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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.


Singh S.C.,Dublin City University | Zeng H.,Nanjing University of Aeronautics and Astronautics
Science of Advanced Materials | Year: 2012

Lasers have shown their appreciable engagements in the synthesis, post processing and characterization of nano-scale materials since its discovery in 1960. Laser ablation in the gaseous media have been widely explored for the fabrication of thin films, nanoparticles and nanostructure of various shapes, size and morphologies, as well as in the spectroscopy of atoms, molecules and clusters. Laser ablates solid target in the gaseous and liquid media for the generation of atomic/molecular clusters in the hot and dense plasma, initiates several photochemical reactions such as polymerization and atomization, dissociate gaseous precursors into their fragments. All these processes are the keys for the synthesis of nanoparticles of various size, shapes, and morphology in the gaseous as well as in the liquid media. Here, we present a current state of art on various laser based approaches for the synthesis of nanomaterials such as conventional pulsed laser deposition, nanoparticle assisted pulsed laser deposition (NAPLD), and thermal assisted pulsed laser deposition (TAPLD) of target materials in the gaseous media for the synthesis of thin films, particles, and nanostructures of desired composition. Laser chemical vapour deposition, and laser pyrolysis, includes laser induced thermal or resonant dissociation of gaseous precursors into their fragments and clustering of some of the dissociated products into nanomaterials of different shapes, size, and composition. Two photon polymerization (TPP) possesses polymerization of three dimensional volume of photoresist material by absorption of two photon from the laser radiation to fabricate 3D microstructures/patterns. Photolithography has the ability to create 1D, 2D and 3D nano/micro patterns on the substrate, and is widely employed by semiconductor industry for the fabrication of nanoscale device to follow Moore's law in future. Continuous research and development in shorter wavelength light sources facilitates this technique to fabricate smaller and smaller electronic devices Liquid assisted pulsed laser ablation is a fastest growing laser based nanomaterials processing method owing to its simplicity, comparatively cheaper, one step process, ability to used stabilizer, in-situ functinalization etc. Liquid assisted laser based nanomaterials processing provides ways for the generation of highly colloidal solution of nanoparticles and nanostructures, nano/microstructuring on the surface of solid, and fabrication of films on the substrates through laser induced forward transfer (LIFT) of particles from colloid to the substrates. Particle generation using liquid assisted pulsed laser ablation (LA-PLA) includes ablation of solid bulk target submerged in the liquid, laser irradiation of liquid suspended particles for their resizing, reshaping, surface modification and phase conversion, as well as laser irradiation of solution of metal salts/liquid precursors. All of these gas and liquid assisted approaches of nanostructures/nanomaterials processing are discussed in brief. © 2012 by American Scientific Publishers. Source


Pan D.,Huazhong University of Science and Technology | Ruan X.,Huazhong University of Science and Technology | Ruan X.,Nanjing University of Aeronautics and Astronautics | Bao C.,Huazhong University of Science and Technology | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2014

This paper investigates the capacitor-current-feedback active damping for the digitally controlled LCL-type grid-connected inverter. It turns out that proportional feedback of the capacitor current is equivalent to virtual impedance connected in parallel with the filter capacitor due to the computation and pulse width modulation (PWM) delays. The LCL-filter resonance frequency is changed by this virtual impedance. If the actual resonance frequency is higher than one-sixth of the sampling frequency (fs/6), where the virtual impedance contains a negative resistor component, a pair of open-loop unstable poles will be generated. As a result, the LCL-type grid-connected inverter becomes much easier to be unstable if the resonance frequency is moved closer to fs/6 due to the variation of grid impedance. To address this issue, this paper proposes a capacitor-current-feedback active damping with reduced computation delay, which is achieved by shifting the capacitor current sampling instant towards the PWM reference update instant. With this method, the virtual impedance exhibits more like a resistor in a wider frequency range, and the open-loop unstable poles are removed; thus, high robustness against the grid-impedance variation is acquired. Experimental results from a 6-kW prototype confirm the theoretical expectations. © 1986-2012 IEEE. Source


Zhao Y.-P.,Nanjing University of Aeronautics and Astronautics
Neural Networks | Year: 2016

Recently, extreme learning machine (ELM) has become a popular topic in machine learning community. By replacing the so-called ELM feature mappings with the nonlinear mappings induced by kernel functions, two kernel ELMs, i.e., P-KELM and D-KELM, are obtained from primal and dual perspectives, respectively. Unfortunately, both P-KELM and D-KELM possess the dense solutions in direct proportion to the number of training data. To this end, a constructive algorithm for P-KELM (CCP-KELM) is first proposed by virtue of Cholesky factorization, in which the training data incurring the largest reductions on the objective function are recruited as significant vectors. To reduce its training cost further, PCCP-KELM is then obtained with the application of a probabilistic speedup scheme into CCP-KELM. Corresponding to CCP-KELM, a destructive P-KELM (CDP-KELM) is presented using a partial Cholesky factorization strategy, where the training data incurring the smallest reductions on the objective function after their removals are pruned from the current set of significant vectors. Finally, to verify the efficacy and feasibility of the proposed algorithms in this paper, experiments on both small and large benchmark data sets are investigated. © 2016 Elsevier Ltd. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

This paper follows on from the earlier study (Part I) which investigated the fatigue behavior of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures. In this paper, a micromechanics approach to predict the fatigue life S−N curves of fiber-reinforced CMCs has been developed considering the fatigue damage mechanism of interface wear or interface oxidation. Upon first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. The two-parameter Weibull model is used to describe fibers strength distribution. The stress carried by broken and intact fibres on the matrix crack plane under fatigue loading is determined based on the Global Load Sharing (GLS) criterion. The fibres failure probabilities under fatigue loading considering the degradation of interface shear stress and fibres strength have been obtained. When the broken fibres fraction approaches critical value, the composite would fatigue fail. The fatigue life S−N curves of unidirectional, cross-ply and 2.5D C/SiC composites at room and elevated temperatures have been predicted. The predicted results agreed with experimental data. © 2015 Springer Science+Business Media Dordrecht Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

An analytical method has been developed to investigate the effect of oxidation on the tensile strength of carbon fiber − reinforced ceramic − matrix composites (CMCs). The Budiansky − Hutchinson − Evans shear − lag model was used to describe the micro stress field of the damaged composite considering fibers failure. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The fiber strength degradation model and oxidation region propagation model have been adopted to analyze the oxidation effect on tensile strength of the composite, which is controlled by diffusion of oxygen gas through matrix cracks. Under tensile loading, the fibers failure probabilities were determined by combining oxidation model and fiber statistical failure model based on the assumption that fiber strength is subjected to two-parameter Weibull distribution and the loads carried by broken and intact fibers statisfy the global load sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength considering oxidation time and temperature have been analyzed. © 2015 Springer Science+Business Media Dordrecht Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

In this paper, the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) under multiple loading stress levels considering interface wear has been investigated using micromechanical approach. Under fatigue loading, the fiber/matrix interface shear stress decreases with the increase of cycle number due to interface wear. Upon increasing of fatigue peak stress, the interface debonded length would propagate along the fiber/matrix interface. The difference of interface shear stress existed in the new and original debonded region would affect the interface debonding and interface frictional slipping between the fiber and the matrix. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading, the interface slip lengths, i.e., the interface debonded length, interface counter-slip length and interface new-slip length, are determined by fracture mechanics approach. The fatigue hysteresis loops models under multiple loading stress levels have been developed. The effects of single/multiple loading stress levels and different loading sequences on fatigue hysteresis loops have been investigated. The fatigue hysteresis loops of unidirectional C/SiC composite under multiple loading stress levels have been predicted. © 2015 Springer Science+Business Media Dordrecht Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

This paper presents an experimental analysis on the fatigue behavior in C/SiC ceramic-matrix composites (CMCs) with different fiber preforms, i.e., unidirectional, cross-ply and 2.5D woven, at room and elevated temperatures in air atmosphere. The experimental fatigue life S − N curves of C/SiC composites corresponding to different stress levels and test conditions have been obtained. The damage evolution processes under fatigue loading have been analyzed using fatigue hysteresis modulus and fatigue hysteresis loss energy. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different peak stress, fiber preforms and test conditions have been estimated. It was found that the degradation of interface shear stress and fibres strength caused by oxidation markedly decreases the fatigue life of C/SiC composites at elevated temperature. © 2015 Springer Science+Business Media Dordrecht Source


Liu F.,Nanjing University of Aeronautics and Astronautics | Yan J.,Bel Power Company | Ruan X.,Huazhong University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2010

This paper proposes a zero-voltage and zero-current-switching (ZVZCS) PWM combined three-level (TL) dc/dc converter, which is a combination of a ZVZCS PWM TL converter with a ZVZCS PWM full-bridge converter. The proposed converter has the following advantages: all power switches suffer only half of the input voltage; the voltage across the output filter is very close to the output voltage, which can reduce the output filter inductance significantly; and the voltage stress of the rectifier diodes is reduced too, so that the converter is very suitable for high input voltage and wide input voltage range applications. The converter also can achieve zero-voltage-switching for the leading switches and ZCS for the lagging switches in a wide load range to achieve higher efficiency. The design considerations and procedures are presented in this paper. The operation principle and characteristics of the proposed converter are analyzed and verified on a 400800-V input and 54-V/20-A output prototype. © 2006 IEEE. Source


Wang J.,Nanjing University of Aeronautics and Astronautics
Shock and Vibration | Year: 2016

The performance of the high speed trains depends critically on the quality of the contact in the pantograph-catenary interaction. Maintaining a constant contact force needs taking special measures and one of the methods is to utilize active control to optimize the contact force. A number of active control methods have been proposed in the past decade. However, the primary objective of these methods has been to reduce the variation of the contact force in the pantograph-catenary system, ignoring the effects of locomotive vibrations on pantograph-catenary dynamics. Motivated by the problems in active control of vibration in large scale structures, the author has developed a geometric framework specifically targeting the remote vibration suppression problem based only on local control action. It is the intention of the paper to demonstrate its potential in the active control of the pantograph-catenary interaction, aiming to minimize the variation of the contact force while simultaneously suppressing the vibration disturbance from the train. A numerical study is provided through the application to a simplified pantograph-catenary model. © 2016 Jiqiang Wang. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

An analytical method has been developed to investigate the effect of interface wear on fatigue hysteresis behavior in carbon fiber-reinforced ceramic-matrix composites (CMCs). The damage mechanisms, i.e., matrix multicracking, fiber/matrix interface debonding and interface wear, fibers fracture, slip and pull-out, have been considered. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. Upon first loading to fatigue peak stress and subsequent cyclic loading, the fibers failure probabilities and fracture locations were determined by combining the interface wear model and fiber statistical failure model based on the assumption that the loads carried by broken and intact fibers satisfy the global load sharing criterion. The effects of matrix properties, i.e., matrix cracking characteristic strength and matrix Weibull modulus, interface properties, i.e., interface shear stress and interface debonded energy, fiber properties, i.e., fiber Weibull modulus and fiber characteristic strength, and cycle number on fibers failure, hysteresis loops and interface slip, have been investigated. The hysteresis loops under fatigue loading from the present analytical method were in good agreement with experimental data. © 2015 Springer Science+Business Media Dordrecht Source


Li L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

When the fiber-reinforced ceramic-matrix composites (CMCs) are first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. Under fatigue loading, the stress–strain hysteresis loops appear as fiber slipping relative to matrix in the interface debonded region upon unloading/reloading. Due to interface wear at room temperature or interface oxidation at elevated temperature, the interface shear stress degredes with increase of the number of applied cycles, leading to the evolution of the shape, location and area of stress–strain hysteresis loops. The evolution characteristics of fatigue hysteresis loss energy in different types of fiber-reinforced CMCs, i.e., unidirectional, cross-ply, 2D and 2.5D woven, have been investigated. The relationships between the fatigue hysteresis loss energy, stress–strain hysteresis loops, interface frictional slip, interface shear stress and interface radial thermal residual stress, matrix stochastic cracking and fatigue peak stress of fiber-reinforced CMCs have been established. © 2015 Springer Science+Business Media Dordrecht Source


Cross E.J.,University of Sheffield | Worden K.,University of Sheffield | Chen Q.,Nanjing University of Aeronautics and Astronautics
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Before structural health monitoring (SHM) technologies can be reliably implemented on structures outside laboratory conditions, the problem of environmental variability in monitored features must be first addressed. Structures that are subjected to changing environmental or operational conditions will often exhibit inherently non-stationary dynamic and quasi-static responses, which can mask any changes caused by the occurrence of damage. The current work introduces the concept of cointegration, a tool for the analysis of non-stationary time series, as a promising new approach for dealing with the problem of environmental variation in monitored features. If two or more monitored variables from an SHM system are cointegrated, then some linear combination of them will be a stationary residual purged of the common trends in the original dataset. The stationary residual created from the cointegration procedure can be used as a damage-sensitive feature that is independent of the normal environmental and operational conditions. This journal is © 2011 The Royal Society. Source


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. Source


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. Source


Yan G.,Nanjing University of Aeronautics and Astronautics
Structural Control and Health Monitoring | Year: 2014

This paper proposes a probabilistic approach for localizing damage in plate-like structures by using particle filter (PF) method with considerations of the uncertainties from modeling and measurement. A piezoelectric sensor network is deployed on the plate-like structures to excite and receive diagnostic Lamb waves before and after damage. The damage-scattered waves that contain characteristic information about the damage are then obtained and used for damage localization. A complex Morlet wavelet transform is employed to highlight the time-of-arrival of the scattered waves in each actuator-sensor path to help measuring the time-of-flight values. After that, damage localization is formulated as a Bayesian state estimation problem with the damage location and the wave velocity as the unknown state parameters. A PF procedure is developed to iteratively estimate the unknown parameters simultaneously. Numerical study for an aluminum plate and experimental study for a stiffened aluminum panel are conducted to demonstrate the effectiveness and applicability of the proposed PF-based localization method. © 2013 John Wiley & Sons, Ltd. Source


Bao C.,Huazhong University of Science and Technology | Ruan X.,Huazhong University of Science and Technology | Ruan X.,Nanjing University of Aeronautics and Astronautics | Wang X.,Huazhong University of Science and Technology | And 3 more authors.
IEEE Transactions on Power Electronics | Year: 2014

The injected grid current regulator and active damping of the LCL filter are essential to the control of LCL-type grid-connected inverters. Generally speaking, the current regulator guarantees the quality of the injected grid current, and the active damping suppresses the resonance peak caused by the LCL filter and makes it easier to stabilize the whole system. Based on the proportional-integral (PI) and proportional-resonant (PR) compensator together with capacitor-current-feedback active-damping which are widely used for their effectiveness and simple implementations, this paper proposes a simple step-by-step controller design method for the LCL-type grid-connected inverter. By carefully dealing with the interaction between the current regulator and active damping, the complete satisfactory regions of the controller parameters for meeting the system specifications are obtained, and from which the controller parameters can be easily picked out. Based on these satisfactory regions, it is more convenient and explicit to optimize the system performance. Besides, the insight of tuning the controller parameters from these satisfactory regions is also discussed. Simulation and experimental results verify the proposed step-by-step design method. © 1986-2012 IEEE. Source


Li L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

An analytical method has been developed to investigate the effect of interface wear on the tensile strength of carbon fiber − reinforced ceramic − matrix composites (CMCs) under multiple fatigue loading. The Budiansky − Hutchinson − Evans shear − lag model was used to describe the micro stress field of the damaged composite considering fibers failure and the difference existed in the new and original interface debonded region. The statistical matrix multicracking model and fracture mechanics interface debonding criterion were used to determine the matrix crack spacing and interface debonded length. The interface shear stress degradation model and fibers strength degradation model have been adopted to analyze the interface wear effect on the tensile strength of the composite subjected to multiple fatigue loading. Under tensile loading, the fibers failure probabilities were determined by combining the interface wear model and fibers failure model based on the assumption that the fiber strength is subjected to two − parameter Weibull distribution and the loads carried by broken and intact fibers satisfy the Global Load Sharing criterion. The composite can no longer support the applied load when the total loads supported by broken and intact fibers approach its maximum value. The conditions of a single matrix crack and matrix multicrackings for tensile strength corresponding to multiple fatigue peak stress levels and different cycle number have been analyzed. © 2015 Springer Science+Business Media Dordrecht Source


Dai Q.,Nanjing University of Aeronautics and Astronautics
Neurocomputing | Year: 2013

Although the Directed Hill Climbing Ensemble Pruning (DHCEP) algorithm has achieved favorable classification performance, it often yields suboptimal solutions to the ensemble pruning problem, due to its limited exploration within the whole solution space, which inspires us with the development of a novel Ensemble Pruning algorithm based on Randomized Greedy Selective Strategy and Ballot (RGSS&B-EP), where randomization technique is introduced into the procedure of greedy ensemble pruning, and the final pruned ensemble is generated by ballot, which are the two major contributions of this paper. Experimental results, including t-tests on the three benchmark classification tasks, verified the validity of the proposed RGSS&B-EP algorithm. © 2013 Elsevier B.V. Source


Zhang W.,Hong Kong Polytechnic University | Wong S.-C.,Hong Kong Polytechnic University | Tse C.K.,Hong Kong Polytechnic University | Chen Q.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2014

Secondary series-and parallel-compensations are widely used in inductive power transfer (IPT) systems for various applications. These compensations are often studied under some isolated constraints of maximum power transfer, optimal efficiency at a particular loading condition, etc. These constraints constitute an insufficient set of requirements for engineers to select appropriate compensation techniques to be used as a voltage converter with optimal efficiency and loading conditions. This paper studies the characteristics of the IPT system at various frequencies of operation utilizing the two compensation techniques to work as a voltage converter. The frequencies that can provide maximum efficiency of operation and load-independent voltage-transfer ratio are analyzed. The optimal frequencies corresponding to the two compensation techniques are found and compared to facilitate the design of voltage converters with efficient power conversion and load-independent frequency of operation. The analysis is supported by experimental measurements. © 2013 IEEE. Source


Wang Y.,Nanjing University of Aeronautics and Astronautics
Xitong Gongcheng Lilun yu Shijian/System Engineering Theory and Practice | Year: 2010

Economic discrepancy of the east, mid and west areas in China is enlarging in recent years, which is closely related to the distribution of foreign direct investment (FDI). Using the time-pooling and cross-section data between 1998 and 2006, the regional distribution imbalance of GDP, investment infixed assets, export, FDI and transaction value in technical market are measured based on the Gini Coefficient. Then the relationship between different factors and the regional economic discrepancy are empirically analyzed by stages using the grey incidence theory. It is found that the unbalancing degree of regional economy is different with diverse index, and though different before and after entering WTO, the regional distribution imbalance of FDI is a significant factor causing the regional economic discrepancy of the east, mid and west areas. Source


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. Source


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. Source


Zhu J.,Nanjing University of Aeronautics and Astronautics | Qiu J.,Xiamen University
Journal of Computational Physics | Year: 2016

In this paper a new simple fifth order weighted essentially non-oscillatory (WENO) scheme is presented in the finite difference framework for solving the hyperbolic conservation laws. The new WENO scheme is a convex combination of a fourth degree polynomial with two linear polynomials in a traditional WENO fashion. This new fifth order WENO scheme uses the same five-point information as the classical fifth order WENO scheme [14,20], could get less absolute truncation errors in L1 and L∞ norms, and obtain the same accuracy order in smooth region containing complicated numerical solution structures simultaneously escaping nonphysical oscillations adjacent strong shocks or contact discontinuities. The associated linear weights are artificially set to be any random positive numbers with the only requirement that their sum equals one. New nonlinear weights are proposed for the purpose of sustaining the optimal fifth order accuracy. The new WENO scheme has advantages over the classical WENO scheme [14,20] in its simplicity and easy extension to higher dimensions. Some benchmark numerical tests are performed to illustrate the capability of this new fifth order WENO scheme. © 2016 Elsevier Inc. Source


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. Source


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. Source


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. Source


Yang W.-A.,Nanjing University of Aeronautics and Astronautics
Journal of Intelligent Manufacturing | Year: 2015

Nowadays, modern computers in general and the PC in particular have made the continuous high-speed acquisition and inspection accessible and during the last decade, multivariate control charts were given more attention and became so popular in real-world manufacturing scenarios. However, most conventional multivariate control charts share the same problem: they can only detect an out-of-control circumstance but cannot directly point out which variable or group of variables has caused the out-of-control signal. This study proposes an effective MSPC model enabled by two-level discrete particle swarm optimization-based selective ensemble of learning vector quantization networks (DPSOSENLVQ) for monitoring and diagnosing of mean shifts in multivariate manufacturing processes. In this model, one DPSOSENLVQ is developed for detecting out-of-control signals in process mean, while the other DPSOSENLVQ is developed for further classifying the detected out-of-control signals as one of the specific mean shift types. The experimental result indicates that the proposed MSPC model can not only efficiently monitor the process state but also accurately diagnose the detected out-of-control signals. Empirical comparisons also showed that the proposed MSPC model outperformed other existing approaches in literature. In addition, a case study is conducted to demonstrate how the proposed MSPC model can function as an effective tool for monitoring and diagnosing of mean shifts in multivariate manufacturing processes. © 2013, Springer Science+Business Media New York. Source


The interface shear stress in C/SiC and SiC/SiC ceramic-matrix composites with different fiber preforms, i.e. unidirectional, cross-ply, 2D woven, 2.5D woven, and 3D braided, under cyclic fatigue loading at room and elevated temperatures have been estimated. An effective coefficient of the fiber volume fraction along the loading direction was introduced to describe the fiber preforms. Based on fiber slipping mechanisms, the hysteresis loops models considering different interface slip cases have been developed. Using the experimental fatigue hysteresis dissipated energy, the interface shear stress degradation rates of C/SiC and SiC/SiC composites with different fiber preforms at room and elevated temperatures have been obtained and compared. It was found that the interface shear stress degradation rate is the highest for 3D braided SiC/SiC at 1300 °C in air, and the lowest for 2D woven C/SiC at room temperature under cyclic fatigue loading. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source


Yang C.-F.,The First Aircraft Institute | Zhang J.-Z.,Nanjing University of Aeronautics and Astronautics
Experimental Thermal and Fluid Science | Year: 2012

Experimental study was conducted to investigate the enhanced cooling performance caused by ridge-shaped tabs located along the upstream edge of the film cooling holes. Three covering ratios of ridge-shaped tab on film hole and four blowing ratios were considered in the present. The results show that the presence of ridge-shaped tabs in the nearby region of the primary film cooling holes mitigates the primary vortices due to mainstream-coolant jet interaction in the downstream region. The lower penetration of coolant jet provides an increment in the film cooling effectiveness and also enhance heat transfer coefficient over the baseline case. The ridge-shaped tabs provide enhancements in cooling effectiveness, but this is at the expense of larger pressure drop, especially for ridge-shaped tabs with bigger covering ratio. © 2011 Elsevier Inc. Source


Cai R.-G.,Hunan Normal University | Cai R.-G.,CAS Institute of Theoretical Physics | Hu Y.-P.,Nanjing University of Aeronautics and Astronautics | Hu Y.-P.,Shanghai JiaoTong University | And 3 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

We present a class of charged black hole solutions in an (n+2)-dimensional massive gravity with a negative cosmological constant, and study the thermodynamics and phase structure of the black hole solutions in both the grand canonical and canonical ensembles. The black hole horizon can have a positive, zero, or negative constant curvature characterized by the constant k. By using the Hamiltonian approach, we obtain conserved charges of the solutions and find that the black hole entropy still obeys the area formula and the gravitational field equation at the black hole horizon can be cast into a form similar to the first law of black hole thermodynamics. In the grand canonical ensemble, we find that the thermodynamics and phase structure depend on the combination k-μ2/4+c2m2 in the four-dimensional case, where μ is the chemical potential and c2m2 is the coefficient of the second term in the potential associated with the graviton mass. When it is positive, the Hawking-Page phase transition can happen; when as it is negative, the black hole is always thermodynamically stable with a positive capacity. In the canonical ensemble, the combination turns out to be k+c2m2 in the four-dimensional case. When it is positive, a first-order phase transition can happen between small and large black holes if the charge is less than its critical value. In the higher-dimensional [(n+2)≥5] case, even when the charge is absent, the small/large black hole phase transition can also appear, and the coefficients for the third (c3m2) and/or fourth (c4m2) terms in the potential associated with the graviton mass in massive gravity can play the same role as that of the charge in the four-dimensional case. © 2015 American Physical Society. Source


Xu J.,Nanjing University of Aeronautics and Astronautics
Zeitschrift fur Angewandte Mathematik und Physik | Year: 2010

This paper is devoted to study the strong relaxation limit of multi-dimensional isentropic Euler equations with relaxation. Motivated by the Maxwell iteration, we generalize the analysis of Yong (SIAM J Appl Math 64:1737-1748, 2004) and show that, as the relaxation time tends to zero, the density of a certain scaled isentropic Euler equations with relaxation strongly converges towards the smooth solution to the porous medium equation in the framework of Besov spaces with relatively lower regularity. The main analysis tool used is the Littlewood-Paley decomposition. © 2010 Birkhäuser Verlag Basel/Switzerland. Source


Wang Z.,Nanjing University of Aeronautics and Astronautics
Science China Earth Sciences | Year: 2015

On 24 August 2005, an impulse of solar wind dynamic pressure (PSW) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of PSW at the trailing edge of the impulse. The results show that the sharp decrease of PSW can excite a global pulsation in the frequency range 4.3–11.6 mHz. The pulsation has a reversal of polarization between two auroral latitude stations, a larger power spectral density (PSD) close to resonant latitude and increasing frequency with decreasing latitude. All these features indicate that the pulsations are associated with field line resonance (FLR). The fundamental resonant frequency (the peak frequency of PSD between 4.3 and 5.8 mHz) is dependent on magnetic local time and is largest around magnetic local noon. This feature is due to the fact that the size of magnetospheric cavity is dependent on local time and smallest at noon. A second harmonic wave at about 10 mHz is also observed, which is strongest in the daytime sector, and becomes heavily attenuated in the night sector. The comparison of the PSDs of the pulsations driven by sharp increase and sharp decrease of PSW shows that the frequency of pulsations is negatively proportional to the size of magnetopause. Since the FLR is excited by compressional cavity/waveguide waves, the above results indicate that the resonant frequency in the magnetospheric cavity/waveguide is controlled not only by solar wind parameters but also by magnetic local time of observation point. © 2015 Science China Press and Springer-Verlag Berlin Heidelberg Source


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. Source


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. Source


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. Source


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. Source


Chen X.,Jiangsu University | Qi J.,Jiangsu University | Shi D.,Nanjing University of Aeronautics and Astronautics
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

In this paper, we demonstrate by the density functional theory calculations that the monolayer CrSiTe3 is an intrinsic ferromagnetic semiconductor. More importantly, ferromagnetic stability can be enhanced significantly by applying an elastic tensile stain, implying their potential applications in spintronic devices at room temperature. In addition, a ferromagnetic-antiferromagnetic transition occurs under the small compression stain. The underlying physical mechanism is attributed to a competition effect of direct antiferromagnetic interaction and indirect ferromagnetic superexchange interaction. © 2014 Elsevier B.V. Source


Feng X.,Nanjing University of Aeronautics and Astronautics | Feng X.,Technical University of Delft | Blote H.W.J.,Technical University of Delft | Blote H.W.J.,Leiden University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

We provide an expression quantitatively describing the specific heat of the Ising model on the simple-cubic lattice in the critical region. This expression is based on finite-size scaling of numerical results obtained by means of a Monte Carlo method. It agrees satisfactorily with series expansions and with a set of experimental results. Our results include a determination of the universal amplitude ratio of the specific-heat divergences at both sides of the critical point. © 2010 The American Physical Society. Source


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Fu J.,Queens University | Liu Y.-F.,Queens University | Sen P.C.,Queens University
IEEE Transactions on Power Electronics | Year: 2011

In this letter, the switching loop inductance was investigated on the current-source drivers (CSDs). The analytical model was developed to predict the switching losses. It is noted that although the CSDs can greatly reduce the switching transition time and switching loss, the switching loop inductance still causes the current holding effect on the CSDs. This results in high turn-off loss for the control MOSFET in a buck converter. An improved layout was proposed to achieve minimum switching loop inductance. The experimental results verified the significant switching loss reduction owing to the proposed layout of a 1-MHz buck converter with 12-V input, and 1.3-V and 30-A output. © 2011 IEEE. Source


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. Source


Wang F.,Nanjing University of Aeronautics and Astronautics
Nonlinear Analysis: Real World Applications | Year: 2011

In this paper, a weak force condition enables the achievement of new existence criteria for positive doubly periodic solutions of a nonlinear telegraph system through a basic application of Schauder's fixed point theorem. A weak singularity will be useful to our proofs. © 2010 Published by Elsevier Ltd. All rights reserved. Source


Wu P.,Nanjing University of Aeronautics and Astronautics
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2010

The theory and the method of measuring displacement direction by double-exposure hologram, that the reference-beam is modulated by the displacement of the wavefront-division mirror, are investigated. In the process of recording double-exposure hologram, the mirror placed on the surface of the measured object is displaced when the object has a micro-displacement, and then the reference beam reflected by the mirror is modulated. The hologram can records the displacing information of the object not only in magnitude but also in direction. Through theoretical analysis, the correlation of the displacement directions between the interference pattern of the hologram and the wavefront-division mirror or the measured object is established when the object displaces, and the correlation formulas are derived. Measured method of displacement direction is described. Experimental result is given. Source


Niu Z.P.,Nanjing University of Aeronautics and Astronautics
European Physical Journal B | Year: 2011

We investigate the thermoelectric effects in a double-dot Aharonov-Bohm interferometer coupled to ferromagnetic leads held at different temperatures. The interplay of Rashba spin-orbit interaction (RSOI) and magnetic flux φ induces various interesting spin-dependent interference phenomena. The thermoelectric transport oscillates with φ. The peak of the thermopower S and figure of merit ZT splits into two new peaks and its splitting increases with the Rashba induced phase factor φ R . With increasing φ R S and ZT at φ = ± 2nπ (n = 0,1,2,...) exhibit a conversion from a peak to a valley. In the presence of the interplay of RSOI and φ by increasing spin polarization the splitting peaks of S (ZT) become asymmetric and ZT is greatly enhanced. The influence of the quantum dot levels on thermoelectric effects is also analyzed. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source


Dai Q.,Nanjing University of Aeronautics and Astronautics
Neural Computing and Applications | Year: 2010

In neural network ensemble, the diversity of its constitutive component networks is a crucial factor to boost its generalization performance. In terms of how each ensemble system solves the problem, we can roughly categorize the existing ensemble mechanism into two groups: data-driven and model-driven ensembles. The former engenders diversity to ensemble members by manipulating the data, while the latter realizes ensemble diversity by manipulating the component models themselves. Within a neural network ensemble, standard back-propagation (BP) networks are usually used as a base component. However, in this article, we will use our previously designed improved circular back-propagation (ICBP) neural network to establish such an ensemble. ICBP differentiates from BP network not only because an extra anisotropic input node is added, but also more importantly, because of the introduction of the extra node, it possesses an interesting property apart from the BP network, i. e., just through directly assigning different sets of values 1 and -1 to the weights connecting the extra node to all the hidden nodes, we can construct a set of heterogeneous ICBP networks with different hidden layer activation functions, among which we select four typical heterogeneous ICBPs to build a dynamic classifier selection ICBP system (DCS-ICBP). The system falls into the category of model-driven ensemble. The aim of this article is to explore the relationship between the explicitly constructed ensemble and the diversity scale, and further to verify feasibility and effectiveness of the system on classification problems through empirical study. Experimental results on seven benchmark classification tasks show that our DCS-ICBP outperforms each individual ICBP classifier and surpasses the performance of combination of ICBP using the majority voting technique, i. e. majority voting ICBP system (MVICBP). The successful simulation results validate that in DCS-ICBP we provide a new constructive method for diversity enforcement for ICBP ensemble systems. © Springer-Verlag London Limited 2009. Source


Lu C.,Nanjing University of Aeronautics and Astronautics
Nanjing Hangkong Hangtian Daxue Xuebao/Journal of Nanjing University of Aeronautics and Astronautics | Year: 2010

The runway capacity assessment is the key of air terminal area planning and constructing, as well as the air traffic flow and the capacity management. But the existing methods of the runway capacity assessment do not consider the real-time and dynamic characteristics of the landing airplane flow. This paper presents the definitions of the T system and confirms that the capacity of the T system is existed and limited. According to the T system characteristics of single runway system, the basic formula of the single runway capacity is derived based on the T system model, and the relationships of parameters are analyzed. The calculation capacity of an airport is in agreement with actual situation. Source


Yuan Q.,Nanjing University of Aeronautics and Astronautics
Mechanical Systems and Signal Processing | Year: 2013

The problem of finding the optimal approximation to analytical stiffness matrix modeled by the finite element method is considered in this paper. Desired matrix properties, including satisfaction of the dynamic equation, symmetry, positive semidefiniteness and physical connectivity, are imposed as side constraints of the minimization problem. To the best of the author's knowledge, the finite element model updating problem containing all these constraints simultaneously has not been proposed in the literature earlier. By partial Lagrangian multipliers technique, the optimization problem is transformed into a matrix linear variational inequality and the proximal-point method is first used to solve the equivalent problem. The results of numerical examples show that the proposed method works well even for incomplete measured data. © 2012 Elsevier Ltd. Source


Xiao Y.,CNRS Chemistry Laboratory | Xiao Y.,Nanjing University of Aeronautics and Astronautics | Dong W.,CNRS Chemistry Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We develop a strategy based on a molecular dynamics method with reactive force fields for large-scale simulations of reacting systems. The considerably enhanced computational efficiency (105 times faster than an ab initio molecular dynamics method) opens an avenue to simulating complex chemical reactions that had been previously nontractable. As a demonstration of feasibility, thorough simulations were performed for H2 dissociation on H-covered Pd(111), which bring insights into the coverage effect on surface reactivity. © 2011 American Physical Society. Source


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. Source


Huang Z.,Nanjing University of Aeronautics and Astronautics
Philosophical Magazine Letters | Year: 2014

Based on a energy flux vector associated with surface energy, the Lagrangian field theory is used to derive a new mixed boundary condition of solid concerned with surface effects. The prediction given by it agrees well with experimental data on the lattice contraction of palladium nanoparticles. Comparison with various existing versions of traction boundary condition is discussed. The results show that the new version is concise in theory and verifiable in experiment. © 2014 © 2014 Taylor & Francis. Source


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. Source


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. Source


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. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2016

In this paper, the effects of temperature, oxidation and fiber preforms on the fatigue life of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) have been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S–N curves and fatigue limits of unidirectional, cross-ply, 2D, 2.5D and 3D C/SiC composites at room temperature, 800 °C in air, 1100, 1300 and 1500 °C in vacuum conditions have been predicted. © 2016 Springer Science+Business Media Dordrecht Source


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. Source


Cao X.,Nanjing University of Aeronautics and Astronautics | Cao X.,Beihang University | Hu L.,University of Chinese Academy of Sciences
Finite Fields and their Applications | Year: 2011

We present two methods for generating linearized permutation polynomials over an extension of a finite field Fq. These polynomials are parameterized by an element of the extension field and are permutation polynomials for all nonzero values of the element. For the case of the extension degree being odd and the size of the ground field satisfying q ≡ 3(mod4), these parameterized linearized permutation polynomials can be used to derive non-parameterized nonlinear permutation polynomials via a recent result of Ding et al. © 2011 Elsevier Inc. All Rights Reserved. Source


Wang J.,Nanjing University of Aeronautics and Astronautics
E-Polymers | Year: 2012

To develop a high dielectric constant composite of poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] and multi-walled carbon-nanotubes (MWCNTs) with desirable homogeneity, MWCNTs were treated with a nitro-sulfuric acid by ultrasonication. Improvement of the dispersibility of chemically modified MWCNTs (a-MWCNTs) in polymer matrix, in comparison with that of unmodified MWCNTs in P(VDF-TrFE), was confirmed by field emission scanning electron microscopy (FESEM)-observed morphologies. Electric behavior of the composites with different volume fraction of dispersed carbon nanotubes phase can be described mainly by percolation theory. The percolation threshold (f c) of composites with a-MWCNTs (f c=0.0308) is larger than that of composites with MWCNTs (f c=0.0216) due to better dispersion of a-MWCNTs in polymer matrix and the reduction of aspect ratio of a-MWCNTs occurred in the modification procedure. The composite with 2.98 vol% (a volume fraction close to the percolation threshold) of a-MWCNTs has a dielectric constant of 592 at 100Hz and room temperature. The composite remains very flexible with an elastic modulus close to that of the parent copolymer. Source


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. Source


Li X.,Nanjing University of Aeronautics and Astronautics | Wu R.,Anhui University
Nonlinear Dynamics | Year: 2014

In this paper, a new fractional-order hyperchaotic system based on the Lorenz system is presented. The chaotic behaviors are validated by the positive Lyapunov exponents. Furthermore, the fractional Hopf bifurcation is investigated. It is found that the system admits Hopf bifurcations with varying fractional order and parameters, respectively. Under different bifurcation parameters, some conditions ensuring the Hopf bifurcations are proposed. Numerical simulations are given to illustrate and verify the results. © 2014, Springer Science+Business Media Dordrecht. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Theoretical and Applied Fracture Mechanics | Year: 2016

In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic-matrix composites (CMCs) at elevated temperatures has been investigated. The interface slip between fibers and the matrix existed in the matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in the longitudinal yarns, are considered as the major reason for hysteresis loops of 2D woven CMCs. The hysteresis loops of 2D SiC/SiC composite corresponding to different peak stresses, test conditions and loading frequencies have been predicted using present analysis. The damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire matrix cracking modes of the composite, and the hysteresis dissipated energy increase with increasing fatigue peak stress. With increasing cycle number, the interface shear stress in the longitudinal yarns decreases, leading to transition of interface slip types of matrix cracking mode 3 and mode 5. © 2016 Elsevier Ltd. Source


Xuan Y.,Nanjing University of Aeronautics and Astronautics
Photonics and Nanostructures - Fundamentals and Applications | Year: 2014

With the rapid development of micro/nanoscaled technologies, we are confronted with more and more challenges related to small-scale thermal radiation. Thorough understanding and handling of micro/nanoscaled radiative heat transfer is vital for many fields of modern science and technology. For example, proper utilization of near-field thermal radiation phenomenon greatly improves light-electric conversion efficiency. This review introduces theoretical and experimental investigation on near-field thermal radiation, especially progress in application and control of micro/nanoscaled radiative heat transfer, which addresses problems in developing renewable and sustainable energy techniques. © 2014 Elsevier B.V. Source


Dong J.,Nanjing University of Aeronautics and Astronautics
Journal of Physics A: Mathematical and Theoretical | Year: 2011

From the three-dimensional space fractional Schrödinger equation, a generalized Lippmann-Schwinger equation for the fractional quantum mechanics is obtained for both scattering and bound states. We apply the generalized integral equation to study the fractional quantum scattering problem and give the approximate scattering wavefunction of first order and higher orders. © 2011 IOP Publishing Ltd. Source


Yuan C.,Anhui University of Technology | Yuan C.,Shandong University | Li J.,Anhui University of Technology | Hou L.,Anhui University of Technology | And 3 more authors.
Journal of Materials Chemistry A | Year: 2013

We have developed a facile yet scalable polymer-assisted chemical solution route to prepare a three-dimensional (3D) hierarchical porous network-like NiCo2O4 framework for advanced electrochemical capacitors (ECs). The unique interconnected hierarchical porous framework is constructed by nanosized spinel NiCo2O4 building blocks of 20-30 nm size, thus, a 3D continuous electron transport expressway, convenient electrolyte penetration-diffusion and large electrode-electrolyte interface are obtained simultaneously. The combination of these appealing structural features in the striking network-like NiCo2O4 framework results in a drastically enhanced kinetic behavior, large specific capacitance (SC) and a remarkable cycling stability at high rates. The unique network-like NiCo 2O4 electrode features a SC of 587 F g-1 at 2 A g-1, and can deliver up to 518 F g-1 at a large current density of 16 A g-1. Also, a SC deterioration of ∼6% of the maximum SC is evident after continuous 3500 charge-discharge cycles at varying current densities, ranging from 2 to 16 A g-1. Furthermore, the synthetic strategy presented here can be easily extended to fabricate other binary complex metal oxides and/or ternary metal oxides with a controlled composition and porous structure, which may be promising candidates for high-performance ECs, and even advanced Li-ion batteries. © 2013 The Royal Society of Chemistry. Source


Chen G.,Nanjing University of Aeronautics and Astronautics
Hangkong Dongli Xuebao/Journal of Aerospace Power | Year: 2012

In order to study the whole aero-engine vibration, a generalized complex rotor-support-casing coupling dynamic model was established. In the model, the rotor and casing systems were modeled by means of the finite elements method; the support systems were modeled by the lumped parameter model, and the nonlinear factors of ball bearings and the squeeze film dampers were also included; the complex structures with multi-rotor and multi-casing was considered. A numerical integral method was used to obtain the system responses. Two aero-engine rotor testers were designed to verify the new model. The coupling dynamic model was established for the tester according to the new method, and the modal tests were carried out. The computation results were compared with the experiments results. The results indicate the effectiveness of the new method. Source


Qing H.,Nanjing University of Aeronautics and Astronautics
Acta Metallurgica Sinica (English Letters) | Year: 2014

The influence of the shape and spatial distribution of reinforced particles on strength and damage of metal matrix composite (MMC) is investigated through finite element method under uniaxial tensile, simple shear, biaxial tensile, as well as combined tensile/shear loadings. The particle shapes change randomly from circular to regular n-sided polygon (3 ≤ n ≤ 10); the particle alignments are determined through a sequentially random number stream and the particle locations are defined through the random sequential adsorption algorithm. The ductile failure in metal matrix and brittle failure in particles are described through damage models based on the stress triaxial indicator and maximum principal stress criterion, respectively, while the debonding behavior of interface between particles and matrix is simulated through cohesive elements. The simulation results show that, under different loadings, interface debonding is the dominated failure mechanism in MMCs and plastic deformation and ductile failure of matrix also play very important roles on the failure of MMCs. © The Chinese Society for Metals and Springer-Verlag 2014. Source


Xu J.,Nanjing University of Aeronautics and Astronautics | Kawashima S.,Kyushu University
Archive for Rational Mechanics and Analysis | Year: 2014

The basic existence theory of Kato and Majda enables us to obtain local-in-time classical solutions to generally quasilinear hyperbolic systems in the framework of Sobolev spaces (in x) with higher regularity. However, it remains a challenging open problem whether classical solutions still preserve well-posedness in the case of critical regularity. This paper is concerned with partially dissipative hyperbolic system of balance laws. Under the entropy dissipative assumption, we establish the local well-posedness and blow-up criterion of classical solutions in the framework of Besov spaces with critical regularity with the aid of the standard iteration argument and Friedrichs' regularization method. Then we explore the theory of function spaces and develop an elementary fact that indicates the relation between homogeneous and inhomogeneous Chemin-Lerner spaces (mixed space-time Besov spaces). This fact allows us to capture the dissipation rates generated from the partial dissipative source term and further obtain the global well-posedness and stability by assuming at all times the Shizuta-Kawashima algebraic condition. As a direct application, the corresponding well-posedness and stability of classical solutions to the compressible Euler equations with damping are also obtained. © 2013 Springer-Verlag Berlin Heidelberg. Source


Zhao Y.,Nanjing University of Aeronautics and Astronautics
JVC/Journal of Vibration and Control | Year: 2010

A practical method for suppressing random vibrations of a quadrilateral plate using the active/ passive hybrid piezoelectric circuits is developed. Firstly, the finite element model of the plate bonded with piezoelectric actuators is established by using the commercial software packages ANSYS ®. Afterwards, matrices in these electromechanically coupled equations are directly imported into MATLAB ® platform for later use. Time histories of the random excitations are obtained from the output of a band-pass FIR filter driven by white noise. Hybrid piezoelectric shunt circuits that combine the passive circuits with active voltage sources are used to suppress random vibrations of plate under the designed loads. Simulation results demonstrate that with appropriate circuit parameters, the hybrid control is more effective than passive or purely active control. © 2010 SAGE Publications Los Angeles, London, New Delhi, Singapore. Source


Han D.,Nanjing University of Aeronautics and Astronautics
Chinese Journal of Aeronautics | Year: 2015

To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluidlastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev (per revolution) pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased. © 2015 The Author. Source


Chen Z.,Nanjing University of Aeronautics and Astronautics
Computer Journal | Year: 2015

This work is primarily inspired by the observation that supervisory control and regulated rewriting have the same nature. Indeed, both of them model a system using some formalism and use a certain formalized control structure to restrict the behavior of the system via some designated control mechanisms. In this paper, we propose the theory of Control Systems (C Systems), which provides a more generic framework to integrate the automaton and grammar representations of control in supervisory control and regulated rewriting. The C system contains two components: the controlled component and the controlling component. The two components are expressed using the same formalism, e.g. automata or grammars. More specifically, we define three types of control systems based on the automaton or grammar representation, namely Automaton Control Systems (AC Systems), Grammar Control Systems (GC Systems) and Leftmost-derivation-based Grammar Control Systems (LGC Systems). We formally study their key theoretical characterizations, such as generative power, equivalence and translation techniques, as well as their connections with supervisory control and regulated rewriting, including the relationships between AC systems and supervisory control, and between GC/LGC systems and regulated rewriting. We also discuss some applications of C systems and finally propose some open questions. © The British Computer Society 2013. All rights reserved. Source


Cui J.,Nanjing University of Aeronautics and Astronautics
Metrology and Measurement Systems | Year: 2015

Power electronic circuits (PECs) are prone to various failures, whose classification is of paramount importance. This paper presents a data-driven based fault diagnosis technique, which employs a support vector data description (SVDD) method to perform fault classification of PECs. In the presented method, fault signals (e.g. currents, voltages, etc.) are collected from accessible nodes of circuits, and then signal processing techniques (e.g. Fourier analysis, wavelet transform, etc.) are adopted to extract feature samples, which are subsequently used to perform offline machine learning. Finally, the SVDD classifier is used to implement fault classification task. However, in some cases, the conventional SVDD cannot achieve good classification performance, because this classifier may generate some so-called refusal areas (RAs), and in our design these RAs are resolved with the one-against-one support vector machine (SVM) classifier. The obtained experiment results from simulated and actual circuits demonstrate that the improved SVDD has a classification performance close to the conventional one-against-one SVM, and can be applied to fault classification of PECs in practice. © 2015 Polish Academy of Sciences. All rights reserved. Source


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. Source


Wang L.,Nanjing University of Aeronautics and Astronautics | Son I.-Y.,Rensselaer Polytechnic Institute | Yazici B.,Rensselaer Polytechnic Institute
Inverse Problems | Year: 2010

We develop a new passive image formation method capable of exploiting information about multiple scattering in the environment, as well as statistics of the objects to be imaged, additive noise and clutter, using measurements from a sparse array of receivers that rely on illumination sources of opportunity. The array of receivers can be distributed spatially in an arbitrary fashion with several hundred wavelengths apart. We use a physics-based approach to model a multiple-scattering environment and develop a statistical model that relates measurements in a given receiver to measurements in other receivers. The model is based on back-propagating measurements in a given receiver to a hypothetical target location and then forward propagating to another receiver location based on the Green's function of the background environment. We next address the imaging problem as a generalized likelihood ratio test (GLRT) for an unknown target location. The GLRT framework allows a priori scene, clutter and noise information to be incorporated into the problem formulation, as well as non-Gaussian data likelihood and a priori models. We address the spatially resolved hypothesis testing problem by constraining the associated discriminant functional to be linear and by maximizing the signal-to-noise ratio of the test statistics. We use the resulting spatially resolved test statistic to form the image. We present the resolution analysis of our imaging algorithms for free-space and a multiple-scattering environment model. Our analysis demonstrates the improvements in the point spread function and the signal-to-noise ratio of the reconstructed images when multiple scattering is exploited, as well as the potential artifacts and limitations. We present numerical experiments to demonstrate the performance of the resulting algorithms and to validate the theoretical findings. © 2010 IOP Publishing Ltd. Source


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. Source


Ye Y.,Nanjing University of Aeronautics and Astronautics | Pan Y.-J.,Dalhousie University | Hilliard T.,Dalhousie University
IEEE/ASME Transactions on Mechatronics | Year: 2013

In this paper, the activeness of bilateral communication with time-varying delay is analyzed. Based on the power-based time-domain passivity control previously proposed, a time-domain passivity control approach is derived for bilateral communication. Teleoperation experimental results verify the effectiveness. © 1996-2012 IEEE. Source


Song D.,Nanjing University of Aeronautics and Astronautics | Lu Y.Y.,City University of Hong Kong
Journal of Modern Optics | Year: 2013

For lamellar gratings and other layered periodic structures, the modal methods (including both analytic and numerical ones) are often the most efficient, since they avoid the discretization of one spatial variable. The pseudospectral modal method (PSMM) previously developed for in-plane diffraction problems of one-dimensional gratings achieves high accuracy for a small number of discretization points, and it outperforms most other modal methods. In this paper, an extension of the PSMM to conical diffraction problems is presented and implemented. Numerical examples are used to demonstrate the high accuracy and excellent convergence property of this method for both dielectric and metallic gratings. © 2013 Taylor & Francis. Source


Wang J.,Nanjing University of Aeronautics and Astronautics
ISA Transactions | Year: 2016

Restricted sensing and actuation control represents an important area of research that has been overlooked in most of the design methodologies. In many practical control engineering problems, it is necessitated to implement the design through a single sensor and single actuator for multivariate performance variables. In this paper, a novel approach is proposed for the solution to the single sensor and single actuator control problem where performance over any prescribed frequency band can also be tailored. The results are obtained for the broad band control design based on the formulation for discrete frequency control. It is shown that the single sensor and single actuator control problem over a frequency band can be cast into a Nevanlinna-Pick interpolation problem. An optimal controller can then be obtained via the convex optimization over LMIs. Even remarkable is that robustness issues can also be tackled in this framework. A numerical example is provided for the broad band attenuation of rotor blade vibration to illustrate the proposed design procedures. © 2016 ISA. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
AIP Advances | Year: 2013

The adhesion between two immiscible polymers stitched together via mobile promoters is studied with large scale molecular simulations employing a coarse-grained bead-spring model. An adhesion model is presented that enables both connector molecular slipping out viscously and bulk dissipation in two dissimilar glassy polymers, in which one is dense melt and another is loose. The contributions to the separation work from thermodynamics and chain suction are studied in dependence of the connector areal density, at constant temperature, and at fixed basic molecular parameters. It is shown that high connector coverage, but below saturation areal density, can enhance the adhesion toughness and interfacial strength. Bulk dissipation is not considerable with low connector areal density in mushroom regime, while becomes more evident in the loose block when the coverage density is increased up to overlapping brush regime. With increasing connector length, both bulk melts are enhanced by the segments of connector chains that penetrated in. The results provide insight into the structure evolution of adhesion interface coupled with promoter molecular, which are useful for future developments of continuum cohesive models for fracture of polymer- polymer interfaces. Copyright © 2013 Author(s). Source


Liu G.,Harbin Institute of Technology | Wang J.,Harbin Institute of Technology | Dang K.,Harbin Institute of Technology | Tang Z.,Nanjing University of Aeronautics and Astronautics
Materials | Year: 2014

A new high strain rate forming process for titanium alloys is presented and named High Pressure Pneumatic Forming (HPPF), which might be applicable to form certain tubular components with irregular cross sections with high efficiency, both with respect to energy cost and time consumption. HPPF experiments were performed on Ti-3Al-2.5V titanium alloy tubes using a square cross-sectional die with a small corner radius. The effects of forming of pressure and temperature on the corner filling were investigated and the thickness distributions after the HPPF processes at various pressure levels are discussed. At the same time, the stress state, strain and strain rate distribution during the HPPF process were numerically analyzed by the finite element method. Microstructure evolution of the formed tubes was also analyzed by using electron back scattering diffraction (EBSD). Because of different stress states, the strain and strain rate are very different at different areas of the tube during the corner filling process, and consequently the microstructure of the formed component is affected to some degree. The results verified that HPPF is a potential technology to form titanium tubular components with complicated geometrical features with high efficiency. © 2014 by the authors. Source


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. Source


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. Source


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. Source


Zhang W.,Nanjing University of Aeronautics and Astronautics
Applied Mechanics and Materials | Year: 2012

As one of the key technologies, preparation of silicon nanospheres is very important for developing the new types of silicon based solar cells. In this paper, with the establishment of a novel electrical discharge machining (EDM) system and the raw material of heavy doped mono-crystalline silicon (0.01Ω•cm), silicon nanospheres of which diameter are ranging from 25nm to 280nm have been successfully prepared by using EDM method. The micro surface topography and the elements composition are analyzed by the SEM and the EDS methods respectively. The formation mechanism of nanospheres has also been studied. © (2012) Trans Tech Publications, Switzerland. Source


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. Source


Dai Q.,Nanjing University of Aeronautics and Astronautics
Knowledge-Based Systems | Year: 2013

Ensemble pruning is crucial for the consideration of both efficiency and predictive accuracy of an ensemble system. This paper proposes a new Competitive technique for Ensemble Pruning based on Cross-Validation (CEPCV). The data to be learnt by neural computing models are mostly drifting with time and environment, therefore a dynamic ensemble pruning method is indispensable for practical applications, while the proposed CEPCV method is just the kind of dynamic ensemble pruning method, which can realize on-line ensemble pruning and take full advantage of potentially valuable information. The algorithm naturally inherits the predominance of cross-validation technique, which implies that those networks regarded as winners in selective competitions and chosen into the pruned ensemble have the "strongest" generalization capability. It is essentially based on the strategy of "divide and rule, collect the wisdom", and might alleviate the local minima problem of many conventional ensemble pruning approaches only at the cost of a little greater computational cost, which is acceptable to most applications of ensemble learning. The comparative experiments among the four ensemble pruning algorithms, including: CEPCV and the state-of-the-art Directed Hill Climbing Ensemble Pruning (DHCEP) algorithm and two baseline methods, i.e. BSM, which chooses the Best Single Model in the initial ensemble based on their performances on the pruning set, and ALL, which reserves all network members of the initial ensemble, on ten benchmark classification tasks, demonstrate the effectiveness and validity of CEPCV. © 2012 Elsevier B.V. All rights reserved. Source


Dai Q.,Nanjing University of Aeronautics and Astronautics
Knowledge-Based Systems | Year: 2013

Ensemble pruning is substantial for the successful application of an ensemble system. A novel method for Ensemble Pruning via BackTracking algorithm (EnPBT) was proposed by us in our previous work. Backtracking algorithm can systematically search for the solutions of a problem in a depth-first and jumping manner, suitable for solving all those large-scale combinatorial problems. The validity of EnPBT algorithm has been verified in our previous work. However, the relatively slow pruning speed might be a drawback of EnPBT. Aiming at this problem, an efficient and novel ensemble pruning algorithm is proposed in this paper, i.e. One-Path and Two-Trips (OPTT) ensemble pruning algorithm. It is very fast in pruning speed, while its classification performance has no significant difference with EnPBT, as demonstrated in the experimental results of this work. In short, OPTT achieves a proper trade-off between pruning effectiveness and efficiency. © 2013 Elsevier B.V. All rights reserved. Source


Zhen Z.-Y.,Nanjing University of Aeronautics and Astronautics
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2016

Preview control can improve control system performance by utilizing future desired or external disturbance information. Therefore, more and more applications are seen in various real engineering fields, attracting a wide spread attention of researchers. This article comprehensively overviews the preview control research achievement since 196's, and especially introduces the theoretical research progress of linear optimal preview control, linear robust preview control and nonlinear preview control. Furthermore, the application developments of preview control in vehicle active suspension systems, electromechanical servo systems, robots, aircraft and power generation systems are summarized. Finally, the research achievements of the preview control are summarized, and the main problems in researches are discussed to forecast the future development direction. The author hopes to promote the integrated development of the theory and applications of the preview control. Copyright © 2016 Acta Automatica Sinica. All rights reserved. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
Computational Materials Science | Year: 2014

First-principles density-functional investigations on H6-carbon of all sp2-bonds are presented, which show that H6-carbon is stable under isotropic deformations and tetragonal deformations of volume-conserving. However, H6-carbon cannot withstand trigonal deformations and may undergo phase transitions under triaxial shear, although it presents a bulk modulus of 273 GPa as a hard material. H6-carbon also exhibits metastability against diamond as the difference of cohesive energy is 0.80 eV. Small electronic energy gap of band structure indicates that H6-carbon is metallic. © 2013 Elsevier Inc. All rights reserved. Source


Dong J.,Nanjing University of Aeronautics and Astronautics
Journal of Mathematical Physics | Year: 2011

We study the Green's function of the time-dependent 3D space-fractional Schrödinger equation for the scattering problem in the fractional quantum mechanics. The Green's function is expressed in terms of Fox's H-function and in a computable series form. We get the asymptotic formula of the Green's function, and apply it to obtain the approximate wave function for the fractional quantum scattering problem. © 2011 American Institute of Physics. Source


Meng L.,Nanjing University of Aeronautics and Astronautics
Materials Science Forum | Year: 2016

Finite element simulations of high speed machining of Ti6Al4V alloy were carried out based on Abaqus. The Johnson-Cook constitutive model was chosen for the titanium alloy Ti6Al4V, the parameters of the constitutive model were obtained through the SHPB (Split Hopkinson Pressure Bar) experiment. The similarity of the chips obtained from the simulations and that from the experiments indicated that the parameters of the constitutive model for titanium alloy Ti6Al4V were reliable. Different cutting parameters and different tool geometric parameters were applied in the simulations to find out their effects to the simulation results. Comparisons were made between the results obtained from the simulations and that from the experiments, a good agreement between them indicated that the finite element simulation of high speed machining of Ti6Al4V in this paper is reliable. It can be concluded that the finite element simulations of high speed machining can be widely used in practice to help the researchers to study more about the machining process and reduce the experimental expenses. © 2016 Trans Tech Publications, Switzerland. Source


Wang D.-S.,Nanjing University of Aeronautics and Astronautics
Journal of Applied Physics | Year: 2012

SrBi 2Ta 2O 9 (SBT) thin films were prepared on Pt/TiO 2/SiO 2/Si substrates by metalorganic decomposition method. The dielectric properties of SBT films strongly depend on annealing conditions and annealing time. Compared with films not annealed in forming gas, the relative dielectric constant and the dissipation factor for SBT films annealed at 400 °C decrease by 23.4 and 30.6, respectively. It implies that the dominant dielectric loss mechanism is related to the degradation of films. Forming gas ambient may have played an important role in the increase of oxygen vacancies in SBT thin films and the degradation of dielectric properties. © 2012 American Institute of Physics. Source


Chen K.,Nanjing University of Aeronautics and Astronautics
International Journal of Production Economics | Year: 2012

This paper investigates the coordination mechanism for supply chain with one manufacturer and multiple competing suppliers in the electronic market. We first study two conventional price-only policies, including wholesale price policy and catalog policy, based on the reverse Vickrey auction, and show that both the buyer and the powerful suppliers (with production cost less than a special threshold value) prefer catalog policy to wholesale price policy, and the powerless suppliers prefer wholesale price policy to catalog policy. Simultaneously, neither policy can coordinate the channel composed of the manufacturer and the winning supplier. We also show that a quantity discount policy cannot coordinate the supply chain with competing suppliers unless a kind of restriction is imposed. The aim of the paper is to explore a coordination mechanism, i.e., the price-restricted quantity-discount policy. Pareto analysis indicates that the manufacturer and the winning supplier will realize the 'win-win' situation, and the channel can also be coordinated. A key managerial implication of our study is that additional restrictive condition may be necessary to eliminate system inefficiency. Some numerical examples are also given to illustrate management insights. © 2012 Elsevier B.V. All rights reserved. Source


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. Source


Liu C.Y.,Nanjing University of Aeronautics and Astronautics
Advanced Materials Research | Year: 2014

Thermal energy sources have been applied for softening the difficult-to-machine material when it is combined with conventional machining processes. Cutting forces has been reduced during the process. To investigate the plastic deformation property of workpiece materials heated by thermal sources, and its influence to the cutting forces, the analytical model of orthogonal cutting is established. The impact of cutting speed and initial temperature of the shear banding to the cutting forces are taken account of, based on adiabatic shear banding model and Johnson-Cook material constitutive law. The shear banding average shear stress failure criteria has been proposed to decide the fracture between workpiece and chip. Simulation has been carried out and compared with experimental data of laser-heat assisted titanium alloy milling, showing good agreement. © (2014) Trans Tech Publications, Switzerland. Source


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. Source


Bhuyan S.,iversity | 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. Source


Zhang M.,Nanjing University of Aeronautics and Astronautics
MATEC Web of Conferences | Year: 2016

In order to response to the increasingly polluted environment, maintain sustainable economic and social development in Jiangsu province, the author calculated the index of the resource environment in Jiangsu, using LMDI(logarithmic-mean Divisia index) decomposition method based on the Commoner model(we can see from formula(2),(5),(6)&(7)), to reflect the three major influencing factors of cumulative effects. In table 2 and figure 3, the research results show the expansion of the size of economy and growth of population make resources consumption increase and environmental pollution aggravate, while technological progress reduce the pressure of resources and environment. According to the findings, the paper proposes the policy recommendations, such as develop circular economy, promote technological innovation and strengthen regional cooperation mechanism and so on to reduce the environmental pollution while economic developing. These will be useful to the policymakers. © Owned by the authors, published by EDP Sciences, 2016. Source


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. Source


Wang P.,Nanjing University of Aeronautics and Astronautics
Mathematical Methods in the Applied Sciences | Year: 2015

In this paper, we develop a continuation principle for general hyperbolic singular limit problems in more general Besov spaces, which covers the cases of usual Sobolev spaces with higher regularity in and the critical Besov space. As an application, we give a simple justification for the low Mach number limit of compressible magnetohydrodynamics equations. More precisely, for the Mach number sufficiently small, the smooth compressible flows exist on the (finite) time interval where the incompressible magnetohydrodynamics equations have smooth solutions, and the definite convergence orders are also obtained. Copyright © 2014 John Wiley & Sons, Ltd. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
Physica B: Condensed Matter | Year: 2013

Experiments show that there is a novel hexagonal carbon polymorph restricted to the space group of P-62c, but the detailed atomic structure is not determined. Here we set carbon atoms occupying P-62c 4f or P-62c 2c and 2d Wyckoff positions, and calculate the total energy of the different cell structures changing the internal parameter by first-principles calculations, which demonstrates that the stable structures in energy (at local minima) are hexagonal carbon (P-62c 2c and 2d) and hexagonal diamond (P-62c 4f, z=1/16). The calculated bulk modulus 437±16 GPa and interlayer distance 2.062 Å of the layered graphene structure P-62c 2c and 2d are in good agreement with those of the proposed new carbon, which indicates that P-62c 2c and 2d is a possible precursor or intermediate hard phase during the structural transformation of carbon. © 2013 Elsevier Ltd. All rights reserved. Source


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

Ring-like vortex is a flow structure at late stages of a transitional boundary layer. Independent to the initial disturbance conditions corresponding to K- and N-scenarios of transition, the vortical structure shows some universal features. The nonlinear evolution of the ring-like vortices, detail flow structures around ring-like vortex and their effects on the surrounding flow were studied by direct numerical simulation with high order accuracy. A detailed enforced spatial transition on a flat-plate boundary layer in the compressible flow was studied. This study reveals the mechanism of the second sweep generation, mechanism of the positive spike formation and mechanism of high shear layer distribution. © 2010 Elsevier Ltd. Source


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. Source


The fatigue behavior of cross-ply C/SiC and 2D woven SiC/SiC composites at elevated temperatures in air or steam condition have been investigated using the hysteresis dissipated energy. The evolution of fatigue hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter of C/SiC and SiC/SiC composites have been analyzed. For SiC/SiC composite at 1000 °C in steam, the experimental fatigue hysteresis dissipated energy lies in the right part of the fatigue hysteresis dissipated energy versus interface shear stress curve, which indicates that the interface partially debonds during cyclic fatigue loading; however, for C/SiC composite at 800 °C in air, the experimental fatigue hysteresis dissipated energy lies in the right and left part of the fatigue hysteresis dissipated energy versus interface shear stress curve, which indicates that the interface completely debonds upon initial cyclic fatigue loading. By comparing the experimental fatigue hysteresis dissipated energy with theoretical computational values, the interface shear stress of C/SiC and SiC/SiC composites have been estimated. The interface shear stress of C/SiC composite at 800 °C in air decreases much more rapidly than that of SiC/SiC composite at higher temperatures in air or steam condition. © 2016. Source


Cui S.,State Key Laboratory of Natural Medicines | Chen H.,State Key Laboratory of Natural Medicines | Zhu H.,State Key Laboratory of Natural Medicines | Tian J.,State Key Laboratory of Natural Medicines | And 4 more authors.
Journal of Materials Chemistry | Year: 2012

Upconversion nanoparticles (UCNPs) have attracted much attention as potential photosensitizer carriers for photodynamic therapy (PDT) in deep tissues. In this study, hydrophilic UCNPs were prepared by coating amphiphilic chitosan (N-succinyl-N′-octyl chitosan, SOC) on the surface of hydrophobic oleic acid-capped NaYF 4 UCNPs (OA-UCNPs). Water-insoluble photosensitizer zinc(ii) phthalocyanine (ZnPc) was loaded into the SOC-coated UCNPs (SOC-UCNPs) via hydrophobic interactions to form a novel drug delivery system for in vivo deep tissue PDT triggered by near-infrared (NIR) light. The ZnPc-loaded SOC-UCNPs exhibited good dispersibility, excellent optical properties and good photostability. Under NIR light irradiation, the measurement of singlet oxygen production indicated that ZnPc effectively generated singlet oxygen induced by the emission from the UCNPs. Cell viability assays showed the low cytotoxicity of the UCNPs after surface modification. In vitro and in vivo therapeutic investigation evidenced the prominent PDT effects of ZnPc-loaded SOC-UCNPs upon NIR light irradiation. Furthermore, NIR imaging of ICG derivative-loaded SOC-UCNPs after intra-tumoral injection indicated the high retention of SOC-UCNPs only in the tumor site. Histological examination confirmed the negligible toxicity of ZnPc-loaded SOC-UCNPs on other organs. All the results demonstrate the promising potential of using SOC-UCNPs as new photosensitizer carriers for PDT of cancer and other diseases in deep tissues. © 2012 The Royal Society of Chemistry. Source


Niu Z.P.,Nanjing University of Aeronautics and Astronautics
EPL | Year: 2013

We investigate thermally induced spin currents through a two-dimensional normal/ferromagnetic/normal graphene (NG/FG/NG) junction with an energy gap in the FG. By applying temperature difference between two NG electrodes, spin-up and spin-down currents flowing in opposite directions cancel each other out, resulting in pure spin currents. These currents can be modulated by adjusting the gate voltage Vg and the Fermi energy and can flow in the same direction. For nonzero Vg fully polarized currents can be observed. When the NG/FG/NG junction is extended to a NG/FG/NG/FG/NG structure a large thermal magnetoresistance is obtained. These devices can be realized with current technologies and may have practical use in spin caloritronics and quantum information. © Copyright EPLA, 2013. Source


Xu J.,Nanjing University of Aeronautics and Astronautics | Kawashima S.,Kyushu University
Archive for Rational Mechanics and Analysis | Year: 2015

We give a new decay framework for the general dissipative hyperbolic system and the hyperbolic–parabolic composite system, which allows us to pay less attention to the traditional spectral analysis in comparison with previous efforts. New ingredients lie in the high-frequency and low-frequency decomposition of a pseudo-differential operator and an interpolation inequality related to homogeneous Besov spaces of negative order. Furthermore, we develop the Littlewood–Paley pointwise energy estimates and new time-weighted energy functionals to establish optimal decay estimates on the framework of spatially critical Besov spaces for the degenerately dissipative hyperbolic system of balance laws. Based on the Lp(ℝn) embedding and the improved Gagliardo–Nirenberg inequality, the optimal Lp(ℝn)-L2(ℝn)(1 ≦ p < 2) decay rates and Lp(ℝn)-Lq(ℝn)(1 ≦ p < 2 ≦ q ≦ ∞) decay rates are further shown. Finally, as a direct application, the optimal decay rates for three dimensional damped compressible Euler equations are also obtained. © 2015, Springer-Verlag Berlin Heidelberg. Source


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. Source


Yan Z.-Y.,Nanjing University of Aeronautics and Astronautics
Journal of Hydrodynamics | Year: 2010

Boundary element method accelerated by the precorrected-FFT (pFFT) algorithm is developed and implemented for acoustic scattering problems. Because models with very fine meshes can be computed using this method, high frequency responses can be simulated. In the implementation, constant triangular elements are applied. An example of a plane acoustic wave scattering by a rigid sphere is simulated to validate the in-house fast BEM code for acoustic scattering problems. Numerical results are compared with the corresponding analytical solutions and the solutions by the conventional boundary element method. As a result, the pFFT accelerated boundary element method greatly improve the computational efficiency and reduce the requirement of storage largely. The accuracy by this method is comparable to that by the conventional boundary element method as the grid-order is no less than 4. © 2010 Publishing House for Journal of Hydrodynamics. Source


Wang L.,Nanjing University of Aeronautics and Astronautics | Cheney M.,Rensselaer Polytechnic Institute | Borden B.,Naval Postgraduate School, Monterey
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

We develop a linearized imaging theory that combines the spatial, temporal, and spectral aspects of scattered waves. We consider the case of fixed sensors and a general distribution of objects, each undergoing linear motion; thus the theory deals with imaging distributions in phase space. We derive a model for the data that is appropriate for narrowband waveforms in the case when the targets are moving slowly relative to the speed of light. From this model, we develop a phase-space imaging formula that can be interpreted in terms of filtered backprojection or matched filtering. For this imaging approach, we derive the corresponding phase-space point-spread function (PSF). We show plots of the phase-space point-spread function for various geometries. We also show that in special cases, the theory reduces to: 1) range-Doppler imaging, 2) inverse synthetic aperture radar (ISAR), 3) synthetic aperture radar (SAR), 4) Doppler SAR, and 5) tomography of moving targets. © 2006 IEEE. Source


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. Source


Dai Z.,Nanjing University of Aeronautics and Astronautics
Nanjing Hangkong Hangtian Daxue Xuebao/Journal of Nanjing University of Aeronautics and Astronautics | Year: 2012

The problems in the development of bionic robots, the biological basis and the future of animal-motion bionics are generally reviewed, and the development opportunities as well as problems to be faced in the animal-motion bionics are discussed. At the same time, it is pointed out that the advanced environment perception technology, the multistep actuator driven by smart material, the multi-bar compound mobile robot and its intelligent control technology, and the research on the law of animal motion will be the developing trend in the future. Source


Qin Y.,Nanjing University of Aeronautics and Astronautics
Zhendong Ceshi Yu Zhenduan/Journal of Vibration, Measurement and Diagnosis | Year: 2012

A method of using the tensor product wavelet theory and the orthogonality of Daubechies wavelet to identify the distributed dynamic load acting on a beam is presented. The method is also named as wavelet Galerkin method. The dynamic equation and the finite element equation of the beam are transformed from time domain into wavelet domain, so the convolution equation is replaced by a simple linear equation group. The simulation example shows that the method can effectively identify the one-dimensional distribution dynamic load and has high calculation efficiency. Source


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. Source


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. Source


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
PLoS ONE | Year: 2012

Accurate prediction of clinical changes of mild cognitive impairment (MCI) patients, including both qualitative change (i.e., conversion to Alzheimer's disease (AD)) and quantitative change (i.e., cognitive scores) at future time points, is important for early diagnosis of AD and for monitoring the disease progression. In this paper, we propose to predict future clinical changes of MCI patients by using both baseline and longitudinal multimodality data. To do this, we first develop a longitudinal feature selection method to jointly select brain regions across multiple time points for each modality. Specifically, for each time point, we train a sparse linear regression model by using the imaging data and the corresponding clinical scores, with an extra 'group regularization' to group the weights corresponding to the same brain region across multiple time points together and to allow for selection of brain regions based on the strength of multiple time points jointly. Then, to further reflect the longitudinal changes on the selected brain regions, we extract a set of longitudinal features from the original baseline and longitudinal data. Finally, we combine all features on the selected brain regions, from different modalities, for prediction by using our previously proposed multi-kernel SVM. We validate our method on 88 ADNI MCI subjects, with both MRI and FDG-PET data and the corresponding clinical scores (i.e., MMSE and ADAS-Cog) at 5 different time points. We first predict the clinical scores (MMSE and ADAS-Cog) at 24-month by using the multimodality data at previous time points, and then predict the conversion of MCI to AD by using the multimodality data at time points which are at least 6-month ahead of the conversion. The results on both sets of experiments show that our proposed method can achieve better performance in predicting future clinical changes of MCI patients than the conventional methods. © 2012 Zhang et al. Source


Wang J.,University of Dayton | Wang J.,Nanjing University of Aeronautics and Astronautics | Chen W.,University of Dayton | Zhan Q.,University of Dayton
Optics Express | Year: 2010

We report a new method to create high purity longitudinally polarized field with extremely long depth of focus in the focal volume of a high numerical aperture (NA) objective lens. Through reversing the radiated field from an electric dipole array situated near the focus of the high-NA lens, the required incident field distribution in the pupil plane for the creation of an ultra-long optical needle field can be found. Numerical examples demonstrate that an optical needle field with a depth of focus up to 8λ is obtainable. Throughout the depth of focus, this engineered focal field maintains a diffraction limited transverse spot size (<0.43λ) with high longitudinal polarization purity. From the calculated pupil plane distribution, a simplified discrete complex pupil filter can be designed and significant improvements over the previously reported complex filters are clearly demonstrated. © 2010 Optical Society of America. Source


Wu Y.,Yancheng Institute of Technology | Kan J.,Yancheng Institute of Technology | Xie S.,Nanjing University of Aeronautics and Astronautics
Dianli Xitong Zidonghua/Automation of Electric Power Systems | Year: 2012

The line impedance is resistive in low voltage microgrids. In order to ensure that the output impedance matches the line impedance, virtual impedance is introduced to the control strategy for inverters. The impact of integral coefficient voltage loop on output impedance is analyzed. The improvement of voltage loop integral coefficient can make the output impedance become resistive provided that the inverter is in a stable operation state. From the analysis on equivalent circuit of a low voltage microgrid, it is concluded that the active power and reactive power can be changed by adjusting the output voltage amplitude and frequency of the inverter respectively. The impact of parameter examination error on output power of the power inverter is analyzed. The amplitude and frequency proportional-integral (PI) regulators are introduced to droop control strategy, which can realize zero-error tracking of the output power. The simulation results verify that the performance of the proposed control strategy is excellent both in grid-connected mode and islanded mode. © 2012 State Grid Electric Power Research Institute Press. Source


Zhou Q.,CAS Research Center for Eco Environmental Sciences | Pan G.,CAS Research Center for Eco Environmental Sciences | Zhang J.,Nanjing University of Aeronautics and Astronautics
Chemosphere | Year: 2013

The hexadecyltrimethylammonium bromide (HDTMAB) immobilized hollow mesoporous silica spheres were prepared for the efficient removal of perfluorooctane sulfonate (PFOS) from aqueous solution. Besides the traditional sorption behavior including sorption kinetics as well as effect of solution pH and temperature, the effect of increasing volume which simulated the natural river where the rate of solute and solvent was relatively constant and solution volume was always changing was investigated. The result indicated that the residual PFOS concentrations in aqueous phase decreased with increasing solution pH and ionic strength, whereas they increased with increasing temperature. The HDTMAB immobilized material still maintained high efficiency after increasing volume, that is, the removal kept more than 99% after the treatment when the initial PFOS concentration was 1mgL-1. The uptake behavior and morphology of spheres which was characterized by transmission electron microscopy (TEM) revealed that the additional HDTMAB and mesoporous shell were responsible for the enhanced sorption of PFOS. It was concluded that electrostatic interaction and Ca-bridge role played an important role in the sorption of PFOS on the mesoporous SiO2 hollow spheres, whereas, hydrophobic interaction contributed to the nice sorption performance of PFOS on the HDTMAB immobilized sorbent. © 2012 Elsevier Ltd. Source


Xudong W.,Nanjing University of Aeronautics and Astronautics
Eurasip Journal on Advances in Signal Processing | Year: 2010

This paper presents a novel ESPRIT algorithm-based joint angle and frequency estimation using multiple-delay output (MDJAFE). The algorithm can estimate the joint angles and frequencies, since the use of multiple output makes the estimation accuracy greatly improved when compared with a conventional algorithm. The useful behavior of the proposed algorithm is verified by simulations. © 2010 Wang Xudong. Source


Yingfei G.,Nanjing Institute of Technology | Jiuhua X.,Nanjing University of Aeronautics and Astronautics | Hui Y.,Beijing Precision Engineering Institute for Aircraft Industry
Wear | Year: 2010

The wear pattern and its mechanisms of single crystal diamond (SCD) and polycrystalline diamond (PCD) tools have been investigated experimentally and theoretically during ultra-precision turning of SiC particle-reinforced 2009 aluminum matrix composite under wet machining conditions. The results showed that microwear, chipping, cleavage, abrasive wear and chemical wear were the dominating wear patterns of SCD tools, and PCD tools mainly suffered from abrasive wear on the rake face and adhesive wear on the flank face. The local temperature increase in the workpiece material adjacent to the contact surface of SCD tool was approximately as high as 505. °C. The combined effects of abrasive wear of SiC particles and catalysis of copper in the aluminum matrix caused the severe graphitization of SCD tool with (rake face 1. 1. 0-flank 1. 1. 0) crystal orientation. The adhesive wear on PCD tool was induced by the intermittent growth and breaking off behavior of build-up-edge. SCD tool with the crystal orientation of (rake face 1. 1. 0-flank 1. 0. 0) had the best cutting performance among the three types of tools, by which the machined surface roughness Ra was less than 49 nm after cutting for over 9 km. PCD tool had a steady and favorable cutting performance and could produce acceptable surface quality when the cutting distance was less than 6 km, during which the value of Ra was less than 46 nm and varied in the range of 12-15 nm. For this tool, adhesive wear on the rake face and abrasive wear on the flank increased gradually with the increase of cutting distance. The flank wear value of PCD was only 50 μm which was slightly higher than that of straight-nose SCD (40 μm) when cutting for 6.22 km. For all the three types of tools, with the increase of cutting distance, the machining induced defects such as craters and scratches increased too. Especially, when cutting distance was long enough to cause severe tool wear, material swelling on the machined surface was severe due to the plastic side flow. The chips formed by PCD tool were more discontinuous and fragmentary than that for straight-nose SCD tool. © 2009. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Journal of Composite Materials | Year: 2015

When fiber-reinforced ceramic-matrix composites (CMCs) are first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. Under fatigue loading, the stress-strain hysteresis loops appear as the frictional slip occurred between the fiber and the matrix in the interface debonded region. The micromechanics fatigue hysteresis loops models of fiber-reinforced CMCs have been developed for different fiber preforms, i.e., unidirectional, cross-ply, and woven CMCs. The interface slip lengths, i.e., the interface debonded length upon first loading, unloading interface counter slip length, and reloading interface new slip length, were determined by fracture mechanics approach. The fatigue hysteresis loops of different interface debonding and slipping cases have been analyzed. The fatigue hysteresis loss energy is formulated in terms of fiber/matrix interface shear stress in the interface debonded region. When the interface shear stress decreases, the fatigue hysteresis loss energy first increases to the maximum value and then decreases to zero. By assuming the mechanical hysteresis behavior of cross-ply and woven CMCs was mainly controlled by interface frictional slip in the 0° plies or longitudinal yarns, considering the effect of matrix multicracking modes in cross-ply or woven CMCs, the fatigue hysteresis loops of fiber-reinforced CMCs with different fiber preforms under different peak stresses corresponding to different number of applied cycles have been predicted. © The Author(s) 2015. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
Solid State Communications | Year: 2014

New H6-Boron (H6-B) is predicted by first-principles calculations of density-functional theory. The proposed boron crystal is a rigid three-dimensional network with covalent sp2 coordination only and short interatomic distance 1.605 Å. Our results show that the novel form of pure boron holds a bulk modulus of 148 GPa and an estimated high hardness of 51 GPa, and it is also metallic without doping with other elements. The cohesive energy is calculated as 6.34 eV/atom, comparable with other boron polymorphs, which indicates that H6-B could be thermodynamically stable at ambient pressure. These results speculate that H6-B is a potential candidate of all sp 2 covalent crystal. © 2013 Elsevier Ltd. All rights reserved. Source


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. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Composites Part B: Engineering | Year: 2016

In this paper, the tensile fatigue hysteresis behavior of unidirectional C/SiC ceramic-matrix composite under multiple loading stress levels has been investigated. The fatigue hysteresis loops and fatigue hysteresis loss energy corresponding to different number of applied cycles have been analyzed. Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading/reloading, the unloading interface counter-slip length and reloading interface new-slip length are determined by fracture mechanics method. The fatigue hysteresis loops models corresponding to different interface slip cases under multiple loading stress levels have been developed. The relationships between fatigue hysteresis loops, fatigue hysteresis loss energy and interface slip have been analyzed. The fatigue hysteresis loops of unidirectional C/SiC composite corresponding to different number of applied cycles under multiple loading stress levels have been predicted. © 2015 Elsevier Ltd. All rights reserved. Source


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. Source


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. Source


Fang T.,Nanjing University of Aeronautics and Astronautics | Ruan X.,Huazhong University of Science and Technology | Tse C.K.,Hong Kong Polytechnic University
IEEE Transactions on Power Electronics | Year: 2010

This paper explores a new configuration for modular inverter systems, namely, input-seriesoutput-series (ISOS) connected inverter systems, which are very suitable for high-input-voltage and high-output-voltage applications. The control objective of such systems is to achieve input voltage sharing (IVS) and output voltage sharing (OVS) among the constituent modules. This paper first reveals the relationship between IVS and OVS and points out that IVS and OVS can be simultaneously achieved only by the application of a compound strategy, which involves controlling IVS as well as controlling the magnitudes or phases of the modules output voltages. Then, a practical implementation of the compound strategy, which combines a method of IVS with synchronization of the output phase angles, is proposed. An analysis of the decoupling of the two control loops, along with the detailed description of their design, is also presented. Finally, experimental results are presented to verify the theoretical analysis. © 2006 IEEE. Source


Zhang X.,Nanjing University of Aeronautics and Astronautics | Chung H.S.-H.,City University of Hong Kong | Ruan X.,Huazhong University of Science and Technology | Ioinovici A.,Holon Institute of Technology
IEEE Transactions on Power Electronics | Year: 2010

A new current-driven soft-switched full-bridge converter is presented in this paper. By connecting a switched-capacitor snubber in parallel with the primary winding of the coupling transformer, all main switches are zero-current-switched (ZCS) and the switches in the snubber are zero-voltage-switched (ZVS). The proposed converter has the following key features. First, the transformer leakage inductance is utilized as a part of the resonant circuit for the soft-switching actions. Second, the snubber capacitor voltage is adaptively controlled: the capacitor is charged to the minimum necessary energy for switching the main switches at zero current, depending on the actual value of the input/load current. Thus, less resonant energy is circulated. Third, there is no extra voltage stress on the switches and the current through the switches is limited to the value of the input current. Consequently, the conduction losses are kept minimum. The cyclical switching operation and control of the converter are described. A tradeoff design of the snubber circuit is given: the requirement of reducing the duration of the resonant intervals for minimizing the duty-cycle loss is superimposed on the requirement of getting ZCS for a very large range of the line voltage and load. A 530-V/15-kV, 5-kW prototype has been built and evaluated. The experimental results confirmed the theoretical predictions. A comparative study on the converter efficiency with and without the proposed snubber circuit is given, showing the superiority of the proposed solution. © 2010 IEEE. Source


Wang L.,Nanjing University of Aeronautics and Astronautics
Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi | Year: 2013

Arterial spin labeling (ASL) technique is a kind of perfusion functional magnetic resonance imaging method that is based on endogenous contrast, and it can measure cerebral blood flow (CBF) noninvasively. The ASL technique has advantages of noninvasiveness, simplicity and relatively lower costs so that it is more suitable for longitudinal studies compared with previous perfusion methods, such as positron emission tomography (PET), single photon emission computed tomography (SPECT), CT and the contrast agent based magnetic resonance perfusion imaging. This paper mainly discusses the current clinical applications of ASL in brain diseases as cerebrovascular diseases, brain tumors, Alzheimer's disease and epilepsy, etc. Source


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. Source


Yan G.,Nanjing University of Aeronautics and Astronautics
Smart Materials and Structures | Year: 2013

This paper presents an investigation of the applicability of a Bayesian system identification theory for localizing damage in plate-like structures, while considering the uncertainties from modeling and measurement. Diagnostic Lamb waves are excited and received by a piezoelectric sensor network before and after damage to obtain scattered waves that contain characteristic information about the damage. After the time-of-flight (ToF) of the scattered waves in each actuator-sensor path is measured by a continuous wavelet transform (CWT), a Bayesian approach is developed to identify the damage location and wave velocity. By combining the prior information and the measured ToF data, Bayes' theorem is used to update the probability distributions of the parameters about the damage location and wave velocity. In particular, a Markov chain Monte Carlo (MCMC) method is employed for sampling the posterior distributions of the unknown parameters. A numerical study for an aluminum plate and experimental studies for a stiffened aluminum panel and a composite laminate are conducted to validate the proposed Bayesian damage localization approach. © 2013 IOP Publishing Ltd. Source


Meyer E.,AMD Inc | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Liu Y.-F.,Queens University
IEEE Transactions on Power Electronics | Year: 2012

A linear/nonlinear digital controller is presented that allows a Buck converter to recover from a load transient event with near-optimal voltage deviation and recovery time. A novel digital double accumulator calculation block is used to calculate the appropriate pulse width modulation switching time instants. The proposed controller possesses many advantages not demonstrated by a single controller in the previous literature. For example, unlike many previously proposed time-optimal digital controllers, the proposed controller provides an excellent transient response as it is capable of reacting asynchronously to a load transient event. In addition, it is demonstrated that the proposed controller can operate without requiring information pertaining to the Buck converters output inductor. Furthermore, the proposed controller can be extended to applications that require load-line regulation. Lastly, unlike all previous digital time-optimal controllers, the proposed controller does not require digital multiplier or divider blocks nor does it require 2-D lookup tables. Thus, the controller can be implemented through the use of low-cost field programmable gate arrays or complex programmable logic devices. © 2011 IEEE. Source


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. Source


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. Source


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. Source


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. Source


Ang H.,Nanjing University of Aeronautics and Astronautics
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2016

In order to explore the overall design method of micro air vehicle (MAV), this paper briefly introduces the concept and technical difficulties of the MAV based on the author's years of MAV research and test, it also proposes some thoughts on MAV design principle, discusses the research MAV and the practical MAV. The design features of different types of MAVs such as fixed wing, flapping wing and rotor MAVs are described. The strategies of MAV design are given and the special characteristics of MAV design are illustrated in terms of the contradiction and coordination of MAV design method and optimization problem. Finally, the development trend of MAV design is prospected, which provides the reference for the overall design of MAV. © 2016, Press of Chinese Journal of Aeronautics. All right reserved. Source


Su Y.,Nanjing University of Aeronautics and Astronautics
Applied Mechanics and Materials | Year: 2012

For the shortcomings of existing SDG modeling methods in fault diagnosis, a data-driven semi-quantitative SDG automatic graphical modeling approach and a direct manual SDG graphical modeling approach are investigated. Function failure analysis procedures and data modeling process based on system principle are introduced in detail, and relevant graphical modeling tool are developed. A fault diagnosis modeling for the air supply system of certain type of aircraft is taken as an illustration to verify the validity of proposed modeling method. © (2012) Trans Tech Publications. Source


A new method for detecting the boundary of an internal defect is proposed in this paper. The proposed method can be used in phase-shifting digital speckle pattern interferometry to detect accurately the boundary of an internal defect based on discontinuity of the second-order gradient of out-of-plane displacement in the direction perpendicular to the defect boundary. Both theoretical analysis and experimental result are presented in this paper. © 2013 Elsevier Ltd. Source


Zhou T.,Nanjing University of Aeronautics and Astronautics
Physical Review Letters | Year: 2011

Based on a four-layered self-doped t-J type model and the slave-boson mean-field approach, we study theoretically the superconductivity in the electron-doped and hole-doped layers. The neighbor layers are coupled through both the single electron interlayer hopping and pair tunneling effect. The superconducting gap magnitude for the electron-doped band is nearly twice that of the hole-doped one, which contrasts with our previous understanding of the electron-hole asymmetry in high-Tc superconductors but is consistent with recent angle-resolved photoemission spectroscopy experiments in four-layered materials Ba2Ca3Cu4O 8F2. Our results propose that the pair tunneling effect is important to examine the multilayered superconducting materials. © 2011 American Physical Society. Source


This paper proposes a new method for detecting the size and centroid of an internal defect based on the Radon transform and morphological operation. This method proposed in the paper can be used in phase-shifting digital speckle pattern interferometry to measure quantitatively the size of the internal defect and to determine accurately the centroid of the internal defect. Theoretical analysis, experimental result, and error calculation are presented in this paper. © 2014 Elsevier Ltd. Source


Fu J.,Queens University | Fu J.,International Rectifier | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Liu Y.-F.,Queens University | Sen P.C.,Queens University
IEEE Transactions on Power Electronics | Year: 2012

A new analytical switching loss model for power MOSFETs driven by the current source driver (CSD) is presented in this paper. The gate current diversion problem, which commonly exists in existing CSDs, is analyzed mathematically. In addition, a new accurate switching loss model considering every switching interval piecewisely is proposed. Based on the proposed loss model, the optimal design of the CSD inductor is achieved to minimize the total power loss for the buck converter. The experimental result verifies the proposed switching loss model and optimal design. The measured loss matches the calculated loss very well; the error between the calculated loss and measured one is less than 10% from 5 A load to 30 A load with 12 V input and 1.3 V output. As compared with the previous study, the efficiency with the optimal CSD inductor is improved from 86.1% to 87.6% at 12 V input and 1.3 V/20 A output and from 82.4% to 84.0% at 12 V input and 1.3 V/30 A output at 1 MHz switching frequency. As compared with the commercial driver-MOSFETs from Renesas and International Rectifier, the buck converter with the optimal CSD still shows better performance. © 2011 IEEE. Source


Fu J.,International Rectifier | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Liu Y.-F.,Queens University | Sen P.C.,Queens University | Ge L.,Anhui University of Technology
IEEE Transactions on Power Electronics | Year: 2012

A novel bipolar current source driver (CSD) for power MOSFETs is proposed in this paper. The proposed bipolar CSD alleviates the gate current diversion problem of the existing CSDs by clamping the gate voltage to a flexible negative value (such as-3.5 V) during turn-off transition. Therefore, the proposed driver is able to turn off the MOSFET much faster with a higher effective gate current. The idea presented in this paper can also be extended to other CSDs to further improve the efficiency with high output currents. The experimental results verify the benefits of the proposed CSD. For buck converters with 12 V input at 1 MHz switching frequency, the proposed driver improves the efficiency from 80.5 using the existing CSD to 82.5% (an improvement of 2%) at 1.2 V/30 A, and at 1.3 V/30 A output, from 82.5% using the existing CSD to 83.9% (an improvement of 1.4%). © 2011 IEEE. Source


Huang Z.,Nanjing University of Aeronautics and Astronautics
Mechanics of Advanced Materials and Structures | Year: 2014

Nonlocal variational formulation is established for continuum with the internal long-range interactions. Applying this theory, we develop a new microbeam model, which is used to investigate the scale effects of a micro-cantilever in micro-electro-mechanical system (MEMS). The calculations show that when the thickness of a micro-cantilever is on the micron-order of magnitude, the static deflection of the micro-cantilever increases with the thickness decreasing, but the eigenfrequency remains almost constant. The prediction for the static deflection agrees well with the existing experimental data. This new model provides a concise interpretation, distinguished from the strain gradient theory and surface elasticity, for the scale effects in MEMS. In this model, the scale effects are regarded due to the long-range interactions within material. Copyright © 2014 Taylor & Francis Group, LLC. Source


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. Source


Shen X.,Nanjing University of Aeronautics and Astronautics
Ferroelectrics | Year: 2011

A new type of large-displacement actuator called RAINBOW (Reduced And Internally Biased Oxide Wafer) was fabricated by a chemical reduction of PSZT antiferroelectric ceramics. It is found that PSZT was easily reduced and the optimal conditions for producing RAINBOW samples were determined to be 870°C for 2∼3 hours. The AFE-FE phase transitions occur at lower field strength for these reduced antiferroelectric ceramics compared with normal ones. Larger axial displacement (about 190 μm) were obtained from the samples. Furthermore, the possibility of the integration between antiferroelectric ceramics and SMA was also explored. PVD (Physical Vapor Deposition) method was applied to depose SMA (shape memory alloy) films on the reduced layers of the ceramic patches. Experimental results show that this integrated material has better mechanical properties and SMA films do contribute actuation to the whole composite actuating structure. So the integration method for these two kinds of functional materials is a reasonable idea to manufacture actuators with better performance. © Taylor & Francis Group, LLC. Source


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. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
Polymer (United Kingdom) | Year: 2013

The adhesion between two immiscible polymers stitched together via mobile chains is studied with large scale molecular simulations employing a coarse-grained bead-spring model. An adhesion model is presented that incorporates both connector molecular slipping out viscously and bulk dissipation in two dissimilar glassy polymers, in which one is dense melt and another is loose. The contributions to the separation work from thermodynamics and chain suction are studied in dependence of the connector length, at constant temperature, and at fixed basic molecular parameters. It is shown that connector length relative to its entanglement length can enhance the adhesion toughness and interfacial strength. Bulk dissipation is not considerable with low connector areal density in mushroom regime, while becomes more evident in the loose melt with increasing connector length when the coverage density is increased up to overlapping brush regime. The results provide insight into the structure evolution of adhesion interface with mobile promoter molecular, which are useful for future developments of continuum cohesive models for fracture of polymer-polymer interfaces. © 2013 Elsevier Ltd. All rights reserved. Source


Ma H.-X.,Nanjing University of Aeronautics and Astronautics
Journal of Applied Optics | Year: 2013

In order to calculate the absorption efficiency of different double-clad optical fibers, two-dimensional analysis, three-dimensional analysis and fiber optics wave coupling theory were adopted in the past. A 3-D method based on Zemax software was introduced in this paper, the absorption efficiency of circular, offset, rectangular, D-shape, octagonal double-clad fibers were investigated by writing ZPL macros, and the results were compared with the data obtained from the 2-D analysis. Data showed that two results were similar and the absorption efficiency trends of different inner-clad fibers were same. The solution based on Zemax had many advantages in comparison with the 2-D analysis. The simulation based on Zemax was more vivid because the relationship between the absorption efficiency and fiber length could be achieved, however, the relationship between the absorption efficiency and reflection times was obtained based on the 2-D analysis. The critical angle could be set in Zemax, rays with arbitrary angle were emitted from the arbitrary point in the inner-clad section in the 2-D analysis ignoring ray total reflection condition in the inner-clad, so the result based on Zemax was more accurate. It was easy to simulate the different inner-clad shapes and the non-sequential ray tracing velocity was very fast, the operation time based on Zemax was 373 seconds, and was 1732 seconds based on 2-D analysis under the same condition for the same rectangular inner-clad fiber, so the calculate speed based on Zemax was more rapid. The absorption efficiency of a new structure double-clad fiber put forward by professor LOU Qi-hong was calculated finally. Source


Bi G.-B.,Anhui University of Science and Technology | Song W.,Anhui University of Science and Technology | Zhou P.,Nanjing University of Aeronautics and Astronautics | Liang L.,Anhui University of Science and Technology
Energy Policy | Year: 2014

Data envelopment analysis (DEA) has gained much popularity in performance measurement of power industry. This paper presents a slack-based measure approach to investigating the relationship between fossil fuel consumption and the environmental regulation of China's thermal power generation. We first calculate the total-factor energy efficiency without considering environmental constraints. An environmental performance indicator is proposed through decomposing the total-factor energy efficiency. The proposed approach is then employed to examine whether environmental regulation affects the energy efficiency of China's thermal power generation. We find that the environmental efficiency plays a significant role in affecting energy performance of China's thermal generation sector. Decreasing the discharge of major pollutants can improve both energy performance and environmental efficiency. Besides, we also have three main findings: (1) The energy efficiency and environmental efficiency were relatively low. (2) The energy and environmental efficiency scores show great variations among provinces. (3) Both energy efficiency and environmental efficiency are of obvious geographical characteristics. According to our findings, we suggest some policy implications. © 2013 Elsevier Ltd. Source


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. Source


Chen K.,Nanjing University of Aeronautics and Astronautics | Yang L.,South China University of Technology
International Journal of Production Research | Year: 2014

This paper considers a supply chain in which a buyer purchases finished items from a contracting supplier to satisfy a stochastic market demand, where the suppliers production is subject to random yield. We assume that the buyer can make up the shortage by sourcing from an emergency backup supplier. We develop two Stackelberg game models, i.e. buyer-Stackelberg (BS) model and supplier-Stackelberg (SS) model, and find that the decentralised BS model results in a higher stocking factor of suppliers input than the decentralised SS model. Compared with BS model, the buyer in SS model performs more explicit order plan, and we find that only when the actual yield of the supplier is insufficient, the buyer would use emergency backup sourcing to make up the shortage. When the manufacturing operation of the supplier is in the good state, the buyer only orders a certain amount and has some leftover. When the actual yield of the supplier is moderate, the buyer uses up every item produced from the supplier regardless of the yield rate. Comparing both channel structures, SS operation is a more effective way of controlling both inventory cost and backup sourcing cost, and it can be beneficial for each player as well as for the whole channel. Finally, we develop the coordination mechanism for each channel to investigate the issues of risk handling and risk sharing for uncertain demand and uncertain yield. © 2014 Taylor & Francis. Source


Zhang W.,Hong Kong Polytechnic University | Wong S.-C.,Hong Kong Polytechnic University | Tse C.K.,Hong Kong Polytechnic University | Chen Q.,Nanjing University of Aeronautics and Astronautics
IEEE Transactions on Power Electronics | Year: 2014

Inductive power transfer (IPT) is an emerging technology that may create new possibilities for wireless power charging and transfer applications. However, the rather complex control method and low efficiency remain the key obstructing factors for general deployment. In a regularly compensated IPT circuit, high efficiency and controllability of the voltage transfer function are always conflicting requirements under varying load conditions. In this paper, the relationships among compensation parameters, circuit efficiency, voltage transfer function, and conduction angle of the input current relative to the input voltage are studied. A design and optimization method is proposed to achieve a better overall efficiency as well as good output voltage controllability. An IPT system design procedure is illustrated with design curves to achieve a desirable voltage transfer ratio, optimizing between efficiency enhancement and current rating of the switches. The analysis is supported with experimental results. © 1986-2012 IEEE. Source


Zhang Z.-Y.,Nanjing University of Aeronautics and Astronautics
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014

We employ density-functional theory to investigate the strain engineering for infinitely long [0001] ZnO nanowires with rectangular cross sections. The structural and electronic properties of ZnO nanowires with uniaxial, lateral and shear strain are systemically calculated. The results show that the band-gaps of ZnONWs will decrease (increase) with increasing (decreasing) tensile (compressive) uniaxial strain. The tensile (compressive) lateral strain on {10 1Ì...0} surfaces will improve (reduce) the band-gaps for ZnONW with clearly nonlinear characteristic, while the change trend of band-gaps for ZnONW with lateral strain on {1 2Ì...10} surfaces is basically opposite. When we enhance shear strain on ZnONWs, the band-gaps are reduced. The increasing shear strain along [10 1Ì...0] direction will sharply reduce the band-gap and the curve is nonlinear, while the band-gap decreases nearly linearly with the increase of shear strain along [1 2Ì...10] direction. © 2014 Elsevier B.V. Source


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. Source


Zhou C.H.,Nanjing University of Aeronautics and Astronautics | Ai J.Q.,Aviation Industry Corporation of China
International Journal for Numerical Methods in Fluids | Year: 2013

In this work, an approach for performing mesh adaptation in the numerical simulation of two-dimensional unsteady flow with moving immersed boundaries is presented. In each adaptation period, the mesh is refined in the regions where the solution evolves or the moving bodies pass and is unrefined in the regions where the phenomena or the bodies deviate. The flow field and the fluid-solid interface are recomputed on the adapted mesh. The adaptation indicator is defined according to the magnitude of the vorticity in the flow field. There is no lag between the adapted mesh and the computed solution, and the adaptation frequency can be controlled to reduce the errors due to the solution transferring between the old mesh and the new one. The preservation of conservation property is mandatory in long-time scale simulations, so a P1-conservative interpolation is used in the solution transferring. A nonboundary-conforming method is employed to solve the flow equations. Therefore, the moving-boundary flows can be simulated on a fixed mesh, and there is no need to update the mesh at each time step to follow the motion or the deformation of the solid boundary. To validate the present mesh adaptation method, we have simulated several unsteady flows over a circular cylinder stationary or with forced oscillation, a single self-propelled swimming fish, and two fish swimming in the same or different directions. Copyright © 2012 John Wiley & Sons, Ltd. In each adaptation period, the mesh is refined in the regions where the solution evolves or the moving bodies pass and is unrefined in the regions where the phenomena or the bodies deviate. There is no lag between mesh and solution, and the adaptation frequency can be controlled to reduce the errors due to solution transferring. The number of mesh nodes can be reduced greatly when using a nonboundary-conforming method to simulate complex moving-boundary flows. © 2012 John Wiley & Sons, Ltd. Source


Niu Z.P.,Nanjing University of Aeronautics and Astronautics
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2011

We investigate the thermoelectric effects in a spin field-effect transistor with ferromagnetic leads held at different temperatures. The thermopower S and thermoelectric figure of merit ZT oscillate with the increase of the Rashba spin-orbit coupling strength. The oscillation amplitude of ZT decreases with increasing the spin polarization. S and ZT are strongly influenced by the interfacial barrier strength Z, exhibiting a nonmonotonous change with Z. The thermoelectric effects are also manipulated by the magnetization configuration of the ferromagnetic leads. It is expected that the present study of the thermoelectric effects is helpful in the design of thermoelectric devices. © 2011 Elsevier B.V. All rights reserved. Source


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. Source


Chen G.,Nanjing University of Aeronautics and Astronautics
Journal of Mechanical Science and Technology | Year: 2015

Blade-casing rubbing experiments, which include single-point rubbing and partial rubbing, are carried out on an aero engine rotor experimental rig with casings. Casing vibration acceleration signals are analyzed for extracting the rubbing faults’ characteristics. The results show that under rubbing, casing signals have obvious impact characteristics: impact frequency is the frequency of blades passing the casing, and it equals the product of rotating frequency and the number of blades; the frequency spectrum shows the blade-passage frequency and its multiple-frequencies; impact strength is modulated by the rotating frequency so that there are families of side bands on both sides of the blade-passage frequency and its multiple frequencies, and the side bands’ interval equals the rotating frequency. There are obvious quefrency components of the rotating frequency and its multiple frequencies in the cepstrum, and there is also a distinct rotating frequency and its multiple frequencies in the wavelet envelope spectrum. Finally, the rubbing characteristics determined in this study are verified by using test data from an actual aero engine. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg. Source


Staroswiecki M.,Ecole Normale Superieure de Cachan | Zhang K.,Nanjing University of Aeronautics and Astronautics | Berdjag D.,Ecole Normale Superieure de Cachan | Abbas-Turki M.,Ecole Normale Superieure de Cachan
IEEE Transactions on Automatic Control | Year: 2012

This note addresses reconfiguration-based fault tolerance under actuator faults, for linear time invariant systems. Based on the concept of bottom-up extensible controls, a fault tolerance scheme that mixes the passive and active approaches is designed to recover all recoverable faults, and an algorithm is proposed to reduce the reliability overcost with respect to previous designs. © 1963-2012 IEEE. Source


Jin K.,Nanjing University of Aeronautics and Astronautics | Xu M.,Virginia Polytechnic Institute and State University | Lee F.C.,Virginia Polytechnic Institute and State University
IEEE Transactions on Power Electronics | Year: 2010

This paper proposes a novel switching-capacitor pulsewidth modulation (PWM) converter. The converter is a combination of a switching-capacitor converter and a PWM converter, and it has the following advantages: 1) zero-voltage switching of all the MOSFETs; 2) with an autotransformer self-driven method, there is no need to adjust the synchronous rectifier control timing, and this reduces body diode conduction loss; 3) its efficiency is not sensitive to the leakage inductor, so a discrete transformer can be used, and it is suitable for both voltage regulator module (VRM) and voltage regulator down (VRD) application; and 4) a single-phase option makes it more flexible, and it can achieve higher efficiency in the whole load range with a phase-shedding control strategy. A 700-kHz 1.2-V/35-A POL prototype and a four-phase 700-kHz 1.2-V/130-A-output VRM prototype were built to verify the analysis. © 2010 IEEE. Source


Jiao S.,Tsinghua University | Xu Z.,Tsinghua University | Xu Z.,Nanjing University of Aeronautics and Astronautics
ACS Applied Materials and Interfaces | Year: 2015

Designing membrane materials from one-atom-thick structures is highly promising in separation and filtration applications for the reason that they offer the ultimate precision in modifying the atomic structures and chemistry for optimizing performance, and thus resolving the permeation-selectivity trade-off. In this work, we explore the molecular dynamics of gas diffusion in the gallery space between functionalized graphene layers as well as within nanopores across the multilayers. We have identified highly selective gas permeation that agrees with recent experimental measurements and is promising for advancing gas separation technologies such as hydrogen separation, helium/nitrogen generation, and CO2 sequestration. The roles of structural and chemical factors are discussed by considering different types of gases including H2, He, CH4, N2, O2, CO, CO2, and H2O. The overall performance of graphene oxide membranes is also discussed with respect to their microstructures, and compared with recent experimental measurements. These understandings could advise high-performance gas-separation membrane development by engineering assemblies of two-dimensional layered structures. © 2015 American Chemical Society. Source


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Meyer E.,Queens University | Liu Y.-F.,Queens University | Sen P.C.,Queens University
IEEE Transactions on Power Electronics | Year: 2010

In this paper, a new self-driven zero-voltage-switching (ZVS) nonisolated full-bridge converter is presented for 12-V input VRM applications. The advantages of the new circuit are: 1)duty cycle extension; 2) ZVS of all the control MOSFETs; 3) lower voltage stress and reduced reverse recovery loss of the synchronous rectifier (SR) MOSFETs; 4) high-drive voltage to reduce R D S(ON) and the conduction loss of the SRs due to gate energy recovery capability; and 5) reduced body-diode conduction and no external drive IC chips with dead time control needed for SRs. Existing multiphase buck controllers and buck drivers can be directly used in the proposed converter. The experimental results verify the principle of operation and significant efficiency improvement. At 12 V input, 1.3 V output voltage, and 1 MHz switching frequency, the proposed converter improves the efficiency, using the buck converter from 80.7% to 83.6% at 50 A, and from 77.9% to 80.5% at 60 A. With two parallel SRs, the efficiency is further improved from 83.6% (single SR) to 84.7% (two SRs) and at 60 A, the efficiency is improved from 80.5% (single SR) to 83.2% (two SRs). © 2010 IEEE. Source


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. Source


Niu Z.P.,Nanjing University of Aeronautics and Astronautics
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014

We study the spin-dependent thermoelectric transport through two-dimensional normal/ferromagnetic/normal/ferromagnetic/normal graphene (NG/FG/NG/FG/NG) junctions. It is found that both charge and spin thermopowers depend on the FGÊs magnetization direction and exhibit an anisotropic behavior. Interestingly, the spin thermopower can be as large as the charge thermopower and even can exceed the latter in magnitude. Moreover, the pure spin thermopower and spin current emerge in this device. The results obtained here suggest a feasible way of enhancing thermospin effects and generating the pure spin current in two-dimensional graphene. © 2013 Elsevier B.V. Source


Huang Z.,Paris West University Nanterre La Defense | Huang Z.,Nanjing University of Aeronautics and Astronautics | Wagner D.,Paris West University Nanterre La Defense | Bathias C.,Paris West University Nanterre La Defense | Paris P.C.,LAMEFIP EA 2727
Acta Materialia | Year: 2010

In the very high cycle regime (Nf < 107 cycles) cracks can nucleate on inclusions, "supergrains" and pores, which leads to fish-eye propagation around the defect. The initiation from an inclusion or other defect is almost equal to the total crack growth lifetime, perhaps much more than 99% of this lifetime in many cases. Integration of the Paris law allows one to predict the number of cycles to crack initiation. A cyclic plastic zone around the crack exists, and recording the surface temperature of the sample during the test may allow one to follow crack propagation and determine the number of cycles to crack initiation. A thermo-mechanical model has been developed. In this study several fish-eyes from various materials have been observed by scanning electron microscopy, and the fractographic results analyzed as they related to the mechanical and thermo-mechanical models. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


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. Source


Zhang Z.,Nanjing University of Aeronautics and Astronautics | Fu J.,Queens University | Liu Y.-F.,Queens University | Sen P.C.,Queens University
IEEE Transactions on Power Electronics | Year: 2010

This paper proposes a new current-source driver (CSD) with discontinuous inductor current. Compared to other CSDs proposed in the previous work, the most important advantage of the proposed CSD is the small inductance (typically, 20nH at 1 MHz switching frequency). This translates into the footprint reduction of as much as 90 compared with the continuous CSDs. Other features of the proposed CSD includes: 1) fast switching speed and reduced switching loss; 2) discontinuous inductor current with low circulating loss; 3) gate energy recovery; and 4) wide range of duty cycle and switching frequency. The experimental results verified the functionality of the proposed CSD. At 12 V input, 1.3 V output, and 1 MHz switching frequency, the new CSD improves the efficiency from 80.7 using a conventional driver to 85.7 at 25 A output, and at 30 A output, from 77.9 to 84.4. © 2011 IEEE. Source


Yang Y.,University of Arkansas | Yang Y.,Nanjing University of Aeronautics and Astronautics | Iniguez J.,CSIC - Institute of Materials Science | Mao A.-J.,University of Sichuan | Bellaiche L.,University of Arkansas
Physical Review Letters | Year: 2014

We report a first-principles study of the recently predicted Pmc21 phase of the multiferroic BiFeO3 material, revealing a novel magnetoelectric effect that makes it possible to control magnetism with an electric field. The effect can be viewed as a two-step process: Switching the polarization first results in the change of the sense of the rotation of the oxygen octahedra, which in turn induces the switching of the secondary magnetic order parameter. The first step is governed by an original trilinear-coupling energy between polarization, octahedral tilting, and an antiferroelectric distortion. The second step is controlled by another trilinear coupling, this one involving the predominant and secondary magnetic orders as well as the oxygen octahedral tilting. In contrast with other trilinear-coupling effects in the literature, the present ones occur in a simple ABO3 perovskite and involve a large polarization. © 2014 American Physical Society. Source


Song D.,Nanjing University of Aeronautics and Astronautics | Lu Y.Y.,City University of Hong Kong
Journal of Lightwave Technology | Year: 2014

For optical waveguides with high index-contrast and sharp corners, it is challenging to develop efficient, accurate and general full-vectorial mode solvers. The classical mode-matching method is capable of computing modes to high accuracy for waveguides with right-angle corners, but it is not convenient to implement when the waveguide has lossy components. Numerical variants of the mode-matching method, such as the Fourier modal method (as a mode solver), are simpler to implement. In this paper, a recently developed pseudospectral modal method for diffraction gratings is reformulated as a full-vectorial waveguide mode solver. As demonstrated in a number of examples, the method can be used to calculate waveguide modes to high accuracy, and it is relatively simple to implement. © 1983-2012 IEEE. Source


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. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Composites Part B: Engineering | Year: 2015

Under fatigue loading, the stress-strain hysteresis loops appear as fiber slipping relative to matrix in the interface debonded region. The area of hysteresis loops, i.e.; the hysteresis dissipated energy, changes with the increase of cycle number, and can reveal fatigue damage mechanisms, i.e.; matrix multicracking, fiber/matrix interface debonding, interface slipping, interface wear, and fibers fracture. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationships between the hysteresis dissipated energy, hysteresis dissipated energy-based damage parameter, stress-strain hysteresis loops, and fatigue damage mechanisms have been established. The effects of fatigue peak stress, stress ratio, matrix crack spacing and fiber volume content on the evolution of hysteresis dissipated energy and hysteresis dissipated energy-based damage parameter as a function of cycle number have been analyzed. It was found that the hysteresis dissipated energy-based damage parameter is much more sensitive to interface debonding and interface frictional slipping compared with the hysteresis dissipated energy under fatigue loading, and can be used to reveal the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs. The experimental fatigue life S-N curves of unidirectional CMCs have been predicted using the present analysis. © 2015 Elsevier Ltd. All rights reserved. Source


Sun J.,Nanjing University of Aeronautics and Astronautics
International Journal of Communication Systems | Year: 2016

Crowd sensing is a new paradigm that leverages pervasive sensor-equipped mobile devices to provide sensing services like forensic analysis, documenting public spaces, and collaboratively constructing statistical models. Extensive user participation is indispensable for achieving good service quality. Nowadays, most of existing mechanisms focus on guaranteeing good service quality based on instantaneous extensive user participation for crowd sensing applications. Little attention has been dedicated to maximizing long-term service quality for crowd sensing applications due to their heterogeneous interests, preferences, selfish behaviors, and so on. To fill these gaps, a closed-form expression of the marginal sensing data quality based on the monopoly aggregation in economics is derived in this paper. Furthermore, we design marginal quality-based incentive mechanisms for long-term crowd sensing applications not only to enhance extensive user participation by maximizing the expected total profits of mobile users but also to stimulate mobile users to produce high-quality contents by applying the marginal quality. Finally, simulation results show that our mechanisms outperform the existing solutions. Copyright © 2015 John Wiley & Sons, Ltd. Source


Ni Q.,Nanjing University of Aeronautics and Astronautics | Qi L.,Hong Kong Polytechnic University
Journal of Global Optimization | Year: 2015

In this paper we propose a quadratically convergent algorithm for finding the largest eigenvalue of a nonnegative homogeneous polynomial map where the Newton method is used to solve an equivalent system of nonlinear equations. The semi-symmetric tensor is introduced to reveal the relation between homogeneous polynomial map and its associated semi-symmetric tensor. Based on this relation a globally and quadratically convergent algorithm is established where the line search is inserted. Some numerical results of this method are reported. © 2014, Springer Science+Business Media New York. Source


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. Source


Li L.,Nanjing University of Aeronautics and Astronautics
Composites Part B: Engineering | Year: 2014

In this paper, the fatigue hysteresis behavior of unidirectional C/SiC ceramic-matrix composite at room and elevated temperatures in air atmosphere has been investigated. The fatigue hysteresis modulus and fatigue hysteresis loss energy corresponding to different cycles have been analyzed. An approach to model fatigue hysteresis loops of unidirectional ceramic composites considering fiber failure has been developed. Based on the damage mechanism of fiber slipping relative to matrix under fatigue loading, the unloading interface counter-slip length and reloading interface new slip length are determined by fracture mechanics approach. The interface shear stress and broken fibers fraction corresponding to different cycles are obtained through comparing the experimental fatigue hysteresis loss energy with theoretical computational value considering fiber failure. The fatigue hysteresis loops of unidirectional C/SiC composite have been predicted for different number of cycles. © 2014 Elsevier Ltd. All rights reserved. Source


Li L.,Nanjing University of Aeronautics and Astronautics
Engineering Fracture Mechanics | Year: 2015

This study investigates the synergistic effect of arbitrary loading sequence and interface wear on the fatigue hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs). Based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region, the interface debonded length, unloading interface counter-slip length and reloading interface new-slip length are determined by fracture mechanics approach. The effects of peak stress, material properties, interface wear and arbitrary loading stress levels on the interface slip and fatigue hysteresis loops have been analyzed. © 2015 Published by Elsevier Ltd. Source


Yuan Y.,Jiangsu University of Science and Technology | Liu H.,Nanjing University of Aeronautics and Astronautics
Meccanica | Year: 2012

Finite element model updating is a procedure to minimize the differences between analytical and experimental results and can be mathematically reduced to solving the following problem. Problem P: Let M a SR n×n and K a SR n×n be the analytical mass and stiffness matrices and λ=diagλ 1,⋯,λ p R p×p and X=[x 1,⋯,x p ] R n×p be the measured eigenvalue and eigenvector matrices, respectively. Find (M, K) ∈ S MK such that | M-M a | 2+| K-K a| 2= min(M,K) ∈ S MK (|M-M a| 2+|K-K a| 2), where SMK=(M,K)| X TMX=I p, MX Λ=K X and ∥·∥ is the Frobenius norm. This paper presents an iterative method to solve Problem P. By the method, the optimal approximation solution (M, K) of Problem P can be obtained within finite iteration steps in the absence of roundoff errors by choosing a special kind of initial matrix pair. A numerical example shows that the introduced iterative algorithm is quite efficient. © 2011 Springer Science+Business Media B.V. Source


The tension-tension fatigue behavior of unidirectional C/SiC ceramic-matrix composite at room temperature and 800 °C under air has been investigated. The fatigue hysteresis modulus and fatigue hysteresis loss energy corresponding to different number of applied cycles have been analyzed. The fatigue hysteresis loops models for different interface slip cases have been derived based on the fatigue damage mechanism of fiber slipping relative to matrix in the interface debonded region upon unloading and subsequent reloading. The fiber/matrix interface shear stress has been estimated for different numbers of applied cycles. By combining the interface shear stress degradation model and fibers strength degradation model with fibers failure model, the tension-tension fatigue life S-N curves of unidirectional C/SiC composite at room temperature and 800 °C under air have been predicted. © 2015 by the author. Source


Dai Q.,Nanjing University of Aeronautics and Astronautics
Applied Soft Computing Journal | Year: 2013

This paper proposes a novel approach, namely, the Back-propagation with diversive curiosity (DCPROP) algorithm, for solving the "flat spot" problem and for escaping from local minima. Representing the diversive curiosity, an internal indicator is designed for BP algorithm, which detects the phenomenon of being trapped in local minima and the occurrence of premature convergence. Upon such detection, the neural network is activated again to explore optimal solution in search space and escape form local minima by means of stochastic disturbance. The proposed DCPROP algorithm is implemented and applied to two well-known face recognition problems, and the results are compared with Standard Back-propagation (SBP). © 2012 Elsevier B.V. Source


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. Source


Qing H.,Nanjing University of Aeronautics and Astronautics
Journal of Nanoscience and Nanotechnology | Year: 2015

The influence of the distribution of particle shapes, locations and orientations on the mechanical behavior of the particle reinforced Metal-Matrix Composite (MMC) is studied through finite element (FE) method under different loading conditions in this investigation. The FE-model with multi-particle is generated through the random sequential adsorption algorithm, with the particles treated respectively as elastic-brittle circular, regular octagon and hexagon and square shape. Ductile failure in metal matrix, brittle fracture of particles and interface debonding are taken into account during the simulations. 2D cohesive element is applied to simulate the debonding behavior of interface. The damage models based on the stress triaxial indicator and maximum principal stress criterion are developed to simulate the ductile failure of metal matrix and brittle cracking of particles, respectively. Simulation results show that the interface debonding dominates the failure process under the loading, while the damage in particle grows at slowest rate compared with those in matrix and interface. Copyright © 2015 American Scientific Publishers Source


Li F.,Nanjing University of Aeronautics and Astronautics
Modern Physics Letters B | Year: 2010

The scaled boundary finite element method is used to determine the seepage free surface of a dam with unbounded base. Two models for the bounded and the unbounded domains are established by using the mentioned method, and the numerical solutions are compared with the analytical results. Also, the free surface seepage of a dam with unbounded base is solved by combining the substructure and scaled boundary finite-element methods. The method has satisfactory accuracy and is quite efficient. © 2010 World Scientific Publishing Company. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Journal of the European Ceramic Society | Year: 2016

An analytical method has been developed to investigate the effect of oxidation on the hysteresis loops of fiber-reinforced ceramic-matrix composites (CMCs) under static fatigue at elevated temperature. The oxidation region propagating model has been adopted to analyze the oxidation effect on the hysteresis loops, which is controlled by interface frictional slip and diffusion of oxygen gas through matrix multicrackings. Based on the damage mechanism of fiber slipping relative to matrix, the hysteresis loops models corresponding to different interface slip cases considering interface oxidation have been established. The relationships between hysteresis loops, hysteresis dissipated energy, interface slip and oxidation time have been established. The effects of stress level, matrix crack spacing, fiber volume content and oxidation temperature on the hysteresis dissipated energy, interface debonding, oxidation and slip lengths versus oxidation time have been analyzed. The experimental hysteresis loops of C/[Si-B-C] composite under static fatigue in air at 1200. °C have been predicted. © 2015 Elsevier Ltd. Source


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. Source


Li B.-Y.,Nanjing University of Aeronautics and Astronautics
Kongzhi yu Juece/Control and Decision | Year: 2010

This paper introduces outside competitive factors to remanufacturing system of closed-loop supply chain. The decision-making of original equipment manufacturer (OEM) remanufacturing and the impact on outside competition and inside competition are studied. In inside competitive environment, the conditions that OEM enters the remanufacturing field are studied by analyzing the decision of OEM. The decision boundary on when competitors can enter is given in outside competitive environment. Study results show that the remanufacturing strategy of manufacturers is not only a profit behavior, but also a prevention strategy, and it can prevent competitors from entering under certain conditions. The decisions of competitors depend on product competitiveness and manufactures' recovery rate. Source


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. Source


Zhou X.,Nanjing University of Aeronautics and Astronautics
Tien Tzu Hsueh Pao/Acta Electronica Sinica | Year: 2013

As an important model for modeling synthetic aperture radar (SAR) image data, G0 distribution has strong modeling ability and good practicability, and therefore draws extensive attentions around the world. The applications of G0 distribution require accurate and effective parameter estimations, and maximum likelihood estimator, which is statistically optimal, has not been applied for the G0 distribution due to the complexity of G0 distribution. In this paper, a new derivation of G0 distribution is first given, based on which, a maximum likelihood parameter estimation method using expectation maximization (EM) algorithm is proposed for the G0 distribution. The proposed method is compared with other G0 parameter estimation methods through extensive experiments, and the results show the effectiveness of the proposed method. Source


Zhao J.,Jiangnan University | Zhao J.,Bauhaus University Weimar | Jiang J.-W.,Bauhaus University Weimar | Jia Y.,Bauhaus University Weimar | And 2 more authors.
Carbon | Year: 2013

Explicit solutions for the cohesive energy between carbon nanotubes, graphene and substrates are obtained through continuum modeling of the van der Waals interaction between them. The dependence of the cohesive energy on their size, spacing and crossing angles is analyzed. Checking against full atom molecular dynamics calculations and available experimental results shows that the continuum solution has high accuracy. The equilibrium distances between the nanotubes, graphene and substrates with minimum cohesive energy are also provided explicitly. The obtained analytical solution should be of great help for understanding the interaction between the nanostructures and substrates, and designing composites and nanoelectromechanical systems. © 2013 Elsevier Ltd. All rights reserved. Source


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. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2015

In this paper, the relationship between hysteresis dissipated energy and temperature rising of the external surface in fiber-reinforced ceramic-matrix composites (CMCs) during the application of cyclic loading has been analyzed. The temperature rise, which is caused by frictional slip of fibers within the composite, is related to the hysteresis dissipated energy. Based on the fatigue hysteresis theories considering fibers failure, the hysteresis dissipated energy and a hysteresis dissipated energy-based damage parameter changing with the increase of cycle number have been investigated. The relationship between the hysteresis dissipated energy, a hysteresis dissipated energy-based damage parameter and a temperature rise-based damage parameter have been established. The experimental temperature rise-based damage parameter of unidirectional, cross-ply and 2D woven CMCs corresponding to different fatigue peak stresses and cycle numbers have been predicted. It was found that the temperature rise-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs. © 2015 Springer Science+Business Media Dordrecht Source


Yang Y.,University of Washington | Gao C.,Nanjing University of Aeronautics and Astronautics | Li J.,University of Washington
Acta Mechanica | Year: 2014

Thermoelectric materials are capable of converting heat directly into electricity and vice versa, and they have been explored for both waste heat recovery and thermal management. In this work, we analyze axially symmetric thermoelectric problems, motivated by energy harvesting using waste heat from an automobile exhaust pipe. Thermoelectric field distributions in both homogeneous shell and core-shell composites are solved, and the effective thermoelectric properties of the core-shell composites are analyzed. Numerical results show that higher thermoelectric conversion efficiency can be achieved in core-shell composites, and the mechanism responsible for the enhanced conversion efficiency is also identified. The analysis thus points to a new direction in developing high-performance thermoelectric materials. © 2014 Springer-Verlag Wien. Source


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. Source


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. Source


Chen G.,Nanjing University of Aeronautics and Astronautics
Zhendong Gongcheng Xuebao/Journal of Vibration Engineering | Year: 2011

In this paper, a new dual rotor-ball bearing-stator coupling dynamic model for practical aero-engine is established. In the coupling system, the rotor and casing systems are modeled by means of the Finite Elements method; the support systems are modeled as the lumped parameter models, and the nonlinear factors of ball bearings and the squeeze film dampers are also included; 5 kinds of supports and connection modes are defined to model the complex rotor-support-casing coupling system of dual rotor aero-engine. A new numerical integral method, which combines the Newmark-β method and the improved Newmark-β method (ZHAI Method), is used to obtain the system responses. Finally, the vibration is analysis for whole aero-engine carried out, the system critical rotating speeds, strain energy, and the sensitivity of unbalance response are analyzed; the vibration suppression characteristics of squeeze film damper (SFD) and the transient responses of sudden unbalance are studied. Source


Yan G.,Nanjing University of Aeronautics and Astronautics
Inverse Problems in Science and Engineering | Year: 2014

This paper proposes a statistical approach for identifying impact location and impact force history on a stiffened composite panel using Bayesian inference, in which uncertainties from modelling error and measurement noise are explicitly included. The impact load identification problem in both space domain (impact location) and time domain (impact force history) is first transformed to a parameter identification problem by representing the impact load using a set of parameters. A forward impact model characterising the dynamic responses of a stiffened composite panel subject to a known impact load is incorporated in the identification procedure. By combining the measured data and the prior information, Bayes' theorem is used to update the probability distributions of the parameters of impact load. In particular, Markov chain Monte Carlo method is employed for sampling the posterior distributions to estimate the impact parameters. Numerical simulation studies using noisy finite element data are conducted to demonstrate the effectiveness of the proposed method. © 2013 © 2013 Taylor & Francis. Source


Chen G.,Nanjing University of Aeronautics and Astronautics
Jixie Gongcheng Xuebao/Journal of Mechanical Engineering | Year: 2011

On the basis of Newland harmonic wavelet, an improved harmonic wavelet is put forward, it has a symmetrical and boxy frequency spectrum, and its expansions and translations will generate a series of wavelet functions which form an orthogonal basis of L2(R) space, the decomposition and reconstitution process of signal by the improved harmonic wavelet is easier than that by the Newland harmonic wavelet, moreover, the improved harmonic wavelet has the same excellent characteristics as the Newland harmonic wavelet. Using the simulation examples, the ability of extracting weak and local signal in strong noise is studied, in comparison to the DB8 wavelet, the effects of the improved harmonic wavelet are better. The improved harmonic wavelet is used to extract the super-harmonics and sub-harmonics components of the rotor faults signals because the harmonics frequencies characteristics reflect the rotor faults very well. The 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 and 5.0 components are extracted by the improved harmonic wavelet from the rotor fault experimental signals including imbalance, misalignment, rubbing, and oil whirling faults, and the results verify the effectiveness and correctness of the new method. © 2011 Journal of Mechanical Engineering. Source


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. Source


Hou W.,Nanjing University of Aeronautics and Astronautics
Sheng wu yi xue gong cheng xue za zhi = Journal of biomedical engineering = Shengwu yixue gongchengxue zazhi | Year: 2012

Ultrasound images are easily corrupted by speckle noise, which limits its further application in medical diagnoses. An image de-noising method combining dual-tree complex wavelet transform (DT-CWT) with nonlinear diffusion is proposed in this paper. Firstly, an image is decomposed by DT-CWT. Then adaptive-contrast-factor diffusion and total variation diffusion are applied to high-frequency component and low-frequency component, respectively. Finally the image is synthesized. The experimental results are given. The comparisons of the image de-noising results are made with those of the image de-noising methods based on the combination of wavelet shrinkage with total variation diffusion, the combination of wavelet/multiwavelet with nonlinear diffusion. It is shown that the proposed image de-noising method based on DT-CWT and nonlinear diffusion can obtain superior results. It can both remove speckle noise and preserve the original edges and textural features more efficiently. Source


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. Source


Qing H.,Nanjing University of Aeronautics and Astronautics
Computational Materials Science | Year: 2014

The influence of particle arrangements and interface strengths on the mechanical behavior of the particle reinforced metal-matrix composite (MMC) is investigated under different loading conditions in this work. During the loading process, three different failure mechanisms are distinguished in MMC: ductile failure in metal matrix, brittle failure in SiC particles and interface debonding between matrix and particles. The damage models based on the stress triaxial indicator and maximum principal stress criterion are developed to simulate the failure process of metal matrix and SiC particles. Meanwhile, 2D cohesive element is utilized to describe the debonding behavior of interface. Series of numerical experiments are performed to study the macroscopic stress-strain relationships and microscale damage evolution in MMCs under different loading conditions. An agreement between the simulation results and the experimental data is obtained. © 2014 Elsevier B.V. All rights reserved. Source


Jiang Y.,Nanjing Southeast University | Jiang Y.,Xian Jiaotong University | Hu J.,Nanjing University of Aeronautics and Astronautics | Lin D.,Japan National Institute of Information and Communications Technology
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2011

Networked multiagent systems are very popular in large-scale application environments. In networked multiagent systems, the interaction structures can be shaped into the form of networks where each agent occupies a position that is determined by such agent's relations with others. To avoid collisions between agents, the decision of each agent's strategies should match its own interaction position, so that the strategies available to all agents are in line with their interaction structures. Therefore, this paper presents a novel decision-making model for networked multiagent strategies based on their interaction structures, where the set of strategies for an agent is conditionally decided by other agents within its dependence interaction substructure. With the presented model, the resulting strategies available to all agents can minimize the collisions of multiagents regarding their interaction structures, and the model can produce the same resulting strategies for the isomorphic interaction structures. Furthermore, this paper uses a multiagent citation network as a case study to demonstrate the effectiveness of the presented decision-making model. © 2011 IEEE. Source


Li L.,Nanjing University of Aeronautics and Astronautics
Materials Science and Engineering A | Year: 2013

The tensile fatigue hysteresis behavior of cross-ply C/SiC composites at room and elevated temperatures in air atmosphere has been investigated in present analysis. The hysteresis modulus and hysteresis loss energy corresponding to different cycles have been analyzed. Based on damage mechanisms of fiber sliding relative to matrix in fiber/matrix interface debonded region upon unloading and subsequent reloading, the hysteresis loops models considering different matrix cracking modes have been developed. The hysteresis loss energy for strain energy lost per volume during corresponding cycle is formulated in terms of fiber/matrix interface shear stress. By comparing experimental hysteresis loss energy with computational values, fiber/matrix interface shear stress of cross-ply C/SiC composites at room and elevated temperatures has been estimated. © 2013 Elsevier B.V. Source


Zhang B.,Nanjing University of Aeronautics and Astronautics
International Journal of Solids and Structures | Year: 2013

Comprehensive molecular dynamics simulations, employing a coarse-grained bead-spring model, are conducted to study the failure of adhesion between two immiscible polymers stitched together via mobile promoters. A realistic model under separating tension is constructed that enables both chain pulling out viscously and bulk dissipation in two dissimilar glassy polymers that one is dense melt and another is loose. The contributions to the adhesion energy from thermodynamics and chain suction are studied for dependence of the strain rate at fixed basic molecular parameters. With low density of connectors, either adhesion toughness or strength changes slightly with separation strain rate as viscous loss is negligible. But rate effects become evident for long connectors with high density, viscoelastic sliding friction and reptation of chains dominate and the fracture energy increases with strain rate. The results provide insights into the evolution of adhesion surfaces coupled with promoter molecular slipping out of bulk melts, which are useful for future developments of continuum models for failure of polymeric interfaces. © 2013 Elsevier Ltd. All rights reserved. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Composites Part B: Engineering | Year: 2013

In this paper, the loading/unloading tensile behavior of cross-ply C/SiC ceramic matrix composites at room temperature has been investigated. The loading/unloading stress-strain curve exhibits obvious hysteresis behavior. An approach to model the hysteresis loops of cross-ply ceranic matrix composites including the effect of matrix cracking has been developed. Based on the damage mechanisms of fiber sliding relative to matrix during unloading and subsequent reloading, the unloading interface reverse slip length and reloading interface new slip length of different matrix cracking modes are obtained by the fracture mechanics approach. The hysteresis loops of cross-ply C/SiC ceramic matrix composites corresponding to different peak stresses have been predicted. © 2013 Elsevier Ltd. All rights reserved. Source


Donga J.,Nanjing University of Aeronautics and Astronautics
Journal of Mathematical Physics | Year: 2014

The 2D space-fractional Schrödinger equation in the time-independent and timedependent cases for the scattering problems in the fractional quantum mechanics is studied.We define the Green's functions for the two cases and give the mathematical expression of them in infinite series form and in terms of some special functions. The asymptotic formulas of the Green's functions are also given, and applied to get the approximate wave functions for the fractional quantum scattering problems. These results contain those in the standard (integer) quantum mechanics as special cases, and can be applied to study the complex quantum systems. © 2014 AIP Publishing LLC. Source


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. Source


Wang Y.,Nanjing University of Aeronautics and Astronautics
Theoretical and Applied Climatology | Year: 2015

Deforestation is expanding and accelerating into the remaining areas of undisturbed forest, and the quality of the remaining forests is declining today. Assessing the climatic impacts of deforestation can help to rectify this alarming situation. In this paper, how historical deforestation may affect global climate through interactive ocean and surface albedo is examined using an Earth system model of intermediate complexity (EMIC). Control and anomaly integrations are performed for 1000 years. In the anomaly case, cropland is significantly expanded since AD 1700. The response of climate in deforested areas is not uniform between the regions. In the background of a global cooling of 0.08 °C occurring with cooler surface air above 0.4 °C across 30° N to 75° N from March to September, the surface albedo increase has a global cooling effect in response to global-scale replacement of forests by cropland, especially over northern mid-high latitudes. The northern mid-latitude (30° N–60° N) suffers a prominent cooling in June, suggesting that this area is most sensitive to cropland expansion through surface albedo. Most regions show a consistent trend between the overall cooling in response to historical deforestation and its resulting cooling due to surface albedo anomaly. Furthermore, the effect of the interactive ocean on shaping the climate response to deforestation is greater than that of prescribed SSTs in most years with a maximum spread of 0.05 °C. This difference is more prominent after year 1800 than that before due to the more marked deforestation. These findings show the importance of the land cover change and the land surface albedo, stressing the necessity to analyze other biogeophysical processes of deforestation using interactive ocean. © 2015 Springer-Verlag Wien Source


The damage evolution of unidirectional C/SiC ceramic-matrix composite (CMC) under cyclic fatigue loading has been investigated using a hysteresis loss energy-based damage parameter at room and elevated temperatures. The experimental fatigue hysteresis modulus and fatigue hysteresis loss energy versus cycle number have been analyzed. By comparing the experimental fatigue hysteresis loss energy with theoretical computational values, the interface shear stress corresponding to different cycle number and peak stress has been estimated. The experimental evolution of fatigue hysteresis loss energy and fatigue hysteresis loss energy-based damage parameter versus cycle number has been predicted for unidirectional C/SiC composite at room and elevated temperatures. The predicted results of interface shear stress degradation, stress–strain hysteresis loops corresponding to different number of applied cycles, fatigue hysteresis loss energy and fatigue hysteresis loss energy-based damage parameter as a functions of cycle number agreed with experimental data. It was found that the fatigue hysteresis energy-based parameter can be used to monitor the fatigue damage evolution and predict the fatigue life of fiber-reinforced CMCs. © 2015 Springer Science+Business Media Dordrecht Source


Yang X.,Nanjing University of Aeronautics and Astronautics
Nonlinear Analysis: Real World Applications | Year: 2015

We prove global-in-time and uniform-in-ε existence of the strong solutions to the 3D compressible Hall-magnetohydrodynamic (MHD) system in a periodic domain double-struck T3, where ε is the Mach number. Consequently, we obtain the convergence of strong solutions to the compressible Hall-MHD system to that of incompressible Hall-MHD system. © 2015 Elsevier Ltd. All rights reserved. Source


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. Source


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. Source


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. Source


Huang Z.,Nanjing University of Aeronautics and Astronautics
Mathematics and Mechanics of Solids | Year: 2012

A representation of the non-local residual is issued in the form of theorem. This representation makes the non-local residual satisfy the zero mean condition automatically. On the basis of this representation, a new theoretical framework and method to establish the non-local damage model are put forth. In this framework, the non-locality of damage and inelastic deformation is characterized by the non-local residual, and it need not introduce the non-local constitutive variables in the Helmholtz free energy and the dissipation potential. According to the new method, non-local quasi-brittle damage model and non-local viscoplastic damage model are established. The constitutive equations and evolution equations of damage are consistently derived from the thermodynamics principles. © 2011 The Author(s). Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
International Journal of Fracture | Year: 2016

In this paper, the damage development behavior in fiber-reinforced ceramic-matrix composites (CMCs) with different fiber architectures, i.e., unidirectional, cross-ply and 2D woven, under cyclic fatigue loading at room and elevated temperatures has been investigated using fatigue hysteresis loops, i.e., fatigue hysteresis modulus, fatigue hysteresis dissipated energy, and fatigue hysteresis dissipated energy-based damage parameter. The relationships between fatigue hysteresis loops, fatigue hysteresis modulus, fatigue hysteresis dissipated energy and fatigue hysteresis dissipated energy-based damage parameter have been established. The effects of fiber volume content, fatigue peak stress, fatigue stress ratio, matrix crack spacing, multiple matrix cracking modes, and woven structures on the damage evolution in fiber-reinforced CMCs have been investigated. The experimental fatigue hysteresis modulus, fatigue hysteresis dissipated energy and fatigue hysteresis dissipated energy-based damage parameter versus cycle number have been predicted for unidirectional, cross-ply and 2D woven CMCs at room and elevated temperatures. It was found that the damage parameters derived from the fatigue hysteresis loops can effectively monitor the damage development and predict the fatigue life of fiber-reinforced CMCs. © 2016 Springer Science+Business Media Dordrecht Source


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. Source


Yang W.-A.,Nanjing University of Aeronautics and Astronautics
Journal of Intelligent Manufacturing | Year: 2014

Many manufacturing processes are multivariate in nature because the quality of a given product is determined by several interrelated quality characteristics. Recently, various machine learning techniques (e.g., artificial neural network, support vector machine, support vector regression or decision tree) have been used as an effective tool to monitor process mean vector and covariance matrix shifts. However, most of these machine learning techniques-based approaches for process mean vector and covariance matrix have been developed separately in literature with the other parameter assumed to be under control. Little attention has been given to simultaneous monitoring of process mean vector and covariance matrix shifts. In addition, these approaches cannot provide more detailed shift information, for example the shift magnitude, which would be greatly useful for quality practitioners to search the assignable causes that give rise to the out-of-control situation. This study presents a hybrid ensemble learning-based model for simultaneous monitoring of process mean vector and covariance matrix shifts. The numerical results indicate that the proposed model can effectively detect and recognize not only mean vector or covariance matrix shifts but also mixed situations where mean vector and covariance matrix shifts exist concurrently. Meanwhile, the magnitude of the shift of each of the shifted quality characteristics can be accurately quantified. Empirical comparisons also show that the proposed model performs better than other existing approaches in detecting mean vector and covariance matrix shifts, while also providing the capability of recognition of shift types and quantification of shift magnitudes. A demonstrative example is provided. © 2014 Springer Science+Business Media New York. Source


Xie J.-L.,Nanjing Institute of Technology | Wang C.-Y.,Nanjing University of Aeronautics and Astronautics
Yuhang Xuebao/Journal of Astronautics | Year: 2011

To solve the problem of detection performance descending of airborne radar, an echo signal model of hypersonic moving target is established in this paper, then the range migration and time-varying Doppler frequency characteristics resulted from target's hypersonic moving are analyzed. Through the inference formula, the Keystone transform is employed to correct the range migration, and the high-order ambiguity function method is used to estimate the Doppler parameter of a hypersonic moving target. The coherent integration process is carried out after compensating the high order of Doppler frequency. Computer simulation results confirm the effectiveness of the proposed method. Source


Longbiao L.,Nanjing University of Aeronautics and Astronautics
Applied Composite Materials | Year: 2016

In this paper, the effect of multiple matrix cracking modes on cyclic loading/unloading hysteresis loops of 2D woven ceramic-matrix composites (CMCs) has been investigated. The interface slip between fibers and the matrix existed in matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, are considered as the major reason for hysteresis loops of 2D woven CMCs. The effects of fiber volume content, peak stress, matrix crack spacing, interface properties, matrix cracking mode proportion and interface wear on interface slip and hysteresis loops have been analyzed. The cyclic loading/unloading hysteresis loops of 2D woven SiC/SiC composite corresponding to different peak stresses have been predicted using the present analysis. It was found that the damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire cracking modes of the composite, increases with increasing peak stress. © 2016 Springer Science+Business Media Dordrecht Source


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