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Analysis of an improved acquisition method for high-dynamic BOC signal

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Journal of Systems Engineering and Electronics 2016年第6期27卷 1158-1167页

作者： Yi Pan Tianqi zhang gang zhang Zhongtao Luo Chongqing Key Laboratory of Signal and Information Processing Chongqing University of Posts and Telecommunications

To reach a compromise between short acquisition time and excellent detection probability for the high-dynamic binary offset carrier (BOC) signal, an overall algorithm based on discrete polynomial-phase transform (DPT) and partial matching filter (PMF)-fast Fourier transform (FFT) algorithm is given. The high order items of received signals are removed by the method of DPT, and the PMF-FFT algorithm is redesigned for the BOC signal. The simulation experiments and theoretical analyses verify that the improved algorithm has attained improvement in acquisition performance. © 2016 Beijing Institute of Aerospace Information.

关键词： Bins Mergers and acquisitions Titration

MoS2-graphene in-plane contact for high interfacial thermal conduction

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Nano Research 2017年第9期10卷 2944-2953页

作者： Xiangjun Liu Junfeng Gao gang zhang Yong-Wei zhang Institute of High Performance Computing A＊STAR Singapore 138632 Singapore

Recent studies have indicated that two-dimensional (2D) MoS2 exhibits low in-plane and inter-plane thermal conductivities. This poses a significant challenge to heat management in MoS2-based electronic devices. To address this challenge, we have designed MoS2-graphene interfaces that fully utilize graphene, a 2D material that exhibits very high thermal conductivity. First, we performed ab initio atomistic simulations to understand bonding and structural stability at the interfaces. The interfaces that we designed, which were connected via strong covalent bonds between Mo and C atoms, were energetically stable. We then performed molecular dynamics simulations to investigate interfacial thermal conductance in these materials. Surprisingly, the interfacial thermal conductance was high and comparable to those of covalently bonded graphene-metal interfaces. Importantly, each interfacial Mo–C bond served as an independent thermal channel, enabling modulation of the interfacial thermal conductance by controlling the Mo vacancy concentration at the interface. The present work provides a viable heat management strategy for MoS2-based electronic devices.

关键词： MoS_2 graphene interfacial thermal conductance thermal management

Graphene-based thermal modulators

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Nano Research 2015年第8期8卷 2755-2762页

作者： Xiangjun Liu gang zhang Yong-Wei zhang Institute of High Performance Computing A＊STAR Singapore 138632 Singapore

The quest for materials and devices that are capable of controlling heat flux continues to fuel research on thermal controlling devices. In this letter, using molecular dynamics simulations, we demonstrate that a partially clamped singlelayer graphene can serve as a thermal modulator. The mismatch in phonon dispersion between the unclamped and clamped graphene sections results in phonon interface scattering, and the strength of interface scattering is tunable by controlling the clamp-graphene distance via applying the external pressure. Owing to the ultra-thin structure of graphene and its highly sensitive phonon dispersion to external physical interaction, the modulation efficiency--which is defined as the ratio of the highest to lowest heat flux-can reach as high as 150% at a moderate pressure of 50 GPa. This modulation efficiency can be further enhanced by arranging a number of clamps in series along the direction of the heat flux.

关键词： graphene thermal modulator molecular dynamics thermal conductivity phonon dispersion

Wind Power Prediction Based on Variational Mode Decomposition and Feature Selection

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Journal of Modern Power Systems and Clean Energy 2021年第6期9卷 1520-1529页

作者： gang zhang Benben Xu Hongchi Liu Jinwang Hou Jiangbin zhang State Key Laboratory of Eco-Hydraulics in Northwest Arid Region Xi’an University of Technology School of Electrical Engineering Xi’an University of Technology The Institute of Water Resources and Hydroelectric Engineering Xi’an University of Technology

Accurate wind power prediction can scientifically arrange wind power output and timely adjust power system dispatching plans. Wind power is associated with its uncertainty,multi-frequency and nonlinearity for it is susceptible to climatic factors such as temperature, air pressure and wind ***, this paper proposes a wind power prediction model combining multi-frequency combination and feature ***, the variational mode decomposition(VMD) is used to decompose the wind power data, and the sub-components with different fluctuation characteristics are obtained and divided into high-, intermediate-, and low-frequency components according to their fluctuation characteristics. Then, a feature set including historical data of wind power and meteorological factors is established, which chooses the feature sets of each component by using the max-relevance and min-redundancy(m RMR) feature selection method based on mutual information selected from the above set. Each component and its corresponding feature set are used as an input set for prediction afterwards. Thereafter, the high-frequency input set is predicted using back propagation neural network(BPNN), and the intermediate-and low-frequency input sets are predicted using least squares support vector machine(LS-SVM). After obtaining the prediction results of each component, BPNN is used for integration to obtain the final predicted value of wind power, and the ramping rate is verified. Finally, through the comparison, it is found that the proposed model has higher prediction accuracy.

关键词： Wind power prediction feature selection variational mode decomposition(VMD) max-relevance and min-redundancy(mRMR)

Numerical Simulation and Innovation on Magnesium Reduction Process

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Journal of Thermal Science 2006年第3期15卷 269-273页

作者： Dehong XIA gang zhang Liang GUO Department of Thermal Engineering University of Science and Technology Beijing Beijing 100083China

The thermal process of ***'s reduction art,widely used in magnesium production,is *** is shown that the thermal efficiency will be highly enhanced with the increase of heat-exchange areaor the intensification of heat exchange between flame and the outer surface of the reduction *** innovationhas been made by fuel-shifting(from coal to Coal-Water Mixture),up-draft reduction furnace configuration,multi-layer jars installation and waste heat recovery.A bench scale furnace has been constructed and put intooperation to identify the simulation and new design.

关键词： magnesium reduction fuel-shifting simulation coal-water mixture.

Smoothness-oriented path optimization for robotic milling processes

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Science China(Technological Sciences) 2020年第9期63卷 1751-1763页

作者： PENG JingFu DING Ye zhang gang DING Han State Key Laboratory of Mechanical System and Vibration Shanghai Jiao Tong UniversityShanghai200240China HUST-Wuxi Research Institute Wuxi214174China

Industrial robots are increasingly used for five-axis machining operations, where the rotation of the end effector along the toolaxis direction is functionally redundant. This functional redundancy should be carefully resolved when planning the robot path according to the tool path generated by a computer-aided manufacturing(CAM) system. Improper planning of the redundancy may cause drastic variations of the joint motions, which could significantly decrease the machining efficiency as well as the machining accuracy. To tackle this problem, this paper presents a new optimization-based methodology to globally resolve the functional redundancy for the robotic milling process. Firstly, a global performance index concerning the smoothness of the robot path at the joint acceleration level is proposed. By minimizing the smoothness performance index while considering the avoidance of joint limits and the singularity and the constraint of the stiffness performance, the resolution of the redundancy is formulated as a constrained optimization problem. To efficiently solve the problem, the sequential linearization programming method is employed to improve the initial solution provided by the conventional graph-based method. Then, simulations for a given tool path are presented. Compared with the graph-based method, the proposed method can generate a smoother robot path in which a significant reduction of the magnitude of the maximum joint acceleration is obtained, resulting in a smoother tool-tip feedrate profile. Finally, the experiment on the robotic milling system is also presented. The results show that the optimized robot path of the proposed method obtains better surface quality and higher machining efficiency, which verifies the effectiveness of the proposed method.

关键词： robot milling functional redundancy path optimization smoothness sequential linear programming

The novel generating algorithm and properties of hybrid-P-ary generalized bridge functions

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Science in China(Series F) 2006年第2期49卷 228-234页

作者： WANG gang zhang Qishan Department of Electronic Engineering Beihang University Beijing 100083 China

In this paper, we develop novel non-sine functions, named hybrid-P-ary generalized bridge functions, based on the copy and shift methods. The generating algorithm of hybrid-P-ary generalized bridge functions is introduced based on the hybrid-P-ary generalized Walsh function＇s copy algorithm. The main property, product property, is also discussed. This function may be viewed as the generalization of the theory of bridge functions. And a lot of non-sine orthogonal functions are the special subset of these novel functions, The hybrid-P-ary generalized bridge functions can be used to search many unknown non-sine functions by defining different parameters.

关键词： hybrid-P-ary generalized Waish functions hybrid-P.ary generalized shift copy hybrid-P-ary generalized bridge functions.

Modulating the thermal conductivity of silicon nanowires via surface amorphization

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Science China(Technological Sciences) 2014年第4期57卷 699-705页

作者： LIU XiangJun zhang gang PEI QingXiang zhang YongWei Institute of High Performance Computing

We perform non-equilibrium molecular dynamics calculations to study the heat transport in crystalline-core amorphous-shell silicon nanowires(SiNWs).It is found that the thermal conductivity of the core-shell SiNWs is closely related to the cross-sectional area ratio of amorphous *** shell amorphization,an 80%reduction in thermal conductivity compared to crystalline SiNWs with the same size can be achieved,due to the non-propagating heat diffusion in the amorphous *** contrast to the strong temperature-dependent thermal conductivity of crystalline SiNWs,the core-shell SiNWs only show weak temperature *** addition,an empirical relation is proposed to accurately predict the thermal conductivity of the core-shell SiNWs based on the rule of *** present work demonstrates that SiNWs with an amorphized shell are promising candidates for thermoelectric applications.

关键词： thermal conductivity thermoelectric molecular dynamics silicon nanowire

Multi-objective interval prediction of wind power based on conditional copula function

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Journal of Modern Power Systems and Clean Energy 2019年第4期7卷 802-812页

作者： gang zhang Zhixuan LI Kaoshe zhang Lei zhang Xia HUA Yongqing WANG Institute of Water Resources and Hydro-Electric Engineering Xi’an University of TechnologyXi’an 710048China State Grid Shaanxi Baoji Electric Power Company Baoji 721000China State Grid Gansu Electric Power Company Gansu Electric Power Research InstituteLanzhou 730050China State Grid Shaanxi Electric Power Company Shaanxi Electric Power Research InstituteXi’an 710054China

Interval prediction of wind power,which features the upper and lower limits of wind power at a given confidence level,plays a significant role in accurate prediction and stability of the power grid integrated with wind ***,the conventional methods of interval prediction are commonly based on a hypothetic probability distribution function,which neglects the correlations among various variables,leading to the decrease of prediction ***,we improve the multi-objective interval prediction based on the conditional copula function,through which we can fully utilize the correlations among variables to improve prediction accuracy without an assumed probability distribution *** use the multi-objective optimization method of nondominated sorting genetic algorithm-II(NSGA-II)to obtain the optimal solution *** particular best solution is weighted by the prediction interval average width(PIAW)and prediction interval coverage probability(PICP)to pick the optimized solution in practical ***,we apply the proposed method to three wind power plants in different cities in China as examples forvalidation and obtain higher prediction accuracy compared with other methods,i.e.,relevance vector machine(RVM),artificial neural network(ANN),and particle swarm optimization kernel extreme learning machine(PSO-KELM).These results demonstrate the superiority and practicability of this method in interval prediction of wind power.

关键词： Wind power prediction Interval prediction Conditional copula function Empirical distribution function Multi-objective optimization algorithm