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... Ferrat et al. (2011) found that the REE are enriched in the sediments smaller than the 32 μm fraction, the provenance tracers such as PAAS-normalized REE ratios, i.e., Y/ΣREE, La/Er, Gd/Er, La/Yb, and Y/Nd, and to a certain extent the europium anomaly Eu/Eu*, are size- independent tracers that represent long-range transported dust, even when bulk samples are used. The ratio of Eu/Sm in Xiashu loess in Nanjing is almost identical in different grain-size fractions, with a small variation within the range of 0.18- 0.21 ( Li et al. 2004). ...
Given the conflicts over the proposed formation mechanisms of Xiashu loess, the question of the provenance of sediments comprising the Xiashu loess in the Yangtze River Delta has not been satisfactorily resolved. In this study, the provenance of aeolian sediments of the Yangtze River Delta, China was examined by applying the detrial zircon U–Pb dating technique, Sr–Nd isotopic and trace element compositional analysis. U-Pb dating analysis was conducted on the Xiashu loess at three locations over the Yangtze River Delta, including Huangnishan (HNS) hill, Shengshan (SS) island and the Xuancheng (XC) area. The Xiashu loess and the sediments of the Yangtze River Valley share considerable similarity in their zircon U-Pb age spectra with the same main age peak and comparable age distribution. By contrast, significant differences in the age spectra, exist between the Xiashu loess and loess deposits of Chinese Loess Plateau (CLP). Coarse grains of the Yangtze River Delta loess may have a proximal material source identical to the sediments from the Yangtze River valley. Sr–Nd isotopic values of the Xiashu loess match those from the northern margin of the Tibetan Plateau. Rare earth element ratios independent of grain size illustrate that the values from loess of the Yangtze River Delta mostly overlap with those of CLP loess. This feature implies that loess from the Yangtze River Delta has a dominant source of distant material similar as the CLP loess. As such, we conclude that multi-proxy analysis of sediments can shed new light on tracing the provenance of aeolian loess in the Yangtze River Delta.
A simple and controllable method is developed to experimentally study the effects of defects on reduced graphene oxide (RGO) sheets for nanoelectronics application. First, a deterministic technique is developed to assemble a single layer graphene oxide sheet onto the gaps of microelectrodes by optimizing the dielectrophoretic parameters (10 Vpp at 1 MHz for 5 s). This is followed by the utilization of atomic force microscopy–based mechanical cutting method to form line defects on RGO sheets. Based on these two procedures, the experimental studies of the effects of line defects on RGO are investigated, which provides an alternative approach to study the influence of defects on graphene. The electric transport measurement results show that the electrical performance of the defected RGO devices generally decrease due to Anderson localization, which supports the theoretical studies of the influence of defects on the electrical properties of RGO.
Uncertainties in paleoenvironmental interpretations for traditional chemical analysis of bulk samples result from different grain-size sub-populations of sediments containing variable distributions of elements and minerals. Therefore, it is important to understand the elemental and mineral distribution in different grain sizes in determining the quantitative relationship between chemical weathering and climatic change. We sieved a series of Xiashu loess samples into three sub-populations of different grain sizes (< 2, 2-45 and > 45 mu m, respectively), and then analyzed each population for rubidium (Rb), strontium (Sr), rare earth elements and magnetic susceptibility. In comparison with elemental concentrations of bulk samples, clay mineralogy and illitic crystallinity, our results show that distinct elemental distributions and magnetic susceptibilities for different grain-size sub-populations are controlled by sorting and/or chemical weathering, although we also suggest that the Xiashu loess may have the same provenance as the Central Chinese Loess. Maximum concentrations of Rb and fine-grained magnetic minerals in the less than 2 mu m sub-population, coupled with our finding of maximum Sr in the larger than 45 mu m fraction, indicate that Sr was lost during chemical weathering. Grain-size sub-population analysis is, therefore, an effective method for extracting paleoenvironmental information, because individual sub-populations show minimal variations in initial Rb/Sr ratios compared to bulk analysis of all sizes together. Furthermore, a negative correlation between Rb/Sr ratios and Sr concentrations for the < 2 mu m fraction (R(2) = 0.97) may indicate that clay is a sensitive indicator of intensity of chemical weathering and is an ideal sub-population for determining Rb/Sr ratios, but not for magnetic susceptibility. (c) 2006 Elsevier Ltd. All rights reserved.
Xiashu loess strata are widely distributed along the middle-lower reaches of the Yangtze River in East China with the stratum near Nanjing, Jiangsu Province being typical. The cyclic variability of the stratum was investigated through comparison of geological features, chemical composition, and swelling-shrinkage properties between the loess and the paleosol layers. Based on the investigation of such a cyclic variability, soil behavior associated with the unsaturated state of the Xiashu loess stratum and its usefulness for geotechnical design and construction in the Nanjing area was analyzed. The stratum consisted of two types of cyclically alternating soil layers, namely the loess and the paleosol layers, which was the major cause for its cyclic variability. The loess and the paleosol layers were formed in Different sedimentary environments. In order to avoid detrimental results from the Differential engineering properties between them, this study suggested for the practitioners the importance of inspecting the variation of water content and controlling the downward net fluxes during geotechnical construction in the Nanjing area.
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