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Now showing items 113 - 128 of 446

  • Sedentism and plant cultivation in northeast China emerged during affluent conditions

    Shelach-Lavi, Gideon   Teng, Mingyu   Goldsmith, Yonaton   Wachtel, Ido   Stevens, Chris J.   Marder, Ofer   Wan, Xiongfei   Wu, Xiaohong   Tu, Dongdong   Shavit, Roi   Polissar, Pratigya   Xu, Hai   Fuller, Dorian Q.  

    The reasons and processes that led hunter-gatherers to transition into a sedentary and agricultural way of life are a fundamental unresolved question of human history. Here we present results of excavations of two single-occupation early Neolithic sites (dated to 7.9 and 7.4 ka) and two high-resolution archaeological surveys in northeast China, which capture the earliest stages of sedentism and millet cultivation in the second oldest center of domestication in the Old World. The transition to sedentism coincided with a significant transition to wetter conditions in north China, at 8.1-7.9 ka. We suggest that these wetter conditions were an empirical precondition that facilitated the complex transitional process to sedentism and eventually millet domestication in north China. Interestingly, sedentism and plant domestication followed different trajectories. The sedentary way of life and cultural norms evolved rapidly, within a few hundred years, we find complex sedentary villages inhabiting the landscape. However, the process of plant domestication, progressed slowly over several millennia. Our earliest evidence for the beginning of the domestication process appear in the context of an already complex sedentary village (late Xinglongwa culture), a half millennia after the onset of cultivation, and even in this phase domesticated plants and animals were rare, suggesting that the transition to domesticated (sensu stricto) plants in affluent areas might have not played a substantial role in the transition to sedentary societies.
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  • Relationships between nutrient, chlorophyll a and Secchi depth in lakes of the Chinese Eastern Plains ecoregion: Implications for eutrophication management.

    Zou, Wei   Zhu, Guangwei   Cai, Yongjiu   Vilmi, Annika   Xu, Hai   Zhu, Mengyuan   Gong, Zhijun   Zhang, Yunlin   Qin, Boqiang  

    Eutrophication and associated algal blooms are principal environmental challenges confronting lakes in China, particularly in the Eastern Plains ecoregion. The empirical relationships between nutrient and chlorophyll a (Chla) level and Secchi depth (SD) are widely used as a theoretical basis for lake eutrophication management. However, these relationships are largely influenced by hydromorphological conditions and biogeochemical processes. Thus, there is a need to establish a type-specific understanding of these interactions. In the current study, lakes in the Chinese Eastern Plains ecoregion were subdivided into four lake types according to water retention time (LRT), water depth, and water area. Regression analyses indicated that the impacts of nutrient (total nitrogen, TN; total phosphorus, TP) concentrations on summer Chla were significantly reduced in lakes with high inorganic suspended solids (ISS) (P<0.05). Meanwhile, the decrease in SD in these lakes were found to relate mainly to non-algal turbidity. In lakes characterized by both short LRT and high ISS content, the Chla exhibited limited response to nutrients. In contrast, in lakes with low ISS content and long LRT, the observed slopes of both Chla=3Df(TP) and SD=3Df(Chla) were significantly steeper (P<0.05). The factors limiting summer algal growth and the development of type-specific nutrient criteria (TN and TP) of all four investigated lake types in the Eastern Plains ecoregion are discussed in the context of specific nutrients. Based on these results, we establish type-specific eutrophication assessment equations of TN, TP, Chla, and SD in our study lakes. Our results may provide essential information for achieving the cost-effective eutrophication management of lakes both in the Eastern Plains ecoregion and elsewhere with similar climatic and hydromorphological conditions. Moreover, we believe that the subdivision of lakes to allow type-specific eutrophication management framework may prove valuable for other ecoregions where the interpretation of empirical nutrient-Chla and SD relationships suffer from similar serious limitations. Copyright =C2=A9 2020 Elsevier Ltd. All rights reserved.
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  • Microstructure Design of Carbonaceous Fibers:A Promising Strategy toward High-Performance Weaveable/Wearable Supercapacitors

    Yu, Chenyang   An, Jianing   Zhou, Ruicong   Xu, Hai   Zhou, Jinyuan   Chen, Qiang   Sun, Gengzhi   Huang, Wei  

    Fiber-based supercapacitors (FSCs) possess great potential as an ideal type of power source for future weaveable/wearable electronics and electronic-textiles. The performance of FSCs is, without doubt, primarily determined by the properties of fibrous electrodes. Carbonaceous fibers, e.g., commercial carbon fibers, newly developed graphene fibers, and carbon nanotube fibers, are deemed as promising materials for weaveable/wearable supercapacitors owing to their exotic properties including high tensile strength and robustness, excellent electrical conductivity, good flexibility, and environmental stability. Nevertheless, bare carbonaceous fiber normally exhibits low capacitance originating from electric double-layer capacitance, which remains unsatisfactory for efficiently powering wearable and portable devices. Numerous efforts have been devoted to tailoring fiber properties by hybridizing pseudocapacitive materials, and impressive progress has been achieved thus far. Herein, the microstructures of pristine carbonaceous fibers are introduced in detail, and the recent advances in rational nano/microstructure design of their hybrids, which provides the feasibility to achieve the synergistic interaction between conductive agents and pseudocapacitive nanomaterials but are normally overlooked, are comprehensively reviewed. Besides, the challenges in developing high-performance fibrous electrodes are also elaborately discussed.
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  • Holocene peatland development along the eastern margin of the Tibetan Plateau

    Xu, Hai   Liu, Bin   Lan, Jianghu   Sheng, Enguo   Che, Shuai   Xu, Sheng  

    Knowledge of peatland initiation, accumulation, and decline or cessation is critical in understanding peatland development and the related carbon source/sink effect. In this study, we investigated the development of three peat profiles along the eastern margin of the Tibetan Plateau (ETP) and compared the results with those of our previous work along this transect. Our work showed that the initiation over the northern ETP is later and the slowdown/cessation earlier than in the middle to southern ETP. The timing of optimum peatland formation over the northern ETP lags the Holocene climatic optimum. These spatio-temporal differences are likely to be related to the intensity of Asian summer monsoon. Our work suggests that some peatlands along the ETP transect have returned or are now returning their previously captured carbon to the atmosphere and thus act as carbon sources. Some peatlands still have net accumulation at present, but the rates have been reduced concomitant with the decreasing summer monsoon intensity. We speculate that more of the previously stored carbon in the ETP peatlands will be re-emitted to the atmosphere if the aridity continues, as might occur under a continuous global-warming scenario. (C) 2013 Published by Elsevier Inc. on behalf of University of Washington.
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  • Human impact on the historical change of CO2 degassing flux in River Changjiang

    Wang, FuShun   Wang, Yuchun   Zhang, Jing   Xu, Hai   Wei, Xiuguo  

    The impact of water quality changes in River Changjiang ( formally known as the Yangtze River) on dissolved CO2 and silicate concentrations and seasonal carbon flux in the past several decades ( 1960s - 2000) was evaluated, based on monitoring data from hydrographic gauge. It was found that dissolved CO2 and silicate in Changjiang decreased dramatically during this decades, as opposed to a marked increase in nutrient ( e. g. NO3-) concentrations. Our analyses revealed that dissolved CO2 in Changjiang was over-saturated with the atmosphere CO2, and its concentration had showed a declining trend since the 1960s, despite that fluvial DIC flux had maintained stable. Analysis results also suggested that the decrease in dissolved CO2 concentration was attributed to changes on the riverine trophic level and river damming activities in the Changjiang drainage basin. Due to the economic innovation ( e. g. agriculture and industry development) across the Changjiang watershed, fertilizers application and river regulations have significantly altered the original state of the river. Its ecosystem and hydrological condition have been evolving toward the " lacustrine/reservoir" autotrophic type prevailing with plankton. Accordingly, average CO2 diffusing flux to the atmosphere from the river had been reduced by three-fourth from the 1960s to 1990s, with the flux value being down to 14.2 mol. m(-2). yr(-1) in the 1990s. For a rough estimate, approximately 15.3 Mt of carbon was degassed annually into the atmosphere from the entire Changjiang drainage basin in the 1990s.
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  • Influence of Ovalbumin on CaCO(3) Precipitation during in Vitro Biomineralization

    Wang, Xiaoqiang   Wu, Congmeng   Tao, Kai   Zhao, Kang   Wang, Jiqian   Xu, Hai   Xia, Daohong   Shan, Honghong   Lu, Jian R.  

    As a major constituent of egg white matrix, ovalbumin has long been perceived to be implicated in the formation of avian eggshells, in particular, the mammillary layer. However, very little is known about the detailed mechanism by which this protein mediates shell calcification. By the combined studies of AFM, SEM, and TEM, we have investigated the influence of ovalbumin on CaCO(3) precipitation under in vitro mineralization conditions. We observed that the influence was multifold. This protein modified the morphology of calcite crystals through a distinct anisotropic process with respect to the four crystal step edges. AFM characterization revealed that the modification was initiated at the obtuse-obtuse step corner and propagated predominantly along the obtuse steps. Furthermore, the protein favored the existence of unstable phases such as amorphous calcium carbonate and crystalline vaterite. In contrast, lysozyme, another protein also present in the system, played a very different role in modifying calcite morphology. The mechanistic understanding gained from this study is clearly also of practical significance in developing advanced inorganic CaCO(3) materials with the aid of morphological manipulation of crystalline structures via different protein mediation.
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  • Preparation of mullite from desilication-flyash

    Guo, Anran   Liu, Jiachen   Xu, Rui   Xu, Hai   Wang, Caifen  

    A novel technique of flyash utilization was presented and mullite ceramics were prepared from flyash and desilication-flyash. The effect of desilication process was analyzed and the result shows that the only difference between flyash and desilication-flyash lies in the silica content, which is caused by the removal of silicate glassy phase during the desilication process. The physical and mechanical properties of flyash sample and desilication-flyash samples were measured. All results indicate that the desilication-flyash is more suitable to be used to prepare the mullite ceramics than flyash. The inner structure of flyash particle was first discovered, which can help us form a new description of the flyash particle and finally benefit the utilization of flyash. Lath-like mullite crystals appeared in high-iron samples and needle-like mullite crystals were observed in low-iron samples. The flexural strength of high-iron sample was higher than that of low-iron sample because of the formation of network structure consisting of many interlocked lath-like mullite crystals in high-iron samples. (C) 2010 Elsevier Ltd. All rights reserved.
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  • Polycarbonates with Potent and Selective Antimicrobial Activity toward Gram-Positive Bacteria

    Nimmagadda, Alekhya   Liu, Xuan   Teng, Peng   Su, Ma   Li, Yaqiong   Qiao, Qiao   Khadka, Nawal K.   Sung, Xiaoting   Pan, Jianjun   Xu, Hai   Li, Qi   Cai, Jianfeng  

    The resistance developed by life-threatening bacteria toward conventional antibiotics has become a major concern in public health. To combat antibiotic resistance, there has been a significant interest in the development of antimicrobial cationic polymers due to the ease of synthesis and low manufacturing cost compared to host-defense peptides (HDPs). Herein, we report the design and synthesis of amphiphilic polycarbonates containing primary amino groups. These polymers exhibit potent antimicrobial activity and excellent selectivity to Gram-positive bacteria, including multidrug resistant pathogens. Fluorescence and TEM studies suggest that these polymers are likely to kill bacteria by disrupting bacterial membranes. These polymers also show law, tendency to elicit resistance in bacteria. Their further development may lead to new antimicrobial agents combating drug-resistance.
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  • SAE Technical Paper Series [SAE International SAE 2007 Commercial Vehicle Engineering Congress & Exhibition - (OCT. 30, 2007)] SAE Technical Paper Series - A Novel Formula for Instantaneous Coefficients of Sliding Friction in Gearing

    Xu, Hai  

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  • Patterned Thermoresponsive Microgel Surfaces to Control Cell Detachment

    Xia, Yongqing   Tang, Ying   He, Xinlong   Pan, Fang   Li, Zonyi   Xu, Hai   Lu, Jian Ren  

    The aim of this work is to examine how adhered individual cells could detach from the patterned, discontinuous thermoresponsive coating substrate and how different patterns in the form of thermoresponsive squares and gaps would affect cell detachment. Microgels prepared from copolymerization of N-isopropylacrylamide and styrene (pNIPAAmSt) were spin-coated on polyethylenimine (PEI) precoated glass coverslips to form a uniform microgel monolayer; then a surface-moisturized PMDS stamp was used to contact the microgel monolayer at room temperature. The thin layer of water on the PDMS stamp surface worked as an ink to penetrate the microgels so that any microgels in direct contact with the wet stamp surface became swollen and could be peeled away, while uncontacted microgels formed patterns. Using this method, various patterns with different thermoisland diameters and gaps could be fabricated. NIH3T3 fibroblast cells were then cultured on these patterns to study their detachment behavior. It was found that cells could detach not only from these discontinuous thermoresponsive coatings, but also from the patterned surfaces with the thermoresponsive area being as low as 20% of the cell spread area.
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  • Synthesis of hierarchical flower-like Bi2MoO6 microspheres as efficient photocatalyst for photoreduction of CO2 into solar fuels under visible light

    Dai, Weili   Yu, Juanjuan   Xu, Hai   Hu, Xu   Luo, Xubiao   Yang, Lixia   Tu, Xinman  

    Hierarchical flower-like Bi2MoO6 microspheres were successfully synthesized via a facile hydrothermal approach, employing PVP as the crystal growth modifier. The building units of the hierarchical flower-like Bi2MoO6 were constructed by two-dimensional thin flakes, which intercrossed with each other and aggregated together to form the three-dimensional flower-like structure. The PVP amount and hydrothermal duration played crucial roles in the formation of the Bi2MoO6 architectures with evolving morphologies. The Bi2MoO6 samples were first evaluated for the photocatalytic reduction of CO2 into methanol and ethanol as solar fuels under visible-light irradiation. It has been found that the hierarchical flower-like Bi2MoO6 exhibits highly efficient photocatalytic activity. After 4 hours of irradiation, the yields of methanol and ethanol were 24.8 and 18.8 mu mol g(cat)(-1) respectively, higher than those obtained over previously-reported Bi2WO6 hollow microspheres. This demonstrates that the hierarchical flower-like Bi2MoO6 is a simple, efficient and promising visible-light-driven photocatalyst for the photoreduction of CO2 into solar fuels.
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  • Deuterated Ethanol as a Probe for Measuring Equilibrium Isotope Effects for Hydroxyl Exchange

    Xu, Hai   Zhao, Siqi   Xiong, Xiang   Yao, Jiayao   Cross, R. James   Saunders, Martin  

    Equilibrium deuterium isotope effects for exchange of hydroxyl deuterons and protons among tert-butanol, phenol, ethanethiol, diethylamine, and ethanol were measured by using NMR and also calculated theoretically. Deuterated ethanol could be used as a probe for measuring equilibrium isotope effects (EIE) for hydroxyl exchange; tert-butanol, phenol, ethanethiol, diethylamine, and pyrrole were used as five representive examples. A procedure called the "one-atom isotope effect" was used to save time in the calculations.
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  • A ''naked-eye'' colorimetric and ratiometric fluorescence probe for trace hydrazine

    Wu, Cuiyan   Xu, Hai   Li, Yaqian   Xie, Ruihua   Li, Peijuan   Pang, Xiao   Zhou, Zile   Li, Haitao   Zhang, Youyu  

    Hydrazine (N2H4) is widely used in industry but also very toxic. Herein, we describe the preparation of a "naked-eye" colorimetric and ratiometric fluorescent probe (DH), bearing alpha,beta-unsaturation carbonyl group as a recognition site, and employ it for the excited-state intramolecular proton transfer based (ESIPT-based) detection of N2H4. The probe can detect N2H4 by colorimetric and ratiometric fluorescence dual signals with high sensitivity and selectivity; the detection limit of N2H4 was 0.063 mu M (2.01 ppb), which was far below the safety level (10 ppb) stated by the U.S. Environmental Protection Agency (EPA). It enables "naked-eye" detection for hydrazine determination in aqueous solution. More importantly, we successfully applied DH to detect N2H4 in real water samples, indicating its potential utility for N2H4 sensing in environmental samples.
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  • Real-time tracking and selective visualization of exogenous and endogenous hydrogen sulfide by a near-infrared fluorescent probe

    Gu, Biao   Su, Wei   Huang, Liyan   Wu, Cuiyan   Duan, Xiaoli   Li, Yaqian   Xu, Hai   Huang, Zhen   Li, Haitao   Yao, Shouzhuo  

    Rapid capture and selective visualization of hydrogen sulfide (H2S) in living systems has remained challenging. In this work, by employing ortho-aldehyde assisted thiolysis of 2,4-dinitrophenyl (DNP) ether approach and utilizing the dicyanomethylene-4H-chromene as the fluorophore, we developed a new fluorescent probe (E)-2-(2-(4-(2,4-dinitrophenoxy)-3-formylstyryl)-4H-chromen-4-ylidene) malo- nonitrile (2-CHO-OH) for this purpose with improved recognition performances. Probe 2-CHO-OH showed the advantage of quick reaction (8 min) with H2S, resulting in a strong near-infrared fluorescence emission (32-fold enhancement) and large Stokes shift (137 nm). More importantly, the probe could highly selectively detect H2S from other biological related species including cysteine, homocysteine and glutathione with distinct dual colorimetric and fluorescent signal changes. The detection limit of H2S was estimated as 8.3 x 10(-8) M, which was much lower than the intracellular concentration. Thanks to these unique features, 2-CHO-OH has been successfully applied for NIR fluorescence imaging of both the exogenous and endogenous H2S in living cells, demonstrating its value of practical application in biology. (C) 2017 Elsevier B.V. All rights reserved.
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  • Variations in DENSE AND ERECT PANICLE 1 (DEP1) contribute to the diversity of the panicle trait in high-yielding japonica rice varieties in northern China

    Zhao, Mingzhu   Sun, Jian   Xiao, Zhiqiu   Cheng, Fei   Xu, Hai   Tang, Liang   Chen, Wenfu   Xu, Zhengjin   Xu, Quan  

    Rice is one of mankind's major food staples, and the erect panicle architecture in rice is an important morphological improvement. The dense and erect panicle 1 (DEP1) locus corresponds with the formation of erect panicles and has been widely used in rice breeding. However, the genetic diversity of DEP1 remains narrow. In order to improve the genetic diversity of DEP1, we used a rice germplasm collection of 72 high yielding japonica rice varieties to analyze the contribution of DEP1 to the panicle traits. We found 45 SNPs and 26 insertions and deletions (indels) within the DNA fragment of DEP1. We further detected 7 haplotypes and found that the replacement of 637 bp by a 12 bp fragment could explain the erect panicle architecture in all 72 germplasms. An SNP (G/C) at the -1253 bp of the promoter region caused a core sequence shift (TGGGCC) of a site II transcriptional regulatory element. The association analysis showed that the SNP(G/C) largely affects the number of primary and secondary branches, and grain number per panicle. Our results provide novel in-sights into the function and genetic diversity of DEPI. The SNP (G/C) at the promoter region will contribute to the flexible application of DEP1 in rice breeding.
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  • Polarity-assisted formation of hollow-frame sheathed nitrogen-doped nanofibrous carbon for supercapacitors

    Gong, Yujiao   Chen, Ruyi   Xu, Hai   Yu, Chenyang   Zhao, Xi   Sun, Yue   Hui, Zengyu   Zhou, Jinyuan   An, Jianing   Du, Zhuzhu   Sun, Gengzhi   Huang, Wei  

    Heteroatom-doped carbon nanostructures with uniform size and morphology, well-designed architectures, and minimized interfacial resistance have been recognized as promising electrode materials for energy storage, but remain a crucial challenge. Herein, we develop a general approach of polarity-induced decoration of a monolayer sheath of metal-organic framework (MOF) particles with excellent uniformity in size and morphology on electrospun polymer nanofibers. These hybrid nanofibers are facilely converted into nitrogen-doped nanofibrous carbon (denoted as N-NFC) during pyrolysis. The thus-obtained N-NFC features (1) a one-dimensional nanofibrous structure with a highly conductive core, (2) a monolayer sheath of hollow carbon-frames with uniform size and morphology, (3) plenty of micro/mesopores with a highly accessible surface area, and (4) a high N-doping level, all of which guarantee its good electrochemical performance with a high capacitance of 387.3 F g(-1) at 1 A g(-1). In a solid-state supercapacitor, it delivers excellent rate capability (78.0 F g(-1) at 0.2 A g(-1) and 64.0 F g(-1) at 1 A g(-1)), an enhanced energy density of 7.9 W h kg(-1) at a power density of 219 W kg(-1), and outstanding cycling stability with 90% capacity retained over 10000 cycles at 1 A g(-1).
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