North China University of Technology is a university in Shijingshan District, Western Beijing, People's Republic of China.North China University of Technology has 9 colleges, 30 majors, 12 teaching and experimental center, and 9 research and design institute. Wikipedia.
Li C.,North China University of Technology
Materials Letters | Year: 2014
This study reports a direct synthesis of AlN nanowires via the reaction of aluminum powder and nitrogen gas at around 800 C without catalyst. The as-prepared AlN nanowires were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The product consists of wurtzite AlN nanowires with diameter of tens of nanometer. The cathodoluminescence (CL) measurements show that the luminescence intensities of the as-prepared AlN nanowires are more than 5 times stronger than that of the commercial AlN powder, which is attributed to the nitrogen vacancies and oxygen-related defects in the nanowires. © 2013 Published by Elsevier B.V. Source
Zhang S.,North China University of Technology
Computers and Mathematics with Applications | Year: 2011
With respect to comprehensive evaluation model for computer network security with linguistic information and incomplete weight information, a new comprehensive evaluation model is proposed. In the method, the 2-tuple linguistic representation developed in recent years is used to aggregate the linguistic assessment information. In order to get the weight vector of the attribute, we establish an optimization model based on the basic ideal of traditional TOPSIS, by which the attribute weights can be determined. Then, the optimal alternative(s) is determined by calculating the shortest distance from the 2-tuple linguistic positive ideal solution (TLPIS) and on the other side the farthest distance of the 2-tuple linguistic negative ideal solution (TLNIS). The method has exact characteristics in linguistic information processing. It avoided information distortion and losing which occurred formerly in linguistic information processing. Finally, a numerical example of the evaluation of network security systems is used to illustrate the use of the proposed method. The result shows the approach is simple, effective and easy to calculate. © 2011 Elsevier Ltd. All rights reserved. Source
Zhang Z.-Y.,North China University of Technology
Journal of Physics A: Mathematical and Theoretical | Year: 2013
In this paper, approximate nonlinear self-adjointness for perturbed PDEs is introduced and its properties are studied. Consequently, approximate conservation laws which cannot be obtained by the approximate Noether theorem are constructed by means of the method. As an application, a class of perturbed nonlinear wave equations is considered to illustrate the effectiveness. © 2013 IOP Publishing Ltd. Source
North China University of Technology | Date: 2014-05-19
A flexible roll-die forming machine for variable cross-section parts includes: a feeding device and a flexible roll-die forming unit; wherein the flexible roll-die forming unit includes at least a set of flexible roll-die forming devices; when two or more sets of the flexible roll-die forming devices are provided, the flexible roll-die forming devices are connected in sequence; wherein the feeding device is arranged at a front end of the flexible roll-die forming unit and is connected to an adjacent flexible roll-die forming device. The present invention effectively solves problems that conventional flexible roll-die forming machines are not able to produce narrow part with variable cross-sections, and the forming accuracy is poor. The present invention also reduces the amount of shafts controlled by servo motors, so as to simplify the controlling system, improve system operation reliability and simplify maintenance.
Zhang Y.,North China University of Technology |
Yang H.,North China University of Technology
IEEE Transactions on Power Electronics | Year: 2014
Model predictive torque control (MPTC) is emerging as a powerful control scheme for high performance control of induction motor (IM) drives. Compared to direct torque control, MPTC is more effective and accurate in voltage vector selection by incorporating the system model directly with the finite switching states. However, for two-level inverter-fed IM drives, the sampling frequency of MPTC has to be high to achieve good performance due to the limited number of voltage vectors. Recently, the concept of duty cycle control was introduced in MPTC by inserting a null vector along with the selected active voltage vector to achieve torque ripple reduction. The active vector is first selected from conventional MPTC and then its duration is determined based on a certain principle. The cascaded processing of active vector and its duration leads to poor low-speed performance and the sampling frequency still has to be high. This paper proposes an improved MPTC with duty cycle control by optimizing the vector selection and its duration simultaneously when minimizing both torque and flux errors. As a result, better steady-state performance at both low and high speeds is achieved, even if the sampling frequency is reduced by half. The effectiveness of the proposed MPTC is verified by both simulation and experimental results. © 2014 IEEE. Source