Browsing by Author "Guo, J"

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    A chronological model for the Late Paleolithic at Shuidonggou Locality 2, North China
    (Public Library of Science (PLoS), 2020-05-27) Peng, F; Lin, SC; Patania, I; Levchenko, VA; Guo, J; Wang, H; Gao, X
    The site of Shuidonggou Locality 2 offers important evidence for the Late Paleolithic sequence of north China. The site not only contains one of the earliest instances of ornamental freshwater shell and ostrich eggshell beads in the region, but also stone artifacts with features arguably resembling the Initial Upper Paleolithic (IUP) blade technology found farther north. The appearance of these innovative archaeological forms have been attributed to the arrival of hominin populations, possibly modern humans, into the region during Marine Isotope Stage 3. Yet, the chronology of the site remains debated due to ambiguities in the existing dates. In this study, we conduct a systematical radiocarbon analysis of charcoal and ostrich eggshell samples obtained throughout the site sequence. Both acid-baseacid and the more stringent acid-base-oxidation pretreatment methods were applied to the charcoal samples. The resulting ages follow an age-depth relationship that is consistent with the stratigraphic profile. In line with previous stratigraphic assessments, Bayesian age modeling suggests that site formation history can be split into two phases: An early phase 43-35 cal kBP associated with a lacustrine depositional environment, and a later phase 35- 28 cal kBP associated with rapid terrestrial silt accumulation. The chronology of the archaeological layers containing IUP-like artifacts are placed at 43-39 cal kBP and 35-34 cal kBP respectively. This finding supports the interpretation that an IUP-like blade technology appeared in the SDG region by at least ∼41 ka. © © 2020 Peng et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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    Hydrogen storage performance and phase transformations in as-cast and extruded Mg-Ni-Gd-Y-Zn-Cu alloys
    (Elsevier, 2023-04-18) Yao, H; Zeng, G; Tan, XF; Gu, QF; Nogita, K; Guo, J; Li, Q
    Thermal-mechanical processing of magnesium-based materials is an effective method to tailor the hydrogen storage performance. In this study, Mg-Ni-Gd-Y-Zn-Cu alloys were prepared by Direct Chill (DC) casting, with and without extrusion process. The influences of microstructure evolution, introduced by DC casting and thermal-mechanical processing, on the hydrogen storage performance of Mg-Ni-Gd-Y-Zn-Cu alloys were comprehensively explored, using analytical electron microscopy and in-situ synchrotron powder X-ray diffraction. The result shows that the extruded alloy yields higher hydrogen absorption capacity and faster hydrogen ab/desorption kinetics. As subjected to extrusion processing, the α-Mg grains in the microstructure were significantly refined and a large number of 14H type long-period stacking ordered (LPSO) phases appeared on the α-Mg matrix. After activation, there were more nanosized Gd hydride/Mg2Ni intermetallics and finer chips. These modifications synergistically enhance the hydrogen storage properties. The findings have implications for the alloy design and manufacturing of magnesium-based hydrogen storage materials with the advantages of rapid mass production and anti-oxidation. © 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.