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Removal of Cr(VI) from aqueous solution by rice husk derived magnetic sorbents
Ruifeng Yang,Shangru Zhai,Yuan Fan,Zhimin Lei,Na Liu,Jialiang Lv,Bin Zhai,Lei Wang 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.4
−A novel magnetic porous sorbent obtained from agricultural waste rice husk was successfully synthesized through a simple carbon-thermal method. The sorbent was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, N2 sorption analysis, and X-ray photoelectron spectroscopy. The removal efficiency of the sorbent for Cr(VI) was also investigated. Chromium adsorption was fitted by the pseudo-second-order and Langmuir models. The maximum chromium adsorption capacity, Brunauer-Emmett-Teller surface area, and average Barrett-Joyner-Halenda pore size of the magnetic sorbent were 157.7mg·g−1, 134.1m2·g−1, and 4.99 nm, respectively. The saturated magnetization of the novel adsorbent was 77.8 emu·g−1, indicating that the material can facilitate separation and recovery from aqueous systems. The removal mechanisms of Cr(VI) were also discussed. The result illustrates that rice husk-derived magnetic carbonaceous materials are a potential adsorbent for Cr(VI) pollution treatment and provide a suitable method for the effective conversion of biomass waste, which may solve the problem of waste disposal and widen the applications of the materials.
On effects of rail fastener failure on vehicle/track interactions
Lei Xu,Jianmin Gao,Wanming Zhai 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5
Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.
On effects of rail fastener failure on vehicle/track interactions
Xu, Lei,Gao, Jianmin,Zhai, Wanming Techno-Press 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5
Rail support failure is inevitably subjected to track geometric deformations. Due to the randomness and evolvements of track irregularities, it is naturally a hard work to grasp the trajectories of dynamic responses of railway systems. This work studies the influence of rail fastener failure on dynamic behaviours of wheel/rail interactions and the railway tracks by jointly considering the effects of track random irregularities. The failure of rail fastener is simulated by setting the stiffness and damping of rail fasteners to be zeroes in the compiled vehicle-track coupled model. While track random irregularities will be transformed from the PSD functions using a developed probabilistic method. The novelty of this work lays on providing a method to completely reveal the possible responses of railway systems under jointly excitation of track random irregularities and rail support failure. The numerical results show that rail fastener failure has a great influence on both the wheel/rail interactions and the track vibrations if the number of rail fastener failure is over three. Besides, the full views of time-dependent amplitudes and probabilities of dynamic indices can be clearly presented against different failing status.
The generalized Fermat type difference equations
Kai Liu,Lei Ma,Xiaoyang Zhai 대한수학회 2018 대한수학회보 Vol.55 No.6
This paper is to consider the generalized Fermat difference equations with different types which ever considered by Li \cite{li}, Ishizaki and Korhonen \cite{IK}, Zhang \cite{zhangjie} and Liu \cite{liuk4,11,1177,liu}, respectively. Some new observations and results on these equations will be given.
Ground Current Crosstalk Analysis and Suppression in High Power Cascaded Chopper Braking Circuit
Peifei Li,Lei Zhang,Xiaofei Zhai,Bin Ouyang 대한전기학회 2019 Journal of Electrical Engineering & Technology Vol.14 No.2
This paper systematically investigates the ground current crosstalk (GCC) of high-power cascaded chopper braking circuit (CCBC). Turning on and off the IGBTs of the CCBC will generate GCC problem between the upper and lower chopper braking circuits. The GCC may cause the freewheeling diode to be hard-off , resulting in strong electromagnetic interference and serious losses, and even causing the freewheeling diode to fail due to reverse recovery. This paper establishes the ground current model of CCBC and the GCC is predicted base on the model. To minimize the infl uence of GCC, the solutions of inserting damping resistors to the ground current path and optimizing IGBT timing are proposed. The correctness of the analysis is verifi ed by simulations and experiments. The proposed methods are of great signifi cance for improving the reliability of high-power cascaded chopper braking devices and reducing electromagnetic interference and losses.
THE GENERALIZED FERMAT TYPE DIFFERENCE EQUATIONS
Liu, Kai,Ma, Lei,Zhai, Xiaoyang Korean Mathematical Society 2018 대한수학회보 Vol.55 No.6
This paper is to consider the generalized Fermat difference equations with different types which ever considered by Li [14], Ishizaki and Korhonen [9], Zhang [26] and Liu [15-18], respectively. Some new observations and results on these equations will be given.