North China University of Technology

www.ncut.edu.cn
Beijing, China

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.

SEARCH FILTERS
Time filter
Source Type

Zhang Z.-Y.,North China University of Technology
Computers and Mathematics with Applications | Year: 2017

Nonlinear self-adjointness method for constructing conservation laws of partial differential equations (PDEs) is further studied. We show that any adjoint symmetry of PDEs is a differential substitution of nonlinear self-adjointness and vice versa. Consequently, each symmetry of PDEs corresponds to a conservation law via a formula if the system of PDEs is nonlinearly self-adjoint with differential substitution. As a byproduct, we find that the set of differential substitutions includes the set of conservation law multipliers as a subset. The results are illustrated by three typical examples. © 2017.


Wang A.,North China University of Technology
Journal of Hypertension | Year: 2017

OBJECTIVE:: To assess whether changes in proteinuria are associated with the incidence of myocardial infarction (MI) in patients with hypertension. METHODS:: The Kailuan study was a prospective longitudinal cohort study on cardiovascular risk factors and events. Hazard ratios with 95% confidence intervals (CIs) were calculated using Cox regression models. RESULTS:: A total of 24?926 hypertensive patients (mean age: 55.2?±?10.9 years) without previous MI were included. After a mean follow-up of 6.8 years, 382 (1.5%) individuals developed MI. Participants with proteinuria at baseline had a 60% higher risk for developing MI as compared with participants without proteinuria at baseline (hazard ratio: 1.60, 95% CI: 1.12–2.29) after adjusting for dyslipidemia, diabetes mellitus and other cardiovascular risk factors. Compared with participants without proteinuria, individuals with incident proteinuria or persistent proteinuria during the follow-up had 54 and 141% higher risks for developing MI, respectively (hazard ratio: 1.54, 95% CI: 1.14–2.09 and hazard ratio: 2.41, 95% CI: 1.59–3.66; all P?


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.


Zhang Y.,North China University of Technology | Xie W.,North China University of Technology
IEEE Transactions on Power Electronics | Year: 2014

Finite control set model predictive control (FCS-MPC) is emerging as a powerful control scheme in the control of power converters, because it takes the discrete nature of power converters into account and offers a flexible way to consider various constraints. However, conventional FCS-MPC requires to evaluate a cost function for each discrete switching states, which poses high computational burden. This paper proposes a low-complexity MPC (LC-MPC), which only requires one prediction to find the best voltage vector. The principle of LC-MPC is inherited from prior direct current control (DCC), but has been generalized by identifying its advantages, limitations, and potential application areas. Furthermore, the relationship between LC-MPC and FCS-MPC is studied and it is found that in some cases, the LC-MPC is completely equivalent to FCS-MPC. This paper presents the application example of LC-MPC in power control of three-phase ac/dc converter. To make it a success, the negative conjugate of complex power in synchronous frame is selected as the control variable. Detailed principle of vector selection is introduced and the reason for requiring only one prediction in the proposed LC-MPC is strictly proven using mathematical tools. The proposed LC-MPC is compared with conventional FCS-MPC and its effectiveness is verified by both simulation and experimental results from a two-level ac/dc converter. © 1986-2012 IEEE.


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.


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.


Patent
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.


Patent
North China University of Technology | Date: 2012-01-13

A temperature sensor, based on magnetic tunneling junction (MTJ) device, includes an MTJ device, a PMOS device and an analog switch. Source electrode of the PMOS device is connected to a power supply; drain electrode of the PMOS device is connected to an input terminal of the MTJ device and is connected to the voltage output terminal of the temperature sensor; an output terminal of the MTJ device is connected to a ground or a circuit via the analog switch; drain electrode of the PMOS device is short circuited with gate electrode of the PMOS device. A negative input terminal of an operational amplifier is connected to the voltage output terminal and a positive input terminal of the operational amplifier is connected to a reference voltage. The sensor is compatible with CMOS process and able to simultaneously perform functions such as temperature detection, over-temperature protection and over-current protection.


Patent
North China University of Technology | Date: 2011-12-30

A monolithically-integrated dual surge protective device and its fabrication method are disclosed. The exemplary dual surge protective device includes a LDMOS device and a diode assembly which is consisted. of multiple diodes series-wound on back-to-back basis and whose one end is connected to drain electrode of the LDMOS device and the other-end is connected to gate electrode of the LDMOS device. The diode assembly can be fabricated directly in the gate electrode area of the LDMOS device after fabrication of the LDMOS device is completed. The protective device is equivalent to combination of diodes and LDMOS in respect to operating principles and structures, with the advantage of enhanced effect of surge prevention and cost reduction of surge device as it can be integrated into a chip.


Patent
North China University of Technology | Date: 2012-01-13

A type of high voltage isolation trench, its fabrication method and an MOS device are disclosed. The isolation trench includes a trench extending to a buried oxide layer of a wafer, with high concentration N^(+) injected to a side wall of the trench, polysilicon being filled in the trench and oxides are being filled between the side wall of the trench and the polysilicon. Multiple composite structures are used to fill the vacant trench to reduce stress brought by trenching so as to improve performance of the device on one hand and to achieve the purpose of increasing breakdown voltage and improving superficial flatness on the other hand.

Loading North China University of Technology collaborators
Loading North China University of Technology collaborators