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Journal Articles

${it Neocalanus cristatus}$ (Copepoda) from a deep sediment-trap; Abundance and implications for ecological and biogeochemical studies

Ikenoue, Takahito*; Otosaka, Shigeyoshi*; Honda, Makio*; Kitamura, Minoru*; Mino, Yoshihisa*; Narita, Hisashi*; Kobayashi, Takuya

Frontiers in Marine Science (Internet), 9, p.884320_1 - 884320_11, 2022/05

We studied seasonal variations of the mesozooplankton swimmer community collected by a sediment trap moored at 873 m in the Kuroshio & Oyashio Transition region off the east coast of Japan from 5 August 2011 to 23 June 2013. The total flux of mesozooplankton swimmers varied between 0 and 11.1 individuals m-2 d-1, with a mean of 3.1 individuals m-2 d-1 during the sampling period. Among the Copepoda, Neocalanus cristatus was the most dominant taxon. The species composition of the swimmers closely reflected the mid-depth mesozooplankton of the Oyashio region. The fluxes of Neocalanus species reflected ontogenetic vertical migration, but may have been overestimates of active fluxes if they included dormant individuals that accidentally entered the sediment trap.

Journal Articles

Vertical and lateral transport of particulate radiocesium off Fukushima

Otosaka, Shigeyoshi; Nakanishi, Takahiro; Suzuki, Takashi; Sato, Yuhi; Narita, Hisashi*

Environmental Science & Technology, 48(21), p.12595 - 12602, 2014/11

 Times Cited Count:22 Percentile:60.08(Engineering, Environmental)

From August 2011 to July 2013, a sediment trap was deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant and sinking particles were collected. Sinking flux of $$^{137}$$Cs decreased over time with seasonal fluctuation. The $$^{137}$$Cs fluxes were mainly affected by two principal modes. One was a rapid sinking of radiocesium-bound particles (moderate mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (turbulence mode). Although the latter process would not drastically change the distribution of sedimentary radiocesium, attention should be paid as this key process redistributing the accident-derived radiocesium may cumulatively affect the long-term distribution.

Journal Articles

Electron compound nature in a surface atomic layer of a two-dimensional hexagonal lattice

Matsuda, Iwao*; Nakamura, Fumitaka*; Kubo, Keisuke*; Hirahara, Toru*; Yamazaki, Shiro*; Choi, W. H.*; Yeom, H. W.*; Narita, Hisashi*; Fukaya, Yuki; Hashimoto, Mie*; et al.

Physical Review B, 82(16), p.165330_1 - 165330_6, 2010/10

 Times Cited Count:9 Percentile:42.3(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Metal co-adsorption induced $$sqrt{21}timessqrt{21}$$ superstructure on Si(111) surface studied by reflection high-energy positron diffraction

Fukaya, Yuki; Matsuda, Iwao*; Hashimoto, Mie; Narita, Hisashi*; Kawasuso, Atsuo; Ichimiya, Ayahiko

e-Journal of Surface Science and Nanotechnology (Internet), 7, p.432 - 435, 2009/04

no abstracts in English

Journal Articles

Atomic scale study of surface structures and phase transitions with reflection high-energy positron diffraction

Kawasuso, Atsuo; Fukaya, Yuki; Hashimoto, Mie; Ichimiya, Ayahiko; Narita, Hisashi*; Matsuda, Iwao*

Materials Science Forum, 607, p.94 - 98, 2008/11

Currently, we are performing the surface study with reflection high-energy positron diffraction (RHEPD). The advantage of this method is the appearance of total reflection of positrons at the first surface layer. In this talk, we will present the recent progress of our research on some unknown surface structures and phase transition mechanisms.

Oral presentation

Hume-Rothery-type electron compound formed in a single-atomic layer of metal alloy

Matsuda, Iwao*; Fukaya, Yuki; Hashimoto, Mie; Narita, Hisashi*; Kawasuso, Atsuo; Ichimiya, Ayahiko

no journal, , 

no abstracts in English

Oral presentation

Structural analysis of Si(111)-$$sqrt{21}timessqrt{21}$$-(Au,Ag) surface using reflection high-energy positron diffraction

Fukaya, Yuki; Matsuda, Iwao*; Hashimoto, Mie; Narita, Hisashi*; Kawasuso, Atsuo; Ichimiya, Ayahiko

no journal, , 

no abstracts in English

Oral presentation

Noble metal adsorption induced Si(111)-$$sqrt{21}timessqrt{21}$$ superstructure studied by reflection high-energy positron diffraction

Fukaya, Yuki; Matsuda, Iwao*; Hashimoto, Mie; Narita, Hisashi*; Kawasuso, Atsuo; Ichimiya, Ayahiko

no journal, , 

no abstracts in English

Oral presentation

Sinking flux of radiocesium in the region off Fukushima

Otosaka, Shigeyoshi; Suzuki, Takashi; Nakanishi, Takahiro; Narita, Hisashi*; Kato, Yoshihisa*

no journal, , 

Between August 2011 and July 2012, sinking particles were collected with a sediment trap deployed at 100 km east of the Fukushima Daiichi Nuclear Power Plant. Concentration of $$^{134}$$Cs in sinking particles varied between 5 and 415 Bq/kg and was highest on December 2011. In this period, sinking particles predominantly consisted of lithogenic particles and the highest carbon/nitrogen ratio was observed, indicating resuspension of seabed sediment in the near-shore regions. From these results, it can be inferred that accident-derived radiocesium in the near-shore seabed was transported to the offshore region and increased $$^{134}$$Cs concentration in sinking particles.

Oral presentation

Sinking fluxes of radiocesium off Fukushima

Otosaka, Shigeyoshi; Sato, Yuhi; Suzuki, Takashi; Narita, Hisashi*

no journal, , 

A sediment trap experiment was conducted between August 2011 and July 2013 and sinking particles were collected at 100 km east of the Fukushima Daiichi Nuclear Power Plant. Sinking flux of $$^{137}$$Cs was the highest in September 2011 (98 mBq/m$$^{2}$$/day), and decreased over time with seasonal fluctuation. The sinking fluxes of particulate radiocesium were controlled by two modes. One was a rapid sinking of radiocesium-bound particles (summer mode). This mode was dominant especially in the early post-accident stage, and was presumed to establish the distribution of radiocesium in the offshore seabed. Another was the secondary transport of particles attributed to turbulence near the seabed and was observed in winter (winter mode). Although the latter process would not change the distribution of sedimentary radiocesium drastically, attention should be paid as a key process redistributing the accident-derived radiocesium over a long duration.

10 (Records 1-10 displayed on this page)
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