Fabrication and characterization of silicon nanostructures based on metal-assisted chemical etching

Wendong Zhang,Jie Hu,Xuge Fan,Shengbo Sang,Pengwei Li,Gang Li,Yongjiao Sun 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.1

We present a facile method to fabricate one-dimensional Si nanostructures based on Ag-induced selective etching of silicon wafers. To obtain evenly distributed Si nanowires (SiNWs), the fabrication parameters have been optimized. As a result, a maximum of average growth rate of 0.15 μm/min could be reached. Then, the fabricated samples were characterized by water contact angle (CA) experiments. As expected, the as-etched silicon samples exhibited a contact angle in the range of 132o-136.5o, whereas a higher contact angle (145o) could be obtained by chemical modification of the SiNWs with octadecyltrichlorosilane (OTS). Additionally, Raman spectra experiments have been carried out on as-prepared nanostructures, showing a typical decreasing from 520.9 cm−1 to 512.4 cm−1 and an asymmetric broadening, which might be associated with the phonon quantum confinement effect of Si nanostructures.

Strength, deformation and failure behavior of bolted rock-like specimen with multiple cracks under uniaxial compression by particle flow simulation

Wendong Yang,Yiwei Li,Ling Wang,Kaicheng Zhang,Zhicheng Gong 한국지질과학협의회 2023 Geosciences Journal Vol.27 No.6

Most of the rock mass in nature contains a large number of joints, faults and other defects, which make the rock mass have the characteristics of discontinuity and anisotropy, and easily lead to instability and failure of rock engineering. A great quantity of engineering practices show that the bolt has a significant supporting effect on jointed rock mass. Therefore, it is of great significance to study the deformation and failure characteristics of jointed rock mass and the crack arrest effect of bolt for the safety and stability of engineering. A reasonable numerical model of bolted rock samples with non-persistent joints is established by using a three-dimensional Particle Flow Code (PFC) based on the laboratory rock specimens, and the uniaxial compression numerical test is carried out. The results indicate that (1) the numerical simulation results are in good agreement with the laboratory test results, and the variation trend of strength is basically consistent; (2) the different joint angles and anchorage angles result in variations in the mechanical properties of bolted specimens with non-persistent joints; (3) the joint angle has a significant effect on the failure mode of the specimen; (4) the existence of bolts can effectively limit the initiation and propagation process of micro-cracks, and greatly improve the mechanical properties of the specimen containing non-persistent joints.

A New Closed-loop Control Allocation Method with Application to Direct Force Control

Wendong Gai,Jie Liu,Jing Zhang,Yuxia Li 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.3

A new closed-loop control allocation method is proposed to distribute the force and moment increment commands among multiple actuators at the same time. An innovative feedback configuration for the force and moment increment produced by the actuators deflections is added into the trajectory and attitude control loop, respectively. In addition, the trajectory and attitude controllers designed by nonlinear dynamic inversion are used to derive the desired force and moment increment commands. Then, the stability of the closed-loop system is guaranteed theoretically when the actuators are healthy and fail, where there is no a fault detection method to identify the failure. Finally, the proposed method is used to achieve direct force control for decoupling the attitude and flight trajectory in the longitudinal flight. The nonlinear simulation using Canard Rotor/Wing (CRW) aircraft longitudinal model in fixed-wing mode demonstrates that this method can achieve two direct force control modes: pitch pointing and direct lift, whether the actuators are healthy or fail.

A Secure and Efficient Remote User Authentication Scheme for Multi-server Environments Using ECC

( Junsong Zhang ),( Jian Ma ),( Xiong Li ),( Wendong Wang ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.8

With the rapid growth of the communication technology, intelligent terminals (i.e. PDAs and smartphones) are widely used in many mobile applications. To provide secure communication in mobile environment, in recent years, many user authentication schemes have been proposed. However, most of these authentication schemes suffer from various attacks and cannot provide provable security. In this paper, we propose a novel remote user mutual authentication scheme for multi-server environments using elliptic curve cryptography (ECC). Unlike other ECC-based schemes, the proposed scheme uses ECC in combination with a secure hash function to protect the secure communication among the users, the servers and the registration center (RC). Through this method, the proposed scheme requires less ECC-based operations than the related schemes, and makes it possible to significantly reduce the computational cost. Security and performance analyses demonstrate that the proposed scheme can solve various types of security problems and can meet the requirements of computational complexity for low-power mobile devices.

Using DFP Algorithm for Nodal Demand Estimation of Water Distribution Networks

Hui Zhang,Kai Wang,Xue Zhou,Wendong Wang 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.8

Nodal demand estimation of a Water Distribution Network (WDN) means calculating the estimated values of nodal demands withsome measured parameter values through mathematical methods. The most existing methods are based on an constrained weightedleast-squares model and repeated computation of Jacobian matrix for optimal solutions. In this paper a new nonlinear modelcombined with pseudo-measurements and pressure constraints was developed for solution uniqueness. Davidon-Fletcher-Powell(DFP) algorithm was proposed to search for the solution by one dimensional optimization and scale matrix calculation, which waseasier than Jacobian matrix computation. Two cases, including a real-life WDN of X city in northwest China, were used to show theperformance of the proposed algorithm. Encouraging results showed that the proposed method was effective and feasiblemacroscopically, and it had potential for practical applications of WDNs.

Nonlinear Adaptive Backstepping with ESO for the Quadrotor Trajectory Tracking Control in the Multiple Disturbances

Jie Liu,Wendong Gai,Jing Zhang,Yuxia Li 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.11

In this paper, we present a nonlinear adaptive backstepping with extended state observer (ESO) trajectory tracking controller for a quadrotor unmanned aerial vehicle (UAV) subject to the multiple disturbances, which include the parametric uncertainties, actuator faults and external disturbance. First, a six-degrees of freedom quadrotor UAV model with the multiple disturbances function is built. Second, the adaptive backstepping controller is designed to track the desired trajectory command aim at internal disturbance. And the adaptive backstepping controller with ESO is designed to track the desired trajectory command aim at external disturbance. Third, the stability of the system is proved by the circle criterion. Finally, under different flight scenarios, simulation results are given to demonstrate the effectiveness of the proposed method.

Flexible and Highly Sensitive Piezoresistive Pressure Sensor with Sandpaper as a Mold

Wendan Jia,Qiang Zhang,Yongqiang Cheng,Dong Zhao,Yan Liu,Wendong Zhang,Shengbo Sang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.7

Flexible pressure sensors based on piezoresistive induction have recently become a research hotspot due to the simple device structure, low energy consumption, easy readout mechanism and excellent performance. For practical applications, flexible pressure sensors with both high sensitivity and low-cost mass production are highly desirable. Herein, this paper presents a high-sensitivity piezoresistive pressure sensor based on a micro-structured elastic electrode, which is low cost and can be mass-produced by a simple method of sandpaper molding. The microstructure of the electrode surface under external pressure causes a change in the effective contact area and the distance between the electrodes, which exhibits great pressure sensitivity. The test results show that the surface structure is twice as sensitive as the planar structure under low pressure conditions. This is because of the special morphology of silver nanowires (AgNWs), which exhibits the tip of nanostructures on the surface and realizes the quantum tunneling mechanism. The sensor has high sensitivity for transmitting signals in real time and it can also be used to detect various contact actions. The low cost mass production and high sensitivity of flexible pressure sensors pave the way for electronic skin, wearable healthcare monitors and contact inspection applications.

Electrical properties and morphology of highly conductive composites based on polypropylene and hybrid fillers

Gu Zheming,Wang Gengchao,Zhang Ling,Cheng Qilin,Li Xiaohui,Wang Wendong,Jin Shilei,Li Chunzhong 한국공업화학회 2010 Journal of Industrial and Engineering Chemistry Vol.16 No.1

Electrically conductive polypropylene/hybrid filler (PP/GO–MWNTs) and PP/MWNTs composite have been prepared via melt blending PP with the hybrid filler (multiwalled carbon nanotubes (MWNTs) and graphite oxide (GO)) and the single filler (MWNTs), respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to research the interior morphology of the GO–MWNTs hybrid filler, and the dispersion of the hybrid filler in the PP matrix is also observed by SEM. The results show that a clear reduction in electrical resistivity and percolation threshold of PP/GO–MWNTs composite can be ascribed to the corporation of GO. The electrical properties of PP composites were improved owing to the effective conductive networks formed by hybrid filler.

Back-stepping Robust Control for Flexible Air-breathing Hypersonic Vehicle via a-filter-based Uncertainty and Disturbance Estimator

Yuhua Yang,Xingling Shao,Yi Shi,Wendong Zhang 제어·로봇·시스템학회 2021 International Journal of Control, Automation, and Vol.19 No.2

In this paper, a robust control scheme using back-stepping and α-filter-based uncertainty and disturbance estimator (UDE) is designed for flexible air-breathing hypersonic vehicle (FAHV) in the presence of severe external disturbances. Firstly, with the aid of back-stepping technique, the longitudinal dynamics of FAHV is separated into velocity and altitude subsystems. Feedback linearization (FL) is utilized to design control laws for each subsystem. Secondly, to enhance robustness of the controller, α-filter-based UDEs are constructed to estimate the lumped disturbances, including aerodynamic parameter uncertainties, flexible effects and external disturbances. More importantly, the performance superiority of α-filter-based UDE is clarified via frequency response analysis and comparisons with an extended state observer (ESO). Furthermore, the issue of tuning design parameter α is analyzed. The stability of closed-loop system is proved by Lyapunov stability theory. Simulation results demonstratethe effectiveness of the proposed control strategy.

Evaluation of a pyramid die extrusion for a hollow aluminum profile using FE simulation

Liang Chen,Guoqun Zhao,Junquan Yu,Wendong Zhang 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.5

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For thispurpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusionprocess was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state,transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load,material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzedand compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were wellconcluded, which should be important information for die designers and makers.