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DEM investigation of angle of repose for super-ellipsoidal particles

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Particuology 2020年第3期18卷 53-66页

作者： Hao Chen Shiwei Zhao xiaowen zhou State Key Laboratory of Subtropical Building Science South China University of TechnologyGuangzhou 510641China

We explore the effect of particle shape on the angle of repose (AoR) in granular packing using a three-dimensional discrete element ***-spherical particles were modeled using super-ellipsoids characterized by aspect ratio and *** relationship between AoR and particle shape was examined,followed by a series of analyses on the origin of AoR from a microscopic *** show that,with blockiness deviating from unity,AoR has an approximate "M" shape that exhibits a strong to weak trend with aspect ratio,matching results of previous *** finding suggests a parabolic relationship between normalized AoR and normalized coordination number,AoR increases with anisotropy related more with the anisotropy of particle orientation than with the anisotropy of contact *** shape is more likely to affect AoR by affecting the tangential force than the normal contact *** analysis based on traction indicates that dips in stress associated with the tangential force (compared with the normal force) and non-spherical particles (compared with spheres) are more *** various particle shapes,AoR is positively correlated with friction mobilization but is negatively correlated with friction mobilization for various coefficient of friction.

关键词： Discrete element Angle of repose Non-spherical particles Granular fabric Packing

A Wiener-Hopf factorization related potential measure for spectrally negative Lévy process

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Frontiers of Mathematics in China 2021年第2期16卷 325-343页

作者： Man CHEN Xianyuan WU xiaowen zhou School of Mathematical Sciences Capital Normal UniversityBeijing 100048China Department of Mathematics and Statistics Concordia UniversityMontrealQC H3G 1M8Canada

For spectrally negative Lévy process (SNLP), we find an expression, in terms of scale functions, for a potential measure involving the maximum and the last time of reaching the maximum up to a draw-down time. As applications, we obtain a potential measure for the reflected SNLP and recover a joint Laplace transform for the Wiener-Hopf factorization for SNLP.

关键词： Spectrally negative Lévy process(SNLP) potential measure draw-down time excursion theory scale function Wiener-Hopf factorization

An occupation time related potential measure for diffusion processes

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Frontiers of Mathematics in China 2017年第3期12卷 559-582页

作者： Ye CHEN Yingqiu LI xiaowen zhou Hunan Province Cooperative Innovation Center for the Construction and Development of Dongting Lake Ecological Economic Zone and College of Mathematics and Computational Science Hunan University of Arts and Science Changde 415000 China School of Mathematics and Statistics Changsha University of Science and TechnologyChangsha 410114 China Department of Mathematics and Statistics Concordia UniversityMontreal Quebec H3G IMS Canada

In this paper, for homogeneous diffusion processes, the approach of Y. Li and X. zhou [Statist. Probab. Lett., 2014, 94： 48-55] is adopted to find expressions of potential measures that are discounted by their joint occupation times over semi-infinite intervals （-∞, a） and （a, ∞）. The results are expressed in terms of solutions to the differential equations associated with the diffusions generator. Applying these results, we obtain more explicit expressions for Brownian motion with drift, skew Brownian motion, and Brownian motion with two-valued drift, respectively.

关键词： Laplace transform occupation time potential measure exit time,time-homogeneous diffusion Brownian motion with two-valued drift skew Brownian motion

Branching particle systems in spectrally one-sided Levy processes

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Frontiers of Mathematics in China 2015年第4期10卷 875-900页

作者： Hui HE Zenghu LI xiaowen zhou Laboratory of Mathematics and Complex Systems School of Mathematical SciencesBeijing Normal University Beijing 100875 China Department of Mathematics and Statistics Concordia UniversityMontreal Quebec H3G 1M8 Canada

We investigate the branching structure coded by the excursion above zero of a spectrally positive Levy process. The main idea is to identify the level of the Levy excursion as the time and count the number of jumps upcrossing the level. By regarding the size of a jump as the birth site of a particle, we construct a branching particle system in which the particles undergo nonlocal branchings and deterministic spatial motions to the left on the positive half line. A particle is removed from the system as soon as it reaches the origin. Then a measure-valued Borel right Markov process can be defined as the counting measures of the particle system. Its total mass evolves according to a Crump- Mode-Jagers （CMJ） branching process and its support represents the residual life times of those existing particles. A similar result for spectrally negative Levy process is established by a time reversal approach. Properties of the measure- valued processes can be studied via the excursions for the corresponding Levy processes.

关键词： Levy process spectrally one-sided subordinator branchingparticle system non-local branching Crump-Mode-Jagers (CMJ) branchingprocess

Random packing of tetrahedral particles using the polyhedral discrete element method

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Particuology 2015年第6期13卷 109-117页

作者： Shiwei Zhao xiaowen zhou Wenhui Liu Chengguang Lai School of Civil Engineering and Transportation South China University of Technology Guangzhou 510640 China State Key Laboratory of Subtropical Building Science Guangzhou 510640 China Key Laboratory of Water Cycle and Water Security in Southern China of Guangdong Higher Education Institutes Cuangzhou 510275 China

The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.

关键词： Discrete element method Random packing Tetrahedral particle Coordination number Packing density

Diffusion occupation time before exiting

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Frontiers of Mathematics in China 2014年第4期9卷 843-861页

作者： Yingqiu LI Suxin WANG xiaowen zhou Na ZHU College of Mathematics and Computing Sciences Changsha University of Science and Technology Changsha 410004 China College of Mathematics Nankai University Tianjin 300071 China Department of Mathematics and Statistics Concordia University MontrealQuebec H3G 1M8 Canada

Using the approach of D. Landriault et al. and B. Li and X. zhou, for a one-dimensional time-homogeneous diffusion process X and constants c 〈 a 〈 b 〈 d, we find expressions of double Laplace transforms of the form Ex[e--θTd--λ∫o Td1a 〈Xs〈b ds; Td 〈 Tc], where Tx denotes the first passage time of level x. As applications, we find explicit Laplace transforms of the corresponding occupation time and occupation density for the Brownian motion with two-valued drift and that of occupation time for the skew Ornstein- Uhlenbeck process, respectively. Some known results are also recovered.

关键词： Diffusion exit problem occupation time occupation density localtime Brownian motion with two-valued drift skew Ornstein-Uhlenbeck (OU)process

Performances improvement of eosin Y sensitized solar cells by modifying TiO_2 electrode with silane-coupling reagent

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Chinese Science Bulletin 2009年第15期54卷 2633-2640页

作者： zhou YanFang LI XuePing ZHANG JingBo zhou xiaowen LIN Yuan CAS Key Laboratory of Photochemistry Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China Graduate University of Chinese Academy of Sciences Beijing 100049 China

Chemical fixing of xanthene dye (eosin Y) on the surface of TiO2 electrode was carried out by modifying the electrode with silane-coupling reagent to obtain stable dye-sensitized TiO2 electrode. Such silane modification can not only evidently enhance the stability of dye-sensitized TiO2 electrode but also im-prove the energy conversion efficiency of the assembled cells by increasing short-circuit photocurrent (JSC) and open-circuit photovoltage (VOC). It was found that the improvements of cell performances differ depending on the composition of the electrolyte. The optimum cell of the cell performance was achieved in the electrolyte with 0.5 mol/L TBAI/0.05 mol/L I2/EC:PC(3:1 w/w), yielding JSC of 4.69 mA·cm?2, VOC of 0.595 V, fill factor (FF) of 0.64 and η of 1.78%. Different spectroscopic techniques including UV-Vis spectra, fluorescence spectra, EIS and dark current measurements were employed to derive reasonable analysis and explanations.

关键词： TiO2电极硅烷偶联剂太阳能电池染料敏化曙红Y 修改表演能量转换效率

Rare earth recovery from fluoride molten-salt electrolytic slag by sodium carbonate roasting-hydrochloric acid leaching

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Journal of Rare Earths 2023年第8期41卷 1242-1249,I0005页

作者： Hao Wu Huashan Yan Yanzhen Liang Sen Qiu xiaowen zhou Dongmei Zhu Tingsheng Qiu Collaborative Innovation Center for Development and Utilization of Rare Metal Resources Co-sponsored by Ministry of Education and Jiangxi Province Jiangxi University of Science and TechnologyGanzhou 341000China Jiangxi Province Key Laboratory of Mining Engineering Jiangxi University of Science and TechnologyGanzhou 341000China School of Resources and Environmental Engineering Jiangxi University of Science and TechnologyGanzhou 341000China

Fluorinated rare earth molten-salt electrolytic slag contains a considerable amount of rare earth elements,as well as a variety of heavy metals and fluorides that cause environmental ***,it is of great importance to fully utilise this *** this study,the transformation mechanism of fluorinated rare earth molten-salt electrolytic slag roasted with sodium carbonate,and the regulation mechanism of rare earth leaching under different roasting conditions were investigated with the help of thermodynamic calculation of the reactions and kinetic *** thermodynamic and differential thermal thermogravimetric(DTA-TG)analysis shows that the transformation of rare earth fluoride to rare earth oxide is promoted at elevated ***,the leaching experimental results show that increasing the temperature,time,hydrochloric acid concentration,and liquid-solid ratio can effectively promote the recovery of rare *** optimum experimental conditions are a roasting temperature of 700℃,roasting time of 2 h,and sodium carbonate to molten salt electrolytic slag mass ratio of 0.6,followed by leaching at 80℃with a liquid-solid ratio of 10:1 by adding 3 moI/L hydrochlo ric acid with stirring for 2 *** these conditions,the rare earths in the molten salt electrolytic slag are biologically transformed at a lower temperature and the leaching efficiency of rare earths exceeds 98%.

关键词： Fluorinated rare earth molten-salt electrolytic slag Sodium carbonate Roasting Transformation mechanism Leaching Rare earths

Synthesis of TiO_(2) nanotubes film and its light scattering property

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Chinese Science Bulletin 2005年第18期50卷 1985-1990页

作者： MA Yutao LIN Yuan XIAO Xurui LI Xueping zhou xiaowen Key Laboratory of Photochemistry Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 100080 China Graduate School of Chinese Academy of Sciences Beijing 100039 China

TiO2 nanotubes with diameters of 10 nm and lengths up to 600 nm were fabricated by directly using com-mercial TiO2 powders P25 as the precursors via sonica-tion-hydrothermal combination approach. TiO2 nanotubes were characterized by means of X-ray powder diffractometer (XRD), scanning electron microscope (SEM), selected area electron diffraction pattern (SAED) and transmission elec-tron microscope (TEM). The light scattering property of film electrodes modified with TiO2 nanotubes was studied and revealed that TiO2 nanotubes can be used as the light scat-tering centers to increase the light absorption in dye- sensi-tized solar cells. The TiO2 nanotubes film electrodes mixed with 10% small nanoparticles TiO2 had both strong light scattering property and fine mechanical characteristics, and this kind of electrodes can be used as electrodes in improving the conversion efficiencies of dye-sensitized solar cells.

关键词：二氧化钛纳米管光散射反射光谱超声波降解法 X射线