Nanjing University of Aeronautics and Astronautics is a university located in Nanjing, Jiangsu province, China. It was established in October 1952. In Chinese, the university name is sometimes shortened to Nanhang . The university is operated by Ministry of Industry and Information Technology and is one of China's leading universities on research and education. It is regarded as one of the top engineering universities in China and also has a great influence on China's aerospace industry. Wikipedia.
Xiao H.,Nanjing Southeast University |
Xie S.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2012
Characterized by low leakage current and low voltage stress of the power device, a neutral point clamped three-level inverter (NPCTLI) is suitable for a transformerless photovoltaic (PV) grid-connected system. Unfortunately, the shoot-through problem of bridge legs still exists in an NPCTLI, so its operation reliability is degraded. An improved three-level grid-connected inverter is proposed based on the NPCTLI and the dual-buck half-bridge inverter (DBHBI), and which avoids the shoot-through problem. The proposed topology guarantees no switching-frequency common-mode voltage and no shoot-through risk. Furthermore, the freewheeling diode of bridge legs of the DBHBI can be removed taking into consideration the unity power factor of grid current, and a straightforward topology is thus derived. The new topology is referred to as split-inductor NPCTLI (SI-NPCTLI). The operation mode, common-mode characteristic, and control strategy are analyzed. Finally, both the simulation and the experimental results of a 1-kW SI-NPCTLI prototype verify the analysis. © 2011 IEEE.
Tan X.,Nanjing University of Aeronautics and Astronautics |
Triggs B.,French National Center for Scientific Research
IEEE Transactions on Image Processing | Year: 2010
Making recognition more reliable under uncontrolled lighting conditions is one of the most important challenges for practical face recognition systems. We tackle this by combining the strengths of robust illumination normalization, local texture-based face representations, distance transform based matching, kernel-based feature extraction and multiple feature fusion. Specifically, we make three main contributions: 1) We present a simple and efficient preprocessing chain that eliminates most of the effects of changing illumination while still preserving the essential appearance details that are needed for recognition; 2) We introduce local ternary patterns (LTP), a generalization of the local binary pattern (LBP) local texture descriptor that is more discriminant and less sensitive to noise in uniform regions, and we show that replacing comparisons based on local spatial histograms with a distance transform based similarity metric further improves the performance of LBP/LTP based face recognition; and 3) We further improve robustness by adding Kernel principal component analysis (PCA) feature extraction and incorporating rich local appearance cues from two complementary sourcesGabor wavelets and LBPshowing that the combination is considerably more accurate than either feature set alone. The resulting method provides state-of-the-art performance on three data sets that are widely used for testing recognition under difficult illumination conditions: Extended Yale-B, CAS-PEAL-R1, and Face Recognition Grand Challenge version 2 experiment 4 (FRGC-204). For example, on the challenging FRGC-204 data set it halves the error rate relative to previously published methods, achieving a face verification rate of 88.1% at 0.1% false accept rate. Further experiments show that our preprocessing method outperforms several existing preprocessors for a range of feature sets, data sets and lighting conditions. © 2010 IEEE.
Qiu H.,Nanjing University of Aeronautics and Astronautics |
Guo W.,Nanjing University of Aeronautics and Astronautics
Physical Review Letters | Year: 2013
In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under a perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to the field-induced disruption of the water-wall interaction induced well-ordered network of the hydrogen bond. This electromelting process should add an important new ingredient to the physics of water. © 2013 American Physical Society.
Dai Q.,Nanjing University of Aeronautics and Astronautics
Knowledge-Based Systems | Year: 2013
Ensemble pruning is crucial for the consideration of both efficiency and predictive accuracy of an ensemble system. This paper proposes a new Competitive technique for Ensemble Pruning based on Cross-Validation (CEPCV). The data to be learnt by neural computing models are mostly drifting with time and environment, therefore a dynamic ensemble pruning method is indispensable for practical applications, while the proposed CEPCV method is just the kind of dynamic ensemble pruning method, which can realize on-line ensemble pruning and take full advantage of potentially valuable information. The algorithm naturally inherits the predominance of cross-validation technique, which implies that those networks regarded as winners in selective competitions and chosen into the pruned ensemble have the "strongest" generalization capability. It is essentially based on the strategy of "divide and rule, collect the wisdom", and might alleviate the local minima problem of many conventional ensemble pruning approaches only at the cost of a little greater computational cost, which is acceptable to most applications of ensemble learning. The comparative experiments among the four ensemble pruning algorithms, including: CEPCV and the state-of-the-art Directed Hill Climbing Ensemble Pruning (DHCEP) algorithm and two baseline methods, i.e. BSM, which chooses the Best Single Model in the initial ensemble based on their performances on the pruning set, and ALL, which reserves all network members of the initial ensemble, on ten benchmark classification tasks, demonstrate the effectiveness and validity of CEPCV. © 2012 Elsevier B.V. All rights reserved.
Pan S.,Nanjing University of Aeronautics and Astronautics |
Zhang Y.,Nanjing University of Aeronautics and Astronautics
Optics Letters | Year: 2012
A novel microwave photonic phase shifter based on a single-sideband (SSB) polarization modulator (PolM) and a polarizer is proposed and demonstrated. In the SSB-PolM, two SSB intensity-modulated signals with a phase difference of π along two orthogonal polarization directions are generated. With the polarizer to combine the two signals, the phase of the optical microwave signal can be tuned from -180 to 180 deg by simply adjusting the polarization direction of the polarizer, whereas the amplitude keeps unchanged. An experiment is carried out. A full-range tunable phase shift in the frequency range of 11-43 GHz is achieved. The flat power response, power independent operation, and high stability of the proposed microwave photonic phase shifter is also confirmed. © 2012 Optical Society of America.
Zhang Y.,Nanjing University of Aeronautics and Astronautics |
Pan S.,Nanjing University of Aeronautics and Astronautics
Optics Letters | Year: 2013
A scheme for the generation of phase-coded microwave signals using an electrically tunable photonic microwave phase shifter is proposed and demonstrated. The photonic phase shifter is based on a single-sideband polarization modulator (PolM), and the tuning of the phase shifter is implemented by a second PolM. By introducing an RF signal to the first PolM and an electrical coding signal to the second PolM, a phase-coded microwave signal with binary phase codes or polyphase codes is achieved. An experiment is performed. The simple and flexible operation, high coding rate, large frequency range, excellent transmission performance, and high stability of the system is confirmed. © 2013 Optical Society of America.
Chen K.,Nanjing University of Aeronautics and Astronautics
International Journal of Production Economics | Year: 2012
This paper investigates the coordination mechanism for supply chain with one manufacturer and multiple competing suppliers in the electronic market. We first study two conventional price-only policies, including wholesale price policy and catalog policy, based on the reverse Vickrey auction, and show that both the buyer and the powerful suppliers (with production cost less than a special threshold value) prefer catalog policy to wholesale price policy, and the powerless suppliers prefer wholesale price policy to catalog policy. Simultaneously, neither policy can coordinate the channel composed of the manufacturer and the winning supplier. We also show that a quantity discount policy cannot coordinate the supply chain with competing suppliers unless a kind of restriction is imposed. The aim of the paper is to explore a coordination mechanism, i.e., the price-restricted quantity-discount policy. Pareto analysis indicates that the manufacturer and the winning supplier will realize the 'win-win' situation, and the channel can also be coordinated. A key managerial implication of our study is that additional restrictive condition may be necessary to eliminate system inefficiency. Some numerical examples are also given to illustrate management insights. © 2012 Elsevier B.V. All rights reserved.
Qing H.,Nanjing University of Aeronautics and Astronautics
Computational Materials Science | Year: 2014
The influence of particle arrangements and interface strengths on the mechanical behavior of the particle reinforced metal-matrix composite (MMC) is investigated under different loading conditions in this work. During the loading process, three different failure mechanisms are distinguished in MMC: ductile failure in metal matrix, brittle failure in SiC particles and interface debonding between matrix and particles. The damage models based on the stress triaxial indicator and maximum principal stress criterion are developed to simulate the failure process of metal matrix and SiC particles. Meanwhile, 2D cohesive element is utilized to describe the debonding behavior of interface. Series of numerical experiments are performed to study the macroscopic stress-strain relationships and microscale damage evolution in MMCs under different loading conditions. An agreement between the simulation results and the experimental data is obtained. © 2014 Elsevier B.V. All rights reserved.
Chen J.,Nanjing University of Aeronautics and Astronautics |
Gong C.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2013
Variable-speed fixed-pitch (VSFP) wind turbines have good prospects in small-to-medium-scale wind power markets due to their simple structure, low cost, and high reliability. One difficulty with VSFP concept wind turbines is to prevent overspeeding and overloading problems at excessive wind velocities, which has rarely been reported in literatures until now. This paper first proposes a sensorless overall power control strategy for a commonly used permanent-magnet-synchronous-generator-based VSFP concept wind power system, with which maximum power point tracking operation, constant speed stalling operation, and constant power soft-stalling operation are all realized. The proposed control scheme has a special advantage of simple structure, i.e., only two regulators are used to realize the three operational modes and also the natural transition between them. An aerodynamic power observer is adopted in the proposed scheme to fasten the MPPT speed. In addition, to enhance system robustness to parameter variations and optimize dynamic and static speed-control performance, an adaptive PI-like fuzzy logic controller is proposed and used as speed regulator in the overall power control scheme. The proposed strategy is verified by simulation and experimental results performed by a 1.2-kW VSFP concept wind turbine prototype. © 1982-2012 IEEE.
Nanjing University of Aeronautics and Astronautics | Date: 2014-11-10
The present invention discloses a method for locating an impact area of a composite structure based on an energy weighted factor, which belongs to the field of structural health monitoring technologies. According to the characteristic that the closest a sensor in an impact occurring sub-area is to the impact position, the most the sensor is affected by the impact, the present invention defines a characteristic parameter of the energy weighted factor, to represent the degree that each sensor is affected by the impact within the entire impact monitoring range, then calculates the degree that each sub-area is affected by the impact within the monitoring range, and finally determines that the sub-area most affected is the impact occurring sub-area. The present invention solves the problems of localization confliction of adjacent nodes and locating blind zones of mid-areas arising during existing multi-node large-scale networking monitoring; the method unites a plurality of nodes to jointly perform impact monitoring through networking, can quickly and accurately perform impact localization on all sub-areas within the network monitoring range, and has good application prospects in the aspect of impact monitoring of large-scale composite structures.