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Changsha, China

National University of Defense Technology is a comprehensive national key university based in Changsha, Hunan Province, China.It is under the dual supervision of the Ministry of National Defense and the Ministry of Education, designated for Project 211 and Project 985, the two national plans for facilitating the development of Chinese higher education. Wikipedia.

Deng X.,China Aerodynamics Research And Development Center | Deng X.,National University of Defense Technology | Min Y.,China Aerodynamics Research And Development Center | Mao M.,China Aerodynamics Research And Development Center | And 3 more authors.
Journal of Computational Physics | Year: 2013

The metrics and Jacobian in the fluid motion governing equations under curvilinear coordinate system have a variety of equivalent differential forms, which may have different discretization errors with the same difference scheme. The discretization errors of metrics and Jacobian may cause serious computational instability and inaccuracy in numerical results, especially for high-order finite difference schemes. It has been demonstrated by many researchers that the Geometric Conservation Law (GCL) is very important for high-order Finite Difference Methods (FDMs), and a proper form of metrics and Jacobian, which can satisfy the GCL, can considerably reduce discretization errors and computational instability. In order to satisfy the GCL for FDM, we have previously developed a Conservative Metric Method (CMM) to calculate the metrics [1] and the difference scheme δ3 in the CMM is determined with the suggestion δ3 = δ2. In this paper, a Symmetrical Conservative Metric Method (SCMM) is newly proposed based on the discussions of the metrics and Jacobian in FDM from geometry viewpoint by following the concept of vectorized surface and cell volume in Finite Volume Methods (FVMs). Interestingly, the expressions of metrics and Jacobian obtained by using the SCMM with second-order central finite difference scheme are equivalent to the vectorized surfaces and cell volumes, respectively. The main advantage of SCMM is that it makes the calculations based on high-order WCNS schemes aroud complex geometry flows possible and somewhat easy. Numerical tests on linear and nonlinear problems indicate that the quality of numerical results may be largely enhanced by utilizing the SCMM, and the advantage of the SCMM over other forms of metrics and Jacobian may be more evident on highly nonuniform grids. © 2012 Elsevier Inc.

Chini M.,University of Central Florida | Wang X.,University of Central Florida | Wang X.,National University of Defense Technology | Cheng Y.,University of Central Florida | And 10 more authors.
Nature Photonics | Year: 2014

The generation of high-order harmonics and attosecond pulses at ultrahigh repetition rates (>1 MHz) promises to revolutionize ultrafast spectroscopy. Such vacuum ultraviolet (VUV) and soft X-ray sources could potentially be driven directly by plasmonic enhancement of laser pulses from a femtosecond oscillator, but recent experiments suggest that the VUV signal is actually dominated by incoherent atomic line emission. Here, we demonstrate a new regime of phase-matched below-threshold harmonic generation, for which the generation and phase matching is enabled only near resonance structures of the atomic target. The coherent VUV line emission exhibits low divergence and quadratic growth with increasing target density up to nearly 1,000 torr mm and can be controlled by the sub-cycle field of a few-cycle driving laser with an intensity of only ∼1/41 × 10 13 W cm ∼'2, which is achievable directly from few-cycle femtosecond oscillators with nanojoule energy. © 2014 Macmillan Publishers Limited.

Wang Y.,National University of Defense Technology | Sefiane K.,University of Edinburgh
International Journal of Thermal Sciences | Year: 2013

Two types of single vapour bubble growth in micro-scale space are experimentally investigated. Degassed pentane and FC-72 are used to study the bubble confined between superheated parallel plates without liquid flow. Liquid properties which are influential on bubble growth are discussed. Effects of plate superheating and plate gap on bubble growth rate are examined. Bubble growth during flow boiling in high aspect ratio micro-channels is also examined to extensively investigate the single bubble growth in a dynamic configuration. The hydraulic diameters of the tested channel are 571 μm, 762 μm and 1454 μm, with an aspect ratio of 20, 20 and 10 respectively. Transparent heating technique is utilised to provide heating power while ensuring sufficient transparency for visualisation. A three-stage bubble growth mode is presented. Moreover, bubble geometry evolution is found to be strongly related to channel cross-sectional geometry but slightly affected by heat flux or mass flux. Bubble growth critical time is defined. Bubble equivalent radius, bubble aspect ratio and width versus length trends are also discussed. © 2012 Elsevier Masson SAS. All rights reserved.

Zhang J.-R.,National University of Defense Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We present a QCD sum rule analysis for the newly observed resonance X c(3250) by assuming it to be a D0*(2400)N molecular state. Technically, contributions of operators up to dimension 12 are included in the operator product expansion (OPE). We find that it is difficult to find the conventional OPE convergence in this work. By releasing the rigid OPE convergence criterion, one could find that the OPE convergence is still under control in the present work, and the numerical result for the D0*(2400)N state is 3.18±0.51 GeV, which is in agreement with the experimental data of Xc(3250). In view of that, the conventional OPE convergence is not obtained here; thus only weak conclusions can be drawn regarding the explanation of Xc(3250) in terms of a D0*(2400)N molecular state. As a byproduct, the mass for the bottom counterpart B̄0*N state is predicted to be 6.50±0.49 GeV. © 2013 American Physical Society.

Li M.,National University of Defense Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Loop invariants play a major role in software verification. Based on random testing, constraint solving and verification, this paper presents a practical approach for generating equality loop invariants. More importantly, we present a practical verification approach of loop invariant based on finite difference technique. This approach is efficient since the constraint system is linear equational system. The effectiveness of the approach is demonstrated on examples. © 2012 Springer-Verlag.

Liu W.,National University of Defense Technology
Optics Express | Year: 2015

We study the light scattering of homogenous radially-anisotropic spherical particles. It is shown that radial anisotropy can be employed to tune effectively the electric resonances, and thus enable flexible overlapping of electric and magnetic dipoles of various numbers, which leads to unidirectional forward super-scattering at different spectral positions. We further reveal that through adjusting the radial anisotropy parameters, electric and magnetic resonances of higher orders can be also made overlapped, thus further collimating the forward scattering lobes. The ultra-directional super-scattering we have obtained with individual homogenous radially anisotropic spherical particles may shed new light to the design of compact and efficient nanoantennas, which may find various applications in solar cells, bio-sensing and many other antenna based researches. © 2015 Optical Society of America.

Zhang L.,Hunan University | Zhang Z.,National University of Defense Technology | Huang L.,Hunan University
Nonlinear Dynamics | Year: 2012

This paper undertakes an analysis of a double Hopf bifurcation of a maglev system with timedelayed feedback. At the intersection point of the Hopf bifurcation curves in velocity feedback control gain and time delay space, the maglev system has a codimension 2 double Hopf bifurcation. To gain insight into the periodic solution which arises from the double Hopf bifurcation and the unfolding, we calculate the normal form of double Hopf bifurcation using the method of multiple scales. Numerical simulations are carried out with two pairs of feedback control parameters, which show different unfoldings of the maglev system and we verify the theoretical analysis. © Springer Science+Business Media B.V. 2011.

Yan G.,Indiana University Kokomo | Wen D.,National University of Defense Technology | Olariu S.,Old Dominion University | Weigle M.C.,Old Dominion University
IEEE Transactions on Intelligent Transportation Systems | Year: 2013

In a series of recent papers, Prof. Olariu and his co-workers have promoted the vision of vehicular clouds (VCs), a nontrivial extension, along several dimensions, of conventional cloud computing. In a VC, underutilized vehicular resources including computing power, storage, and Internet connectivity can be shared between drivers or rented out over the Internet to various customers. Clearly, if the VC concept is to see a wide adoption and to have significant societal impact, security and privacy issues need to be addressed. The main contribution of this work is to identify and analyze a number of security challenges and potential privacy threats in VCs. Although security issues have received attention in cloud computing and vehicular networks, we identify security challenges that are specific to VCs, e.g., challenges of authentication of high-mobility vehicles, scalability and single interface, tangled identities and locations, and the complexity of establishing trust relationships among multiple players caused by intermittent short-range communications. Additionally, we provide a security scheme that addresses several of the challenges discussed. © 2000-2011 IEEE.

Sun S.,East China Normal University | Xu X.,National University of Defense Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2011

This paper proposes a new variational approximation for infinite mixtures of Gaussian processes. As an extension of the single Gaussian process regression model, mixtures of Gaussian processes can characterize varying covariances or multimodal data and reduce the deficiency of the computationally cubic complexity of the single Gaussian process model. The infinite mixture of Gaussian processes further integrates a Dirichlet process prior to allowing the number of mixture components to automatically be determined from data. We use variational inference and a truncated stick-breaking representation of the Dirichlet process to approximate the posterior of hidden variables involved in the model. To fix the hyperparameters of the model, the variational EM algorithm and a greedy algorithm are employed. In addition to presenting the variational infinite-mixture model, we apply it to the problem of traffic flow prediction. Experiments with comparisons to other approaches show the effectiveness of the proposed model. © 2006 IEEE.

Zhang J.-R.,National University of Defense Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In the framework of QCD sum rules, we present an improved study of our previous work, particularly on the D̄D* molecular state, to investigate the possibility that the newly observed Zc(3900) is a S-wave D̄D* molecular state. To ensure the quality of QCD sum rule analysis, contributions of up to dimension nine are calculated to test the convergence of operator product expansion (OPE). We find that the two-quark condensate âŸ̈q̄q⟩ is very large and makes the standard OPE convergence (i.e. the perturbative at least larger than each condensate contribution) happen at very large values of Borel parameters. By releasing the rigid OPE convergence criterion, one could find that the OPE convergence is still under control. We arrive at the numerical result 3.86±0.27 GeV for D̄D*, which agrees with the mass of Zc(3900) and could support the explanation of Zc(3900) in terms of a S-wave D̄D* molecular state. © 2013 American Physical Society.

Wang Y.,National University of Defense Technology | Wang Y.,University of Edinburgh | Sefiane K.,University of Edinburgh
International Journal of Heat and Mass Transfer | Year: 2012

Experiments on flow boiling heat transfer in high aspect ratio micro-channels with FC-72 were carried out. Three channels with different hydraulic diameters (571, 762 and 1454 μm) and aspect ratios (20, 20 and 10) were selected. The tested mass fluxes were 11.2, 22.4 and 44.8 kg m -2 s -1 and heat fluxes ranging from 0-18.6 kW m -2. In the present study, boiling curves with obvious temperature overshoots are presented. Average heat transfer coefficient and local heat transfer coefficient along stream-wise direction are measured as a function of heat flux and vapour quality respectively. Slug-annular flow and annular flow are the main flow regimes. Convective boiling is found to be the dominant heat transfer mechanism. Local heat transfer coefficient increases with decreasing hydraulic diameter. Moreover, the effect of hydraulic diameter is more significant when mass flux is higher. The unique channel geometry is considered as the decisive reason of the flow regimes as well as heat transfer mechanisms. © 2012 Elsevier Ltd. All rights reserved.

Zhou Y.,Queen Mary, University of London | Zhou Y.,National University of Defense Technology | Fenton N.,Queen Mary, University of London | Neil M.,Queen Mary, University of London
International Journal of Approximate Reasoning | Year: 2014

One of the hardest challenges in building a realistic Bayesian Network (BN) model is to construct the node probability tables (NPTs). Even with a fixed predefined model structure and very large amounts of relevant data, machine learning methods do not consistently achieve great accuracy compared to the ground truth when learning the NPT entries (parameters). Hence, it is widely believed that incorporating expert judgments can improve the learning process. We present a multinomial parameter learning method, which can easily incorporate both expert judgments and data during the parameter learning process. This method uses an auxiliary BN model to learn the parameters of a given BN. The auxiliary BN contains continuous variables and the parameter estimation amounts to updating these variables using an iterative discretization technique. The expert judgments are provided in the form of constraints on parameters divided into two categories: linear inequality constraints and approximate equality constraints. The method is evaluated with experiments based on a number of well-known sample BN models (such as Asia, Alarm and Hailfinder) as well as a real-world software defects prediction BN model. Empirically, the new method achieves much greater learning accuracy (compared to both state-of-the-art machine learning techniques and directly competing methods) with much less data. For example, in the software defects BN for a sample size of 20 (which would be considered difficult to collect in practice) when a small number of real expert constraints are provided, our method achieves a level of accuracy in parameter estimation that can only be matched by other methods with much larger sample sizes (320 samples required for the standard machine learning method, and 105 for the directly competing method with constraints). © 2014 Elsevier B.V. All rights reserved.

Gu F.,University of Huddersfield | Shao Y.,Chongqing University | Hu N.,National University of Defense Technology | Naid A.,University of Huddersfield | Ball A.D.,University of Huddersfield
Mechanical Systems and Signal Processing | Year: 2011

This paper presents the use of the induction motor current to identify and quantify common faults within a two-stage reciprocating compressor based on bispectrum analysis. The theoretical basis is developed to understand the nonlinear characteristics of current signals when the motor undertakes a varying load under different faulty conditions. Although conventional bispectrum representation of current signal allows the inclusion of phase information and the elimination of Gaussian noise, it produces unstable results due to random phase variation of the sideband components in the current signal. A modified bispectrum based on the amplitude modulation feature of the current signal is then adopted to combine both lower sidebands and higher sidebands simultaneously and hence characterise the current signal more accurately. Based on this new bispectrum analysis a more effective diagnostic feature, namely normalised bispectral peak, is developed for fault classification. In association with the kurtosis value of the raw current signal, the bispectrum feature gives rise to reliable fault classification results. In particular, the low feature values can differentiate the belt looseness from the other fault cases and different degrees of discharge valve leakage and inter-cooler leakage can be separated easily using two linear classifiers. This work provides a novel approach to the analysis of stator current for the diagnosis of motor drive faults from downstream driving equipment. © 2010 Published by Elsevier Ltd. All rights reserved.

Huang W.,National University of Defense Technology
Journal of Zhejiang University: Science A | Year: 2015

Drag reduction and thermal protection is very important for hypersonic vehicles, and a counterflowing jet and its combinations is one of the most promising drag and heat release reduction strategies. In the current survey, research progress on the drag and heat release reduction induced by a counterflowing jet and its combinations is summarized. Three combinatorial configurations are considered, namely the combination of the counterflowing jet and a forward-facing cavity, the combination of the counterflowing jet and an aerospike, and the combination of the counterflowing jet and energy deposition. In conclusion, some recommendations are provided, especially for jet instability protection, for the tradeoff between drag and heat release reductions, and for the critical points for the operational and geometric parameters in the flow mode transition. © 2015, Zhejiang University and Springer-Verlag Berlin Heidelberg.

Cao X.-Q.,National University of Defense Technology
Wuli Xuebao/Acta Physica Sinica | Year: 2013

A new numerical method is presented to solve optimal control problem of a chaotic system based on Gauss pseudospectral method (GPM). Firstly, the Lagrange interpolation polynomials are constructed on Legendre-Gauss nodes and used to parameterize the state and control the trajectories in optimal control of the chaotic system. Then, the chaotic optimal control problem in the continuous space is transformed into a nonlinear programming (NLP) problem through GPM. Furthermore, the NLP problem is solved by the sequential quadratic programming algorithm. Finally, the proposed method is applied to the optimal control of the typical Lorenz, Chen, and Liu chaotic systems respectively. The simulation processes indicate that the GPM is effective, fast and feasible for solving optimal control problems of chaotic systems. © 2013 Chinese Physical Society.

Yin J.,University of Liverpool | Yin J.,National University of Defense Technology | Hopkins C.,University of Liverpool
Journal of Sound and Vibration | Year: 2015

The inclusion of rib-stiffened plates within the framework of Statistical Energy Analysis (SEA) is a challenge in the field of engineering noise control for the low- and mid-frequency ranges. This paper focuses on periodic ribbed plates with symmetric ribs and assesses different approaches using SEA to model bending wave transmission when one or both of the rectangular plates that form an L-junction are a periodic ribbed plate. SEA is compared with measurements and Finite Element Methods (FEM) with all plate boundaries pinned to give boundary conditions that are representative of engineering structures typically used for noise control. When one or both plates are ribbed, and the ribs are parallel to the junction, the closest agreement between measurements and FEM is with SEA models that use a combination of Bloch theory and wave theory to determine the coupling loss factors. However, when both plates are ribbed plates, one with ribs orientated perpendicular to the junction and the other with ribs parallel to the junction, the available SEA models which assume an effective isotropic plate, or an equivalent isotropic plate or angle-dependent bending stiffness all underestimate the energy level difference. © 2015 Elsevier Ltd. All rights reserved.

Li Y.,Goethe University Frankfurt | Li Y.,National University of Defense Technology | He L.,Goethe University Frankfurt | Hofstetter W.,Goethe University Frankfurt
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We numerically simulate strongly correlated ultracold bosons coupled to a high-finesse cavity field, pumped by a laser beam in the transverse direction. Assuming a weak classical optical lattice added in the cavity direction, we model this system by a generalized Bose-Hubbard model, which is solved by means of bosonic dynamical mean-field theory. The complete phase diagram is established, which contains two novel self-organized quantum phases, lattice supersolid and checkerboard solid, in addition to conventional phases such as superfluid and Mott insulator. At finite but low temperature, thermal fluctuations are found to enhance the buildup of the self-organized phases. We demonstrate that cavity-mediated long-range interactions can give rise to stable lattice supersolid and checkerboard solid phases even in the regime of strong s-wave scattering. In the presence of a harmonic trap, we discuss coexistence of these self-organized phases, as relevant to experiments. © 2013 American Physical Society.

Liu L.,Australian National University | Wang L.,Australian National University | Wang L.,University of Wollongong | Liu X.,Australian National University | Liu X.,National University of Defense Technology
Proceedings of the IEEE International Conference on Computer Vision | Year: 2011

In object recognition, soft-assignment coding enjoys computational efficiency and conceptual simplicity. However, its classification performance is inferior to the newly developed sparse or local coding schemes. It would be highly desirable if its classification performance could become comparable to the state-of-the-art, leading to a coding scheme which perfectly combines computational efficiency and classification performance. To achieve this, we revisit soft-assignment coding from two key aspects: classification performance and probabilistic interpretation. For the first aspect, we argue that the inferiority of soft-assignment coding is due to its neglect of the underlying manifold structure of local features. To remedy this, we propose a simple modification to localize the soft-assignment coding, which surprisingly achieves comparable or even better performance than existing sparse or local coding schemes while maintaining its computational advantage. For the second aspect, based on our probabilistic interpretation of the soft-assignment coding, we give a probabilistic explanation to the magic max-pooling operation, which has successfully been used by sparse or local coding schemes but still poorly understood. This probability explanation motivates us to develop a new mix-order max-pooling operation which further improves the classification performance of the proposed coding scheme. As experimentally demonstrated, the localized soft-assignment coding achieves the state-of-the-art classification performance with the highest computational efficiency among the existing coding schemes. © 2011 IEEE.

Wang G.,National University of Defense Technology
Guangxue Xuebao/Acta Optica Sinica | Year: 2010

In high-low temperature experiments, the null shift of the four-mode laser gyro whose beam intensity is stablely controlled in two different modes is very different. The null shift vibrates in one mode but changes linearly with temperature in the other one. Aiming at this phenomenon, through the analysis based on the basic theory, the physical reason that the differential lose null shift and the constant magnetism biasing null shift change differently with temperature in different modes is found. If using temperature compensation to improve the precision of the four-mode laser gyro, the coefficient must be gotten in the same mode which is selected by actual use.

Zhao J.,Space Time Research | Zhao J.,National University of Defense Technology | Lein M.,Space Time Research
Physical Review Letters | Year: 2013

From the numerical solution of the time-dependent Schrödinger equation, we obtain the times of ionization and return of the laser-driven electron in high-order harmonic generation by probing the dynamics with a second harmonic field polarized orthogonal to the fundamental field and observing the harmonic emission in dependence on the two-color delay. Our retrieval method using complex-time evolution gives ionization and return times in excellent agreement with the quantum-orbit model, while a retrieval based on real-time classical dynamics can introduce substantial errors. Because of the imaginary parts, the harmonic signal polarized along the probe field is nonzero for any two-color delay. The tunneling time can be retrieved under an assumption for the return time. © 2013 American Physical Society.

Shu Y.,National University of Defense Technology | Kim D.W.,University of Arizona | Martin H.M.,University of Arizona | Burge J.H.,University of Arizona
Optics Express | Year: 2013

A generalized model is developed to quantitatively describe the smoothing effects from different polishing tools used for optical surfaces. The smoothing effect naturally corrects mid-to-high spatial frequency errors that have features small compared to the size of the polishing lap. The original parametric smoothing model provided a convenient way to compare smoothing efficiency of different polishing tools for the case of sinusoidal surface irregularity, providing the ratio of surface improvement via smoothing to the bulk material removal. A new correlation-based smoothing model expands the capability to quantify smoothing using general surface data with complex irregularity. For this case, we define smoothing as a band-limited correlated component of the change in the surface and original surface. Various concepts and methods, such as correlation screening, have been developed and verified to manipulate the data for the calculation of smoothing factor. Data from two actual polishing runs from the Giant Magellan Telescope off-axis segment and the Large Synoptic Survey Telescope monolithic primary-tertiary mirror were processed, and a quantitative evaluation for the smoothing efficiency of a large pitch lap and a conformal lap with polishing pads is provided. © 2013 Optical Society of America.

Wang F.-Y.,CAS Institute of Automation | Wang F.-Y.,National University of Defense Technology
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2015

Knowledge automation is the organic integration of intelligentization, human-machine, automation etc. From the perspective of social signals and Merton systems, we address issues related to the significance and development of knowledge automation. Key topics discussed are technical foundation for smart algorithms and knowledge robots, software-defined systems and processes from the viewpoint of systems engineering, and the important role played by knowledge automation in parallel systems for the control and management of complex systems. Copyright © 2015 Acta Automatica Sinica. All rights reserved.

Li Y.,CAS Institute of Semiconductors | Yue Q.,National University of Defense Technology
Physica B: Condensed Matter | Year: 2013

The structural, electronic and magnetic properties of stage-I and -2 FeCl3-based graphite intercalation compounds (GIC5) are studied in the framework of the GGA+U implementation of density functional theory. The intercalation process extends the c-axis remarkably and modulates the band structure of graphite to p-type doped. A linearly dispersing band structure is observed for stage-I GIC. The carrier density shows a weak descending tendency from stage-I GIC to stage-2 GIC. The dependence of the energy level positions of Fe 3d orbitals on parameter U is strong. With the increase of U, the spin-up states move to the deeper energy levels, while the spin-down states move to the shallower energy levels. Stage-I GIC has antiferromagnetic (AFM) order and stage-2 GICs has ferromagnetic (FM) orders at the ground states, and two combinative effects are proposed to explain the origin of the magnetic transformation from stage-I GIC to stage-2 GIC. © 2013 Elsevier BY. All rights reserved.

Chini M.,University of Central Florida | Wang X.,University of Central Florida | Wang X.,National University of Defense Technology | Cheng Y.,University of Central Florida | Chang Z.,University of Central Florida
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2014

We present theoretical simulations of the attosecond transient absorption of singly-excited states of helium atoms in the presence of a dressing near-infrared or infrared laser. In particular, we aim to address several unresolved questions in the transient absorption of helium and to resolve the remaining discrepancies between theory and experiment. We initially focus on the forklike structures in the Autler-Townes splitting of the 1s2p state and the effects of resonant coupling to the 1s2s and 1s3s states. We find that the delay-dependent features of the Autler-Townes doublet depend strongly on both the laser frequency detuning from resonance and on the laser pulse duration, and explain the lack of such structures in current experimental data. Next, we identify the interference mechanism which causes the half-cycle oscillations in the absorption spectrum below the excited state manifold. Finally, we observe for the first timethe presence of quantum beating in the simulated transient absorption spectrogram, and discuss the conditions under which such wavepacket dynamics could be observed experimentally. © 2014 IOP Publishing Ltd.

Xu X.,National University of Defense Technology
Applied Soft Computing Journal | Year: 2010

Anomaly detection is an important problem that has been popularly researched within diverse research areas and application domains. One of the open problems in anomaly detection is the modeling and prediction of complex sequential data, which consist of a series of temporally related behavior patterns. In this paper, a novel sequential anomaly detection method based on temporal-difference (TD) learning is proposed, where the anomaly detection problem of multi-stage cyber attacks is considered as an application case. A Markov reward process model is presented for the anomaly detection and alarming process of sequential data and it is verified that when the reward function is properly defined, the anomaly probabilities of sequential behaviors are equivalent to the value functions of the Markov reward process. Therefore, TD learning algorithms in the reinforcement learning literature can be used to efficiently construct anomaly detection models of complex sequential behaviors by estimating the value functions of the Markov reward process. Compared with other machine learning methods for anomaly detection, the proposed approach has the advantage of simplified labeling process using delayed evaluative signals and the prediction accuracy can be improved even if labeled training data are limited. Based on the experimental results on intrusion detection of host computers using system call data, it was shown that the proposed anomaly detection method can achieve higher or at least comparable detection accuracies than other approaches including SVMs, and HMMs. © 2009 Elsevier B.V. All rights reserved.

Zhang Z.,Nanyang Technological University | Seah H.S.,Nanyang Technological University | Quah C.K.,Nanyang Technological University | Sun J.,National University of Defense Technology
IEEE Transactions on Multimedia | Year: 2013

Compared to monocular pose tracking, 3D articulated body pose tracking from multiple cameras can better deal with self-occlusions and meet less ambiguities. Though considerable advances have been made, pose tracking from multiple images has not been extensively studied: very seldom existing work can produce a solution comparable to that of a marker-based system which generally can recover accurate 3D full-body motion in real-time. In this paper, we present a multi-view approach to 3D body pose tracking. We propose a pose search method by introducing a new generative sampling algorithm with a refinement step of local optimization. This multi-layer search method does not rely on strong motion priors and generalizes well to general human motions. Physical constraints are incorporated in a novel way and 3D distance transform is employed for speedup. A voxel subject-specific 3D body model is created automatically at the initial frame to fit the subject to be tracked. We design and develop the optimized parallel implementations of time-consuming algorithms on GPU (Graphics Processing Unit) using CUDA (Compute Unified Device Architecture), which significantly accelerates the pose tracking process, making our method capable of tracking full body movements with a maximum speed of 9 fps. Experiments on various 8-camera datasets and benchmark datasets (HumanEva-II) captured by 4 cameras demonstrate the robustness and accuracy of our method. © 1999-2012 IEEE.

Liu Z.-M.,National University of Defense Technology
IEEE Transactions on Vehicular Technology | Year: 2014

This paper proposes a Bayesian method to address the farfield narrowband direction-of-arrival (DOA) estimation problem with time-varying arrays, whose elements relatively move in an arbitrary but known way. The measurements associated with different array geometries are formulated with distinct and spatially overcomplete observation systems, and a joint Bayesian model is established to combine those measurements and yield unified DOA estimates. The joint reconstruction process of the multiple measurements falls into the multitask learning category; thus, the proposed method is named DOA estimation via multitask learning (DEML). Theoretical results focusing on the uniqueness of the solution and the global convergence of the Bayesian learning process are also given, which indicate the maximal separable signal number and the global convergence of the proposed method in the considered array processing scenarios. Numerical examples are also provided to demonstrate the DOA estimation performance of the proposed method and support the theoretical results. © 2014 IEEE.

Han S.,National University of Defense Technology | Wang J.,University of New South Wales
GPS Solutions | Year: 2012

A dual-rate Kalman Filter (DRKF) has been developed to integrate the time-differenced GPS carrier phases and the GPS pseudoranges with INS measurements. The time-differenced GPS carrier phases, which have low noise and millimeter measurement precision, are integrated with INS measurements using a Kalman Filter with high update rates to improve the performance of the integrated system. Since the time-differenced GPS carrier phases are only relative measurements, when integrated with INS, the position error of the integrated system will accumulate over time. Therefore, the GPS pseudoranges are also incorporated into the integrated system using a Kalman Filter with a low update rate to control the accumulation of system errors. Experimental tests have shown that this design, compared to a conventional design using a single Kalman Filter, reduces the coasting error by two-thirds for a medium coasting time of 30 s, and the position, velocity, and attitude errors by at least one-half for a 45-min field navigation experiment. © 2011 Springer-Verlag.

Li D.D.-U.,University of Strathclyde | Yu H.,University of Strathclyde | Yu H.,National University of Defense Technology | Chen Y.,University of Strathclyde
Optics Letters | Year: 2015

A new hardware-friendly bi-exponential fluorescence lifetime imaging (FLIM) algorithm has been proposed. Compared to conventional FLIM software, the proposed algorithms are noniterative offering direct calculation of lifetimes and therefore suitable for real-time applications. They are applicable to single-channel or 2D multichannel time-correlated single-photon counting (TCSPC) systems. The proposed methods have been tested on both synthesized and realistic FLIM data, and we have compared their performances with other recently proposed nonfitting bi-exponential techniques showing promising applications in future massive solid-state TCSPC imagers. © 2015 Optical Society of America.

Luo A.-M.,National University of Defense Technology
Guofang Keji Daxue Xuebao/Journal of National University of Defense Technology | Year: 2010

System cohesion is an important evaluation factor in information system architecture. Based on the architecture framework, the formal description of system interfaces and system functions were provided. In terms of functions and data relationships, the function cohesion and data cohesion were defined respectively, and the system cohesion evaluation method was proposed. Furthermore, an application example was presented. The method is helpful in system design, function assignment, and improving the quality of architecture development.

Li M.,National University of Defense Technology
Information Processing Letters | Year: 2014

Loop invariants play a major role in software verification. In this paper, based on finite difference techniques, a formal characterization for equality loop invariants is presented. Integrating the formal characterization with the automatic verification approach in [5], the algorithm for automatic proving or disproving equality loop invariants is presented. The effectiveness of the algorithm is demonstrated with the experimental results. © 2014 Elsevier B.V. All rights reserved.

Wang G.-C.,National University of Defense Technology
Zhongguo Guanxing Jishu Xuebao/Journal of Chinese Inertial Technology | Year: 2010

In view that our current-stabilized power supply doesn't meet the requirement of laser gyro's theory, this paper discusses the theory, function, realization and difficulty of beam intensity stability control of laser gyro, and puts forward a scheme for restraining the coupling effects between three types of control. Based on the scheme, an all-digital integration circuitry of laser gyro based on TMS320F2812 is designed, and the beam intensity stability power supply of laser gyro is realized. Various experiments on a four-frequency laser gyro are conducted using the designed circuits. The results shows that the digital integration circuit is effective and can be applied in controlling coupling, and the four-frequency laser gyro's null shift vibration can be effectively controlled under the high- and low-temperature process. Both the theory and the experiment verify that the current-stabilized power supply does not meet the principle's requirements, and should be replaced by the beam intensity stability power supply.

Liang D.C.,National University of Defense Technology
IET Conference Publications | Year: 2015

Real-time processors are growly used in embedded applications. Considering that the time cost in data transfer among devices is much more than the time used for computation and operation, it's important to design a high-speed real-time bus structure in real-time systems. This paper offers a deep investigation to the characteristics of real-time systems as well as the basic structure of real-time processors and real-time buses. We designed a high-speed and time-predictable bus architecture called RTBus, where high-performance AXI protocol is employed. To accurately calculate the bus access time for master devices, a two-level real-time bus arbitration algorithm, which adopts the warning-line judgment mechanism and simulated annealing algorithm, is proposed for the operation of the RTBus. Finally, it is proved that RTBus provides a good solution to the conflicts when sharing resources in real-time processors.

Yan S.,National University of Defense Technology
Proceedings of 2011 IEEE CIE International Conference on Radar, RADAR 2011 | Year: 2011

The paper presents a cost-effective real-time motion compensation (MOCO) strategy of airborne UWB SAR based on single GPS receiver and Phase Gradient Autofocus (PGA). The real-time imaging result is present to validate its feasibility. © 2011 IEEE.

Liu B.,National University of Defense Technology
International Journal of Sensor Networks | Year: 2015

The Internet of Things based on sensors is bound to trigger an epoch-making revolution in military affairs. However, the multitudinous sensors increase the processing time of a computer. This makes battlefield simulation get into great trouble. In addition, the outcome of a war is affected by many factors and an excellent battlefield simulation should consider these factors comprehensively. The supercomputer with the capabilities of ultra computation and communication should be applied into this kind of simulation. After introducing the hardware architecture of a high performance simulation supercomputer, this paper presents several techniques in our battlefield simulation software such as its monitoring policy, design principles and scheduling algorithm. These techniques are helpful to monitor the status of the supercomputer with numerous multi-core CPUs and enormous samples of a battlefield programme can be easily deployed and executed in batch. The evaluation conclusion of different samples for the battlefield situation can provide powerful support for the commander. Copyright © 2015 Inderscience Enterprises Ltd.

Feng J.,National University of Defense Technology
Hangkong Dongli Xuebao/Journal of Aerospace Power | Year: 2011

The premise of predicting storage life from accelerated storage test data is the consistency of failure mechanism between use condition and raised stresses. Nonparametric consistent test method for accelerated storage degradation failure mechanism was proposed based on Spearman rank correlation coefficient. If the failure mechanism is consistent in different stresses, the shape of the degradation path is the same. This is essential to consistent test. The Spearman rank correlation coefficient was proposed to measure the difference of the curve shape in different stresses. At last, two examples were given to illustrate the validity of the method.

Yang R.,Changsha University | He Y.,National University of Defense Technology | Gao B.,University of Electronic Science and Technology of China | Tian G.Y.,University of Electronic Science and Technology of China | Tian G.Y.,Northumbria University
Applied Physics Letters | Year: 2014

Emissivity variation introduces illusory temperature inhomogeneity and results in false alarms in infrared thermography, thus, it is important to separate the influence of surface emissivity variation. This letter experimentally demonstrates the advantages of phase information to reduce or enlarge the effect of surface emissivity variation with inductive pulsed phase thermography, where inductive excitation is emissivity-independent and avoids the effect of emissivity variation in heating process. The directly heated area and the indirectly heated area are divided in the phasegrams. The emissivity variation is removed or enlarged perfectly at the specific frequency and defect detectability is improved remarkably. © 2014 AIP Publishing LLC.

Liu Y.,National University of Defense Technology | Zhu H.,Oxford Brookes University
Software - Practice and Experience | Year: 2010

This paper surveys the research on power management techniques for high-performance systems. These include both commercial high-performance clusters and scientific high-performance computing (HPC) systems. Power consumption has rapidly risen to an intolerable scale. This results in both high operating costs and high failure rates so it is now a major cause for concern. It has imposed new challenges to the development of high-performance systems. In this paper, we first review the basic mechanisms that underlie power management techniques. Then we survey two fundamental techniques for power management: metrics and profiling. After that, we review the research for the two major types of high-performance systems: commercial clusters and supercomputers. Based on this, we discuss the new opportunities and problems presented by the recent adoption of virtualization techniques, and again we present the most recent research on this. Finally, we summarize and discuss the future research directions. Copyright © 2010 John Wiley & Sons, Ltd.

Pan Z.,National University of Defense Technology | Balakrishnan N.,McMaster University
Reliability Engineering and System Safety | Year: 2011

Many highly reliable products usually have complex structure, with their reliability being evaluated by two or more performance characteristics. In certain physical situations, the degradation of these performance characteristics would be always positive and strictly increasing. In such a case, the gamma process is usually considered as a degradation process due to its independent and non-negative increments properties. In this paper, we suppose that a product has two dependent performance characteristics and that their degradation can be modeled by gamma processes. For such a bivariate degradation involving two performance characteristics, we propose to use a bivariate BirnbaumSaunders distribution and its marginal distributions to approximate the reliability function. Inferential method for the corresponding model parameters is then developed. Finally, for an illustration of the proposed model and method, a numerical example about fatigue cracks is discussed and some computational results are presented. © 2011 Elsevier Ltd.

Li J.,National University of Defense Technology | Lu C.-Y.,Chinese Academy of science | Lu C.-Y.,Hefei University of Technology
Neurocomputing | Year: 2013

The sparse representation based classification (SRC) method attracts much attention in recent years, due to its promising result and robustness for face recognition. Different from the previous improved versions of SRC which emphasize more on sparsity, we focus on the decision rule of SRC. SRC predicts the label of a given test sample based on the residual which measures the representational capability of the training data of each class. Such decision rule is the same as the nearest feature classifiers (NFCs), but not optimal for SRC which is based on the mechanism of sparsity. In this paper, we first review the NFCs, and rewrite them in a unified formulation. We found that the objective of NFCs is different from SRC but they use the same decision rule. In order to capture more discriminative information from the sparse coding coefficient, we propose a new decision rule, sum of coefficient (SoC), which matches well with SRC. SoC is based on the fact that the sparse coefficient reflects the similarities between data, which are able to take full advantage of sparsity for classification. SoC can be regarded as the voting decision rule which is widely used in ensemble learning, i.e. Adaboost, Bagging. We compare our method with the original SRC on three representative face databases and show that SoC is much more discriminative and accurate. © 2012.

Guoxin C.,National University of Defense Technology
Review of Scientific Instruments | Year: 2015

In recent years, several calibration-independent transmission/reflection methods have been developed to determine the complex permittivity of liquid materials. However, these methods experience their own respective defects, such as the requirement of multi measurement cells, or the presence of air gap effect. To eliminate these drawbacks, a fast calibration-independent method is proposed in this paper. There are two main advantages of the present method over those in the literature. First, only one measurement cell is required. The cell is measured when it is empty and when it is filled with liquid. This avoids the air gap effect in the approach, in which the structure with two reference ports connected with each other is needed to be measured. Second, it eliminates the effects of uncalibrated coaxial cables, adaptors, and plug sections; systematic errors caused by the experimental setup are avoided by the wave cascading matrix manipulations. Using this method, three dielectric reference liquids, i.e., ethanol, ethanediol, and pure water, and low-loss transformer oil are measured over a wide frequency range to validate the proposed method. Their accuracy is assessed by comparing the results with those obtained from the other well known techniques. It is demonstrated that this proposed method can be used as a robust approach for fast complex permittivity determination of liquid materials. © 2015 AIP Publishing LLC.

Radetzki M.,University of Stuttgart | Feng C.,National University of Defense Technology | Zhao X.,KTH Royal Institute of Technology | Jantsch A.,KTH Royal Institute of Technology
ACM Computing Surveys | Year: 2013

Networks-on-Chip constitute the interconnection architecture of future, massively parallel multiprocessors that assemble hundreds to thousands of processing cores on a single chip. Their integration is enabled by ongoing miniaturization of chip manufacturing technologies followingMoore's Law. It comes with the downside of the circuit elements' increased susceptibility to failure. Research on fault-tolerant Networks-on-Chip tries to mitigate partial failure and its effect on network performance and reliability by exploiting various forms of redundancy at the suitable network layers. The article at hand reviews the failure mechanisms, fault models, diagnosis techniques, and fault-tolerance methods in on-chip networks, and surveys and summarizes the research of the last ten years. It is structured along three communication layers: the data link, the network, and the transport layers. The most important results are summarized and open research problems and challenges are highlighted to guide future research on this topic. © 2013 ACM.

Zhang Z.,National University of Defense Technology
Review of Scientific Instruments | Year: 2015

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation. © 2015 AIP Publishing LLC.

Li R.,CAS Institute of Semiconductors | Yue Q.,National University of Defense Technology | Wei Z.,CAS Institute of Semiconductors
Journal of Materials Chemistry C | Year: 2013

High-quality Bi2S3 nanowires are synthesized and their photoresponses are investigated in detail. Our results show that the photoresponsive curves have distinctly different characteristics at low-temperature (50 K) compared to those at room temperature (290 K). The transferred-electron effect is believed to cause this difference. A first principle calculation shows that Bi2S3 has many energy valleys, which agree with our experimental analysis. At low temperature, due to the lack of sufficient phonon energy, the photoexcited electrons in Bi 2S3 mainly aggregate at the bottom of the conduction band. When this electron concentration increased to a high enough level after illumination, an electron transfer between the energy valleys happened and the photocurrent began to decrease slowly after the rapid increase in the first stage. After the transfer process reaches equilibrium, the photocurrent reaches a minimum, thus the trap states play a dominant role and the photocurrent rises slowly again. Furthermore, photocurrent curves at different temperatures were recorded to estimate the phonon energy value needed to assist the electron transitions. The required phonon energy is calculated to be about 16.3 meV (corresponding to 190 K), which fits well with previous results. © 2013 The Royal Society of Chemistry.

Wang R.,University of Sheffield | Wang R.,National University of Defense Technology | Purshouse R.C.,University of Sheffield | Fleming P.J.,University of Sheffield
IEEE Transactions on Evolutionary Computation | Year: 2013

The simultaneous optimization of many objectives (in excess of 3), in order to obtain a full and satisfactory set of tradeoff solutions to support a posteriori decision making, remains a challenging problem. The concept of coevolving a family of decision-maker preferences together with a population of candidate solutions is studied here and demonstrated to have promising performance characteristics for such problems. After introducing the concept of the preference-inspired coevolutionary algorithm (PICEA), a realization of this concept, PICEA-g, is systematically compared with four of the best-in-class evolutionary algorithms (EAs); random search is also studied as a baseline approach. The four EAs used in the comparison are a Pareto-dominance relation-based algorithm (NSGA-II), an ε-dominance relation-based algorithm [ε-multiobjective evolutionary algorithm (MOEA)], a scalarizing function-based algorithm (MOEA/D), and an indicator-based algorithm [hypervolume-based algorithm (HypE)]. It is demonstrated that, for bi-objective problems, all of the multi-objective evolutionary algorithms perform competitively. As the number of objectives increases, PICEA-g and HypE, which have comparable performance, tend to outperform NSGA-II, ε-MOEA, and MOEA/D. All the algorithms outperformed random search. © 1997-2012 IEEE.

The rapid fuel-air mixing enhancement is one of the important issues for the efficient operation of scramjet engines, and it attracts an increasing attention all over the world. The influence of jet-to-crossflow pressure ratio arrangement on the turbulent mixing in the staged transverse injection flow field has been investigated numerically, and the multiport injection system with four square-shaped portholes arranged in tandem has been employed as the simplest configuration in the current study. The numerical approach has been validated against the available experimental data in the open literature, and the predicted wall static pressure distributions show reasonable agreement with the experimental data for the cases with different jet-to-crossflow pressure ratios. The obtained results show that the larger jet-to-crossflow pressure ratio of the primary injector is beneficial to the mixing improvement irrespective of the arrangement of the other jet-to-crossflow pressure ratios, and the evolution of the vortex structure keeps nearly the same irrespective of the jet-to-crossflow pressure ratio of the primary injector. When the jet-to-crossflow pressure ratio of the injector 3 is larger than that of the injector 4, it is beneficial to the evolution of the vortex structure, and this would induce the mixing improvement, as well as the flame holding ability. The largest mixing efficiency is 73.6% at the cross-sectional plane x = 340 mm just downstream of the last injector in the range considered in this article. © 2014 Elsevier Ltd.

Li Y.,Goethe University Frankfurt | Li Y.,National University of Defense Technology | He L.,Goethe University Frankfurt | Hofstetter W.,Goethe University Frankfurt
New Journal of Physics | Year: 2013

We theoretically investigate the pair-superfluid phase of two-component ultracold gases with attractive inter-species interactions in an optical lattice. We establish the phase diagram for filling n = 1 at zero and finite temperatures, by applying bosonic dynamical mean-field theory, and observe stable pair-superfluid and charge-density wave quantum phases for asymmetric hopping of the two species. While the pair superfluid is found to be robust in the presence of a harmonic trap, we observe that it is destroyed already by a small population imbalance of the two species. © IOP Publishing and Deutsche Physikalische Gesellschaft.

Yin H.,Aston University | Yin H.,National University of Defense Technology | Gbadebo A.,Aston University | Turitsyna E.G.,Aston University
Optics Letters | Year: 2015

We examined the possibility of using noise or pseudorandom variations of the refractive index in the design of fiber Bragg gratings (FBGs). We demonstrated theoretically and experimentally that top-hat FBGs may be designed and fabricated using this approach. The reflectivity of the fabricated top-hat FBG matches quite well with that of the designed one. © 2015 Optical Society of America.

Han X.,National University of Defense Technology | Han X.,University College London | Jones P.H.,University College London
Optics Letters | Year: 2015

In this Letter, we demonstrate stable optical binding of spherical microparticles in counter-propagating evanescent optical fields formed by total reflection at a dielectric interface. The microspheres are observed to form onedimensional chains oriented parallel to the direction of propagation of the beams. We characterize the strength of the optical binding interaction by measuring the extent of Brownian position fluctuations of the optically bound microspheres and relating this to a binding spring constant acting between adjacent particles. A stronger binding interaction is observed for particles near the middle of the chain, and the dependence of the binding strength on incident laser power and number of particles in the chain is determined. © 2015 Optical Society of America.

Zhang L.,CAS Shanghai Institute of Optics and fine Mechanics | Zhang L.,University of Chinese Academy of Sciences | Hu J.,CAS Shanghai Institute of Optics and fine Mechanics | Hu J.,University of Chinese Academy of Sciences | And 3 more authors.
Optics Letters | Year: 2012

We report on a tunable all-fiber dissipative-soliton laser with a multimode interference filter that consists of a multimode fiber spliced between two single-mode fibers. By carefully selecting the fiber parameters, a filter with a central wavelength at 1032 nm and a bandwidth of 7.6 nm is constructed and used for spectral filtering in an all-normaldispersion mode-locked ytterbium-doped fiber laser based on nonlinear polarization evolution. The laser delivers 31 mW of average output power with positively chirped 7 ps pulses. The repetition rate of the pulses is 15.3 MHz, and pulse energy is 2.1 nJ. Tunable dissipative-soliton over 12 nm is achieved by applying tension to the single-mode-multimode-single-mode filter. © 2012 Optical Society of America.

Zeng G.,National University of Defense Technology | Ru M.,Academy of Equipment Command and Technology | Yao R.,Academy of Equipment Command and Technology
Acta Astronautica | Year: 2012

A new relative orbit estimation method and practical control scheme for satellite formation keeping is developed. We present the general formation description method based on the relative orbital elements and employ the extended particle filter for the relative orbit estimation using the relative distance, elevation, and azimuth measurements. The stability of the formation configuration is analyzed in the presence of the perturbation and atmospheric drag. We propose a new control scheme for formation keeping, including the triple-impulse strategy for the in-plane motion, the single- impulse maneuver for the cross-track motion, and the time-optimal aerodynamic control for the along-track separation. The full analytical fuel-optimal triple-impulse solutions are then derived, which do not cause additional along-track drift compared with the conventional dual-impulse method. Effects of the thruster errors are also analyzed. Furthermore, the time-optimal aerodynamic control law for the along-track drift is presented. Simulation results show that the relative position estimation errors are within 2 × 10 -2 m, and that of the relative velocity estimation are within 1 × 10 -4 m/s. Moreover, the triple-impulse strategy is simple and effective, and the along-track aerodynamic control precision is under 50 m. © 2012 Elsevier Ltd.

Liu H.,National University of Defense Technology
Proceedings - 2010 International Conference on Communications and Intelligence Information Security, ICCIIS 2010 | Year: 2010

To solve the inefficiencies and high false alarm probability problem of the target detection in synthetic aperture radar (SAR) images and to improve the weakness of the two-parameter CFAR detector, a fast constant false alarm rate(CFAR) algorithm based on Weighted Parzen-window clustering (WPWC) is proposed. The principles and flow of the WPWC algorithm is introduced and a fast two parameter CFAR detector taking WPWC as a preprocessing, which reduced the effect of clutter and eliminated many false target detections from background. According to the theoretical performance analysis and the experiment results of some typical SAR images, the proposed algorithm is shown to be of good performance and strong practicability. Meanwhile, the corresponding fast algorithm greatly reduces the computational load. © 2010 IEEE.

Jin G.,University of Waterloo | Jin G.,National University of Defense Technology | Matthews D.E.,University of Waterloo | Zhou Z.,Hunan University
Reliability Engineering and System Safety | Year: 2013

The paper presents a Bayesian framework consisting of off-line population degradation modeling and on-line degradation assessment and residual life prediction for secondary batteries in the field. We use a Wiener process with random drift, diffusion coefficient and measurement error to characterize the off-line population degradation of secondary battery capacity, thereby capturing several sources of uncertainty including unit-to-unit variation, time uncertainty and stochastic correlation. Via maximum likelihood, and using observed capacity data with unknown measurement error, we estimate the parameters in this off-line population model. To achieve the requirements for on-line degradation assessment and residual life prediction, we exploit a particle filter-based state and static parameter joint estimation method, by which the posterior degradation model is updated iteratively and the degradation state of an individual battery is estimated at the same time. A case study of some Li-ion type secondary batteries not only shows the effectiveness of our method, but also provides some useful insights regarding the necessity of on-line updating and the apparent differences between the population and individual unit degradation modeling and assessment problems. © 2012 Elsevier Ltd.

Wu X.,National University of Defense Technology
ICRMS'2011 - Safety First, Reliability Primary: Proceedings of 2011 9th International Conference on Reliability, Maintainability and Safety | Year: 2011

Traditional phased mission system (PMS) requires that mission phases are connected one after another. However, there is a kind of PMS with mission phases that are not connected consecutively because of idle phase existing among them. Component repair can occur in idle phase, but there is no mission requirement in such phase. This is a new kind of PMS that has not been investigated thoroughly in literature. In this paper, mission reliability is defined as the probability that the system successfully complete missions in all phases except in idle phases. By define absorbing states as the failure states corresponding to the systems mission failure, a continuous time Markov chain (CTMC) models are built for each mission phase. The transition probabilities of system states are obtained by solving CTMC models. Based on these probabilities, mission reliability can be calculated for such kind of PMS. Finally, a numerical example is provided to show the effectiveness of the proposed approach. © 2011 IEEE.

Guo J.Y.,Ohio State University | Duan X.J.,Ohio State University | Duan X.J.,National University of Defense Technology | Shum C.K.,Ohio State University
Geophysical Journal International | Year: 2010

We present a new non-isotropic Gaussian filter for smoothing mass changes computed from Gravity Recovery and Climate Experiment (GRACE) L2 products and a new method to reduce land-ocean signal leakage caused by Gaussian smoothing. The kernel of our non-isotropic filter is the product of two Gaussian functions with distinct latitudinal and longitudinal smoothing radii. When expressed as number of kilometres at the Earth's surface, the longitudinal smoothing radius, defined as a fixed longitude interval, is longer at the equator, and shorter at higher latitude. This is principally in accordance with the resolution of the GRACE data, and permits us to produce homogeneously smoothed results without excessive smoothing in latitudinal direction. This filter is not applicable in polar regions, where we choose to use the classical isotropic Gaussian filter. A smoothing radius choice scheme is proposed for the two filters to mesh seamlessly. In our leakage reduction method, the inputs are the mass change data after smoothing using a Gaussian filter. Along coasts where mass change signal on land is far larger than that over ocean (or signal over ocean is reduced to a very small magnitude by removing a model beforehand, and adding the model back afterwards), our method approximately recovers a smoothed mass change signal over both land and ocean sides as if a regional Gaussian filter with the same smoothing radius were applied over land and ocean separately, in which no signal leakages appear. The side lobe problem does not appear in our approach. Our leakage reduction method could also be used to study mass changes within a region where signal is far larger than that in surrounding regions, or where signal in surrounding regions could be reduced to very low magnitude by removing a model. © 2010 The Authors Journal compilation © 2010 RAS.

Gao G.,National University of Defense Technology
IEEE Geoscience and Remote Sensing Letters | Year: 2011

This letter proposes a Parzen-window-kernel-based algorithm for ship detection in synthetic aperture radar (SAR) images. First, the data-driving kernel functions of Parzen window are utilized to approximate the histogram of real SAR image, in order to complete the accurate modeling of SAR images. Then, a threshold of global constant false alarm rate is given theoretically, and the numerical solution of the threshold is also derived. The experimental results of the real data of typical targets demonstrate that the algorithm presented is effective. © 2010 IEEE.

Wang R.,University of Sheffield | Wang R.,National University of Defense Technology | Fleming P.J.,University of Sheffield | Purshouse R.C.,University of Sheffield
Information Sciences | Year: 2014

Many real-world problems have multiple competing objectives and can often be formulated as multi-objective optimisation problems. Multi-objective evolutionary algorithms (MOEAs) have proven very effective in obtaining a set of trade-off solutions for such problems. This research seeks to improve both the accuracy and the diversity of these solutions through the local application of evolutionary operators to selected sub-populations. A local operation-based implementation framework is presented in which a population is partitioned, using hierarchical clustering, into a pre-defined number of sub-populations. Environment-selection and genetic-variation are then applied to each sub-population. The effectiveness of this approach is demonstrated on 2- and 4-objective benchmark problems. The performance of each of four best-in-class MOEAs is compared with their modified local operation-based versions derived from this framework. In each case the introduction of the local operation-based approach improves performance. Further, it is shown that the combined use of local environment-selection and local genetic-variation is better than the application of either local environment-selection or local genetic-variation alone. Preliminary results indicate that the selection of a suitable number of sub-populations is related to problem dimension as well as to population size. © 2013 Elsevier Inc. All rights reserved.

Wan G.,National University of Defense Technology | Sharf A.,Ben - Gurion University of the Negev
Computers and Graphics (Pergamon) | Year: 2012

Recent advances in scanning technologies allow large-scale scanning of urban scenes. Commonly, such acquisition incurs imperfections: large regions are missing, significant variation in sampling density, noise and outliers. Nevertheless, building facades often consist structural patterns and self-similarities of local geometric structures. Their highly structured nature, makes 3D facades amenable to model-based approaches and in particular to grammatical representations. We present an algorithm for reconstruction of 3D polygonal models from scanned urban facades. We cast the problem of 3D facade segmentation as an optimization problem of a sequence of derivation rules with respect to a given grammar. The key idea is to segment scanned facades using a set of specific grammar rules and a dictionary of basic shapes that regularize the problem space while still offering a flexible model. We utilize this segmentation for computing a consistent polygonal representation from extrusions. Our algorithm is evaluated on a set of complex scanned facades that demonstrate the (plausible) reconstruction. © 2012 Elsevier Ltd.

Han S.,National University of Defense Technology | Wang J.,University of New South Wales
Journal of Navigation | Year: 2011

Modern attitude and heading reference systems (AHRS) generally use Kalman filters to integrate gyros with some other augmenting sensors, such as accelerometers and magnetometers, to provide a long term stable orientation solution. The construction of the Kalman filter for the AHRS is flexible, while the general options are the methods based on quaternion, Euler angles, or Euler angle errors. But the quaternion and Euler angle based methods need to model system angular motions, and, meanwhile, all these three methods suffer from nonlinear problems which will increase the system complexities and the computational difficulties. This paper proposes a novel implementation method for the AHRS integrating IMU and magnetometer sensors. In the proposed method, the Kalman filtering is implemented to use the Euler angle errors to express the local level frame (l frame) errors, rather than express the body frame (b frame) errors as the customary methods do. A linear system error model based on the Euler angles errors expressing the l frame errors for the AHRS has been developed and the corresponding system observation model has been derived. This proposed method for AHRS does not need to model system angular motions and also avoids the nonlinear problem which is inherent in the commonly used methods. The experimental results show that the proposed method is a promising alternative for the AHRS. © 2011 The Royal Institute of Navigation.

Li J.,National University of Defense Technology
Optimal Control Applications and Methods | Year: 2016

This paper investigates the classical time-optimal rest-to-rest three-axis reorientation of the inertially symmetric rigid spacecraft. First-order necessary optimality conditions are derived from the Pontryagin's maximum principle. Then, control structures (i.e., switching times and control torques) for the time-optimal solution with five, six, and seven switches are given. For any five-switch, six-switch, or seven-switch time-optimal solution, a finite number of control structures exist, and relations among the control structures and their associated time-optimal solutions are analytically derived. By utilizing the control structure, efficient numerical optimization algorithm based on multiple-interval Radau pseudospectral method is proposed. Numerical results show that, after rounding to integer, five-switch and six-switch time-optimal solutions exist for rotation angles on the interval [1,180] deg, and s es on the interval [1,72] deg. Finally, time-optimal solutions for typical rotation angles are given to illustrate and validate the new findings. © 2016 John Wiley & Sons, Ltd.

Jiang W.-D.,National University of Defense Technology
Xi Tong Gong Cheng Yu Dian Zi Ji Shu/Systems Engineering and Electronics | Year: 2010

With the research on ballistic missile penetration and defense growing profoundly, target feature extraction becomes more rigorous. Flexible control of warhead and decoys' features is important so as to gain better penetration, while various features extracted from multi-sensors' data are key steps for distinguishing warhead and decoys in ballistic missile defense system. The achievements and technique on electromagnetic feature extraction of ballistic missile and decoy are investigated including the ISAR of complex motion targets, the geometrical characteristics extraction of ballistic targets, and the micro-Doppler feature extraction. Finally, the difficulties of ballistic target feature extraction are pointed out and some feature extraction ideas are given.

Huang L.,National University of Defense Technology
Proceedings -Design, Automation and Test in Europe, DATE | Year: 2014

Coherent data prediction is introduced as a promising architectural technique for reducing cache-to-cache accesses in directory protocol. However, limited on-chip resources cause the accuracy of current prediction to be generally low. Low accuracy would result in a large number of unnecessary or incorrect predictions, which would consequently generate excessive network traffic. This leads to large power and performance overhead for coherent memory access. This paper proposes an early abort mechanism (EBT) that leverages NoC design to reduce the negative effect of wrong prediction operations, thus facilitating overall performance improvement and traffic reduction. Using detailed full-system simulations, we conclude that EBT provides a cost-effective solution for designing efficient multicore processors. To the best of our knowledge, this study is the first to leverage on-chip network for the prediction optimization on multicore coherence. © 2014 EDAA.

Xu W.,National University of Defense Technology
Xi Tong Gong Cheng Yu Dian Zi Ji Shu/Systems Engineering and Electronics | Year: 2010

To improve the reliability of multidisciplinary design optimization (MDO) solving, this paper proposes a new global optimization genetic algorithm called GACOM by combining the genetic algorithm which has good global searching capability and the complex algorithm which has local convergence characteristic. Then this paper establishes double optimization MDF (DO-MDF) and single optimization MDF (SO-MDF) by applying GACOM to the system analysis solution of multidisciplinary feasible (MDF). Finally, by contrasting the optimization result of five calculation frames solving MDO, DO-MDF and SO-MDF have better calculating capability.

Wu G.,National University of Defense Technology
Information Sciences | Year: 2016

Population-based search algorithms (PBSAs), including swarm intelligence algorithms (SIAs) and evolutionary algorithms (EAs), are competitive alternatives for solving complex optimization problems and they have been widely applied to real-world optimization problems in different fields. In this study, a novel population-based across neighborhood search (ANS) is proposed for numerical optimization. ANS is motivated by two straightforward assumptions and three important issues raised in improving and designing efficient PBSAs. In ANS, a group of individuals collaboratively search the solution space for an optimal solution of the optimization problem considered. A collection of superior solutions found by individuals so far is maintained and updated dynamically. At each generation, an individual directly searches across the neighborhoods of multiple superior solutions with the guidance of a Gaussian distribution. This search manner is referred to as across neighborhood search. The characteristics of ANS are discussed and the concept comparisons with other PBSAs are given. The principle behind ANS is simple. Moreover, ANS is easy for implementation and application with three parameters being required to tune. Extensive experiments on 18 benchmark optimization functions of different types show that ANS has well balanced exploration and exploitation capabilities and performs competitively compared with many efficient PBSAs (Related Matlab codes used in the experiments are available from http://guohuawunudt.gotoip2.com/publications.html). © 2015 Published by Elsevier B.V.

Zhou P.,University of Arizona | Shu Y.,National University of Defense Technology | Zhao C.,University of Arizona | Burge J.H.,University of Arizona
Optics Express | Year: 2012

Aspheric surfaces are often measured using interferometers with null correctors, either refractive or diffractive. The use of null correctors allows high accuracy in the measurement, but also introduces imaging aberrations, such as mapping distortion and field curvature. These imaging aberrations couple with diffraction effects and limit the accuracy of the measurements, causing high frequency features in the surface under test to be filtered out and creating artifacts near boundaries, especially at edges. We provide a concise methodology for analyzing these effects using the astigmatic field curves to define the aberration, and showing how this couples with diffraction as represented by the Talbot effect and Fresnel edge diffraction. The resulting relationships are validated with both computer simulations and direct measurements from an interferometer with CGH null corrector. © 2012 Optical Society of America.

Deng X.,National University of Defense Technology | Xie J.,Tsinghua University | Xiong H.,Tsinghua University
International Journal of Production Economics | Year: 2013

In a recent paper [Wang C.; Webster S.; 2007. Channel coordination for a supply chain with a risk-neutral manufacturer and a loss-averse retailer. Decision Sciences 38 (3), 361-389.], the authors study a supply chain consisting of a risk neutral manufacturer and a loss averse retailer and show that the supply chain can be coordinated by three contracts: buy back (BB), gain/loss sharing (GL) and gain/loss sharing and buy back (GLB). They assume that the retailer's degree of loss aversion is common knowledge. However, this assumption cannot reflect real situations, since in the real industry, one party's degree of loss aversion is usually unknown by other parties. In the present paper, we propose a principal-agent model, assuming the retailer's degree of loss aversion to be asymmetric information. Within the principal-agent framework, we obtain the following results: (1) An optimal MGL (modified GL) contract menu, which is based on the GL contract studied in Wang and Webster (2007), is derived for the manufacturer (the principal) by mechanism design theory; (2) Under the MGL contract menu, information asymmetry lowers the production quantity, decreases the manufacturer's profit and deteriorates supply chain performance, while increasing the retailer's utility; (3) The MGL contract menu can coordinate the supply chain with asymmetric information in an implementable way if the wholesale price is endogenously determined by the manufacturer and its lower bound is 0. © 2012 Elsevier B.V.

Wu Y.,National University of Defense Technology
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

Significant weakness in the proposed alternative justification for the Bortz equation are highlighted. The rotation vector is an important concept and tool in understanding 3D rigid rotation and implementing inertial navigation algorithm. screw vector was employed to consider rotation and translation simultaneously in the dual quaternion based inertial navigation algorithm design. The rotation vector is used to describe the rotation from the reference frame N to the body frame. Studies concluded that the fundamental problem with attitude integration is the rotating measurement frame of gyroscopes. Later it was found that the exactness of attitude integration is related not to the expressed/measured frame but to the physical direction of the angular velocity.

Zeng G.,National University of Defense Technology | Hu M.,Academy of Equipment Command and Technology
Acta Astronautica | Year: 2012

The current paper investigates the electromagnetic formation flight control problem using the finite-time control technique. The electromagnetic force model is presented, and the effects of the Earths magnetic field on the EMFF satellites are analyzed. The equations of relative motion and general formation description method are then established. A robust sliding mode controller is designed to achieve trajectory tracking in the presence of model uncertainties and external disturbances. The proposed controller, which combines the advantages of linear and terminal sliding mode controls, can guarantee the convergence of tracking errors in finite time rather than in the asymptotic sense. By constructing a particular Lyapunov function, the closed-loop system is proven globally stable and convergent. Numerical simulations of formation maintenance and reconfiguration are then presented to show the effectiveness of the developed controller. © 2012 Elsevier Ltd. All rights reserved.

Wu J.-X.,Central South University | Li X.-F.,Central South University | Tang G.-J.,National University of Defense Technology
Physica B: Condensed Matter | Year: 2012

This article studies transverse waves propagating in carbon nanotubes (CNTs) embedded in a surrounding medium. The CNTs are modeled as a nonlocal elastic beam, whereas the surrounding medium is modeled as a bi-parameter elastic medium. When taking into account the effect of rotary inertia of cross-section, a governing equation is acquired. A comparison of wave speeds using the Rayleigh and EulerBernoulli theories of beams with the results of molecular dynamics simulation indicates that the nonlocal Rayleigh beam model is more adequate to describe flexural waves in CNTs than the nonlocal EulerBernoulli model. The influences of the surrounding medium and rotary inertia on the phase speed for single-walled and double-walled CNTs are analyzed. Obtained results turn out that the surrounding medium plays a dominant role for lower wave numbers, while rotary inertia strongly affects the phase speed for higher wave numbers. © 2011 Elsevier B.V. All rights reserved.

Wang F.,National University of Defense Technology
Guangdianzi Jiguang/Journal of Optoelectronics Laser | Year: 2012

This paper studies the problem of image inpainting and image interpolation. By transforming the inpainting and interpolation model under the scheme of compressed sensing, we establish a new model of inpainting and interpolation, which is corresponding to the reconstruction model in compressed sensing. To solve this new reconstruction model, this paper gives an iterated hard threshold method based on the sparsity of images decomposed on the complex wavelet. Simulated and real image results demonstrate the effectiveness of the proposed method.

Wang S.,National University of Defense Technology | Wang X.,Columbia University
IEEE Transactions on Circuits and Systems II: Express Briefs | Year: 2010

We consider chaotic digital communications in multiple-inputmultiple-output (MIMO) wireless multipath fading channels. In particular, we focus on systems that employ M-ary differential chaos shift keying (M-DCSK). We consider two transceiver schemes, both of which require no channel state information at either the transmitter or the receiver. The first one employs a distinct chaotic sequence at each transmit antenna to spread the same data symbol and transmits omnidirectionally. At each receive antenna, the corresponding differential detection statistic is formed, and these statistics are then combined with equal gain for symbol detection. The second scheme employs a single chaotic spreading sequence and makes use of adaptive transmit and receive beamforming. The beamformers are updated by using a simple stochastic gradient method that is based on the received signal power and a finite-rate feedback strategy. Simulation results show that both schemes can effectively exploit the spatial diversity of the underlying MIMO system, and the adaptive beamforming scheme significantly outperforms the omnidirectional transmission. © 2010 IEEE.

Jin G.,National University of Defense Technology | Jin G.,University of Waterloo | Matthews D.,University of Waterloo
Quality and Reliability Engineering International | Year: 2014

This article concerns the optimization of measurement plans in the design of bivariate degradation tests for bivariate Wiener processes. After describing an unbalanced measurement scheme for bivariate degradation tests, we derive the likelihood function and provide a method for estimating the model parameters that is based on maximum likelihood and least squares. From the corresponding Fisher information matrix, we deduce an important insight, namely that longer degradation tests and longer intervals between measurements in the test design result in more precise parameter estimates. We introduce a model for optimizing the degradation test measurement plan that incorporates practical constraints and objectives in the test design framework. We also present a search-based algorithm to identify the optimal test measurement plan that is based on the aforementioned measurement rule. Via a simulation study and a case study involving the Rubidium Atomic Frequency Standard, we demonstrate the characteristics of optimal measurement plans for bivariate degradation test design and show the superiority of longer duration tests involving fewer samples compared to alternative designs that specify testing more samples over shorter periods of time. © 2013 John Wiley & Sons, Ltd.

Cheng C.,University of Auckland | Xu W.,University of Auckland | Shang J.,National University of Defense Technology
IEEE Transactions on Industrial Electronics | Year: 2016

A redundantly actuated parallel robot of the 6RSS mechanism involving two point-contact higher kinematic pairs (HKPs) has been developed for the evaluation of food texture changes during the process of mastication. To accomplish this, a fundamental capability of reproducing complex mandibular motions of human subjects in a biomimetic manner is required. In this paper, first, the mechanism and experimental setup of the robot are described, followed by five performance criteria proposed for the torque distribution across the robot. Second, the distributed torque is employed as a feedforward to enhance the independent joint control for the tracking of the mandibular movement. The frictional effects are compensated for to further improve the tracking accuracy. Finally, experiments are carried out to evaluate and compare the proposed control algorithms with the robot being commanded to reproduce a real human mandibular motion in free chewing, chewing a silicone gel, and chewing a wooden stick. The results illustrate that the robot is able to emulate complex mandibular motions, the distributed-torque-based joint control significantly enhances the motion tracking accuracy, and the friction compensation can further improve the motion tracking performance. © 1982-2012 IEEE.

Zhang J.-R.,National University of Defense Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Theoretically, some works have proposed the hadronic resonances Σc(2800) and Λc(2940)+ to be S-wave DN and D*N molecular candidates, respectively. In the framework of QCD sum rules, we investigate whether Σc(2800) and Λc(2940)+ could be explained as the S-wave DN state with JP=12- and the S-wave D*N state with JP=32-, respectively. Technically, contributions of operators up to dimension 12 are included in the operator product expansion. The final results are 3.64±0.33GeV and 3.73±0.35GeV for the S-wave DN state of JP=12- and the S-wave D*N state of JP=32-, respectively. They are somewhat bigger than the experimental data of Σc(2800) and Λc(2940)+, respectively. Since corresponding molecular currents are constructed from local operators of hadrons, the possibility of Σc(2800) and Λc(2940)+ as molecular states cannot be arbitrarily excluded merely from these disagreements between molecular masses using local currents and experimental data. But then these results imply that Σc(2800) and Λc(2940)+ could not be compact states. This may suggest a limitation of the QCD sum rule using the local current to determine whether some state is a molecular state or not. As by-products, masses for their bottom partners are predicted to be 6.97±0.34GeV for the S-wave B̄N state of JP=12- and 6.98±0.34 GeV for the S-wave B̄*N state of JP=32-. © 2014 American Physical Society.

Wu Q.-Y.,National University of Defense Technology
Ruan Jian Xue Bao/Journal of Software | Year: 2013

Middleware is a kind of fundamental software that boomed in 1990s with the rapid development of computer networks. Its main function is to effectively support the development, deployment, operation and management of the network application software systems. With a new connotation, the network computing middleware has encountered a breakthrough of information networks technology and service-oriented software engineering. The former part of this paper, which starts with the network computing environment, gives a comprehensive interpretation on the basic concepts and main technologies of basic middleware, application integration middleware and domain application framework; the second half focuses on hot research topics such as cloud computing, Internet of things, and indicates a number of concerned research directions as well as several challenges and key technologies that need deep exploration from the point view of middleware. © 2013 ISCAS.

Grinstein B.,University of California at San Diego | Stone D.,University of California at San Diego | Stergiou A.,Yale University | Zhong M.,University of California at San Diego | Zhong M.,National University of Defense Technology
Physical Review Letters | Year: 2014

The possibility of a strong a theorem in six dimensions is examined in multiflavor φ3 theory. Contrary to the case in two and four dimensions, we find that, in perturbation theory, the relevant quantity ã increases monotonically along flows away from the trivial fixed point. ã is a natural extension of the coefficient a of the Euler term in the trace anomaly, and it arises in any even spacetime dimension from an analysis based on Weyl consistency conditions. We also obtain the anomalous dimensions and beta functions of multiflavor φ3 theory to two loops. Our results suggest that some new intuition about the a theorem is in order. © 2014 American Physical Society.

Jiang J.,National University of Defense Technology
Xitong Gongcheng Lilun yu Shijian/System Engineering Theory and Practice | Year: 2015

The evidential network model is proposed, on the basis of the Dempster-Shafer theory of evidence and the graph theory, for management problems with uncertainty and complex correlation. The definition and parameter model of evidential network is presented before the advantages of evidential network are concluded. The reasoning problem, reasoning framework and reasoning process are proposed. Then the forward and backward reasoning algorithms are deduced. Finally, a number example is explored to demonstrate the algorithm and process. The evidential network model will be provided as an efficient method for analyzing and resolving the problems in the research fields of decision analysis and system engineering. ©, 2015, Systems Engineering Society of China. All right reserved.

Guo D.,National University of Defense Technology | Li M.,Nanyang Technological University
IEEE Transactions on Knowledge and Data Engineering | Year: 2013

In this paper, we study the set reconciliation problem, in which each member of a node pair has a set of objects and seeks to deliver its unique objects to the other member. How could each node compute the set difference, however, is challenging in the set reconciliation problem. To address such an issue, we propose a lightweight but efficient method that only requires the pair of nodes to represent objects using a counting Bloom filter (CBF) of size (O(d)) and exchange with each other, where (d) denotes the total size of the set differences. A receiving node then subtracts the received CBF from its local one via minus operation proposed in this paper. The resultant CBF can approximately represent the union of the set differences and thus the set difference to each node can be identified after querying the resultant CBF. In this paper, we propose a novel estimator through which each node can accurately estimate not only the value of (d) but also the size of the set difference to each node. Such an estimation result can be used to optimize the parameter setting of the CBF to achieve less false positives and false negatives. Comprehensive analysis and evaluation demonstrates that our method is more efficient than prior BF-based methods in terms of achieving the same accuracy with less communication cost. Moreover, our reconciliating method needs no prior context logs and it is very useful in networking and distributed applications. © 1989-2012 IEEE.

Feng J.,National University of Defense Technology
Gaodianya Jishu/High Voltage Engineering | Year: 2010

In order to improve the prediction precision of high voltage pulse capacitors' storage life, an equal-probability-interval virtual-samples-regression-analysis method based on Bootstrap and regression was proposed, which considered capacitance degradation rule in storage. By analyzing the data collected for 8 months with 10 400nF-composite-medium capacitors, the normal distribution of storage life was got and the 0.8-reliable-life was about 85 months. The interval length of reliability-storage-life was 27.192 based on the analysis of original 10 products data, while with the proposed virtual sample method (N=100), the length was improved to be 4.444. Thus, by using the virtual sample method, the prediction precision of storage life can be remarkably improved. When the number of virtual samples added to above 1500, the precision will little change.

Shi J.,University of Windsor | Shi J.,National University of Defense Technology | Zhang G.,University of Windsor
International Journal of Production Economics | Year: 2010

We consider the joint acquisition and pricing problem where the retailer sells multiple products with uncertain demands and the suppliers provide all unit quantity discounts. The problem is to determine the optimal acquisition quantities and selling prices so as to maximize the retailer's expected profit, subject to a budget constraint. This is the first extension to consider supplier discounts in the constrained multi-product newsvendor pricing problem. We establish a mixed integer nonlinear programming (MINLP) model to formulate the problem, and develop a Lagrangian-based solution approach. Computational results for the test problems involving up to thousand products are reported, which show that the proposed approach can obtain high quality solutions in a very short time. © 2010 Elsevier B.V.All rights reserved.

Chen Y.,University of Graz | Chen Y.,National University of Defense Technology | Ranftl R.,University of Graz | Pock T.,University of Graz
IEEE Transactions on Image Processing | Year: 2014

This paper addresses a new learning algorithm for the recently introduced co-sparse analysis model. First, we give new insights into the co-sparse analysis model by establishing connections to filter-based MRF models, such as the field of experts model of Roth and Black. For training, we introduce a technique called bi-level optimization to learn the analysis operators. Compared with existing analysis operator learning approaches, our training procedure has the advantage that it is unconstrained with respect to the analysis operator. We investigate the effect of different aspects of the co-sparse analysis model and show that the sparsity promoting function (also called penalty function) is the most important factor in the model. In order to demonstrate the effectiveness of our training approach, we apply our trained models to various classical image restoration problems. Numerical experiments show that our trained models clearly outperform existing analysis operator learning approaches and are on par with state-of-the-art image denoising algorithms. Our approach develops a framework that is intuitive to understand and easy to implement. © 2014 IEEE.

Hu H.,Max Planck Institute for Nuclear Physics | Hu H.,National University of Defense Technology | Muller C.,Max Planck Institute for Nuclear Physics
Physical Review Letters | Year: 2011

Electron-positron pair annihilation into a single photon is studied when a second free electron is present. Focussing on the relativistic regime, we show that the photon emitted in the three-lepton interaction may exhibit distinct angular distributions and polarization properties. Moreover, the process can dominate over two-photon annihilation in relativistic electron-positron plasmas of few-MeV temperature. An analogy with three-body recombination of electrons with ions is drawn. © 2011 American Physical Society.

Lei Y.,University of Sichuan | Lei Y.,University of Western Australia | Bennamoun M.,University of Western Australia | Hayat M.,University of Western Australia | And 2 more authors.
Pattern Recognition | Year: 2014

This paper presents a computationally efficient 3D face recognition system based on a novel facial signature called Angular Radial Signature (ARS) which is extracted from the semi-rigid region of the face. Kernel Principal Component Analysis (KPCA) is then used to extract the mid-level features from the extracted ARSs to improve the discriminative power. The mid-level features are then concatenated into a single feature vector and fed into a Support Vector Machine (SVM) to perform face recognition. The proposed approach addresses the expression variation problem by using facial scans with various expressions of different individuals for training. We conducted a number of experiments on the Face Recognition Grand Challenge (FRGC v2.0) and the 3D track of Shape Retrieval Contest (SHREC 2008) datasets, and a superior recognition performance has been achieved. Our experimental results show that the proposed system achieves very high Verification Rates (VRs) of 97.8% and 88.5% at a 0.1% False Acceptance Rate (FAR) for the "neutral vs. nonneutral" experiments on the FRGC v2.0 and the SHREC 2008 datasets respectively, and 96.7% for the ROC III experiment of the FRGC v2.0 dataset. Our experiments also demonstrate the computational efficiency of the proposed approach. © 2013 Elsevier Ltd.

Belal M.,University of Southampton | Song Z.-Q.,University of Southampton | Song Z.-Q.,National University of Defense Technology | Jung Y.,University of Southampton | And 2 more authors.
Optics Express | Year: 2010

In this paper we demonstrate a compact current sensor using the optic fiber micro wire, based on the idea of interferometrically measuring the thermally induced optical phase shifts as a result of heat produced due to the flow of electric current over short transit lengths. A responsivity of 1.28 x 10 -4 rad/I2 at 50Hz of current signal has been shown, with capability of measuring alternating current signals up to 500Hz. © 2010 Optical Society of America.

Yao X.-Y.,National University of Defense Technology
Xitong Fangzhen Xuebao / Journal of System Simulation | Year: 2010

4-tier hiberarchy was put forward as the standard architecture of distributed real-time simulation system, and KD-DRT was introduced as a supporting platform. A radar RF signal simulation system for precisely guided missile was constructed based on KD-DRT. The system modules were arranged to different layer according to its time restriction and the time synchronization method of the distributed system was studied. At last, the simulation system was constructed and the efficiency of KD-DRT in simulation of radar signal was proved.

Wang L.,University of New Brunswick | Wang X.,National University of Defense Technology
Journal of Theoretical Biology | Year: 2012

The number of temporary migrant workers from rural areas to urban areas in emerging market economies like China has increased dramatically since the early 1980s. Temporary migrant workers have been labeled as the major driving force for the rising incidence of infectious diseases in cities. However, it has not been well recognized that temporary migration indeed may have tremendous impacts on the spread of infectious diseases in migrants' home villages. In this paper, by proposing a delay differential equation model, we provide a framework to study the influence of temporary migration on the transmission of infectious diseases in a migrant workers' home village. The model is shown to admit a unique positive equilibrium which is locally asymptotically stable and is globally asymptotically stable under certain conditions. This implies that the disease always persists at a constant level. Considering tuberculosis as an example, we explore various disease prevention and control strategies numerically to demonstrate how migration related parameters affect the early outbreak of the disease. We find that a single control strategy, such as reducing the migration time period alone, has little effect on reducing the disease endemic level. For disease prevention and control, temporary migrant workers should be identified as the top target group, and a combination of several prevention strategies should be implemented. © 2012 Elsevier Ltd.

Zhao S.,National University of Defense Technology
Chinese Control Conference, CCC | Year: 2015

In this paper, a general observer based data-driven control algorithm is proposed to adaptive control for discrete system using input and output (I/O) data. In contrast to model based controller, data-driven control fully utilizes the I/O data measured from the object, whose accurate mathematics model is difficulty to confirm. we deploy pseudo gradient (PG) parameters of full form dynamic linearization (FFDL), which are obtained via adaptive observer based on the method model free adaptive control (MFAC). The observer proposed has more degree of freedom (DOF) and is more flexible. The tracking error is guaranteed converging to 0 and the stability analysis of the controller proposed is presented. Simulation results in MATLAB environment show the effectiveness and applicability of the control law. © 2015 Technical Committee on Control Theory, Chinese Association of Automation.

Xu K.,National University of Defense Technology
Chinese Control Conference, CCC | Year: 2015

To deal with the requirement of high-performance controller of single leg foot force for improving the flexibility of complex environment for quadruped robot, the inaccuracies of dynamical model of quadruped robot, and the model of force control changing through the load changes, through analysis of hydraulic system and single leg dynamical model, hydraulic actuated leg model is built for foot force controlling. Combined with the characteristic of force control, a feed-forward paralleled Active Disturbance Rejection Controller (ADRC) for foot-end-force control of support leg is designed, which have not only the model flexibility of ADRC but also a fast responding as feed-forward. Proved by RecurDyn/Matlab united simulation platform and quadruped bionic robot prototype system, the force controller gives accurate, stabile performance and fast responding. As a basic of force control frame of quadruped robot, the force controller plays an important role in following research of quadruped robot. © 2015 Technical Committee on Control Theory, Chinese Association of Automation.

Wan H.,National University of Defense Technology | Ruda H.E.,University of Toronto
Journal of Materials Science: Materials in Electronics | Year: 2010

ZnO nanowires were grown by CVD process using both pure Zn powder and a mixture of ZnO and graphite powders as the Zn source, and the key factors controlling nanowire growth were identified. In both processes, the partial pressure of zinc vapor determines the prevailing growth morphology and is sensitive to the growth conditions. In the case of Zn powder as the source, the predominant growth mechanism is driven by self-catalyzed growth on the Si substrate, and in the case of a mixture of ZnO and graphite used as the source, the formation of ZnO nanowires is controlled by the vapor-liquid-solid mechanism, where the gold particles serve as catalyst. © 2010 Springer Science+Business Media, LLC.

Chen Y.,University of Bath | Chen Z.,University of Bath | Chen Z.,National University of Defense Technology | Wadsworth W.J.,University of Bath | Birks T.A.,University of Bath
Optics Express | Year: 2013

The distinct disperion properties of higher-order modes in optical fibers permit the nonlinear generation of radiation deeper into the ultraviolet than is possible with the fundamental mode. This is exploited using adiabatic, broadband mode convertors to couple light efficiently from an input fundamental mode and also to return the generated light to an output fundamental mode over a broad spectral range. For example, we generate visible and UV supercontinuum light in the LP02 mode of a photonic crystal fiber from sub-ns pulses with a wavelength of 532 nm. © 2013 Optical Society of America.

Huang W.,National University of Defense Technology
International Journal of Hydrogen Energy | Year: 2014

The information in the three-dimensional transverse injection flow field is very important for the design of a scramjet combustor, and it should be explored by using the data mining and multi-objective design optimization methods. In the current study, the three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations coupled with the two equation SST k-ω turbulence model has been utilized to simulation the transverse injection flow field with a freestream Mach number 3.75, and the influence of the turbulence model on the flow field properties has been evaluated as well. At the same time, three grid scales have been employed to perform the grid independency analysis, and the predicted results have been compared with the available experimental data in the open literature in order to carry out the code validation process. Further, the effect of the injector geometric configuration on the mixing efficiency of the transverse injection flow field has been investigated, and four different configurations have been considered in the current study, namely the square port, the diamond port, the equilateral triangular port and the circular port. The obtained results show that the case with the square injection port can obtain the largest mixing efficiency, and it can offer the rapidest near-field mixing between the injectant and the air. At last, the transverse injection flow field with the square injection port has been optimized by the surrogate-based evolutionary algorithm, and the relationships between the design variables and the objective functions have been explored by the variance analysis method. It is shown that the jet-to-crossflow pressure ratio has a high remarkable impact on the total pressure recovery efficiency, as well as the number of the injection ports on the drag force performance. The drag force increases with the increase of the number of the injection ports due to the deeper penetration of the rear jets. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Yang S.,CAS Institute of Semiconductors | Kang J.,CAS Institute of Semiconductors | Yue Q.,National University of Defense Technology | Yao K.,CAS Changchun Institute of Applied Chemistry
Journal of Physical Chemistry C | Year: 2014

Various stacking patterns have been predicted in few-layer MoS2, strongly influencing its electronic properties. Bilayer MoS2 nanosheets have been synthesized by vapor phase growth. It is found that both A-B and A-A′ stacking configurations are present in bilayer MoS 2 nanosheets through optical images, and the different stacking patterns exhibit distinctive line shapes in the Raman spectra. By theory calculation, it is also concluded that the A-B and A-A′ stacking are the most stable and lowest-energy stacking in the five predicted stacking patterns of bilayer MoS2 nanosheets, which proves the experimental observations. © 2014 American Chemical Society.

Zhang J.,Fudan University | Wang F.-Y.,CAS Institute of Automation | Wang F.-Y.,University of Arizona | Wang K.,CAS Institute of Automation | And 3 more authors.
IEEE Transactions on Intelligent Transportation Systems | Year: 2011

For the last two decades, intelligent transportation systems (ITS) have emerged as an efficient way of improving the performance of transportation systems, enhancing travel security, and providing more choices to travelers. A significant change in ITS in recent years is that much more data are collected from a variety of sources and can be processed into various forms for different stakeholders. The availability of a large amount of data can potentially lead to a revolution in ITS development, changing an ITS from a conventional technology-driven system into a more powerful multifunctional data-driven intelligent transportation system (D2ITS): a system that is vision, multisource, and learning algorithm driven to optimize its performance. Furthermore, D2ITS is trending to become a privacy-aware people-centric more intelligent system. In this paper, we provide a survey on the development of D2ITS, discussing the functionality of its key components and some deployment issues associated with D2ITS. Future research directions for the development of D2ITS is also presented. © 2011 IEEE.

Kong J.,National University of Defense Technology
Proceedings - 10th IEEE International Conference on Computer and Information Technology, CIT-2010, 7th IEEE International Conference on Embedded Software and Systems, ICESS-2010, ScalCom-2010 | Year: 2010

Cloud computing can provide users dynamically scalable, shared resources over the internet, but users usually fear about security threats and loss of control of data and systems. This paper presents a practical architecture to protect the data confidentiality for guest virtual machines. With this solution, even the cloud computing service providers cannot access the private data of their clients. This is very important and attractive for the cloud clients. In our work, we utilize virtualization technology and trusted computing technology to construct a secure and robust virtualization platform. On this platform, we customize the guest virtual machine operating system, strengthen the isolation between virtual machines, and therefore, greatly improve the data privacy of cloud services. With our solution, the cloud service provider can compromise the availability, but not the confidentiality of the guest virtual machines. © 2010 IEEE.

Huang W.,National University of Defense Technology
Journal of Mechanical Science and Technology | Year: 2015

The Reynolds averaged Navier-Stokes (RANS) equations coupled with the renormalization group (RNG) k-ε and the single-step chemical reaction mechanism have been used to evaluate the influence of the radius of the strut tip, the half-angle of the strut and the strut location relative to the combustor entrance on the combustion performance of the combustor has been discussed. At the same time, the numerical method has been validated by the available experimental shadowgraph, velocity measurements and temperature measurements in the open literature. With the increasing of the radius of the strut tip, the separation region generated due to the strong interaction between the shock wave and the boundary layer becomes broader, and accordingly, a bifurcated shock wave appears at the front of the strut, then a shock wave train. The shock waves generated at the intersectional points between the walls of the strut and the sonic lines play an important role in the generation of the separation zone, and they can improve the combustion efficiency to a certain extent. Further, the mixing process is more intensive than the chemical reaction process in the vicinity of the strut base, and the combustion efficiency increases nearly monotonically with the increasing of the horizontal distance in the range considered in the current study. When the intersectional point between the leading shock wave and the upper wall overlaps with the divergence point, the combustion efficiency at the exit of the combustor becomes the largest, and its value is nearly 96.2%. © 2015, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Yang R.,Changsha University | He Y.,National University of Defense Technology
Composite Structures | Year: 2016

Polymer-matrix composites (PMCs) such as glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP) are being increasingly used in fields of aerospace, renewable energy, civil and architecture. Damages such as broken fibre, impact and delamination are inevitable during either fabrication or lifetime of PMC structures or components. This work proposed selectively heating thermography (SeHT) through electromagnetic induction and infrared temperature measurement for CFRP characterisation and damage inspection. Broken carbon fibres can be easily identified through SeHT whilst inside delamination is difficult to be inspected due to negative influence of temperature gradient, lateral blur effect, and periodic structures. In order to solve this problem, cross correlation (CC) matched filtering algorithm was proposed to enhance the inspection results. Six CFRP laminate samples with impact damages from 2 to 12 J were tested to verify the proposed methods. The experimental studies show that SeHT is capable of characterising fibres and inspecting surface broken area, whilst CC phasegram is capable of inspecting inner delamination due to elimination of non-uniform heating effect and lateral blurring effect. The dependence of damage for CFRP sample on impact energy was also investigated. Through SeHT and CC matched filtering, characterisation and inspection for CFRP can be achieved. © 2016 Elsevier Ltd.

Zhang S.,National University of Defense Technology | Dulieu-Barton J.M.,University of Southampton | Thomsen O.T.,University of Southampton
Composite Structures | Year: 2015

The influence of elevated temperature on the stability of sandwich structures is investigated. A new analytical solution is proposed that enables the calculation of the critical wrinkling stress in sandwich beams subjected to load and elevated temperatures. The effect of a through thickness temperature gradient is accounted for by imposing different stiffnesses of the core for the different temperatures. The sandwich beam studied in the paper is loaded in a simply supported four-point bending configuration, where one of the face sheets is heated. The experimental approach utilises high-speed imaging where the strains are calculated from measured displacements obtained from digital image correlation (DIC). A shift of the failure mode from face sheet yielding to face sheet wrinkling is observed with increasing temperatures. The results from the new analytical method agree well with corresponding experimental results. Finite element analysis is also conducted, which shows excellent correspondence with the theory and the experimental data. The work clearly demonstrates that under certain conditions the load response of the sandwich beam can become nonlinear and unstable, and hence will fail well below face sheet yielding load because of the loss of stiffness of the core material. © 2014 Elsevier Ltd.

Kong J.,National University of Defense Technology
Proceedings - 2010 International Symposium on Intelligence Information Processing and Trusted Computing, IPTC 2010 | Year: 2010

Virtualization has been widely used in cloud computing systems to cut costs, and to provide dynamically scalable resources over the internet. Many ideas have been proposed to increase the security of the virtualized systems. But, a big unspoken assumption of these ideas is that the cloud users have to trust the cloud provider totally and unconditionally. In reality, however, this assumption can't always hold water, host administrator, for one reason or another, is prone to illegally access the sensitive data stored in the guest virtual machines. In this paper, we put forward ideas to protect the confidentiality of virtual machines when the host administrator is untrusted. Based on virtualization environment, we define our threat model and analyze a set of security aspects which are of real-world concerns. Leveraging trusted computing technologies, we propose possible solutions to these security threats. The solutions can provide better confidentiality to cloud users, and have practical value to the future cloud construction. © 2010 IEEE.

Wu Q.,Nanjing Southeast University | Wu Q.,Hong Kong Polytechnic University | Law R.,Hong Kong Polytechnic University | Xu X.,National University of Defense Technology
Expert Systems with Applications | Year: 2012

In recent years, Gaussian process (GP) models have been popularly studied to solve hard machine learning problems. The models are important due to their flexible non-parametric modeling abilities using Mercer kernels and the Bayesian framework for probabilistic inference. In this paper, we propose a sparse GP regression (GPR) model for tourism demand forecasting in Hong Kong. The sparsification procedure of the GPR model not only decreases the computational complexity but also improves the generalization ability. We experiment the proposed model with monthly demand data that are relevant to Hong Kong's tourism industry, and compare the performance of the sparse GPR model with those of various kernel-based models to show its effectiveness. The proposed sparse GPR model shows that its forecasting capability outperforms those of the ARMA model and the two state-of-the-art SVM models. © 2011 Elsevier Ltd. All rights reserved.

Liu Z.,National University of Defense Technology
Chinese Journal of Aeronautics | Year: 2015

This paper addresses the problem of direction-of-arrival (DOA) and polarization estimation with polarization sensitive arrays (PSA), which has been a hot topic in the area of array signal processing during the past two or three decades. The sparse Bayesian learning (SBL) technique is introduced to exploit the sparsity of the incident signals in space to solve this problem and a new method is proposed by reconstructing the signals from the array outputs first and then exploiting the reconstructed signals to realize parameter estimation. Only 1-D searching and numerical calculations are contained in the proposed method, which makes the proposed method computationally much efficient. Based on a linear array consisting of identically structured sensors, the proposed method can be used with slight modifications in PSA with different polarization structures. It also performs well in the presence of coherent signals or signals with different degrees of polarization. Simulation results are given to demonstrate the parameter estimation precision of the proposed method. © 2015 The Author. Production and hosting by Elsevier Ltd. on behalf of CSAA & BUAA.

Zhang Y.,National University of Defense Technology | Liu L.,Georgia Institute of Technology
Future Generation Computer Systems | Year: 2013

Resource discovery in large-scale Peer-to-Peer (P2P) networks is challenging due to lack of effective methods for guiding queries. Based on the observation that the effectiveness of P2P resource discovery is determined by the utilization of hints, i.e., a summary of where the resources are, scattered in the network, in this paper we propose the distance-aware bloom filters (DABF) that disseminate hint information to faraway nodes by decaying BFs with different deterministic masks. Based on DABF, we design a novel Collaborative P2P Search (CPS) mechanism, which supports intelligent message behaviors including suspend, resume, terminate, move, reside, dispatch, notify and order. The effectiveness of our proposals is demonstrated through theoretical analysis and extensive simulations, in which we observed a remarkable reduction in search latency over previous approaches. © 2012 Elsevier B.V. All rights reserved.

Lei P.,National University of Defense Technology
Proceedings of 2011 IEEE CIE International Conference on Radar, RADAR 2011 | Year: 2011

A multi-channel equalization algorithm combined with spectrum correction is proposed, suitable for SAR/GMTI system with small time-bandwidth chirp signal. The experimental results show the algorithm not only can compensate the channel mismatch, but also obtain satisfied pulse compression performance. © 2011 IEEE.

Huang W.,National University of Defense Technology
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering | Year: 2014

The staged injection scheme has drawn an increasing attention for the airbreathing hypersonic propulsion system, and the fuel injection angle has a large impact on the mixing improvement between the fuel and the supersonic cross flow. The Reynolds-averaged Navier-Stokes equations associated with the SST k- turbulence model have been employed to investigate the interaction mechanism in the staged sonic injection flow field, and the influences of the injection angle, the injection angle arrangement, and the distance between the injectors on the flow field characteristics have been analyzed comprehensively. At the same time, three grid scales have been used to perform the grid independency analysis, and the predicted results have been compared with the experimental data in the open literature for the single transverse injection scheme. The obtained results show that the penetration height for the cases with the distance between the injectors being 1 mm is the highest in the range considered in the current study, and this may be due to the strongest shock wave/shock wave interaction between the injectors. At the same time, due to the blockage of the fuel injection, the penetration height increases as the supersonic air stream flows downstream, and the influence of the wave system generated by the first and third injectors cannot propagate downstream and upstream, respectively. The multi-port injection scheme can provide better fuel penetration performance than the single one when the flow flux keeps constant, and the multi-port injection scheme with a certain angle can provide a higher total pressure recovery efficiency than the staged transverse injection scheme. Further, the staged transverse injection flow field can provide a better recirculation zone for the mixing between the fuel jet and the boundary layer, and the separation length increases with the increase of the distance between the injectors. © © IMechE 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Liang W.,Australian National University | Luo J.,National University of Defense Technology
Proceedings - Conference on Local Computer Networks, LCN | Year: 2011

In this paper we deal with the network lifetime maximization problem under multiple mobile sink environments, namely, the h-hop-constrained multiple mobile sink problem, which is defined as follows. Given a stationary sensor network with K mobile sinks that traverse and sojourn in a given space of locations in the monitoring area, assume that the total travel distance of each sink is bounded by a given value L and the maximum number of hops from each sensor to a sink is bounded by an integer h ≥ 1, the problem is to find an optimal trajectory for each mobile sink and determine the sojourn time at each sojourn location in the trajectory such that the network lifetime is maximized. We first formulate this problem as a joint optimization problem consisting of finding an optimal trajectory and determining the sojourn time at each chosen location. We then show that the problem is NP-hard. We instead devise a novel three-stage heuristic, which consists of calculating the sojourn time profile at each potential sojourn location, finding a high-quality trajectory for each mobile sink, and determining the actual sojourn time at each sojourn location. We finally conduct extensive experiments by simulations to evaluate the performance of the proposed algorithm in terms of network lifetime. We also investigate the impact of constraint parameters on the network lifetime. The experimental results demonstrate that the performance of the proposed heuristic is highly comparable to the optimal one, and the ratios of network lifetime of the proposed algorithm to the optimal network lifetime are ranged from 56% to 93%. © 2011 IEEE.

Li Y.,National University of Defense Technology
Dianzi Yu Xinxi Xuebao/Journal of Electronics and Information Technology | Year: 2016

The performance of low frequency Ultra-Wide-Band (UWB) Synthetic Aperture Radar (SAR) is seriously affected by narrow band Radio Frequency Interference (RFI) in the VHF/UHF band. RFI suppression, by placing notches over the energy spectra to remove the RFI spikes, results energy loss of the wide-band signals and raises the range direction side-lobes. This paper presents an approach to suppress the side-lobe in range direction caused by adaptive filtering. After clipping main energy of strong scatterers in range compression domain before RFI estimation, the interference signals are estimated using an Adaptive Line Enhancer (ALE) and subtracted from the radar echo. The clipping approach makes use of the different time-domain characteristics between wide-band signal and narrow band interference, and by using pulse compression technology the method can be processed efficiently. To investigate the performance of RFI suppression, clipping of strong scatterers is combined to the ALE based on Normalized Least Mean Square (NLMS) algorithm. Simulation results and experimental data test compared with the conventional algorithms suggest that side-lobes of the strong scatters can be reduced effectively in RFI suppression. © 2016, Science Press. All right reserved.

Han K.,National University of Defense Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2016

In the all-fiber optical parametric oscillator (OPO) based on four wave mixing (FWM), the signal laser gets effective gain only in a short distance. The increasing trend of signal laser in photonic crystal fiber (PCF) is measured by optical time domain reflecting (OTDR) technology, and the backscatter signal light is measured. The parametric gain distribution in PCF is calculated, and the distance between the start of the PCF and the sharp drop in the parametric gain is defined as the effective interaction length. Moreover, the results are verified by PCF heating experiment. The results show that there is only 10 m of the effective interaction length in the 34.5 m PCF. The signal laser keeps growing exponentially only in the first 10 m PCF, and cannot increase any more in the rest 24.5 m PCF for the signal and the pump light is no longer meet the phase matching conditions. An effective method for measuring the parametric gain distribution is proposed, and the result is useful for optimizing the configuration and improving the efficiency of all-fiber OPO. © 2016, Chinese Lasers Press. All right reserved.

Yang R.,Changsha University | He Y.,National University of Defense Technology
Applied Physics Letters | Year: 2015

Anisotropy and inhomogeneity of carbon fiber reinforced polymers (CFRPs) result in that many traditional non-destructive inspection techniques are inapplicable on the delamination evaluation. This letter introduces eddy current pulsed phase thermography (ECPPT) for CFRPs evaluation considering volumetric induction heating due to small electrical conductivity, abnormal thermal wave propagation, and Fourier analysis. The proposed methods were verified through experimental studies under transmission and reflection modes. Using ECPPT, the influence of the non-uniform heating effect and carbon fiber structures can be suppressed, and then delamination detectability can be improved dramatically over eddy current pulsed thermography. © 2015 AIP Publishing LLC.

Shi J.R.,CAS National Astronomical Observatories | Gehren T.,Universitats Sternwarte Munich | Zeng J.L.,National University of Defense Technology | Mashonkina L.,CAS National Astronomical Observatories | And 2 more authors.
Astrophysical Journal | Year: 2014

Non-local thermodynamic equilibrium (NLTE) line formation for neutral copper in the one-dimensional solar atmospheres is presented for the atomic model, including 96 terms of Cu I and the ground state of Cu II. The accurate oscillator strengths for all the line transitions in model atom and photoionization cross sections were calculated using the R-matrix method in the Russell-Saunders coupling scheme. The main NLTE mechanism for Cu I is the ultraviolet overionization. We find that NLTE leads to systematically depleted total absorption in the Cu I lines and, accordingly, positive abundance corrections. Inelastic collisions with neutral hydrogen atoms produce minor effects on the statistical equilibrium of Cu I in the solar atmosphere. For the solar Cu I lines, the departures from LTE are found to be small, the mean NLTE abundance correction of THK∼0.01 dex. It was found that the six low-excitation lines, with excitation energy of the lower level E exc ≤ 1.64 eV, give a 0.14 dex lower mean solar abundance compared to that from the six E exc > 3.7 eV lines, when applying experimental gf-values of Kock & Richter. Without the two strong resonance transitions, the solar mean NLTE abundance from 10 lines of Cu I is logε(Cu) = 4.19 ± 0.10, which is consistent within the error bars with the meteoritic value 4.25 ± 0.05 of Lodders et al. The discrepancy between E exc = 1.39-1.64 eV and E exc > 3.7 eV lines can be removed when the calculated gf-values are adopted and a mean solar abundance of logε(Cu) = 4.24 ± 0.08 is derived. © 2014. The American Astronomical Society. All rights reserved..

Wang K.,National University of Defense Technology | Wang K.,Chinese Academy of Sciences | Shen Z.,Chinese Academy of Sciences
IEEE Intelligent Systems | Year: 2011

It is challenging to establish accurate mathematical models for complex systems, and experiments on them are generally costly or even impossible, making it difficult to analyze, control, and manage them. The ACP approach provides a way to attack this difficulty. However, with the agent technologies for the A (artificial societies) part, the burdens from computing agent behaviors and the algorithms' evaluating process are usually very heavy. Fortunately, computing hardware is going through a revolution with the development of graphics processing units (GPUs). A single GPU can provide numerous threads running together and is suitable for parallel computing. This article focuses on the C (computational experiments) part of the ACP approach. It explains the advantages of cloud computing and GPUs and presents the architectures of the GPU-based cloud computing for the transportation systems. © 2006 IEEE.

Xu K.,Shenzhen VisuCA Key Laboratory SIAT | Xu K.,National University of Defense Technology | Zhang H.,Simon Fraser University | Cohen-Or D.,Tel Aviv University | Chen B.,Shenzhen VisuCA Key Laboratory SIAT
ACM Transactions on Graphics | Year: 2012

We introduce set evolution as a means for creative 3D shape modeling, where an initial population of 3D models is evolved to produce generations of novel shapes. Part of the evolving set is presented to a user as a shape gallery to offer modeling suggestions. User preferences define the fitness for the evolution so that over time, the shape population will mainly consist of individuals with good fitness. However, to inspire the user's creativity, we must also keep the evolving set diverse. Hence the evolution is "fit and diverse", drawing motivation from evolution theory. We introduce a novel part crossover operator which works at the finer-level part structures of the shapes, leading to significant variations and thus increased diversity in the evolved shape structures. Diversity is also achieved by explicitly compromising the fitness scores on a portion of the evolving population. We demonstrate the effectiveness of set evolution on man-made shapes. We show that selecting only models with high fitness leads to an elite population with low diversity. By keeping the population fit and diverse, the evolution can generate inspiring, and sometimes unexpected, shapes. © 2012 ACM 0730-0301/2012/08-ART57.

Li J.,National University of Defense Technology
Advances in Space Research | Year: 2016

This paper investigates the time-optimal rest-to-rest three-axis reorientation of asymmetric rigid spacecraft. First, time-optimal solutions for the inertially symmetric rigid spacecraft (ISRS) three-axis reorientation are briefly reviewed. By utilizing initial costates and reorientation time of the ISRS time-optimal solution, the homotopic approach is introduced to solve the asymmetric rigid spacecraft time-optimal three-axis reorientation problem. The main merit is that the homotopic approach can start automatically and reliably, which would facilitate the real-time generation of open-loop time-optimal solutions for attitude slewing maneuvers. Finally, numerical examples are given to illustrate the performance of the proposed method. For principle axis reorientation, numerical results and analytical derivations show that, multiple time-optimal solutions exist and relations between them are given. For generic reorientation problem, though mathematical rigorous proof is not available to date, numerical results also indicated the existing of multiple time-optimal solutions. © 2016 COSPAR.

Feng J.,National University of Defense Technology
Tien Tzu Hsueh Pao/Acta Electronica Sinica | Year: 2011

For products whose failures are defined in terms of performance characteristics exceeding their critical values, reliability assessment can be based on degradation measurements by using degradation models. Since the time-to-failure depends on the level of critical value, more life data can be obtained by tightening the critical value. This paper presents a method for the estimation of life distribution for long life products by using life data from degradation measurements. The relationship between life and critical value and stress is modeled and used to estimate the life distribution at a usual critical value design stress. The model parameters are estimated by using maximum likelihood and least square method. At last, an example is used to illustrate the validity of the method.

Yang R.,Changsha University | He Y.,National University of Defense Technology
Infrared Physics and Technology | Year: 2014

Longitudinal heat conduction from surface to inside of solid material could be used to evaluate the subsurface defects. Considering that the skin depth of high frequency eddy current in metal is quite small, this paper proposed logarithmic analysis of eddy current thermography (ECT) to quantify the depth of subsurface defects. The proposed method was verified through numerical and experimental studies. In numerical study, ferromagnetic material and non-ferromagnetic material were both considered. Results showed that the temperature-time curve in the logarithm domain could be used to detect subsurface defects. Separation time was defined as the characteristic feature to measure the defect's depth based on their linear relationships. The thermograms reconstructed by logarithm of temperature can improve defect detectability. © 2014 Elsevier B.V. All rights reserved.

Li Z.,Chinese Academy of Sciences | Chen C.,Chinese Academy of Sciences | Wang K.,National University of Defense Technology
IEEE Intelligent Systems | Year: 2011

Agent-based traffic management systems can use the autonomy, mobility, and adaptability of mobile agents to deal with dynamic traffic environments. Cloud computing can help such systems cope with the large amounts of storage and computing resources required to effectively use of traffic strategy agents and mass transport data. This article reviews the history of the development of traffic control and management systems within the evolving computing paradigm and shows the state of traffic control and management systems based on mobile multiagent technology. An intelligent transportation cloud could provide services such as decision support, a standard development environment for traffic management strategy, and so on. Moreover, the cloud can generate, store, manage, test, optimize, and use mobile traffic strategy agents to maximize advantages of cloud computing and agent technology to effectively control and manage urban-traffic systems. © 2011 IEEE.

Chen L.-H.,National University of Defense Technology
Xi Tong Gong Cheng Yu Dian Zi Ji Shu/Systems Engineering and Electronics | Year: 2011

An algorithm of directions of arrival estimation for multicomponet frequency-hopping signals based on spatial time-frequency analysis is proposed, which can realize direction-of-arrival (DOA) estimation in underdetermined condition. First, a clear time-frequency representation is gained by short-time-Fourier-transform (STFT) and smoothed-pseudo-Wigner-Ville distribution (SPWVD) synthesis method, which can obtain robust results with good time-frequency concentration and suppression cross-term interference performance. Then, effective hops are selected from the time-frequency distribution, and every hop's spatial time-frequency matrix is built. Finally, every hop's DOA is estimated by three methods: linear spatial time-frequency method, bilinear spatial time-frequency method, and root-MUSIC. The simulation results demonstrate that the estimation algorithm is effective.

Belal M.,University of Southampton | Song Z.,University of Southampton | Song Z.,National University of Defense Technology | Jung Y.,University of Southampton | And 2 more authors.
Optics Letters | Year: 2010

We demonstrate a compact optical fiber microwire current sensor based on the Faraday effect with gigahertz frequency of current sensing capabilities. © 2010 Optical Society of America.

Zhang K.,National University of Defense Technology
Electronics Letters | Year: 2013

Two QPSK-like global navigation satellite system signals with unequal power are multiplexed as a constant-envelope signal analytically. It is further generalised as an extended AltBOC signal that has unbalanced power on the upper and the lower sidebands by the phase rotating technique. The modulations provide additional power control flexibility than the traditional DualQPSK and AltBOC signals and are demonstrated as optimum analytical implementations that maximise the power efficiency. © The Institution of Engineering and Technology 2013.

Dang Z.,National University of Defense Technology
Aerospace Science and Technology | Year: 2013

The inner-formation flying system with two proof-masses (IFFS-II) in the same cavity of a big satellite is an innovative satellite formation flying system which can be used in the Earth gravity measurement. In IFFS-II, two proof-masses freely fly in the nearly pure gravitational orbit since the satellite shields them from the outer environmental disturbances. In IFFS-II, the self-gravitational attraction among proof-masses and outer satellite is a special disturbance and modeled for the first time. In addition, other disturbances like J2 non-spherical shape perturbation and atmospheric drag, etc. also influence the formation flying of IFFS-II. In regard to these problems, a relative translational controller combined with a disturbance feedback and a coordinate controller defined by the hyperbolic tangent function is designed. The global stability of the system with the proposed controller is proved by the Barbalat lemma in theory. Then a simulation is performed and the corresponding control effects are tested. The simulation results demonstrate that the controller stabilizes the system. © 2013 Elsevier Masson SAS. All rights reserved.

Zhong Q.,National University of Defense Technology
Lecture Notes in Electrical Engineering | Year: 2012

The increasing number of rules used in Network Intrusion Detection System(NIDS) based on pattern matching lead to the performance diminishing. An efficient algorithm(Multi-AC) for Packet Pre-filtering is proposed to improve the performance of Packet Pre-filtering and NIDS. By making Multilevel AC finite automata, it reduces the number of rules that are candidates for a full match. Experiments based on Snort show that the rules' number can be reduced to 11%-14% by using Multi-AC algorithm. © Springer-Verlag Berlin Heidelberg 2012.

Wu Y.,Central South University | Pan X.,National University of Defense Technology
IEEE Transactions on Aerospace and Electronic Systems | Year: 2013

The in-flight alignment is a critical stage for airborne inertial navigation system/Global Positioning System (INS/GPS) applications. The alignment task is usually carried out by the Kalman filtering technique that necessitates a good initial attitude to obtain a satisfying performance. Due to the airborne dynamics, the in-flight alignment is much more difficult than the alignment on the ground. An optimization-based coarse alignment approach that uses GPS position/velocity as input, founded on the newly-derived velocity/position integration formulae is proposed. Simulation and flight test results show that, with the GPS lever arm well handled, it is potentially able to yield the initial heading up to 1 deg accuracy in 10 s. It can serve as a nice coarse in-flight alignment without any prior attitude information for the subsequent fine Kalman alignment. The approach can also be applied to other applications that require aligning the INS on the run. © 1965-2011 IEEE.

Wu Y.,Central South University | Pan X.,National University of Defense Technology
IEEE Transactions on Aerospace and Electronic Systems | Year: 2013

Inertial navigation applications are usually referenced to a rotating frame. Consideration of the navigation reference frame rotation in the inertial navigation algorithm design is an important but so far less seriously treated issue, especially for super high-speed flying vehicles or the future ultraprecision navigation system of several meters per hour. A rigorous approach is proposed to tackle the issue of navigation frame rotation in velocity/position computation by use of the newly-devised velocity/position integration formulae in the Part I companion paper. The two integration formulae set a well-founded cornerstone for the velocity/position algorithms' design that makes the comprehension of the inertial navigation computation principle more accessible to practitioners, and different approximations to the integrals involved give birth to various velocity/position update algorithms. Two-sample velocity and position algorithms are derived to exemplify the design process. In the context of level-flight airplane examples, the derived algorithm is analytically and numerically compared with the typical algorithms that exist in the literature. The results throw light on the problems in existing algorithms and the potential benefits of the derived algorithm. © 1965-2011 IEEE.

Chen G.Y.,University of Southampton | Zhang X.L.,University of Southampton | Zhang X.L.,National University of Defense Technology | Brambilla G.,University of Southampton | Newson T.P.,University of Southampton
Optics Letters | Year: 2011

The proof-of-concept demonstration of a microfiber-based flexural disc accelerometer is presented. The reduced microfiber size and bending radii give rise to high device compactness and responsivity. A flexural disc accelerometer manufactured from a 10mm long microfiber showed a performance of ∼ 2:2 rad=g, with the responsivity expected to increase proportionally with the microfiber length. © 2011 Optical Society of America.

Yang J.,National University of Defense Technology | Yang J.,University of Edinburgh | Thompson J.,University of Edinburgh | Huang X.,University of Edinburgh | And 2 more authors.
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

The compressed sensing (CS) synthetic aperture radar (SAR) imaging scheme can use random undersampled data to reconstruct images of sparse or compressible targets. However, compared to Nyquist sampling, the cost of the CS imaging scheme is the long reconstruction time, particularly for the conventional reconstruction strategy, which reconstructs the whole scene in one process. It also needs a large memory to access the sensing matrix used for reconstruction. In this paper, a segmented reconstruction strategy for the CS SAR imaging scheme is proposed. The whole scene is split into a set of small subscenes, so that the reconstruction time can be reduced significantly. The proposed method also needs much less memory for computation than the conventional method. In this proposed method, the range profiles are reconstructed first, and then, the range profiles can be split into subpatches. Subscenes can be reconstructed by using the subpatch data, and the whole scene can be obtained by combining the reconstructed subscenes. Simulation and experimental results are shown to demonstrate the validity of the proposed method. © 1980-2012 IEEE.

Li B.C.,Hunan University | Jiang C.,Hunan University | Han X.,Hunan University | Li Y.,National University of Defense Technology
Fatigue and Fracture of Engineering Materials and Structures | Year: 2014

Based on the critical plane approach, a new path-dependent multiaxial fatigue model in low-cycle fatigue is proposed. The proposed model includes damage contribution from four sources: the normal strain amplitude, the shear strain amplitude on the critical plane, the hydrostatic mean strain and a new path-dependent factor. The effect of mean strain is considered by the hydrostatic mean strain. The experimental data of 11 kinds of materials are used to demonstrate the effectiveness of this new model under both zero and non-zero mean strain multiaxial loading path. © 2013 Wiley Publishing Ltd.

Xing L.,National University of Defense Technology
Lecture Notes in Electrical Engineering | Year: 2015

The interaction between learning and evolution has recently become a popular research direction. Many scholars make use of knowledge to strengthen the guidance process in intelligent optimization methods. We review knowledge guidance in intelligent optimization approaches, which is normally carried out through artificial intelligence approaches and special knowledge models. Some researchers have also proposed algorithms with a double-layer evolution mechanism. These improved methods are able to discover some knowledge from previous iterations and to use the discovered knowledge to guide subsequent iterations. © Springer-Verlag Berlin Heidelberg 2015.

Zhou W.-Y.,University of Southampton | Zhou W.-Y.,National University of Defense Technology | Aglietti G.S.,University of Southampton | Zhang Z.,University of Southampton
Journal of Sound and Vibration | Year: 2011

The micro-vibrations generated by equipment onboard spacecraft can significantly affect the performance of sensitive payloads; in particular mid to high frequency band micro-vibrations, are difficult to model and control. This study focuses on the micro-vibrations emitted by a wheel assembly (WA) implementing a soft (flexible) suspension system. Both the soft and a conventional rigid design were tested using a Seismic Micro-Vibration Measurement System (SMVMS). A NewtonEuler method was employed to develop an analytical model of the WA and the test system, which was then used to model and analyze the micro-vibrations emitted by the reaction/momentum WA, due to the static and dynamic imbalance of the flywheel. When compared with the traditional rigid design, the soft suspension system is shown to effectively reduce the high frequency disturbances, and the mathematical model effectively represents the fundamental harmonic disturbances. In addition, the results confirm that the SMVMS shows relatively high measurement accuracy. © 2011 Published by Elsevier Ltd. All rights reserved.

Zhang Y.,College of William and Mary | Li Q.,College of William and Mary | Yu G.,College of William and Mary | Wang B.,National University of Defense Technology
Proceedings - IEEE INFOCOM | Year: 2011

In a dynamic spectrum access (DSA) network, communication rendezvous is the first step for two secondary users to be able to communicate with each other. In this step, the pair of secondary users meet on the same channel, over which they negotiate on the communication parameters, to establish the communication link. This paper presents ETCH, Efficient Channel Hopping based MAC-layer protocols for communication rendezvous in DSA networks. We propose two protocols, SYNC-ETCH and ASYNC-ETCH. Both protocols achieve better time-to-rendezvous and throughput compared to previous work. © 2011 IEEE.

Han S.,National University of Defense Technology | Han S.,University of New South Wales | Wang J.,University of New South Wales
IEEE Sensors Journal | Year: 2011

In this paper, modeling approaches for quantization and colored noises have been proposed. To accommodate the quantization noise, a modified inertial navigation system (INS) error dynamics is developed in this paper, and the quantization noise is incorporated into the modified INS error dynamics as augmenting driving noise. The three kinds of colored noises are modeled by using an equivalent differential equation driven by a unit white noise, and a technique is developed in this paper to augment the Kalman Filter of GPS/INS integration using this equivalent differential equation. Experimental test results show that the proposed stochastic error modeling approaches for quantization and colored noises significantly improves the accuracies of the estimated inertial drifts and the navigation solutions. © 2010 IEEE.

Yu T.-P.,Heinrich Heine University Dusseldorf | Yu T.-P.,National University of Defense Technology | Pukhov A.,Heinrich Heine University Dusseldorf | Shvets G.,University of Texas at Austin | And 2 more authors.
Physical Review Letters | Year: 2010

By using multidimensional particle-in-cell simulations, we present a new regime of stable proton beam acceleration which takes place when a two-ion-species shaped foil is illuminated by a circularly polarized laser pulse. In the simulations, the lighter protons are nearly instantaneously separated from the heavier carbon ions due to the charge-to-mass ratio difference. The heavy ion layer expands in space and acts to buffer the proton layer from the Rayleigh-Taylor-like (RT) instability that would have otherwise degraded the proton beam acceleration. A simple three-interface model is formulated to explain qualitatively the stable acceleration of the light ions. In the absence of the RT instability, the high quality monoenergetic proton bunch persists even after the laser-foil interaction ends. © 2010 The American Physical Society.

Xu F.,College of William and Mary | Qin Z.,College of William and Mary | Tan C.C.,Temple University | Wang B.,National University of Defense Technology | Li Q.,College of William and Mary
Proceedings - IEEE INFOCOM | Year: 2011

Recent studies have revealed security vulnerabilities in implantable medical devices (IMDs). Security design for IMDs is complicated by the requirement that IMDs remain operable in an emergency when appropriate security credentials may be unavailable. In this paper, we introduce IMDGuard, a comprehensive security scheme for heart-related IMDs to fulfill this requirement. IMDGuard incorporates two techniques tailored to provide desirable protections for IMDs. One is an ECG based key establishment without prior shared secrets, and the other is an access control mechanism resilient to adversary spoofing attacks. The security and performance of IMDGuard are evaluated on our prototype implementation. © 2011 IEEE.

Wang G.,National University of Defense Technology
ICACTE 2010 - 2010 3rd International Conference on Advanced Computer Theory and Engineering, Proceedings | Year: 2010

As one of the most popular many-core architecture, GPUs have illustrated power in many non-graphic applications. Traditional general purpose computing systems tend to integrate GPU as the co-processor to accelerate parallel computing tasks. Meanwhile, GPUs also result in high power consumption, which accounts for a large proportion of the total system power consumption. In this paper, we mainly focus on the power analysis and optimizations for GPU architecture. The main contributions of this paper are: firstly, we establish a GPU power reserach platform, which is extended from an existing GPU simulator with several power models; secondly, we validate that, as the gap between shader core and memory speed becomes larger and larger, integrating more shader cores or enhancing running frequencies may not bring better performance, but results in higher energy consumption; thirdly, we show that traditional power optimization methods for CPUs, such as dynamic frequency scaling and concurrencythrottling, could be effectively applied on GPU architectures for better power efficiency, especially for memory-intensive applications. © 2010 IEEE.

Hu M.,National University of Defense Technology
2015 IEEE 12th International Conference on Electronic Measurement and Instruments, ICEMI 2015 | Year: 2016

Based on the fault feature locus with the change of the component parameters in node-voltage space, a fault diagnosis method based on AC iterative simulation before test is proposed. The slope fault model under AC sinusoidal excitation is analyzed first, the idea of the AC iterative simulation before test and the fault diagnosis after test according to the parameter scanning simulation result is proposed; secondly, the procedure of the AC iterative simulation before test and fault diagnosis algorithm after test are both described. Furthermore, the test system of hardware and software for practical experiment is designed, mainly realized the signal acquisition and data analysis. The experiments of simulation and the practical circuit-board are implemented to validate the efficiency of the proposed method. © 2015 IEEE.

Peng W.,National University of Defense Technology | Zhang Q.,University of Essex
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Multiobjective evolutionary algorithms (MOEAs) have attracted growing attention recently. Problem-specific operators have been successfully used in single objective evolutionary algorithms and it is widely believed that the performance of MOEAs can be improved by using problem-specific knowledge. However, not much work have been done along this direction. Taking a network topology planning problem as an example, we study how to incorporate problem-specific knowledge into the multiobjective evolutionary algorithm based on decomposition (MOEA/D). We propose objective-guided operators for the network topology planning problem and use them in MOEA/D. Experiments are conducted on two test networks and the experimental results show that the MOEA/D algorithm using the proposed operators works very well. The idea in this paper can be generalized to other multiobjective optimization problems. © 2012 Springer-Verlag.

Li J.,National University of Defense Technology
Advances in Space Research | Year: 2016

This paper investigates fuel-optimal low-thrust formation reconfiguration near circular orbit. Based on the Clohessy-Wiltshire equations, first-order necessary optimality conditions are derived from the Pontryagin's maximum principle. The fuel-optimal impulsive solution is utilized to divide the low-thrust trajectory into thrust and coast arcs. By introducing the switching times as optimization variables, the fuel-optimal low-thrust formation reconfiguration is posed as a nonlinear programming problem (NLP) via direct transcription using multiple-phase Radau pseudospectral method (RPM), which is then solved by a sparse nonlinear optimization software SNOPT. To facilitate optimality verification and, if necessary, further refinement of the optimized solution of the NLP, formulas for mass costate estimation and initial costates scaling are presented. Numerical examples are given to show the application of the proposed optimization method. To fix the problem, generic fuel-optimal low-thrust formation reconfiguration can be simplified as reconfiguration without any initial and terminal coast arcs, whose optimal solutions can be efficiently obtained from the multiple-phase RPM at the cost of a slight fuel increment. Finally, influence of the specific impulse and maximum thrust magnitude on the fuel-optimal low-thrust formation reconfiguration is analyzed. Numerical results shown the links and differences between the fuel-optimal impulsive and low-thrust solutions. © 2016 COSPAR.

Huang H.,National University of Defense Technology
Measurement: Journal of the International Measurement Confederation | Year: 2014

Multi-baseline and multi-frequency band can improve the performance of phase unwrapping. This paper, taking the multi-baseline InSAR (interferometric synthetic aperture radar) system as an example, proposes a fast method for multiple-baseline and multi-frequency band phase unwrapping in the frequency domain. The basic idea is to perform a least-squares minimization of the differences between the estimated and absolute phase gradients on all interferograms simultaneously, which are all in the frequency domain. Results on real and simulated data show that the frequency-domain method yields results similar to those of the time-domain method while improving efficiency by avoiding mirroring operations. © 2013 Elsevier Ltd. All rights reserved.

Gao G.,National University of Defense Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

To design a highly automatic and practical method for target discrimination in synthetic aperture radar images, we propose in this paper an improved scheme consisting of the framework and algorithms for target discrimination. Our main contribution in this scheme comprises four aspects. First, an integrative frame sequentially combining the algorithm based on feature extraction and the knowledge of target group has been presented. Second, three new features for target discrimination have been introduced. Third, a genetic algorithm-based feature-selection algorithm has been presented. The results show that this algorithm can evaluate the goodness-of-feature better. Finally, to improve the accuracy of the discriminator, we have designed a weighted quadratic distance discriminator, which has been observed to improve the performance of target discrimination. We have analyzed the performance of the proposed scheme comprehensively and specifically using some measured data, and carried out comparisons of the existing algorithms. The results show that the proposed scheme could improve the application ability in target discrimination. © 2006 IEEE.

Chen S.-W.,Tohoku University | Wang X.-S.,National University of Defense Technology | Sato M.,Tohoku University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2012

Most polarimetric synthetic aperture radar interferometry (PolInSAR) data processing procedures and their applications are based on the polarimetric complex coherence descriptor. The reliable estimation of the complex coherence requires selecting sufficient homogeneous pixels for generating an unbiased estimator. In this paper, two indicators using only polarimetric and both polarimetric and interferometric information are derived as the similarity measures for complex Wishart distributed PolInSAR covariance matrix, respectively. Using these indicators, a double similarity test scheme, which shows high sensitivity to both polarimetric and interferometric properties, is proposed for similar pixel selection. The full information utilization could characterize the homogeneous pixels more accurately. Furthermore, since the similarity test has the potential to reject the pixels with different populations, it is suitable to be applied in a large searching area (e.g., 15 × 15 window) to accept sufficient homogeneous pixels. Thereby, combining with unbiased estimator, reliable estimation is achieved. The efficiency and advantage of the proposed estimation scheme are demonstrated with the aid of simulated and real PolInSAR data sets. © 1980-2012 IEEE.

Wang X.,National University of Defense Technology | Wang X.,Australian National University | Yu C.,Australian National University | Yu C.,Shandong Computer Science Center
Systems and Control Letters | Year: 2013

This paper provides a unified solution for the attitude and position tracking problem of a rigid body in 3-dimensional space, using the concept of the unit dual quaternion. The error dynamics described by a unit dual quaternion are deduced after the dual-quaternion-based dynamics of a single rigid body are given. Then by utilizing the feedback linearization principle, a unit dual quaternion based tracker is proposed based on the error dynamics, which is proven to render the equilibrium point of the closed loop system asymptotically stable, and includes the attitude and position regulation problems as particular cases. Furthermore, to solve the two equilibria problem, a switching parameter is introduced to improve the tracker, which causes the system to converge to the 'nearer' equilibrium with a 'shorter' path. Both the trackers uniquely deal with the rotational and translational dynamics simultaneously with non-singularity and maintain the interconnection between rotation and translation. Finally, the proposed control schemes with applications to the regulation problem and the tracking problem are simulated to illustrate the theoretical results. © 2012 Elsevier B.V. All rights reserved.

Duan D.-L.,Engineering University of Armed Police | Wu X.-Y.,National University of Defense Technology
Wuli Xuebao/Acta Physica Sinica | Year: 2014

To better explore the robustness against cascading failures on complex networks, according to the redistribution rule of the real networks always lie between global preferential rule and local preferential rule or between even shared rule and extremely heterogeneous rule. A new cascading model is proposed based on a tunable load redistribution model. It can tune the load redistribution range and the redistribution heterogeneity of extra load respectively by a redistribution range coefficient and a redistribution heterogeneity coefficient. With this model, we further investigate cascading failures on scale-free networks in terms of numerical simulation and theoretical analysis respectively. Numerical simulation and analytic results show that the model can achieve better robustness against cascading failure than the previous model by adjusting the redistribution range and heterogeneity. © Chinese Physical Society.

Zhang L.,National University of Defense Technology | Zhang L.,University of Kiel | Koch R.,University of Kiel
Journal of Visual Communication and Image Representation | Year: 2014

We address the problem of structure and motion from line correspondences, which ranges from the representation of lines, their projections and the initialization procedure to the final adjustment. The Cayley representation of spatial lines is developed, which is a nonlinear minimal parametrization circumventing the tiresome Plücker constraint. The relationships between different line representations are given. Based on these relationships, we derive a novel line projection function which is consistent with the previous results. After building the line observation model, we employ a closed-form solution for the first image triplet, then develop an incremental initialization approach to initialize the motion and structure parameters. Finally, the sparse bundle adjustment (SBA) is applied to refine the parameters, which updates the spatial lines by using the Cayley representation with an unconstrained optimization engine. The experiments show that the proposed algorithm outperforms the previous works both in efficiency and accuracy. © 2014 Elsevier Inc. All rights reserved.

Li L.,Tsinghua University | Wen D.,National University of Defense Technology | Yao D.,Tsinghua University
IEEE Transactions on Intelligent Transportation Systems | Year: 2014

During the last 60 years, incessant efforts have been made to improve the efficiency of traffic control systems to meet ever-increasing traffic demands. Some recent works attempt to enhance traffic efficiency via vehicle-to-vehicle communications. In this paper, we aim to give a survey of some research frontiers in this trend, identifying early-stage key technologies and discussing potential benefits that will be gained. Our survey focuses on the control side and aims to highlight that the design philosophy for traffic control systems is undergoing a transition from feedback character to feedforward character. Moreover, we discuss some contrasting preferences in the design of traffic control systems and their relations to vehicular communications. The first pair of contrasting preferences are model-based predictive control versus simulation-based predictive control. The second pair are global planning-based control versus local self-organization-based control. The third pair are control using rich information that may be highly redundant versus control using concise information that is necessary. Both the potentials and drawbacks of these control strategies are explained. We hope these comparisons can shed some interesting light on future traffic control studies. © 2013 IEEE.

Sun L.,National University of Defense Technology
Spectroscopy Letters | Year: 2015

In new-generation hyperspectral sensors, the electronic noise is not dominant and the photon noise has to be taken into account. Therefore, a parametric model that accounts for both signal-dependent and signal-independent noise on the useful signal is established. A novel algorithm to estimate the parameters of the model is proposed, which consists of two steps. First, the residual image is calculated by the multiple linear regression in spectral domain to decouple the strong spectral correlation. Then, local sample statistics of the hyperspectral image and its residual image are calculated, and the system of linear equations with respect to the signal-dependent and signal-independent noise variances is established. The least square solution of the equations is the estimation of the signal-dependent and signal-independent noise variances. Experiments on the simulated hyperspectral data analyze the accuracy of the method and experiments on the real-life data show its effectiveness. © 2015 Copyright © Taylor & Francis Group, LLC.

Zhang Z.-Y.,Hunan Institute of Science and Technology | Zhang Z.-Y.,National University of Defense Technology
Romanian Journal of Physics | Year: 2015

In this paper, we investigate the modified Korteweg-de Vries-Zakharov-Kuznetsov and the Hirota equations and obtain exact travelling wave solutions by using Jacobi elliptic function expansion method together with the symbolic computation system Mathematica. For some limit cases, the obtained periodic solutions degenerate to the corresponding solitary wave solutions and other types of solutions. © 2015, Editura Academiei Romane. All rights reserved.

Quan W.,University of Amsterdam | Pimentel A.D.,National University of Defense Technology
Proceedings - Design Automation Conference | Year: 2013

The application workloads in modern MPSoC-based embedded systems are becoming increasingly dynamic. Different applications concurrently execute and contend for resources in such systems which could cause serious changes in the intensity and nature of the workload demands over time. To cope with the dynamism of application workloads at run time and improve the efficiency of the underlying system architecture, this paper presents a novel scenario-based run-time task mapping algorithm. This algorithm combines a static mapping strategy based on workload scenarios and a dynamic mapping strategy to achieve an overall improvement of system efficiency. We evaluated our algorithm using a homogeneous MPSoC system with three real applications. From the results, we found that our algorithm achieves an 11.3% performance improvement and a 13.9% energy saving compared to running the applications without using any run-time mapping algorithm. When comparing our algorithm to three other, well-known run-time mapping algorithms, it is superior to these algorithms in terms of quality of the mappings found while also reducing the overheads compared to most of these algorithms. Copyright © 2013 ACM.

Guo G.,National University of Defense Technology | Guo G.,University of Rostock | Bittig A.,University of Rostock | Uhrmacher A.,University of Rostock
Journal of Computational Physics | Year: 2015

The observation of an increasing number of anomalous diffusion phenomena motivates the study to reveal the actual reason for such stochastic processes. When it is difficult to get analytical solutions or necessary to track the trajectory of particles, lattice Monte Carlo (LMC) simulation has been shown to be particularly useful. To develop such an LMC simulation algorithm for the Galilei variant anomalous diffusion, we derive explicit solutions for the conditional and unconditional first passage time (FPT) distributions with double absorbing barriers. According to the theory of random walks on lattices and the FPT distributions, we propose an LMC simulation algorithm and prove that such LMC simulation can reproduce both the mean and the mean square displacement exactly in the long-time limit. However, the error introduced in the second moment of the displacement diverges according to a power law as the simulation time progresses. We give an explicit criterion for choosing a small enough lattice step to limit the error within the specified tolerance. We further validate the LMC simulation algorithm and confirm the theoretical error analysis through numerical simulations. The numerical results agree with our theoretical predictions very well. © 2015 Elsevier Inc.

Yue D.,National University of Defense Technology
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Excimer Pumped Alkali Laser (XPAL) is a hopeful choice to solve Diode Pumped Alkali Laser (DPAL)'s disadvantages. Theoretical and experimental investigations of Rb-Ar XPAL were carried out in this paper. Time dependent rate equation model illustrated that extreme pump strength was needed to exceed threshold and to assure efficient cw running. 780nm lasing of four level Rb-Ar excimer was realized with a surrogate 15 ns pulsed optical parametric oscillator (OPO). Possible resonator configuration may increase pumping strength was proposed. © 2012 SPIE.

Cai H.,National University of Defense Technology | Mikolajczyk K.,University of Surrey | Matas J.,Czech Technical University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2011

In this paper, we present Linear Discriminant Projections (LDP) for reducing dimensionality and improving discriminability of local image descriptors. We place LDP into the context of state-of-the-art discriminant projections and analyze its properties. LDP requires a large set of training data with point-to-point correspondence ground truth. We demonstrate that training data produced by a simulation of image transformations leads to nearly the same results as the real data with correspondence ground truth. This makes it possible to apply LDP as well as other discriminant projection approaches to the problems where the correspondence ground truth is not available, such as image categorization. We perform an extensive experimental evaluation on standard data sets in the context of image matching and categorization. We demonstrate that LDP enables significant dimensionality reduction of local descriptors and performance increases in different applications. The results improve upon the state-of-the-art recognition performance with simultaneous dimensionality reduction from 128 to 30. © 2011 IEEE.

Feng T.,National University of Defense Technology
IEEE Signal Processing Letters | Year: 2016

Traditional binary offset carrier (BOC) tracking algorithms process the upper and lower sideband signals together, and thus, the sampling frequency and computational requirements are much higher than that required for binary phase-shift keying tracking algorithms, especially for high-order BOC signals. Addressing existing limitations, this letter proposes a decimation double-phase estimator (DDPE) tracking algorithm for BOC signals. The algorithm uses a normal carrier and a subcarrier with a constant frequency to shift the upper and lower sideband signals of BOC to the zero frequency and decimates the signal before processing by the correlator. The residual carrier and the subcarrier are then tracked by the double-phase estimator algorithm. Decimating the signals significantly reduces the computational complexity, and for a BOC(6n, n) signal, the DDPE is found to reduce 86% of correlator operations with a signal-to-noise ratio loss of 0.5 dB. © 1994-2012 IEEE.

Chen F.,National University of Defense Technology | Huang X.,Tsinghua University | Zhou J.,Tsinghua University
IEEE Transactions on Image Processing | Year: 2013

Fingerprints and palmprints are the most common authentic biometrics for personal identification, especially for forensic security. Previous research have been proposed to speed up the searching process in fingerprint and palmprint identification systems, such as those based on classification or indexing, in which the deterioration of identification accuracy is hard to avert. In this paper, a novel hierarchical minutiae matching algorithm for fingerprint and palmprint identification systems is proposed. This method decomposes the matching step into several stages and rejects many false fingerprints or palmprints on different stages, thus it can save much time while preserving a high identification rate. Experimental results show that the proposed algorithm can save almost 50% searching time compared with traditional methods and illustrate its effectiveness. © 1992-2012 IEEE.

Xie H.,National University of Defense Technology
Proceedings International Radar Symposium | Year: 2013

A novel bistatic fast factorized back projection (BFFBP) method for one-stationary bistatic low frequency ultra wide band synthetic aperture radar (UWB SAR) imaging is proposed in this study. This method can precisely deal with azimuth-variance of range cell migrations and motion errors, and achieve computational performance in parity with frequency-domain algorithms. First, the imaging geometry with motion errors in elliptical polar coordinate is provided. Then, based on the subaperture imaging model, the analytical expressions for sampling requirements are derived from the bandwidth angle. Finally, the concrete realization and practical computational load of the BFFBP algorithm are discussed. Simulation data processing results are shown to demonstrate the validity of the proposed approach. © 2013 German Inst of Navigation.

Chen D.X.,National University of Defense Technology | Deng X.,Beijing Jiaotong University | Yang W.Q.,University of Manchester
Review of Scientific Instruments | Year: 2010

The capacitance of a single electrode is usually measured by injecting a current to the electrode and measuring the resultant voltage on the electrode. In this case, a voltage-controlled current source with a high bandwidth is needed because the impedance is inversely proportional to the excitation frequency. In this design note, three different current sources are discussed: (1) the Howland current source, (2) a modified Howland current source, and (3) a dual op-amp current source. The principle and dynamic performances are presented and compared. Simulation and experimental results show that although the Howland current source has the lowest (i.e., worst) output impedance, its output is the most stable among the three current sources when the frequency changes. Therefore, it is suitable for single-electrode capacitance measurement. Initial tests have proven the feasibility of single-electrode capacitance sensor with the Howland current source. © 2010 American Institute of Physics.

Song C.,University College London | Samuel Schwarzkopf D.,University College London | Lutti A.,University College London | Li B.,University College London | And 3 more authors.
Journal of Neuroscience | Year: 2013

Visual perception depends strongly on spatial context. A classic example is the tilt illusion where the perceived orientation of a central stimulus differs from its physical orientation when surrounded by tilted spatial contexts. Here we show that such contextual modulation of orientation perception exhibits trait-like interindividual diversity that correlates with interindividual differences in effective connectivity within human primary visual cortex. We found that the degree to which spatial contexts induced illusory orientation perception, namely, the magnitude of the tilt illusion, varied across healthy human adults in a trait-like fashion independent of stimulus size or contrast. Parallel to contextual modulation of orientation perception, the presence of spatial contexts affected effective connectivity within human primary visual cortex between peripheral and foveal representations that responded to spatial context and central stimulus, respectively. Importantly, this effective connectivity from peripheral to foveal primary visual cortex correlated with interindividual differences in the magnitude of the tilt illusion. Moreover, this correlation with illusion perception was observed for effective connectivity under tilted contextual stimulation but not for that under iso-oriented contextual stimulation, suggesting that it reflected the impact of orientation-dependent intra-areal connections. Our findings revealed an interindividual correlation between intra-areal connectivity within primary visual cortex and contextual influence on orientation perception. This neurophysiological-perceptual link provides empirical evidence for theoretical proposals that intra-areal connections in early visual cortices are involved in contextual modulation of visual perception. © 2013 the authors.

Chen S.-W.,National University of Defense Technology | Chen S.-W.,Tohoku University | Sato M.,Tohoku University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

This paper explores the use of full polarimetric synthetic aperture radar (PolSAR) images for tsunami damage investigation from the polarimetric viewpoint. The great tsunami induced by the earthquake of March 11th, 2011, which occurred beneath the Pacific off the northeastern coast of Japan, is adopted as the study case using the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar multitemporal PolSAR images. The polarimetric scattering mechanism changes were quantitatively examined with model-based decomposition. It is clear that the observed reduction in the double-bounce scattering was due to a change into odd-bounce scattering, since a number of buildings were completely washed away, leaving relatively a rough surface. Polarization orientation (PO) angles in built-up areas are also investigated. After the tsunami, PO angle distributions from damaged areas spread to a wider range and fluctuated more strongly than those from the before-tsunami period. Two polarimetric indicators are proposed for damage level discrimination at the city block scale. One is the ratio of the dominant double-bounce scattering mechanism observed after-tsunami to that observed before-tsunami, which can directly reflect the amount of destroyed ground-wall structures in built-up areas. The second indicator is the standard deviation of the PO angle differences, which is used to interpret the homogeneity reduction of PO angles. Experimental results from after-and before-tsunami comparisons validate the efficiency of these indexes, since the built-up areas with different damage levels can be well discriminated. In addition, comparisons between before-tsunami pairs further confirm the stability of the two polarimetric indexes over a long temporal duration. These interesting results also demonstrate the importance of full polarimetric information for natural disaster assessment. © 1980-2012 IEEE.

Gou Y.,National University of Defense Technology | Geng J.,University of Bristol | Richards S.-J.,University of Warwick | Burns J.,University of Warwick | And 2 more authors.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2013

Synthetic glycopolymers are important natural oligosaccharides mimics for many biological applications. To develop glycopolymeric drugs and therapeutic agents, factors that control the receptor-ligand interaction need to be investigated. A library of well-defined glycopolymers has been prepared by the combination of copper mediated living radical polymerization and CuAAC click reaction via post-functionalization of alkyne-containing precursor polymers with different sugar azides. Employing Concanavalin A as the model receptor, we explored the influence of the nature and densities of different sugars residues (mannose, galactose, and glucose) on the stoichiometry of the cluster, the rate of the cluster formation, the inhibitory potency of the glycopolymers, and the stability of the turbidity through quantitative precipitation assays, turbidimetry assays, inhibitory potency assays, and reversal aggregation assays. The diversities of binding properties contributed by different clustering parameters will make it possible to define the structures of the multivalent ligands and densities of binding epitopes tailor-made for specific functions in the lectin-ligand interaction. © 2013 Wiley Periodicals, Inc.

Zhang M.,National University of Defense Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2011

The composition of the angle random walk in the four-mode ring laser gyro (RLG) has been researched. It escapes the trouble from the type of random walk caused by crossing the dead band contained in the dithered RLG. By changing the current of the gyro, the time order pulse output of the gyro in different laser intensities is measured. Then the random walk coefficients of the corresponding laser intensities are calculated. According to the feature of the quantum noise, the random walk can be separated into two parts: the random walk due to spontaneously emitted photons and the random walk due to other causes. The experimental results show that the random walk due to other causes plays a more important role in the current status of technology. If the part of random walk could be eliminated or weakened, the value of the random walk would be reduced, and the performance of the gyro would be improved.

Hu P.,National University of Defense Technology
IET Conference Publications | Year: 2015

Passive bistatic radars (PBR) using illuminators of opportunity have attracted much attention over the last years. However, most PBR systems have been rather experimental set-ups tailored to a single frequency band or implemented as laboratory test devices. In case of PBR exploiting transmitters for sources of illumination, there is a problem that radar transmitting signal parameters are unknown, and radar signal processing cannot be conducted accurately. This paper presents a study to demonstrate the feasibility of using a Digital Array Passive Bistatic Radar (DA-PBR) system in weak target detection. The design considerations and the resulting DA-PBR structure are described and the evaluations of various measurement campaigns with this system are summarized.

Fang Q.,National University of Defense Technology
ICCAS 2015 - 2015 15th International Conference on Control, Automation and Systems, Proceedings | Year: 2015

Observability is an important aspect of the state-estimation problem in the initial alignment of the inertial navigation system(INS). In most previous research, the authors focus on determining the observable states and unobservable states of a system, while this analysis does not provide sufficient information on the performance of error estimators. In order to provide more insight into the system error estimators, it is necessary to analysis the observable degree of the observable states. For the analysis of the degree of observability, an analysis based on information theory of an inertial navigation system in ground alignment with Bar-Itzhack and Bermans error model is presented. It is shown that through the method based on mutual information, we can not only determine which state is observable and which is not, but also calculate the exact degree of observability of the system states. Simulation results indicate that the observable degree indexes are able to predict Kalman filtering errors of system states, and demonstrate the validity of the method. © 2015 Institute of Control, Robotics and Systems - ICROS.

Wang Q.,Otto Von Guericke University of Magdeburg | Zhou Y.,National University of Defense Technology
Advances in Mathematics of Communications | Year: 2014

Zero-difference balanced (ZDB) functions can be employed in many applications, e.g., optimal constant composition codes, optimal and perfect difference systems of sets, optimal frequency hopping sequences, etc. In this paper, two results are summarized to characterize ZDB functions, among which a lower bound is used to achieve optimality in applications and determine the size of preimage sets of ZDB functions. As the main contribution, a generic construction of ZDB functions is presented, and many new classes of ZDB functions can be generated. This construction is then extended to construct a set of ZDB functions, in which any two ZDB functions are related uniformly. Furthermore, some applications of such sets of ZDB functions are also introduced.

Huan-Yao D.,National University of Defense Technology
Applied Mathematics and Information Sciences | Year: 2012

We present a simple and novel design for alternating polarized array (APA) antenna which process anti-interference ability. The APA received signal model is established. By utilizing the different polarization property of target and the interference, the interference effect on desired signal detection will be eliminated through adaptive polarization filter technique. The predicted results are verified with simulation test and the pattern synthesis of APA is given. The anti-interference performance is indicated. The APA can reduce the complexity of the communication system which has good application prospect in the future. © 2012 NSP Natural Sciences Publishing Cor.

Liu L.,National University of Defense Technology | Fieguth P.,University of Waterloo
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

Inspired by theories of sparse representation and compressed sensing, this paper presents a simple, novel, yet very powerful approach for texture classification based on random projection, suitable for large texture database applications. At the feature extraction stage, a small set of random features is extracted from local image patches. The random features are embedded into a bag-of-words model to perform texture classification; thus, learning and classification are carried out in a compressed domain. The proposed unconventional random feature extraction is simple, yet by leveraging the sparse nature of texture images, our approach outperforms traditional feature extraction methods which involve careful design and complex steps. We have conducted extensive experiments on each of the CUReT, the Brodatz, and the MSRC databases, comparing the proposed approach to four state-of-the-art texture classification methods: Patch, Patch-MRF, MR8, and LBP. We show that our approach leads to significant improvements in classification accuracy and reductions in feature dimensionality. © 2012 IEEE.

Lin C.,National University of Defense Technology
IET Conference Publications | Year: 2015

In case of passive bistatic radar (PBR) using a phased array radar (PAR) as the non-cooperative illuminator, there are problems that signal parameters of the transmitter are unknown and signal coherence is damaged. Aiming at the issues, this article presents a target detection method for PBR using PAR as the non-cooperative illuminator. Firstly, the method uses the direct wave to estimate signal parameters, and then pulse compresses scattered wave. Secondly, the compressed wave is aligned by fast-time dimension so that a Range-Time (R-T) map can be obtained. Finally, the target is detected according to the trajectory in R-T map. The field experimental results demonstrate the effectiveness of this method.

Yang R.,Changsha University | He Y.,National University of Defense Technology | Gao B.,University of Electronic Science and Technology of China | Yun Tian G.,University of Electronic Science and Technology of China | Peng J.,Southwest Jiaotong University
Measurement: Journal of the International Measurement Confederation | Year: 2015

Rail tread oblique crack, initiated by rolling contact fatigue (RCF) damage, is one of the most significant phenomena and has serious influence on rail industry. Electromagnetic non-destructive testing (EM NDT) methods are usually used in rail regular inspection. However, the conventional EM NDT methods based on eddy current field distribution are difficult to detect the cracks parallel to the inductive coil (parallel cracks) and natural oblique cracks. This paper studied lateral heat conduction (LHC) induced by eddy current for detection of these defects. The proposed method was verified through both numerical and experimental studies as well as the investigation of characteristic of LHC. Due to significant temperature gradient in the direction of lateral heat conduction, the spatial derivative and gradient were proposed to improve the defect detectability on the thermograms. Finally, the test of natural oblique cracks on a rail was conducted to validate the proposed methods. © 2015 Elsevier Ltd. All rights reserved.

Chen H.,Sun Yat Sen University | He X.,Sun Yat Sen University | He X.,National University of Defense Technology
Molecular Biology and Evolution | Year: 2016

The essence of Darwin's theory is that evolution is driven by purposeless mutations that are subsequently selected by natural environments, so there is often no predefined destination in organismal evolution. Using gene expressions of 107 cell types, we built a functional space of human cells to trace the evolutionary trajectory of 18 types of solid tumor cancers. We detected a dominant evolving trend toward the functional status of embryonic stem cells (ESC) for approximately 3,000 tumors growing in distinct tissue environments. This pattern remained the same after excluding known cancer/ESC signature genes (∼3,000 genes) or excluding all oncogenic gene sets (∼12,000 genes) annotated in MSigDB, suggesting a convergent evolution of the overall functional status in cancers. In support of this, the functional distance to ESC served as a common prognostic indicator for cancers of various types, with shorter distance corresponding to poor prognosis, which was true even when randomly selected gene sets were considered. Thus, regardless of the external environments, cancer evolution is a directional process toward a defined cellular destination, a finding reconciling development and evolution, the two seemingly incompatible philosophies both adopted by the cancer research community, and also raising new questions to evolutionary biology. © The Author 2015. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Huang W.,National University of Defense Technology
Aerospace Science and Technology | Year: 2016

The mixing and combustion process plays an important role in the realization of the scramjet engine, and the transverse injection from a wall orifice is widely employed for the simplest and most promising of its configurations. In the current survey, the research progress on the transverse jet in supersonic crossflows has been summarized systematically from four aspects, namely single injection, multiport injection, interaction between jet and vortex generator, and interaction between jet and shock wave, and the basic principle of the transverse injection has been provided as well. At last, some promising recommendations have been proposed, namely the refined vortex structure capture, the mixing and combustion process in the novel injector and multiport flow fields, especially with the incident shock wave interaction, and the combinatorial operating and optimization process between the fuel injection and the vortex generator. © 2016 Elsevier Masson SAS.

Kotsia I.,Queen Mary, University of London | Guo W.,National University of Defense Technology | Patras I.,Queen Mary, University of London
Pattern Recognition | Year: 2012

This work addresses the two class classification problem within the tensor-based large margin classification paradigm. To this end, we formulate the higher rank Support Tensor Machines (STMs), in which the parameters defining the separating hyperplane form a tensor (tensorplane) that is constrained to be the sum of rank one tensors. Subsequently, we propose two extensions in which the separating tensorplanes take into consideration the spread of the training data along the different tensor modes. More specifically, we first propose the higher rank Σ/ Σw STMs that use the total or the within-class covariance matrix in order to whiten the data and thus provide invariance to affine transformations. Second, we propose the higher rank Relative Margin Support Tensor Machines (RMSTMs) that bound from above the distance of the data samples from the separating tensorplane while maximizing the margin from it. The corresponding optimization problem is solved in an iterative manner utilizing the CANDECOMP/PARAFAC (CP) decomposition, where at each iteration the parameters corresponding to the projections along a single tensor mode are estimated by solving a typical Support Vector Machine (SVM)-type optimization problem. The efficiency of the proposed method is illustrated on the problems of gait and action recognition where we report results that improve, in some cases considerably, the state of the art. © 2012 Elsevier Ltd.

He H.,University of Rhode Island | Chen S.,Stevens Institute of Technology | Li K.,Queens University of Belfast | Xu X.,National University of Defense Technology
IEEE Transactions on Neural Networks | Year: 2011

Recent years have witnessed an incredibly increasing interest in the topic of incremental learning. Unlike conventional machine learning situations, data flow targeted by incremental learning becomes available continuously over time. Accordingly, it is desirable to be able to abandon the traditional assumption of the availability of representative training data during the training period to develop decision boundaries. Under scenarios of continuous data flow, the challenge is how to transform the vast amount of stream raw data into information and knowledge representation, and accumulate experience over time to support future decision-making process. In this paper, we propose a general adaptive incremental learning framework named ADAIN that is capable of learning from continuous raw data, accumulating experience over time, and using such knowledge to improve future learning and prediction performance. Detailed system level architecture and design strategies are presented in this paper. Simulation results over several real-world data sets are used to validate the effectiveness of this method. © 2011 IEEE.

Sun H.,National University of Defense Technology | Wang C.,Xiamen University | Wang B.,Xiamen University | El-Sheimy N.,University of Calgary
Neurocomputing | Year: 2011

This paper presents a robust real-time pedestrian detection approach from infrared (IR) videos using binary pattern features. A novel pyramid binary pattern (PBP) feature is first proposed for IR pedestrian appearance representation. Both symmetry and spatial layout of texture cells have been encapsulated in the PBP feature. PBP outperforms several state-of-the-art binary pattern features for IR pedestrian images classification. Motivated by the recent success of motion-enhanced pedestrian detector, we then extend the PBP feature to 3D spatial-temporal volumes. The dynamic PBP feature combines both motion and appearance for IR pedestrian description and achieves better performance in comparison to the static PBP feature. Finally, a keypoint based sliding window support vector machine (SVM) classifier is used to detect pedestrians in IR videos. The keypoint based scanning strategy reduces the number of candidate sub-windows dramatically. The proposed approach has been implemented on an experimental vehicle equipped with a forward-looking infrared (FLIR) camera. Experimental results in various urban scenarios demonstrate the effectiveness and robustness of our approach. In addition, even though our approach is presented for IR imageries, it can also be applied to pedestrian detection in visual images. © 2010 Elsevier B.V.

Yuan Y.,National University of Defense Technology | Wu K.,University of Victoria | Jia W.,City University of Hong Kong | Jiang Y.,Norwegian University of Science and Technology
IEEE Transactions on Parallel and Distributed Systems | Year: 2011

Network coding allows a network node to code the information flows before forwarding them. While it has been theoretically proved that network coding can achieve maximum network throughput, the theoretical results usually do not consider the burstiness of data traffic, delays, and the stochastic nature in information processing and transmission. There is currently no theory to systematically model and evaluate the performance of network coding, especially when node's capacity (i.e., coding and transmission) becomes stochastic. Without such a theory, the performance of network coding under various system settings is far from clear. To fill the vacancy, we develop an analytical approach by extending the stochastic network calculus theory to tackle the special difficulties in the evaluation of network coding. We prove the new properties of the stochastic network calculus and design an algorithm to obtain the performance bounds for acyclic stochastic networks with network coding. The tightness of theoretical bounds is validated with simulation. © 2011 IEEE.

Mo H.,Changsha University of Science and Technology | Wang F.-Y.,CAS Institute of Automation | Wang F.-Y.,National University of Defense Technology | Zhou M.,Changsha University of Science and Technology | And 3 more authors.
Information Sciences | Year: 2014

In the paper, a new and comprehensible definition is proposed for type-2 fuzzy sets (T2 FSs), and the primary and secondary memberships function are defined respectively by using multi valued mapping. A new definition and formula for the footprint of uncertainty (FOU) is presented, and based on the new definitions, the relation between FOU and the original definition of T2 FS is discussed. Finally, the partition method of FOU is provided to represent the primary membership grade, the FOU and the interval type-2 fuzzy sets (IT2 FS) when the upper and lower membership functions (UMF, LMF) of FOU are given. © 2014 Elsevier Inc. All rights reserved.

Wu H.,Academy of Military Medical Science | Sun Z.,Academy of Military Medical Science | Chen J.,National University of Defense Technology
Optics and Laser Technology | Year: 2013

We present an effective method to improve performances of the optical systems with Cassegrain-telescope receivers by using vortex sources and phase optimizations. A typical model of optical systems with Cassegrain-telescope receivers is established, theory of beam propagation through the optical system is analyzed and principle of the new method is illuminated in detail. We classify the optical systems with Cassegrain-telescope receivers into two types and analyze the system performance evaluating factors: the first type is that the received beam is converted to signals, and power efficiency of the received beam is used as the system performance evaluating factor; the second type is that the received beam is used as a new source for further propagation after being cleaned up, and the product of power efficiency and beam quality (Strehl ratio) of the received beam is used as the system performance evaluating factor. Under the H-V 5/7 turbulent model, performances of the two systems with vortex sources and phase optimized by the stochastic parallel gradient descent algorithm are calculated. Results show that power efficiency of the received beam in the first type optical system can get 97.86, and the system performance evaluating factor of the second type system can be improved from 0.8560 to 0.9398. © 2012 Elsevier Ltd.

Yang X.,National University of Defense Technology
Advances in Space Research | Year: 2016

For designers, operators and users, the ability to accurately predict thermal behavior and trajectory of stratospheric airships is very important. Thermal models and dynamic models of stratospheric airships during ascent are developed, including solar radiation, infrared radiation, convection heat transfer and gas expulsion equation. Based on the model, performance parameters of a stratospheric airship during ascent are obtained, including film temperature, helium gas temperature, air temperature, pressure differential, altitude and ascent velocity, changing regulation for these parameters are discussed, and influence of initial helium gas volume and film radiation properties on thermal behavior is analyzed. Simulation results show that, (1) stratospheric airships experience supercooling during ascent, the maximum value is about 30. K, supercooling causes loss of net buoyancy, and affects ascent velocity and trajectory in the end, (2) stratospheric airships experience superheating at the floating altitude, and the maximum value is about 51. K, (3) initial volume ratio of helium gas and the solar radiation absorptivity of film have important effect on thermal behavior and trajectory during ascent, the larger the initial volume ratio is, the faster the ascent velocity will be, and the bigger the solar radiation absorptivity of film is, the smaller the temperature differential between helium gas and outside atmosphere will be. © 2016 COSPAR.

Yang W.L.,CAS Wuhan Institute of Physics and Mathematics | Hu Y.,Huazhong University of Science and Technology | Yin Z.Q.,University of Chinese Academy of Sciences | Deng Z.J.,National University of Defense Technology | Feng M.,CAS Wuhan Institute of Physics and Mathematics
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We propose a potentially practical scheme for creating entanglement between two distant nitrogen-vacancy-center (N-V) spin ensembles using a current-biased Josephson junction superconducting qubit and transmission line resonators. The idea provides a scalable way to an N-V ensemble-based quantum network, which is close to the reach with currently available technology. © 2011 American Physical Society.

Gao M.,Tsinghua University | Gao M.,National University of Defense Technology | Liu Y.-X.,Tsinghua University | Wang X.-B.,Tsinghua University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We propose a hybrid system to realize long information storage and fast quantum operation via Rydberg atoms and superconducting qubits (SCQs). The internal states of a Rydberg atom are coupled to a nanomechanical resonator. The atom-resonator coupling is achieved via an electric field generated by the quantized motions of the resonator and temporarily exciting the atom to Rydberg states. The coupling can be made large enough to allow quantum manipulation and measurement of the resonator via the atom. The resonator can also be coupled to a SCQ, and therefore the tripartite system can provide a quantum interface between the SCQ and the atom via the nanomechanical resonator. © 2011 American Physical Society.

He B.,University of Calgary | MacRae A.,University of Calgary | Han Y.,University of Calgary | Han Y.,National University of Defense Technology | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

The multimode character of quantum fields imposes constraints on the implementation of high-fidelity quantum gates between individual photons. So far this has only been studied for the longitudinal degree of freedom. Here we show that effects due to the transverse degrees of freedom significantly affect quantum gate performance. We also discuss potential solutions, in particular separating the two photons in the transverse direction. © 2011 American Physical Society.

Cheng Z.,National University of Defense Technology
Journal of Vibroengineering | Year: 2015

A hybrid prognostics approach for the monioring of a planetary gearbox with the local defect is presented. This hybrid method can predict the remaining useful life (RUL) of planetary gearbox with a fatigue crack. The method consists of a dynamical model for simulation data generation, a statistical algorithm for feature selection and weighting, and a modified grey model for RUL prediction. Experimental studies are conducted to validate and demonstrate the feasibility of the proposed method for RUL prediction of a cracked sun gear in planetary gearbox. And the validation has a promising result. © JVE INTERNATIONAL LTD.

Hu H.,Max Planck Institute for Nuclear Physics | Hu H.,National University of Defense Technology | Muller C.,Max Planck Institute for Nuclear Physics | Keitel C.H.,Max Planck Institute for Nuclear Physics
Physical Review Letters | Year: 2010

Electron-positron pair creation by multiphoton absorption in the collision of a relativistic electron with a strong laser beam is calculated within laser-dressed quantum electrodynamics. Total production rates, positron spectra, and relative contributions of different reaction channels are obtained in various interaction regimes. We study the process in a manifestly nonperturbative domain which is shown accessible to future experiments utilizing the electron beam lines at novel x-ray laser facilities or all-optical setups based on laser acceleration. Our theory moreover allows us to add further insights into the experimental data from SLAC.

Zhang Z.,Samsung | Pi Z.,Samsung | Liu B.,National University of Defense Technology
IEEE Transactions on Biomedical Engineering | Year: 2014

Heart rate monitoring using wrist-type photoplethysmographic signals during subjects' intensive exercise is a difficult problem, since the signals are contaminated by extremely strong motion artifacts caused by subjects' hand movements. So far few works have studied this problem. In this study, a general framework, termed TROIKA, is proposed, which consists of signal decomposiTion for denoising, sparse signal RecOnstructIon for high-resolution spectrum estimation, and spectral peaK trAcking with verification. The TROIKA framework has high estimation accuracy and is robust to strong motion artifacts. Many variants can be straightforwardly derived from this framework. Experimental results on datasets recorded from 12 subjects during fast running at the peak speed of 15 km/h showed that the average absolute error of heart rate estimation was 2.34 beat per minute, and the Pearson correlation between the estimates and the ground truth of heart rate was 0.992. This framework is of great values to wearable devices such as smartwatches which use PPG signals to monitor heart rate for fitness. © 2014 IEEE.

Zhao J.,Space Time Research | Zhao J.,National University of Defense Technology | Lein M.,Space Time Research
New Journal of Physics | Year: 2012

In this paper autoionizing states in the one-dimensional helium atom are investigated by numerical solution of the time-dependent twoelectron Schrodinger equation. The atom is irradiated by an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared few-cycle laser pulse. The XUV pulse populates a superposition of doubly excited states, leading to Fano resonances in the photoelectron spectrum. It is demonstrated that the Fano line profile is strongly modified by the presence of the laser field. Laser-induced coupling between the different doubly excited states causes the population of autoionizing states that cannot be reached by absorbing a single XUV photon from the ground state. The resulting additional peaks in the photoelectron spectrum are modulated as a function of time delay. Furthermore, the photoelectron spectrum exhibits a fringe pattern that is determined by the time delay but is independent of the details of the laser pulse. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Wei C.,Jiangsu University | Shen X.,Jiangsu University | Song F.,Jiangsu University | Zhu Y.,Nanjing University of Aeronautics and Astronautics | Wang Y.,National University of Defense Technology
Materials and Design | Year: 2012

The microwave absorption properties of the nanocrystalline NiZn ferrite (Zn0.5Ni0.5Fe2O4) and iron (α-Fe) microfibers with single-layer and double-layer structures were investigated in the frequency range of 2-18GHz. The double-layer absorbers have much better microwave absorption properties than the single-layer absorbers, and the microwave absorption properties of the double-layer structure are influenced by the coupling interactions between the absorbing layer and matching layer. With the absorbing layer thickness 0.7mm of α-Fe microfibers-wax composite and the matching layer thickness 1.5mm of Zn0.5Ni0.5Fe2O4 microfibers-wax composite, the minimum reflection loss (RL) reaches about -71dB at 16.2GHz and the absorption band width is about 9.2GHz ranging from 8.8 to 18GHz with the RL value exceeding -10dB. While, when the absorbing layer is the Zn0.5Ni0.5Fe2O4 microfibers-wax composite with thickness 1.8mm and the matching layer is the α-Fe microfibers-wax composite with thickness 0.2mm, the RL value achieves the minimum about -73dB at 13.8GHz and the absorption band width is about 10.2GHz ranging from 7.8 to 18GHz with the RL value exceeding -10dB, which covers the whole X-band (8.2-12.4GHz) and Ku-band (12.4-18GHz). © 2011 Elsevier Ltd.

Wang X.,National University of Defense Technology | Yu C.,Australian National University | Yu C.,Shandong Computer Science Center | Lin Z.,Zhejiang University
IEEE Transactions on Robotics | Year: 2012

This paper focuses on finding a dual quaternion solution to attitude and position control for multiple rigid body coordination. Representing rigid bodies in 3-D space by unit dual quaternion kinematics, a distributed control strategy, together with a specified rooted-tree structure, are proposed to control the attitude and position of networked rigid bodies simultaneously with notion concision and nonsingularity. A property called pairwise asymptotic stability of the overall system is then analyzed and validated by an example of seven quad-rotor formation in the Urban Search And Rescue Simulation (USARSim) platform. As a separate but related issue, a maximum depth condition of the rooted tree is found with respect to error accumulation along each path using dual quaternion algebra, such that a given safety bound on attitude and position errors can be satisfied. © 2012 IEEE.

Zhou Y.L.,National University of Defense Technology | Ortner M.,University of Innsbruck | Ortner M.,Austrian Academy of Sciences | Rabl P.,Austrian Academy of Sciences
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

We describe a simple scheme for the implementation and control of effective spin-spin interactions in self-assembled crystals of cold polar molecules. In our scheme, spin states are encoded in two long-lived rotational states of the molecules and coupled via state-dependent dipole-dipole forces to the lattice vibrations. We show that, by choosing an appropriate time-dependent modulation of the induced dipole moments, the resulting phonon-mediated interactions compete with the direct dipole-dipole coupling and lead to long-range and tunable spin-spin interaction patterns. We illustrate how this technique can be used for the generation of multiparticle entangled spin states and the implementation of spin models with long-range and frustrated interactions, which exhibit nontrivial phases of magnetic ordering. © 2011 American Physical Society.

Li Q.,National University of Defense Technology
Proceedings - 2012 International Conference on Intelligent Systems Design and Engineering Applications, ISDEA 2012 | Year: 2012

According to the HP memristor model with linear do pant drift, the electrical characteristics of memristor are analyzed. Then, the transmission characteristics of memristor based noninverting op amplifier are investigated. The theoretical results are well demonstrated by the SPICE circuit simulation with a published memristor sub circuit with linear do pant drift. © 2012 IEEE.

Zhang P.,National University of Defense Technology
Proceedings of the 2011 2nd International Conference on Digital Manufacturing and Automation, ICDMA 2011 | Year: 2011

a novel approach to extracting visual saLiency based on receptive field is described in this paper. Visual saLiency may be appLied potentially in object recognition and image retrieval etc. In this paper, its two key problems are solved: saLiency measurement and scale detection. Based on the receptive field hypothesis in psychology, the approach measures visual saLiency in terms of the statistical features difference between target region and background region, and detects the scale of target region adaptively with a set of multi-scale measurements in the multi-resolution framework. Its definition of visual saLiency is more close to feeLing of human vision than current ones by introduction of the theories in psychology and physiology. It is capabiLity of detecting the target varying in a wide scale range with low computation burden by combing multi-scale template with multi-resolution framework. The satisfying experimental results on real images of remote sense and natural scene show the approach is effective. © 2011 IEEE.

Wu Y.,Central South University | Wang J.,University of New South Wales | Hu D.,National University of Defense Technology
IEEE Transactions on Signal Processing | Year: 2014

Integration of inertial navigation system (INS) and global navigation satellite system (GNSS) is usually implemented in engineering applications by way of Kalman-like filtering. This form of INS/GNSS integration is prone to attitude initialization failure, especially when the host vehicle is moving freely. This paper proposes an online constrained-optimization method to simultaneously estimate the attitude and other related parameters including GNSS antenna's lever arm and inertial sensor biases. This new technique benefits from self-initialization in which no prior attitude or sensor measurement noise information is required. Numerical results are reported to validate its effectiveness and prospect in high accurate INS/GNSS applications. © 2014 IEEE.

Wang X.,National University of Defense Technology | Yu C.,University of Canberra
IEEE International Symposium on Intelligent Control - Proceedings | Year: 2010

The main contribution of this paper is the design of a unit dual quaternion-based attitude and position regulator. The dynamic model of rigid body represented by unit dual quaternion is derived firstly from the rotational and the translational dynamics. And then an output feedback regulator, which ensures asymptotical stability, is proposed using unit dual quaternion. To the best of our knowledge, this study is the first to relate dual quaternion to dynamic control of rigid body without requiring decoupling attitude and position. The simulation results are provided to verify the performance. © 2010 IEEE.

Hu S.,National University of Defense Technology
8th Annual IEEE International Conference on Nano/Micro Engineered and Molecular Systems, IEEE NEMS 2013 | Year: 2013

This paper presents a novel method of structural trimming to reduce the mode coupling error with the focus on micro-gyroscopes. A UV nanosecond laser was used to remove materials with determined size at certain point on the vibratory structure of the micro-gyroscope. The peak-peak voltage of the mode coupling error signal of the gyroscope prototype studied in this paper could be reduced from 3.52V to 0.082V. Furthermore, the zero-velocity output of the same gyroscope prototype was decreased from 244mV to 14mV after coarse trimming and fine trimming. Demonstrated theoretically and experimentally, this structural trimming by UV nanosecond laser is an effective way to reduce mode coupling error for improving the micro-gyroscope performance. © 2013 IEEE.

Lee L.H.,National University of Singapore | Pujowidianto N.A.,National University of Singapore | Li L.-W.,National University of Defense Technology | Chen C.-H.,National Taiwan University | And 2 more authors.
IEEE Transactions on Automatic Control | Year: 2012

We develop a new Optimal Computing Budget Allocation (OCBA) approach for the ranking and selection problem with stochastic constraints. The goal is to maximize the probability of correctly selecting the best feasible design within a fixed simulation budget. Based on some approximations, we derive an asymptotic closed-form allocation rule which is easy to compute and implement and can help provide more insights about the allocation. The numerical testing shows that our approach can enhance the simulation efficiency. © 2012 IEEE.

Zhu H.,Oxford Brookes University | Zhang Y.,National University of Defense Technology
IEEE Transactions on Services Computing | Year: 2012

Software testers are confronted with great challenges in testing Web Services (WS) especially when integrating to services owned by other vendors. They must deal with the diversity of implementation techniques used by the other services and to meet a wide range of test requirements. However, they are in lack of software artifacts, the means of control over test executions and observation on the internal behavior of the other services. An automated testing technique must be developed to be capable of testing on-the-fly nonintrusively and nondisruptively. Addressing these problems, this paper proposes a framework of collaborative testing in which test tasks are completed through the collaboration of various test services that are registered, discovered, and invoked at runtime using the ontology of software testing STOWS. The composition of test services is realized by using test brokers, which are also test services but specialized in the coordination of other test services. The ontology can be extended and updated through an ontology management service so that it can support a wide open range of test activities, methods, techniques, and types of software artifacts. The paper presents a prototype implementation of the framework in semantic WS and demonstrates the feasibility of the framework by running examples of building a testing tool as a test service, developing a service for test executions of a WS, and composing existing test services for more complicated testing tasks. Experimental evaluation of the framework has also demonstrated its scalability. © 2008 IEEE.

Tan D.-F.,National University of Defense Technology
Xitong Gongcheng Lilun yu Shijian/System Engineering Theory and Practice | Year: 2013

The classic Lanchester equations reveal size effect of combat, but their assumption is challenged in the modern warfare that the battlefield is universal sensible and direct targeting. Through the semiotical analysis of the combat information flow in microscopic view, it is suggested that the modern battlefield is networked universal sensible and direct targeting, and by combining the Albert's "removal of node" operation with the stochastic duel based on the global network efficiency, a novel model - stochastic duel of networks - is put forward which represents combat behavior and cooperation behavior in an unitary form. The network effect of networked combat system (NCS) has been characterized in the model: (1) Lanchester square law is the optimized special case of network effect of NCS; (2) a NCS loses its attritionrate along with the combat process, which relates not only the generative factors of effective combat power, such as its weapon performance and the structure of the network, but also the rate of target redundancy; (3) the scale-free network is more superiority, robust yet fragile than the random network in combat.

Mo H.,Changsha University of Science and Technology | Wang T.,National University of Defense Technology
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2012

The conventional fuzzy sets are type-1 fuzzy sets whose point-values are two-dimensional, and the point-values of type-2 fuzzy sets (T2 FSs) are three-dimensional. So it is more difficult for T2 FS to be understood and computed than the corresponding type-1. To make T2 FS be better understood and extensively applied, in this paper, we present the definition of generalized interval type-2 fuzzy sets (GIT2 FSs), and divide them into three types: discrete type, partial discrete type, and continuous type. Then, the corresponding mathematical representation of every type is given to get the extension principle formula of GIT2 FS. Lastly, computing methods are proposed to discuss computing with words of GIT2 FS by two different fuzzy logic operators. Copyright © 2012 Acta Automatica Sinica. All rights reserved.

Guo W.,National University of Defense Technology | Kotsia I.,Queen Mary, University of London | Patras I.,Queen Mary, University of London
IEEE Transactions on Image Processing | Year: 2012

In this paper, we exploit the advantages of tensorial representations and propose several tensor learning models for regression. The model is based on the canonical/parallel-factor decomposition of tensors of multiple modes and allows the simultaneous projections of an input tensor to more than one direction along each mode. Two empirical risk functions are studied, namely, the square loss and ε-insensitive loss functions. The former leads to higher rank tensor ridge regression (TRR), and the latter leads to higher rank support tensor regression (STR), both formulated using the Frobenius norm for regularization. We also use the group-sparsity norm for regularization, favoring in that way the low rank decomposition of the tensorial weight. In that way, we achieve the automatic selection of the rank during the learning process and obtain the optimal-rank TRR and STR. Experiments conducted for the problems of head-pose, human-age, and 3-D body-pose estimations using real data from publicly available databases, verified not only the superiority of tensors over their vector counterparts but also the efficiency of the proposed algorithms. © 2011 IEEE.

Zhu M.,National University of Defense Technology
IET Conference Publications | Year: 2015

Multiple-copy routing is widely used in sparse vehicular ad hoc networks (VANETs). Recently, we proposed a novel architecture named software-defined vehicular networks (SDVNs) that can provide a global view of the whole network and centralized control over vehicular switches. However, existing multiple-copy routing protocols cannot utilize the benefits of SDVNs to improve routing efficiency. In this paper, we propose a Spray-and-Prey multiple-copy routing protocol for SDVNs. The Spray-and-Prey protocol uses graph-based minimum communication hops to define the utility of carriers and utilize two copies cooperation schemes to reduce delivery delay. Further more, the proposed protocol can clear other copies in the network when one copy arrives at the destination with low cost. Simulation experiment demonstrates that spray-and-prey protocol has lower delivery delay and network resource cost than other protocol in sparse SDVNs scenarios.

Li Y.,Goethe University Frankfurt | Li Y.,National University of Defense Technology | Bakhtiari M.R.,Goethe University Frankfurt | He L.,Goethe University Frankfurt | Hofstetter W.,Goethe University Frankfurt
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We theoretically investigate finite-temperature thermodynamics and demagnetization cooling of two-component Bose-Bose mixtures in a cubic optical lattice, by using bosonic dynamical mean-field theory (BDMFT). We calculate the finite-temperature phase diagram, and remarkably find that the system can be heated from the superfluid into the Mott insulator at low temperature, analogous to the Pomeranchuk effect in 3He. This provides a promising many-body cooling technique. We examine the entropy distribution in the trapped system and discuss its dependence on temperature and an applied magnetic field gradient. Our numerical simulations quantitatively validate the spin-gradient demagnetization cooling scheme proposed in recent experiments. © 2012 American Physical Society.

Zhang J.,University of Southampton | Zhang J.,National University of Defense Technology | MacDonald K.F.,University of Southampton | Zheludev N.I.,University of Southampton | Zheludev N.I.,Nanyang Technological University
Optics Letters | Year: 2014

We demonstrate that resonant optical forces generated within all-dielectric planar photonic metamaterials at nearinfrared illumination wavelengths can be an order of magnitude larger than in corresponding plasmonic metamaterials, reaching levels many tens of times greater than the force resulting from radiation pressure. This is made possible by the dielectric structures' freedom from Joule losses and the consequent ability to sustain Fano-resonances with high quality factors that are unachievable in plasmonic nanostructures. Dielectric nano-optomechanical metamaterials can thus provide a functional platform for a range of novel dynamically controlled and self-adaptive nonlinear, tunable/switchable photonic metamaterials. © 2014 Optical Society of America.

Zhou Y.L.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

We present a scheme of quantum simulation of many-body interactions with trapped ions via the exchange of virtual phonons, where the motion from both the longitudinal and the transverse directions is considered. By tuning the detunings of Raman lasers, the long-range and locally tunable interaction is easily obtained between different spins. We show that the competing spin-spin couplings mediated by all motion modes can give rise to higher levels of frustration and richer phase transitions than the conventional approaches based on the longitudinal or the transverse phonon modes alone. © 2014 American Physical Society.

National University of Defense Technology | Date: 2014-12-12

The disclosure discloses a dynamic attitude measurement method of a star sensor based on gyros precise angular correlation. On the basis that a dynamic compensation is performed on each of the measurement exposure frames of the star sensor and a fixed star matching vector matrix having dynamic error and noise influence is obtained in a prior art, a transform matrix between every two adjacent measurement frames of the star sensor is precisely measured by a unit including three gyros fixedly coupled with the star sensor. The transform matrix correlates the matched vector matrixes of the adjacent measurement frames of the star sensor. Finally, a correlated measurement equation is established with a series of correlated measurement frames, which is corresponding to processing a series of measurement frames as a single measurement frame.

Fan J.C.,KTH Royal Institute of Technology | Fan J.C.,Anhui University of Technology | Sreekanth K.M.,KTH Royal Institute of Technology | Sreekanth K.M.,Amrita University | And 3 more authors.
Progress in Materials Science | Year: 2013

In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p-n junction are the key steps to realize these applications. However, the reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (VO and Zni) and/or hydrogen incorporation. Considerable efforts have been made to obtain p-type ZnO by doping different elements with various techniques. Remarkable progresses have been achieved, both theoretically and experimentally. In this paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, VZn and O i act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Theoretically, the principles of selection of p-type dopant, codoping method and XZn-2VZn acceptor model are introduced. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band-gap engineering and room temperature ferromagnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials. © 2013 Elsevier Ltd. All rights reserved.

Wu H.,Microsoft | Feng Z.,Microsoft | Feng Z.,National University of Defense Technology | Guo C.,Microsoft | Zhang Y.,Microsoft
IEEE/ACM Transactions on Networking | Year: 2013

Transport Control Protocol (TCP) incast congestion happens in high-bandwidth and low-latency networks when multiple synchronized servers send data to the same receiver in parallel. For many important data-center applications such as MapReduce and Search, this many-to-one traffic pattern is common. Hence TCP incast congestion may severely degrade their performances, e.g., by increasing response time. In this paper, we study TCP incast in detail by focusing on the relationships between TCP throughput, round-trip time (RTT), and receive window. Unlike previous approaches, which mitigate the impact of TCP incast congestion by using a fine-grained timeout value, our idea is to design an Incast congestion Control for TCP (ICTCP) scheme on the receiver side. In particular, our method adjusts the TCP receive window proactively before packet loss occurs. The implementation and experiments in our testbed demonstrate that we achieve almost zero timeouts and high goodput for TCP incast. © 1993-2012 IEEE.

Zhu F.,CAS Institute of Automation | Wen D.,National University of Defense Technology | Chen S.,CAS Institute of Automation
IEEE Transactions on Intelligent Transportation Systems | Year: 2013

The Artificial societies, Computational experiments, and Parallel execution (ACP) approach provides us an opportunity to look into new methods that address transportation problems from new perspectives. In this paper, we present our work and results of applying the ACP approach on modeling and analyzing transportation systems, particularly carrying out computational experiments based on artificial transportation systems (ATSs). Two aspects in the modeling process are analyzed. The first is growing an ATS from the bottom up using agent-based technologies. The second is modeling environmental impacts under the principle of 'simple is consistent.' Finally, three computational experiments are carried out on one specific ATS, i.e., Jinan-ATS, and numerical results are presented to illustrate the applications of our method. © 2000-2011 IEEE.

Ye P.,CAS Institute of Automation | Wen D.,National University of Defense Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2013

Generating travel behavior based on artificial population and an activity plan is a conventional method for traffic simulation. As a complicated and important constituent of travel behavior, destination selection is a decision-making process for space transfer and has been studied extensively in the disaggregate model. However, existing selection models only focus on the psychology or custom of individuals from a microscopic perspective and rarely take account of the actual traffic state. This causes a large deviation in simulation results and thus results in some obstacles for application. In this paper, a new destination selection model based on link flows is proposed. Further, a searching algorithm for an observed link set is given, and compressed sensing is used in the model solution. Experiments demonstrate that this model can predict the actual traffic state in rush hours quite well. Therefore, it contributes to the credible simulation and computational experiments. © 2000-2011 IEEE.

Wang D.,National University of Defense Technology
Applied Physics Letters | Year: 2012

As an alternative to conventional magnetic field, the effective spin-orbit field in transition metals, derived from the Rashba field experienced by itinerant electrons confined in a spatial inversion asymmetric plane through the s-d exchange interaction, is proposed for the manipulation of magnetization. Magnetization switching in ferromagnetic thin films with perpendicular magnetocrystalline anisotropy can be achieved by current induced spin-orbit field, with small in-plane applied magnetic field. Spin-orbit field induced by current pulses as short as 10 ps can initiate ultrafast magnetization switching effectively, with experimentally achievable current densities. The whole switching process completes in about 100 ps. © 2012 American Institute of Physics.

Tian B.,CAS Institute of Automation | Li Y.,CAS Institute of Automation | Li B.,CAS Institute of Automation | Wen D.,National University of Defense Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2014

Traffic surveillance is an important topic in intelligent transportation systems. Robust vehicle detection and tracking is one challenging problem for complex urban traffic surveillance. This paper proposes a rear-view vehicle detection and tracking method based on multiple vehicle salient parts using a stationary camera. We show that spatial modeling of these vehicle parts is crucial for overall performance. First, the vehicle is treated as an object composed of multiple salient parts, including the license plate and rear lamps. These parts are localized using their distinctive color, texture, and region feature. Furthermore, the detected parts are treated as graph nodes to construct a probabilistic graph using a Markov random field model. After that, the marginal posterior of each part is inferred using loopy belief propagation to get final vehicle detection. Finally, the vehicles' trajectories are estimated using a Kalman filter, and a tracking-based detection technique is realized. Experiments in practical urban scenarios are carried out under various weather conditions. It can be shown that our method adapts to partial occlusion and various lighting conditions. Experiments also show that our method can achieve real-time performance. © 2000-2011 IEEE.

Li P.,National University of Defense Technology | Sun Y.,Beijing Normal University
International Journal of Communication Systems | Year: 2014

Research on social networks has received remarkable attention, because an increasing number of people use social networks to broadcast information and stay connected with their friends. However, because of the information overload in social networks, it becomes increasingly difficult for users to find useful information. This paper takes Facebook-like social networks into account and proposes models to capture the characters such as the network, the user behaviors, and the process of information diffusion under information overload. The term type influence is introduced to characterize the information diffusion efficiency for users of a given type, which can be analyzed theoretically on the basis of the proposed models. Having noticed the inaccuracy of using type influence to estimate the information diffusion efficiency for a given user, we further introduce the term individual influence and propose a scalable approach to estimate it. We verify the accuracy of this approach by simulations and show that considering more nearby users leads to more computational costs, but more accurate results. Copyright © 2014 John Wiley & Sons, Ltd.

A variable near-null compensator for measuring aspheric surfaces by subaperture stitching includes a pair of counter-rotating CGH phase plates, each of the phase plates having a phase function including two terms Z5 and Z7 of Zernike polynomials. The phase plates are mounted on a pair of precision rotary center-through tables, wherein rotational axes of the pair of precision rotary center-through tables coincide with the optical axes of the phase plates. A figure metrology apparatus includes a wavefront interferometer, the test mirror mount, the near-null compensator and the mechanical adjustment components therefor. The optical axis of the near-null compensator coincides with the optical axis of the interferometer. A method for measuring aspheric surfaces by subaperture stitching includes the steps of mounting the test mirror, measuring the subapertures with the figure metrology apparatus, and finally processing the data by stitching.

National University of Defense Technology | Date: 2011-04-29

A side lobe suppression method for an SAR image based on the deformation of a spatial spectral support area is provided. Using the relationship between the spatial spectral support area distribution of an SAR system and an impulse response, the trend of a side lobe in the impulse response is changed by deforming the spatial spectral support area; two SAR images with different side lobe trends are obtained by calculation; the difference information of the side lobe trends between the two SAR images is finally utilized to realize the mutual separation of a target main lobe and the side lobe, thus realizing effective side lobe suppression. The method has an obvious effect on side lobe suppression without losing image resolution, at the same time, can be realized simply, has less calculation amount, is not sensitive to noise, is also very convenient to implement, and can be directly used for processing an original SAR image.

News Article | November 19, 2015
Site: www.techtimes.com

China is rapidly loading up on its supercomputers. According to a BBC News report, the country has nearly tripled its amount of supercomputers. Based on the biannual Top500 list of supercomputers, China now has 109 high-performance computing (HPC) systems, which marks a whopping 196 percent increase from just over three years ago. In addition, China scored the top supercomputer of them all, the Tianhe-2, which was ranked first on the Top500 for the sixth straight time. Created by China's National University of Defense Technology, the Tianhe-2 can generate a mind-numbing 33.86 quadrillion calculations per second, easily making it the most sophisticated supercomputer in the world. In comparison, the United States' number of supercomputers has suffered a slide. Although the U.S. counts 200 supercomputers in the Top500, that's its lowest number since the list began being compiled back in 1993, according to the BBC. Rajnish Arora, vice president of computing research firm IDC Asia Pacific, told the BBC that China's advancement with supercomputers is a global sign of the times. "When China started off appearing on the center stage of the global economy in the '80s and '90s, it was predominately a manufacturing hub," he told the BBC. "All the IP or design work would happen in Europe or the U.S. and the companies would just send manufacturing or production jobs to China. Now as these companies become bigger, they want to invest in technical research capabilities, so that they can create a lot more innovation and do basic design and engineering work." David Schibeci, from the Pawsey Supercomputing Center in Western Australia, told the BBC: "Nations like China have a great opportunity to take a leading role in the HPC (high-performance computing) space but it's important that they focus on research support and up-skilling of staff rather than just raw numbers for the Top500."

Zhang H.,National University of Defense Technology | Li Z.,National University of Defense Technology
Nonlinear Analysis: Real World Applications | Year: 2011

In this paper we study the existence of periodic and homoclinic solutions for a class of second order differential equations of the form q+Vq(t,q)=f(t) with impulsive conditions Δq(sk)=gk(q(sk)) via variational methods. Our results show that under appropriate conditions such a system possesses at least one non-zero periodic solution and at least one non-zero homoclinic solution and these solutions are generated by impulses when f≡0. Furthermore, one of the results gives us a lower bound of the number of periodic solutions generated by impulses and this lower bound is determined by the number of impulses of the system in a period of the solution. © 2010 Published by Elsevier Ltd. All rights reserved.

Meng X.-L.,National University of Defense Technology | Wang Z.-Z.,National University of Defense Technology
Zidonghua Xuebao/Acta Automatica Sinica | Year: 2011

An image diffusion algorithm based on visual masking effect is proposed. In view of properties of human visual system, inhomogeneity underlying an image is employed to define a novel noise masking function. It is a measure of contextual discontinuities, and could efficiently distinguish noise from edges. The resultant noise visibility function is used as diffusivity function of anisotropic diffusion. Due to the combined use of local spatial gradient and contextual information of larger neighborhood, the proposed algorithm could preserve nontrivial features more efficiently while removing noise. Further, it avoids the difficulty of estimating the gradient threshold in traditional algorithms. Comparative experiments certify that the proposed algorithm outperforms several existing typical diffusion methods in terms of noise removal and feature preservation. © 2011 Acta Automatica sinica. All rights reserved.

Liu B.,National University of Defense Technology | Chang W.,National University of Defense Technology
Progress in Electromagnetics Research | Year: 2013

One of the di±culties for frequency stepped chirp radar (FSCR) is to resolve the range-Doppler coupling due to relative motion between the radar and the target. Motion compensation is usually adopted to solve the problem in realizing synthetic high range resolution profile (HRRP) for a moving target. For missile- borne FSCR, the range migration of target echo during a coherent processing interval, which is resulted from the high speed motion of missile, is serious and will affect target detection and synthetic high range resolution profile. Therefore, range migration correction and motion compensation are very important for missile-borne FSCR signal processing. In the paper, with the background of terminal guidance anti-ship FSCR seeker, the range alignment is accomplished in frequency domain during the process of real-time digital pulse compression. Then an effective velocity estimation algorithm based on the waveform entropy of the Doppler amplitude spectrum of target echoes is addressed and the velocity estimation accuracy is derived. Finally, the simulation indicates that the new method can estimate the radial velocity accurately and reconstruct the distorted HRRP successfully. In addition, the method has good anti-noise performance and works in the scenario of multi-target with different velocities as well.

Zhan R.-H.,National University of Defense Technology | Zhang J.,National University of Defense Technology
Xi Tong Gong Cheng Yu Dian Zi Ji Shu/Systems Engineering and Electronics | Year: 2011

Feature-aided data association (FADA), as a novel and effective approach for improving track maintenance, has been a hot spot in the area of targets tracking under complicated environment such as dense clutter or multiple near spaced targets, and it has a good prospect of application. Based on the extensive investigation of published literatures, the foundational principle of FADA is represented at the beginning of this paper, followed by scientific categorization of the target features and association algorithms. The typical FADA application instances are surveyed in detail, and the direction of future progress is also discussed.

Zhan Y.,National University of Defense Technology | Yin J.,National University of Defense Technology
Neurocomputing | Year: 2011

Recently manifold learning has attracted extensive interest in machine learning and related communities. This paper investigates the noise manifold learning problem, which is a key issue in applying manifold learning algorithm to practical problems. We propose a robust version of LTSA algorithm called RLTSA. The proposed RLTSA algorithm makes LTSA more robust from three aspects: firstly robust PCA algorithm based on iterative weighted PCA is employed instead of the standard SVD to reduce the influence of noise on local tangent space coordinates; secondly RLTSA chooses neighborhoods that are well approximated by the local coordinates to align with the global coordinates; thirdly in the alignment step, the influence of noise on embedding result is further reduced by endowing clean data points and noise data points with different weights into the local alignment errors. Experiments on both synthetic data sets and real data sets demonstrate the effectiveness of our RLTSA when dealing with noise manifold. © 2011 Elsevier B.V.

Jiang J.-P.,National University of Defense Technology | Li D.-X.,National University of Defense Technology
JVC/Journal of Vibration and Control | Year: 2011

The multi-panel deployable solar array structure is the most common system utilized for spacecraft power system. To effectively suppress vibration of the solar array structure is still a challenging task. The present works focus on dynamic modeling and robust H∞ vibration control for a large flexible spacecraft solar array structure using piezoelectric actuators and velocity sensors. The structural dynamic model of the solar array structure with piezoelectric actuators is generated by using finite element techniques. The order of the system is reduced by employing Modal Hankel Singular Value method. Based on Linear Matrix Inequality technique, a robust H∞ dynamic output feedback controller is designed to suppress the vibrations caused by external disturbances. The simulation results show that the vibration can be significantly suppressed with permitted actuator voltages by the controller. The robust H∞ controller can avoid the spillover due to mode truncation. © 2010 The Author(s).

Chen W.,National University of Defense Technology | Chen W.,Tsinghua University | Zhang S.,Tsinghua University | Long X.,National University of Defense Technology
Optics Letters | Year: 2013

We introduce a technique for simultaneous measurement of thickness and refractive index of birefringent materials. The principle is based on the laser feedback effect that laser polarization states flip between two orthogonal directions when a birefringent material is placed into the external cavity. The position of polarization flipping is determined by the phase-retardation magnitude of the birefringent material. Some feature points in the laser intensity curve can be used to calculate phase retardation. We derive an expression for phase retardation and rotation angle of a birefringent material to calculate thickness and refractive index. This technique is noncontact and compatible with in situ thickness and refractive-index measurement. The measurement precision of thickness is 59 nm and of refractive index is 0.0006. © 2013 Optical Society of America.

Zhu F.,CAS Institute of Automation | Li G.,National University of Defense Technology | Li Z.,CAS Institute of Automation | Chen C.,CAS Institute of Automation | Wen D.,National University of Defense Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2011

A new traffic signal control system (TSCS) evaluation method that uses computational experiments based on artificial transportation systems (ATSs) is proposed in this paper. Some basic ideas of the method are discussed, i.e., generating reasonable travel demand, modeling the influence of environment, and designing communication interface. Using a 30-day computational experiment on ATSs, a case study is carried out to evaluate three TSCSs, which are implemented using fixed-time (FT), queue-based responsive (QBR), and adaptive dynamic program (ADP) algorithms, respectively. Aside from normal weather, three types of adverse weather, i.e., rain, wind, and fog, are modeled in the computational experiment. After analyzing aggregate data and detailed operating record, reliable evaluation results are obtained from this case study. Furthermore, several interesting phenomena are observed in this case study, which have yet to be noticed by previous work. © 2011 IEEE.

Chen M.-S.,National University of Defense Technology | Jiang H.-M.,National University of Defense Technology
Guangxue Jingmi Gongcheng/Optics and Precision Engineering | Year: 2011

An experiment of 975 nm continuous wave laser irradiating carbon-fiber reinforced resin composites was studied, while the front surface of a target was with and without tangential airflow loadings. The results show that the dynamic responses are obviously different for two different cases. While the front surface of the target is without tangential airflow loading, the ejected inner pyrolysis products ignite surface combustion which is accompanied by dense smoke and flame after laser irradiation for 1.28 s. While the front surface of the target is with tangential airflow loading, there is not obvious combustion flame, but a burn-like bright spot is in the laser-irradiated zone and a little particles spill into the air intermittently. Analysis indicates that the out overflows of pyrolysis products will inhibit the diffusion of oxygen to the target surface, which has a protective effect on the carbon fiber. The presence of tangential airflow not only undermine the protective effect of pyrolysis products on the carbon fiber, but also promote the diffusion of oxygen to the surface. Therefore, the loading of tangential airflow will result in the carbon fiber suffered from oxidative ablation at the low temperature (850°C).

Xu X.,National University of Defense Technology | Li G.,National University of Defense Technology
Proceedings - IEEE International Symposium on Distributed Simulation and Real-Time Applications | Year: 2013

This paper outlines a management and control infrastructure that integrates heterogeneous simulations into a synthetic experiment environment. Concepts and functionality of the infrastructure are discussed, and architecture design along with detailed analysis is given to illustrate its support for the whole process of conducting experiments. We consider two key challenges, time management and data exchange mechanism that support constructing the infrastructure, and propose proper design. In particular, real-time constrains satisfaction is considered as a critical problem in our work. The presented infrastructure adopts a GPS-based approach to meet highprecision time synchronization requirement, and takes DDS (Data Distribution Service) as the network middleware to implement data organization and transmission. We propose a case study to illustrate this infrastructure's feasibility and advantages in terms of simulation integration and management issues. © 2013 IEEE.

Wang H.,National University of Defense Technology | Wang Z.-W.,National University of Defense Technology
Composites Part A: Applied Science and Manufacturing | Year: 2016

This paper presents a linear discretized theoretical model on the basis of the ideal theoretical model to evaluate elastic constants of plain-weave composite by using the statistics of the feature parameters of yarn measured from Micro CT data. A finite element method is utilized to calculate the elastic constants of the composite using the modified and global mean feature parameters of yarn, respectively. Uniaxial tensile and in-plane shear experiments are then completed to measure in-plane elastic constants of the composite. Finally, comparisons among the predictions of two theoretical models, FEM and experimental results are conducted. The results show that the stochastic fluctuations of yarn feature parameters decrease the in-plane elastic moduli and increase the in-plane shear moduli and Poisson's ratios of the plain-weave composite. The discretized theoretical model with taking account of real yarn stochastic features can predict more accurate elastic constants of the composite than deterministic models. © 2016 Elsevier Ltd. All rights reserved.

Xi Y.,National University of Defense Technology | Burr A.,University of York | Wei J.,National University of Defense Technology | Grace D.,University of York
IEEE Transactions on Wireless Communications | Year: 2011

We propose a new analytical approach to evaluate the average packet error rate (PER) of a conventional packet transmission system over a quasi static fading channel, by presenting an integral inequality lemma. The basic idea of the approach is that, given the PER for the AWGN channel as a function of signal-to-noise ratio (SNR), the average PER over Rayleigh fading channel can be generally upper bounded by a quite simple inequality, i.e.,1 - exp( - w0/γ̄), for both coded and uncoded schemes, where w0, defined by an integral expression, corresponds exactly to the inversion of coding gain; and this bound is tight in the high SNR region or for long packet systems. We further apply the integral inequality to extend our research to more general Nakagami-m fading channel. © 2011 IEEE.

Xing L.-N.,National University of Defense Technology | Rohlfshagen P.,University of Birmingham | Chen Y.-W.,National University of Defense Technology