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- 저자 : Yamamoto Tomohiko (검색결과 3 건)
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Yamamoto Tomohiko,Kato Atsushi,Hayakawa Masato,Shimoyama Kazuhito,Ara Kuniaki,Hatakeyama Nozomu,Yamauchi Kanau,Eda Yuhei,Yui Masahiro 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.3
In a secondary cooling system of a sodium-cooled fast reactor (SFR), rapid detection of hydrogen due to sodiumwater reaction (SWR) caused by water leakage from a heat exchanger tube of a steam generator (SG) is important in terms of safety and property protection of the SFR. For hydrogen detection, the hydrogen detectors using atomic transmission phenomenon of hydrogen within Ni-membrane were used in Japanese proto-type SFR “Monju”. However, during the plant operation, detection signals of water leakage were observed even in the situation without SWR concerning temperature up and down in the cooling system. For this reason, the study of a new hydrogen detector has been carried out to improve stability, accuracy and reliability. In this research, the authors focus on the difference in composition of hydrogen and the difference between the background hydrogen under normal plant operation and the one generated by SWR and theoretically estimate the hydrogen behavior in liquid sodium by using ultra-accelerated quantum chemical molecular dynamics (UA-QCMD). Based on the estimation, dissolved H or NaH, rather than molecular hydrogen (H2), is the predominant form of the background hydrogen in liquid sodium in terms of energetical stability. On the other hand, it was found that hydrogen molecules produced by the sodium-water reaction can exist stably as a form of a fine bubble concerning some confinement mechanism such as a NaH layer on their surface. At the same time, we observed experimentally that the fine H2 bubbles exist stably in the liquid sodium, longer than previously expected. This paper describes the comparison between the theoretical estimation and experimental results based on hydrogen form in sodium in the development of the new hydrogen detector in Japan.
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Endoscopic features of gastrointestinal stromal tumor in the small intestine
Yutaro Ihara,Takehiro Torisu,Tomohiko Moriyama,Junji Umeno,Atsushi Hirano,Yasuharu Okamoto,Yoshifumi Hori,Hidetaka Yamamoto,Takanari Kitazono,Motohiro Esaki 대한장연구학회 2019 Intestinal Research Vol.17 No.3
Background/Aims: Gastrointestinal stromal tumor (GIST) is one of the most common types of submucosal tumors (SMTs). Because of GIST’s malignant potential, it is crucial to differentiate it from other SMTs. The present study aimed to identify characteristic endoscopic findings of GISTs in the small intestine. Methods: We reviewed the clinicopathological and endoscopic findings of 38 patients with endoscopically or surgically resected SMTs in the small intestine. SMTs were classified into GIST and non-GIST groups, and clinicopathological and endoscopic findings were compared between the 2 groups. Results: Fifteen patients had GIST and 23 patients had other types of SMTs in the small intestine. Comparison of the endoscopic findings between the 2 groups revealed that dilated vessels in the surrounding mucosa were significantly more in number in the GIST group than in the non-GIST group (P<0.05). However, there were no other differences in endoscopic findings between the 2 groups. Among patients with GISTs, the presence of dilated vessels in the surrounding mucosa was not associated with bleeding risk, tumor size, or metastasis rate at diagnosis. Conclusions: Dilated vessels in the surrounding mucosa, identified during balloon-assisted endoscopy, may be a diagnostic indicator for GIST in the small intestine. However, its clinical significance should be further analyzed.
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Mitsuru UESAKA,Atsushi FUKASAWA,Fumito SAKAMOTO,Haruyuki OGINO,Junji URAKAWA,Katsuhiro DOBASHI,Kazutaka TAKAO,Mitsuo AKEMOTO,Tomohiko YAMAMOTO,Toshinobu MIYOSHI,Toshiyasu HIGO 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.1
A Compton scattering X-ray source consisting of an X-band (11.424 GHz) electron linear accelerator (linac) and Q-switched Nd:YAG laser is currently under construction. Monochromatic hard X-rays are required for a variety of medical and biological applications. The new hard X-ray source produces monochromatic X-rays via collision between a 35-MeV multi-bunch (104 bunches in a 1 μs RF pulse) electron beam and 1.4 J/10 ns (532 nm) Nd:YAG laser beam. The linac uses an X-band 3.5-cell thermionic cathode RF gun and an alpha magnet as an injector. The thermionic cathode RF gun is the first of its kind and can generate a high current (2 μA) and a multi-bunch 2-MeV electron beam. To increase the efficiency of the X-ray yield, a laser pulse circulation system is adopted, that can increase the X-ray intensity by up to 50 times. This scheme can produce monochromatic tunable X-rays (10 40 keV) with intensities of 108 109 photons/sec. In addition, the X-ray energy can be changed rapidly over 40 ms by two different wavelength lasers (YAG fundamental (1064 nm), 2nd harmonic (532 nm)) and an optical switch. This quick energy change is very important for living specimens and is very difficult to achieve in light sources such as a large SR (Synchrotron Radiation) source. The system can be used for dual-energy X-ray CT and subtraction X-ray CT to determine the 3D distribution of the atomic number density and electron density, and specified atomic distribution, respectively. In this paper, we describe the details of the system, report on experiments on the X-band thermionic cathode RF gun, and discuss applications of monochromatic X-rays.?
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