Beijing, China
Beijing, China

Beihang University, previously known as Beijing University of Aeronautics and Astronautics is a major public research university located in Beijing, China.It is a member of China's Project 211 and Project 985 group of key state universities, with a heavy focus on high level technological and scientific research. BUAA was founded on October 25, 1952 with an area of over 100 hectares, BUAA is one of China's leading universities on research and education. It is regarded as one of the best engineering universities in China and has a great influence on China's aeronautical and astronautical industry. Wikipedia.

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Beihang University and The General Hospital Of The Peoples Libration Army | Date: 2014-09-19

A master-slave same structure teleoperation fracture reduction mechanism includes a frame assembly, two parallel platform assemblies, a top platform connecting plate (9), an operating handle assembly, two fixing assemblies, a controller (15), six movement assemblies and 24 hydraulic pipes (26). The operating handle assembly is located in the middle of the upper platform (5), and the two fixing assemblies are located on the top of the parallel platform assembly. The two parallel platform assemblies are disposed on the frame assembly; the controller (15) and the six movement assemblies are disposed on the frame assembly; A top platform connecting plate (9) is connected to the fixing assembly parallel platform assembly. The hydraulic pipes (26) is in communication with motion hydraulic cylinders (7a) and the other end of the hydraulic pipes is in communication with one of platform hydraulic cylinders (7b). The invention assists a doctor to achieve fracture reduction.

Sheng Z.-Y.,Beihang University
Proceedings of 2016 IEEE Advanced Information Management, Communicates, Electronic and Automation Control Conference, IMCEC 2016 | Year: 2016

To solve the problems of motor's data acquisition system's low automation level, too less data channel, limited apply areas. This paper introduced a kind of motor's data acquisition and analyzation system which were developed based on producer/consumer model and LabVIEW program. This system can fulfil the tasks of multi-channel data acquisition, data analyzation and display, data saving and loading. By setting two different data acquiring frequencies, that's 2kHz and 20kHz, to acquire the same signal that produced by the signal generator and analyzing the data that were acquired. According to the analysis and data fitting results the benefits and short comes was concluded. These tests suggested that the signal can be represented by this two kind of data acquiring frequency and the standard error that the 2kHz had is bigger than that of 20kHz had. So, the test's result proved that this system works well and easy to realize. © 2016 IEEE.

Zhou Y.,Beihang University | Zhao L.-D.,Beihang University
Journal of Solid State Chemistry | Year: 2017

BaBiTe3, a material with low thermal conductivity, is an inferior thermoelectric material due to the poor electrical properties originated from its narrow band gap. We choose two types of dopants, K and La, trying to optimize its electrical transport properties. The minority carriers, which harm the Seebeck coefficient in this system, are suppressed by La doping. With the increase of both electrical conductivity and Seebeck coefficient, the power factor of 3% La doped BaBiTe3 reaches 3.7 μW cm−1 K−2 which increased by 40% from undoped BaBiTe3. Besides high power factor, the thermal conductivity is also reduced in it. Eventually, a high ZT value, 0.25 at 473 K, for n-type BaBiTe3 is achieved in 3% La doped BaBiTe3. © 2017 Elsevier Inc.

Chen Z.,University of Science and Technology Beijing | Du F.,Beihang University
Measurement: Journal of the International Measurement Confederation | Year: 2017

In the large-size product assembly process, the inspection of the large-size components and quality assurance of the product requires advanced digital metrologies, which include high-precision and high-efficiency measuring devices, and corresponding measuring approaches. The single measuring device or measurement field usually cannot meet the demands of measuring in the large-size assembly site; instead, a measurement network based on the combination of multi devices, is a better choice for the manufacturers. In this paper, a measurement network constructed by iGPS and portable scanner is proposed. The measuring principles of the two kinds of measuring devices are studied firstly, as well as the characteristics of their layouts and measurement uncertainties, based on simulating and actual measuring experiments. Then, the measuring principle, structure and uncertainty characteristics of the measurement network are discussed in detail, with measurement data analysis of the measuring experiments. Finally, a few conclusions and the future work are illustrated. © 2017 Elsevier Ltd

Li H.,Beihang University | Li H.,China 2 Collaborative Innovation Center for Advanced Aerospace Engine
Ultrasonics | Year: 2017

Air-coupled ultrasonic testing systems are usually restricted by low signal-to-noise ratios (SNR). The use of pulse compression techniques based on P4 Polyphase codes can improve the ultrasound SNR. This type of codes can generate higher Peak Side Lobe (PSL) ratio and lower noise of compressed signal. This paper proposes the use of P4 Polyphase sequences to code ultrasound with a NDT system based on air-coupled piezoelectric transducer. Furthermore, the principle of selecting parameters of P4 Polyphase sequence for obtaining optimal pulse compression effect is also studied. Successful results are presented in molded composite material. A hybrid signal processing method for improvement in SNR up to 12.11 dB and in time domain resolution about 35% are achieved when compared with conventional pulse compression technique. © 2017 Elsevier B.V.

Fang L.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2017

We rigorously show that the truncation at low wave numbers always leads to background scalar-level anisotropy at large scales. Neither the resolution nor the spectral low-pass filter is dominant for this anisotropy, while the shape of the energy spectrum at low wave numbers is an important influence factor. Quantitative results are shown to provide references to the statistics in future postprocessing studies. Also, a simplified analytical model is introduced to explain the single-mode effects for this anisotropy. © 2017 American Physical Society.

Hu Y.,Beihang University | Liu D.,China Aerospace Science and Technology Corporation | Wu Y.,Beihang University
2016 1st IEEE International Conference on Computer Communication and the Internet, ICCCI 2016 | Year: 2016

Topology control is one of the key technologies in ad hoc network. Recently some topology control algorithms focus on reducing the end-to-end delay have been proposed. However, they do not consider the delay which is caused by contending for the shared channel and collision at MAC layer. In this paper, we put forward a new delay model to character the link delay which is composed by the transmission delay, access delay and collision delay. We obtain the probability of waiting to access the channel according to the probability of transmission and the nodes' distribution. In particular, the delay model takes into account the impact of the capture effect and the collision caused by hidden terminals. Then a distributed topology control algorithm is put forward to make sure that the final topology is composed of the minimum delay paths. Finally, abundant simulations prove that the topology built by our algorithm can reduce the network delay efficiently. © 2016 IEEE.

She C.,Beihang University | Yang C.,Beihang University | Quek T.Q.S.,Singapore University of Technology and Design
2016 IEEE Global Communications Conference, GLOBECOM 2016 - Proceedings | Year: 2016

To ensure the low end-to-end (E2E) delay for tactile internet, short frame structures will be used in 5G systems. As such, transmission errors with finite blocklength channel codes should be considered to guarantee the high reliability requirement. In this paper, we study cross-layer transmission optimization for tactile internet, where both queueing delay and transmission delay are accounted for in the E2E delay, and different packet loss/error probabilities are considered to characterize the reliability. We show that the required transmit power becomes unbounded when the allowed maximal queueing delay is shorter than the channel coherence time. To satisfy quality-of-service requirement with finite transmit power, we introduce a proactive packet dropping mechanism, and optimize a queue state information and channel state information dependent transmission policy. Since the resource and policy for transmission and the packet dropping policy are related to the packet error probability, queueing delay violation probability, and packet dropping probability, we optimize the three probabilities and obtain the policies related to these probabilities. We start from single-user scenario and then extend our framework to the multi-user scenario. Simulation results show that the optimized three probabilities are in the same order of magnitude. Therefore, we have to take into account all these factors when we design systems for tactile internet applications. © 2016 IEEE.

Zhou R.,Beihang University | Chan A.H.S.,City University of Hong Kong
Work | Year: 2017

BACKGROUND: In order to compare existing usability data to ideal goals or to that for other products, usability practitioners have tried to develop a framework for deriving an integrated metric. However, most current usability methods with this aim rely heavily on human judgment about the various attributes of a product, but often fail to take into account of the inherent uncertainties in these judgments in the evaluation process. OBJECTIVE: This paper presents a universal method of usability evaluation by combining the analytic hierarchical process (AHP) and the fuzzy evaluation method. By integrating multiple sources of uncertain information during product usability evaluation, the method proposed here aims to derive an index that is structured hierarchically in terms of the three usability components of effectiveness, efficiency, and user satisfaction of a product. METHODS: With consideration of the theoretical basis of fuzzy evaluation, a two-layer comprehensive evaluation index was first constructed. After the membership functions were determined by an expert panel, the evaluation appraisals were computed by using the fuzzy comprehensive evaluation technique model to characterize fuzzy human judgments. Then with the use of AHP, the weights of usability components were elicited from these experts. RESULTS AND CONCLUSIONS: Compared to traditional usability evaluation methods, the major strength of the fuzzy method is that it captures the fuzziness and uncertainties in human judgments and provides an integrated framework that combines the vague judgments from multiple stages of a product evaluation process. © 2017 - IOS Press and the authors. All rights reserved.

Zheng B.,Beihang University | Xu J.,Beihang University
Carbon | Year: 2017

Nanoscale homogeneous single-walled carbon nanotube lattice exhibits extraordinary attenuation performance and ultrahigh specific energy absorption upon high-velocity impact. However, upon relatively low impact velocity (for example, < 1000 m/s), this system does not possess a good stress wave attenuation performance where severe damage may still occur. To overcome this disadvantage, a new attenuation mechanism is introduced to carbon nanotube lattice via the creation of mass mismatch, i.e. carbon nanotube dimer lattice. Under specific mass ratio, a strong inherent resonance happens, resulting in an evident attenuation of the propagating pulse. The joint effect of mass mismatch-induced resonance and dissipative nature of carbon nanotube lattice make it ideal for both high and low-velocity impacts. Additionally, specific energy absorption is improved due to the mass reduction. This work reveals the possibility to achieve much higher energy dissipation by exploiting the system's inherent dynamics, suggesting a new strategy of lightweight design of protective devices and the potential of technological applications of nanoscale nonlinear granular crystals. © 2017 Elsevier Ltd

Tong Y.,Beihang University | She J.,Hong Kong University of Science and Technology | Ding B.,Microsoft | Chen L.,Hong Kong University of Science and Technology | And 2 more authors.
Proceedings of the VLDB Endowment | Year: 2016

Recently, with the development of mobile Internet and smartphones, the online minimum bipartite matching in real time spatial data (OMBM) problem becomes popular. Specifically, given a set of service providers with specific locations and a set of users who dynamically appear one by one, the OMBM problem is to find a maximum-cardinality matching with minimum total distance following that once a user appears, s/he must be immediately matched to an unmatched service provider, which cannot be revoked, before subsequent users arrive. To address this problem, existing studies mainly focus on analyzing the worst-case competitive ratios of the proposed online algorithms, but study on the performance of the algorithms in practice is absent. In this paper, we present a comprehensive experimental comparison of the representative algorithms of the OMBM problem. Particularly, we observe a surprising result that the simple and efficient greedy algorithm, which has been considered as the worst due to its exponential worst-case competitive ratio, is significantly more effective than other algorithms. We investigate the results and further show that the competitive ratio of the worst case of the greedy algorithm is actually just a constant, 3.195, in the average-case analysis. We try to clarify a 25-year misunderstanding towards the greedy algorithm and justify that the greedy algorithm is not bad at all. Finally, we provide a uniform implementation for all the algorithms of the OMBM problem and clarify their strengths and weaknesses, which can guide practitioners to select appropriate algorithms for various scenarios. © 2016 VLDB Endowment 21508097/16/08.

Liu Z.,Beihang University | Huang Y.,Beihang University
Key Engineering Materials | Year: 2017

Numerical simulation of the moving interface is widely investigated in the fields of two-phase flow, crystal growth, molten metal casting and so on. To simulate accurately and quickly motion state of the moving interface, two types of interface-capturing method, LSM (level set method) and MCLS (mass-conserving LSM coupled with VOF (volume of fluid)), were comparatively analysed and studied. Two kinds of moving interface, rotation motion of Zaleska slotted disk interface and shearing deformation of the circle interface, were simulated. The level set advection equation was solved with IATVD (the characteristic integral-averaging finite volume method), RK-WENO (the third order Runge-Kutta method with WENO (weighted essentially non-oscillatory)), or the low order method, respectively. The level set function was re-initialized with modified Godunov method. Computation was implemented in different size mesh. When it is independent with mesh size, results show that the high order method, IATVD and RK-WENO, can get higher computing accuracy in LSM without topological geometry change. But computing time cost of RK-WENO is much greater than that of IATVD. For the low order method, LSM captures the moving interface in bad, however, MCLS's numerical result is very good. But computing time cost of MCLS is much and much greater than that of LSM. For interface-capturing with topological geometry change, these two high order methods all can not capture the moving interface in good in LSM. Nevertheless, the resulting interfaces all are same as original interface in MCLS. These indicate that an appropriate numerical method and interface-capturing method can be chosen to accurately and quickly capture the related moving interface. © 2017 Trans Tech Publications.

Peng C.,Beihang University
Optics and Laser Technology | Year: 2017

The effect of laser shock peening (LSP) on bending fatigue performance of AISI 9310 steel spur gear has been investigated in this study. To help to explain bending fatigue test results, residual stress distribution induced by LSP is studied by means of finite element modelling, results of which are verified by X-ray diffraction analysis. It is found that a compressive layer of desirable depth can be induced on the gear root fillet after LSP, and both magnitude and depth of compressive stress increase with laser energy. The bending fatigue test is conducted using the single-tooth bending method to compare fatigue performance of laser peened teeth and non-peened teeth, which is followed by relevant statistical analysis. S-N curves acquired from the fatigue test reveal that bending fatigue lives of gear teeth has been significantly improved after LSP in comparison with those non-peened teeth, and the bending fatigue limit is enhanced correspondingly. It is noticeable that higher laser energy does not necessarily lead to much better fatigue performance of test gears. © 2017

Qiu Z.,Beihang University | Lv Z.,Beihang University
International Journal for Numerical Methods in Engineering | Year: 2017

This work gives new statement of the vertex solution theorem for exact bounds of the solution to linear interval equations and its novel proof by virtue of the convex set theory. The core idea of the theorem is to transform linear interval equations into a series of equivalent deterministic linear equations. Then, the important theorem is extended to find the upper and lower bounds of static displacements of structures with interval parameters. Following discussions about the computational efforts, a coupled framework based on vertex method (VM) is established, which allows us to solve many large-scale engineering problems with uncertainties using deterministic finite element software. Compared with the previous works, the contribution of this work is not only to obtain the exact bounds of static displacements but also lay the foundation for development of an easy-to-use interval finite element software. Numerical examples demonstrate the good accuracy of VM. Meanwhile, the implementation of VM and availability of the coupled framework are demonstrated by engineering example. © 2017 John Wiley & Sons, Ltd.

Cai Y.,Beihang University | Huo L.,Beihang University | Sun Y.,Beihang University
Advanced Materials | Year: 2017

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liu Z.,Beihang University | Lu S.,Beihang University
International Journal of Computer Mathematics | Year: 2017

We consider the initial boundary value problem of the long-short wave equations on the whole line. A fully discrete spectral approximation scheme is developed based on Chebyshev rational functions in space and central difference in time. A priori estimates are derived which are crucial to study numerical stability and convergence of the fully discrete scheme. Then, unconditional numerical stability is proved. Convergence of the fully discrete scheme is shown by the method of error estimates. Finally, numerical experiments are presented to demonstrate the efficiency and accuracy of the convergence results. © 2017 Informa UK Limited, trading as Taylor & Francis Group

Fu R.-R.,Beihang University
Proceedings - 2016 6th International Conference on Instrumentation and Measurement, Computer, Communication and Control, IMCCC 2016 | Year: 2016

An algorithm of recognizing radar compound jamming signals including additive, multiplicative and convolution signals of typical blanket jamming and deception jamming based on neural networks is proposed in this article. Firstly, all signals of echo, jamming and noise received in one pulse repetition interval are acquired as signal sources. Then the features of the signal sources are extracted in time domain, frequency domain and fractal dimensions. Finally, classifier based on neural networks is established, by which compound signals are recognized. Results of the experiment indicate that the algorithm has the ability to recognize not only compound modes but also signal types, which enhances the accuracy of recognition. © 2016 IEEE.

Liang L.,Beihang University | Xu X.,Beihang University
International Conference on Signal Processing Proceedings, ICSP | Year: 2017

Strong background clutter exists in many cases such as inverse synthetic aperture radar (ISAR) imagery of turntable objects, which results in severely corrupted images. This work mainly aims at the reduction of zero-Doppler clutter (ZDC) for fixed background in high resolution radar imaging of rotating targets. Existing signal processing techniques for ZDC suppression are first addressed. An improved procedure is developed to avoid the defects of existing techniques. Experimental results using outdoor range measurements are presented to demonstrate the usefulness of the proposed technique. © 2016 IEEE.

Yang X.,Beihang University | Fan T.,Beihang University
International Conference on Signal Processing Proceedings, ICSP | Year: 2017

Multi-frame super resolution has been well studied in recent years, but blur kernel is always assumed to be known in video super resolution problem. Most blind deconvolution algorithm can both estimate the blur kernel and the sharp image. In this paper, we originally adopt a fast single image blind deconvolution algorithm in video super resolution to estimate high-resolution image and blur kernel. In super resolution part, we use a Bayesian framework to estimate motion, noise parameters and high-resolution image simultaneously. In blind deconvolution part, we use the first reconstructed high-resolution image as blurred image to restore the sharp image and blur kernel, and smooth sparse prior is used here. By introducing blind deconvolution, super resolution algorithm only needs several iteration to reach promising results. © 2016 IEEE.

Wang H.,Beihang University | Xu X.,Beihang University
International Conference on Signal Processing Proceedings, ICSP | Year: 2017

The paper proposes an approach for pixel-by-pixel orbit registration between wide swaths of passive sensors and narrow traces of active sensors, where a rough-to-fine process is implemented step by step. Take a granule of one passive sensor and the corresponding orbit of an active sensor as example. First, a part of the trace is extracted according to the latitude and longitude of the granule. Second, the granule is constrained roughly on the basis of the latitude and longitude of the extracted trace. Finally, a cost function verr of latitude and longitude is defined and the most matching pixel is selected from the constrained granule for each pixel of the active sensor along the extracted trace according verr and a given threshold. Moderate Resolution Imaging Spectroradiometer (MODIS) on Aqua and Cloud Profiling Radar (CPR) on CloudSat are chosen to validate the proposed method. Estimated results are compared with geographic data provided by CloudSat team, demonstrating that the algorithm performs well. © 2016 IEEE.

Kang Y.,Beihang University | Wang J.,Beihang University
International Conference on Signal Processing Proceedings, ICSP | Year: 2017

Time-of-arrival (TOA) is a range-based positioning method with high positioning precision. However, TOA-based methods require strict time synchronization between nodes, which puts forward high requirements on the hardware and power consumption of sensor nodes. For the high cost hardware problem of TOA-based methods, we propose a TOA-based iterative algorithm (iTOA) that can be applied to the wireless system under the condition of low time synchronization precision to achieve high positioning precision. Without the restriction of strict time synchronization, iTOA can reduce the difficulty of hardware implementation. iTOA eliminates the time synchronization error via iteration and minimizes the non-line-of-sight propagation error by using the weighted least square method at the same time. Moreover, iTOA can be applied to the network with changing beacons. The simulation results show that the average positioning precision improves at least 27.2% and 38.3% compared to CCTG and LOP, respectively. As the time synchronization precision decreases, the positioning precision improvement is more obvious compared to CCTG and LOP. For a low time synchronization precision system, the positioning error of iTOA is almost 99.99% less than both CCTG and LOP. © 2016 IEEE.

Jie C.,Beihang University | Zhuo L.,Beihang University
International Conference on Signal Processing Proceedings, ICSP | Year: 2017

A strategy for compensating time-variant ionospheric effect on GEO SAR is proposed. A HF band radar is is deployed on GEO SAR platform to simultaneously measure TEC variation for compensation. The sounding principle is presented and key system parameters of HF-radar are designed. Preliminary simulation results show that HF-radar sounding result may compensate the linear error in GEO SAR azimuth signal. © 2016 IEEE.

Zou Y.,Beihang University
International Journal of Robust and Nonlinear Control | Year: 2017

This paper exploits a nonlinear robust adaptive hierarchical sliding mode control approach for quadrotors subject to thrust constraint and inertial parameter uncertainty to accomplish trajectory tracking missions. Because of under-actuated nature of the quadrotor, a hierarchical control strategy is available; and position and attitude loop controllers are synthesized according to adaptive sliding mode control projects, where adaptive updates with projection algorithm are developed to ensure bounded estimations for uncertain inertial parameters. Further, during the position loop controller development, an auxiliary dynamic system is introduced, and selection criteria for controller parameters are established to maintain the thrust constraint and to ensure the non-singular requirement of command attitude extraction. It has demonstrated that, the asymptotically stable trajectory tracking can be realized by the asymptotically stable cascaded closed-loop system and auxiliary dynamic system. Simulations validate and highlight the proposed control approach. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Lei P.,Beihang University | Zheng L.,Beihang University
Robotics and Computer-Integrated Manufacturing | Year: 2017

Alignment is a crucial issue for finish machining the assembly interfaces of a large-scale component before final assembly in the aviation industry, as it affects the distribution of machining allowance and is time and effort consuming in the current manual way. This study presents an automated and in-situ alignment approach with the assistance of computer numerical controlled (CNC) positioners and laser trackers. The aligning process mainly consists of three steps, that is, measurement, posture evaluation, and posture adjustment. For measuring using laser tracker, a closed-loop method is proposed to establish a global reference frame (GRF) on the shop floor to unify measuring results from multi-stations based on the machine tool coordinate system. Therefore, the large-scale component is aligned to the machine tool as long as it is adjusted to the nominal posture in the GRF. As regards posture evaluation, the key characteristics (KCs) of the large-scale component are considered in the evaluation process based on the geometrical meaning of the singular value decomposition (SVD) to reduce the residual error of the KC with higher importance. An in-process calibration method is proposed during the adjustment process to calculate the actual position of the sphere hinge center and avoid the alignment accuracy loss in the kinematic backward transformation. A vertical tail of a certain large passenger aircraft is then used to validate the proposed alignment system and methods. The experimental results show that: (1) the GRF is accurately established on the shop floor; (2) the proposed posture evaluation algorithm enhances the transformation accuracy of the KC with greater importance; (3) the center position of the sphere hinge is calibrated, such that it hardly affects the alignment accuracy; and (4) the large component is aligned to the machine tool, satisfying all the tolerance requirements. © 2017 Elsevier Ltd

Yu X.,Beihang University | Lin Y.,Beihang University
IEEE Transactions on Automatic Control | Year: 2017

Recently, an adaptive backstepping quantized control scheme was proposed. In this note, for a class of general nonlinear systems, it is shown that with a simple yet novel transformation of the control signal, all the strict assumptions on the system in early works can be relaxed, a coarser quantization can be achieved, and the stabilization error can be steered to within an arbitrarily small neighborhood of the origin. © 1963-2012 IEEE.

Meng D.,Beihang University | Moore K.L.,Colorado School of Mines
IEEE Transactions on Automatic Control | Year: 2017

This technical note proposes a robust iterative learning control (ILC) strategy to regulate iteratively-operated, finite-duration nonrepetitive systems characterized by iteration-varying uncertainties in initial states, external disturbances, plant model matrices and desired reference trajectories. Our convergence analysis exploits results on input-to-state stability of discrete parameterized systems. For a class of multiple-input, multiple-output discrete-time linear systems, with all iteration-varying uncertainties bounded, we give one condition that ensures boundedness of all system trajectories and an additional, second condition that ensures convergence of tracking error. Notably, we do not require the standard ILC contraction mapping requirement to hold at each iteration. Moreover, we show that it is possible to achieve perfect output tracking if the iteration-varying uncertainties all converge with increasing iteration. © 1963-2012 IEEE.

Yang J.,Beihang University | Liu M.,Beihang University
Acta Astronautica | Year: 2017

The theory of molecular motion was used to study the wall cell Reynolds number method, and it found that the height of the first grid point off wall is related to the molecular mean free path near wall. A wall grid scale criterion based on the molecular mean free path at the stagnation point was proposed by considering both the flow parameters and the wall temperature boundaries. The criterion was verified through numerical calculations and comparative analyses of the wall heat flux in different hypersonic flow fields. Research results draw the following conclusions: The optimal height of the first grid point off wall is a molecular mean free path. The influence of height of the first grid point off wall on aerodynamic heat is much greater than that of aerodynamic force. The criterion is not only effective for the wall heat flux predictions in air conditions, but also useful to that of non air environments. With the weakening of aerodynamic heating along the flow direction, the effect of wall grid scale on the wall heat flux gradually decreases. © 2017

Meng D.,Beihang University
Automatica | Year: 2017

This paper considers a class of bipartite containment tracking problems for leader-following networks associated with signed digraphs. It admits multiple leaders which can be not only stationary but also dynamically changing via interactions between them and their neighbored leaders. It is shown that the followers can converge to the convex hull containing each leader's trajectory as well as its symmetric trajectory which is the same as it in modulus but different in sign. In particular, if the adjacency weight matrix of the digraph is not signed but nonnegative, then the leader-following network achieves the traditional containment tracking. Simulation tests are performed to illustrate the observed bipartite containment tracking performances of signed networks. © 2017 Elsevier Ltd

Meng D.,Beihang University | Moore K.L.,Colorado School of Mines
Automatica | Year: 2017

This paper studies the robust convergence properties of iterative learning control (ILC) for single-input, single-output (SISO), nonrepetitive systems subject to iteration-dependent uncertainties that arise in not only initial states and external disturbances but also plant models. Given an extended relative degree condition, it is possible to propose necessary and sufficient (NAS) conditions for robust ILC convergence. The tracking error bound is shown to depend continuously on the bounds of the iteration-dependent uncertainties. When the iteration-dependent uncertainties are bounded, NAS conditions exist to guarantee bounded system trajectories and output tracking error. If the iteration-dependent uncertainties converge, then NAS conditions ensure bounded system trajectories and zero output tracking error. The results are also extended to a class of affine nonlinear systems satisfying a Lipschitz condition. Simulation tests on a representative batch process demonstrate the validity of the obtained robust ILC convergence results. © 2017 Elsevier Ltd

Xu Y.,Beihang University | Jiao Z.,Beihang University
Journal of Fluids and Structures | Year: 2017

The axial vibration of liquid-pipes, considering the fluid-structure interaction (FSI), can be described by a four-equation model consisting of two equations for the fluid and the other two for the pipe wall. When distributed friction and damping were neglected, the model could be solved with an exact solution developed from the method of characteristics (MOC). The exact solution with a simple recursion process was presented instead of meshing the distance-time plane, introducing no numerical error, while the only weakness was the high time cost. An improved method based on this exact solution is proposed in this work, using the time-line interpolation rather than the recursive algorithm to speed the calculation. As numerical diffusion and oscillation affect the accuracy a lot, various interpolation techniques are investigated and compared. The mean absolute error (MAE) and the structural similarity index measure (SSIM) are employed to assess the accuracy of proposed methods, and the latter was originally developed for the image quality assessment. A hybrid interpolation scheme, mixing the cubic spline and linear interpolation, is proposed and achieves the highest accuracy and the quadratic-linear interpolation is found to be a good choice considering both accuracy and efficiency. The solution method developed here improves the efficiency significantly while retains an acceptable level of the accuracy, especially suitable for the long duration event. © 2017 Elsevier Ltd

An H.,Beihang University | Huang H.,Beihang University
AIAA Journal | Year: 2017

This paper discusses the integrated topology and sizing optimization of frame structures where beam elements are used in the structural analysis model. Based on the ground structure approach, discrete variables (0, 1) representing the absence or presence of beam members and continuous sizing variables for beam cross sections are involved in the problem. A two-level multipoint approximation strategy is introduced to address this mixed-variable problem. A first-level approximate problem is first constructed using the branched multipoint approximate function involving both discrete and continuous variables. For solving this problem, discrete variables are optimized through a genetic algorithm, and when calculating the fitness in the genetic algorithm, a second-level approximate problem solved by the dual method is established to optimize the cross sections for the retained beam members. Temporal deletion techniques are used for displacement and stress constraints. Meanwhile, by considering local vibration modes in frequency-constrained problems, material density is assigned with an extremely small value for the removed beams to avoid these local modes. Thence, the singularities encountered in stress, displacement, and frequency constraints are overcome. Typical examples and a satellite application are given to verify the feasibility and efficiency of this method in handling the integrated topology and sizing optimization for frame structures. © 2016 by Hai Huang and Haichao An.

Zhu W.,Beihang University | Deng Y.,Beihang University | Cao L.,Beihang University
Nano Energy | Year: 2017

In this study, we prepared a multi-functional thin-film thermoelectric device for small-scale energy harvesting and self-powered light sensing. A comprehensive optimization was conducted in terms of thermoelectric material, device, and system integration. The thermoelectric thin films in the device were prepared using the sputtering method together with a post-annealing process. A Fresnel lens was incorporated into the thin-film thermoelectric device for energy concentration. In addition, a simulation procedure was used to facilitate the optimization of the heat sink, which can provide fast heat dissipation and mechanical support for the thin-film thermoelectric device. The electricity generation and light sensing performance was then characterized under solar irradiation, followed by a feasibility study for sensor application. The results indicate that our thin-film thermoelectric device exhibits high voltage output and greatly enhanced responsivity. This work presents a significant progress toward an integrated design of an applicable and multifunctional thin-film thermoelectric sensor for detecting sunlight intensity. © 2017 Elsevier Ltd

Bian Y.,Beihang University | Gao Z.,Beihang University
Journal of Sound and Vibration | Year: 2017

A semi-active vibration absorption method is put forward to attenuate nonlinear vibration of a flexible arm based on the internal resonance. To maintain the 2:1 internal resonance condition and the desirable damping characteristic, a virtual vibration absorber is suggested. It is mathematically equivalent to a vibration absorber but its frequency and damping coefficients can be readily adjusted by simple control algorithms, thereby replacing those hard-to-implement mechanical designs. Through theoretical analyses and numerical simulations, it is proven that the internal resonance can be successfully established for the flexible arm, and the vibrational energy of flexible arm can be transferred to and dissipated by the virtual vibration absorber. Finally, experimental results are presented to validate the theoretical predictions. Since the proposed method absorbs rather than suppresses vibrational energy of the primary system, it is more convenient to reduce strong vibration than conventional active vibration suppression methods based on smart material actuators with limited energy output. Furthermore, since it aims to establish an internal vibrational energy transfer channel from the primary system to the vibration absorber rather than directly respond to external excitations, it is especially applicable for attenuating nonlinear vibration excited by unpredictable excitations. © 2017 Elsevier Ltd.

Liu H.,Beihang University | Yang J.,Beihang University
Composite Structures | Year: 2017

A theoretical model is obtained to predict the dynamic response of a clamped sandwich beam with thick weak core impacted centrally by a projectile. The core is weak and thick enough that only part or all of the front face sheet and the core undergo permanent plastic deformations, while the back face sheet undergoes an elastic vibration. The core is taken to be rigid-plastic and the front face sheet is treated as an individual rigid-plastic beam resting on a foundation. The back face sheet is modeled as an Euler–Bernoulli beam. Based on the rigid-perfectly theory and Galerkin method, two types of the sandwich beam response are given, i.e., intermediate strength and low strength core type responses. The critical kinetic energy of the projectile as the back face sheet reaches its elastic limit is studied. The localized indentation and response history of the sandwich beam are presented. It is found that the dynamic response of the sandwich beam is sensitive to the core strength, mass ratio, breadth and impact velocity of the projectile. The finite element (FE) simulation is also carried out to verify the analytical predictions and a good agreement is achieved. © 2017 Elsevier Ltd

Zou Y.,Beihang University
International Journal of Systems Science | Year: 2017

This paper exploits a singularity-free adaptive fault-tolerant controller for vertical take-off and landing (VTOL) unmanned airborne vehicles (UAVs) to fulfill trajectory tracking manoeuvres, which is robust against parametric uncertainties, actuator faults and unexpected disturbances. Under the hierarchical control framework, the position and attitude loop controls are developed in sequence based on adaptive sliding mode control schemes. Initially, using the saturation property of the hyperbolic tangent function, a position loop controller is synthesised, and a criterion for choosing control parameters is established to guarantee the singularity-free command attitude extraction. Then, in the attitude loop, to avoid singularity which occurs when the pitch reaches (Formula presented.), a novel sliding mode surface is introduced, and an attitude control project with the associated initial condition constraint is put forward. In addition, adaptive algorithms are developed to estimate and compensate the uncertainties arising from unknown inertial parameters, thrust and torque faults and undesired disturbances. It is demonstrated in terms of Lyapunov theorem that, with the proposed controller, the closed-loop position and attitude error subsystems of the VTOL UAV are asymptotically stable, respectively. Eventually, simulations validate the tracking performance of the controller. © 2017 Informa UK Limited, trading as Taylor & Francis Group

Meng D.,Beihang University
International Journal of Control | Year: 2017

This paper aims at solving convergence problems on directed signed networks with multiple nodes, where interactions among nodes are described by signed digraphs. The convergence analysis is achieved by matrix-theoretic and graph-theoretic tools, in which M-matrices play a central role. The fundamental digon sign-symmetry assumption upon signed digraphs can be removed with the proposed analysis approach. Furthermore, necessary and sufficient conditions are established for semi-positive and positive stabilities of Laplacian matrices of signed digraphs, respectively. A benefit of this result is that given strong connectivity, a directed signed network can achieve bipartite consensus (or state stability) if and only if the signed digraph associated with it is structurally balanced (or unbalanced). If the interactions between nodes are described by a signed digraph only with spanning trees, a directed signed network can achieve interval bipartite consensus (or state stability) if and only if the signed digraph contains a structurally balanced (or unbalanced) rooted subgraph. Simulations are given to illustrate the developed results by considering signed networks associated with digon sign-unsymmetric signed digraphs. © 2017 Informa UK Limited, trading as Taylor & Francis Group

Hao K.,Beihang University
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

For a reentry warhead with single moving mass, the goal of control in this paper is tracking and stabilization in roll and yaw channel, respectively. Firstly, a detailed model of warhead is established using Kane method, and the affine nonlinear form for the control design is derived. Then PID is combined with the nonlinear dynamic inverse to form the attitude controller of the warhead. And the disturbance observer based on extended state observer (ESO) is designed, which is used to observe and compensate for the inaccuracy of the under-actuated controller. The Moving Mass Nonlinear Controller (MMNC) is composed of the controller and the disturbance observer. At last, simulation and comparison are carried out, the results show that the MMNC has better system response, better adaptability and stronger robustness than the traditional PID controller. © 2016 IEEE.

Tie L.,Beihang University
2016 European Control Conference, ECC 2016 | Year: 2016

Small-controllable systems are controllable under arbitrarily small control inputs. In this paper, small-controllability of a class of discrete-time bilinear systems is studied. A necessary and sufficient condition for the systems to be small-controllable is presented. Furthermore, a new notion, defined as near-reachability, is introduced to describe the systems when they are uncontrollable but own a strong reachability property, and a necessary and sufficient condition for the systems to be nearly-reachable is also obtained. Finally, examples are given to illustrate the results of this paper. © 2016 EUCA.

Zheng Z.,Beihang University | Tian J.,Beihang University
Risk, Reliability and Safety: Innovating Theory and Practice - Proceedings of the 26th European Safety and Reliability Conference, ESREL 2016 | Year: 2017

Manufacturing industry is a complex socio-technological system which include not only technological, but also human and organizational components. Slight deviations from the expected output are ubiquitous in every activity during the manufacture process. The aggregation of deviations in a given scenario or set of conditions may have great impact on the quality of the product, or even directly lead to the rejection of the product. The undesired event occurred in the manufacture process maybe the emergence of many factors and may not involve any component failure, the analysis of which is out of the capability of traditional failure-based methods. Therefore, the need for a new approach which is well-suited for analyzing the problem of nonlinear interrelationships in the manufacture process is perceived as strongly evident. © 2017 Taylor & Francis Group, London.

Han R.,Beihang University | Wang S.,Beihang University
Risk, Reliability and Safety: Innovating Theory and Practice - Proceedings of the 26th European Safety and Reliability Conference, ESREL 2016 | Year: 2017

As the development of avionics system, the system integration degree enhances gradually, which increases the complexity of the system safety problem. Integrated modular avionics systems present the improvement of functionality and performance of the system and the reduction of cost of aircraft life cycle, as well as a series of system safety problems which come with the resource sharing mechanism. The problems presented above refer to complex situations in which the states of system correlates each other and a system runs with dynamic behaviors when a fault happened. © 2017 Taylor & Francis Group, London.

Zhong S.,Beihang University
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

Missile spins can reduce the disturbance caused by asymmetric body, the eccentric of mass and other problem, and can also lead to the attitude control of missile being more complicated. Dynamic model of a spin missile is established in quasi-body coordinates. The system is divided into inner and outer subsystems through time-scale separation principle. And the controllers of inner loop and the outer loop are both designed by the active disturbance rejection controller (ADRC). The main idea of ADRC is putting the uncertainty of the model, parameters perturbation and unmodelled dynamic as a system of total disturbance, and observing it through the extended state observer, and compensating to system timely. Simulation shows that the system in the conditions of parameters change and disturbance exist can maintain a good dynamic performance. © 2016 IEEE.

Lu W.,Beihang University
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

For an air-breathing Hypersonic Air Vehicle (HAV) in cruise flight, the model is strongly nonlinear and coupled and includes uncertain parameters. A pseudo-linear model is obtained by input/output feedback linearization, and a model reference adaptive controller is applied to it. Single Hidden Layer (SHL) Perceptron Neural Network (NN) is used to cancel model error online because of its good nonlinear approximation. Considering that large-span maneuver or strong disturbance can cause control surface saturation, Pseudo-Control Hedging (PCH) is introduced. Simulation results show that the proposed adaptive control system has well tracking performance, strong robustness and anti-input-saturation characteristics. © 2016 IEEE.

Zhao T.,Beihang University
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

As the application of unmanned aerial vehicles(UAVs) becoming more widely, a demand for precise autonomous landing is rising quickly. AR.Drone 2.0 is a high-tech low-cost flying toy that is able to take role as UAV. In this paper, we present a system for the drone to implement autonomous landing. The image flow from the camera of the drone is obtained and rectified by camera calibration. Then the image frames are processed by a marker recognition package to detect the AR marker which is used as a landing pad, and calculate the position and orientation relation between the drone and the landing pad. Next a PID controller is used to control the drone's velocity to stably hovering on the center of the landing pad. A laptop computer running Ubuntu and ROS is used to communicate with the drone via Wi-Fi, throughout the landing process. Several experiments are made to verify the feasibility of the whole system. © 2016 IEEE.

Liu X.,Beihang University
CGNCC 2016 - 2016 IEEE Chinese Guidance, Navigation and Control Conference | Year: 2016

This paper focuses on the hypersonic vehicle in consideration of oscillation and aerodynamic heating problems during reentry process, for trajectory optimization, penalty function method and ϵ level comparison are introduced for transforming the unconstrained waterweeds algorithm into constrained algorithm to solve multi-objective optimization problems, in which a novel and more precise criterion based on time-scales separation guidance for oscillation optimization is put forward indicating waterweeds algorithm to get a better optimal result. The algorithm transformed is successfully applied to trajectory design. © 2016 IEEE.

Wu C.F.,Qingdao University of Science and Technology | Zhao Q.H.,Beihang University
Scientia Iranica | Year: 2015

One of the important issues in inventory management is permissible delay in payments. Previous inventory lot-size models allowing permissible delay in payments implicitly assumed that the demand rate is constant and inventory-dependent. However, this paper, unlike most existing models, this paper develops an Economic Order Quantity (EOQ) model for deteriorating items with a current inventory-dependent and linearly increasing time-varying demand under trade credit, which fits a more general inventory feature. An efficient solution procedure is shown to determine the optimal replenishment cycle of the model. Furthermore, this study deduces some previously published results as special cases of the proposed model. Finally, numerical examples are presented to illustrate the optimization procedure, and a sensitivity analysis is performed for changes in the parameters to obtain important and relevant findings on managerial implication. © 2015 Sharif University of Technology. All rights reserved.

Jiang J.,Beihang University
IMA Journal of Mathematical Control and Information | Year: 2016

For a linear time invariant system, the system stability is equivalent to the stability of the system matrix. Thus, finding the conditions for the matrix stability becomes a key to analysis and design of large-scale linear systems. This paper is aimed at studying the large-scale matrix stability problem by means of matrix partitioning. The sufficient conditions for the large-scale matrix stability are proposed. For matrices with normal block diagonal submatrices, a concise and practical expression for testing matrix stability is derived. Additionally, for block diagonally dominant matrices, a sufficient condition, which is used to determine whether the matrix is stable, is proposed. Finally, numerical examples are provided that not only validate theoretical results obtained in this paper, but also demonstrate the analysis and design of large-scale linear systems. © The authors 2015. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.

Liu C.,Beihang University | Liu G.,Beihang University | Fang J.,Beihang University
IEEE Transactions on Industrial Electronics | Year: 2017

To effectively reject the influence of moving gimbal effect and parameter variation on the control performance of the rotor-active magnetic bearings (AMBs) system in a double gimbal magnetically suspended control moment gyro (MSCMG), this paper proposes a feedback linearization and extended state observer (ESO) based control (FLESOBC) strategy, which can attenuate the matched and mismatched system uncertainties simultaneously. First, considering the voltage-type power amplifier used in the MSCMG for space applications, the rotor dynamics is modeled completely and then rearranged into translation and tilt motion subsystems according to modal separation control, where the lumped system uncertainties are adopted to represent the external disturbances and the parameter variations. Then, feedback linearization based on differential geometry theory is performed to transform the original system into the integral chain pseudo-linear system, making the mismatched uncertainties in the same channel as the new virtual input. Afterwards, the ESO is designed to estimate the lumped uncertainties. To combine the merits of compensation control and robust control, a PIDD controller (PID with second order differential) is designed to guarantee the closed loop stability and avoid the power amplifier saturation. Finally, simulations and experiments are carried out to demonstrate the effectiveness of the proposed method. © 2016 IEEE.

Wang Z.,Beihang University | Bao W.,China Aerospace Science and Technology Corporation | Li H.,Beihang University
IEEE Transactions on Industrial Electronics | Year: 2017

This paper deals with the second-order dynamic sliding-mode control (SODSMC) problem for nonminimum phase underactuated hypersonic vehicles. First, the underactuated hypersonic vehicle attitude control model is introduced. The normal form and the nonminimum phase nature for the vehicle are discussed. Thus, the nonminimum phase system is divided into the minimum phase subsystem and the nonminimum phase subsystem via the system decomposition approach. Second, the SODSMC scheme is developed. The conventional sliding-mode controller and the second-order dynamic sliding-mode controller are designed for the two subsystems. Besides, the dynamic sliding manifold is provided for the nonminimum phase subsystem. Simulation results for the nonminimum phase underactuated hypersonic vehicle are presented to demonstrate the effectiveness and robustness of the proposed control scheme. © 2017 IEEE.

Yang J.,Nanjing Southeast University | Chen W.-H.,Loughborough University | Li S.,Nanjing Southeast University | Guo L.,Beihang University | Yan Y.,Nanjing Southeast University
IEEE Transactions on Industrial Electronics | Year: 2017

This paper gives a comprehensive overview on disturbance/uncertainty estimation and attenuation (DUEA) techniques in permanent-magnet synchronous motor (PMSM) drives. Various disturbances and uncertainties in PMSM and also other alternating current (ac) motor drives are first reviewed which shows they have different behaviors and appear in different control loops of the system. The existing DUEA and other relevant control methods in handling disturbances and uncertainties widely used in PMSM drives, and their latest developments are then discussed and summarized. It also provides in-depth analysis of the relationship between these advanced control methods in the context of PMSM systems. When dealing with uncertainties, it is shown that DUEA has a different but complementary mechanism to widely used robust control and adaptive control. The similarities and differences in disturbance attenuation of DUEA and other promising methods such as internal model control and output regulation theory have been analyzed in detail. The wide applications of these methods in different ac motor drives (in particular in PMSM drives) are categorized and summarized. Finally, the paper ends with the discussion on future directions in this area. © 2017 IEEE.

Zuo Z.,Beihang University | Mallikarjunan S.,Unmanned Dynamics
IEEE Transactions on Industrial Electronics | Year: 2017

This paper addresses the trajectory tracking control (i.e., outer-loop control) problem for unmanned aerial vehicles (UAVs) in the presence of modeling uncertainties and external disturbances. The kinematics and dynamics of the trajectory tracking problem are always in strict feedback form. While there is no uncertainty in the kinematics, rapidly changing uncertainties present in the dynamics makes this problem an ideal candidate for Ⅎ1 adaptive backstepping control. The trajectory tracking controller serves as the outer-loop in a cascaded design architecture and supplies a reference quaternion and thrust to the inner-loop controller. The inner-loop controller in turn generates a moment demand for the control allocation module. Such an inner-outer loop architecture is modular and does away with the requirement that the commanded trajectory be four times differentiable as would be required if a single monolithic backstepping control law where to be used. Both simulations and flight tests are used to demonstrate the effectiveness of the proposed controller and how the controller tracks any twice differentiable trajectory, respectively. © 2017 IEEE.

Tang J.,Beihang University | Wang K.,Beihang University | Xiang B.,Beihang University
IEEE Transactions on Industrial Electronics | Year: 2017

The rotor's stable suspension is one of elementary requirements for the superconducting attitude control and energy storage flywheel with active magnetic bearings (AMBs) due to its prominent gyroscopic effect. To suspend the high-speed rotor stably, the dynamic model of rotor is established, the decoupling control method is introduced to decouple the radial translations modal and tilting modal of rotor, and the displacement cross-feedback is adopted to suppress the rotor's vibration. When the rotor speeds up to 50 000 r/min, research results indicate that the trace of rotor's vibration is a circle with radius 0.005 mm, which is far smaller than its magnetic gap. All that verified the force linearization of both superconducting MB and AMBs is reasonable, the dynamic model of rotor is suitable and the cross-feedback control is one effective method to suppress the vibration of the high-speed discal rotor. © 2016 IEEE.

Tan D.,Beihang University | Lv H.,Longdong University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

Impulsive noise usually has adverse effect on image processing. It has been proved that adaptive median filter is effective to impulsive noise removal. However, high percentage impulsive noise is still a challenge to adaptive median filter. Thus, a sequential median filter is proposed in this paper. Adaptive median filter and median filter are combined in sequence to handle high percentage impulsive noise. Moreover, variable window sizes are employed in the sequential median filter. Experimental results indicate that the sequential median filter is effective for high percentage impulsive noise removal. © 2017 SPIE.

Liu Y.,Beihang University | Xue B.,Beihang University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

We propose a faster method for video motion magnification, which can make imperceptible motion visible for human eyes. Motion-magnified videos produced by our framework are of comparable quality to those produced with Riesz pyramid, but our method has higher computational efficiency. We use median filter to eliminate the grid noises at motion area edges. Experiments show our method is effective and efficient. © 2017 SPIE.

Xue P.,Beihang University | Fu G.,Beihang University | Zhang D.,Beihang University
IEEE Transactions on Power Electronics | Year: 2017

In this study, a physics-based compact model for high-speed buffer layer insulated gate bipolar transistor (IGBT) is proposed. The model utilizes the 1-D Fourier-based solution of ambipolar diffusion equation (ADE) implemented in MATLAB and Simulink. Based on the improved understanding on the inductive switching behavior of a high-speed buffer layer IGBT, the ADE is solved for all injection levels instead of high-level injection only as usually done. Assuming high-level injection condition in the buffer layer, the excess carrier transport, redistribution and recombination in the buffer layer are redescribed. Moreover, some physical characteristics such as the low conductivity of N-base at turn-on transient and free holes appeared in the depletion layer during turn-off process are also considered in the model. Finally, the double-pulse switching tests for a commercial field stop IGBT and a light punch-through carrier-stored trench bipolar transistor are used to validate the proposed model. The simulation results are compared with experiment results and good agreement is obtained. © 1986-2012 IEEE.

Su H.,Beihang University
Journal of Pragmatics | Year: 2017

This study explores the possibility and the feasibility of developing a set of local grammars to account adequately for speech acts, exemplifying the exploration with a local grammar of request. It mainly aims to further speech act studies and to ultimately contribute to the on-going development of corpus pragmatics. Using a corpus compiled of transcripts of the sitcom The Big Bang Theory, instances containing conventionalised forms of request are first extracted and then manually examined to make sure that all the remaining instances express requests and thus qualify for further analysis. Functional elements (e.g. Requester, Requestee, Requested action) designed specifically for a local grammar analysis of request are proposed. The subsequent analyses lead to the identification of 10 local grammar patterns of requests. The study shows that it is promising, though at the same time challenging, to develop local grammars of speech acts. The opportunities and challenges of using a local grammar approach to account for speech acts are further discussed. Implications and applications are also briefly discussed. © 2017 Elsevier B.V.

Huang M.,Beihang University
CIE 2016: 46th International Conferences on Computers and Industrial Engineering | Year: 2016

To improve the robustness of modular product to requirements change, a robust module partition method is proposed by introducing the robust design idea. Generalized and personalized or changeable requirements are identified as key noise factors. Components and modules change caused by requirements change is analyzed as influence of variation. For each module partition, the influence concentration degree is calculated as the robustness principle based on change-influence matrix between requirement noises and components, and the internal clustering and external independence are calculated simultaneously as the aggregation principle based on integrated interactions matrix. Bi-objective optimization model is established and an improved multi-objective evolutionary algorithm is used to address the problem and find the Pareto-optimal set. A selection method considering robustness is also used to select the best compromise Pareto solution. Finally, an industrial case study of coal mining machine is given to illustrate the practical application and rationality of the research.

Yan W.,Beihang University
CIE 2016: 46th International Conferences on Computers and Industrial Engineering | Year: 2016

To solve the process discontinuity and data asynchronism problems between product data management and computer aided quality systems which were used in engineering change order execution process, the engineering change management process in those two information systems were analysed. The objective difference was recognized and data exchange interfaces were identified. Then a cross-system collaboration model and a cross-system data exchange model were proposed. A case study in an aircraft manufacture company proved the validity and effectiveness of the proposed models.

Yang Y.,Beihang University | Zhang X.,Beihang University
Soft Computing | Year: 2017

In this note, we correct three non-trivial classes of Birkhoff–Pierce’s classification of two-dimensional associative lattice-ordered real algebras. © 2017 Springer-Verlag Berlin Heidelberg

Wu Y.,Beihang University | Yang Y.,Beihang University
Soft Computing | Year: 2017

In this paper, we study the exclusion problem concerning the classes of involutive bounded lattices, logics, and quantum logics (i.e., orthomodular lattices). We also obtain that a logic is a quantum logic if and only if it is a paraconsistent logic. Moreover, we give some considerations on an open question to find sufficient conditions for the existence of an orthomodular orthocomplementation on lattices. Furthermore, we revisit the Dedekind–MacNeille completion of involutive bounded posets and correct a widely cited error in quantum logics. © 2017 Springer-Verlag Berlin Heidelberg

Luan C.,Beihang University | Yang Y.,Beihang University
Soft Computing | Year: 2017

We show that every MV-algebra A can be naturally equipped with a filter topology such that A is a topological MV-algebra, which improves the main results on C-topological lattice-ordered groups in both Yang (Sci China Ser A 52(11):2397–2403, 2009) and Gusić (Proc Am Math Soc 126(9):2593–2597, 1998). Furthermore, for a 2-divisible MV-algebra A, we show that the filter topological space is Hausdorff if and only if A is semisimple. © 2017 Springer-Verlag Berlin Heidelberg

Chen Y.,Fujian Commercial College | Yang Y.,Beihang University
Soft Computing | Year: 2017

We give a lattice theoretic proof of the well-known result that a finite group G is cyclic iff G has at most one subgroup of each order dividing |G|. Consequently, we show that a division ring D is a field iff D has at most one maximal subfield. © 2017 Springer-Verlag Berlin Heidelberg

Tie L.,Beihang University
2016 IEEE 55th Conference on Decision and Control, CDC 2016 | Year: 2016

In this paper, we consider a class of n-dimensional discrete-time bilinear systems which can be nearly controllable. We first show that, to achieve near-controllability, at least n+1 control inputs are required. That is, the minimum time to steer the class of systems between any given pair of states is no less than n + 1 time steps. We then prove by applying the root locus theory that the systems can be nearly controllable with exactly n + 1 control inputs only if a corresponding matrix has no Jordan block with dimension greater than two and, meanwhile, has no more than one Jordan block with dimension two in its Jordan canonical form. Finally, we give examples to demonstrate the results of this paper. © 2016 IEEE.

Sun D.,Beihang University | Liu B.,Shandong Computer Science Center National Supercomputer Center in Jinan
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2017

With the development of new web technologies, the Massive Open Online Course (MOOC) which aims at unlimited participation and access is emerging. In contrast to traditional education, learners could get access to filmed lectures and tests online anytime and anywhere. However, there still exists some problems with MOOCs. Currently, one major problem is the imbalance between teachers and learners online. In many courses, thousands of learners enroll in a class with a single instructor which could lead to bad learning effect and very low completion rates, so we propose crowdsourcing based teaching assistant assignment for MOOC in order to optimize the reasonable disposal of manpower. We present effective algorithms for the selection and assignment of teaching assistants. With experiments on various datasets, we verify the effectiveness of our proposed methods. © Springer International Publishing AG 2017.

Liang Y.,Beihang University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2017

Massive open online courses (MOOCs) provide an opportunity for learners to access free courses offered by top universities in the world. However, with contrast to large scale enrollment, the completion rate of these courses is really low. One of the reasons for students to quit learning process is that they could not study the courses with their friends. In order to improve the completion rate, we address the importance of content interest and social friendship for courses arrangement for learners in MOOCs. We first develop a greedy algorithm to solve the arrangement according to the friendship of learners and the content of courses. Then we used the game theoretic framework to improve greedy algorithm performance. Finally, we verify the effectiveness and efficiency of the proposed solutions through extensive experiments on both real and synthetic datasets. © Springer International Publishing AG 2017.

Gao Y.,Beihang University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2017

With larger and larger numbers of students participating in Massive Open Online Courses (MOOCs), finding top-k suitable courses increasingly becomes a challenging issue for students in terms of course quality, which is hard for computer to compare. Thanks to emerging crowdsourcing platforms, the crowd are assigned to compare the objects and infer the top − k objects based on the crowdsourced comparison results. In this paper, we focus on one such function, top − k, that finds the former k ranked objects. We then provide heuristic functions to recommend the top−k elements given evidence.We experimentally evaluate our functions to highlight their strengths and weaknesses. © Springer International Publishing AG 2017.

Zhong R.,Beihang University
Proceedings of the International Astronautical Congress, IAC | Year: 2016

With the dramatically growing number of states capable of launching their own satellites into orbits, the near earth orbits are becoming increasingly crowded. Among all possible solutions of space debris removal, the tethered space-tug (TST) carrying a space net to capture and deorbit the space debris by a tether appears one of the most effective and promising methods. However, it is challenging to prevent the TST system from failures due to the tether slack, tether libration and the attitude motion of the tug during the propulsion stage. This work concerns the dynamic stability of TST systems in the propulsion phase of a Hohmann orbital transfer that raises space debris from the geostationary orbit to the graveyard orbit by 300km. Operational constraints, such as bounded motion both for the tether libration and the tug attitude motion, positive tension and constant propulsion, are considered. The stability control of the tug system is achieved by regulating the reel-in/out acceleration of tether, the control toque and the orientation of the propulsion force acting on the tug. The authors develop a computationally efficient algorithm to solve the optimal control problem of the Hohnmann transfer for onboard implementation. Studies show that the orbital and libration motions of tethered space systems change at different timescales. Based on their time variation rates, the states and control inputs are separated into fast and slow categories and they are discretized by Legendre-Gauss-Lobatto method with different discretization grids. The resulted openloop optimal control generates an optimal trajectory with minimum propulsion time and stable states of TST systems (zero libration of tether and zero attitude of tug) at the end of propulsion stage of the Hohmann transfer. Then, a closed-loop sliding mode controller is used to reduce errors introduced by the approximation of timescale separation and the direct discretization using polynomials. Finally, the efficiency and accuracy of the timescale separate optimal control strategy is demonstrated by numerical simulation. Furthermore, It is demonstrated that the proposed timescale separation scheme is effective in reducing the computational burden of the optimal control by about 30 percent with acceptable control accuracy.

Wei Q.,Beihang University | Yang B.,Beihang University
IEEE Sensors Journal | Year: 2017

This paper presents an adaptable roadside vehicle detection and speed estimation system for various traffic conditions on urban roads based on tri-axial anisotropic magnetoresistive sensors and wireless sensor network. The system consists of one master node and two sensor nodes, which are placed along the roadsides and can measure the earth's local magnetic field disturbance caused by passing vehicles. A dynamic threshold detection algorithm is proposed for vehicle detection, especially considering the actual variable traffic condition. The vehicle speed is estimated on the basis of the maximum values and the cross correlation of effective parts extracted from two sensor signals. We have tested the vehicle information at several roads under different traffic conditions. Validation study has revealed a high detection accuracy of 97.92% when using a dynamic threshold compared with 92.3% when using a fixed threshold. And, the average accuracy of speed estimation can reach up to 97.11% on the roads. The proposed algorithm has a significant increase in accuracy, reliability, and practicability compared with the fixed threshold algorithm. © 2017 IEEE.

Sun Z.-Y.,Qufu Normal University | Zhang C.-H.,Qufu Normal University | Wang Z.,Beihang University
Automatica | Year: 2017

This paper investigates the problem of adaptive disturbance attenuation for a class of generalized high-order uncertain nonlinear systems. The control strategy is on the basis of continuous domination and delicate adaptive technique, and it can cope with serious coexistence among uncertainties, including time-varying control coefficients which have unknown upper and lower bounds, nonlinear parameters and external disturbances. Adaptive state-feedback controller is one-dimensional irrespective of the number of unknown parameters, and its performance is evaluated in terms of L2-L2p gain. © 2017 Elsevier Ltd

Xu J.,Beihang University | Zheng B.,Beihang University
Carbon | Year: 2017

One-dimensionally arrayed C60 system, a nanoscale counterpart of traditional macroscale granular crystals, supports solitary wave propagation. In this paper, it is shown that inserting a series of short carbon nanotubes to C60 system may achieve quantitative tuning of C60-based solitary wave based on molecular dynamics simulations. A concept of energy tunnel is suggested which explains the change of transmitted energy in carbon nanotubes. Based on the energy tunnel theory, the amplitude and wave speed can be quantitatively tuned, which, to the authors’ knowledge, has not been achieved at macroscale. This study may be instructive to the design of nanoscale wave-tailoring devices as well as stress wave monitoring measurements. © 2016 Elsevier Ltd

Fu Y.,Beihang University | Yan M.,Beihang University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2017

This article briefly describes the overall structure of the loading test rig; establish mathematical model of loading EMA, analyze its stability, surplus force and other properties in MATLAB; propose a compound control strategy combined speed feedback, PID and feed-forward compensation based on structure invariance principle. To verify the effectiveness of the control strategy, do a co-simulation by designing a controller based on the control strategy above in MATLAB and building the EMA model in AMESim. The results show that the compound control strategy can significantly improve dynamic tracking accuracy and reduce surplus force. © 2017 SPIE.

Wu F.,Beihang University
Information (Switzerland) | Year: 2017

Dependency parsing is an important subtask of natural language processing. In this paper, we propose an embedding feature transforming method for graph-based parsing, transform-based parsing, which directly utilizes the inner similarity of the features to extract information from all feature strings including the un-indexed strings and alleviate the feature sparse problem. The model transforms the extracted features to transformed features via applying a feature weight matrix, which consists of similarities between the feature strings. Since the matrix is usually rank-deficient because of similar feature strings, it would influence the strength of constraints. However, it is proven that the duplicate transformed features do not degrade the optimization algorithm: the margin infused relaxed algorithm. Moreover, this problem can be alleviated by reducing the number of the nearest transformed features of a feature. In addition, to further improve the parsing accuracy, a fusion parser is introduced to integrate transformed and original features. Our experiments verify that both transform-based and fusion parser improve the parsing accuracy compared to the corresponding feature-based parser.

Tu P.,Guangdong University of Technology | Liu X.,Beihang University
Experimental Mechanics | Year: 2017

Digital image correlation (DIC) is a widely used optical metrology for surface deformation measurement. In DIC, the square root of the mean square error (RMS error) and standard deviation error (SD error) are used as quantitative criteria in order to evaluate the accuracy and robustness of a DIC method\algorithm. However, RMS and SD error criteria are computed from prescribed and measured displacements, which indicates that the prescribed displacement fields must be precisely generated. Therefore, it is difficult to quantitatively evaluate the accuracy and robustness of an algorithm\method in practical DIC measurements because imposed displacements are unknown (that’s why DIC measurements are needed). Moreover, the accuracy of DIC measurements highly relies on parameters selection, especially the selections of subset size and shape function. In practice, the subset size and shape function are usually selected according to experience because there are numerous factors (e.g. the quality of speckle image, local displacement field) and uncertainties (e.g. noise level, out-of-plane motion, illumination lighting fluctuation during image capturing) that affect the parameters selection, which makes it difficult to select optimal parameters based on previous works which mainly focused on theoretical deduction in ideal condition. In this paper, an error criterion for evaluating the accuracy of practical DIC measurements with unknown displacements is proposed. Numerical experiments are used to validate the effectiveness and feasibility of the proposed criterion for accuracy evaluation. It is concluded that the square root of the sum of squared forward and backward displacements difference (SFBD) error has a significant positive linear correlation with the widely used SD error in most practical DIC measurements where the mismatch between the frequently-used first- and second-order shape functions and the actual field is usually small. Also, an application of the proposed criterion is presented by real experiments for subset size and shape function selections, which verifies that the proposed error criterion can be effectively used for DIC parameters selection. © 2017 Society for Experimental Mechanics

Zhou J.,Beihang University | Jiang Y.,Beihang University | Doi M.,Beihang University
Physical Review Letters | Year: 2017

When a liquid film of a colloidal solution consisting of particles of different sizes is dried on a substrate, the colloids often stratify, where smaller colloids are laid upon larger colloids. This phenomenon is counterintuitive because larger colloids which have a smaller diffusion constant, are expected to remain near the surface during the drying process, leaving a layer of larger colloids on top of smaller colloids. Here we show that the phenomenon is caused by the interaction between the colloids, and can be explained by a diffusion model accounting for the interaction between the colloids. By studying the evolution equations both numerically and analytically, we derive the condition at which the stratified structures are obtained. © 2017 American Physical Society.

Fang L.,Beihang University | Ge M.-W.,North China Electrical Power University
Chinese Physics Letters | Year: 2017

To shed light on the subgrid-scale (SGS) modeling methodology of nonlinear systems such as the Navier Stokes turbulence, we define the concepts of assumption and restriction in the modeling procedure, which are shown by generalized derivation of three general mathematical constraints for different combinations of restrictions. These constraints are verified numerically in a one-dimensional nonlinear advection equation. This study is expected to inspire future research on the SGS modeling methodology of nonlinear systems. copy; 2017 Chinese Physical Society and IOP Publishing Ltd.

News Article | April 17, 2017

By mimicking the way some fishes eat, a new membrane easily separates and collects spilled oil on water without getting clogged (ACS Nano 2017, DOI: 10.1021/acsnano.6b07918). It could be an efficient and cost-effective way to clean up large oil spills, its developers say. Disaster responders typically clean up large oil spills by containing the slick with floating booms and using skimmers to remove it. Many researchers are developing separation membranes that could potentially be faster and cheaper. These are designed to repel water or attract oil, which helps them separate the two liquids. But the membranes’ pores tend to get clogged with oil, which makes them ineffective after a while. Dongliang Tian of Beihang University, Ziqi Sun of the University of Wollongong, and their colleagues designed a new filter inspired by the throat structures of filter-feeding fish. To filter out tiny prey suspended in water, these fish have bony arches in their throats that get narrower and more closely spaced deeper into the throat. Water flows into the throat, gradually seeping out from the spaces between the arches and out through the gills, while food particles collect at the back. To mimic that process, the researchers made a 3-cm-long stainless steel membrane containing five mesh sections with gradually decreasing pore size—from 150 nm to 30 nm—from one end to the other. They coated the membrane with nanosheets of cobalt oxide which intertwine with each other, forming tiny pockets that lock in water, making the membrane water-attracting, or hydrophilic. Then they tilted the membrane so that the large pores were at the bottom and pushed it with a controller attached to the top, emulating how a ship might push the angled membrane, bottom edge first, through the water. When the driving system moves the membrane through an oil-water mixture, the liquids stream up the membrane. Water permeates the membrane and forms a layer along its hydrophilic surface, preventing oil from clogging the pores. The large pores at the bottom, which encounter the highest water flux, allow water to flow through faster, Tian explains, while the water-logged small pores at the top repel oil, allowing it to easily flow over the top of the membrane into a container. Though oil may pass through the large pores on the first pass, the system makes multiple sweeps through a contaminated area, capturing more oil with each pass. The researchers tested the system in a 100-cm-long, 10-cm-wide sink filled with a mixture of water and one of a variety of oils: crude oil, diesel fuel, corn oil, or hydraulic fluid. They were able to continually collect oil at a calculated rate of 50 liters per minute for each meter length of the membrane, pushing the membrane along the sink more than 2,000 times over 100 minutes. The efficiency drops by less than 3% after those uses, and Tian says cleaning the membrane would restore its efficiency. By comparison, when the team tested a conventional setup by pouring an oil-water mixture through a 90-µm pore size membrane, the membrane became clogged and unusable after 50 uses. This novel filtration technique could enable “one-step, fast, continuous, and high-throughput spilled oil collection,” says Lin Feng of Tsinghua University. The technique has promise for use in large-scale oil spills, especially on lakes and quiet seas, she says. Waves could be a challenge since the water could spill over the top of the membrane into the oil-collection vessel and reduce the membrane’s efficiency.

The first C919 passenger jet made by the Commercial Aircraft Corporation of China (COMAC) is seen during a test in Shanghai, China April 16, 2017. Picture taken April 16, 2017. REUTERS/Stringer ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY. CHINA OUT. NO COMMERCIAL OR EDITORIAL SALES IN CHINA. SHANGHAI (Reuters) - China's home-grown C919 passenger jet is set to take to the skies on its long-delayed maiden flight on Friday, a major step for Beijing as it looks to boost its profile in the global aviation market. The narrow-body aircraft, which will compete with Boeing's 737 and the Airbus A320, is a key symbol of China's ambitions to muscle into a global jet market estimated to be worth $2 trillion over the next 20 years. The jet will take to the skies at the Shanghai Pudong International Airport on China's affluent east coast, at a ceremony expected to be broadcast live on state TV. The C919, made by state-owned Commercial Aircraft Corporation of China (COMAC) [CMAFC.UL], has seen its test flight pushed back at least twice since 2014 due to production issues, underlining the scale of the task facing Beijing. "The significance is huge, it's the first ever large-frame aircraft made in China," said Xiong Yuexi, a professor and plane design expert at Beihang University in Beijing. "It has a great impact for the Chinese people and the domestic market." China first gave the world a glimpse of the plane, which will be able to carry 158-168 passengers, in November 2015 when it rolled it out at a ceremony in Shanghai. For a FACTBOX on the C919, click Analysts, however, say the production delays mean the C919 will lag technologically behind improved versions of the A320 and 737 which will enter service in the next two years. China Eastern Airlines <600115.SS> is the launch customer for the plane, which COMAC says has 570 orders from 23 customers. The plane also relies on an array of overseas technology, with CFM International, a joint venture between General Electric's aerospace arm and a unit of French firm Safran , supplying the engines. Others include Honeywell International Inc , United Technologies Corp subsidiary Goodrich, Rockwell Collins Inc and a unit of Parker-Hannifin Corp . Conceived in 2008, China wants the C919 to eventually take market share from Boeing and Airbus in the lucrative narrow-body market which accounts for more than 50 percent of the aircraft in service worldwide. For a TIMELINE on the C919, click However, the jet likely faces a lengthy journey from first flight to commercial usage. China's first home-made jet, the regional ARJ-21, received its type certification in December 2014, six years after its first flight and more than 12 years after it was conceived. It made its maiden passenger flight in June last year. Then there is also the daunting task of selling the jet in a global market dominated by Boeing and Airbus. "Aviation is a complex market and you need experience over a long time. Boeing has 100 years, Airbus has over 40 years," said Sinolink Securities analyst Si Jingzhe, adding COMAC still lagged far behind in terms of supply chain know-how. China is pushing for recognition globally of its certification by European and U.S. regulators. Without their certification, China would only be able to sell the jet to a handful of countries that accept its certification standards. Beijing is also already looking beyond the C919, with plans to develop a wide-body long-haul jet with Russia. In November COMAC and its partner United Aircraft Corp said they have started the hunt to find suppliers.

News Article | May 5, 2017

WUXI, China, May 6, 2017 /PRNewswire/ -- The final round of the 2017 ASC Student Supercomputer Challenge (ASC17) ended in Wuxi. Tsinghua University stood out from 20 teams from around the world after a fierce one-week competition, becoming grand champion and winning the prize. As the world's largest supercomputing competition, ASC17 received applications from 230 universities around the world, 20 of which got through to the final round held this week at the National Supercomputing Center in Wuxi after the qualifying rounds. During the final round, the university student teams were required to independently design a supercomputing system under the precondition of a limited 3000W power consumption. They also had to operate and optimize standard international benchmark tests and a variety of cutting-edge scientific and engineering applications including AI-based transport prediction, genetic assembly, and material science. Moreover, they were required to complete high-resolution maritime simulation on the world's fastest supercomputer, "Sunway TaihuLight". The grand champion, team Tsinghua University, completed deep parallel optimization of the high-resolution maritime data simulation mode MASNUM on TaihuLight, expanding the original program up to 10,000 cores and speeding up the program by 392 times. This helped the Tsinghua University team win the e Prize award. MASNUM was nominated in 2016 for the Gordon Bell Prize, the top international prize in the supercomputing applications field. The runner-up, Beihang University, gave an outstanding performance in the popular AI field. After constructing a supercomputing system which received massive training based on past big data of transportation provided by Baidu, their self-developed excellent deep neural network model yielded the most accurate prediction of road conditions during the morning peak. The first-time finalist, Weifang University team, constructed a highly optimized advanced heterogeneous supercomputing system with Inspur's supercomputing server, and ran the international HPL benchmark test, setting a new world record of 31.7 TFLOPS for float-point computing speed. The team turned out to be the biggest surprise of the event and won the award for best computing performance. Moreover, Ural Federal University, National Tsing Hua University, Northwestern Polytechnical University and Shanghai Jiao Tong University won the application innovation award. The popular choice award was shared by Saint-Petersburg State University and Zhengzhou University. "It is great to see the presence of global teams in this event," Jack Dongarra, the Chairman of the ASC Expert Committee, founder of the TOP500 list that ranks the 500 most powerful supercomputer systems in the world, and professor at the Oak Ridge National Laboratory of the United States and the University of Tennessee, said in an interview. "This event inspired students to gain advanced scientific knowledge. TaihuLight is an amazing platform for this event. Just imagine the interconnected computation of everyone's computer in a gymnasium housing 100,000 persons, and TaihuLight's capacity is 100 times of such a gym. This is something none of the teams will ever be able to experience again." According to Wang Endong, initiator of the ASC competition, academician of the Chinese Academy of Engineering, and the chief scientist of Inspur Group, the rapid development of AI at the moment is significantly changing human society. At the core of such development are computing, data and algorithms. With this trend, supercomputers will become an important infrastructure for intelligent society in the future, and their speed of development and standards will be closely related to social development, improvement in livelihood, and progress of civilization. ASC competition is always committed to cultivating future-oriented, inter-disciplinary supercomputing talents to extend the benefits to the greater population. ASC17 is jointly organized by the Asian Supercomputing Community, Inspur Group, the National Supercomputing Center in Wuxi, and Zhengzhou University. Initiated by China, the ASC supercomputing challenge aims to be the platform to promote exchanges among young supercomputing talent from different countries and regions, as well as to groom young talent. It also aims to be the key driving force in promoting technological and industrial innovations by improving the standards in supercomputing applications and research. To view the original version on PR Newswire, visit:

News Article | May 5, 2017

The grand champion, team Tsinghua University, completed deep parallel optimization of the high-resolution maritime data simulation mode MASNUM on TaihuLight, expanding the original program up to 10,000 cores and speeding up the program by 392 times. This helped the Tsinghua University team win the e Prize award. MASNUM was nominated in 2016 for the Gordon Bell Prize, the top international prize in the supercomputing applications field. The runner-up, Beihang University, gave an outstanding performance in the popular AI field. After constructing a supercomputing system which received massive training based on past big data of transportation provided by Baidu, their self-developed excellent deep neural network model yielded the most accurate prediction of road conditions during the morning peak. The first-time finalist, Weifang University team, constructed a highly optimized advanced heterogeneous supercomputing system with Inspur's supercomputing server, and ran the international HPL benchmark test, setting a new world record of 31.7 TFLOPS for float-point computing speed. The team turned out to be the biggest surprise of the event and won the award for best computing performance. Moreover, Ural Federal University, National Tsing Hua University, Northwestern Polytechnical University and Shanghai Jiao Tong University won the application innovation award. The popular choice award was shared by Saint-Petersburg State University and Zhengzhou University. "It is great to see the presence of global teams in this event," Jack Dongarra, the Chairman of the ASC Expert Committee, founder of the TOP500 list that ranks the 500 most powerful supercomputer systems in the world, and professor at the Oak Ridge National Laboratory of the United States and the University of Tennessee, said in an interview. "This event inspired students to gain advanced scientific knowledge. TaihuLight is an amazing platform for this event. Just imagine the interconnected computation of everyone's computer in a gymnasium housing 100,000 persons, and TaihuLight's capacity is 100 times of such a gym. This is something none of the teams will ever be able to experience again." According to Wang Endong, initiator of the ASC competition, academician of the Chinese Academy of Engineering, and the chief scientist of Inspur Group, the rapid development of AI at the moment is significantly changing human society. At the core of such development are computing, data and algorithms. With this trend, supercomputers will become an important infrastructure for intelligent society in the future, and their speed of development and standards will be closely related to social development, improvement in livelihood, and progress of civilization. ASC competition is always committed to cultivating future-oriented, inter-disciplinary supercomputing talents to extend the benefits to the greater population. ASC17 is jointly organized by the Asian Supercomputing Community, Inspur Group, the National Supercomputing Center in Wuxi, and Zhengzhou University. Initiated by China, the ASC supercomputing challenge aims to be the platform to promote exchanges among young supercomputing talent from different countries and regions, as well as to groom young talent. It also aims to be the key driving force in promoting technological and industrial innovations by improving the standards in supercomputing applications and research. To view the original version on PR Newswire, visit:

Chen H.-X.,Beijing University of Technology | Chen H.-X.,Beihang University | Chen W.,University of Saskatchewan | Liu X.,Lanzhou University | And 2 more authors.
Physics Reports | Year: 2016

In the past decade many charmonium-like states were observed experimentally. Especially those charged charmonium-like Zc states and bottomonium-like Zb states cannot be accommodated within the naive quark model. These charged Zc states are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. Recently, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this work, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states. © 2016 Elsevier B.V..

Mackintosh R.S.,Open University Milton Keynes | Pang D.Y.,Beihang University
Physical Review C - Nuclear Physics | Year: 2013

The scattering of proton-halo nucleus 8B from 208Pb at 170.3 MeV is shown to reveal a distinctive pattern in the change in |SL| that is induced by coupling to breakup channels. The same pattern had been found for 8B scattering from 58Ni at 30 MeV, an energy near the Coulomb barrier, and has been linked to various other respects in which scattering for this proton-halo nucleus differs from that of other light, weakly bound nuclei. The increase in |SL| for L<80, induced by breakup coupling, is associated with a substantial repulsive region in the dynamic polarization potential as determined by exact inversion. This repulsion appears to reduce the penetration of the projectile into the absorptive region of the interaction. This accounts for the fact that the increase in the total reaction cross section, due to breakup, is much less than the breakup cross section, and is consistent with the relatively small effect of breakup on the elastic scattering angular distribution compared with the large breakup cross section. © 2013 American Physical Society.

Chen H.-X.,Beihang University | Chen W.,University of Saskatchewan | Liu X.,Lanzhou University | Steele T.G.,University of Saskatchewan | And 2 more authors.
Physical Review Letters | Year: 2015

Inspired by Pc(4380) and Pc(4450) recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anticharmed meson and a charmed baryon. Our results suggest that Pc(4380) and Pc(4450) have quantum numbers JP=3/2- and 5/2+, respectively. Furthermore, two extra hidden-charm pentaqurks with configurations D¯Σc∗ and D¯∗Σc∗ are predicted, which have spin-parity quantum numbers JP=3/2- and JP=5/2+, respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of Pc(4380) and Pc(4450) are especially accessible at future experiments like LHCb and BelleII. © 2015 American Physical Society.

Yang S.A.,Singapore University of Technology and Design | Pan H.,Beihang University | Zhang F.,University of Texas at Dallas
Physical Review Letters | Year: 2015

We generalize a semiclassical theory and use the argument of angular momentum conservation to examine the ballistic transport in lightly doped Weyl semimetals, taking into account various phase-space Berry curvatures. We predict universal transverse shifts of the wave-packet center in transmission and reflection, perpendicular to the direction in which the Fermi energy or velocities change adiabatically. The anomalous shifts are opposite for electrons with different chirality, and they can be made imbalanced by breaking inversion symmetry. We discuss how to utilize local gates, strain effects, and circularly polarized lights to generate and probe such a chirality-dependent Hall effect. © 2015 American Physical Society.

Du J.,CAS Institute of Process Engineering | Lai X.,CAS Institute of Process Engineering | Yang N.,CAS Institute of Process Engineering | Zhai J.,Beihang University | And 4 more authors.
ACS Nano | Year: 2011

Hierarchically ordered macro-mesoporous titania films have been produced through a confinement self-assembly method within the regular voids of a colloidal crystal with three-dimensional periodicity. Furthermore, graphene as an excellent electron-accepting and electron-transporting material has been incorporated into the hierarchically ordered macro-mesoporous titania frameworks by in situ reduction of graphene oxide added in the self-assembly system. Incorporation of interconnected macropores in mesoporous films improves the mass transport through the film, reduces the length of the mesopore channel, and increases the accessible surface area of the thin film, whereas the introduction of graphene effectively suppresses the charge recombination. Therefore, the significant enhancement of photocatalytic activity for degrading the methyl blue has been achieved. The apparent rate constants for macro-mesoporous titania films without and with graphene are up to 0.045 and 0.071 min-1, respectively, almost 11 and 17 times higher than that for pure mesoporous titania films (0.0041 min-1). © 2011 American Chemical Society.

Bai L.,Beihang University | Choi J.,University of Swansea
IEEE Transactions on Wireless Communications | Year: 2013

For iterative detection and decoding (IDD) in multiple-input multiple-output (MIMO) systems, although the maximum a posteriori probability (MAP) detector is desirable in terms of performance, it is difficult to be employed due to its prohibitively high complexity as an exhaustive search is used. In this paper, a lattice reduction (LR)-based MIMO detection method is studied to achieve near MAP performance with reasonably low complexity for IDD. The a priori information (API), which is available from a soft-input soft-output (SISO) decoder, is taken into account to generate a list with a randomized successive interference cancellation (SIC) method. More specifically, a joint Gaussian distribution is used to convert the API into the LR domain and a modified sampling distribution, which was originally adopted for near optimal LR-based detection in non-IDD MIMO systems, is derived for random sampling to build a list of candidate vectors of high a posteriori probability (APP) with low complexity. It is shown that the IDD receiver with the proposed method outperforms those with the conventional LR-based methods, where no API is taken into account to build a list. Furthermore, the trade-off between performance and complexity is exploited with varying list length. © 2002-2012 IEEE.

Du H.,East China University of Science and Technology | Ge S.S.,National University of Singapore | Liu J.K.,Beihang University
IET Control Theory and Applications | Year: 2011

In this study, an output feedback-based adaptive neural controller is presented for a class of uncertain non-affine pure-feedback non-linear systems with unmodelled dynamics. Two major technical difficulties for this class of systems lie in: (i) the few choices of mathematical tools in handling the non-affine appearance of control in the systems, and (ii) the unknown control direction embedded in the unknown control gain functions, in great contrast to the standard assumptions of constants or bounded time-varying coefficients. By exploring the new properties of Nussbaum gain functions, stable adaptive neural network control is possible for this class of systems by using a strictly positive-realness-based filter design. The closed-loop system is proven to be semi-globally uniformly ultimately bounded, and the regulation error converges to a small neighbourhood of the origin. The effectiveness of the proposed design is verified by simulations. © 2011 The Institution of Engineering and Technology.

Tao F.,Beihang University | Laili Y.,Beihang University | Xu L.,Old Dominion University | Zhang L.,Beihang University
IEEE Transactions on Industrial Informatics | Year: 2013

In order to realize the full-scale sharing, free circulation and transaction, and on-demand-use of manufacturing resource and capabilities in modern enterprise systems (ES), Cloud manufacturing (CMfg) as a new service-oriented manufacturing paradigm has been proposed recently. Compared with cloud computing, the services that are managed in CMfg include not only computational and software resource and capability service, but also various manufacturing resources and capability service. These various dynamic services make ES more powerful and to be a higher-level extension of traditional services. Thus, as a key issue for the implementation of CMfg-based ES, service composition optimal-selection (SCOS) is becoming very important. SCOS is a typical NP-hard problem with the characteristics of dynamic and uncertainty. Solving large scale SCOS problem with numerous constraints in CMfg by using the traditional methods might be inefficient. To overcome this shortcoming, the formulation of SCOS in CMfg with multiple objectives and constraints is investigated first, and then a novel parallel intelligent algorithm, namely full connection based parallel adaptive chaos optimization with reflex migration (FC-PACO-RM) is developed. In the algorithm, roulette wheel selection and adaptive chaos optimization are introduced for search purpose, while full-connection parallelization in island model and new reflex migration way are also developed for efficient decision. To validate the performance of FC-PACO-RM, comparisons with 3 serial algorithms and 7 typical parallel methods are conducted in three typical cases. The results demonstrate the effectiveness of the proposed method for addressing complex SCOS in CMfg. © 2005-2012 IEEE.

Wang Z.-J.,Zhejiang University of Finance and Economics | Wang Z.-J.,Beihang University | Li K.W.,University of Windsor
Information Sciences | Year: 2012

This article investigates the consistency of interval fuzzy preference relations based on interval arithmetic, and new definitions are introduced for additive consistent, multiplicative consistent and weakly transitive interval fuzzy preference relations. Transformation functions are put forward to convert normalized interval weights into consistent interval fuzzy preference relations. By analyzing the relationship between interval weights and consistent interval fuzzy preference relations, goal-programming-based models are developed for deriving interval weights from interval fuzzy preference relations for both individual and group decision-making situations. The proposed models are illustrated by a numerical example and an international exchange doctoral student selection problem. © 2011 Elsevier Inc. All rights reserved.

Guo H.,Beihang University | Shen S.-Q.,University of Hong Kong | Feng S.,Beijing Normal University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We show the existence of the fractional topological phase (FTP) in a one-dimensional interacting fermion model using exact diagonalization, in which the noninteracting part has flat bands with nontrivial topology. In the presence of the nearest-neighboring interaction V 1, the FTP at filling factor ν=1/3 appears. It is characterized by the threefold degeneracy and the quantized total Berry phase of the ground states. The FTP is destroyed by a next-nearest-neighboring interaction V 2, and the phase diagrams in the (V 1,V 2) plane are determined. We also present a physical picture of the phase and discuss its existence in the nearly flat band. Within the picture, we argue that the FTP at other filling factors can be generated by introducing proper interactions. The present study contributes to a systematic understanding of the FTPs and can be realized in cold-atom experiments. © 2012 American Physical Society.

Wang Z.-J.,Zhejiang University of Finance and Economics | Wang Z.-J.,Beihang University | Li K.W.,University of Windsor
Expert Systems with Applications | Year: 2012

This article proposes a framework to handle multiattribute group decision making problems with incomplete pairwise comparison preference over decision alternatives where qualitative and quantitative attribute values are furnished as linguistic variables and crisp numbers, respectively. Attribute assessments are then converted to interval-valued intuitionistic fuzzy numbers (IVIFNs) to characterize fuzziness and uncertainty in the evaluation process. Group consistency and inconsistency indices are introduced for incomplete pairwise comparison preference relations on alternatives provided by the decision-makers (DMs). By minimizing the group inconsistency index under certain constraints, an auxiliary linear programming model is developed to obtain unified attribute weights and an interval-valued intuitionistic fuzzy positive ideal solution (IVIFPIS). Attribute weights are subsequently employed to calculate distances between alternatives and the IVIFPIS for ranking alternatives. An illustrative example is provided to demonstrate the applicability and effectiveness of this method. © 2012 Elsevier Ltd. All rights reserved.

Sun Y.,Peking University | Liu Y.,Beihang University
IEEE Signal Processing Magazine | Year: 2012

The Internet has created vast opportunities to interact with strangers. The interactions can be fun, informative, and even profitable [1]. However, there is also risk involved. Will an eBay seller ship the product in time? Is the advice from a self-proclaimed expert on trustworthy? Does a product from have high quality as described? © 2012 IEEE.

Tao F.,Beihang University | Zhang L.,Beihang University | Nee A.Y.C.,National University of Singapore
International Journal of Production Research | Year: 2011

Grid technology has been recognised as a promising paradigm for the next generation manufacturing systems. Researchers have attempted to apply grid technology to product design, manufacturing resource integration and sharing, enterprise management, enterprise collaboration, resource optimal allocation and scheduling, and to enable the digitalisation of enterprise information as an implementation methodology. It has been already close to a decade since the first appearance of the concept of manufacturing grid (MGrid). Many projects on the application of grid technologies in manufacturing have been carried out, and a large number of research papers on MGrid have been published. In order for MGrid to be better known and accepted by researchers in the manufacturing community, this study aims to describe the connotation of MGrid through investigating existing research studies on MGrid. The contributions of this study are: (1) highlighting the motivations and driving forces of MGrid; (2) detailed description of the connotation of MGrid, such as the concept of MGrid; (3) presenting the key research contents and technologies of MGrid, including its four commonly known categories and 31 items; (4) investigating and summarising existing research on MGrid theories and applications; and (5) projecting several key future research issues of MGrid. © 2011 Taylor & Francis.

Wang L.,Beihang University | Wang Q.-G.,National University of Singapore
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2011

This Letter investigates synchronization issues of complex dynamical networks with switching topology. By constructing a common Lyapunov function, we show that local and global synchronization for a linearly coupled network with switching topology can be evaluated by the time average of second smallest eigenvalues corresponding to the Laplacians of switching topology. This result is quite powerful and can be further used to explore various switching cases for complex dynamical networks. Numerical simulations illustrate the effectiveness of the obtained results in the end. © 2011 Elsevier B.V. All rights reserved.

Wang L.,Beihang University | Wang Q.-G.,National University of Singapore
International Journal of Systems Science | Year: 2013

This article investigates synchronisation of a nonlinear networked system with switching topology. By defining a common synchronisation manifold for each possible switching topology, exponential synchronisation of a nonlinear networked system can be assessed by the exponential stability of a reduced nonlinear system corresponding to the concerned system, wherein the communication graph can be directed and weighted and the inner-linking matrix might be singular. In particular, a synchronisation criterion consisting of the self-dynamics of isolated nodes and the consensus dynamics of a linear switched system is given. Two numerical simulations of synchronisation are presented to illustrate the effectiveness of the analytical results for the periodic and random switching cases. © 2013 Copyright Taylor and Francis Group, LLC.

Chao K.-T.,Beijing University of Technology | Chao K.-T.,Peking University | Ma Y.-Q.,Beijing University of Technology | Ma Y.-Q.,Brookhaven National Laboratory | And 3 more authors.
Physical Review Letters | Year: 2012

With nonrelativistic QCD factorization, we present a full next-to-leading order computation of the polarization observable for J/ψ production at hadron colliders including all important Fock states, i.e., S1[1,8]3, S0[8]1, and PJ[8]3. We find the PJ[8]3 channel contributes a positive longitudinal component and a negative transverse component, so the J/ψ polarization puzzle may be understood as the transverse components canceling between the S1[8]3 and PJ[8]3 channels, which results in mainly the unpolarized (even slightly longitudinally polarized) J/ψ. This may give a possible solution to the long-standing J/ψ polarization puzzle. Predictions for J/ψ polarization at the LHC are also presented. © 2012 American Physical Society.

MacKintosh R.S.,Open University Milton Keynes | Pang D.Y.,Beihang University
Physical Review C - Nuclear Physics | Year: 2012

For deuteron scattering from 58Ni at laboratory energies of 56, 79, and 120 MeV, we study the dynamic polarization potentials (DPPs) induced by S-wave and D-wave breakup (BU), separately and together, in order to gain insight into the nature of the DPP as well as a counterintuitive property: the existence of L values for which the BU coupling increases |S L|, a 'wrong-way' effect. The effect is associated with the existence of emissive regions in the imaginary DPP, suggesting a connection with the nonlocal nature of the DPP. The same relationship was previously found for 6Li scattering, indicating a generic effect bearing on the dynamics of nuclear reactions. © 2012 American Physical Society.

Pang D.Y.,Beihang University | MacKintosh R.S.,Open University Milton Keynes
Physical Review C - Nuclear Physics | Year: 2011

For 6Li scattering from 12C at five laboratory energies from 90 to 318 MeV, we study the dynamic polarization potential, DPP, due to the breakup of the projectile. The breakup is evaluated using standard continuum discretized coupled-channels formalism applied to a two-body cluster model of the projectile. The DPP is evaluated over a wide radial range using both direct S-matrix-to-potential inversion and trivially equivalent local potential methods which yield substantially and systematically different results. The radius at which the real DPP changes from external repulsion to interior attraction varies systematically with energy. This should be experimentally testable because, according to notch tests, this crossover radius is within a radial range to which elastic scattering should be sensitive. The imaginary DPP has an emissive (generative) region at the lower energies; this may be associated with counterintuitive properties of |S L|. © 2011 American Physical Society.

Cao X.,Peking University | Cao X.,Capital Medical University | Wang N.,Beihang University | Jia S.,Beihang University | Shao Y.,Peking University
Analytical Chemistry | Year: 2013

A series of novel bimetallic PtCu nanochains have been synthesized through a water-based mild chemical route, and their compositions (PtxCu 1-x) can be conveniently tuned at the mesoscopic scale by a facile dealloying process. These nanomaterials have been characterized by transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray powder diffraction (XRD), and elemental analysis. They have different compositions (Pt 88Cu12, Pt75Cu25, and Pt 50Cu50) but have similar morphology. Electrochemical activity of these nanomaterials is compared to Pt and nanochains of Pt when they are chemically modified onto a glassy carbon electrode. Electrochemical measurements demonstrate that the sensors made by these PtCu nanomaterials are very sensitive and selective for glucose detection due to the wiring of dispersed crystals, porous nanostructure, clean surface, and synergetic electronic effects of the alloyed atoms. Among them, the modified electrode made of Pt75Cu25 shows the best performance. The superior catalytic activity and selectivity make nanomaterials, via the green synthesis, very promising for applications in direct biosensing of glucose. © 2013 American Chemical Society.

Dai P.,Peking University | Chen Z.,Peking University | Chen Z.,Beihang University | Chen S.,Peking University | Ju Y.,Princeton University
Proceedings of the Combustion Institute | Year: 2015

Usually different autoignition modes can be generated by a hot spot in which ignition occurs earlier than that in the surrounding mixture. However, for large hydrocarbon fuels with negative temperature coefficient (NTC) behavior, ignition happens earlier at lower temperature than that at higher temperature when the temperature is within the NTC regime. Consequently, a cool spot may also result in different autoignition modes. In this study, the modes of reaction front propagation caused by temperature gradient in a one dimensional planar configuration are investigated numerically for n-heptane/air mixture at initial temperature within and below the NTC regime. For the first time, different supersonic autoignition modes caused by a cool spot with positive temperature gradient are identified. It is found that the initial temperature gradient has strong impact on autoignition modes. With the increase of the positive temperature gradient of the cool spot, supersonic autoignitive deflagration, detonation, shock-detonation, and shock-deflagration are sequentially observed. It is found that shock compression of the mixture between the deflagration wave and leading shock wave produces an additional ignition kernel, which determines the autoignition modes. Furthermore, the cool spot is compared with the hot spot with temperature below the NTC regime. Similar autoignition modes are observed for the hot and cool spots. Different autoignition modes in the considered simplified configuration are summarized in terms of the normalized temperature gradient and acoustic-to-excitation time scale ratio. It is shown that the transition between different autoignition modes is not greatly affected by the NTC behavior. Therefore, our 1-D simulation indicates that like hot spot, the cool spot may also generate knock in engines when fuels with NTC behavior is used and the temperature is within the NTC regime. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Pan B.,Beihang University | Li K.,Shanghai University | Tong W.,Southern Methodist University
Experimental Mechanics | Year: 2013

High-efficiency and high-accuracy deformation analysis using digital image correlation (DIC) has become increasingly important in recent years, considering the ongoing trend of using higher resolution digital cameras and common requirement of processing a large sequence of images recorded in a dynamic testing. In this work, to eliminate the redundant computations involved in conventional DIC method using forward additive matching strategy and classic Newton-Raphson (FA-NR) algorithm without sacrificing its sub-pixel registration accuracy, we proposed an equivalent but more efficient DIC method by combining inverse compositional matching strategy and Gauss-Newton (IC-GN) algorithm for fast, robust and accurate full-field displacement measurement. To this purpose, first, an efficient IC-GN algorithm, without the need of re-evaluating and inverting Hessian matrix in each iteration, is introduced to optimize the robust zero-mean normalized sum of squared difference (ZNSSD) criterion to determine the desired deformation parameters of each interrogated subset. Then, an improved reliability-guided displacement tracking strategy is employed to achieve further speed advantage by automatically providing accurate and complete initial guess of deformation for the IC-GN algorithm implemented on each calculation point. Finally, an easy-to-implement interpolation coefficient look-up table approach is employed to avoid the repeated calculation of bicubic interpolation at sub-pixel locations. With the above improvements, redundant calculations involved in various procedures (i.e. initial guess of deformation, sub-pixel displacement registration and sub-pixel intensity interpolation) of conventional DIC method are entirely eliminated. The registration accuracy and computational efficiency of the proposed DIC method are carefully tested using numerical experiments and real experimental images. Experimental results verify that the proposed DIC method using IC-GN algorithm and the existing DIC method using classic FA-NR algorithm generate similar results, but the former is about three to five times faster. The proposed reliability-guided IC-GN algorithm is expected to be a new standard full-field displacement tracking algorithm in DIC. © 2013 Society for Experimental Mechanics.

Yang S.A.,Singapore University of Technology and Design | Pan H.,Beihang University | Zhang F.,University of Texas at Dallas | Zhang F.,University of Pennsylvania | Zhang F.,University of California at Santa Barbara
Physical Review Letters | Year: 2014

We introduce the concept of three-dimensional Dirac (Weyl) superconductors (SC), which have protected bulk fourfold (twofold) nodal points and surface Majorana arcs at zero energy. We provide a sufficient criterion for realizing them in centrosymmetric SCs with odd-parity pairing and mirror symmetry. Pairs of Dirac nodes appear in a mirror-invariant plane when the mirror winding number is nontrivial. Breaking mirror symmetry may gap Dirac nodes producing a topological SC. Each Dirac node evolves to a nodal ring when inversion-gauge symmetry is broken, whereas it splits into a pair of Weyl nodes when, and only when, time-reversal symmetry is broken. © 2014 American Physical Society.

Wang L.,Beihang University | Xu L.D.,Shanghai JiaoTongUniversity | Xu L.D.,Old Dominion University | Bi Z.,Indiana University - Purdue University Fort Wayne | Xu Y.,China National Institute of Standardization
IEEE Transactions on Industrial Informatics | Year: 2014

Today's manufacturing environments are very dynamic and turbulent. Traditional enterprise information systems (EISs) have mostly been implemented upon hierarchical architectures, which are inflexible to adapt changes and uncertainties promptly. Next-generation EISs must be agile and adaptable to accommodate changes without significant time delays. It is essential for an EIS to obtain real-time data from the distributed and dynamic manufacturing environment for decision making. Wireless sensor networks (WSNs) and radio-frequency identification (RFID) systems provide an excellent infrastructure for data acquisition, distribution, and processing. In this paper, some key challenges related to the integration of WSN and RFID technologies are discussed. A five-layer system architecture has been proposed to achieve synergistic performance. For the integration of WSN and RFID, one of the critical issues is the low efficiency of communication due to redundant data as redundant data increases energy consumption and causes time delay. To address it, an improved data cleaning algorithm has been proposed; its feasibility and effectiveness have been verified via simulation and a comparison with a published algorithm. To illustrate the capacity of the developed architecture and new data cleaning algorithm, their application in relief supplies storage management has been discussed. © 2005-2012 IEEE.

Zheng Y.F.,Peking University | Gu X.N.,Beihang University | Witte F.,Charité - Medical University of Berlin
Materials Science and Engineering R: Reports | Year: 2014

After decades of developing strategies to minimize the corrosion of metallic biomaterials, there is now an increasing interest to use corrodible metals in a number of medical device applications. The term "biodegradable metal" (BM) has been used worldwide to describe these new kinds of degradable metallic biomaterials for medical applications and there were many new findings reported over the last decade. In this paper, the definition of BM and its classification are given for the first time, along with the summary of the degradation mechanisms of BMs and its environmental influencing factors, which includes the degeneration of mechanical integrity and the metabolism of the degradation products. The recently-developed representative Mg-based BMs (pure Mg, Mg-Ca alloy, Mg-Zn alloy, etc.), Fe-based BMs (pure Fe, Fe-Mn-based alloys, etc.) and other BMs (pure W, pure Zn and its alloys, Ca-based and Sr-based bulk metallic glasses, etc.) were comprehensively reviewed with emphases on their microstructures, mechanical properties and degradation behaviors, in vitro and in vivo performances, pre-clinical and clinical trials. Moreover, current approaches to control their biodegradation rates to match the healing rates of the host tissues with various surface modification techniques and novel structural designs are summarized. Finally, this paper comprehensively discusses the directions of future development and the challenges of transitioning BMs from raw materials to semi-products to final medical devices. All in all, BM belongs to "bioactive" biomaterials and its future research and development direction should lean towards "third-generation biomedical materials" with "multifunctional capabilities" in a controllable manner to benefit the local tissue reconstruction. © 2014 Elsevier B.V.

Chen X.,Beihang University | Zou D.,Beihang University | Zhou S.Z.,National University of Singapore | Zhao Q.,Beihang University | Tan P.,National University of Singapore
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

In this paper we propose a novel alpha matting method with local and nonlocal smooth priors. We observe that the manifold preserving editing propagation [4] essentially introduced a nonlocal smooth prior on the alpha matte. This nonlocal smooth prior and the well known local smooth prior from matting Laplacian complement each other. So we combine them with a simple data term from color sampling in a graph model for nature image matting. Our method has a closed-form solution and can be solved efficiently. Compared with the state-of-the-art methods, our method produces more accurate results according to the evaluation on standard benchmark datasets. © 2013 IEEE.

Li K.,CAS Beijing National Laboratory for Molecular | Ju J.,CAS Beijing National Laboratory for Molecular | Xue Z.,CAS Beijing National Laboratory for Molecular | Ma J.,CAS Beijing National Laboratory for Molecular | And 4 more authors.
Nature Communications | Year: 2013

Environmental protection agencies and the petroleum industry require effective methods to separate micron-sized oil droplets from water. However, for most existing separation methods, phase separation occurs in the oil-water mixture. The remaining micron-scale oil droplets, which are not affected by phase separation, are difficult to handle with conventional methods on a large scale because of either a lack of separation ability or drawbacks in throughput capacity. Here we develop an oleophilic array of conical needle structures for the collection of micron-sized oil droplets, inspired by the collection of similar sized water droplets on conical cactus spines. Underwater, these structures mimic cacti and can capture micron-sized oil droplets and continuously transport them towards the base of the conical needles. Materials with this structure show obvious advantages in micron-sized oil collection with high continuity and high throughput. © 2013 Macmillan Publishers Limited.

Cao X.,Capital Medical University | Wang N.,Beihang University | Jia S.,Beihang University | Guo L.,Beihang University | Li K.,Peking University
Biosensors and Bioelectronics | Year: 2013

The recent development in the nanotechnology has paved the way for a large number of alloyed nanomaterials and devices of desirable properties which have useful functions for electrochemical sensor and biosensor applications. In this paper, bimetallic AuPt nanochains were synthesized through a mild chemical method, with which anti-horseradish peroxidase-conjugated anti-carcinoembryonic antigen (HRP-anti-CEA-NCAuPt) was developed for electrochemical detection of carcinoembryonic antigen (CEA) in a sandwich-type immunoassay format. The alloyed nanocrystals exhibit not only sound signal amplification effect of Au nanoparticles, but also further new combination of interfacial, electrical and structural properties arising from the disparate AuPt components. As a result, the electrochemical signal was significantly amplified by using the HRP-anti-CEA-NCAuPt as tracer and hydrogen peroxide as enzyme substrate. The linear range of the developed immunosensor is 0.01-200. ng/mL and the detection limit is 0.11. pg/mL of CEA, which makes the biometallic nanochains promising candidates for the next-generation sandwich-type electrochemical immunoassays. © 2012 Elsevier B.V..

Gai K.,Tsinghua National Laboratory for Information Sciences and Technology | Shi Z.,Beihang University | Zhang C.,Tsinghua National Laboratory for Information Sciences and Technology
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2012

We address the problem of blind separation of multiple source layers from their linear mixtures with unknown mixing coefficients and unknown layer motions. Such mixtures can occur when one takes photos through a transparent medium, like a window glass, and the camera or the medium moves between snapshots. To understand how to achieve correct separation, we study the statistics of natural images in the Labelme data set. We not only confirm the well-known sparsity of image gradients, but also discover new joint behavior patterns of image gradients. Based on these statistical properties, we develop a sparse blind separation algorithm to estimate both layer motions and linear mixing coefficients and then recover all layers. This method can handle general parameterized motions, including translations, scalings, rotations, and other transformations. In addition, the number of layers is automatically identified, and all layers can be recovered, even in the underdetermined case where mixtures are fewer than layers. The effectiveness of this technology is shown in experiments on both simulated and real superimposed images. © 2012 IEEE.

Qian H.,Beihang University | Zhang J.,Beihang University | Yin L.,Shanghai University
RSC Advances | Year: 2013

A new single-phased white light-emitting phosphor, Y2WO 6:Sm3+, was synthesized via conventional solid-state reaction calcining in air. The Y2WO6:Sm3+ samples were characterized using powder X-ray diffraction and refined with Rietveld methods. The phosphors exhibit a green emission from the host as well as a red emission from the dopant under ultraviolet excitation (300-380 nm). The color coordinates can be gradually tuned from green (0.247, 0.380) through white-light (0.319, 0.382) toward orange (0.335, 0.390) in the visible spectral region by systematically changing the Sm3+ dopant concentration. In addition, combining a 365 nm near-ultraviolet chip and Y2WO 6:0.02Sm3+ phosphor produced a white light-emitting diode, which exhibited an excellent color rendering index (Ra) of 92.3, a correlated color temperature of 5916 K and CIE coordinates of x = 0.3246, y = 0.3242. © The Royal Society of Chemistry 2013.

Liu L.,Beihang University | Li X.,Beihang University | Hu F.Q.,Old Dominion University
Journal of Computational Physics | Year: 2010

With many superior features, Runge-Kutta discontinuous Galerkin method (RKDG), which adopts Discontinuous Galerkin method (DG) for space discretization and Runge-Kutta method (RK) for time integration, has been an attractive alternative to the finite difference based high-order Computational Aeroacoustics (CAA) approaches. However, when it comes to complex physical problems, especially the ones involving irregular geometries, the time step size of an explicit RK scheme is limited by the smallest grid size in the computational domain, demanding a high computational cost for obtaining time accurate numerical solutions in CAA. For computational efficiency, high-order RK method with nonuniform time step sizes on nonuniform meshes is developed in this paper. In order to ensure correct communication of solutions on the interfaces of grids with different time step sizes, the values at intermediate-stages of the Runge-Kutta time integration on the elements neighboring such interfaces are coupled with minimal dissipation and dispersion errors. Based upon the general form of an explicit p-stage RK scheme, a linear coupling procedure is proposed, with details on the coefficient matrices and execution steps at common time-levels and intermediate time-levels. Applications of the coupling procedures to Runge-Kutta schemes frequently used in simulation of fluid flow and acoustics are given, including the third-order TVD scheme, and low-storage low dissipation and low dispersion (LDDRK) schemes. In addition, an analysis on the stability of coupling procedures on a nonuniform grid is carried out. For validation, numerical experiments on one-dimensional and two-dimensional problems are presented to illustrate the stability and accuracy of proposed nonuniform time-step RKDG scheme, as well as the computational benefits it brings. Application to a one-dimensional nonlinear problem is also investigated. © 2010 Elsevier Inc.

Bai L.,Peking University | Huang X.,Beihang University
Journal of the Acoustical Society of America | Year: 2011

In the field of noise identification with microphone arrays, conventional delay-and-sum (DAS) beamforming is the most popular signal processing technique. However, acoustic imaging results that are generated by DAS beamforming are easily influenced by background noise, particularly for in situ wind tunnel tests. Even when arithmetic averaging is used to statistically remove the interference from the background noise, the results are far from perfect because the interference from the coherent background noise is still present. In addition, DAS beamforming based on arithmetic averaging fails to deliver real-time computational capability. An observer-based approach is introduced in this paper. This so-called observer-based beamforming method has a recursive form similar to the state observer in classical control theory, thus holds a real-time computational capability. In addition, coherent background noise can be gradually rejected in iterations. Theoretical derivations of the observer-based beamforming algorithm are carefully developed in this paper. Two numerical simulations demonstrate the good coherent background noise rejection and real-time computational capability of the observer-based beamforming, which therefore can be regarded as an attractive algorithm for acoustic array signal processing. © 2011 Acoustical Society of America.

Liu C.,Beihang University | Du W.-B.,Beihang University | Wang W.-X.,Beijing Normal University
PLoS ONE | Year: 2014

The particle swarm optimization (PSO) algorithm, in which individuals collaborate with their interacted neighbors like bird flocking to search for the optima, has been successfully applied in a wide range of fields pertaining to searching and convergence. Here we employ the scale-free network to represent the inter-individual interactions in the population, named SF-PSO. In contrast to the traditional PSO with fully-connected topology or regular topology, the scale-free topology used in SF-PSO incorporates the diversity of individuals in searching and information dissemination ability, leading to a quite different optimization process. Systematic results with respect to several standard test functions demonstrate that SF-PSO gives rise to a better balance between the convergence speed and the optimum quality, accounting for its much better performance than that of the traditional PSO algorithms. We further explore the dynamical searching process microscopically, finding that the cooperation of hub nodes and non-hub nodes play a crucial role in optimizing the convergence process. Our work may have implications in computational intelligence and complex networks. © 2014 Liu et al.

Di C.,Beijing Normal University | Yang X.,Beijing Normal University | Wang X.,Beihang University
PLoS ONE | Year: 2014

Hydrological time series forecasting remains a difficult task due to its complicated nonlinear, non-stationary and multi-scale characteristics. To solve this difficulty and improve the prediction accuracy, a novel four-stage hybrid model is proposed for hydrological time series forecasting based on the principle of 'denoising, decomposition and ensemble'. The proposed model has four stages, i.e., denoising, decomposition, components prediction and ensemble. In the denoising stage, the empirical mode decomposition (EMD) method is utilized to reduce the noises in the hydrological time series. Then, an improved method of EMD, the ensemble empirical mode decomposition (EEMD), is applied to decompose the denoised series into a number of intrinsic mode function (IMF) components and one residual component. Next, the radial basis function neural network (RBFNN) is adopted to predict the trend of all of the components obtained in the decomposition stage. In the final ensemble prediction stage, the forecasting results of all of the IMF and residual components obtained in the third stage are combined to generate the final prediction results, using a linear neural network (LNN) model. For illustration and verification, six hydrological cases with different characteristics are used to test the effectiveness of the proposed model. The proposed hybrid model performs better than conventional single models, the hybrid models without denoising or decomposition and the hybrid models based on other methods, such as the wavelet analysis (WA)-based hybrid models. In addition, the denoising and decomposition strategies decrease the complexity of the series and reduce the difficulties of the forecasting. With its effective denoising and accurate decomposition ability, high prediction precision and wide applicability, the new model is very promising for complex time series forecasting. This new forecast model is an extension of nonlinear prediction models. © 2014 Di et al.

Huang Q.,Beihang University | Diao Q.,University of California at Davis | Lin S.,University of California at Davis | Abdel-Ghaffar K.,University of California at Davis
IEEE Transactions on Information Theory | Year: 2012

This paper is concerned with construction and structural analysis of both cyclic and quasi-cyclic codes, particularly low-density parity-check (LDPC) codes. It consists of three parts. The first part shows that a cyclic code given by a parity-check matrix in circulant form can be decomposed into descendant cyclic and quasi-cyclic codes of various lengths and rates. Some fundamental structural properties of these descendant codes are developed, including the characterization of the roots of the generator polynomial of a cyclic descendant code. The second part of the paper shows that cyclic and quasi-cyclic descendant LDPC codes can be derived from cyclic finite-geometry LDPC codes using the results developed in the first part of the paper. This enlarges the repertoire of cyclic LDPC codes. The third part of the paper analyzes the trapping set structure of regular LDPC codes whose parity-check matrices satisfy a certain constraint on their rows and columns. Several classes of finite-geometry and finite-field cyclic and quasi-cyclic LDPC codes with large minimum distances are shown to have no harmful trapping sets of size smaller than their minimum distances. Consequently, their error-floor performances are dominated by their minimum distances. © 2011 IEEE.

Diao Q.,University of California at Davis | Huang Q.,Beihang University | Lin S.,University of California at Davis | Abdel-Ghaffar K.,University of California at Davis
IEEE Transactions on Information Theory | Year: 2012

A matrix-theoretic approach for studying quasi-cyclic codes based on matrix transformations via Fourier transforms and row and column permutations is developed. These transformations put a parity-check matrix in the form of an array of circulant matrices into a diagonal array of matrices of the same size over an extension field. The approach is amicable to the analysis and construction of quasi-cyclic low-density parity-check codes since it takes into account the specific parity-check matrix used for decoding with iterative message-passing algorithms. Based on this approach, the dimension of the codes and parity-check matrices for the dual codes can be determined. Several algebraic and geometric constructions of quasi-cyclic codes are presented as applications along with simulation results showing their performance over additive white Gaussian noise channels decoded with iterative message-passing algorithms. © 1963-2012 IEEE.

Hong L.,University of California at Davis | Hong L.,Beihang University | Pan T.,University of California at Davis
Microfluidics and Nanofluidics | Year: 2011

Surface microfluidics can be of potential use in a variety of emerging applications, including biological and chemical analysis, cellular detection and manipulation, high-throughput pharmaceutical screening, and etc. In comparison with the conventional closed-channel microfluidic system, surface microfluidics shows the distinct advantages of simple construction, direct surface access, no cavitation or interphase obstruction, clear optical path, easy fluidic packaging, and device reusability. In this article, we first present surface microfluidic networks microfabricated by a single-step lithographic process using a novel superhydrophobic photosensitive nanocomposite formula. The photopatternable superhydrophobic nanocomposite (PSN) incorporates PTFE nanoparticles into a SU-8 matrix, in which superhydrophobicity (contact angle of above 160°) is primarily contributed by the extremely low chemical energy and nano-topology of PTFE nanoparticles, while the SU-8 polymer matrix offers photopatternability (lithographic resolution of 10 μm) and substrate adhesion. Moreover, an additive intermediate layer with hydrophilic sidewall considerably reduces flow resistance while improving the substrate adhesion, as a crucial improvement from the previous surface flow configuration. Furthermore, self-propelled microfluidic networks driven by surface tension-induced pressure gradient have been fabricated and characterized to demonstrate the applicability of the novel nanocomposite fabrication approach. © 2010 The Author(s).

Wang L.,Beihang University | Wang Q.-G.,National University of Singapore
Journal of Physics A: Mathematical and Theoretical | Year: 2012

This paper introduces an average contraction analysis for nonlinear switched systems and applies it to investigating the synchronization of complex networks of coupled systems with switching topology. For a general nonlinear system with a time-dependent switching law, a basic convergence result is presented according to average contraction analysis, and a special case where trajectories of a distributed switched system converge to a linear subspace is then investigated. Synchronization is viewed as the special case with all trajectories approaching the synchronization manifold, and is thus studied for complex networks of coupled oscillators with switching topology. It is shown that the synchronization of a complex switched network can be evaluated by the dynamics of an isolated node, the coupling strength and the time average of the smallest eigenvalue associated with the Laplacians of switching topology and the coupling fashion. Finally, numerical simulations illustrate the effectiveness of the proposed methods. © 2012 IOP Publishing Ltd.

Liang H.,Beijing University of Technology | Liang H.,RIKEN | Meng J.,Beijing University of Technology | Meng J.,Beihang University | And 3 more authors.
Physics Reports | Year: 2015

Symmetry plays a fundamental role in physics. The quasi-degeneracy between single-particle orbitals (n,l,j=l+1/2) and (n-1,l+2,j=l+3/2) indicates a hidden symmetry in atomic nuclei, the so-called pseudospin symmetry (PSS). Since the introduction of the concept of PSS in atomic nuclei, there have been comprehensive efforts to understand its origin. Both splittings of spin doublets and pseudospin doublets play critical roles in the evolution of magic numbers in exotic nuclei discovered by modern spectroscopic studies with radioactive ion beam facilities. Since the PSS was recognized as a relativistic symmetry in 1990s, many special features, including the spin symmetry (SS) for anti-nucleon, and many new concepts have been introduced. In the present Review, we focus on the recent progress on the PSS and SS in various systems and potentials, including extensions of the PSS study from stable to exotic nuclei, from non-confining to confining potentials, from local to non-local potentials, from central to tensor potentials, from bound to resonant states, from nucleon to anti-nucleon spectra, from nucleon to hyperon spectra, and from spherical to deformed nuclei. Open issues in this field are also discussed in detail, including the perturbative nature, the supersymmetric representation with similarity renormalization group, and the puzzle of intruder states. © 2015 Elsevier B.V.

Pan B.,Beihang University | Li K.,Shanghai University
Optics and Lasers in Engineering | Year: 2011

Fast and high-accuracy deformation analysis using digital image correlation (DIC) has been increasingly important and highly demanded in recent years. In literature, the DIC method using the NewtonRapshon (NR) algorithm has been considered as a gold standard for accurate sub-pixel displacement tracking, as it is insensitive to the relative deformation and rotation of the target subset and thus provides highest sub-pixel registration accuracy and widest applicability. A significant drawback of conventional NR-algorithm-based DIC method, however, is its extremely huge computational expense. In this paper, a fast DIC method is proposed deformation measurement by effectively eliminating the repeating redundant calculations involved in the conventional NR-algorithm-based DIC method. Specifically, a reliability-guided displacement scanning strategy is employed to avoid time-consuming integerpixel displacement searching for each calculation point, and a pre-computed global interpolation coefficient look-up table is utilized to entirely eliminate repetitive interpolation calculation at sub-pixel locations. With these two approaches, the proposed fast DIC method substantially increases the calculation efficiency of the traditional NR-algorithm-based DIC method. The performance of proposed fast DIC method is carefully tested on real experimental images using various calculation parameters. Results reveal that the computational speed of the present fast DIC is about 120200 times faster than that of the traditional method, without any loss of its measurement accuracy © 2011 Elsevier Ltd. All rights reserved.

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

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

News Article | February 27, 2017

GUIYANG, China, 27. Februar 2017 /PRNewswire/ -- Guian New Area, die vom chinesischen Staat auf nationaler Ebene genehmigte New Area in Guizhou im mittleren Westen Chinas, hilft Unternehmen sektorübergreifend bei der Nutzung von Chancen in Virtual Reality durch die Gründung der Beidouwan VR Town, einer Initiative, die von bevorzugten Maßnahmen zur Förderung der Entwicklung der schnell wachsenden VR-Branche unterstützt wird. Das Beidou Bay VR Village, liegt im Gaofeng County der Guian New Area und ist eine neue Art von Standort, der fünf Funktionen integriert: Industrieplanung und -ausstellungen, wissenschaftliche Bildung und Förderung, Exkursionen und Erfahrungen, Innovation und Unternehmertum sowie eine Handels- und Vorführungsplattform. Man erwartet, dass sich bis 2019 etwa 50 Unternehmen mit einer Gesamtproduktionskapazität von 1,5 Millionen Einheiten VR-bezogener Ausrüstung niederlassen werden. Zusätzlich sollten diese Unternehmen 500.000 Transaktionen mit Softwareinhalten sowie 100.000 Lösungssets mit Sektoren, wie dem Gesundsheits- und Bauwesen, Planung und Bildung abgeschlossen haben. Der Standort sollte 1 Milliarde Yuan (USD $ 145,490 Millionen) Jahresumsatz erwirtschaften, 80 Millionen Yuan (USD $ 11,6 Millionen) an Steuern abführen und 3.500 neue Arbeitsplätze schaffen. Die Beidouwan VR Town der Guian New Area ist auf die Unterstützung wirtschaftlicher Entwicklung durch den Aufbau der vollständigen Infrastruktur ausgerichtet, die für Forschung, Entwicklung, Produktion und Dienstleistungen zur Unterstützung der mit VR verbundenen Branchen erforderlich ist. Die Initiative schließt Gründer- und Vorführzentren, Handelsdienstleistungen und sogar die Unterstützung von Tourismus ein. Das Gebiet feierte unlängst die Fertigstellung seiner vier wichtigen Zentren: des Weiai Education Pavilion, eines Industrieplanungszentrums, eines VR-Anwendungszentrums und eines VR-Tourismuszentrums für landwirtschaftliche Erfahrung, die alle unterschiedliche Funktionen bei der Vorstellung von VR-Anwendungen und Innovationen erfüllen. Weitere Entwicklungen sind bereits in Umsetzung und die erste Phase der Beidouwan VR Town sollte bis Mai 2017 fertiggestellt sein. Im Oktober 2016 war die Guian New Area Gastgeber des 2016 Guian Virtual Reality Summit das den Slogan „Collaboration in Virtual and Reality" [Zusammenarbeit in Virtualität und Realität] zum Thema hatte. Das Summit zog führende Internetakteure und -entwickler an, darunter Vertreter von HTC, Facebook, der Peking University und Beijings Beihang University, die Branchenerkenntnisse bei der Anwendung von VR-Technologie in Bildung, im Tourismus und bei Gaming austauschten und Entwicklungen bei erweiterter Realität diskutierten. Während des Summits erklärte die Regierung von Guian ihre volle Hilfestellung und Unterstützung bei der Umsetzung der zehn Richtlinien zur Förderung des VR-bezogenen Geschäfts in der Guian New Area. Im Rahmen der Initiative bietet die Verwaltung Prämien und Zuwendungen zur Unterstützung von Content-Entwicklung, Investitionsvorhaben und Industriegründerzentren an, die sich in der New Area niederlassen. Chinesische Organisationen und Forschungsinstitute, die geistiges Eigentum im Wert von RMB 2 Millionen (USD $ 290.782) generieren, erhalten Prämien von RMB 1 Million (USD $ 145.390). Eine Einmalzuwendung von bis zu RMB 5 Millionen (USD $ 726.955) steht Förderern von VR-Gründerzentren zur Verfügung. Die Guian New Area ist die achte nationale New Area in China mit drei Hauptverantwortungen: Haupttreiber von Wirtschaftswachstum in Westchina, Pionier bei der wirtschaftlichen Öffnung und Benchmark für solide und dynamische Ökosystemzonen.

Agency: European Commission | Branch: FP7 | Program: CSA | Phase: INFRA-2010-3.3 | Award Amount: 1.57M | Year: 2010

Over the past 6 years, the EC has invested to extend the European eInfrastructure technology and European eInfrastructure (and particularly Grid) operational and organisational principles to a number of regions in the world, and reinforcing the close collaboration and exchange of know-how with similar technologies in other areas. A number of different collaboration models have thus been established between Europe and the rest of the world, while the projects implementing these collaborations have had impacts typically focused on their regions. The CHAIN project aims to coordinate and leverage these efforts and their results with a vision of a harmonised and optimised interaction model for eInfrastructure and specifically Grid interfaces between Europe and the rest of the world. The project will elaborate a strategy and define the instruments in order to ensure coordination and interoperation of the European Grid Infrastructures with other external e-Infrastructures. The CHAIN consortium, consisting of leading organisations in all the regions addressed by the project, will ensure global coverage, European leadership, and most efficient leveraging of results with respect to preceding regional initiatives. First, the project will define a coherent operational and organisational model, where a number of EU countries/regions will possibly act, in collaboration with, as bridges/gateways to other Regions/Continents. Further, the project will validate this model by supporting the extension and consolidation of worldwide virtual communities, which increasingly require distributed facilities (large instruments, distributed data and databases, digital repositories, etc.) across the regions for trans-continental research. Finally, the project will act as a worldwide policy-watch and coordination instrument, by exploring and proposing concrete steps for the coordination with other initiatives and studying the evolution of e-Infrastructures.

Agency: European Commission | Branch: FP7 | Program: CSA | Phase: INFRA-2012-3.3. | Award Amount: 2.12M | Year: 2012

CHAIN-REDS vision is to promote and support technological and scientific collaboration across different eInfrastructures established and operated in various continents, in order to facilitate their uptake and use by established and emerging Virtual Research Communities (VRCs) but also by single researchers, promoting instruments and practices that can facilitate their inclusion in the community of users. The project aims to support and disseminate the best practices currently adopted in Europe and other continents, and promote and facilitate interoperability among different regional eInfrastructures. CHAIN-REDS gathers the main stakeholders of regional eInfrastructures, collectively engaged in studying and defining a path towards a global eInfrastructure ecosystem that will allow VRCs, research groups and even single researchers to access and efficiently use worldwide distributed resources (i.e. computing, storage, data, services, tools, applications). The core objective of CHAIN-REDS project is to promote, coordinate and support the effort of a critical mass of non-European eInfrastructures for Research and Education to collaborate with Europe addressing interoperability and interoperation of Grids and other Distributed Computing Infrastructures. From this perspective, CHAIN-REDS will optimise the interoperation of European infrastructures with those present in other 6 regions of the world, both from development and use point of view, and catering to different communities.\nOverall, CHAIN-REDs will provide input for future strategies and decision-making regarding collaboration with other regions on eInfrastructure deployment and availability of related data; it will raise the visibility of eInfrastructures towards intercontinental audiences, covering most of the world and will provide support to establish globally connected and interoperable infrastructures, in particular between EU and the developing regions.

News Article | February 27, 2017

GUIYANG, China, Feb. 27, 2017 /PRNewswire/ -- Guian New Area, China's state approved national-level new area in Guizhou, mid-Western China, is helping businesses across sectors to realize opportunities in virtual reality by establishing Beidouwan VR Town, an initiative backed by preferential policies to support development in the fast-growing VR industry. Beidou Bay VR Village, located in the Gaofeng County of Guian New Area, is a new type of village that integrates five functions -- industry planning & exhibition, scientific education & promotion, field trip & experiences, innovation & entrepreneurship, and a platform for trading and showcase. By 2019, the village is expected to house 50 companies with total annual capacity of producing 1.5 million pieces of VR-related hardware equipment. In addition, these companies are expected to have completed 500,000 transactions of software content, and 100,000 sets of solutions to industries including healthcare, construction, planning and education. The village is expected to have annual revenue of 1 billion yuan (USD $145,490 million), and contribute to 80 million yuan (USD $11.6 million) in fiscal taxes, as well as 3,500 new jobs. Guian New Area's Beidouwan VR Town aims to support industrial development by building the entire infrastructure required for research, development, manufacturing and servicing support for VR related industries. The initiative includes incubator support, demonstration centers, trading services, training and even tourism support. The area recently celebrated the completion of its four major centers -- Weiai Education Pavilion, an industrial planning center, a VR application center, a tourism VR center featuring farming experience -- all serving different functions to showcase VR applications and innovations. More developments are now underway with the first phase of Beidouwan VR Town due to complete in May, 2017. In October, 2016, Guian New Area hosted the 2016 Guian Virtual Reality Summit under the slogan 'Collaboration in Virtual and Reality'. The summit attracted top internet players and developers including representatives from HTC, Facebook, Peking University and Beijing's Beihang University to share industrial insights in applying VR technology in education, tourism, gaming and discuss developments of augmented reality. During the summit, the Guian government showed full backing and support by releasing ten policies to support the development of VR related business in the Guian New Area. Under the initiative, the administration will offer rewards and grants to support content development, investment ventures, and industrial incubators that set up in the new area. A reward of RMB1 million (USD $145,390) is available to Chinese organizations and research institutes that generate intellectual property with a value of RMB2 million (USD $290,782) or above. A one-off grant of up to RMB5 million (USD $726,955) will be available to VR incubator support providers. Guian New Area is the eighth national-level new area in China, shoulders three major responsibilities - key driver of economic growth in western China, breaking new ground in economic opening, and the benchmark of sound and vibrant eco-system zone.

GUIYANG, China, Feb. 27, 2017 /PRNewswire/ -- Guian New Area, China's state approved national-level new area in Guizhou, mid-Western China, is helping businesses across sectors to realize opportunities in virtual reality by establishing Beidouwan VR Town, an initiative backed by preferential policies to support development in the fast-growing VR industry. Beidou Bay VR Village, located in the Gaofeng County of Guian New Area, is a new type of village that integrates five functions -- industry planning & exhibition, scientific education & promotion, field trip & experiences, innovation & entrepreneurship, and a platform for trading and showcase. By 2019, the village is expected to house 50 companies with total annual capacity of producing 1.5 million pieces of VR-related hardware equipment. In addition, these companies are expected to have completed 500,000 transactions of software content, and 100,000 sets of solutions to industries including healthcare, construction, planning and education. The village is expected to have annual revenue of 1 billion yuan (USD $145,490 million), and contribute to 80 million yuan (USD $11.6 million) in fiscal taxes, as well as 3,500 new jobs. Guian New Area's Beidouwan VR Town aims to support industrial development by building the entire infrastructure required for research, development, manufacturing and servicing support for VR related industries. The initiative includes incubator support, demonstration centers, trading services, training and even tourism support. The area recently celebrated the completion of its four major centers -- Weiai Education Pavilion, an industrial planning center, a VR application center, a tourism VR center featuring farming experience -- all serving different functions to showcase VR applications and innovations. More developments are now underway with the first phase of Beidouwan VR Town due to complete in May, 2017. In October, 2016, Guian New Area hosted the 2016 Guian Virtual Reality Summit under the slogan 'Collaboration in Virtual and Reality'. The summit attracted top internet players and developers including representatives from HTC, Facebook, Peking University and Beijing's Beihang University to share industrial insights in applying VR technology in education, tourism, gaming and discuss developments of augmented reality. During the summit, the Guian government showed full backing and support by releasing ten policies to support the development of VR related business in the Guian New Area. Under the initiative, the administration will offer rewards and grants to support content development, investment ventures, and industrial incubators that set up in the new area. A reward of RMB1 million (USD $145,390) is available to Chinese organizations and research institutes that generate intellectual property with a value of RMB2 million (USD $290,782) or above. A one-off grant of up to RMB5 million (USD $726,955) will be available to VR incubator support providers. Guian New Area is the eighth national-level new area in China, shoulders three major responsibilities - key driver of economic growth in western China, breaking new ground in economic opening, and the benchmark of sound and vibrant eco-system zone. 

News Article | October 12, 2016

Physicists at The University of Texas at Arlington have shown that using microwaves to activate photosensitive nanoparticles produces tissue-heating effects that ultimately lead to cell death within solid tumors. “Our new method using microwaves can propagate through all types of tissues and target deeply situated tumors,” says Wei Chen, UTA professor of physics and lead author of the study published this month in The Journal of Biomedical Nanotechnology titled “A new modality of cancer treatment-nanoparticle mediated microwave induced photodynamic therapy.” Photodynamic therapy kills cancer cells when a nanoparticle introduced into tumor tissue generates toxic singlet oxygen after being exposed to light. Singlet oxygen is a highly reactive type of oxygen that irreversibly damages cell mitochondria and eventually causes cell death. “Up to now, photodynamic therapy, which depends on visible, ultraviolet or near infrared light, was considered effective for skin cancers or cancers close to the skin surface,” Chen says. “Our new concept combining microwaves with photodynamic therapy opens up new avenues for targeting deeper tumors and has already proven effective in rapidly and safely reducing tumor size.” In prior studies, the researchers had identified a new type of nanoparticle, copper-cysteamine or Cu-Cy, that could be activated by X-rays to produce singlet oxygen and slow the growth of tumors. X-ray radiation, however, poses significant risks to patients and can harm healthy tissue. In this new lab study, the team demonstrated that the nanoparticle Cu-Cy also can be activated by microwaves, which can be targeted directly at the tumor itself without harming surrounding tissue. “Our new microwave-induced photodynamic therapy offers numerous advantages, the most significant of which is increased safety,” Chen says. “Our nanoparticle Cu-Cy also demonstrates very low toxicity, is easy to make and inexpensive, and also emits intense luminescence, which means it can also be used as an imaging agent.” The researchers demonstrated that both in vitro and in vivo studies on an osteosarcoma cell line showed significant cell destruction using copper cysteamine nanoparticles under microwave activation. The heating effects and the release of copper ions from copper cysteamine upon activation was the main mechanism for the generation of the reactive oxygen needed for cancer cell destruction. Chen was joined on this research by Lun Ma, a UTA research assistant professor in physics, as well as Mengyu Yao, Lihua Li and Yu Zhang from the Guangdong Key Laboratory of Orthopaedic Technology and Implant Materials in Guangzhou, China, and Junying Zhang from the Physics Department at Beihang University in Beijing, China. The U.S. Army Medical Research Acquisition Activity, the National Science Foundation and Department of Homeland Security’s joint Academic Research Initiative program, the National Basic Research Program of China, the National Natural Science Foundation of China, and the five-year plan of the Chinese Military, all supported this research. “This new invention is largely based on the new photosensitizer copper cysteamine that we invented and are patenting, and I would like to thank all our team members, particularly Dr. Lun Ma, for the time and energy spent on this project,” Chen says. Alex Weiss, UTA chair of the Physics Department, emphasized the importance of this research in the context of UTA’s increasing focus on health and the human condition within the Strategic Plan 2020: Bold Solutions|Global Impact. “Dr. Chen’s research into nanoparticle activation has led to important discoveries that could potentially transform cancer treatment,” Weiss says.  “This new paper on the possibilities of microwave activation demonstrates yet again how Dr. Chen’s search for new modalities of therapy could play a key role in finding safe, viable and inexpensive treatments for cancer.” Chen came to UTA in 2006 following an international career in the United States, Canada, Sweden, and China. He received his doctorate in chemistry from Peking University in Beijing, China. Source: The University of Texas at Arlington

Fu H.S.,Swedish Institute of Space Physics | Fu H.S.,Beihang University | Khotyaintsev Y.V.,Swedish Institute of Space Physics | Vaivads A.,Swedish Institute of Space Physics | And 2 more authors.
Nature Physics | Year: 2013

The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares, substorms, and disruptions in fusion experiments. Observations in the solar chromosphere an. The Earth's magnetosphere indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent. Here we show that energetic electron acceleration is caused by unsteady reconnection. I. The Earth's magnetosphere an. The solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady, so energetic electrons are absent. The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain fo. The peak observed fluxes. © 2013 Macmillan Publishers Limited. All rights reserved.

Meng D.,Beihang University | Jia Y.,Beihang University | Du J.,Beijing University of Posts and Telecommunications | Yu F.,Henan Polytechnic University
Systems and Control Letters | Year: 2012

In this paper, the tracking control problem for multi-agent systems is considered, where all agents in a directed graph are enabled to track a time-varying reference trajectory perfectly over a finite interval. A unified algorithm is presented for agents described by both discrete-time and continuous-time models through using the iterative learning approach. Even under the condition that the reference trajectory is available to not all but only a portion of agents, all agents can be guaranteed to (1) obtain the finite-time tracking except the initial time step in the discrete-time domain and (2) follow the reference trajectory with constant shifts at all the time in the continuous-time domain. If an initial rectifying action is used to continuous-time agents, then the finite-time tracking can be derived on an interval that can be specified. The proposed algorithms are also extended to achieve the formation control for multi-agent systems. Moreover, design conditions are developed for all algorithms, and two examples are given to demonstrate the effectiveness of the theoretical results. © 2012 Elsevier Ltd. All rights reserved.

Cao M.,Beihang University | Ju J.,CAS Beijing National Laboratory for Molecular | Li K.,CAS Beijing National Laboratory for Molecular | Dou S.,University of Wollongong | And 2 more authors.
Advanced Functional Materials | Year: 2014

Although clean drinking water is a basic human need, freshwater scarcity has been identified as a major global problem of the 21st century. Nature has long served as a source of inspiration for human beings to develop new technology. The cactus in the desert possesses a multifunctional integrated fog collection system originating from the cooperation of a Laplace pressure gradient and the wettability difference. In this contribution, inspired by the cactus, an artificial fog collector on a large scale is first fabricated through integrating cactus spine-like hydrophobic conical micro-tip arrays with the hydrophilic cotton matrix. The novel cactus-inspired fog collector can spontaneously and continuously collect, transport, and preserve fog water, demonstrating high fog collection efficiency and promising applications in the regions with drinking water scarcity. Furthermore, the present approach is simple, time-saving and cost-effective, which provides a potential device and new idea to solve the global water crisis. Inspired by the fog-harvesting behavior of the cactus, a novel fog collector in large scale is first fabricated through integrating cactus spine-like hydrophobic conical micro-tip arrays with a hydrophilic cotton matrix, which can spontaneously and continuously collect, transport, and preserve fog water. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhou W.,University of Illinois at Urbana - Champaign | Zhou W.,Beihang University | Wu J.,University of Illinois at Urbana - Champaign | Yang H.,University of Illinois at Urbana - Champaign
Nano Letters | Year: 2013

Highly uniform Pt icosahedral nanocrystals with an edge length of 8.8 nm were synthesized in nonhydrolytic systems using the hot injection-assisted GRAILS (gas reducing agent in liquid solution) method. The results show the key factors for the shape control include fast nucleation, kinetically controlled growth, and protection from oxidation by air. The effect of oxygen molecules on the Pt morphology was experimentally confirmed based on the study of shape evolution of icosahedral crystals upon exposure to oxygen gas. The Pt icosahedral catalysts obtained had an area-specific activity of 0.83 mA/cm 2 Pt, four times that of 0.20 mA/cm2 Pt for typical Pt/C catalysts, in an oxygen reduction reaction (ORR). © 2013 American Chemical Society.

Zhang J.,University of Illinois at Urbana - Champaign | Xiao J.,Northwestern University | Meng X.,Beihang University | Monroe C.,University of Illinois at Urbana - Champaign | And 2 more authors.
Physical Review Letters | Year: 2010

Graphene, like a sheet of paper, folds under mechanical forces. The stability of folded graphene, however, depends on the folding direction and the resulted graphene stacking. Suspended graphene in liquids folds freely under random ultrasonic stimulations. We determined the structure of ∼100 folded graphene edges by electron nanodiffraction. About 1/3 are armchair and 1/3 are zigzag. The results are explained by the energetics of graphene folding and atomic simulation. The zigzag edge has AB stacking, while in the armchair edge, AB stacking is achieved in some areas by a small twist. © 2010 The American Physical Society.

Yin L.,Nanjing University of Information Science and Technology | Guo L.,Beihang University
International Journal of Systems Science | Year: 2012

This article considers a new tracking control problem for a class of nonlinear stochastic descriptor systems where the tracked target is a given joint probability density function (JPDF). The controlled plants can be represented by multivariate discrete-time descriptor systems with non-Gaussian disturbances and nonlinear output equations. The control objective is to find crisp algorithms such that the conditional output JPDFs can follow the given target JPDF. A direct relationship is established between the JPDFs of the transformed tracking error and the stochastic input. An optimisation approach is presented such that the distances between the output JPDF and the desired one are minimised. Furthermore, a stabilisation suboptimal control strategy is proposed using the linear matrix inequality-based Lyapunov theory. Finally, simulations are provided to demonstrate the effectiveness of the stochastic tracking control algorithms. © 2011 Copyright Taylor and Francis Group, LLC.

Wang Q.,Beihang University | Chen G.,City University of Hong Kong | Perc M.,University of Maribor
PLoS ONE | Year: 2011

This paper investigates the dependence of synchronization transitions of bursting oscillations on the information transmission delay over scale-free neuronal networks with attractive and repulsive coupling. It is shown that for both types of coupling, the delay always plays a subtle role in either promoting or impairing synchronization. In particular, depending on the inherent oscillation period of individual neurons, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as wellexpressed minima in the measure for spatiotemporal synchrony. For attractive coupling, the minima appear at every integer multiple of the average oscillation period, while for the repulsive coupling, they appear at every odd multiple of the half of the average oscillation period. The obtained results are robust to the variations of the dynamics of individual neurons, the system size, and the neuronal firing type. Hence, they can be used to characterize attractively or repulsively coupled scalefree neuronal networks with delays. © 2011 Wang et al.

Zu C.-X.,CAS Institute of Physics | Zu C.-X.,Beihang University | Li H.,CAS Institute of Physics
Energy and Environmental Science | Year: 2011

The average increase in the rate of the energy density of secondary batteries has been about 3% in the past 60 years. Obviously, a great breakthrough is needed in order to increase the energy density from the current 210 Wh kg -1 of Li-ion batteries to the ambitious target of 500-700 Wh kg -1 to satisfy application in electrical vehicles. A thermodynamic calculation on the theoretical energy densities of 1172 systems is performed and energy storage mechanisms are discussed, aiming to determine the theoretical and practical limits of storing chemical energy and to screen possible systems. Among all calculated systems, the Li/F 2 battery processes the highest energy density and the Li/O 2 battery ranks as the second highest, theoretically about ten times higher than current Li-ion batteries. In this paper, energy densities of Li-ion batteries and a comparison of Li, Na, Mg, Al, Zn-based batteries, Li-storage capacities of the electrode materials and conversion reactions for energy storage, in addition to resource and environmental concerns, are analyzed. © 2011 The Royal Society of Chemistry.

Yang Y.,Beihang University | Munoa J.,Ideko Danobat Group | Altintas Y.,University of British Columbia
International Journal of Machine Tools and Manufacture | Year: 2010

Chatter is more detrimental to machining due to its instability than forced vibrations. This paper presents design and optimal tuning of multiple tuned mass dampers (TMDs) to increase chatter resistance of machine tool structures. Chatter free critical depth of cut of a machine is inversely proportional to the negative real part of frequency response function (FRF) at the toolworkpiece interface. Instead of targeting reduction of magnitude, the negative real part of FRF of the machine is reduced by designing single and multiple TMD systems. The TMDs are designed to have equal masses, and their damping and stiffness values are optimized to improve chatter resistance using minimax numerical optimization algorithm. It is shown that multiple TMDs need more accurate tuning of stiffness and natural frequency of each TMD, but are more robust to uncertainties in damping and input dynamic parameters in comparison with single TMD applications. The proposed tuned damper design and optimization strategy is experimentally illustrated to increase chatter free depth of cuts. © 2010 Elsevier Ltd. All rights reserved.

Sun M.-J.,Beihang University | Li M.-F.,CAS Institute of Physics | Wu L.-A.,CAS Institute of Physics
Applied Optics | Year: 2015

The Hanbury Brown and Twiss (HBT) effect is a classical intensity correlation effect, but it is also widely used in the quantum optics regime, and has led to many important breakthroughs in both basic and applied physics, among which ghost imaging (GI) has aroused particular interest. In this article, the positive and negative intensity correlations in HBT correlation are analyzed, based on which we describe experiments on thermal light nonlocal imaging of a reflective object using the positive and negative correlations of correspondence imaging. An improvement of 16.3% in the signal-to-noise ratio of the reconstructed image has been achieved, indicating that this method may have promising potential in future GI applications where noise is a serious problem and smaller sampling numbers are necessary. © 2015 Optical Society of America.

Chen J.,Shanghai JiaoTong University | Zhou X.,Beihang University
Journal of Materials Processing Technology | Year: 2010

For sheet metals, the endurance to fracture under different strain paths may be different. Based on plastic deformation energy, the sheet metal forming limit is calculated, and the relationship model between maximum allowable integral value of the general plastic work criterion and the strain path is built. In addition, the strain-hardening exponent, anisotropy coefficient and the initial thickness of the material are also taken into account to consider their effects on forming limit. In order to simplify the process of parameter determination, only uniaxial tension test is used to calculate the material property parameters and necessary limit strain, and the expression of the criterion is determined finally. Then the limit strains under other strain paths between uniaxial tension to equi-biaxial tension are predicted by the criterion combined with numerical simulation of the forming process. The criterion is also applied to limit strain prediction under bilinear strain path. © 2009 Elsevier B.V. All rights reserved.

Liu J.,Beihang University | Zhang D.,Beihang University | Qin L.,Chengdu Aircraft Industrial Co. | Yan L.,Beihang University
International Journal of Machine Tools and Manufacture | Year: 2012

Carbon fiber reinforced plastics (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. However, when CFRP are machined, rapid tool wear and delamination are troublesome. Therefore, cost effective and excellent quality machining of CFRP remains a challenge. In this paper, the rotary ultrasonic elliptical machining (RUEM) using core drill is proposed for drilling of holes on CFRP panels. This method combines advantages of core-drill and elliptical tool vibration towards achieving better quality, delamination free holes. The cutting force model and chip-removal phenomenon in ultrasonic elliptical vibration cutting are introduced and analyzed. The feasibility to machine CFRP for RUEM is verified experimentally. The results demonstrate that compared to conventional drilling (CD), the chip-removal rate has been improved, tool wear is reduced, precision and surface quality around holes is enhanced, delamination at hole exits has been prevented and significant reduction in cutting force has been achieved. © 2011 Elsevier Ltd All rights reserved.

Zhu C.,Max Planck Institute for Solid State Research | Yu Y.,Beihang University | Gu L.,CAS Institute of Physics | Weichert K.,Max Planck Institute for Solid State Research | Maier J.,Max Planck Institute for Solid State Research
Angewandte Chemie - International Edition | Year: 2011

From the spinning room: LiFePO4 is a promising cathode material for lithium batteries, but it suffers from slow mass and charge transport. Electrospinning is able to produce single-crystalline LiFePO4 nanowires coated with amorphous carbon (see TEM images and small-angle electron diffraction pattern). Networks of these wires show very short diffusion lengths, thus leading to high rate performance and cycling capability. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ren Y.,Academy of Equipment Command and Technology | Su D.,Beihang University | Fang J.,Beihang University
IEEE Transactions on Power Electronics | Year: 2013

To intuitively analyze the absolute and relative stability of the forward and backward whirling modes of the high-speed magnetically suspended flywheel rotor with significant gyroscopic effects and bending modes, this paper presents a whirling modes stability criterion based on complex coefficient frequency characteristics method. Through variable reconstruction, the multiple-input multiple-output magnetically suspended rotor system is converted into a single-input single-output (SISO) system with complex coefficients. The stability equivalence of the systems before and after variable reconstruction has been proven. Based on this, the inherent relationships between the distribution of the closed-loop poles of the complex coefficient SISO system and the whirling modes stability are revealed, and the Nyquist stability criterion is further extended by applying the argument principle. All of these lay the foundation for the whirling modes stability theorem, and then, their stability criterion is further developed. Simulation and experimental results prove the effectiveness and correctness of the presented criterion. © 1986-2012 IEEE.

Yi M.,Beihang University | Yi M.,TU Darmstadt | Shen Z.,Beihang University
Journal of Materials Chemistry A | Year: 2015

Mass production and commercial availability are prerequisites for the viability and wide application of graphene. The exfoliation of graphite to give graphene is one of the most promising ways to achieve large-scale production at an extremely low cost. This review focuses on discussing different exfoliation techniques based on a common mechanical mechanism; because a deep understanding of the exfoliation mechanism can provide fruitful information on how to efficiently achieve high-quality graphene by optimizing exfoliation techniques. We highlight the recent progress on mechanical exfoliation for graphene production during the last decade. The emphasis is set on the widely used sonication method with the latest insight into sonication-induced defects, the newly explored ball milling method, the fluid dynamics method that has emerged in the last three years, and the innovative supercritical fluid method. We also give an outlook on how to achieve high-quality graphene efficiently using mechanical exfoliation techniques. We hope this review will point towards a rational direction for the scalable production of graphene. © The Royal Society of Chemistry 2015.

Wang L.,North China Electrical Power University | Gao Y.-T.,Beihang University | Qi F.-H.,Beijing University of Posts and Telecommunications
Annals of Physics | Year: 2012

Under investigation in this paper is a variable-coefficient modified Kortweg-de Vries (vc-mKdV) model describing certain situations from the fluid mechanics, ocean dynamics and plasma physics. N-fold Darboux transformation (DT) of a variable-coefficient Ablowitz-Kaup-Newell-Segur spectral problem is constructed via a gauge transformation. Multi-solitonic solutions in terms of the double Wronskian for the vc-mKdV model are derived by the reduction of the N-fold DT. Three types of the solitonic interactions are discussed through figures: (1) Overtaking collision; (2) Head-on collision; (3) Parallel solitons. Nonlinear, dispersive and dissipative terms have the effects on the velocities of the solitonic waves while the amplitudes of the waves depend on the perturbation term. © 2012 Elsevier Inc.

Sun Q.,Beihang University | Wang S.,CAS Institute of Physics | Wang R.,Beihang University
Journal of Physical Chemistry C | Year: 2012

Synthesis and manipulation of advanced bimetallic nanomaterials via a green and low-cost wet chemical route are of great importance for the industrialization potential. Materials design integrating the synthesis of nanomaterials through an environmentally benign route with a simple manipulation method is a challenge. The CoPt hollow nanochains have been successfully synthesized in aqueous solution with shell thickness of about 5 nm and tunable length from 300 nm to 2 μm. The as-prepared CoPt hollow nanochains can be easily aligned by the external magnetic fields and can be attached onto substrates, such as silicon wafer. The synthesis strategy is characterized by room temperature reaction (300 K), low cost, and utilization of facile reagents (water as solvent). Growth kinetics investigation shows the magnetostatic interactions between Co clusters together with the spontaneous galvanic replacement between Co clusters and Pt ions are indispensable for the formation of aligned hollow nanochains. Magnetic measurements indicate that the shape anisotropy of 1D aligned nanochains plays a dominant role on the good controllable behavior. © 2012 American Chemical Society.

Meng D.,Beihang University | Jia Y.,Beihang University | Du J.,Beijing University of Posts and Telecommunications | Zhang J.,Beihang University
Automatica | Year: 2014

This paper deals with formation control problems for multi-agent systems with nonlinear dynamics and switching network topologies. Using the nearest neighbor knowledge, a distributed algorithm is constructed by employing the iterative learning control approach. Sufficient conditions are given to obtain the desired relative formations of agents, which benefits from the strict positiveness of products of stochastic matrices. It is shown that the derived results can effectively work, although the network topologies dynamically change along both time and iteration axes and the corresponding directed graphs may not have spanning trees. Such result is also illustrated via numerical simulations. © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

Mo L.,Beijing Technology and Business University | Jia Y.,Beihang University
IET Control Theory and Applications | Year: 2011

This study is devoted to the consensus problems for high-order multi-agent systems with external disturbances. A dynamic neighbour-based protocol is adopted for the agents with the consideration of communication time delay and external disturbances. Sufficient conditions are derived to make all agents reach consensus with H∞ performance. Finally, simulation results are provided for demonstrating the effectiveness of the results presented. © 2011 The Institution of Engineering and Technology.

Guo D.,University of Electronic Science and Technology of China | Guo D.,Okinawa Institute of Science and Technology | Wang Q.,Beihang University | Perc M.,University of Maribor
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

Networks of fast-spiking interneurons are crucial for the generation of neural oscillations in the brain. Here we study the synchronous behavior of interneuronal networks that are coupled by delayed inhibitory and fast electrical synapses. We find that both coupling modes play a crucial role by the synchronization of the network. In addition, delayed inhibitory synapses affect the emerging oscillatory patterns. By increasing the inhibitory synaptic delay, we observe a transition from regular to mixed oscillatory patterns at a critical value. We also examine how the unreliability of inhibitory synapses influences the emergence of synchronization and the oscillatory patterns. We find that low levels of reliability tend to destroy synchronization and, moreover, that interneuronal networks with long inhibitory synaptic delays require a minimal level of reliability for the mixed oscillatory pattern to be maintained. © 2012 American Physical Society.

Krzakala F.,CNRS Gulliver Laboratory | Mezard M.,University Paris - Sud | Sausset F.,University Paris - Sud | Sun Y.F.,CNRS Gulliver Laboratory | And 2 more authors.
Physical Review X | Year: 2012

Compressed sensing has triggered a major evolution in signal acquisition. It consists of sampling a sparse signal at low rate and later using computational power for the exact reconstruction of the signal, so that only the necessary information is measured. Current reconstruction techniques are limited, however, to acquisition rates larger than the true density of the signal. We design a new procedure that is able to reconstruct the signal exactly with a number of measurements that approaches the theoretical limit, i.e., the number of nonzero components of the signal, in the limit of large systems. The design is based on the joint use of three essential ingredients: a probabilistic approach to signal reconstruction, a messagepassing algorithm adapted from belief propagation, and a careful design of the measurement matrix inspired by the theory of crystal nucleation. The performance of this new algorithm is analyzed by statistical-physics methods. The obtained improvement is confirmed by numerical studies of several cases.

Guo F.-K.,University of Bonn | Meissner U.-G.,University of Bonn | Meissner U.-G.,Jülich Research Center | Shen C.-P.,Beihang University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

Heavy quark spin symmetry is useful to make predictions on ratios of decay or production rates of systems involving heavy quarks. The breaking of spin symmetry is generally of the order of O(ΛQCD/mQ), with ΛQCD the scale of QCD and mQ the heavy quark mass. In this paper, we will show that a small S- and D-wave mixing in the wave function of the heavy quarkonium could induce a large breaking in the ratios of partial decay widths. As an example, we consider the decays of the ϒ{hooked}(10860) into the χbJω (J=0, 1, 2), which were recently measured by the Belle Collaboration. These decays exhibit a huge breaking of the spin symmetry relation were the ϒ{hooked}(10860) a pure 5S bottomonium state. We propose that this could be a consequence of a mixing of the S-wave and D-wave components in the ϒ{hooked}(10860). Prediction on the ratio Γ(ϒ{hooked}(10860)→χb0ω)/Γ(ϒ{hooked}(10860)→χb2ω) is presented assuming that the decay of the D-wave component is dominated by the coupled-channel effects. © 2014 The Authors.

Yi M.,Beihang University | Yi M.,TU Darmstadt | Shen Z.,Beihang University
Carbon | Year: 2014

The application of a kitchen blender for producing high-quality few-layer graphene (FLG) is demonstrated. The obtained FLG flakes, with an average thickness of ∼1.5 nm (∼20% ≤ 1 nm), are high-quality and free of oxidation and basal-plane defects. With a rotating impeller, the kitchen blender can induce multiple fluid dynamics events which are featured by shear, turbulence, and collisions. These fluid dynamics events and their cooperative effects are responsible for the exfoliation mechanism, resulting in a gentle lateral-force-dominated way for graphite self-exfoliation through its lateral self-lubricating ability. © 2014 Elsevier Ltd. All rights reserved.

Yan H.,Shanghai JiaoTong University | Pan B.,Beihang University
Optics Letters | Year: 2014

A new simultaneous three-dimensional (3D) displacement measurement technique based on the combination of digital holography (DH) and digital imaging correlation (DIC) is proposed. The current DH-based 3D displacement measurement technique needs three sets of DH setups, and only the phase images are utilized in measurements, with all the intensity images discarded. In contrast, the proposed new technique only adopts a single off-axis DH setup. In the proposed technique, the phase images are used to extract out-of-plane displacements, but the intensity images (instead of being discarded) are processed by an intensity correlation algorithmto retrieve in-plane displacement components. Because the proposed technique fully takes advantage of all the information obtained by an offaxis DH without additional optical arrangements, it is simpler and more practical than the existing DH-based 3D displacement measurement technique. Experiments performed on a United States Air Force (USAF) target demonstrate that both the in-plane and out-of-plane displacements can be accurately determined by the proposed technique. © 2014 Optical Society of America.

Yu Y.,Beihang University | Gu L.,CAS Institute of Physics | Lang X.,Tohoku University | Zhu C.,Max Planck Institute for Solid State Research | And 3 more authors.
Advanced Materials | Year: 2011

3D nanoporous Au supported nano-crystalline tin thin-film anodes for Liion batteries are prepared by dealloying followed by electroless plating. When used as an electrode for Liion batteries, this special Sn structure can effectively accommodate large volume variations during cycling in a lithium cell, resulting in improved capacity retention. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

News Article | March 1, 2017

COLUMBUS, Ohio - Even nations can have friends of friends, a new study has found. Results suggest these indirect relationships have a surprisingly strong ability to prevent major conflicts, and that international military alliances may matter more than we typically expect. Many studies have shown that nations with military alliances are less likely to go to war. But this new study is the first to show that neighboring countries without direct alliances are still unlikely to have serious conflicts, as long as they are indirectly connected through an ally in common. In fact, this peace dividend extends up to three degrees of separation without getting weaker: Nations are much less likely to have wars with their allies, the allies of their allies, and the allies of their allies' allies. "The peacemaking impact of an alliance between two countries goes beyond the two that signed the agreement," said Skyler Cranmer, lead author of the study and the Phillips & Henry associate professor of political science at The Ohio State University. "It permeates the network of alliances, like ripples in a pond, to prevent conflicts beyond the two countries that have the alliance." The researchers were surprised that the strength of these indirect relationships didn't decline until they went beyond three degrees, said co-author Aisha Bradshaw, a Ph.D. candidate in political science at Ohio State. "We didn't expect that. We thought the effect would decline with each degree of separation," Bradshaw said The study was published today in the journal Science Advances. The researchers examined all serious military conflicts worldwide from 1965 to 2000. This included all conflicts in which one country made a deliberate choice to deploy military force against another. They focused on conflicts between neighboring states, since very few nations have the ability to wage war beyond their borders. Results showed that the probability of a new conflict between two neighboring countries in a given year was between 3 and 4 percent for nations within three degrees of separation. But the probability of conflict nearly doubled for countries at four degrees of separation from each other. "The probability of conflict jumps dramatically once you get to four degrees," Cranmer said. "At that point, it appears that countries have much less in common that will keep the peace." There are many examples of these indirect alliances helping keep the peace. One is the lack of conflict between Turkey and Iran from 1965 to 1979, a period during which they were indirectly connected at two degrees of separation. After losing this connection in 1980, disputes arose between the neighbors, reaching a peak in 1987 when they had a militarized dispute with fatalities. What's the difference between three degrees and four degrees of separation between nations that dramatically changes the probability of conflict? In order to figure that out, the researchers divided the world into different communities of nations. A community of nations was defined as a group of countries that were more closely connected to each other - through their alliances - than they were to those outside of the community. "Not every member of a community is necessarily tied to every other member, but there is usually a short and clear path between them all," Cranmer said. The researchers found that nearly all members of each of these communities of nations were within three degrees of each other, which helped explain why the probability of conflict was so much lower for these countries. But any two countries that had four or more degrees of separation were almost always in different communities of nations. "At four degrees, the countries no longer share membership in common communities that represent shared interests," he said. But these communities, by themselves, couldn't explain the probability of war between any two countries. Results suggested that these overall community structures helped explain how the indirect ties worked to prevent conflict. Still, both factors played independent roles in keeping the peace. These results fit in with a growing body of evidence in science. "There's emerging evidence that this three-degree horizon of influence seems to be relatively common in human networks and can be found in political attitudes, health behaviors and the likelihood of smoking," Cranmer said. "But this is the first evidence of anything like this in a political network." The study shows the importance of ties between two countries, which can sometimes be forgotten in the conversation about the future of alliances like NATO, Bradshaw said. "An alliance between two countries can make peace more likely among a larger group of countries than just those two countries," she said. Other co-authors were Caitlin Clary, a Ph.D. candidate at Ohio State, and Weihua Li of Beihang University in China. Funding for the study came from the National Science Foundation and the Alexander von Humboldt Foundation's Fellowship for Experienced Researchers.

Wang N.,Guangxi Normal University | Liu M.,Guangxi Normal University | Wu X.,China Institute of Atomic Energy | Meng J.,Beijing University of Technology | Meng J.,Beihang University
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

By taking into account the surface diffuseness correction for unstable nuclei, the accuracy of the macroscopic-microscopic mass formula is further improved. The rms deviation with respect to essentially all the available mass data falls to 298 keV, crossing the 0.3 MeV accuracy threshold for the first time within the mean-field framework. Considering the surface effect of the symmetry potential which plays an important role in the evolution of the "neutron skin" toward the "neutron halo" of nuclei approaching the neutron drip line, we obtain an optimal value of the symmetry energy coefficient J = 30.16 MeV. With an accuracy of 258 keV for all the available neutron separation energies and of 237 keV for the α-decay Q-values of super-heavy nuclei, the proposed mass formula is particularly important not only for the reliable description of the r process of nucleosynthesis but also for the study of the synthesis of super-heavy nuclei. © 2014 The Authors.

Wang J.,University of Chinese Academy of Sciences | Li Y.,Beihang University | Zhang Y.,Beihang University
Advanced Functional Materials | Year: 2014

Hydrous hydrazine (H2NNH2·H2O) has generally been considered a promising hydrogen storage carrier because of inherent advantages such as its high hydrogen content and easy recharging as a liquid. Unfortunately, the decomposition of hydrous hydrazine to H2 is terribly sluggish and/or not entirely favored - a competing decomposition to ammonia may be preferred. This has been the case using noble-metal catalysts and using non-precious-metal-based catalysts, even at elevated temperatures. To overcome this challenge, non-precious-metal-based Cu@Fe5Ni5 core@shell nanocatalysts are prepared using an in situ seeding-growth approach. Unexpectedly, the catalyst exerts 100% H 2 selectivity and excellent activity and stability toward the complete decomposition of hydrous hydrazine, which is due to the synergistic effect of the core@shell structure. These promising results will certainly promote the effective application of hydrous hydrazine as a potential hydrogen storage material. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA.

Zhang Q.,Beihang University | Hu Z.,Beihang University | Liu Z.,Beihang University | Zhai J.,Beihang University | Jiang L.,Beihang University
Advanced Functional Materials | Year: 2014

Bioinspired artificial nanochannels exhibiting ion transport properties similar to biological ion channels have been attracting some attention for biosensors, separation technologies, and nanofluidic diodes. Herein, an easily available artificial heterogeneous nanochannel shows both ion gating and ion rectification characteristics when irradiated by ultraviolet light. The fabrication of heterogeneous nanochannels includes the coating of an anatase TiO2 porous layer on an alumina porous supporter, followed by a chemical modification with octadecyltrimethoxysilane (OTS) molecules. The irreversible decomposition of OTS molecules by TiO2 photocatalysis under ultraviolet light results in a change of surface wettability and an asymmetric distribution of surface negative charges simultaneously, which contributes to the ion gating and ion rectification. The asymmetric distribution of negative charges in the TiO2 porous layer can be controlled by the irradiation time of ultraviolet light, which regulates the ion rectification characteristic. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liu T.,Beihang University | Pang Y.,Beihang University | Zhu M.,Beihang University | Kobayashi S.,Iwate University
Nanoscale | Year: 2014

Nanoporous metal materials with many potential applications have been synthesized by a chemical dealloying approach. The fabrication of nanoporous metal nanoparticles (NPs), however, is still challenging due to the difficulties in producing suitable nanoscale precursors. Herein, nanoporous Co NPs of 31 nm have been successfully prepared by dealloying Co-Al NPs, and surprisingly they possess micropores in a range from 0.7 to 1.7 nm and a large surface area of 50 m2 g-1. The crystalline size of the microporous NPs is 2-5 nm. Through the passivation process, the microporous Co NPs covered with CoO (Co@CoO) are generated as a result of the surface oxidation of Co. They exhibit better microwave absorption properties than their nonporous counterpart. An enhanced reflection loss (RL) value of -90.2 dB is obtained for the microporous Co@CoO NPs with a thickness of merely 1.3 mm. The absorption bandwidth corresponding to the RL below -10 dB reaches 7.2 GHz. The microwave absorption mechanism is discussed in terms of micropore morphology, core@shell structure and nanostructure. This novel microporous material may open new routes for designing high performance microwave absorbers. © 2014 The Royal Society of Chemistry.

Feng W.,Beihang University
Systems and Control Letters | Year: 2012

Global stability has been shown for network congestion control algorithms in the absence of propagation delays by use of the conventional Lyapunov function method. When heterogeneous delays are taken into account, this problem becomes harder and is partly answered until the latest work of Papachristodoulou et al., where a Lyapunov-Krasovskii functional argument is used to analyze global stability of nonlinear congestion control algorithms, but only applicable to the single-path case. In this paper, we develop a new multi-path extension to the dual algorithm in the presence of delays. By finding a reasonable Lyapunov-Krasovskii functional candidate, usually difficult to do in a constructive way, we establish a new sufficient condition for robust global stability to delays, which includes Papachristodoulou's as a special case. Finally, we verify the results through simulations. © 2012 Elsevier B.V. All rights reserved.

Zhang B.,Beihang University | Gao Y.,Griffith University | Zhao S.,Griffith University | Liu J.,Chinese University of Hong Kong
IEEE Transactions on Image Processing | Year: 2010

This paper proposes a novel high-order local pattern descriptor, local derivative pattern (LDP), for face recognition. LDP is a general framework to encode directional pattern features based on local derivative variations. The nth-order LDP is proposed to encode the (n-1)th-order local derivative direction variations, which can capture more detailed information than the first-order local pattern used in local binary pattern (LBP). Different from LBP encoding the relationship between the central point and its neighbors, the LDP templates extract high-order local information by encoding various distinctive spatial relationships contained in a given local region. Both gray-level images and Gabor feature images are used to evaluate the comparative performances of LDP and LBP. Extensive experimental results on FERET, CAS-PEAL, CMU-PIE, Extended Yale B, and FRGC databases show that the high-order LDP consistently performs much better than LBP for both face identification and face verification under various conditions. © 2010 IEEE.

Tian G.,Beihang University | Bi X.,Beihang University
Surface and Coatings Technology | Year: 2010

FeSi (12 wt.% Si) and Si were alternatively deposited on pure iron (Fe) substrates by direct current magnetron sputtering. Subsequent annealing in vacuum at 1150-1190 °C results in penetration of Si into the substrate. Cross-sectional microstructure and Si concentration were investigated by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The penetration mechanism is found to depend greatly on Si amount in the as-deposited films. When FeSi/Si/FeSi/Si/FeSi was deposited on the Fe substrate, the Si penetration is controlled by phase-boundary migration, while a diffusion-controlling penetration is observed in FeSi/Si/FeSi deposited samples. Fe-6.5 wt.% Si sheet with thickness of 0.35 mm is obtained through the deposition of FeSi/Si multilayer on a Fe-3 wt.% Si sheet together with subsequent annealing at 1180 °C for 2 h. © 2009 Elsevier B.V. All rights reserved.

Guan C.,Beihang University | Jiao Z.,Beihang University
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science | Year: 2014

Stack-type piezoelectric actuators, which usually consist of several ceramic layers connected in series, are widely used in piezoelectric direct-drive servo valves (PDDSV). However, poor pulling force capacity of this kind of actuators affects the performances of the direct-drive servo valves. This article presents a new type of PDDSV, whose spool-driving mechanism is composed of a set of independent parts that are not fixed together but are in contact with each other. This multi-body contacting spool-driving mechanism provides bidirectional movement of the spool by a preloaded stack-type piezoelectric actuator and a driving disc spring. This prevents the stack-type piezoelectric actuator from bearing the pulling force due to the inertia and friction of the spool. Design of the proposed servo valve is illustrated in detail and its characteristics are also predicted. Based on a nonlinear dynamic model of the multi-body contacting spool-driving mechanism, a comprehensive dynamic simulation model of the proposed PDDSV is established. Static and dynamic characteristics of the proposed PDDSV have been studied experimentally and good agreements between experimental and simulation results are observed. The dynamic performances of the proposed PDDSV are compared with the existing piezoelectric servo valves, which demonstrate that the proposed PDDSV has satisfactory dynamic characteristics for high-frequency applications. © IMechE 2013.

Wang L.-L.,Beihang University | Zhang D.-F.,Beihang University | Guo L.,Beihang University
Nanoscale | Year: 2014

The phase-segregated Pt-Ni chain-like nanostructures, composed of monometallic counterparts attached to each other, were synthesized via a modified polyol process with the assistance of a small amount of PVP. The molar ratio between Pt and Ni was tuned by simply adjusting the feed ratio of the precursors. High-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS) results reveal that atomic diffusion occurred at the interface of the granular subunits. The negative shift of the Pt4f 7/2 peak in the XPS spectra indicates the electron transfer from Ni to Pt atoms, while the strong peaks at around 855.7 eV suggest the surface oxidation of the Ni nanoparticles, which was further confirmed by the cyclic voltammetry (CV) measurement. The electrocatalytic activities of the methanol oxidation reaction (MOR) were found to be higher for the phase-segregated structures relative to those for pure Pt nanoparticles, and the activities followed the sequences of Pt1Ni1 > Pt 3Ni1 ∼ Pt2Ni3 > pure Pt. We believe that the modified electronic structures and the existence of nickel hydroxide both contributed to the improved catalytic activities. © 2014 the Partner Organisations.

Yang M.,CAS Shanghai Institute of Ceramics | Gao Q.,CAS Shanghai Institute of Ceramics | Gao Q.,Beihang University
Microporous and Mesoporous Materials | Year: 2011

A composite of leaf-shaped copper oxide (CuO) nanoparticles mainly covered on the ordered mesoporous carbon CMK-3 is synthesized by a facile precipitation method. This material (CuO/CMK-3) has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption. Electrochemical analyses show that the material possesses excellent cycling stability and high rate capability with an average discharge capacity of 171 mAh g-1 at 25 C using as the anode material for lithium-ion battery. © 2011 Elsevier Inc. All rights reserved.

Zhai K.,University of Hong Kong | Jiang B.,Beihang University | Chan W.K.,University of Hong Kong
IEEE Transactions on Services Computing | Year: 2014

Location-based services (LBS) are widely deployed. When the implementation of an LBS-enabled service has evolved, regression testing can be employed to assure the previously established behaviors not having been adversely affected. Proper test case prioritization helps reveal service anomalies efficiently so that fixes can be scheduled earlier to minimize the nuisance to service consumers. A key observation is that locations captured in the inputs and the expected outputs of test cases are physically correlated by the LBS-enabled service, and these services heuristically use estimated and imprecise locations for their computations, making these services tend to treat locations in close proximity homogenously. This paper exploits this observation. It proposes a suite of metrics and initializes them to demonstrate input-guided techniques and point-of-interest (POI) aware test case prioritization techniques, differing by whether the location information in the expected outputs of test cases is used. It reports a case study on a stateful LBS-enabled service. The case study shows that the POI-aware techniques can be more effective and more stable than the baseline, which reorders test cases randomly, and the input-guided techniques. We also find that one of the POI-aware techniques, cdist, is either the most effective or the second most effective technique among all the studied techniques in our evaluated aspects, although no technique excels in all studied SOA fault classes. © 2014 IEEE.

Wang X.-L.,Beihang University | Li Y.-F.,Beihang University
Aerospace Science and Technology | Year: 2012

In the traditional strapdown inertial navigation system/global positioning system (SINS/GPS) ultra-tight integration structure, the mutual aiding between SINS and GPS forms a positive feedback loop, through which measurement errors of both subsystems are coupled deeply. In signal jamming or/and dynamic conditions, the Doppler aiding error derived from the SINS using low-grade inertial measurement unit (IMU) can increase rapidly, and cause GPS measurement errors to be correlated with the SINS velocity errors. Such correlations can result in poor estimation accuracy of the integration Kalman filter, losing lock of tracking loops or even yielding system instability. To solve this problem, we propose to model tracking errors of the SINS aided phase lock loop and to derive a new tracking-error estimator. Then, an innovative scheme for SINS/GPS ultra-tight integration using low-grade IMU is investigated. Simulations experiments are implemented to verify this innovative scheme under challenging environments. © 2011 Elsevier Masson SAS © 2011 Elsevier Masson SAS. All rights reserved.

Huang J.,Beihang University | Hu X.,Beihang University | Geng X.,Beihang University
Electric Power Systems Research | Year: 2011

Targeting the characteristics of machinery vibration signals of high voltage circuit breaker (CB), a new method based on improved empirical mode decomposition (EMD) energy entropy and multi-class support vector machine (MSVM) to diagnose fault for high voltage CB is proposed. In the fault diagnosis for the high voltage CB, the feature extraction based on improved EMD energy entropy is detailedly analyzed. A new multi-layered classification of SVM named 'one against others' algorithm approach is proposed and applied to machinery fault diagnosis of high voltage CB. The extracted features are applied to MSVM for estimating fault type. Compared with back-propagation network (BPN), the test results of MSVM demonstrate that the applying of improved EMD energy entropy to vibration signals is superior to that based on wavelet packet analysis (WPT) and hence estimating fault type on machinery condition of high voltage CB accurately and quickly. © 2010 Elsevier B.V. All rights reserved.

Pan B.,Beihang University | Wang Z.,Catholic University of America | Lu Z.,Beihang University
Optics Express | Year: 2010

Digital image correlation (DIC) is an easy-to-implement yet powerful optical metrology for deformation measurement. The technique measures the displacement of a point of interest by matching the subsets surrounding the same point located in the reference image and the deformed image. Although the technique is simple in principle, the existing DIC technique has several deficiencies. For example, for the points located near or at the boundaries of a specified region of interest (ROI), the selected square subsets surrounding these points may contain unwanted or foreign pixels from background image or other regions. In the existing DIC method, these points are either intentionally excluded from calculation or automatically removed after calculation, and leads to the absence of deformation information for the boundary points. Besides, existing DIC technique is prone to yield erroneous measurement for specimen with geometric discontinuities. In this paper, two approaches are developed to overcome the deficiencies of existing DIC technique. First, a modified Zero-mean Normalized Sum of Squared Differences (ZNSSD) criterion is defined for the correlation analysis of subsets surrounding the boundary points. Second, considering the possible complex shape of the ROI, a scanning strategy guided by the correlation coefficients of computed points is proposed to ensure reliable computation between consecutive points. With these two measures, the deformation of all the points including those located near or at the ROI boundaries can be automatically, reliably, and accurately determined. The improved DIC technique is universally applicable to the genuine full-field deformation measurement of objects with complex or arbitrary shapes. Two typical experimental image pairs are processed to evaluate the performance of the proposed method, and the results successfully demonstrate its effectiveness and practicality. © 2009 Optical Society of America.

Wen M.,Beihang University | Kang R.,Beihang University
Applied Soft Computing Journal | Year: 2011

Facility location-allocation (FLA) problem is widely used in practical life. Many papers have introduced the problem with the random or fuzzy demands of customers, but few give the case that the customers' demands are random fuzzy. In this paper, the expected cost minimization model, (α,β)- cost minimization model and chance maximization model are presented with random fuzzy demands. In order to solve these random fuzzy models, the simplex algorithm, random fuzzy simulations and genetic algorithm are integrated to produce a hybrid intelligent algorithm. Finally, some numerical examples are provided for the sake of illustration. © 2010 Elsevier B.V. All rights reserved.

Infrared image enhancement is a crucial technique for improving the quality of infrared images. And, the clear image details are important information for infrared image analysis. To effectively enhance infrared image and make image details clear, a multi-scale sequential toggle operator based algorithm is proposed in this paper. Firstly, the sequential toggle operator, which uses opening and closing as primitives, is constructed and discussed. Secondly, the feature extraction in infrared image through the sequential toggle operator is given, and the multi-scale extension of the feature extraction is discussed in details. Finally, the extracted final features of infrared image are constructed and imported into the original infrared image to produce the enhanced image. In the enhanced image, the image features are enhanced well and the image details are clear. Infrared images which obtained from different environments are used in the experiment. The results show that, the proposed algorithm is very effective for infrared image enhancement. ©2014 Elsevier B.V. All rights reserved.

Bai X.,Beihang University
Infrared Physics and Technology | Year: 2015

Effectively extracting the features of the original images is crucial for infrared and visual image fusion. To well maintain the information of the original infrared and visual images and make the fusion image clear, a sequential toggle operator based algorithm through feature extraction is proposed in this paper. Firstly, sequential toggle operator based on multi-scale theory is discussed. Secondly, the features in the original infrared and visual images are extracted. Thirdly, the final fusion features are calculated from the extracted multi-scale image features through the weight strategy and considering the image details. Finally, after the base image is calculated from the original images, the final fusion image is obtained through enlarging the contrast between the final fusion features by using the base image. Experimental results on different types of infrared and visual images show that, the fusion result effectively combines the information of the original images and the result is clear. So, the fusion result is effective for different infrared image related applications, such as target detection, recognition, and surveillance. © 2015 Elsevier B.V. All rights reserved.

Wen L.,CAS Beijing National Laboratory for Molecular | Hou X.,CAS National Center for Nanoscience and Technology | Tian Y.,CAS Beijing National Laboratory for Molecular | Zhai J.,Beihang University | Jiang L.,CAS Beijing National Laboratory for Molecular
Advanced Functional Materials | Year: 2010

Inspired by the light-driven, cross-membrane proton pump of biological systems, a photoelectric conversion system based on a smart-gating, protondriven nanochannel is constructed. In this system, solar energy is the only source of cross-membrane proton motive force that induces a diffusion potential and photocurrent flowing through the external circuit. Although the obtained photoelectric conversion performance is lower than that of conventional solid photovoltaic devices, it is believed that higher efficiencies can be generated by enhancing the protonation capacity of the photo-acid molecules, optimizing the membrane, and synthesizing high-performance photosensitive molecules. This type of facile and environmentally friendly photoelectric conversion has potential applications for future energy demands such as the production of power for in vivo medical devices. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liu T.,Beihang University | Yang C.,Beihang University
IEEE Transactions on Signal Processing | Year: 2013

In this paper, we analyze the feasibility of linear interference alignment (IA) for multi-input-multi-output (MIMO) interference broadcast channel (MIMO-IBC) with constant coefficients. We pose and prove the necessary conditions of linear IA feasibility for general MIMO-IBC. Except for the proper condition, we find another necessary condition to ensure a kind of irreducible interference to be eliminated. We then prove the necessary and sufficient conditions for a special class of MIMO-IBC, where the numbers of antennas are divisible by the number of data streams per user. Since finding an invertible Jacobian matrix is crucial for the sufficiency proof, we first analyze the impact of sparse structure and repeated structure of the Jacobian matrix. Considering that for the MIMO-IBC the sub-matrices of the Jacobian matrix corresponding to the transmit and receive matrices have different repeated structure, we find an invertible Jacobian matrix by constructing the two sub-matrices separately. We show that for the MIMO-IBC where each user has one desired data stream, a proper system is feasible. For symmetric MIMO-IBC, we provide proper but infeasible region of antenna configurations by analyzing the difference between the necessary conditions and the sufficient conditions of linear IA feasibility. © 1991-2012 IEEE.

Chen M.,Beihang University | Lu Z.,Beihang University
Composite Structures | Year: 2015

In this paper, the load transfer mechanism of the composites incorporating nanohybrid shish-kebab structures is analyzed by an improved shear-lag model. The discontinuity of the matrix and interface, which is introduced by the specific periodical morphology of nanohybrid shish-kebab structure, is incorporated in the newly developed shear-lag model. A satisfying agreement is obtained between the stress distributions derived by the present model and finite element simulation. The "load transfer back" phenomenon is found for the nanohybrid shish-kebab structure, which can be attributed to the redistribution of the axial loads according to the variation of elastic modulus of matrix along the axial direction. Besides, considerable improvement of load transfer efficiency is observed due to the enhancement of the mechanical property of the interface. The parametric study shows that the elastic modulus and morphology of the nanohybrid shish-kebab structure both have pronounced effects on the load transfer characteristics of the composites, while the effect of the van der Waals interaction is very limited. © 2014 Elsevier Ltd.

Huang K.,Beihang University | Mao X.,Beihang University
Infrared Physics and Technology | Year: 2010

Selecting the most appropriate algorithms for detecting small targets in varied infrared image scenes is frequently needed, since the relative characteristics between small targets and backgrounds in varied scenes are disparate. To solve that problem, a novel criterion is proposed in this article to measure the difficulty in distinguishing small targets from infrared images, which is named detectability of infrared small targets (DIST). Then a new method to detect small targets based on it was introduced. Detection probability and false alarm probability were employed to evaluate the performance. The results from the experiments further demonstrated the robustness of the proposed methodology under different backgrounds. © 2009 Elsevier B.V. All rights reserved.

Pan B.,Beihang University | Lu Z.,Beihang University | Xie H.,Tsinghua University
Optics and Lasers in Engineering | Year: 2010

Digital image correlation (DIC) is an image-based optical metrology for full-field deformation measurement. In DIC technique, the test object surface must be covered with a random speckle pattern, which deforms together with the object surface as a carrier of deformation information. In practice, the speckle patterns may show distinctly different intensity distribution characteristics and have an important influence on DIC measurements. How to assess the overall quality of different speckle patterns with a simple yet effective parameter is an interesting but confusing problem, and is also helpful to the optimal use of the technique. In this paper, a novel, simple, easy-to-calculate yet effective global parameter, called mean intensity gradient, is proposed for quality assessment of the speckle patterns used in DIC. To verify the correctness and effectiveness of the new concept, five different speckle patterns are numerically translated, and the displacements measured with DIC are compared with the exact ones. The errors are evaluated in terms of mean bias error and standard deviation error. It is shown that both mean bias error and standard deviation of the measured displacement are closely related to the mean intensity gradient of the speckle pattern used, and a so-called good speckle pattern should be of large mean intensity gradient. © 2009 Elsevier Ltd. All rights reserved.

Guo J.-H.,Beihang University | Lu Z.-X.,Beihang University
International Journal of Solids and Structures | Year: 2010

The anti-plane problem of multiple cracks originating from a circular hole in a magnetoelectroelastic solid is investigated under remotely uniform anti-plane mechanical loading and in-plane electromagnetic loadings. The boundary value problem is reduced to a Cauchy integral equation by a new mapping function and the complex variable method, which is further solved exactly. The analytic expressions of the complex potentials, the field intensity factors and the energy release rate are derived in closed-form under the assumption that the surfaces of the cracks and hole are both electrically and magnetically impermeable. The effects of crack configurations and combined loadings on the energy release rate are shown graphically. Several useful results which may have potential applications to the design and fracture analysis of magnetoelectroelastic structures are given. © 2010 Elsevier Ltd. All rights reserved.

Liu Z.,University of Nevada, Reno | Liu Z.,Beihang University | Misra M.,University of Nevada, Reno
ACS Nano | Year: 2010

Dye-sensitized photovoltaic wires (DSPVWs) are developed using anodized Ti wires that contain ordered arrays of TiO2 nanotubes. The prototype DSPVW consists of N719 dye-adsorbed TiO2 nanotube arrays around a Ti wire as a working electrode, a platinum wire as a counter electrode, and an organic electrolyte encased in a capillary glass tube. The effect of length of nanotube arrays on the photovoltaic performance of DSPVWs is studied systematically. A solar-to-electric conversion efficiency of 2.78% is achieved with 55 μm long nanotubes under 98.3 mW/cm2 AM 1.5 simulated full light. The prototype device is capable of achieving a long distance transport of photocurrent and harvesting all light from any direction in surroundings to generate electricity. © 2010 American Chemical Society.

Shan R.Q.,Beihang University | Wang J.J.,Beihang University
Sensors and Actuators, A: Physical | Year: 2010

This paper studies the influences of two dimensionless parameters, the Reynolds number and dimensionless stroke, on an axisymmetric synthetic jet by using flow visualization and particle image velocimetry (PIV) techniques. The flow visualization results and the relevant analyses, such as the formation and state of the vortex ring, the time-averaged streamwise velocity and kinetic energy of the fluctuating motion, etc., are provided. It was found that the Reynolds number does not influence the formation location of vortex rings; however, with increasing Reynolds number, the vortex rings go through the laminar-turbulent transition and tend to lose stability, leading to breakdown. In addition, the similarity of the jet kinetic energy distribution of fluctuating motion can be reached in a short distance downstream from the orifice, and the characteristics of conventional turbulent jets also appear as the Reynolds number is increased to a certain value. The dimensionless stroke strongly influences the formation and development of vortex rings. Furthermore, the experimental investigations on an axisymmetric synthetic jet actuated by a novel actuator signal, proposed by Zhang and Wang [16], are implemented in the present paper, and the 'actual efficient stroke' concept is introduced. © 2009 Elsevier B.V. All rights reserved.

Gao Z.,Hong Kong University of Science and Technology | Zhao J.,Hong Kong University of Science and Technology | Yao Y.,Beihang University
International Journal of Solids and Structures | Year: 2010

Experimental evidence shows that the strength of geomaterials, such as soils and rocks, is significantly influenced by inherent anisotropy and other factors such as shear banding and the intermediate principal stress, which cannot be properly described by an isotropic failure criterion. This paper presents a generalized failure criterion for geomaterials with cross-anisotropy. To account for the influence of cross-anisotropy, we introduce an anisotropic variable in terms of the invariants and joint invariants of the stress tensor and the fabric tensor into the frictional coefficient of the failure criterion. The anisotropic failure criterion is formulated in both the deviatoric plane and the meridian plane which collectively offer a general three-dimensional description of strength anisotropy. All the parameters introduced in the criterion can be conveniently determined by conventional laboratory tests. We demonstrate that the new criterion is general and robust in describing the variation of strength with loading direction for a wide range of materials. The failure criterion has been applied to the prediction of strength for several clays, sands and rocks reported in the literature. The predictions compare favorably with available experimental data. Further discussion is made on possible improvement of the new criterion to address other materials with complex strength characteristics, as well as its potential usefulness for constitutive modeling of anisotropic geomaterials. © 2010 Elsevier Ltd. All rights reserved.

Guo Z.,Beihang University
Proceedings of the World Congress on Intelligent Control and Automation (WCICA) | Year: 2016

Design of product maintainability, involving analysis, verification, and training, can be pre-conducted with the aid of virtual environment - virtual maintenance. Unlike non-immersive virtual simulation, immersive virtual simulation offers a more realistic and effective path for maintainability design. However, in the current maintenance simulation environment, the actions of human beings who act as the subject of recognition are always observed and analyzed externally, where little sensory information acquired from human beings can be adopted for further interaction. Meanwhile, current maintenance simulation is conducted based on personal experiences and skills where the users may be disoriented without a natural and reasonable interaction pattern and model. To solve the problem of human-computer interaction in virtual maintenance system, we adapt the driver class of data gloves and optical tracking devices to expatiate the method of maintenance action data acquisition and disposal strategy, combined with the virtual environment. With the use of gloves and a 3D data tracker for motion capture, gesture recognition, and mapping of command, we expound the realization of human-computer interaction methods in the DELMIA virtual environment. We operate a virtual model of parts and components maintenance via a virtual hand. The focus is to achieve a virtual entity that manipulates the process in direct and concrete ways, relying on optical tracking, data gloves, and other peripherals. Finally, a virtual maintenance case is presented to verify the proposed method. © 2016 IEEE.

Zhang J.,Beihang University | Liu F.,Beihang University | Zhao L.,Beihang University | Fei B.,Beihang University
Composite Structures | Year: 2014

A novel characteristic curve determined by tensile, compressive and shear-out characteristic length is presented to predict failure load and failure mode of mechanically fastened composite joints. In contrast to the existing curves, the novel one introduces a shear-out characteristic length and provides capability to predict shear-out failure. A mathematics formulation of the novel curve is proposed based on the expression of Chang's characteristic curve and shear-out characteristic length. A series of tests were carried out and nonlinear finite element analyses were conducted to obtain the tensile, compressive and shear-out characteristic lengths for the novel curve. Following tensile tests of two-bolt and three-bolt joints were performed, and the failure loads and modes were numerically predicted by the characteristic curve method with the novel curve and Chang's. The numerical results obtained from the curve presented show good agreements with the experimental outcomes and better accuracy on both failure load and failure mode. © 2013 Elsevier Ltd.

Wang J.-J.,Beihang University | Choi K.-S.,University of Nottingham | Feng L.-H.,Beihang University | Jukes T.N.,University of Nottingham | Whalley R.D.,University of Nottingham
Progress in Aerospace Sciences | Year: 2013

Flow control using DBD (dielectric-barrier-discharge) plasma actuators is a relatively new, but rapidly expanding area of research. There are a number of review papers available on this subject, but few discuss on their latest developments. The purpose of the present article is to "fill the gap" by reviewing the recent trend of plasma actuator design and to summarise aerodynamic control techniques. Here, we review new plasma actuators, such as plasma synthetic jet actuators, plasma spark jet actuators, three-dimensional plasma actuators and plasma vortex generators, which can induce three-dimensional flows away from the wall. We also review the starting vortex that leads to formation of a plasma wall jet. This is an important subject not only for a better understanding of the flow induced by DBD plasma actuators, but also as a database that can be used to calibrate the numerical models for plasma flow control. Design of DBD plasma actuators to obtain turbulent skin-friction reduction is shown and the modifications to near-wall turbulence structures are summarised. Novel applications of DBD plasma actuators for aerodynamic control are then discussed, including pitch and roll control, plasma jet vectoring, circulation control and plasma flap, showing a potential of DBD plasma actuators for replacing movable, aircraft control surfaces. Finally, vortex shedding control techniques by a number of different plasma actuators are surveyed. © 2013 Elsevier Ltd. All rights reserved.

Yu L.,Beihang University | Pan B.,Beihang University
Optics and Lasers in Engineering | Year: 2016

A low-cost, easy-to-implement but practical single-camera stereo-digital image correlation (DIC) system using a four-mirror adapter is established for accurate shape and three-dimensional (3D) deformation measurements. The mirrors assisted pseudo-stereo imaging system can convert a single camera into two virtual cameras, which view a specimen from different angles and record the surface images of the test object onto two halves of the camera sensor. To enable deformation measurement in non-laboratory conditions or extreme high temperature environments, an active imaging optical design, combining an actively illuminated monochromatic source with a coupled band-pass optical filter, is compactly integrated to the pseudo-stereo DIC system. The optical design, basic principles and implementation procedures of the established system for 3D profile and deformation measurements are described in detail. The effectiveness and accuracy of the established system are verified by measuring the profile of a regular cylinder surface and displacements of a translated planar plate. As an application example, the established system is used to determine the tensile strains and Poisson׳s ratio of a composite solid propellant specimen during stress relaxation test. Since the established single-camera stereo-DIC system only needs a single camera and presents strong robustness against variations in ambient light or the thermal radiation of a hot object, it demonstrates great potential in determining transient deformation in non-laboratory or high-temperature environments with the aid of a single high-speed camera. © 2016 Elsevier Ltd

Yao Y.,Beihang University | Gao Z.,Hong Kong University of Science and Technology | Zhao J.,Hong Kong University of Science and Technology | Wan Z.,Beihang University
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2012

Most clays, either naturally deposited or man-made, possess a certain degree of overconsolidation owing to tamping, cyclic loading, erosion, excavation, and/or changes in groundwater tables. An easy-to-use constitutive model for overconsolidated clays is useful for relevant engineering applications. In this paper, a simple model is proposed for overconsolidated clays based on the unified-hardening (UH) model. To evaluate the potential peak stress ratio of overconsolidated clays, a parabolic Hvorslev envelope rather than a straight envelope (used in the original UH model) is adopted. The proposed parabolic Hvorslev envelope passes through the origin of the mean stress-deviatoric stress plane. It hasa slope of 3 as the overconsolidation ratio (OCR) approaches infinity and intersects withthe critical state line as the OCR reaches unity. This modification leads to more realistic predictions for highly overconsolidated clays than does the original UH model with a straight Hvorslev envelope and is consistent with the critical state soil mechanics in which the higher peak stress ratio in overconsolidated clays is a result of interlocking (ordilatancy) rather than cohesion. The modified UH model retains the same parameters as those in the modified Cam-clay model. Reasonable agreement between the model predictions andexperimental data demonstrates that the modified model is capable of addressing the fundamental behavior of overconsolidated clays. The present model is developed for reconstituted clays with an isotropic fabric. The potential improvement of the model, taking into account anisotropy and structural effects, is discussed. © 2012 American Society of Civil Engineers.

Wang J.-L.,Beihang University | Wu H.-N.,Beihang University
International Journal of Control | Year: 2012

In this article, two kinds of leader-following formation control problems for second-order nonlinear multi-agent systems are investigated, that is, the cases with fixed topology and with switching topology. For the former, by constructing an appropriate Lyapunov functional and utilising linear matrix inequality (LMI) method, we propose a formation control algorithm which makes the nonlinear multi-agent systems converge to a desired formation. In addition, a formation control algorithm is also developed for coupled double-integrators with a constant reference velocity. Then we extend these results to the case when the interaction topology is switching. Numerical simulations are presented finally to demonstrate the effectiveness of the proposed results. © 2012 Taylor & Francis.

Yang X.,Beihang University | Wang X.,Beihang University | Wang L.,Beihang University
Bioresource Technology | Year: 2010

For a better sewage sludge disposal and more efficient energy reclamation, transforming of components and energy in sludge by thermal and WAO pretreatment followed by two-phase anaerobic UASB process were studied in the pilot scale. Biogas outputs and the qualities and quantities of the effluent and solid residue were compared with a traditional anaerobic sludge digestion. Sludge components, including carbon, nitrogen, phosphorus, sulphur, were observed and mass balances were discussed throughout the process. The input and output energy balance was also studied. Results showed different trait to compare with biogas outputs in terms of COD added and raw sludge added. Pretreatment improved the transformation of carbon substances into biogas production with higher carbon removal and higher VSS removal. Comparing the energy obtained from biogas production with energy inputs required for pretreatment, energy output in the whole process decreased with higher pretreatment temperature. © 2009 Elsevier Ltd. All rights reserved.

Khan A.W.,Beihang University | Chen W.,Beihang University
International Journal of Advanced Manufacturing Technology | Year: 2011

To enhance the accuracy, an efficient methodology was developed and described for systematic geometric error correction and their compensation in five-axis machine tools. The methodology is capable of compensating the overall effect of all position-dependent and position-independent errors which contribute to volumetric workspace. It was implemented on a five-axis grinding machine for error compensation and for the check of its effectiveness. Error compensation algorithm was designed, and a routine was written in Matlab software. The developed technique and software are based on an error table which interprets the function of axis through cubic spline technique and synthesis modeling of a machine tool. Recursive compensation methodology was used to remove the machine errors from the actual tool path and inverse technique was implemented to find the corrected positions of prismatic and rotary joints. Moreover, it can convert the corrected tool paths into practical compensated NC codes. The generated, corrected and modified NC codes directly fed to the controller of a five-axis machine tool. Validation of the technique was preceded by repeated experimentation of measurement and through machining of typical standard workpieces with some additional specific features. Experimental results exhibit effective compensation and remarkable improvement in the parametric and volumetric-workspace accuracy of the five-axis machine tool. © 2010 Springer-Verlag London Limited.

Zhao G.,Beihang University | Yang C.,Beihang University | Li G.Y.,Georgia Institute of Technology | Li D.,Huawei | Soong A.C.K.,Huawei
IEEE Journal on Selected Topics in Signal Processing | Year: 2011

In this paper, we investigate power and channel allocation for cooperative relay in a three-node cognitive radio network. Different from conventional cooperative relay channels, cognitive radio relay channels can be divided into three categories: direct, dual-hop, and relay channels, which provide three types of parallel end-to-end transmission. In the context, those spectrum bands available at all three nodes may either perform relay diversity transmission or assist the transmission in direct or dual-hop channels. On the other hand, the relay node involves both dual-hop and relay diversity transmission. In this paper, we develop power and channel allocation approaches for cooperative relay in cognitive radio networks that can significantly improve the overall end-to-end throughput. We further develop a low complexity approach that can obtain most of the benefits from power and channel allocation with minor performance loss. © 2011 IEEE.

Bi S.,Beihang University | Liang J.,Beihang University
International Journal of Advanced Manufacturing Technology | Year: 2011

Manual drilling in titanium structures is a tedious and labor-intensive work. To reduce man-hour requirements while concurrently improving hole quality, we developed a robotic drilling system for this application. The lean system contains the product holding fixture, the industrial robot, the end effector, the control and sensor system, and the offline programming. The system functions include locating workpiece with a calibration stick or the vision system, weld mark inspection, one-sided clamping, drilling and reaming hole in material stack combinations of titanium and aluminum, and real-time thrust force feedback. The positional accuracy and the repeatability of the system have successfully been placed within the specification's 0.3 mm tolerance and 0.2 mm tolerance, respectively. The dimensional accuracy of drilled holes in both Ti alloy and Al alloy materials is within H9 tolerance. © Springer-Verlag London Limited 2010.

Cao Y.,Beihang University | Wu Z.,Beihang University | Xu Z.,Beihang University
Progress in Aerospace Sciences | Year: 2014

Rainfall has been considered as an important meteorological factor to threat aircraft flight safety. Adverse effects of rainfall on aircraft aerodynamics have been a constantly hot subject in meteorological aviation community for decades. This paper presents a systematic and comprehensive overview of the effects of rainfall on aircraft aerodynamics. The overview includes an introduction of rain-induced aviation accidents, a list of the hazards of rainfall to aircraft, the natural characteristics of rain, the existing rain research techniques, some aerodynamic considerations for rainfall simulation and the current state-of-the-art research achievements in the field of effects of rainfall on aircraft aerodynamics. Raindrop impingement, splashback and flow of the formed water film upon lifting surfaces effectively degrade aircraft aerodynamic performance, leading to severe aviation accidents. The previous lessons learned should be disseminated and accepted by later generations to avoid aviation accidents due to flight in heavy rain. © 2014 Elsevier Ltd.

Shang Y.,Beihang University | Zhang D.,Beihang University | Guo L.,Beihang University
Journal of Materials Chemistry | Year: 2012

Surfactant-directed self-assembly (SDSA) had become a promising approach towards the synthesis of ordered mesoporous oxide materials in recent years. A key step in this method is to control the hydrolysis-condensation rates of inorganic precursors for good co-assembly with a structure-directing agent (SDA). Based on the principle of solubility product, we propose a new strategy, namely using water-insoluble intermediates as a "buffer" to retard the hydrolysis rates of inorganic species and thus facilitate the cooperative organization process to construct ordered mesoporous materials. Cuprous oxide mesoporous spheres (Cu 2O MPS) with short-range-ordered structure were obtained with the assistance of triblock copolymers Pluronic P123 (EO 20PO 70EO 20) to demonstrate this concept. The as-prepared unique structures exhibit excellent adsorption ability, and the maximum adsorption capacities is 3.4 times that of commercial activated carbon, at room temperature with methyl orange as pollutant. With the advantage of simple, easy control and high yield, it may provide a good idea for the preparation of other mesoporous structured materials. © The Royal Society of Chemistry 2011.

Wang S.,Beihang University | Xing Y.,Beihang University | Xu H.,Beihang University | Zhang S.,Beihang University
ACS Applied Materials and Interfaces | Year: 2014

Interdispersed MnO nanoparticles that are anchored and encapsulated in a three-dimensional (3D) porous carbon framework (MnO@CF) have been constructed, which display nanosphere architecture with rich porosity, well-defined carbon framework configuration, and excellent structure stability. When evaluated as an anode material, the MnO@CF exhibits relatively high specific capacity of 939 mA h g-1 at current rate of 0.2 A g-1 over 200 cycles and excellent rate capability of 560.2 mA h g-1 at 4 A g-1. By virtue of its mechanical stability and desirable ionic/electronic conductivity, the specific design can be a promising approach to fabricate high-performance lithium-ion batteries. © 2014 American Chemical Society.

Tsai W.-T.,Arizona State University | Wu W.,Beihang University | Huhns M.N.,University of South Carolina
IEEE Internet Computing | Year: 2014

In addition to providing large-scale, highly available computational resources, clouds also enable a new methodology for software development via crowdsourcing, in which crowd participants either collaborate or compete to contribute software. Using a crowd to develop software is predicted to take its place alongside established methodologies, such as agile, scrum, pair programming, service-oriented computing, and the traditional waterfall. © 2014 IEEE.

Liu Y.,Beihang University | Jia Y.,Beihang University
International Journal of Control, Automation and Systems | Year: 2011

This paper is devoted to the robust H ∞ consensus control of multi-agent systems with model parameter uncertainties and external disturbances. In particular, switching networks of multiple agents with general linear dynamics are considered, and uncertain communication delays are also taken into account. It shows that a sufficient condition in terms of linear matrix inequalities (LMIs) is derived for the robust consensus performance with a given H ∞ disturbance attenuation level, and meanwhile the unknown feedback matrix of the proposed distributed state feedback protocol is also determined. A numerical example is included to validate the theoretical results. © ICROS, KIEE and Springer 2011.

Bai X.,Beihang University
Microscopy Research and Technique | Year: 2013

To well enhance the mineral image and image details obtained by microscopes, an effective mineral image enhancement algorithm through feature extraction using the morphological center operator is proposed in this work. First, mineral image feature extraction based on the morphological center operator is proposed and discussed. Second, the multiscale extension of the mineral image feature extraction is given by using the multiscale structuring elements. Third, the important mineral image features at multiscales of image are extracted and used to construct the final mineral features for mineral image enhancement. Finally, the original mineral image is well enhanced through importing the extracted final mineral image features into the original mineral image. Experimental results on different types of microscopy images of minerals verified the effective performance of the proposed algorithm for microscopy mineral image enhancement. © 2012 Wiley Periodicals, Inc.

Wu Z.,Nanjing University of Finance and Economics | Wu J.,Beihang University | Cao J.,Nanjing University of Finance and Economics | Tao D.,Intelligent Systems Technology, Inc.
Proceedings of the ACM SIGKDD International Conference on Knowledge Discovery and Data Mining | Year: 2012

Shilling attackers apply biased rating profiles to recommender systems for manipulating online product recommendations. Although many studies have been devoted to shilling attack detection, few of them can handle the hybrid shilling attacks that usually happen in practice, and the studies for real-life applications are rarely seen. Moreover, little attention has yet been paid to modeling both labeled and unlabeled user profiles, although there are often a few labeled but numerous unlabeled users available in practice. This paper presents a Hybrid Shilling Attack Detector, or HySAD for short, to tackle these problems. In particular, HySAD introduces MC-Relief to select effective detection metrics, and Semi-supervised Naive Bayes (SNB-lambda) to precisely separate Random-Filler model attackers and Average-Filler model attackers from normal users. Thorough experiments on MovieLens and Netflix datasets demonstrate the effectiveness of HySAD in detecting hybrid shilling attacks, and its robustness for various obfuscated strategies. A real-life case study on product reviews of is also provided, which further demonstrates that HySAD can effectively improve the accuracy of a collaborative-filtering based recommender system, and provide interesting opportunities for in-depth analysis of attacker behaviors. These, in turn, justify the value of HySAD for real-world applications. © 2012 ACM.

Zhao J.,Beihang University | Dong L.,Beihang University | Wu J.,Beihang University | Xu K.,Beihang University
Proceedings of the ACM SIGKDD International Conference on Knowledge Discovery and Data Mining | Year: 2012

Recent years have witnessed the explosive growth of online social media. Weibo, a Twitter-like online social network in China, has attracted more than 300 million users in less than three years, with more than 1000 tweets generated in every second. These tweets not only convey the factual information, but also reflect the emotional states of the authors, which are very important for understanding user behaviors. However, a tweet in Weibo is extremely short and the words it contains evolve extraordinarily fast. Moreover, the Chinese corpus of sentiments is still very small, which prevents the conventional keyword-based methods from being used. In light of this, we build a system called MoodLens, which to our best knowledge is the first system for sentiment analysis of Chinese tweets in Weibo. In MoodLens, 95 emoticons are mapped into four categories of sentiments, i.e. angry, disgusting, joyful, and sad, which serve as the class labels of tweets. We then collect over 3.5 million labeled tweets as the corpus and train a fast Naive Bayes classifier, with an empirical precision of 64.3%. MoodLens also implements an incremental learning method to tackle the problem of the sentiment shift and the generation of new words. Using MoodLens for real-time tweets obtained from Weibo, several interesting temporal and spatial patterns are observed. Also, sentiment variations are well captured by MoodLens to effectively detect abnormal events in China. Finally, by using the highly efficient Naive Bayes classifier, MoodLens is capable of online real-time sentiment monitoring. The demo of MoodLens can be found at © 2012 ACM.

Chen H.-X.,Beihang University
Advances in High Energy Physics | Year: 2013

We systematically study the chiral structure of local tetraquark currents of flavor singlet and J P = 0 +. We also investigate their chiral partners, including scalar and pseudoscalar tetraquark currents of flavor singlet, octet, 10, 10 ̄, and 27. We study their chiral transformation properties. Particularly, we use the tetraquark currents belonging to the "nonexotic" [ (3 -, 3) ⊕ (3, 3 -) ] chiral multiplets to calculate the masses of light scalar mesons through QCD sum rule. The two-point correlation functions are calculated including all terms and only the connected parts (Weinberg (2013), Coleman (1985), and Page (2003)). The results are consistent with the experimental values. © 2013 Hua-Xing Chen.

Yang T.,Beihang University | Zhang Y.,Beihang University | Li C.,Beihang University
Journal of Alloys and Compounds | Year: 2014

Tungsten oxide nanotubes were synthesized by solvothermal process without template. The steric effect and the concentration of WCl6 are the dominant factors for the formation mechanism of the nanotube. The steric effect was experimentally and systematically studied with solvents including ethanol, isopropanol, n-propanol and butylalcohol, which have different molecular configuration and length, while the effect of concentration was investigated by characterizing the nanostructured productions. The samples have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The surface chemistry of the nanotube is characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the solvents species and WCl6 concentration obviously diversified the morphologies of the products; the nanotubes synthesized with isopropanol composed of W18O49 phase; the crystal defects (O atom vacancy) formed during rapid crystallization could be modified by heat treatment. The DC electrical response of the nanotube thin film to hydrogen was measured the temperature range from 200 C to 300 C, which indicated a decline in electrical resistance with good sensitivity, and showed the mechanism that the reaction limited process works at low temperature, whereas the diffusion limited process works at higher temperature. © 2013 Elsevier B.V. All rights reserved.

Li Y.,Beihang University
2010 International Conference on Measuring Technology and Mechatronics Automation, ICMTMA 2010 | Year: 2010

A synthetic function for time optimal control of the second-order discrete-time system without control constraint is derived in this paper. It is proved that by the use of the function, any non-zero initial state of the system can be driven to the origin in two steps. Based on this synthetic function, a high speed discrete tracking-differentiator with simple form is presented. Numerical simulation shows that the proposed tracking-differentiator can quickly track input signal with excellent filtering performance and produce a good differential signal of the input. © 2010 IEEE.

Liu B.,Beihang University | Xing Y.F.,Beihang University | Qatu M.S.,Central Michigan University | Ferreira A.J.M.,University of Porto
Composite Structures | Year: 2012

This paper presents an analytical procedure and closed-form vibration solutions with analytically determined coefficients for orthotropic circular cylindrical shells having classical boundary conditions. This analysis is based upon the Donnell-Mushtari shell theory. This is the simplest thin shell theory and its results for the lowest frequencies of a closed cylinder may not be as accurate. It is known that the exact procedure is complicated for orthotropic shells and this complexity has apparently prevented most researchers from getting results. Using the separation of variables method, the closed-form natural frequencies are successfully obtained in this work. They are found in a compact form. Moreover, the characteristics of the eigenvalues are examined. The exact solutions are validated through numerical comparisons with available solutions in literatures and the semi-analytical differential quadrature finite element method (S-DQFEM) solutions calculated by the authors. © 2011 Elsevier Ltd.

Jin-Long L.V.,Beihang University | Hong-Yun L.,Beihang University
Materials Chemistry and Physics | Year: 2012

The degree of sensitization for tensile pre-strain (0%, 10%, 20%, 30%, 40%) of AISI 304 stainless steels and sensitization at 575°C was investigated by the double loop electrochemical potentiokinetic reactivation technique and scanning electron microscopes (SEMs). The properties of passive films of all the sensitized specimens in borate buffer solution (pH = 9.2) with 5000 ppm Cl - were investigated by the Mott-Schottky analysis. The degree of sensitization results showed that two reactivation current peak values were obtained for the sensitized specimens after 30% and 40% pre-strain. The degree of sensitization was decreased by pre-strain, except for specimen with 10% pre-strain. The results were further confirmed by the Mott-Schottky analysis. © 2012 Elsevier B.V. All rights reserved.

Song Y.,Beihang University
Nanoscale | Year: 2013

We demonstrate a simple and clean physical methodology for fabricating such nanoparticle assemblies (dense arrays and/or dendrites) related to the interfacial interaction between the constructed materials and the anodized aluminum oxide (AAO) porous templates. The interfacial interaction can be regulated by the surface tension of the constructed materials and the AAO membrane, and the AAO-template structure, such as pore size, membrane thickness and surface morphologies. Depending on the interfacial interaction between the constructed materials and the AAO templates, NP arrays with mean particle diameters from 3.8 ± 1.0 nm to 12.5 ± 2.9 nm, mean inter-edge spacings from 3.5 ± 1.4 nm to 7.9 ± 3.4 nm and areal densities from 5.6 × 10(11) NPs per cm(2) to 1.5 × 10(12) NPs per cm(2) are fabricated over large areas (currently ~2 cm × 3 cm). The fabrication process includes firstly thermal evaporation of metal layers no more than 10 nm thick on the pre-coated Si wafer by AAO templates with a thickness of less than 150 nm and mean pore sizes no more than 12 nm, and then removal of the AAO templates. The NP arrays can be stable for hours at a temperature slightly below the melting point of the constructed materials (e.g., ~800 °C for Au NPs for 4 hours) with little change in size and inter-particle separation. Using one of them (e.g., 11.8 nm Au NPs) as growth-oriented catalysts, ultra-thin (12.1 ± 2.3 nm) dense nanowires can be conveniently obtained. Furthermore, dendrite superstructures can be generated easily from eutectic alloy NPs with diameters of ~10 nm pre-formed by thermal evaporation of metal layers more than 20 nm thick on surface-patterned thick AAO templates (e.g., 500 nm). The resulting dendrites, dense arrays and other superstructures (i.e., nanorods and nanowires) formed using NP arrays as catalysts, should have broad applications in catalysis, information technology, photovoltaics and biomedical engineering.

Vo M.,Catholic University of America | Wang Z.,Catholic University of America | Pan B.,Beihang University | Pan T.,Catholic University of America
Optics Express | Year: 2012

Fringe-projection-based (FPB) three-dimensional (3D) imaging technique has become one of the most prevalent methods for 3D shape measurement and 3D image acquisition, and an essential component of the technique is the calibration process. This paper presents a framework for hyper-accurate system calibration with flexible setup and inexpensive hardware. Owing to the crucial improvement in the camera calibration technique, an enhanced governing equation for 3D shape determination, and an advanced flexible system calibration technique as well as some practical considerations on accurate fringe phase retrieval, the novel FPB 3D imaging technique can achieve a relative measurement accuracy of 0.010%. The validity and practicality are verified by both simulation and experiments. © 2012 Optical Society of America.

Pan B.,Beihang University | Wu D.,Beihang University | Yu L.,Beihang University
Applied Optics | Year: 2012

An optimized 3D digital image correlation (3D-DIC) system using active optical imaging is developed for accurate shape and 3D deformation measurements in nonlaboratory conditions or extreme hightemperature environments. In contrast to a conventional 3D-DIC system using white or natural light illumination, the proposed active imaging 3D-DIC system is based on a combination of monochromatic lighting and bandpass filter imaging. Because the bandpass filter attached before the imaging lenses allows only the actively illuminated monochromatic light to pass through and blocks all light outside of its bandpass range, the active imaging 3D-DIC system is therefore insensitive to serious variations in ambient light in nonlaboratory environments and to the thermal radiation of hot objects in extreme high-temperature environments. Two challenging experiments that cannot be performed by a conventional 3D-DIC system were carried out to verify the robustness and accuracy of the developed active imaging 3D-DIC system. Because a much wider application range can be achieved with relatively simple and easy-to-implement improvements, the proposed active imaging 3D-DIC system is highly recommended for practical use instead of the conventional 3D-DIC system. © 2012 Optical Society of America.

Zhou Y.,Fudan University | Pan B.,Beihang University | Chen Y.Q.,Fudan University
Applied Optics | Year: 2012

In digital image correlation, the iterative spatial domain cross-correlation algorithm is considered as a gold standard for matching the corresponding points in two images, but requires an accurate initial guess of the deformation parameters to converge correctly and rapidly. In this work, we present a fully automated method to accurately initialize all points of interest for the deformed images in the presence of large rotation and/or heterogeneous deformation. First, a robust computer vision technique is adopted to match feature points detected in reference and deformed images. The deformation parameters of the seed point are initialized from the affine transform, which is fitted to the matched feature points around it. Subsequently, the refined parameters are automatically transferred to adjacent points using a modified quality-guided initial guess propagation scheme. The proposed method not only ensures a rapid and correct convergence of the nonlinear optimization algorithm by providing a complete and accurate initial guess of deformation for each measurement point, but also effectively deals with deformed images with relatively large rotation and/or heterogeneous deformation. Tests on both simulated speckle images and real-world foam compression experiment verify the effectiveness and robustness of the proposed method. © 2012 Optical Society of America.

Combing the useful information of multisensor or multifocus images is important for producing effective optical images. To extract and combine the image features of the original images for image fusion well, an algorithm through feature extraction by using the sequentially combined toggle and top-hat based contrast operator is proposed in this paper. Sequentially combining toggle contrast operator and top-hat based contrast operator could be used to identify well the effective bright and dark image features. Furthermore, through multiscale extension, the effective bright and dark image features at multiscales of an image are extracted. After the final bright and dark fusion features are constructed by using the pixel-wise maximum operation on the multiscale image features from different images, the final fusion result is obtained by importing the final bright and dark fusion features into the base image. Experimental results on different types of images show that the proposed algorithm performs well for image fusion, which may be widely used in different applications, such as security surveillance, object recognition, and so on. © 2012 Optical Society of America.

Luo B.,Beihang University | Wu H.-N.,Beihang University
Journal of Process Control | Year: 2012

In this paper, the linear quadratic (LQ) optimal control problem is considered for a class of linear distributed parameter systems described by first-order hyperbolic partial differential equations (PDEs). Reinforcement learning (RL) technique is introduced for adaptive optimal control design from the design-then-reduce (DTR) framework. Initially, a policy iteration (PI) algorithm is proposed, which learns the solution of the space-dependent Riccati differential equation (SDRDE) online without requiring the internal system dynamics of the PDE system. To prove its convergence, the PI algorithm is shown to be equivalent to an iterative procedure of a sequence of space-dependent Lyapunov differential equations (SDLDEs). Then, the convergence is established by showing that the solutions of SDLDEs are a monotone non-increasing sequence that converges to the solution of the SDRDE. For implementation purpose, an online least-square method is developed for the approximation of the solutions of the SDLDEs. Finally, the proposed design method is applied to the distributed control of a steam-jacketed tubular heat exchanger to illustrate its effectiveness. © 2012 Elsevier Ltd. All rights reserved.

Chen J.,Beihang University | Quegan S.,University of Sheffield
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

Spaceborne synthetic aperture radar (SAR) systems operating at lower frequencies, such as P-band, are significantly affected by Faraday rotation (FR) effects. A novel algorithm for calibrating the circular-transmit-and-linear- receive (CTLR) mode spaceborne compact polarimetric SAR using mixed calibrators is proposed, which is able to correct precisely both FR and radar system errors (i.e., channel imbalance and crosstalk). Six sets of mixed calibrators, consisting of both passive calibrators and polarimetric active radar calibrators (PARCs), are investigated. Theoretical analysis and simulations demonstrate that the optimal calibration scheme combines four polarimetric selective mixed calibrators, including two gridded trihedrals and two PARCs, together with total-electron-content measurements by the Global Navigation Satellite System system. © 2011 IEEE.

Li W.,Beihang University | Jia Y.,Beihang University
IEEE Transactions on Industrial Electronics | Year: 2012

In this paper, we consider the problem of mobile location estimation in a rough wireless environment. To mitigate the non-line-of-sight (NLOS) effects, the transition between the line of sight and the NLOS is described by a discrete-time Markov chain. The multiple-model approach is applied first time for locating a mobile station (MS), and a location estimation algorithm is developed by employing the basic interacting-multiple-model approach to a jump Markov system with two independent switching parameters. The data fusion of the time of arrival and the received signal strength measurements is utilized, and the cubature Kalman filter is applied for nonlinear estimation. Simulations are presented to illustrate the effectiveness of the proposed algorithm involving locating an MS with maneuvers. © 2011 IEEE.

Chen T.,Beihang University | Xu S.,Beihang University
Journal of Guidance, Control, and Dynamics | Year: 2011

Based on double-line-of-sight measuring relative navigation method, an approach guidance law with the trianglemeasuring constraint is presented for autonomous rendezvous. The observability of double-line-of-sight measuring relative navigation system is analyzed using the state estimation error covariance matrix. The triangle-measuring navigation constraint is described as a keep-out cone. The approach guidance law is designed via artificial potential function method. It is ensured that there is a high region of potential in the keep-out cone and the potential still has a unique minimum at the goal position. Numerical simulations are undertaken to verify the guidance method proposed. The results indicate that the control impulses of the potential function guidance ensure convergence of the chase spacecraft to reach the goal position without violating the navigation keep-out zone. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Hou Y.,Beihang University | Wang Q.,Beihang University | Dong C.,Beihang University
Journal of Guidance, Control, and Dynamics | Year: 2011

A study was conducted to propose a gain-scheduled controller synthesis approach on the basis of stability theory for switched systems evolving on locally overlapped switching law. Switched systems consisted of a collection of subsystems, along with a switching law that specified the switchings between the subsystems. These systems had a wide range of applications in the aerospace field when the switching was with the 'locally overlapped' property. A switched polytopic system was established to describe the plant dynamics within the full flight envelope. Every polytopic subsystem represented the system dynamics in a part of flight envelope and its vertices were the subsystems of a locally overlapped switched system (LOSS) which described the dynamics on operating points within this part of flight envelope. It was proved that the switched polytopic system was input-to-state uniformly bounded on the condition that vertices of any polytopic subsystem shared a common Lyapunov function.

Zhang L.,Beihang University | Liu J.,Beihang University
IET Control Theory and Applications | Year: 2012

This study addresses the problem of trajectory control of a flexible two-link manipulator on the basis of the partial differential equation (PDE) dynamic model. One of the key contributions of this study is that a novel non-linear PDE observer is proposed to estimate distributed positions and velocities along flexible links, which cannot be achieved by the typical ordinary differential equation observer. In addition, the rigidity-flexibility coupling dynamics is decomposed using the singular perturbation approach, thus providing convenience for control design. Based on the proposed observer and the decoupled PDE model, a boundary control scheme is designed to regulate the end effector along reference trajectory in task space and suppress vibration simultaneously. The asymptotic stability of both the proposed observer and the control algorithm is validated by theoretical analysis and demonstrated by simulation results, respectively. © 2012 The Institution of Engineering and Technology.

Li S.,Beihang University | Wang B.,Beihang University | Liu J.,Beihang University | Yu M.,Beihang University
Electrochimica Acta | Year: 2014

A facile method is developed to in situ one-step synthesize CoFe 2O4/graphene (CFO/GN) nanocomposites as a promising high-performance anode for lithium-ion batteries. This method involves two processes occurring simultaneously: Co2+ and Fe2+ ions co-precipitate homogeneously on the surface of graphene oxides by using urea as the precipitant, while in situ reduction process reduces graphene oxides at the same time. As a consequence, the nanocomposites of CFO/GN self-assembled into a three-dimensional (3D) network architecture, in which CoFe2O 4 nanoparticles with the diameter of 50-80 nm uniformly dispersed on graphene sheets. The as-synthesized CFO/GN nanocomposites exhibit a high specific reversible capacity up to 937.73 mAh g-1 with high charge/discharge reversibility at high current densities of 1000 mA g -1. In addition, it shows superior rate capability and good capacity retention of 69.5% after 50 cycles. The improved cyclic stability can be attributed to the synergistic interaction between uniformly dispersed CoFe 2O4 nanoparticles and graphene, which offers the fast diffusion of Li ions (diffusion coefficient: 1.29 × 10-13 cm2 s-1) and low internal resistance (equivalent series resistance: 138.49 Ω cm-2). © 2014 Elsevier Ltd.

Wei L.,Beihang University | Jun W.,Beihang University
IEEE Geoscience and Remote Sensing Letters | Year: 2011

In this letter, a new improved step transform (IST) algorithm is developed for highly squint stripmap synthetic aperture radar (SAR) imaging. Different from the previous step transform algorithms, such as the time-varying step transform algorithm, the new algorithm compensates the cubic phase term and the phase term caused by the varying chirp rate using estimation of the target position focused in the coarse-resolution fast Fourier transform, and these undesirable phase terms can be compensated more appropriately. The algorithm can process SAR imaging under a squint angle of up to 75° in X-band. Simulation results show that the IST algorithm is effective. © 2010 IEEE.

Tie L.,Beihang University | Cai K.-Y.,Beihang University
Systems and Control Letters | Year: 2011

In this paper, the near-controllability and stabilizability of a class of discrete-time bilinear systems are studied. A necessary and sufficient condition for the near-controllability of the systems is first derived. Then, on the basis of the corresponding near-controllability criterion, the stabilizability problem of the systems is solved in turn. © 2011 Elsevier B.V. All rights reserved.

Jia G.Z.,Beihang University | Bai M.,Beihang University
Computers and Industrial Engineering | Year: 2011

Today most research related to manufacturing strategy development concentrates on descriptive processes and conceptual models, and therefore lacks the capability of assessing the supportive degree of manufacturing strategy to competitive priorities, and is also difficult to assess the congruence among various decisions of the manufacturing strategy. This paper proposes an approach for manufacturing strategy development based on quality function deployment (QFD). The study starts by analyzing the process of manufacturing strategy development and the features of QFD. Thereafter, a methodology related to manufacturing strategy development based on QFD is developed, which comprises two stages and eleven steps. This approach uses QFD as a transforming device to link competitive factors with manufacturing decision categories such as structural decision categories and infrastructural categories, and uses QFD as a main tool in different stages of manufacturing strategy development process. This paper also integrates fuzzy set theory and house of quality (HOQ) in order to provide a structural tool to capture the inherent imprecision and vagueness of decision-relevant inputs and to facilitate the analysis of decision-relevant QFD information. A case is given to illustrate the utilization of the proposed approach at the end of this paper. © 2010 Elsevier Ltd. All rights reserved.

Wang J.,Beihang University | Zhao J.,Beihang University | Wang X.,Beihang University
Computers and Industrial Engineering | Year: 2011

In this study, a hybrid manufacturing/remanufacturing system for a kind of short life cycle product with stochastic demand and stochastic returned products was investigated. The objective is to minimize the total cost of the hybrid system. The impacts of the amount of products manufactured and the proportion of the remanufactured part to the returned products on the total cost of the system were analyzed. Through theoretic analyses and numerical experiments, the relationship between the total cost of the system and the two influential factors were identified. The total cost of the hybrid system could be reduced significantly by setting optimum values of the amount of products manufactured and the proportion of the remanufactured part to the returned products. The sensitivity of the optimum values of the decision variables and the minimum cost with respect to the system parameters were also investigated. © 2010 Elsevier Ltd. All rights reserved.

Meng X.G.,Beihang University | Sun M.,Beihang University
Physics of Fluids | Year: 2013

Corrugation gives an insect-wing the advantages of low mass, high stiffness, and low membrane stress. Researchers are interested to know if it is also advantageous aerodynamically. Previous works reported that corrugation enhanced the aerodynamic performance of wings at gliding flight. However, Reynolds numbers considered in these studies were higher than that of gliding insects. The present study showed that in the Reynolds number range of gliding insects, corrugation had negative aerodynamic effects. We studied aerodynamic effects of corrugation at gliding motion using the method of computational fluid dynamics, in the Reynolds number range of Re = 200-2400. Different corrugation patterns were considered. The effect of corrugation on aerodynamic performance was identified by comparing the aerodynamic forces between the corrugated and flat-plate wings, and the underlying flow mechanisms of the corrugation effects were revealed by analyzing the flow fields and surface pressure distributions. The findings are as follows: (1) the effect of corrugation is to decrease the lift, and change the drag only slightly (at 15°-25° angles of attack, lift is decreased by about 16%; at smaller angles of attack, the percentage of lift reduction is even larger because the lift is small). (2) Two mechanisms are responsible for the lift reduction. One is that the pleats at the lower surface of the corrugated wing produce relatively strong vortices, resulting in local low-pressure regions on the lower surface of the wing. The other is that corrugation near the leading edge pushes the leading-edge-separation layer slightly upwards and increases the size of the separation bubble above the upper surface, reducing the "suction pressure," or increasing the pressure, on the upper surface. © 2013 AIP Publishing LLC.

Correctly and effectively quantifying the clarity of microscopy mineral image is important and useful to produce clear image for mineral analysis. To well quantify the clarity of mineral image, an effective measure constructed using the sequentially combined toggle and top-hat based contrast operator is proposed in this article. First, the sequentially combined toggle and top-hat based contrast operator is used to extract the effective features which represent the clarity of mineral image. Second, the multiscale clarity features corresponding to each scale are extracted. Finally, after combining the multiscale clarity features in one feature image, the mean value of the feature image is constructed as the measure of mineral image clarity. Because the sequentially combined toggle and top-hat based contrast operator could effectively extract the clarity features, the clarity features are directly used as the measure of image clarity. Therefore, the proposed measure is effective and reasonable. The experimental results on different types of microscopy mineral images verified the effective performance of the proposed measure. © 2013 Wiley Periodicals, Inc.

Zhang K.,Beihang University | Gu Y.,Beihang University | li M.,Beihang University | Zhang Z.,Beihang University
Materials and Design | Year: 2014

Long processing cycle makes vacuum assisted resin infusion molding (VARIM) only suitable for low and medium volumes of production, and shortening of curing time is critical to improving the processing efficiency of automotive composite parts. In this paper, unidirectional carbon fiber reinforced composite laminates were fabricated by VARIM. Three different processes (namely quick, quick-post and preheating) were employed, in which a kind of rapid curing epoxy resin is used. The preheating of mold and fiber was conducted to shorten the filling time compared with that of quick process. Quick-post process with a post cure stage was investigated to verify the composite properties fabricated by quick process. The cycle time was 16. min for preheating process, about 30% shorter than that of quick process, simultaneously, flexural strength and interlaminar shear strength (ILSS) were respectively improved by 29% and 7% compared with those of quick process. The non-uniformity of mechanical properties at different positions along resin flow direction under preheating process was found, but the processing quality of composite was good. The preheating process is confirmed to be suitable for the improvement of processing efficiency of VARIM with good mechanical properties. In addition, the composite fabricated by quick-post process has better mechanical properties, which is attributed to the alleviation of residual stress during post curing process. © 2013 Elsevier Ltd.

Yang L.-J.,Beihang University | Fu Q.-F.,Beihang University
Journal of Propulsion and Power | Year: 2012

The linear-temporal and spatiotemporal instability behavior of a confined gas-liquid shear flow was investigated theoretically. The practical situation which motivated this investigation is the recessed gas-liquid shear coaxial injector, usually used in liquid propellant rocket engines. The corresponding dispersion relation between the complex wave growth rate and the complex wave number was derived. The temporal stability analysis shows that a more strongly confined gas-liquid shear flow exhibits a larger temporal growth rate than a weakly confined gas- liquid shear flow. A larger nondimensional outer injector radius, a larger liquid-to-gas density ratio and velocity ratio, and a smaller liquid Weber number would stabilize the confined gas-liquid shear flow. In spatiotemporal mode, when the confinement is strong, flow is absolutely unstable. When the confinement becomes weak, the flow can transit to become convectively unstable. Under strong confinement, the confined jet is always absolutely unstable.

Qian Z.,Beihang University | Lee C.-H.,Beihang University
Journal of Computational Physics | Year: 2011

A large time step (LTS) Godunov scheme firstly proposed by LeVeque is further developed in the present work and applied to Euler equations. Based on the analysis of the computational performances of LeVeque's linear approximation on wave interactions, a multi-wave approximation on rarefaction fan is proposed to avoid the occurrences of rarefaction shocks in computations. The developed LTS scheme is validated using 1-D test cases, manifesting high resolution for discontinuities and the capability of maintaining computational stability when large CFL numbers are imposed. The scheme is then extended to multidimensional problems using dimensional splitting technique; the treatment of boundary condition for this multidimensional LTS scheme is also proposed. As for demonstration problems, inviscid flows over NACA0012 airfoil and ONERA M6 wing with given swept angle are simulated using the developed LTS scheme. The numerical results reveal the high resolution nature of the scheme, where the shock can be captured within 1-2 grid points. The resolution of the scheme would improve gradually along with the increasing of CFL number under an upper bound where the solution becomes severely oscillating across the shock. Computational efficiency comparisons show that the developed scheme is capable of reducing the computational time effectively with increasing the time step (CFL number). © 2011 Elsevier Inc.

Wei Y.,Microsoft | Tao L.,Beihang University
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2010

Many computer vision problems rely on computing histogram-based objective functions with a sliding window. A main limiting factor is the high computational cost. Existing computational methods have a complexity linear in the histogram dimension. In this paper, we propose an efficient method that has a constant complexity in the histogram dimension and therefore scales well with high dimensional histograms. This is achieved by harnessing the spatial coherence of natural images and computing the objective function in an incremental manner. We demonstrate the significant performance enhancement by our method through important vision tasks including object detection, object tracking and image saliency analysis. Compared with state-of-the-art techniques, our method typically achieves from tens to hundreds of times speedup for those tasks. ©2010 IEEE.

Zhao Q.,Beihang University | Lin Y.,Beihang University
International Journal of Systems Science | Year: 2011

In this article, an output-feedback adaptive dynamic surface control (DSC) is proposed for a class of nonlinear systems. It is proved that, by using the new scheme, the explosion of the complexity problem in a traditional backstepping design can be eliminated, the semi-global stability of a closed-loop system can be guaranteed and, in particular, by choosing the design parameters and initialising the filters and the update law properly, we show that the L∞ performance of the system-tracking error can be achieved without over-parametrisation. Another advantage of the proposed scheme compared with those traditional backstepping control and current adaptive DSC schemes, whose adaptive control law is obtained through a series of steps recursively, is that the adaptive law is needed only at the first design step, and therefore significantly reduces the design procedure. © 2011 Taylor & Francis.

Xu L.,Beihang University | Liu T.,Beihang University
Journal of Computational Physics | Year: 2011

Since the (original) ghost fluid method (OGFM) was proposed by Fedkiw et al. in 1999 [5], a series of other GFM-based methods such as the gas-water version GFM (GWGFM), the modified GFM (MGFM) and the real GFM (RGFM) have been developed subsequently. Systematic analysis, however, has yet to be carried out for the various GFMs on their accuracies and conservation errors. In this paper, we develop a technique to rigorously analyze the accuracies and conservation errors of these different GFMs when applied to the multi-medium Riemann problem with a general equation of state (EOS). By analyzing and comparing the interfacial state provided by each GFM to the exact one of the original multi-medium Riemann problem, we show that the accuracy of interfacial treatment can achieve " third-order accuracy" in the sense of comparing to the exact solution of the original mutli-medium Riemann problem for the MGFM and the RGFM, while it is of at most " first-order accuracy" for the OGFM and the GWGFM when the interface approach is actually near in balance. Similar conclusions are also obtained in association with the local conservation errors. A special test method is exploited to validate these theoretical conclusions from the numerical viewpoint. © 2011 Elsevier Inc.

Wang J.,Beihang University | Feng L.,Beihang University | Tang Y.,Beihang University | Zhi Y.,Beihang University
Optics Letters | Year: 2015

A resonator integrated optic gyro (RIOG) employing trapezoidal phase modulation (TZPM) technique is proposed, analyzed, and demonstrated for the first time. This technique can provide more information about the whole gyro system without complicating the light circuit structure, making it possible to compensate the gyro output in real time. The experimental results of the RIOG prototype show that the standard deviation is greatly reduced after compensation, which proves the viability and effectiveness of the TZPM technique. A bias stability of 0.09 deg/s with an integration time of 10 s over 3000 s is achieved, which is, to our knowledge, the best long-term performance that ever been reported in a RIOG based on a silica waveguide ring resonator. © 2015 Optical Society of America.

Zhao L.,Beihang University
Optics Express | Year: 2015

We exploit the giant cross-Kerr nonlinearity of electromagnetically induced transparency (EIT) system in ultracold atoms to implement vortex-based multimode manipulation of stored light at low light levels. Using image-bearing signal light fields with angular intensity profiles, sinusoidal grating structures with phase-only modulation can be azimuthally imprinted on the stored probe light field, where the nonlinear absorption loss can be ignored. Upon retrieval of the probe light, collinearly superimposed vortex modes can be generated in the far field. Considering the finite size of atomic gas, the Fraunhofer diffraction patterns of the retrieved probe fields and their spiral spectra are numerically investigated, where the diffracted vortex modes can be efficiently controlled by tuning the weak signal fields. Our studies not only exhibit a fundamental diffraction phenomenon with angular grating structures in EIT system, but also provide a fascinating opportunity to realize multidimensional quantum information processing for stored light in an all-optical manner. © 2015 Optical Society of America.

Wang J.-L.,Beihang University | Wu H.-N.,Beihang University
Neurocomputing | Year: 2012

In this paper, the robust global exponential stability and robust passivity are investigated for a class of parabolic complex networks with multiple time-varying delays. By constructing appropriate Lyapunov functionals and utilizing inequality techniques, several criteria for robust global exponential stability and robust passivity are established. Finally, a numerical example is also given to illustrate the effectiveness of the obtained results. © 2012 Elsevier B.V.

Wang J.,Beihang University | Cheng Q.,Beihang University | Lin L.,State Oceanic Administration | Jiang L.,Beihang University
ACS Nano | Year: 2014

Inspired by the layered aragonite platelet/nanofibrillar chitin/protein ternary structure and integration of extraordinary strength and toughness of natural nacre, artificial nacre based on clay platelet/nanofibrillar cellulose/poly(vinyl alcohol) is constructed through an evaporation-induced self-assembly technique. The synergistic toughening effect from clay platelets and nanofibrillar cellulose is successfully demonstrated. The artificial nacre achieves an excellent balance of strength and toughness and a fatigue-resistant property, superior to natural nacre and other conventional layered clay/polymer binary composites. © 2014 American Chemical Society.

Hua N.,Fujian University of Technology | Zhang T.,Beihang University
Journal of Alloys and Compounds | Year: 2014

The effects of partial substitution of Ni by Ag in Zr56Al 16(Ni1-xAgx) 28 (at.%, x = 0, 0.1, 0.2, 0.3, and 0.4) alloys on their glass-forming ability (GFA), crystallization kinetics, mechanical property, and corrosion behavior were investigated. The critical diameter for glass formation of Zr56Al16Ni28 alloy is significantly enhanced by partially substituting Ag for Ni. The Zr56Al16(Ni 0.7Ag0.3)28 BMG exhibits the best GFA and its critical diameter for glass formation is 20 mm. Ag-bearing Zr-based BMG presents a lower Avrami exponent n than that of Ag-free Zr-Al-Ni BMG, indicating the nucleation rate is reduced by the addition of Ag. The corrosion resistance of Zr-Al-Ni BMG is improved by Ag alloying, and the Zr-Al-Ni-Ag BMG exhibits higher corrosion resistance than that of other known Zr-based BMGs with high GFA. Moreover, the BMGs possess high compressive yield strength of 1830-2000 MPa, large plastic strain of 2.7-3.1%, and high specific strength of 274-312 MPa cm3/g. © 2014 Elsevier B.V. All rights reserved.

Chen D.-R.,Beihang University | Li H.,Beihang University
Neurocomputing | Year: 2012

Based on m randomly drawn vectors in a separable Hilbert space, we investigate the consistency of the regularized regression learning algorithm by using Rademacher averages techniques. Furthermore, random projection technique for speeding up the regression learning algorithm is used. The learning rates of the regularized regression learning algorithm with random projection are established. Theoretical analysis shows that it is possible to learn directly in the projected domain. Our results reflect a tradeoff between accuracy and computational complexity when one uses regularized least square regression algorithm after random projection of the data to a finite dimensional space. © 2012 Elsevier B.V..

Yang X.P.,Beihang University | Zhang G.L.,Beihang University | Zhang H.Q.,China Institute of Atomic Energy
Physical Review C - Nuclear Physics | Year: 2013

The barrier parameters of weakly and tightly bound nuclei on different target nuclei are obtained by the São Paulo potential, and the total reaction cross sections are obtained from analyzing the experimental elastic scattering data. In order to explore the breakup effects we systematically analyze the total reaction function F(x) of weakly and tightly bound projectiles on light, medium-mass, and heavy target nuclei in comparison with the universal function F0(x). From this comparison, we conclude that the breakup effect is not important for weakly bound projectiles on the light target nuclei, is suppressed on medium-mass and heavy target nuclei above the Coulomb barrier, and, oppositely, is enhanced for some weakly bound projectiles at energies near and below the Coulomb barrier. More experiments need to be performed for some unstable weakly bound nuclei on medium-mass and heavy target nuclei at low energies especially at sub-barrier energies. © 2013 American Physical Society.

Sun Z.-Y.,Beihang University | Gao Y.-T.,Beihang University | Yu X.,Beihang University | Liu Y.,Beihang University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2013

We respectively investigate breakup and switching of the Manakov-typed bound vector solitons (BVSs) induced by two types of stochastic perturbations: the homogenous and nonhomogenous. Symmetry-recovering is discovered for the asymmetrical homogenous case, while soliton switching is found to relate with the perturbation amplitude and soliton coherence. Simulations show that soliton switching in the circularly-polarized light system is much weaker than that in the Manakov and linearly-polarized systems. In addition, the homogenous perturbations can enhance the soliton switching in both of the Manakov and non-integrable (linearly- and circularly-polarized) systems. Our results might be helpful in interpreting dynamics of the BVSs with stochastic noises in nonlinear optics or with stochastic quantum fluctuations in Bose-Einstein condensates. © 2013 Elsevier B.V. All rights reserved.

Liang J.,Beihang University | Wang T.,Beihang University | Wen L.,Beihang University
Journal of Field Robotics | Year: 2011

Research on biomimetic robotic fish has been undertaken for more than a decade. Various robotic fish prototypes have been developed around the world. Although considerable research efforts have been devoted to understanding the underlying mechanism of fish swimming and construction of fish-like swimming machines, robotic fish have largely remained laboratory curiosities. This paper presents a robotic fish that is designed for application in real-world scenarios. The robotic fish adopts a rigid torpedo-shaped body for the housing of power, electronics, and payload. A compact parallel four-bar mechanism is designed for propulsion and maneuvering. Based on the kinematic analysis of the tail mechanism, the motion control algorithm of joints is presented. The swimming performance of the robotic fish is investigated experimentally. The swimming speed of the robotic fish can reach 1.36 m/s. The turning radius is 1.75 m. Powered by the onboard battery, the robotic fish can operate for up to 20 h. Moreover, the advantages of the biomimetic propulsion approach are shown by comparing the power efficiency and turning performance of the robotic fish with that of a screw-propelled underwater vehicle. The application of the robotic fish in a real-world probe experiment is also presented. © 2010 Wiley Periodicals, Inc.

Xu N.,Beihang University | Sun M.,Beihang University
Bioinspiration and Biomimetics | Year: 2014

Many insects hover with their wings beating in a horizontal plane ('normal hovering'), while some insects, e.g., hoverflies and dragonflies, hover with inclined stroke-planes. Here, we investigate the lateral dynamic flight stability of a hovering model hoverfly. The aerodynamic derivatives are computed using the method of computational fluid dynamics, and the equations of motion are solved by the techniques of eigenvalue and eigenvector analysis. The following is shown: The flight of the insect is unstable at normal hovering (stroke-plane angle equals 0) and the instability becomes weaker as the stroke-plane angle increases; the flight becomes stable at a relatively large stroke-plane angle (larger than about 24°). As previously shown, the instability at normal hovering is due to a positive roll-moment/side-velocity derivative produced by the 'changing-LEV-axial-velocity' effect. When the stroke-plane angle increases, the wings bend toward the back of the body, and the 'changing-LEV-axial-velocity' effect decreases; in addition, another effect, called the 'changing-relative-velocity' effect (the 'lateral wind', which is due to the side motion of the insect, changes the relative velocity of its wings), becomes increasingly stronger. This causes the roll-moment/side-velocity derivative to first decrease and then become negative, resulting in the above change in stability as a function of the stroke-plane angle. © 2014 IOP Publishing Ltd.

Pei Y.-L.,Beihang University | Wu H.,South University of Science and Technology of China | Wu D.,South University of Science and Technology of China | Zheng F.,South University of Science and Technology of China | He J.,South University of Science and Technology of China
Journal of the American Chemical Society | Year: 2014

We report a greatly enhanced thermoelectric performance in a BiCuSeO system, realized by improving carrier mobility through modulation doping. The heterostructures of the modulation doped sample make charge carriers transport preferentially in the low carrier concentration area, which increases carrier mobility by a factor of 2 while maintaining the carrier concentration similar to that in the uniformly doped sample. The improved electrical conductivity and retained Seebeck coefficient synergistically lead to a broad, high power factor ranging from 5 to 10 W cm-1 K-2. Coupling the extraordinarily high power factor with the extremely low thermal conductivity of 0.25 W m-1 K-1 at 923 K, a high ZT - 1.4 is achieved in a BiCuSeO system. © 2014 American Chemical Society.

Wang W.,Beihang University | Zhou C.,Beihang University
Corrosion Science | Year: 2013

Hot corrosion behaviour of Nb-16Si-24Ti-6Cr-6Al-2Hf (at.%) in the mixture of Na2SO4 and NaCl melts at 900°C was studied. The results show that the corrosion kinetics of the alloy fit parabolic law. The oxides consist of a loose and porous outer layer and an internal oxidation zone. Outer oxides are mainly composed of TiO2, TiNb2O7, Nb2O5, CrNbO4 and SiO2 while the internal oxidation zone is composed of TiO2. Hot corrosion mechanism of the alloy in the presence of Na2SO4 and NaCl deposits is discussed. © 2013 Elsevier Ltd.

Cai J.-Y.,University of Wisconsin - Madison | Cai J.-Y.,Beihang University | Chen X.,University of Southern California
Proceedings - Annual IEEE Symposium on Foundations of Computer Science, FOCS | Year: 2010

The complexity of graph homomorphism problems has been the subject of intense study. It is a long standing open problem to give a (decidable) complexity dichotomy theorem for the partition function of directed graph homomorphisms. In this paper, we prove a decidable complexity dichotomy theorem for this problem and our theorem applies to all non-negative weighted form of the problem: given any fixed matrix A with non-negative algebraic entries, the partition function Z A(G) of directed graph homomorphisms from any directed graph G is either tractable in polynomial time or #P-hard, depending on the matrix A. The proof of the dichotomy theorem is combinatorial, but involves the definition of an infinite family of graph homomorphism problems. The proof of its decidability is algebraic using properties of polynomials. © 2010 IEEE.

Luo X.,Beihang University | Li R.,Beihang University | Huang L.,Beihang University | Zhang T.,Beihang University
Corrosion Science | Year: 2013

Mg90-xCuxY10 glassy precursors have been used to synthesize nanoporous copper (NPC) by electrochemical dealloying in H2SO4 aqueous solution. The formation mechanism of NPC during electrochemical dealloying of Mg90-xCuxY10 metallic glasses is mainly governed by dissolution and diffusion processes at the precursor/solution interfaces. A diffusion growth model was provided to reveal a quantitative relationship between the ligament size and the dealloying conditions. The ligament size of NPC shows a linear correlation with Cu content in the glassy precursors. Moreover, the ligaments can be significantly coarsened with prolongation of leaching time or elevation of leaching temperature. © 2012 Elsevier Ltd.

Guan P.,Johns Hopkins University | Lu S.,Beihang University | Spector M.J.B.,Johns Hopkins University | Valavala P.K.,Johns Hopkins University | Falk M.L.,Johns Hopkins University
Physical Review Letters | Year: 2013

Molecular dynamics simulations of cavitation in a Zr50Cu 50 metallic glass exhibit a waiting time dependent cavitation rate. On short time scales nucleation rates and critical cavity sizes are commensurate with a classical theory of nucleation that accounts for both the plastic dissipation during cavitation and the cavity size dependence of the surface energy. All but one parameter, the Tolman length, can be extracted directly from independent calculations or estimated from physical principles. On longer time scales strain aging in the form of shear relaxations results in a systematic decrease of cavitation rate. The high cavitation rates that arise due to the suppression of the surface energy in small cavities provide a possible explanation for the quasibrittle fracture observed in metallic glasses. Published by the American Physical Society under the terms of the © 2013 American Physical Society.

Xu Y.P.,Beihang University | Pang D.Y.,Beihang University
Physical Review C - Nuclear Physics | Year: 2013

A systematic nucleus-nucleus potential is proposed based on an optical model analysis of angular distributions of differential cross sections of 6Li and 7Li elastic scattering from targets with A≥40 with incident energies between 5 and 40 MeV/nucleon. A single-folding model based on the Bruyères Jeukenne-Lejeune-Mahaux (JLMB) model nucleon-nucleus potentials was used. Systematics in energy dependence of the potential parameters were obtained. This systematics was found to give reasonable account for both elastic scattering and total reaction cross sections for projectiles with mass numbers up to A∼40, including both stable and unstable nuclei, for incident energies from the vicinity of the Coulomb barrier to about 100 MeV/nucleon. © 2013 American Physical Society.

Wang Z.F.,University of Utah | Jin S.,Beihang University | Liu F.,University of Utah
Physical Review Letters | Year: 2013

A graphene nanoribbon with sawtooth edges has a ferromagnetic ground state. Using first-principles and tight-binding model calculations, we show that, under a transverse electrical field, the sawtooth graphene nanoribbons become a spin semiconductor whose charge carriers are not only spin polarized in energy space but also spatially separated at different edges. Low-energy excitation produces spin-up electrons localized at one edge and spin-down holes at the opposite edge, and the excitation energy of spin carries can be tuned by the electric field to reach a new state of spin gapless semiconductor. Also, the spin semiconducting states are shown to be robust against at least 10% edge disorder. These features demonstrate a good tunability of spin carriers for spintronics applications. © 2013 American Physical Society.

Qiao M.,Beihang University | Zhou C.,Beihang University
Corrosion Science | Year: 2013

Based on the results of thermochemical analysis, NH4I+NH4Cl proved to be a more favorable activator for codepositing Co-Al-Y compared to NH4I or NH4Cl. Coating deposition experiments were also demonstrated that codeposition of Co-Al-Y with high concentration of Co and minute quantities of Y could be achieved at 1323K in the NH4I+NH4Cl activated packs. The coating exhibited the best cyclic oxidation resistance at 1323K when NH4I+NH4Cl were used as activator. © 2013.

Guo H.-M.,Beihang University
Science China: Physics, Mechanics and Astronomy | Year: 2016

Recently one-dimensional topological phases are gaining increasing attentions. Like two- and three-dimensional ones, Onedimensional systems are important in a complete understanding of the topological properties. One-dimensional topological phases have been realized using current experimental setups. Specially the signatures of Majorana fermions have been observed in onedimensional topological superconductors engineered with Rashiba nanowires. From the many studies, the paper reviews typical theoretical models of one-dimensional topological insulators and superconductors. For one-dimensional topological insulators, we introduce the Su-Schrieffer-Heeger, superlattices and Creutz models, while for topological superconductors the Kitaev model and Rashiba nanowire are introduced. These models not only provide an overview of one-dimensional topological phases, but also are the starting points for further studies. © 2016, Science China Press and Springer-Verlag Berlin Heidelberg.

Wei Z.,Beihang University | Liu X.,Beihang University
Optics Express | Year: 2015

Based on analyzing the measurement model of binocular vision sensor, we proposed a new flexible calibration method for binocular vision sensor using a planar target with several parallel lines. It only requires the sensor to observe the planar target at a few (at least two) different orientations. Relying on vanishing feature constraints and spacing constraints of parallel lines, linear method and nonlinear optimization are combined to estimate the structure parameters of binocular vision sensor. Linear method achieves the separation of the rotation matrix and translation vector which reduces the complexity of computation; Nonlinear algorithm ensures the calibration results for the global optimization. Towards the factors that affect the accuracy of the calibration, theoretical analysis and computer simulation are carried out respectively consequence in qualitative analysis and quantitative result. Real data shows that the accuracy of the proposed calibration method is about 0.040mm with the working distance of 800mm and the view field of 300 × 300mm. The comparison with Bougust toolbox and the method based on known length indicates that the proposed calibration method is precise and is efficient and convenient as its simple calculation and easy operation, especially for onsite calibration and selfcalibration. © 2015 Optical Society of America.

Cao X.,Capital Medical University | Cao X.,Beihang University | Wang N.,Beihang University
Analyst | Year: 2011

Fe 2O 3 was generally considered to be biologically and electrochemically inert, and its electrocatalytic functionality has been rarely realized directly in the past. In this work, Fe 2O 3 nanowire arrays were synthesized and electrochemically characterized. The as prepared Fe 2O 3 nanomaterial was proved to be an ideal electrode material due to the intrinsic peroxidase-like catalytic activity. The Fe 2O 3 nanowire array modified glucose sensor exhibited excellent biocatalytic performance towards the oxidation of glucose with a response time of <6 s, a linear range between 0.015-8 mM, and sensitivity of 726.9 μA mM -1cm -1. Additionally, a high sensing selectivity towards glucose oxidation in the presence of ascorbic acid (AA) and dopamine (DA) has also been obtained at their maximum physiological concentrations, which makes the Fe 2O 3 nanomaterial promising for the development of effective electrochemical sensors for practical applications. © 2011 The Royal Society of Chemistry.

Bing P.,Beihang University | W D.,Beihang University | Xia Y.,Tsinghua University
Optics and Lasers in Engineering | Year: 2012

Conventional digital image correlation (DIC) technique using a fixed reference image provides high-accuracy measurements but normally fails when serious decorrelation effect occurs in the deformed images due to large deformation, serious illumination fluctuations or other reasons. In this paper, an incremental reliability-guided digital image correlation (RG-DIC) technique, by combining the recently developed RG-DIC technique and an automatic reference image updating scheme, is proposed for large deformation measurement. In the incremental RG-DIC technique, a seed point is defined in the original reference image and searched in the deformed images, if the estimated correlation coefficient is larger than a preset threshold, which means no serious decorrelation effect exists in the deformed image, the RG-DIC technique is used to continue correlation analysis to obtain full-field displacements. Otherwise, the image recorded just before the current deformed image is chosen as an updated reference image to proceed with correlation analysis. Afterwards, the incremental displacements extracted by comparing the current deformed image and the updated reference image can be cumulated to determine the overall deformation. The effectiveness of the proposed technique is demonstrated by retrieving the full-field deformation of a foam sample subjected to large compressive deformation. © 2011 Elsevier Ltd. All rights reserved.

Zhou J.R.,Beihang University | Sha J.B.,Beihang University
Intermetallics | Year: 2013

This paper deals with phase constitutions, microstructural evolutions, and mechanical properties of Nb-16Si-xFe in-situ composites (where x = 2, 4, 6 at.%, referred as to 2Fe, 4Fe and 6Fe alloys, hereafter) prepared by arc-melting. It is found that with additions of Fe, Nb4FeSi silicide arises and microstructures of as-cast samples are consisted of dendritic-like NbSS phase, Nb3Si block, and Nb4FeSi matrix in the 2Fe and 4Fe alloys, and of the dendritic-like NbSS phase and Nb4FeSi matrix in the 6Fe alloy. When heat-treated at 1350°C for 100 h, part of the Nb3Si phase decomposes in the 2Fe and 4Fe alloys, and the 6Fe alloy shows no change in microstructure as compared with the as-cast one. The Nb4FeSi silicide is found to be brittle, its fracture toughness and elastic modulus are first obtained, having values about 1.22 MPa m1/2, and 310 GPa, respectively. The fracture toughness of the bulk as-cast and heat-treated Nb-16Si-xFe samples are changed slightly by the Fe additions, which is in a range of 9.03-10.19 MPa m1/2. It is interesting that at room temperature, strength is improved by the Fe additions, whereas at 1250°C and 1350°C the strength decreases. As the Fe content increased from 2 at.% to 6 at.%, for example, the 0.2% yield strength increases from 1410 MPa to 1580 MPa at room temperature, decreases from 479 MPa to 385 MPa at 1250°C. © 2012 Elsevier Ltd. All rights reserved.

Wu H.-N.,Beihang University | Luo B.,Beihang University
Industrial and Engineering Chemistry Research | Year: 2012

This work considers the optimal control problem of linear continuous-time hyperbolic partial differential equation (PDE) systems with partially unknown system dynamics. To respect the infinite-dimensional nature of the hyperbolic PDE system, the problem can be reduced to finding a solution of the space-dependent Riccati differential equation (SDRDE), which requires the full system model. Therefore, a heuristic dynamic programming (HDP) algorithm is proposed to achieve online optimal control of the hyperbolic PDE system, which online collects data accrued along system trajectories and learns the solution of the SDRDE without requiring the internal system dynamics. The convergence of HDP algorithm is established by showing that the HDP algorithm generates a nondecreasing sequence which uniformly converges to the solution of the SDRDE. For implementation purposes, the HDP algorithm is realized by developing an approximate approach based on the method of weighted residuals. Finally, the application on a steam-jacketed tubular heat exchanger demonstrates the effectiveness of the developed control approach. © 2012 American Chemical Society.

Cao Y.,Beihang University | Zhou C.,Beihang University
Journal of Magnetism and Magnetic Materials | Year: 2012

Soft magnetism and magnetic anisotropy properties of CoZrNb thin films deposited on polyethylene terephthalate (PET) substrate by magnetron sputtering were investigated. As the film thickness increases, the coercivity of films decreases from 7 to 4 Oe. It exhibits an in-plane uniaxial magnetic anisotropy as the thickness of CoZrNb thin films increases. An easy axis is observed in CoZrNb films along the direction transverse to the rolling direction of the polymer web. © 2012 Elsevier B.V. All rights reserved.

Liang Y.-J.,Beihang University | Liu D.,Beihang University | Wang H.-M.,Beihang University
Scripta Materialia | Year: 2014

The mechanical behavior of commercial purity Ti (CP-Ti)/Ti-6Al-2Zr-1Mo-1 V structurally graded materials (SGMs) fabricated by laser additive manufacturing was investigated via uniaxial tensile experiments. Although the strength of all SGM specimens is higher than that of the monolithic CP-Ti specimens, only the SGM specimen of ∅10 mm gauge diameter with bulky α-grains exhibits excellent plasticity comparable to the CP-Ti specimen under the same conditions. The SGM presents a potential for use as load-bearing components due to its good strength-ductility balance. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Wan T.,Boston University | Zhu C.,Beihang University | Qin Z.,Beihang University
Pattern Recognition Letters | Year: 2013

Multifocus image fusion has emerged as a major topic in computer vision and image processing community since the optical lenses for most widely used imaging devices, such as auto-focus cameras, have a limiting focus range. Only objects at one particular depth will be truly in focus while out-of-focus objects will become blurry. The ability to create a single image where all scene areas appear sharp is desired not only in digital photography but also in various vision-related applications. We propose a novel image fusion scheme for combining two or multiple images with different focus points to generate an all-in-focus image. We formulate the problem of fusing multifocus images as choosing the most significant features from a sparse matrix obtained by a newly developed robust principal component analysis (RPCA) decomposition method to form a composite feature space. The local sparse features that represent salient information of the input images (i.e. sharp regions) are integrated to construct the resulting fused image. Experimental results have demonstrated that it is consistently superior to the other existing state-of-the-art fusion methods in terms of visual and quantitative evaluations. © 2013 Elsevier B.V.

Song Y.,Beihang University
Nano-Micro Letters | Year: 2010

One process based on phase inversion of fillers in microstructures for the fabrication of multi-level three-dimensional (3-D) microstructures is described using SU-8, a kind of epoxy photoresist, as the model constructing materials. This process is depicted by use of the routine photolithography technique to construct the top layer of 3-D microstructures on the bottom layer of 3-D microstructures layer by layer. This process makes it possible to fabricate multi-level 3-D microstructures with connectors at desired locations, and to seal long span microstructures (e.g. very shallow channels with depth less than 50 μm and width more than 300 μm) without blockage. In addition, this process can provide a sealing layer by the solidification of a liquid polymer layer, which can be as strong as the bulk constructing materials for microstructures due to a complete contact and cross-linking between the sealing layer and the patterned layers. The hydrodynamic testing indicates that this kind of sealing and interconnection can endure a static pressure of more than 10 MPa overnight and a hydrodynamic pressure drop of about 5.3 MPa for more than 8 hours by pumping the tetrahydrofuran solution through a 60 μm wide micro-channels.

Wang Y.,Beihang University | Xu S.,Beihang University
Nonlinear Dynamics | Year: 2014

The full dynamics of a spacecraft around an asteroid, in which the gravitational orbit–attitude coupling is considered, has been shown to be of great value and interest. Nonlinear stability of the relative equilibria of the full dynamics of a rigid spacecraft around a uniformly rotating asteroid is studied with the method of geometric mechanics. The non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are given in the differential geometric method. A classical kind of relative equilibria of the spacecraft is determined from a global point of view, at which the mass center of the spacecraft is on a stationary orbit, and the attitude is constant with respect to the asteroid. The conditions of nonlinear stability of the relative equilibria are obtained with the energy-Casimir method through the semi-positive definiteness of the projected Hessian matrix of the variational Lagrangian. Finally, example asteroids with a wide range of parameters are considered, and the nonlinear stability criterion is calculated. However, it is found that the nonlinear stability condition cannot be satisfied by spacecraft with any mass distribution parameters. The nonlinear stability condition by us is only the sufficient condition, but not the necessary condition, for the nonlinear stability. It means that the energy-Casimir method cannot provide any information about nonlinear stability of the relative equilibria, and more powerful tools, which are the analogues of the Arnold’s theorem in the canonical Hamiltonian system with two degrees of freedom, are needed for a further investigation. © 2014, Springer Science+Business Media Dordrecht.

Tang T.,Beihang University | Shi W.,Beihang University | Shang H.,Capital University of Economics and Business | Wang Y.,Beihang University
Nonlinear Dynamics | Year: 2014

In this paper, we construct a new car-following model with inter-vehicle communication (IVC) to study the driving behavior under an accident. The numerical results show that the proposed model can qualitatively describe the effects of IVC on each vehicle's speed, acceleration, movement trail, and headway under an accident and that the new model can overcome the full velocity difference (FVD) model's shortcoming that collisions occur under an accident, which illustrates that the new model can better describe the driving behavior under an accident than the FVD model. © 2014 Springer Science+Business Media Dordrecht.

Zhang X.-J.,Beihang University | Wang G.-S.,Beihang University | Wei Y.-Z.,Beihang University | Guo L.,Beihang University | Cao M.-S.,Beijing Institute of Technology
Journal of Materials Chemistry A | Year: 2013

Novel reduced graphene oxide (RGO)/CuS nanocomposites, featuring CuS microspheres embedded in reduced graphene oxide (RGO) layers, are successfully fabricated by using an in situ growth approach in the presence of cexadecyl trimethyl ammonium bromide (CTAB) under mild wet-chemical conditions (140 °C). Characterization of the nanocomposites indicates that the CuS complex microspheres with relatively uniform size are embedded in the RGO layers to form unique core-shell nanostructures. A simple hot-press process is employed to synthesize the RGO/CuS/PVDF composites. With a filler loading of 15 wt%, the dielectric constant of the composites can reach 36 at 2 GHz, which is 10 times higher than that of pure PVDF. The composites with a filler loading of 5 wt% exhibit high values of reflection loss and the maximum loss is 32.7 dB at 10.7 GHz when the thickness is just 2.5 mm, and it can be adjusted by the thickness. The enhanced mechanism is also explained based on the Debye dipolar relaxation of the composites. The composite with a high dielectric constant is a promising material in high capacitance, while the composite with enhanced absorption can decrease the environmental pollution caused by microwave irradiation. © 2013 The Royal Society of Chemistry.

Gao H.,Beihang University | Zhang Y.,Beihang University
Nonlinear Dynamics | Year: 2014

In this paper, the nonlinear vibration characteristics of geared rotor bearing system and the interactions among gears, shafts, and plain journal bearings were studied. First, with the consideration of backlash, transmission error, time-varying mesh stiffness, and layout parameters, the dynamic model of geared rotor bearing system featuring confluence transmission was proposed. The nonlinear oil-film forces were computed with the Reynolds equation for finite-length journal bearings. Second, the responses of meshing vibration and bearing vibration were discussed. The numerical results revealed that the system exhibited a diverse range of periodic, sub-harmonic, and chaotic behaviors. Under different ranges of rolling frequency, the system got into chaos state through different roads. Moreover, in lower frequency, meshing vibration showed coexist of different periodic motions. Lastly, couplings of nonlinear oil-film force and nonlinear gear mesh force were discussed through a range of rolling frequencies. Gear-bearing dynamic interactions were demonstrated through the analysis of dynamic gear loads and dynamic bearing loads, and the coupling effect behaved different when rolling frequency changed. © 2014 Springer Science+Business Media Dordrecht.

Guo R.-Y.,Inner Mongolia University | Huang H.-J.,Beihang University
Journal of Statistical Mechanics: Theory and Experiment | Year: 2011

A method for formulating the route choice behavior of pedestrians in evacuation in closed areas with internal obstacles is proposed. The method is implemented in a pedestrian model, in which the route choice is determined by the potential of discrete space. The potential measures the total effect of such factors affecting route choice as route distance, pedestrian congestion and route capacity. Using scenario simulations, the proposed method is compared with several existing methods. Simulation results indicate that the proposed method can simulate two classes of phenomena that cannot be reproduced accurately by those existing methods. In addition, two examples of inefficient evacuation as regards route choice are given. The two examples illustrate that, for improving the efficiency of evacuation, excessive or limited sensitivity of pedestrians to the route capacity may be unhelpful, and adding an extra route may be inefficient. © 2011 IOP Publishing Ltd and SISSA.

Xiang Y.,Beihang University | Lu S.,Beihang University | Jiang S.P.,Curtin University Australia
Chemical Society Reviews | Year: 2012

As one of the most effective synthesis tools, layer-by-layer (LbL) self-assembly technology can provide a strong non-covalent integration and accurate assembly between homo- or hetero-phase compounds or oppositely charged polyelectrolytes, resulting in highly-ordered nanoscale structures or patterns with excellent functionalities and activities. It has been widely used in the developments of novel materials and nanostructures or patterns from nanotechnologies to medical fields. However, the application of LbL self-assembly in the development of highly efficient electrocatalysts, specific functionalized membranes for proton exchange membrane fuel cells (PEMFCs) and electrode materials for supercapacitors is a relatively new phenomenon. In this review, the application of LbL self-assembly in the development and synthesis of key materials of PEMFCs including polyelectrolyte multilayered proton-exchange membranes, methanol-blocking Nafion membranes, highly uniform and efficient Pt-based electrocatalysts, self-assembled polyelectrolyte functionalized carbon nanotubes (CNTs) and graphenes will be reviewed. The application of LbL self-assembly for the development of multilayer nanostructured materials for use in electrochemical supercapacitors will also be reviewed and discussed (250 references). © 2012 The Royal Society of Chemistry.

Song C.,Beihang University | Zheng Y.,Beihang University
Journal of Colloid and Interface Science | Year: 2014

Creatures have evolved the unique wetting-controlled strategies on their surfaces to collect water for the sake of survival, such as Beetle back, spider silk and plant leaf as well, which inspires us to open the area of novel researches. In this feature article, we review the theoretical basis of wetting-controlling regarding of wettability and highlight the biological wetting-controlled strategies in water transport, and water collection, and also introduce some bio-inspired materials with water collection properties. It is significant to design the novel materials that would be used in the fields of responsive, smart catalysis, filtration and sensing besides water collection. © 2013.

Image decomposition and reconstruction is an important way for image analysis. To be effective for image decomposition and reconstruction, a method using extracted features through top-hat transform-based morphological contrast operator (MCOTH) is proposed in this paper. First, the morphological contrast operator constructed using the top-hat transforms is discussed. Then, extracting the bright and dark image features in the result of MCOTH is given. Based on the extracted bright and dark image features, the original images are decomposed into multiscale complete decompositions using multiscale structuring elements. After processing the decomposed images following different application purposes, the final result image can be reconstructed from the processed decomposition images. To verify the effectiveness of the proposed image analysis method through image decomposition and reconstruction, the application of image enhancement and fusion are discussed. The experimental results show that because the proposed image decomposition and reconstruction method reasonably decomposes the original image into complete decomposition with useful image features at different scales, the useful image features could be easily used for different applications. After the useful image features are processed, the final result image could be reconstructed. Moreover, different types of images are used in the experiments of image enhancement and fusion, and the results are effective. Therefore, the proposed image decomposition and reconstruction method in this paper are effective methods for image analysis and could be widely used in different applications. © 2013 Optical Society of America.

Wang Q.,Beihang University | Chen G.,City University of Hong Kong
Chaos | Year: 2011

We study the dependence of synchronization transitions in scale-free networks of bursting neurons with hybrid synapses on the information transmission delay and the probability of inhibitory synapses. It is shown that, irrespective of the probability of inhibitory synapses, the delay always plays a subtle role during synchronization transition of the scale-free neuronal networks. In particular, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as well-expressed minima in the measure for spatiotemporal synchrony. In addition, it is found that, for smaller and larger probability of inhibitory synapses, intermittent synchronization transition is relatively profound, while for the moderate probability of inhibitory synapses, synchronization transition seems less profound. More interestingly, it is found that as the probability of inhibitory synapses is large, regions of synchronization are upscattering. © 2011 American Institute of Physics.

Zhang T.,Beihang University | Shi Z.,Beijing Jiaotong University
Smart Materials and Structures | Year: 2011

An analytical model of the dynamic properties of the 2-2 cement based piezoelectric transducer is proposed using the piezoelectric effect, based on Li's experiments. Then, the exact solutions are obtained by using the displacement method; comparison and discussion with Li's experimental results in related literature are also given and good agreement is found, which could be used for better understanding of Li's experiment. A theoretical method for applying the cement based piezoelectric composite in civil engineering is provided. © 2011 IOP Publishing Ltd.

Pan B.,Beihang University
Experimental Mechanics | Year: 2011

In this paper, we report the following important progress recently made in the basic theory and practical implementation of digital image correlation (DIC) for deformation measurement. First, we answer a basic but confusing question to the users of DIC: what is a good speckle pattern for DIC? We present a simple, easy-to-compute yet effective global parameter, called mean intensity gradient, for quality assessment of the entire speckle pattern. Second, we provide an overview of various correlation criteria used in DIC for evaluating the similarity of the reference and deformed subsets, and demonstrate the equivalence of three robust and most widely used correlation criteria, i. e., a zero-mean normalized cross-correlation (ZNCC) criterion, a zero-mean normalized sum of squared difference (ZNSSD) criterion and a parametric zero-mean normalized sum of squared difference (PSSD ab) criterion with two additional unknown parameters, which elegantly unifies these correlation criteria for subset-based pattern matching. Third, we describe an iterative least squares (ILS) algorithm for accurate subpixel motion detection, which is proved to be equivalent to the existing Newton-Raphson algorithm, but the principle and implementation of ILS algorithm is more straightforward and easier. Finally, to overcome the two limitations of existing subset-based DIC technique, we introduce a robust and generally applicable reliability-guided DIC technique, in which the calculation path is guided by the ZNCC coefficients of computed points, to determine the genuine full-field deformation of an object with complex shape. © 2010 Society for Experimental Mechanics.

Jiancheng F.,Beihang University | Sheng Y.,Beihang University
IEEE Transactions on Instrumentation and Measurement | Year: 2011

The Position and Orientation measurement System (POS) is a dedicated Strapdown Inertial Navigation System (SINS)/Global Positioning System (GPS) integrated system for airborne remote sensing. In-flight alignment (IFA) is an effective way to improve the accuracy and speed of initial alignment for an airborne POS. During IFA, the GPS provides the position and velocity references for the SINS, so the alignment accuracy will be degraded by unstable GPS measurements. To improve the alignment accuracy under unstable GPS measurement, an adaptive filtering algorithm of an extended Kalman filter (EKF) combined with innovation-based adaptive estimation is proposed, which introduces the calculated innovation covariance into the computation of the filter gain matrix directly. Then, this innovation adaptive EKF algorithm is used for the IFA of the POS with a large initial heading error. Moreover, it is optimized by blocked matrix multiplication to reduce the computational burden and improve the real-time performance. To validate the proposed algorithm, the car-mounted IFA experiment is carried out for the prototype of the airborne POS (TX-D10) under a turning maneuver, taking Applanix's POS/AV510 as a reference and changing the GPS measurement artificially. The experiment results demonstrate that the proposed algorithm can reach a better alignment accuracy than the EKF under unknown GPS measurement noises. © 2006 IEEE.

Lin P.,University of Electronic Science and Technology of China | Lin P.,Beihang University | Jia Y.,Beihang University
Automatica | Year: 2011

This paper investigates consensus problems in networks of continuous-time agents with diverse time-delays and jointly-connected topologies. For convergence analysis of the networks, a class of LyapunovKrasovskii functions is constructed which contains two parts: one describes the current disagreement dynamics and the other describes the integral impact of the dynamics of the whole network over the past. By a contradiction approach, sufficient conditions are derived under which all agents reach consensus, even though the communication structures between agents dynamically change over time and the corresponding graphs may not be connected. The obtained conditions are composed of a sum of decoupled parts corresponding to each possible connected component of the communication topology. Finally, numerical examples are included to illustrate the obtained results. Copyright © 2011 Published by Elsevier Ltd. All rights reserved.

Chen H.-X.,University of Valencia | Chen H.-X.,Beihang University | Oset E.,University of Valencia
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

The aim of this paper is to investigate an efficient strategy that allows one to obtain ππ phase shifts and ρ meson properties from QCD lattice data with high precision. For this purpose we evaluate the levels of the ππ system in the ρ channel in finite volume using chiral unitary theory. We investigate the dependence on the π mass and compare this with other approaches which use QCD lattice calculations and effective theories. We also illustrate the errors induced by using the conventional Lüscher approach instead of a more accurate one that was recently developed that takes into account exactly the relativistic two-meson propagators. Finally, we make use of this latter approach to solve the inverse problem, getting ππ phase shifts from "synthetic" lattice data, providing an optimal strategy and showing which accuracy is needed in these data to obtain the ρ properties with a desired accuracy. © 2013 American Physical Society.

Bai X.,Beihang University | Zhou F.,Beihang University | Xue B.,Beihang University
Optics Express | Year: 2011

Fusion of infrared and visual images is an important research area in image analysis. The purpose of infrared and visual image fusion is to combine the image information of the original images into the final fusion result. So, it is crucial to effectively extract the image information of the original images and reasonably combine them into the final fusion image. To achieve this purpose, an algorithm by using multi scale center-surround top-hat transform through region extraction is proposed in this paper. Firstly, multi scale center-surround top-hat transform is discussed and used to extract the multi scale bright and dim image regions of the original images. Secondly, the final extracted image regions for image fusion are constructed from the extracted multi scale bright and dim image regions. Finally, after a base image is calculated from the original images, the final extracted image regions are combined into the base image through a power strategy to form the final fusion result. Because the image information of the original images are well extracted and combined, the proposed algorithm is very effective for image fusion. Comparison experiments have been performed on different image sets, and the results verified the effectiveness of the proposed algorithm. © 2011 Optical Society of America.

Ling Y.,Beihang University
Applied Mechanics and Materials | Year: 2014

This paper designs a single neuron PID controller for the loading system which can simulate the load in the process of landing gear turning. As artificial neurons have the adaptive, self-learning and more fault-tolerant characteristics, the controller based on single neuron PID can improve performance of loading system. To assess the effectiveness of controller, united simulation between Matlab/Simulink and AMESim was conducted. Obtained results show the proposed approach is satisfactory in fast response, small overshoot, high control accuracy, strong anti-interference ability and robustness when compared with traditional PID controller. © (2014) Trans Tech Publications, Switzerland.

Wang Z.,Beihang University | Xu Y.,Beihang University | Suman B.,Clinic Heath Care Pvt. Ltd.
Ultrasonics Sonochemistry | Year: 2015

This paper presents an overview of research status and development trend of ultrasonic oil production technique for Enhanced Oil Recovery in China. As one of EOR techniques, ultrasonic oil production attracts more attention due to its simplicity, lower expenses, good applicability and no reservoir pollution. Through the comparison of the development of ultrasonic oil production both in China and other countries, this paper summarize the recent research progress in ultrasonic oil production techniques and practices in China. Finally, the development of oil production equipment and development trend of ultrasonic oil production technique in China are given. © 2015 Elsevier B.V. All rights reserved.

Liu B.,Beihang University | Xing Y.,Beihang University
European Journal of Mechanics, A/Solids | Year: 2011

All possible exact solutions are successfully obtained for the first time in terms of 10 sets of distinct eigensolutions for the free in-plane vibration of orthotropic rectangular plates when two opposite plate edges are either type of simple support, the other two edges are any combination of classical edge conditions. The exact solutions are validated through both mathematical proof and comparisons with the solutions of differential quadrature method. Some unusual phenomena are revealed in free in-plane vibrations of rectangular plates due to one of the eigenvalues being zero. This work constitutes a natural extension of very recent corresponding work for isotropic rectangular plates by the same authors. Moreover, this work substantially simplified both solution forms and solving procedure of the early work. It is expected that results tabulated here can serve as the benchmarks for the validation of the numerical methods. © 2011 Elsevier Masson SAS. All rights reserved.

Luo Y.,Beihang University | Luo Y.,George Washington University
Journal of Mechanics in Medicine and Biology | Year: 2015

It has gradually developed into an undisputable fact that sharkskin surface has the obvious drag reduction effect compared with the absolutely smooth skins, and it has been put into application widely, which has brought great advantages and profits in daily life, industry and agriculture. Because some problems in turbulence are not resolved completely and perfectly, the drag reduction mechanism of real sharkskin has also not been understood absolutely and thoroughly so far. However, many researchers have carried out lots of the relevant experiments and analyses, very plentiful and important conclusions are obtained, which can explain some certain phenomena of sharkskin drag reduction effect. An overview of exploring drag reduction mechanism of real sharkskin surface is systemically presented in detail. These mechanisms include inhibition of turbulence using micro/nano structured morphology, influence of scale's attack angles, nano-long chains and boundary layer slipping based on superhydrophobicity. This paper will improve the comprehension of the drag reduction mechanism and expand biomimetic sharkskin technology into more applications. © 2015 World Scientific Publishing Company.

Jinji S.,Beihang University | Jiancheng F.,Beihang University
Journal of Magnetism and Magnetic Materials | Year: 2011

The paper proposes a novel structure for a permanent-magnet-biased radial hybrid magnetic bearing. Based on the air gap between the rotor and stator of traditional radial hybrid magnetic bearings, a subsidiary air gap is first constructed between the permanent magnets and the inner magnetic parts. Radial magnetic bearing makes X and Y magnetic fields independent of each other with separate stator poles, and the subsidiary air gap makes control flux to a close loop. As a result, magnetic field coupling of the X and Y channels is decreased significantly by the radial hybrid magnetic bearing and makes it easier to design control systems. Then an external rotor structure is designed into the radial hybrid magnetic bearing. The working principle of the radial hybrid magnetic bearing and its mathematical model is discussed. Finally, a non-linear magnetic network method is proposed to analyze the radial hybrid magnetic bearing. Simulation results indicate that magnetic fields in the two channels of the proposed radial hybrid magnetic bearing decouple well from each other. © 2010 Published by Elsevier B.V.

Liu M.,CAS National Center for Nanoscience and Technology | Liu M.,University of Chinese Academy of Sciences | Jiang L.,CAS Institute of Chemistry | Jiang L.,Beihang University
Advanced Functional Materials | Year: 2010

Construction and application of surfaces with switchable liquidsolid adhesion have generated worldwide interest during the past a few years. These surfaces are of great importance not only for fundamental research but for various practical applications in smart and fluid-controllable devices. This Feature Article reviews several techniques that have been developed to switch the adhesion on liquid/solid interfaces, including tuning the surface chemical composition, tailoring the surface morphology, and applying external stimuli. Particular attention is paid to superhydrophobic surfaces with reversible switching between low- and high-adhesion to water droplets in response to external stimuli. The dynamic behavior of water droplets on such surfaces can be controlled ranging from rolling to pinning state, while maintaining superhydrophobic states. In addition, smart adhesion in oil/water/solid system and platelet/water/solid system are also discussed, which is of importants for application in designing novel anti-bioadhesion materials. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Feng L.-H.,Beihang University | Wang J.-J.,Beihang University
Experiments in Fluids | Year: 2012

A synthetic jet generated by a non-sinusoidal waveform is used to control flow separation around a circular cylinder at Reynolds number 950. The synthetic jet is positioned at the rear stagnation point. The suction duty cycle factor defined as the ratio of the time duration of the suction cycle to the blowing cycle is introduced as the determining parameter. Increasing the suction duty cycle factor, the exit velocity and entrainment effect of the synthetic jet are enhanced, flow separation is delayed, and drag reduction by up to 29 % is achieved. Different mechanisms for separation control during both the blowing cycle and the suction cycle have been revealed. It is suggested that a better control effect can be obtained during the blowing cycle. © Springer-Verlag 2012.

Huang H.,Rice University | Huang H.,Nanjing University of Science and Technology | Yang S.,Rice University | Yang S.,Beihang University | And 3 more authors.
Advanced Materials | Year: 2014

Homogeneous dispersion of ultrafine Pt nanoparticles on 3D architectures constructed of graphene and exfoliated graphitic carbon nitride results in hybrids with 3D porous structures, large surface area, high nitrogen content, and good electrical conductivity. This leads to excellent electrocatalytic activity, unusually high poison tolerance, and reliable stability for methanol oxidation, making them of interest as catalysts in direct methanol fuel cells. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cui W.,Beihang University | Li M.,CAS Institute of Chemistry | Liu J.,Beihang University | Wang B.,Georgia Institute of Technology | And 3 more authors.
ACS Nano | Year: 2014

Demands of the strong integrated materials have substantially increased across various industries. Inspired by the relationship of excellent integration of mechanical properties and hierarchical nano/microscale structure of the natural nacre, we have developed a strategy for fabricating the strong integrated artificial nacre based on graphene oxide (GO) sheets by dopamine cross-linking via evaporation-induced assembly process. The tensile strength and toughness simultaneously show 1.5 and 2 times higher than that of natural nacre. Meanwhile, the artificial nacre shows high electrical conductivity. This type of strong integrated artificial nacre has great potential applications in aerospace, flexible supercapacitor electrodes, artificial muscle, and tissue engineering. © 2014 American Chemical Society.

Afzal F.,Beihang University
MATEC Web of Conferences | Year: 2016

The notion of characteristic sets, which are a special kind of triangular sets, is introduced by J. F Ritt and W.T. Wu. Wu extended Ritt's work and developed the characteristic set method not only in theory but in algorithms, efficiency and its numerous applications. Triangular sets are widely considered as a good representation for the solution of polynomial systems. After the introduction of characteristic sets by Ritt, triangular sets have become an alternative tool for representing the ideal besides the Gröbner bases. This paper is about implementation and applications of generalized characteristic sets of ordinary differential polynomial sets defined by author. © The Authors, published by EDP Sciences, 2016.

Liu D.,Beihang University | Yang C.,Beihang University
IEEE Journal on Selected Areas in Communications | Year: 2016

Caching popular contents at base stations (BSs) can reduce the backhaul cost and improve the network throughput. Yet whether locally caching at the BSs can improve the energy efficiency (EE), a major goal for fifth generation cellular networks, remains unclear. Due to the entangled impact of various factors on EE such as interference level, backhaul capacity, BS density, power consumption parameters, BS sleeping, content popularity, and cache capacity, another important question is what are the key factors that contribute more to the EE gain from caching. In this paper, we attempt to explore the potential of EE of the cache-enabled wireless access networks and identify the key factors. By deriving closed-form expression of the approximated EE, we provide the condition when the EE can benefit from caching, find the optimal cache capacity that maximizes the network EE, and analyze the maximal EE gain brought by caching. We show that caching at the BSs can improve the network EE when power efficient cache hardware is used. When local caching has EE gain over not caching, caching more contents at the BSs may not provide higher EE. Numerical and simulation results show that the caching EE gain is large when the backhaul capacity is stringent, interference level is low, content popularity is skewed, and when caching at pico BSs instead of macro BSs. © 2016 IEEE.

Gao J.,Beihang University | Gao J.,China Aerodynamics Research And Development Center
Journal of Computational Physics | Year: 2013

Overlap grid is usually used in numerical simulation of flow with complex geometry by high order finite difference scheme. It is difficult to generate overlap grid and the connectivity information between adjacent blocks, especially when interpolation is required for non-coincident overlap grids. In this study, an interface flux reconstruction (IFR) method is proposed for numerical simulation using high order finite difference scheme with multi-block structured grids. In this method the neighboring blocks share a common face, and the fluxes on each block are matched to set the boundary conditions for each interior block. Therefore this method has the promise of allowing discontinuous grids on either side of an interior block interface. The proposed method is proven to be stable for 7-point central DRP scheme coupled with 4-point and 5-point boundary closure schemes, as well as the 4th order compact scheme coupled with 3rd order boundary closure scheme. Four problems are numerically solved with the developed code to validate the interface flux reconstruction method in this study. The IFR method coupled with the 4th order DRP scheme or compact scheme is validated to be 4th order accuracy with one and two dimensional waves propagation problems. Two dimensional pulse propagation in mean flow is computed with wavy mesh to demonstrate the ability of the proposed method for non-uniform grid. To demonstrate the ability of the proposed method for complex geometry, sound scattering by two cylinders is simulated and the numerical results are compared with the analytical data. It is shown that the numerical results agree well with the analytical data. Finally the IFR method is applied to simulate viscous flow pass a cylinder at Reynolds number 150 to show its capability for viscous problem. The computed pressure coefficient on the cylinder surface, the frequency of vortex shedding, the lift and drag coefficients are presented. The numerical results are compared with the data of other researchers, and a good agreement is obtained. The validations imply that the proposed IFR method is accurate and effective for inviscid and viscous problems with complex geometry. © 2013 Elsevier Inc.

Li C.,Beihang University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Verdet constants of beta-barium borate (BBO) and lead molybdate (PMO) crystals are measured experimentally by the method of comparison with a block of terbium-doped glass with a known Verdet constant. Experimental setups mainly include two prism polarizers, a solenoid and ac current supply, and signal processing circuits. The influences of light intensity fluctuation, applied magnetic field and signal processing circuits on measurement result of Verdet constant can be removed by using the method of comparison. For light wavelength of 635nm, the measured Verdet constants respectively are 5.80±0.06 rad/(T.m) for the BBO crystal and 54.6±1.1 rad/(T.m) for the PMO crystal. A novel optical current sensor based on electrooptic compensation is designed in principle using the BBO crystal. © 2013 SPIE.

Lu Z.,Beihang University | Xia B.,Beihang University | Yang Z.,Beihang University
Computational Materials Science | Year: 2013

Longitudinal tensile behaviors of three-dimensional full five-directional (3DF5D) braided composites are simulated using finite element methods (FEMs). A representative volume cell (RVC) with periodical boundary conditions is adopted to calculate the mechanical properties of the composites. In addition, the yarns are considered as uniaxial fiber-reinforced composites, and the effective mechanical properties are obtained from a RVC of yarns by using the collision algorithm. Based on the Linde failure criterion, a new damage model is proposed to describe the damage initiation and evolution in yarns, and then the longitudinal tensile strengths are predicted. Beyond this, deformation of braided preforms and pore defects are also considered in the computational model. Numerical results show that the longitudinal damage in yarns contributes to the failure of composites, and the prediction is compared with the experimental results with good agreement achieved. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.

Li H.,Beihang University | Xu Q.,Beihang University
Electronics Letters | Year: 2011

A new design methodology is presented for detecting spiking signals from complex brain neural potentials, which applies ultra-low-power technology to implement a nonlinear energy operator (NEO)-based spike detector. The NEO spike detector achieves a differentiator with a differential structure and a multiplier based on the dynamic translinear principle using a sub-threshold technique. As is demonstrated by the simulation results, the proposed circuit has detected the instantaneous energy of the input signals well, which focus in the range 5Hz to 10kHz. © 2011 The Institution of Engineering and Technology.

Wu H.-N.,Beihang University | Wang J.-W.,Beihang University | Shi P.,University of South Wales | Shi P.,Victoria University of Melbourne
Automatica | Year: 2011

This paper investigates the problem of L2L∞ filter design for a class of stochastic systems with time-varying delay. The addressed problem is the design of a full order linear filter such that the error system is asymptotically mean-square stable and a prescribed L 2L∞ performance is satisfied. In order to develop a less conservative filter design, a new Lyapunov-Krasovskii functional (LKF) is constructed by decomposing the delay interval into multiple equidistant subintervals, and a new integral inequality is established in the stochastic setting. Then, based on the LKF and integral inequality, the delay-dependent conditions for the existence of L2L∞ filters are obtained in terms of linear matrix inequalities (LMIs). The resulting filters can ensure that the error system is asymptotically mean-square stable and the peak value of the estimation error is bounded by a prescribed level for all possible bounded energy disturbances. Finally, two examples are given to illustrate the effectiveness of the proposed method. © 2011 Elsevier Ltd. All rights reserved.

Luo W.,Beihang University | Wang L.,Beihang University
Diangong Jishu Xuebao/Transactions of China Electrotechnical Society | Year: 2011

A wind speed forecasting model for wind farm based on support vector machine is proposed. Through wavelet decomposition and genetic algorithm, the data are preprocessed and the parameters are optimized. The model includes data processing unit, parameter optimization and support vector machine unit. The historical wind speed data is input to the model, and the model outputs the future wind speed data. Meanwhile, the adjustable parameters of the model is introduced, in order to improve the general adaptability for the different wind speed data. The simulation results show that the forecast wind speed is following the true value, what's more, the model can adapt to different wind data.

Xiaojuan W.,Beihang University | Xinlong W.,Beihang University
Acta Astronautica | Year: 2011

According to the flight characteristics of vehicle under high dynamic conditions, the impact of linear, angular, and vibrational motion on star sensor imaging was researched. Then, the mathematical model of motion blur corresponding to various flight conditions was deduced, and the star centroiding accuracy affected by motion blur was analyzed subsequently. On this basis, the mechanism of multiple blur was discussed. In order to ensure the accuracy of star sensor in high dynamic environment, a restoration method was proposed to remove the multiple blur. Finally, simulations are implemented to validate the restoration method. © 2011 Elsevier Ltd. All rights reserved.

Chen Z.,CAS Beijing National Laboratory for Molecular | Cui Z.-M.,Beihang University | Niu F.,CAS Beijing National Laboratory for Molecular | Jiang L.,Beihang University | Song W.-G.,CAS Beijing National Laboratory for Molecular
Chemical Communications | Year: 2010

A true nanoreactor composed of mesoporous silica hollow spheres and Pd nanoparticles residing inside the spheres shows superior activity in Suzuki coupling reactions with 99.5% yield in 3 min. © 2010 The Royal Society of Chemistry.

Zhao Q.,Beihang University | Lin Y.,Beihang University
Asian Journal of Control | Year: 2011

This paper aims at exploring an adaptive fuzzy dynamic surface control (DSC) with prespecified tracking performance for a class of nonlinear systems in strict-feedback form. Incorporating DSC technique into fuzzy logic systems (FLSs), it is shown that the design procedure and the computational burden can be greatly reduced. Moreover, by introducing a performance function in controller design, the prespecified tracking performance, i.e. the convergence rate, the allowed maximum overshoot and the steady state error, can be achieved. Simulation results are presented to demonstrate the efficiency of the proposed scheme. © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.

Wu H.-N.,Beihang University | Luo B.,Beihang University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2012

It is well known that the nonlinear H∞ state feedback control problem relies on the solution of the Hamilton-Jacobi-Isaacs (HJI) equation, which is a nonlinear partial differential equation that has proven to be impossible to solve analytically. In this paper, a neural network (NN)-based online simultaneous policy update algorithm (SPUA) is developed to solve the HJI equation, in which knowledge of internal system dynamics is not required. First, we propose an online SPUA which can be viewed as a reinforcement learning technique for two players to learn their optimal actions in an unknown environment. The proposed online SPUA updates control and disturbance policies simultaneously; thus, only one iterative loop is needed. Second, the convergence of the online SPUA is established by proving that it is mathematically equivalent to Newton's method for finding a fixed point in a Banach space. Third, we develop an actor-critic structure for the implementation of the online SPUA, in which only one critic NN is needed for approximating the cost function, and a least-square method is given for estimating the NN weight parameters. Finally, simulation studies are provided to demonstrate the effectiveness of the proposed algorithm. © 2012 IEEE.

Li Y.,Key Laboratory of Dynamics and Control of Flight Vehicle | Li Y.,Tsinghua University | Song J.,Tsinghua University | Yang J.,Beihang University
Renewable and Sustainable Energy Reviews | Year: 2015

To address the demand for vehicles using fuel cell energy with high-performance electrodes, this paper discusses the energy storage model, nano-scale characterization technology, nanoenergy system and the structural design for fuel cell graphene electrodes while giving special attention to three characteristics: electrode conversion efficiency, specific power and cost. The structural stability model, evolutionary mechanism and the construction process of graphene electrodes of fuel cell technology are introduced. By analyzing electron and ion transmission and characterizing the electrode structure, energy system, surface and interface property at the nano-scale level, this paper reveals the intrinsic link between how an energy system is structured and performs. It combines the system model with the application of high-performance electrodes to highlight the compatibility between graphene and the electrode. By addressing progress in the applicability of renewable energy and the sustainability of energy technology during recent years, this paper provides scientific and experimental support for the practicality of fuel cell energy while also addressing bottleneck issues such as conversion efficiency, specific power and the cost of electrodes. © 2014 Elsevier Ltd. All rights reserved.

Tu Y.,Beihang University | Lin G.P.,Beihang University
Journal of Aircraft | Year: 2011

The mathematical model and calculation method of three-wheel environmental control system with the highpressure water separation are developed in this paper. The component models are created based on the Flowmaster software platform, and the environmental control system simulation model is established using these component models. The dynamical response of environmental control system is simulated. With the simulation results, a general idea of the dynamical characteristic of the environm