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.


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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.


Chen S.,National University of Defense Technology | Chen S.,University of Victoria | Jin S.,National University of Defense Technology | Gordon R.,University of Victoria
Optics Express | Year: 2014

A theory is presented for the transmission of transverse magnetic waves through a finite number of subwavelength slits in metal film. While a single slit achieves the single channel limit on resonance, multiple slits show super-transmission exceeding the single channel limit. The phenomenon of super-transmission is revealed as a result of cross-coupling of modes and confirmed by simulations. The influence of finite permittivity in the IR and microwave regime is included by perturbative corrections to the theory. The theory agrees quantitatively with past experiments and finite-difference time-domain simulations. By considering two or more modes in the slit region, our theory provides an approach to the analysis of cross-coupling among slits, which allows for super-transmission and features of a Fano resonance. © 2014 Optical Society of America.


Liu L.,National University of Defense Technology | Fieguth P.,University of Waterloo | Kuang G.,National University of Defense Technology | Zha H.,Peking University
Proceedings of the IEEE International Conference on Computer Vision | Year: 2011

This paper presents a simple and highly effective system for robust texture classification, based on (1) random local features, (2) a simple global Bag-of-Words (BoW) representation, and (3) Support Vector Machines (SVMs) based classification. The key contribution in this work is to apply a sorting strategy to a universal yet information-preserving random projection (RP) technique, then comparing two different texture image representations (histograms and signatures) with various kernels in the SVMs. We have tested our texture classification system on six popular and challenging texture databases for exemplar based texture classification, comparing with 12 recent state-of-the-art methods. Experimental results show that our texture classification system yields the best classification rates of which we are aware of 99.37% for CUReT, 97.16% for Brodatz, 99.30% for UMD and 99.29% for KTH-TIPS. Moreover, combining random features significantly outperforms the state-of-the-art descriptors in material categorization. © 2011 IEEE.


Sun Y.,National University of Defense Technology | Lu R.,University of Waterloo | Lin X.,University of Ontario Institute of Technology | Shen X.,University of Waterloo | Su J.,National University of Defense Technology
IEEE Transactions on Vehicular Technology | Year: 2010

In this paper, we propose an efficient pseudonymous authentication scheme with strong privacy preservation (PASS), for vehicular communications. Unlike traditional pseudonymous authentication schemes, the size of the certificate revocation list (CRL) in PASS is linear with the number of revoked vehicles and unrelated to how many pseudonymous certificates are held by the revoked vehicles. PASS supports the roadside unit (RSU)-aided distributed certificate service that allows the vehicles to update certificates on road, but the service overhead is almost unrelated to the number of updated certificates. Furthermore, PASS provides strong privacy preservation to the vehicles so that the adversaries cannot trace any vehicle, even though all RSUs have been compromised. Extensive simulations demonstrate that PASS outperforms previously reported schemes in terms of the revocation cost and the certificate updating overhead. © 2006 IEEE.


Chen S.,National University of Defense Technology | Chen S.,University of Victoria | Jin S.,National University of Defense Technology | Gordon R.,University of Victoria
Physical Review X | Year: 2014

Radiationless electromagnetic interference (REI) has been used to achieve focusing below Abbe's diffraction limit. Here, we demonstrate an approach to REI that uses the Fano resonance of subwavelength slits to achieve subdiffraction focusing. Two main features of the Fano resonance are critical: (1) The Fano resonance suppresses radiation by destructive interference, thereby allowing for REI, and (2) the Fano resonance creates a resonant field enhancement allowing one to overcome evanescent decay, which is different from past approaches to REI. An analytic theory is introduced to explain these results. While the analytic theory is formulated for a perfect electric conductor, comprehensive numerical simulations show the applicability in the visible regime, where losses and plasmonic effects play a role.


Yang J.,Peking University | Yang J.,National University of Defense Technology | Zhou Z.,Peking University | Jia H.,National University of Defense Technology | And 2 more authors.
Optics Letters | Year: 2011

A high-performance and compact fiber-to-waveguide binary blazed subwavelength grating coupler was designed based on silicon-on-insulator. By the appropriate choice of waveguide/grating parameters, including thicknesses, periods, height, and fill factor, to optimize the mode matching, a relatively high coupling efficiency was obtained for the fiber and waveguide interface. Moreover, perfectly vertical fiber coupling is achieved by using an asymmetric subgrating structure in which a period consists of two subgratings with identical etching height and different widths. Coupling efficiency as high as 69% at a wavelength of 1:52 ?m and 65% at a wavelength of 1:55 ?m is calculated. Simultaneously, the 1 dB wavelength bandwidth is around 80nm. The coupling efficiency can reach up to 80% or so if Bragg reflector layers are added. Finally, the device layout is simple, feasible, one-step etched, and compatible with standard complementary metal-oxide semiconductor technology processing. © 2011 Optical Society of America.


Ren K.,National University of Defense Technology | Xiao N.,National University of Defense Technology | Chen J.,Swinburne University of Technology
IEEE Transactions on Services Computing | Year: 2011

Although semantic-based composition approaches have brought some comprehensive advantages such as higher precisions and recalls, they are far from the real practice and hard to be applied in real-world applications due to the several challenging issues such as performance issues of time-consuming ontology reasoning, exponentially expanded searching time in large service repositories, lack of available and consensus ontologies, and higher using thresholds for users who do not have much semantic knowledge. To reduce these issues, in this paper, we present an innovative composition technique by building an Extended Quick Service Query List (EQSQL) for supporting more efficient and more realistic service composition. In EQSQL, data structures are specially designed to record service information and their associated semantic concepts by in advance processing semantic-related computing during service publication period. Particularly, WordNet and semantic similarities among multiple heterogeneous ontologies are exploited in our developed algorithms for forming EQSQL. As a result, EQSQL-based planning algorithm can not only achieve a quick response for a composition request, but guarantee the semantic composition quality as well. More importantly, our approaches can be scalable to the large service repositories and also significantly alleviate users or developers from the burden of using complicated semantic service composition, thus making service composition easier and more realistic. Our final experiments further demonstrate the feasibility and the efficiency of our proposed approaches. © 2011 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.


Zhou D.F.,National University of Defense Technology | Hansen C.H.,University of Adelaide | Li J.,National University of Defense Technology
Journal of Sound and Vibration | Year: 2011

The self-excited vibration that occurs between a stationary Electromagnetic Suspension (EMS) maglev vehicle and a girder is a practical problem that greatly degrades the performance of a maglev system. As of today, this problem has not been fully solved. In this article, the principle underlying the self-excited vibration problem is explored, and it is found that the fundamental resonance frequency of the maglev girder plays a vital role in the initiation of the self-excited vibration. To suppress the self-excited vibration, a scheme applying a tuned mass damper (TMD) to the maglev girder is proposed, and the stability of the combined system is analyzed. Furthermore, a novel concept of a virtual TMD is introduced, which uses an electromagnetic force to emulate the force of a real TMD acting on the girder. However, in the presence of the time delay caused by the inductance of the electromagnets, the stability analysis of the levitation system combined with the virtual TMD becomes complex. Analysis of the stability shows that there exist some repeated time delay zones within which the overall system is stable. Based on this rule, time delay control is introduced to stabilize the system with a virtual TMD, and a procedure to determine the optimal time delay and gain is proposed. Numerical simulation indicates that the proposed virtual TMD scheme can significantly suppress the self-excited vibration caused by one unstable vibration mode, and is suitable for application to EMS maglev systems. © 2010 Elsevier Ltd.


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.


Shi J.,University of Windsor | Shi J.,National University of Defense Technology | Zhang G.,University of Windsor | Sha J.,National University of Defense Technology
Computers and Operations Research | Year: 2011

We study the production planning problem for a multi-product closed loop system, in which the manufacturer has two channels for supplying products: producing brand-new products and remanufacturing returns into as-new ones. In the remanufacturing process, used products are bought back and remanufactured into as-new products which are sold together with the brand-new ones. The demands for all the products are uncertain, and their returns are uncertain and price-sensitive. The problem is to maximize the manufacturer's expected profit by jointly determining the production quantities of brand-new products, the quantities of remanufactured products and the acquisition prices of the used products, subject to a capacity constraint. A mathematical model is presented to formulate the problem and a Lagrangian relaxation based approach is developed to solve the problem. Numerical examples are presented to illustrate the model and test the solution approach. Computational results show that the proposed approach is highly promising for solving the problems. The sensitivity analysis is also conducted to generate managerial insights. © 2010 Elsevier Ltd. All rights reserved.


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.


Shi J.,National University of Defense Technology | Shi J.,University of Windsor | Zhang G.,University of Windsor | Sha J.,National University of Defense Technology
Resources, Conservation and Recycling | Year: 2011

A closed loop system is investigated, in which the manufacturer has two channels to satisfy the demand: manufacturing brand-new products and remanufacturing returns into as-new products. Remanufactured products have no difference from brand-new products and can be sold in the same market at the same price. The demand is uncertain and sensitive to the selling price, while the return is also stochastic and sensitive to the acquisition price of used products. A mathematical model is developed to maximize the overall profit of the system by simultaneously determining the selling price, the production quantities for brand-new products and remanufactured products, and the acquisition price of used products. Some properties of the problem are analyzed, based on which a solution procedure is presented. Through a numerical example, the impacts of the uncertainties of both demand and return on the production plan, selling price, and the acquisition price of used products are analyzed. © 2010 Elsevier B.V. All rights reserved.


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.


Qu L.,National University of Defense Technology | Tan Y.,National University of Singapore | Tan C.H.,National University of Singapore | Li C.,National University of Defense Technology
IEEE Transactions on Information Theory | Year: 2013

Many block ciphers use permutations defined on f22k with low differential uniformity, high nonlinearity, and high algebraic degree as their S-boxes to provide confusion. It is well known that, for a function on ,f 2n the lowest differential uniformity is 2 and the functions achieving this lower bound are called almost perfect nonlinear (APN) functions. However, due to the lack of knowledge on APN permutations on f22k, differentially 4-uniform permutations are usually chosen as S-boxes. For example, the currently endorsed Advanced Encryption Standard chooses one such function, the multiplicative inverse function, as its S-box. By a recent survey on differentially 4-uniform permutations over f22k, there are only five known infinite families of such functions, and most of them have small algebraic degrees. In this paper, we apply the powerful switching method to discover many CCZ-inequivalent infinite families of such functions f 22k on with optimal algebraic degree, where k is an arbitrary positive integer. This greatly expands the list of differentially 4-uniform permutations and hence provide more choices for the S-boxes. Furthermore, lower bounds for the nonlinearity of the functions obtained in this paper are presented and they imply that some infinite families have high nonlinearity. © 2013 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.


Guan N.,National University of Defense Technology | Tao D.,Intelligent Systems Technology, Inc. | Luo Z.,National University of Defense Technology | Yuan B.,Shanghai JiaoTong University
IEEE Transactions on Image Processing | Year: 2011

Nonnegative matrix factorization (NMF) has become a popular data-representation method and has been widely used in image processing and pattern-recognition problems. This is because the learned bases can be interpreted as a natural parts-based representation of data and this interpretation is consistent with the psychological intuition of combining parts to form a whole. For practical classification tasks, however, NMF ignores both the local geometry of data and the discriminative information of different classes. In addition, existing research results show that the learned basis is unnecessarily parts-based because there is neither explicit nor implicit constraint to ensure the representation parts-based. In this paper, we introduce the manifold regularization and the margin maximization to NMF and obtain the manifold regularized discriminative NMF (MD-NMF) to overcome the aforementioned problems. The multiplicative update rule (MUR) can be applied to optimizing MD-NMF, but it converges slowly. In this paper, we propose a fast gradient descent (FGD) to optimize MD-NMF. FGD contains a Newton method that searches the optimal step length, and thus, FGD converges much faster than MUR. In addition, FGD includes MUR as a special case and can be applied to optimizing NMF and its variants. For a problem with 165 samples in R1600 , FGD converges in 28 s, while MUR requires 282 s. We also apply FGD in a variant of MD-NMF and experimental results confirm its efficiency. Experimental results on several face image datasets suggest the effectiveness of MD-NMF. © 2011 IEEE.


Guan N.,National University of Defense Technology | Tao D.,University of Technology, Sydney | Luo Z.,National University of Defense Technology | Yuan B.,Shanghai JiaoTong University
IEEE Transactions on Neural Networks | Year: 2011

In this paper, we present a non-negative patch alignment framework (NPAF) to unify popular non-negative matrix factorization (NMF) related dimension reduction algorithms. It offers a new viewpoint to better understand the common property of different NMF algorithms. Although multiplicative update rule (MUR) can solve NPAF and is easy to implement, it converges slowly. Thus, we propose a fast gradient descent (FGD) to overcome the aforementioned problem. FGD uses the Newton method to search the optimal step size, and thus converges faster than MUR. Experiments on synthetic and real-world datasets confirm the efficiency of FGD compared with MUR for optimizing NPAF. Based on NPAF, we develop non-negative discriminative locality alignment (NDLA). Experiments on face image and handwritten datasets suggest the effectiveness of NDLA in classification tasks and its robustness to image occlusions, compared with representative NMF-related dimension reduction algorithms. © 2011 IEEE.


Cao Y.,National University of Defense Technology | Yang L.,Electronic Equipments and System Engineering Corporation
Proceedings 2010 IEEE International Conference on Information Theory and Information Security, ICITIS 2010 | Year: 2010

This paper presents a survey of identity management from the perspectives of development stages and functions variety of Identity Management. The definition and core concepts of identity and identity management have been discussed deeply. Identity Management models including isolated model, centralized model, and federated model are grouped by components varying and functions changing. Based on the transformation of core design principles, paradigms of identity management are classified into network centric paradigm, service centric paradigm, and user centric paradigm. Comparisons of these paradigms and models have been presented. And we give a rough classification of current systems to the corresponding paradigms and models. © 2010 IEEE.


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.


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.


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.


Guan N.,National University of Defense Technology | Tao D.,Intelligent Systems Technology, Inc. | Luo Z.,National University of Defense Technology | Yuan B.,Shanghai JiaoTong University
IEEE Transactions on Signal Processing | Year: 2012

Nonnegative matrix factorization (NMF) is a powerful matrix decomposition technique that approximates a nonnegative matrix by the product of two low-rank nonnegative matrix factors. It has been widely applied to signal processing, computer vision, and data mining. Traditional NMF solvers include the multiplicative update rule (MUR), the projected gradient method (PG), the projected nonnegative least squares (PNLS), and the active set method (AS). However, they suffer from one or some of the following three problems: slow convergence rate, numerical instability and nonconvergence. In this paper, we present a new efficient NeNMF solver to simultaneously overcome the aforementioned problems. It applies Nesterov's optimal gradient method to alternatively optimize one factor with another fixed. In particular, at each iteration round, the matrix factor is updated by using the PG method performed on a smartly chosen search point, where the step size is determined by the Lipschitz constant. Since NeNMF does not use the time consuming line search and converges optimally at rate O(1/k2) in optimizing each matrix factor, it is superior to MUR and PG in terms of efficiency as well as approximation accuracy. Compared to PNLS and AS that suffer from numerical instability problem in the worst case, NeNMF overcomes this deficiency. In addition, NeNMF can be used to solve L 1-norm, L 2-norm and manifold regularized NMF with the optimal convergence rate. Numerical experiments on both synthetic and real-world datasets show the efficiency of NeNMF for NMF and its variants comparing to representative NMF solvers. Extensive experiments on document clustering suggest the effectiveness of NeNMF. © 2012 IEEE.


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.


Qian Y.,National University of Defense Technology | Lu Z.,KTH Royal Institute of Technology | Dou W.,National University of Defense Technology
IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems | Year: 2010

In network-on-chip (NoC), computing worst-case delay bounds for packet delivery is crucial for designing predictable systems but yet an intractable problem. This paper presents an analysis technique to derive per-flow communication delay bound. Based on a network contention model, this technique, which is topology independent, employs network calculus to first compute the equivalent service curve for an individual flow and then calculate its packet delay bound. To exemplify this method, this paper also presents the derivation of a closed-form formula to compute a flow's delay bound under all-to-one gather communication. Experimental results demonstrate that the theoretical bounds are correct and tight. © 2010 IEEE.


Guan N.,National University of Defense Technology | Tao D.,Intelligent Systems Technology, Inc. | Luo Z.,National University of Defense Technology | Yuan B.,Shanghai JiaoTong University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2012

Nonnegative matrix factorization (NMF) has become a popular dimension-reduction method and has been widely applied to image processing and pattern recognition problems. However, conventional NMF learning methods require the entire dataset to reside in the memory and thus cannot be applied to large-scale or streaming datasets. In this paper, we propose an efficient online RSA-NMF algorithm (OR-NMF) that learns NMF in an incremental fashion and thus solves this problem. In particular, OR-NMF receives one sample or a chunk of samples per step and updates the bases via robust stochastic approximation. Benefitting from the smartly chosen learning rate and averaging technique, OR-NMF converges at the rate of in each update of the bases. Furthermore, we prove that OR-NMF almost surely converges to a local optimal solution by using the quasi-martingale. By using a buffering strategy, we keep both the time and space complexities of one step of the OR-NMF constant and make OR-NMF suitable for large-scale or streaming datasets. Preliminary experimental results on real-world datasets show that OR-NMF outperforms the existing online NMF (ONMF) algorithms in terms of efficiency. Experimental results of face recognition and image annotation on public datasets confirm the effectiveness of OR-NMF compared with the existing ONMF algorithms. © 2012 IEEE.


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.


Zhu Y.,National University of Defense Technology | Su Y.,National University of Defense Technology | Yu W.,Shanghai JiaoTong University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

With the inverse synthetic aperture radar (ISAR) imaging model, targets should move smoothly during the coherent processing interval (CPI). Since the CPI is quite long, fluctuations of a target's velocity and gesture will deteriorate image quality. This paper presents a multiple-inputmultiple-output (MIMO)-ISAR imaging method by combining MIMO techniques and ISAR imaging theory. By using a special M-transmitter N-receiver linear array, a group of M orthogonal phase-code modulation signals with identical bandwidth and center frequency is transmitted. With a matched filter set, every target response corresponding to the orthogonal signals can be isolated at each receiving channel, and range compression is completed simultaneously. Based on phase center approximation theory, the minimum entropy criterion is used to rearrange the echo data after the target's velocity has been estimated, and then, the azimuth imaging will finally finish. The analysis of imaging and simulation results show that the minimum CPI of the MIMO-ISAR imaging method is 1/MN of the conventional ISAR imaging method under the same azimuth-resolution condition. It means that most flying targets can satisfy the condition that targets should move smoothly during CPI; therefore, the applicability and the quality of ISAR imaging will be improved. © 2006 IEEE.


Tang M.,National University of Defense Technology | Chen X.,National University of Defense Technology | Hu W.,National University of Defense Technology | Yu W.,Shanghai JiaoTong University
Information Sciences | Year: 2012

This study considers probabilistic fuzzy systems constructed using Mamdani probabilistic fuzzy rules. As a generalisation of deterministic fuzzy systems, Mamdani probabilistic fuzzy systems better model practical complex systems involving uncertainty because they combine the interpretability of fuzzy systems with the statistical properties of probabilistic systems. Using probabilistic fuzzy rules, both probabilistic uncertainty and linguistic ambiguity are handled simultaneously with a single framework. Considering that the information available often consists of a training set of input-output data pairs, a general method for generating Mamdani probabilistic fuzzy rule bases from numerical data pairs is presented. A fuzzy reasoning method is used on the generated probabilistic fuzzy rule base to derive a map leading from the input space to the output space, and a probabilistic fuzzy system is constructed. We use this probabilistic fuzzy modelling method for nonlinear regression analysis. The effectiveness of the proposed method is demonstrated by a comparison with similar regression techniques. © 2012 Elsevier Inc. All rights reserved.


Yu T.-P.,National University of Defense Technology | Yu T.-P.,Heinrich Heine University Düsseldorf | Pukhov A.,Heinrich Heine University Düsseldorf | Sheng Z.-M.,Shanghai JiaoTong University | And 3 more authors.
Physical Review Letters | Year: 2013

By using multidimensional particle-in-cell simulations, we study the electromagnetic emission from radiation pressure acceleration of ultrathin mass-limited foils. When a circularly polarized laser pulse irradiates the foil, the laser radiation pressure pushes the foil forward as a whole. The outer wings of the pulse continue to propagate and act as a natural undulator. Electrons move together with ions longitudinally but oscillate around the latter transversely, forming a self-organized helical electron bunch. When the electron oscillation frequency coincides with the laser frequency as witnessed by the electron, betatronlike resonance occurs. The emitted x rays by the resonant electrons have high brightness, short durations, and broad band ranges which may have diverse applications. © 2013 American Physical Society.


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.


Ganichev I.,University of California at Berkeley | Dai B.,National University of Defense Technology | Godfrey P.B.,University of Illinois at Urbana - Champaign | Shenker S.,UCB
SIGCOMM'10 - Proceedings of the SIGCOMM 2010 Conference | Year: 2010

Multipath routing is a promising technique to increase the Internet's reliability and to give users greater control over the service they receive. However, past proposals choose paths which are not guaranteed to have high diversity. In this paper, we propose yet another multipath routing scheme (YAMR) for the interdomain case. YAMR provably constructs a set of paths that is resilient to any one inter-domain link failure, thus achieving high reliability in a systematic way. Further, even though YAMR maintains more paths than BGP, it actually requires significantly less control traffic, thus alleviating instead of worsening one of the Internet's scalability problems. This reduction in churn is achieved by a novel hiding technique that automatically localizes failures leaving the greater part of the Internet completely oblivious.


Shen Z.-B.,National University of Defense Technology | Tang G.-J.,National University of Defense Technology | Zhang L.,China Airborne Missile Academy | Li X.-F.,Central South University
Computational Materials Science | Year: 2012

This paper studies free vibration of double-walled carbon nanotubes (DWCNTs) based nanomechanical sensor under initial axial stress. A bridged DWCNT carrying a nanoparticle at any position of the outer tube is modeled as two clamped nonlocal Euler-Bernoulli beams, and the interaction between two tubes is governed by van der Waals force. For comparison, a bridged single-walled carbon nanotube (SWCNT) based nanomechanical sensor is considered in a similar way. Using the transfer function method, the critical buckling stress and natural frequencies of these nanomechanical sensors are computed. Under small initial stress, the effects of the attached nanoparticle, and the small scale parameter on the frequency shift are discussed. The obtained results show that when the mass of the nanoparticle increases or its location is closed to the beam center, the natural frequency decreases, but frequency shift increases. Initial tensile stress increases the natural frequency, while initial compressive stress decreases the natural frequency. In comparison with SWCNT sensor, DWCNT is more stable, but less sensitive for smaller attached mass. Obtained results are helpful to the design of DWCNT-based resonator as nanomechanical sensor. © 2012 Elsevier B.V. All rights reserved.


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.


Guoji S.,National University of Defense Technology | McLaughlin S.,Heriot - Watt University | Yongcheng X.,National University of Defense Technology | White P.,University of Southampton
Mechanical Systems and Signal Processing | Year: 2014

Condition monitoring and fault diagnosis is an important issue for gearbox maintenance and safety. The critical process involved in such activities is to extract reliable features representative of the condition of the gears or gearbox. In this paper a framework is presented for the application of bispectrum to the analysis of gearbox vibration. The bispectrum of a composite signal consisting of multiple periodic components has peaks at the bifrequencies that correspond to closely related components which can be produced by any nonlinearity. As a result, biphase verification is necessary to decrease false-alarming for any bispectrum-based method. A model based on modulated signals is adopted to reveal the bispectrum characteristics for the vibration of a faulty gear, and the corresponding amplitude and phase of the bispectrum expression are deduced. Therefore, a diagnostic approach based on the theoretical result is derived and verified by the analysis of a set of vibration signals from a helicopter gearbox. © 2013 Elsevier Ltd. 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 | 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.


Ko D.-H.,Pohang University of Science and Technology | Ren W.,National University of Defense Technology | Kim J.-O.,Pohang University of Science and Technology | Wang J.,National University of Defense Technology | And 4 more authors.
ACS Nano | Year: 2016

Gas and liquid streams are invariably separated either by a solid wall or by a membrane for heat or mass transfer between the gas and liquid streams. Without the separating wall, the gas phase is present as bubbles in liquid or, in a microsystem, as gas plugs between slugs of liquid. Continuous and direct contact between the two moving streams of gas and liquid is quite an efficient way of achieving heat or mass transfer between the two phases. Here, we report a silicon nanowire built-in microsystem in which a liquid stream flows in contact with an underlying gas stream. The upper liquid stream does not penetrate into the lower gas stream due to the superamphiphobic nature of the silicon nanowires built into the bottom wall, thereby preserving the integrity of continuous gas and liquid streams, although they are flowing in contact. Due to the superamphiphobic nature of silicon nanowires, the microsystem provides the best possible interfacial mass transfer known to date between flowing gas and liquid phases, which can achieve excellent chemical performance in two-phase organic syntheses. © 2015 American Chemical Society.


Deng Z.J.,National University of Defense Technology | Deng Z.J.,Beijing Computational Science Research Center | Li Y.,Beijing Computational Science Research Center | Gao M.,National University of Defense Technology | Wu C.W.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Cooling mechanical resonators to a quantum regime at high temperatures is important in terms of exploring and applying their quantum effects unrestricted by low environmental temperatures. It has been suggested by M. Bhattacharya that quadratic coupling could be used to help cool a membrane in membrane-in-the-middle optomechanical systems (MMOSs) at room temperature to a state with a mean phonon number smaller than 1. Its cooling effect is actually overestimated because of the unconsidered factor that it is limited by the small frequency difference between the quadratically coupled cavity mode and its neighboring mode, which imposes an upper bound on the input trapping laser power and therefore restricts its cooling effect. Based on the MMOS and by taking the above factors into consideration, we have concretely investigated the performance of this cooling method by a more rigorous calculation. Our calculation shows that the cooling effect is indeed ultimately limited by the input trapping laser power, but one can still cool a membrane close to a quantum regime at 77 K with parameters approaching experimental values. © 2012 American Physical Society.


Dong D.,National University of Defense Technology | Li M.,Nanyang Technological University | Liu Y.,Tsinghua University | Liu Y.,Hong Kong University of Science and Technology | And 2 more authors.
IEEE/ACM Transactions on Networking | Year: 2011

Wormhole attack is a severe threat to wireless ad hoc and sensor networks. Most existing countermeasures either require specialized hardware devices or make strong assumptions on the network in order to capture the specific (partial) symptom induced by wormholes. Those requirements and assumptions limit the applicability of previous approaches. In this paper, we present our attempt to understand the impact and inevitable symptom of wormholes and develop distributed detection methods by making as few restrictions and assumptions as possible. We fundamentally analyze the wormhole problem using a topology methodology and propose an effective distributed approach, which relies solely on network connectivity information, without any requirements on special hardware devices or any rigorous assumptions on network properties. We formally prove the correctness of this design in continuous geometric domains and extend it into discrete domains. We evaluate its performance through extensive simulations. © 2011 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.


Chen Z.-Y.,National University of Defense Technology | Cattani C.,University of Salerno | Zhong W.-P.,China University of Mining and Technology
Advances in Mathematical Physics | Year: 2014

From the signal processing point of view, the nondifferentiable data defined on the Cantor sets are investigated in this paper. The local fractional Fourier series is used to process the signals, which are the local fractional continuous functions. Our results can be observed as significant extensions of the previously known results for the Fourier series in the framework of the local fractional calculus. Some examples are given to illustrate the efficiency and implementation of the present method. © 2014 Zhi-Yong Chen et al.


Zhang Y.,National University of Defense Technology | Chen L.,Hong Kong University of Science and Technology | Lu X.,National University of Defense Technology | Li D.,National University of Defense Technology
IEEE Journal on Selected Areas in Communications | Year: 2010

DHTs are scalable, self-organizing, and adaptive to underlying topology changes, thus being a promising infrastructure for realizing autonomic communications in distributed systems. To provide the above advantages, however, DHTs sacrifice flexibility, that is, all messages are routed by using a common algorithm in a DHT on the assumption that all participant nodes are homogeneous. In practice, nodes in largescale systems might be heterogeneous with respect to their capabilities, reputations, affiliations of administrative domains, and so on, which consequently makes it preferable to distinguish the heterogeneity of participant nodes and enable flexible control of routing destinations and paths. To achieve this, in this paper we propose a novel approach that supports organizing nodes into groups and enables routing control in a DHT. The effectiveness of our proposals is demonstrated through theoretical analysis and extensive simulations. © 2010 IEEE.


Chen T.,Bioinformatics Group | Chen L.,Hong Kong University of Science and Technology | Ozsu M.T.,University of Waterloo | Xiao N.,National University of Defense Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2013

Query processing over uncertain data streams, in particular top-k query processing, has become increasingly important due to its wide application in many fields such as sensor network monitoring and internet traffic control. In many real applications, multiple top-k queries are registered in the system. Sharing the results of these queries is a key factor in saving the computation cost and providing real-time response. However, due to the complex semantics of uncertain top-k query processing, it is nontrivial to implement sharing among different top-k queries and few works have addressed the sharing issue. In this paper, we formulate various types of sharing among multiple top-k queries over uncertain data streams based on the frequency upper bound of each top-k query. We present an optimal dynamic programming solution as well as a more efficient (in terms of time and space complexity) greedy algorithm to compute the execution plan of executing queries for saving the computation cost between them. Experiments have demonstrated that the greedy algorithm can find the optimal solution in most cases, and it can almost achieve the same performance (in terms of latency and throughput) as the dynamic programming approach. © 2012 IEEE.


He H.,University of Rhode Island | Chen S.,Stevens Institute of Technology | Li K.,Queen's 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.


Li W.,National University of Defense Technology | Ghogho M.,University of Leeds | Ghogho M.,International University of Rabat | Chen B.,National University of Defense Technology | Xiong C.,National University of Defense Technology
IEEE Communications Letters | Year: 2012

A novel approach for ensuring confidential wireless communication is proposed and analyzed from an information-theoretic standpoint. In this approach, the legitimate receiver generates artificial noise (AN) to impair the intruder's channel. This method is robust because it does not need the feedback of channel state information (CSI) to the transmitter and does not assume that the number of Eve's antennas should be smaller than that of Bob. Furthermore, we propose a new concept of outage secrecy region to evaluate the secrecy performance from a geometrical perspective. This should be useful if we need to know what zone should be protected (or militarized). Analysis and simulation results in practical environments show that the proposed method has a good performance. © 2012 IEEE.


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."


Fu J.,Wuhan University of Technology | Cao S.,Wuhan University of Technology | Yu J.,Wuhan University of Technology | Yu J.,King Abdulaziz University | And 2 more authors.
Dalton Transactions | Year: 2014

Photocatalytic reduction of CO2 into renewable hydrocarbon fuels using semiconductor photocatalysts is considered as a potential solution to the energy deficiency and greenhouse effect. In this work, mesoporous TiO 2 nanofibers with high specific surface areas and abundant surface hydroxyl groups are prepared using an electrospinning strategy combined with a subsequent calcination process, followed by a solvothermal treatment. The solvothermally treated mesoporous TiO2 nanofibers exhibit excellent photocatalytic performance on CO2 reduction into hydrocarbon fuels. The significantly improved photocatalytic activity can be attributed to the enhanced CO2 adsorption capacity and the improved charge separation after solvothermal treatment. The highest activity is achieved for the sample with a 2-h solvothermal treatment, showing 6- and 25-fold higher CH4 production rate than those of TiO2 nanofibers without solvothermal treatment and P25, respectively. This work may also provide a prototype for studying the effect of solvothermal treatment on the structure and photocatalytic activity of semiconductor photocatalysts. © the Partner Organisations 2014.


Dang Z.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Zhang Y.,Tsinghua University
Advances in Space Research | Year: 2013

Navigation sharing among distributed satellites is quite important for coordinated motion and collision avoidance. This paper proposes optimization methods of the communication network topology to achieve navigation sharing. The whole communication network constructing by inter-satellite links are considered as a topology graph. The aim of this paper is to find the communication network topology with minimum communication connections' number (MCCN) in different conditions. It has found that the communication capacity and the number of channels are two key parameters affecting the results. The model of MCCN topology for navigation sharing is established and corresponding method is designed. Two main scenarios, viz., homogeneous case and heterogeneous case, are considered. For the homogeneous case where each member has the same communication capacity, it designs a construction method (Algorithm 1) to find the MCCN topology. For the heterogeneous case, it introduces a modified genetic algorithm (Algorithm 2) to find the MCCN topology. When considering the fact that the number of channels is limited, the Algorithm 2 is further modified by adding a penalized term in the fitness function. The effectiveness of these algorithms is all proved in theoretical. Three examples are further tested to illustrate the methods developed in this paper. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.


Li L.,Tsinghua University | Wen D.,National University of Defense Technology | Zheng N.-N.,Xi'an Jiaotong University | Shen L.-C.,National University of Defense Technology
IEEE Transactions on Intelligent Transportation Systems | Year: 2012

This paper provides a survey of recent works on cognitive cars with a focus on driver-oriented intelligent vehicle motion control. The main objective here is to clarify the goals and guidelines for future development in the area of advanced driver-assistance systems (ADASs). Two major research directions are investigated and discussed in detail: 1) stimuli-decisions-actions, which focuses on the driver side, and 2) perception enhancement-action-suggestion- function-delegation, which emphasizes the ADAS side. This paper addresses the important achievements and major difficulties of each direction and discusses how to combine the two directions into a single integrated system to obtain safety and comfort while driving. Other related topics, including driver training and infrastructure design, are also studied. © 2011 IEEE.


Chen F.,National University of Defense Technology | Zhou J.,Tsinghua University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Conventional algorithms for fingerprint recognition are mainly based on minutiae information. However, the small number of minutiae in partial fingerprints is still a challenge in fingerprint matching. In fingerprint recognition systems, there are frequently appeared partial fingerprints, such as incompletely touching in fingerprint scanning or latent fingerprints. In this paper, we studied the influence of the fingerprint area in partial fingerprint recognition. First, a simulation scheme was proposed to construct a serial of partial fingerprints with different area. Then, the influence of the fingerprint area in partial fingerprint recognition is studied. By comparing the performance of partial fingerprint recognition with different fingerprint area, some useful conclusions can be drawn: (1) The decrease of the fingerprint area degrades the performance of partial fingerprint recognition; (2) When the fingerprint area decreases, the genuine matching scores will decrease, whereas the imposter matching scores will increase; (3) When the area of partial fingerprints is smaller than 20,000 pixels (about fifth of the normal full fingerprints), the performance of partial fingerprint recognition becomes very poor; (4) The threshold value of a given false accept rate increases when the area of partial fingerprints decrease a lot, but it remains almost the same if the area of partial fingerprints decrease not so much, e.g., greater than 50,000 pixels (about half of the normal full fingerprint). These observations can be helpful in improving the performance of partial fingerprint recognition in the future. © 2012 Springer-Verlag.


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.


Cui C.-Y.,Military School of Engineering | Liu Y.-L.,National University of Defense Technology | Huang M.-Q.,National University of Defense Technology
European Physical Journal C | Year: 2013

We investigate whether the newly observed narrow resonance Zc(4025) can be described as a D*D̄* molecular state with quantum numbers JP=1+. Using QCD sum rules, we consider contributions up to dimension six in the operator product expansion and work at leading order of αs. The mass obtained for this state is (4.05±0.28) GeV. It is concluded that the D*D̄* molecular state is a possible candidate for Zc(4025). © 2013 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica.


Hou C.,National University of Defense Technology | Nie F.,University of Texas at Arlington | Zhang C.,Tsinghua University | Yi D.,National University of Defense Technology | Wu Y.,National University of Defense Technology
Pattern Recognition | Year: 2014

Matrices, or more generally, multi-way arrays (tensors) are common forms of data that are encountered in a wide range of real applications. How to classify this kind of data is an important research topic for both pattern recognition and machine learning. In this paper, by analyzing the relationship between two famous traditional classification approaches, i.e., SVM and STM, a novel tensor-based method, i.e., multiple rank multi-linear SVM (MRMLSVM), is proposed. Different from traditional vector-based and tensor based methods, multiple-rank left and right projecting vectors are employed to construct decision boundary and establish margin function. We reveal that the rank of transformation can be regarded as a tradeoff parameter to balance the capacity of learning and generalization in essence. We also proposed an effective approach to solve the proposed non-convex optimization problem. The convergence behavior, initialization, computational complexity and parameter determination problems are analyzed. Compared with vector-based classification methods, MRMLSVM achieves higher accuracy and has lower computational complexity. Compared with traditional supervised tensor-based methods, MRMLSVM performs better for matrix data classification. Promising experimental results on various kinds of data sets are provided to show the effectiveness of our method. © 2013 Elsevier Ltd. All rights reserved.


Liu Y.-L.,National University of Defense Technology | Cui C.-Y.,Military School of Engineering | Huang M.-Q.,National University of Defense Technology
European Physical Journal C | Year: 2014

The improved light-cone distribution amplitudes (LCDAs) of the Λ baryon are examined on the basis of the QCD conformal partial wave expansion approach. The calculations are carried out to the next-to-leading order of conformal spin accuracy with consideration of twist 6. The next leading order conformal expansion coefficients are related to the nonperturbative parameters defined by the local three-quark operator matrix elements with different Lorentz structures with a covariant derivative. The nonperturbative parameters are determined with the QCD sum rule method. The explicit expressions of the LCDAs are provided as the main results. © 2014, The Author(s).


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.


Chen W.,Tsinghua University | Chen W.,National University of Defense Technology | Zhang S.,Tsinghua University | Long X.,National University of Defense Technology
Optics Letters | Year: 2012

Internal stress in material detracts from its usefulness. In this Letter, a stress measurement instrument is reported. The instrument principle is based on a laser feedback effect where the polarization state of the laser with an anisotropic feedback cavity will flip between two orthogonal directions, while the feedback mirror is tuned by piezoelectric transducer sawtooth voltage. The position of polarization flipping in one period on curves reflects the birefringence or material internal stress of the feedback cavity. Hence, when a piece of internal stress material is placed in a feedback cavity, its internal stress can be measured by the polarization flipping position. The internal stress of the vacuum tube, Nd:YAG crystal, and GaN semiconductor are measured, which proved this instrument has very high precision. © 2012 Optical Society of America.


Tao C.-A.,National University of Defense Technology | Wang J.,National University of Defense Technology | Qin S.,National University of Defense Technology | Lv Y.,Hunan Normal University | And 3 more authors.
Journal of Materials Chemistry | Year: 2012

A novel graphene oxide (GO)-based hydrogel with drug molecules as crosslinking agents was fabricated. Metformin hydrochloride (MFH), which has no aromatic groups, but only has N-containing functionalities, was chosen as a model drug. When a very small amount of MFH was introduced into a GO solution, a supramolecular assembled hydrogel was rapidly formed without any polymers or chemical additives. The gelation process can be influenced by the weight ratio of MFH to GO. The driving forces were hydrogen bonding and electrostatic attraction. Both air-dried and freeze-dried samples of GO-MFH hydrogels were utilized for controlled drug release in water (pH = 7) and hydrochloric acid (pH = 1, 3 and 5). The release mechanism of capsulated MFH was Fickian diffusion according to the fitted results. Both the freeze-dried and air-dried samples released around 74% of the MFH in a strongly acidic medium after 70 h, but only 50% in a neutral solution. This pH-sensitivity makes it a potential candidate for the controlled release of drugs in the acidic environment of the stomach. © The Royal Society of Chemistry 2012.


Huang Z.-P.,National University of Defense Technology | Huang Z.-P.,CAS Institute of Theoretical Physics | Wu Y.-L.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The observed acceleration of the present Universe is shown to be well explained by the holographic dark energy characterized by the total comoving horizon of the Universe (ηHDE). It is of interest to notice that the very large primordial part of the comoving horizon generated by the inflation of the early Universe makes the ηHDE behave like a cosmological constant. As a consequence, both the fine-tuning problem and the coincidence problem can reasonably be understood with the inflationary universe and holographical principle. We present a systematic analysis and obtain a consistent cosmological constraint on the ηHDE model based on the recent cosmological observations. It is found that the ηHDE model gives the best-fit result Ω m0=0.270 (Ω de0=0.730) and the minimal χmin2=542.915 which is compatible with χΛCDM2=542.919 for the ΛCDM model. © 2012 American Physical Society.


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

An instrument for angle measurement based on laser feedback has been designed. The measurement technique is based on the principle that when a wave plate placed into a feedback cavity rotates, its phase retardation varies. Phase retardation is a function of the rotating angle of the wave plate. Hence, the angle can be converted to phase retardation. The phase retardation is measured at certain characteristic points identified in the laser outputting curve that are then modulated by laser feedback. The angle of a rotating object can be measured if it is connected to the wave plate. The main advantages of this instrument are: high resolution, compact, flexible, low cost, effective power, and fast response. © 2013 Optical Society of America.


Dang Z.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Zhang Y.,Tsinghua University
Acta Astronautica | Year: 2011

Inner-Formation Gravity Measurement Satellite System (IFGMSS) is used to map the gravity field of the Earth. The IFGMSS consists of two satellites, in which one is the inner satellite; the other is the outer satellite. The inner satellite flies in the cavity of the outer satellite and is affected only by the Earth gravitational force. To detect the relative position of the inner satellite in real time, it has suggested an optical scheme to observe the mass center of the inner satellite. This paper describes a modified Unscented Kalman Filter (UKF) algorithm to estimate the relative motion between inner satellite and outer satellite. An integrated relative rotational and translational dynamics is constructed when the outer satellite tracking the inner satellite. Particular attention is given to the nonlinearity due to the coupled dynamics between the translational and rotational motion equations. Simulation results are presented in order to validate the proposed estimation scheme with and without control. Three different scenarios are simulated to validate the effectiveness of this approach. And the results showed that the estimation accuracy is affected by the nonlinearity of the dynamics. Through analysis, the proposed estimation algorithm is able to provide high accurate relative attitude and position estimation for the IFGMSS. © 2011 Elsevier Ltd.


Zhang J.-R.,National University of Defense Technology | Zhong M.,National University of Defense Technology | Zhong M.,CAS Institute of Theoretical Physics | Huang M.-Q.,National University of Defense Technology
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

Assuming the newly observed structure Zb(10610) as a bottomonium-like molecular state B *B̄, we calculate its mass in the framework of QCD sum rules. The numerical result is 10.54±0.22 GeV for B *B̄, which coincide with the mass of Zb(10610). This consolidates the statement made by Belle Collaboration that the Zb(10610) resonance could be a B *B̄ molecular state. © 2011 Elsevier B.V.


Liu Y.-L.,National University of Defense Technology | Cui C.-Y.,Military School of Engineering | Huang M.-Q.,National University of Defense Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The light-cone distribution amplitudes (LCDAs) of the Σ± baryons up to twist-6 are investigated on the basis of the QCD conformal partial wave expansion approach. The calculations are carried out to the next-to-leading order of conformal spin accuracy. The nonperturbative parameters relevant to the LCDAs are determined in the framework of the QCD sum rule method. The explicit expressions of the LCDAs are given as the main results. © 2014 American Physical Society.


Wang P.,National University of Defense Technology | Wang P.,University of Heidelberg | Reinelt G.,University of Heidelberg | Gao P.,National University of Defense Technology | Tan Y.,National University of Defense Technology
Computers and Industrial Engineering | Year: 2011

China plans to launch four small optical satellites and four small SAR satellites to form a natural disaster monitoring constellation. Data can be obtained by the constellation in all weather conditions for disaster alert and environmental damage analysis. The scheduling problem for the constellation consists of selecting and timetabling the observation activities to acquire the requested images of the earth surface and scheduling the download activities to transmit the image files to a set of ground stations. The scheduling problem is required to be solved every day in a typical 1-day horizon and it must respect complex satellite operational constraints as well as request preferences, such as visibility time windows, transition time between consecutive observations or downloads, memory capacity, energy capacity, polygon target requests and priorities. The objective is to maximize the rewards of the images taken and transmitted. We present a nonlinear model of the scheduling problem, develop a priority-based heuristic with conflict-avoided, limited backtracking and download-as-needed features, which produces satisfactory feasible plans in a very short time. A decision support system based on the model and the heuristic is also provided. The system performance shows a significant improvement with respect to faster and better scheduling of an earth observing satellite constellation. © 2010 Elsevier Ltd. All rights reserved.


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.


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.


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.


Chen S.-W.,National University of Defense Technology | Chen S.-W.,Tohoku University | Wang X.-S.,National University of Defense Technology | Li Y.-Z.,National University of Defense Technology | Sato M.,Tohoku University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

The overestimation of volume scattering power and the scattering mechanism ambiguity are still present in model-based decompositions even with the implementation of the deorientation processing. These effects are demonstrated and investigated. One possible reason is because of the limited dynamic range of the models themselves that are not fully satisfied for the mixed scene cases. An empirical volume scattering model is proposed, using the repeat-pass polarimetric synthetic aperture radar interferometry (PolInSAR) coherence, to extend the model dynamic range to be more adaptive. PolInSAR coherence is sensitive to different types of forests and terrains. The proposed model inherits these characteristics. In addition, it considers the cross-polarization power induced by oriented man-made structures. Thereby, a model-based polarimetric decomposition scheme is developed. The efficiency of the proposed method is demonstrated using E-SAR airborne and ALOS/PALSAR spaceborne repeat-pass PolInSAR datasets. Comparative experiments are carried out and show that the proposed decomposition overcomes the scattering mechanism ambiguity between forests and oriented built-up areas, since it successfully identifies the oriented buildings as double-or odd-bounce man-made structures while keeping the volume scattering dominant for the forests. Besides, the stable decomposition performance over the oriented built-up patches with quite different orientation angles also validates the improvement of the proposed decomposition. In addition, the demonstrations with short and long temporal baselines validate the generality of the proposed method. © 2013 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.


Chen S.-W.,National University of Defense Technology | Chen S.-W.,Tohoku University | Wang X.-S.,National University of Defense Technology | Xiao S.-P.,National University of Defense Technology | Sato M.,Tohoku University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

Orientation angle compensation was incorporated into model-based decomposition to cure overestimation of the volume scattering contribution for interpretation of polarimetric synthetic aperture radar (PolSAR) data. The compensation is based on rotating the coherency matrix to minimize the cross-polarization term. However, this processing cannot always guarantee that the double-and odd-bounce scattering components will be rotated back to zero orientation angle and left with zero cross-polarization power. As a result, built-up patches with large orientation angles may still suffer from the scattering mechanism ambiguity. In this paper, double-and odd-bounce scattering models were generalized to fit the cross-polarization and off-diagonal terms, by separating their independent orientation angles. A general decomposition framework is proposed that utilizes all elements of a coherency matrix. The residual minimization criterion is used for model inversion. All the model parameters are simultaneously obtained using a nonlinear least squares optimization technique. The manual intervention, branch conditions, and negative power issues are avoided. The performance and advantages of this approach are demonstrated and evaluated with spaceborne L-band ALOS/PALSAR and airborne X-band Pi-SAR PolSAR data sets. Comparison studies are also carried out and demonstrate that further improved decomposition performance is achieved by the proposed method, especially in oriented built-up areas. © 2013 IEEE.


Wang X.,National University of Defense Technology | Luo J.,National University of Defense Technology | Liu Y.,Tsinghua University | Li S.,National University of Defense Technology | Dong D.,National University of Defense Technology
IEEE/ACM Transactions on Networking | Year: 2011

Localization is crucial for wireless ad hoc and sensor networks. As the distance-measurement ranges are often less than the communication ranges for many ranging systems, most communication-dense wireless networks are localization-sparse. Consequently, existing algorithms fail to provide accurate localization supports. In order to address this issue, by introducing the concept of component, we group nodes into components so that nodes are able to better share ranging and anchor knowledge. Operating on the granularity of components, our design, CALL, relaxes two essential restrictions in localization: the node ordering and the anchor distribution. Compared to previous designs, CALL is proven to be able to locate the same number of nodes using the least information. We evaluate the effectiveness of CALL through extensive simulations. The results show that CALL locates 90% nodes in a network with average degree 7.5 and 5% anchors, which outperforms the state-of-the-art design Sweeps by about 40%. © 2006 IEEE.


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.


Chen S.-W.,National University of Defense Technology | Wang X.-S.,National University of Defense Technology | Sato M.,Tohoku University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2014

This paper presents the development of a uniform polarimetric matrix rotation theory in the rotation domain along the radar line of sight for polarimetric synthetic aperture radar (PolSAR) data interpretation. The uniform representation of each coherency matrix element is a sinusoidal function in the rotation domain. A set of oscillation parameters, including oscillation amplitude, oscillation center, angular frequency, and initial angle, is proposed to fully characterize the scattering behavior in the rotation domain. A set of rotation angle parameters, including stationary angle, null angle, and minimization/maximization angles, is derived to indicate specific states of the rotation property. The rotation relationships between the coherency and covariance matrices with linear and circular polarization bases are established. A look-up table for these parameters is provided, and their physical meanings are interpreted. These derived parameters directly link to the Huynen parameters. Therefore, the proposed theory has the ability to achieve a desired state of one Huynen parameter by rotating the polarimetric matrix at a designated rotation angle. This theory also generalizes both the classic polarization orientation angle originally derived from the covariance matrix in a circular polarization basis and the deorientation theory developed from the minimization of the cross-polarization term. The roll-invariant terms have also been summarized. Finally, multifrequency Pi-SAR and AIRSAR PolSAR data sets are used to demonstrate the derived parameters. One oscillation amplitude parameter has been verified to be especially suitable for characterization of oriented man-made targets. Two angle parameters are sensitive to the reflection symmetry condition and crop types. Therefore, a simple unsupervised classification scheme has been developed and demonstrated. Further utilization perspectives of the proposed theory have been discussed. © 2013 IEEE.


Du X.,National University of Defense Technology | Cheng L.,National University of Defense Technology | Chen D.,Military School of Engineering
Neurocomputing | Year: 2014

This paper addresses the sparse recovery problem by l0 minimization, which is of central importance in the compressed sensing theory. We model the problem as a combinatorial optimization problem and present a novel algorithm termed SASR based on simulated annealing (SA) and some greedy pursuit (GP) algorithms. In SASR, the initial solution is designed using the simple thresholding algorithm, and the generating mechanism is designed using the strategies existed in the subspace pursuit algorithm and the compressed sampling matching pursuit algorithm. On both the random Gaussian data and the face recognition task, the numerical simulation results illustrate the efficiency of SASR. Compared with the existing sparse recovery algorithms, SASR is more efficient in finding global optimums and performs relatively fast in some good cases. That is, SASR inherits the advantage of SA in finding global optimums and the advantage of GP in fast speed to some extent. © 2013 Elsevier B.V.


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.


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.


Wu G.,National University of Defense Technology | Dou Y.,National University of Defense Technology | Sun J.,Marvell Semiconductor Inc. | Peterson G.D.,University of Tennessee at Knoxville
IEEE Transactions on Computers | Year: 2012

LU decomposition for dense matrices is an important linear algebra kernel that is widely used in both scientific and engineering applications. To efficiently perform large matrix LU decomposition on FPGAs with limited local memory, a block LU decomposition algorithm on FPGAs applicable to arbitrary matrix size is proposed. Our algorithm applies a series of transformations, including loop blocking and space-time mapping, onto sequential nonblocking LU decomposition. We also introduce a high performance and memory efficient hardware architecture, which mainly consists of a linear array of processing elements (PEs), to implement our block LU decomposition algorithm. Our design can achieve optimum performance under various hardware resource constraints. Furthermore, our algorithm and design can be easily extended to the multi-FPGA platform by using a block-cyclic data distribution and inter-FPGA communication scheme. A total of 36 PEs can be integrated into a Xilinx Virtex-5 XC5VLX330 FPGA on our self-designed PCI-Express card, reaching a sustained performance of 8.50 GFLOPS at 133 MHz for a matrix size of 16,384, which outperforms several general-purpose processors. For a Xilinx Virtex-6 XC6VLX760, a newer FPGA, we predict that a total of 180 PEs can be integrated, reaching 70.66 GFLOPS at 200 MHz. Compared to the previous work, our design can integrate twice the number of PEs into the same FPGA and has significantly higher performance. © 2012 IEEE.


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.


Dang Z.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Zhang Y.,Tsinghua University
Advances in Space Research | Year: 2012

Inner-Formation Gravity Measurement Satellite System (IFGMSS) is used to map the gravity field of Earth. The IFGMSS consists of two satellites in which one is called "inner satellite" and the other one is named as "outer satellite". To measure the pure Earth gravity, the inner satellite is located in the cavity of the outer satellite. Because of the shield effect of the cavity, the inner satellite is affected only by the gravitational force, so it can sense Earth gravity precisely. To avoid the collision between the inner satellite and the outer satellite, it is best to perform a real-time control on the outer satellite. In orbit, the mass of the outer satellite decreases with the consumption of its propellant. The orbit angular rate of the inner satellite varies with time due to various disturbing forces. These two parameters' uncertainties make the C-W function be not so accurate to describe the formation behavior of these two satellites. Furthermore, the thrusters also have some uncertainties due to the unmodelled dynamics. To cancel the effects caused by the above uncertainties, we have studied the robust control method based on the μ-synthesis. This μ-synthesis eliminates the conservativeness and improves the control efficiency comparing with the H ∞ method. Finally, to test the control method, we simulate an IFGMSS mission in which the satellite runs in a sun synchronous circular orbit with an altitude of 300 km. The simulation results show the effectiveness of the robust control method. The performances of the closed-loop system with the μ-controller are tested by the μ-analysis. It has found that the nominal performance, the robust stability and the robust performance are all achieved. The transient simulation results further prove the control response is fast and the accuracy of the relative position meets the demand of the gravity measurement. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.


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.


News Article | November 16, 2015
Site: www.scientificcomputing.com

For the sixth consecutive time, Tianhe-2, a supercomputer developed by China’s National University of Defense Technology, has maintained its position as the world’s No. 1 system, according to the 46th edition of the twice-yearly TOP500 list of the world’s most powerful supercomputers. Overall, change at the top of the list is again minor, with only two new systems in the Top 10: #6: the Trinity supercomputer built by Cray and jointly deployed by the Department of Energy’s (DOE) Los Alamos and Sandia national laboratories #8: the Hazel-Hen system built by Cray and installed at the HLRS - Höchstleistungsrechenzentrum Stuttgart in Germany In the bigger picture, China nearly tripled the number of systems on the latest list, while the number of systems in the United States has fallen to the lowest point since the TOP500 list was created in 1993. China is also carving out a bigger share as a manufacturer of high performance computers with multiple Chinese manufacturers becoming more active in this field. Tianhe-2, which means Milky Way-2, led the list with a performance of 33.86 petaflop/s (quadrillions of calculations per second or Pflop/s) on the Linpack benchmark. Keeping its hold on the No. 2 spot is Titan, a Cray XK7 system installed at DOE’s Oak Ridge National Laboratory. Titan, the top system in the United States and one of the most energy-efficient systems on the list, achieved 17.59 petaflop/s on the Linpack benchmark. The only new entries in the Top 10 supercomputers on the latest list are Trinity and Hazel-Hen. Six of the Top 10 systems were installed in 2011 or 2012, Tianhe-2 in 2013 and only Trinity, Hazel-Hen, and Shaheen II in Saudi Arabia were installed in 2015. This low level of turnover among the top supercomputers reflects a slowing trend that began in 2008. For more information about the sites and systems in the list, click on the links or view the complete list.


Xing L.-N.,National University of Defense Technology | Rohlfshagen P.,University of Birmingham | Chen Y.-W.,National University of Defense Technology | Yao X.,University of Birmingham
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2011

The capacitated arc routing problem (CARP) is representative of numerous practical applications, and in order to widen its scope, we consider an extended version of this problem that entails both total service time and fixed investment costs. We subsequently propose a hybrid ant colony optimization (ACO) algorithm (HACOA) to solve instances of the extended CARP. This approach is characterized by the exploitation of heuristic information, adaptive parameters, and local optimization techniques: Two kinds of heuristic information, arc cluster information and arc priority information, are obtained continuously from the solutions sampled to guide the subsequent optimization process. The adaptive parameters ease the burden of choosing initial values and facilitate improved and more robust results. Finally, local optimization, based on the two-opt heuristic, is employed to improve the overall performance of the proposed algorithm. The resulting HACOA is tested on four sets of benchmark problems containing a total of 87 instances with up to 140 nodes and 380 arcs. In order to evaluate the effectiveness of the proposed method, some existing capacitated arc routing heuristics are extended to cope with the extended version of this problem; the experimental results indicate that the proposed ACO method outperforms these heuristics. © 2011 IEEE.


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.


Wang Z.,University of Bath | Wang Z.,National University of Defense Technology | Belardi W.,University of Bath | Yu F.,University of Bath | And 2 more authors.
Optics Express | Year: 2014

We report 3.1-3.2 μm mid-infrared emission from acetylene-filled low loss antiresonant hollow-core fiber pumped with an amplified, modulated, narrowband, tunable 1.5 μm diode laser. The maximum power conversion efficiency of ∼30%, with respect to the absorbed pump power, is obtained with a 10.5 m length of fiber at 0.7 mbar. The maximum efficiency with respect to the total incident pump power (∼20%) and the minimum pump laser energy required (<50 nJ) are both improved compared to similar work reported previously using an optical parametric oscillator as a pump source. This paper provides an effective route to obtain compact mid-infrared fiber lasers. ©2014 Optical Society of America.


Qin J.,Australian National University | Yu C.,Australian National University | Gao H.,Harbin Institute of Technology | Wang X.,National University of Defense Technology
Proceedings of the IEEE Conference on Decision and Control | Year: 2011

This paper investigates the leaderless consensus control problem for a group of agents under fixed or switching directed interaction topology, where each agent is modeled as a generic linear system rather than the single- or double-integrator dynamics. For the case with fixed topology, it is shown that consensus can be reached by assigning an appropriate feedback matrix if the interaction topology has a directed spanning tree; while for the switching case, by imposing the balanced condition on the interaction topology, sufficient conditions are provided for the agents to reach consensus under arbitrary switching signal. Furthermore, the consensus equilibria are specified for both cases. © 2011 IEEE.


Feng J.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Jiang Y.,National University of Defense Technology | Zhao N.,Northwest Institute of Nuclear Technology
ACS Applied Materials and Interfaces | Year: 2011

Carbon fiber-reinforced carbon aerogel composites (C/CAs) for thermal insulators were prepared by copyrolysis of resorcinol-formaldehyde (RF) aerogels reinforced by oxidized polyacrylonitrile (PAN) fiber felts. The RF aerogel composites were obtained by impregnating PAN fiber felts with RF sols, then aging, ethanol exchanging, and drying at ambient pressure. Upon carbonization, the PAN fibers shrink with the RF aerogels, thus reducing the difference of shrinkage rates between the fiber reinforcements and the aerogel matrices, and resulting in C/CAs without any obvious cracks. The three point bend strength of the C/CAs is 7.1 ± 1.7 MPa, and the thermal conductivity is 0.328 W m -1 K -1 at 300 °C in air. These composites can be used as high-temperature thermal insulators (in inert atmospheres or vacuum) or supports for phase change materials in thermal protection system. © 2011 American Chemical Society.


Zhang Q.,National University of Defense Technology | Antoniou M.,University of Birmingham | Chang W.,National University of Defense Technology | Cherniakov M.,University of Birmingham
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015

This paper analyzes the spatial decorrelation between repeat-pass bistatic synthetic aperture radar (BSAR) images with Global Navigation Satellite Systems as transmitters and a fixed receiver. This study is needed in the development of such a system to monitor temporal changes in a scene. The main challenge is that, in this bistatic configuration, spatial coherence heavily depends on the data acquisition geometry. The appropriate theoretical framework to describe spatial coherence for this case is developed by extending well-established monostatic models and, in principle, can be applied to any fixed-receiver BSAR with a spaceborne transmitter. Theoretical results are initially supported by Monte Carlo simulations. Finally, the validity of the model is confirmed by comparing real images. © 2014 IEEE.


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 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.


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.


Xing L.,National University of Defense Technology | Rohlfshagen P.,University of Birmingham | Chen Y.,National University of Defense Technology | Yao X.,University of Birmingham
IEEE Transactions on Evolutionary Computation | Year: 2010

The capacitated arc routing problem (CARP) is a challenging vehicle routing problem with numerous real world applications. In this paper, an extended version of CARP, the multidepot capacitated arc routing problem (MCARP), is presented to tackle practical requirements. Existing CARP heuristics are extended to cope with MCARP and are integrated into a novel evolutionary framework: the initial population is constructed either by random generation, the extended random path-scanning heuristic, or the extended random Ulusoy's heuristic. Subsequently, multiple distinct operators are employed to perform selection, crossover, and mutation. Finally, the partial replacement procedure is implemented to maintain population diversity. The proposed evolutionary approach (EA) is primarily characterized by the exploitation of attributes found in near-optimal MCARP solutions that are obtained throughout the execution of the algorithm. Two techniques are employed toward this end: the performance information of an operator is applied to select from a range of operators for selection, crossover, and mutation. Furthermore, the arc assignment priority information is employed to determine promising positions along the genome for operations of crossover and mutation. The EA is evaluated on 107 instances with up to 140 nodes and 380 arcs. The experimental results suggest that the integrated evolutionary framework significantly outperforms these individual extended heuristics. © 2006 IEEE.


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..


Wei D.,National University of Defense Technology | Wei D.,University of Zürich | Wang T.,National University of Defense Technology | Wang J.,National Laboratory for Parallel and Distributed Processing | Bernstein A.,University of Zürich
Journal of Web Semantics | Year: 2011

As the number of publicly available services grows, discovering proper services becomes an important issue and has attracted amount of attempts. This paper presents a new customizable and effective matchmaker, called SAWSDL-iMatcher. It supports a matchmaking mechanism, named iXQuery, which extends XQuery with various similarity joins for SAWSDL service discovery. Using SAWSDL-iMatcher, users can flexibly customize their preferred matching strategies according to different application requirements. SAWSDL-iMatcher currently supports several matching strategies, including syntactic and semantic matching strategies as well as several statistical-model-based matching strategies which can effectively aggregate similarity values from matching on various types of service description information such as service name, description text, and semantic annotation. Besides, we propose a semantic matching strategy to measure the similarity among SAWSDL semantic annotations. These matching strategies have been evaluated in SAWSDL-iMatcher on SAWSDL-TC2 and Jena Geography Dataset (JGD). The evaluation shows that different matching strategies are suitable for different tasks and contexts, which implies the necessity of a customizable matchmaker. In addition, it also provides evidence for the claim that the effectiveness of SAWSDL service matching can be significantly improved by statistical-model-based matching strategies. Our matchmaker is competitive with other matchmakers on benchmark tests at S3 contest 2009. © 2011 Elsevier B.V. All rights reserved.


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.


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.


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.


News Article | July 11, 2014
Site: www.techtimes.com

The National Nuclear Security Administration (NNSA) has turned to Cray for a supercomputer that will be used for managing nuclear weapons. Called Trinity, the supercomputer is expected to be one of the world's fastest. In a deal worth $174 million, Cray is being tapped by the US government to create a supercomputer that will let the NNSA manage the country's stockpile of nuclear weapons without resorting to underground testing. When it's built, Trinity will aid the NNSA in keeping the stockpiles safe, secure, and reliable possibly through virtual simulations to test the performance of the weapons. Virtual simulation is necessary because it takes away underground testing without affecting the NNSA's ability to understand how nuclear weapons age and how newly developed weapons will work. It is not clear, however, if Trinity will take part in managing weapons when a nuclear conflict arises. Trinity will be different from the usual high-performance computers used by internet companies such as Facebook and Google because it will be vertically integrated. Internet companies typically parallel processing which breaks computing jobs into small bits to be farmed into multiple commodity servers at the same time. "For certain applications, such as modeling, simulation and certain types of analytics, a vertically integrated system works best. That's because those applications often rely on sequential calculations that must be completed in a certain order," explains Peter Ungaro, Cray CEO. The world's fastest computer at the moment is China's Tianhe-2 located in the National University of Defense Technology. Tianhe-2 is capable of 33.86 petaflops at peak performance. The world's second fastest is US' Titan which the Department of Energy uses at the Oak Ridge National Laboratory. Made by Cray, Titan peaks at 17.59 petaflops. It has not been released how fast Trinity will be once it is made but it is planned to take the top spot for the world's fastest. As part of the NNSA Advanced Simulation and Computing Program, Trinity will entail cooperation between the Los Alamos National Laboratory's New Mexico Alliance for Computing at Extreme Scale and the Sandia National Laboratories. Trinity is scheduled to be delivered mid-2015. It will be at least eight times better compared to Cielo, the current supercomputer that the NNSA uses in Los Alamos.


Liu L.,National University of Defense Technology | Long Y.,National University of Defense Technology | Fieguth P.W.,University of Waterloo | Lao S.,National University of Defense Technology | Zhao G.,University of Oulu
IEEE Transactions on Image Processing | Year: 2014

In this paper, we propose a simple, efficient, yet robust multiresolution approach to texture classification - binary rotation invariant and noise tolerant (BRINT). The proposed approach is very fast to build, very compact while remaining robust to illumination variations, rotation changes, and noise. We develop a novel and simple strategy to compute a local binary descriptor based on the conventional local binary pattern (LBP) approach, preserving the advantageous characteristics of uniform LBP. Points are sampled in a circular neighborhood, but keeping the number of bins in a single-scale LBP histogram constant and small, such that arbitrarily large circular neighborhoods can be sampled and compactly encoded over a number of scales. There is no necessity to learn a texton dictionary, as in methods based on clustering, and no tuning of parameters is required to deal with different data sets. Extensive experimental results on representative texture databases show that the proposed BRINT not only demonstrates superior performance to a number of recent state-of-the-art LBP variants under normal conditions, but also performs significantly and consistently better in presence of noise due to its high distinctiveness and robustness. This noise robustness characteristic of the proposed BRINT is evaluated quantitatively with different artificially generated types and levels of noise (including Gaussian, salt and pepper, and speckle noise) in natural texture images. © 2014 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.


Liu L.,National University of Defense Technology | Zhao L.,National University of Defense Technology | Long Y.,National University of Defense Technology | Kuang G.,National University of Defense Technology | Fieguth P.,University of Waterloo
Image and Vision Computing | Year: 2012

This paper presents a novel approach for texture classification, generalizing the well-known local binary pattern (LBP) approach. In the proposed approach, two different and complementary types of features (pixel intensities and differences) are extracted from local patches. The intensity-based features consider the intensity of the central pixel (CI) and those of its neighbors (NI); while for the difference-based feature, two components are computed: the radial-difference (RD) and the angular-difference (AD). Inspired by the LBP approach, two intensity-based descriptors CI-LBP and NI-LBP, and two difference-based descriptors RD-LBP and AD-LBP are developed. All four descriptors are in the same form as conventional LBP codes, so they can be readily combined to form joint histograms to represent textured images. The proposed approach is computationally very simple: it is totally training-free, there is no need to learn a texton dictionary, and no tuning of parameters. We have conducted extensive experiments on three challenging texture databases (Outex, CUReT and KTHTIPS2b). Outex results show significant improvements over the classical LBP approach, which clearly demonstrates the great power of the joint distributions of these proposed descriptors for gray-scale and rotation invariant texture classification. The proposed method produces the best classification results on KTHTIPS2b, and results comparable to the state-of-the-art on CUReT. © 2012 Elsevier B.V. All rights reserved.


Lv S.,National University of Defense Technology | Zhuang W.,University of Waterloo | Wang X.,National University of Defense Technology | Zhou X.,National University of Defense Technology
Proceedings - IEEE INFOCOM | Year: 2011

Successive interference cancellation (SIC) is an effective way of multipacket reception (MPR) to combat interference in wireless networks. To understand the potential MPR advantages, we study link scheduling in an ad hoc network with SIC at the physical layer. The fact that the links detected sequentially by SIC are correlated at the receiver poses key technical challenges. We characterize the link dependence and propose simultaneity graph (SG) to capture the effect of SIC. Then interference number is defined to measure the interference of a link. We show that scheduling over SG is NP-hard and the maximum interference number bounds the performance of maximal greedy schemes. An independent set based greedy scheme is explored to efficiently construct a maximal feasible schedule. Moreover, with careful selection of link ordering, we present a scheduling scheme that improves the bound. The performance is evaluated by both simulations and measurements in testbed. The throughput gain is on average 40% and up to 120% over IEEE 802.11. The complexity of SG is comparable with that of conflict graph, especially when the network size is not large. © 2011 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.


Liu L.,National University of Defense Technology | Fieguth P.,University of Waterloo | Clausi D.,University of Waterloo | Kuang G.,National University of Defense Technology
Pattern Recognition | Year: 2012

This paper presents a simple, novel, yet very powerful approach for robust rotation-invariant texture classification based on random projection. The proposed sorted random projection maintains the strengths of random projection, in being computationally efficient and low-dimensional, with the addition of a straightforward sorting step to introduce rotation invariance. At the feature extraction stage, a small set of random measurements is extracted from sorted pixels or sorted pixel differences in local image patches. The rotation invariant random features are embedded into a bag-of-words model to perform texture classification, allowing us to achieve global rotation invariance. The proposed unconventional and novel random features are very robust, yet by leveraging the sparse nature of texture images, our approach outperforms traditional feature extraction methods which involve careful design and complex steps. We report extensive experiments comparing the proposed method to six state-of-the-art methods, RP, Patch, LBP, WMFS and the methods of Lazebnik et al. and Zhang et al., in texture classification on five databases: CUReT, Brodatz, UIUC, UMD and KTH-TIPS. Our approach leads to significant improvements in classification accuracy, producing consistently good results on each database, including what we believe to be the best reported results for Brodatz, UMD and KTH-TIPS. © 2011 Elsevier Ltd. All rights reserved.


Chen D.,National University of Defense Technology | Yang W.,University of Manchester | Pan M.,National University of Defense Technology
IEEE Transactions on Instrumentation and Measurement | Year: 2011

Impedance measuring circuits play a crucial role in an electrical impedance tomography system, in which capacitance and resistance need to be measured accurately at a high speed. Several impedance measuring circuits based on phase-sensitive demodulation (PSD) have been designed, tested, and presented in this paper. The measurement error is analyzed, and the mismatch of the measured capacitance and resistance is considered to be the main cause of the measurement error. A new impedance measuring circuit with dual-frequency PSD has been designed to solve this problem. It has been proven by experiment that this circuit can be used to measure both capacitance and resistance with an uncertainty of less than 0.5%. © 2006 IEEE.


Yu T.-P.,Heinrich Heine University Düsseldorf | Yu T.-P.,National University of Defense Technology | Pukhov A.,Heinrich Heine University Düsseldorf | 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.


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.


Huang X.,University of Manchester | Huang X.,National University of Defense Technology | Hu Z.,University of Manchester | Liu P.,National University of Defense Technology
AIP Advances | Year: 2014

This paper proposes a new type of graphene based tunable radar absorbing screen. The absorbing screen consists of Hilbert curve metal strip array and chemical vapour deposition (CVD) graphene sheet. The graphene based screen is not only tunable when the chemical potential of the graphene changes, but also has broadband effective absorption. The absorption bandwidth is from 8.9GHz to 18.1GHz, ie., relative bandwidth of more than 68%, at chemical potential of 0eV, which is significantly wider than that if the graphene sheet had not been employed. As the chemical potential varies from 0 to 0.4eV, the central frequency of the screen can be tuned from 13.5GHz to 19.0GHz. In the proposed structure, Hilbert curve metal strip array was designed to provide multiple narrow band resonances, whereas the graphene sheet directly underneath the metal strip array provides tunability and averagely required surface resistance so to significantly extend the screen operation bandwidth by providing broadband impedance matching and absorption. In addition, the thickness of the screen has been optimized to achieve nearly the minimum thickness limitation for a nonmagnetic absorber. The working principle of this absorbing screen is studied in details, and performance under various incident angles is presented. This work extends applications of graphene into tunable microwave radar cross section (RCS) reduction applications. © 2014 Author(s).


Zhang C.,National University of Defense Technology | Yin J.,National University of Defense Technology | Cai Z.,National University of Defense Technology | Chen W.,California University of Pennsylvania
IEEE Communications Letters | Year: 2010

The existing Random Early Detection (RED) algorithm and its variants are found vulnerable to emerging attacks, especially the Low-rate Denial-of-Service (LDoS) attacks. In this letter we propose a Robust RED (RRED) algorithm to improve the TCP throughput against LDoS attacks. The basic idea behind the RRED is to detect and filter out attack packets before a normal RED algorithm is applied to incoming flows. We conduct a set of simulations to evaluate the performance of the proposed RRED algorithm. The results show that, compared to existing RED-like algorithms, the RRED algorithm nearly fully preserves the TCP throughput in the presence of LDoS attacks. © 2010 IEEE.


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.


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.


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.


Wang D.-W.,Wuhan Radar Academy | Ma X.-Y.,Wuhan Radar Academy | Chen A.-L.,The Academy of Management | Su Y.,National University of Defense Technology
IEEE Transactions on Image Processing | Year: 2010

Imaging a fast maneuvering target has been an active research area in past decades. Usually, an array antenna with multiple elements is implemented to avoid the motion compensations involved in the Inverse synthetic aperture radar (ISAR) imaging. Nevertheless, there is a price dilemma due to the high level of hardware complexity compared to complex algorithm implemented in the ISAR imaging system with only one antenna. In this paper, a wideband multiple-input multiple-output (MIMO) radar system with two distributed arrays is proposed to reduce the hardware complexity of the system. Furthermore, the system model, the equivalent array production method and the imaging procedure are presented. As compared with the classical real aperture radar (RAR) imaging system, there is a very important contribution in our method that the lower hardware complexity can be involved in the imaging system since many additive virtual array elements can be obtained. Numerical simulations are provided for testing our system and imaging method. © 2010 IEEE.


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.


Xu X.,National University of Defense Technology | Lian C.,National University of Defense Technology | Zuo L.,National University of Defense Technology | He H.,University of Rhode Island
IEEE Transactions on Control Systems Technology | Year: 2014

In the past decade, there has been considerable research interest in learning control methods based on reinforcement learning (RL) and approximate dynamic programming (ADP). As an important class of function approximation techniques, kernel methods have been recently applied to improve the generalization ability of RL and ADP methods but most previous works were only based on simulation. This paper focuses on experimental studies of real-time online learning control for nonlinear systems using kernel-based ADP methods. Specifically, the kernel-based dual heuristic programming (KDHP) method is applied and tested on real-time control systems. Two kernel-based online learning control schemes are presented for uncertain nonlinear systems by using simulation data and online sampling data, respectively. Learning control experiments were performed on a single-link inverted pendulum system as well as a double-link inverted pendulum system. From the experimental results, it is shown that both online learning control schemes, either using simulation data or using real sampling data, are effective for approximating near-optimal control policies of nonlinear dynamical systems with model uncertainties. In addition, it is demonstrated that KDHP can achieve better performance than conventional DHP, which uses multilayer perceptron neural networks. © 2013 IEEE.


Zhang Y.,National University of Defense Technology | Zhu H.,Oxford Brookes University
Proceedings - International Computer Software and Applications Conference | Year: 2011

This paper proposes an intelligent broker approach to service composition and collaboration. The broker employs a planner to generate service composition plans according to service usage and workflow knowledge, dynamically searches for services according to the plan, then invokes and coordinates the executions of the selected services at runtime. A prototype called I-Broker has been implemented to support the approach, which can be instantiated by populating the knowledge-base with domain specific knowledge to form domain specific brokers. This paper also reports experiments that evaluate the scalability of the approach. © 2011 IEEE.


Xu X.,National University of Defense Technology | Hou Z.,Beijing Jiaotong University | Lian C.,National University of Defense Technology | He H.,University of Rhode Island
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

In the past decade, adaptive critic designs (ACDs), including heuristic dynamic programming (HDP), dual heuristic programming (DHP), and their action-dependent ones, have been widely studied to realize online learning control of dynamical systems. However, because neural networks with manually designed features are commonly used to deal with continuous state and action spaces, the generalization capability and learning efficiency of previous ACDs still need to be improved. In this paper, a novel framework of ACDs with sparse kernel machines is presented by integrating kernel methods into the critic of ACDs. To improve the generalization capability as well as the computational efficiency of kernel machines, a sparsification method based on the approximately linear dependence analysis is used. Using the sparse kernel machines, two kernel-based ACD algorithms, that is, kernel HDP (KHDP) and kernel DHP (KDHP), are proposed and their performance is analyzed both theoretically and empirically. Because of the representation learning and generalization capability of sparse kernel machines, KHDP and KDHP can obtain much better performance than previous HDP and DHP with manually designed neural networks. Simulation and experimental results of two nonlinear control problems, that is, a continuous-action inverted pendulum problem and a ball and plate control problem, demonstrate the effectiveness of the proposed kernel ACD methods. © 2013 IEEE.


Ni Z.,University of Rhode Island | He H.,University of Rhode Island | Wen J.,Huazhong University of Science and Technology | Xu X.,National University of Defense Technology
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

Goal representation heuristic dynamic programming (GrHDP) is proposed in this paper to demonstrate online learning in the Markov decision process. In addition to the (external) reinforcement signal in literature, we develop an adaptively internal goal/reward representation for the agent with the proposed goal network. Specifically, we keep the actor-critic design in heuristic dynamic programming (HDP) and include a goal network to represent the internal goal signal, to further help the value function approximation. We evaluate our proposed GrHDP algorithm on two 2-D maze navigation problems, and later on one 3-D maze navigation problem. Compared to the traditional HDP approach, the learning performance of the agent is improved with our proposed GrHDP approach. In addition, we also include the learning performance with two other reinforcement learning algorithms, namely {\rm Sarsa}(\lambda) and Q-learning, on the same benchmarks for comparison. Furthermore, in order to demonstrate the theoretical guarantee of our proposed method, we provide the characteristics analysis toward the convergence of weights in neural networks in our GrHDP approach. © 2012 IEEE.


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.


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.


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.


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 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.


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.


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.


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.


Cheng J.,National University of Defense Technology | Cheng J.,University of New South Wales | Yang L.,University of New South Wales | Li Y.,University of New South Wales | Zhang W.,National University of Defense Technology
Physical Communication | Year: 2014

This paper describes an integrated navigation system that can be used for pedestrian navigation in both outdoor and indoor environments. With the aid of Global Positioning System (GPS) positioning solutions, an Inertial Navigation System (INS) can provide stable and continuous outdoor navigation. When moving indoors, WIFI positioning can replace the GPS in order to maintain the integrated system's long-term reliability and stability. On the other hand, the position from an INS can also provide a priori information to aid WIFI positioning. Signal strength-based WIFI positioning is widely used for indoor navigation. A new fingerprinting method is proposed so as to improve the performance of WIFI stand-alone positioning. For pedestrian navigation applications, a step detection method is implemented to constrain the growth of the INS error using an Extended Kalman Filter (EKF). Experiments have been conducted to test this system and the results have demonstrated the feasibility of this seamless outdoor/indoor navigation system. © 2014 Elsevier B.V.


Zhu X.,National University of Defense Technology | Qin X.,Auburn University | Qiu M.,University of Kentucky
IEEE Transactions on Computers | Year: 2011

Fault-tolerant scheduling plays a significant role in improving system reliability of clusters. Although extensive fault-tolerant scheduling algorithms have been proposed for real-time tasks in parallel and distributed systems, quality of service (QoS) requirements of tasks have not been taken into account. This paper presents a fault-tolerant scheduling algorithm called QAFT that can tolerate one node's permanent failures at one time instant for real-time tasks with QoS needs on heterogeneous clusters. In order to improve system flexibility, reliability, schedulability, and resource utilization, QAFT strives to either advance the start time of primary copies and delay the start time of backup copies in order to help backup copies adopt the passive execution scheme, or to decrease the simultaneous execution time of the primary and backup copies of a task as much as possible to improve resource utilization. QAFT is capable of adaptively adjusting the QoS levels of tasks and the execution schemes of backup copies to attain high system flexibility. Furthermore, we employ the overlapping technology of backup copies. The latest start time of backup copies and their constraints are analyzed and discussed. We conduct extensive experiments to compare our QAFT with two existing schemesNOQAFT and DYFARS. Experimental results show that QAFT significantly improves the scheduling quality of NOQAFT and DYFARS. © 2011 IEEE.


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.


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.


Zhu C.,National University of Defense Technology | Zhou H.,Beijing Institute of Technology | Wang R.,National University of Defense Technology | Guo J.,National University of Defense Technology
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

Ship detection from remote sensing imagery is very important, with a wide array of applications in areas such as fishery management, vessel traffic services, and naval warfare. This paper focuses on the issue of ship detection from spaceborne optical images (SDSOI). Although advantages of synthetic-aperture radar (SAR) result in that most of current ship detection approaches are based on SAR images, disadvantages of SAR still exist, such as the limited number of SAR sensors, the relatively long revisit cycle, and the relatively lower resolution. With the increasing number of and the resulting improvement in continuous coverage of the optical sensors, SDSOI can partly overcome the shortcomings of SAR-based approaches and should be investigated to help satisfy the requirements of real-time ship monitoring. In SDSOI, several factors such as clouds, ocean waves, and small islands affect the performance of ship detection. This paper proposes a novel hierarchical complete and operational SDSOI approach based on shape and texture features, which is considered a sequential coarse-to-fine elimination process of false alarms. First, simple shape analysis is adopted to eliminate evident false candidates generated by image segmentation with global and local information and to extract ship candidates with missing alarms as low as possible. Second, a novel semisupervised hierarchical classification approach based on various features is presented to distinguish between ships and nonships to remove most false alarms. Besides a complete and operational SDSOI approach, the other contributions of our approach include the following three aspects: 1) it classifies ship candidates by using their class probability distributions rather than the direct extracted features; 2) the relevant classes are automatically built by the samples appearances and their feature attribute in a semisupervised mode; and 3) besides commonly used shape and texture features, a new texture operator, i.e., local multiple patterns, is introduced to enhance the representation ability of the feature set in feature extraction. Experimental results of SDSOI on a large image set captured by optical sensors from multiple satellites show that our approach is effective in distinguishing between ships and nonships, and obtains a satisfactory ship detection performance. © 2006 IEEE.


Zhang K.,National University of Defense Technology | Zhou H.,Beijing Institute of Technology | Wang F.,National University of Defense Technology
GPS Solutions | Year: 2013

With the proposed new GNSS signals, enhanced navigation performance is expected in both civil and military applications. However, these new signals introduce the difficulty of combining multiple signal components into a constant-envelope signal. For the Compass B1 band, the problem is to multiplex a QPSK(2) signal and a new multiplexed binary offset carrier (MBOC) signal with a center frequency difference of 14. 322 MHz. One approach for multiplexing spreading codes is the phase-optimized constant-envelope transmission (POCET) method proposed for the GPS L1 band. However, only binary spreading codes are considered in POCET. We first generalize the POCET method as a multilevel POCET (MPOCET) algorithm for multilevel coded signals. A new implementation of the alternative binary offset carrier (AltBOC) generator is derived from MPOCET. Secondly, the multiplexing problem for Compass is modeled by MPOCET. Multilevel subcarriers of AltBOC are adopted in the model. As a result, an 8-PSK unbalanced AltBOC (UAltBOC) modulation, which has a QPSK(2) signal at the lower sideband and a TMBOC signal at the upper sideband, is obtained. Simulations for signal model validation and power spectrum analysis are conducted. Numerical results indicate that UAltBOC successfully combines the QPSK and TMBOC signals with only 0. 16-dB additional combining loss compared to AltBOC. The proposed MPOCET technique is demonstrated as a unified multiplexing method for navigation signals. © 2012 Springer-Verlag.


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.


Yang X.,National University of Defense Technology | Wang Z.,National University of Defense Technology | Xue J.,University of New South Wales | Zhou Y.,National University of Defense Technology
IEEE Transactions on Computers | Year: 2012

Reliability is a key challenge to be understood to turn the vision of exascale supercomputing into reality. Inevitably, large-scale supercomputing systems, especially those at the peta/exascale levels, must tolerate failures, by incorporating fault-tolerance mechanisms to improve their reliability and availability. As the benefits of fault-tolerance mechanisms rarely come without associated time and/or capital costs, reliability will limit the scalability of parallel applications. This paper introduces for the first time the concept of "Reliability Wall to highlight the significance of achieving scalable performance in peta/exascale supercomputing with fault tolerance. We quantify the effects of reliability on scalability, by proposing a reliability speedup, defining quantitatively the reliability wall, giving an existence theorem for the reliability wall, and categorizing a given system according to the time overhead incurred by fault tolerance. We also generalize these results into a general reliability speedup/wall framework by considering not only speedup but also costup. We analyze and extrapolate the existence of the reliability wall using two representative supercomputers, Intrepid and ASCI White, both employing checkpointing for fault tolerance, and have also studied the general reliability wall using Intrepid. These case studies provide insights on how to mitigate reliability-wall effects in system design and through hardware/software optimizations in peta/exascale supercomputing. © 1968-2012 IEEE.


Guo J.,National University of Defense Technology | Zhou H.,Beijing Institute of Technology | Zhu C.,National University of Defense Technology
Information Sciences | Year: 2013

Wepresent a novel cascaded classification approach by exploiting various contexts on different levels for high resolution remote sensing (HRRS) images. The contexts mentioned in our article are defined according to objects from a set of regions resulting from segmentation. The cascaded procedure comprises three stages: (1) initializing the classification using the object's inner context (i.e., the gray constraints of different pixels in an object), (2) correcting the classification using the object's neighbor context (i.e., the characteristic constraints of different objects adjacent to the concerned object), and (3) refining classification using the object's scene context (i.e., the distribution constraint of different objects' labels and their feature vectors in the whole scene). The proposed algorithm has the following distinctions. First, it uses an object's neighbor context to bridge the gap between its inner context and its scene context because the latter two types of contexts have inevitable drawbacks when being used for classification alone. Second, it carries on a cascaded classification procedure in which the previous stage provides a better initial classification for the following stage, and the result is gradually refined by integrating different contexts. The effectiveness and practicability of the proposed algorithm is demonstrated through a set of completely experimental results and substantiated using quantitative criteria. © 2012 Elsevier Inc. All rights reserved.


Chang X.,PLA Fourth Military Medical University | Shen H.,National University of Defense Technology | Wang L.,National University of Defense Technology | Liu Z.,Central South University | And 3 more authors.
Brain Research | Year: 2014

The complex symptoms of schizophrenia have recently been linked to disrupted neural circuits and corresponding malfunction of two higher-order intrinsic brain networks: The default mode network (DMN) and the fronto-parietal network (FPN). These networks are both functionally heterogeneous and consist of multiple subsystems. However, the extent to which these subsystems make differential contributions to disorder symptoms and to what degree such abnormalities occur in unaffected siblings have yet to be clarified. We used resting-state functional MRI (rs-fMRI) to examine group differences in intra- and inter-connectivity of subsystems within the two neural networks, across a sample of patients with schizophrenia (n=24), their unaffected siblings (n=25), and healthy controls (n=22). We used group independent component analysis (gICA) to identify four network subsystems, including anterior and posterior portions of the DMN (aDMN, pDMN) as well as left- and right-lateralized portions of the FPN (lFPN, rFPN). Intra-connectivity is defined as neural coherence within a subsystem whereas inter-connectivity refers to functional connectivity between subsystems. In terms of intra-connectivity, patients and siblings shared dysconnection within the aDMN and two FPN subsystems, while both groups preserved connectivity within the pDMN. In terms of inter-connectivity, all groups exhibited positive connections between FPN and DMN subsystems, with patients having even stronger interaction between rFPN and aDMN than the controls, a feature that may underlie their psychotic symptoms. Our results implicate that DMN subsystems exhibit different liabilities to the disease risk while FPN subsystems demonstrate distinct inter-connectivity alterations. These dissociating manners between network subsystems explicitly suggest their differentiating roles to the disease susceptibility and manifestation. © 2014 Elsevier B.V. All rights reserved.


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.


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.


Ren T.P.,63790 Troops | Guan Y.L.,Nanyang Technological University | Yuen C.,Singapore University of Technology and Design | Zhang E.Y.,National University of Defense Technology
IEEE Journal on Selected Topics in Signal Processing | Year: 2011

Full-rate space time codes (STCs) with rate = number of transmit antennas have high multiplexing gain, but high decoding complexity even when decoded using reduced-complexity decoders such as sphere or QRDM decoders. In this paper, we introduce a new code property of STC called block-orthogonal property, which can be exploited by QR-decomposition-based decoders to achieve significant decoding complexity reduction without performance loss. We show that such complexity reduction principle can benefit the existing algebraic codes such as Perfect and DjABBA codes due to their inherent (but previously undiscovered) block-orthogonal property. In addition, we construct and optimize new full-rate block-orthogonal STC (BOSTC) that further maximize the QRDM complexity reduction potential. Simulation results of bit error rate (BER) performance against decoding complexity show that the new BOSTC outperforms all previously known codes as long as the QRDM decoder operates in reduced-complexity mode, and the code exhibits a desirable complexity saturation property. © 2011 IEEE.


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.


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.


Yang W.Q.,National University of Defense Technology | Zhang B.,National University of Defense Technology | Hou J.,National University of Defense Technology | Xiao R.,Beijing Institute of Radiation Medicine | And 2 more authors.
Laser Physics Letters | Year: 2013

A simultaneously gain-switched and mode-locked Tm/Ho-codoped fiber laser with a central wavelength of 1958 nm is reported for the first time to the authors' knowledge. The repetition rates of the gain-switched pulse envelopes and mode-locked sub-pulses are 20 kHz and 14.8 MHz, respectively. Using this laser as a seed source, a flat mid-IR supercontinuum is generated from a Tm-doped fiber amplifier. For the maximum output power of 2.17 W, the long wavelength edge of the supercontinuum spectrum is extended to 2750 nm, and the supercontinuum has a 10 dB bandwidth of 640 nm (a spectral range of ∼1953-2593 nm). © 2013 Astro Ltd.


Zhao K.,University of Central Florida | Zhang Q.,University of Central Florida | Chini M.,University of Central Florida | Wu Y.,University of Central Florida | And 3 more authors.
Optics Letters | Year: 2012

A single isolated attosecond pulse of 67 as was composed from an extreme UV supercontinuum covering 55-130 eV generated by the double optical gating technique. Phase mismatch was used to exclude the single-atom cutoff of the spectrum that possesses unfavorable attochirp, allowing the positive attochirp of the remaining spectrum to be compensated by the negative dispersion of a zirconium foil. Two algorithms, PROOF and FROG-CRAB, were employed to retrieve the pulse from the experimental spectrogram, yielding nearly identical results. © 2012 Optical Society of America.


Peng Y.,National University of Defense Technology | Hou J.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Huang Z.,National University of Defense Technology | And 2 more authors.
Optics Letters | Year: 2013

A compact temperature sensor based on a selectively liquid-filled photonic crystal fiber (PCF) is proposed using controlled hole collapse in PCF post-processing. The first ring around the core is filled with liquid of higher refractive index than the matrix, while the outer rings of holes are filled with air. The bandgap (BG)-like effect of the high refractive index ring is analyzed. Absorption loss spectra of the fiber are found to be quite sensitive to the refractive index of liquid when the liquid is lossy. Using the BG-like effect, a fiber temperature sensor is fabricated by selectively injecting a mixture of dimethyl sulfoxide and aqueous gold colloids with a high thermo-optic coefficient to the PCF. Temperature sensitivity up to -5.5 nm/°C is experimentally confirmed. © 2013 Optical Society of America.


Yang W.Q.,National University of Defense Technology | Zhang B.,National University of Defense Technology | Hou J.,National University of Defense Technology | Xiao R.,Beijing Institute of Radiation Medicine | And 2 more authors.
Laser Physics Letters | Year: 2013

We demonstrate all-fiber-integrated mid-IR supercontinuum generation in a Tm/Ho codoped fiber amplifier, where the codoped fiber is both nonlinear and a gain medium. The observed supercontinuum spectrum ranges from 1760 to 2600 nm and has an extremely high spectral flatness, with a 3 dB bandwidth ∼635 nm (from 1845 to 2480 nm). In the Tm/Ho codoped fiber, as well as the nonlinear optical processes, the Tm3+ and Ho3+ ions also play important roles in mid-IR supercontinuum generation. The 3F 4-3H6 transition for Tm3+ radiates a laser in the 1.8-2.1 μm spectral region, the 5I7- 5I8 transition for Ho3+ radiates a laser around 2.1 μm and the 3H4-3H5 transition for Tm3+ radiates a laser in the 2.2-2.5 μm spectral region. All of these energy level transitions contribute towards supercontinuum generation. © 2013 Astro Ltd.


Meng Y.,National University of Defense Technology | Hao R.,National University of Defense Technology | Chen Q.,Hunan University
Acta Astronautica | Year: 2014

The attitude stability of a dual-spin spacecraft in libration point orbits is investigated. The equations of rotational motion of a spacecraft in libration point orbits are provided. Considering the case of a rigid spacecraft located at a libration point, the rotation equations are simplified, and the stability conditions are determined and illustrated with figures. In the case of a spacecraft that occupies a halo orbit far from a libration point, a semi-analytical approach was proposed. By approaching the gravity gradient torque with a multi-segment series, the rotational motion of the spacecraft can be expressed as a series of three modes of motion, which can be used to explain the mechanism of attitude motion of a dual-spin spacecraft in libration point orbits. Numerical simulations show the validity of the semi-analytical approach. © 2014 Published by Elsevier Ltd. on behalf of IAA.


He Y.,National University of Defense Technology | He Y.,Northumbria University | Tian G.,Northumbria University | Tian G.,University of Electronic Science and Technology of China | And 2 more authors.
Applied Physics Letters | Year: 2013

This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth. © 2013 AIP Publishing LLC.


Zhang L.,Hunan University | Huang L.,Hunan University | Zhang Z.,National University of Defense Technology
Mathematical and Computer Modelling | Year: 2010

This paper investigates the local dynamics around the trivial solution of suspension system of maglev train with time-delayed feedback signals. With characteristic root method, the linear stability analysis of the maglev system is obtained, which implies that a Hopf bifurcation may occur when time delay exceeds a critical value. To gain insight into the periodic motion, the pseudo-oscillator analysis is used to calculate the bifurcated periodic solution, and to determine the direction of the bifurcation. Unlike the widely used methods such as manifold reduction, the pseudo-oscillator analysis involves simple computation and gives prediction of the local dynamics with high accuracy. Numerical simulation results show that the existence of the Hopf bifurcation and the amplitude of the periodic solution can be determined by time delay and control parameters. So appropriately selecting them can restrain vibration between vehicle and guideway of the system effectively. © 2010 Elsevier Ltd.


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.


Quo F.,National University of Defense Technology | Ho K.C.,University of Missouri
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2011

This paper proposes a new closed-form solution for the position and velocity of a moving source obtained from the time differences of arrival(TDOAs) and frequency differences of arrival(FDOAs) of its emitted signal arrived at a number of receivers. The method uses weighted least-squares formulation and imposes quadratic constraints among the positioning variables to improve performance. The proposed solution can achieve the Cramer-Rao lower bound(CRLB) accuracy for Gaussian TDOA and FDOA noise with a higher noise threshold than the previous method [7]. Simulations are included to examine the performance of the proposed solution and compare with the previous method. © 2011 IEEE.


Li X.-F.,Central South University | Li X.-F.,Dalian University of Technology | Tang G.-J.,National University of Defense Technology | Shen Z.-B.,National University of Defense Technology | Lee K.Y.,Dalian University of Technology
Ultrasonics | Year: 2015

Free vibration and mass detection of carbon nanotube-based sensors are studied in this paper. Since the mechanical properties of carbon nanotubes possess a size effect, the nonlocal beam model is used to characterize flexural vibration of nanosensors carrying a concentrated nanoparticle, where the size effect is reflected by a nonlocal parameter. For nanocantilever or bridged sensor, frequency equations are derived when a nanoparticle is carried at the free end or the middle, respectively. Exact resonance frequencies are numerically determined for clamped-free, simply-supported, and clamped-clamped resonators. Alternative approximations of fundamental frequency are given in closed form within the relative error less than 0.4%, 0.6%, and 1.4% for cantilever, simply-supported, and bridged sensors, respectively. Mass identification formulae are derived in terms of the frequency shift. Identified masses via the present approach coincide with those using the molecular mechanics approach and reach as low as 10-24 kg. The obtained results indicate that the nonlocal effect decreases the resonance frequency except for the fundamental frequency of nanocantilever sensor. These results are helpful to the design of micro/nanomechanical zeptogram-scale biosensor. © 2014 Elsevier B.V. All rights reserved.


He Y.,National University of Defense Technology | He Y.,Northumbria University | Tian G.,Northumbria University | Tian G.,University of Electronic Science and Technology of China | And 3 more authors.
Composite Structures | Year: 2014

With the growing interest to use engineering composite structures, much attention is devoted to the development of non-destructive testing (NDT) techniques for impact evaluation. Eddy current pulsed thermography (ECPT) is an emerging NDT technique, which is firstly investigated for crack evaluation in carbon fiber reinforced plastic (CFRP) in 2011 and the preliminary results have shown the significant potential. However, the research is limited by the experimental conditions. In this work, the detection mechanism for carbon fiber structure and impact are analyzed through theoretic analysis and validated by experimental studies under reflection and transmission modes. Laminates impacted with different energies from 4. J to 12. J are characterised. The qualitative and quantitative conclusions for impact behavior understanding are outlined, which is helpful to develop the reliable instruments for quality control and in-service inspection of CFRP. © 2013 Elsevier Ltd.


Huang Q.,National University of Defense Technology | Ghogho M.,University of Leeds | Wei J.,National University of Defense Technology | Ciblat P.,ENST
IEEE Transactions on Signal Processing | Year: 2010

In this paper, we investigate the timing and carrier frequency offset (CFO) synchronization problem in decode and forward cooperative systems operating over frequency selective channels. A training sequence which consists of one orthogonal frequency-division multiplexing (OFDM) block having a tile structure in the frequency domain is proposed to perform synchronization. Timing offsets are estimated using correlation-type algorithms. By inserting some null subcarriers in the proposed tile structure, we propose a computationally efficient subspace decomposition-based algorithm for CFO estimation. The issue of optimal tile length is studied both theoretically and through simulations. By judiciously designing the tile size of the pilot, the proposed algorithms are shown to have better performance, in terms of synchronization errors and bit error rate, than the time-division multiplexing-based training method and the computationally demanding space-alternating generalized expectation-maximization algorithm. © 2010 IEEE.


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.


Li J.,National University of Defense Technology | Levine M.D.,McGill University | An X.,National University of Defense Technology | Xu X.,National University of Defense Technology | He H.,National University of Defense Technology
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

We address the issue of visual saliency from three perspectives. First, we consider saliency detection as a frequency domain analysis problem. Second, we achieve this by employing the concept of nonsaliency. Third, we simultaneously consider the detection of salient regions of different size. The paper proposes a new bottom-up paradigm for detecting visual saliency, characterized by a scale-space analysis of the amplitude spectrum of natural images. We show that the convolution of the image amplitude spectrum with a low-pass Gaussian kernel of an appropriate scale is equivalent to an image saliency detector. The saliency map is obtained by reconstructing the 2D signal using the original phase and the amplitude spectrum, filtered at a scale selected by minimizing saliency map entropy. A Hypercomplex Fourier Transform performs the analysis in the frequency domain. Using available databases, we demonstrate experimentally that the proposed model can predict human fixation data. We also introduce a new image database and use it to show that the saliency detector can highlight both small and large salient regions, as well as inhibit repeated distractors in cluttered images. In addition, we show that it is able to predict salient regions on which people focus their attention. © 1979-2012 IEEE.


Xiong J.,National University of Defense Technology | Xiong J.,Australian Defence Force Academy | Xing L.-N.,National University of Defense Technology | Chen Y.-W.,National University of Defense Technology
International Journal of Production Economics | Year: 2013

This study addresses robust scheduling for a flexible job-shop scheduling problem with random machine breakdowns. Two objectives - makespan and robustness - are simultaneously considered. Robustness is indicated by the expected value of the relative difference between the deterministic and actual makespan. Utilizing the available information about machine breakdowns, two surrogate measures for robustness are developed. Specifically, the first suggested surrogate measure considers the probability of machine breakdowns, while the second surrogate measure considers the location of float times and machine breakdowns. To address this problem, a multi-objective evolutionary algorithm is presented in this paper. The experimental results indicate that, compared with several other existing surrogate measures, the first suggested surrogate measure performs better for small cases, while the second surrogate measure performs better for both small and relatively large cases. © 2012 Elsevier B.V. All rights reserved.


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.


Lu X.,National University of Defense Technology | Wang H.,National University of Defense Technology | Wang J.,National University of Defense Technology | Xu J.,University of Leeds | Li D.,National University of Defense Technology
Future Generation Computer Systems | Year: 2013

The two dominating characteristics of new and emerging Internet applications are ultra-large scales and utility. Centralized data centers alone are often inadequate for running such applications. In this paper we introduce the concept of an Internet-based Virtual Computing Environment (iVCE), which aims to provide Cloud services by a dynamic combination of data centers and other multi-scale computing resources on the Internet. We present a model that addresses two critical challenges in iVCE: multi-scale resource aggregation and elastic binding. We then describe the design and implementation of our iVCE software platform that embodies the model. Comprehensive experiments show that iVCE provides a novel, promising way to deal with scalability and utility, thereby enabling economical and elastic Cloud Computing. © 2011 Elsevier B.V. All rights reserved.


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.


Ma S.,National University of Defense Technology | Ma S.,University of Toronto | Jerger N.E.,University of Toronto | Wang Z.,National University of Defense Technology
Proceedings - International Symposium on High-Performance Computer Architecture | Year: 2012

Routing algorithms for networks-on-chip (NoCs) typically only have a small number of virtual channels (VCs) at their disposal. Limited VCs pose several challenges to the design of fully adaptive routing algorithms. First, fully adaptive routing algorithms based on previous deadlock-avoidance theories require a conservative VC re-allocation scheme: a VC can only be re-allocated when it is empty, which limits performance. We propose a novel VC re-allocation scheme, whole packet forwarding (WPF), which allows a non-empty VC to be re-allocated. WPF leverages the observation that the majority of packets in NoCs are short. We prove that WPF does not induce deadlock if the routing algorithm is deadlock-free using conservative VC re-allocation. WPF is an important extension of previous deadlock-avoidance theories. Second, to efficiently utilize WPF in VC-limited networks, we design a novel fully adaptive routing algorithm which maintains packet adaptivity without significant hardware cost. Compared with conservative VC re-allocation, WPF achieves an average 88.9% saturation throughput improvement in synthetic traffic patterns and an average 21.3% and maximal 37.8% speedup for PARSEC applications with heavy network loads. Our design also offers higher performance than several partially adaptive and deterministic routing algorithms. © 2012 IEEE.


Chen S.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Zhao D.,National University of Defense Technology | And 2 more authors.
Corrosion Science | Year: 2013

Ablation behavior of 3D C/ZrC-SiC composite was tested under an oxyacetylene flame and an ablation mechanism was proposed. A five-layer microstructure formed after ablation, including the ZrO2-melting layer, the porous layer, the SiO2-rich layer, the SiC-depleted layer and the composite substrate. The ablation rate is controlled by oxidations of carbon fibers, SiC and ZrC in the first stage, and then controlled by the scouring away of ZrO2-SiO2 binary melt by gas flow and the oxygen diffusion through the glassy ZrO2-SiO2 layer. Finally the evaporation of SiO2 controls the ablation rate cooperative with the last mentioned two ablation behavior. © 2012.


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.


Ma S.,National University of Defense Technology | Jerger N.E.,University of Toronto | Wang Z.,National University of Defense Technology
Proceedings - International Symposium on Computer Architecture | Year: 2011

With the emergence of many-core architectures, it is quite likely that multiple applications will run concurrently on a system. Existing locally and globally adaptive routing algorithms largely overlook issues associated with workload consolidation. The shortsightedness of locally adaptive routing algorithms limits performance due to poor network congestion avoidance. Globally adaptive routing algorithms attack this issue by introducing a congestion propagation network to obtain network status information beyond neighboring nodes. However, they may suffer from intra-and inter-application interference during output port selection for consolidated workloads, coupling the behavior of otherwise independent applications and negatively affecting performance. To address these two issues, we propose Destination-Based Adaptive Routing (DBAR). We design a novel low-cost congestion propagation network that leverages both local and non-local network information for more accurate congestion estimates. Thus, DBAR offers effective adaptivity for congestion beyond neighboring nodes. More importantly, by integrating the destination into the selection function, DBAR mitigates intra-and inter-application interference and offers dynamic isolation among regions. Experimental results show that DBAR can offer better performance than the best baseline algorithm for all measured configurations; it is well suited for workload consolidation. The wiring overhead of DBAR is low and DBAR provides improvement in the energy-delay product for medium and high injection rates. Copyright 2011 ACM.


Guo D.,National University of Defense Technology | Wu J.,Temple University | Chen H.,National University of Defense Technology | Yuan Y.,Northeastern University China | Luo X.,National University of Defense Technology
IEEE Transactions on Knowledge and Data Engineering | Year: 2010

A Bloom filter is an effective, space-efficient data structure for concisely representing a set, and supporting approximate membership queries. Traditionally, the Bloom filter and its variants just focus on how to represent a static set and decrease the false positive probability to a sufficiently low level. By investigating mainstream applications based on the Bloom filter, we reveal that dynamic data sets are more common and important than static sets. However, existing variants of the Bloom filter cannot support dynamic data sets well. To address this issue, we propose dynamic Bloom filters to represent dynamic sets, as well as static sets and design necessary item insertion, membership query, item deletion, and filter union algorithms. The dynamic Bloom filter can control the false positive probability at a low level by expanding its capacity as the set cardinality increases. Through comprehensive mathematical analysis, we show that the dynamic Bloom filter uses less expected memory than the Bloom filter when representing dynamic sets with an upper bound on set cardinality, and also that the dynamic Bloom filter is more stable than the Bloom filter due to infrequent reconstruction when addressing dynamic sets without an upper bound on set cardinality. Moreover, the analysis results hold in stand-alone applications, as well as distributed applications. © 2006 IEEE.


Dai F.,University of Toronto | Chen R.,University of Toronto | Chen R.,National University of Defense Technology | Iqbal M.J.,University of Toronto | Xia K.,University of Toronto
International Journal of Rock Mechanics and Mining Sciences | Year: 2010

The cracked chevron notch Brazilian disc (CCNBD) method is widely used in characterizing rock fracture toughness. We explore here the possibility of extending the CCNBD method to dynamic rock fracture testing. In dynamic rock fractures, relevant fracture parameters are the initiation fracture toughness, the fracture energy, the fracture propagation toughness, and the fracture velocity. The dynamic load is applied with a split Hopkinson pressure bar (SHPB) apparatus. A strain gauge is mounted on the sample surface near the notch tip to detect the fracture-induced strain release, and a laser gap gauge (LGG) is used to monitor the crack surface opening distance (CSOD) during the test. With dynamic force balance achieved in the tests, the stable-unstable transition of the crack propagation crack is observed and the initiation fracture toughness is obtained from the peak load. The dynamic fracture initiation toughness values obtained for the chosen rock (Laurentian granite) using this method are consistent with those measured using other methods. The dynamic fracture initiation toughness is in the range 2.5-4.6MPam1/2 and the propagation fracture toughness is in the range 7.1-10.6MPam1/2, which is consistently larger than the initiation toughness. © 2010 Elsevier Ltd.


Wang J.,National University of Defense Technology | Wang J.,CAS Shanghai Institute of Optics and fine Mechanics | Cui S.,CAS Shanghai Institute of Optics and fine Mechanics | Si L.,National University of Defense Technology | And 2 more authors.
Optics Express | Year: 2013

An all-fiber single-mode actively Q-switched laser at 1120 nm is demonstrated. The laser cavity consists of a 5 m long Yb-doped polarization maintaining gain fiber, an acousto-optical modulator and a pair of FBGs. At a pump power of 2.5 W, a peak power of 0.8 kW is achieved with a pulse duration of 140 ns at a repetition rate of 1 kHz. A slope efficiency of 16.9% with respect to launched pump power is obtained at 10 kHz. The low achievable gain at 1120 nm, imposed by the parasitic lasing limit at conventional Yb lasing wavelength, has a major role in laser performance. © 2013 Optical Society of America.


Liu Y.P.,National University of Defense Technology | Gao C.,National University of Defense Technology | Zeng J.L.,National University of Defense Technology | Yuan J.M.,National University of Defense Technology | Shi J.R.,CAS National Astronomical Observatories
Astrophysical Journal, Supplement Series | Year: 2014

A complete set of atomic data of Cu I, including the energy levels, oscillator strengths, and photoionization cross sections, is theoretically studied to investigate element abundance including nonlocal thermodynamic equilibrium (NLTE) effects. The calculations are carried out by using the R-matrix method in the LS-coupling scheme. Twenty terms of Cu II are utilized as target states, and extensive configuration interactions are included to properly delineate the quantum states of Cu II and Cu I. One hundred thirteen bound states and 1699 oscillator strengths for E1 transitions between these states are obtained. Photoionization cross sections for all bound states are calculated in a photon energy range covering 1.28 Ry from the threshold of the respective state. Resonances shown in the photoionization cross sections are identified, and some strong resonances are expected to play an important role in NLTE modeling. The atomic data in this work represent the first complete data set for copper abundance studies. Our results are compared with the experimental and other theoretical data wherever available. © 2014. The American Astronomical Society. All rights reserved..


Qiao J.,University of Toronto | Qiao J.,National University of Defense Technology | Shang J.,National University of Defense Technology | Goldenberg A.,University of Toronto
IEEE/ASME Transactions on Mechatronics | Year: 2013

In-pipe robots are used to carry sensors and some other repairing instruments to perform inspection and maintenance jobs inside pipelines. In this paper, a self-locking mechanism is presented to improve the traction ability of in-pipe robots and avoid their traditional limitations. The structure of this type of inpipe robot is presented and some critical design issues on the principle of self-locking mechanism are discussed. Prototypes of 19mm diameter were produced, and related experiments were performed on specially designed test platform. The traction ability of the proposed in-pipe robot was measured experimentally to be 15.2 N, far beyond itsmaximum static friction of 0.35N with the inner surface of pipeline. It means that this development has broken the traditional limitation of in-pipe robot whose traction ability was smaller than its maximum static friction with the pipeline. © 2012 IEEE.


Wang F.,Fudan University | Wang F.,National University of Defense Technology | Shen D.,Fudan University | Fan D.,Fudan University | Lu Q.,National University of Defense Technology
Optics Letters | Year: 2010

We report on high-power operation of a widely tunable dual-wavelength Tm:fiber laser in the 2 μm spectral region using volume Bragg gratings and a simple resonator configuration for wavelength selection. The wavelength splitting range is continuously tunable from 1 to 50 nm (0.1-3.8 THz), with > 115W of diffraction-limited total output power for wavelength separations of < 40 nm. A maximum output power of 118 W was obtained for 279 W of launched pump power at 792 nm, corresponding to a slope efficiency with respect to launched pump power of 45%. The prospects for further improvement in performance are discussed. © 2010 Optical Society of America.


Wang F.,National University of Defense Technology | Wang F.,Fudan University | Shen D.,Fudan University | Fan D.,Fudan University | Lu Q.,National University of Defense Technology
Optics Express | Year: 2010

Efficient operation of a cladding pumped high power Tm: fiber laser with a volume Bragg grating (VBG) as wavelength selective and spectrally narrowing element is reported. The laser yielded over 112 W of diffraction limited output at 1988 nm with a spectral linewidth of ∼12 pm for 279 W of launched pump power, corresponding to a slope efficiency with respect to launched pump power of 43.4%. No discernable difference was observed in terms of output power and slope efficiency when using a broadband highly reflective mirror in place of the VBG. ©2010 Optical Society of America.


Dong J.,National University of Defense Technology | Fu D.,China Aerospace Science and Technology Corporation | Yang X.,National University of Defense Technology
Journal of Applied Optics | Year: 2013

A real-time algorithm for detecting and tracking ground moving target by using unmanned aerial vehicle(UAV) video was proposed. Two images were matched based on the correspondence of feature points, and the change detection was proceeded on the basis of the matched images. Then according to the changing and moving information, target was detected and part of false alarm was eliminated. If tracking failed, the target could be correctly relocated to obtain full trace of moving target finally by combining detecting with tracking. The test result of groud vehicle image by UAV implies that the moving target can be detected and tracked at a real-time processing speed of more than 25 f/s by using our algorithm.


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.


Liu Y.P.,National University of Defense Technology | Gao C.,National University of Defense Technology | Zeng J.L.,National University of Defense Technology | Shi J.R.,CAS National Astronomical Observatories
Astronomy and Astrophysics | Year: 2011

Aims. We calculate the energy levels, oscillator strengths, and photoionization cross-sections of Zn I to provide atomic data for the study of element abundances in astrophysics. Methods. The calculations are carried out by using the R-matrix method in the LS-coupling scheme. The lowest 12 terms of Zn II are utilized as target states and extensive configuration interaction is included to properly delineate the quantum states of Zn II and Zn I. Results. The 3443 oscillator-strength values are calculated in both length and velocity forms, for the dipole-allowed transitions between 235 bound states of Zn I. The photoionization cross-section of each bound state is presented in a photon energy range from the first threshold to about 1.5 Ry. Some resonance structures are identified in the photoionization cross-sections. Conclusions. A set of atomic data to derive the spectral characteristics of neutral zinc is obtained. Comparisons are made with available experimental and other theoretical results. © 2011 ESO.


Jianxiong Z.,National University of Defense Technology | Zhiguang S.,National University of Defense Technology | Xiao C.,National University of Defense Technology | Qiang F.,China Aerospace Science and Technology Corporation
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

This paper proposes a synthetic aperture radar (SAR) automatic target recognition approach based on a global scattering center model. The scattering center model is established offline using range profiles at multiple viewing angles, so the original data amount is much less than that required for establishing SAR image templates. Scattering center features at different target poses can be conveniently predicted by this model. Moreover, the model can be modified to predict features for various target configurations. For the SAR image to be classified, regional features in different levels are extracted by thresholding and morphological operations. The regional features will be matched to the predicted scattering center features of different targets to arrive at a decision. This region-to-point matching is much easier to implement and is less sensitive to nonideal factors such as noise and pose estimation error than point-to-point matching. A matching scheme going through from coarse to fine regional features in the inner cycle and going through different pose hypotheses in the outer cycle is designed to improve the efficiency and robustness of the classifier. Experiments using both data predicted by a high-frequency electromagnetic (EM) code and data measured in the MSTAR program verify the validity of the method. © 2011 IEEE.


Chen S.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Zhao D.,National University of Defense Technology | And 2 more authors.
Materials and Design | Year: 2013

Silicon carbide (SiC) interphase was introduced by chemical vapor deposition (CVD) process to prevent carbon fiber degradation and improve fiber-matrix interface bonding of C/ZrC composite prepared via precursor infiltration and pyrolysis (PIP) process. Moderate thickness of SiC interphase in fiber bundles could increase the density of the composite, but when the thickness of SiC interphase was over 0.5μm, more close pores formed and the density of the composite decreased. The SiC interphase could protect carbon fiber effectively from carbo-thermal reduction, but could not enhance the mechanical properties of C/ZrC composite. The flexural strength and fracture toughness of C/ZrC composites with 0.05μm thickness SiC layer were 252MPa and 13.6MPam1/2, and for those with 0.5μm thickness SiC layer 240MPa and 12.8MPam1/2, both close to the value of the composite without SiC interphase (254MPa and 14.5MPam1/2), while those with 0.7μm thickness SiC layer were only 191MPa and 10.8MPam1/2, respectively. Moderate content of SiC interphase could improve the ablation property of C/ZrC composites; however excessive content of SiC interphase would decrease the ablation property. © 2012.


Wang J.,CAS Shanghai Institute of Optics and fine Mechanics | Wang J.,National University of Defense Technology | Hu J.,CAS Shanghai Institute of Optics and fine Mechanics | Zhang L.,CAS Shanghai Institute of Optics and fine Mechanics | And 3 more authors.
Optics Express | Year: 2012

A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical efficiency of 50% was demonstrated. The laser consists of a 4.2 m long Yb-doped polarization maintaining fiber with a core diameter of 10 μm and a pair of FBGs written in matched passive fiber. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Pulsed operations with square shaped pulses varying from 100 μs to 1 ms duration are achieved without relaxation oscillation. © 2012 Optical Society of America.


Ma X.-C.,National University of Defense Technology | Ma X.-C.,University of Toronto | Sun S.-H.,National University of Defense Technology | Jiang M.-S.,National University of Defense Technology | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

Measurement-device-independent quantum key distribution (MDI-QKD), leaving the detection procedure to the third partner and thus being immune to all detector side-channel attacks, is very promising for the construction of high-security quantum information networks. We propose a scheme to implement MDI-QKD, but with continuous variables instead of discrete ones, i.e., with the source of Gaussian-modulated coherent states, based on the principle of continuous-variable entanglement swapping. This protocol not only can be implemented with current telecom components but also has high key rates compared to its discrete counterpart; thus it will be highly compatible with quantum networks. © 2014 American Physical Society.


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.


Liu W.,National University of Defense Technology | Liu W.,Henan University | Wang T.,National University of Defense Technology
Knowledge and Information Systems | Year: 2012

Email spam causes a serious waste of time and resources. This paper addresses the email spam filtering problem and proposes an online active multi-field learning approach, which is based on the following ideas: (1) Email spam filtering is an online application, which suggests an online learning idea; (2) Email document has a multi-field text structure, which suggests a multi-field learning idea; and (3) It is costly to obtain a label for a real-world email spam filter, which suggests an active learning idea. The online learner regards the email spam filtering as an incremental supervised binary streaming text classification. The multi-field learner combines multiple results predicted by field classifiers in a novel compound weight schema, and each field classifier calculates the arithmetical average of multiple conditional probabilities calculated from feature strings according to a data structure of string-frequency index. Comparing the current variance of field classifying results with the historical variance, the active learner evaluates the classifying confidence and takes the more uncertain email as the more informative sample for which to request a label. The experimental results show that the proposed approach can achieve the state-of-the-art performance with greatly reduced label requirements and very low space-time costs. The performance of our online active multi-field learning, the standard (1-ROCA)% measurement, even exceeds the full feedback performance of some advanced individual text classification algorithms. © 2011 Springer-Verlag London Limited.


Hou C.,National University of Defense Technology | Nie F.,University of Texas at Arlington | Yi D.,National University of Defense Technology | Wu Y.,National University of Defense Technology
IEEE Transactions on Image Processing | Year: 2013

The problem of image classification has aroused considerable research interest in the field of image processing. Traditional methods often convert an image to a vector and then use a vector-based classifier. In this paper, a novel multiple rank regression model (MRR) for matrix data classification is proposed. Unlike traditional vector-based methods, we employ multiple-rank left projecting vectors and right projecting vectors to regress each matrix data set to its label for each category. The convergence behavior, initialization, computational complexity, and parameter determination are also analyzed. Compared with vector-based regression methods, MRR achieves higher accuracy and has lower computational complexity. Compared with traditional supervised tensor-based methods, MRR performs better for matrix data classification. Promising experimental results on face, object, and hand-written digit image classification tasks are provided to show the effectiveness of our method. © 1992-2012 IEEE.


Wang Y.,National University of Defense Technology | Wang Y.,Nanjing University | Jiang Y.,Nanjing University | Wu Y.,National University of Defense Technology | Zhou Z.-H.,Nanjing University
IEEE Transactions on Neural Networks | Year: 2011

Spectral clustering (SC) is a large family of grouping methods that partition data using eigenvectors of an affinity matrix derived from the data. Though SC methods have been successfully applied to a large number of challenging clustering scenarios, it is noteworthy that they will fail when there are significant intersections among different clusters. In this paper, based on the analysis that SC methods are able to work well when the affinity values of the points belonging to different clusters are relatively low, we propose a new method, called spectral multi-manifold clustering (SMMC), which is able to handle intersections. In our model, the data are assumed to lie on or close to multiple smooth low-dimensional manifolds, where some data manifolds are separated but some are intersecting. Then, local geometric information of the sampled data is incorporated to construct a suitable affinity matrix. Finally, spectral method is applied to this affinity matrix to group the data. Extensive experiments on synthetic as well as real datasets demonstrate the promising performance of SMMC. © 2011 IEEE.


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.


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.


Han B.,University of Tsukuba | Li J.,University of Tsukuba | Su J.,National University of Defense Technology | Cao J.,Hong Kong Polytechnic University
IEEE Journal on Selected Areas in Communications | Year: 2012

One of the challenging issues for supporting emergency services in wireless networks is coordinating the network under emergent situations. Cooperative communication (CC) is a promising approach which can offer significant enhancements in multi-hop wireless networks. This paper investigates the potential issues in using this communication paradigm to support emergency services. We focus on promoting energy-efficient and congestion-aware cooperative networking for emergency services based on the idea of Do-It-Yourself. We propose a novel cross-layer design which jointly considers the problems of route selection in network layer, congestion and non-cooperation avoidance among multiple links in MAC layer under cooperative multi-hop wireless environments. We formulate the multi-hop cooperative flow routing and relay node selection process as an optimization problem. Based on the formulations and models, we propose a self-supported networking scheme including three novel components that make the solution procedure highly efficient. Analysis and simulation results show that our approaches significantly achieve better network performance and typically satisfy the requirements for emergency services in multi-hop wireless networks. © 2006 IEEE.


Chen S.-W.,National University of Defense Technology | Li Y.-Z.,National University of Defense Technology | Wang X.-S.,Chinese Institute of Electronics | Xiao S.-P.,National University of Defense Technology | Sato M.,Geoscience and Remote Sensing Society GRSS
IEEE Signal Processing Magazine | Year: 2014

Polarimetric target decomposition is a powerful technique to interpret scattering mechanisms in polarimetric synthetic aperture radar (PolSAR) data. Eigenvalue-?eigenvector-based and model-based methods are two main categories within the incoherent decomposition techniques. Eigenvalue-eigenvector-based decomposition becomes relatively mature since it has a clearer mathematical background and has only one decomposition solution. In contrast, model-based decompositions can obtain different decomposition solutions in terms of various scattering models. Meanwhile, conventional methods with models or assumptions that do not fit the observations may induce deficiencies. Thereby, the development of effective model-based decompositions has received considerable attention and many advances have been reported. This article aims to provide a review for these notable advances, mainly including the incorporation of orientation compensation processing, nonnegative eigenvalue constraint, generalized scattering models, complete information utilization, full-parameter inversion schemes, and fusion of polarimetry and interferometry. Airborne Pi-SAR data sets are used for demonstration. Besides, natural disaster damage evaluation using model-based decomposition is carried out based on advanced land-observing satellite/phased array type L-band synthetic aperture radar (ALOS/PALSAR) data. Finally, further development perspectives are presented and discussed. © 2014 IEEE.


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.


Xiong J.,National University of Defense Technology | Wong K.-K.,University College London | Ma D.,National University of Defense Technology | Wei J.,National University of Defense Technology
IEEE Communications Letters | Year: 2012

In this letter, we aim to achieve secure communication for a multiple-input single-output (MISO) wiretap channel in the presence of multiple non-colluding eavesdroppers. It is assumed that the eavesdroppers' channels are unavailable to the transmitter, and artificial noise (AN) is used to provide masked beamforming for degrading the eavesdroppers' channels. First, we derive the secrecy rate outage probability for the masked beamforming system and then the optimal power allocation between data and AN is obtained in closed form for minimizing the secrecy rate outage probability under a total power constraint. The effects of the number of transmit antennas, the transmit power, and the target secrecy rate on the optimal power allocation parameter are characterized. Numerical results are presented to show the performance of our proposed power allocation scheme. © 2012 IEEE.


Hu T.,National University of Defense Technology | Low K.H.,Nanyang Technological University | Shen L.,National University of Defense Technology | Xu X.,National University of Defense Technology
IEEE/ASME Transactions on Mechatronics | Year: 2014

Robotic models have been used as one of the approaches to study fish locomotion. Therefore, this paper proposes an effective control scheme that enables robotic models to mimic fin-ray undulation kinematics of live fish. We found in the experiments of robotic fin undulation that the difference between the desired and actual trajectories can be significant. It is believed that the difference might be caused by the phase lagging effect. To tackle the phase tracking problem, a modified iterative learning control (ILC) scheme is proposed and implemented on the robotic fish model. Furthermore, a memory clearing operator is proposed to satisfy the Lipschitz condition. This is necessary for the convergence and feasibility of the ILC scheme. Finally, experimental results illustrate the effectiveness of the proposed learning control approach, including the memory clearing operator. © 1996-2012 IEEE.


Liu F.,National University of Defense Technology | Liu F.,Beijing University of Technology
Proc. - 14th IEEE Int. Conf. on Computational Science and Engineering, CSE 2011 and 11th Int. Symp. on Pervasive Systems, Algorithms, and Networks, I-SPA 2011 and 10th IEEE Int. Conf. on IUCC 2011 | Year: 2011

Digest Access Authentication was originally proposed to provide peer authentication and data encryption in HTTP protocols. It has been widely employed along with the deployment of SASL. In this paper, we implement a password recovery attack to Digest Access Authentication that can recover passwords as long as 48 characters in overall off-line computation about 2 35 MD5 compressions and 8084 on-line queries. This confirms that the security of Digest Access Authentication is totally broken, and all applications based on that must be re-evaluated seriously. Further, we prove that the security of the hashing scheme H(C∥P), where H is a hash function, C is a challenge and P is a shared password, is totally dependent on the collision resistance of H, instead of the pre-image resistance. Such scheme can't be used in challenge and response protocols to protect the shared password. Finally, we prove that some hashing schemes like H(H(C∥P)) provide no more security than H(C∥P), in the aspect of collision resistance. © 2011 IEEE.


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 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.


Lv P.,National University of Defense Technology | Wang X.,The University of Michigan - Shanghai Jiao Tong University Joint Institute | Xu M.,National University of Defense Technology
Ad Hoc Networks | Year: 2012

Network virtualization of a wireless mesh network (WMN) is an economical way for different subscribers to customize their exclusive access networks through a common network infrastructure. The most critical task of network virtualization is virtual network embedding, which can be divided into two sub-problems: node mapping and link mapping. Although there exist approaches to virtual network embedding in wired networks, the characteristics of WMNs make virtual network embedding become a unique and challenging problem. In this paper, virtual access network embedding is studied for WMNs. To support flexible resource allocation in virtual access network embedding, each access node is designed based on orthogonal frequency division multiple access (OFDMA) dual-radio architecture. Through subcarrier allocation on each link, virtual access networks are gracefully separated from each other. To coordinate channel assignment across different links under the constraint of a limited number of orthogonal channels, a novel channel allocation algorithm is proposed to exploit partially-overlapped channels to improve resource utilization. Since the virtual access network embedding problem is NP-hard, a heuristic algorithm is developed based on an enhanced genetic algorithm to obtain an approximate but effective solution. Simulation results illustrate that the virtual access network embedding framework developed in this paper works effectively in WMNs. © 2012 Elsevier B.V. All rights reserved.


Van Kaick O.,Simon Fraser University | Xu K.,National University of Defense Technology | Zhang H.,Simon Fraser University | Wang Y.,National University of Defense Technology | And 3 more authors.
ACM Transactions on Graphics | Year: 2013

We introduce an unsupervised co-hierarchical analysis of a set of shapes, aimed at discovering their hierarchical part structures and revealing relations between geometrically dissimilar yet functionally equivalent shape parts across the set. The core problem is that of representative co-selection. For each shape in the set, one representative hierarchy (tree) is selected from among many possible interpretations of the hierarchical structure of the shape. Collectively, the selected tree representatives maximize the within-cluster structural similarity among them. We develop an iterative algorithm for representative co-selection. At each step, a novel cluster-and-select scheme is applied to a set of candidate trees for all the shapes. The tree-to-tree distance for clustering caters to structural shape analysis by focusing on spatial arrangement of shape parts, rather than their geometric details. The final set of representative trees are unified to form a structural co-hierarchy. We demonstrate co-hierarchical analysis on families of man-made shapes exhibiting high degrees of geometric and finer-scale structural variabilities. Copyright © ACM 2013.


Chen Y.,Nanjing Normal University | Wang C.,Nanjing Medical University | Zhu X.,National University of Defense Technology | Tan Y.,Nanjing Medical University | Zhong Y.,Nanjing Normal University
Journal of Affective Disorders | Year: 2015

Abstract Background Convergent studies have highlighted the dysfunction of default mode network (DMN) in major depressive disorder (MDD). The altered connectivity in posterior cingulate cortex (PCC) and medial prefrontal cortex (mPFC) was especially found to be of interest in the resting state functional connectivity analysis. Recently, more attention has turned to the internal functional connectivity within the DMN. However, the internal connection patterns within the DMN remain unclear at the initial onset of MDD. Methods Resting-state fMRI was performed on 38 first-episode, treatment-naïve MDD patients along with 38 matched healthy controls. Seed-based analysis was used to define the DMN and then a region-to-region connectivity analysis was performed to inspect the functional connectivity within the DMN. Spearman's rank correlation analysis was performed between significantly abnormal connectivities in MDD patients and clinical measurements. Results Decreased region-to-region connectivities within DMN were found between the PCC and dorsal medial prefrontal cortex (dmPFC), between PCC and the right inferior parietal gyrus/angular, as well as between the left thalamus and cerebellar tonsil. No significant increase in connectivity was found. Moreover, functional connectivity between the left thalamus and cerebellar tonsil revealed a marginal significant negative correlation with clinical Hamilton Depression Rating Scale (HDRS) scores. Limitations Noteworthiness in morbidity, a high risk of mortality, and a high rate of medical service utilization of MDD make the current results uncertain to apply to the more complicated situations. Conclusions Each region within DMN may have a specific, individual functional role. The reason to identify the pathological mechanism of MDD may not lie in the abnormal DMN functional connectivity, but rather in the abnormal functional connectivity within DMN. © 2015 Elsevier B.V.


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.


Liu Y.,National University of Defense Technology | Luo X.,Hong Kong Polytechnic University | Chang R.K.C.,Hong Kong Polytechnic University | Su J.,National University of Defense Technology
IEEE Journal on Selected Areas in Communications | Year: 2013

Rerouting is not uncommon in nowadays Internet because it can be triggered by many root causes, such as network faults, routing attacks, etc. However, few methods effectively characterize rerouting in the whole Internet. In this paper, inspired by a well known network science metric-betweenness centrality, we propose a new approach to characterize inter-domain reroutings. By defining and analysing the variation of AS betweenness centrality for neighbouring- destination routes and global routes separately, our method empowers users to identify the temporal, topological, and relational characteristics of route changes. We apply our method to investigate the Internet's reactions to four different disruptive events, including Japan earthquake in March 2011, SEA-ME-WE 4 cable fault in April 2010, routing attack on YouTube in February 2008, and AS4761 hijacking event in January 2011. This examination reveals many new insights. For example, the route flapping and the congestion caused by the side-effect of rerouting after cable faults significantly degraded path quality. Moreover, direct providers of attackers and victims are the most critical positions for amplifying impact of prefix hijacking attacks. Such results shed light on how to implement effective reactions to network faults and how to deploy efficient defense mechanisms against routing attacks. © 1983-2012 IEEE.


Su L.,National University of Defense Technology | Wang L.,National University of Defense Technology | Shen H.,National University of Defense Technology | Feng G.,Beijing Jiaotong University | Hu D.,National University of Defense Technology
Frontiers in Human Neuroscience | Year: 2013

Background: Dysfunctional integration of distributed brain networks is believed to be the cause of schizophrenia, and resting-state functional connectivity analyses of schizophrenia have attracted considerable attention in recent years. Unfortunately, existing functional connectivity analyses of schizophrenia have been mostly limited to linear associations. Objective: The objective of the present study is to evaluate the discriminative power of non-linear functional connectivity and identify its changes in schizophrenia. Method: A novel measure utilizing the extended maximal information coefficient was introduced to construct non-linear functional connectivity. In conjunction with multivariate pattern analysis, the new functional connectivity successfully discriminated schizophrenic patients from healthy controls with relative higher accuracy rate than the linear measure. Result: We found that the strength of the identified non-linear functional connections involved in the classification increased in patients with schizophrenia, which was opposed to its linear counterpart. Further functional network analysis revealed that the changes of the non-linear and linear connectivity have similar but not completely the same spatial distribution in human brain. Conclusion: The classification results suggest that the non-linear functional connectivity provided useful discriminative power in diagnosis of schizophrenia, and the inverse but similar spatial distributed changes between the non-linear and linear measure may indicate the underlying compensatory mechanism and the complex neuronal synchronization underlying the symptom of schizophrenia. © 2013 Su, Wang, Shen, Feng and Hu.


Tang Y.,National University of Defense Technology | Xiao B.,Hong Kong Polytechnic University | Lu X.,National University of Defense Technology
IEEE Transactions on Computers | Year: 2011

Network-based signature generation (NSG) has been proposed as a way to automatically and quickly generate accurate signatures for worms, especially polymorphic worms. In this paper, we propose a new NSG system-PolyTree, to defend against polymorphic worms. We observe that signatures from worms and their variants are relevant and a tree structure can properly reflect their familial resemblance. Hence, in contrast to an isolated view of generated signatures in previous approaches, PolyTree organizes signatures extracted from worm samples into a tree structure, called signature tree, based on the formally defined "more specific relation of simplified regular expression signatures. PolyTree is composed of two components, signature tree generator and signature selector. The signature tree generator implements an incremental signature tree generation algorithm from worm sample clustering, up-to-date signature refinement to efficient tree construction. The incremental signature tree construction gives insight on how the worm variants evolve over time and allows signature refinement upon a new worm sample arrival. The signature selector chooses a set of signatures for worm detection from a benign traffic pool and the current signature tree constructed by the signature tree generator. Experiments show that PolyTree cannot only generate accurate signatures for polymorphic worms with noise, but these signatures are well organized in the signature tree to reflect the inherent relations of worms and their variants. © 2011 IEEE.


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.


Pei M.,National University of Defense Technology | Wei J.,National University of Defense Technology | Wong K.-K.,University College London | Wang X.,National University of Defense Technology
IEEE Transactions on Wireless Communications | Year: 2012

This letter investigates masked beamforming schemes for multiuser multiple-input multiple-output (MIMO) downlink systems in the presence of an eavesdropper. With noisy and outdated channel state information (CSI) at the base station (BS), we aim to maximize the transmit power of an artificial noise, which is broadcast to jam any potential eavesdropper, while meeting individual minimum mean square error (MMSE) constraints of the desired user links. To this end, we adopt a Bayesian approach and derive an average MSE uplink-downlink duality with imperfect CSI. Using the duality, a robust beamforming algorithm is proposed. Simulation results show the effectiveness of the proposed scheme. © 2012 IEEE.


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.


Xu K.,National University of Defense Technology | Xu K.,Simon Fraser University | Zheng H.,Zhejiang University | Zhang H.,Simon Fraser University | And 3 more authors.
ACM Transactions on Graphics | Year: 2011

We introduce an algorithm for 3D object modeling where the user draws creative inspiration from an object captured in a single photograph. Our method leverages the rich source of photographs for creative 3D modeling. However, with only a photo as a guide, creating a 3D model from scratch is a daunting task. We support the modeling process by utilizing an available set of 3D candidate models. Specifically, the user creates a digital 3D model as a geometric variation from a 3D candidate. Our modeling technique consists of two major steps. The first step is a user-guided image-space object segmentation to reveal the structure of the photographed object. The core step is the second one, in which a 3D candidate is automatically deformed to fit the photographed target under the guidance of silhouette correspondence. The set of candidate models have been pre-analyzed to possess useful high-level structural information, which is heavily utilized in both steps to compensate for the ill-posedness of the analysis and modeling problems based only on content in a single image. Equally important, the structural information is preserved by the geometric variation so that the final product is coherent with its inherited structural information readily usable for subsequent model refinement or processing. © 2011 ACM.


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 X.,National University of Defense Technology | Yang Y.-H.,University of Alberta | Han Z.,National University of Defense Technology | Wang H.,National University of Defense Technology | Gao C.,National University of Defense Technology
ACM Computing Surveys | Year: 2013

Object class detection, also known as category-level object detection, has become one of the most focused areas in computer vision in the new century. This article attempts to provide a comprehensive survey of the recent technical achievements in this area of research. More than 270 major publications are included in this survey covering different aspects of the research, which include: (i) problem description: key tasks and challenges; (ii) core techniques: appearance modeling, localization strategies, and supervised classification methods; (iii) evaluation issues: approaches, metrics, standard datasets, and state-of-the-art results; and (iv) new development: particularly new approaches and applications motivated by the recent boom of social images. Finally, in retrospect of what has been achieved so far, the survey also discusses what the future may hold for object class detection research. © 2013 ACM.


Liu W.,National University of Defense Technology | Xie W.,Wuhan Radar Academy | Liu J.,Xidian University | Wang Y.,Wuhan Radar Academy
IEEE Transactions on Signal Processing | Year: 2014

In this two-part paper, we consider the problem of adaptive multidimensional/multichannel signal detection in Gaussian noise with unknown covariance matrix. The test data (primary data) is assumed as a collection of sample vectors, arranged as the columns of a rectangular data array. The rows and columns of the signal matrix are both assumed to lie in known subspaces, but with unknown coordinates. Due to this feature of the signal structure, we name this kind of signal as the double subspace signal. Part I of this paper focuses on the adaptive detection in homogeneous environments, while Part II deals with the adaptive detection in partially homogeneous environments. Precisely, in this part, we derive the generalized likelihood ratio test (GLRT), Rao test, Wald test, as well as their two-step variations, in homogeneous environments. Three types of spectral norm tests (SNTs) are also introduced. All these detectors are shown to possess the constant false alarm rate (CFAR) property. Moreover, we discuss the differences between them and show how they work. Another contribution is that we investigate various special cases of these detectors. Remarkably, some of them are well-known existing detectors, while some others are still new. At the stage of performance evaluation, conducted by Monte Carlo simulations, both matched and mismatched signals are dealt with. For each case, more than one scenario is considered. © 1991-2012 IEEE.


Liu W.,National University of Defense Technology | Xie W.,Wuhan Radar Academy | Liu J.,Xidian University | Wang Y.,Wuhan Radar Academy
IEEE Transactions on Signal Processing | Year: 2014

In this part of the paper, we continue to study the problem of detecting a double subspace signal in Gaussian noise. Precisely, we address the detection problem in partially homogeneous environments, where the primary and secondary data share the same covariance matrix up to an unknown scaling factor. We derive the generalized likelihood ratio test (GLRT), Rao test, Wald test, and their two-step versions. We also introduce three spectral norm tests (SNTs). All these detectors possess the constant false alarm rate (CFAR) property. Moreover, various kinds of special cases of these detectors are given. At the stage of performance evaluation, we consider two cases. One is the case of no signal mismatch. The other is more general, namely, the case of signal mismatch, including the column-space signal mismatch and row-space signal mismatch. © 1991-2012 IEEE.


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.


Liu W.,National University of Defense Technology | Liu W.,Wuhan Radar Academy | Wang Y.,Wuhan Radar Academy | Xie W.,Wuhan Radar Academy
Signal Processing | Year: 2014

The Fisher information matrix (FIM) is an important tool in signal processing. In this paper, we investigate the FIM with respect to the complex-valued quantities, and show its application in signal processing, such as the design of the Rao and Wald tests, and the derivation of the Cramér-Rao bound for the unbiased estimate. Some examples are also given. © 2013 Published by Elsevier B.V. All rights reserved.


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.


Wang K.,National University of Defense Technology | Wang K.,Intelligent Systems Technology, Inc. | Shen Z.,Chinese Academy of Sciences
Proceedings of 2012 IEEE International Conference on Service Operations and Logistics, and Informatics, SOLI 2012 | Year: 2012

Traffic micro-simulation is an important tool in the Intelligent Transportation Systems (ITS) research. In the micro-simulation, a bottom up system can be built up by the interactions of vehicle agents, road agents, traffic lights agents, etc. The Artificial societies, Computational experiments, and Parallel execution (ACP) approach suggests integrating other metropolitan systems such as logistic, infrastructure, legal and regulatory, weather and environmental systems to build an Artificial Transportation System (ATS) to help solve ITS problems. This is reasonable as the transportation system is complex that is affected by many systems interacting with each other. However, there is a challenge that the computing burden can be very heavy as there can be many agents of different kinds interacting in parallel in ATS. In recent years, the Graphics Processing Units (GPUs) have been applied successfully in many areas for parallel computing. Compared with the traditional CPU cluster, GPU has an obvious advantage of low cost of hardware and electricity consumption. In this paper, we build a parallel traffic simulation module of ATS with GPU. The simulation results are reasonable and a maximum speedup factor of 105 is obtained compared with the CPU implementations. © 2012 IEEE.


Wang D.-W.,Wuhan Radar Academy | Ma X.-Y.,Wuhan Radar Academy | Su Y.,National University of Defense Technology
IEEE Transactions on Image Processing | Year: 2010

This paper presents a system model and method for the 2-D imaging application via a narrowband multiple-input multiple-output (MIMO) radar system with two perpendicular linear arrays. Furthermore, the imaging formulation for our method is developed through a Fourier integral processing, and the parameters of antenna array including the cross-range resolution, required size, and sampling interval are also examined. Different from the spatial sequential procedure sampling the scattered echoes during multiple snapshot illuminations in inverse synthetic aperture radar (ISAR) imaging, the proposed method utilizes a spatial parallel procedure to sample the scattered echoes during a single snapshot illumination. Consequently, the complex motion compensation in ISAR imaging can be avoided. Moreover, in our array configuration, multiple narrowband spectrum-shared waveforms coded with orthogonal polyphase sequences are employed. The mainlobes of the compressed echoes from the different filter band could be located in the same range bin, and thus, the range alignment in classical ISAR imaging is not necessary. Numerical simulations based on synthetic data are provided for testing our proposed method. © 2010 IEEE.


Zenghui Z.,National University of Defense Technology | Jubo Z.,National University of Defense Technology | Yongliang W.,Wuhan Radar Academy
IET Radar, Sonar and Navigation | Year: 2012

Space-time adaptive processing (STAP) is an advanced technique for airborne radar to mitigate clutter and detect moving targets effectively. Based on adaptive radar theory, the degrees-of-freedom of a STAP processor should be larger than that of a clutter. In this study, the local degrees-of-freedom (LDOF) of clutter for reduced-dimensional STAP (RD-STAP) methods with subarray configurations are studied. The LDOF formulas are proposed and verified by simulations. With these formulas, the LDOFs of clutter will collapse under certain radar configurations, which are favourable for clutter mitigation. Therefore these formulas could be used as guidance for STAP radar to choose appropriate system parameters and processing methods. © 2012 The Institution of Engineering and Technology.


Liu W.,National University of Defense Technology | Xie W.,Wuhan Radar Academy | Wang Y.,Wuhan Radar Academy
IEEE Signal Processing Letters | Year: 2013

In this letter, we consider the problem of detecting a distributed target with unknown signal steering in the Gaussian noise. We derive the Rao and Wald tests. It is found that the Rao test coincides with the so-called modified two-step generalized likelihood ratio test (M2S-GLRT), while the Wald test is equivalent to the plain two-step GLRT (2S-GLRT). We also give some intuitive interpretations about the Rao and Wald tests, as well as other existing detectors. © 2013 IEEE.


Wang X.,National University of Defense Technology | Liu L.,Georgia Institute of Technology | Su J.,National University of Defense Technology
IEEE Transactions on Services Computing | Year: 2012

Reputation-based trust systems provide important capability in open and service-oriented computing environments. Most existing trust models fail to assess the variance of a reputation prediction. Moreover, the summation method, widely used for reputation feedback aggregation, is vulnerable to malicious feedbacks. This paper presents a general trust model, called RLM, for a more comprehensive and robust reputation evaluation. Concretely, we define a comprehensive reputation evaluation method based on two attributes: reputation value and reputation prediction variance. The reputation predication variance serves as a quality measure of the reputation value computed based on aggregation of feedbacks. For feedback aggregation, we propose the novel Kalman aggregation method, which can inherently support robust trust evaluation. To defend against malicious and coordinated feedbacks, we design the Expectation Maximization algorithm to autonomously mitigate the influence of a malicious feedback, and further apply the hypothesis test method to resist malicious feedbacks precisely. Through theoretical analysis, we demonstrate the robustness of the RLM design against adulating and defaming attacks, two popular types of feedback attacks. Our experiments show that the RLM model can effectively capture the reputation's evolution and outperform the popular summation-based trust models in terms of both accuracy and attack resilience. Concretely, under the attack of collusive malicious feedbacks, RLM offers higher robustness for the reputation prediction and a lower false positive rate for the malicious feedback detection. © 2008 IEEE.


Guo Y.,National University of Defense Technology | Guo Y.,University of Western Australia | Sohel F.,University of Western Australia | Bennamoun M.,University of Western Australia | And 2 more authors.
International Journal of Computer Vision | Year: 2013

Recognizing 3D objects in the presence of noise, varying mesh resolution, occlusion and clutter is a very challenging task. This paper presents a novel method named Rotational Projection Statistics (RoPS). It has three major modules: local reference frame (LRF) definition, RoPS feature description and 3D object recognition. We propose a novel technique to define the LRF by calculating the scatter matrix of all points lying on the local surface. RoPS feature descriptors are obtained by rotationally projecting the neighboring points of a feature point onto 2D planes and calculating a set of statistics (including low-order central moments and entropy) of the distribution of these projected points. Using the proposed LRF and RoPS descriptor, we present a hierarchical 3D object recognition algorithm. The performance of the proposed LRF, RoPS descriptor and object recognition algorithm was rigorously tested on a number of popular and publicly available datasets. Our proposed techniques exhibited superior performance compared to existing techniques. We also showed that our method is robust with respect to noise and varyingmesh resolution. Our RoPS based algorithm achieved recognition rates of 100, 98.9, 95.4 and 96.0% respectively when tested on the Bologna, UWA, Queen's and Ca' Foscari Venezia Datasets. © Springer Science+Business Media New York 2013.


Xie G.,Lanzhou University | Xi P.,Lanzhou University | Liu H.,Lanzhou University | Chen F.,Lanzhou University | And 6 more authors.
Journal of Materials Chemistry | Year: 2012

A superparamagnetic graphene oxide-Fe 3O 4 hybrid composite (GO-Fe 3O 4) was prepared via a simple and effective chemical method. Amino-functionalized Fe 3O 4 (NH 2-Fe 3O 4) particles are firmly deposited on the graphene oxide sheets. The graphene oxide sheets could prevent NH 2-Fe 3O 4 particles from agglomeration and enable a good dispersion of these oxide particles. The as-prepared GO-Fe 3O 4 hybrid composite had a much higher thermal stability than graphene oxide. The amount of NH 2-Fe 3O 4 loaded on GO was estimated to be 23.6 wt% by atomic absorption spectrometry. The specific saturation magnetization (M s) of the GO-Fe 3O 4 hybrid composite is 15 emu g -1. The magnetic GO-Fe 3O 4 composite has been employed as adsorbent for the magnetic separation of dye contaminants from water. The adsorption test of dyes (Methylene Blue (MB) and Neutral Red (NR)) demonstrates that it only takes 30 min for MB and 90 min for NR to attain equilibrium. The adsorption capacities for MB and NR in the concentration range studied are 167.2 and 171.3 mg g -1, respectively. The GO-Fe 3O 4 hybrid composite can be easily manipulated in magnetic field for desired separation, leading to the removal of dyes from polluted water. These GO-Fe 3O 4 hybrid composites have great potential applications in removing organic dyes from polluted water. © The Royal Society of Chemistry 2011.


Guo Y.,National University of Defense Technology | Guo Y.,University of Western Australia | Bennamoun M.,University of Western Australia | Sohel F.,University of Western Australia | And 2 more authors.
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2014

3D object recognition in cluttered scenes is a rapidly growing research area. Based on the used types of features, 3D object recognition methods can broadly be divided into two categories - global or local feature based methods. Intensive research has been done on local surface feature based methods as they are more robust to occlusion and clutter which are frequently present in a real-world scene. This paper presents a comprehensive survey of existing local surface feature based 3D object recognition methods. These methods generally comprise three phases: 3D keypoint detection, local surface feature description, and surface matching. This paper covers an extensive literature survey of each phase of the process. It also enlists a number of popular and contemporary databases together with their relevant attributes. © 1979-2012 IEEE.


He Y.,National University of Defense Technology | He Y.,Northumbria University | Pan M.,National University of Defense Technology | Luo F.,National University of Defense Technology | Tian G.,Northumbria University
NDT and E International | Year: 2011

Hidden defect characterisation in some complex structures is difficult. Pulsed Eddy Current (PEC) imaging based on rectangular excitation coil is investigated in this paper and hidden defect nondestructive testing and evaluation (detection, classification, and quantification) is carried out based on the various C-scan images. Experimental results have illustrated that hidden defects can be identified effectively by particular character in C-scan imaging results and sub-surface defects can be discriminated to correct class by selecting the rising time from response in time domain. The quantification information of hidden defects is preliminarily obtained based on the contour and 3D images. In addition, PEC imaging and frequency spectrum analysis are effective to detect, classify, and evaluate the sub-surface defects under the influence of edge effect of specimen. To sum up, PEC imaging is an effective approach to characterise hidden defects and sub-surface defects. © 2011 Elsevier Ltd. All rights reserved.


Wang X.,National University of Defense Technology | Balakrishnan N.,McMaster University | Guo B.,National University of Defense Technology
Reliability Engineering and System Safety | Year: 2014

The issue of residual life (RL) estimation, which has been widely studied recently, plays an important role in scheduling maintenance. In this work, we present an adaptive method of RL estimation based on a generalized Wiener degradation process which subsumes several existing models as limiting cases. The nonlinearity, the temporal uncertainty, and the product-to-product variability of the degradation are jointly taken into account in the proposed degradation model. Under a mild assumption, an analytical approximation to the probability density function of the RL is derived in a closed-form, which becomes quite useful in maintenance decision making. The unknown parameters of the model that characterize the population-based degradation characteristics are obtained by using the maximum likelihood approach, while the parameters that describe the online product-specific characteristic are estimated by using the Markov chain Monte Carlo (MCMC) method. Once new degradation data information of the target product becomes available, the degradation model is first updated based on the degradation history up to the current time through a strong tracking filter, and then the RL is estimated sequentially. In this way, the RL of a product can be estimated in an adaptive manner. Finally, the validity of the proposed method is demonstrated with an illustrative example concerning fatigue cracks. © 2013 Elsevier Ltd.


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.


He Y.,National University of Defense Technology | He Y.,Northumbria University | Tian G.,Northumbria University | Pan M.,National University of Defense Technology | Chen D.,National University of Defense Technology
Composites Part B: Engineering | Year: 2014

With the growing interest to use composite materials and honeycomb sandwich panels in industrial fields, much attention is devoted to the development of non-destructive testing (NDT) techniques for the detection and evaluation of defects. In this work, scanning pulsed eddy current (PEC) was investigated and two features, representing the magnetic field intensity and conductivity, were used to characterise the different types of defects in carbon fibre reinforced plastics (CFRP) laminates and honeycomb sandwich panels. The experimental results show that the low energy impact from 4 J to 12 J, conductive and non-conductive insert defects can be effectively detected and evaluated using the proposed methods. The effectiveness was verified and the advantages of scanning PEC were addressed through comparative studies with flash thermography and shearography. © 2013 Elsevier Ltd. All rights reserved.


Wang X.,National University of Defense Technology | Liu T.,New York University | Qin J.,Australian National University
IET Control Theory and Applications | Year: 2012

This study proposes a distributed non-linear consensus protocol for second-order non-linear multi-agent systems with unknown locally Lipschitz dynamics and connected graph. The main analysis is based on a blend of graph-theoretic and non-linear-theoretic tools with the notion of input-to-state stability (ISS) playing a central role. Through the backstepping design, the closed-loop multi-agent system is transformed into a two-cascade interconnected system with proven ISS properties. Correspondingly, the recently developed cyclic-small-gain theorem is then employed to guarantee the asymptotic stability of the closed-loop multi-agent system, which implies consensus. © 2012 The Institution of Engineering and Technology.


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.


Lei H.,National University of Defense Technology | Laporte G.,HEC Montréal | Laporte G.,Interuniversity Research Center on Enterprise Networks | Guo B.,National University of Defense Technology
Computers and Operations Research | Year: 2011

The capacitated vehicle routing problem with stochastic demands and time windows is an extension of the capacitated vehicle routing problem with stochastic demands, in which demands are stochastic and a time window is imposed on each vertex. A vertex failure occurring when the realized demand exceeds the vehicle capacity may trigger a chain reaction of failures on the remaining vertices in the same route, as a result of time windows. This paper models this problem as a stochastic program with recourse, and proposes an adaptive large neighborhood search heuristic for its solution. Modified Solomon benchmark instances are used in the experiments. Computational results clearly show the superiority of the proposed heuristic over an alternative solution approach. © 2011 Elsevier Ltd. All rights reserved.


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.


He Y.,National University of Defense Technology | Pan M.,National University of Defense Technology | Pan M.,Northumbria University | Luo F.,National University of Defense Technology
Review of Scientific Instruments | Year: 2012

Pulsed eddy current (PEC) thermography (a.k.a. induction thermography) has been successfully applied to detect defects (corrosion, cracks, impact, and delamination) in metal alloy and carbon fiber reinforced plastic. During these applications, the defect detection mechanism is mainly investigated based on the eddy current interaction with defect. In this paper, defect characterisation for wall thinning defect and inner defect in steel is investigated based on heat diffusion. The paper presents the PEC thermography testing, which integrates the reflection mode and transmission mode by means of configuring two cameras on both sides of sample. The defect characterisation methods under transmission mode and reflection mode are investigated and compared through 1D analytical analysis, 3D numerical studies, and experimental studies. The suitable detection mode for wall thinning and inner defects quantification is concluded. © 2012 American Institute of Physics.


Xie Z.,National University of Defense Technology | Zhu J.,Zhejiang University | Kong D.,Zhejiang University | Li J.,National University of Defense Technology
Physica A: Statistical Mechanics and its Applications | Year: 2015

The theory of random geometric graph enables the study of complex networks through geometry. To analyze evolutionary networks, time-varying geometries are needed. Solutions of the generalized hyperbolic geometric flow are such geometries. Here we propose a scale-free network model, which is a random geometric graph on a two dimensional disc. The metric of the disc is a Ricci flat solution of the flow. The model is used to physically simulate the growth and aggregation of a type of cancer cell. © 2015 Elsevier B.V. All rights reserved.


Chen S.,National University of Defense Technology | Zhao C.,Arizona Optical Metrology LLC | Dai Y.,National University of Defense Technology | Li S.,National University of Defense Technology
Optics Express | Year: 2014

In off-Axis subapertures of most aspheres, astigmatism and coma dominate the aberrations with approximately quadratic and linear increase as the off-Axis distance increases. A pair of counter-rotating Zernike plates is proposed to generate variable amount of Zernike terms Z4 and Z6, correcting most of the astigmatism and coma for subapertures located at different positions on surfaces of various aspheric shapes. The residual subaperture aberrations are then reduced within the vertical dynamic range of measurement of the interferometer. The plates are fabricated with computer generated holograms and the experimental results show the variable aberration correction effect without ghost fringes. The same plates are reconfigurable by counter-rotating to enable near-null test of various aspheres flexibly. © 2014 Optical Society of America.


Ju S.,National University of Defense Technology | Shenoi R.A.,University of Southampton | Jiang D.,National University of Defense Technology | Sobey A.J.,University of Southampton
Composite Structures | Year: 2013

A multi-parameter optimization approach for a lightweight FRP composite triangular truss under nonlinear structural response constraints is presented in this paper. The composite truss exhibited bilinear behavior under three-point bending which was observed by both experimental and numerical investigation. Sensitivity analysis was conducted to evaluate the effects of geometric parameters on the flexural performance of the composite truss. A response surface, developed from a finite element analysis, was employed to replicate the outputs of nonlinear structural responses with respect to four key geometric parameters. Gradient-based and Genetic Algorithm optimization processes were selected and implemented from the MATLAB Optimization Toolbox. Final adjustments to the optimal design, obtained using MATLAB, were made according to the results of sensitivity analysis. The results show that significant improvement in terms of weight saving were achieved by adopting the proposed optimization design procedure. © 2012 Elsevier Ltd.


Ma J.,National University of Defense Technology | Huang M.,National University of Defense Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2012

With the development of laser technology, laser imaging radar gradually possesses vast application in complicated battlefield of modern warfare. At present automatic target recognition technology for laser imaging radar is a hot problem at home and abroad. Target recognition algorithm based on combination moments for laser imaging radar is put forward. Combination moments feature including lower-order Zernike moments, Hu moments and central moments is extracted from range image of laser imaging radar target, this feature is not sensitive to range image noise. Radial base function (RBF) neural network is used to recognize three kinds of ground targets. Experimental result shows that comparing this algorithm with using Zernike moments and Hu moments feature to recognize targets, the average recognition rate of three kinds of ground targets of laser imaging radar is raised by 1.0% and 3.7% separately under high carrier-to-noise ratio (CNR) (20 dB); the average recognition rate is raised by 11.8% and 42.5% separately under low CNR (10 dB); when CNR is higher than 17 dB, the average recognition rate of this algorithm is 100%. Therefore this algorithm gains good recognition effect.


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

The four-mode laser gyro's null shift is very complex under the high-low temperature process. It often vibrates when temperature changes linearly, which is a very difficult problem that cannot be explained and solved. Beam intensity changing along with temperature is simulated by changing the discharge current at room temperature, and the null shift also vibrates. So it can be concluded that temperature change induces beam intensity change, and then the null shift vibrates. If beam intensity of four-mode laser gyro can be kept constant in the high-low temperature, the null shift vibration will be effectually controlled. The conclusion is proved by the high-low temperature experiment with intensity stability.


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.


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.


Chen W.,National University of Defense Technology | Meng Z.,National University of Defense Technology
Chinese Optics Letters | Year: 2012

The characteristic of intensity noise is degraded when stimulated Brillouin scattering (SBS) occurs in the fiber transmission systems. We use the localized fluctuating model to study SBS and obtain the curves of intensity fluctuations versus the single-pass gain. Corresponding experiments are also conducted. For the forward light, the relative intensity noise (RIN) dramatically increases at first and gradually stabilizes when the input power is above the SBS threshold. For the backward light, the RIN increases dramatically with the input power near the threshold. As the input power continues to increase, the RIN decreases quickly at first and subsequently decreases slowly. This observation is attributed to the lower frequencies. © 2012 Chinese Optics Letters.


Wei G.,National University of Defense Technology | Long X.,National University of Defense Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2010

In order to evaluate the performance of high-accuracy ring laser gyroscope (RLG) more precisely, a new method of analyzing the collecting data of high-accuracy dithered RLG using dynamic Allan variance (DAVAR) is proposed. The theory of DAVAR is introduced in detail and applied in the study of stochastic errors in dithered RLG. The result shows that the analysis method of DAVAR can not only refine and identify RLG's stochastic error terms, while confirming the ratio of each error term to the overall error, but also analyze the stability of RLG's stochastic errors. Compared with Allan variance, DAVAR can represent the characterization of stochastic errors in RLG more completely.


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.


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.


Xu T.,National University of Defense Technology | Ma Q.,National University of Defense Technology | Chen Z.,National University of Defense Technology
Materials Letters | Year: 2011

Silicon oxycarbide (SiOC) and aluminum-containing silicon oxycarbide (SiAlOC) glasses were obtained through pyrolysis in argon atmosphere at 1000 °C of a polymethyl(phenyl)siloxane resin and aluminum trisec-butoxide- derived siloxane networks. These glasses were further annealed at 1200, 1300, and 1400 °C in vacuum atmosphere to investigate their high-temperature behavior. The two types of glasses were characterized by X-ray diffraction, 29SiMASNMR, 27AlMASNMR, and chemical element analysis. The aluminum incorporated into structure plays a major role on the thermal stability of SiOC by hindering carbothermal reductions. It can be found that introducing aluminum into structure should be an effective way to enhance the thermal stability of SiOC glasses. © 2010 Elsevier B.V. All rights reserved.


Ma X.-C.,National University of Defense Technology | Sun S.-H.,National University of Defense Technology | Jiang M.-S.,National University of Defense Technology | Liang L.-M.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We consider the security of practical continuous-variable quantum-key-distribution implementation with the local oscillator (LO) fluctuating in time, which opens a loophole for Eve to intercept the secret key. We show that Eve can simulate this fluctuation to hide her Gaussian collective attack by reducing the intensity of the LO. Numerical simulations demonstrate that if Bob does not monitor the LO intensity and does not scale his measurements with the instantaneous intensity values of LO, the secret key rate will be compromised severely. © 2013 American Physical Society.


Zeng J.,National University of Defense Technology | Liu P.,National University of Defense Technology | Xiang W.,National University of Defense Technology | Yuan J.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Auger decay including direct double processes of Ar 2p-1 hole levels is investigated in the framework of perturbation theory implemented by distorted wave approximation with balanced large-scale configuration interaction among the successive ions being taken into account. The complex transition amplitude obtained from the second perturbation theory for the direct double Auger decay (DAD) is decomposed into approximate formulas according to two generally agreed mechanisms of shake-off and knock-out. Practical computations showed that the knock-out condition is fulfilled and thus justified such a decomposition treatment of knock-out mechanism. The contribution to the DAD probability from knock-out mechanism is larger than shake-off by an order of magnitude and therefore the former is dominant. The interference effect between the knock-out and shake-off mechanisms should be trivial and neglecting it we obtained a branching ratio of 12.0% for the direct DAD into triply charged states of Ar3+. By including cascade double decay, a total branching ratio of 14.9% is obtained. Our result explained recent experimental results on the branching ratio into triply charged ion, and should be useful for further detailed experimental investigations. © 2013 American Physical Society.


Gao Q.,National University of Defense Technology | Jiang Z.,National University of Defense Technology | Yi S.,National University of Defense Technology | Wang X.,National University of Defense Technology
Optics Letters | Year: 2013

The tilt of the aero-optical aberration caused by the supersonic turbulent boundary layer is obtained by analyzing the center wandering of the far-field optical pattern, and its characteristics are examined from the viewpoint of statistics. When the diameter of the beam propagating through the flow is small compared with the boundary layer thickness, the probability density function (PDF) of the tilt coefficient is centered and can be approximated with a Gaussian distribution. For a larger beam diameter, the PDF of the tilt in the spanwise direction can still be regarded as centered and Gaussian, but the tilt in the streamwise direction clearly deviates from a Gaussian distribution. The correlation of the tilts in the two directions is investigated by computing the correlation coefficient, and the results indicate that the correlation is negative and strong for a small beam diameter and becomes positive and weak for a large beam diameter. These characteristics are explained by the hairpin vortex structures in the boundary layer, which prevail and meander for a very long distance streamwise. © 2013 Optical Society of America.


Wang X.,National University of Defense Technology | Zhou P.,National University of Defense Technology | Xiao H.,National University of Defense Technology | Liu Z.,National University of Defense Technology
Optics Express | Year: 2014

We demonstrate the nanosecond-level pulses in Tm-doped fiber laser generated by passively harmonic mode-locking. Nonlinear polarization rotation performed by two polarization controllers (PCs) is employed to induce the self-starting harmonic mode-locking. The fundamental repetition rate of the laser is 448.8 kHz, decided by the length of the cavity. Bundles of pulses with up to 17 uniform subpulses are generated due to the split of pulse when the pump power increases and the PCs are adjusted. Continuous harmonic mode-locked pulse trains are obtained with 1st to 6th and even more than 15th order when the positions of the PCs are properly fixed and the pump power is scaled up. The widths of all the uniform individual pulses are mostly 3-5 ns, and pulse with width of 304 ns at fundamental repetition rate can also be generated by adjusting the PCs. Hysteresis phenomenon of the passively harmonic mode-locked pulses' repetition frequency versus pump power is observed. The rather wide 3dB spectral bandwidth of the pulse train (25 nm) indicates that they may resemble noise-like pulses. © 2014 Optical Society of America.


Sun K.,National University of Defense Technology | Huang L.,National University of Defense Technology | Cheng X.,National University of Defense Technology | Jiang H.,National University of Defense Technology
Optics Express | Year: 2011

The phenomenon of secondary spots is observed in the experiment of TDI CCD camera irradiated by CW He-Ne laser. It is considered to be related to the scattering of the slit in front of the sensor and the reflection of the window of the TDI CCD chip. Additional experiments and ray tracing simulation are performed to study the mechanism of the secondary spots. The experimental and simulated results demonstrated that the scattering of the side walls of the slit is the main source of the secondary spots. Furthermore, the operation mode of rotary scanning provides the chance of scattering incident beam to the side wall of the slit. This paper will provide a preliminary hint to the optimum design of slit in camera to reduce the effects of the secondary spots to the image quality. © 2011 Optical Society of America.


Yang W.,National University of Defense Technology | Zhang B.,National University of Defense Technology | Yin K.,National University of Defense Technology | Zhou X.,National University of Defense Technology | Hou J.,National University of Defense Technology
Optics Express | Year: 2013

High power all fiber mid-IR supercontinuum (SC) generation in a ZBLAN fiber pumped by a 2 μm master oscillator power amplifier (MOPA) system is demonstrated. A semiconductor saturable absorber mirror (SESAM) passively mode-locked laser with pulse width of 26 ps at 1960 nm is used as the seed of the MOPA system. A laser spectrum extending from ~1.9 μm to beyond 2.6 μm is generated in a subsequent thulium-doped fiber amplifier (TDFA). Then, the spectrum is further broadened to the mid-IR region in the ZBLAN fiber. A mid-IR SC extending from 1.9 to 3.9 μm with 7.11 W average output power is obtained based on a large mode area TDFA, the SC power for wavelengths longer than 2.5 μm is 3.52 W with a power ratio of 49.5% with respect to the total SC power. The overall optical conversion efficiency from the 790 nm pump of the large mode area TDFA to the total SC output is 10.4%. To the best of our knowledge, both the 7.11 W total average power and 3.52 W average power in wavelengths beyond 2.5 μm are the highest power ever reported for a mid-IR SC generation in ZBLAN fiber pumped by 2 μm fiber lasers and TDFAs. © 2013 Optical Society of America.


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
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.


Kang Y.,National University of Defense Technology | Chu Z.,National University of Defense Technology | Zhang D.,National University of Defense Technology | Li G.,National University of Defense Technology | And 3 more authors.
Carbon | Year: 2013

This work demonstrates the conversion of graphene oxide into BCN hybrid nanosheets by reaction with boric acid and urea at 900 C, during which boron and nitrogen atoms are incorporated into the graphene atomic sheets. X-ray diffraction pattern and X-ray photoelectron spectroscopy reveal the existence of h-BN. High-resolution electron microscopy and Raman spectrum indicate the presence of graphene-like layers with h-BN nanodomains. The content of h-BN in the BCN nanosheets can also be tuned by further heat-treatment in an ammonia environment, which in turn affects the band gap of these nanosheets. The electromagnetic parameters suggest that these samples can be used as good microwave absorbing materials at G band (5.6-8.2 GHz) and X band (8.2-12.4 GHz). This study provides a simple route to BCN hybrid nanosheets with tunable band gap and adjustable conductivity for microwave absorbing applications. © 2013 Elsevier Ltd. All rights reserved.


Zhang H.,National University of Defense Technology | Xiao H.,National University of Defense Technology | Zhou P.,National University of Defense Technology | Wang X.,National University of Defense Technology | Xu X.,National University of Defense Technology
IEEE Photonics Technology Letters | Year: 2013

An all-fiberized, laser-diode-pumped, high-power, 1120-nm Yb-doped fiber laser with master oscillator power amplifier configuration was demonstrated. The seed was a 178-W single-mode fiber laser with an optical efficiency of nearly 70%. An amplifier stage was built to boost the power to 309 W with the slope efficiency of 80%. The M2 factors, measured in the end of the amplifier at output power of 253 W, are 2.45 and 2.82 in x-and y-directions, respectively. A numerical model was also proposed to evaluate the ability of seed power level in suppressing amplified spontaneous emission in the fiber amplifier. The result indicates that the ratio of the pump power and seed power should not be higher than four for our amplifier if there is no special design to suppress amplified spontaneous emission. © 2013 IEEE.


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.


Ma H.,National University of Defense Technology | Liu Z.,National University of Defense Technology | Xu X.,National University of Defense Technology | Chen J.,National University of Defense Technology
Optics Letters | Year: 2013

We propose and demonstrate the simultaneous adaptive control of a dual deformable mirror system for full-field beam shaping based on an improved stochastic parallel gradient descent (SPGD) algorithm and dual-phase-only liquid crystal spatial light modulators (LC-SLMs). One LC-SLM adaptively redistributes the intensity of the input beam and the other adaptively compensates the wavefront of the output beam. However, the intensity redistribution and wavefront compensation closed loops run simultaneously. In addition, the intensity redistribution and wave-front compensation closed loops adopt their respective metric functions independently. Experimental results show that the improved SPGD algorithm can not only be used for controlling dual deformable mirror configuration to adaptively generate near diffraction-limited flattop beams with desired intensity distributions, but also can greatly improve the control bandwidth. © 2013 Optical Society of America.


Yang B.,National University of Defense Technology | Ye W.-M.,National University of Defense Technology | Yuan X.-D.,National University of Defense Technology | Zhu Z.-H.,National University of Defense Technology | Zeng C.,National University of Defense Technology
Optics Letters | Year: 2013

Based on an analysis of the surface admittance of a plasmonic film with a substrate, we propose an ultrathin quarter-wave plate consisting of a periodic plane array of symmetrical L-shaped plasmonic antennas. The period, which determines the coupling among L-shaped antennas, is an important parameter for optimizing the performance of the structure. Numerical simulation results show that an Au quarter-wave plate designed in this Letter can efficiently convert a linearly polarized light at normal incidence into circularly polarized light, whose ellipticity is 0.994 at an operating wavelength of 1550 nm. The thickness is only 30 nm, which is nearly 1/50 of the wavelength of incident light. © 2013 Optical Society of America.


Ge L.,National University of Defense Technology | Hua W.,National University of Defense Technology | Wang H.,National University of Defense Technology | Yang Z.,National University of Defense Technology | Xu X.,National University of Defense Technology
Optics Letters | Year: 2013

We use the optogalvanic method to calculate the concentration of rubidium ions produced by photoionization in a Rb diode-pumped alkali laser gain medium. With bias voltage added across the electrodes of a rubidium hollow cathode lamp, the measured optogalvanic current is 2.3 × 10-7 A. Further study shows that the rubidium ion concentration is proportional to the pump intensity, and the drift velocity of rubidium ions is proportional to the bias voltage. When the photoionization process reaches dynamic equilibrium, the rubidium ion concentration will not increase with growing rubidium atom density. The calculated rubidium ion concentration is 1.5 × 105-10 6 according to the experiment, and the ionization degree is less than 2.4 × 10-7. © 2013 Optical Society of America.


Liu D.,National University of Defense Technology | Cheng H.,National University of Defense Technology | Zhu X.,National University of Defense Technology | Wang G.,National University of Defense Technology | Wang N.,National University of Defense Technology
ACS Applied Materials and Interfaces | Year: 2013

We developed an analog memristor based on the thickening/thinning of Ag nanofilaments in amorphous La1-xSrxMnO3 (a-LSMO) thin films. The Ag/a-LSMO/Pt memristor exhibited excellent pinched hysteresis loops under high-excitation frequency, and the areas enclosed by the pinched hysteresis loops shrank with increasing excitation frequency, which is a characteristic typical of a memristor. The memristor also showed continuously tunable synapselike resistance and stable endurance. The a-LSMO thin films in the memristor acted as a solid electrolyte for Ag+ cations, and only the Ag/a-LSMO/Pt memristor electroformed with a larger current compliance easily exhibited high-frequency pinched hysteresis loops. On the basis of the electrochemical metallization (ECM) theory and electrical transport models of quantum wires and nanowires, we concluded that the memristance is ultimately determined by the amount of charge supplied by the external current. The state equations of the memristor were established, and charge was the state variable. This study provides a new analog memristor based on metal nanofilaments thickening/thinning in ECM cells, which can be extended to other resistive switching materials. The new memristor may enable the development of beyond von Neumann computers. © 2013 American Chemical Society.


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.


Chen M.,National University of Defense Technology | Meng Z.,National University of Defense Technology | Tu X.,National University of Defense Technology | Zhou H.,National University of Defense Technology
Optics Letters | Year: 2013

We demonstrate a low-noise Brillouin/erbium fiber laser (BEFL), which uses only 1.5 m polarization-maintaining erbium-doped fiber as both the Brillouin and erbium gain media. This BEFL presentsa phase noise of -125 dB/Hz1/2 at 1 kHz frequency, at 2 mW Brillouin pump (∼3 MHz linewidth) power and 200 mW 980 nm pump power. The polarization extinction ratio of the laser output light is 31 dB. Stable (∼2 h) single-mode operation is observed. This BEFL presents potential applications in distributed Brillouin fiber sensors, inteferometric fiber sensors, and optical communications. © 2013 Optical Society of America.


Sun S.-H.,National University of Defense Technology | Gao M.,State Key Laboratory of Mathematical Engineering and Advanced Computing | Li C.-Y.,National University of Defense Technology | Liang L.-M.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

Measurement-device-independent quantum key distribution (MDI-QKD) is immune to all the detection attacks; thus when it is combined with the decoy-state method, the final key is unconditionally secure, even if a practical weak coherent source is used by Alice and Bob. However, until now, the analysis of decoy-state MDI-QKD with a weak coherent source is incomplete. In this paper, we derive, with only vacuum+weak decoy state, some tight formulas to estimate the lower bound of yield and the upper bound of error rate for the fraction of signals in which both Alice and Bob send a single-photon pulse to the untrusted third party Charlie. The numerical simulations show that our method with only vacuum+weak decoy state can asymptotically approach the theoretical limit of the infinite number of decoy states. Furthermore, the statistical fluctuation due to the finite length of date is also considered based on the standard statistical analysis. © 2013 American Physical Society.


Yuan J.,National University of Defense Technology | Long X.,National University of Defense Technology | Chen M.,National University of Defense Technology
Optics Express | Year: 2011

To the best of our knowledge, the generalized ray matrix, an augmented 5×5 ray matrix for a spherical mirror reflection with all the possible perturbation sources including three kinds of displacements and its detailed deducing process have been proposed in this paper for the first time. Square ring resonators and monolithic triaxial ring resonators have been chosen as examples to show its application, and some novel results of the optical-axis perturbation have been obtained. A novel method to eliminate the diaphragm mismatching error and the gain capillary mismatching error in monolithic triaxial ring resonators more effectively has also been proposed. Both those results and method have been confirmed by related experiments and the experimental results have been described with diagrammatic representation. This generalized ray matrix is valuable for ray analysis of various kinds of resonators. These results are important for the cavity design, cavity improvement and alignment of high accuracy and super high accuracy ring laser gyroscopes. © 2011 Optical Society of America.


Ma X.-C.,National University of Defense Technology | Sun S.-H.,National University of Defense Technology | Jiang M.-S.,National University of Defense Technology | Liang L.-M.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We present the wavelength attack on a practical continuous-variable quantum-key-distribution system with a heterodyne protocol, in which the transmittance of beam splitters at Bob's station is wavelength dependent. Our strategy is proposed independent of but analogous to that of Huang [arXiv:1206.6550v1 [quant-ph]], but in that paper the shot noise of the two beams that Eve sends to Bob, transmitting after the homodyne detector, is unconsidered. However, shot noise is the main contribution to the deviation of Bob's measurements from Eve's when implementing the wavelength attack, so it must be considered accurately. In this paper, we first analyze the solutions of the equations specifically that must be satisfied in this attack, which is not considered rigorously by Huang Then we calculate the shot noise of the homodyne detector accurately and conclude that the wavelength attack can be implemented successfully in some parameter regime. © 2013 American Physical Society.


Yin K.,National University of Defense Technology | Zhang B.,National University of Defense Technology | Yang W.,National University of Defense Technology | Chen H.,National University of Defense Technology | Hou J.,National University of Defense Technology
Optics Express | Year: 2013

In this paper, we report on cascaded Raman scattering (RS) in a highly germanium-doped silica fiber (HGDF) pumped by a picosecond pulsed master oscillator power amplifier (MOPA) system at 1064 nm in the normal dispersion regime. Benefited by the higher Raman gain of germanium (GeO2) than silica in the core, the length of the HGDF is only several meters. The broadest output spectrum comprises of 10 orders Raman stokes waves and eventually evolves into a supercontinuum (SC) spanning from 1000 to beyond 2100 nm with an output average power up to Watt scale. To the best of our knowledge, this is the first time to obtain such a broad cascaded RS spectrum in a short length of GeO2-doped step index silica fiber. We also numerically investigate the propagation of picosecond pulses in this HGDF based on the generalized nonlinear Schrödinger equation (GNLSE) which includes most of the dispersive and nonlinear effects, and the simulation results are in fairly good agreement with our experiments. It is believed that the numerical approach adopted in this paper is very beneficial for designing customized cascaded Raman fiber lasers before experimental implementations. © 2013 Optical Society of America.


Huang W.,National University of Defense Technology | Zhang Q.,Army Aviation Institute
Procedia Engineering | Year: 2012

The hardware-in-the-loop simulation plays an important role in aerocraft design. In hardware-in-the-loop simulation on launch vehicle, some hardware components are connected to the simulation loop and then work driven by data from the running computer which yield different operand quantities in different coordinate frames. According to the analysis on characteristic of the ballistics in the inertial launch reference frame, a hardware-in-the-loop simulation system for a small launch vehicle containing IMU, rocket-borne computer and rudder is established. Simulation results indicate the control scheme is accurate, the algorithm of navigation, guidance and attitude control are valid, and the calculation reduction quantity benefited from using the data in the inertial launch reference frame rather than in launch reference is worked out. © 2011 Published by Elsevier Ltd.


Wu J.,National University of Defense Technology | Wu J.,Imperial College London | Barahona M.,Imperial College London | Tan Y.-J.,National University of Defense Technology | Deng H.-Z.,National University of Defense Technology
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2011

We introduce the concept of natural connectivity as a measure of structural robustness in complex networks. The natural connectivity characterizes the redundancy of alternative routes in a network by quantifying the weighted number of closed walks of all lengths. This definition leads to a simple mathematical formulation that links the natural connectivity to the spectrum of a network. The natural connectivity can be regarded as an average eigenvalue that changes strictly monotonically with the addition or deletion of edges. We calculate both analytically and numerically the natural connectivity of three typical networks: regular ring lattices, random graphs, and random scale-free networks. We also compare the proposed natural connectivity to other structural robustness measures within a scenario of edge elimination and demonstrate that the natural connectivity provides sensitive discrimination of structural robustness that agrees with our intuition. © 2011 IEEE.


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.


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.


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.


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.


Zhang Y.,National University of Defense Technology | Lu K.,National University of Defense Technology | Gao Y.,National University of Defense Technology | Xu K.,National University of Defense Technology
Quantum Information Processing | Year: 2013

The power of quantum mechanics has been extensively exploited to meet the high computational requirement of classical image processing. However, existing quantum image models can only represent the images sampled in Cartesian coordinates. In this paper, quantum log-polar image (QUALPI), a novel quantum image representation is proposed for the storage and processing of images sampled in log-polar coordinates. In QUALPI, all the pixels of a QUALPI are stored in a normalized superposition and can be operated on simultaneously. A QUALPI can be constructed from a classical image via a preparation whose complexity is approximately linear in the image size. Some common geometric transformations, such as symmetry transformation, rotation, etc.; can be performed conveniently with QUALPI. Based on these geometric transformations, a fast rotation-invariant quantum image registration algorithm is designed for log-polar images. Performance comparison with classical brute-force image registration method reveals that our quantum algorithm can achieve a quartic speedup. © 2013 Springer Science+Business Media New York.


Wang X.,National University of Defense Technology | Zhou P.,National University of Defense Technology | Xiao H.,National University of Defense Technology | Si L.,National University of Defense Technology
Optics Express | Year: 2013

We demonstrate a high power all-fiber single frequency Tmdoped fiber amplifier. The maximum output power reached 102 W and the central wavelength was 1.97 μm. The single frequency laser signal from a seed laser was amplified based on a monolithic master oscillator power amplifier (MOPA) configuration. The slope efficiency was about 50% against the absorbed pump power. Neither parasitic lasing nor nonlinear effect was observed in the monolithic fiber amplifier. The SBS threshold of the single frequency Tm-doped fiber amplifier was analyzed and estimated. The output power is not limited by the SBS threshold and could be further improved by increasing the pump power. To the best of our knowledge, this is the first demonstration of average power exceeding 100 W from monolithic all-fiber laser near 2 μm wavelength.©2013 Optical Society of America. © 2013 Optical Society of America.


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.


Zhang Y.,National University of Defense Technology | Lu K.,National University of Defense Technology | Gao Y.,National University of Defense Technology | Wang M.,National University of Defense Technology
Quantum Information Processing | Year: 2013

Quantum computation is becoming an important and effective tool to overcome the high real-time computational requirements of classical digital image processing. In this paper, based on analysis of existing quantum image representations, a novel enhanced quantum representation (NEQR) for digital images is proposed, which improves the latest flexible representation of quantum images (FRQI). The newly proposed quantum image representation uses the basis state of a qubit sequence to store the gray-scale value of each pixel in the image for the first time, instead of the probability amplitude of a qubit, as in FRQI. Because different basis states of qubit sequence are orthogonal, different gray scales in the NEQR quantum image can be distinguished. Performance comparisons with FRQI reveal that NEQR can achieve a quadratic speedup in quantum image preparation, increase the compression ratio of quantum images by approximately 1.5X, and retrieve digital images from quantum images accurately. Meanwhile, more quantum image operations related to gray-scale information in the image can be performed conveniently based on NEQR, for example partial color operations and statistical color operations. Therefore, the proposed NEQR quantum image model is more flexible and better suited for quantum image representation than other models in the literature. © 2013 Springer Science+Business Media New York.


Ren X.G.,National University of Defense Technology
Applied Mechanics and Materials | Year: 2014

OpenFOAM is a widely used open source computational fluid dynamics (CFD), and the performance of its application is critical for the CFD user, and many researchers try to optimize it from various perspectives. In this paper, we try to optimization OpenFOAM application from the compiler perspective, which is the simplest way to get the optimization affect. We compare two mainstream compilers: Intel compiler icc and an open source compiler, as well as a serious of optimization option flags. Through the experiment, we find that Intel compiler has a much better performance than gcc, which is up to 9.88%, and a suitable combination of the optimization option flags is important to the compile performance. © (2014) Trans Tech Publications, Switzerland.


Zhou J.,National University of Defense Technology | Long X.,National University of Defense Technology
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2010

An idea of using laser Doppler velocimeter(LDV) to offer velocity in vehicle inertial navigation system was proposed. The principle of measuring its own velocity with laser Doppler was expounded while reference-beam LDV was designed. And Doppler signal was processed using tracking filter, frequency spectrum refinement and frequency spectrum correction. The results of theory and experiment showed that: reference-beam LDV solved the problem that dual-beam LDV can not measure the velocity while out of focus; background signal and part of noise were eliminated, Doppler signal was tracked so that signal-to-noise ratio was raised; distinguishability of spectrum was improved, Doppler frequency was more agreed with the actual value, and the error of the system was decreased by frequency spectrum refinement and correction technology. So LDV can offer valid velocity for vehicle inertial navigation system.


Yang W.,National University of Defense Technology | Cui F.,National University of Defense Technology | Li X.,National University of Defense Technology | Liu J.,National University of Defense Technology
Proceedings - 2011 IEEE International Conference on Computer Science and Automation Engineering, CSAE 2011 | Year: 2011

In the multi-sensor data fusion system, the data acquired by each sensor which will be fused should be at the same time level so that the correct state can be worked out. In this work, several usual time registration algorithms are analyzed and a new method based on the filtering algorithms is proposed. This proposed method can solve the time registration problem effectively and the results of simulation prove that the method has good performance. © 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).


Zhao D.,National University of Defense Technology | Zhang C.,National University of Defense Technology | Hu H.,National University of Defense Technology | Zhang Y.,National University of Defense Technology
Composites Science and Technology | Year: 2011

Ablation property of three dimensional carbon fiber reinforced zirconium carbide composite (3D C/ZrC composite) was determined using oxyacetylene torch test with a heat flux of 4187kW/m2 and flame temperature of over 3000°C. C/ZrC composite exhibited an excellent configurational stability with a surface temperature of over 2000°C during 60-300s period, while 3D C/SiC composite was perforated at 55s. After ablation for 300s, the composite showed a mass loss rate of 0.006g/s and a linear recession rate of 0.004mm/s. The formation of zirconia melt on the surface of the C/ZrC composite contributed mainly the ablation property improvement. The C/ZrC composite after ablation showed four different layers due to the temperature and pressure gradients: the melting layer, the loose tree-coral-like ZrO2 layer, the undersurface oxidation layer, and the composite layer. © 2011 Elsevier Ltd.


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.


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.


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.


Li P.,National University of Defense Technology | Zheng Z.-Q.,National University of Defense Technology
Kongzhi Lilun Yu Yingyong/Control Theory and Applications | Year: 2011

A nonlinear integral sliding mode control approach is proposed for a class of uncertain nonlinear systems. To promote the performance of the traditional integral sliding mode control, this approach incorporates a new nonlinear saturation function which enhances small errors and will be saturated with large errors in shaping the tracking errors. While maintaining the tracking accuracy of the traditional integral sliding mode control, this approach provides better transient performances. Using Lyapunov stability theory and LaSalle invariance principle, we prove that the proposed approach ensures the zero steady-state error in the presence of a constant disturbance or an asymptotically constant disturbance. When the control input is constrained, the saturated controller operates like a PD controller with a nonlinear I term. Simulation example is given to demonstrate the effectiveness and robustness of the proposed approach.


Zhu H.,National University of Defense Technology | Song S.,National University of Defense Technology | Tang Y.,CAS Academy of Mathematics and Systems Science
Computer Physics Communications | Year: 2011

In this paper, we develop a novel multi-symplectic wavelet collocation method for solving multi-symplectic Hamiltonian system with periodic boundary conditions. Based on the autocorrelation function of Daubechies scaling functions, collocation method is conducted for the spatial discretization. The obtained semi-discrete system is proved to have semi-discrete multi-symplectic conservation laws and semi-discrete energy conservation laws. Then, appropriate symplectic scheme is applied for time integration, which leads to full-discrete multi-symplectic conservation laws. Numerical experiments for the nonlinear Schrödinger equation and Camassa-Holm equation show the high accuracy, effectiveness and good conservation properties of the proposed method. © 2010 Elsevier B.V. All rights reserved.


Jiang M.-S.,National University of Defense Technology | Sun S.-H.,National University of Defense Technology | Li C.-Y.,National University of Defense Technology | Liang L.-M.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Any imperfections in a practical quantum key distribution (QKD) system may be exploited by an eavesdropper (Eve) to collect information about the key without being discovered. For example, without the decoy-state method, Eve can perform the photon-number-splitting (PNS) attack and get full information without introducing any perturbation, since weak laser pulses are widely used in practical systems instead of single-photon sources. However, the decoy-state method against PNS attack itself may introduce another loophole while closing the loophole of multiphoton pulses. In this paper, a fatal loophole of practical decoy-state plug-and-play QKD systems has been exploited and a wavelength-selected photon-number-splitting (WSPNS) attack scheme against plug-and-play QKD systems with the decoy-state method is proposed. Theoretical analysis shows that the eavesdropper can get full information about the key generated between the legitimate parties just like the PNS attack was performed in plug-and-play QKD systems without the decoy-state method. © 2012 American Physical Society.


Zhang B.,National University of Defense Technology | Yuan J.,National University of Defense Technology | Zhao Z.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We investigate the strong-field ionization for the ground state of H 2 + by numerically solving the three-dimensional (3D) time-dependent Schrödinger equation (TDSE), and comparisons have been made among the TDSE, the different versions of molecular strong-field approximation (MO-SFA) and the molecular Ammosov-Delone-Krainov (MO-ADK) approximation. The study shows that, for the TDSE results, the ratio of ionization rates between perpendicular and parallel alignments displays a step-like structure against the Keldysh parameter γ. For small internuclear distances, the transition between the steps are found to be around γ-1 and is recognized as the competition between the multiphoton ionization (MPI) and tunneling ionization (TI). The ionization is more isotropic in the MPI regime. For large internuclear distances, the transition position shifts to larger γ due to the charge-resonance-enhanced ionization (CREI). Different versions of strong-field ionization theories are compared against the TDSE results. © 2012 American Physical Society.


Sun S.-H.,National University of Defense Technology | Gao M.,National University of Defense Technology | Jiang M.-S.,National University of Defense Technology | Li C.-Y.,National University of Defense Technology | Liang L.-M.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Phase randomization is a very important assumption in the Bennett-Brassard 1984 quantum key distribution (QKD) system with a weak coherent source. Thus an active phase modulator is needed to randomize the phase of source. However, it is hard to check whether the phase of source is randomized totally or not in practical QKD systems. In this paper a partially random phase attack is proposed to exploit this imperfection. Our analysis shows that Eve can break the security of a two-way QKD system by using our attack, even if an active phase randomization is adopted by Alice. Furthermore, the numerical simulation shows that in some parameter regimes, our attack is immune to the one-decoy-state method. © 2012 American Physical Society.


Luo C.,National University of Defense Technology | Zhang Y.,National University of Defense Technology | Xie W.-X.,National University of Defense Technology
Journal of Information Hiding and Multimedia Signal Processing | Year: 2014

In order to solve the problem that the node are respond slowly and unsteadily in the existing congestion control algorithms for sensor network traffic control with dynamic changes of network status, an algorithm based on traffic regulation is proposed. In the algorithm, congestion can be avoided and controlled by sending Traffic Regulating Factors from the father node to the children nodes according to the queue size and current traffic arrival rate of the father node. In order to produce traffic regulating factors, pre-assigned rates in bottleneck nodes are considered for the control of packet round-trip delay. At the same time, the Sink node makes reverse transmission of traffic regulating factors one hop-by-hop according to Minimum Event Detection Degrees. Based on the traffic regulating factors, the source nodes can adjust the data packet generation rate adaptively, and the congestion problem can be fundamentally resolved. Simulation results show that the proposed algorithm is an effective algorithm for congestion control, which can raise network throughput, reduce packet loss rate, and stabilize node queue length. © 2013 ISSN 2073-4212.


Zhang S.,National University of Defense Technology | Wu C.-W.,National University of Defense Technology | Chen P.-X.,National University of Defense Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We propose a dark-state cooling scheme of trapped ion systems using standing waves in the Lamb-Dicke limit. By exploiting the property of standing waves, the heating effects caused by the carrier and the blue sideband transitions vanish and lower final phonon number can be achieved. Different from other dark-state cooling schemes, our scheme is more robust under the fluctuations of laser intensities. © 2012 American Physical Society.


Yin K.,National University of Defense Technology | Zhang B.,National University of Defense Technology | Xue G.,National University of Defense Technology | Li L.,National University of Defense Technology | Hou J.,National University of Defense Technology
Optics Express | Year: 2014

Power scaling of an all-fiber wavelength-tunable thulium doped fiber laser (TDFL) based on a monolithic master oscillator power amplifier (MOPA) system is presented. The whole configuration is comprised of a low-power seed oscillator and two stages of double-cladding thulium doped fiber amplifiers (TDFAs). The tuning of the operating wavelength is realized by inserting a spectral tunable filter into the seed oscillator. Maximum average output power of 115 W is obtained at 1950 nm with a linearly fitted slope efficiency of 51.7%. This laser has superior spectral characteristics with wavelength tunable from 1940 nm to 2070 nm. To the best of our knowledge, this is the first demonstration of an all-fiber wavelength-tunable TDFL at 2 μm with output power exceeding 100 W. The results are of great interest for many application areas. © 2014 Optical Society of America.


Chen H.,National University of Defense Technology | Chen S.-P.,National University of Defense Technology | Jiang Z.-F.,National University of Defense Technology | Hou J.,National University of Defense Technology
Optics Express | Year: 2014

We demonstrate nanosecond scale rectangular wave-breaking-free pulse generation in an actively mode locked Yb-doped fiber laser based on a combined action of active periodic cavity loss modulation and nonlinear polarization rotation effect. The pulse width of the laser can be controlled in the range of 890 ps to above 124 ns instantaneously by adjusting the electrical signal applied on the modulator. As high as 19.8 nJ wave-breaking-free pulse is achieved with maximum available pump power. The output pulse temporal dynamics exhibit various distinct characteristics under different modulation and polarization control. The laser presents unusually flexible tunabilities in pulse width, pulse energy and pulse shape. ©2014 Optical Society of America


Dai J.,National University of Defense Technology | Hou Y.,National University of Defense Technology | Yuan J.,National University of Defense Technology
Physical Review Letters | Year: 2010

Electron-ion interactions are central to numerous phenomena in the warm dense matter (WDM) regime and at higher temperature. The electron-ion collisions induced friction at high temperature is introduced in the procedure of ab initio molecular dynamics using the Langevin equation based on density functional theory. In this framework, as a test for Fe and H up to 1000 eV, the equation of state and the transition of electronic structures of the materials with very wide density and temperature can be described, which covers a full range of WDM up to high energy density physics. A unified first principles description from condensed matter to ideal ionized gas plasma is constructed. © 2010 The American Physical Society.


Fang Q.,National University of Defense Technology | Huang S.X.,National University of Defense Technology
IEEE Sensors Journal | Year: 2013

An unscented Kalman filter (UKF) is derived for integrating vision with inertial measurements from gyros and accelerometers sensors based on three-view geometry. The main goal of the proposed method is to provide better estimations compared to the implicit extended Kalman filter introduced by Indelman. The UKF uses a selected set of points to more accurately map the probability distribution of the measurement model than the linearization of the extended Kalman filter, leading to faster convergence from inaccurate initial conditions in estimation problems. The proposed method is validated using a statistical study based on simulated navigation and synthetic images data. © 2001-2012 IEEE.


Zhang Y.,National University of Defense Technology | Liu J.,National University of Defense Technology
Laser and Particle Beams | Year: 2013

In this paper, a new kind of solid-state Marx generator based on synchronous transformer type magnetic switches (TTMS) is put forward, and the TTMSs with new winding structures are used to substitute all the spark gaps in the traditional Marx generator for the purposes of solidification and long life time. As the new type of TTMS with high step-up ratio and low saturated inductances is employed, the proposed Marx generator becomes a compact combination of pulse transformer, magnetic switch, and Marx capacitors. The stages of the Marx capacitors can be synchronously charged in parallel before the magnetic core saturates, and these Marx capacitors also can synchronously discharge in series. The establishing time of the proposed Marx generator is at ns range. As the new type of self-reset TTMS is used, the input voltage of the Marx generator decreases to a low level less than 1 kV while the output voltage can easily reach a high level ranging from dozens of kV to hundreds of kV. Copyright © Cambridge University Press 2013.


Zhang H.,National University of Defense Technology | Xiao H.,National University of Defense Technology | Zhou P.,National University of Defense Technology | Wang X.,National University of Defense Technology | Xu X.,National University of Defense Technology
IEEE Photonics Journal | Year: 2013

We report a high-power high-efficiency single-mode all-fiber Raman fiber laser (RFL) operating at 1173 nm. With the core pumped by a 144-W 1120-nm Yb-doped fiber laser, an output power of 119 W at a wavelength of 1173 nm was obtained, corresponding to an optical efficiency of 82%. To the best of our knowledge, it is the highest power at the 1150-1200-nm laser band by using common silica fiber. The optical efficiency of the RFL with high output coupler (OC) reflectivity and short fiber length is discussed. We also carefully measured the output Raman spectrums under different cavity parameters and presented primary analysis. The results show that the bandwidth increases near linearly with laser output power, rather than a square-root law concluded for high Q-value and long-cavity RFLs in previous published literatures. Increasing the length of the gain fiber and the reflectivity of the OC would also broaden the output spectral bandwidth. © 2009-2012 IEEE.


Ma P.,National University of Defense Technology | Tao R.,National University of Defense Technology | Wang X.,National University of Defense Technology | Ma Y.,National University of Defense Technology | And 2 more authors.
Optics Express | Year: 2014

In this manuscript, we report on coherent polarization beam combination (CPBC) of a four-channel pulsed amplifier array in the picosecond regime by using single frequency dithering technique. By employing a photo-detector with low-pass bandwidth (8.5 MHz at 10 dB gain) to filter the intensity fluctuation and obtain phase errors for feedback, a combined laser pulse with~480 ps pulse width at~60 MHz repetition rate is obtained with an average power of 88 W. By adjusting the optical path differences (OPDs) and controlling the pump power to ensure the synchronizations and alleviate the influence of nonlinear phases among each channel, more than 90% combining efficiency is achieved with excellent beam quality (M2~1.1). Finally, the efficiency loss of the system along with the power scaling process is discussed. © 2014 Optical Society of America.


Liao W.,National University of Defense Technology | Dai Y.,National University of Defense Technology | Xie X.,National University of Defense Technology | Zhou L.,National University of Defense Technology
Optics Express | Year: 2014

Ion sputtering of Zerodur material often results in the formation of nanoscale microstructures on the surfaces, which seriously influences optical surface quality. In this paper, we describe the microscopic morphology evolution during ion sputtering of Zerodur surfaces through experimental researches and theoretical analysis, which shows that preferential sputtering together with curvature-dependent sputtering overcomes ion-induced smoothing mechanisms leading to granular nanopatterns formation in morphology and the coarsening of the surface. Consequently, we propose a new method for ion beam smoothing (IBS) of Zerodur optics assisted by deterministic ion beam material adding (IBA) technology. With this method, Zerodur optics with surface roughness down to 0.15nm root mean square (RMS) level is obtained through the experimental investigation, which demonstrates the feasibility of our proposed method. © 2014 Optical Society of America.


Yang J.,National University of Defense Technology | Shu T.,National University of Defense Technology | Fan Y.,National University of Defense Technology
Laser and Particle Beams | Year: 2013

A combination of electrical and optical diagnostics has been used to investigate the time evolution of the two-dimensional expansion velocity distributions of the cathode plasma in pulsed high-power diodes. The perveance model based on the Child-Langmuir law was used to calculate the expansion velocity of the diode plasmas from voltage and current profiles. Additionally, a four-channel high speed framing camera was used to observe the formation and subsequent movement of the cathode plasma. More accurate and valuable information about the dynamics of the cathode plasma was also acquired by utilizing the digital image processing methods. Results from the experiments and theoretical analysis were compared. In this paper, the experiments have been performed using a high-voltage pulse generator with 200Â kV output voltage and 110Â ns pulse duration. Current densities up to 440 A/cm2 were produced. The observation of the cathode plasma expansion in transverse direction indicated that the diode current was cathode-limited in the current rising stage (the first 60Â ns of the current pulse). The perveance model should be modified taking in account the time dependent expanding plasma surface (i.e., not the whole cathode surface) for this period. The velocity in the direction parallel to the cathode surface (transverse velocity) was much larger than that in the direction perpendicular to the cathode surface (longitudinal velocity), and further, it dropped from 90Â cm/μs to nearly 20Â cm/μs rapidly. It was shown that, during the current flattop stage, the plasma filled out all the surface of cathode and the diode current was space-charge-limited. The values of the transverse velocity and longitudinal velocity were nearly the same and decreased relatively slowly. The satisfactory coincidence of experimental and calculated (both were in the range of 6-8Â cm/μs) values of the cathode plasma expansion velocities was obtained. Copyright © Cambridge University Press 2013.


Zhou W.,National University of Defense Technology | Li D.,National University of Defense Technology
Journal of Sound and Vibration | Year: 2013

This paper focuses on experimental research on a vibration isolation platform for momentum wheel assembly (MWA). A vibration isolation platform, consisting of four folded beams, was designed to isolate the microvibrations produced by MWA during operation. The performance of the platform was investigated with an impact test to verify the natural frequencies and damping coefficients of the system when the MWA was at rest, and with a measurement system consisting of a Kistler table and an optical tabletop to monitor the microvibrations produced when the MWA operated at stable speed. The results show that although the sixth natural frequency of the system is 26.29 Hz (1577 rev/min) when the MWA is at rest, the critical speed occurs at 2600 rev/min due to the gyroscopic effect of the flywheel, and that the platform can effectively isolate the high frequency disturbances in the 100-300 Hz range in all six degrees of freedom. Thus, the gyroscopic effect force deserves more attention in the design and analysis of vibration isolation platform for rotating wheel assembly, and the platform in this paper is particularly effective for MWA, which generally operates at high rotating speed range. Crown Copyright © 2012 Published by Elsevier Ltd. All rights reserved.


Zhang H.,National University of Defense Technology | Xiao H.,National University of Defense Technology | Zhou P.,National University of Defense Technology | Wang X.,National University of Defense Technology | Xu X.,National University of Defense Technology
Optics Express | Year: 2014

We demonstrated a high power Yb-Raman combined nonlinear fiber amplifier. The seed is a 30 W dual-wavelength Yb-doped fiber laser formed by 1070 nm and 1120 nm lasers. The gain medium in the amplifier stage is a 45-meters-long Yb-doped fiber, which power scaled the 1070 nm laser and Raman amplified the 1120 nm laser simultaneously. A record 1120 nm power of 732 W is obtained with pump power of 890 W. Numerical study taking into account of both Yb and Raman gain has been conducted to analyze the output characters and power evolution in the amplifier under different conditions. The numerical results are in good agreement with the experiment. This amplifier is also suitable to amplify laser in the wavelength range of 1100-1150 nm. © 2014 Optical Society of America.


Zhang J.,National University of Defense Technology | Liu W.,National University of Defense Technology | Zhu Z.,National University of Defense Technology | Yuan X.,National University of Defense Technology | Qin S.,National University of Defense Technology
Optics Express | Year: 2014

Strong subwavelength field enhancement has often been assumed to be unique to plasmonic nanostructures. Here we propose a type of all-dielectric metamaterials based on split bar resonators. The nano gap at the centre of the resonant elements results in large local field enhancement and light localization in the surrounding medium, which can be employed for strong light-matter interactions. In a Fano-resonant dielectric metamaterial comprising pairs of asymmetric split silicon bars, the enhancement of electric field amplitude in the gap exceeds 120 while the averaged electromagnetic energy density is enhanced by more than 7000 times. An optical refractive index sensor with a potential sensitivity of 525 nm/RIU is designed based on the proposed metamaterials. The proposed concept can be applied to other types of dielectric nanostructures and may stimulate further research of dielectric metamaterials for applications ranging from nonlinear optics and sensing to the realization of new types of active lasing devices. © 2014 Optical Society of America.