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Su, Dawei,Han Seo, Dong,Ju, Yuhang,Han, ZhaoJun,Ostrikov, Kostya,Dou, Shixue,Ahn, Hyo-Jun,Peng, Zhangquan,Wang, Guoxiu Nature Publishing Group 2016 NPG Asia Materials Vol.8 No.-
<P>The electrochemical performance of lithium-oxygen (Li-O-2) batteries can be markedly improved through designing the architecture of cathode electrodes with sufficient spaces to facilitate the diffusion of oxygen and accommodate the discharge products, and optimizing the cathode catalyst to promote the oxygen reduction reaction and oxygen evolution reaction (OER). Herein, we report the synthesis of ruthenium (Ru) nanocrystal-decorated vertically aligned graphene nanosheets (VGNS) grown on nickel (Ni) foam. As an effective binder-free cathode catalyst for Li-O-2 batteries, the Ru-decorated VGNS@Ni foam can significantly reduce the charge overpotential via the effects on the OER and achieve high specific capacity, leading to an enhanced electrochemical performance. The Ru-decorated VGNS@Ni foam electrode has demonstrated low charge overpotential of similar to 0.45 V and high reversible capacity of 23 864 mAh g(-1) at the current density of 200 mA g(-1), which can be maintained for 50 cycles under full charge and discharge testing condition in the voltage range of 2.0-4.2 V. Furthermore, Ru nanocrystal decorated VGNS@Ni foam can be cycled for more than 200 cycles with a low overpotential of 0.23 V under the capacity curtained to be 1000 mAh g(-1) at a current density of 200 mA g-1. Ru-decorated VGNS@Ni foam electrodes have also achieved excellent high rate and long cyclability performance. This superior electrochemical performance should be ascribed to the unique three-dimensional porous nanoarchitecture of the VGNS@Ni foam electrodes, which provide sufficient pores for the diffusion of oxygen and storage of the discharge product (Li2O2), and the effective catalytic effect of Ru nanocrystals on the OER, respectively. Ex situ field emission scanning electron microscopy, X-ray diffraction, Raman and Fourier transform infrared measurements revealed that Ru-decorated VGNS@Ni foam can effectively decompose the discharge product Li2O2, facilitate the OER and lead to a high round-trip efficiency. Therefore, Ru-decorated VGNS@Ni foam is a promising cathode catalyst for rechargeable Li-O-2 batteries with low charge overpotential, long cycle life and high specific capacity.</P>
Dawei Tian,Binyuan Liu,Li Zhang,Xiaoyang Wang,Wei Zhang,Lina Han,Dae Won Park 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.4
Four novel bifunctional aluminum–salen complexes (2a, 2b, 2c, and 2d) containing both Lewis acidic metal center and Lewis base quaternary phosphonium salt sites within one molecule and an aluminum–salen complex with a neutral tert-butyl group (2f) for comparison were synthesized and characterized by UV–vis, IR, 1H, 13C, 27Al NMR spectroscopy and Elemental analysis (EA). Their catalytic efficiencies as single-component catalysts toward the coupling reaction of carbon dioxide and propylene oxide were evaluated. These complexes exhibit catalytic activity in the order 2d > 2a > 2b > 2c 2f. 27Al NMR spectra reveal the existence of five- and six-coordinated metal centers in the aluminum–salen complexes bearing a quaternary phosphonium salt group, whereas only five-coordinate aluminum species were found in the aluminum–salen complex with a neutral tert-butyl group. This indicates the importance of the six-coordinate aluminum center in enhancing the catalytic activity as well as an intramolecular cooperative effect in bifunctional aluminum–salen complexes 2a–d. The effects of reaction variables on the catalytic performance were investigated in detail. These new catalysts are highly stable to moisture and air and robust to impurities in the coupling reaction.
Yu Dai,Xiao Wu,Dawei Sha,Ming Chen,Han Zou,Jie Ren,Jingjing Wang,Xuehua Yan 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.6
Graphene-like dichalcogenides with huge surface area and nanostructuredtransition metal oxides with extraordinarily high theoretical capacities could becomposited as promising electrode candidates for supercapacitors. In this work,monolayer and few-layers WS2 nanosheets were exfoliated by combination ofball-milling and sonication. A facile strategy for the hierarchical self-assembly ofFe3O4 nanoparticles (Fe3O4NPs) on WS2 nanosheets was developed to synthesizeFe3O4NPs@WS2 nanocomposites via hydrothermal method. Fe3O4NPs areuniformly dispersed on the WS2 nanosheets without aggregation. The particlesize of Fe3O4NPs is about 3 nm. The nanocomposite shows strong enhancementsof electrochemical behaviors. This self-assembly synthesis strategy may havegreat prospects for other 0D/2D nanocomposites in supercapacitors and otherenergy devices.
A Ghost-Imaging System Based on a Microfluidic Chip
Kaimin Wang,Xiaoxuan Han,Hualong Ye,Zhaorui Wang,Leihong Zhang,Jiafeng Hu,Meiyong Xu,Xiangjun Xin,Dawei Zhang 한국광학회 2021 Current Optics and Photonics Vol.5 No.2
Microfluidic chip technology is a research focus in biology, chemistry, and medicine, for example. However, microfluidic chips are rarely applied in imaging, especially in ghost imaging. Thus in this work we propose a ghost-imaging system, in which we deploy a novel microfluidic chip modulator (MCM) constructed of double-layer zigzag micro pipelines. While in traditional situations a spatial light modulator (SLM) and supporting computers are required, we can get rid of active modulation devices and computers with this proposed scheme. The corresponding simulation analysis verifies good feasibility of the scheme, which can ensure the quality of data transmission and achieve convenient, fast ghost imaging passively.
Chunxian Tao,Zhaoxia Han,Jun Ruan,Shunpeng Shu,Zhongrong Lu,Ruijin Hong,Dawei Zhang 한국광학회 2017 Current Optics and Photonics Vol.1 No.4
In order to investigate the ultraviolet-excited photoluminescence properties of phosphor coatings andtheir relationship to thickness, Lumogen coatings with different thicknesses were deposited on quartzsubstrates and charge-coupled device chips by thermal evaporation. The variation of the film thicknessaffected the crystallite size, surface roughness and fluorescence signal. It was found that the Lumogencoating with the thickness of 420 nm has the largest luminescent signal and conversion efficiency, andthe corresponding coated charge-coupled devices had the maximum quantum efficiency in the ultraviolet. These results provided one key parameter for improving the sensitivity of Lumogen coated charge-coupleddevices to ultraviolet light.
Quantitative Process Design of 1-D Crystallization for Pure Melt
Lunyong Zhang,Hongbo Zuo,Dawei Xing,Jiecai Han,Jianfei Sun 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.5
A 1-D crystallization process has been analyzed for thermal diffusion by solving the Fourier equation. The expressions of thermal fields indicate that the temperature decreases as the crystal grows and the temperature decreases in the solid phase as the crystal growth rate decreases. The trend of temperature variation is the opposite in the liquid phase. Meanwhile the temperature gradient decays along the crystal growth direction in both the solid and liquid phases. An obvious temperature layer gradually appears as the crystal growth rate increases when the crystal grows in an undercooled melt. According to these results, the following guidelines are suggested for the quantitative process design of the 1-D crystallization at a constant crystal growth rate: (1) the heater temperature must be decreased as the crystal grows along a route established using a formula, (2) the linear simplification of temperature distribution is applicable to the process design of crystallization only below a high growth rate limit, and (3) in order to keep the crystal growing in a non-undercooled melt, its growth rate cannot exceed a maximum.
Kwon, Moonhyuk,Kwon, Hyun-Han,Han, Dawei Elsevier 2018 Journal of hydrology Vol.564 No.-
<P><B>Abstract</B></P> <P>A multivariate stochastic soil moisture (SM) estimation approach based on a Gaussian-mixture nonstationary hidden Markov model (GM-NHMM) is introduced in this study to spatially disaggregate the AMSR2 SM data for multiple locations in the Yongdam dam watershed in South Korea. Rainfall and air temperature are considered as additional predictors in the proposed modeling framework. In GM-NHMM, a six-state model is constructed with three predictors representing an unobserved state associated with SM. It is clearly seen that the rainfall predictor plays a substantial role in achieving the overall predictability. Using weather variables (i.e., rainfall and temperature) can be effective in picking up some of the predictability of local SM that is not captured by the AMSR2 data. On the other hand, larger scale dynamic features identified from the AMSR2 data seem to facilitate the identification of regional spatial patterns of SM. The efficiency of the proposed model is compared with that of an ordinary regression model (OLR) using the same predictors. The mean correlation coefficient of the proposed model is about 0.78, which is significantly greater than that of the OLR at about 0.49. The proposed GM-NHMM method not only provides a better representation of the observed SM than the OLR model but also preserves the spatial coherence across all stations reasonably well.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A nonstationary HMM model is employed to spatially downscale the soil moisture data. </LI> <LI> Rainfall predictor plays a substantial role in achieving the overall predictability. </LI> <LI> Climate data are effective in picking up the predictability of local soil moisture. </LI> <LI> The proposed model preserves the spatial coherence across stations reasonably well. </LI> </UL> </P>
The Complete Genome Sequence of Southern rice black-streaked dwarf virus Isolated from Vietnam
Dinh, Thi-Sau,Zhou, Cuiji,Cao, Xiuling,Han, Chenggui,Yu, Jialin,Li, Dawei,Zhang, Yongliang The Korean Society of Plant Pathology 2012 Plant Pathology Journal Vol.28 No.4
We determined the complete genome sequence of a Vietnamese isolate of Southern rice black-streaked dwarf virus (SRBSDV). Whole genome comparisons and phylogenetic analysis showed that the genome of the Vietnamese isolate shared high nucleotide sequence identities of over 97.5% with those of the reported Chinese isolates, confirming a common origin of them. Moreover, the greatest divergence between different SRBSDV isolates was found in the segments S1, S3, S4 and S6, which differs from the sequence alignment results between SRBSDV and Rice black streaked dwarf virus (RBSDV), implying that SRBSDV evolved in a unique way independent of RBSDV. This is the first report of a complete nucleotide sequence of SRBSDV from Vietnam and our data provides new clues for further understanding of molecular variation and epidemiology of SRBSDV in Southeast Asia.