Browsing by Author "Wu, Z"

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    In situ neutron-diffraction study of the Ti38V30Cr14Mn18 structure during hydrogenation
    (Elsevier Science BV, 2013-11-01) Fei, Y; Kong, X; Wu, Z; Li, HH; Peterson, VK
    The phase transformations of the Ti38V30Cr14Mn18 alloy during hydrogenation and dehydrogenation using deuterium (D2) were investigated using in situ neutron powder diffraction (NPD) at various D2 pressures up to 2 MPa. Initially, the first hydride that formed, Ti38V30Cr14Mn18D15, had the same body centered cubic (BCC) crystal structure as the starting alloy. Upon further hydrogenation, the system displays a distinct two-phase mixture of the intermediate BCC and body-centered tetragonal (BCT) phases, that exist in a ration of 1.38:1.42, respectively. At the end of the deuterium absorption, the phase pure Ti38V30Cr14Mn18D183 material forms, with a face-centered cubic (FCC) structure. Upon dehydrogenation, all hydride phases eventually returned to the initial alloy phase without any amorphization or disproportionation. Using standard Rietveld refinement, information on the variation of the deuterium site occupancy, the lattice symmetry, and the cell volume were determined during these phase changes and are presented. © 2013, Elsevier Ltd.
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    Isochron 26A1/10Be burial dating of Xihoudu: evidence for the earliest human settlement in northern China
    (Elsevier, 2020-12) Shen, G; Wang, Y; Tu, H; Tong, H; Wu, Z; Kuman, K; Fink, D; Granger, DE
    The mainstream school of human evolution posits that Homo erectus was the earliest species to leave Africa at ∼1.85 million years (Ma) ago. Recent discoveries from the Shangchen loess-palaeosol sequence near the Lantian hominid site in northern China, however, show lithic artifacts up to 2.12 Ma, pre-dating the fossil record of H. erectus. Here we apply the recently established isochron 26Al/10Be burial dating, whose reliability has been verified by intercomparison with 40Ar/39Ar dating, to two locations at the Palaeolithic site of Xihoudu ∼100 km east of Shangchen. The results show that the stone tools found within river gravels there are 2.43 ± 0.06 Ma (1σ) old, making them the earliest radio-isotopically dated evidence for human occupation in Eurasia. The new date is supported by relative dating of the associated fauna, by consistent simple burial ages of quartz sand from deep cores, and by agreement between the two isochrons. Although the validity of the Xihoudu artifacts has been previously debated because of marked fluvial abrasion, there is clear evidence of intentional flaking. In particular, in addition to two cores with small amounts of cortex, a number of flakes lack original rock cortex, which indicate multiple and sustained removals that do not occur naturally. The great antiquity of the Xihoudu artifacts renders firm support to an earlier “Out of Africa I” that approaches the emergence of the genus Homo and the Oldowan industry. © 2020 Elsevier Masson SAS.