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Now showing items 49 - 64 of 89

  • Topological properties of the intermetallic compounds Sc-TM(TM =3D Cd,Ag,Cu,Hg,Au)

    Shang, Fanfan   Wang, Guangtao  

    We studied the electronic structure and topological properties of the intermetallic compounds (IMCs) Sc-TM (TM =3D Cd, Ag, Cu, Hg, Au), by using the first-principle calculations. We find that these IMCs are topologically nontrivial Mull-Nodal-Lines semimetals in the absence of the spin-orbit coupling (SOC). Unlike the previously reported nodal-line semimetals with nodal-lines inside their Brillouin-zones (BZ), the nodal-lines of the Sc-TM IMCs lie on six BZ surfaces, protected by the space inversion and time-reversal symmetries. The nodal-line induced drumhead liked surface states are obtained on the (001)-surface. When the SOC is included, a small band gap opens along the nodal lines. This indicates that these IMCs become topological insulators (TIs), on contrary to the general expectation that IMCs will be metals.
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  • Orbital ordering in Mott-insulators La(2)O(3)Fe(2)Se(2) and La(2)O(3)Co(2)Se(2)

    Wang, Guangtao   Zhang, Minping   Zheng, Lihua   Yang, Zongxian  

    The electronic structure and magnetic properties of new layered oxyselenide compounds La(2)O(3)Fe(2)Se(2) and La(2)O(3)Co(2)Se(2) are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe As-based superconductors. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
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  • Topological properties of the intermetallic compounds Sc-TM(TM = Cd, Ag, Cu, Hg, Au)

    Shang, Fanfan   Wang, Guangtao  

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  • The first-principles studying LaOMnSe: A possible parent compound of superconductor

    Wang, Guangtao   Zheng, Lihua   Zhang, Minping   Yang, Zongxian  

    By the first-principles calculations, we studied the structure, electronic and magnetic properties of LaOMnSe. The band structure and Fermi surface of LaOMnSe are very similar to those of LaOFeAs, where there are three hole-like Fermi surfaces around Gamma-point and two electron-like Fermi surfaces around M-point. The hole-like Fermi surfaces will strongly overlap with electron-like Fermi surfaces if they are shifted by the q vector (pi, pi, 0). Such Fermi surfaces nesting will induce magnetic instability and spin density wave (SDW), which is similar to LaOFeAs. Because of so much similarity to LaOFeAs, LaOMnSe is expected to become superconductor with electron or hole doping. (C) 2009 Published by Elsevier B.V.
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  • High-speed maglev noise impacts on residents: A case study in Shanghai

    Chen, Xiaohong   Tang, Feng   Huang, Zhaoyi   Wang, Guangtao  

    High-speed maglev trains offer competitive journey-times to automobile and air transport in markets of 60-1000 miles but they have potentially adverse noise impacts. This paper considers the noise characteristics of the Shanghai Maglev Train on residents within 300 in to the track. It shows that the system is about 4-8 dBA quieter than other high-speed systems at comparable speeds with their guideways at a similar distance. One of the train's noise characteristics is that L-ASmax drops 7-10 dBA as distance from the guideway doubles. The onset rate within 30 m-distance to the maglev track is more than 20 dB/s, and 86.51%, of respondents complained they had been startled when traveling beneath the guideway when it was in use. High speed maglev noise annoyance is not found to be strongly related to demographic variables, other than that home owners are more annoyed than renters. The linear dose-response relationships between HA% and L-ASmax is developed to evaluate the impacts of high-speed rail systems, with the finding that L-ASmax is more appropriate than calculated L-Acq to as a descriptor of noise level and limit boundary. (c) 2007 Elsevier Ltd. All rights reserved.
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  • Thermoelectric and optical properties of half-Heusler compound TaCoSn:A first-principle study

    Wei, Junhong   Wang, Guangtao  

    Based on first-principles simulation and semi-classical Boltzmann transport theory, we investigated the electronic structures and optical and thermoelectric properties of ternary half-Heusler compound TaCoSn. Results indicated that TaCoSn is a narrow-gap semiconductor. The accidental degeneracy of the valence-band maximum resulted in higher p-type Seebeck coefficients than n-type doping, in which the highest value reached 660 mu V/K at 900 K. The optimum carrier concentration is approximately 10(19) cm(3). In comparison to the experimental results of TaCoSn, we obtained the electrical conductivity and power factor of TaCoSn as a function of temperature and carrier concentrations, respectively. TaCoSn exhibits a large power factor of 10.93 mu W cm(-1) K-2 at 820 K. The calculated electrical conductivity and optical absorption coefficient agree well with the reported experimental data. ZT, shows a relatively high value for carrier concentrations at approximately 10(19) cm(3), and the p-type is superior to the n-type. These results indicate that TaCoSn can be used as an important photoelectric and thermoelectric material in the future. (C) 2018 Published by Elsevier B.V.
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  • The electronic structure and magnetism of a new layered iron selenide superconductor: LiOHFeSe

    Wang, Guangtao   Yi, Xia   Shi, Xianbiao  

    Highlights • Study the electronic and magnetic properties of LiOHFeSe. • Find the Fermi surfaces nesting induced spin density wave. • Explain the superconductivity in Li0.8Fe0.2OHFeSe, and predict the superconductivity in Li1 − xOHFeSe. Abstract We studied the electronic structure and magnetic properties of LiOHFeSe with first-principle calculations. The strong Fermi-surface nesting in the nonmagnetic state induces magnetic instability and the spin-density-wave state, which is more stable than the other states. The calculated bare susceptibility χ0(q) χ 0 ( q ) peaked at the M-point and it was obviously suppressed with increasing electron and hole doping.
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  • Goaf Compaction Evaluation Based on Integrity and Permeability Measurement of the Overburden Strata

    Zhai, Xiaorong   Wang, Guangtao   Wu, Jiwen   Bi, Yaoshan  

    Groundwater outbursts from coal mine goafs, which are widely distributed in China with the increase in the number of abandoned coal mines, demonstrate an impartible relationship with the permeability of goaf overburden strata. A research on rock mass integrity and permeability characteristics of goaf overburden strata is necessary to assess waterinrush risk induced by goaf water. Two goafs in two adjacent coal mines located at the Huaibei mining area in the Anhui Province of China were considered as the research targets. A ground exploration hole was conducted in each goaf. The rock mass integrity and fracture development of goaf overburden strata were determined on the basis of rock quality designation (RQD) and borehole television. The permeability of goaf overburden strata was measured by performing a field packer test. Results are as follows: (1) The fracture development of the borehole wall of the production mine is favorable, and a water drenching phenomenon occurs. The RQD is approximately 20.8-35.6%, which indicates that the integrity of the goaf overburden strata of the production mine is poor. The unit water inflow (q) is 0.133 L/s.m, and the average permeability coefficient is 0.26 m/d, which reveals that the goaf overburden strata of the production mine exhibit medium water abundance and permeable strata. (2) The overburden strata parameters of the abandoned mine goaf are as follows: the q is 0.012-0.014 L/s.m, and the average permeability coefficient is 0.005 m/d, which suggests that the goaf overburden strata exhibit poor water abundance and low permeable strata. The results demonstrate that the overburden strata compaction of the two goafs is different and the results can provide a reference for adjacent mines to access the water inrush risk induced by the goaf water of the abandoned coal mines.
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  • and

    Wang, Guangtao   Zhang, Minping   Zheng, Lihua   Yang, Zongxian  

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  • One-step synthesis of hydrophilic graphene-Fe3O4-PVA composite film:Micromorphology and performance

    Wang, Pengjun   Zhang, Mengyi   Liu, Yang   Wang, Liqiu   Lv, Qiulan   Xu, Daxing   Liu, Xiu   Wang, Guangtao   Yang, Wan   Wang, Pengchen   Yu, Tengbo   Xing, Shichao  

    Multifunctional polymers have wide applications in smart materials. In this study, the multifunctional polymer (hydrophilic graphene-Fe3O4-PVA, GFP composite films) were synthesized by mixing with hydrophilic graphene (HG), ferrous ammonium sulfate, and ferric chloride in PVA solution through one-pot coprecipitation method. GFP composite films were characterized by XRD, FT-IR. Their morphology and particle size of Fe3O4 in GFP composite film were observed by TEM, SEM, and AFM. The results indicated that the morphology of Fe3O4 in GFP could be modulated from sphere shape to rod structure by the loading quantity of HG. Besides, many properties of GFP composite films were investigated. Firstly, GFP composite films demonstrated the fast magnetic response and high thermal stability. Secondly, the introduction of HG not only simultaneously enhanced the stiffness and ductility of GFP composite films, but also improved their flame retarding performance. Finally, HG regulating effect for the morphology of Fe3O4 in GFP and improvement mechanism of HG for mechanical performance of GFP composite films were illustrated. Both of them might be contributed to the hydrogen bonds effect among Fe3O4, PVA, and HG. Thus, these multifunctional GFP composite films can be applicable as the basis of fabricating smart materials in different fields. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48174.
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  • An improved data characterization method and its application in classification algorithm recommendation

    Wang, Guangtao   Song, Qinbao   Zhu, Xiaoyan  

    Picking up appropriate classification algorithms for a given data set is very important and useful in practice. One of the most challenging issues for algorithm selection is how to characterize different data sets. Recently, we extracted the structural information of a data set to characterize itself. Although these kinds of characteristics work well in identifying similar data sets and recommending appropriate classification algorithms, the extraction method can only be applied to binary data sets and its performance is not high. Thus, in this paper, an improved data set characterization method is proposed to address these problems. For the purpose of evaluating the effectiveness of the improved method on algorithm recommendation, the unsupervised learning method EM is employed to build the algorithm recommendation model. Extensive experiments with 17 different types of classification algorithms are conducted upon 84 public UCI data sets; the results demonstrate the effectiveness of the proposed method.
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  • Synergistically optimizing interdependent thermoelectric parameters of n-type PbSe through alloying CdSe

    Qian, Xin   Wu, Haijun   Wang, Dongyang   Zhang, Yang   Wang, Jinfeng   Wang, Guangtao   Zheng, Lei   Pennycook, Stephen J.   Zhao, Li-Dong  

    PbSe is an alternative of the well-known moderate-temperature thermoelectric material PbTe, and has attracted much attention because of its advantages of high earth-abundance and low price of Se compared with Te. To enhance the thermoelectric performance of PbSe, its several shortcomings should be overcome, such as poor electrical conductivity, small Seebeck coefficient and bipolar thermal conductivity. Simultaneously improving these properties is a big challenge in the thermoelectric community. In this work, we successfully addressed these problems with PbSe by introducing just one component, CdSe, which has a similar crystal structure and larger band gap compared to PbSe. The introduction of CdSe realizes four positive effects: (1) improving the effective mass through flattening the conduction band; (2) decreasing the lattice thermal conductivity enormously by introducing hierarchical sub-nano defects; (3) keeping a high carrier mobility due to the nanostructure-free matrix; (4) suppressing the bipolar thermal conductivity via enlarging the band gap of PbSe. Due to all the above synergistically optimized electrical and thermal transport properties, a superior ZT value of B1.4 and ZTave of B0.7 are achieved in n-type PbSe through CdSe alloying, and the calculated conversion efficiency can reach 10.5%. Our results indicate that PbSe is a robust candidate for medium-temperature thermoelectric applications.
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  • Synergistically optimized electrical and thermal transport properties of polycrystalline SnSe via alloying SnS

    Zhao, Qian   Wang, Dongyang   Qin, Bingchao   Wang, Guangtao   Qiu, Yuting   Zhao, Li-Dong  

    SnSe crystals were reported to possess extraordinary thermoelectric performance, while the polycrystals were less marked due to the inferior carrier and phonon transport properties. Herein, we fully take advantage of the complex band structure and strong point scattering via alloying SnS. The carrier concentration and Seebeck coefficient were synergistically optimized via activating multiple valance bands and enlarging band effective mass, which contribute to a maximum power factor similar to 7.53 mu Wcm(-1)K(-2) at 793 K. Meanwhile, the lattice thermal conductivity was greatly reduced to similar to 0.92 Wm(-1)K(-1) due to the effective phonon scattering from point defects, as well demonstrated by the Callaway model. Combining a high power factor with low thermal conductivity, relatively high ZT of 1.2 at 793 K was obtained in polycrystalline Sn0.98Na0.02Se0.9S0.1. Our work demonstrates that alloying is simple yet effective approach for enhancing thermoelectric performance for polycrystalline SnSe, and SnSe system is one of promising thermoelectric candidates.
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  • Synergistically optimized electrical and thermal transport properties of polycrystalline SnSe via alloying SnS

    Zhao, Qian   Wang, Dongyang   Qin, Bingchao   Wang, Guangtao   Qiu, Yuting   Zhao, Li-Dong  

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  • The electronic structure of LaCo\r 2\r B\r 2

    Wang, Guangtao   Zhang, Minping   Li, Zhen   Yang, Zongxian  

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  • Electronic structure and optical properties of Cs(2)AX(2)' X-4 (A=3DGe,Sn,Pb; X,' X=3DCl,Br,I)

    Wang, Guangtao   Wang, Dongyang   Shi, Xianbiao  

    We studied the crystal structures, electronic structures and optical properties of Cs(2)AX(2)'X-4 (A=3DGe, Sn, Pb; X', X=3DCl, Br, I) compounds using the first-principles calculation. Our optimized structures agree well with experimental and theoretical results. Band structure calculations, using the modified Becke-Johnson (mBJ) potential method, indicate that these compounds (with the exception of Cs2PbX2'I-4) are semiconductors with the direct band gap ranging from 0.36 to 4.09 eV. We found the compounds Cs2GeBr2I4, Cs2GeCl2I4, Cs2GeI2Br4, Cs2SnI6, and Cs2SnBr2I4 may be good candidates for lead-free solar energy absorber materials. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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