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  • 11
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    The 2‐D Structure of Foreshock‐Driven Field Line Resonances Observed by THEMIS Satellite and Ground‐Based Imager Conjunctions (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Recent studies of Pc5‐band (150–600 s) ultralow frequency waves found that foreshock disturbances can be a driver of dayside compressional waves and field line resonance, which are two typical Pc5 wave modes in the dayside magnetosphere. However, it is difficult to find spatial structure of dayside Pc5 waves using a small number of satellites or ground magnetometers. This study determines 2‐D structure of dayside Pc5 waves and their driver by utilizing coordinated observations by the THEMIS satellites and the all‐sky imager at South Pole during two series of Pc5 waves on 29 June 2008. These Pc5 waves were found to be field line resonances (FLRs) and driven by foreshock disturbances. The ground‐based all‐sky imager at South Pole shows that periodic poleward moving arcs occurred simultaneously with the FLRs near the satellite footprints over ~3° latitude and had the same frequencies as FLRs. This indicates that they are the auroral signature of the FLRs. The azimuthal distribution of the FLRs in the magnetosphere and their north‐south width in the ionosphere were further determined in the 2‐D images. In the first case, the FLRs distribute symmetrically in the prenoon and postnoon regions with out‐of‐phase oscillation as the odd toroidal mode in the equatorial plane. In the second case, the azimuthal wavelengths of the 350–500 s and 300–450 s period waves were ~8.0 and ~5.2 Re in the equatorial plane. It also shows a fine azimuthal structure embedded in the large‐scale arcs, indicating that a high azimuthal wave number (m ~ 140) mode wave coupled with the low‐wave number FLRs.
    Print ISSN: 2169-9380
    Electronic ISSN: 2169-9402
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 12
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    Microstructural evidence for the deep pulverization in a lower crustal meta‐anorthosite (2018)
    Wiley
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    Publication Date: 2018
    Description: Abstract We report on the evidence of the pulverization in a deep‐seated meta‐anorthosite in the Eidsfjord shear zone, Vesterålen, northern Norway. Some plagioclase porphyroclasts comprise a few large relict clasts and many fine grains that preserve the outlines of the original grains. The fine‐grained plagioclase does not show any plastic‐deformation microstructures and has strong crystallographic preferred orientations, which are inherited from the twinned porphyroclast. Misorientation‐axis distributions indicate that the grains have rotated randomly, so that the misorientation axes are not aligned with either the crystallographic or kinematic axes. The observed grain‐size distribution has a fractal dimension, suggesting their fracturing/fragmentation origin. The microstructures are characterized by the fracturing/fragmentation with a very low shear strain, indicating that it may be associated with pulverization at ~20–25 km depth.
    Print ISSN: 0954-4879
    Electronic ISSN: 1365-3121
    Topics: Geosciences
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  • 13
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    The warming of the Chukchi slope through the Barrow Canyon outflow in the 2016‐2017 winter (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The shallow Chukchi Sea is a gateway to the Arctic Ocean for Pacific‐origin waters. While a substantial portion of the Pacific‐origin waters flows through Barrow Canyon in the northeast corner of the Chukchi Sea, little is known on the hydrography of the surrounding regions in winter. We present profiles of wintertime hydrography on the Chukchi slope from an autonomous profiling instrument, and mooring records in Barrow Canyon. The central and western sectors of Barrow Canyon in December 2016 ‐ February 2017 (DJF 2016‐2017) were anomalously warm (∼0.5 ° C warmer than the climatology) with the flow orienting toward the Arctic Ocean. Unlike the summertime warming near the surface, the warm outflow has a temperature maximum at 80 dbar, and this outflow modifies the water mass properties on the Chukchi slope 70 km north of the canyon. Based on our Barrow Canyon mooring records starting in 2002, this is the first time that such warming is recorded on the outflow in winter. We discuss that this is due to the combination of the Barrow Canyon outflow favourable wind pattern and warming in the southern Chukchi Sea (the Gulf of Alaska and the Bering Sea) before the winter.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 14
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    Late Holocene changes on erosion pattern on a lacustrine environment: landscape stabilization by volcanic activity versus human activity (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The most recent eruption of Mt. Fuji (Japan), the VEI 5 Hōei plinian eruption (CE 1707) heavily impacted Lake Yamanaka, a shallow lake located at the foot of Mt. Fuji. Here, we discuss the influence of the Hōei eruption on the lacustrine sedimentation of Lake Yamanaka using high resolution geophysical and geochemical measurements on gravity cores. Hōei scoria fall‐out had two major impacts on Lake Yamanaka: (i) reduction of the sedimentation rate (from ~0.16 cm/yr to ~0.09 cm/yr); and (ii) the increase of in‐situ lake productivity. Sedimentation rates after the eruption were relatively low due to the thick scoria layer, trapping underlying sediments in the catchment. The lacustrine system took over more than ~170 years to begin to recover from the Hōei eruption: sedimentation recovery have been accelerated by changes in land use. Since the beginning of the 20th Century, vegetated strips delimited cultivated parcels, trapping sediment and minimizing the anthropogenic impacts on the sedimentation rate. Over the last decade, the decline of agriculture and the increase of other human activities led to an increase in the sedimentation rate (~1 cm/yr). This study highlights the effect of the grainsize of the volcanic ejecta on the sedimentation rate following a volcanic eruption. Coarse‐grained tephra are difficult to erode. Therefore, their erosion and remobilization is largely limited to intense typhoons when porous scoria deposits are saturated by heavy rains. Moreover, this study suggests that recent anthropogenic modifications of the catchment had a greater impact on the sedimentation rate than the Hōei eruption.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 15
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    Multi-decadal trends of oxygen and their controlling factors in the western North Pacific (2015)
    Wiley
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    Publication Date: 2015-06-10
    Description: The rate of change of dissolved oxygen (O 2 ) concentrations was analyzed over 1987–2011 for the high-frequency repeat section along 165°E in the western North Pacific. Significant trends towards decreasing O 2 were detected in the northern subtropical to subtropical-subarctic transition zones over a broad range of isopycnal horizons. On 25.3σ θ between 25°N-30°N in North Pacific Subtropical Mode Water, the rate of O 2 decrease reached −0.45 ± 0.16 µmol kg −1 yr −1 . It is largely attributed to a deepening of isopycnal horizons and to a reduction in oxygen solubility associated with ocean warming. In North Pacific Intermediate Water, the rate of O 2 decrease was elevated (−0.44 ± 0.14 µmol kg −1 yr −1 on 26.8σ θ ) and was associated with net increases in apparent oxygen utilization in the source waters. On 27.3σ θ in the subtropical Oxygen Minimum Layer (OML) between 32.5°N-35°N, the rate of O 2 decrease was significant (−0.22 ± 0.05 µmol kg −1 yr −1 ). It was likely due to the increases in westward transport of low-oxygen water. These various drivers controlling changes in O 2 along the 165°E section are the same as those acting along 137°E (analyzed previously), and also account for the differences in the rate of O 2 decrease between these sections. Additionally, in the tropical OML near 26.8σ θ between 5°N-10°N, significant trends toward increasing O 2 were detected in both sections (+0.36 ± 0.04 µmol kg −1 yr −1 in the 165°E section). These results demonstrate that warming and circulation changes are causing multi-decadal changes in dissolved O 2 over wide expanses of the western North Pacific.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 16
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    Near-Field Tsunami Inundation Forecast Using the Parallel TUNAMI-N2 Model: Application to the 2011 Tohoku-Oki Earthquake Combined with Source Inversions (2015)
    Wiley
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    Publication Date: 2015-02-04
    Description: To contribute to tsunami early warning systems, we investigated the currently achievable speed of tsunami inundation simulations on a parallel computer as well as the benefits of high-resolution and faster-than-real-time inundation predictions. We found that 5-m resolution inundation simulation can be 75 times faster than real time, requiring only 1.5 min to overview the inundation situation in Sendai City for the 2011 Tohoku tsunami. We developed a novel parallel tsunami model based on the well-known TUNAMI-N2 model and achieved 9.17 TFLOPS on 9,469 CPU cores. The present model can accurately hindcast the observed inundated regions of the 2011 Tohoku tsunami using tsunami source estimations of the tFISH and tFISH/RAPiD inversion algorithms, which can be instantly derived from real-time observation data. The present high-resolution predictions can provide clear images of imminent hazards/disasters and can provide guidance for appropriate evacuation actions.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 17
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    Nutrient supply and biological response to wind-induced mixing, inertial motion, internal waves, and currents in the northern Chukchi Sea (2015)
    Wiley
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    Publication Date: 2015-02-19
    Description: A fixed-point observation station was set up in the northern Chukchi Sea during autumn 2013, and for about 2 weeks conductivity-temperature-depth (CTD)/water samplings (6-hourly) and microstructure turbulence measurements (two to three times a day) were performed. This enabled us to estimate vertical nutrient fluxes and the impact of different types of turbulent mixing on biological activity. There have been no such fixed-point observations in this region, where incoming low-salinity water from the Pacific Ocean, river water, and sea-ice meltwater promote a strong pycnocline (halocline) that stabilizes the water column. Previous studies have suggested that because of the strong pycnocline wind-induced ocean mixing could not change the stratification to impact biological activity. However, the present study indicates that a combined effect of an uplifted pycnocline accompanied by wind-induced inertial motion and turbulent mixing caused by intense gale-force winds (〉10 m s -1 ) did result in increases in upward nutrient fluxes, primary productivity, and phytoplankton biomass, particularly large phytoplankton such as diatoms. Convective mixing associated with internal waves around the pycnocline also increased the upward nutrient fluxes and might have an impact on biological activity there. For diatom production at the fixed-point observation station, it was essential that silicate was supplied from a subsurface silicate maximum, a new feature that we identified during autumn in the northern Chukchi Sea. Water mass distributions obtained from wide-area observations suggest that the subsurface silicate maximum water was possibly derived from the ventilated halocline in the Canada Basin. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 18
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    Thermal dependency of shell growth, microstructure, and stable isotopes in laboratory-reared Scapharca broughtonii (Mollusca: Bivalvia) (2015)
    Wiley
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    Publication Date: 2015-07-04
    Description: We experimentally examined the growth, microstructure, and chemistry of shells of the bloody clam, Scapharca broughtonii (Mollusca: Bivalvia), reared at five temperatures (13, 17, 21, 25, and 29°C) with a constant p CO 2 condition (∼450 ppm). In this species, the exterior side of the shell is characterized by a composite prismatic structure, on the interior side it has a crossed lamellar structure on the interior surface. We previously found a negative correlation between temperature and the relative thickness of the composite prismatic structure in field-collected specimens. In the reared specimens, the relationship curve between temperature and the growth increment of the composite prismatic structure was humped-shaped, with a maximum at 17°C, which was compatible with the results obtained in the field-collected specimens. In contrast, the thickness of the crossed lamellar structure was constant over the temperature range tested. These results suggest that the composite prismatic structure principally accounts for the thermal dependency of shell growth, and this inference was supported by the finding that shell growth rates were significantly correlated with the thickness of the composite prismatic structure. We also found a negative relationship between the rearing temperature and δ 18 O of the shell margin, in close quantitative agreement with previous reports. The findings presented here will contribute to the improved age determination of fossil and recent clams based on seasonal microstructural records. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 19
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    FliH and FliI ensure efficient energy coupling of flagellar type III protein export in Salmonella (2016)
    Wiley
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    Publication Date: 2016-02-26
    Description: For construction of the bacterial flagellum, flagellar proteins are exported via its specific export apparatus from the cytoplasm to the distal end of the growing flagellar structure. The flagellar export apparatus consists of a transmembrane (TM) export gate complex and a cytoplasmic ATPase complex consisting of FliH, FliI, and FliJ. FlhA is a TM export gate protein and plays important roles in energy coupling of protein translocation. However, the energy coupling mechanism remains unknown. Here, we performed a cross-complementation assay to measure robustness of the energy transduction system of the export apparatus against genetic perturbations. Vibrio FlhA restored motility of a Salmonella Δ flhA mutant but not that of a Δ fliH-fliI flhB(P28T) Δ flhA mutant. The flgM mutations significantly increased flagellar gene expression levels, allowing Vibrio FlhA to exert its export activity in the Δ fliH-fliI flhB(P28T) Δ flhA mutant. Pull-down assays revealed that the binding affinities of Vibrio FlhA for FliJ and the FlgN–FlgK chaperone–substrate complex were much lower than those of Salmonella FlhA. These suggest that Vibrio FlhA requires the support of FliH and FliI to efficiently and properly interact with FliJ and the FlgN–FlgK complex. We propose that FliH and FliI ensure robust and efficient energy coupling of protein export during flagellar assembly. FlhA requires the support of FliH and FliI to efficiently and properly interact with FliJ and the flagellar type III secretion chaperone–substrate complexes.
    Electronic ISSN: 2045-8827
    Topics: Biology , Medicine
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  • 20
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    Investigation of the arrangement of oxide ion vacancies and their effect on the crystal structure of BaFe0.9In0.1O3−δ (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The crystal structure of BaFe0.9In0.1O3−δ, which was prepared via heating in N2 (BFI010‐N2), was evaluated using high‐temperature X‐ray diffraction (XRD) and in situ convergent‐beam electron diffraction (CBED) at room temperature and 700°C. Although the crystal structure of BFI010‐N2 at room temperature was assigned to a cubic perovskite‐type structure based on the XRD results, the CBED patterns indicated that the space group of its crystal structure was not (No. 221), which corresponds to an ideal cubic perovskite. When the temperature was increased to 700°C, the symmetries for the space group of cubic perovskite were directly observed by means of in situ CBED, indicating that the partial ordering and/or clustering of oxide ion vacancies in the BFI010‐N2 vanished and that the oxide ion vacancy arrangements became completely random. The change in crystal symmetry agreed with a sudden decrease in the activation energy of oxide ion conduction at 600°C. The crystal symmetry of the BaFe0.9In0.1O3−δ sample that was prepared via heating in O2 (BFI010‐O2) and had a decreased δ value was compared with that of the BFI010‐N2 sample. It was concluded that the same phase transition also occurred by a decrease in δ, similar to phase transitions caused by increasing the temperature.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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