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Three-dimensionally ordered macro-porous Pt/TiO_2 catalyst used for water-gas shift reaction

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Journal of Natural Gas Chemistry 2008年第4期17卷 403-408页

作者： Hao Liang yuan Zhang yuan liu Department of Catalysis Science and Technology School of Chemical Engineering and Technology Tianjin University Tianjin 300072 China

Three-dimensionally ordered macro-porous （3DOM） Pt/TiO2 catalysts were prepared by template and impregnation methods, and the resultant samples were characterized by using TG-DTA, XRD, SEM, TEM, and TPR techniques. The catalytic performance for water-gas shift （WGS） reaction was tested, and the influences of some conditions, such as reduction temperature of catalysts, the amount of Pt loadings and space velocity on catalytic performance were investigated. It was shown that Pt particles were homogeneously dispersed on 3DOM TiO2. The reduction of TiO2 surface was important for the catalytic performance. The activity test results showed that the 3DOM Pt/TiO2 catalysts exhibited very good catalytic performance for WGS reaction even at high space velocity, which was owing to the better mass transfer of 3DOM porous structure besides the high intrinsic activity of Pt/TiO2.

关键词： three-dimensionally ordered macro-porous water-gas shift platinum titania

Explicit Convergence Rates of the Embedded M/G/1 Queue

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Acta Mathematica Sinica,English Series 2007年第7期23卷 1289-1296页

作者： yuan yuan liu Zhen Ting HOU School of Mathematics Central South University

This paper investigates the explicit convergence rates to the stationary distribution π of the embedded M/G/1 queue; specifically, for suitable rate functions r（n） which may be polynomial with r（n） = n^l, l 〉 0 or geometric with r（n） = α^n, a 〉 1 and ＂moments＂ f ≥ 1, we find the conditions under which Σ∞n=0 r（n）｜｜P^n（i,·） - π（·）｜｜f ≤ M（i） for all i ∈ E. For the polynomial case, the explicit bounds on M（i） are given in terms of both ＂drift functions＂ and behavior of the first hitting time on the state O; and for the geometric case, the largest geometric convergence rate α＊ is obtained.

关键词： convergence rate Markov chains queues polynomial ergodicity geometric ergodicity

Local Asymptotics of a Markov Modulated Random Walk with Heavy-tailed Increments

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Acta Mathematica Sinica,English Series 2011年第9期27卷 1843-1854页

作者： Bing Chang WANG yuan yuan liu Institute of Systems Science Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing 100190 P. R. China School of Mathematics Railway Campus Central South University Changsha 410075 P. R. China

In this paper, we obtain sufficient and necessary conditions for local asymptotics for the maximum of a Markov modulated random walk with long-tailed increments and negative drifts, where the local asymptotics means asymptotic behaviour of P（ ∈ （x,x ＋ z]） for each z 〉 0, as x→∞ Our results extend and improve the existing ones in the literature.

关键词： Mavkov modulated random walk local asymptotics long-tailed distributions subexpo- nential distributions Wiener-Hopf factorization

Monolithic macroporous catalysts—a new route for miniaturization of water-gas shift reactor

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Journal of Natural Gas Chemistry 2009年第4期18卷 436-440页

作者： Hao Liang yuan Zhang yuan liu Department of Catalysis Science and Technology School of Chemical Engineering and Technology Tianjin University Tianjin 300072 China

Monolithic macroporous Pt/CeO2/Al2O3 catalysts were prepared using concentrated emulsions synthesis route, and the obtained samples were characterized with SEM, TG, TEM, XRD and TPR techniques. These monolithic catalysts were applied to water gas shift （WGS） reaction in reformed gases. The SEM and TEM results indicated that the monoliths possessed macroporosity, and that the platinum particles homogeneously dispersed on the supports with the particle size in the range of 1-2 nm. The reducibility of the catalysts was characterized by TPR method, and it was shown that the monolithic PtOx/CeO2/Al2O3 exhibited the similar reducibility property to that of the particle PtOx/CeO2 reported in literatures. The CO conversion over the monolithic catalysts is higher than that over micro-reactor catalysts for WGS reaction in the reformed gases conditions, indicating that the monolithic macroporous catalysts is a potential new route for miniaturization of WGS reactor.

关键词： macroporous monolith miniaturization water gas shift platinum

3D stress simulation and parameter design during twin-roll casting of 304 stainless steel based on the Anand model

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International Journal of Minerals,Metallurgy and Materials 2014年第7期21卷 666-673页

作者： Jing Guo yuan-yuan liu Li-gang liu Yue Zhang Qing-xiang Yang State Key Laboratory of Metastable Materials Science & Technology Yanshan University Nanjing Iron & Steel Co. School of Material Science and Engineering University of Science and Technology Beijing

This study first investigated cracks on the surface of an actual steel strip. Formulating the Anand model in ANSYS software, we then simulated the stress field in the molten pool of type 304 stainless steel during the twin-roll casting process. Parameters affecting the stress distribution in the molten pool were analyzed in detail and optimized. After twin-roll casting, a large number of transgranular and intergranular cracks resided on the surface of the thin steel strip, and followed a tortuous path. In the molten pool, stress was enhanced at the exit and at the roller contact positions. The stress at the exit decreased with increasing casting speed and pouring temperature. To ensure high quality of the fabricated strips, the casting speed and pouring temperature should be controlled above 0.7 m/s and 1520℃, respectively.

关键词： stainless steel strip metal roll casting stress surface cracks numerical analysis

Enhancements of Passive Film and Pitting Resistance in Chloride Solution for 316LX Austenitic Stainless Steel After Sn Alloying

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Acta Metallurgica Sinica(English Letters) 2019年第1期32卷 98-106页

作者： yuan-yuan Yang yuan-yuan liu Man-Lang Cheng Nian-Wei Dai Min Sun Jin Li Yi-Ming Jiang Department of Materials Science Fudan University

In the present work, the electrochemical behavior and properties of the passive film of a new Sn-alloyed 316 LX austenitic stainless steel were investigated. With the increase in Sn content in 316 LX austenitic stainless steel from 0 to 0.21%, the critical pitting temperature value increased from 32.6 to 38.8 °C, and the pitting potential increased from 0.252 V_(SCE) to 0.317 V_(SCE). Electrochemical impedance spectroscopy results showed that the corrosion resistance of passive film rose with the increase in Sn content, indicating a more stable passive film. The Mott–Schottky measurement revealed an n-type passive film with a decreased carrier concentration on the 316 LX austenitic stainless steel surface. The Cr, Sn^(2+) and Sn^(4+)(SnO, SnOHCl or SnO_2) enrichments were observed in the passive layer by X-ray photoelectron spectroscopy. The enrichment of Sn and Cr in the passive film can account for the enhanced pitting resistance of 316 LX austenitic stainless steel in chloride solution.

关键词： Austenitic stainless steel Sn alloying Pitting Chloride solution

The Maximum Surplus Distribution before Ruin in an Erlang（n） Risk Process Perturbed by Diffusion

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Acta Mathematica Sinica,English Series 2011年第9期27卷 1869-1880页

作者： Zhen Zhong ZHANG Jie Zhong ZOU yuan yuan liu College of Science Donghua University Shanghai 201620 P. R. China andSchool of Mathematics Central South University Changsha 410075 P. R. China School of Mathematics Central South University Changsha 410075 P. R. China

In this paper, we consider the distribution of the maximum surplus before ruin in a generalized Erlang（n） risk process （i.e., convolution of n exponential distributions with possibly different parameters） perturbed by diffusion. It is shown that the maximum surplus distribution before ruin satisfies the integro-differential equation with certain boundary conditions. Explicit expressions are obtained when claims amounts are rationally distributed. Finally, the surplus distribution at the time of ruin and the surplus distribution immediately before ruin are presented.

关键词： Sparre Anderson risk model generalized Erlang(n) inter-claim times integro-differential equation diffusion process maximum surplus distribution

On the Positivity of Linear Weights in WENO Approximations

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Acta Mathematicae Applicatae Sinica 2009年第3期25卷 503-538页

作者： yuan-yuan liu Chi-wang Shu Meng-ping Zhang Department of Mathematics University of Science and Technology of China Hefei 230026 China Division of Applied Mathematics Brown University Providence RI 02912 USA

High order accurate weighted essentially non-oscillatory （WENO） schemes have been used extensively in numerical solutions of hyperbolic partial differential equations and other convection dominated problems. However the WENO procedure can not be applied directly to obtain a stable scheme when negative linear weights are present. In this paper, we first briefly review the WENO framework and the role of linear weights, and then present a detailed study on the positivity of linear weights in a few typical WENO procedures, including WENO interpolation, WENO reconstruction and WENO approximation to first and second derivatives, and WENO integration. Explicit formulae for the linear weights are also given for these WENO procedures. The results of this paper should be useful for future design of WENO schemes involving interpolation, reconstruction, approximation to first and second derivatives, and integration procedures.

关键词： Weighted essentially non-oscillatory (WENO) scheme hyperbolic partial differential equations WENO interpolation WENO reconstruction WENO approximation to derivatives WENO integration

Synthesis,characterization,and theoretical study of N,S-codoped nano-TiO_2 with photocatalytic activities

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International Journal of Minerals,Metallurgy and Materials 2011年第5期18卷 606-614页

作者： Hong-tao Gao yuan-yuan liu Cui-hong Ding Dong-mei Dai Guang-jun liu State Key Laboratory of Crystal materials Shandong University Jinan 250100 China College of Chemistry and Molecular Engineering Qingdao University of Science and Technology Qingdao 266042 China Department of Chemistry and Chemical Engineering Jining University Qufu 273155 China

Nitrogen and sulfur doped titanium dioxide photocatalysts were prepared by the sol-gel *** products were characterized by X-ray diffraction （XRD）,transmission electron microscopy （TEM）,and UV-visible diffuse reflectance spectra （DRS）.Photocatalytic activities of the samples were investigated on the degradation of methyl orange （MO）.The effect of the dopants on the electronic structure of TiO2 was studied by the first-principles calculations based on the density functional theory （DFT）.The orbital hybridization resulted in energy gap narrowing and electronic delocalization in the crystal of doped *** electrons of varied energetic states could offer enhanced electron transfer,together with optical absorption *** results show that the doping elements of N and S play a cooperative role in the modification of electronic structure,which enhances the photocatalytic *** experimentally observed absorption edges of N-doped TiO2,S-doped TiO2,and N,S-codoped TiO2 are 420,413,and 429 nm,respectively,which can be explained by the theoretical calculation results.

关键词： titanium dioxide doping electronic structure red shift photocatalysis nanoparticles