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Articles by Wei Zhou
Total Records ( 12 ) for Wei Zhou
  Wei Zhou , Lin Luo , Hongzhou Xu and Dongxiao Wang
  An intensive observation and a three-dimensional finite-difference model of Environmental Fluid Dynamic Code were used to study saltwater intrusion in the Pearl River Estuary. The model simulation was carried out for December 2007 to February 2008, which covered the in situ observation. The model was forced by observed winds, tidal elevation at open boundaries, and river discharges from eight inlets in the Pearl River Estuary. The agreements with observation were verified in terms of current, salinity and tide elevation. Using the computed tidal current, the residual current was also calculated to estimate material transport. In addition, the Lagrangian method was used to track the trajectory of particles from the mouth of Humen and Modaomen inlets. By computing the flushing time of these two channels, the authors find that there exists close relationship between flushing time and saltwater intrusion. Potential impact of sea-level rise on saltwater intrusion was also studied. Sensitivity experiments indicate that sea-level rise can impact on the saltwater intrusion in the Pearl River Estuary, such as increasing salinity concentration and intrusion distance, especially during neap tide in winter (dry season).
  Peng Yu , Wei Zhou , Yu Zhao , Hui Sun , Jian Liu and Yan Liu
  Keeping the wind power constant is essential for the large-scale integration of wind power into electric power system. In this study, we classify the wind power fluctuation and propose a method of suppressing the fluctuant wind power by an Active-Parallel Hybrid Energy Storage System (APHESS). The APHESS consists of a battery, a supercapacitor and two charge-discharge controllers. By designing the configuration logically, the APHESS obtains the enhanced energy storage performance and the low investment cost. In order to realize the wind power suppression, the method of controlling the APHESS to exchange power precisely with the wind power system is developed in this study. For the purpose of making the battery and supercapacitor balance, respectively different kinds of fluctuation classified in this study, the power within APHESS is allocated reasonably between the battery and the supercapacitor. By the method proposed in this study, the fluctuant wind power can be balanced effectively and the service life of energy storage system can be prolonged.
  Wei Zhou , Weiren Shi , Peng Gao , Hongde Zhang and Xiaogang Wang
  Localization is a crucial issue and acts as a fundamental element in wireless sensor networks. The location accuracy of sensor node increases with the number of beacon points which can provide reference information for localization. However, the more beacons are used, the higher implementation cost is. In the study, a distributed algorithm called RSS-assisted range-free is proposed to locate sensor nodes using mobile beacons. The proposed algorithm only uses three beacon points to estimate the position of the sensor node. In the proposed scheme, two beacon points are used to obtain candidate positions of the sensor node and the third beacon point is used to determine which one of the candidates would be the actual position of the sensor node. To improve the location accuracy, the study estimates sensor position from possible candidate regions by using geometric conjecture and Received Signal Strength (RSS) constraints. The simulation results have shown that the proposed algorithm is feasible and significantly improves on location accuracy.
  Peng Gao , Wei-Ren Shi , Wei Zhou , Hong-Bing Li and Xiao-Gang Wang
  Node localization is a fundamental problem in many wireless sensor networks applications. In this study, based on simulated annealing approach, an adaptive RSSI compensation strategy in cooperative localization (called SA-ARC-CL algorithm) is proposed. Firstly, we built cooperative localization model and then extract the localization problem based on this model. The core problem is to find the right RSSI compensation of each Access Point (AP). After that, an improved simulated annealing approach is proposed to solve this problem, in which some new rules are proposed to make this solution more effective. Finally, based on RSSI compensation, WCL algorithm is used to obtain the final position of each UN. Simulation results show that the proposed algorithm performs better than WCL algorithm using only a few APs and has a good RSSI adaptive ability in indoor localization applications.
  Hongde Zhang , Weiren Shi , Hui Han and Wei Zhou
  This study analyses the performance of the random waypoint mobile model in mobile sensor network based on asymptotic spatial distribution theory, which is mainly aimed at analyzing the connectivity and coverage performances of the network, in order to obtain the maximized coverage with connectivity performance. Meanwhile, it also analyses the relationship between the length of the longest edge of the Minimum Spanning Tree (MST) and the minimum transmission distance of node in Geometric Random Graphs and provides the minimum transmission distance of mobile sensor network for ensuring connectivity. Finally, the theoretical analysis results are verified based on the method of experimental simulation, which shows that the bigger the number of the node, the more consistent the results of theoretical analysis and experimental result, higher reliability.
  Wei Zhou , Wen-Qi Liu , Dong-Liang Wang , Gui-Xiang Zhu , Ying-Jie Hu and Yong-Feng Zhan
  With the increasing utilization of telemedicine/tele health services, a vast number of medical images are now transmitted over the Internet and through wireless networks. Consequently, how to effectively protect the patients’ privacy has become an important issue. Recently, chaos-based encryption approaches have been suggested and it is reported that they are more effective than traditional encryption algorithms when processing images. In this study, a novel permutation-diffusion architecture based medical image protection scheme is suggested. The new scheme introduces a parallel chaotic keystream generation mechanism so as to reduce the runtime cost on diffusion. Various intensive experiments are carried out to evaluate effectiveness and efficiency of the proposed cryptosystem. Computational results indicate that the cryptosystem can withstand all kinds of main attacks including brute-force attack, differential attack, known/chosen plain-text attack and various statistical attacks. We also show that the efficiency of the proposed cryptosystem is effectively improved.
  Ke-Chiun Chang , Chien-Chung Yuan , Chang-Liang Lin and Wei Zhou
  Technological diversification has positive influence on corporate performance, however, previous studies have only presumed as a linear relationship. As business environment nowadays has became more dynamic and uncertain, it is important to explore the possible non-linear relationship between the technological diversification and its consequents. This study uses panel negative binomial fixed effect model to explore the nonlinear relationships between technological diversification and corporate patent performance. The result indicates that technological diversification has nonlinear effect of which an inverted U-shape on the corporate patent performance. Technological diversification is positively related with corporate patent performance when the value of technological diversification is below the critical point and vice-versa. This finding has important implication for corporate management.
  Wei Zhou and Yonghai Wang
  Using a sample population of CEOs from listed companies in China, we studied empirical important corporate risk index-risk-taking level by examining whether or not the CEO characteristics help explain their level of corporate risk taking. As corporate risk-taking level reflects CEOs’risk preference which was formed from their characteristics. We found that CEOs’ age and education level are significant negatively related with corporate risk taking level. Female CEOs tend to maintain less leverage than male CEOs. Risk-taking level is greater at firms where CEOs are younger. CEOs with a higher level of education tend to maintain low volatility of earnings and have significant less leverage. These results help understanding corporate risk control and management in China.
  Wei Zhou and Katsunori Sato
  The effects of high fat diet on obesity and susceptibility to diabetics in Alloxan-induced diabetes-susceptible mice were studied. A total of 40 mice were divided equally (n = 10 per group) into four groups: (i) male high fat (40%) diet group (ii) female high fat (40% fat) diet group (iii) male control (7% fat) diet group and (iv) female control (7% fat) diet group. The body weight and blood glucose level of high fat male diet group were significantly (p<0.01; p<0.001) higher than those of other groups at 5 to 20 weeks of age. The high fat male and female mice produced significantly higher (p<0.05; p<0.001) perinephrium fat and mesenteric fat than those for corresponding control groups. However, the high fat female mice produced significantly (p<0.001) higher epididymal and high fat male mice produced significantly (p<0.001) lower epididymal fat than those for corresponding control groups. The high fat female mice produced significantly (p<0.01) higher retroperitoneal fat than that for control female group. The percentages of pancreas and genital organ trended to decrease and percentage of liver tended to increase for high fat male mice and percentage of pancreas and liver tended to decrease in high fat female mice than those for corresponding control group. However, the difference between two dietary groups in female mice for genital organ was insignificant. Only the male group fed with high fat diet developed diabetes (rate of incidence of glycosuria) with the earliest onset in strains occurred at the age of 10 weeks, followed by increasing to 100% disease at the age of 18 weeks and the phenomenon had been kept till the 20 weeks of age. Results of this study have shown that high fat diet male mice developed diabetics and dysfunction of glucose metabolism.
  Wei Zhou , Ran Ran and Zongping Shao
 

Solid-oxide fuel cells (SOFCs) convert chemical energy directly into electric power in a highly efficient way. Lowering the operating temperature of SOFCs to around 500–800 °C is one of the main goals in current SOFC research. The associated benefits include reducing the difficulties associated with sealing and thermal degradation, allowing the use of low-cost metallic interconnectors and suppressing reactions between the cell components. However, the electrochemical activity of the cathode deteriorates dramatically with decreasing temperature for the typical La0.8Sr0.2MnO3-based electrodes. The cathode becomes the limiting factor in determining the overall cell performance. Therefore, the development of new electrodes with high electrocatalytic activity for oxygen reduction becomes a critical issue for intermediate-temperature (IT)-SOFCs. Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite oxide was first reported as a potential IT-SOFC cathode material in 2004 by Shao and Haile. After that, the BSCF cathode has attracted considerable attention. This paper reviews the current research activities on BSCF-based cathodes for IT-SOFCs. Emphasis will be placed on the understanding and optimization of BSCF-based materials. The issues raised by the BSCF cathode are also presented and analyzed to provide some guidelines in the search for the new generation of cathode materials for IT-SOFCs.

  Wei Zhou , Wenhua Su , Xi Cheng , Yuanjiang Xiang , Xiaoyu Dai and Shuangchun Wen
  Nonlinear coupled equations describing the copropagation of two light pulses of different central frequencies in metamaterials (MMs) are derived. Based on the derived equations and the Drude model for dispersive MMs, the modulation instabilities (MIs) induced by cross-phase modulation (XPM) for different combination of the signs of refractive index experienced by the two optical pulses, respectively, are analyzed. It is shown that, in the absence of group-velocity mismatch, the property of MI only depends on the sign of group-velocity dispersion the two pulses experience, irrespective of the sign of refractive index. The group-velocity mismatch plays an important role in the occurrence of MI, especially when the central frequencies of the two pulses near the electric or magnetic plasma frequency of the MM. The theoretical results are confirmed by numerical simulations.
  Wei Zhou , Jinling Yang , Yan Li , An Ji , Fuhua Yang and Yude Yu
  The mechanical properties and fracture behavior of silicon nitride (SiNx) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiNx thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiNx films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiNx thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiNx thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiNx layer during SiO2 removal.
 
 
 
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