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Journal Articles

Identification of coral spawn source areas around Sekisei Lagoon for recovery and poleward habitat migration by using a particle-tracking model

Takeda, Naoya*; Kashima, Motohiko*; Odani, Sachika*; Uchiyama, Yusuke*; Kamidaira, Yuki; Mitarai, Satoshi*

Scientific Reports (Internet), 11(1), p.6963_1 - 6963_10, 2021/03

 Times Cited Count:6 Percentile:65.91(Multidisciplinary Sciences)

A massive coral bleaching event occurred in 2016 in the interior of Japan's largest coral lagoon, the Sekisei Lagoon, located in the Kuroshio upstream region in southwestern Japan. Recovery of the coral lagoon will require the influx of coral spawn and larvae; therefore, it is important to identify and conserve source sites. A surface particle tracking simulation of coral spawn and larvae was used to identify source areas in the exterior Sekisei Lagoon for restoration of the interior lagoon. The northern coastal zone of Iriomote Island, including Hatoma Island, was identified as a major source area. Hatoma Island was also identified as a key source for the Kuroshio downstream region, making it one of the most important source areas in the Nansei Archipelago.

Journal Articles

Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex, 2; Neutron scattering instruments

Nakajima, Kenji; Kawakita, Yukinobu; Ito, Shinichi*; Abe, Jun*; Aizawa, Kazuya; Aoki, Hiroyuki; Endo, Hitoshi*; Fujita, Masaki*; Funakoshi, Kenichi*; Gong, W.*; et al.

Quantum Beam Science (Internet), 1(3), p.9_1 - 9_59, 2017/12

The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.

Journal Articles

Principles of neutron reflectometry

Torikai, Naoya*; Takeda, Masayasu

Hamon, 18(4), p.221 - 227, 2008/10

Neutron reflectometry is a non-destructive structural analysis method utilizing optical property of neutron at interfaces between two media, and is indispensable for structural analysis on material interfaces due to high depth resolution of a sub-nm scale. The specular reflection of neutron at the interface can be described by the Shr$"{o}$dinger equation with the one-dimensional square well potential for a plane wave. Here, the principles of neutron reflectometry are explained using a typical few examples from a single ideal interface to a multi-layer system.

Journal Articles

Buried H monolayer at hetero-interface between highly mismatched Sr films and Si substrates

Yamazaki, Tatsuya; Asaoka, Hidehito; Takeda, Masayasu; Yamazaki, Dai; Taguchi, Tomitsugu; Torikai, Naoya*; Toyoshima, Yasutake*; Shamoto, Shinichi

Transactions of the Materials Research Society of Japan, 33(3), p.611 - 614, 2008/09

Strontium and SrO are well-known templates on Si for SrTiO$$_{3}$$, highly-desirable transistor gate material. When stacked on Si, Srlayer becomes amorphous due to its large lattice mismatch of 12%. By introducing a monatomic hydrogen layer on Si, we succeeded in making the Sr (and subsequent SrO) layer(s) grow epitaxially with atomically abrupt interface. However, it is some what mysterious how the monatomic hydrogen layer behaves to manage this large mismatch. In order to identify its behavior, we have employed compound analysis by neutron reflectometer as well as multiple-internal-reflection fourier-transform infrared spectroscopy (MIR-FTIR) to investigate the buried heterointerface of Sr grown on Si(111)1$$times$$1: monohydride. We have found difference between the H- and D-terminated substrates in the reflectivity profiles, and changes in Si-H bonding features with the Sr growth (mainly at the initial monolayer stage) in the FTIR spectra. From these, existence of buried H layer at the heterointerfaceis confirmed with its bonding environment.

Journal Articles

Exchange bias and uncompensated spins in a Fe/Cr(100) bilayer

Kim, K. Y.*; Hwang, Y. S.*; Park, J.-G.*; Torikai, Naoya*; Takeda, Masayasu; Han, S. W.*; Shin, S. C.*

Physica Status Solidi (B), 244(12), p.4499 - 4502, 2007/12

 Times Cited Count:1 Percentile:6.71(Physics, Condensed Matter)

We have investigated the effect of the field cooling on the exchange bias and the coercivity in an exchange-biased Fe/Cr(100) bilayer using SQUID magnetometer. After the field cooling, magnetization shifted upwards, indicative of surplus magnetic moments, which could be interpreted as an evidence of pinned and uncompensated Cr magnetic moments induced by the cooling field. Interestingly enough, we also discovered that not all the pinned and uncompensated spins seem to be involved in producing the exchange bias, although they contribute to increasing the coercivity and inducing the surplus magnetization.

Journal Articles

Resonance spin-echo option on neutron reflectometers for the study of dynamics of surfaces and interfaces

Yamazaki, Dai; Soyama, Kazuhiko; Ebisawa, Toru*; Takeda, Masayasu; Torikai, Naoya*; Tasaki, Seiji*; Matsuoka, Hideki*

Physica B; Condensed Matter, 356(1-4), p.229 - 233, 2005/02

 Times Cited Count:1 Percentile:6.25(Physics, Condensed Matter)

The application of neutron reflectometry to study dynamic phenomena at surface and interfaces have been restricted so far. It was mainly due to the low intensity of neutron sources, but now high-intensity spallation neutron sources are under construction in Japan (J-PARC) and U.S. (SNS). We have a plan to install a spin-echo option on the J-PARC neutron reflectometer with horizontal sample geometry for studies on dynamics of surfaces and interfaces. This option is based on the resonance spin-echo method and aimed at dynamics upto hundreds of nanoseconds. In this contribution, the plan and status of development are introduced together with the principle and characteristics of this option.

Journal Articles

Recent activities and progress on PORE reflectometer

Takeda, Masayasu; Torikai, Naoya*; Ino, Takashi*; Tasaki, Seiji*

KENS Report-XIV, p.205 - 206, 2003/00

no abstracts in English

Oral presentation

Future prospects of neutron reflectometry in Japan

Takeda, Masayasu; Yamazaki, Dai; Soyama, Kazuhiko; Torikai, Naoya*

no journal, , 

no abstracts in English

Oral presentation

Buried hetero-interface of H, D monolayer

Asaoka, Hidehito; Takeda, Masayasu; Soyama, Kazuhiko; Shamoto, Shinichi; Yamazaki, Tatsuya; Torikai, Naoya*

no journal, , 

no abstracts in English

Oral presentation

Neutron reflectivity study on buried hetero-interfacial structure of H, D monolayer

Asaoka, Hidehito; Takeda, Masayasu; Yamazaki, Dai; Yamazaki, Tatsuya; Taguchi, Tomitsugu; Shamoto, Shinichi; Torikai, Naoya*

no journal, , 

no abstracts in English

Oral presentation

Extraction behavior of Mo and W from H$$_{2}$$SO$$_{4}$$ with Aliquat336 as homologues of seaborgium (Sg)

Mitsukai, Akina; Toyoshima, Atsushi; Asai, Masato; Tsukada, Kazuaki; Sato, Tetsuya; Kaneya, Yusuke; Takeda, Shinsaku*; Nagame, Yuichiro; Komori, Yukiko*; Murakami, Masashi*; et al.

no journal, , 

We have started studying sulphate-complex formation of a transactinide element, seaborgium (Sg). In this study, we report on the extraction behavior of carrier-free radioisotopes $$^{93m}$$Mo and $$^{181}$$W which are lighter homologs of Sg, from aqueous H$$_{2}$$SO$$_{4}$$ solution with amine extractant, Aliquat336, dissolved in toluene by a batch method. These radioisotopes were produced in the $$^{nat}$$Zr($$alpha$$,${it 2}$)$$^{93m}$$Mo and $$^{181}$$Ta(${it d}$,x${it n}$)$$^{181}$$W reactions at the RIKEN K70 AVF cyclotron. Results of the extraction experiments showed that the distribution ratios of Mo and W increase sharply above ~3.0 M H$$_{2}$$SO$$_{4}$$. Based on the slope analysis, it was indicated that anionic sulphate-complex of [MO$$_{2}$$(SO$$_{4}$$)$$_{2}$$]$$^{2-}$$ (M = Mo, W) are formed in $$>$$ 5 M H$$_{2}$$SO$$_{4}$$. These results suggest that the present system is applicable to the extraction of Sg.

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