Nanjing, China

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.


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Ma J.,Nanjing University of Aeronautics and Astronautics | Li D.,Nanjing University of Aeronautics and Astronautics
Pacific Asia Conference on Information Systems, PACIS 2016 - Proceedings | Year: 2016

Modern online social networks and traditional face-to-face interactions are important social media for information spreading, and these two media are usually interconnected each other. We present a two-layer social network model to study the rumor spreading process. The model consists of two layers of networks with one layer is online social network (e.g. Facebook, Twitter and Sina Microblog, etc.) and the other is offline social network (also called as physical contact network, e.g. face-to-face communication). The rumor spreading dynamics under the interaction of online social network and offline social network is theoretical investigated. Through numerical simulations we find that the two-layered networks could enhance the spreading speed and expand the spreading scale under the action of online social network. Besides, although different network layers in the two-layered social network are interacted each other, the spreading rate in one layer only affects the spreading process within the same layer but almost have no effect on the spreading process in the other layer. Finally, the number of spreaders that transfers from offline social network is less effective than that from online social network.


Fang T.,Nanjing University of Aeronautics and Astronautics | Shen L.,Nanjing University of Aeronautics and Astronautics | He W.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2017

Input-series-output-parallel (ISOP) inverter system is very suitable for high input voltage and large output current power conversion applications. One of many merits of this assembly system lies in that its characteristic of multimodule series-parallel combination can significantly improve the reliability of the operation. To address this point, redundancy should be realized for the whole system. However, the existing methods for the ISOP inverter system all belong to centralized control, which restricts the modularity of the system. From the above perspective, this paper proposes a new scheme to achieve both power balance and distributed configuration according to the conception of compound control. Also, the relationship of control loops is analyzed and the design procedure of them is given. Based on the fully modular system actualized by the distributed control, the hot-swap technique is then raised to get a redundant system with superior reliability. Here, the way of bypassing other than cutting off is adopted to fulfill withdrawal of the faulty module from the system due to series connection at the input terminal. In addition, the detailed timing sequence of system operation is provided to ensure the smooth transition during the hot-plugging transient. Finally, a three-module prototype is built and the experimental results validate the effectiveness of the presented strategy. © 2016 IEEE.


In this paper, the synergistic effects of temperature, oxidation, loading frequency and stress-rupture on damage evolution of cross-ply ceramic-matrix composites (CMCs) under cyclic fatigue loading at elevated temperatures in oxidizing atmosphere have been investigated. The Budiansky-Hutchinson-Evans shear-lag model was used to describe the micro stress field of the damaged composite considering interface wear and interface oxidation. The damage parameters of fatigue hysteresis dissipated energy, fatigue hysteresis modulus, and fatigue peak strain have been used to monitor the damage evolution inside of CMCs. The relationships between damage parameters and internal damage of matrix cracking, interface debonding and slipping have been established. The experimental fatigue hysteresis, interface slip lengths and peak strain of cross-ply SiC/MAS composite under cyclic fatigue loading at different testing temperatures, loading frequency and stress-rupture time in air condition have been predicted. © 2017 Elsevier Ltd


Chen Z.,Nanjing University of Aeronautics and Astronautics
Information Processing Letters | Year: 2017

In this article, we solve an important open problem – the computational complexity of parametric runtime verification against regular properties. To achieve this, we first formulate the membership problem of existential and universal parametric languages, then show that the membership problem of existential parametric regular languages is NP-complete, and the membership problem of universal parametric regular languages is coNP-complete. These computational complexity results show that parametric runtime verification of regular properties is NP-complete and coNP-complete. This gives a rigorous proof and a formal explanation of the inherent intractability of parametric runtime verification, which has been shown by the empirical experiments in the literature. In this sense, our work has moved one significant step on the theoretical aspect of runtime monitoring and verification. © 2017 Elsevier B.V.


Chen S.,Huazhong Agricultural University | Shen J.,Nanjing University of Aeronautics and Astronautics
Circuits, Systems, and Signal Processing | Year: 2017

This paper considers the effect of multiple quantizers and channel packet dropouts in state estimation of networked system. Taking into account the limit capacity of the quantizer, multiple quantizers in the networked system with respect to the multichannels are modeled firstly. In addition, channel packet dropouts with different packet loss probabilities in different channels are also proposed in this paper. To minimize the effect of the quantizers and the disturbances, state estimators are constructed under a given performance requirement. Finally, a simulation example is used to illustrate the effectiveness of the theoretical results. © 2016, Springer Science+Business Media New York.


Liao F.,Nanjing University of Aeronautics and Astronautics | Zhang L.,Nanjing University of Aeronautics and Astronautics
International Journal of Computer Mathematics | Year: 2017

In this article, a decoupled and linearized compact difference scheme is investigated to solve the coupled Schrödinger–Boussinesq equations numerically. We establish the convergence rates for the error at the order of (Formula presented.) in the (Formula presented.)-norm with the time step τ and mesh size h. The linear scheme is proved to conserve the total energy which is defined as a recursion relationship. Due to the difficulty in obtaining the priori estimate from the discrete energy, we utilize cut-off function technique to prove the convergence. The numerical results are reported to verify the theoretical analysis, and the numerical comparison between our scheme with previous methods are conducted to show the efficiency of our scheme. © 2017 Informa UK Limited, trading as Taylor & Francis Group


Msr M.,Nanjing University of Aeronautics and Astronautics | Sebag M.,University Paris - Sud
Artificial Intelligence | Year: 2017

Algorithm selection (AS), selecting the algorithm best suited for a particular problem instance, is acknowledged to be a key issue to make the best out of algorithm portfolios. This paper presents a collaborative filtering approach to AS. Collaborative filtering, popularized by the Netflix challenge, aims to recommend the items that a user will most probably like, based on the previous items she liked, and the items that have been liked by other users. As first noted by Stern et al. [47], algorithm selection can be formalized as a collaborative filtering problem, by considering that a problem instance “likes better“ the algorithms that achieve better performance on this particular instance. Two merits of collaborative filtering (CF) compared to the mainstream algorithm selection (AS) approaches are the following. Firstly, mainstream AS requires extensive and computationally expensive experiments to learn a performance model, with all algorithms launched on all problem instances, whereas CF can exploit a sparse matrix, with a few algorithms launched on each problem instance. Secondly, AS learns a performance model as a function of the initial instance representation, whereas CF builds latent factors to describe algorithms and instances, and uses the associated latent metrics to recommend algorithms for a specific problem instance. A main contribution of the proposed algorithm recommender ALORS system is to handle the cold start problem – emitting recommendations for a new problem instance – through the non-linear modeling of the latent factors based on the initial instance representation, extending the linear approach proposed by Stern et al. [47]. The merits and generality of ALORS are empirically demonstrated on the ASLib [6] and OpenML [53] benchmarks. © 2016 Elsevier B.V.


Lin Y.,Nanjing University of Aeronautics and Astronautics | Chen Q.,Nanjing University of Aeronautics and Astronautics
Huagong Xuebao/CIESC Journal | Year: 2017

Non-stationary process monitoring based on common trends model was proposed, because conventional multivariate statistical process control methods with stationary data assumption were inapplicable to non-stationary process monitoring. The new common trends model was capable of identifying common factors from co-integrated non-stationary multiple variables and decomposing each non-stationary process variable into summation of a non-stationary common trends component and a stationary counterpart. Contrary to existing non-stationary process monitoring technique from cointegration model, the common trends model captured the stationary component of each non-stationary process variable, eliminated effects of non-stationary common factors and unveiled overall dynamic equilibrium relationships among variables. Hence, non-stationary process monitoring was transformed to an application of common trends model, which involved obtaining stationary component of each process variable, creating estimation for the stationary components by conventional multivariate statistical methods and setting up monitoring on corresponding control limits. A case study of monitoring petroleum distillation process showed that the proposed approach possessed more reliable process monitoring performance than the method of cointegration model. © All Right Reserved.


Wang Y.,Nanjing University of Aeronautics and Astronautics | Wu Q.,Nanjing University of Aeronautics and Astronautics
Aerospace Science and Technology | Year: 2017

This paper presents an adaptive non-affine control scheme for the longitudinal short-period model of a generic hypersonic flight vehicle (HFV). Firstly, the non-affine nonlinear characteristics of the aerodynamic coefficients are analyzed, which have great influence on the flight dynamical behaviors. Secondly, without ignoring the non-affine nonlinear aerodynamics, a fuzzy sliding mode adaptive non-affine controller is designed. Under the existence of external disturbances and unmodeled dynamics, the controller can still ensure that the angle of attack tracks the desired signal robustly and asymptotically. Furthermore, the proposed controller does not require the exact bound values of the external disturbances and unmodeled dynamics, which is very important for hypersonic vehicles because the values usually cannot be obtained at hypersonic flight conditions. Finally, the simulation results are provided to illustrate the feasibility and effectiveness of the proposed scheme. © 2017 Elsevier Masson SAS


Kang Y.,Linyi Normal University | Tang D.,Nanjing University of Aeronautics and Astronautics
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2016

To solve the problem of the lack of optimization tools in the matrix-based solving process of the functional chain design solution, an optimization method based on computational matrix combined with ant colony algorithm is proposed. The similarity theory is analyzed, and similarity and generalized distance are used to characterize the compatibility of the two adjacent elements. The similarity matrix is defined, and the design solution matrix containing similarity information is acquired by the calculation of the similarity matrix and the design solution matrix. The design scheme evaluation model and the ant colony algorithm based optimization model are defined, and the calculation method of the evaluation criterion, weight and value is proposed. As the evaluation score of components is pheromone and as the length of generalized distance is the path of adjacent nodes, the pheromone matrix and probability matrix is structured. The problem of solution solving is converted to the optimal path problem of combinatorial optimization. The design solution contained in the design solution matrix is optimized with ant colony algorithm, and the optimized design solution meeting the functional requirements, structural requirements and the evaluation target is obtained. Finally, the effectiveness of the proposed method is verified with an example of three-axis servo drive. © 2016 Journal of Mechanical Engineering.


Tao Y.,Nanjing University of Aeronautics and Astronautics | Zhang G.,Nanjing University of Aeronautics and Astronautics
IEEE Signal Processing Letters | Year: 2016

This letter proposes a novel pulse accumulation scheme via structured measurement matrix in compressive sensing radar for better detection performance in the presence of high-level additive noise. The measurement matrix allows radar accumulate pulses with both coherent and noncoherent accumulation. The range migration can be accurately compensated via time delay compensation matrix based on frequency domain weighting. A modified algorithm is derived to recover the structured joint sparse vectors. By implementing numerical simulations, it is demonstrated that better detection performance and more accuracy can be achieved through the proposed scheme. © 2016 IEEE.


Li L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2017

In this paper, the fatigue hysteresis behavior of unidirectional SiC/Si3N4 ceramic-matrix composite at elevated temperature has been investigated. The hysteresis loops models considering interface friction between fibers and the matrix have been developed to establish the relationships between the fatigue hysteresis loops, fatigue hysteresis dissipated energy and the interface frictional coefficient. Using the experimental fatigue hysteresis dissipated energy, the interface frictional coefficient of SiC/Si3N4 composite at 1000 °C were obtained for different cycle numbers and fatigue peak stresses. The effects of fatigue peak stress, test temperature and cycle number on the evolution of fatigue hysteresis dissipated energy and interface frictional coefficient have been analyzed. It was found that the fatigue hysteresis dissipated energy can be used to monitor the interface debonding and damage evolution inside of the composite. © 2017 Springer Science+Business Media Dordrecht


Cui S.,Nanjing University of Aeronautics and Astronautics | Chen H.-H.,Nanjing University of Aeronautics and Astronautics | He X.-D.,Nanjing University of Aeronautics and Astronautics
Journal of Sound and Vibration | Year: 2017

This paper presents a time-domain method for multi-exciter random environment tests. Traditional random environment test theory has been formulated in the frequency domain, where an important step is taking the inverse of the frequency response function matrices (FRFMs). The accuracy of this inversion tends to be poor, particularly at frequencies near lightly damped resonances. The currently used control algorithms face difficulties in suppressing abnormal spectral lines caused by this inverse problem. In this paper, traditional formulations of the environment test are reformed, and the time-domain method is adopted; this results in a more precise inverse operation in environment tests. To achieve this, reference spectra are converted into time-domain response signals. The finite long driving signals are derived by the state-space method with estimated state vectors. During the process, the inverse of rank-deficient Toeplitz matrices are stabilized with truncated singular value decomposition (TSVD) to suppress all abnormally high-level components in the driving forces; thus, overall, the spectra lines produced by noise within the frequency band are filtered out. A numerical simulation of a single-axis random vibration test of a cantilever beam is conducted using the traditional frequency-domain procedure (FDP) and the proposed time-domain procedure (TDP). The response spectra generated by both procedures are tested by control algorithms, and the result shows that responses generated by the proposed TDP are more easily controlled. The conditions of stability for both the FDP and the TDP are also determined and introduced in the simulation. Moreover, a multi-axis vibration experiment further validates the effectiveness of the TDP. © 2017 Elsevier Ltd


Wang X.,Nanjing University of Aeronautics and Astronautics
Composite Structures | Year: 2017

The discrete singular convolution (DSC) is used for free vibration analysis of three-layer angle-ply symmetric laminated plates with free boundaries, including laminated plates with two adjacent free edges. During formulating the weighting coefficients of derivatives having different orders, two Taylor series expansions with different orders are used to eliminate the degrees of freedom at fictitious points outside the physical domain. Thus, the difficulty in handling free boundary conditions by using the DSC is overcome. Results are presented and compared with either exact solutions or the ones obtained by the differential quadrature method (DQM). It is shown that the DSC with the novel way to apply the boundary conditions yields very accurate lower mode frequencies as well as relatively accurate higher mode frequencies. The excellent performance of the DSC on high mode frequencies of beams and isotropic plates is retained and also independent of boundary conditions. © 2017 Elsevier Ltd


Liu F.,Jiangsu Key Laboratory of New Energy Generation and Power Conversion | Chen Y.,SinopecNanjing Engineering Incorporation | Chen X.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2017

A three-phase three-level (TPTL) converter is an optimal alternative for high-input and high-power dc/dc conversion system. The voltage stress on the primary switch is only half of the input voltage due to its three-level (TL) structure, and the current rating of power devices can be reduced by the three-phase configuration. To achieve soft switching and improve efficiency, the resonant tank can be introduced to optimize the performance of the converter. In this paper, a novel TPTL LC-type series resonant converter with few switches and simple configuration is proposed. The voltage stress on all switches can be reduced to the half of the input voltage, and the voltage across output rectifiers is clamped to the output voltage; as a result, the proposed converter is suitable for high-input/output applications. Meanwhile, the ripple frequency of the output current can be increased significantly, resulting in a reduced filter requirement. Variable frequency control strategy is adopted in order to obtain zero-voltage switching for all switches and zero-current switching for all rectifier diodes in wide input voltage and load range. In this paper, the comprehensive analysis on the proposed converter is carried out, including the operation mode classification, the operating mechanism under different operation mode, along with the circuit model, and gain characteristics of the converter by the fundamental harmonic analysis. Experimental results from a 440-590 V input and 400 V/5 A output are presented to verify the theoretical analysis and the performance of the converter. © 2016 IEEE.


Watjen J.I.,Georgia Institute of Technology | Liu X.L.,Georgia Institute of Technology | Liu X.L.,Nanjing University of Aeronautics and Astronautics | Zhao B.,Georgia Institute of Technology | Zhang Z.M.,Georgia Institute of Technology
Journal of Heat Transfer | Year: 2017

Near-field thermophotovoltaic (NFTPV) devices have received much attention lately as an alternative energy harvesting system, whereby a heated emitter exchanges super-Planckian thermal radiation with a photovoltaic (PV) cell to generate electricity. This work describes the use of a grating structure to enhance the power throughput of NFTPV devices, while increasing the energy conversion efficiency by ensuring that a large portion of the radiation entering the PV cell is above the band gap. The device contains a high-temperature tungsten grating that radiates photons to a room-temperature In0.18Ga0.82Sb PV cell through a vacuum gap of several tens of nanometers. Scattering theory is used along with the rigorous coupled-wave analysis (RCWA) to calculate the radiation energy exchange between the grating emitter and the TPV cell. A parametric study is performed by varying the grating depth, period, and ridge width in the range that can be fabricated using available fabrication technologies. It is found that the power output can be increased by 40% while improving the efficiency from 29.9% to 32.0% with a selected grating emitter as compared to the case of a flat tungsten emitter. Reasons for the enhancement are found to be due to the enhanced energy transmission coefficient close to the band gap. This work shows a possible way of improving NFTPV and sheds light on how grating structures interact with thermal radiation at the nanoscale. Copyright © 2017 by ASME.


Hu J.,Nanjing University of Aeronautics and Astronautics
Journal of Harbin Institute of Technology (New Series) | Year: 2016

Nano manipulation technology has great potential applications in the assembly, measurement and fabrication of nano materials, actuating and high-sensitivity sensing of biological samples, manufacture of nano sensors, decontamination of air and water, etc. As an actuating technology which is far from being mature, the nano manipulation still faces lots of challenges in the device principles, design, scaling up, sample safety, etc. The ultrasonic nano manipulation, in which nanoscale objects are handled and actuated by controlled ultrasound, is an emerging technology to meet some of challenges in nano manipulations. The author's research team and other groups have proposed and realized a series of nano manipulation functions such as trapping, transfer, rotation and concentration since 2012, by controlled ultrasound. Compared with other nano manipulating techniques, the ultrasonic method has the merits such as very low temperature rise at the manipulation area, little selectivity to the material properties of manipulated samples, capability of being implemented on the substrates without MENS or NEMS structure, etc. This paper reviews the progresses in principles, functions, structures and characteristics of the ultrasonic devices for nano manipulations. © 2016, The Editorial Department of Journal of Harbin Institute of Technology. All right reserved.


He S.,Nanjing University of Aeronautics and Astronautics | Chen H.,Nanjing University of Aeronautics and Astronautics
IEEE Sensors Journal | Year: 2017

Sound source direction-of-arrival (DOA) estimation in reverberant environments with low-computational complexity remains a challenging problem, especially for small-sized microphone arrays. To address the problem, a promising method is based on the sound intensity (SI) measurement using differential microphone arrays (DMAs), which can give a closed-form solution and, hence, is computationally efficient. Unfortunately, the SI-based method has been shown to be sensitive to room reverberation, and therefore, more works need to be done to improve its performance in reverberant environments. In this paper, we propose an SI-based closed-form DOA estimation algorithm through the joint temporal-spectral-spatial processing by using two orthogonal first-order DMAs. The proposed method consists of two stages. In the first stage, it focuses on temporal-spectral processing to improve the SI-based DOA estimation, and a preliminary DOA estimate is made through a dual-threshold technique inspired by the local DOA variance weighting scheme in the time-frequency domain. In the second stage, the preliminary DOA estimate is then refined through the spatial processing, where the two first-order orthogonal DMAs are further utilized to construct a first-order steerable DMA for dereverberation, which is shown to be useful when the signal to noise ratio is not too low. Simulations and real-world experiments in reverberant environments have demonstrated the superior performance of the proposed closed-form DOA estimation method. © 2016 IEEE.


Wang Y.,Nanjing University of Aeronautics and Astronautics | Deng Z.,Nanjing University of Aeronautics and Astronautics
IET Electric Power Applications | Year: 2017

The open-winding permanent magnet generator (OWPMG) systems, having the advantages such as high power density, relatively few power switches, high degree of integration and easy to realise power distribution, are suitable for applications like renewable energy power generation systems with multiple power sources. The non-overlapping concentrated winding switched-flux permanent magnet (NOWSFPM) machines, having relatively high torque density and big flux-weakening inductance, are good choices when used in OWPMG systems. The electromagnetic performance of the 6/10 NOWSFPM machine, the 6/7 E-core NOWSFPM machine, the 6/7 E-core NOWSFPM machine with pole shoe and the 6/19 multi-tooth NOWSFPM machine are compared and analysed. Based on the results and according to two defined factors, namely the proportion factor of the power distribution and the speed range, this study mainly focuses on the influence of the flux-weakening coefficient (ρ) on the capability of the power distribution control. The analysis conclusions are verified by experimental results, indicating that the 6/19 multi-tooth NOWSFPM machine (ρ ~ 1) has relatively strong power distribution capability. © The Institution of Engineering and Technology 2016.


Li L.,Nanjing University of Aeronautics and Astronautics
Journal of Composite Materials | Year: 2017

The fatigue hysteresis behavior in fiber-reinforced ceramic-matrix composites under multiple loading stress levels has been investigated. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading/reloading, the fatigue hysteresis loops models corresponding to different interface slip cases under multiple loading stress levels have been derived. The fatigue hysteresis loss energy and interface slip corresponding to single/multiple loading stress levels and different loading sequences have been investigated. The fatigue hysteresis loops of unidirectional SiC/CAŜ'II composite under multiple loading stress levels have been predicted. © The Author(s) 2016.


Li H.-S.,Nanjing University of Aeronautics and Astronautics | Gu R.-J.,Nanjing University of Aeronautics and Astronautics | Zhao X.,Nanjing University of Aeronautics and Astronautics
Composites Part B: Engineering | Year: 2017

This paper presents the development of a novel methodology for global sensitivity analysis of multi-bolt composite joints. Two sources of uncertainty were considered, i.e., the mechanical properties of composite plies and the bolt-hole clearance which comes from assembly phase. The uncertainty propagation in the composite plate was derived through the classical laminate theory, while the load distribution within bolts and the joint displacement were determined by an analytical spring-based method. A kind of Monte Carlo simulation was used to calculate the variance-based sensitivity indices. Furthermore, the proposed methodology was applied to a generic single-lap composite joint, which can also be extended to represent double-lap joints, to identify the significant input random variables with respect to structural responses of the joint. Useful conclusions for the design of multi-bolt composite joints were obtained from the computational results and discussions. © 2017 Elsevier Ltd


Tang Z.,Nanjing University of Aeronautics and Astronautics | Pan S.,Nanjing University of Aeronautics and Astronautics
2016 IEEE International Topical Meeting on Microwave Photonics, MWP 2016 | Year: 2016

A photonic microwave image-reject and singlesideband mixer is proposed based on a dual-polarization dualdrive Mach-Zehnder modulator. Results show that the image-and sideband-reject ratios of the proposed IRM and SSM are larger than 60 and 30 dB, respectively, and the LO leakage is largely suppressed. © 2016 IEEE.


Jing Q.,Nanjing University of Aeronautics and Astronautics | Wu J.,Panda Electronics Group Co.
Radioelectronics and Communications Systems | Year: 2017

Due to the crowded orbits and shortage of frequency resources, the use of MIMO technology to improve spectrum efficiency and an increase of the capacity have become a necessary trend of broadband satellite communication. Firstly, we analyze the main influenced factors and compare the bit error rate (BER) performance of space-time block code (STBC) scheme and space-time trellis code (STTC) scheme. Then we build up the model of land mobile satellite (LMS) channel under different environments by using 3-state Markov chain. This paper emphatically studies the BER performance of STTC and STBC in the MIMO satellite channel. The main emphasis is placed on the effects of different factors, such as terminal environment and elevation angles, on the BER performance of STBC and STTC schemes. Simulation results indicate that performance of STTC in Rayleigh channel is obviously improved with the increasing number of transmitting and receiving antennas, but the encoder state has little impact on the performance. In the Rayleigh channel, the performance of Alamouti code is better than that of STTC. In the LMS channel, performance of these two kinds of space-time coding in open area is optimal, and in the urban area it is the worst. Nevertheless, performance of STTC is slightly superior to the performance of STBC under different circumstances. Under the same environmental conditions, BER of STBC and STTC reduces with the increase of the satellite altitude angle, and therefore, the BER curves of STTC fall faster. © 2017, Allerton Press, Inc.


Du J.,Nanjing University of Aeronautics and Astronautics | Huang P.,Nanjing University of Aeronautics and Astronautics
Guti Lixue Xuebao/Acta Mechanica Solida Sinica | Year: 2017

With the rapid development of microelectronics technology, more attention has been paid to the major failure mode of Copper interconnects. Based on the classical theory of surface diffusion and evaporation-condensation and its weak statement, a finite-element method is developed for simulating the shape instability of intergranular microcracks in Copper caused by the electromigration-induced surface diffusion. A detailed discussion has been given about the impacts of the electric field χ, the aspect ratio β, and the ratio of grain boundary energy to surface energy on the shape instability of intergranular microcracks. The results show that the evolution of the intergranular microcracks has two trends when they migrate along the electric field direction and the grain boundary: being a cylinder or splitting into two small intergranular microcracks (one is relatively larger than the other). There exist critical values of the aspect ratio βcand the electric field χc. When β≥βc or χ≥χc, the intergranular microcrack will split into two smaller intergranular microcracks. The splitting time of the intergranular microcrack decreases with an increase in the electric field or the aspect ratio, indicating that the increase of electric field or aspect ratio accelerates microcrack splitting. The critical electric field χc decreases as the aspect ratio increases, and the critical aspect ratio βc decreases as the electric field increases. In other words, the increase of the electric field or the aspect ratio is beneficial to microcrack splitting. In addition, the splitting time of the intergranular microcracks is less than that of the intragranular microcracks. The existence of grain boundary accelerates microcrack splitting. © 2017, Editorial Department Chinese Journal of Solid Mechanics. All right reserved.


Wu D.,Nanjing University of Aeronautics and Astronautics
Zhendong Ceshi Yu Zhenduan/Journal of Vibration, Measurement and Diagnosis | Year: 2017

With its high spatial resolution and excellent detection capability, high-frequency ultrasound is a valuable tool in clinical studies, biomedical research, and nondestructive testing (NDT) of high value manufacturing (HVM). However, a major bottleneck in further progress is the development of ultrasonic transducers for high-frequency applications. In the paper, we introduce basic principles of ultrasonic transducers and briefly review existing ultrasonic transducer techniques. Following this, we address current technical challenges of high-frequency ultrasonic transducer techniques and provide practical solutions, illustrating our recent efforts to develop state-of-the-art high-frequency ultrasonic transducer arrays. Finally, we discuss the future prospects of high-frequency ultrasonic transducer techniques. © 2017, Editorial Department of JVMD. All right reserved.


Zheng L.-K.,Nanjing University of Aeronautics and Astronautics | Xuan Y.-M.,Nanjing University of Aeronautics and Astronautics
Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics | Year: 2017

Full spectrum anti-reflectance surface micro-structure has become increasingly significant in efficient utilization of solar energy since the photovoltaics-thermoelectric hybrid system was proposed. In this paper, a composited structure that combines conventional TiO2/SiO2 antireection coatings and silicon nanorod is proposed and investigated through the finite difference time domain (FDTD) method. By means of calculating and analyzing the reflectance of structures with various parameters, an optimized structure which possesses full spectrum anti-reflectance properties is obtained, achieving a low reflectance of 0.032. © 2017, Science Press. All right reserved.


Li R.,Nanjing University of Aeronautics and Astronautics | Shi B.,Nanjing University of Aeronautics and Astronautics
Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics | Year: 2017

For analysis of scattering solar radiation influence on limb atmospheric infrared radiation, based on the scattering model, with the sun on atmospheric radiative transfer limb was calculated by using MODTRAN mid-latitude winter and summer in 3~14 μm infrared radiation of atmospheric components. For 3~5 μm and 8~14 μm band, was calculated under different Angle of the sun's atmosphere mode scattering solar radiation values and accounts for the proportion of the total radiation atmosphere. Results show that the sun angles around 20° scattering radiation is strongest, and the higher the latitude, the lower the temperature the more scattering solar radiation. In a short infrared band scattering solar radiation for a long band of 30 times, shorter infrared wavelengths scattering solar radiation, the proportion of atmospheric radiation is higher, up to 80%, in the long wave band ratio less than 0.1%, can be ignored. © 2017, Science Press. All right reserved.


Liu X.,Nanjing University of Aeronautics and Astronautics | Xuan Y.,Nanjing University of Aeronautics and Astronautics
Solar Energy | Year: 2017

Plasmonic nanoshell-based nanofluids have recently been demonstrated to be promising candidates for efficient solar thermal conversion. During the nanoshells’ fabrication processes, more often than not, only part of the dielectric core is covered by metals. However, there are few reports on how these particle defects affect the solar thermal conversion. In this paper, we find that the coverage defects of TiO2/Ag nanoshells, instead of deteriorating, may enhance the solar absorption of nanofluids. The underlying mechanism mainly lies in the redshift of the symmetric localized surface plasmon resonance from the visible region for perfect nanoshells to the near-infrared in the presence of particle defects. The poor absorption of perfect nanoshells based nanofluids in the near-infrared is thus improved. The redshift can be quantitatively predicted and understood by an effective medium approach. This work opens a new route to enhance the solar thermal conversion of nanofluids by mediating the resonance absorption of composite nanoparticles via defects, and helps to deepen the understanding of plasmonic absorption properties of non-perfect nanoshells. © 2017 Elsevier Ltd


Wang Y.,Nanjing University of Aeronautics and Astronautics | Deng Z.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Energy Conversion | Year: 2017

The open winding permanent magnet generator system is suitable for applications such as renewable energy power generation systems with multiple power sources, due to its high power density, relatively few power switches, and high degree of integration. However, for this system, it is difficult to quantitatively control the power distribution between different energy sources. In this paper, an open winding hybrid excitation generator system is presented, and for this system, a controllable power distribution strategy is investigated. In the proposed strategy, the excitation current is regulated according to the error in the current loop of the auxiliary energy source, which can achieve the regulation of the output power of the generator and finally realize the power quantitative control of the auxiliary energy source. Then, the topologies of the hybrid excitation machine are analyzed and chosen with emphasize on the influence of the flux regulation capability on the control capability of system power distribution. The experiments are carried out on a parallel hybrid excitation flux-switching (PHEFS) generator system, and the results verify the correctness and effectiveness of the proposed controllable power distribution strategy and the power distribution capability of the PHEFS generator. © 2016 IEEE.


Liu X.F.,Anhui University of Technology | Wang Y.,Anhui University of Technology | Liu W.H.,Nanjing University of Aeronautics and Astronautics
Applied Thermal Engineering | Year: 2017

In this paper, we present our theoretical investigations on thermo-mechanical conditions inside the piston of a diesel engine. For the theoretical analysis, the operational parameters of such piston, semi-empirical formula and empirical model were employed to determine the boundary conditions such as temperature and stress fields. Using the finite element method (FEM), the stress loading and fatigue life were calculated. Based on the available experiment data, the used empirical formula and models can be improved well. Furthermore, the harsh conditions were simulated using the FEM, and the results were verified using the accelerated life testing. Moreover, the relationships between the piston life and stress under the thermal load, mechanical load, and thermal-mechanical coupling conditions were established based on the above simulated data. The results showed that in different thermal, mechanical, and thermal-mechanical coupling conditions, their relationships obeyed Arrhenius model, Inverse power law model, and Generalized Eyring model, respectively. © 2017 Elsevier Ltd


In this paper, the synergistic effects of stress rupture and cyclic loading on the strain response of fiber-reinforced ceramic-matrix composites (CMCs) at elevated temperature in air have been investigated. The stress-strain relationships considering interface wear and interface oxidation in the interface debonded region under stress rupture and cyclic loading have been developed to establish the relationship between the peak strain, the interface debonded length, the interface oxidation length and the interface slip lengths. The effects of the stress rupture time, stress levels, matrix crack spacing, fiber volume fraction and oxidation temperature on the peak strain and the interface slip lengths have been investigated. The experimental fatigue hysteresis loops, interface slip lengths, peak strain and interface oxidation length of cross-ply SiC/MAS (magnesium alumino-silicate, MAS) composite under cyclic fatigue and stress rupture at 566 and 1093 °C in air have been predicted. © 2017 by the authors.


Xiao L.,Nanjing University of Aeronautics and Astronautics | Guo Z.,University of New South Wales | D'Ambra J.,University of New South Wales
Information and Management | Year: 2017

Given the enormous growth and significant impacts of group buying on Internet business marketplaces, this study aims to understand consumer goal structure in online group buying (OGB) contexts using a means-end chain approach. Using the laddering interview technique, 52 OGB consumers were interviewed. From the interview data, we identified 27 goals consumers pursued and their goal striving paths that are summarized in the hierarchical goal structure. This study has the potential to make significant contributions to both information systems research and e-commerce by utilizing a different approach to explain consumer technology adoption behavior. © 2017 Elsevier B.V.


Wu W.,Nanjing University of Aeronautics and Astronautics
5th Asian-Australian Rotorcraft Forum, ARF 2016 | Year: 2016

The maneuverability is a key factor to determine whether a helicopter could finish certain flight mission successfully or not. The inverse simulation is commonly used to calculate the controls of a helicopter to complete certain kind of maneuver flight and to assess the maneuverability. A general method for inverse simulation of maneuver flight to helicopters with flight control system online is developed in this paper. A describing function is established to provide general mathematical descriptions of different kinds of maneuvers. A comprehensive control solver based on the optimal linear quadratic regulator theory is developed to calculate the pilot controls of different maneuvers. The coupling problem between pilot controls and flight control system outputs is well solved by taking the flight control system model into control solver. The inverse simulation of three different kinds of maneuvers with different agility requirements defined in the ADS-33E-PRF is implemented based on the developed method for a UH-60 helicopter. The results show that the method developed in this paper can solve the closed-loop inverse simulation problem of helicopter maneuver flight with high reliability as well as efficiency. Copyright © 2016 by the American Helicopter Society International, Inc. All rights reserved.


Chen Z.,Nanjing University of Aeronautics and Astronautics | Liu X.,Nanjing University of Aeronautics and Astronautics
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2017

Noise-induced escape from the domain of attraction of a nonhyperbolic chaotic attractor in a periodically excited nonlinear oscillator is further investigated. Deviations are found to be amplified at the primary homoclinic tangency from which the optimal force begins to fluctuate dramatically. Escaping trajectories turn out to possess several modes to pass through the saddle cycle on the basin boundary, and each mode corresponds to a certain type of value of the action plot, respectively. A subset of the pattern of fluctuational paths from the chaotic attractor is obtained, showing the existence of complicated singularities. © 2017 American Physical Society.


Jiang C.,Nanjing University of Aeronautics and Astronautics | Wu Y.-H.,Nanjing University of Aeronautics and Astronautics
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

Spacecraft on-orbit serving is vital important for future space missions and is of interest of many countries. Relative motion determination is the major problem for spacecraft on-orbit servicing. Due to the advantages of monocular vision navigation system, it has been widely proposed for spacecraft approaching for the final stage. However, due to the model uncertainty and state mobility of the target spacecraft, a strong tracking filter is proposed to overcome the above issues in estimating relative position and attitude. This article first introduces how to set up, select and match feature markers. Followed by establishing a 6DOF spacecraft dynamics model and an imaging observation model based on quaternion. Then, the recursive process of Suboptimal Fading Extended Kalman Filter is implemented. Finally, numerical simulations are carried out to verify the effectiveness of the proposed algorithm. © 2016 IEEE.


Ye Q.,Nanjing University of Aeronautics and Astronautics | Liu C.,Nanjing University of Aeronautics and Astronautics
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

A method of a SMC (sliding mode control)-based guidance law design is proposed for an exoatmospheric missile with constant positive acceleration. By analyzing the nonlinear kinematic equations of the missile, a class of nominal motions that requires no maneuver effort can be defined. The unique time-to-go, the corresponding nominal heading angle and the nominal heading angular rate can be solved from the equations that are derived from the properties of the nominal motions to guarantee a perfect interception with a desired impact angle. A nonsingular SMC-based guidance law is designed for the disturbed heading angle tracking system such that the tracking is guaranteed in finite time. © 2016 IEEE.


Zhang T.,Nanjing University of Aeronautics and Astronautics | Yang Z.,Nanjing University of Aeronautics and Astronautics
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

This paper presents a vision method for a multi-rotor Unmanned Aerial Vehicle (UAV) to track a moving object using combined algorithm of Camshift and Kalman predictor. Because of the real-time performance demanded by the control system, vision algorithm should calculate navigation data quickly. Camshift is a tracking algorithm based on histogram matching and color probability distribution, which has a lot of advantages such as strong adaptability and precise tracking accuracy. However, the center of tracking box generated by Camshift algorithm cannot remain stable because of inevitable noise due to the change of light and camera shaking. Thusly, Kalman predictor is implemented to erase this noise as well as predict the position of moving object when it is temporarily lost by UAV. Experimental results show that through this method, UAV can continuously tracking a moving vehicle under different background environment even object is temporarily occluded or lost by UAV. © 2016 IEEE.


Qian M.,Nanjing University of Aeronautics and Astronautics | Gao Z.,Nanjing University of Posts and Telecommunications
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

This paper addresses an adaptive fault tolerant flight control design for an unmanned aerial vehicle (UAV) in the presence of multiple actuator faults. With a reference model and control allocation implemented to evaluate dynamic tracking error performance of flight control systems (FCS) in fault free case, the proposed control can converge to an optimal solution and make faulty FCS asymptotically track a reference system online. Finally, simulation results are given to demonstrate the effectiveness of the proposed development. © 2016 IEEE.


Zhang X.,Nanjing University of Aeronautics and Astronautics | Yang Z.,Nanjing University of Aeronautics and Astronautics
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

In this paper, a quaternion based extended Kalman filter (EKF) is developed for determining the attitude and heading of multi-rotor UAVs from the outputs of a self-designed nano Inertial Measurement Unit (nIMU), which consists of low-cost MEMS sensors including a triaxial gyroscope, a triaxial accelerometer and a triaxial magnetometer. In the proposed filtering design, the quaternion associated with the rotation of the quadrotor is included in the state vector with the bias of the sensors. The Gauss-Newton method for parameter optimization is utilized along with Kalman filtering. Preprocessing of sensors' measurements using the Gauss-Newton method yields a computed quaternion input for the Kalman filter, which reduces the dimension of the state vector and linearizes the measurement equations, hence the filter design is significantly simplified. Experimental results have validated the filter design and show good performance of the self-designed nIMU used on quadrotors. © 2016 IEEE.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Qi D.,North University of China
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

Drawing upon small gain criteria and robust analysis techniques, lower bounds on the largest allowable time-varying delay are derived with the use of rational approximation functions. These results are computationally efficient and conceptually appealing. Moreover, when specialized to specific situations, the results provide analytical expressions which exhibit explicit dependence of the bounds on the pole and zero and show how fundamentally unstable poles and nonminimum phase zeros may limit the range of delays over which a plant may be stabilized. © 2016 IEEE.


Lei X.,Nanjing University of Aeronautics and Astronautics
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

Model prediction control (MPC) is adopted in this work to solve the Gust Load Alleviation (GLA) system performance, which is seriously influenced by some uncertain factors. Based on receding optimization strategy, it can overcome the negative influence of modeling errors and uncertain environmental disturbance, which helps achieve strong robustness. Especially, one kind of large aircraft is chosen and the state-space form of aircraft-gust model is proposed. As for the synthesized system model, model prediction control technology is used to design a control law on gust load alleviation. Simulation and comparison results show that the designed controller can mitigate the impact of gust on the aircraft effectively and achieve strong robustness. © 2016 IEEE.


Zheng D.,Nanjing University of Aeronautics and Astronautics | Zheng D.,Yancheng Institute of Technology | Chen W.,Nanjing University of Aeronautics and Astronautics
Tribology International | Year: 2017

To predict thermal behaviors of high-speed angular contact ball bearings is essential for operating precision. Particularly, the characteristics of high-speed angular contact ball bearings depend on their thermal performances. However, most researchers only considered the convection effect between housings and ambient air, whereas the coolant/lubricant and specific structural constraints effect were not integrated. In this investigation, the load equilibrium model of angular contact ball bearings with thermal expansion was first established to calculate bearing loads. The coolant/lubricant, radial and axial structural constraints and assembly constraints were fully taken into account to study the heat generation and transfer of bearings, and then a novel muti-node thermal network model for angular contact ball bearings was proposed. Applying this muti-node model, an integrated comprehensive thermal grid model for the front bearing of high-speed spindle and its surroundings was established to forecast the bearing temperature. Next Euler's method was employed to solve the equations by Matlab and the node temperature was calculated. Finally, the bearing temperature rise was tested and the comparative analysis was made with the numerical results. The results indicate that both series of results agree well. So, the thermal grid model established is verified. © 2017 Elsevier Ltd


Yu H.,Nanjing University of Aeronautics and Astronautics | Ma H.,Nanjing University of Aeronautics and Astronautics | Yan K.,Nanjing Gardens Planning and Design Institute Ltd. Co.
Construction and Building Materials | Year: 2017

The present study uses the dynamic modulus of elasticity as the damage variable and derives an equation that can be used to determine the freeze-thaw fatigue damage in concrete under water and deicing salt freeze-thaw conditions based on the mechanical fatigue damage theory. The present study derives a model for predicting the service life of concrete subjected to freeze-thaw cycles under different freeze-thaw systems. Accumulative model is also presented for predicting the service life of concrete subjected to freeze-thaw cycles under a combination of different freeze-thaw systems in natural environmental conditions; this model uses the fatigue damage accumulation theory along with the fact that the mechanism of freeze-thaw damage in concrete is the same in the natural freeze-thaw environment as it is under standard laboratory rapid freeze-thaw conditions. The equation for determining the freeze-thaw fatigue damage in concrete and the model for predicting the service life of concrete subjected to freeze-thaw cycles are verified based on a large amount of test data. The relationship between the number of freeze-thaw cycles concrete undergoes under laboratory condition and natural environmental conditions is recalculated. In addition, applying the cumulative model for predicting the service life of concrete subjected to freeze-thaw cycles under natural environmental conditions is discussed. The results show that the curves of the freeze-thaw fatigue damage for different types of concrete obtained from the proposed equation have the same trends and are in good agreement with the curve of the measured relative dynamic modulus of elasticity. Furthermore, the relative errors between the values calculated from the model for predicting the service life of concrete subjected to freeze-thaw cycles and the values measured under different cooling rates are less than 3%; this result indicates that the model for predicting the service life of concrete subjected to freeze-thaw cycles and its cumulative model can satisfactorily predict the natural fatigue life of concrete subjected to freeze-thaw cycles in an actual freeze-thaw environment. The analysis and calculation of the measured laboratory condition and natural environmental conditions data shows that the ratio of the standard fatigue life of concrete subjected to freeze-thaw cycles under rapid laboratory freeze-thaw conditions to the natural fatigue life of the same concrete subjected to freeze-thaw cycles in the actual environment is approximately 1:8–1:9, instead of the previously reported range of 1:10–1:15. © 2017 Elsevier Ltd


Wan Y.,Nanjing University of Aeronautics and Astronautics
Bulletin of the Polish Academy of Sciences: Technical Sciences | Year: 2017

In this paper, a new control scheme is proposed to achieve stability for a single-machine infinite-bus power system. A power system model simultaneously considering input saturation and time-varying uncertainties is presented. A sufficient condition for the system convergence is given and based on this result, a switching excitation control law with auxiliary system is designed. The stability analysis and simulation results all show that the developed controller is effective.


Zhang Y.,Nanjing University of Aeronautics and Astronautics | Tao G.,University of Virginia | Chen M.,Nanjing University of Aeronautics and Astronautics | Wen L.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Fuzzy Systems | Year: 2017

This paper conducts a new study for adaptive Takagi-Sugeno (T-S) fuzzy approximation-based control of multi-input and multi-output (MIMO) noncanonical-form nonlinear systems. Canonical-form nonlinear systems have explicit relative degree structures, whose approximation models can be directly used to derive desired parameterized controllers. Noncanonical-form nonlinear systems usually do not have such a feature, nor do their approximation models, which are also in noncanonical forms. This paper shows that it is desirable to reparameterize noncanonical-form T-S fuzzy system models with smooth membership functions for adaptive control, and such system reparameterization can be realized using relative degrees, a concept yet to be studied for MIMO noncanonical-form T-S fuzzy systems. This paper develops an adaptive feedback linearization scheme for control of such general system models with uncertain parameters, by first deriving various relative degree structures and normal forms for such systems. Then, a reparameterization procedure is developed for such system models, based on which adaptive control designs are derived, with desired stability and tracking properties analyzed. A detailed example is presented with simulation results to show the new control design procedure and desired control system performance. © 1993-2012 IEEE.


Wu S.-X.,Nanjing University of Aeronautics and Astronautics | Chen C.,Nanjing University of Aeronautics and Astronautics
Proceedings of the 2016 Symposium on Piezoelectricity, Acoustic Waves and Device Applications, SPAWDA 2016 | Year: 2016

In this paper, a dual ring ultrasonic motor based on out of plane bending vibration mode is proposed, fabricated and characterized. This motor is composed of a stator constituted with two ring and one rod-shaped transducer at the middle and two disk shaped rotors. There are four piezoelectric ceramic plates are bolted at the middle of the rod-shaped transducer and used to excite the stator's blending vibration mode. The ring is used to amplify the vibration amplitude of the rod-shaped transducer. The rotor pressed on the conical surface of the stator can be driven to rotate by the friction force induced by the traveling wave vibration of the stator. It can be seen from experimental results that proposed motor can rotate at the maximum value of 65 rpm and the maximum output torque is 0.07N•m, while applied with the driving voltage of 250 Vp-p. This motor can be designed double output shaft has a great potential for applications of the actuator control. © 2016 IEEE.


Yu C.-B.,Nanjing University of Aeronautics and Astronautics | Gao C.-F.,Nanjing University of Aeronautics and Astronautics
Proceedings of the 2016 Symposium on Piezoelectricity, Acoustic Waves and Device Applications, SPAWDA 2016 | Year: 2016

The plane problem of a circular-arc crack in an infinite thermoelectric medium under remote thermal-electric loads is studied in this paper. The crack surface boundary conditions are assumed to be electrically and thermally impermeable. The explicit solutions are presented based on the complex variable method. Expressions for the electric flux, energy flux, thermal flux, and temperature and stress fields are derived. It is found that these fields exhibit traditional square-root singularity at the crack tip. Then the electric flux, the energy flux and stress intensity factors at the crack tip are obtained. The results show that the electric flux intensity factor and the energy flux intensity factor depend on the far-field electric flux loads and the applied total energy flux loads, respectively. In addition, the simultaneous existence of mode-I and mode-II stress intensity factors are found to be dependent on the angle of electric flux, the electric conductivity, the angle of thermal flux, the thermal conductivity, the central angle of the crack and thermal-elastic isotropy. © 2016 IEEE.


Zhang R.-F.,Nanjing University of Aeronautics and Astronautics | Gao C.-F.,Nanjing University of Aeronautics and Astronautics
Proceedings of the 2016 Symposium on Piezoelectricity, Acoustic Waves and Device Applications, SPAWDA 2016 | Year: 2016

Based on the XFEM, an elliptical hole edge-cracks problem in piezoelectric materials is analyzed. The stress field and the electrical displacement field around the crack tip are derived. The virtual crack closure method is used to calculate the energy release rate of different crack length under the mechanical load and electromechanical coupling load, respectively. According to the relationship between the energy release rate and the stress intensity factor, the crack tip stress intensity factor and the electric displacement intensity factor are calculated. The obtained results are excellent agreement with those from the analytical solutions. The influences of the geometries and the external loads on the field intensity factors are discussed. To show the accuracy of the present method, the numerical results from the XFEM are compared with the analytical reference solutions available in the literature and excellent agreements are found. © 2016 IEEE.


Peng Y.-S.,Nanjing University of Aeronautics and Astronautics | Hu J.-H.,Nanjing University of Aeronautics and Astronautics
Proceedings of the 2016 Symposium on Piezoelectricity, Acoustic Waves and Device Applications, SPAWDA 2016 | Year: 2016

In this report, ultrasound based molecular transport from gas onto a solid material surface is demonstrated, and the molecular transport is confirmed by the detection based on a gas sensor. In the experiments, a standing wave ultrasonic field of 46.25 kHz was used to transport CO gas molecules onto the surface of a SnO2 sensing layer. The experimental results show that the CO molecules can be transported onto the sensing layer when the ultrasound exists in the vicinity of the sensing layer, and the molecular transport can be enhanced by making the ultrasonic field resonant or stronger. © 2016 IEEE.


Liu H.,Nanjing University of Aeronautics and Astronautics | Xu J.,Nanjing University of Aeronautics and Astronautics
Mechanical Systems and Signal Processing | Year: 2017

In this paper, we consider the partial eigenvalue assignment problem of high order control systems. Based on the orthogonality relations, we propose a new method for solving this problem by which the undesired eigenvalues are moved to desired values and keep the remaining eigenvalues unchanged. Using the inverse of Cauchy matrix, we give the solvable condition and the explicit solutions to this problem. Numerical examples show that our method is effective. © 2017 Elsevier Ltd


Zhang S.,Nanjing University of Aeronautics and Astronautics | Cai Z.,Nanjing University of Aeronautics and Astronautics
International Journal of Control, Automation and Systems | Year: 2017

Electrical wiring interconnection system (EWIS) of civil aircraft has been paid more attention in recent years, and intermittent failure detection of electrical connectors in EWIS is a challenging problem. This paper presents a sliding mode observer (SMO) approach for the intermittent failure detection of an aircraft electrical system with multiple connector failures. The mathematical model of the aircraft electrical system which contains multiple connector failures is established for transforming the intermittent failure detection problem into observerbased multiplicative faults isolation and estimation problems. A set of adaptive sliding mode observers are designed to locate the failure connectors preliminarily, the observers can adapt the unknown upper bound of the faults. Furthermore, a fault-reconstruction scheme applying the equivalent output error injection principle is proposed for fault estimation, where the characteristic parameters of connecters are reconstructed to identify the failures. Finally, a numerical example is provided to show the effectiveness of the proposed method. © 2017 Institute of Control, Robotics and Systems and The Korean Institute of Electrical Engineers and Springer-Verlag Berlin Heidelberg


Qi T.,South China University of Technology | Zhu J.,Nanjing University of Aeronautics and Astronautics | Chen J.,City University of Hong Kong
IEEE Transactions on Automatic Control | Year: 2017

This paper concerns the stabilization of linear time-invariant (LTI) systems subject to uncertain, possibly time-varying delays. The fundamental issue under investigation, referred to as the delay margin problem, addresses the question: What is the largest range of delay such that there exists a single LTI feedback controller capable of stabilizing all the plants for delays within that range? Drawing upon analytic interpolation and rational approximation techniques, we derive fundamental bounds on the delay margin, within which the delay plant is guaranteed to be stabilizable by a certain LTI output feedback controller. Our contribution is threefold. First, for single-input single-output (SISO) systems with an arbitrary number of plant unstable poles and nonminimum phase zeros, we provide an explicit, computationally efficient bound on the delay margin, which requires computing only the largest real eigenvalue of a constant matrix. Second, for multi-input multi-output (MIMO) systems, we show that estimates on the variation ranges of multiple delays can be obtained by solving LMI problems, and further, by finding bounds on the radius of delay variations. Third, we show that these bounds and estimates can be extended to systems subject to time-varying delays. When specialized to more specific cases, e.g., to plants with one unstable pole but possibly multiple nonminimum phase zeros, our results give rise to analytical expressions exhibiting explicit dependence of the bounds and estimates on the pole and zeros, thus demonstrating how fundamentally unstable poles and nonminimum phase zeros may limit the range of delays over which a plant can be stabilized by a LTI controller. © 2016 IEEE.


Xu L.,Nanjing University of Science and Technology | Nallanathan A.,King's College London | Song X.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Wireless Communications | Year: 2017

In this paper, a joint video scheduling, subchannel assignment, and power allocation problem in cognitive heterogeneous networks are modeled as a mixed integer non-linear programming (MINLP), which maximizes the minimum video transmission quality among different secondary mobile terminals (MTs) subject to the total available energy at each secondary, the total interference power at each primary base station, the total available capacity at each radio interface of each secondary MTs, and the video sequence encoding characteristic. In order to solve it, we decompose the original MINLP as joint subchannel and power allocation problem and video packet scheduling problem. Then, we model the joint subchannel and power allocation problem as a max-min fractional programming, and transform it as a convex optimization problem. Finally, we utilize dual decomposition method to design a joint subchannel and power allocation algorithm, and propose a video packet scheduling scheme based on auction theory to maximize the video quality for each secondary MT. Simulation results demonstrate that the proposed framework not only improves the video transmission quality significantly, but also guarantees the fairness among different secondary MTs. © 2017 IEEE.


Chen M.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2017

In this paper, a robust tracking control scheme is proposed for wheeled mobile robots with skidding, slipping, and input disturbance. Considering the existing skidding and slipping, a desired disturbance-observer-based virtual velocity control law is first designed. Then, the robust tracking control scheme is developed by considering the prescribed tracking performance requirement and using the disturbance observer. In the tracking control scheme design, the prescribed performance function method is employed to guarantee the desired tracking performance. To handle the skidding, slipping, and input disturbance, the disturbance observer is developed in the control scheme design. Experiment results demonstrate the effectiveness of the proposed tracking control scheme for wheeled mobile robots with skidding, slipping, and input disturbance. © 2017 IEEE.


Zhao Q.,Nanjing University of Aeronautics and Astronautics | Ye Y.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2017

Repetitive control (RC) can offer a promising accurate voltage control scheme for constant-voltage constant-frequency (CVCF) pulse width modulation (PWM) inverters to compensate the harmonic distortion caused by nonlinear loads. However, limited by digital sampling, conventional RC with integer phase lead compensation cannot exactly compensate the system phase lag, which may result in instability in the case of low sampling frequency. In this paper, a fractional phase lead compensation RC (FPLC-RC) scheme is proposed to enable the phase lead step to be fractional, which can enlarge the stability region and improve the tracking accuracy. A newly devised finite-impulse response fractional lead filter based on Lagrange interpolation is applied to approximate the fractional lead items. Meanwhile, the synthesis and analysis of fractional phase lead RC for a single PWM inverter are given. Furthermore, simulations and experiments are provided to demonstrate the validity of the proposed FPLC-RC scheme. © 2017 IEEE.


Xue M.,Nanjing University of Aeronautics and Astronautics | Pan S.,Nanjing University of Aeronautics and Astronautics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

Most of the efforts devoted to the area of optical communications were on the improvement of the optical spectral efficiency. Varies innovative optical devices are thus developed to finely manipulate the optical spectrum. Knowing the spectral responses of these devices, including the magnitude, phase and polarization responses, is of great importance for their fabrication and application. To achieve high-resolution characterization, optical vector analyzers (OVAs) based on optical single-sideband (OSSB) modulation have been proposed and developed. Benefiting from the mature and highresolution microwave technologies, the OSSB-based OVA can potentially achieve a resolution of sub-Hz. However, the accuracy is restricted by the measurement errors induced by the unwanted first-order sideband and the high-order sidebands in the OSSB signal, since electrical-to-optical conversion and optical-to-electrical conversion are essentially required to achieve high-resolution frequency sweeping and extract the magnitude and phase information in the electrical domain. Recently, great efforts have been devoted to improve the accuracy of the OSSB-based OVA. In this paper, the influence of the unwanted-sideband induced measurement errors and techniques for implementing high-accurate OSSB-based OVAs are discussed. © 2016 SPIE.


Li Y.,Nanjing University of Aeronautics and Astronautics | Zhang J.,Nanjing University of Aeronautics and Astronautics | Xuan Y.,Nanjing University of Aeronautics and Astronautics
Applied Thermal Engineering | Year: 2017

The interaction between the rotor and fuselage of a helicopter is a three-dimensional and highly unsteady phenomenon. Meanwhile, the exhaust plume of the turbo-shaft engine which has the characteristics of high exhaust temperature and velocity, is subjected to the interference of rotor flow field. The flow interaction has a great influence on the temperature distribution and infrared radiation performance, especially in the engine affecting area. Numerical calculation is established for simulating the downwash of the isolated rotor at hovering condition based on CFD analysis by using three different methods. The “actuator disk” method is applied to form a new simulation for rotor-fuselage interaction flow field in forward flight. We also calculate and analyze the temperature distribution on the helicopter fuselage and exhaust plume. Ultimately, based on the characterization of the flow and temperature fields, the helicopter solid wall infrared radiation has been investigated by utilizing a ray tracing method. © 2017 Elsevier Ltd


Yu Y.,Nanjing University of Aeronautics and Astronautics | Wang W.,Nanjing University of Aeronautics and Astronautics | Hickey M.P.,Embry - Riddle Aeronautical University
Journal of Geophysical Research: Space Physics | Year: 2017

Ionospheric fluctuations inferred from observations of total electron content have previously been attributed to tsunamis and have confirmed the strong coupling between Earth's ocean and ionosphere via atmospheric gravity waves (AGWs). To further advance our understanding of this wave coupling process we employ a linear full-wave model and a nonlinear time-dependent model to examine the ionospheric response to the AGW perturbations induced by the 2004 Sumatra and the 2011 Tohoku tsunamis. In the 2004 case, our modeling analyses reveal that one component of the propagating AGWs becomes dynamically unstable in the E-region ionosphere at a range exceeding 2000km in a direction 340° clockwise from north. Another component becomes convectively unstable in the E-region ionosphere at a range exceeding 700km in a direction 250° clockwise from north. In the 2011 case, a significant enhancement in the ionospheric disturbance occurs in a direction northwest from the epicenter about 1h following the tsunami onset, in general agreement with observations. Our simulations also indicate that the AGW propagating toward the southeast is responsible for a traveling ionospheric disturbance that remains of an observable amplitude for over 4h during which time it propagates horizontally almost 4000km. © 2017. American Geophysical Union. All Rights Reserved.


Wang X.,Nanjing University of Aeronautics and Astronautics | Yuan Z.,Georgia Institute of Technology
Composite Structures | Year: 2017

Although many engineering sandwich panel theories are available, however, they cannot recover all stress components accurately for the sandwich panels with non-homogeneous functionally graded (FG) soft-cores. In this paper, a novel method is proposed to accurately analyze the static behavior of sandwich panels with FG soft-cores. Two combinations of boundary conditions and three types of loading are considered. Due to the severe transverse variations in the material properties and the discontinuity of the first order derivative of material parameters at the middle plane of the core, the problem is challenging for point discrete methods and thus is solved by the weak form quadrature element method (QEM). Based on the differential quadrature (DQ) rule, a novel quadrature sandwich panel element is established. Explicit formulations are worked out and the element can be implemented adaptively. Sandwich panels involving seven different core materials are investigated. The results are verified with ABAQUS data by using very fine meshes. Numerical results are presented to investigate effects of the power-law exponent of the material prosperities’ variation, boundary conditions, and different types of loading on the distributions of displacement and stress of the sandwich panel with FG soft-core. © 2016 Elsevier Ltd


Wei L.,Nanjing University of Aeronautics and Astronautics | Dang Y.-G.,Nanjing University of Aeronautics and Astronautics
2016 IEEE International Conference on Systems, Man, and Cybernetics, SMC 2016 - Conference Proceedings | Year: 2016

In order to overcome the shortcomings of the conventional model GM (1,N), a new optimized model which is based on the development trends of multiple driving variables, termed TMGM (1,N), is proposed in this study. The new model has improved the theory from the following aspects. First, a new forecast model of the development trend of the driving variables is established which can make better use of the information of the driving variables. Meanwhile, the time response formula of the TMGM(1,N) are based on the convolution integral which can better simulate the driving variables' function on the system sequence which can improve the accuracy of the prediction. Finally, the forecast of China's grain yield is adopted for demonstration. The results indicate that the new model has higher accuracy of the output than model GM (1,N) and model TGM (1,N). © 2016 IEEE.


Hu M.-L.,Nanjing University of Aeronautics and Astronautics | Ding L.,Nanjing University of Aeronautics and Astronautics
2016 IEEE International Conference on Systems, Man, and Cybernetics, SMC 2016 - Conference Proceedings | Year: 2016

Some scholars have already proposed a lot of dominance relation and its corresponding rough model under incomplete information system in order to deal with the problem of preference decision which has incomplete information. In the incomplete information system no matter use any dominance relation to construct a rough set model the result is uncertain. In order to reduce the misclassification caused by uncertainty, this paper put forward the concept of grey dominance relation and its rough model. Firstly the analyses of the sectors which cause the uncertainty of classification are presented in this paper. Secondly the concepts of difference coefficient and grey dominance relation are definite. Besides, rough approximation model based on grey dominance relation is constructed. Finally, through the example new model proves to have better classification performance. © 2016 IEEE.


Xu H.,Nanjing University of Aeronautics and Astronautics | Lei L.,Nanjing University of Aeronautics and Astronautics
2016 3rd International Conference on Systems and Informatics, ICSAI 2016 | Year: 2016

This article propose a directional MAC protocol of ad hoc networks based on busy tone, which is a modification of the IEEE 802.11 DCF(distributed coordination function), namely TBTMA/DA(Triple Busy Tone Medium Access protocol with Directional Antennas). According to the directional busy tone, our protocol can avoid data conflict, which will solve the 'deaf' and directional 'hidden terminal' and other new problems that caused by the directional transmission. Compared with some other typical directional MAC schemes like DBTMA/DA(Double Busy Tone Medium Access protocol with Directional Antennas) and the traditional IEEE 802.11 DCF, simulation results show that our protocol can obtain higher network throughput, and better fairness of the link between 'deaf' nodes. © 2016 IEEE.


Huang X.,Nanjing University of Aeronautics and Astronautics | Zhou Y.,Nanjing University of Aeronautics and Astronautics
ISAPE 2016 - Proceedings of the 11th International Symposium on Antennas, Propagation and EM Theory | Year: 2016

The rapid development of modern wireless communication system has greatly promoted the development of the reconfigurable filters. This paper presents a hexagonal structure reconfigurable filter which operates at five different frequencies. The resonant characteristics of stepped impedance resonator (SIR) is utilized by equaling the transmission line of low impedance to multiple parallel lines of high impedance. And four PIN diodes are loaded to control the access state of equivalent lines of high impedance. The filter operates at 2GHz, 2.3GHz, 2.5GHz, 2.7GHz and 3GHz, with 3dB absolute bandwidth of constant 100MHz. Experimental results agree well with theoretical and simulated predications. © 2016 IEEE.


Gao F.,Nanjing University of Aeronautics and Astronautics | Niu Z.,Nanjing University of Aeronautics and Astronautics
ISAPE 2016 - Proceedings of the 11th International Symposium on Antennas, Propagation and EM Theory | Year: 2016

The investigation into the effect of the wind turbines (WTs) on the radar system is increasing with the growing demands for wind farms. In order to evaluate the Doppler spectrum features of the rotational WT, a simplified WT model with high reliability is proposed and the simulation results are conducted in this paper. Then the Doppler effect under different characteristics are also analyzed by utilizing quasi-stationary method as well as the Fast Fourier Transform (FFT). © 2016 IEEE.


Tao C.,Nanjing University of Aeronautics and Astronautics | Qiu J.,Nanjing University of Aeronautics and Astronautics
AIP Conference Proceedings | Year: 2017

Composite laminates suffer from fatigue damages under cyclic loads and one direct result is the stiffness degradation due to transverse matrix cracks in off-axis plies. Since the Lamb wave velocities are decided by the stiffness properties of materials, it is reasonable to use Lamb wave velocity to characterize the fatigue damages in composite laminates. For this to be achieved, an explicit solution for 0-frequency S0-mode and SH0-mode phase velocities are deduced in this work, based on which a velocity degradation model is further proposed using a shear-lag model approximation and Paris model. The proposed velocity degradation model was then used to characterize fatigue damages in cross-ply GFRP laminates ([0/903/0/903]S), where the experimental S0-mode phase velocity was obtained by a laser ultrasonic scanning system. The proposed damage model shows good correlation with experimental results. With the proposed velocity degradation model, it is possible for future work to be done to inspect and predict the residual fatigue life of composite laminates using Lamb wave velocities. © 2017 Author(s).


Hu D.L.,Hohai University | Liu X.B.,Nanjing University of Aeronautics and Astronautics | Chen W.,Hohai University
Nonlinear Dynamics | Year: 2017

In this paper, the moment Lyapunov exponent and stochastic stability of binary airfoil under combined harmonic and Gaussian white noise excitation are investigated. Via the singular perturbation method, the first-order expansions of the moment Lyapunov exponent are obtained, which agree well with the results obtained by the Monte Carlo simulation. Finally, the effects of the noise and parametric resonance (such as subharmonic resonance and combination additive resonance) on the stochastic stability of the binary airfoil system are discussed. © 2017 Springer Science+Business Media Dordrecht


He D.,Nanjing University of Aeronautics and Astronautics | Chen S.,Nanjing University of Aeronautics and Astronautics
Moshi Shibie yu Rengong Zhineng/Pattern Recognition and Artificial Intelligence | Year: 2017

To improve the clustering performance, an incomplete data imputation clustering algorithm based on difference of convex functions programming (DCP) is proposed. DCP is applied to optimize the kernel-based fuzzy C-means objective function, and the alternative optimization process for DCP clustering and missing completion is given. The convergence of the alternating optimization is proved theoretically. Experiments show the superiority of the proposed algorithm in missing completion and clustering performance. © 2017, Science Press. All right reserved.


Yu H.,Nanjing University of Aeronautics and Astronautics | Wang T.,Nanjing University of Aeronautics and Astronautics
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2017

In this paper, we proposed a fast algorithm for circle detection and measurement, which uses a lookup table and bitwise center accumulator (LUT-BCA). The LUT-BCA is a two-stage procedure. The first stage determines the candidate circle centers with normal lines produced by the lookup table and recorded by the bitwise center accumulator. The second stage computes the radius of each candidate circle center and validates these centers, which eliminates the false detections. The proposed LUT-BCA can also be easily implemented on massively parallel high-performance graphics hardware using the compute unified device architecture. Experimental results indicate that the LUT-BCA can locate circle centers and measure their radii accurately and is very suitable for real-time circle detection and measurement. © 2017 Optical Society of America.


Wang Y.,Nanjing University of Aeronautics and Astronautics | Qin N.,University of Sheffield | Zhao N.,Nanjing University of Aeronautics and Astronautics
Communications in Computational Physics | Year: 2017

A novel mesh deformation technique is developed based on the Delaunay graph mapping method and the inverse distance weighting (IDW) interpolation. The algorithm maintains the advantages of the efficiency of Delaunay graph mapping mesh deformation while it also possesses the ability of better controlling the near surface mesh quality. The Delaunay graph is used to divide the mesh domain into a number of sub-domains. On each sub-domain, the inverse distance weighting interpolation is applied, resulting in a similar efficiency as compared to the fast Delaunay graph mapping method. The paper will show how the near-wall mesh quality is controlled and improved by the new method. © 2017 Global-Science Press.


Pan S.,Nanjing University of Aeronautics and Astronautics | Xue M.,Nanjing University of Aeronautics and Astronautics
Journal of Lightwave Technology | Year: 2017

Knowing magnitude, phase, and polarization responses is of great importance for fabrication and application of optical devices. A large variety of parameters such as insertion loss, dispersion, group delay, polarization-dependent loss, and polarization mode dispersion can be obtained based on these responses. Conventional approaches achieve the optical spectral responses by sweeping the wavelength of a laser source. Restricted by the low-wavelength accuracy and poor wavelength stability of the wavelength-swept laser source, the resolution of the optical vector analyzers (OVAs) are usually poor (>1.6 pm). To achieve ultrahigh resolution measurement, an OVA based on optical single-sideband (OSSB) modulation has been proposed and developed, which potentially has a sub-Hz resolution. However, electrical-to-optical and optical-to-electrical conversions are required to implement the electrical frequency sweeping and to detect the phase and magnitude information in the electrical domain, which limits the spectral measurement range, accuracy, and dynamic range. In the past decade, great efforts have been devoted to deal with these problems. In this paper, techniques for constructing high-performance OSSB-based OVAs are discussed with an emphasis on the system architectures and operation principles for improving the spectral measurement range, accuracy, and dynamic range of the measurement system. Possible future research directions are also discussed. © 2016 IEEE.


Tang Q.,Nanjing University of Aeronautics and Astronautics | Wang X.,Nanjing University of Aeronautics and Astronautics | Hu J.,Nanjing University of Aeronautics and Astronautics
Applied Physics Letters | Year: 2017

A strategy to concentrate nanoscale materials on the boundary between a nano suspension droplet and non-vibration substrate is demonstrated and analyzed. It employs the spiral vortex of acoustic streaming, generated by an ultrasonically vibrating needle parallel to and above the non-vibration substrate. The vortex drags nanoscale materials to the center of itself, forming a concentration spot. For 250 nm-diameter SiO2 nano particle suspension with an initial concentration of 0.09 mg/ml, the diameter of the concentration spot can be up to several hundred microns. The dependency of the spiral vortex field on the vibration distribution of the acoustic needle in the droplet is also clarified by experiments and computation, and the concentration conditions are obtained by analyzing the nano particle dynamics in the spiral vortex. © 2017 Author(s).


Li C.,Nanjing University of Aeronautics and Astronautics | Wang X.,Nanjing University of Aeronautics and Astronautics
Proceedings - 2016 9th International Congress on Image and Signal Processing, BioMedical Engineering and Informatics, CISP-BMEI 2016 | Year: 2016

Based on the analysis of GPS deception jamming theory, this paper considers the control feathers of the UAV GPS/INS integrated navigation system and designs an innovation detection rule for the UAV navigation system state estimation. Methods of direct track deception and track fusion are used to achieve the intrusive control of the navigation system and the control of the UAV's trajectory through the GPS deception jamming. The normalized innovation squared under two control modes is given through theoretical derivation and simulation analysis. The results show that the method of track fusion not only can realize the cheating of UAV trajectory, but also not easy to be checked, which provides an effective means of interference for GPS countermeasures. © 2016 IEEE.


Ju M.,Nanjing University of Aeronautics and Astronautics | Wang L.,Nanjing University of Aeronautics and Astronautics
Proceedings of 2016 Prognostics and System Health Management Conference, PHM-Chengdu 2016 | Year: 2016

Arc fault in DC system is an un-negligible hazard which should to be cut off immediately for system safety. In order to describe the character of the arc fault, an accurate arc model is in urgent need. This paper proposed a new method to confirm the parameters of Habedank model which used in DC system. The volt-Ampere characteristics of arc from simulation and experiment are compared. Comparison shows that the method this paper proposed can simulate the characteristics of impedance of DC arc fault well. © 2016 IEEE.


A "self-heating" boron catalyst that makes particularly efficient use of sunlight to reduce carbon dioxide (CO2) serves as a light harvester, photothermal converter, hydrogen generator, and catalyst in one. In the journal Angewandte Chemie, researchers introduce a photothermocatalytic reaction that requires no additives beyond water. This could form the basis of a new, more efficient process for converting the greenhouse gas CO2 into a useful carbon source for the production of fuels and chemical products. The ideal route for making CO2 useful is considered to be reduction aided by a photocatalyst to use sunlight as the only source of energy—a process that corresponds to the first step of photosynthesis. Despite decades of research, processes for converting CO2 are still too inefficient. "This is largely due to the insufficient utilization of solar light, the high energy barrier for CO2 activation, and the sluggish kinetics of the multiple electron and proton transfer processes," explains Jinhua Ye. Working with a team for the National Institute for Materials Science (NIMS) in Tsukuba, Ibaraki, and Hokkaido University in Sapporo (Japan), as well as Tianjin University and Nanjing University of Aeronautics and Astronautics (China), Ye is now pursuing a strategy that uses both the light and thermal energy provided by sunlight. When the sun shines on a surface, it is heated. The researchers want to use this ordinary photothermic effect to increase the efficiency of catalytic systems. Their material of choice is powdered elemental boron, which very strongly absorbs sunlight and efficiently converts it photothermically, heating itself up remarkably. This allowed the team to carry out the efficient reduction of CO2 to form carbon monoxide (CO) and methane (CH4) under irradiation in the presence of water, with no additional reagents or co-catalysts. Irradiation causes the boron particles to heat up to about 378 °C. At this temperature it reacts with water, forming hydrogen and boron oxides in situ. The boron oxides act as "traps" for CO2 molecules. The hydrogen is highly reactive and, in the presence of the light-activated boron catalyst, efficiently reduces the CO2 by providing the necessary protons (H+) and electrons. "The key to our success lies in the favorable properties of the boron powder, which make it an all-in-one catalyst: light harvester, photothermic converter, hydrogen source, and catalyst," says Ye. "Our study confirms the highly promising potential of a photothermocatalytic strategy for the conversion of CO2 and potentially opens new vistas for the development of other solar-energy-driven reaction systems." Explore further: Hydrogen from sunlight—but as a dark reaction More information: Guigao Liu et al. Elemental Boron for Efficient Carbon Dioxide Reduction under Light Irradiation, Angewandte Chemie International Edition (2017). DOI: 10.1002/anie.201701370


Zhou C.H.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore
Computers and Fluids | Year: 2012

This paper is the first endeavor to present the local domain-free discretization (DFD) method for the solution of the three-dimensional Navier-Stokes equations. The computational domain may contain complex moving boundaries. The strategy of DFD is that the discrete form of partial differential equations at an interior point may involve some points outside the solution domain. The functional values at the exterior dependent points are evaluated by the approximate form of solution near the boundary. Compared to the previous work, the tedious task of constructing new interpolation tetrahedrons is eliminated, and this reduces the complexity of DFD implementation. An efficient algorithm for classifying mesh points is also presented. Simulation of flow around a stationary sphere is used to validate the numerical method, and three distinct flow regimes have been obtained with varied Reynolds numbers of up to 300. The ability of the method for flows with complex moving boundary is demonstrated by simulating flows over an undulating fish-like body. The results of force coefficient, structure of wake patterns and propulsive efficiency at critical Strouhal number have been presented. All predictions show a good agreement with the reference data. © 2012 Elsevier Ltd.


Zhou C.H.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore
International Journal for Numerical Methods in Fluids | Year: 2012

The local domain-free discretization method is extended in this work to simulate fluid-structure interaction problems, the class of which is exemplified by the self-propelled anguilliform swimming of deforming bodies in a fluid medium. Given the deformation of the fish body in its own reference frame, the translational and rotational motions of the body governed by Newton's Law are solved together with the surrounding flow field governed by Navier-Stokes equations. When the body is deforming and moving, no mesh regeneration is required in the computation. The loose coupling strategy is employed to simulate the fluid-structure interaction involved in the self-propelled swimming. The local domain-free discretization method and an efficient algorithm for classifying the Eulerian mesh points are described in brief. To validate the fluid-structure interaction solver, we simulate the 'lock-in' phenomena associated with the vortex-induced vibrations of an elastically mounted cylinder. Finally, we demonstrate applications of the method to two-dimensional and three-dimensional anguilliform-swimming fish. The kinematics and dynamics associated with the center of mass are shown and the rotational movement is also presented via the angular position of the body axis. The wake structure is visualized in terms of vorticity contours. All the obtained numerical results show good agreement with available data in the literature. © 2011 John Wiley & Sons, Ltd.


Wu J.,Nanjing University of Aeronautics and Astronautics | Wu J.,National University of Singapore | Shu C.,National University of Singapore
Journal of Computational Physics | Year: 2011

A stencil adaptive lattice Boltzmann method (LBM) is developed in this paper. It incorporates the stencil adaptive algorithm developed by Ding and Shu [26] for the solution of Navier-Stokes (N-S) equations into the LBM calculation. Based on the uniform mesh, the stencil adaptive algorithm refines the mesh by two types of 5-points symmetric stencils, which are used in an alternating sequence for increased refinement levels. The two types of symmetric stencils can be easily combined to form a 9-points symmetric structure. Using the one-dimensional second-order interpolation recently developed by Wu and Shu [27] along the straight line and the D2Q9 model, the adaptive LBM calculation can be effectively carried out. Note that the interpolation coefficients are only related to the lattice velocity and stencil size. Hence, the simplicity of LBM is not broken down and the accuracy is maintained. Due to the use of adaptive technique, much less mesh points are required in the simulation as compared to the standard LBM. As a consequence, the computational efficiency is greatly enhanced. The numerical simulation of two dimensional lid-driven cavity flows is carried out. Accurate results and improved efficiency are reached. In addition, the steady and unsteady flows over a circular cylinder are simulated to demonstrate the capability of proposed method for handling problems with curved boundaries. The obtained results compare well with data in the literature. © 2010 Elsevier Inc.


Yan X.,Nanjing Forestry University | Xu G.,Nanjing University of Aeronautics and Astronautics
Progress in Organic Coatings | Year: 2012

Surface of copper (Cu) powder was chemically modified using silane coupling agent (KH550) in order to improve the interfacial interaction between Cu and polyurethane (PU) polymer, and therefore, expectable corrosion resistance of the Cu/PU coating with low infrared emissivity was acquired. Infrared spectra reveal an obvious interaction between Cu and PU induced by the addition of KH550. The corrosion behavior of Cu/PU coating has been investigated with potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results have shown that the proper amount of KH550 is benefit to the dispersion of Cu and induces the strong chemical interfacial interaction, which often keeps the low infrared emissivity and increases the corrosion resistance of the Cu/PU coating. © 2011 Elsevier B.V. All rights reserved.


Wang X.,Nanjing University of Posts and Telecommunications | Wang X.,Nanjing University of Aeronautics and Astronautics | Zheng J.,Nanjing University of Posts and Telecommunications | Xuan Y.,Nanjing University of Posts and Telecommunications | And 2 more authors.
Optics Express | Year: 2013

NaYbF4:Tm3+@SiO2 core-shell micro-particles were synthesized by a hydrothermal method and subsequent ultrasonic coating process. Optical temperature sensing has been observed in NaYbF4: Tm3+@SiO2 core-shell micro-particles with a 980 nm infrared laser as excitation source. The fluorescence intensity ratios, optical temperature sensitivity, and temperature dependent population re-distribution ability from the thermally coupled 1D 2/1G4 and 3F2/ 3H4 levels of the Tm3+ ion have been analyzed as a function of temperature in the range of 100~700 K in order to check its availability as a optical temperature sensor. A better behavior as a lowtemperature sensor has been obtained with a minimum sensitivity of 5.4 × 10-4 K-1 at 430 K. It exhibits temperature induced population re-distribution from 1D2/1G 4 thermally coupled levels at higher temperature range. © 2013 Optical Society of America.


Yao K.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Mao X.,Nanjing University of Aeronautics and Astronautics | Ye Z.,LiteOn Technology Power NJ R and D Center
IEEE Transactions on Power Electronics | Year: 2012

The discontinuous current mode boost power factor correction (PFC) converter automatically achieves PFC when the duty cycle is kept constant in a line cycle; however, there is large third harmonic in the input current, and the third harmonic has the initial phase of in respect of the fundamental component. Therefore, the input power factor is low, and a large storage capacitor is needed. Injecting appropriate third harmonic with initial phase of zero into the input current could reduce the storage capacitor. This paper proposes the variable duty cycle control to inject the required third harmonic into the input current to meet the requirement of IEC 61000-3-2 Class D or Energy Star. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. The experimental results from a 120-W universal input prototype are given to verify the effectiveness of the proposed method. © 2011 IEEE.


Wu J.,Nanjing University of Aeronautics and Astronautics | Wu J.,National University of Singapore | Shu C.,National University of Singapore
International Journal for Numerical Methods in Fluids | Year: 2012

An improved immersed boundary-lattice Boltzmann method (IB-LBM) developed recently [28] was applied in this work to simulate three-dimensional (3D) flows over moving objects. By enforcing the non-slip boundary condition, the method could avoid any flow penetration to the wall. In the developed IB-LBM solver, the flow field is obtained on the non-uniform mesh by the efficient LBM that is based on the second-order one-dimensional interpolation. As a consequence, its coefficients could be computed simply. By simulating flows over a stationary sphere and torus [28] accurately and efficiently, the proposed IB-LBM showed its ability to handle 3D flow problems with curved boundaries. In this paper, we further applied this method to simulate 3D flows around moving boundaries. As a first example, the flow over a rotating sphere was simulated. The obtained results agreed very well with the previous data in the literature. Then, simulation of flow over a rotating torus was conducted. The capability of the improved IB-LBM for solving 3D flows over moving objects with complex geometries was demonstrated via the simulations of fish swimming and dragonfly flight. The numerical results displayed quantitative and qualitative agreement with the date in the literature. © 2011 John Wiley & Sons, Ltd.


Mao Z.,Tsinghua National Laboratory for Information Sciences and Technology | Mao Z.,Nanjing University of Aeronautics and Astronautics | Jiang B.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales
Journal of the Franklin Institute | Year: 2011

In this paper, an observer-based fault-tolerant control (FTC) method is proposed for a class of networked control systems (NCSs) with transfer delays. Markov chain is employed to characterize the transfer delays. Then, such kind of networked control systems are modelled as Markovian jump systems. An observer-based FTC scheme using the delayed state information and the estimated fault value is presented to guarantee the stability of the faulty systems. An inverted pendulum example is used to illustrate the efficiency of the proposed method. © 2011 Published by Elsevier Ltd. on behalf of The Franklin Institute.


Liu S.L.,Nanjing University of Posts and Telecommunications | Zhou T.,Nanjing University of Aeronautics and Astronautics
Journal of Physics Condensed Matter | Year: 2012

We study theoretically the effect of transition-metal (TM) substitution in iron-based superconductors through treating all of the TM ions as randomly distributed impurities. The extra electrons from TM elements are localized at the impurity sites. In the meantime the chemical potential shifts upon substitution. The phase diagram is mapped out and it seems that the TM elements can act as effective dopants. The local density of states (LDOS) is calculated and the bottom becomes V-shaped as the impurity concentration increases. The LDOS at the Fermi energy ρ(ω = 0) is finite and reaches the minimum at the optimal doping level. Our results are in good agreement with scanning tunneling microscopy experiments. © 2012 IOP Publishing Ltd.


Gu L.,Nanjing University of Aeronautics and Astronautics | Jin K.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Xu M.,Fsp Powerland Technology Inc. | Lee F.C.,Bradley University
IEEE Transactions on Power Electronics | Year: 2014

In conventional PWM converters, the dynamic performance is limited by the inductor. Switching capacitor converters utilize the capacitor as the energy transmitter and have good transient response. However, their output voltage cannot be regulated by the duty cycle. To combine the advantages of the above two kinds of converters, this paper proposes a family of switching capacitor regulators which are derived from basic switching capacitor cells and basic regulator cells. Each of the derived converters is the combination of a switching capacitor converter and a PWM converter. And they have the following advantages: 1) fast transient response and 2) the regulated output voltage. A 12 V/16 A isolated converter and a 1.2 V/130 A voltage regulator module prototype were built in the lab to verify the theoretical analysis. © 1986-2012 IEEE.


Wu J.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Zhao N.,Nanjing University of Aeronautics and Astronautics
Journal of Fluids and Structures | Year: 2014

Flow control through the interaction between a fixed circular cylinder and a detached flexible plate is numerically investigated in this study. Based on the diameter of the cylinder (d), the laminar flow with a Reynolds number of 100 is considered in this work. A flexible plate undergoing fish-like motion is placed in either the downstream or upstream of the cylinder. The gap between the cylinder and the plate (S), the oscillation frequency (Stf) and the oscillation amplitude (A) are crucial parameters. When the flexible plate is in the downstream of the cylinder, a stable flow pattern is generated under some conditions (for example, Stf=0.4 together with A/d=0.1 at S/d=0.1-2.5 and Stf=0.2 with A/d=0.2-0.4 at S/d=1). Meanwhile, compared to the case of the rigid plate, a further drag reduction is obtained due to the motion of the flexible plate (the maximum drag reduction is 2.9% at A/d=0.2, Stf=0.2 and S/d=1). In addition, the net saving can also be found, which means that both drag reduction and energy saving can be achieved (the maximum net saving is 98.54% at A/d=0.5, Stf=0.1 and S/d=2.5). In contrast, when the flexible plate is in the upstream of the cylinder, a much smaller drag can be achieved compared to the case of the flexible plate in the downstream. Moreover, a significant drag reduction can be attained compared to the rigid plate case (the maximum drag reduction is approximately 28% at A/d=0.5, Stf=0.5 and S/d=2). The established results in this study imply that the flexibility of the plate is of importance in controlling the flow over a bluff body. © 2014 Elsevier Ltd.


Zhou C.H.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore
International Journal for Numerical Methods in Fluids | Year: 2011

This paper presents a local domain-free discretization (DFD) method for the simulation of unsteady flows over moving bodies governed by the incompressible Navier-Stokes equations. The discretization strategy of DFD is that the discrete form of partial differential equations at an interior point may involve some points outside the solution domain. All the mesh points are classified as interior points, exterior dependent points and exterior independent points. The functional values at the exterior dependent points are updated at each time step by the approximate form of solution near the boundary. When the body is moving, only the status of points is changed and the mesh can stay fixed. The issue of 'freshly cleared nodes/cells' encountered in usual sharp interface methods does not pose any particular difficulty in the presented method. The Galerkin finite-element approximation is used for spatial discretization, and the discrete equations are integrated in time via a dual-time-stepping scheme based on artificial compressibility. In order to validate the present method for moving-boundary flow problems, two groups of flow phenomena have been simulated: (1) flows over a fixed circular cylinder, a harmonic in-line oscillating cylinder in fluid at rest and a transversely oscillating cylinder in uniform flow; (2) flows over a pure pitching airfoil, a heaving-pitching airfoil and a deforming airfoil. The predictions show good agreement with the published numerical results or experimental data. © 2010 John Wiley & Sons, Ltd.


Wu J.,Nanjing University of Aeronautics and Astronautics | Qiu Y.L.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Zhao N.,Nanjing University of Aeronautics and Astronautics
Physics of Fluids | Year: 2014

A numerical investigation on the power extraction of a pitching-motion-activated flapping foil near solid walls is performed by using an immersed boundary-lattice Boltzmann method in this study. The flapping motions of the foil include a forced pitching component and an induced plunging component. The foil is placed either near a solid wall or between two parallel plane walls. Compared to previous work on the flapping foil for power extraction, the effect of the walls is first considered in this work. At a Reynolds number of 1100 and with the position of the foil pitching axis at third chord, the influences of the mechanical parameters (such as damping coefficient and spring constant) of the foil, the amplitude and frequency of the pitching motion and the clearance between the foil pitching axis and the wall on the power extraction performance of the flapping foil are systematically evaluated. Compared to the situation of free stream, the power extraction performance of the foil near the wall is improved. For given amplitude and frequency, as the clearance decreases the net power extraction efficiency improves. Moreover, as the foil is placed near one wall, there is a transverse shift to the plunging motion that consequently weakens the improvement of net power extraction efficiency. In contrast, the shift can be significantly eliminated as the foil is placed between two walls, which can further improve the net power extraction efficiency. In addition, it is found that the efficiency improvement is essentially from the increased power extraction, which is due to the generation of high lift force. © 2014 AIP Publishing LLC.


Wu J.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Zhao N.,Nanjing University of Aeronautics and Astronautics
Physics of Fluids | Year: 2014

The flow characteristics of the vortex-induced vibration of an elastically mounted circular cylinder with a hinged flat plate are investigated numerically in this study. By fixing the Reynolds number, the mass ratio, the damping ratio, and the plate length, we systematically examine the influence of the reduced velocities of cylinder and plate as well as the ratio of moment of inertia on the flow behaviors.With the help of the hinged plate, the cylinder vibration and the force fluctuations can be efficiently suppressed. Meanwhile, the drag force can also be reduced significantly compared to the situation of an isolated cylinder. Moreover, because of the large pitching angle of the hinged plate, smoother vortex shedding can be observed. © 2014 AIP Publishing LLC.


Chen M.,Nanjing University of Aeronautics and Astronautics | Ge S.S.,Interactive Digital Media Institute IDMI | Ge S.S.,National University of Singapore | How B.V.E.,National University of Singapore
IEEE Transactions on Neural Networks | Year: 2010

In this paper, robust adaptive neural network (NN) control is investigated for a general class of uncertain multiple-inputmultiple-output (MIMO) nonlinear systems with unknown control coefficient matrices and input nonlinearities. For nonsymmetric input nonlinearities of saturation and deadzone, variable structure control (VSC) in combination with backstepping and Lyapunov synthesis is proposed for adaptive NN control design with guaranteed stability. In the proposed adaptive NN control, the usual assumption on nonsingularity of NN approximation for unknown control coefficient matrices and boundary assumption between NN approximation error and control input have been eliminated. Command filters are presented to implement physical constraints on the virtual control laws, then the tedious analytic computations of time derivatives of virtual control laws are canceled. It is proved that the proposed robust backstepping control is able to guarantee semiglobal uniform ultimate boundedness of all signals in the closed-loop system. Finally, simulation results are presented to illustrate the effectiveness of the proposed adaptive NN control. © 2010 IEEE.


Liu L.,Nanjing University of Aeronautics and Astronautics | Xu J.,Nanjing University of Aeronautics and Astronautics | Xie Z.-H.,University of Adelaide | Munroe P.,University of New South Wales
Journal of Materials Chemistry A | Year: 2013

A novel TiC-Ti5Si3 nanocomposite film was successfully engineered onto a Ti-6Al-4V substrate using a double glow discharge plasma technique. This type of film exhibits a self-toughened, hierarchical structure, consisting of cauliflower-like Ti5Si3 grains together with TiC nanoparticles distributed at the boundaries. The electrochemical behavior and electronic properties of the passive layers formed on the TiC-Ti5Si3 nanocomposite film were compared to a monolithic Ti5Si3 film and uncoated Ti-6Al-4V in a 3.5 wt% NaCl solution by various electrochemical analytical techniques, including low frequency impedance, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization and Mott-Schottky analysis. The results showed that the corrosion resistance of the TiC-Ti5Si 3 nanocomposite film was comparable to that of the monolithic Ti 5Si3 film, but was significantly higher than that of uncoated Ti-6Al-4V. The TiC-Ti5Si3 nanocomposite film is thus an attractive candidate for surface protection of components against mechanical and chemical attacks. This journal is © The Royal Society of Chemistry 2013.


Sun K.,Tsinghua University | Zhang L.,Nanjing University of Aeronautics and Astronautics | Xing Y.,Nanjing University of Aeronautics and Astronautics | Guerrero J.M.,Polytechnic University of Catalonia | Guerrero J.M.,University of Aalborg
IEEE Transactions on Power Electronics | Year: 2011

Modular generation system, which consists of modular power conditioning converters, is an effective solution to integrate renewable energy sources with conventional utility grid to improve reliability and efficiency, especially for photovoltaic generation. A distributed control strategy based on improved dc bus signaling is proposed for a modular photovoltaic (PV) generation system with battery energy storage elements. In this paper, the modular PV generation system is composed of three modular dc/dc converters for PV arrays, two grid-connected dc/ac converters, and one dc/dc converter for battery charging/discharging and local loads, which is available of either grid-connected operation or islanding operation. By using the proposed control strategy, the operations of a modular PV generation system are categorized into four modes: islanding with battery discharging, grid-connected rectification, grid-connected inversion, and islanding with constant voltage (CV) generation. The power balance of the system under extreme conditions such as the islanding operation with a full-charged battery is taken into account in this control strategy. The dc bus voltage level is employed as an information carrier to distinguish different modes and determine mode switching. Control methods of modular dc/dc converters, battery converter, and grid-connected converter are addressed. An autonomous control method for modular dc/dc converters is proposed to realize smooth switching between CV operation and maximum power point tracking operation, which enables the dc bus voltage regulation capability of modular dc/dc converters. Seamless switching of a battery converter between charging and discharging and that of a grid-connected converter between rectification and inversion are ensured by the proposed control methods. Experiments verify the practical feasibility and the effectiveness of the proposed control strategies. © 2006 IEEE.


Han X.,Peking University | Kou L.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zhu X.,Peking University | And 4 more authors.
Advanced Materials | Year: 2012

The table of contents image ilustrates the strain-gradient effect on the optical-electronic properties in a bent ZnO microwire, with a much stronger red-shift on the outer tensile side than a blue-shift on the inner compressive side. The low temperature cathodoluminescence cross-sectional scanning spectra on the strain-neutral middle-plane are highlighted by thicker black lines, which clearly shows a strain-gradient induced red-shift. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Li Y.,Nanjing Forestry University | Shen Y.,Nanjing University of Aeronautics and Astronautics
Polymer Engineering and Science | Year: 2014

Polymeric materials used in memory devices have attracted significant scientific interest due to their several advantages, such as low cost, solution processability, and possible development of three-dimensional stacking devices. Polythiophenes, including tethered alkyl substituted polythiophenes and block copolymers, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and composites, are one of the most attractive polymeric systems for memory applications because of their commercial availability, high conductivity, and mechanical strength. In this article, recent studies of functional polythiophene for memory applications are reviewed, mostly focusing on the role of the materials in the memory functionality, optimizing the chemical structure of the polythiophene and the component of each layer in memory device. A critical summary of the proposed mechanisms, including filament formation, electric field-induced charge transfer and reductionoxidation (redox) driven, is given to explain the resistive switching phenomena in the polythiophene system. In addition, the challenges facing the research and development in the field of polythiophene electronic memories are summarized. © 2013 Society of Plastics Engineers.


Chen M.,Nanjing University of Aeronautics and Astronautics | Ge S.S.,National University of Singapore | Ge S.S.,University of Electronic Science and Technology of China
IEEE Transactions on Industrial Electronics | Year: 2015

In this paper, an adaptive neural output feedback control scheme is proposed for uncertain nonlinear systems that are subject to unknown hysteresis, external disturbances, and unmeasured states. To deal with the unknown nonlinear function term in the uncertain nonlinear system, the approximation capability of the radial basis function neural network (RBFNN) is employed. Using the approximation output of the RBFNN, the state observer and the nonlinear disturbance observer (NDO) are developed to estimate unmeasured states and unknown compounded disturbances, respectively. Based on the RBFNN, the developed NDO, and the state observer, the adaptive neural output feedback control is proposed for uncertain nonlinear systems using the backstepping technique. The first-order sliding-mode differentiator is employed to avoid the tedious analytic computation and the problem of "explosion of complexity" in the conventional backstepping method. The stability of the whole closed-loop system is rigorously proved via the Lyapunov analysis method, and the satisfactory tracking performance is guaranteed under the integrated effect of unknown hysteresis, unmeasured states, and unknown external disturbances. Simulation results of an example are presented to illustrate the effectiveness of the proposed adaptive neural output feedback control scheme for uncertain nonlinear systems. © 1982-2012 IEEE.


Yang L.M.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Wu J.,Nanjing University of Aeronautics and Astronautics
Computers and Fluids | Year: 2013

Based on the idea of constructing equilibrium distribution functions directly from the conservation forms of moments, a platform for developing non-free parameter lattice Boltzmann models is presented in this work. It is found that the existing compressible lattice Boltzmann models such as D1Q4L2 and D1Q5L2 models of Qu et al. [28,29] and D1Q5 model of Kataoka and Tsutahara [22] can be derived by the platform. This paper goes further to determine the lattice velocities of a non-free parameter D1Q4 model by incorporating two additional higher order conservation forms of moments. Since the lattice velocities are determined physically rather than specified artificially, the non-free parameter D1Q4 model can be applied to simulate compressible flows with a wide range of Mach numbers. The developed non-free parameter D1Q4 model is then applied to a local Riemann problem at the cell interface to establish a new Riemann flux solver for the solution of Euler equations by the finite volume method (FVM). Some test problems, such as Sod shock tube, shock reflection, compressible flows around NACA0012 airfoil, hypersonic flows around a blunt body and double Mach reflection, are simulated to illustrate the capability of present solver. Numerical results show that the present non-free parameter D1Q4 model can provide accurate results with faster convergence rate. © 2013 Elsevier Ltd.


Yarman C.E.,Schlumberger | Wang L.,Nanjing University of Aeronautics and Astronautics | Yazici B.,Rensselaer Polytechnic Institute
Inverse Problems | Year: 2010

In this paper we consider passive airborne receivers that use backscattered signals from sources of opportunity transmitting single-frequency or ultra-narrowband waveforms. Because of its combined passive synthetic aperture and the single-frequency nature of the transmitted waveforms, we refer to the system under consideration as Doppler synthetic aperture hitchhiker (DSAH). We present a novel image formation method for DSAH. Our method first correlates the windowed signal obtained from one receiver with the windowed, filtered, scaled and translated version of the received signal from another receiver. This processing removes the transmitter-related variables from the phase of the Fourier integral operator that maps the radiance of the scene to the correlated signal. Next, we use microlocal analysis to reconstruct the scene radiance by the weighted backprojection of the correlated signal. The image reconstruction method is applicable to both cooperative and non-cooperative sources of opportunity using one or more airborne receivers. It has the desirable property of preserving the visible edges of the scene radiance. Additionally, it is an analytic reconstruction technique that can be made computationally efficient. We present numerical simulations to demonstrate the performance of the image reconstruction method and to verify the theoretical results. © 2010 IOP Publishing Ltd.


Yang Y.,University of Arkansas | Yang Y.,Nanjing University of Aeronautics and Astronautics | Ren W.,University of Arkansas | Ren W.,Shanghai University | And 2 more authors.
Physical Review Letters | Year: 2012

Ab initio computations are performed to investigate properties of bulk material and epitaxial films made of EuTiO3 (ETO). A whole family of nanoscale twinned phases, that present complex oxygen octahedra tilting (OOT) and unusual antiferroelectricity, is found to be degenerate in energy with simpler phases (all possessing typical OOT) in bulk ETO. Such degeneracy provides a successful explanation of recently observed anomalous phenomena. The calculations also lead to revisiting the (rich) phase diagram of ETO films. © 2012 American Physical Society.


Chen Y.,Nanjing University of Aeronautics and Astronautics | Li K.W.,University of Windsor | Liu S.-F.,Nanjing University of Aeronautics and Astronautics
Expert Systems with Applications | Year: 2011

A hybrid approach integrating OWA (Ordered Weighted Averaging) aggregation into TOPSIS (technique for order performance by similarity to ideal solution) is proposed to tackle multiple criteria decision analysis (MCDA) problems. First, the setting of extreme points (ideal and anti-ideal points) in TOPSIS is redefined and extended for handling the multiple extreme points situation where a decision maker (DM) or multiple DMs can provide more than one pair of extreme points. Next, three different aggregation schemes are designed to integrate OWA into the TOPSIS analysis procedure. A numerical example is provided to demonstrate the proposed approach and the results are compared for different aggregation settings and confirm the robustness of rankings from different scenarios. © 2010 Elsevier Ltd. All rights reserved.


Ang B.W.,National University of Singapore | Zhou P.,Nanjing University of Aeronautics and Astronautics | Tay L.P.,National University of Singapore
Energy Policy | Year: 2011

We present five performance indicators for electricity generation for 129 countries using the 2005 data. These indicators, measured at the national level, are the aggregate CO2 intensity of electricity production, the efficiencies of coal, oil and gas generation and the share of electricity produced from non-fossil fuels. We conduct a study on the potential for reducing global energy-related CO2 emissions from electricity production through simple benchmarking. This is performed based on the last four performance indicators and the construction of a cumulative curve for each of these indicators. It is found that global CO2 emissions from electricity production would be reduced by 19% if all these indicators are benchmarked at the 50th percentile. Not surprisingly, the emission reduction potential measured in absolute terms is the highest for large countries such as China, India, Russia and the United States. When the potential is expressed as a percentage of a country's own emissions, few of these countries appear in the top-five list. © 2011 Elsevier Ltd.


Chen M.,Nanjing University of Aeronautics and Astronautics | Ge S.S.,University of Electronic Science and Technology of China | Ge S.S.,National University of Singapore
IEEE Transactions on Cybernetics | Year: 2013

In this paper, the direct adaptive neural control is proposed for a class of uncertain nonaffine nonlinear systems with unknown nonsymmetric input saturation. Based on the implicit function theorem and mean value theorem, both state feedback and output feedback direct adaptive controls are developed using neural networks (NNs) and a disturbance observer. A compounded disturbance is defined to take into account of the effect of the unknown external disturbance, the unknown nonsymmetric input saturation, and the approximation error of NN. Then, a disturbance observer is developed to estimate the unknown compounded disturbance, and it is established that the estimate error converges to a compact set if appropriate observer design parameters are chosen. Both state feedback and output feedback direct adaptive controls can guarantee semiglobal uniform boundedness of the closed-loop system signals as rigorously proved by Lyapunov analysis. Numerical simulation results are presented to illustrate the effectiveness of the proposed direct adaptive neural control techniques. © 2012 IEEE.


Qi J.,Jiangsu University | Qi J.,Nanjing University of Aeronautics and Astronautics | Qian X.,Massachusetts Institute of Technology | Qi L.,Massachusetts Institute of Technology | And 5 more authors.
Nano Letters | Year: 2012

Two-dimensional atomic sheets such as graphene and boron nitride monolayers represent a new class of nanostructured materials for a variety of applications. However, the intrinsic electronic structure of graphene and h-BN atomic sheets limits their direct application in electronic devices. By first-principles density functional theory calculations we demonstrate that band gap of zigzag BN nanoribbons can be significantly tuned under uniaxial tensile strain. The unexpected sensitivity of band gap results from reduced orbital hybridization upon elastic strain. Furthermore, sizable dipole moment and piezoelectric effect are found in these ribbons owing to structural asymmetry and hydrogen passivation. This will offer new opportunities to optimize two-dimensional nanoribbons for applications such as electronic, piezoelectric, photovoltaic, and opto-electronic devices. © 2012 American Chemical Society.


Wang Y.,Nanjing University of Posts and Telecommunications | Chen S.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

Though semi-supervised classification learning has attracted great attention over past decades, semi-supervised classification methods may show worse performance than their supervised counterparts in some cases, consequently reducing their confidence in real applications. Naturally, it is desired to develop a safe semi-supervised classification method that never performs worse than the supervised counterparts. However, to the best of our knowledge, few researches have been devoted to safe semi-supervised classification. To address this problem, in this paper, we invent a safety-control mechanism for safe semi-supervised classification by adaptive tradeoff between semi-supervised and supervised classification in terms of unlabeled data. In implementation, based on our recent semi-supervised classification method based on class memberships (SSCCM), we develop a safety-aware SSCCM (SA-SSCCM). SA-SSCCM, on the one hand, exploits the unlabeled data to help learning (as SSCCM does) under the assumption that unlabeled data can help learning, and on the other hand, restricts its prediction to approach that of its supervised counterpart least-square support vector machine (LS-SVM) under the assumption that unlabeled data can hurt learning. Therefore, prediction by SA-SSCCM becomes a tradeoff between those by semi-supervised SSCCM and supervised LS-SVM, respectively, in terms of the unlabeled data. As in SSCCM, the optimization problem in SA-SSCCM can be efficiently solved by the alternating iterative strategy, and the iteration convergence can theoretically be guaranteed. Experiments over several real datasets show the promising performance of SA-SSCCM compared with LS-SVM, SSCCM, and off-the-shelf safe semi-supervised classification methods. © 2012 IEEE.


Wang L.,Nanjing University of Aeronautics and Astronautics | Yarman C.E.,Schlumberger | Yazici B.,Rensselaer Polytechnic Institute
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

In this paper, we present a novel synthetic aperture radar imaging modality that uses ultranarrowband sources of opportunity and passive airborne receivers to form an image of the ground. Due to its combined passive synthetic aperture and high Doppler resolution of the transmitted waveforms, we refer to this modality as the Doppler Synthetic Aperture Hitchhiker or Doppler-hitchhiker for short. Our imaging method first correlates the windowed signal obtained from one receiver with the scaled and translated version of the received signal in another window from the same or another receiver. We show that this correlation processing removes the transmitter-related variables from the phase of the resulting operator that maps the radiance of the scene to the correlated signals. We define a concept of passive Doppler scale factor using the radial velocities of the receivers. Next, we show that the scaled, translated, and correlated signal is the projection of the scene radiance onto the contours that are formed by the intersection of the surfaces of constant passive Doppler scale factor and ground topography. We use microlocal analysis to design a generalized filtered-backprojection operator to reconstruct the scene radiance from its projections. Our analysis shows that the resolution of the reconstructed images improves with the increased time duration and center frequency of the transmitted ultranarrowband signals. Our reconstruction method is analytic and therefore can be made computationally efficient. Furthermore, it easily accommodates arbitrary flight trajectories, nonflat topography, and system-related parameters. We present numerical simulations to demonstrate the performance of our imaging method. © 2011 IEEE.


Zhou P.,Nanjing University of Aeronautics and Astronautics | Ang B.W.,National University of Singapore | Zhou D.Q.,Nanjing University of Aeronautics and Astronautics
Applied Energy | Year: 2012

This paper proposes a parametric frontier approach to estimating economy-wide energy efficiency performance from a production efficiency point of view. It uses the Shephard energy distance function to define an energy efficiency index and adopts the stochastic frontier analysis technique to estimate the index. A case study of measuring the economy-wide energy efficiency performance of a sample of OECD countries using the proposed approach is presented. It is found that the proposed parametric frontier approach has higher discriminating power in energy efficiency performance measurement compared to its nonparametric frontier counterparts. © 2011 Elsevier Ltd.


Ang B.W.,National University of Singapore | Mu A.R.,National University of Singapore | Zhou P.,Nanjing University of Aeronautics and Astronautics
Energy Economics | Year: 2010

Many differences can be found among the existing accounting systems for tracking economy-wide energy efficiency trends. There is a need for greater uniformity in the design and application of such systems but a formal study does not exist. This paper seeks to fill some of the gaps. It begins by introducing the basic concepts, indicators and terminology in this study area. This is followed by a review of the existing economy-wide energy efficiency accounting systems with a focus on the analytical framework. The merit of having a precise and meaningful relationship between two basic energy indicators, the energy efficiency index and the energy savings due to efficiency improvement, is elaborated. An accounting framework based on the LMDI decomposition technique which possesses a number of desirable properties is proposed. Numerical examples are presented to highlight these properties and show the differences among the various accounting frameworks. Several methodological and application issues are discussed, and the study concludes with key findings and recommendations. © 2010 Elsevier B.V.


Shen Q.,Nanjing University of Aeronautics and Astronautics | Shen Q.,Yangzhou University | Jiang B.,Nanjing University of Aeronautics and Astronautics | Shi P.,Victoria University of Melbourne | Shi P.,University of Adelaide
IEEE Transactions on Fuzzy Systems | Year: 2014

It is well known that there always exist some level of time delay between fault occurrence and fault accommodation, which is called as the time delay due to fault diagnosis (TDDTFD) in this paper. TDDTFD may cause severe loss of system performance and stability. This paper investigates the TDDTFD's adverse effect on the system performance. First, a fault diagnosis (FD) model is constructed to diagnose sensor faults which integrate time-varying gain and bias faults, where a novel FD algorithm is proposed, which removes the classical assumption that the time derivative of the output error should be known. Meanwhile, the time spent at each step in FD and its analytical expression are derived strictly. Further, the analysis of the system performance degraded by TDDTFD is developed, and the conditions under which the magnitudes of sensor faults should be satisfied such that the state of the faulty system controlled by the normal controller remains bounded during TDDTFD are derived. In addition, the corresponding solutions are proposed to minimize the adverse effect of the time delay. Finally, simulation results of near-space vehicle attitude dynamics are presented to demonstrate the efficiency of the proposed approach. © 1993-2012 IEEE.


Chen M.,Nanjing University of Aeronautics and Astronautics | Ge S.S.,University of Electronic Science and Technology of China | Ge S.S.,National University of Singapore | How B.V.E.,National University of Singapore | Choo Y.S.,National University of Singapore
IEEE Transactions on Control Systems Technology | Year: 2013

In this paper, robust adaptive control with dynamic control allocation is proposed for the positioning of marine vessels equipped with a thruster assisted mooring system, in the presence of parametric uncertainties, unknown disturbances and input nonlinearities. Using neural network approximation and variable structure based techniques in combination with backstepping and Lyapunov synthesis, the positioning control is developed to handle the uncertainties, input saturation and dead-zone characteristics of the mooring lines and thrusters. Full state feedback with all states measurable and output feedback using high gain observer to estimate unmeasurable states are considered. Dynamic control allocation is presented for actuation of the position mooring system. Under the proposed robust adaptive control, semi-global uniform boundedness of the closed-loop signals are guaranteed. Numerical simulations are carried out to show the effectiveness of the proposed control. © 2012 IEEE.


Shen Q.,Nanjing University of Aeronautics and Astronautics | Shen Q.,Yangzhou University | Jiang B.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of Adelaide | And 2 more authors.
IEEE Transactions on Fuzzy Systems | Year: 2014

In this paper, the cooperative adaptive fault tolerant fuzzy tracking control (CAFTFTC) problem of networked high-order multiagent with time-varying actuator faults is studied, and a novel CAFTFTC scheme is proposed to guarantee that all follower nodes asymptotically synchronize a leader node with tracking errors converging to a small adjustable neighborhood of the origin in spite of actuator faults. The leader node is modeled as a higher order nonautonomous nonlinear system. It acts as a command generator giving commands only to a small portion of the networked group. Each follower is assumed to have nonidentical unknown nonlinear dynamics, and the communication network is also assumed to be a weighted directed graph with a fixed topology. A distributed robust adaptive fuzzy controller is designed for each follower node such that the tracking errors are cooperative uniform ultimate boundedness (CUUB). Moreover, these controllers are distributed in the sense that the controller designed for each follower node only requires relative state information between itself and its neighbors. The adaptive compensation term of the optimal approximation errors and external disturbances is adopted to reduce the effects of the errors and disturbances, which removes the assumption that the upper bounds of unknown function approximation errors and disturbances should be known. Analysis of stability and parameter convergence of the proposed algorithm are conducted that are based on algebraic graph theory and Lyapunov theory. Comparing with results in the literature, the CAFTFTC scheme can minimize the time delay between fault occurrence and accommodation and reduce its adverse effect on system performance. In addition, the FTC scheme requires no additional fault isolation model, which is necessary in the traditional active FTC scheme. Finally, an example is provided to validate the theoretical results. © 2014 IEEE.


Guo Y.-D.,Nanjing University of Aeronautics and Astronautics | Yan X.-H.,Nanjing University of Aeronautics and Astronautics | Yan X.-H.,Nanjing University of Posts and Telecommunications | Xiao Y.,Nanjing University of Aeronautics and Astronautics
Journal of Physical Chemistry C | Year: 2012

We propose a single-electron transistor (SET)-based nanopore sensor for DNA sequencing, which consists of source, drain, and gate electrodes, as well as a nanopore where the DNA molecule is pulled through. For nanopore sensors based on transverse electronic transport, generally, the tunneling current is relatively small due to the weak coupling between the molecule and electrodes. We take full advantage of this feature by introducing SET to make the device operate in Coulomb-blockade regime. Through first-principles simulations, the charge stability diagrams of the nucleobases within the SET-nanopore environment are demonstrated to be distinctive for each molecule and, more importantly, independent of the nucleobase orientation, which can be served as electronic fingerprint for detection. We show that identifying the nucleobases can be achieved only though several specific regions or points in the diagram. © 2012 American Chemical Society.


Zhou P.,Nanjing University of Aeronautics and Astronautics | Ang B.W.,National University of Singapore | Han J.Y.,National University of Singapore
Energy Economics | Year: 2010

This paper introduces a Malmquist CO2 emission performance index (MCPI) for measuring changes in total factor carbon emission performance over time. The MCPI is derived by solving several data envelopment analysis models. Bootstrapping MCPI is proposed to perform statistical inferences on the MCPI results. Using the index the emission performance of the world's 18 top CO2 emitters from 1997 to 2004 is studied. The results obtained show that the total factor carbon emission performance of the countries as a whole improved by 24% over the period and this was mainly driven by technological progress. The results of a cross-country regression analysis to investigate the determinants of the resulting MCPI are presented. © 2009 Elsevier B.V. All rights reserved.


Wu J.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Zhao N.,Nanjing University of Aeronautics and Astronautics
European Journal of Mechanics, B/Fluids | Year: 2014

The flow characteristics around a stationary circular cylinder with an undulatory plate have been numerically investigated in this work. This is the extension of our previous study on flows over a cylinder with a rigid flapping plate (Wu and Shu, 2011). In this study, the effect of plate flexibility on the flow characteristics is extensively examined by varying the frequency and amplitude of motion and the length of the plate. The laminar flow at Reynolds number of Re=100 is considered. Based on the numerical results obtained, some interesting flow patterns and drag reduction are observed. Meanwhile, the physical mechanisms elucidating good performance of the undulatory plate are also provided. As compared with the rigid plate, the flexible plate performs better in the flow control of bluff body. © 2014 Elsevier Masson SAS. All rights reserved.


Su B.,National University of Singapore | Huang H.C.,National University of Singapore | Ang B.W.,National University of Singapore | Zhou P.,National University of Singapore | Zhou P.,Nanjing University of Aeronautics and Astronautics
Energy Economics | Year: 2010

Energy-related CO2 emissions embodied in international trade have been widely studied by researchers using the input-output analysis framework. These studies are often conducted at a specific level of sector aggregation and the choice made to a large extent is dictated by economic and energy data availability. We investigate analytically the possible effects of sector aggregation on the study results. We conduct empirical studies using the data of China and Singapore where energy-related CO2 emissions embodied in their exports are estimated at different levels of sector aggregation. A finding from the studies is that levels around 40 sectors appear to be sufficient to capture the overall share of emissions embodied in a country's exports. Another finding is that in approximating the "ideal" situation the hybrid data treatment approach produces better results than the uniformly distributed data treatment approach. Other findings and some recommendations are also presented. © 2009 Elsevier B.V. All rights reserved.


Chen M.,Nanjing University of Aeronautics and Astronautics | Chen M.,National University of Singapore | Ge S.S.,University of Electronic Science and Technology of China | Ge S.S.,National University of Singapore | Ren B.,National University of Singapore
Automatica | Year: 2011

In this paper, adaptive tracking control is proposed for a class of uncertain multi-input and multi-output nonlinear systems with non-symmetric input constraints. The auxiliary design system is introduced to analyze the effect of input constraints, and its states are used to adaptive tracking control design. The spectral radius of the control coefficient matrix is used to relax the nonsingular assumption of the control coefficient matrix. Subsequently, the constrained adaptive control is presented, where command filters are adopted to implement the emulate of actuator physical constraints on the control law and virtual control laws and avoid the tedious analytic computations of time derivatives of virtual control laws in the backstepping procedure. Under the proposed control techniques, the closed-loop semi-global uniformly ultimate bounded stability is achieved via Lyapunov synthesis. Finally, simulation studies are presented to illustrate the effectiveness of the proposed adaptive tracking control. © 2011 Elsevier Ltd. All rights reserved.


Wu J.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore
Physics of Fluids | Year: 2011

The laminar flow over a stationary circular cylinder with a flapping plate is simulated in this study to investigate the flow characteristics by using our recently developed boundary condition-enforced immersed boundary-lattice Boltzmann method [Wu and Shu, J. Comput. Phys.228, 1963 (2009); Wu et al. Int. J. Numer. Methods Fluids62, 327 (2010); Wu and Shu, Comm. Comp. Phys.7, 793 (2010)]. The purpose of this work is to study the flow control behind a bluff body by an alternative way different from the rotationally oscillating motion. The idea is in fact from the tadpole locomotion, where the bluff head-body is modeled by a circular cylinder, and the thin tail is simplified by a rigid plate with flapping motion. In this work, only the laminar flow is considered and thus the Reynolds number is chosen as 100. Similar to the case of rotationally oscillating cylinder, the flow wake behind the cylinder and flapping plate is strongly affected by the flapping amplitude and frequency of plate. On the other hand, because of the existence of flapping plate, the length of plate can also modify the flow structures. Due to flapping motion of plate, some typical flow patterns and drag reduction are found, and two different vortex interaction modes, known as constructive interaction and destructive interaction, are observed. © 2011 American Institute of Physics.


Yang L.M.,Nanjing University of Aeronautics and Astronautics | Shu C.,National University of Singapore | Wu J.,Nanjing University of Aeronautics and Astronautics
Journal of Computational Physics | Year: 2014

In this work, a simple distribution function-based gas-kinetic scheme for simulation of viscous flows is presented. The work applies the finite volume method to discretize the governing differential equations, and inviscid and viscous fluxes at the cell interface are evaluated simultaneously by local reconstruction of solution for the continuous Boltzmann equation. Differently from the conventional gas-kinetic scheme [13-15], in the present work, the Maxwellian distribution function is simplified by a simple distribution function, and integrals in the infinity domain of phase space are reduced to integrals around a circle. As a consequence, the computational efficiency is greatly improved. Since the simple distribution function is defined on the circle, for simplicity, it is termed as circular function hereafter. The present work is the extension of our previous work [20], where the circular function-based gas-kinetic scheme is presented to simulate inviscid flows. Only the equilibrium distribution function is considered in [20]. To solve viscous flows, the non-equilibrium part of density distribution function has to be considered. One of major contributions in this work is to present a simple way to compute the non-equilibrium part of the distribution function. It can be calculated by the difference of equilibrium distribution functions at the cell interface and its surrounding point. As a result, the formulations for computing the conservative flow variables and fluxes at the cell interface can be given explicitly. The present solver can simulate both incompressible and compressible viscous flows. To validate the proposed new gas-kinetic scheme, several incompressible and compressible viscous flows are simulated. Numerical results showed that the circular function-based gas-kinetic scheme can provide accurate numerical results with the same computational cost as that needed by conventional Navier-Stokes solver. © 2014 Elsevier Inc.


Grant
Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: AAT.2010.4.2.-7 | Award Amount: 3.49M | Year: 2010

Reynolds stress is the most important quantity affecting the mean flow as it is responsible for a major part of the momentum transfer in the wall bounded turbulent flow. It has a direct relevance to both skin friction and flow separation. Manipulation of the Reynolds stress can directly lead to changes in the viscous stress at the wall so as to effectively control the flow for effective flow control. However, there is a lack of current understanding of the inter-relationship between the various flow control devices and the Reynolds stresses in the flow field they produced. An improved understanding can potentially significantly improve the effectiveness of flow control as the Reynolds stresses are closely related to the flow behaviour at the surface for effective separation control or drag reduction. A variety of control devices are available and new ones are invented but which one for what purpose is an open question yet to be fully answered. MARS proposal proposes to reverse that process and consider the long term goal of controlling dynamic structures that influence the Reynolds stress that changes the mean flow. This radical approach recognises we are still some way away from hardware to implement it at flight scales but if successful, would establish a first important step towards our ultimate ambition. The focus of MARS will be on the effects of a number of active flow control devices on the discrete dynamic components of the turbulent shear layers and the Reynolds stress. From the application point of view, MARS provides a positive and necessary step in the right direction wherein it will demonstrate the capability to control individual structures that are larger in scale and lower in frequency compared to the richness of the time and spatial scales in a turbulent boundary layer. MARS will investigate active flow control means rather than passive controls.


Ji X.,University of Portsmouth | Ji X.,Nanjing University of Aeronautics and Astronautics | Ji X.,Shenyang Institute of Engineering | Liu H.,University of Portsmouth
IEEE Transactions on Systems, Man and Cybernetics Part C: Applications and Reviews | Year: 2010

As viewpoint issue is becoming a bottleneck for human motion analysis and its application, in recent years, researchers have been devoted to view-invariant human motion analysis and have achieved inspiring progress. The challenge here is to find a methodology that can recognize human motion patterns to reach increasingly sophisticated levels of human behavior description. This paper provides a comprehensive survey of this significant research with the emphasis on view-invariant representation, and recognition of poses and actions. In order to help readers understand the integrated process of visual analysis of human motion, this paper presents recent development in three major issues involved in a general human motion analysis system, namely, human detection, view-invariant pose representation and estimation, and behavior understanding. Public available standard datasets are recommended. The concluding discussion assesses the progress so far, and outlines some research challenges and future directions, and solution to what is essential to achieve the goals of human motion analysis.


Bhuyan S.,S O A University | Hu J.,Nanjing University of Aeronautics and Astronautics
Energy | Year: 2013

We report a natural battery constructed by lake water and its soil bank. A DC (direct current) open-circuit electric voltage and short-circuit current is generated between two metal electrodes dipped inside lake water and its soil bank. The open-circuit voltage, short-circuit electric current and maximum output power are up to 486 mV, 70 μA and 8.2 μW, depending on the distance from the metal electrode inserted into soil to the one immersed in lake water. The small power of the battery is generated by the pH value difference between the lake water and soil bank, and the oxidation of organic matter around the electrode in soil. The natural battery provides an easy and essential method to harvest small energy from the environment for the drive of low power electronic systems. © 2013 Elsevier Ltd.


Su D.,University of Technology, Sydney | Dou S.,University of Wollongong | Wang G.,University of Technology, Sydney | Wang G.,Nanjing University of Aeronautics and Astronautics
Chemistry of Materials | Year: 2015

Amorphous TiO2@C nanospheres were synthesized via a template approach. After being sintered under different conditions, two types of polyphase TiO2 hollow nanospheres were obtained. The electrochemical properties of the amorphous TiO2 nanospheres and the TiO2 hollow nanospheres with different phases were characterized as anodes for the Na-ion batteries. It was found that all the samples demonstrated excellent cyclability, which was sustainable for hundreds of cycles with little capacity fading, although the anatase TiO2 presented a capability that was better than that of the mixed anatase/rutile TiO2 or the amorphous TiO2@C. Through crystallographic analysis, it was revealed that the anatase TiO2 crystal structure supplies two-dimensional diffusion paths for Na-ion intercalation and more accommodation sites. Density functional theory calculations indicated lower energy barriers for the insertion of Na+ into anatase TiO2. Therefore, anatase TiO2 hollow nanospheres show excellent high-rate performance. Through ex situ field emission scanning electron microscopy, it was revealed that the TiO2 hollow nanosphere architecture can be maintained for hundreds of cycles, which is the main reason for its superior cyclability. © 2015 American Chemical Society.


Ye Y.,Nanjing University of Aeronautics and Astronautics | Liu P.X.,Carleton University
IEEE/ASME Transactions on Mechatronics | Year: 2010

For wave-variable-based teleoperation systems, the performance of trajectory tracking is not ensured due to a bias term introduced by the wave communication channel. This paper proposes a new method that can improve the trajectory tracking performance. The key idea is that the wave in the forward path is augmented by the user-perceived force and slave control force. The passivity of the augmented teleoperation system can be maintained by tuning the bandwidth of the low-pass filter, as demonstrated via an example. Therefore, the system stability can be always guaranteed. Both the simulation and experimental results verify the effectiveness of the scheme. © 2009 IEEE.


Zhang H.,Nanjing University of Information Science and Technology | Zhou D.,Nanjing University of Aeronautics and Astronautics | Cao J.,Nanjing University of Information Science and Technology
Renewable and Sustainable Energy Reviews | Year: 2011

Energy strategy evolution of China and US is assessed quantitatively based on Bai and Perron' s structure breaks test. Results indicate no break for time series of energy intensity, while series of carbon emissions per GDP, proportion of renewable energy production and oil importing reliance are characterized as segmented trend stationary process around one or two structural breaks. Execution of China and US energy strategies does not change the growth path of carbon emissions per GDP, and the pollution caused by energy production and consumption is one of the problems to be solved urgently. The impact of China energy strategy on the proportion of renewable energy production is inconsistent with that of US, suggesting that China can learn from the diversified energy supply, renewable energy quota system policies, and R&D incentive policies of US. Energy strategies in China and US pose a significant impact on the oil importing reliance, indicating that the strategy to reduce the oil dependence from US is not working. © 2010 Elsevier Ltd.


Kan J.,Yancheng Institute of Technology | Xie S.,Nanjing University of Aeronautics and Astronautics | Tang Y.,Nanjing University of Aeronautics and Astronautics | Wu Y.,Yancheng Institute of Technology
IEEE Transactions on Power Electronics | Year: 2014

A new voltage-fed isolated bidirectional dc/dc converter (BDC) based on immittance network (IMN) is proposed. The operations of the BDC are analyzed in the buck mode and the boost mode, respectively. Compared to the conventional dual active bridges (DAB) BDC, the proposed converter can obtain unity power factor at both ac terminals of the high voltage side (HVS) bridge and the low voltage side (LVS) bridge. The unity power factor working is resulted from the characteristic of the IMN and it is helpful to improve the converter's efficiency. The quantitative relationship of the proposed converter is deduced. The optimal design guidance of transformer and IMN is presented. The analysis is verified by the experimental results from a 500 W prototype. © 2013 IEEE.


Tang Z.,Nanjing University of Aeronautics and Astronautics | Periaux J.,Polytechnic University of Catalonia
Computer Methods in Applied Mechanics and Engineering | Year: 2012

A new robust optimization method is introduced to extend single point design to more realistic problems in aerodynamics taking into account uncertainties. It is well known that single point design techniques produce solutions that perform well for the selected design point but have poor off-design performance. Following ideas of Taguchi's robust control theory, a design with uncertainties is replaced by an optimization problem with two objectives which are mean performance and variance. Here, this two-objective optimization problem is solved by Pareto and Nash game strategies combined with the adjoint method, in the sense that solutions are less sensitive to uncertainties of input parameters. A constrained Nash strategy is implemented for performing multi-criteria optimization problems with constraints. Starting from a statistical definition of stability, the method simultaneously captures, Pareto and Nash equilibrium solutions ensuring performance and stability. © 2012 Elsevier B.V.


Yao Z.,Nanjing University of Aeronautics and Astronautics | Xiao L.,Yancheng Institute of Technology | Yan Y.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2010

This paper presents a novel seamless transfer of single-phase grid-interactive inverters between grid-connected and stand-alone modes. The grid-connected inverter should operate in grid-tied and off-grid modes in order to provide power to the emergency load during system outages. However, the grid current controller and the output voltage controller are switched between the two modes, so the outputs of both controllers may not be equal during the transfer instant, which will cause the current or voltage spikes during the switching process. The transfer between the two controllers does not exist in the proposed method. In grid-tied mode, the voltage controller is used for compensating the filter capacitor current, and the current controller is used to control the grid current. In stand-alone mode, the voltage controller is used to regulate the output voltage, whereas the output of the current controller is zero. With the proposed control method, the seamless transfer can be achieved between both modes, even in polluted grid voltage. The principle and realization conditions of the control methods at both modes are analyzed. The detailed process of the seamless transfer between the two modes is illustrated. Finally, the simulation and experimental results verify the theoretical analysis. © 2006 IEEE.


Yin Y.H.,Shanghai JiaoTong University | Zhou C.,Shanghai JiaoTong University | Zhu J.Y.,Nanjing University of Aeronautics and Astronautics
CIRP Annals - Manufacturing Technology | Year: 2010

Pipe system design like aero-engine, not only a typical NP-hard problem in limited 3D space, must also extraordinarily depend on human experience. This paper presents a methodology for designing compact pipe systems by fully imitating human's imaginal thinking based on image. The feasible workspace is represented as images of the holistic layout of pipes on the basis of human experience. The improved visible graph imitating human pipe-routing behaviour is conducted to form possible edge sequence tree. Moreover, the global optimal pipe path is generated from the tree. The simulation demonstrated the effectiveness of the pipe route design methodology. © 2010 CIRP.


Fang L.,Nanjing University of Aeronautics and Astronautics | Susilo W.,University of Wollongong | Ge C.,Nanjing University of Aeronautics and Astronautics | Wang J.,Nanjing University of Aeronautics and Astronautics
Information Sciences | Year: 2013

The notion of public key encryption with keyword search (PEKS) was put forth by Boneh et al. to enable a server to search from a collection of encrypted emails given a "trapdoor" (i.e., an encrypted keyword) provided by the receiver. The nice property in this scheme allows the server to search for a keyword, given the trapdoor. Hence, the verifier can merely use an untrusted server, which makes this notion very practical. Following Boneh et al.'s work, there have been subsequent works that have been proposed to enhance this notion. Two important notions include the so-called keyword guessing attack and secure channel free, proposed by Byun et al. and Baek et al., respectively. The former realizes the fact that in practice, the space of the keywords used is very limited, while the latter considers the removal of secure channel between the receiver and the server to make PEKS practical. Unfortunately, the existing construction of PEKS secure against keyword guessing attack is only secure under the random oracle model, which does not reflect its security in the real world. Furthermore, there is no complete definition that captures secure channel free PEKS schemes that are secure against chosen keyword attack, chosen ciphertext attack, and against keyword guessing attacks, even though these notions seem to be the most practical application of PEKS primitives. In this paper, we make the following contributions. First, we define the strongest model of PEKS which is secure channel free and secure against chosen keyword attack, chosen ciphertext attack, and keyword guessing attack. In particular, we present two important security notions namely IND-SCF-CKCA and IND-KGA. The former is to capture an inside adversary, while the latter is to capture an outside adversary. Intuitively, it should be clear that IND-SCF-CKCA captures a more stringent attack compared to IND-KGA. Second, we present a secure channel free PEKS scheme secure without random oracle under the well known assumptions, namely DLP, DBDH, SXDH and truncated q-ABDHE assumption. Our contributions fill the gap in the literature and hence, making the notion of PEKS very practical. We shall highlight that our scheme is IND-SCF-CKCA secure. © 2013 Elsevier Inc.


An Q.L.,Shanghai JiaoTong University | Fu Y.C.,Nanjing University of Aeronautics and Astronautics | Xu J.H.,Nanjing University of Aeronautics and Astronautics
International Journal of Machine Tools and Manufacture | Year: 2011

Titanium alloys, as difficult-to-cut materials, have poor machinability due to their superior mechanical properties, heat resistance and corrosion resistance. High cutting temperature that will greatly accelerate tool wear often occurs in titanium alloy cutting process. In this paper, cold water mist jet (CWMJ) cooling method, an eco-friendly cooling method, was used to obtain a lower cutting temperature during TC9 titanium alloy turning process. The effects of CWMJ were mainly discussed as compared with cold air jet and flood cooling methods. A comprehensive evaluation on the cooling effects of CWMJ was carried out by hydrodynamic tests, heat transfer tests and turning tests, respectively. Experimental results indicated that CWMJ had better cooling effects as compared with other two cooling methods. Cutting temperature was greatly reduced, and tool life was improved with CWMJ during TC9 turning process. Machined surface quality and chip morphology were also acceptable. © 2011 Elsevier Ltd. All rights reserved.


Yao Z.,Nanjing University of Aeronautics and Astronautics | Xiao L.,Yancheng Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2013

This paper presents a control of single-phase grid-interactive inverters with nonlinear loads. The utility-connected inverter should operate at both stand-alone and grid-connected modes. However, the waveform qualities of the grid current in grid-connected mode and the output voltage in stand-alone mode are poor under the nonlinear critical load with the conventional control. The impact of the nonlinear load on the grid current is analyzed. The proposed control is illustrated in detail. By adding the load current into the filter inductor current loop, the influence of the nonlinear load on the grid current can be eliminated, and the waveform quality of the output voltage in stand-alone mode can be improved. The control method is simple and easy to be achieved. The grid-connected inverter is stable at both modes. The filter inductor is chosen. Simulation and experimental results from a 1-kW dual-buck full-bridge grid-interactive inverter with a diode rectifier load verify the theoretical analysis. © 2012 IEEE.


Liu M.,Shanghai JiaoTong University | Liu M.,University of North Carolina at Chapel Hill | Zhang D.,University of North Carolina at Chapel Hill | Zhang D.,Nanjing University of Aeronautics and Astronautics | Shen D.,University of North Carolina at Chapel Hill
Human Brain Mapping | Year: 2014

Pattern classification methods have been widely investigated for analysis of brain images to assist the diagnosis of Alzheimer's disease (AD) and its early stage such as mild cognitive impairment (MCI). By considering the nature of pathological changes, a large number of features related to both local brain regions and interbrain regions can be extracted for classification. However, it is challenging to design a single global classifier to integrate all these features for effective classification, due to the issue of small sample size. To this end, we propose a hierarchical ensemble classification method to combine multilevel classifiers by gradually integrating a large number of features from both local brain regions and interbrain regions. Thus, the large-scale classification problem can be divided into a set of small-scale and easier-to-solve problems in a bottom-up and local-to-global fashion, for more accurate classification. To demonstrate its performance, we use the spatially normalized grey matter (GM) of each MR brain image as imaging features. Specifically, we first partition the whole brain image into a number of local brain regions and, for each brain region, we build two low-level classifiers to transform local imaging features and the inter-region correlations into high-level features. Then, we generate multiple high-level classifiers, with each evaluating the high-level features from the respective brain regions. Finally, we combine the outputs of all high-level classifiers for making a final classification. Our method has been evaluated using the baseline MR images of 652 subjects (including 198 AD patients, 225 MCI patients, and 229 normal controls (NC)) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. The experimental results show that our classification method can achieve the accuracies of 92.0% and 85.3% for classifications of AD versus NC and MCI versus NC, respectively, demonstrating very promising classification performance compared to the state-of-the-art classification methods. © 2013 Wiley Periodicals, Inc.


Xue H.,Nanjing Southeast University | Chen S.,Nanjing University of Aeronautics and Astronautics | Chen S.,Nanjing University | Yang Q.,Hong Kong University of Science and Technology
IEEE Transactions on Neural Networks | Year: 2011

Support vector machine (SVM), as one of the most popular classifiers, aims to find a hyperplane that can separate two classes of data with maximal margin. SVM classifiers are focused on achieving more separation between classes than exploiting the structures in the training data within classes. However, the structural information, as an implicit prior knowledge, has recently been found to be vital for designing a good classifier in different real-world problems. Accordingly, using as much prior structural information in data as possible to help improve the generalization ability of a classifier has yielded a class of effective structural large margin classifiers, such as the structured large margin machine (SLMM) and the Laplacian support vector machine (LapSVM). In this paper, we unify these classifiers into a common framework from the concept of structural granularity and the formulation for optimization problems. We exploit the quadratic programming (QP) and second-order cone programming (SOCP) methods, and derive a novel large margin classifier, we call the new classifier the structural regularized support vector machine (SRSVM). Unlike both SLMM at the cross of the cluster granularity and SOCP and LapSVM at the cross of the point granularity and QP, SRSVM is located at the cross of the cluster granularity and QP and thus follows the same optimization formulation as LapSVM to overcome large computational complexity and non-sparse solution in SLMM. In addition, it integrates the compactness within classes with the separability between classes simultaneously. Furthermore, it is possible to derive generalization bounds for these algorithms by using eigenvalue analysis of the kernel matrices. Experimental results demonstrate that SRSVM is often superior in classification and generalization performances to the state-of-the-art algorithms in the framework, both with the same and different structural granularities. © 2011 IEEE.


Theodoulidis T.,University of Western Macedonia | Wang H.,Nanjing University of Aeronautics and Astronautics | Tian G.Y.,Northumbria University
NDT and E International | Year: 2012

Calculations are carried out to evaluate pulsed eddy-current interaction with a crack in a planar conductor. The field is excited by a coil carrying current pulses and crack signals are detected by measuring changes in the magnetic field above the conductor. The model is based on the Fourier superposition concept, where the current pulses are decomposed into distinct frequencies. An existing boundary element method model for eddy current inspection of narrow cracks is used for each frequency and the final transient crack signal is synthesized by the individual frequency responses. The model is verified by a 3D finite element commercial package with a time-stepping technique. Computation times for the presented approach are orders of magnitudes shorter and allow rapid parametric studies of the transient signals for identification of principal component characteristics as well as for inversion purposes. © 2011 Elsevier Ltd. All rights reserved.


Zhang H.-F.,Nanjing University of Aeronautics and Astronautics | Zhang H.-F.,Nanjing Artillery Academy of the PLA | Liu S.-B.,Nanjing University of Aeronautics and Astronautics | Liu S.-B.,Nanjing Southeast University | Kong X.-K.,Nanjing University of Aeronautics and Astronautics
Journal of Lightwave Technology | Year: 2013

Dispersion properties of two types of three-dimensional plasma photonic crystals are theoretically investigated by a modified plane wave expansion method, which is composed of isotropic dielectric and nomagnetized plasma. The eigenvalue equations of two types of structures depend on the diamond lattice realization (dielectric spheres inserted in plasma background or vice versa), are deduced respectively. The band structures can be obtained by solving the nonlinear eigenvalue equations. The influences of relative dielectric constant and plasma frequency with different filling factors on dispersive relation are demonstrated, respectively. The numerical results show that the band structures can be modulated by the parameters for the two types of plasma photonic crystals. © 1983-2012 IEEE.


Tang J.,Tsinghua University | Fong A.C.M.,Auckland University of Technology | Wang B.,Nanjing University of Aeronautics and Astronautics | Zhang J.,Tsinghua University
IEEE Transactions on Knowledge and Data Engineering | Year: 2012

Despite years of research, the name ambiguity problem remains largely unresolved. Outstanding issues include how to capture all information for name disambiguation in a unified approach, and how to determine the number of people K in the disambiguation process. In this paper, we formalize the problem in a unified probabilistic framework, which incorporates both attributes and relationships. Specifically, we define a disambiguation objective function for the problem and propose a two-step parameter estimation algorithm. We also investigate a dynamic approach for estimating the number of people K. Experiments show that our proposed framework significantly outperforms four baseline methods of using clustering algorithms and two other previous methods. Experiments also indicate that the number K automatically found by our method is close to the actual number. © 1989-2012 IEEE.


Han J.,Nanjing University of Aeronautics and Astronautics | Xu G.,Nanjing University of Aeronautics and Astronautics | Ding B.,Nanjing University of Aeronautics and Astronautics | Pan J.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Journal of Materials Chemistry A | Year: 2014

Porous nitrogen-doped hollow carbon spheres (PNHCS) had been prepared by pyrolysis of hollow polyaniline spheres (HPS), which were synthesized by the use of sulfonated polystyrene spheres (SPS) as a hard template. PNHCS have a specific surface area of 213 m2 g-1 and a pore volume of 0.24 cm3 g-1. At a current density of 0.5 A g -1, the specific capacitance of the PNHCS prepared is ca. 213 F g-1. The capacity retention after 5000 charge/discharge cycles at a current density of 1 A g-1 is more than 91%. The enhanced electrochemical performance can be attributed to the unique carbon nanostructure and nitrogen-doping of the PNHCS electrodes. The hollow macro-structure plays the role of an "ion-buffering" reservoir. The micropores of the PNHCS enlarge the specific surface area, while the mesopores offer larger channels for liquid electrolyte penetration. Nitrogen groups in the PNHCS not only improve the wettability of the carbon surface, but also enhance the capacitance by addition of a pseudocapacitive redox process. © 2014 the Partner Organisations.


Liu Y.,Nanjing University of Aeronautics and Astronautics | Dou W.B.,Nanjing Southeast University | Zhao Y.J.,Nanjing University of Aeronautics and Astronautics
Progress in Electromagnetics Research | Year: 2010

In this paper, we present a tri-band filter design using tri-mode T-shaped branches connected by A/4 transmission lines. By analyzing the input admittance of a T-shape branch with commensurate electrical lengths, three resonant modes with two transmission zeros between are found and design formulas are derived. The filter can be regarded as a combination of three bandpass filters with only one set of coupling elements. To realize different bandwidths for each, the admittance slope of each resonating mode is set as required. A genetic algorithm is used in solving related equations to obtain the impedance of each line in a T-shape branch, followed by a final optimization. A three-pole tri-band filter having passbands of 0.60.9, 1.35-1.65 and 2.1-2.4 GHz, is designed, fabricated and measured with low passband insertion losses of < 0.7 dB and high rejection of > 60 dB between the passband regions. As a generalization, necessary to achieve a tri-band filter with arbitrary passbands, a non-commensurate version of the T-shape branch is introduced. An example filter design is given with the passbands asymmetrically located at 0.7-1, 1.65-1.95, and 2.2-2.3 GHz. This technique is able to achieve good design flexibility with respect to bandwidth ratios. This is validated by studying the maximum impedance variations of a T-shape branch when the bandwidth ratios vary.


Wu T.,Nanjing University of Aeronautics and Astronautics | Ding G.,CAS Shanghai Institute of Microsystem and Information Technology | Shen H.,Nanjing University of Aeronautics and Astronautics | Wang H.,CAS Shanghai Institute of Microsystem and Information Technology | And 4 more authors.
Advanced Functional Materials | Year: 2013

A simple but efficient strategy to synthesize millimeter-sized graphene single crystal grains by regulating the supply of reactants in the chemical vapor deposition (CVD) process is demonstrated. Polystyrene is used as a carbon source. Pulse heating on the carbon source is utilized to minimize the nucleation density of graphene on copper foil, while a gradual increase in the temperature of the carbon source and the flow rate of hydrogen is adapted to drive the continuous growth of the graphene grains. As a result, the nucleation density of graphene grain can be controlled to as low as ≈100 nuclei/cm 2, and a single crystal grain can grow up to dimensions of ≈1.2 mm. Raman spectroscopy, transmission electron microscopy (TEM), and electrical-transport measurements show that the graphene grains obtained are of high quality. The strategy presented provides very good controllability and enables the possibility of large graphene single crystals, which is of vital importance for practical applications. The key to synthesizing large graphene grains by ambient pressure chemical vapor deposition (APCVD) is to maintain a low nucleation rate and to provide a continuous drive for graphene growth. An optimized process enables ≈100 nuclei/cm2 on a finely polished and annealed substrate. A continuous increase in carbon supply and flow rate drives the graphene growth to ≈1.2 mm, the largest reported on a Cu substrate. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Xiao H.,Nanjing Southeast University | Xie S.,Nanjing University of Aeronautics and Astronautics
IET Power Electronics | Year: 2012

The double-switch buck-boost converter, characterised with non-inverting and step-up/step-down conversion, is suitable for the front stage of the two-stage photovoltaic (PV) grid-connected inverter. However, one strategy for the converter, named as 'synchronisation control', requires a considerable inductor and another control strategy, named as 'combined control', is sophisticated to control the operation modes transition smoothly. In order to reduce the inductance in synchronisation control strategy and to resolve the control complexity in combined control strategy, an interleaving control strategy for a double-switch buck-boost converter is proposed. This paper analyses the operation principle and characteristics of the proposed control strategy, and compares several switching strategies. Finally, the interleaving operation principle is verified by a 3 kW two-stage PV grid-connected inverter prototype. © 2012 The Institution of Engineering and Technology.


Cao Y.,Nanjing University | Hu X.-Y.,Nanjing University | Li Y.,Nanjing Southeast University | Zou X.,Nanjing University | And 5 more authors.
Journal of the American Chemical Society | Year: 2014

Supramolecular binary vesicles based on the host-guest complexation of water-soluble pillar[6]arene (WP6) and SAINT molecule have been successfully constructed, which showed pH-, Ca2+-, and thermal-responsiveness. These supramolecular vesicles can efficiently encapsulate model substrate calcein, which then can be efficiently released either by adjusting the solution pH to acidic condition due to the complete disruption of vesicular structure, or particularly, by adding a certain amount of Ca2+ due to the Ca2+-induced vesicle fusion and accompanied by the structure disruption. More importantly, drug loading and releasing experiments demonstrate that an anticancer drug, DOX, can be successfully encapsulated by the supramolecular vesicles, and the resulting DOX-loaded vesicles exhibit efficient release of the encapsulated DOX with the pH adjustment or the introduction of Ca2+. Cytotoxicity experiments suggest that the resulting DOX-loaded supramolecular vesicles exhibit comparable therapeutic effect for cancer cells as free DOX and the remarkably reduced damage for normal cells as well. The present multistimuli-responsive supramolecular vesicles have great potential applications in the field of controlled drug delivery. In addition, giant supramolecular vesicles (∼3 μm) with large internal volume and good stability can be achieved by increasing the temperature of WP6 ⊃ SAINT vesicular solution, and they might have potential applications for bioimaging. © 2014 American Chemical Society.


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.


Li S.,Nanjing University of Aeronautics and Astronautics | Peng Y.,Shanghai Institute of Satellite Engineering
Advances in Space Research | Year: 2012

In order to accurately deliver an entry vehicle through the Martian atmosphere to the prescribed parachute deployment point, active Mars entry guidance is essential. This paper addresses the issue of Mars atmospheric entry guidance using the command generator tracker (CGT) based direct model reference adaptive control to reduce the adverse effect of the bounded uncertainties on atmospheric density and aerodynamic coefficients. Firstly, the nominal drag acceleration profile meeting a variety of constraints is planned off-line in the longitudinal plane as the reference model to track. Then, the CGT based direct model reference adaptive controller and the feed-forward compensator are designed to robustly track the aforementioned reference drag acceleration profile and to effectively reduce the downrange error. Afterwards, the heading alignment logic is adopted in the lateral plane to reduce the crossrange error. Finally, the validity of the guidance algorithm proposed in this paper is confirmed by Monte Carlo simulation analysis. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.


Li S.,Nanjing University of Aeronautics and Astronautics | Peng Y.-M.,Shanghai Institute of Satellite Engineering
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2012

To deliver a Mars entry vehicle through the Martian atmosphere to the prescribed parachute deployment point, active Mars entry guidance and control is essential. This article addresses the problem of Mars atmospheric entry control by a neural network-based sliding mode variable structure control (NNSMVSC) to reduce the effect of the bounded uncertainties on the atmospheric density and aerodynamic coefficients. First, NNSMVSC is designed to robustly track the prescribed nominal trajectory under high uncertainties and to effectively reduce the downrange error. Then, the heading alignment logic is adopted in the lateral plane to reduce the cross-range error. Finally, the validity of the control algorithm proposed in this article is demonstrated by computer simulation analysis. © IMechE 2011.


Wang S.,Nanjing University of Aeronautics and Astronautics | Liu S.,Nanjing University of Aeronautics and Astronautics | Liu S.,Nanjing Southeast University
Optics Express | Year: 2012

Based on the transformation media theory, we proposed a way to control the scattering of a cavity, or trench, located on a metallic plane. Specifically, we show how is possible to design transformation medium to fill up a cavity with arbitrary cross section, which is capable of enhancing the specularly reflection wave. As the inverse problem, we also address the design of transformation medium coating, which is laid on the metallic plane, to mimic the scattering of the cavity. Based on the effective medium theory, the transformation medium for the case of a polygonal cavity can be realized by oblique layered structures, and each layered structure is consisting of two kinds of isotropic dielectrics, thus leading an ease of practical fabrication. © 2012 Optical Society of America.


Qi J.S.,University of Pennsylvania | Qi J.S.,Nanjing University of Aeronautics and Astronautics | Huang J.Y.,Sandia National Laboratories | Feng J.,University of Pennsylvania | And 2 more authors.
ACS Nano | Year: 2011

Graphene is an interesting electronic material. However, flat monolayer graphene does not have significant gap in the electronic density of states, required for a large on-off ratio in logic applications. We propose here a novel device architecture, composed of self-folded carbon nanotube-graphene hybrids, which have been recently observed experimentally in Joule-heated graphene. These experiments demonstrated the feasibility of cutting, folding, and welding few-layer graphene in situ to form all-carbon nanostructures with complex topologies. The electronic gap of self-folded nanotubes can be combined with the semimetallicity of graphene electrodes to form a "metal-semiconductor- metal" junction. By ab initio calculations we demonstrate large energy gaps in the transmission spectra of such junctions, which preserve the intrinsic transport characteristics of the semiconducting nanotubes despite topologically necessary disinclinations at the flat graphene-curved nanotube interface. These all-carbon devices are proposed to be constructed by contact probe cutting and high-temperature annealing and, if produced, would be chemically stable at room temperature under normal gas environments. © 2011 American Chemical Society.


Xu J.,Nanjing University of Aeronautics and Astronautics | Liu L.,Nanjing University of Aeronautics and Astronautics | Lu X.,Nanjing University of Aeronautics and Astronautics | Jiang S.,Nanjing Southeast University
Electrochemistry Communications | Year: 2011

The nanocrystalline Ti5Si3 and Ti5Si 3C0.8 films with an average grain size of 15 nm were prepared on Ti-6Al-4V alloy substrate by double glow discharge plasma technique. The electrochemical behaviour of two nanocrystalline films has been characterised by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The electronic properties of the passive films were investigated by Mott-Schottky analysis. The results revealed that the calculated donor densities are lower and the space charge region thicker for nanocrystalline Ti5Si3C0.8 film as compared to nanocrystalline Ti5Si3 film, suggesting that the passive layer formed is more protective. © 2010 Elsevier B.V. All rights reserved.


Xu J.,Nanjing University of Aeronautics and Astronautics | Wang Y.,Nanjing University of Aeronautics and Astronautics | Jiang S.,Nanjing Southeast University
Nanoscale | Year: 2010

A series of nanocrystalline (MoxCr1-x) 5Si3 films with an average grain size of 8 nm has been prepared on Ti-6A1-4V alloy substrates by glow discharge. The effect of substitution of Cr for Mo on the hardness, elastic modulus and plastic deformability of the nanocrystalline (MoxCr1-x) 5Si3 film was investigated using the nanoindentation method. The results reveal that the hardness of nanocrystalline (Mo xCr1-x)5Si3 films slightly decreases with increasing Cr content. In contrast, the plastic deformability significantly increases with increasing Cr content. © 2010 The Royal Society of Chemistry.


Xu J.,The Interdisciplinary Center | Cao L.-M.,The Interdisciplinary Center | Cao L.-M.,CAS Institute of Theoretical Physics | Hu Y.-P.,Nanjing University of Aeronautics and Astronautics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We study the P-V criticality and phase transition in the extended phase space of charged anti-de Sitter black holes in canonical ensemble of ghost-free massive gravity, where the cosmological constant is viewed as a dynamical pressure of the black hole system. We give the generalized thermodynamic first law and the Smarr relation with massive gravity correction. We find that not only when the horizon topology is spherical but also in the Ricci flat or hyperbolic case, there appear the P-V criticality and phase transition up to the combination k+c02c2m2 in the four-dimensional case, where k characterizes the horizon curvature and c2m2 is the coefficient of the second term of massive potential associated with the graviton mass. The positivity of such combination indicate the van der Waals-like phase transition. When the spacetime dimension is larger then four, the Maxwell charge there seems unnecessary for the appearance of critical behavior, but a infinite repulsion effect needed, which can also be realized through negative valued c3m2 or c4m2, which is third or fourth term of massive potential. When c3m2 is positive, a Hawking-Page-like black hole to vacuum phase transition is shown in the five-dimensional chargeless case. For the van der Waals-like phase transition in four and five spacetime dimensions, we calculate the critical exponents near the critical point and find they are the same as those in the van der Waals liquid-gas system. © 2015 American Physical Society.


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Rice University | Guo W.,Nanjing University of Aeronautics and Astronautics | Yakobson B.I.,Rice University
Nanoscale | Year: 2013

Using hybrid density functional theory calculations with van der Waals correction, we show that polar boron nitride (BN) nanoribbons can be favorably aligned via substantial hydrogen bonding at the interfaces, which induces significant interface polarizations and sharply reduces the band gap of insulating ribbons well below the silicon range. The interface polarization can strongly couple with carrier doping or applied electric fields, yielding not only enhanced stability but also widely tunable band gap for the aligned ribbons. Furthermore, similar layer-by-layer alignment also effectively reduces the band gap of a 2D hydrogenated BN sheet and even turns it into metal. This novel strategy for band gap control appears to be general in semiconducting composite nanostructures with polar nonbonding interfaces and thus offers unique opportunities for developing nanoscale electronic and optical devices. © 2013 The Royal Society of Chemistry.


Wang L.,Anhui Polytechnic University | Tang D.-B.,Nanjing University of Aeronautics and Astronautics
Expert Systems with Applications | Year: 2011

An improved adaptive genetic algorithm (IAGA) for solving the minimum makespan problem of job-shop scheduling problem (JSP) is presented. Though the traditional genetic algorithm (GA) exhibits implicit parallelism and can retain useful redundant information about what is learned from previous searches by its representation in individuals in the population, yet GA may lose solutions and substructures due to the disruptive effects of genetic operators and is not easy to regulate GA's convergence. The proposed IAGA is inspired from hormone modulation mechanism, and then the adaptive crossover probability and adaptive mutation probability are designed. The proposed IAGA is characterized by simplifying operations, high search precision, overcoming premature phenomenon and slow evolution. The proposed method by employing operation-based encoding is effectively applied to solve a dynamic job-shop scheduling problem (DJSP) and a complicated contrastive experiment of JSP in manufacturing system. Meanwhile, in order to ensure to create a feasible solution, a new method for crossover operation is adopted, named, partheno-genetic operation (PGO). The computational results validate the effectiveness of the proposed IAGA, which can not only find optimal or close-to-optimal solutions but can also obtain both better and more robust results than the existing genetic algorithms reported recently in the literature. By employing IAGA, machines can be used more efficiently, which means that tasks can be allocated appropriately, production efficiency can be improved, and the production cycle can be shortened efficiently. © 2010 Elsevier Ltd. All rights reserved.


Nai S.E.,Institute for Infocomm Research | Ser W.,Nanyang Technological University | Yu Z.L.,South China University of Technology | Chen H.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Signal Processing | Year: 2011

Based on worst-case performance optimization, the recently developed adaptive beamformers utilize the uncertainty set of the desired array steering vector to achieve robustness against steering vector mismatches. In the presence of large steering vector mismatches, the uncertainty set has to expand to accommodate the increased error. This degrades the output signal-to- interference-plus-noise ratios (SINRs) of these beamformers since their interference-plus-noise suppression abilities are weakened. In this paper, an iterative robust minimum variance beamformer (IRMVB) is proposed which uses a small uncertainty sphere (and a small flat ellipsoid) to search for the desired array steering vector iteratively. This preserves the interference-plus-noise suppression ability of the proposed beamformer and results in a higher output SINR. Theoretical analysis and simulation results are presented to show the effectiveness of the proposed beamformer. © 2010 IEEE.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Qiu J.,Xiamen University
Communications in Computational Physics | Year: 2014

In this paper, we present a new type of Hermite weighted essentially nonoscillatory (HWENO) schemes for solving the Hamilton-Jacobi equations on the finite volume framework. The cell averages of the function and its first one (in one dimension) or two (in two dimensions) derivative values are together evolved via time approaching and used in the reconstructions. And the major advantages of the new HWENO schemes are their compactness in the spacial field, purely on the finite volume framework and only one set of small stencils is used for different type of the polynomial reconstructions. Extensive numerical tests are performed to illustrate the capability of the methodologies.© 2014 Global-Science Press.


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Rice University | Liu X.,Nanjing University of Aeronautics and Astronautics | Yakobson B.I.,Rice University | Guo W.,Nanjing University of Aeronautics and Astronautics
Journal of the American Chemical Society | Year: 2012

We report a two-dimensional tetragonal Titanium Carbide (TiC) monolayer sheet with distinguished structure and properties based on comprehensive first-principles calculations. The TiC sheet exhibits a novel zigzag-shaped buckling structure with all atoms being quasiplanar tetracoordinate, as favored by strong in-plane C2p-Ti3d bonding and synergetic out-of-plane electronic delocalization. This unique structure endows the sheet with high kinetic stability and anisotropic mechanical properties. Moreover, the TiC sheet displays orientation-dependent electronic properties derived from its special rectangular symmetry, with indirect band gap of ∼0.2 eV and substantial ferromagnetism along its edges, thus promising for wide applications in nanoelectronics. © 2012 American Chemical Society.


Zhou P.,Nanjing University of Aeronautics and Astronautics | Zhou X.,Nanjing University of Aeronautics and Astronautics | Fan L.W.,Hohai University
Applied Energy | Year: 2014

Undesirable outputs (or bads) refer to the byproducts accompanied with desirable outputs (or goods) in a production process, e.g. sulfur dioxide and carbon dioxide in coal-fired power generation. The shadow price of undesirable output, which may be interpreted as the opportunity cost of abating one additional unit of undesirable output in terms of the loss of desirable output, could provide valuable reference information for policy analysis and making. A prevalent practice is to use the Shephard or directional distance function to derive the shadow price, which can be further calculated by parametric or nonparametric efficiency models. In application, earlier studies have estimated shadow prices at plant, sector and even economy levels. This study aims to conduct a systematic review of the studies on estimating shadow prices of undesirable outputs with efficiency models. We first introduce the methodological framework for deriving shadow prices as well as the nonparametric/parametric efficiency models for calculating their values. A systematic summary of over forty earlier studies in this field is then conducted, through which the key features of the existing studies are summarized and possible future research directions are identified. © 2014 Elsevier Ltd.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Zhong X.,Michigan State University | Shu C.-W.,Brown University | Qiu J.,Xiamen University
Journal of Computational Physics | Year: 2013

In this paper we generalize a new type of limiters based on the weighted essentially non-oscillatory (WENO) finite volume methodology for the Runge-Kutta discontinuous Galerkin (RKDG) methods solving nonlinear hyperbolic conservation laws, which were recently developed in [32] for structured meshes, to two-dimensional unstructured triangular meshes. The key idea of such limiters is to use the entire polynomials of the DG solutions from the troubled cell and its immediate neighboring cells, and then apply the classical WENO procedure to form a convex combination of these polynomials based on smoothness indicators and nonlinear weights, with suitable adjustments to guarantee conservation. The main advantage of this new limiter is its simplicity in implementation, especially for the unstructured meshes considered in this paper, as only information from immediate neighbors is needed and the usage of complicated geometric information of the meshes is largely avoided. Numerical results for both scalar equations and Euler systems of compressible gas dynamics are provided to illustrate the good performance of this procedure. © 2013 Elsevier Inc.


Tao G.,University of Virginia | Tao G.,Nanjing University of Aeronautics and Astronautics
Automatica | Year: 2014

Adaptive control is a control methodology capable of dealing with uncertain systems to ensure desired control performance. This paper provides an overview of some fundamental theoretical aspects and technical issues of multivariable adaptive control, and a thorough presentation of various adaptive control schemes for multi-input-multi-output systems, literature reviews on adaptive control foundations and multivariable adaptive control methods, and related technical problems. It covers some basic concepts and issues such as certainty equivalence, stability, tracking, robustness, and parameter convergence. It discusses some of the most important topics of adaptive control: plant uncertainty parametrization, stable controller adaptation, and design conditions for different adaptive control schemes. The paper also presents a detailed study of well-developed multivariable model reference adaptive control theory and design techniques. It provides an introduction to multivariable adaptive pole placement and adaptive nonlinear control, and it concludes by identifying some open research problems.


Zhang L.,Tsinghua University | Sun K.,Tsinghua University | Hu H.,Nanjing University of Aeronautics and Astronautics | Xing Y.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2014

A European efficiency enhancement strategy for the grid-tied inverters with common dc bus and ac bus in parallel operation is proposed in this paper. Based on the inherent relationship between the dc bus voltage and the grid-feeding power, two dc bus voltage regulators with different output limits are employed in each grid-tied inverter. The operation of the dc bus voltage regulators depends on the grid-feeding power level. Therefore, the grid-tied inverter has priority up to the maximum efficiency operation point, and then, to operate at full load mode with the increase of the grid-feeding power. As a result, the European efficiency of the grid-tied system is improved without any communication link and extra hardware cost. The operation principle of the grid-tied inverter system is analyzed in detail with the implementation of the proposed control, and the design guidelines for key parameters are given and discussed. A prototype with three grid-tied inverters in parallel operation is built and experimental tests have been conducted on it in terms of steady-state performances and dynamic performances. The experimental results show that the operation modes of each grid-tied inverter depend on its sensing gain of the dc bus voltage. The European efficiency of the grid-tied inverter system with the conventional control and with the proposed control are 94.74% and 95.17%, respectively, which means the European efficiency has been enhanced by 0.43%. These results verify the feasibility and effectiveness of the proposed control strategy. © 2013 IEEE.


Zhang L.,Tsinghua University | Sun K.,Tsinghua University | Xing Y.,Nanjing University of Aeronautics and Astronautics | Xing M.,State Grid Corporation of China
IEEE Transactions on Power Electronics | Year: 2014

Transformerless inverters are widely used in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency and low cost. Various transformerless inverter topologies have been proposed to meet the safety requirement of leakage currents, such as specified in the VDE-4105 standard. In this paper, a family of H6 transformerless inverter topologies with low leakage currents is proposed, and the intrinsic relationship between H5 topology, highly efficient and reliable inverter concept (HERIC) topology, and the proposed H6 topology has been discussed as well. One of the proposed H6 inverter topologies is taken as an example for detail analysis with operation modes and modulation strategy. The power losses and power device costs are compared among the H5, the HERIC, and the proposed H6 topologies. A universal prototype is built for these three topologies mentioned for evaluating their performances in terms of power efficiency and leakage currents characteristics. Experimental results show that the proposed H6 topology and the HERIC achieve similar performance in leakage currents, which is slightly worse than that of the H5 topology, but it features higher efficiency than that of H5 topology. © 1986-2012 IEEE.


Zhang L.,Tsinghua University | Sun K.,Nanjing University of Aeronautics and Astronautics | Wu T.,Tsinghua University | Xing Y.,Tsinghua University
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2013

In order to optimize energy utilization and realize system stability, an energy conversion and management control based on improved DC bus signaling (DBS) is proposed for DC microgrid based on photovoltaic (PV) generation. The DC microgrid is composed of three modular DC-DC converters for PV arrays, two bidirectional grid-tied DC-AC converters, one DC-DC converter for battery charging/discharging and local loads, which is available of either grid-tied operation or islanding operation. The operations of system are categorized into four modes: islanding with battery discharging, grid-tied rectification, grid-tied inversion and islanding with constant voltage generation. The DC bus voltage level is employed as an information carrier to determine operation mode switching. Hence, there is no centralized controller, and the reliability is enhanced. Control methods of PV converter, grid-tied converter, and battery converter are presented. The power balance of the system under extreme conditions such as the islanding operation with full-charged battery is taken into account. Experimental results verify the practical feasibility and effectiveness of the proposed control strategy.


Bu Z.,Nanjing University of Aeronautics and Astronautics | Bu Z.,University of Alabama at Birmingham | Zhang C.,University of Alabama at Birmingham | Xia Z.,Nanjing University of Aeronautics and Astronautics | Wang J.,Nanjing University of Aeronautics and Astronautics
Knowledge-Based Systems | Year: 2013

As information technology has advanced, people are turning more frequently to electronic media for communication, and social relationships are increasingly found in online channels. Discovering the latent communities therein is a useful way to better understand the properties of a virtual social network. Traditional community-detection tasks only consider the structural characteristics of a social organization, but more information about nodes and edges such as semantic information cannot be exploited. What is more, the typical size of virtual spaces is now counted in millions, if not billions, of nodes and edges, most existing algorithms are incapable to analyze such large scale dense networks. In this paper, we first introduce an interesting social network model (Interest Network) in which links between two IDs are built if they both participate to the discussions about one or more topics/stories. In this case, we say both of the connected two IDs have the similar interests. Then, the edges of the initial network are updated using the attitude consistency information of the connected ID pairs. For a given ID pair i and j, they may together reply to some topics/IDs. The implicit orientations/attitudes of these two IDs to their together-reply topics/IDs may not be the same. We use a simple statistical method to calculate the attitude consistency, the value of which is between 0 and 1, and the higher value corresponds to a greater degree of consistency of the given ID pair to topics/IDs. The updated network is called Similar-View Network (SVN). In the second part, a fast parallel modularity optimization algorithm (FPMQA) that performs the analogous greedy optimization as CNM and FUC is used to conduct community discovering. By using the parallel manner and sophisticated data structures, its running time is essentially fast, O(kmax(kmax+〈k〉logkmax)). Finally, we propose an evaluation metric, which is based on the reliable ground truths, for online network community detection. In the experimental work, we evaluate our method using real datasets and compare our approach with several previous methods; the results show that our method is more effective and accurate in find potential online communities. © 2013 Elsevier B.V. All rights reserved.


Jiang B.,Nanjing University of Aeronautics and Astronautics | Zhang K.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne | Shi P.,University of South Australia
IEEE Transactions on Fuzzy Systems | Year: 2011

This paper addresses the problem of integrated robust fault estimation (FE) and accommodation for discrete-time TakagiSugeno (TS) fuzzy systems. First, a multiconstrained reduced-order FE observer (RFEO) is proposed to achieve FE for discrete-time TS fuzzy models with actuator faults. Based on the RFEO, a new fault estimator is constructed. Then, using the information of online FE, a new approach for fault accommodation based on fuzzy-dynamic output feedback is designed to compensate for the effect of faults by stabilizing the closed-loop systems. Moreover, the RFEO and the dynamic output feedback fault-tolerant controller are designed separately, such that their design parameters can be calculated readily. Simulation results are presented to illustrate our contributions. © 2010 IEEE.


Dong Y.,Nanjing University of Aeronautics and Astronautics | Dong Y.,Tsinghua University | Li J.,Tsinghua University
Chemical Communications | Year: 2015

The direct synthesis of tungsten nitride (WN) nanoparticles on nitrogen-doped carbon black (N-carbon black) was achieved through facile nucleation and growth of WN nanoparticles on simultaneously generated N-carbon black under ammonia annealing. As a noble-metal-free catalyst, the WN/N-carbon black hybrid exhibited excellent performance in ORR, coupled with superior methanol tolerance and long-term stability in comparison to commercial Pt/C catalysts, through an efficient four-electron-dominant ORR process. © 2015 The Royal Society of Chemistry.


Xie X.,University of Technology, Sydney | Ao Z.,University of Technology, Sydney | Su D.,University of Technology, Sydney | Zhang J.,University of Technology, Sydney | And 2 more authors.
Advanced Functional Materials | Year: 2015

Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfides (MoS2, WS2, SnS, and SnS2) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfides and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS2/reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS2 to RGO. When used as anode materials for sodium-ion batteries, the synergistic effect contributing to the enhanced reversible capacity of MoS2/RGO nanocomposites is closely related with the heterointerfacial area. The computational results demonstrate that Na prefers to be adsorbed on MoS2 in the MoS2/RGO heterostructure rather than intercalate into the MoS2/RGO heterointerface. Interestingly, the MoS2/RGO heterointerfaces can significantly increase the electronic conductivity of MoS2, store more Na ions, while maintaining the high diffusion mobility of Na atoms on MoS2 surface and high electron transfer efficiency from Na to MoS2. It is expected that the efforts to establish the correlation between the two-dimensional heterointerface and the electrochemical sodium-ion storage performance offer fundamental understanding for the rational design of layered metal sulfides/graphene composites as high-performance electrode materials for sodium-ion batteries. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Rice University | Guo W.,Nanjing University of Aeronautics and Astronautics
Nano Letters | Year: 2012

We show by density functional theory calculations with both hybrid and semilocal functionals that cubic boron nitride (111) nanofilms are intrinsically metallic and even turn into semiconductors once the thickness is less than 0.69 nm, which is in sharp contrast to the known insulating nature of boron nitride materials. The exceptional metallic or semiconducting band gap is due to a combined effect of thickness-dependent inbuilt electric polarization and labile near-gap states unique in the polar nanofilms. The band gap and dipole moment of the nanofilms can be further significantly tuned by applying an in-plane strain. These distinguished features of the boron nitride nanofilms are robust to surface passivation and can be enhanced by hybridizing with diamond films, thereby opening an exciting prospect of using the versatile cubic nanofilms in future electronic and piezoelectric devices. © 2012 American Chemical Society.


Mao Z.,Nanjing University of Aeronautics and Astronautics | Jiang B.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne | Shi P.,University of South Australia
Automatica | Year: 2010

In this paper, a fault-tolerant control (FTC) scheme is developed for a class of nonlinear sampled-data systems. First, a Euler approximate discrete model is used to describe the plant under the sampling. Under this model, an observer-based fault estimation method is proposed. To guarantee the accuracy of both the state and fault estimation values, the conditions to make the approximate model consistent with the exact model are presented. Then, an active fault-tolerant controller, which has a constraint condition for the sampling time, is designed to make the faulty system stable. Finally, an inverted pendulum is used to show the efficiency of the proposed method. © 2010 Elsevier Ltd. All rights reserved.


Qi R.,Nanjing University of Aeronautics and Astronautics | Tao G.,Nanjing University of Aeronautics and Astronautics | Tao G.,University of Virginia | Jiang B.,Nanjing University of Aeronautics and Astronautics
Automatica | Year: 2014

This paper studies a new solution framework for adaptive control of a class of MIMO time-varying systems with indicator function based parametrization, motivated by a general discrete-time MIMO Takagi-Sugeno (T-S) fuzzy system model in an input-output form with unknown parameters. An indicator (membership) function based parametrization has some favorable capacity to deal with certain large parameter variations. A new discrete-time MIMO system prediction model is derived for approximating a nonlinear dynamic system, and its system properties are clarified. An adaptive control scheme is developed, with desired controller parametrization and stable parameter estimation for control of such uncertain MIMO time-varying systems. A control singularity problem is addressed and the closed-loop stability and output tracking properties are analyzed. This work provides a new method for multivariable T-S fuzzy system modeling and adaptive control. An illustrative example and simulation results are presented to demonstrate the proposed novel concepts and to verify the desired adaptive control system performance. © 2014 Elsevier Ltd. All rights reserved.


Wu F.,Nanjing University of Aeronautics and Astronautics | Fan L.W.,Hohai University | Zhou P.,Nanjing University of Aeronautics and Astronautics | Zhou D.Q.,Nanjing University of Aeronautics and Astronautics
Energy Policy | Year: 2012

Global awareness on energy security and climate change has created much interest in assessing economy-wide energy efficiency performance. A number of previous studies have contributed to evaluate energy efficiency performance using different analytical techniques among which data envelopment analysis (DEA) has recently received increasing attention. Most of DEA-related energy efficiency studies do not consider undesirable outputs such as CO 2 emissions in their modeling framework, which may lead to biased energy efficiency values. Within a joint production framework of desirable and undesirable outputs, in this paper we construct both static and dynamic energy efficiency performance indexes for measuring industrial energy efficiency performance by using several environmental DEA models with CO 2 emissions. The dynamic energy efficiency performance indexes have further been decomposed into two contributing components. We finally apply the indexes proposed to assess the industrial energy efficiency performance of different provinces in China over time. Our empirical study shows that the energy efficiency improvement in China's industrial sector was mainly driven by technological improvement. © 2012 Elsevier Ltd.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Qiu J.,Xiamen University | Qiu J.,Nanjing University
Communications in Computational Physics | Year: 2012

This paper further considers weighted essentially non-oscillatory (WENO) and Hermite weighted essentially non-oscillatory (HWENO) finite volume methods as limiters for Runge-Kutta discontinuous Galerkin (RKDG) methods to solve problems involving nonlinear hyperbolic conservation laws. The application discussed here is the solution of 3-D problems on unstructured meshes. Our numerical tests again demonstrate this is a robust and high order limiting procedure, which simultaneously achieves high order accuracy and sharp non-oscillatory shock transitions. © 2012 Global-Science Press.


Jiang B.,Nanjing University of Aeronautics and Astronautics | Gao Z.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales | Xu Y.,Victoria University of Melbourne
IEEE Transactions on Fuzzy Systems | Year: 2010

Based on the adaptive-control technique, this paper deals with the problem of fault-tolerant tracking control for near-space-vehicle (NSV) attitude dynamics. First, TakagiSugeno (TS) fuzzy models are used to describe the NSV attitude dynamics; then, an actuator-fault model is developed. Next, an adaptive fault-tolerant tracking-control scheme is proposed based on the online estimation of actuator faults, in which a compensation control term is introduced in order to reduce the effect of actuator faults. Compared with some existing results of fault-tolerant control (FTC) in nonlinear systems, the technique presented in this paper is not dependent on fault detection and isolation (FDI) mechanism and is easy to implement in aerospace-engineering applications. Finally, simulation results are given to illustrate the effectiveness and potential of the proposed FTC scheme. © 2010 IEEE.


Jiang B.,Nanjing University of Aeronautics and Astronautics | Mao Z.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne | Shi P.,University of South Australia
IEEE Transactions on Fuzzy Systems | Year: 2010

This paper is concerned with H∞-design for a class of networked control systems (NCSs) with multiple state-delays via the TakagiSugeno (TS) fuzzy model. The transfer delays and packet loss that are induced by the limited bandwidth of communication networks are considered. The focus of this paper is on the analysis and design of a full-order H∞ filter, such that the filtering-error dynamics are stochastically stable, and a prescribed H∞ attenuation level is guaranteed. Sufficient conditions are established for the existence of the desired filter in terms of linear-matrix inequalities (LMIs). An example is given to illustrate the effectiveness and applicability of the proposed design method. © 2006 IEEE.


Xie X.,University of Technology, Sydney | Ao Z.,University of Technology, Sydney | Su D.,University of Technology, Sydney | Zhang J.,University of Technology, Sydney | Wang G.,Nanjing University of Aeronautics and Astronautics
Advanced Functional Materials | Year: 2015

Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfides (MoS2, WS2, SnS, and SnS2) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfides and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS2/reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS2 to RGO. When used as anode materials for sodium-ion batteries, the synergistic effect contributing to the enhanced reversible capacity of MoS2/RGO nanocomposites is closely related with the heterointerfacial area. The computational results demonstrate that Na prefers to be adsorbed on MoS2 in the MoS2/RGO heterostructure rather than intercalate into the MoS2/RGO heterointerface. Interestingly, the MoS2/RGO heterointerfaces can significantly increase the electronic conductivity of MoS2, store more Na ions, while maintaining the high diffusion mobility of Na atoms on MoS2 surface and high electron transfer efficiency from Na to MoS2. It is expected that the efforts to establish the correlation between the two-dimensional heterointerface and the electrochemical sodium-ion storage performance offer fundamental understanding for the rational design of layered metal sulfides/graphene composites as high-performance electrode materials for sodium-ion batteries. MoS2/reduced graphene oxide nano-composites are prepared as anode materials for sodium-ion batteries. The performance of MoS2/reduced graphene oxide nano-composites is closely related to the heterointerfacial areas. Computational investigations reveal that the 2D MoS2/reduced graphene oxide heterointerface can increase the conductivity of MoS2, adsorb more Na atoms, and maintain high diffusion mobility of Na on MoS2 surface and electron transfer efficiency from Na to MoS2. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yuan J.,Rice University | Najmaei S.,Rice University | Zhang Z.,Rice University | Zhang Z.,Nanjing University of Aeronautics and Astronautics | And 4 more authors.
ACS Nano | Year: 2015

Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide-molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide-black phosphorus or molybdenum disulfide-black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide-molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications. © 2015 American Chemical Society.


Wu J.,Nanjing University of Aeronautics and Astronautics | Cheng X.,Tsinghua University
International Journal of Heat and Mass Transfer | Year: 2013

Entransy is a novel concept developed in recent years to measure the transport ability of heat in heat transfer processes. In order to analyze and optimize thermal radiation process more conveniently and intuitively, we develop the entransy-theory-based method to the field of thermal radiation problems to define the generalized thermal resistance for multi-dimensional steady state thermal radiation systems, with a consistent dimension of those for heat conduction and convection systems proposed in previous studies. Based on it, the minimum generalized thermal resistance principle for thermal radiation is developed and its equivalence with the entransy dissipation extremum principle can be concluded by defining the concept of heat flux weighted average temperature difference for thermal radiation systems. We point out that these two principles emphasize particularly on the optimization of the mean performance for heat transfer processes. A steady state thermal radiation process in an enclosure with three opaque surfaces is taken as an example to illustrate the applicability and reliability of generalized thermal radiation resistance when it is used to optimize thermal radiation problems. Finally, a comparison between the principles of minimum generalized thermal resistance and minimum entropy generation is discussed to show that the latter might not be appropriate to optimize some thermal radiation problems. © 2012 Elsevier Ltd. All rights reserved.


Zhang L.,Nanjing University of Aeronautics and Astronautics | Sun K.,Tsinghua University | Feng L.,Delta Electronics Inc | Wu H.,Nanjing University of Aeronautics and Astronautics | Xing Y.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2013

Transformerless inverter topologies have attracted more attentions in photovoltaic (PV) generation system since they feature high efficiency and low cost. In order to meet the safety requirement for transformerless grid-tied PV inverters, the leakage current has to be tackled carefully. Neutral point clamped (NPC) topology is an effective way to eliminate the leakage current. In this paper, two types of basic switching cells, the positive neutral point clamped cell and the negative neutral point clamped cell, are proposed to build NPC topologies, with a systematic method of topology generation given. A family of single-phase transformerless full-bridge topologies with low-leakage current for PV grid-tied NPC inverters is derived including the existing oH5 and some new topologies. A novel positive-negative NPC (PN-NPC) topology is analyzed in detail with operational modes and modulation strategy given. The power losses are compared among the oH5, the full-bridge inverter with dc bypass (FB-DCBP) topology, and the proposed PN-NPC topologies. A universal prototype for these three NPC-type topologies mentioned is built to evaluate the topologies at conversion efficiency and the leakage current characteristic. The PN-NPC topology proposed exhibits similar leakage current with the FB-DCBP, which is lower than that of the oH5 topology, and features higher efficiency than both the oH5 and the FB-DCBP topologies. © 1986-2012 IEEE.


Zhou X.,Nanjing University of Aeronautics and Astronautics | Fan L.W.,Hohai University | Zhou P.,Nanjing University of Aeronautics and Astronautics
Energy Policy | Year: 2015

Shanghai, one of the most developed cities in China, is implementing a pilot regional carbon emission trading scheme. Estimating the marginal abatement costs of CO2 emissions for the industrial sectors covered in Shanghai's emission trading scheme provides the government and participating firms useful information for devising compliance policies. This paper employs multiple distance function approaches to estimating the shadow prices of CO2 emissions for Shanghai industrial sectors. Our empirical results show that the overall weighted average of shadow price estimates by different approaches ranges between 394.5 and 1906.1Yuan/ton, which indicates that model choice truly has a significant effect on the shadow price estimation. We have also identified a negative relationship between the shadow price of CO2 emissions and carbon intensity, and the heavy industries with higher carbon intensities tend to have lower shadow prices. It has been suggested that Shanghai municipal government take various measures to improve its carbon market, e.g. using the marginal abatement costs of participating sectors/firms as a criterion in the initial allocation of carbon emission allowances. © 2014 Elsevier Ltd.


Zhang K.,Nanjing University of Aeronautics and Astronautics | Jiang B.,Nanjing University of Aeronautics and Astronautics | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne
IEEE Transactions on Fuzzy Systems | Year: 2012

This paper studies the problem of robust fault estimation (FE) observer design for discrete-time Takagi-Sugeno (T-S) fuzzy systems via piecewise Lyapunov functions. Both the full-order FE observer (FFEO) and the reduced-order FE observer (RFEO) are presented. The objective of this paper is to establish a novel framework of the FE observer with less conservatism. First, under the multiconstrained design, an FFEO is proposed to achieve FE for discrete-time T-S fuzzy models. Then, using a specific coordinate transformation, an RFEO is constructed, which results in a new fault estimator to realize FE using current output information. Furthermore, by the piecewise Lyapunov function approach, less conservative results on both FFEO and RFEO are derived by introducing slack variables. Simulation results are presented to illustrate the advantages of the theoretic results that are obtained in this paper. © 2012 IEEE.


Chen H.,Yancheng Teachers University | Chen H.,Nanjing University of Aeronautics and Astronautics
Journal of Magnetism and Magnetic Materials | Year: 2012

We studied the magnetic properties of Mn/Fe codoped ZnS comparatively with and without defects using first-principle calculation. The calculated results indicate that the Mn/Fe codoped ZnS system tends to stabilize in a ferrimagnetic (FiM) configuration. To obtain a ferromagnetic (FM) configuration, we consider the doped system with defects, such as S or Zn vacancy. The calculated results indicate that the doped system with Zn vacancy favors FiM states. Although the FM states of the doped system with S vacancy are more stable than the FiM states in negative charge states, the FM states are not stable enough to exist. Finally, we replaced an S atom by a C atom in the doped system. The C atom prefers to substitute the S atom connecting Mn and Fe atoms. The formation energy of this defect is -0.40 eV, showing that Mn/Fe/C codoped ZnS can be fabricated easily by experiments. Furthermore, the FM state was lower in energy than the FiM state by 114 meV. Such a large energy difference between the FM and FiM states implies that room temperature ferromagnetism could be expected in such a system. © 2012 Elsevier B.V. All rights reserved.


Li Y.,Nanjing University of Aeronautics and Astronautics | Liu X.,Nanjing University of Aeronautics and Astronautics | Gao J.X.,University of Greenwich | Maropoulos P.G.,University of Bath
CIRP Annals - Manufacturing Technology | Year: 2012

This paper presents a new, dynamic feature representation method for high value parts consisting of complex and intersecting features. The method first extracts features from the CAD model of a complex part. Then the dynamic status of each feature is established between various operations to be carried out during the whole manufacturing process. Each manufacturing and verification operation can be planned and optimized using the real conditions of a feature, thus enhancing accuracy, traceability and process control. The dynamic feature representation is complementary to the design models used as underlining basis in current CAD/CAM and decision support systems. © 2012 CIRP.


Zeng H.,Japan International Center for Materials Nanoarchitectonics | Zhi C.,Japan International Center for Materials Nanoarchitectonics | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Wei X.,Japan International Center for Materials Nanoarchitectonics | And 4 more authors.
Nano Letters | Year: 2010

Inspired by rich physics and functionalities of graphenes, scientists have taken an intensive interest in two-dimensional (2D) crystals of h-BN (analogue of graphite, so-called "white" graphite). Recent calculations have predicted the exciting potentials of BN nanoribbons in spintronics due to tunable magnetic and electrical properties; however no experimental evidence has been provided since fabrication of such ribbons remains a challenge. Here, we show that few- and single-layered BN nanoribbons, mostly terminated with zigzag edges, can be produced under unwrapping multiwalled BN nanotubes through plasma etching. The interesting stepwise unwrapping and intermediate states were observed and analyzed. Opposed to insulating primal tubes, the nanoribbons become semiconducting due to doping-like conducting edge states and vacancy defects, as revealed by structural analyses and ab initio simulations. This study paves the way for BN nanoribbon production and usage as functional semiconductors with a wide range of applications in optoelectronics and spintronics. © 2010 American Chemical Society.


Dreaden E.C.,Georgia Institute of Technology | MacKey M.A.,Georgia Institute of Technology | Huang X.,Georgia Institute of Technology | Huang X.,University of Memphis | And 3 more authors.
Chemical Society Reviews | Year: 2011

Gold nanoparticles possess a unique combination of properties which allow them to act as highly multifunctional anti-cancer agents (X. H. Huang, P. K. Jain, I. H. El-Sayed and M. A. El-Sayed, Nanomedicine, 2007, 2, 681-693; P. Ghosh, G. Han, M. De, C. K. Kim and V. M. Rotello, Adv. Drug Delivery Rev., 2008, 60, 1307-1315; S. Lal, S. E. Clare and N. J. Halas, Acc. Chem. Res., 2008, 41, 1842-1851; D. A. Giljohann, D. S. Seferos, W. L. Daniel, M. D. Massich, P. C. Patel and C. A. Mirkin, Angew. Chem., Int. Ed., 2010, 49, 3280-3294). Not only can they be used as targeted contrast agents for photothermal cancer therapy, they can serve as scaffolds for increasingly potent cancer drug delivery, as transfection agents for selective gene therapy, and as intrinsic antineoplastic agents. This tutorial review will highlight some of the many forms and recent applications of these gold nanoparticle conjugates by our lab and others, as well as their rational design and physiologic interactions. © 2011 The Royal Society of Chemistry.


Zhang L.,Harbin Institute of Technology | Jiang B.,Nanjing University of Aeronautics and Astronautics
International Journal of Innovative Computing, Information and Control | Year: 2010

In this paper, the problems of stability for continuous and discrete-time polytopic uncertain switched linear systems with average dwell time switching are investigated. Firstly, the exponential stability result of general continuous-time switched systems using a discontinuous piecewise Lyapunov function approach is revisited, and the discretetime counterpart is then presented by the following similar lines in continuous-time case. Based on these and by further constructing a discontinuous piecewise parameterdependent Lyapunov function, the exponential stability criteria for both uncertain continuous and discrete-time polytopic uncertain switched linear systems with average dwell time switching are derived and formulated in terms of a set of linear matrix inequalities, respectively. Furthermore, the minimal average dwell time is obtained from the corresponding stability conditions for a given decay degree, and the admissible switching signals are consequently found such that the underlying system is robustly exponentially stable. Numerical examples are included to demonstrate the effectiveness and less conservativeness of the developed theoretical results. © 2010 ICIC International.


Song J.,Nanjing University of Science and Technology | Song J.,Nanjing University of Aeronautics and Astronautics | Kulinich S.A.,Tokai University | Kulinich S.A.,Aston University | And 4 more authors.
Angewandte Chemie - International Edition | Year: 2015

For all-solution-processed (ASP) devices, transparent conducting oxide (TCO) nanocrystal (NC) inks are anticipated as the next-generation electrodes to replace both those synthesized by sputtering techniques and those consisting of rare metals, but a universal and one-pot method to prepare these inks is still lacking. A universal one-pot strategy is now described; through simply heating a mixture of metal-organic precursors a wide range of TCO NC inks, which can be assembled into high-performance electrodes for use in ASP optoelectronics, were synthesized. This method can be used for various oxide NC inks with yields as high as 10 g. The formed NCs are of high crystallinity, uniform morphology, monodispersity, and high ink stability and feature effective doping. Therefore, the inks can be readily assembled into films with a surface roughness of 1.6 nm. Typically, a sheet resistance of 110 Ω sq-1 can be achieved with a transmittance of 88%, which is the best performance for TCO NC ink-based electrodes described to date. These electrodes can thus drive a polymer light-emitting diode (PLED) with a luminance of 2200 cdm-2 at 100 mA cm-2. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.


Li S.,Nanjing University of Aeronautics and Astronautics | Guo H.,Nanjing University of Aeronautics and Astronautics | Li D.,Weifang Xiaotuo Tractor Co.
Yi Qi Yi Biao Xue Bao/Chinese Journal of Scientific Instrument | Year: 2013

Vibration signal processing method has been an active research topic all the time, and the equipment vibration monitoring and fault diagnosis are crucial. Though the vibration signal processing methods developed fast in recent years, they still need to be improved and optimized. Some typical approaches referring to recent literatures are classified and summarized in this paper. The developments, features and applications are presented and discussed for amplitude domain analysis, Fourier transform, correlation analysis in traditional methods, and Wigner-Ville distribution, spectral analysis, wavelet analysis, blind source separation, Hilbert-Huang transform, higher order statistics analysis in modern methods. Finally, we make a conclusion for this paper and an overview is made to guide the future development in this field.


Chen X.,Nanjing University of Aeronautics and Astronautics | Chen X.,Xidian University | Chen H.-H.,National Cheng Kung University | Meng W.,Harbin Institute of Technology
IEEE Communications Surveys and Tutorials | Year: 2014

Cognitive Radio has been recognized as a promising way to improve spectrum efficiency of wireless communications by exploiting under-utilized licensed spectrum in temporal, frequency, and spatial domains. As a remedy to the limited capability of a single node or network, cooperative communication technique has a potential to further improve the performance of cognitive networks, especially for spectrum sensing based cognitive networks. Given that spectrum efficiency of a cognitive network is determined jointly by spectrum sensing and access capabilities, it makes sense to employ cooperative techniques to enhance their performance. This article offers a tutorial on various cooperative techniques in cognitive networks, with its emphasis on spectrum sensing and access based cooperation, interference constraint based adaptive cooperative feedback, rateless network coding based cooperative transmission, and limited cooperation based interference coordination. Finally, numerical results are given to showcase advantages of the proposed cooperative schemes for cognitive networks. © 2014 IEEE.


Pei Y.,Xiangtan University | Pal R.,University of Nebraska - Lincoln | Liu C.,Xiangtan University | Gao Y.,University of Nebraska - Lincoln | And 2 more authors.
Journal of the American Chemical Society | Year: 2012

Atomic structure of a recently synthesized ligand-covered cluster Au 24(SR) 20 [J. Phys. Chem. Lett., 2010, 1, 1003] is resolved based on the developed classical force-field based divide-and-protect approach. The computed UV-vis absorption spectrum and powder X-ray diffraction (XRD) curve for the lowest-energy isomer are in good agreement with experimental measurements. Unique catenane-like staple motifs are predicted for the first time in core-stacked thiolate-group (RS-) covered gold nanoparticles (RS-AuNPs), suggesting the onset of structural transformation in RS-AuNPs at relatively low Au/SR ratio. Since the lowest-energy structure of Au 24(SR) 20 entails interlocked Au 5(SR) 4 and Au 7(SR) 6 oligomers, it supports a recently proposed growth model of RS-AuNPs [J. Phys. Chem. Lett., 2011, 2, 990], that is, Au n(SR) n-1 oligomers are formed during the initial growth of RS-AuNPs. By comparing the Au-core structure of Au 24(SR) 20 with other structurally resolved RS-AuNPs, we conclude that the tetrahedral Au 4 motif is a prevalent structural unit for small-sized RS-AuNPs with relatively low Au/SR ratio. The structural prediction of Au 24(SR) 20 offers additional insights into the structural evolution of thiolated gold clusters from homoleptic gold(I) thiolate to core-stacked RS-AuNPs. Specifically, with the increase of interfacial bond length of Au(core)-S in RS-AuNPs, increasingly larger "metallic" Au-core is formed, which results in smaller HOMO-LUMO (or optical) gap. Calculations of electronic structures and UV-vis absorption spectra of Au 24(SR) 20 and larger RS-AuNPs (up to ∼2 nm in size) show that the ligand layer can strongly affect optical absorption behavior of RS-AuNPs. © 2012 American Chemical Society.


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.


Pan X.,Weifang University | Zhang L.,Nanjing University of Aeronautics and Astronautics
Mathematical Problems in Engineering | Year: 2012

Numerical solutions for the general Rosenau-RLW equation are considered and an energy conservative linearized finite difference scheme is proposed. Existence of the solutions for the difference scheme has been shown. Stability, convergence, and a priori error estimate of the scheme are proved using energy method. Numerical results demonstrate that the scheme is efficient and reliable. © 2012 Xintian Pan and Luming Zhang.


Li C.,Nanjing University of Aeronautics and Astronautics | Yue Q.,Nanjing University of Aeronautics and Astronautics | Li F.,Nanjing University of Aeronautics and Astronautics | Li F.,Zaozhuang University
Finite Fields and their Applications | Year: 2014

Let Fr be an extension of a finite field Fq with r=qm. Let each gi be of order ni in r * and gcd(ni,nj)=1 for 1≤i≠j≤u. We define a cyclic code over Fq byC(q,m, n1,n2,.,nu)={C(a1, a2,.,au):a1,a2,.,a u⋯Fr}, whereC(a1,a2,., au)=(Trr/q(Σi=1uaigi0),.,Trr/ q(Σi=1uaigin-1)) and n=n1 n2⋯nu. In this paper, we present a method to compute the weights of C(q,m,n1,n2,.,nu). Further, we determine the weight distributions of the cyclic codes C(q,m, n1,n2) and C(q,m,n1,n2,1). © 2014 Elsevier Inc.


Gondal M.A.,King Fahd University of Petroleum and Minerals | Chang X.F.,King Fahd University of Petroleum and Minerals | Chang X.F.,Nanjing University of Aeronautics and Astronautics | Yamani Z.H.,King Fahd University of Petroleum and Minerals
Chemical Engineering Journal | Year: 2010

The sorption and photocatalytic decolorization (under irradiation of monochromaticitic 355nm-pulsed-laser) behaviors of Rhodamine 6G (Rh 6G) in presence of BiOCl semiconductor in aqueous solution were studied in this paper. The sorption kinetic and isotherm behaviors of Rh 6G over BiOCl catalyst were investigated and discussed through pseudo-second-order/intraparticle diffusion models and Langmuir/Freundlich models, respectively. The effect of critical parameters such as catalyst dosage, initial concentration of Rh 6G, and laser pulse energy on the photocatalytic decolorization process was investigated. The photocatalytic decolorization and photonic efficiency of BiOCl was compared with standard catalyst (TiO2) and the obtained results were discussed in terms of their band edge position. Finally, the chemical stability of BiOCl photocatalyst was studied by measuring the X-ray diffraction (XRD) pattern of BiOCl samples after the reaction. © 2010 Elsevier B.V.


Xu K.,Nanjing University of Aeronautics and Astronautics | Das K.C.,Sungkyunkwan University | Balachandran S.,SASTRA University
Match | Year: 2014

For a (molecular) graph, the first and second Zagreb indices (M1 and M2) are two well-known topological indices in chemical graph theory introduced in 1972 by Gutman and Trinajstić. Let Gn,m be the set of connected graphs of order n and with m edges. In this paper we characterize the extremal graphs from Gn,m with n + 2 ≥ m ≥ 2n-4 with maximal first Zagreb index and from Gn,m with m-n = (k 2)-k for k ≥ 4 with maximal second Zagreb index, respectively. Finally a related conjecture has been proposed to the extremal graphs with respect to second Zagreb index.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Hipel K.W.,University of Waterloo
Information Sciences | Year: 2012

The method of grey target decision making based on a multiple stages linguistic label is extended in this research. Firstly, the multi-granularity linguistic term sets are transformed into the same linguistic set. Next, the choice rule of a target is put forward and the calculation of a target distance is developed. Furthermore, weight models of criteria and of stages, which are based on the requirement of maximum difference of alternatives and restriction of stage harmony, are suggested. In addition, a model of lower and upper value of a target distance is put forward. Moreover, the method is extended to the group decision making environment. This model can help to avoid faulty decision making due to uncertainty. The suggested method is applied to vendor evaluation of a commercial airplane in China. © 2012 Elsevier Inc. All rights reserved.


Zhong W.,Nanjing University of Aeronautics and Astronautics | Zhao D.,Nanjing University of Aeronautics and Astronautics | Wang X.,Nanchang Hangkong University
International Journal of Machine Tools and Manufacture | Year: 2010

Green manufacturing is the theme of manufacturing industry in the 21st century. In order to realize green manufacturing, it is critical to decrease the usage of cutting fluid in machining as much as possible. Presently, there are still a lot of difficulties in the adoption of dry cutting and MQL cutting for various reasons. This paper presents a new method called little quantity lubrication (LQL) in machining and a comparative study on dry milling and LQL milling based on vibration signals. The vibration signals were acquired from workpiece surface in peripheral milling and were analyzed in time domain, frequency domain and timefrequency domain. The results show that vibration signals can be significantly affected by cutting fluid in milling process. For the sake of reducing vibration and cutting fluid usage, process parameters should be considered while deciding whether or not and how to apply cutting fluid. This research gives a valuable insight in applying LQL in machining. © 2010 Elsevier Ltd. All Rights reserved.


Yao L.,Zhengzhou University | Yao L.,Nanjing University of Aeronautics and Astronautics | Qin J.,Zhengzhou University | Wang H.,University of Manchester | Jiang B.,Nanjing University of Aeronautics and Astronautics
Automatica | Year: 2012

New fault diagnosis (FD) and fault tolerant control (FTC) algorithms for non-Gaussian singular stochastic distribution control (SDC) systems are presented in this paper. Different from general SDC systems, in singular SDC systems, the relationship between the weights and the control input is expressed by a singular state space model, which increases the difficulty in the FD and FTC design. The proposed approach relies on an iterative learning observer (ILO) for fault estimation. The fault may be constant, fast-varying or slow-varying. Based on the estimated fault information, the fault tolerant controller can be designed to make the post-fault probability density function (PDF) still track the given distribution. Simulations are given to show the effectiveness of the proposed FD and FTC algorithms. © 2012 Elsevier Ltd. All rights reserved.


Li C.,Nanjing University of Aeronautics and Astronautics | Yue Q.,Nanjing University of Aeronautics and Astronautics | Li F.,Nanjing University of Aeronautics and Astronautics | Li F.,Zaozhuang University
IEEE Transactions on Information Theory | Year: 2014

Cyclic codes are an interesting type of linear codes and have wide applications in communication and storage systems due to their efficient encoding and decoding algorithms. In this paper, let Fr be a finite field with r = qm. Suppose that g1, g2 ε F* r are not conjugates over Fq, ord(g1) = n1, ord(g2) = n2, d = gcd(n1, n2), and n = n1n2/d. Let Fq (g1) = Fqm1 , Fq(g2) = F q m2, and Ti denote the trace function from Fqmi to F q for i = 1, 2. We define a cyclic code C(q,m,n1,n2) = {c(a, b) : a ε Fq m1 , b ε dbl;Fq m2 }, where c(a, b) = (T1(ag0 1) + T2(bg0 2 ), T1(ag1 1) + T2(bg1 2), ⋯ , T 1(agn-1 1 ) + T2(bg n-1 2 )). We mainly use Gauss periods to present the weight distribution of the cyclic code C(q,m,n1,n2). As applications, we determine the weight distribution of cyclic code C(q,m,qm1-1,qm2-1) with gcd(m1, m2) = 1; in particular, it is a three-weight cyclic code if gcd(q -1, m1-m2) = 1. We also explicitly determine the weight distributions of some classes of cyclic codes including several classes of four-weight cyclic codes. © 2014 IEEE.


Das K.Ch.,Sungkyunkwan University | Xu K.,Nanjing University of Aeronautics and Astronautics | Gutman I.,University of Kragujevac
Match | Year: 2013

The first (M1) and second (M2) Zagreb indices and the Harary index (H) are graph invariants that found applications in chemistry. We present several new estimates for M1 and M2 and characterize the extremal trees. Lower and upper bounds on Harary index are obtained in terms of independence and matching numbers, as well as M1 and M2, and the extremal trees are characterized.


Yao Y.,Nanchang Hangkong University | Zhang J.-Z.,Nanjing University of Aeronautics and Astronautics | Wang L.-P.,Nanjing University of Aeronautics and Astronautics
International Journal of Thermal Sciences | Year: 2013

Experimental investigation was conducted in the current study to investigate the film cooling performance of a single row of consoles on a large-scale curved-plate model simulating the blade suction side, and an aided numerical study was also made to reveal the detailed film cooling features of consoles on the curved surface. A comparison in contrast to cylindrical hole was made. For the console cooling geometry, the interaction between coolant jet from inclined console and the mainstream flow results in reasonable vortices configuration to reduce mainstream-coolant interaction. And additional corner vortices are observed in the intersection of two consoles on the convex surface. The console row shows great potential in the blade film cooling application to produce high cooling effectiveness, especially at large blowing ratios. But this is at the expense of greater pressure drop. And the heat transfer coefficient ratio for the console is a little bigger than conventional cylindrical hole. Furthermore, the effects of major factors on the film cooling effectiveness, heat transfer coefficient and discharge coefficient were explored, including film hole location, blowing ratio and primary flow Reynolds number. © 2012 Elsevier Masson SAS. All rights reserved.


Lin J.,Nanjing University of Aeronautics and Astronautics | Lin J.,Weifang University | Chen Q.,Nanjing University of Aeronautics and Astronautics
Mechanical Systems and Signal Processing | Year: 2013

Vibration data of faulty rolling bearings are usually nonstationary and nonlinear, and contain fairly weak fault features. As a result, feature extraction of rolling bearing fault data is always an intractable problem and has attracted considerable attention for a long time. This paper introduces multifractal detrended fluctuation analysis (MF-DFA) to analyze bearing vibration data and proposes a novel method for fault diagnosis of rolling bearings based on MF-DFA and Mahalanobis distance criterion (MDC). MF-DFA, an extension of monofractal DFA, is a powerful tool for uncovering the nonlinear dynamical characteristics buried in nonstationary time series and can capture minor changes of complex system conditions. To begin with, by MF-DFA, multifractality of bearing fault data was quantified with the generalized Hurst exponent, the scaling exponent and the multifractal spectrum. Consequently, controlled by essentially different dynamical mechanisms, the multifractality of four heterogeneous bearing fault data is significantly different; by contrast, controlled by slightly different dynamical mechanisms, the multifractality of homogeneous bearing fault data with different fault diameters is significantly or slightly different depending on different types of bearing faults. Therefore, the multifractal spectrum, as a set of parameters describing multifractality of time series, can be employed to characterize different types and severity of bearing faults. Subsequently, five characteristic parameters sensitive to changes of bearing fault conditions were extracted from the multifractal spectrum and utilized to construct fault features of bearing fault data. Moreover, Hilbert transform based envelope analysis, empirical mode decomposition (EMD) and wavelet transform (WT) were utilized to study the same bearing fault data. Also, the kurtosis and the peak levels of the EMD or the WT component corresponding to the bearing tones in the frequency domain were carefully checked and used as the bearing fault features. Next, MDC was used to classify the bearing fault features extracted by EMD, WT and MF-DFA in the time domain and assess the abilities of the three methods to extract fault features from bearing fault data. The results show that MF-DFA seems to outperform each of envelope analysis, statistical parameters, EMD and WT in feature extraction of bearing fault data and then the proposed method in this paper delivers satisfactory performances in distinguishing different types and severity of bearing faults. Furthermore, to further ascertain the nature causing the multifractality of bearing vibration data, the generalized Hurst exponents of the original bearing vibration data were compared with those of the shuffled and the surrogated data. Consequently, the long-range correlations for small and large fluctuations of data seem to be chiefly responsible for the multifractality of bearing vibration data. © 2013 Elsevier Ltd.


Li X.,Nanjing University of Aeronautics and Astronautics | Deng Z.,Nanjing University of Aeronautics and Astronautics | Chen Z.,Shanghai Aircraft Research Institute | Fei Q.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2011

The main objective of this paper is to simplify the implementation of continuous and discontinuous 3-D space vector pulsewidth modulations (SVPWMs). This paper analyzes the relationships, whether in abc or αβO coordinates, between three-phase voltages and the following elements: the tetrahedron in which the reference vector resides, three adjacent active switching vectors (or three switching states), and their duration times. Based on the analysis, the calculation of the turn-on time of each switch in the actual implementation is simplified, and discontinuous PWM (DPWM) methods in three-leg inverters can be extended to four-leg inverters without the phase angle. In addition, two more DPWM methods that are peculiar to 3-D SVPWM are presented. This simplified algorithm does not use irrational operations or look-up tables, and it alleviates the computation burden of the processor. The simulation and experimental results are provided to validate the effectiveness of the proposed algorithm. © 2011 IEEE.


Li B.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Shen Y.,Nanjing University of Aeronautics and Astronautics | Hu W.,Nanjing Institute of Technology | Luo L.,Nanjing University of Aeronautics and Astronautics
Materials and Design | Year: 2014

Friction stir welding (FSW) technique is considered to offer advantages over fusion welding in terms of dissimilar jointing. However, some challenges still exist in the butt FSW of dissimilar Ti and Al metals. The present research employed a modified butt joint configuration into the FSW of Ti-6Al-4V alloy to Al-6Mg alloy with a special pin plunge setup, aiming to obtain a high-quality Ti-to-Al joint, avoid butt flaw or Al melting, and reduce the tool shoulder attrition. Under different FSW process conditions, the examinations and analyses of macro/micro-structures, mechanical tensile properties and fractographies of the dissimilar joints were conducted. The joint mechanical tensile strength can reach more than 92% of the parent Al alloy strength, with a tensile fracture path within the Al alloy butt side. The characteristics and formation mechanisms of the diffusion typed and reaction typed Ti-Al butt-welded interface structures were detailed. The bulky intermetallic compounds (IMC) interlayer at the butt-welded interface had a negative effect on the joint tensile strength, comparing with the Ti-Al diffusion bonding interlayer of ~2μm in thickness, which was produced via lower tool rotating speed and lower pin-offset value towards Ti alloy butt side. © 2014 Elsevier Ltd.


Kou L.,University of Nevada, Las Vegas | Kou L.,Nanjing University of Aeronautics and Astronautics | Tang C.,University of Nevada, Las Vegas | Guo W.,Nanjing University of Aeronautics and Astronautics | Chen C.,University of Nevada, Las Vegas
ACS Nano | Year: 2011

We examine the magnetic properties of two-dimensional graphene with topological line defect using first-principles calculations and predict a weak ferromagnetic ground state with spin-polarized electrons localized along the extended line defect. Our results show that tensile strain along the zigzag direction can greatly enhance local magnetic moments and ferromagnetic stability of the system. In sharp contrast, tensile strain applied along the armchair direction quickly diminishes these magnetic moments. A detailed analysis reveals that this intriguing magnetism modulation by strain stems from the redistribution of spin-polarized electrons induced by local lattice distortion. It suggests a sensitive and effective way to control magnetic properties of graphene which is critical for its applications in nanoscale devices. © 2011 American Chemical Society.


Tang C.,University of Nevada, Las Vegas | Tang C.,Nanjing University of Aeronautics and Astronautics | Guo W.,Nanjing University of Aeronautics and Astronautics | Chen C.,University of Nevada, Las Vegas
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We report molecular dynamics simulations of structural and mechanical properties of partially unzipped carbon nanotubes. Our results show that in the absence of edge passivation, partially unzipped carbon nanotubes are unstable with rising temperature depending on the geometry of cutting. When the length-to-width ratio of the graphene segment is not sufficiently large, the dangling bonds at the cutting front tend to reconnect to each other and form back to carbon nanotube structure; otherwise the structures roll up at the graphene end due to the competition of bending stiffness between longitudinal direction and transverse direction. When the graphene edges are hydrogen saturated, the self-healing behavior is suppressed. Tensile tests show that partially unzipped carbon nanotubes exhibit brittle fracture behavior, with a Young's modulus around 700 GPa, which is comparable to that of carbon nanotubes and graphene. © 2011 American Physical Society.


Jiang Y.,University of Shizuoka | Yang H.,Nanjing University of Aeronautics and Astronautics | Tohgo K.,University of Shizuoka
Composite Structures | Year: 2011

This paper deals with a constitutive model of particulate-reinforced composites (PRCs) which can describe the evolution of debonding damage, matrix plasticity and particle size effects on deformation and damage. An incremental damage model of PRC based on Mori-Tanaka's mean field concept has been extended to three-phase composites for interpreting particle size effect. The interphase was perfectly incorporated into the present micromechanics model as a third phase with the help of double-inclusion model. Progressive damage was controlled by a critical energy criterion for particle-matrix interfacial separation. Based on the developed model, influences of progressive debonding damage, particle size and interphase properties on the overall stress-strain response of PRC were discussed. Finally, particle size effect on the mechanical behaviors of composites was clearly interpreted from the role of the interphase, which is different from all the existing researches. © 2010 Elsevier Ltd.


Guo Y.,Nanjing University of Aeronautics and Astronautics | Guo Y.,University of Nevada, Las Vegas | Guo W.,Nanjing University of Aeronautics and Astronautics | Chen C.,University of Nevada, Las Vegas
Journal of Physical Chemistry C | Year: 2010

Our first-principles calculations show that the electronic properties of spin-resolved zigzag bilayer graphene nanoribbons (ZBGNRs) of antiferromagnetic edges are highly sensitive to the interlayer distance between nanoribbons. The energy gap of the antiferromagnetic ZBGNR decreases and the semiconducting ZBGNR finally becomes a metal with decreasing interlayer spacing. Coupling with a transverse electric field, the ZBGNR exhibits a semiconducting to half-metallic to metallic transition via interlayer distance compression. The charge redistribution of spin-up and spin-down and the change of the density of states on the edge atoms, which are driven by the coupled effect of nanomechanical compression and the electric field, contribute to the exceptional modification on the band structure of the ZBGNR. © 2010 American Chemical Society.


Xu K.,Nanjing University of Aeronautics and Astronautics | Ch. Das K.,University of Suwon
Match | Year: 2012

For a (molecular) graph G with vertex set V(G) and edge set E(G), the first Zagreb index of G is defined as M1(G) = Σ∈V(G) dG(ε)2 where dG(ε) is the degree of vertex ε in G. The alternative expression for M1(G) is Σε∈E(G)(dG(u)+dG(ε)). Very recently, Eliasi, Iranmanesh and Gutman [7] introduced a new graphical invariant Π1(G) = Πu∈E(G)(dG(u) + dG (ε)) as the multiplicative version of M1. Here we call this new index the multiplicative sum Zagreb index. We characterize the trees, unicylcic, and bicyclic graphs extremal (maximal and minimal) with respect to the multiplicative sum Zagreb index. Moreover, we use a method different but shorter than that in [7] for determining the minimal multiplicative sum Zagreb index of trees.


Zhang H.,Nanjing University of Aeronautics and Astronautics | Zhang H.,Zhangzhou Normal University | Pan S.,Nanjing University of Aeronautics and Astronautics
IEEE Microwave and Wireless Components Letters | Year: 2013

A novel microwave frequency measurement scheme based on a dual-parallel Mach-Zehnder modulator (DPMZM) is proposed and demonstrated. By simply adjusting the bias voltage of the DPMZM, the measurement range can be divided into several parts and each part has very high resolution. Thus, the system can be used in a two-stage instantaneous frequency measurement scheme, in which the first stage coarsely determines the frequency band of the intercepted microwave signal, and then the proposed scheme measures the frequency with high resolution. An experiment is performed. Instantaneous frequency measurement with a frequency measurement range of 2.3-18.7 GHz and a measurement resolution of ±0.20 GHz is achieved. © 2001-2012 IEEE.


Wang J.,Southwest Jiaotong University | Bao B.,Changzhou University | Xu J.,Southwest Jiaotong University | Zhou G.,Southwest Jiaotong University | Hu W.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2013

Equivalent series resistance (ESR) of output capacitor has a significant effect on the control performance of constant on-time (COT) controlled switching dc-dc converters. In this paper, a discrete-time model of COT-controlled buck converter, with variable sampling frequency, is established. Based upon which, the dynamical effects of the ESR of output capacitor on COT-controlled buck converter are revealed and analyzed. The time-domain numerical simulations of the exact switched state equations, the bifurcation diagrams, and maximal Lyapunov exponents of the discrete-time model are obtained. These results verified by experimental circuit indicate that the ESR of output capacitor is a critical factor for COT-controlled buck converter, which can eliminate the unique pulse bursting phenomenon and shift operation mode from discontinuous conduction mode to continuous conduction mode, as well as control stability. © 2012 IEEE.


Gu R.,Nanjing University of Finance and Economics | Chen H.,Nanjing University of Aeronautics and Astronautics | Wang Y.,Nanjing University of Finance and Economics
Physica A: Statistical Mechanics and its Applications | Year: 2010

The multifractal nature of WTI and Brent crude oil markets is studied employing the multifractal detrended fluctuation analysis. We find that two crude oil markets become more and more efficient for long-term and two Gulf Wars cannot change time scale behavior of crude oil return series. Considering long-term influence caused by Gulf Wars, we find such "turning windows" in generalized Hurst exponents obtained from three periods divided by two Gulf Wars so that WTI and Brent crude oil returns possess different properties above and below the windows respectively. Comparing with the results obtained from three periods we conclude that, before the First Gulf War, international crude oil markets possessed the highest multifractality degree, small-scope fluctuations presented the strongest persistence and large-scope fluctuations presented the strongest anti-persistence. We find that, for two Gulf Wars, the first one made a greater impact on international oil markets; for two markets, Brent was more influenced by Gulf Wars. In addition, we also verified that the multifractal structures of two markets' indices are not only mainly attributed to the broad fat-tail distributions and persistence, but also affected by some other factors. © 2010 Elsevier B.V. All rights reserved.


Liu M.,Nanjing University of Aeronautics and Astronautics | Liu M.,University of North Carolina at Chapel Hill | Liu M.,Taishan University | Zhang D.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Human Brain Mapping | Year: 2015

Multi-atlas based methods have been recently used for classification of Alzheimer's disease (AD) and its prodromal stage, that is, mild cognitive impairment (MCI). Compared with traditional single-atlas based methods, multiatlas based methods adopt multiple predefined atlases and thus are less biased by a certain atlas. However, most existing multiatlas based methods simply average or concatenate the features from multiple atlases, which may ignore the potentially important diagnosis information related to the anatomical differences among different atlases. In this paper, we propose a novel view (i.e., atlas) centralized multi-atlas classification method, which can better exploit useful information in multiple feature representations from different atlases. Specifically, all brain images are registered onto multiple atlases individually, to extract feature representations in each atlas space. Then, the proposed view-centralized multi-atlas feature selection method is used to select the most discriminative features from each atlas with extra guidance from other atlases. Next, we design a support vector machine (SVM) classifier using the selected features in each atlas space. Finally, we combine multiple SVM classifiers for multiple atlases through a classifier ensemble strategy for making a final decision. We have evaluated our method on 459 subjects [including 97 AD, 117 progressive MCI (p-MCI), 117 stable MCI (s-MCI), and 128 normal controls (NC)] from the Alzheimer's Disease Neuroimaging Initiative database, and achieved an accuracy of 92.51% for AD versus NC classification and an accuracy of 78.88% for p-MCI versus s-MCI classification. These results demonstrate that the proposed method can significantly outperform the previous multi-atlas based classification methods. © 2015 Wiley Periodicals, Inc.


Hu L.,Nanjing University of Aeronautics and Astronautics | Yue Q.,Nanjing University of Aeronautics and Astronautics | Wang M.,University of Hong Kong
IEEE Transactions on Information Theory | Year: 2012

In this paper, we mainly get three results. First, let p, q be distinct primes with \gcd ((p-1)p,(q-1)q)=\gcd (p-1,q-1)=e ; we give a method to compute the linear complexity of Whiteman's generalized cyclotomic sequences of period p^{m+1}q n+1. Second, if e=4, we compute the exact linear complexity of Whiteman's generalized cyclotomic sequences. Third, if p \equiv q \equiv 5∼({\rm mod}∼8), \gcd (p-1, q-1)=4, and we fix a common primitive root g of both p and q, then 2\in H-{0}=(g), which is a subgroup of the multiplicative group Z-{pq} \ast, if and only if Whiteman's generalized cyclotomic numbers of order 4 depend on the decomposition pq=a^{2}+4b 2 with 4\vert b. © 1963-2012 IEEE.


Zhou T.,Nanjing University of Aeronautics and Astronautics | Zhou T.,University of Hong Kong | Wang Z.D.,University of Hong Kong
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We here explore Majorana fermion states in an s-wave superfluid of cold atoms in the presence of spin-orbital coupling and an additional harmonic potential. The superfluid boundary is induced by a harmonic trap. Two locally separated Majorana fermion states are revealed numerically based on the self-consistent Bogoliubov-de Gennes equations. The local density of states is calculated, through which the signatures of Majorana excitations may be indicated experimentally. © 2013 American Physical Society.


Ke C.,Nanjing University of Aeronautics and Astronautics | Huang Z.,Nanjing University of Aeronautics and Astronautics | Tang M.,Nanjing University of Finance and Economics
Knowledge-Based Systems | Year: 2013

Cloud computing have become a software paradigm, providing services dynamically according to user requirements. However, it is difficult to control personal privacy information because of the opening, virtualization, multi-tenancy and service outsourcing characters. Therefore how to protect user privacy information has become a research focus in cloud computing. Considering the service outsourcing character, we propose a privacy information description method and negotiation mechanism. Firstly, we describe privacy property with Privacy Negotiation Language (PNL) based on description logic. Secondly, we get privacy attribute sequence through pre-negotiation between user and service composer. Thirdly, though exchanging privacy disclosure assertion, we obtain privacy policy that satisfying both parties. In the end, we put forward privacy policy negotiation algorithm. Through case study we proved the feasibility and correctness of this method. © 2013 Elsevier B.V. All rights reserved.


Zhang X.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Kim H.,Korea University | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2013

Connecting converters in cascade is a basic configuration of dc distributed power systems (DPS). The impedance interaction between individually designed converters may make the cascaded system unstable. The previous presented approaches of stabilizing the cascaded systems need to modify the source and/or load converter's internal structure such as the topology and control circuit that are contradictory to the modularization characteristic of dc DPS. In this paper, an adaptive active capacitor converter (AACC) is introduced to stabilize the cascaded system. The AACC is connected in parallelwith the cascaded system's intermediate bus and only needs to detect the bus voltage without any change of the existing subsystems. Hence, it can be designed as a standard module for dc DPS. The AACC serves as an equivalent bus capacitor to reduce the output impedance of the source converter, thus avoiding the intersection with the load converter's input impedance, and as a result, the cascaded system becomes stable. The equivalent bus capacitor emulated by the AACC is adaptive according to the output power of the cascaded system, and thus, the power loss of AACC is minimized and the dynamic response of the system is better than that of the system using a passive capacitor. Furthermore, since no electrolytic capacitor is needed in the AACC, the cascaded system's lifetime is prolonged. The operation principle, control, and design consideration of the AACC are discussed in this paper, and a 480 W cascaded system comprising two phase-shifted full-bridge converters has been built and evaluated. The experimental results verify the validity of the proposed AACC. © 2012 IEEE.


Zhou W.,Nanjing University of Aeronautics and Astronautics | Dang Y.,Nanjing University of Aeronautics and Astronautics | Gu R.,Nanjing University of Finance and Economics
Physica A: Statistical Mechanics and its Applications | Year: 2013

We apply the multifractal detrending moving average (MFDMA) to investigate and compare the efficiency and multifractality of 5-min high-frequency China Securities Index 300 (CSI 300). The results show that the CSI 300 market becomes closer to weak-form efficiency after the introduction of CSI 300 future. We find that the CSI 300 is featured by multifractality and there are less complexity and risk after the CSI 300 index future was introduced. With the shuffling, surrogating and removing extreme values procedures, we unveil that extreme events and fat-distribution are the main origin of multifractality. Besides, we discuss the knotting phenomena in multifractality, and find that the scaling range and the irregular fluctuations for large scales in the F q(s) vs s plot can cause a knot. © 2012 Elsevier B.V. All rights reserved.


Jie B.,Nanjing University of Aeronautics and Astronautics | Jie B.,University of North Carolina at Chapel Hill | Zhang D.,Nanjing University of Aeronautics and Astronautics | Zhang D.,University of North Carolina at Chapel Hill | And 3 more authors.
Human Brain Mapping | Year: 2014

Recently, brain connectivity networks have been used for classification of Alzheimer's disease and mild cognitive impairment (MCI) from normal controls (NC). In typical connectivity-networks-based classification approaches, local measures of connectivity networks are first extracted from each region-of-interest as network features, which are then concatenated into a vector for subsequent feature selection and classification. However, some useful structural information of network, especially global topological information, may be lost in this type of approaches. To address this issue, in this article, we propose a connectivity-networks-based classification framework to identify accurately the MCI patients from NC. The core of the proposed method involves the use of a new graph-kernel-based approach to measure directly the topological similarity between connectivity networks. We evaluate our method on functional connectivity networks of 12 MCI and 25 NC subjects. The experimental results show that our proposed method achieves a classification accuracy of 91.9%, a sensitivity of 100.0%, a balanced accuracy of 94.0%, and an area under receiver operating characteristic curve of 0.94, demonstrating a great potential in MCI classification, based on connectivity networks. Further connectivity analysis indicates that the connectivity of the selected brain regions is different between MCI patients and NC, that is, MCI patients show reduced functional connectivity compared with NC, in line with the findings reported in the existing studies. © 2013 Wiley Periodicals, Inc.


Jie B.,Nanjing University of Aeronautics and Astronautics | Jie B.,Anhui Normal University | Zhang D.,Nanjing University of Aeronautics and Astronautics | Cheng B.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Human Brain Mapping | Year: 2015

Multimodality based methods have shown great advantages in classification of Alzheimer's disease (AD) and its prodromal stage, that is, mild cognitive impairment (MCI). Recently, multitask feature selection methods are typically used for joint selection of common features across multiple modalities. However, one disadvantage of existing multimodality based methods is that they ignore the useful data distribution information in each modality, which is essential for subsequent classification. Accordingly, in this paper we propose a manifold regularized multitask feature learning method to preserve both the intrinsic relatedness among multiple modalities of data and the data distribution information in each modality. Specifically, we denote the feature learning on each modality as a single task, and use group-sparsity regularizer to capture the intrinsic relatedness among multiple tasks (i.e., modalities) and jointly select the common features from multiple tasks. Furthermore, we introduce a new manifold-based Laplacian regularizer to preserve the data distribution information from each task. Finally, we use the multikernel support vector machine method to fuse multimodality data for eventual classification. Conversely, we also extend our method to the semisupervised setting, where only partial data are labeled. We evaluate our method using the baseline magnetic resonance imaging (MRI), fluorodeoxyglucose positron emission tomography (FDG-PET), and cerebrospinal fluid (CSF) data of subjects from AD neuroimaging initiative database. The experimental results demonstrate that our proposed method can not only achieve improved classification performance, but also help to discover the disease-related brain regions useful for disease diagnosis. © 2014 Wiley Periodicals, Inc.


Li C.,Fuzhou University | Liu S.,Nanjing University of Aeronautics and Astronautics
Computers and Industrial Engineering | Year: 2014

Supply chains in reality face a highly dynamic and uncertain environment, especially the uncertain end-customer demands and orders. Since the condition of product market changes frequently, the tasks of order management, product planning, and inventory management are complex and difficult. It is imperative for companies to develop new ways to manage the randomness and uncertainty in market demands. Based on the graphical evaluation and review technique, this paper provides a simple but integrated stochastic network mathematical model for supply chain ordering time distribution analysis. Then the ordering time analysis model is extended so that the analysis of inventory level distribution characteristics of supply chain members is allowed. Further, to investigate the effects of different end-customer demands on upstream orders and relative inventory levels, model-based sensitivity analysis algorithms for ordering fluctuations and inventory fluctuations are developed. A detailed numerical example is presented to illustrate the application of the proposed models to a multi-stage supply chain system, and the results of which shows the effectiveness and flexibility of the proposed stochastic network models and algorithms in order and inventory management. © 2014 Published by Elsevier Ltd.


Wang C.,Nanjing University of Aeronautics and Astronautics | Shu C.-W.,Brown University
Journal of Computational Physics | Year: 2010

The high-order accurate Runge-Kutta discontinuous Galerkin (RKDG) method is applied to the simulation of compressible multi-medium flow, generalizing the interface treating method given in Chertock et al. (2008) [9]. In mixed cells, where the interface is located, Riemann problems are solved to define the states on both sides of the interface. The input states to the Riemann problem are obtained by extrapolation to the cell boundary from solution polynomials in the neighbors of the mixed cell. The level set equation is solved by using a high-order accurate RKDG method for Hamilton-Jacobi equations, resulting in a unified DG solver for the coupled problem. The method is conservative if we include the states in the mixed cells, which are however not used in the updating of the numerical solution in other cells. The states in the mixed cells are plotted to better evaluate the conservation errors, manifested by overshoots/undershoots when compared with states in neighboring cells. These overshoots/undershoots in mixed cells are problem dependent and change with time. Numerical examples show that the results of our scheme compare well with other methods for one and two-dimensional problems. In particular, the algorithm can capture well complex flow features of the one-dimensional shock entropy wave interaction problem and two-dimensional shock-bubble interaction problem. © 2010 Elsevier Inc.


Chen X.,Nanjing University of Aeronautics and Astronautics | Chen X.,Xidian University | Yuen C.,Singapore University of Technology and Design | Zhang Z.,Zhejiang University
IEEE Transactions on Vehicular Technology | Year: 2014

In this paper, we consider a multiantenna system where the receiver should harvest energy from the transmitter by wireless energy transfer to support its wireless information transmission. To maximize the harvesting energy, we propose the performance of adaptive energy beamforming according to the instantaneous channel state information (CSI). To help the transmitter obtain the CSI for energy beamforming, we further propose a win-win CSI quantization feedback strategy to improve the efficiencies of both power and information transmission. The focus of this paper is on the tradeoff of wireless energy and information transfer by adjusting the transfer duration with a total duration constraint. By revealing the relationship between transmit power, transfer duration, and feedback amount, we derive two wireless energy and information transfer tradeoff schemes by maximizing an upper bound and an approximate lower bound of the average information transmission rate, respectively. Moreover, the impact of imperfect CSI at the receiver is investigated, and the corresponding wireless energy and information transfer tradeoff scheme is also given. Finally, numerical results validate the effectiveness of the proposed schemes. © 2013 IEEE.


Wang B.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Yao K.,Nanjing University of Aeronautics and Astronautics | Xu M.,Fsp Powerland Technology Inc. | Xu M.,Virginia Polytechnic Institute and State University
IEEE Transactions on Power Electronics | Year: 2010

This paper proposes a concept of electrolytic capacitor-less light-emitting diode (LED) driver, which converts the commercial ac voltage to a pulsating current with twice the line frequency driving high-brightness LEDs. As no electrolytic capacitor is used, this driver possesses the unique advantage of long lifetime to match with that of LEDs. A method of injecting the third and fifth harmonics into the input current to reduce the peak-to-average ratio of the output current is also proposed. While ensuring that the input power factor is higher than 0.9 to meet regulation standards such as ENERGY STAR, the proposed method allows the peak-to-average ratio of the output current to be reduced to 1.34 theoretically, which is beneficial for the safe operation of the LEDs. As an example, a flyback-based electrolytic capacitor-less LED driver is proposed, and its operation is analyzed. In order to inject the third and fifth harmonics into the input current, the function of the duty cycle in a half-line cycle is derived. It is then simplified to a fitting function, which can be easily implemented with the input voltage sensing. A 25 V, 0.35 A output prototype is built and tested in the laboratory, and the experimental results are presented to verify the effectiveness of the electrolytic capacitor-less LED driver and its control method. © 2010 IEEE.


Zhang L.,Nanjing University of Aeronautics and Astronautics | Wang T.,Nanjing University of Aeronautics and Astronautics | Tamura Y.,Tokyo Polytechnic University
Mechanical Systems and Signal Processing | Year: 2010

Following a brief review of the development of operational modal identification techniques, we describe a new method named frequency-spatial domain decomposition (FSDD), with theoretical background, formulation and algorithm. Three typical applications to civil engineering structures are presented to demonstrate the procedure and features of the method: a large-span stadium roof for finite-element model verification, a highway bridge for damage detection and a long-span cable-stayed bridge for structural health monitoring. © 2009 Elsevier Ltd. All rights reserved.


Yang Y.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Zhang L.,Nanjing University of Aeronautics and Astronautics | He J.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Lite-On Technology
IEEE Transactions on Power Electronics | Year: 2014

In order to achieve high-efficiency, high-power-factor, high-reliability, and low-cost, a flicker-free electrolytic capacitor-less single-phase ac/dc light emitting diode (LED) driver is investigated in this paper. This driver is composed of a power-factor-correction (PFC) converter and a bidirectional converter. The bidirectional converter is used to absorb the second harmonic component in the output current of the PFC converter, thus producing a pure dc output to drive the LEDs. The spectrum of the output capacitor voltage of the bidirectional converter is analyzed, indicating that the output capacitor voltage contains harmonic components at multiples of twice the line frequency apart from the dc component and second harmonic component. A feed-forward control scheme with a series of calculation operation is proposed to obtain the desired modulation signal, which contains the corresponding harmonic components, to ensure the bidirectional converter fully absorb the second harmonic current in the output of the PFC converter. Finally, a 33.6 W prototype is fabricated and tested in the lab, and the experiment results show that the proposed control scheme greatly reduces the ripple of the LED driving current. © 1986-2012 IEEE.


Hu H.,Nanjing University of Aeronautics and Astronautics | Fang X.,University of Central Florida | Chen F.,University of Central Florida | Shen Z.J.,University of Central Florida | Batarseh I.,University of Central Florida
IEEE Transactions on Power Electronics | Year: 2013

This paper proposed a modified LLC converter with two transformers in series, which has four operation configurations, covering the range of four times the minimum input voltage. To optimize the proposed LLC converter in an attempt to achieve good efficiency, a numericalmethod is developed based on the LLC converter's steady-state equations. In order to minimize the magnetizing current and thus minimize the conduction and core losses, an optimal objective is proposed to find themaximum magnetizing inductance. An optimization procedure and a design example are given. A 250-W 210-V output prototype with input voltage ranging from 25 to 100V is built to verify the developed numerical model and optimal design method. The dc gain obtained from experimental data agrees pretty well with that from the developed numerical model. Two conventional LLC converters are designed using fundamental harmonic approximation and the proposed optimal design, respectively, to make comparison with the proposed LLC converter and validate the proposed optimal design. Experimental results show that the proposed converter with proposed optimal design can achieve the peak efficiency up to 98%, while maintaining a very wide input voltage range. © 2012 IEEE.


Ruan X.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Tan S.-C.,Hong Kong Polytechnic University | Yang Y.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Lite-On Technology
IEEE Transactions on Power Electronics | Year: 2012

The electrolytic capacitor is the key component that limits the operating lifetime of LED drivers. If an ac-dc LED driver with power factor correction (PFC) control is allowed to output a pulsating current for driving the LEDs, the electrolytic capacitor will no longer be required. However, this pulsating current will introduce light flicker that varies at twice the power line frequency. In this paper, a configuration of flicker-free electrolytic capacitor-less single-phase ac-dc driver for LED lighting is proposed. The configuration comprises an electrolytic capacitor-less PFC converter and a bidirectional converter, which serves to absorb the ac component of the pulsating current of the PFC converter, leaving only a dc component to drive the LEDs. The output filter capacitor of the bidirectional converter is intentionally designed to have a large voltage ripple, thus its capacitance can be greatly reduced. Consequently, film capacitors can be used instead of electrolytic capacitors, leading to the realization of a flicker-free ac-dc LED driver that has a long lifetime. The proposed solution is generally applicable to all single-phase PFC converters. A prototype with 48-V, 0.7-A output is constructed and tested. Experimental results are presented to verify the effectiveness of the flick-free electrolytic capacitor-less ac-dc LED driver. © 2012 IEEE.


Fang X.,University of Central Florida | Hu H.,University of Central Florida | Hu H.,Nanjing University of Aeronautics and Astronautics | Shen Z.J.,University of Central Florida | Batarseh I.,University of Central Florida
IEEE Transactions on Power Electronics | Year: 2012

With the advantage of achieving zero voltage switching for a wide input voltage range, the LLC resonant topology has become increasingly popular for use in high power density and high-efficiency power converter applications. However, when the LLC converter is applied to wide input voltage range applications, the widely used fundamental harmonic approximation is incapable of guiding the design due to its inaccuracy. Thus an accurate LLC converter model is desired. In this paper, a generalized mode analysis is presented that provides highly accurate prediction on resonant current and voltage behavior and dc gain characteristic. Also, because operation modes are affected by load, frequency, and gain conditions, the boundaries and distribution of modes are discussed and illustrated. Based on the mode analysis, an approximation method is developed to estimate the peak gain point, which is useful in LLC design. This approximation demonstrates high accuracy within the simulation results. An experimental prototype is built to verify the analysis. © 2011 IEEE.


Liang L.,Nanjing University of Aeronautics and Astronautics | Han D.,Nanjing University of Aeronautics and Astronautics | Ma R.,Nanjing Agricultural University | Peng T.,Nanjing University of Aeronautics and Astronautics
Desalination | Year: 2013

A double-effect mechanical vapor re-compression (MVR) evaporation system for the treatment of highly concentrated inorganic salt wastewater was investigated, and its characteristics were analyzed taking ammonium sulfate wastewater as the treated solution. Mathematical models were established based on the energy and mass balance equations as well as correlations of the thermophysical properties and the heat-transfer coefficients. A parametric study was performed to observe the effects of the temperature rise in the heater, the emission concentration of the first effect, the evaporation temperature and the temperature difference between the condensing steam and the boiling solution on the power consumption and on the heat-transfer area. The results showed that the temperature rise should be in the range of 2.5 to 4. °C. The power consumption increased as the evaporation temperature decreased and reached a minimum when the first effect emission concentration was approximately 32%. The heat-transfer area decreased as the emission concentration of first effect, the evaporation temperature or the temperature difference between the condensing steam and the boiling solution increased. The model results were found to be consistent with published industrial data. Compared to the single-effect MVR system, the power consumption of double-effect MVR system was lower. Therefore, the system can be used to treat highly concentrated inorganic salt wastewater and can save energy. © 2013 Elsevier B.V.


Song J.,Nanjing University of Aeronautics and Astronautics | Song J.,Nanjing University of Science and Technology | Li J.,Nanjing University of Science and Technology | Xu J.,Shanghai Institute of Technology | And 2 more authors.
Nano Letters | Year: 2014

Low cost and high conductivity make copper (Cu) nanowire (NW) electrodes an attractive material to construct flexible and stretchable electronic skins, displays, organic light-emitting diodes (OLEDs), solar cells, and electrochromic windows. However, the vulnerabilities that Cu NW electrodes have to oxidation, bending, and stretching still present great challenges. This work demonstrates a new Cu@Cu4Ni NW conductive elastomer composite with ultrahigh stability for the first time. Cu@Cu4Ni NWs, facilely synthesized through a one-pot method, have highly crystalline alloyed shells, clear and abrupt interfaces, lengths more than 50 μm, and smooth surfaces. These virtues provide the NW-elastomer composites with a low resistance of 62.4 ohm/sq at 80% transparency, which is even better than the commercial ITO/PET flexible electrodes. In addition, the fluctuation amplitude of resistance is within 2 ohm/sq within 30 days, meaning that at ΔR/R0 = 1, the actual lifetime is estimated to be more than 1200 days. Neither the conductivity nor the performances of OLED with elastomers as conductive circuits show evident degradation during 600 cycles of bending, stretching, and twisting tests. These high-performance and extremely stable NW elastomeric electrodes could endow great chances for transparent, flexible, stretchable, and wearable electronic and optoelectronic devices. © 2014 American Chemical Society.


Yao K.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Mao X.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Lite-On Technology
IEEE Transactions on Industrial Electronics | Year: 2011

A discontinuous-current-mode (DCM) boost power factor correction (PFC) converter features zero-current turn-on for the switch, no reverse recovery in diode, and constantfrequency operation. However, the input power factor (PF) is relatively low when the duty cycle is constant in a half line cycle. This paper derives the expressions of the input current and PF of the DCM boost PFC converter, and based on that, variable-duty-cycle control is proposed so as to improve the PF to nearly unity in the whole inputvoltage range. A method of fitting the duty cycle is further proposed for simplifying the circuit implementation. Other than a higher PF, the proposed variable-duty-cycle control achieves a lower outputvoltage ripple and a higher efficiency over constant-duty-cycle control. The experimental results from a 120-W universal input prototype are presented to verify the effectiveness of the proposed method. © 2010 IEEE.


Chen X.,Nanjing University of Aeronautics and Astronautics | Yuen C.,Singapore University of Technology and Design
IEEE Transactions on Vehicular Technology | Year: 2013

In this paper, we design an efficient resource-allocation strategy for a multiuser multiple-input-multiple-output (MU-MIMO) rateless-coded cognitive radio network (CRN) with quality-of-service (QoS) provisioning. We consider a limited feedback MU-MIMO CRN, where zero-forcing beamforming (ZFBF) is performed under imperfect channel state information (CSI) at a cognitive base station to mitigate both interand intranetwork interferences. To minimize the total feedback amount while satisfying the interference constraint and QoS requirements simultaneously, we propose to adaptively adjust the transmit power, select the transmission mode, and choose the feedback codebook size according to the interference constraint, CSI, and QoS requirements. The optimization problem is shown to be an integer programming problem, and we propose a heuristic algorithm that can provide an optimal solution for most practical scenarios. Results show that our resource-allocation strategy can decide the feedback amount and transmission mode adaptively based on the delay requirements. © 2012 IEEE.


Liu Y.,Shanghai Institute of Technology | Zhang X.,Nanjing University of Aeronautics and Astronautics
Solid State Ionics | Year: 2013

A simple approach to synthesize Co3O4 in mass production by using surfactant (CTAB) and cosurfactants (C5H 12O and C8H12O) via the microemulsion treatment has been developed. By changing the reaction times, the prepared Co 3O4 was readily regulated in its morphologies varying from the chrysanthemum-like microspheres in bud to in full bloom. The sample reacted for 6 h maintains 565.5 mAh·g- 1 after 30 cycles at a current density of 60 mA·g- 1, and 495.1 mAh·g- 1 after 40 cycles at a current density of 80 mA·g- 1. Although the cycling performance at a current density of 50 mA·g- 1 started to fall off in the initial 20 cycles, the capacities were still comparable to the theoretical capacity of graphite (372 mAh·g - 1) after more than 100 cycles. The above 95% capacity retention after 20 cycles is believed to benefit from unique structural features, particularly clusters of nanofibers. The chrysanthemum-like nanostructures with larger BET specific surface area created an easier and shorter diffusion pathway for ionic and electronic diffusion, which resulted in good power performance. © 2012 Elsevier B.V.


Zeng H.,Nanjing University of Aeronautics and Astronautics | Zeng H.,CAS Hefei Institutes of Physical Science | Du X.-W.,Tianjin University | Singh S.C.,Dublin City University | And 4 more authors.
Advanced Functional Materials | Year: 2012

Laser ablation of solid targets in the liquid medium can be realized to fabricate nanostructures with various compositions (metals, alloys, oxides, carbides, hydroxides, etc.) and morphologies (nanoparticles, nanocubes, nanorods, nanocomposites, etc.). At the same time, the post laser irradiation of suspended nanomaterials can be applied to further modify their size, shape, and composition. Such fabrication and modification of nanomaterials in liquid based on laser irradiation has become a rapidly growing field. Compared to other, typically chemical, methods, laser ablation/irradiation in liquid (LAL) is a simple and "green" technique that normally operates in water or organic liquids under ambient conditions. Recently, the LAL has been elaborately developed to prepare a series of nanomaterials with special morphologies, microstructures and phases, and to achieve one-step formation of various functionalized nanostructures in the pursuit of novel properties and applications in optics, display, detection, and biological fields. The formation mechanisms and synthetic strategies based on LAL are systematically analyzed and the reported nanostructures derived from the unique characteristics of LAL are highlighted along with a review of their applications and future challenges. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Chen X.,Nanjing University of Aeronautics and Astronautics | Chen X.,China Mobile | Yuen C.,Singapore University of Technology and Design
IEEE Transactions on Signal Processing | Year: 2014

In this paper, we address the problem of interference alignment (IA) over MIMO interference channels with limited channel state information (CSI) feedback based on quantization codebooks. Due to limited feedback and, hence, imperfect IA, there are residual interferences across different links and different data streams. As a result, the performance of IA is greatly related to the CSI accuracy (namely number of feedback bits) and the number of data streams (namely transmission mode). In order to improve the performance of IA, it makes sense to optimize the system parameters according to the channel conditions. Motivated by this, we first give a quantitative performance analysis for IA under limited feedback and derive a closed-form expression for the average transmission rate in terms of feedback bits and transmission mode. By maximizing the average transmission rate, we obtain an adaptive feedback allocation scheme, as well as a dynamic mode selection scheme. Furthermore, through asymptotic analysis, we obtain several clear insights on the system performance and provide some guidelines on the system design. Finally, simulation results validate our theoretical claims and show that obvious performance gain can be obtained by adjusting feedback bits dynamically or selecting transmission mode adaptively. © 2014 IEEE.


Yang F.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Ji Q.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Lite-On Technology
IEEE Transactions on Power Electronics | Year: 2013

In this paper, the differential-mode (DM) electromagnetic interference (EMI) noise of a single-phase boost power factor correction converter operating in critical current mode was analyzed. The DM noise spectra are calculated based on the mathematical model of EMI receiver and the required corner frequencies of DM filter are obtained. It can be seen that the minimum corner frequencies are determined by the maximum noises at 150kHz. With the relation between the magnitude of the inductor current ripple and the DM noise, the characteristics of noise at 150kHz are obtained by analyzing the current ripple magnitude at 150kHz; thus, the worst conditions which have the maximum noise value are figured out. Meanwhile, the maximum noises at 150kHz for different input voltages are identical, so the DM filter can be designed based on one worst spectrum at one input voltage without testing the spectra in other conditions. © 2012 IEEE.


Wu G.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Nanjing University of Aeronautics and Astronautics | Ye Z.,Lite-On Technology
IEEE Transactions on Industrial Electronics | Year: 2015

In a photovoltaic (PV)-or fuel-cell-based grid-connected power system, a high step-up dc-dc converter is required to boost the low voltage of a PV or fuel cell to a relatively high bus voltage for the downstream dc-ac grid-connected inverter. To integrate the advantages of the high voltage gain of a switched-capacitor (SC) converter and excellent output regulation of a switching-mode dc-dc converter, a method of combining the two types of converters is proposed in this paper. The basic idea is that when the switch is turned on, the inductor is charged, and the capacitors are connected in series to supply the load, and when the switch is turned off, the inductor releases energy to charge multiple capacitors in parallel, whose voltages are controlled by a pulsewidth modulation technique. Thus, a high voltage gain of the dc-dc converter can be obtained with good regulation. Based on this principle, a series of new topologies are derived, and the operating principles and voltage gains of the proposed converters are analyzed. Finally, the design of the proposed converter is given, and the experiment results are provided to verify the theoretical analysis. © 1982-2012 IEEE.


Wu M.,University of Nebraska - Lincoln | Zhang Z.,University of Nebraska - Lincoln | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zeng X.C.,University of Nebraska - Lincoln
Applied Physics Letters | Year: 2010

Based on the first-principles calculations, we predict that strong ferromagnetism and half metallicity can be induced via charge injection in single-layer hexagonal boron nitride (BN) and BN nanoribbons. This phenomenon can be understood based on the Stoner criterion and the relationship between induced magnetic moment and charge density. Other group-III/V two-dimensional honeycomb systems such as boron phosphide (BP), aluminum nitride (AlN), and aluminum phosphide (AIP) exhibit similar ferromagnetic behavior upon charge injection. Like BN, the single-layer hexagonal AlN can be converted to a half metal at certain positive charge states. © 2010 American Institute of Physics.


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,University of Nebraska - Lincoln | Zeng X.C.,University of Nebraska - Lincoln | Guo W.,Nanjing University of Aeronautics and Astronautics
Journal of Physical Chemistry C | Year: 2011

Using ab initio calculations and quantum molecular dynamics simulations, we demonstrate that a few layers of graphene sandwiched between hexagonal boron nitride (h-BN) layers can undergo spontaneous transformation into hybrid cubic BN-diamond (c-BN/Dmd) nanofilms upon fluorination. This spontaneous transformation stems from the remarkably higher stability of thin c-BN/Dmd nanofilm with sp3 hybridization over the precursor multilayer with sp2 hybridization and is promoted by strong selectivity of fluorination with the boron atoms of the coating BN layers. Upon increasing the total number of multilayers, however, the transformation is no longer spontaneous due to emergence of the energy barrier. Nevertheless, adding more h-BN layers to the hybrid nanofilm can assist the transformation into c-BN/Dmd nanofilms upon fluorination. The electronic properties of the c-BN/Dmd nanofilms can be tuned by controlling the ratio of the BN component and film thickness, which can yield narrow-gap semiconductors for novel electronic applications. In addition, the energy gap in the nanofilms can be modulated linearly by applying external electric fields. © 2011 American Chemical Society.


Lu P.,Nanjing University of Aeronautics and Astronautics | Lu P.,University of Nebraska - Lincoln | Wu X.,CAS Hefei Key Laboratory of Materials for Energy Conversion | Wu X.,Anhui University of Science and Technology | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2012

We investigate the strain-dependent electronic and magnetic properties of two-dimensional (2D) monolayer and bilayer MoS 2, as well as 1D MoS 2 nanoribbons and nanotubes using first-principles calculations. For 2D monolayer MoS 2 subjected to isotropic or uniaxial tensile strain, the direct band gap of MoS 2 changes to an indirect gap that decreases monotonically with increasing strain; while under the compressive strain, the original direct band gap is enlarged first, followed by gap reduction when the strain is beyond -2%. The effect of isotropic strain is even stronger than that of uniaxial strain. For bilayer MoS 2 subjected to isotropic tensile strain, its indirect gap reduces monotonically to zero at strain about 6%; while under the isotropic compressive strain, its indirect gap increases first and then reduces and turns into direct gap when the strain is beyond -4%. For strained 1D metallic zigzag MoS 2 nanoribbons, the net magnetic moment increases slightly with axial strain from about -5% to 5%, but drops to zero when the compressive strain is beyond -5% or increases with a power law beyond 5%. For 1D armchair MoS 2 nanotubes, tensile or compressive axial strain reduces or enlarges the band gap linearly, and the gap can be fully closed for nanotubes with relatively small diameter or under large tensile strain. For zigzag MoS 2 nanotubes, the strain effect becomes nonlinear and the tensile strain can reduce the band gap, whereas compressive strain can initially enlarge the band gap and then decrease it. The strain induced change in projected orbitals energy of Mo and the coupling between the Mo atom d orbital and the S atom p orbital are analyzed to explain the strong strain effect on the band gap and magnetic properties. © 2012 the Owner Societies.


Wu W.,Nanjing University of Aeronautics and Astronautics | Wu W.,University of Nebraska - Lincoln | Guo W.,Nanjing University of Aeronautics and Astronautics | Zeng X.C.,University of Nebraska - Lincoln
Nanoscale | Year: 2013

Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (α, β, γ, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the α-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag α-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between π* and π subbands. Unlike α- and 6,6,12-GyNRs, both zigzag β-GyNRs and zigzag γ-GyNRs exhibit NDR behavior regardless of the symmetry. © The Royal Society of Chemistry 2013.


Ding Z.,Nanjing University of Aeronautics and Astronautics | Ding Z.,Delta Electronics Inc | Yang C.,Nanjing University of Aeronautics and Astronautics | Zhang Z.,Nanjing University of Aeronautics and Astronautics | And 3 more authors.
IEEE Transactions on Power Electronics | Year: 2014

A novel multiport isolated bidirectional dc-dc converter for hybrid battery and supercapacitor applications is presented, which can achieve zero voltage switching for all switches in the whole load range. The bidirectional power flow between any two of the ports is free, and the circulating power is low for the well matching of the transformer voltages of all time regardless of the voltage variations of the battery and supercapacitor. Moreover, the current ripples are greatly decreased by interleaved control, which is good for battery and supercapacitor. The converter topology and the operation principle are introduced. Detailed analysis on soft-switching of all switches is given. On the basis of theoretical analysis, the principle and method for parameter designing are provided. A hybrid energy management strategy combining bus voltage control and energy management of the energy storage devices is proposed and the control scheme is presented. Moreover, detailed parameter design of a prototype converter is given for a 380-V dc-bus microgrid lab system. Effectiveness of the control strategy, correctness of the analysis on soft-switching, and the parameter design methods are verified by the simulation and experimental results. © 2013 IEEE.


Liu Y.,Nanjing University of Aeronautics and Astronautics | Li Y.,Shenyang Aerospace University
Journal of Computational Information Systems | Year: 2012

Human action recognition in video has been a difficult challenge due to the diversity of different action of different actor. In this paper, distance image volume is proposed to describe actions in videos, which is combined with sparse coding method for human action recognition. Different from other approaches that use both appearance and motion features or temporal-spatial interest points for better recognition performance, our approach only uses the distance image volumes that can present the appearance and motion information of human action but with low computation. For action recognition, we propose the use of sparse coding (SC), in which dictionary is represented by distance image volumes of training action videos. Each test video is then constructed by a linear combination of the basis vectors of the dictionary. The residuals between the test video and each action class are computed for determining the identity. The experiments are conducted on publicly available data set Weizmann. The results demonstrate that distance image volume feature combined with sparse coding method helps in achieving improved performance. © 2011 by Binary Information Press.


Qiu H.,Nanjing University of Aeronautics and Astronautics | Zeng X.C.,University of Nebraska - Lincoln | Guo W.,Nanjing University of Aeronautics and Astronautics
ACS Nano | Year: 2015

Phase behavior and the associated phase transition of water within inhomogeneous nanoconfinement are investigated using molecular dynamics simulations. The nanoconfinement is constructed by a flat bottom plate and a convex top plate. At 300 K, the confined water can be viewed as a coexistence of monolayer, bilayer, and trilayer liquid domains to accommodate the inhomogeneous confinement. With increasing liquid density, the confined water with uneven layers transforms separately into two-dimensional ice crystals with unchanged layer number and rhombic in-plane symmetry for oxygen atoms. The monolayer water undergoes the transition first into a puckered ice nanoribbon, and the bilayer water transforms into a rhombic ice nanoribbon next, followed by the transition of trilayer water into a trilayer ice nanoribbon. The sequential localized liquid-to-solid transition within the inhomogeneous confinement can also be achieved by gradually decreasing the temperature at low liquid densities. These findings of phase behaviors of water under the inhomogeneous nanoconfinement not only extend the phase diagram of confined water but also have implications for realistic nanofluidic systems and microporous materials. © 2015 American Chemical Society.


O' Mahony T.,Dublin Institute of Technology | Zhou P.,Nanjing University of Aeronautics and Astronautics | Sweeney J.,National University of Ireland, Maynooth
Energy Policy | Year: 2012

Ireland recorded significant growth in energy-related carbon emissions from 1990 to 2007 as the country underwent rapid economic development. Using the LMDI decomposition analysis method, this paper aims to identify and analyse the driving forces of CO 2 emissions in eleven final energy consuming sectors. This multi-sectoral analysis is based on four economic sectors, the residential sector and gives a detailed representation of transport in keeping with UNFCCC recommendations. Scale, structure and intensity effects are explored and substantial heterogeneity in sectoral performance is observed. Scale growth in economic and transport activity was considerable. Some improvements in energy intensity were recorded in the economic sectors. In transport, increases in intensity contributed to a significant increase in emissions, while energy intensity decreased in the residential sector. The declining emissions coefficient of electricity was important in limiting emissions but renewable energy has been slow to penetrate the demand side. The results have relevance in considering development paths and can aid in identifying policy measures required to address the key driving forces of emissions in the sectors. The rapid increase in transport emissions in particular raises concerns of future lock-in to a higher emissions trajectory. © 2012 Elsevier Ltd.


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Zeng X.C.,University of Nebraska - Lincoln | Guo W.,Nanjing University of Aeronautics and Astronautics
Journal of the American Chemical Society | Year: 2011

Cubic boron nitride (c-BN) possesses a number of extreme properties rivaling or surpassing those of diamond. Especially, owing to the high chemical stability, c-BN is desired for fabricating electronic devices that can stand up to harsh environments. However, realization of c-BN-based functional devices is still a challenging task due largely to the subtlety in the preparation of high-quality c-BN films with uniform thickness and controllable properties. Here, we present a simple synthetic strategy by surface fluorination of few-layered hexagonal boron nitride (h-BN) sheets to produce thermodynamically favorable F-terminated c-BN nanofilms with an embedded N-N bond layer and strong inbuilt electric polarization. Due to these specific features, the fluorinated c-BN nanofilms have controllable band gap by thickness or inbuilt and applied electric fields. Especially, the produced nanofilms can be tuned into substantial ferromagnetism through electron doping within a reasonable level. The electron-doping-induced deformation ratio of the c-BN nanofilms is found to be 1 order of magnitude higher than those of carbon nanotubes and graphene. At sufficient high doping levels, the nanofilm can be cleaved peculiarly along the N-N bond layer into diamond-like BN films. As the proposed synthesis strategy of the fluorinated c-BN nanofilms is well within the reach of current technologies, our results represent an extremely cost-effective approach for producing high-quality c-BN nanofilms with tunable electronic, magnetic, and electromechanical properties for versatile applications. © 2011 American Chemical Society.


Zhang N.,Jiangxi University of Finance and Economics | Kong F.,Jiangxi University of Finance and Economics | Choi Y.,Inha University | Zhou P.,Nanjing University of Aeronautics and Astronautics
Energy Policy | Year: 2014

This paper examines the effect of size control policy on the energy and carbon efficiency for Chinese fossil fuel power industry. For this purpose, we propose two non-radial directional distance functions for energy/carbon efficiency analysis of fossil fuel electricity generation. One is named a total-factor directional distance function that incorporates the inefficiency of all input and output factors to measure the unified (operational and environmental) efficiency of fossil fuel power plants, and the other is called an energy-environmental directional distance function that can be used to measure the energy-environmental performance of fossil fuel electric power plants. Several standardized indicators for measuring unified efficiency and energy-environmental performance are derived from the two directional distance functions. An empirical study of 252 fossil fuel power plants in China is conducted by using the proposed approach. Our empirical results show that there exists a significant positive relationship between the plant size and unified efficiency, the five state-owned companies show lower unified efficiency and energy-environmental performance than other companies. It is suggested that Chinese government might need to consider private incentives and deregulation for its state-owned enterprises to improve their performance proactively. © 2014 Elsevier Ltd.


Zhang X.,Nanjing University of Aeronautics and Astronautics | Zhang X.,Huaihai Institute of Technology | Gong C.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Industrial Electronics | Year: 2013

Micro-dc grid is a novel power system focused on the development of renewable resources. However, two-wire transmitting power mode is generally accepted in a micro-dc grid, which is usually not suitable for the requirements of the input voltage levels of different power converters and loads. In order to meet the requirements, a half-bridge voltage balancer was introduced in a micro-dc grid, which can convert a two-wire mode into a three-wire mode in a micro-dc grid via a neutral line. However, the shoot-through problem existing in bridge-type converters degrades the reliability of the voltage balancer. In this paper, a dual-buck half-bridge voltage balancer and a control strategy are proposed, which can avoid the shoot-through problem. The small-signal model of the voltage balancer is derived for designing the control parameters and the current relationships of the inductors; the capacitors and the unbalanced loads are analyzed particularly. Finally, a prototype, which can deal with 2-kW unbalance ability, is built to verify that the proposed voltage balancer may have a good ability of balancing the voltage by building a neutral line. © 1982-2012 IEEE.


Shen L.,Nanjing University of Aeronautics and Astronautics | Yuan C.,Anhui University of Technology | Luo H.,Nanjing University of Aeronautics and Astronautics | Zhang X.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Journal of Materials Chemistry | Year: 2010

A novel approach has been developed to synthesize hierarchically porous Li4Ti5O12 microspheres assembled by well-crystalline nanoparticles. The fabrication process is very simple, involving only hydrothermal treatment of commercial anatase TiO2 powder in LiOH solution and a following calcination procedure without employing any surfactants or templates. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption/desorption analysis were used to characterize their morphologies and structures. Such Li4Ti5O12 nano/microspherical superstructures, with sizes of ca. 4 μm in diameter, exhibits rich hierarchical pores and a specific surface area of 57.5 m2 g -1. A possible growth mechanism of the nano/microspherical superstructure is further discussed. The calcination temperature has a great effect on the crystal structure and electrochemical properties of the materials. The hierarchically porous Li4Ti5O12 microspheres annealed at 700 °C have the perfect crystallization and optimal particle size, which can deliver good coulombic efficiency, ultrahigh rate capability at high rates, and excellent capacity retention over 200 cycles. © 2010 The Royal Society of Chemistry.


Zhang N.,Inha University | Zhou P.,Nanjing University of Aeronautics and Astronautics | Choi Y.,Inha University | Choi Y.,Nanjing University of Aeronautics and Astronautics
Energy Policy | Year: 2013

This paper proposes a meta-frontier non-radial directional distance function to model energy and CO2 emission performance in electricity generation. This approach allows for the consideration of the group heterogeneity of electricity generation, non-radial slacks, and undesirable outputs simultaneously. We extend several standardized indices to measure total-factor energy efficiency, CO2 emission performance, and technology gaps in electricity generation. We estimate the potential reductions in energy use and CO2 emissions under different technology assumptions. We conduct an empirical analysis of fossil fuel electricity generation in Korea by using the proposed approach. The results indicate that coal-fired power plants show higher levels of total-factor energy efficiency and CO2 emission performance than oil-fired ones. Under the meta-frontier technology assumption, coal-fired power plants show a smaller technology gap than oil-fired ones. This suggests that the Korean government should promote technological innovation to reduce technology gaps for oil-fired plants, thereby improving energy and CO2 emission performance and meeting emission reduction targets in the electricity generation industry. © 2013 Elsevier Ltd.


Qu N.S.,Nanjing University of Aeronautics and Astronautics | Qu N.S.,Jiangsu Key Laboratory of Accuracy and Micro Manufacturing Technology | Xu Z.Y.,Nanjing University of Aeronautics and Astronautics
International Journal of Advanced Manufacturing Technology | Year: 2013

Electrochemical machining (ECM) is well-established in certain areas, such as the aerospace, defence, and medical industries for machining complex parts. ECM is an effective way to produce compression blades. However, with advances in the development of aero engines, the accuracy of blades becomes higher and their shapes have also become more complex. Thus, considerable attention has been devoted to improving the machining accuracy of blades by ECM. In blades machined by ECM, the angle between the cathode feeding directions and the normal of the anode profile greatly affects the accuracy of the ECM process, and it is determined by the angle combination of the anode installation and the cathodes feeding direction. It is very important to determine the best angle combinations that could minimise the angle between the cathode feeding directions and the normal of the anode profile. The present paper focuses on the optimization method of the angle combinations of the cathode feeding directions and anode installation. A theoretical model describing the optimization method of the cathode feeding directions and position of the anode was developed, and the experimental investigations were conducted in order to evaluate the rationality of the optimization method. The results show that with the optimized combination of the cathode feeding directions and position of the anode, the maximum angle between the cathodes feeding directions and the normal of the anode profile is minimised and the inter-electrode gap between the cathode and anode is more uniform. Thus, the machining accuracy could be clearly improved and the maximum errors of the convex part and concave part were only 0.054 and 0.047 mm, respectively. © 2013 Springer-Verlag London.


Cai J.,Nanjing University of Aeronautics and Astronautics | Shi L.,PLA University of Science and Technology | Yuan S.,Nanjing University of Aeronautics and Astronautics | Shao Z.,PLA University of Science and Technology
Smart Materials and Structures | Year: 2011

Lamb waves are widely used in structural health monitoring (SHM) of plate-like structures. Due to the dispersion effect, Lamb wavepackets will be elongated and the resolution for damage identification will be strongly affected. This effect can be automatically compensated by the time reversal process (TRP). However, the time information of the compensated waves is also removed at the same time. To improve the spatial resolution of Lamb wave detection, virtual time reversal (VTR) is presented in this paper. In VTR, a changing-element excitation and reception mechanism (CERM) rather than the traditional fixed excitation and reception mechanism (FERM) is adopted for time information conservation. Furthermore, the complicated TRP procedure is replaced by simple signal operations which can make savings in the hardware cost for recording and generating the time-reversed Lamb waves. After the effects of VTR for dispersive damage scattered signals are theoretically analyzed, the realization of VTR involving the acquisition of the transfer functions of damage detecting paths under step pulse excitation is discussed. Then, a VTR-based imaging method is developed to improve the spatial resolution of the delay-and-sum imaging with a sparse piezoelectric (PZT) wafer array. Experimental validation indicates that the damage scattered wavepackets of A 0 mode in an aluminum plate are partly recompressed and focalized with their time information preserved by VTR. Both the single damage and the dual adjacent damages in the plate can be clearly displayed with high spatial resolution by the proposed VTR-based imaging method. © 2011 IOP Publishing Ltd.


Choi Y.,Inha University | Zhang N.,Inha University | Zhou P.,Nanjing University of Aeronautics and Astronautics
Applied Energy | Year: 2012

This paper uses nonparametric efficiency analysis technique to estimate the energy efficiency, potential emission reductions and marginal abatement costs of energy-related CO2 emissions in China. We employ a non-radial slacks-based data envelopment analysis (DEA) model for estimating the potential reductions and efficiency of CO2 emissions for China. The dual model of the slacks-based DEA model is then used to estimate the marginal abatement costs of CO2 emissions. An empirical study based on China's panel data (2001-2010) is carried out and some policy implications are also discussed. © 2012 Elsevier Ltd.


Wang X.-L.,Nanjing University of Aeronautics and Astronautics | Zhong Q.-C.,Loughborough University | Deng Z.-Q.,Nanjing University of Aeronautics and Astronautics | Yue S.-Z.,Nanjing University of Aeronautics and Astronautics | Yue S.-Z.,Shanghai Aerospace Sharp Electrical Technologies Company
IEEE Transactions on Industrial Electronics | Year: 2012

The fault-tolerant control of bearingless motors is vital for their safe and robust operation. In this paper, the operation of current-controlled multiphase slice permanent-magnet bearingless motors (PMBMs) with different open-circuited faulty phases is analyzed, and their fault-tolerant controllability in the general case is investigated. As an example, the feasibility of fault-tolerant control with arbitrary single, double, or triple open-circuited faulty phase(s) for a six-phase slice PMBM is discussed in detail. Simulation results from finite-element analysis are presented to demonstrate the operation of the motor under the proposed fault-tolerant control strategy. Moreover, experimental results are also provided to further verify the theoretical development. © 2006 IEEE.


Wang Z.H.,PLA University of Science and Technology | Du M.L.,Nanjing University of Aeronautics and Astronautics
Shock and Vibration | Year: 2011

Fractional-order derivative has been shown an adequate tool to the study of so-called "anomalous" social and physical behaviors, in reflecting their non-local, frequency- and history-dependent properties, and it has been used to model practical systems in engineering successfully, including the famous Bagley-Torvik equation modeling forced motion of a rigid plate immersed in Newtonian fluid. The solutions of the initial value problems of linear fractional differential equations are usually expressed in terms of Mittag-Leffler functions or some other kind of power series. Such forms of solutions are not good for engineers not only in understanding the solutions but also in investigation. This paper proves that for the linear SDOF oscillator with a damping described by fractional-order derivative whose order is between 1 and 2, the solution of its initial value problem free of external excitation consists of two parts, the first one is the 'eigenfunction expansion' that is similar to the case without fractional-order derivative, and the second one is a definite integral that is independent of the eigenvalues (or characteristic roots). The integral disappears in the classical linear oscillator and it can be neglected from the solution when stationary solution is addressed. Moreover, the response of the fractionally damped oscillator under harmonic excitation is calculated in a similar way, and it is found that the fractional damping with order between 1 and 2 can be used to produce oscillation with large amplitude as well as to suppress oscillation, depending on the ratio of the excitation frequency and the natural frequency. © 2011 IOS Press and the authors. All rights reserved.


Chen X.,Nanjing University of Aeronautics and Astronautics | Chen X.,China Mobile | Yin R.,Zhejiang University
IEEE Wireless Communications Letters | Year: 2013

Channel state information (CSI) at the transmitter is of importance to the performance of physical layer security based on multi-antenna networks. Specifically, CSI is not only beneficial to improve the capacity of the legitimate channel, but also can be used to degrade the performance of the eavesdropper channel. Thus, the secrecy rate increases accordingly. This letter focuses on the quantitative analysis of the ergodic secrecy sum-rate in terms of feedback amount of the CSI from the legitimate users in multiuser multi-antenna downlink networks. Furthermore, the asymptotic characteristics of the ergodic secrecy sum-rate in two extreme cases is investigated in some detail. Finally, our theoretical claims are confirmed by the numerical results. © 2013 IEEE.


Du M.,PLA University of Science and Technology | Wang Z.,PLA University of Science and Technology | Wang Z.,Nanjing University of Aeronautics and Astronautics | Hu H.,Nanjing University of Aeronautics and Astronautics
Scientific Reports | Year: 2013

Fractional derivative has a history as long as that of classical calculus, but it is much less popular than it should be. What is the physical meaning of fractional derivative? This is still an open problem. In modeling various memory phenomena, we observe that a memory process usually consists of two stages. One is short with permanent retention, and the other is governed by a simple model of fractional derivative. With the numerical least square method, we show that the fractional model perfectly fits the test data of memory phenomena in different disciplines, not only in mechanics, but also in biology and psychology. Based on this model, we find that a physical meaning of the fractional order is an index of memory.


Wang S.S.,Nanjing University of Aeronautics and Astronautics | Zhou D.Q.,Nanjing University of Aeronautics and Astronautics | Zhou P.,Nanjing University of Aeronautics and Astronautics | Wang Q.W.,Nanjing University of Aeronautics and Astronautics | Wang Q.W.,Soochow University of China
Energy Policy | Year: 2011

This paper examines the causal relationships between carbon dioxide emissions, energy consumption and real economic output using panel cointegration and panel vector error correction modeling techniques based on the panel data for 28 provinces in China over the period 1995-2007. Our empirical results show that CO2 emissions, energy consumption and economic growth have appeared to be cointegrated. Moreover, there exists bidirectional causality between CO2 emissions and energy consumption, and also between energy consumption and economic growth. It has also been found that energy consumption and economic growth are the long-run causes for CO2 emissions and CO2 emissions and economic growth are the long-run causes for energy consumption. The results indicate that China's CO2 emissions will not decrease in a long period of time and reducing CO2 emissions may handicap China's economic growth to some degree. Some policy implications of the empirical results have finally been proposed. © 2011 Elsevier Ltd.


Tang Z.,Nanjing University of Aeronautics and Astronautics | Zhang T.,Nanjing University of Aeronautics and Astronautics | Zhang T.,Nanjing University | Zhang F.,Nanjing University of Aeronautics and Astronautics | Pan S.,Nanjing University of Aeronautics and Astronautics
Optics Letters | Year: 2013

A compact scheme for photonic generation of a phase-coded microwave signal using a dual-drive Mach-Zehnder modulator (DMZM) is proposed and experimentally demonstrated. In the proposed scheme, the radio frequency (RF) carrier and the coding signal are sent to the two RF ports of the DMZM, respectively. By properly setting the amplitude of the coding signal and the bias voltage of the DMZM, an exact p-phase-shift phase-coded microwave signal is generated. The proposed scheme has a simple structure since only a single DMZM is required. In addition, good frequency tunability is achieved because no frequency-dependent electrical devices or wavelength-dependent optical devices are applied. The feasibility of the proposed scheme is verified by experiment. 2 or 2.5 Gb/s phasecoded 10 and 20 GHz microwave signals are successfully generated. © 2013 Optical Society of America.


Zhao Y.-P.,Nanjing University of Science and Technology | Sun J.-G.,Nanjing University of Aeronautics and Astronautics
Expert Systems with Applications | Year: 2011

In many real life realms, many unknown systems own different data trends in different regions, i.e.; some parts are steep variations while other parts are smooth variations. If we utilize the conventional kernel learning algorithm, viz. the single kernel linear programming support vector regression, to identify these systems, the identification results are usually not very good. Hence, we exploit the nonlinear mappings induced from the kernel functions as the admissible functions to construct a novel multikernel semiparametric predictor, called as MSLP-SVR, to improve the regression effectiveness. The experimental results on the synthetic and the real-world data sets corroborate the efficacy and validity of our proposed MSLP-SVR. Meantime, compared with other multikernel linear programming support vector algorithm, ours also takes advantages. In addition, although the MSLP-SVR is proposed in the regression domain, it can also be extended to classification problems. © 2010 Elsevier Ltd. All rights reserved.


Xuan Y.,Nanjing University of Aeronautics and Astronautics | Xuan Y.,Nanjing University of Science and Technology | Duan H.,Nanjing University of Science and Technology | Li Q.,Nanjing University of Science and Technology
RSC Advances | Year: 2014

Combined with the solar irradiation spectrum, the optical properties of both TiO2/Ag composite nanoparticles and water-based nanofluids composed of different nanoparticles are studied. The solar energy absorption features are compared among these nanofluids based on TiO2, Ag and TiO2/Ag composite nanoparticles. Due to the localized surface plasmon resonance (LSPR) effect excited on the Ag surface, the optical absorption of TiO2/Ag plasmonic nanofluid is remarkably enhanced. The enhanced absorption by LSPR excitation is introduced in solar thermal conversion. The photothermal experiments of different nanofluids conducted under the same conditions reveal that TiO2/Ag plasmonic nanofluid exhibits a higher temperature compared with that of TiO2 based nanofluid. Although the temperatures of Ag nanofluid and TiO2/Ag nanofluid are the same, the cost of TiO2/Ag based nanofluid is much lower. The effect of nanoparticle concentration on the photothermal performance of TiO2/Ag plasmonic nanofluid is also studied in this paper. This journal is © the Partner Organisations 2014.


Yang H.,Nanjing University of Aeronautics and Astronautics | Staroswiecki M.,Ecole Normale Superieure de Cachan | Jiang B.,Nanjing University of Aeronautics and Astronautics | Liu J.,Nanjing University of Aeronautics and Astronautics
Systems and Control Letters | Year: 2011

This paper studies the target aggregation problem for a class of nonlinear multi-agent systems with the time varying interconnection topology. The general neighboring rule-based linear cooperative protocol is developed and a sufficient aggregation condition is derived. Moreover, it is shown that in the presence of agent faults, the target point is still reached by adjusting some weights of the cooperative protocol without changing the structure of the topology. An unmanned aerial vehicle team example illustrates the efficiency of the proposed approach. © 2011 Elsevier B.V. All rights reserved.


Zhang Y.,Nanjing University of Aeronautics and Astronautics | Zhang Y.,Soochow University of China | Ruan X.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2014

By adopting the concept of virtual quadrature source (VQS), a novel method for power transmission control-ac-ac converter with controllable phase and amplitude (ACCPA) was proposed, which has two control variables and is able to continuously regulate the phase and the amplitude of its output voltage independently. The operation principle was studied in detail, and the relationship with the optimization of control parameters of ACCPA's two duty ratios was analyzed for regulating the phase and amplitude of its output voltage. The phase is regulated in the front part, and the amplitude is regulated in the back part. For phase regulation, two methods were proposed to select optimal control parameters dynamically. The curves followed by two methods are crossed at the reference phase angle and have the same initial control parameters. It is necessary to adjust two independent control parameters for method 1 and one parameter for method 2. So method 2 is simple, easy to implement and has high control stability in comparison with method 1. The control strategy of ACCPA was presented and a prototype of single-phase ACCPA was manufactured. The experimental results verified the correctness of the theory and the feasibility of the control strategy. © 2014 IEEE.


Jin C.,Nanjing University of Aeronautics and Astronautics | Jin C.,Nantong University | Wang X.,Nanjing University of Aeronautics and Astronautics
Composite Structures | Year: 2015

Based on the classical beam theory (CBT) and differential quadrature (DQ) rule, an N-node novel weak form quadrature functionally graded (FG) beam element is established. Both Young's modulus and mass density of the beam materials vary exponentially through the thickness. The element node points can be different from the integration points. Either Gauss-Lobatto-Legendre (GLL) quadrature or Gauss quadrature can be used to obtain the element stiffness matrix and mass matrix. Detailed formulations are given. Convergence study is performed. For verification, results are compared with available solutions in literature. It is shown that the proposed thin beam element can yield very accurate frequencies with relatively small number of nodal points. New accurate results are presented for functionally graded beams with nine different boundary conditions. The tabulated results will be a reference with which other researchers can compare their results during developing new numerical method. © 2015 Elsevier Ltd.


Liu C.,University of Texas at Arlington | Chen L.,University of Texas at Arlington | Chen L.,Nanjing University of Aeronautics and Astronautics
Computers and Fluids | Year: 2011

A new DNS using compact high order scheme and MPI parallel computation has been conducted with 1920 × 241 × 128 grid points for non-linear stages of flow transition. The coherent vortex structure of the late flow transition stages and the mechanism of formation of single vortex ring, multiple vortex rings, and small length scales are discussed. The ring-like vortex formation from the Λ-vortex is the result of the interaction of two pairs of counter-rotating primary and secondary streamwise vortices. The formation of the multiple ring structure follows the first Helmholtz vortex conservation law. A bridge must be formed to link two Λ-vortex legs. The bridge finally develops as a new ring. This process keeps going onto form a multiple ring structure. The U-shaped vortices are part of existing coherent large vortex structure. Actually, the U-shaped vortex, which is a third level vortex, serves as a second neck to supply vorticity to the multiple rings. The multiple ring-like vortex structure is found quite stable and can travel for a long distance. The " hairpin vortex breakdown" does not happen. The small vortices can be found on the bottom of the boundary layer near the wall surface. It is believed that the small vortices are generated by the interaction of higher level vortices with the solid wall, but not by the " vortex breakdown" © 2010 Elsevier Ltd.


Zheng J.,Nanjing University of Aeronautics and Astronautics | Lv H.,Nanjing University of Aeronautics and Astronautics | Lin X.,Nanjing University of Aeronautics and Astronautics | Ji G.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Journal of Alloys and Compounds | Year: 2014

Fe3O4/graphene nanosheet (Fe3O 4/GNS) composites were prepared from acetylacetone iron (III) and graphene oxide (GO) with ethylene glycol (EG) as the solvent and reducing agent. The SEM and TEM images show that the Fe3O4 nanoparticles with relatively uniform size are well-distributed on the surface of graphene nanosheet. The structure guiding agents have a great influence on the size and surface property of Fe3O4 particles by control the nucleation and growth of Fe3O4. The effect of GNS in the composites was also discussed by regulation the mass ratio of acetylacetone iron (III) and GO. The optimal Fe3O4/GNS composites have significantly enhanced dielectric properties when compared with pure Fe 3O4. Especially, it can be found that the calculated minimum RL for Fe3O4/GNS composites with a thickness of 1.5 mm is -8.75 dB at 8.11 GHz, the microwave absorption values less than -5 dB is in the ranges of 7.78-10.36 GHz, moreover, it can be modulated by tuning the mass ratio of Fe3O4 and GO. Therefore, the composites with the thin, light-weighted and broadband absorbing properties probably have a huge potential for electromagnetic wave absorption applications. © 2013 Elsevier B.V.


Zhang H.,Nanjing University of Aeronautics and Astronautics | Zhang H.,Nanjing University | Pan S.,Nanjing University of Aeronautics and Astronautics | Huang M.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Optics Letters | Year: 2012

A novel integrable modulator consisting of a polarization modulator and a polarizer is proposed for constructing a high-performance analog photonic link. By adjusting a polarization controller placed before the modulator, both amplitude modulation and phase modulation with adjustable ratio between them are implemented. This feature is used to shift the peak of the frequency response of a dispersive link to any desired frequency, so the dispersion- induced power fading around the frequency is compensated. A proof-of-concept experiment is performed. The compensation of the dispersion-induced power fading in the proposed analog photonic link increases the spur-free dynamic range as large as 12.5 dB. © 2012 Optical Society of America.


Zhou Y.,Nanjing University of Science and Technology | Li Y.,Nanjing University of Aeronautics and Astronautics | Wang W.,Nanjing University of Aeronautics and Astronautics
Robotics and Computer-Integrated Manufacturing | Year: 2011

In fixture design for the manufacturing of aircraft structural parts, there are various challenges and serious problems in industry, such as difficulty in design knowledge capture and reuse, and the arbitrary or non-standard nature of design, which influence the efficiency and quality of fixture design. This paper proposes a feature-based fixture design methodology in which previous fixture design cases and design rules are described in association with features and thus the design knowledge is integrated with geometric information of aircraft structural parts, which are the main concern of this project. In this methodology, machining features of the structural parts and their associated attributes are identified by feature recognition technique from the 3 dimensional (3D) part models defined based on model-based definition (MBD) technique. The feature-based part information models are then established and are used to retrieve previous fixture design cases and design rules stored in the knowledge base. Fixture designers will choose the appropriate retrieved design cases as the starting point for new fixture design or use previous designs to assess his/her current design. In this way the process of new fixture design can be improved. In the current stage of the research, a prototype feature-based fixture design system based on CATIA for the manufacturing of aircraft structural parts has been developed and used by a large airplane manufacturer. © 2011 Elsevier Ltd. All rights reserved.


Zhu J.,Nanjing University of Aeronautics and Astronautics | Qiu J.,Nanjing University
Journal of Computational Physics | Year: 2011

The local discontinuous Galerkin (LDG) method is a spatial discretization procedure for convection-diffusion equations, which employs useful features from high resolution finite volume schemes, such as the exact or approximate Riemann solvers serving as numerical fluxes and limiters, which is termed as Runge-Kutta LDG (RKLDG) when TVD Runge-Kutta method is applied for time discretization. It has the advantage of flexibility in handling complicated geometry, h-p adaptivity, and efficiency of parallel implementation and has been used successfully in many applications. However, the limiters used to control spurious oscillations in the presence of strong shocks are less robust than the strategies of essentially non-oscillatory (ENO) and weighted ENO (WENO) finite volume and finite difference methods. In this paper, we investigated RKLDG methods with WENO and Hermite WENO (HWENO) limiters for solving convection-diffusion equations on unstructured meshes, with the goal of obtaining a robust and high order limiting procedure to simultaneously obtain uniform high order accuracy and sharp, non-oscillatory shock transition. Numerical results are provided to illustrate the behavior of these procedures. © 2010 Elsevier Inc.


Shen L.,Nanjing University of Aeronautics and Astronautics | Shen L.,University of Washington | Zhang X.,Nanjing University of Aeronautics and Astronautics | Li H.,Nanjing University of Aeronautics and Astronautics | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2011

Nanocrystalline TiO 2 grown on conducting graphene nanosheets (GNS) and multiwalled carbon nanotubes (CNTs) via a solution-based method to form a threedimensional (3D) hierarchical structure for fast lithium storage. CNTs in the unique hybrid nanostructure not only prevent the restacking of GNS to increase the basal spacing between graphene sheets but also provides an additional electron-transport path besides the graphene layer underneath of TiO 2 nanomaterials, increasing the electrolyte/electrode contact area and facilitating transportation of the electrolyte ion and electron into the inner region of the electrode. Such a 3D TiO 2-GNS-CNT nanocomposite had a large specific surface area of 291.2 m 2 g -1 and exhibited ultrahigh rate capability and good cycling properties at high rates. © 2011 American Chemical Society.


Wang Y.,Nanjing University of Aeronautics and Astronautics | Chen S.,Nanjing University of Aeronautics and Astronautics | Zhou Z.-H.,Nanjing University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2012

The cluster assumption, which assumes that 'similar instances should share the same label,' is a basic assumption in semi-supervised classification learning, and has been found very useful in many successful semi-supervised classification methods. It is rarely noticed that when the cluster assumption is adopted, there is an implicit assumption that every instance should have a crisp class label assignment. In real applications, however, there are cases where it is difficult to tell that an instance definitely belongs to one class and does not belong to other neighboring classes. In such cases, it is more adequate to assume that 'similar instances should share similar label memberships' rather than sharing a crisp label assignment. Here 'label memberships' can be represented as a vector, where each element corresponds to a class, and the value at the element expresses the likelihood of the concerned instance belonging to the class. By adopting this modified cluster assumption, in this paper we propose a new semi-supervised classification method, that is, semi-supervised classification based on class membership (SSCCM). Specifically, we try to solve the decision function and adequate label memberships for instances simultaneously, and constrain that an instance and its 'local weighted mean' (LWM) share the same label membership vector, where the LWM is a robust image of the instance, constructed by calculating the weighted mean of its neighboring instances. We formulate the problem in a unified objective function for the labeled, unlabeled data and their LWMs based on the square loss function, and take an alternating iterative strategy to solve it, in which each step generates a closed-form solution, and the convergence is guaranteed. The solution will provide both the decision function and the label membership function for classification, their classification results can verify each other, and the reliability of semi-supervised classification learning might be enhanced by checking the consistency between those two predictions. Experiments show that SSCCM obtains encouraging results compared to state-of-the-art semi-supervised classification methods. © 2012 IEEE.


Shen L.,Nanjing University of Aeronautics and Astronautics | Shen L.,University of Washington | Uchaker E.,University of Washington | Zhang X.,Nanjing University of Aeronautics and Astronautics | Cao G.,University of Washington
Advanced Materials | Year: 2012

Self-supported Li4Ti5O12 nanowire arrays with high conductivity architectures are designed and fabricated for application in a Li-ion battery. The Li4Ti5O12 nanowire arrays grow directly on Ti foil by a facile solution-based method, further enhancing Li-ion storage properties by creating Ti3+ sites through hydrogenation. This configuration ensures that every Li4Ti 5O12 nanowire participates in the fast electrochemical reaction, enabling remarkable rate performance and a long cycle life. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yang B.,Nanjing University of Aeronautics and Astronautics | Yang B.,Tonghua Normal University | Chen S.,Nanjing University of Aeronautics and Astronautics
Neurocomputing | Year: 2010

Graph construction plays a key role on learning algorithms based on graph Laplacian. However, the traditional graph construction approaches of -neighborhood and k-nearest-neighbor need to predefine the same neighbor parameter (or k) for all samples, which usually suffers from the difficulty of parameter selection and generally fail to effectively fit intrinsic structures of data. To mitigate these limitations to a certain extent, in this paper we present a novel and sample-dependent approach of graph construction, and name the so-constructed graph as Sample-dependent Graph (SG). Specifically, instead of predefining the same neighbor parameter for all samples, the SG depends on samples in question to determine neighbors of each sample and similarities between sample pairs. As a result, it not only avoids the intractability and high expense of neighbor parameter selection but also can more effectively fit the intrinsic structures of data. Further, in order to show the effectiveness of the SG, we apply it to the dimensionality reduction based on graph embedding, and incorporate it into the state-of-the-art off-the-shelf unsupervised locality preserving projection (LPP) to develop the sample-dependent LPP (SLPP). SLPP naturally inherits the merits of SG and maintains the attractive properties of the traditional LPP. The experiments on the toy and benchmark (UCI, face recognition, object category and handwritten digits recognition) datasets show the effectiveness and feasibility of the SG and SLPP with promising results. © 2010 Elsevier B.V.


Shen L.,Nanjing University of Aeronautics and Astronautics | Ding B.,Nanjing University of Aeronautics and Astronautics | Nie P.,Nanjing University of Aeronautics and Astronautics | Cao G.,University of Washington | Zhang X.,Nanjing University of Aeronautics and Astronautics
Advanced Energy Materials | Year: 2013

Current battery technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Li+ in intercalation electrodes materials. Not only the use of nanostructure materials but also the design of electrode architectures can lead to more advanced properties. Here, advanced electrode architectures consisting of carbon textiles conformally covered by Li4Ti5O12 nanocrystal are rationally designed and synthesized for lithium ion batteries. The efficient two-step synthesis involves the growth of ultrathin TiO2 nanosheets on carbon textiles, and subsequent conversion into spinel Li4Ti 5O12 through chemical lithiation. Importantly, this novel approach is simple and general, and it is used to successfully produce LiMn 2O4/carbon composites textiles, one of the leading cathode materials for lithium ion batteries. The resulting 3D textile electrode, with various advantages including the direct electronic pathway to current collector, the easy access of electrolyte ions, the reduced Li+/e- diffusion length, delivers excellent rate capability and good cyclic stability over the Li-ion batteries of conventional configurations. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Da Y.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Aeronautics and Astronautics
Optics Express | Year: 2013

Nanostructured light trapping is a promising way to improve the efficiency in thin-film solar cells recently. In this work, both the optical and electrical properties of thin-film solar cells with 1D periodic grating structure are investigated by using photoelectric coupling model. It is found that surface recombination plays a key role in determining the performance of nanostructured thin-film solar cells. Once the recombination effect is considered, the higher optical absorption does not mean the higher conversion efficiency as most existing publications claimed. Both the surface recombination velocity and geometric parameters of structure have great impact on the efficiency of thin-film solar cells. Our simulation results indicate that nanostructured light trapping will not only improve optical absorption but also boost the surface recombination simultaneously. Therefore, we must get the tradeoffs between optical absorption and surface recombination to obtain the maximum conversion efficiency. Our work makes it clear that both the optical absorption and electrical recombination response should be taken into account simultaneously in designing the nanostructured thin-film solar cells. ©2013 Optical Society of America.


Duan H.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Aeronautics and Astronautics
Solar Energy Materials and Solar Cells | Year: 2014

The Ag/CdS core/shell nanoparticles are synthesized by a facile method. The synthesis steps are simple and easy to be manipulated. The core/shell nanostructures are characterized by the transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-vis spectrometry techniques. Compared with bare Ag and CdS nanoparticles, the optical absorption of Ag/CdS composite nanostructures is greatly enhanced in a wide range of visible light. It can also be demonstrated in the simulations based on DDA method. The enhanced absorption of light is mainly due to the localized surface plasmon resonance (LSPR) effect excited on silver core. The optical response of such core/shell nanostructures is extended to longer wavelengths. © 2013 Elsevier B.V. All rights reserved.


Yang L.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Science and Technology | Xuan Y.,Nanjing University of Aeronautics and Astronautics | Tan J.,Nanjing University of Science and Technology
Optics Express | Year: 2011

In order to improve the optical absorption of hydrogenated amorphous silicon (a-Si:H) thin film solar cells, a new structure consisted of ITO layer with the nonresonant nanoparticles embedded in it and a-Si:H layer, is proposed. By optimizing both the thickness of a-Si:H layer and nanoparticles size, the effects of Fabry-Perot resonance and the scattering of incident light are discussed and analyzed. It is demonstrated that the enhanced optical absorption can be achieved due to the coupling of incident light and nanostructure, simultaneously the proposed structure can be considered as gradient refractive index structure to restrain the reflection at the interface of ITO and a-Si:H thin film. © 2011 Optical Society of America.


Wang X.,Nanjing University of Aeronautics and Astronautics | Wang X.,Nanjing University | Yan X.,Nanjing University of Aeronautics and Astronautics | Yan X.,Nanjing University
Optics Letters | Year: 2011

A synergistic effect between UV down-conversion and IR up-conversion is witnessed in YbF3:Er3+ phosphors by employing the dual wavelength (369nm and 980nm) excitation source. The synergistic effect originates from an abnormal energy transfer between Er34+ ions, in which the Er34+ ions in metastable states excited by 369 nm photons are excited again by the 980nmIR photons. The dual wavelength excited red emission intensity is 1.1 times the total red emission intensities from 369 nm and 980 nm single excitation. The synergistic effect refers us to a way to convert both high-energy and low-energy photons into one middle-energy photon with high quantum yield. © 2011 Optical Society of America.


Shen L.,Nanjing University of Aeronautics and Astronautics | Shen L.,University of Washington | Li H.,Nanjing University of Aeronautics and Astronautics | Uchaker E.,University of Washington | And 2 more authors.
Nano Letters | Year: 2012

Because of its extreme safety and outstanding cycle life, Li 4Ti5O12 has been regarded as one of the most promising anode materials for next-generation high-power lithium-ion batteries. Nevertheless, Li4Ti5O12 suffers from poor electronic conductivity. Here, we develop a novel strategy for the fabrication of Li4Ti5O12/carbon core-shell electrodes using metal oxyacetyl acetonate as titania and single-source carbon. Importantly, this novel approach is simple and general, with which we have successfully produce nanosized particles of an olivine-type LiMPO4 (M = Fe, Mn, and Co) core with a uniform carbon shell, one of the leading cathode materials for lithium-ion batteries. Metal acetylacetonates first decompose with carbon coating the particles, which is followed by a solid state reaction in the limited reaction area inside the carbon shell to produce the LTO/C (LMPO 4/C) core-shell nanostructure. The optimum design of the core-shell nanostructures permits fast kinetics for both transported Li+ ions and electrons, enabling high-power performance. © 2012 American Chemical Society.


Yang H.,Nanjing University of Aeronautics and Astronautics | Jiang B.,Nanjing University of Aeronautics and Astronautics | Staroswiecki M.,Ecole Normale Superieure de Cachan
International Journal of Systems Science | Year: 2012

This article provides an approach to evaluate the fault recoverability of switched systems (SS) under given energetic constraints. Such evaluation reveals the capability of the SS to tolerate the worst faults over a prescribed set under possible energy constraints. The evaluation is achieved by using the smallest eigenvalue of a proposed switched-system controllability Gramian'. Simulation results about a longitudinal flight control process example are presented to show the effectiveness of the proposed method. © 2011 Copyright Taylor and Francis Group, LLC.


Niu Z.P.,Nanjing University of Aeronautics and Astronautics | Xing D.Y.,Nanjing University
European Physical Journal B | Year: 2010

The spin filter effect and magnetoresistance (MR) in the graphene nanoribbons with zigzag edges have been investigated by the non-equilibrium Green's function method. Due to the spin-dependent current blocking effect, the ferromagnetic graphene/normal graphene junction can filter the spin in one direction, so a fully spin-polarized current is found. As the on-site energy μ R in the right lead goes from negative to positive, the spin-down transmission would suddenly transforms from an 'ON' state to an 'OFF' state, however the spin-up transmission transforms from an 'OFF' state to an 'ON' state, so we can choose the current's spin polarized direction by tuning μ R. For the ferromagnetic graphene/ferromagnetic graphene junction the current for the antiparallel magnetization configuration is blocked, a very large MR is obtained. It is expected that these features may serve as a type of useful spintronic devices in future. © 2009 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.


Wang Q.W.,Soochow University of China | Wang Q.W.,Nanjing University of Aeronautics and Astronautics | Zhou P.,Nanjing University of Aeronautics and Astronautics | Shen N.,Soochow University of China |