysis of the step-scaling function. Results are compared with a perturbative evaluation, and reasonable behavior is observed.
Komatsu, Kazumi*; Seki, Takeshi*; Naganawa, Akihiro*; Oka, Kiyoshi*; Nishimura, Akihiko
Hozengaku, 16(3), p.89 - 95, 2017/10
no abstracts in English
Terada, Takaya; Nishimura, Akihiko; Oka, Kiyoshi; Moriyama, Taku*; Matsuda, Hiroyasu*
Hozengaku, 13(4), p.87 - 94, 2015/01
Oshikawa, Takumi*; Funakoshi, Yoshihiko*; Imaoka, Hiroshi*; Yoshikawa, Kohei*; Maari, Yasutaka*; Iguchi, Masahide; Sakurai, Takeru; Nakahira, Masataka; Koizumi, Norikiyo; Nakajima, Hideo
Proceedings of 19th International Forgemasters Meeting (IFM 2014), p.254 - 259, 2014/09
ITER is a large-scale experiment that aims to demonstrate that it is possible to produce commercial energy from fusion. ITER Toroidal Field Coil Case (hereinafter referred to as "ITER TFCC") is one of the important components of ITER. The ITER TFCC materials are made of high nitrogen austenitic stainless steel and having various configurations. The ITER TFCC material which manufactured by JCFC has a complex configuration with heaver thickness than other materials. It is difficult to form near net shape to delivery configuration by ordinary open die forging method such as upset and stretching, because the ITER TFCC materials manufactured by JCFC have a complex configuration. Therefore ingot weight and lead time of machining increase when ITER TFCC materials are forged by ordinary open die forging method. Moreover, in order to get good attenuation at Ultrasonic examination, it is necessarily to make fine and uniform grain of the material. However, it is impossible to control grain size of austenitic stainless steel by heat treatment. The grain becomes fine and uniform by only forging process with suitable condition. Therefore, JCFC has studied suitable forging method to become near net shape to delivery configuration and also to get fine grain of center of the material. Based on these result, ITER TFCC materials were manufactured. This innovative forging process led to reduce the weight of ingot compared with general forging. And it had good Ultrasonic attenuation. It was confirmed that the results of material test and nondestructive examination satisfied the requirements of Japan domestic agency (hereinafter referred to as "JADA"). Moreover, the test coupons were taken from center of thick part of product and used for various tests. As the result of tests, it was confirmed that results of material test satisfied the requirements of JADA. It is clear that this innovative forging method is very suitable process for manufacturing of ITER TFCC materials.
As by 320 MeV Au irradiation in single crystals and by high-pressure sintering in powder-in-tube wiresPyon, S.*; Taen, Toshihiro*; Otake, Fumiaki*; Tsuchiya, Yuji*; Inoue, Hiroshi*; Akiyama, Hiroki*; Kajitani, Hideki; Koizumi, Norikiyo; Okayasu, Satoru; Tamegai, Tsuyoshi*
Applied Physics Express, 6(12), p.123101_1 - 123101_4, 2013/12
Times Cited Count：21 Percentile：63.34(Physics, Applied)We demonstrate a large enhancement of critical current density (
) up to 1.0 
10
A/cm
at 5 K under self-field in (Ba,K)FeAs single crystals by irradiating 320 MeV Au ions. With the very promising potential of this material in mind, we have fabricated a (Ba,K)FeAs superconducting wire through a powder-in-tube method combined with the hot isostatic pressing technique, whose effectiveness has been proven in industrial Bi2223 tapes. The Jc in the wire at 4.2 K has reached 37 kA/cm under self-field and 3.0 kA/cm at 90 kOe. Magneto-optical imaging of the wire confirmed the large intergranular Jc in the wire core.
Oka, Kiyoshi; Seki, Takeshi; Akatsu, Tomohiro
Kogaku, 41(11), p.576 - 578, 2012/11
no abstracts in English
Shigetomi, Hiroshi*; Oka, Kiyoshi; Oi, Hidekazu*; Furukawa, Naoto*; Yoshida, Shozo*; Kawaguchi, Ryuji*; Nagai, Akira*; Haruta, Shoji*; Yanase, Yasuhito*; Akasaka, Julia*; et al.
Nihon Reza Igakkai-Shi, 33(2), p.131 - 135, 2012/08
no abstracts in English
Yamashita, Hiromasa*; Oka, Kiyoshi; Yamanaka, Noriaki*; Seki, Takeshi; Kim, K.*; Kuwana, Kenta*; Masamune, Ken*; Naganawa, Akihiro*; Dohi, Takeyoshi*; Chiba, Toshio*
Nihon Reza Igakkai-Shi, 33(2), p.122 - 130, 2012/08
no abstracts in English
Naganawa, Akihiro*; Oka, Kiyoshi
Tateishi Kagaku Gijutsu Shinko Zaidan Josei Kenkyu Seikashu, 21, p.74 - 77, 2012/00
no abstracts in English
Oka, Kiyoshi; Seki, Takeshi; Nishimura, Akihiko
Oyo Butsuri, 80(12), p.1069 - 1072, 2011/12
A composite-type optical fiberscope was developed for maintenance research and development of nuclear facilities by JAEA. It can coaxially deliver both a high energy laser beam for micro processing and an image from processing targets. Development of minimally invasive laser treatment devices were introduced by use of the composite-type optical fiber scope.
Nagaoka, Shinichi*; Fukuzawa, Hironobu*; Pr
mper, G.*; Takemoto, Mai*; Takahashi, Osamu*; Yamaguchi, Takuhiro*; Kakiuchi, Takuhiro*; Tabayashi, Kiyohiko*; Suzuki, Isao*; Harries, J.; et al.
Journal of Physical Chemistry A, 115(32), p.8822 - 8831, 2011/07
Times Cited Count：29 Percentile：71.09(Chemistry, Physical)Oka, Kiyoshi; Seki, Takeshi; Naganawa, Akihiro*; Kim, K.*; Chiba, Toshio*
Surgical Endoscopy, 25(7), p.2368 - 2371, 2011/07
Times Cited Count：4 Percentile：22.9(Surgery)We developed an ultrasmall composite-type optical fiberscope (1.1-mm diameter) with a central cauterizing laser fiber surrounded by imaging and illumination fibers as a tool for various surgical applications. Porcine mesenteric blood vessels were laser irradiated in vivo and the procedure was filmed using ultrahigh-speed (max 1,000,000 frames per second) and thermographic cameras. Blood flow was decreased by 81.7% after laser irradiation and the diameter of the vessels at the irradiated point was approximately 46-48% smaller than that of the unirradiated vessels. Medical doctors also confirmed that the blood vessel was blocked after the experiments. From these results, it was shown that this device is applicable to all medical regions.
Seki, Takeshi*; Naganawa, Akihiro*; Oka, Kiyoshi; Yoshino, Junji*
Keisoku Jido Seigyo Gakkai Sangyo Rombunshu, 10(2), p.7 - 16, 2011/05
Enteroscopy was usually performed by the double balloon or capsule endoscopes. However, it is difficult to use these endoscopes in patients who suffer from intestinal obstruction and adhesion. We have developed a new endoscope that can be used in patients who suffer from these problems; the instrument consists of an ileus tube and an optical fiberscope (diameter 1.1 mm). The entire small intestine can be observed by controlling the internal pressure of the balloon in the ileus tube and by pulling the tube out at a constant speed. In our previous study, we developed an internal pressure control device that consists of a balloon attached to an ileus tube and a medical syringe. We also verified the control performance of this device. In this study, we have designed a new two-degrees-of-freedom control system having self-tuning capabilities that enhances the control performance for various types of syringes doctors use usually. The effects of the proposed method are illustrated by the experiment. The obtained results show that balloon pressure in the reference response satisfactorily tracks the output of the reference model and can be settled within 
2% in steady state. In addition, the disturbance rejection properties of the PID control method were affected by the changes in balloon pressure, but this problem can be solved by using the proposed control system.
Nishimura, Akihiko; Shobu, Takahisa; Oka, Kiyoshi; Yamaguchi, Toshihiko; Shimada, Yukihiro; Mihalache, O.; Tagawa, Akihiro; Yamashita, Takuya
Reza Kako Gakkai-Shi, 17(4), p.207 - 212, 2010/10
A prototype probe system with a hybrid optical fiber scope was designed for inspecting and re-pairing the micro cracks on heat exchanger tubes in fast breeder reactors (FBRs). It comprised a laser processing head combined with an eddy current testing unit. Ultrashort laser pulse ablation was used to remove work-hardened layers. And spot laser welding was used to repair the micro cracks. This system has both safe and economical options for the maintenance of FBRs because it extends the lifetime of the heat exchangers.
Seki, Takeshi; Naganawa, Akihiro*; Oka, Kiyoshi; Ishikawa, Shinji*; Yoshino, Junji*
Nihon Kikai Gakkai Rombunshu, C, 76(766), p.1645 - 1647, 2010/06
Recently, by development of double balloon and capsule endoscopes, small intestinal whole area observation was enabled. However, it is difficult to use these endoscopes in patients with intestinal obstruction and adhesion. We developed a new endoscope that can be used in patients with intestinal obstruction and adhesion; this instrument consists of an ileus tube and an optical fiberscope (diameter, 1.1 mm). The complete observation of small intestinal is to be planned by controlling internal pressure of balloon in ileus tube, and pulling the tube out at constant speed. In our previous study, we have developed an internal pressure control device which consists of a balloon of ileus and an industrial cylinder, and we confirmed the utility. In this study, we developed a new control device combined with a general medical syringe, which enables to be sterilized easily and also to give less anxiety to patients. As the results of performance experiment of the device, the control accuracy was within 0.5% error. Furthermore, in a disturbance response, the pressure fluctuation was limited down to 12%, compared with a case without any control.
Oka, Kiyoshi; Seki, Takeshi*; Naito, Takehito*; Watanabe, Shinya*; Wakabayashi, Takao*; Naganawa, Akihiro*; Inui, Kazuo*; Yoshino, Junji*
Nihon Gazo Igaku Zasshi, 28(1), p.12 - 24, 2010/05
Focusing on the measurement function loaded on our rigid-typed endoscope for the fetal surgery treatment, we proposed that its combination with a generally used digestive endoscope enabled calibration of lesion size in stomach. While adding the function, with which the target size is to be easily measured, on the endoscope, we simplified the system structure as much as possible. We also tried to minimize the total cost by using the generally used endoscope, instead of making it from scratch. Combining another development, the composite-type optical fiberscope with diameter of 1.1mm, with a generally used endoscope, we proposed the following as the features: (1)acquisition of fiberscope image, (2)laser irradiation for treatments, (3)applying the real time measurement function of distance and blood flow by semiconductor laser to the generally used endoscope. We have operated the clinical study to the gastric wall of person with no health problem, using this system and confirmed it was available for practical use.
Seki, Takeshi*; Naganawa, Akihiro*; Oka, Kiyoshi; Chiba, Toshio*
Keisoku Jido Seigyo Gakkai Sangyo Rombunshu, 9(10), p.70 - 75, 2010/04
The fetoscopic laser photocoagulation of chorionic plate anastomosing vessels is main treatment for the twin-twin transfusion syndrome. However, in this treatment, it is required highly endoscopic technologies, for example, blood flow measurement, estimation of distance between placental vessels and irradiation fiber tip and so on. We research and develop a composite-type optical fiberscope (2.2 mm in diameter), which has centrally-located cautery laser fiber and surrounding located fiberglasses for viewing. The laser transmitting efficiency of our fiberscope was very high (84.7%), and certain degree of cauterization was performed with from 20 to 40W laser power, when the distance between irradiated area and fiber tip was 10 mm. In addition, we emitted the laser to porcine liver for laser power control using a thermocouple as a basic research for intercepting placental blood flow, and we controlled the temperature of irradiation spot within 0.3
C error in previous paper. In this study, we emitted the laser to in vivo porcine mesenteric vessel with blood flow for laser power control under temperature measurement. From the experimental result, the target temperature of 60 and 70C with feedback control system using thermocouple was controlled low power of about 17W maintain target temperature within 2.0C error. Moreover, we measured the blood flow before and after laser irradiation by a laser Doppler blood-flow meter, and confirmed quantitatively the blood flow blocking.
Oka, Kiyoshi; Seki, Takeshi; Naganawa, Akihiro*; Yamashita, Hiromasa*; Kim, K.*; Chiba, Toshio*
Minimally Invasive Therapy and Allied Technologies, 19(2), p.94 - 99, 2010/04
Times Cited Count：6 Percentile：30.06(Surgery)We developed a new laser device using a composite-type optical fiberscope for laser surgery to treat twin-twin transfusion syndrome. The composite-type optical fiberscope (2.2 mm in external diameter) consists of a centrally located single fiber for laser treatment (0.1mm in diameter) and its surrounding fibers for diagnosis. This fiberscope enables transmission of 40-W Yb fiber laser. The Yb fiber laser can be focused to 10 mm focal length using two lenses on the tip of the fiberscope. In this research, we emitted the laser to in vivo porcine mesenteric vessel with blood flow both with an established laser fiber of 0.6-mm diameter (0.6-mm normal fiber) and with our composite-type optical fiberscope to compare the cautery performance of those devices.
