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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.

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.

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.

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.

Sun L.,Beihang University | Gibson R.F.,University of Nevada, Reno | Gordaninejad F.,University of Nevada, Reno
Engineering Fracture Mechanics | Year: 2011

A combined micromechanics analysis and global-local finite element method is proposed to study the interaction of particles and matrix at the nano-scale near a crack tip. An analytical model is used to obtain the effective elastic modulus of nanoparticle-reinforced composites, then a global-local multi-scale finite element model with effective homogeneous material properties is used to study the fracture of a compact tension sample. For SiO 2 particle-reinforced epoxy composites with various volume fractions, the simulation results for effective elastic modulus, fracture toughness, and critical strain energy release rate show good agreement with previously published experimental data. It is demonstrated that the proposed parametric multi-scale model can be used to efficiently study the toughness mechanisms at both the macro and nano-scale. © 2011 Elsevier Ltd.

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.

A novel magnetooptic sensor is proposed which is based on electrogyration compensation for the Faraday rotation angle in single lead molybdate (PbMoO4, PMO) crystal. The optical sensing unit is only composed of two polarizers and one single PMO crystal exhibiting both the Faraday and electrogyration effects. AC 50-Hz magnetic field in the range of 167 Gs has been measured by the method of electrogyration compensation, and the nonlinear error is <1.2%. The compensating voltage is ∼ 16 V/Gs for a block of PMO crystal with 5 mm in length. Verdet constant of the PMO crystal sample has also been measured for light wavelength of 635 nm, and it is ∼ 51.6 ± 1.1 rad. T-1. m-1. The proposed magnetooptic sensor provides a promising closed-loop measurement method of current, magnetic field, and Verdet constant. © 2016 IEEE.

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.

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.

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.

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.

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.

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.

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.

Liu K.,Beihang University | Tian Y.,CAS Beijing National Laboratory for Molecular | Jiang L.,CAS Beijing National Laboratory for Molecular
Progress in Materials Science | Year: 2012

Through evolution, nature has arrived at what is optimal. Inspired by the biomaterials with special wettability, superhydrophobic materials have been well-investigated and -covered by several excellent reviews. The construction of superoleophobicity is more difficult than that of superhydrophobicity because the surface tension of oil or other organic liquids is lower than that of water. However, superoleophobic surfaces have drawn a great deal of attention for both fundamental research and practical applications in a variety of fields. In this contribution, we focus on recent research progress in the design, fabrication, and application of bio-inspired superoleophobic and smart surfaces, including superoleophobic-superhydrophobic surfaces, oleophobic-hydrophilic surfaces, underwater superoleophobic surfaces, and smart surfaces. Although the research of bio-inspired superoleophobicity is in its infancy, it is a rapidly growing and enormously promising field. The remaining challenges and future outlook of this field are also addressed. Multifunctional integration is a inherent characteristic for biological materials. Learning from nature has long been a source of bio-inspiration for scientists and engineers. Therefore, further cross-disciplinary cooperation is essential for the construction of multifunctional advanced superoleophobic surfaces through learning the optimized biological solutions from nature. We hope this review will provide some inspirations to the researchers in the field of material science, chemistry, physics, biology, and engineering. © 2012 Elsevier Ltd. All rights reserved.

Li Y.,Beijing Institute of Technology | Li Y.,Tsinghua University | Song J.,Tsinghua University | Yang J.,Beihang University
Renewable and Sustainable Energy Reviews | Year: 2014

Structure properties of lithium-ion battery determine the specific energy and specific power of renewable energy vehicle and have attracted extensive concerns. Fundamental innovations in battery system depend on the structure properties, of which graphene and concentration gradient structures become increasingly prospective. As the performance of structure closely relates to the battery performance and the advancement of battery technologies, the paper, based on the research work at our laboratory, discusses about the structure model and energy system design and analyzes the evolution of lithium batteries to provide scientific insights and technical advices for the development of renewable energy vehicle. The review shows that nano and graphene models, with their corresponding energy systems, significantly improve the performance of lithium batteries, thus supporting longer mileage and service life, while providing new ideas for the design of renewable energy vehicles. Compared with other power batteries, lithium-ion batteries are advantageous in addressing the requirements raised by battery electric vehicles, such as, long mileage, high-current charging, and safety. Therefore, lithium batteries are reliable and feasible for the deployment in battery electric vehicles. © 2014 Elsevier Ltd.

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.

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.

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..

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.

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.

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.

Guo H.,Beihang University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

We study the hard-core bosons in one-dimensional (1D) interacting topological bands at different filling factors using exact diagonalization. At the filling factor ν=1 and in the presence of the on-site Hubbard interaction, we find no sign of the existence of the bosonic topological phase, which is in contrast to the fermionic case. Instead by studying the momentum distribution and the condensate fraction we find a superfluid to Mott-insulator transition driven by the Hubbard interaction. At the filling factor ν=1/3 and in the presence of longer-ranged interactions, we identify the bosonic fractional topological phase whose ground states are characterized by a threefold degeneracy and a quantized total Berry phase, which is very similar to the fermionic case. Finally we discuss the reason for the different behaviors of hard-core bosons at different filling factors by mapping them to spinless fermions. Our results can be realized in cold-atom experiments. © 2012 American Physical 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.

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.

Guan J.,Fudan University | Chen K.,Beihang University
Scientometrics | Year: 2010

This paper proposes a novel methodological framework for effectively measuring the production frontier performance (PFP) of macro-scale (regional or national) R&D activities themselves associated with two improved models: a non-radial data envelopment analysis (DEA) model and a nonradial Malmquist index. In particular, the framework can provide multidimensional information to benchmark various R&D efficiency indexes (i. e., technical efficiency, pure technical efficiency and scale efficiency) as well as the total factor R&D productivity change (determined by three components: "catch-up" of R&D efficiency, "frontier shift" of R&D technology as well as "exploitation" of R&D scale economics effect) at a comparable production frontier. It can be used to not only investigate the potential and sustainable capacity of innovation but also screen and finance R&D projects at the regional or national level. We have applied the framework to a province-level panel dataset on R&D activities of 30 selected Chinese provinces. © Akadémiai Kiadó, Budapest, Hungary 2009.

Sun M.,Beihang University
Reviews of Modern Physics | Year: 2014

Insects can hover, fly forward, climb, and descend with ease while demonstrating amazing stability, and they can also maneuver in impressive ways as no other organisms can. Is their flight inherently stable? If so, how can they maneuver so well? In recent years, significant progress has been made in revealing the dynamic flight stability and flight control mechanisms of insects and has partially answered these questions. Here the most recent advances in this active area are reviewed. The aim is to provide the background necessary to do research in the area and raise questions that need to be addressed in the future. This review begins with an overview of the flapping kinematics and aerodynamics of insect flight. It is followed by a summary of the governing equations of insect motion and the simplified theoretical models used for analysis of dynamic stability and control. Next, the stability properties of hovering flight and forward flight are scrutinized. Then the flight control properties are explored, dealing in turn with flight stabilization control, steady-state control for changing from hovering to forward flight and from one forward-flight speed to another, and control for maneuvers near hovering. Finally, remarks are given on the state of the art of this research field and speculation is made on its outlook in the near future. © 2014 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.

Luo K.,Beihang University
Computers and Industrial Engineering | Year: 2015

This study develops a more general model for scheduling problems with learning effects. Compared with the existent general models, the proposed time- and position-dependent model simultaneously covers the normal and actual processing cases. Moreover, the model has many new properties that the previous work did not study. In this paper, a distinctive proof technique is developed based on the adding-and-subtracting-terms operation and the Lagrange Mean Value Theorem. The proof technique is easier to use than the method based on multiple identical or similar lemmas employed in a large number of literatures. © 2015 Elsevier Ltd. All rights reserved.

Li W.,Beihang University
Science in China, Series F: Information Sciences | Year: 2010

This paper shows that the discovery processes of Einstein's special theory of relativity and Darwin's theory of evolution of species can be formally verified by R-calculus which is a logical inference system. The aim of R-calculus is to delete the principles of scientific theories which contradict empirical evidence. The paper shows that the special theory of relativity is the only and correct choice for physics to meet the experimental evidence given at the time. As far as the biology of Darwin's time is concerned, however, the R-calculus has derived three logically correct but different theories, which are all consistent with the empirical evidence provided by Darwin and his principle of natural selection. Darwin's theory of evolution matches one of the three theories derived by R-calculus. This theory has a logical consequence that is "each species has been independently created is erroneous". But the other two theories support the negation of the above statement. The existence of the other two theories may be a reason of the controversies over Darwin's theory. © 2010 Science China Press and Springer-Verlag Berlin Heidelberg.

Tian Q.,Beihang University
Transportmetrica A: Transport Science | Year: 2016

This paper investigates the drivers’ microscopic curbside parking behaviours under random distribution of vacant parking spaces. For each trip, the driver has a preferred arrival time at the destination and may incur schedule delay cost due to the uncertainty of searching process. The expected trip costs include the in-transit travel cost, the cruising cost, the walking cost, the schedule delay cost and the parking fee. To minimize the expected trip cost, there are two decisions require the driver to make, namely how long before the specified arrival time to initiate the trip and how far away ahead of the destination to search for a vacant parking position. Two possible searching state of the driver are illustrated. The ‘fastest parker’ refers to the possible state of the driver parking successfully when just starts cruising with zero searching distance, and the ‘luckiest parker’ refers to the possible state that driver parks exactly on her/his destination and incurs zero walking distance. Based on the schedule delay states of being the fastest parker and the luckiest parker, three searching strategies are distinguished. The ‘Early-park-early-arrival’ strategy refers to the driver has the expectation that arrives at the destination early when being the fastest parker; the ‘Early-park-late-arrival’ strategy refers to the driver has the expectation that arrives at the destination late when being the fastest parker and arrives early when being the luckiest parker; the ‘Never-early’ strategy refers to the driver has the expectation of late arrival whatever being the fastest or the luckiest parker. The analytical proofs reach some interesting findings: the ‘Never-early’ strategy can never be optimal; if the unit time cost of early arrival is larger than that of late arrival, the optimal parking strategy is ‘Early-park-late-arrival’; if the ‘Early-park-early-arrival’ strategy is optimal, the driver’s possibility of parking before the destination is larger than 50%. Several numerical results are illustrated to verify the analytical propositions and show that the ‘Early-park-early-arrival’ strategy is preferred to the ‘Early-park-late-arrival’ strategy under higher parking charge and higher unit time cost of walking. © 2016 Hong Kong Society for Transportation Studies Limited

Lang B.,Beihang University
Science in China, Series F: Information Sciences | Year: 2010

Trust brings a new method for building scalable and fine-grained access control mechanism in P2P systems. The quantificational expression of trust and the calculation of trust in a trust network are the basis of trust degree based access control. In this paper, the properties of trust is analyzed by referring to the fruits from social science; the semantics of trust in the context of access control is described, and a trust degree based access control model named TDBAC is introduced. Basing on the properties and semantics of trust, a computational trust model which includes a multilevel comprehensive evaluation method for expressing direct trust and calculators for computing recommended trust is put forward. To compute trust in a trust network, an algorithm that transforms a trust network to a computable expression is given. The algorithm simplifies the computation process and is also flexible. © 2010 Science China Press and Springer-Verlag Berlin Heidelberg.

This paper investigates the fixed-time consensus tracking problem for second-order multi-agent systems in networks with directed topology. Global well-defined nonlinear consensus protocols are constructed with the aid of a newly-designed sliding surface for each double-integrator agent dynamics. In particular, the proposed framework eliminates the singularity and the settling time is assignable for any initial conditions. This makes it possible for network consensus problems to design and estimate the convergence time off-line. Finally, simulation is included to demonstrate the performance of the new protocols. © 2015 Elsevier Ltd.

Zuo Z.,Beihang University
JVC/Journal of Vibration and Control | Year: 2013

The design of a flight controller capable of not only stabilizing attitude but also tracking a trajectory accurately for a quadrotor aircraft in presence of parametric uncertainties and external disturbances is more challenging than that in the absence of uncertainties. In this paper we propose an adaptive trajectory tracking control algorithm, based on the relationship between attitude and linear acceleration, using online adaptive approximator to estimate unknown aerodynamic parameters and external disturbance upper bounds, and a linear tracking-differentiator to eliminate the timescale separation assumption between attitude and linear dynamics in control system design. The stability of the closed-loop control system is proven subsequently. Finally, the validity and the improvement of this proposed algorithm relative to the previous work are demonstrated through numerical simulations of tracking a circular trajectory under several conditions, including basic parametric uncertainty, exogenous wind disturbance and control input oscillation eliminating via a hyperbolic tangent function instead of a sign function. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Lei L.,Beihang University
Journal of Convergence Information Technology | Year: 2012

Data-Intensive Computing emerges as the fourth paradigm for modern scientific discoveries. MapReduce, a programming paradigm for large-scale data-parallel applications, is widely applied to web indexing, machine learning, and scientific simulations in industries as well as in academia. Recently, the virtualized "utility computing" environments, provided by cloud computing services, are becoming an important scenario to run MapReduce jobs. However, in such a virtualized computing environment, the network bandwidth between pair of virtual machines degrades badly, which makes the data-locality a more crucial goal to guarantee the performance of a virtual Hadoop cluster(VHC). With deployment and benchmark on our testbed, two problems were found to compromise the performance of MapReduce application most in a VHC. The first is the data replica distribution scheme and the second is the speculative executions in fault recovery. HDFS, the distributed file system of Hadoop, depends on the rack awareness scheme to distribute the data block replicas in a physical cluster. However, this scheme fails to work in a virtual computing environment due the underlying assumption of network distance breaks in virtual network topology. Moreover, for a MapReduce job, the straggler tasks may dominate the response time and delay the whole job. Various speculation schemes have been proposed to alleviate such problem, however, most of them implicitly assume that the time cost for data movement on launching speculative map tasks is trivial, which does not always hold for the virtualized Hadoop clusters. In this paper, to the data block replica distribution problem, we propose a mechanism to discover the cohesiveness of virtual machines and designed a novel scheme to distribute the data block replicas, Clustering based Replica Arrangement in Virtual Environment(CRAVE). Concerning the performance problem in speculative execution, we propose a novel approach, Combination Re-Execution Scheduling Technology(CREST), which can achieve the optimal running time for speculative map tasks and decrease the response time of MapReduce jobs. The deployment evaluation validates our approaches and shows that CRAVE boosts the data read speed and decrease the data transportation cost in MapReduce applications. Also, the simulation demonstrates that CREST can reduce the running time of a speculative map task by 70% with best cases and 50% on average, comparing with LATE.

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.

Feng Z.,Beihang University
Journal of Convergence Information Technology | Year: 2012

A semi-physical simulation system is developed based on the RT-LAB real-time simulation environment which is used to process simulation test of missile guidance controlling system. The system adopts design idea of modularization, development of all sub-system together and it integrates the Hi-fi missile aerodynamics environment, missile boron computer system, inertia measurement unit, high accurate aviation posture simulator, real missile boron port equipment, three-dimensional view and data backup system into one so that the performance of guidance controlling algorithm could be reflected comprehensively, directly and really. According to the comparison between test result of digital simulation and semi-physical system simulation, the feasibility of semi-physical simulation could be certified so that under the semi-physical simulation environment, more real and effective test could be checked for guidance controlling algorithm.

Guan J.,Fudan University | Wang G.,Beihang University
Scientometrics | Year: 2010

This paper explores the relationship between patenting and publishing in the field of nanotechnology for Chinese universities. With their growing patents, Chinese universities are becoming main technological source for nanotechnology development that is extremely important in China. Matching names of patentees to names of research paper authors in Chinese universities, we find 6,321 authors with patents, i.e. inventor-authors, and 65,001 without any patent. Research performance is measured using three indicators-publication counts, total citations and h-index received by each researcher. It is found that research performance of authors who are also inventors holding patents is better than that of those authors who do not have a patent, and that most of high quality research is performed by inventor-authors. Our findings indicate that patent-oriented research may produce better results. © 2010 Akadémiai Kiadó, Budapest, Hungary.

Liu Y.,Micron Technology Inc. | Wang H.M.,Beihang University
Wear | Year: 2013

The MgZn2 type Laves phase of Co3Mo2Si has very attractive super high hardness and covalent dominated bonding nature for wear resistance applications. To make it feasible for real application, its inherent brittleness was effectively balanced by toughening it with the ductile cobalt solid solution (Coss) by the laser melting process. The toughening effect was evaluated qualitatively by the observation of the indentation behaviors and the micro-hardness variations of the alloys. The wear properties of the Coss toughened Co3Mo2Si alloys were evaluated in the dry sliding wear test condition at room temperature. Results indicated that the Coss toughened Co3Mo2Si alloys have excellent combination of strength and ductility, and display exceptional wear property. © 2012 Elsevier B.V.

Sun M.,Northeastern University China | Jia Y.,Beihang University
IET Control Theory and Applications | Year: 2010

In this study, a delay-dependent H∞ performance criterion that possess decoupling structure is derived for a class of time-delay systems. It is then extended to H∞ state-feedback synthesis for time-delay systems with polytopic uncertainty and multichannel H ∞ dynamic output-feedback synthesis for time-delay systems. All the conditions are given in terms of the linear matrix inequalities. In some previous descriptor methods, the products of controller matrices and Lyapunov matrices are completely separated in performance analysis, whereas it is not the case in controller synthesis. However, with the method in the paper, the weakness is eliminated. Numerical examples illustrate the effectiveness of our solutions as compared to results obtained by other methods. © 2010 The Institution of Engineering and Technology.

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.

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.

Chen K.,Beihang University | Chen K.,CAS Institute of Policy and Management | Guan J.,University of Chinese Academy of Sciences
Technovation | Year: 2011

The research about the innovation production process (IPP) is burgeoning. Our understanding of the interdependent interactions between functionally distinct innovation activities during it from a systemic perspective is rather unclear, yet, which is beneficial to empirical innovation management. This study, based on systems thinking, presents a novel analytical framework to empirically and quantitatively map the IPP jointly associated with a path modeling approach, which helps in untangling the interactive mechanism between stage-specific innovation activities with distinct functions within an IPP from accumulative advantage to economic outcomes. We use the attractive analytical framework to guide an empirical investigation to the Chinas high-tech industries IPP at the macro-regional level. Our empirical study confirms the dominant role of previous innovation capital accumulation in the whole IPP embedded into regional innovation systems of Chinas high-tech industries. That is, we prove the existence of accumulative advantage phenomenon in the regional IPP. The examination results show that there is a significant Matthew effect of technological innovation accumulation on technological innovation inputs as well as the Path dependence of technological innovation outputs/outcomes on technological innovation accumulation. This indicates that the innovation-practitioners should promote innovation capital accumulation for sustainable innovations and economic profits in a long time. At the same time, our findings suggest that, in order to alleviate the cross-regional unbalance of innovation development and promote radial innovations in Chinas high-tech industries, both policy-makers and innovation-practitioners should try to get rid of the dependence on the previous accumulated innovation capital. © 2011 Elsevier Ltd.

Yue Y.,Beihang University | Zheng K.,Beijing University of Technology
Applied Physics Letters | Year: 2014

With electron-beam (e-beam) off, in-situ tensile experiments on amorphous silica nanowires (NWs) were performed inside a transmission electron microscope (TEM). By controlling the loading rates, the strain rate can be adjusted accurately in a wide range. The result shows a strong strain rate effect on the plasticity of amorphous silica NWs. At lower strain rate, the intrinsic brittle materials exhibit a pronounced elongation higher than 100% to failure with obvious necking near ambient temperature. At the strain rate higher than 5.23 × 10- 3/s, the elongation of the NW decreased dramatically, and a brittle fracture feature behavior was revealed. This ductile feature of the amorphous silica NWs has been further confirmed with the in-situ experiments under optical microscopy while the effect of e-beam irradiation could be eliminated. © 2014 AIP Publishing LLC.

Huang X.,Beihang University
AIAA Journal | Year: 2012

Spinning modal decomposition and detection of an aeroengine are quite important for the urgent development of silent aircraft. An induct circular microphone array has to be used for the existing measurement techniques. To accurately decompose high spinning modes, the number of microphones should be as many as possible, which is, however, quite inconvenient for practical tests. In this work, a new testing algorithm that only needs a single sensor is developed, which constitutes the main contribution of this paper. The fundamental idea behind the testing method is the Kalman filter that was originally developed for ordinary differential equations. The three-dimensional partial differential equations describing spinning modes propagation was therefore simplified to the two-dimensional ordinary differential equations in this work. Although the main attention of this paper is focused on theoretical development, some primitive results of numerical simulations were given to demonstrate the proposed new method. In sumary, this Kalman filter based new method is believed to hold great potential in both scaled model tests and practical engine health monitoring. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Ye H.,Central South University | Jiang Z.-P.,New York University | Jiang Z.-P.,Beihang University | Gui W.,Central South University | Yang C.,Central South University
Automatica | Year: 2012

This paper investigates the problem of decentralized stabilization via saturated delayed feedback. First, a new class of saturated delayed feedback controllers is proposed for a class of single-input feedforward nonlinear systems. Then, this design scheme is generalized for the setting of decentralized feedforward systems using saturated time-delayed feedback. The stability analysis for the closed-loop decentralized systems is rather simple based on the proposed feedback structure. © 2011 Elsevier Ltd. All rights reserved.

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.

A heuristic called RAND was used by Q. Li [Li, Q., 2004. Solving the multi-buyer joint replenishment problem with the RAND method. Computers & Industrial Engineering, 46, 755-762] to solve the multi-buyer joint replenishment problem. In this paper, errors made in the proposed RAND procedure of Q. Li (2004) are rectified. Furthermore, modifications to the proposed RAND procedure are also given. © 2010 Elsevier Ltd. All rights reserved.

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.

Li C.,Beihang University | Yoshino T.,Kaisei Academy
Applied Optics | Year: 2012

A novel magneto-optic sensor with electrically adjustable sensitivity is proposed that is based on the approximate multiplication correlation between the linear electro-optic phase retardation and the Faraday magneto-optic rotation angle in a single bismuth germanate crystal. The measurement sensitivity and its temperature stability, linear and monotonic measurement ranges of the proposed sensor can be controlled in real time by adjusting the modulating voltage applied to the sensing crystal. In particular, the proposed sensor can be used for the precise measurement of dc magnetic field or dc current. The basic sensing performance is theoretically analyzed and experimentally demonstrated by dc current measurement. © 2012 Optical Society of America.

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.

Pan B.,Beihang University
Optics and Lasers in Engineering | Year: 2013

In digital image correlation (DIC), the iterative spatial domain cross-correlation algorithm using high-order B-spline interpolation algorithms has been strongly recommended for accurate sub-pixel displacement measurement. However, the magnitude of the position-dependent bias error increases with the increase of noise level, which dramatically reduces the registration accuracy of DIC for real experimental images. In this paper, a simple method, based on pre-smoothing the speckle images with a 5×5 pixels Gaussian low-pass filter prior to correlation analysis, is proposed for reducing the bias error in measured displacements. Both numerical simulations and real experiments reveal that the proposed technique is capable of reducing the bias error in measured displacement to a negligible degree for both noisy and noiseless images, even though a simple bicubic interpolation is used. © 2013 Elsevier Ltd.

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.

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.

Zhou X.,CAS National Center for Nanoscience and Technology | Liu G.,CAS National Center for Nanoscience and Technology | Yu J.,Wuhan University of Technology | Fan W.,Beihang University
Journal of Materials Chemistry | Year: 2012

Harvesting abundant and renewable sunlight in energy production and environmental remediation is an emerging research topic. Indeed, research on solar-driven heterogeneous photocatalysis based on surface plasmon resonance has seen rapid growth and potentially opens a technologically promising avenue that can benefit the sustainable development of global energy and the environment. This review briefly summarizes recent advances in the synthesis and photocatalytic properties of plasmonic composites (e.g., hybrid structures) formed by noble metal (e.g., gold, silver) nanoparticles dispersed on a variety of substrates that are composed of metal oxides, silver halides, graphene oxide, among others. Brief introduction of surface plasmon resonance and the synthesis of noble metal-based composites are given, followed by highlighting diverse applications of plasmonic photocatalysts in mineralization of organic pollutants, organic synthesis and water splitting. Insights into surface plasmon resonance-mediated photocatalysis not only impact the basic science of heterogeneous photocatalysis, but generate new concepts guiding practical technologies such as wastewater treatment, air purification, selective oxidation reactions, selective reduction reactions, and solar-to-hydrogen energy conversion in an energy efficient and environmentally benign approach. This review ends with a summary and perspectives. © 2012 The Royal Society of Chemistry.

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.

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.

Cao C.-Y.,CAS Beijing National Laboratory for Molecular | Cao C.-Y.,Harbin Institute of Technology | Guo W.,CAS Beijing National Laboratory for Molecular | Cui Z.-M.,Beihang University | And 2 more authors.
Journal of Materials Chemistry | Year: 2011

A rapid method based on an efficient gas/liquid interfacial microwave-assisted process has been developed to synthesize flowerlike NiO hollow nanosphere precursors, which were then transformed to NiO by simple calcinations. The wall of the sphere is composed of twisted NiO nanosheets that intercalated with each other. Such hollow structure is different from widely reported flowerlike nanostructures with solid cores. An Ostwald ripening mechanism was proposed for the formation of the hollow nanostructures. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, energy-dispersive X-ray analysis, and N2 adsorption-desorption methods. These flowerlike NiO hollow nanospheres have high surface area of 176 m2 g-1. Electrochemical properties show a high specific capacitance of 585 F g-1 at a discharge current of 5 A g-1 and excellent cycling stability, suggesting its promising potentials in supercapacitors. © The Royal Society of Chemistry 2011.

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.

Guo H.,Beihang University | Chen S.,CAS Institute of Physics
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We identify the existence of various symmetry-protected topological states in one-dimensional superlattices with periodically modulated hopping amplitudes or on-site potentials, which can be characterized by the quantized Berry phase π or the emergence of a pair of degenerate boundary states. It is shown that there may exist three types of topological phases, which are protected by inversion symmetry, chiral symmetry, and both of them, respectively, depending on the modulations, the odd, or the even modulation period. The connection between the hopping and potential modulations is also discussed. Furthermore, we demonstrate that the topological phase protected by the inversion symmetry can be realized in the interacting boson systems trapped in the same superlattices. The results can very possibly be studied experimentally in superlattice systems engineered with state-of-the-art technologies. © 2015 American Physical Society.

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.

Liu M.,CAS Beijing National Laboratory for Molecular | Xue Z.,CAS Beijing National Laboratory for Molecular | Liu H.,Beihang University | Jiang L.,CAS Beijing National Laboratory for Molecular
Angewandte Chemie - International Edition | Year: 2012

Interfacial phenomena: A solid-phase-independent strategy for tuning the surface wettability is presented. Lewis acid-base interactions at the oil-water interface can greatly decrease the liquid-liquid interfacial tension and induce oleophilic to superoleophobic wetting transition on a nonresponsive microstructured surface (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Xin W.,Beihang University
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2015

Excitation frequency and pulsed width were two important factors in the study of the minor hysteresis characteristics of ferromagnetic materials under pulsed current excitation. With pulsed current peak remaining unchanged, different minor hysteresis curves were obtained through changing frequency and pulsed width. The higher frequency is and the narrower pulsed width is, the more pulsed numbers of excitation current were needed to stabilize minor hysteresis curves. This phenomenon was caused by the magnetic aftereffect of magnetic flux density. To describe the impact of frequency and pulsed width on the minor hysteresis characteristics, the curve fitting method was used to establish mathematic relation between fitting functions of different minor hysteresis curves according to the change law of frequency, pulsed width and the magnetic flux density turning points values. Compared with experimental results, in a certain range, the simulation results prove that the mathematic expression can effectively reflect the influence law of frequency and pulsed width, and accurately simulate the minor hysteresis characteristics of ferromagnetic material when frequency and pulsed width of pulsed current are varied. ©2015 Chin.Soc.for Elec.Eng.

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.

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.

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.

Bao R.,Beihang University | Zhang X.,Cranfield University
International Journal of Fatigue | Year: 2010

This paper presents a study of crack growth behaviour in aluminium alloys 2324-T39 and 7050-T7451 subjected to flight-by-flight load spectra at different low-stress truncation levels. Crack branching was observed in the higher truncation levels for the 2324 and in all truncation levels for the 7050. Mode I crack growth life can be predicted for the 2324 alloy by the NASGRO equation and the Generalised Willenborg retardation model. However, quantitative prediction of the fatigue life of a significantly branched crack is still a problem. Material properties, test sample's orientation and applied stress intensity factor range all play dominant roles in the fracture process. © 2009 Elsevier Ltd.

Zou Y.,Beihang University
Nonlinear Dynamics | Year: 2016

This paper investigates an adaptive trajectory tracking control approach for a model-scaled helicopter with rotation matrix describing its attitude kinematics. The helicopter is decomposed into a cascaded form with some unmodeled dynamics, so that a hierarchical strategy is applicable. First, in the outer position loop, based on an integral-quadratic Lyapunov function, a position control law with hyperbolic tangent functions is designed to accomplish the position tracking. Then, a command rotation matrix is extracted with the minimum rotation principle. Finally, in the inner attitude loop, based on a barrier-quadratic Lyapunov function, a singularity-free attitude control law is designed to realize the attitude tracking. In addition, the bounds of the unmodeled dynamics are estimated and compensated with adaptive algorithms. Simulations on a model-scaled helicopter confirm the proposed control approach. © 2015, Springer Science+Business Media Dordrecht.

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.

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.

Sha J.B.,Beihang University | Sha J.B.,Japan National Institute of Materials Science | Yamabe-Mitarai Y.,Japan National Institute of Materials Science
Intermetallics | Year: 2013

This paper investigates the strength response of Ir-xHf-yNb alloys (x = 3, 4, 5, 8, 9, 10 at.%, and y = 5, 6, 7, 11, 13, 15 at.%) with a dual-phase fcc/L1 2 microstructure at room and high temperatures. The experimental strength at 1950 °C was compared with that obtained by the rule of mixture. The results showed that in the fcc/L1 2 structure the fcc phase always shows higher strength than the L1 2 phase, at both room and high temperatures. A dual-phase fcc/L1 2 microstructure with different fcc to L1 2 fraction ratio formed when Hf and Nb contents in the Ir-xHf-yNb ternary alloys were larger than 3 at.% and 5 at.%, respectively, and the pure L1 2 microstructure was obtained at 10 at.% Hf and 15 at.% Nb. The Ir-5Hf-7Nb alloy, possessing an fcc-dominant microstructure in which the optimization fcc fraction is about 78%, has an outstanding 0.2% yield compressive strength of 270 MPa even at 1950 °C. This ultra-high strength is attributed to strong interface hardening by the large lattice misfit between the fcc and L1 2 phases. The failure mode of the Ir-Hf-Nb ternary alloys is by debonding of the grain boundary. © 2012 Elsevier Ltd. All rights reserved.

Zhou Y.,Beihang University
Materials and Structures/Materiaux et Constructions | Year: 2015

Based on the dynamic characteristics obtained with a three-dimension finite element method, a reduced mechanical model and parameters for the ship lift can be modified and obtained. Simulated analysis shows that the reduced mechanical model can adequately represent the dynamic characteristics of the ship lift. The wind-induced vibrations and seismic responses of the structure were calculated respectively. A fuzzy semi-active control strategy for seismic response reduction using a magnetorheological damper was presented. A roof intelligent isolation system was also proposed. Simulation analysis results show that the fuzzy semi-active control with a magnetorheological smart damper is beneficial in suppressing the seismic whiplash effect on the top workshop and confirm that the fuzzy semi-active control strategy is valid in this scenario. © 2014, RILEM.

Zhang J.,Beihang University
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2011

Airspace surveillance system includes all the equipment for surveillance of flight movements of aircraft in the airspace. Airspace surveillance technology works as an important means to guarantee flight safety and increase operation efficiency. In this article, firstly, with the development of airborne avionics, we particularly analyze the progress of airspace surveillance technology, and point out that the development of airspace surveillance technology depends on the support of airborne avionics. Secondly, aimed at the new challenges of airspace surveillance technology, we analyze some new problems, and summarize new methods and application achievement focusing on the collaborative airspace surveillance technology in recent years. We mainly elaborate the influence of navigation integrity on the airspace surveillance performance and methods to increase surveillance credibility. Finally, we discuss some typical applications of airspace surveillance technology and indicate its future trend, combining with the newest operation concepts in the next generation air traffic management system.

Lin P.,University of Electronic Science and Technology of China | Jia Y.,Beihang University
Systems and Control Letters | Year: 2010

This paper investigates collective rotating motions of second-order multi-agent systems. We first consider rotating consensus problems. Using local relative information, we propose a protocol and give a necessary and sufficient condition for rotating consensus of the system. Then, we consider rotating formation control problems. With the help of Lyapunov theory for complex systems, we propose rotating formation protocols and give sufficient conditions to make all agents move with a specific structure in a circular channel. Finally, simulation results are provided to demonstrate the effectiveness of our theoretical results. © 2010 Elsevier B.V. All rights reserved.

Chen H.-X.,Beihang University
European Physical Journal C | Year: 2012

We systematically investigate tri-local (non-local) three-quark baryon fields with U L(2)×U R(2) chiral symmetry, according to their Lorentz and isospin (flavor) group representations. We note that they can also be called "nucleon wave functions" due to this full non-locality. We study their chiral transformation properties and find all the possible chiral multiplets consisting of J=1/2 and J=3/2 baryon fields. We find that the axial coupling constant {pipe}g A{pipe} = 5/3 is only for nucleon fields belonging to the chiral representation (1/2,1) ⊕ (1,1/2), which contains both nucleon and Δ fields. Moreover, all the nucleon fields belonging to this representation have {pipe}g A{pipe} = 5/3. © 2012 Springer-Verlag / Società Italiana di Fisica.

Liu F.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We present a characteristic function method to calculate the probability density functions of the inclusive work in adiabatic two-level quantum Markovian master equations. These systems are steered by some slowly varying parameters and the dissipations may depend on time. Our theory is based on the interpretation of the quantum jump for the master equations. In addition to the calculation, we also find that the fluctuation properties of the work can be described by the symmetry of the characteristic functions, which is exactly the same as in the case of isolated systems. A periodically driven two-level model is used to demonstrate the method. © 2014 American Physical Society.

Tie L.,Beihang University
Journal of Systems Science and Complexity | Year: 2013

If a linear time-invariant system is uncontrollable, then the state space can be decomposed as a direct sum of a controllable subspace and an uncontrollable subspace. In this paper, for a class of discrete-time bilinear systems which are uncontrollable but can be nearly controllable, by studying the nearly-controllable subspaces and defining the near-controllability index, the controllability properties of the systems are fully characterized. Examples are provided to illustrate the conceptions and results of the paper. © 2013 Institute of Systems Science, Academy of Mathematics and Systems Science, CAS and Springer-Verlag Berlin Heidelberg.

In this paper, controllability and near-controllability of discrete-time inhomogeneous bilinear systems without drift are studied. Necessary and sufficient conditions for controllability and near-controllability of the systems are respectively presented. In particular, algorithms for computing the control inputs to achieve the transition of a given pair of states for the controllable systems and nearly controllable systems are also provided. Examples are shown to demonstrate the conceptions and results of the paper. © 2014 Elsevier Ltd. All rights reserved.

Near-controllability is defined for those systems that are uncontrollable but have a large controllable region. It is a property of nonlinear control systems introduced recently, and it has been demonstrated on two classes of discrete-time bilinear systems. This paper studies near-controllability of discrete-time upper-triangular bilinear systems, which are uncontrollable and are more general than the two classes mentioned. A necessary and sufficient condition for the systems in dimension two to be nearly controllable is presented, which covers the existing results. For the systems with high dimensions, necessary conditions and sufficient conditions of near-controllability are provided, which generalize the existing results. In particular, the obtained near-controllability results are applied to controllability of discrete-time bilinear systems. An example also is given to demonstrate the effectiveness, which shows that the controllability problems of discrete-time bilinear systems can be solved by near-controllability. © 2013 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.

Li C.,Beihang University | Zeng R.,Tsinghua University
IEEE Sensors Journal | Year: 2014

A novel optical voltage sensor is proposed by the use of single Fresnel rhomb bismuth germanate crystal. The optical sensing unit is only composed of one voltage sensing crystal and two prism polarizers. The distinguished feature is that the voltage sensing crystal is simultaneously used as a Fresnel rhomb quarter waveplate. An optical phase bias of π/2 is produced by two times of total internal reflection of light wave in the sensing crystal itself, thus additional quarter waveplate usually used in conventional voltage sensor can be removed. Besides the compact optical configuration, the proposed voltage sensor demonstrates larger linear measurement range and good temperature stability in experiments. The ac voltage in the range of 2000 V was measured with a nonlinear error <0.82% and a measurement sensitivity of 2.2 mV/V, and corresponding temperature drift of the output voltage was <0.9% for ambient temperature change in the range of (-10~+50)°. © 2001-2012 IEEE.

Cai G.-B.,Beihang University
Tuijin Jishu/Journal of Propulsion Technology | Year: 2012

The characteristics, development history and current situation of hybrid rocket motor were presented. The potential application of hybrid rocket motor was analyzed based on the astronautic development in China. The hybrid rocket motor can be used in sounding rockets, low cost target drones and missiles, suborbital vehicles, large launch boosters, advanced upper stages and orbital transfer systems. Thus, the application prospect of hybrid rocket motor is extensive. The design method for hybrid sounding rocket in Beijing University of Aeronautics and Astronautics was summarized. The key technologies which affect the developments and applications of hybrid rocket motors were analyzed.

Chen Y.,Beihang University | Chen Y.,Ohio State University | Ghosh S.,Johns Hopkins University
International Journal of Plasticity | Year: 2012

This paper is intended to study the effect of microstructural morphology and loading characteristics on micromechanical stress-wave propagation leading to different damage mechanisms, energy absorption and dissipation characteristics. The composite material microstructure is represented by brittle fibers in a ductile matrix in different arrangements. The matrix material behavior is modeled using a strain-rate dependent elastic-viscoplastic constitutive model with damage evolution based on the Gurson-Tvergaard-Needleman model with a Johnson-Cook type hardening law. Damage in the fiber is modeled by an isotropic continuum damage mechanics (CDM) model. The microstructural failure modes and energy absorption and dissipation properties show strong dependence on the load types, volume fractions and microstructures, with relatively lower dependence on strain rates. The studies show that for the SiC fiber/Al7075-T6 composites, the microstructures with 15-20% unidirectional hexagonal arrangement of fibers are good designs for energy absorption and dissipation. © 2011 Elsevier Ltd. All rights reserved.

Liu F.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We present two kinds of Bochkov-Kuzovlev work equalities in a two-level system that is described by a quantum Markovian master equation. One is based on multiple time correlation functions and the other is based on the quantum trajectory viewpoint. We show that these two equalities are indeed equivalent. Importantly, this equivalence provides us a way to calculate the probability density function of the quantum work by solving the evolution equation for its characteristic function. We use a numerical model to verify these results. © 2014 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.

Huang B.,Tsinghua University | Li C.,Tsinghua University | Tao F.,Beihang University
Enterprise Information Systems | Year: 2014

This article investigates the problem of cloud service composition optimal-selection (CSCOS) in cloud manufacturing (CMfg). The categories of cloud services and their QoS (quality of service) indexes are established. From the perspective of QoS indexes, the relationship among QoS key factors for different kinds of cloud services are analysed and elaborated, and the corresponding objective functions and constraints of CSCOS are proposed. A new chaos control optimal algorithm (CCOA) is designed to address the CSCOS problem, and the simulation results demonstrate that the proposed algorithm can search better solutions with less time-consumption than widely used algorithms such as genetic algorithm (GA) and typical chaotic genetic algorithm (CGA). © 2013 © 2013 Taylor & Francis.

Lu J.,Curtin University Australia | Lu J.,Nanyang Technological University | Lu S.,Beihang University | Jiang S.P.,Curtin University Australia
Chemical Communications | Year: 2011

A highly ordered mesoporous Nafion membrane with a remarkable water retention ability was synthesized via a micelle templating method with self-assembled Pluronic F108 surfactants and its capability to operate under completely dry gas streams is demonstrated. © 2011 The Royal Society of Chemistry.

Shao H.-S.,Beijing University of Technology | Zhang Y.-J.,Beihang University
Journal of High Energy Physics | Year: 2012

The complete set of Feynman rules for the rational part R of QCD corrections in the MSSM are calculated at the one-loop level, which can be very useful in the next-to-leading order calculations in supersymmetric models. Our results are expressed in the 't Hooft-Veltman regularization scheme and in the Four Dimensional Helicity scheme with non-anticommutating and anticommutating γ 5 strategies. © 2012 SISSA.

Streets J.,University of California at Irvine | Tian G.,Beihang University | Tian G.,Princeton University
Nuclear Physics B | Year: 2012

In Streets and Tian (2010) [1] the authors introduced a parabolic flow for pluriclosed metrics, referred to as pluriclosed flow. We also demonstrated in Streets and Tian (2010) (preprint) [2] that this flow, after certain gauge transformations, gives a class of solutions to the renormalization group flow of the nonlinear sigma model with B-field. Using these transformations, we show that our pluriclosed flow preserves generalized Kähler structures in a natural way. Equivalently, when coupled with a nontrivial evolution equation for the two complex structures, the B-field renormalization group flow also preserves generalized Kähler structure. We emphasize that it is crucial to evolve the complex structures in the right way to establish this fact. © 2012 Elsevier B.V.

Bu H.,Beihang University
Energy Economics | Year: 2014

This paper examines the behavior of crude oil futures price volatility and investigates how the EIA weekly crude oil inventory reports announcements, especially information shocks, impact crude oil price movement and volatility. This study focuses on inventory information shocks using a new measure rather than on inventory changes themselves. The empirical results reveal that inventory information shocks rather than actual inventory changes negatively affect crude oil returns on the day the EIA releases the inventory information, although inventory shocks have no effect on daily conditional variance, which mainly follows a GARCH(1,1) process. To test the robustness of our model, we re-estimate the models for three subsamples. According to all results, we find that the effect of inventory shocks is weakened in rapid growth periods and disappears in steep fall markets. © 2014 Elsevier B.V.

Zhao Z.,Peking University | Chen Z.,Peking University | Chen Z.,Beihang University
International Journal of Hydrogen Energy | Year: 2012

Correlations for the laminar burning velocity of premixed CH 4/H 2/O 2/N 2 mixtures were developed using the method of High Dimensional Model Representation (HDMR). Based on experiment data over a wide range of conditions reported in the literature, two types of HDMR correlation (i.e. global and piecewise HDMR correlations) were obtained. The performance of these correlations was assessed through comparison with experimental results and the correlation reported in the literature. The laminar burning velocity predicted by the piecewise HDMR correlations was shown to agree very well with those from experiments. Therefore, the piecewise HDMR correlations can be used as an effective replacement for the full chemical mechanism when the prediction of the laminar burning velocity is needed in certain combustion modeling. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Feng R.,Beihang University
Communications in Computational Physics | Year: 2012

The Cubic-Polynomial Interpolation scheme has been developed and applied to many practical simulations. However, it seems the existing Cubic-Polynomial Interpolation scheme are restricted to uniform rectangular meshes. Consequently, this scheme has some limitations to problems in irregular domains. This paper will extend the Cubic-Polynomial Interpolation scheme to triangular meshes by using some spline interpolation techniques. Numerical examples are provided to demonstrate the accuracy of the proposed schemes. © 2012 Global-Science Press.

Qu Y.,Beihang University | Yang H.,Key Laboratory of Precision Opto Mechatronics Technology of Education Ministry
Journal of Microscopy | Year: 2015

The axial imaging range of optical microscopy is restricted by its fixed working plane and limited depth of field. In this paper, the axial capabilities of an off-the-shelf microscope is improved by inserting a liquid lens, which can be controlled by a driving electrical voltage, into the optical path of the microscope. First, the numerical formulas of the working distance and the magnification with the variation of the focus of the liquid lens are inferred using a ray tracing method and conclusion is obtained that the best position for inserting a liquid lens with consistent magnification is the aperture plane and the rear focal plane of the objective lens. Second, with the liquid lens embedded in the microscope, the numerical relationship between the magnification and the working distance of the proposed flexible-axial-capability microscope and the liquid lens driving voltage is calibrated and fitted using the inferred numerical formulas. Third, techniques including autofocus, extending depth of field and three-dimensional imaging are researched and applied, improving the designed microscope to not only flexibly control its working distance, but also to extend the depth of field near the variable working plane. Experiments show that the presented flexible-axial-capability microscope has a long working distance range of 8 mm, and by calibrating the magnification curve within the working distance range, samples can be observed and measured precisely. The depth of field can be extended to 400 μm from the variable working plane and is 20 times that of the off-the-shelf microscope. © 2015 Royal Microscopical Society.

Cui J.-Y.,Beihang University
Chinese Critical Care Medicine | Year: 2012

Objective: To compare the effect of albumin as a resuscitation fluid with other fluids in lowering the mortality of patients with sepsis. Methods: By searching MEDLINE, Embase, Cochrane Central Registration of Controlled Trials databases, the metaRegister of Controlled Trials, the Medical Editors Trial Amnesty Register, and retrieval of the randomized controlled trial (RCT) literature to compare the result of resuscitation using albumin-containing fluid and other fluids. The study population included adult patients who were diagnosed to have sepsis, and the patients with sepsis who were studied as subgroup. The RevMan 5.0 software was used for Meta-analysis, and the main outcome was the mortality of the hospitalized patients. Results: In the 14 RCTs, 1729 patients received the albumin-containing fluid resuscitation or resuscitation with other fluids. It was found that the patients with sepsis were the only research objects in five studies, and in other nine studies patients with sepsis were studied as subgroup. P=0.98, I 2=0%, i.e. no heterogenicity, and the fixed effect model was used for combining results. There was no evident difference between the group of patients with sepsis resuscitated by albmin-containing fluids and other fluids [odds ratio (OR) was 0.87, 95% confidence interval (95%G7) 0.71-1.07, P=0.18j. The pooled OiR of resuscitation using high concentration albumin solution (20%) was 1.11, 95%Cf 0.71-1.73, P=0.65, the pooled OR of resuscitation using low concentration albumin solution (4%, 5%) was 0.82, 95% CI 0.65-1.03, P= 0.09. Resuscitation with different concentration of albmin-containing fluids was identical with the whole research results. After rejecting six articles of Boldt and other authors, and also saline versus albumin fluid evaluation (SAFE) study, the sensitivity analysis of the study was performed in order to check whether the data produced decisive significance to the whole research results or not. The whole results did not change after their rejection(Boldt studies were rejected: OR 0.82, 95%CI 0.65-1.02, P=0.08; SAFE study was rejected OR: 1.05, 95%CI 0.71-1.55, P=0.82). Therefore the analysis results were satisfactory. Conclusion: The Meta-analysis shows that by using albmin-containing fluids for resuscitation can not lower the mortality of sepsis as compared with other fluids.

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.

Pei S.,Beihang University | Pei S.,City College of New York | Makse H.A.,City College of New York
Journal of Statistical Mechanics: Theory and Experiment | Year: 2013

Searching for influential spreaders in complex networks is an issue of great significance for applications across various domains, ranging from epidemic control, innovation diffusion, viral marketing, and social movement to idea propagation. In this paper, we first display some of the most important theoretical models that describe spreading processes, and then discuss the problem of locating both the individual and multiple influential spreaders respectively. Recent approaches in these two topics are presented. For the identification of privileged single spreaders, we summarize several widely used centralities, such as degree, betweenness centrality, PageRank, k-shell, etc. We investigate the empirical diffusion data in a large scale online social community - LiveJournal. With this extensive dataset, we find that various measures can convey very distinct information of nodes. Of all the users in the LiveJournal social network, only a small fraction of them are involved in spreading. For the spreading processes in LiveJournal, while degree can locate nodes participating in information diffusion with higher probability, k-shell is more effective in finding nodes with a large influence. Our results should provide useful information for designing efficient spreading strategies in reality. © 2013 IOP Publishing Ltd and SISSA Medialab srl.

In a recent article (Ma and Gupta, 2012), the input-to-state stability (ISS) of a hybrid system with packet dropouts is analyzed. Theorem 10 in the article requires stronger assumptions than those listed in its statement. Specifically, it must be assumed that the packet dropout effect μ should be sufficiently small. © 2014 Elsevier Ltd. All rights reserved.

Li Y.-Z.,Beihang University
International Journal of Hydrogen Energy | Year: 2012

The cooling capacity and cooling load of a fuel-cell cooling loop govern the operating temperature of the fuel-cell module and its electrical output, efficiency and other thermodynamic aspects. The aim of this work was to analyze the performance of a polymer-electrolyte-membrane fuel-cell (PEMFC) under changing cooling conditions. A back-iteration algorithm was employed to determine the operating temperature of a PEMFC for which thermodynamic performance models were developed for the entropy generation, exergy-destruction and second-law efficiency using an entropy-analysis method. Electrochemical equations for the calculation of the voltage, power and first-law efficiency of the cell were also formulated. A parametric study was performed to evaluate the effects of varying cooling conditions on the energy and exergy efficiency of the PEMFC. The parameters considered include the electric-current density governing the cooling load, the mass flow rate of the coolant and the external thermal resistance of the cooler, which together determine the cooling ability of the fuel-cell cooling loop. Their influences on operating temperature, voltage, power, energy and exergy efficiencies were numerically investigated. The results indicate that although the power output and exhaust heat of PEMFC is mainly dominated by the electric-current density, the impacts of the coolant's mass flow rate and the cooler's external thermal resistance on the voltage, energy and exergy efficiencies of PEMFC module can't be neglected. In the investigated ranges, the gross energy and exergy efficiencies increase with the cooler's external thermal resistance by 3.2% and 2.45%, and decrease with the increase in coolant's mass flow rate by 1.2% and 0.92%, respectively. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Yang X.,Beihang University | Xiao T.,University of Oxford | Edwards P.P.,University of Oxford
International Journal of Hydrogen Energy | Year: 2011

CuO/TiO2 photocatalysts were prepared and shown to enhance the rate of CO2 photoreduction and the production of total organic carbon (TOC), including HCOOH, HCHO and CH3OH. Resulting TOC could act as electron donors for enhancing visible light hydrogen evolution from Pt/TiO 2 photocatalysts. The impacts on CO2 photoreduction were investigated including the effect of Cu dopant, pH, irradiation time and using Na2SO3 as a sacrificial agent, and those on hydrogen evolution was also studied including TOC concentration and Pt doping. The CO2 photoreduction mechanisms with respect to pH and CO2 reduction potentials were discussed. CuO/TiO2 and Pt/TiO2 photocatalysts were characterized by X-ray diffraction, Raman spectroscopy and diffuse reflection UV-vis spectrophotometry. Both photocatalysts showed a visible light response in comparison with pure TiO2. The photocatalytic experiments and FT-IR spectra indicated that photoproduct desorption was the rate-limiting step in the CO2 photoreduction. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Bos W.J.T.,Ecole Centrale Lyon | Fang L.,Ecole Centrale Lyon | Fang L.,Beihang University
Physics of Fluids | Year: 2012

Direct numerical simulation data show that the variance of the coupling term in passive scalar advection by a random velocity field is smaller than it would be if the velocity and scalar fields were statistically independent. This effect is analogous to the "depression of nonlinearity" in hydrodynamic turbulence. We show that the trends observed in the numerical data are qualitatively consistent with the predictions of closure theories related to Kraichnan's direct interaction approximation. The phenomenon is demonstrated over a range of Prandtl numbers. In the inertial-convective range the depletion is approximately constant with respect to wavenumber. The effect is weaker in the Batchelor range. © 2012 American Institute of Physics.

Sun Y.,Carnegie Mellon University | Sun Y.,Beihang University | Jallerat Q.,Carnegie Mellon University | Szymanski J.M.,Carnegie Mellon University | Feinberg A.W.,Carnegie Mellon University
Nature Methods | Year: 2015

Our Patterning on Topography (PoT) printing technique enables fibronectin, laminin and other proteins to be applied to biomaterial surfaces in complex geometries that are inaccessible using traditional soft lithography techniques. Engineering combinatorial surfaces that integrate topographical and biochemical micropatterns enhances control of the biotic-abiotic interface. Here, we used this method to understand cardiomyocyte response to competing physical and chemical cues in the microenvironment.

Diao P.,Beihang University | Liu Z.,CAS Beijing National Laboratory for Molecular
Advanced Materials | Year: 2010

Single-walled carbon nanotubes (SWNTs), as one of the most promising one-dimension nanomaterials due to its unique structure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct ordered alignments. Vertically aligned SWNTs (v-SWNTs) have been successfully prepared by using direct growth and chemical assembly strategies. In this review, we focus explicitly on the v-SWNTs fabricated via chemical assembly strategy. We provide the readers with a full and systematic summary covering the advances in all aspects of this area, including various approaches for the preparation of v-SWNTs using chemical assembly techniques, characterization, assembly kinetics, and electrochemical properties of v-SWNTs. We also review the applications of v-SWNTs in electrochemical and bioelectrochemical sensors, photoelectric conversion, and scanning probe microscopy. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

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.

This article studies the influence of local knowledge on the impact of science on institutional change in ecological and environmental management. Based on an empirical study on desertification control in 12 counties in north China, the study found the following major results: (1) although there was a cubic relationship between the extent and effect of local knowledge, local knowledge significantly influenced the impact of science on institutional change; (2) local knowledge took effect mainly through affecting formal laws and regulations, major actors, and methods of desertification control in institutional change but had no significant impact on the types of property rights; and (3) local knowledge enhanced the impact of science on the results of desertification control through affecting the impact of science on institutional change. These findings provide a reference for researchers, policy makers, and practitioners, both in China and in other regions of the world, to further explore the influence of local knowledge on the impact of science on institutional change and the roles of local knowledge or knowledge in institutional change and governance. © 2014, Springer Science+Business Media New York.

Li C.-S.,Beihang University
Wuli Xuebao/Acta Physica Sinica | Year: 2014

In the applications of two external fields, such as stresses and electric fields, the optical modulation properties of some crystals are theoretically analyzed using the method of index ellipsoid. Simple mathematical formulas for the calculations of the field-induced principal refractive indexes of some crystals and corresponding azimuthal angles of their principal axes can be deduced from the equation of index ellipsoid if there exists only one nonzero cross term in the equation, e.g. x1x2. According to these simple formulas, we can find out some crystals exhibiting dual transverse electrooptic effect, e.g. crystals of the 6̄ symmetry point group. Under two simultaneously applied external stresses, elastooptic birefringence of a crystal is proportional to the difference between the two external stresses, and the orientations of their birefringent axes are unchanged. When a stress and an electric field are simultaneously and perpendicularly applied to some crystals such as cubic crystals of 4̄3m point group, the field-induced birefringence of the crystal is proportional to the weighted geometric mean of the applied stress and electric field, and the orientations of their birefringent axes only depend on the ratio of the applied electric field and stress. The above electrooptic and elastooptic modulation properties are useful to the design of novel optical modulators and sensors. © 2014 Chinese Physical Society.

Li Y.-Z.,Beihang University | Lee K.-M.,Georgia Institute of Technology
IEEE Transactions on Industrial Electronics | Year: 2011

This paper presents the dynamic model, analysis, and fuzzy control of a microchannel-heat-exchanger (MHE) space cooling network for dissipating exhaust heat of onboard electronic components inside spacecraft to the outer space environment. Along with a method for modeling a nonlinear fluid resistance network, a detailed analysis of flow rate changes and temperature transients of the MHE cooling network is given, providing a basis for developing a fuzzy coordination control strategy. The fuzzy controller employs two synergic PID controllers to simultaneously control both fluid- and radiation-based cooling mechanisms. The fuzzy coordination controller has been numerically evaluated, demonstrating a better performance than single-input PID controllers in terms of its ability to leverage between two actuators in rejecting disturbances and preventing overmanipulation. This unique feature will benefit the operating reliability of the MHE cooling network under stiff space working conditions. © 2011 IEEE.

Wang Y.,Beihang University
Kongzhi Lilun Yu Yingyong/Control Theory and Applications | Year: 2012

The variable-pump controlling variable-motor (VPCVM) is an essential nonlinear system with dual-input, single-output and coupling, for which regular control algorithms are ineffective to achieve the required control performances. Based on linearization theory for VPCVM, we propose an improved Bang-Bang control algorithm for tackling the nonlinearity and the unsolvable coupling. First we develop a mathematical model of VPCVM involving the multiplication nonlinearity with the output variable; and then, we linearize the model by using the feedback linearization theory. Based on the linearized model, we develop the improved Bang-Bang control algorithm to achieve the rapid control for VPCVM. Simulation results demonstrate that the proposed algorithm realizes the desired rapid control on VPCVM with performances higher than that of conventional control methods. Furthermore, this algorithm exhibits a strong robustness against the variations of rotational speed and load.

Guan J.,University of Chinese Academy of Sciences | Guan J.,Fudan University | Chen K.,CAS Institute of Policy and Management | Chen K.,Beihang University
Research Policy | Year: 2012

Although a large amount of past research has theorized about the character of national innovation systems (NISs), there has been limited process-oriented empirical investigation of this matter, possibly for methodological reasons. In this paper, we first propose a relational network data envelopment analysis (DEA) model for measuring the innovation efficiency of the NIS by decomposing the innovation process into a network with a two-stage innovation production framework, an upstream knowledge production process (KPP) and a downstream knowledge commercialization process (KCP). Although the concept of innovation efficiency is a simplification of the innovation process, it may be a useful tool for guiding policy decisions. We subsequently use a second-step partial least squares regression (PLSR) to examine the effects of policy-based institutional environment on innovation efficiency, considering statistical problems such as multicollinearity, small datasets and a small number of distribution assumptions. The hybrid two-step analytical procedure is used to consider 22 OECD (Organisation for Economic Co-operation and Development) countries. A significant rank difference, which indicates a non-coordinated relationship between upstream R&D (research and development) efficiency and downstream commercialization efficiency, is identified for most countries. The evidence also indicates that the overall innovation efficiency of an NIS is mainly subject to downstream commercial efficiency performance and that improving commercial efficiency should thus be a primary consideration in future innovation policy-making in most OECD countries. Finally, the results obtained using PLSR show that the various factors chosen to represent the embedded policy-based institutional environment have a significant influence on the efficiency performance of the two individual component processes, confirming the impact of public policy interventions undertaken by the government on the innovation performance of NISs. Based on these key findings, some country-specific and process-specific innovation policies have been suggested. © 2011 Elsevier B.V. All rights reserved.

Ma H.,Beihang University | Ma H.,Shandong University of Science and Technology | Zhang W.,Shandong University of Science and Technology | Hou T.,Shandong University of Science and Technology
Automatica | Year: 2012

In this paper we consider the infinite horizon H2 H∞ control problem for discrete-time time-varying linear systems subject to Markov jump parameters and state-multiplicative noise. A stochastic version of a bounded real lemma is firstly developed for a general class of discrete-time time-varying Markov jump systems with state- and disturbance-multiplicative noise. By which we present a necessary and sufficient condition for the solvability of the H2H∞ control problem in terms of four coupled discrete-time Riccati equations. Moreover, the obtained design is applied to a macroeconomic problem to verify its effectiveness. © 2012 Elsevier Ltd. All rights reserved.

In this paper, we develop a helicopter's formation flying model with telegraph poles and electrical wire to study each helicopter's flying behavior in the low airspace. The numerical results show that the proposed model can qualitatively describe the influences of the telegraph poles and electrical wire on the helicopter's formation flying behavior in the low airspace and that the effects will be related to each helicopter's initial conditions. © 2011 Springer Science+Business Media B.V.

Li P.,Anhui University of Architecture | Deng S.-H.,Beihang University | Huang J.,Anhui University of Architecture
Applied Physics Letters | Year: 2011

Based on first-principles calculations, we suggest that the P Zn-2VZn complex is the dominant acceptor in phosphorus-doped ZnO with a calculated transition level of 150 meV. We suggest that the out-diffusion of zinc interstitials will indirectly favor the formation of the PZn-2VZn complex. According to this mechanism, an upper limit of annealing temperature of about 860 C is obtained, which is high enough to activate the doped ZnO from n- to p-type. This mechanism applies to the other group-V dopants. The above results are in agreement with the experimental reports. © 2011 American Institute of Physics.

Yu Y.,Beihang University | Shi J.,Tokyo Institute of Technology | Nakamura Y.,Tokyo Institute of Technology
Acta Materialia | Year: 2012

Magnetic anisotropy of CoPt/AlN multilayer films has been studied by systematically varying the nominal thickness of CoPt layers, t CoPt (1-10 nm), and the annealing temperature, T a (300-500 °C). The as-deposited films show in-plane magnetic anisotropy in the full range of t CoPt, whereas the annealed films show perpendicular magnetic anisotropy (PMA) within small t CoPt but change to in-plane magnetic anisotropy when t CoPt is over a certain thickness. The critical thickness for such anisotropic transformations increases as the T a increases. The maximum PMA obtained in this work is 1.13 × 10 7 erg cm -3. The interface roughness was analyzed by cross-sectional high-resolution electron microscopy and X-ray reflectivity using an abrupt interface model with a Debye exponent shape. The internal stress was analyzed by X-ray diffraction using an equal biaxial stress model. The results show that the CoPt/AlN interface roughness decreases from 0.385 nm to 0.158 nm and the internal stress increases from -2.36 GPa (compressive) to 1.73 GPa (tensile), as the T a increases to 500 °C. The roles of the interface roughness and the internal stress in the magnetic anisotropy of CoPt/AlN multilayer films are studied. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Chen H.-X.,Beihang University
European Physical Journal C | Year: 2012

We investigate the chiral (flavor) structure of tetraquarks, and study chiral transformation properties of the "non-exotic" [(3,3)⊕(3,3)] and [(8,1)⊕(1,8)] tetraquark chiral multiplets. We find that as long as this kind of tetraquark states contains one quark and one antiquark having the same chirality, such as qLqLq̄Lq̄R +qRqRq̄Rq̄L, they transform in the same way as the lowest level q̄q chiral multiplets under chiral transformations. There is only one [(3,3)⊕(3,3)] chiral multiplet whose quark-antiquark pairs all have the opposite chirality (qLqLq̄Rq̄R + qRqRq̄Lq̄L), and it transforms differently from others. Based on these studies, we construct local tetraquark currents belonging to the [(3,3)⊕(3,3)] and having quantum numbers J PC=1 -+. © 2012 The Author(s).

Chen H.-X.,Beihang University
European Physical Journal C | Year: 2012

We study the structure of local baryon fields using the method of QCD sum rule. We only consider the single baryon fields and calculate their operator product expansions. We find that the octet baryon fields belonging to the chiral representations [(3,3)⊕(3,3)] and [(8,1)⊕(1,8)] and the decuplet baryon fields belonging to the chiral representations [(3,6)⊕(6,3)] lead to the baryon masses which are consistent with the experimental data of ground baryon masses. We also calculate their decay constants, check our normalizations for baryon fields in Chen et al. (Phys. Rev. D 81:054002, 2009) and find that they are well-defined. © 2012 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica.

Enhancing mineral image especially making mineral image details clear is very useful for mineral analysis. To effectively enhance mineral image, an algorithm based on the toggle contrast operator and top-hat based contrast operator is proposed in this paper. Sequentially combining the toggle contrast operator and top-hat based contrast operator could be used to identify image features especially the image details. So, appropriately exacting the identified image features by the sequentially combined toggle and top-hat based contrast operator is important for mineral image enhancement, which is analyzed firstly in this paper. After that, the multi-scale extension of feature extraction is given and used to construct the final features for mineral image enhancement. By importing the final extracted image features into the original mineral image through contrast enlargement, the original mineral image is well enhanced and the mineral image details are very clear. Experimental results on different types of mineral images verified the effective performance of the proposed algorithm. © 2012 Elsevier Ltd.

Xiao Y.,Prefectural University of Hiroshima | Wang J.,Beihang University
IEEE Signal Processing Letters | Year: 2011

Performance of the conventional broadband active noise control (ANC) system may degrade severely if its primary and reference noise signals contain both wideband and narrowband components simultaneously. In this letter, we propose a new feedforward hybrid ANC system capable of reducing such primary noise signals. First, typical simulation results are provided to show the performance deterioration of the conventional system in the presence of mixture of wideband and narrowband components. Next, a new hybrid ANC system is proposed to tackle the problem. The new system consists of three subsystems, i.e., a sinusoidal noise canceller, a broadband and a narrowband ANC subsystem, which work in harmony. Extensive simulations are conducted to demonstrate the effectiveness of the proposed system. © 2011 IEEE.

Xiao L.,Defective Product Administrative Center | Gao F.,Beihang University
IEEE Transactions on Intelligent Transportation Systems | Year: 2011

In this paper, the practical string stability of both homogeneous and heterogeneous platoons of adaptive cruise control (ACC) vehicles, which apply the constant time headway spacing policy, is investigated by considering the parasitic time delays and lags of the actuators and sensors when building the vehicle longitudinal dynamics model. The proposed control law based on the sliding-mode controller can guarantee both homogeneous and heterogeneous string stability, if the control parameters and system parameters meet certain requirements. The analysis of the negative effect of the parasitic time delays and lags on the string stability indicates that the negative effect of the time delays is larger than that of the time lags. This paper provides a practical means to evaluate the ACC systems applying the sliding-mode controller and provides a reasonable proposal to design the ACC controller from the perspective of the practical string stability. © 2011 IEEE.

Wei X.,Ludong University | Guo L.,Beihang University
International Journal of Robust and Nonlinear Control | Year: 2010

A novel type of control scheme combining the disturbance-observer-based control (DOBC) with H∞ control is proposed for a class of complex continuous models with disturbances. The disturbances are supposed to include two parts. One part in the input channel is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modeling perturbations. The other part is supposed to have the bounded H 2-norm. Parametric uncertainties exist both in concerned plant and in exogenous subsystem. The disturbance observers based on regional pole placement and D-stability theory are designed and integrated with conventional H∞ control laws. The new composite DOBC and H∞ control scheme is applied to complex continuous models for the case with known and unknown nonlinearity, respectively. Then the first type of disturbances can be estimated and rejected, and the second type can be attenuated; simultaneously, the desired dynamic performances can be guaranteed. Simulations for a flight control system are given to demonstrate the effectiveness of the results and compare the proposed results with the previous schemes. Copyright © 2009 John Wiley & Sons, Ltd.

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.

Xue S.,Beihang University | Lu P.,Iowa State University
Journal of Guidance, Control, and Dynamics | Year: 2010

A fully constrained predictor-corrector entry guidance algorithm for horizontal landing X-33 vehicles is investigated. The quasi-equilibrium-glide condition (QEGC), a zeroth-order solution in an asymptotic expansion of the trajectory about a equilibrium-glide path, is used in entry flight mechanics. The three-degree-of-freedom dynamics for an entry vehicle over a spherical rotating Earth are described by dimensionless equations of motion. The bank-angle histories reveal that for missions with small cross-ranges, the guidance algorithm commands two bank reversals. The impact of these significant dispersions can be seen from the wide spread of the terminal area energy management (TAEM) velocity azimuth angle in a range of 40 deg, which indicates very different ground tracks near the TAEM interface, due to the large dispersions.

Zhong M.,Beihang University | Zhou D.,Tsinghua University | Ding S.X.,University of Duisburg - Essen
IEEE Transactions on Automatic Control | Year: 2010

This technical note deals with the problem of finite horizon H∞ fault detection for linear discrete time-varying systems. Using an observer-based fault detection filter (FDF) with residual feedback as a residual generator, a new problem formulation of fault detection is first presented. Then the design of finite horizon H∞ -FDF is converted into a minimum problem of certain quadratic form. Through building a relationship with Krein space projection and applying innovation analysis, a sufficient and necessary condition for the minimum is derived and a solution to the H∞-FDF is obtained by recursively computing Riccai recursions. Numerical examples are given to show the effectiveness of the proposed method. © 2006 IEEE.

Lin L.,Sun Yat Sen University | Luo P.,Sun Yat Sen University | Chen X.,Beihang University | Zeng K.,Sun Yat Sen University
Pattern Recognition | Year: 2012

Natural image patches are fundamental elements for visual pattern modeling and recognition. By studying the intrinsic manifold structures in the space of image patches, this paper proposes an approach for representing and recognizing objects with a massive number of local image patches (e.g. 17×17 pixels). Given a large collection (>104) of proto image patches extracted from objects, we map them into two types of manifolds with different metrics: explicit manifolds of low dimensions for structural primitives, and implicit manifolds of high dimensions for stochastic textures. We define these manifolds grown from patches as the ε-balls, where ε corresponds to the perception residual or fluctuation. Using these ε-balls as features, we present a novel generative learning algorithm by the information projection principle. This algorithm greedily stepwise pursues the object models by selecting sparse and independent ε-balls (say 103 for each category). During the detection and classification phase, only a small number (say 20) of features are activated by a fast KD-tree indexing technique. The proposed method owns two characters. (1) Automatically generating features (ε-balls) from local image patches rather than designing marginal feature carefully and category-specifically. (2) Unlike the weak classifiers in the boosting models, these selected ε-ball features are used to explain object in a generative way and are mutually independent. The advantage and performance of our approach is evaluated on several challenging datasets with the task of localizing objects against appearance variance, occlusion and background clutter. © 2011 Elsevier Ltd. All rights reserved.

Tian Y.,CAS Beijing National Laboratory for Molecular | Su B.,CAS Beijing National Laboratory for Molecular | Jiang L.,CAS Beijing National Laboratory for Molecular | Jiang L.,Beihang University
Advanced Materials | Year: 2014

Engineering the wettability of solid materials is a traditional, yet key issue in surface science and attracts tremendous interest by researchers in diverse fields. Recently, different superwetting phenomena have been discovered in both nature and experimental results. Therefore, in this review, various superwetting states, leading to a "superwettability" system, are summarized and predicted. Fundamental rules for understanding superwettability are discussed, mainly taking superhydrophobicity in air as an example. Then, some recent application progress of individual members of this "superwettability" system are introduced. Notably, several novel application fields, mainly gas, water, oil and/or other liquid environments, are presented in the following section. By combining different members of this "superwettability" system, new interfacial functions can be generated, allowing unexpected applications, such as in environmental protection, energy, green industry, and many other important domains. Finally, the future development of this interesting "superwettability" system is discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

He L.,Beijing Normal University | Guo L.,Beihang University
Applied Physics Letters | Year: 2010

Here we report the competition of superexchange and double exchange interactions in the molecule [(NH3)4 Co (OH)2 Co (NH3)4]4+. Magnetic data reveal a S=3 ground state arising from the competition. The canting angle between the magnetic moments of the Co2+ and Co4+ ions is about 92.5°. The double exchange parameter is estimated to be sevenfold of the superexchange parameter. The result presented here opens a way to introducing of ferromagnetic double exchange interaction to the single molecular magnets via the charge disproportionation between valence-variable transition-metal ions. © 2010 American Institute of Physics.

Yao Y.P.,Beihang University | Zhou A.N.,Institute of Chemical Technology
Geotechnique | Year: 2013

A constitutive, non-isothermal unified hardening (UH) model is presented to interpret the thermo-elasto-plastic behaviours of normally consolidated and overconsolidated clays. Two yield surfaces are adopted in the proposed model: the current yield surface and the reference yield surface. A UH parameter (H) is developed to describe the evolution of the current yield surface, and the plastic volumetric strain is employed to quantify the hardening of the reference yield surface. The similarity ratio (RT) between the current yield surface and the reference yield surface, which is a function of the temperature and the plastic volumetric strain, is developed to govern the volume change behaviour and the shear strength of soils with different stress histories and at varying temperatures. The performance of the proposed model is then discussed in five typical scenarios: isotropic heating and cooling, drained/undrained triaxial compression with constant temperatures, and heating under constant non-isotropic states (drained/undrained). The mechanisms for thermal contraction/swelling and thermal failure are interpreted within the framework of the proposed non-isothermal UH model. Finally, the proposed model is validated through test results in the literature: heating/cooling tests, temperaturecontrolled drained triaxial compressions, and temperature-controlled undrained triaxial compressions.

Liu N.,Huazhong University of Science and Technology | Jiang Y.,Beihang University | Zhou Y.,CAS Beijing National Laboratory for Molecular | Xia F.,Huazhong University of Science and Technology | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2013

Pore me another one: Sub-nanomolar sequence-specific DNA detection and sub-micromolar small-molecule (ATP) detection was shown by way of self-assembly and disassembly of DNA superstructures within solid-state nanopores (see scheme). These DNA structures provide a built-in amplification mechanism to increase the signal strength and sensitivity. This sensor was also shown to work within complex mixtures, such as mammalian serum. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zheng Z.,University of Chinese Academy of Sciences | Gao Q.,University of Chinese Academy of Sciences | Gao Q.,Beihang University
Journal of Power Sources | Year: 2011

Hierarchical porous carbons are prepared by an easy one-step process of carbonization and activation derived from phenol-formaldehyde resins, in which potassium hydroxide acts as both the catalyst of polymerization and the activation reagent. The simple one-step preparation saves the cost of carbons and leads to high yield. The porous carbons have high surface areas with abundant pore structures. The plenty of micropores and small mesopores increase the capacitance and make the electrolyte ions diffuse fast into the pores. These hierarchical porous carbons show high performance for supercapacitors possessing of the optimized capacitance of 234 F g-1 in aqueous electrolyte and 137 F g-1 in organic electrolyte with high capacitive retention. © 2010 Elsevier B.V.

Pan B.,Beihang University | Xie H.,Tsinghua University | Wang Z.,Catholic University of America
Applied Optics | Year: 2010

In digital image correlation (DIC), to obtain the displacements of each point of interest, a correlation criterion must be predefined to evaluate the similarity between the reference subset and the target subset. The correlation criterion is of fundamental importance in DIC, and various correlation criteria have been designed and used in literature. However, little research has been carried out to investigate their relations. In this paper, we first provide a comprehensive overview of various correlation criteria used in DIC. Then we focus on 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 sum of squared difference (PSSDab) criterion with two additional unknown parameters, since they are insensitive to the scale and offset changes of the target subset intensity and have been highly recommended for practical use in literature. The three correlation criteria are analyzed to establish their transversal relationships, and the theoretical analyses clearly indicate that the three correlation criteria are actually equivalent, which elegantly unifies these correlation criteria for pattern matching. Finally, the equivalence of these correlation criteria is further validated by numerical simulation and actual experiment. © 2010 Optical Society of America.

Hoang T.,Catholic University of America | Pan B.,Beihang University | Nguyen D.,Catholic University of America | Wang Z.,Catholic University of America
Optics Letters | Year: 2010

Fringe-projection profilometry is one of the most commonly used noncontact methods for acquiring the threedimensional (3D) shape information of objects. In practice, the luminance nonlinearity caused by the gamma effect of a digital projector and a digital camera yields undesired fringe intensity changes, which substantially reduce the measurement accuracy. In this Letter, we present a robust and simple scheme to eliminate the intensity nonlinearity induced by the gamma effect by combining a universal phase-shifting algorithm with a gamma correction method. First, by using three-step and large-step phase-shifting techniques, the gamma value involved in the measurement system can be detected. Then, a gamma pre-encoding process is applied to the system for actual 3D shape measurements. With the proposed technique, high accuracy of measurement can be achieved with the conventional smallstep phase-shifting algorithm. The validity of the technique is verified by experiments. © 2010 Optical Society of America.

Zhao Q.P.,Beihang University
Science China Information Sciences | Year: 2011

Virtual natural phenomena obtained through mathematical-physical modeling and simulation as well as graphics emulation can meet the user's requirements for sensory experiences to a certain extent but they can hardly have the same accurate physical consistency as real natural phenomena. The technology for data acquisition and natural phenomena simulation can enable us to obtain multi-dimensional and multi-modal data directly from real natural phenomena and, based on these real data, to establish digital models highly consistent with real natural phenomena in appearance, physics, behavior or many other aspects, thus making a virtual natural phenomenon a direct mapping of real natural phenomenon. This approach is conducive to resolving problems concerning the reliability and availability of virtual reality. At present the technology for acquiring and simulating dada of natural phenomena is still in its initial stage. This paper gives a review of the related investigations. Firstly, we briefly introduce the basic methods and techniques concerned, then, based on the difference between the basic elements of various natural phenomena, we discuss the current studies on such natural phenomena as light, water, fire, smoke, dynamic terrain, etc., and finally, in connection with issues in the present research and possible future direction of development, we put forth a number of theoretical and technical problems, hoping they can be resolved in the near future. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

In the biomedical domain, there are immense data and tremendous increase of genomics and biomedical relevant publications. The wealth of information has led to an increasing amount of interest in and need for applying information retrieval techniques to access the scientific literature in genomics and related biomedical disciplines. In many cases, the desired information of a query asked by biologists is a list of a certain type of entities covering different aspects that are related to the question, such as cells, genes, diseases, proteins, mutations, etc. Hence, it is important of a biomedical IR system to be able to provide relevant and diverse answers to fulfill biologists' information needs. However traditional IR model only concerns with the relevance between retrieved documents and user query, but does not take redundancy between retrieved documents into account. This will lead to high redundancy and low diversity in the retrieval ranked lists. In this paper, we propose an approach which employs a topic generative model called Latent Dirichlet Allocation (LDA) to promoting ranking diversity for biomedical information retrieval. Different from other approaches or models which consider aspects on word level, our approach assumes that aspects should be identified by the topics of retrieved documents. We present LDA model to discover topic distribution of retrieval passages and word distribution of each topic dimension, and then re-rank retrieval results with topic distribution similarity between passages based on N-size slide window. We perform our approach on TREC 2007 Genomics collection and two distinctive IR baseline runs, which can achieve 8% improvement over the highest Aspect MAP reported in TREC 2007 Genomics track. The proposed method is the first study of adopting topic model to genomics information retrieval, and demonstrates its effectiveness in promoting ranking diversity as well as in improving relevance of ranked lists of genomics search. Moreover, we proposes a distance measure to quantify how much a passage can increase topical diversity by considering both topical importance and topical coefficient by LDA, and the distance measure is a modified Euclidean distance.

Liu F.,Beihang University | Miranda-Saavedra D.,Northumbria University
Gene | Year: 2014

Transcription factors (TFs) bind to specific DNA regions, although their binding specificities cannot account for their cell type-specific functions. It has been shown in well-studied systems that TFs combine with co-factors into transcriptional regulatory modules (TRMs), which endow them with cell type-specific functions and additional modes of regulation. Therefore, the prediction of TRMs can provide fundamental mechanistic insights, especially when experimental data are limiting or when no regulatory proteins have been identified. Our method rTRM predicts TRMs by integrating genomic information from TF ChIP-seq data, cell type-specific gene expression and protein-protein interaction data. Here we present a freely available web interface to rTRM (http://www.rTRM.org/) supporting all the options originally described for rTRM while featuring flexible display and network calculation parameters, publication-quality figures as well as annotated information on the list of genes constituting the TRM. © 2014 Elsevier B.V.

Sun Y.-H.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

The focusing nonlinear Schrödinger equation (NLSE) describes propagation of quasimonochromatic waves in weakly nonlinear media. The aim of this study is to determine conditions of soliton synchronization in the NLSE in terms of the solitons' position and phase parameters. For this purpose, the concept of asymptotic middle states of solitons in the NLSE is first introduced. With soliton solutions of the NLSE, it is shown that soliton synchronization can be achieved by synchronizing the asymptotic middle states of the solitons, and conditions of soliton synchronization in terms of the solitons' position and phase parameters are given. Although the interaction of the solitons is nonlinear, the conditions are linear equations. Then, aided with the synchronization conditions, simple initial conditions are presented for producing synchronized interaction of solitons without the need to obtain analytic expressions for the synchronized interaction of the solitons. The initial conditions are summations of fundamental solitons with no mutual overlap, so they might be convenient to implement in applicative contexts. © 2016 American Physical Society.

Wang Y.,North China Electrical Power University | Liu J.,Beihang University
International Journal of Advanced Manufacturing Technology | Year: 2013

Assembly sequence planning is a typical of NP-complete problem which will spend a large amount of computation time or disk memory once the assembly becomes complex. The complex product or assembly is composed of many parts and the number of assembly relationships between them is numerous. To decrease the difficulty of assembly sequence planning of complex products, the subassembly identification methods are focused on. It aims to decompose a complex assembly into a limitative number of subassemblies. Each subassembly contains a relatively smaller number of parts and the assembly sequence planning tasks of them can be handled efficiently. The subassembly identification methods for assembly sequence planning are summarized with respect to assembly constraints. The assembly constraints including the topological, geometrical, and process constraints are considered and merged into the assembly models for subassembly identification. The assembly models are generally represented as directed or undirected assembly diagrams including these considered constraints. It is generally taken as the input information to generate appropriate subassemblies complying with the requirements. The graph theories and graph search algorithms, integer programming methods and the emerging techniques, such as the knowledge-based methods, the intelligent algorithms and the virtual technology, etc. are advocated to resolve the subassembly identification problem with respect to the assembly models. The hierarchical assembly tree is widely used to represent the results of subassembly identification. These useful methods are not only used to subassembly identification for assembly sequence planning, but also successfully referred to by product disassembly. © 2013 Springer-Verlag London.

Bai H.,CAS National Center for Nanoscience and Technology | Bai H.,University of Chinese Academy of Sciences | Ju J.,CAS Beijing National Laboratory for Molecular | Ju J.,University of Chinese Academy of Sciences | And 2 more authors.
Advanced Materials | Year: 2012

Spider silk has been an attractive biopolymer since ancient times. Learning from both its excellent properties and spinning process, silk provides people with inspiration to develop functional fibers. Recently, inspired by shiny water droplets on a spider's web, we revealed that the capture silk of the cribellate spider would deform to have a special periodic spindle-knots structure and hence displayed unique wettability, making it efficient at directional water-collecting. This provides insights in designing functional fibers with unique wettability, by either creating special structures on the fiber surface, or modifying it with responsive molecules. These bioinspired functional fibers may find applications in many fields, such as water collection, smart catalysis, filtration, and sensing. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Su B.,CAS Beijing National Laboratory for Molecular | Wang S.,CAS Beijing National Laboratory for Molecular | Wu Y.,CAS Beijing National Laboratory for Molecular | Chen X.,Beihang University | And 2 more authors.
Advanced Materials | Year: 2012

Elaborately programmed fluorescent calcein nanowire arrays can be prepared with the aid of superhydrophobic pillar-structured surfaces with high adhesion. Each nanowire can be precisely positioned by well designed tip-structured micropillars, indicating an advance in the methodologies of controlling small molecular 1D organic nanostructures. The as-prepared fluorescent nanowire arrays can serve as a ferrous salt sensing device. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Liu F.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2016

I present a technical report indicating that the two methods used for calculating characteristic functions for the work distribution in weakly driven quantum master equations are equivalent. One involves applying the notion of quantum jump trajectory [Phys. Rev. E 89, 042122 (2014)PLEEE81539-375510.1103/PhysRevE.89.042122], while the other is based on two energy measurements on the combined system and reservoir [Silaev, Phys. Rev. E 90, 022103 (2014)PLEEE81539-375510.1103/PhysRevE.90.022103]. These represent backward and forward methods, respectively, which adopt a very similar approach to that of the Kolmogorov backward and forward equations used in classical stochastic theory. The microscopic basis for the former method is also clarified. In addition, a previously unnoticed equality related to the heat is also revealed. © 2016 American Physical Society.

Cui L.,Beihang University
Infrared Physics and Technology | Year: 2016

Experiments and theoretical investigations have shown that the atmosphere turbulence exhibits both anisotropic and non-Kolmogorov properties. In this paper, based on the anisotropic generalized von Karman spectrum and the Rytov approximation theory, new expression for the irradiance scintillation index of optical waves is derived for Gaussian beam propagating through weak anisotropic non-Kolmogorov turbulence. Compared with previously published results, it considers simultaneously the asymmetry property of turbulence cells or eddies in the orthogonal xy-plane, the general spectral power law in the range 3–4 instead of constant value of 11/3 for the Kolmogorov turbulence, and the finite turbulence inner and outer scales. Two anisotropic factors are introduced to parameterize the anisotropy of turbulence cells or eddies in horizontal and vertical directions. In the special cases of these two anisotropic factors equaling one and the finite turbulence inner and outer scales equaling separately zero and infinite, the derived expression can reduce correctly to the previously published results. Calculations are performed to analyze the derived results. © 2016 Elsevier B.V.

Doi M.,Beihang University
European Physical Journal: Special Topics | Year: 2016

Dynamic coarse graining is a procedure to map a dynamical system with large degrees of freedom to a system with smaller degrees of freedom by properly choosing coarse grained variables. This procedure has been conducted mainly by empiricisms. In this paper, I will discuss a theoretical principle which may be useful for this procedure. I will discuss how to choose coarse grained variables (or slow variables), and how to set up their evolution equations. To this end, I will review the classical example of dynamic coarse graining, i.e., the Brownian motion theory, and show a variational principle for the evolution of the slow variables. The principle, called the Onsager principle, is useful not only to derive the evolution equations, but also to solve the problems. © 2016 EDP Sciences and Springer

Lang R.,Beihang University
Match | Year: 2010

For any arbitrary real number a, the general Randić index R α(G) of a graph G, is defined as Σ uvεE(G)(d(u)d(v)) α, where uv is an edge of G, d(u) is the degree of vertex u in G. In this paper we characterize the structures of extremal chemical trees with the minimum general Randić index and give the structure of chemical graphs with minimum general Randić index, for -1 < α < 0.

Wang G.,Beihang University | Guan J.,Fudan University
Journal of Informetrics | Year: 2010

Scientists from universities are becoming more proactive in their efforts to commercialize research results. Patenting, as an important channel of university knowledge transfer, has initiated a controversy on potential effects for the future of scientific research. This paper contributes to the growing study on the relationship between patenting and publishing among faculty members with China's evidence in the field of nanotechnology. Data from top 32 most prolific universities in patenting are used to examine the relationship, consisting of 6321 confirmed academic inventors who both publish and patent over the time period 1991-2008. By controlling for heterogeneity of patenting activities, patenting experience, institutional affiliation and collaboration with foreign researchers, the findings in China's nanotechnology generally support earlier investigations concluding that patenting activity does not adversely affect research output. Patenting, however, has negative impacts on both quantity and quality of university researchers' publication output, when the assignee lists include corporations or scientists themselves. © 2010 Elsevier Ltd.

Wu Y.,CAS Institute of Chemistry | Su B.,CAS Institute of Chemistry | Jiang L.,CAS Institute of Chemistry | Jiang L.,Beihang University
ACS Nano | Year: 2012

The nanotechnology world is being more and more attracted toward high aspect ratio one-dimensional nanostructures due to their potentials as building blocks for electronic/optical devices. Here, we propose a novel method to generate nanowire patterns with assistance of superhydrophobic flexible polydimethylsiloxane (PDMS) substrates. Micropillar gaps are tunable via a stretching process of the PDMS surface; thus, diverse nanowire patterns can be formed by stretching the same PDMS surface in various ways. Importantly, square nanowire loops with alternative compositions can be generated through a double-stretching process, showing an advanced methodology in controlling the alignment of nanowires. Since alternative fluorescent molecules will be quenched by diverse chemical substances, this alternative nanowire loop shows a selective detection for diverse target compounds, which greatly improves the application of this nanowire patterning approach. Furthermore, such alternative nanowire patterns can be transferred from pillar-structured surfaces to flat films, indicating further potentials in microcircuits, sensitive sensors, and other organic functional nanodevices. © 2012 American Chemical Society.

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 Epinion.com trustworthy? Does a product from Amazon.com have high quality as described? © 2012 IEEE.

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.

Tian X.,CAS Institute of Chemistry | Bai H.,CAS National Center for Nanoscience and Technology | Zheng Y.,Beihang University | Jiang L.,CAS Institute of Chemistry
Advanced Functional Materials | Year: 2011

Inspired by the geometric structure of ecribellate spider capture silk and its spinning characteristics, we propose a one-step electrohydrodynamic method to fabricate bead-on-string heterostructured fibers (BSHFs). By combining electrospinning and electrospraying strategies using a sprayable outer fluid with low viscosity and a spinnable inner fluid with high viscosity in a coaxial jetting process, hydrophilic poly(ethylene glycol) beads are successfully imprinted on a hydrophobic polystyrene string. It is demonstrated that the BSHFs are capable of intelligently responding to environmental change. With a change in relative humidity, the fibers show a segmented swelling and shrinking behavior in the "bead" parts whereas the "string" parts remain the same. The elastic BSHFs with alternating hydrophilic and hydrophobic surface characteristics represent a type of mesoscale analogues that block copolymers and may bring about new properties and applications. Moreover, the combined electrohydrodynamic approach developed herein should open new routes to multifunctional one-dimensional heterostructured materials. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dou Y.,Beihang University | Niculescu M.F.,Georgia Institute of Technology | Wu D.J.,Georgia Institute of Technology
Information Systems Research | Year: 2013

Firms nowadays are increasingly proactive in trying to strategically capitalize on consumer networks and social interactions. In this paper, we complement an emerging body of research on the engineering of word-of-mouth effects by exploring a different angle through which firms can strategically exploit the value-generation potential of the user network. Namely, we consider how software firms should optimize the strength of network effects at utility level by adjusting the level of embedded social media features in tandem with the right market seeding and pricing strategies in the presence of seeding disutility. We explore two opposing seeding cost models where seeding-induced disutility can be either positively or negatively correlated with customer type. We consider both complete and incomplete information scenarios for the firm. Under complete information, we uncover a complementarity relationship between seeding and building social media features that holds for both disutility models. When the cost of any of these actions increases, rather than compensating by a stronger action on the other dimension to restore the overall level of network effects, the firm will actually scale back on the other initiative as well. Under incomplete information, this complementarity holds when seeding disutility is negatively correlated with customer type but may not always hold in the other disutility model, potentially leading to fundamentally different optimal strategies. We also discuss how our insights apply to asymmetric networks. © 2013 INFORMS.

Ma F.,Lanzhou University | Qin Y.,Lanzhou University | Li Y.-Z.,Beihang University
Applied Physics Letters | Year: 2010

Co nanoflakes are synthesized through a low temperature hydrothermal method. The single-phased hexagonal close-packed Co nanoflakes have a diameter of several micrometers and a thickness about 80 nm. Magnetic hysteresis loops are quite different along different directions deviating from the nanoflakes plane, which shows Co nanoflakes have strong magnetic anisotropy. Flakelike morphology influence the performance of complex permeability in gigahertz frequency. Natural resonance peak happens at 5.74 GHz with the contribution of shape anisotropy. Multiple resonance phenomenon appears due to the exchange resonance effect, which makes Co nanoflakes a broadband candidate for microwave absorbing material. © 2010 American Institute of Physics.

Su Z.-X.,Beihang University
International Journal of Information Technology and Decision Making | Year: 2011

The paper investigates fuzzy multi-attribute group decision-making (FMAGDM) problems. The important weights of the attributes and the ratings of the alternatives with respect to each attribute provided by multiple decision-makers are described by the linguistic variables expressed in triangular fuzzy numbers or trapezoidal fuzzy numbers. A hybrid fuzzy approach is proposed, which assesses each alternative in terms of distance measure calculated by a modified VIKOR method as well as similarity measure calculated by a modified gray relational analysis (GRA) method, to the positive ideal alternative and the negative ideal alternative. A new relative closeness coefficient is established to rank alternatives by aggregating the distance and the similarity measures. Two numerical examples for reverse logistics applications are presented to illustrate the proposed method. © 2011 World Scientific Publishing Company.

Doi M.,Beihang University
Chinese Physics B | Year: 2015

Onsager principle is the variational principle proposed by Onsager in his celebrated paper on the reciprocal relation. The principle has been shown to be useful in deriving many evolution equations in soft matter physics. Here the principle is shown to be useful in solving such equations approximately. Two examples are discussed: the diffusion dynamics and gel dynamics. Both examples show that the present method is novel and gives new results which capture the essential dynamics in the system. © 2015 Chinese Physical Society and IOP Publishing Ltd.

Wang L.,Beihang University | Sun Y.-x.,Zhejiang University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2010

This Letter studies the robustness problem of pinning a general complex dynamical network toward an assigned synchronous evolution. Several synchronization criteria are presented to guarantee the convergence of the pinning process locally and globally by construction of Lyapunov functions. In particular, if a pinning strategy has been designed for synchronization of a given complex dynamical network, then no matter what uncertainties occur among the pinned nodes, synchronization can still be guaranteed through the pinning. The analytical results show that pinning control has a certain robustness against perturbations on network architecture: adding, deleting and changing the weights of edges. Numerical simulations illustrated by scale-free complex networks verify the theoretical results above-acquired. Crown Copyright © 2010.

Li G.,Beihang University
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences | Year: 2013

The wide application of FMEA in reliability engineering is generally appreciated, and how to identify the failure modes is the key to it. Failure modes, however, rely only on specific components rather than the system architecture, and therefore could be reused in different FMEAs. A novel ontology-based method, to recognize and reuse specific failure modes in existing databases, is provided here, and a light weight tool is developed for this method. The method and the tool can also be used in other fields with similar scenarios. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.

Tie L.,Beihang University
IET Control Theory and Applications | Year: 2013

In this study, controllability of discrete-time bilinear systems is studied. Necessary conditions and sufficient conditions for the systems to be controllable are presented. In particular, the sufficient conditions improve some existing results and the necessary conditions are new and easy to verify. Examples and simulations are provided to demonstrate the results of the paper. © 2013 The Institution of Engineering and Technology.

Xiao Z.,Beihang University
IEEE Communications Letters | Year: 2013

This letter revisits the equal-gain (EG) spatial diversity technique, which was proposed to combat the human-induced shadowing for 60 GHz wireless local area network, under a more practical frequency-selective multi-input multi-output channel. Subsequently, a suboptimal spatial diversity scheme called maximal selection (MS) is proposed by tracing the shadowing process, owing to a considerably high data rate. Comparisons show that MS outperforms EG in terms of link margin and saves computation complexity. © 1997-2012 IEEE.

An optical stress sensor is proposed by using a single crystal with both electro-optic and photoelastic effects. Different from previous crystal-based stress sensors, the proposed sensor is based on electro-optic compensation for stress-induced birefringence and does not need an additional quarter-wave plate or modulator, because the stress-sensing element is simultaneously used as an electro-optic compensator. Candidate sensing materials include electro-optic crystals of the 3m symmetry group and all glass with large Kerr coefficients. A primary experiment has demonstrated that the stress-induced birefringence in lithium niobate crystal can be compensated by its electro-optic birefringence. The proposed stress sensor is compact and low cost, and it is possible to achieve closed-loop stress measurement. © 2011 Optical Society of America.

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.

Chen L.,Beihang University | Stone R.,University of Oxford | Richardson D.,Jaguar Land Rover
Fuel | Year: 2012

The effect of gasoline/ethanol blends in different blending proportions (E0, E10, E20, E50, E70, E85 as #% by volume) on the characteristics of size-resolved particulate number and mass concentrations was investigated in a single-cylinder optical access engine using a differential mobility spectrometer (DMS500) under cold and warm conditions (20°C, 80°C) at a stoichiometric condition (1500 rpm, 0.5 bar manifold absolute pressure). The effects on the fuel spray characteristics were also investigated by capturing the injection images and by post-processing to compare the temporal development of the spray with the different fuels. In-cylinder fFID (fast Flame Ionisation Detector) measurements were undertaken to assess the mixture in-homogeneity in the region of the spark plug. As the ethanol volumetric percentage increases, both the total Pn (Particulate number) and Pm (Particulate mass) increase by a maximum of 16 and 11 for cold conditions and 7 and 8 for warm conditions. This is in agreement with the natural flame chemiluminescence images which showed that fuels with high ethanol proportions generated more soot than fuels with small blending percentages of ethanol. Spray images and combustion analysis showed that ethanol addition results in protracted injection and combustion periods. The effect on spray characteristics is more profound under cold conditions than under warm conditions. The mixture in-homogeneity increases as the ethanol content increases for E50, E70, and E85 and this would explain the increased level of particulate emissions, although the trend is less clear for the lower ethanol content fuels. © 2012 Elsevier Ltd. All rights reserved.

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.

Yang B.,Beihang University
Journal of Computational Information Systems | Year: 2011

This paper addresses the problem of accurately classifying image categories without any human interaction. In current latent topic model, the relationship between different categories is not considered. In fact the parts of different categories may have similar properties. A shared parts latent topic model with Dirichlet process is presented to share mixture components between categories. Different categories share the similar parts which make the model more accurate. As the number of components is unknown and is to be inferred from the train set, the Dirichlet process is introduced into the model to provide a nonparametric prior for the number of mixture components within each category. The object shape feature modeled by Wishart distribution is adopted in the model and Gibbs sampler is applied to estimate the parameters. A number of classification experiments are used to verify the success of our model. Copyright © 2011 Binary Information Press.

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.

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.

Ding Q.,Shandong University | Zhong M.,Beihang University
International Journal of Innovative Computing, Information and Control | Year: 2010

This paper deals with the problem of robust fault detection for Markovian jump linear systems with polytopic uncertainties. Using a generalized form of observer-based fault detection filter (FDF) as a residual generator, the design of robust FDF is formulated in the framework of stochastic H∞ filtering. Based on analyzing the robust mean square stability and stochastic H∞performance of the FDF, sufficient conditions on the existence of both mode-dependent and mode-independent H∞ FDFs are respectively derived and solutions to the H∞ FDFs are given in terms of linear matrix inequalities. A numerical example is given to show the effectiveness of the proposed method. ©2010 ISSN 1349-4198.

Luo K.,Beihang University
Applied Mechanics and Materials | Year: 2012

For vehicle routing problem, its model is easy to state and difficult to solve. The shuffled frog leaping algorithm is a novel meta-heuristic optimization approach and has strong quickly optimal searching power. The paper applies herein this algorithm to solve the vehicle routing problem; presents a high-efficiency encoding method based on the nearest neighborhood list; improves evolution strategies of the algorithm in order to keep excellent characteristics of the best frog. This proposed algorithm provides a new idea for solving VRP. © (2012) Trans Tech Publications, Switzerland.

Wang H.,Tsinghua University | Wang H.,Beihang University | Feng H.,Tsinghua University | Li J.,Tsinghua University
Small | Year: 2014

Being confronted with the energy crisis and environmental problems, the exploration of clean and renewable energy materials as well as their devices are urgently demanded. Two-dimensional (2D) atomically-thick materials, graphene and grpahene-like layered transition metal dichalcogenides (TMDs), have showed vast potential as novel energy materials due to their unique physicochemical properties. In this Review, we outline the typical application of graphene and grpahene-like TMDs in energy conversion and storage fields, and hope to promote the development of 2D TMDs in this field through the analysis and comparisons with the relatively natural graphene. First, a brief introduction of electronic structures and basic properties of graphene and TMDs are presented. Then, we summarize the exciting progress of these materials made in both energy conversion and storage field including solar cells, electrocatalysis, supercapacitors and lithium ions batteries. Finally, the prospects and further developments in these exciting fields of graphene and graphene-like TMDs materials are also suggested. This review summarizes recent progress of graphene and graphene-like layered transition metal dichalcogenide in energy conversion and storage application, including solar cells, electrocatalysis, supercapacitors, and lithium-ion batteries. Prospects and further developments in this exciting field are also discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Guo R.-Y.,Inner Mongolia University | Huang H.-J.,Beihang University
Transportation Research Part C: Emerging Technologies | Year: 2012

When the microscopic pedestrian models, in which pedestrian space is continuously represented, are used to simulate pedestrian movement in the buildings with internal obstacles, some issues arise and need be dealt with in detail. This paper discusses two of the issues, namely formulating the desired direction of each pedestrian in the buildings and determining the region around each pedestrian, other individuals and obstacles in which affect his or her movement. The methods for computing the desired direction and effect region are proposed, using the algorithms for the potential of pedestrian space. By numerical experiments, the performance results of three proposed formulae for the desired direction are compared, the method for the effect region is tested, and the validity of the method for computing the desired direction as considering the border effect of obstacles is verified. Numerical results indicate that the proposed methods can be used to formulate pedestrian movement, especially in the buildings with internal obstacles, in the microscopic models with continuous space representation. © 2012 Elsevier Ltd.

Chen Z.,Beihang University | Guan J.,Fudan University
Journal of Informetrics | Year: 2010

This paper investigates the impact of small world properties and the size of largest component on innovation performance at national level. Our study adds new evidence to the limited literature on this topic with an empirical investigation for the patent collaboration networks of 16 main innovative countries during 1975-2006. We combine small world network theory with statistical models to systematically explore the relationship between network structure and patent productivity. Results fail to support that the size of largest component enhances innovative productivity significantly, which is not consistent with recent concerns regarding positive effects of largest component on patent output. We do find that small-world structure benefits innovation but it is limited to a special range after which the effects inversed and shorter path length always correlates with increased innovation output. Our findings extend the current literature and they can be implicated for policy makers and relevant managers when making decisions for technology, industry and firm location. © 2009 Elsevier Ltd. All rights reserved.

Yuan H.,Beihang University
Procedia Engineering | Year: 2011

Fault diagnosis and failure analysis is crucial issue in the process of health management and predicative maintenance for large complex system. Fault propagation and its cause-effect relationship in the system are of priority with regard to the fault diagnosis. The fundamentals for modeling the network topology are presented according to the characteristics of the electrical control system connection relationship and its functionality, a complex network topology model was built subsequently. The cause and effect relationships of the components are mapped to the relationships of the vertices in a complex network. The search method for the fault propagation path from the source vertex to the target vertex is studied using node coordinates connections, and application research of electrical control system fault propagation is shown and discussed in the paper. The proposed method is practical in dealing with the fault analysis and evaluation for large complex systems. © 2011 Published by Elsevier Ltd.

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.

Tang Z.,Harbin Institute of Technology | Zhang B.,Beihang University
Composites Part B: Engineering | Year: 2012

Macro/micromulti-scale analysis based on the efficient implementation of the Generalized Method of Cells coupled with classical lamination theory was conducted to predict failure of composite laminates, applying failure criteria at the constituent level, including fiber, matrix and interface. Representative unit cells with different fiber arrays were constructed in order to study the effect of reinforcement architecture and failure criteria on strength prediction of composite laminates. In order to compare the micromechanics model's accuracy with commonly-used macroscopic failure theories, the experimental data obtained from the Worldwide Failure Exercise (WWFE) was utilized, and a quantitative assessment method for failure envelopes was developed to evaluate the model's performance. Finally, the types of representative unit cell architectures and failure theories which are applicable for different layups were identified. The results indicate that the predictive performance of the employed micromechanics-based model is closest to the three leading macroscopic failure criteria of Puck, Cuntze and Tsai-Wu, and better than all other microscopic-based failure criteria (Chamis, Mayes, Huang), employed in the WWFE study. © 2011 Elsevier Ltd. All rights reserved.

Ding Y.,Beihang University
PloS one | Year: 2013

OpenMP, a typical shared memory programming paradigm, has been extensively applied in high performance computing community due to the popularity of multicore architectures in recent years. The most significant feature of the OpenMP 3.0 specification is the introduction of the task constructs to express parallelism at a much finer level of detail. This feature, however, has posed new challenges for performance monitoring and analysis. In particular, task creation is separated from its execution, causing the traditional monitoring methods to be ineffective. This paper presents a mechanism to monitor task-based OpenMP programs with interposition and proposes two demonstration graphs for performance analysis as well. The results of two experiments are discussed to evaluate the overhead of monitoring mechanism and to verify the effects of demonstration graphs using the BOTS benchmarks.

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.

Chen K.,Beihang University | Guan J.,Fudan University
Regional Studies | Year: 2012

Chen K. and Guan J. Measuring the efficiency of China's regional innovation systems: application of network data envelopment analysis (DEA), Regional Studies. This study applies a relational network data analysis envelopment to the systematic evaluation of the innovation efficiency of China's regional innovation systems by decomposing the innovation process into the two connecting sub-processes, technological development and subsequent technological commercialization. The results show that only one-fifth of China's regional innovation systems are operating on the empirical best-practice frontier during the whole process from technological development to commercialization. Furthermore, it is found that substantial inconsistencies exist between technological development capacity and commercialization capacity in most regional innovation systems, and that downstream commercialization capacity plays a more important role in the innovation performance of regional innovation systems. Chen K. et Guan J. Evaluer l'efficacité des systèmes d'innovation régionaux en Chine: l'application de la DEA en réseau, Regional Studies. Cet article cherche à appliquer une analyse DEA (data envelopment analysis) relationnelle en réseau à l'évaluation systématique de l'efficacité innovatrice des systèmes d'innovation régionaux en Chine à partir d'une décomposition du processus d'innovation en deux sous-processus, à savoir le développement technologique et la commercialisation technologique qui en découle. Les résultats laissent voir que seulement un cinquième des systèmes d'innovation régionaux en Chine fonctionnent à la frontière empirique des pratiques d'excellence tout au long du processus qui va du développement technologique à la commercialisation. Qui plus est, il s'avère que d'importantes contradictions s'imposent entre la capacité de développement technologique et la capacité de commercialisation dans la plupart des systèmes d'innovation régionaux, et que la capacité de commercialisation en aval joue un rôle plus important quant à la performance innovatrice des systèmes d'innovation régionaux. Systèmes d'innovation régionaux Processus d'innovation Efficacité technologique Analyse DEA en réseau Amorçage ChineChen K. und Guan J. Messung der Effizienz der regionalen Innovationssysteme von China: eine Anwendung der Netzwerk-Dateneinhüllanalyse, Regional Studies. In dieser Studie wird eine relationale Netzwerk-Dateneinhüllanalyse auf die systematische Beurteilung der Innovationseffizienz der regionalen Innovationssysteme von China angewandt. Hierfür wird der Innovationsprozess in die beiden zusammenhängenden Subprozesse aufgegliedert: technologische Entwicklung und die anschließende technologische Kommerzialisierung. Aus den Ergebnissen geht hervor, dass nur ein Fünftel der regionalen Innovationssysteme von China während des gesamten Prozesses von der technologischen Entwicklung zur Kommerzialisierung an der Grenze der besten empirischen Praxis arbeiten. Darüber hinaus stellen wir fest, dass zwischen der Kapazität für technologische Entwicklung und der Kapazität für Kommerzialisierung erhebliche Unregelmäßigkeiten bestehen und dass die Kapazität der prozessabwärts angelagerten Kommerzialisierung für die Innovationsleistung von regionalen Innovationssystemen eine wichtigere Rolle spielt.Regionale Innovationssysteme Innovationsprozess Technische Effizienz Netzwerk-Dateneinhüllanalyse Bootstrap-Ansatz ChinaChen K. y Guan J. Medición de la eficiencia de los sistemas de innovación regional de China: aplicación de un análisis envolvente de datos de redes, Regional Studies. En este estudio aplicamos un análisis envolvente de datos relacionales de redes para la evaluación sistemática de la eficiencia de la innovación de los sistemas de innovación regional de China descomponiendo el proceso de innovación en los dos subprocesos conectados: el desarrollo tecnológico y la posterior comercialización tecnológica. Los resultados muestran que solamente una quinta parte de los sistemas de innovación regional operan en la frontera empírica de las mejores prácticas durante todo el proceso desde el desarrollo tecnológico hasta la comercialización. Asimismo se observa que existen considerables incoherencias entre la capacidad de desarrollo tecnológico y la capacidad de comercialización en la mayoría de sistemas de innovación regional y que la capacidad de comercialización desempeña un papel más importante en el rendimiento de innovación de los sistemas de innovación regional.Sistemas de innovación regional Proceso de innovación Eficacia técnica Análisis envolvente de datos de redes (DEA) Enfoque Bootstrap China. © 2012 Copyright Regional Studies Association.

Bai X.,Beihang University
Optics and Laser Technology | Year: 2013

Constructing alternating sequential operators is the important way of improving the efficiency of morphological operations for image processing. And, the alternating sequential filters (ASFs), which are constructed by using the morphological opening and closing, have been the important alternating sequential operators of mathematical morphology. However, because the morphological opening and closing operations have the defect of image detail smoothing, ASFs could not perform very well for some detail preserving image processing applications. Center-surround top-hat transform has been proposed through reconstructing the used structuring elements following the properties of image regions, which ensures that the main operations in center-surround top-hat transform could protect some image details; and, the main operations in center-surround top-hat transform achieve the similar function as opening and closing for bright and black feature extraction. Therefore, based on center-surround top-hat transform, some new and effective alternating sequential operators may be constructed. In light of this, a new class of alternating sequential operators with improved performance based on the center-surround top-hat transform is proposed in this paper. The definition and properties of the new alternating sequential operators are given and analyzed. Also, an application of impulsive noise suppression is used to show the improved performance of the new alternating sequential operators comparing with ASFs. Moreover, because the new alternating sequential operators constructed in this paper have some superiorities over ASFs, they could be also widely used in different applications in which the ASFs perform well, which indicates that the new alternating sequential operators may be also a class of useful morphological operators for image analysis. © 2012 Elsevier Ltd. All rights reserved.

In this study, silkworm moth (Bombyx mori L.) larvae were regarded as an animal protein source for astronauts in the bioregenerative life support system during long-term deep space exploration in the future. They were fed with mulberry and stem lettuce leaves during the first three instars and the last two instars, respectively. In addition, this kind of environmental approach, which utilised inedible biomass of plants to produce animal protein of high quality, can likewise be applied terrestrially to provide food for people living in extreme environments and/or impoverished agro-ecosystems, such as in polar regions, isolated military bases, ships, submarines, etc. Respiration characteristics of the larvae during development under two main physiological conditions, namely eating and not-eating of leaves, were studied. Nutrient compositions of silkworm powder (SP), ground and freeze-dried silkworms on the 3rd day of the 5th instar larvae, including protein, fat, vitamins, minerals and fatty acids, were measured using international standard methods. Silkworms' respiration rates, measured when larvae were eating mulberry leaves, were higher than those of similar larvae that hadn't eaten such leaves. There was a significant difference between silkworms fed on mulberry leaves and those fed on stem lettuce in the 4th and 5th instars (P<0.01). Amounts of CO2 exhaled by the silkworms under the two physiological regimes differed from each other (P<0.01). There was also a significant difference between the amount of O2 inhaled when the insects were under the two physiological statuses (P<0.01). Moreover, silkworms' respiration quotient under the eating regime was larger than when under the not-eating regime. The SP was found to be rich in protein and amino acids in total; 12 essential vitamins, nine minerals and twelve fatty acids were detected. Moreover, 359 kcal could be generated per 100 gram of SP (dry weight).

An image enhancement algorithm based on multiscale top-hat by reconstruction is proposed in this paper. Firstly, multiscale top-hat by reconstruction using multiscale structuring elements is discussed. Then, multiscale bright and black image regions are extracted. Thirdly, useful image regions for image enhancement are obtained from the extracted multiscale bright and black image regions. Finally, after a base image is calculated from the results of the opening and closing by reconstruction operations, the original image is enhanced through combing the useful image regions into the base image. Experimental results on different types of images show that the proposed algorithm is efficient. © 2013 Elsevier GmbH.

Zhao L.,Beihang University
Science China: Physics, Mechanics and Astronomy | Year: 2011

When the initial position error or the altimeter measurement noise is large, the BUAA Inertial Terrain-Aided Navigation (BITAN) algorithm based on extended Kalman filtering can not be located accurately. To solve this problem, we propose a modified BITAN algorithm based on nonlinear optimal filtering. The posterior probability density correction is obtained by using the prior probability density of the system's state transition model and the most recent observations. Hence, the local unobservable system caused by the measurement equation through terrain linearization is avoided. This algorithm is tested by using the digital elevation model and flight data, and is compared with BITAN. Results show that the accuracy of the proposed algorithm is higher than BITAN, and the robustness of the system is improved. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

Tang H.,Beihang University
Science China: Physics, Mechanics and Astronomy | Year: 2011

Dispersion of metal particles in fluids can be used to manufacture magnetorheologic fluids (MRF). Properties of these dispersion systems are mainly determined by the arrangements and contacts among particles. In this paper, particles with smaller sizes than those in the target dispersion system are added using iron particles dispersed in silicon oil as a model to control the arrangements and contacts. The result suggests that these small-sized particles have a significant effect on the viscoelastic properties of the dispersion. The maximum packing density and the fluid viscosity depend mainly on the adhesion of small particles, which is directly related to the fraction of small particles in the model dispersion system. Under a magnetic field, the yield stress of the dispersion system is proportional to the concentration of iron particles, suggesting that the yield stress relies directly on the presence of small particles. These small particles in the fluid determine the difference in stress of the magnetorheological fluid (MRF) with or without a magnetic field. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

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.

Li Mao-Qing,Beihang University
Kongzhi Lilun Yu Yingyong/Control Theory and Applications | Year: 2010

The controller design technique based on controlled Lagrangians (CL) for the mechanical systems with underactuation degree one is applied to control a planar vertical takeoff-and-landing (PVTOL) aircraft system with input coupling. Under the matching condition between the explicit gyroscopic forces, we develop a smooth feedback control law which ensures almost globally asymptotic stabilization for the system. Compared with the results obtained with existing similar methods, this matching controller is simpler in construction while retaining the same convergence performance.

Xie F.,Beihang University | Bovik A.C.,University of Texas at Austin
Pattern Recognition | Year: 2013

A novel dermoscopy image segmentation algorithm is proposed using a combination of a self-generating neural network (SGNN) and the genetic algorithm (GA). Optimal samples are selected as seeds using GA; taking these seeds as initial neuron trees, a self-generating neural forest (SGNF) is generated by training the rest of the samples using SGNN. Next the number of clusters is determined by optimizing the SD index of cluster validity, and clustering is completed by treating each neuron tree as a cluster. Since SGNN often delivers inconsistent cluster partitions owing to sensitivity relative to the input order of the training samples, GA is combined with SGNN to optimize and stabilize the clustering result. In the post-processing phase, the clusters are merged into lesion and background skin, yielding the segmented dermoscopy image. A series of experiments on the proposed model and the other automatic segmentation methods (including Otsu's thresholding method, k-means, fuzzy c-means (FCM) and statistical region merging (SRM)) reveals that the optimized model delivers better accuracy and segmentation results. © 2012 Elsevier Ltd.

Li C.-S.,Beihang University
Wuli Xuebao/Acta Physica Sinica | Year: 2015

Mutual compensation property between electrooptic and magnetooptic modulations in a crystal with electrooptic and magnetooptic effects and its application to magnetooptic sensor are investigated theoretically and experimentally. Under the condition of light intensity modulation, electrooptic and magnetooptic modulation effects can compensate for each other, so that the transmitted light intensity through the crystal can be kept at a certain fixed value. Based on this mutual compensation property, a novel optical current (or magnetic field) sensor is proposed and demonstrated experimentally by use of a single bismuth germanate (Bi4Ge3O12, BGO) crystal. The optical sensing unit is composed mainly of two polarizers and a block of BGO crystal with the shape of parallelogram. The BGO crystal itself can produce an optical phase bias of π/2, and it can be used as both a current sensing element and an electrooptic compensator. The change of magnetooptic rotation angle through the crystal can be compensated in real time by the change of electrooptic phase retardation caused by the applied voltage, thus the closed-loop optical measurement of current (or magnetic field) can be achieved. The 50 Hz ac current within 5 A is measured experimentally. The required compensating ac voltage is about 21.2 V/A in root-mean-square value. Experimental data show a good linear relationship between measured current and compensating voltage, and the nonlinear error is less than 1.7%. ©, 2015, Institute of Physics, Chinese Academy of Sciences. All right reserved.

Guo H.,Beihang University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014

We study one-dimensional topological models with dimerization and trimerization and show that these models can be generated using interaction or optical superlattice. The topological properties of these models are demonstrated by the appearance of edge states and the mechanism of dimerization and trimerization is analyzed. Then we show that a quantum pumping process can be constructed based on each one-dimensional topological model. The quantum pumping process is explicitly demonstrated by the instantaneous energy spectrum and local current. The result shows that the pumping is assisted by the gapless states connecting the bands and one charge is pumped during a cycle, which also defines a nonzero Chern number. Our study systematically shows the connection of one-dimensional topological models and quantum pumping, and is useful for the experimental studies on topological phases in optical lattices and photonic quasicrystals. © 2014 Elsevier B.V.

A fast, robust and accurate digital image correlation (DIC) method, which uses a robust zero-mean normalized sum of squared difference correlation criterion, a sophisticated reliability-guided displacement tracking strategy and an efficient inverse compositional Gauss-Newton (IC-GN) algorithm, was recently proposed for full-field deformation measurement. As an iterative local optimization algorithm, IC-GN algorithm iteratively solves for the incremental warp assumed on the reference subset until the preset convergence criteria are satisfied. In the literature, different convergence criteria have been set for iterative optimization algorithms. However, on the one hand, stringent convergence criteria lead to increased number of iterations and lessen the computational efficiency. On the other hand, too loose convergence conditions enhance the computational efficiency but may decrease the registration accuracy. Understanding the impact of prescribed convergence criteria on DIC measurement and how to choose proper convergence criteria are therefore fundamental problems in realizing high-efficiency yet high-accuracy DIC analysis. In this paper, the convergence characteristics of IC-GN algorithm are investigated in terms of convergence speed and radius of convergence using real experimental images. The effect of various convergence criteria on the efficiency and accuracy of IC-GN algorithm are carefully examined. Recommendations are given to select proper convergence criteria for more efficient implement of IC-GN algorithm. © 2013 Wiley Publishing Ltd.

Guo H.,Beihang University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The topological property of a boson-fermion mixture in a one-dimensional optical superlattice is studied and the topological insulating phase of an interacting boson-fermion mixture characterized by a nontrivial Berry phase is identified. The single-particle and boson-fermion exchanging excitation spectrums are calculated and we identify the boson-fermion exchanging excitation as the gapless topological excitation in the topological phase of the mixture. The different kinds of excitations are explained explicitly from the competition among the bulk gap, the on-site boson-boson, and boson-fermion interactions. The Hamiltonian studied has been partly realized in the state-of-art cold atom experiments, and the results are very relevant to the experiments. © 2015 American Physical Society. ©2015 American Physical Society.

Lei J.,Tsinghua University | Song Y.,Beihang University
Bulletin of Mathematical Biology | Year: 2010

The importance of morphogens is a central concept in developmental biology. Multiple-fate patterning and the robustness of the morphogen gradient are essential for embryo development. The ways by which morphogens diffuse from a local source to form long distance gradients can differ from one morphogen to the other, and for the same morphogen in different organs. This paper will study the mechanism by which morphogens diffuse through the aid of membrane-associated non-receptors and will investigate how the membrane-associated non-receptors help the morphogen to form long distance gradients and to achieve good robustness. Such a mechanism has been reported for some morphogens that are rapidly turned over. We will establish a set of reaction-diffusion equations to model the dynamical process of morphogen gradient formation. Under the assumption of rapid morphogen degradation, we discuss the existence, uniqueness, local stability, approximation solution, and the robustness of the steady-state gradient. The results in this paper show that when the morphogen is rapidly turned over, diffusion of the morphogen through membrane-associated non-receptors is a possible strategy to form a long distance multiple-fate gradient that is locally stable and is robust against the changes in morphogen synthesis rate. © 2009 Society for Mathematical Biology.

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.

Zhong M.,Beihang University | Ding S.X.,University of Duisburg - Essen | Ding E.L.,Gelsenkirchen University of Applied Sciences
Automatica | Year: 2010

This paper deals with the problem of observer-based fault detection for linear discrete time-varying (LDTV) systems. A problem formulation is first proposed to address the optimization of the fault detection filter (FDF) design, which is expressed in terms of maximizing a finite horizon H ∞/H∞ or H-/H∞ performance index. This formulation can be applied to FDF design of LDTV systems subject to l2-norm bounded unknown inputs or stochastic noise sequences. It is shown that a unified optimal solution to the FDF can be obtained by solving the discrete time Riccati equation and the optimal FDF is not unique. A numerical example is given to illustrate the proposed method. © 2010 Elsevier Ltd. All rights reserved.

Hong L.,University of California at Davis | Hong L.,Beihang University | Pan T.,University of California at Davis
Journal of Microelectromechanical Systems | Year: 2010

In this paper, we first report on direct-photolithography-based microfabrication of transparent superhydrophobic micropatterns using novel photodefinable nanocomposites, combining the nanomorphology and hydrophobicity of polytetrafluoroethylene (PTFE) nanoparticles and the photopatternability and transparency of an SU-8 photoresist using both direct-mixing and coating-immobilization methods. The direct mixture of PTFESU-8 nanocomposite can be reliably spin-coated and photopatterned onto transparent substrates (e.g., glass or polymers) with a minimal feature resolution of 50 μ\hbox{m}. The resulting nanocomposite film possesses a contact angle of water at 150, although its optical transparency is less than 30%. Furthermore, a modified coating-immobilization approach, employing spray coating and thermal immobilization of PTFE nanoparticles onto an SU-8 polymer matrix, significantly enhances superhydrophobicity, lithography resolution, as well as optical transparency. The highest optical transparency of 80% and a minimal feature resolution of 10 μhbox{m} have been achieved using the standard photolithography approach, while the contact angle of water above 165 enables extraordinary superhydrophobicity with low hysteresis. The novel PTFESU-8 nanocomposites provide a unique combination of superhydrophobicity, optical transparency, and photopatternability, along with excellent adaptability and simple processability, which offer great extension to rapidly evolving micronanoengineering applications. © 2006 IEEE.

Dong Z.,CAS Beijing National Laboratory for Molecular | Ma J.,CAS Beijing National Laboratory for Molecular | Jiang L.,CAS Beijing National Laboratory for Molecular | Jiang L.,Beihang University
ACS Nano | Year: 2013

There is rapidly increasing research interest focused on manipulating and dispensing tiny droplets in nanotechnology and biotechnology. A micro/nanostructured superhydrophobic nozzle surface is one promising candidate for the realization of tiny droplet manipulating applications. Here, we explore the feasibility of using superhydrophobicity for guided dispensing of tiny water droplets. A facile dip-coating method is developed to prepare superhydrophobic needle nozzles (SNNs) based on commercial needle nozzles with reduced inner diameter. The SNNs can manipulate tiny droplets of different volumes by only changing the inner diameter of the nozzle, rather than reducing the nozzle size as a whole. Different from the previous electric-field-directed process or pyroelectrodynamic-driven technique, quasi-stable water drops down to the picoliter scale can be produced by SNNs without employing any extra driving mechanisms. Due to their intrinsic superhydrophobic nature, the SNNs also possess the properties of reducing sample liquid retention, improving sample volume transfer accuracy, and saving expensive reagents. In addition, this kind of dip-coating method can also be applied to micropipet tips, inkjet or bio-printer heads, etc. As the issues of reducing drop size and increasing drop volume accuracy are quite important in the laboratory and industry, this facile but effective superhydrophobic nozzle-coating method for manipulating tiny droplets could be of great help to make breakthroughs in next-generation liquid transport and biometric and inkjet printing devices. © 2013 American Chemical Society.

Guo W.,CAS Beijing National Laboratory for Molecular | Cheng C.,Monash University | Wu Y.,Monash University | Jiang Y.,Beihang University | And 3 more authors.
Advanced Materials | Year: 2013

An electrogenetic layered graphene hydrogel membrane (GHM) possesses ultra-large interlayer spacing of about 10 nm, forming charged 2D nanocapillaries between graphene sheets that selectively permeate counter-ions and exclude co-ions. When an electrolyte flow goes through the GHM, it functions as an integrated 2D nanofluidic generator converting hydraulic motion into electricity. The maximum streaming conductance density approaches 16.8 μA cm-2 bar-1. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Li J.,China Academy of Space Technology | Fang J.,Beihang University
IEEE Transactions on Instrumentation and Measurement | Year: 2013

Inertial sensor errors include deterministic errors and stochastic errors. Deterministic errors can be calibrated in laboratory by simple computation technique. Stochastic errors can be determined during calibration by adopting special methods because of their random character. The simplest method to determine the stochastic errors for inertial sensors is the Allan variance. This kind of method needs large data to fully characterize the stochastic errors. The normal nonoverlapped Allan variance has quite poor estimation accuracy in long cluster time. The fully overlapping Allan variance and traditional total variance have better estimation accuracy in long cluster time but are quite time consuming for large data set. The not fully overlapping Allan variance and nonoverlapped total variance are suitable for large data set to improve the estimation accuracy in long cluster time with much less time, but their accuracy is still relatively poor in comparison with not fully overlapping total variance. Whereas the not fully overlapping total variance is relatively time consuming and, compared with Allan variance, there is a bias which is not easy to be corrected. This paper proposes a sliding average Allan variance that has comparable estimation accuracy with total variance. The data are not required to extend as the total variance; thus the calculation burden could be reduced greatly. Therefore, it is more suitable for large data set. In addition this method has no bias in comparison with Allan variance, which means no bias correction is required. This method is applied to 12-h static data of three gyroscopes from a position and orientation system with good performance. © 2013 IEEE.

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.

Hu J.,University of Technology, Sydney | Zhu J.,University of Technology, Sydney | Zhang Y.,North China University of Technology | Platt G.,Energy Technology of Commonwealth Scientific and Industrial Research Organization | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2013

Predictive direct torque control of the electric motors has been well developed. It is simple and has excellent steady state and transient performance. However, further developments are still under investigation for applications in the field of power generation. This paper presents a predictive direct virtual torque and power control strategy for a doubly fed induction generator, which allows fast and smooth grid synchronization, and flexible active and reactive power regulation. In the no-load mode, predictive direct virtual torque control is employed to meet the grid synchronization conditions. In the grid-connected mode, predictive direct power control is utilized to achieve flexible active and reactive power regulation. To simplify the control system structure and improve the reliability, a sensorless rotor position scheme is proposed. Furthermore, a model-based predictive scheme is introduced to compensate for a one-step delay in the digital implementation. The proposed control strategy is very simple and robust. There is constant switching frequency, while the requirement of smooth and fast grid synchronization is fulfilled. The transition from no load to flexible power regulation is achieved without changing the switching table. The proposed control strategy was tested by simulation using MATLAB/Simulink and experimentally validated on a 20-kW laboratory prototype. © 2013 IEEE.

Yang J.,Nanjing Southeast University | Li S.,Nanjing Southeast University | Sun C.,Nanjing Southeast University | Guo L.,Beihang University
IEEE Transactions on Aerospace and Electronic Systems | Year: 2013

The work presented here is concerned with the robust flight control problem for the longitudinal dynamics of a generic airbreathing hypersonic vehicles (AHVs) under mismatched disturbances via a nonlinear-disturbance-observer-based control (NDOBC) method. Compared with other robust flight control method for AHV, the proposed method obtains not only promising robustness and disturbance rejection performance but also the property of nominal performance recovery. The merits of the proposed method are validated by simulation studies. © 1965-2011 IEEE.

Chen H.-X.,Beihang University
European Physical Journal C | Year: 2013

We investigate the chiral structure of local vector and axial-vector tetraquark currents, and study their chiral transformation properties. We consider the charge-conjugation parity and classify all the isovector vector and axial-vector local tetraquark currents of quantum numbers I G J PC=1-1-+, I G J PC=1+1--, I G J PC=1-1++ and I G J PC=1+1+-. We find that there is a one to one correspondence among them. Using these currents, we perform QCD sum rule analyses. Our results suggest that there is a missing b 1 state having I G J PC=1+1+- and a mass around 1.47-1.66 GeV. © 2013 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica.

Kou Y.,Beihang University | Morton Y.,Miami University Ohio
IEEE Transactions on Aerospace and Electronic Systems | Year: 2013

Software-based Global Positioning System (GPS) receivers have been recognized as an effective research platform in recent years. The impact of oscillator frequency offset on hardware receiver and software receiver signal processing is contrasted based on a refined signal model and cross correlation function (CCF) analysis. Several online clock error correction algorithms are presented to produce unbiased measurements and clock error estimates with known and unknown front end frequency plans and with and without signal tracking and navigation solutions for single- and dual-frequency receivers on both static and dynamic platforms. The CCF formulation and the clock correction performance are validated using simulated signals and real single- and dual-frequency GPS data. The raw frequency error measurements with 0.02 s time resolution for an oven controlled crystal oscillator (OCXO) using real GPS signal report an Allan deviation (ADEV) of 1.3E-11 and a standard deviation of 1.56E-11. © 2013 IEEE.

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.

Guo X.,Beihang University | Vavilov V.,Tomsk Polytechnic University
Infrared Physics and Technology | Year: 2013

Ultrasound-stimulated IR thermography, thanks to its large-area imaging capability, high test productivity and safety, is a powerful tool for the inspection of cracks in heavy aluminum structures. In thick aluminum parts, the most important defect detection parameters are the differential temperature signal and signal-to-noise ratio (SNR), which typically reach their maximums at shortly (under 1 s) after the beginning of the ultrasonic excitation. In the IR inspection of non-metals, the ultrasonic excitation may be relatively long, while in the case of highly-conductive aluminum, short-pulse (burst) stimulation (from 0.4 to 1 s) is sufficient The crack detectability can be improved by evaluating temperature images at the times when maximum SNR values occur. Further enhancement of test results can be achieved by applying some data processing algorithms which can be 1D, i.e. applied to temperature evolutions in time, or 2D, i.e. applied to spatial coordinates, or a single image. © 2013 Published by Elsevier B.V.

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.

Nowadays, the issue of Electromagnetic Compatibility is of great importance and urgency. In this paper, we propose a novel hybrid automatic identification system for power quality disturbances, which lays foundations for further analyzing the electromagnetic compatibility. Specifically, we firstly extract features by using the FFT and envelope detection method. Then we utilize the attribute weighted artificial immune evolutionary Classifier (AWAIEC) for classification of power quality disturbance events. Experimental results have shown that the proposed method performs better than existing approaches. © (2014) Trans Tech Publications, Switzerland.

Yang Z.-Q.,Beihang University
Wuli Xuebao/Acta Physica Sinica | Year: 2010

Transitions of different neuronal firing patterns in the Chay model are explored by numerical simulation of three firing sequences observed in experiments on neural pacemakers, and the bifurcation analysis of limit cycle. Firstly, the transitions of periodic firing patterns through a pair of period-doubling bifurcations are obtained. Secondly, a supercritical and a subcritical period-doubling bursting sequences with different appearances lead to chaos, and then transit to an inverse period-doubling spiking sequence in different ways, separately. Finally, we reveal the true nature of period-adding bursting sequence without chaotic bursting, which is closely related to period-doubling bifurcation. © 2010 Chin. Phys. Soc.

Wang G.,Hefei University of Technology | Wang G.,Beihang University
ACS Applied Materials and Interfaces | Year: 2010

Three-phase-percolative composites with ZnO radial nanoclusters (R-ZnO) and BaTiO3 (BT) nanoparticles embedded into polyvinylidene fluoride (PVDF) were prepared by using a simple blending and hot-molding technique. The BT + PVDF composite with a volume fraction of 30 vol % BT particles were employed as a thermoplastic-ceramic matrix. Compared with the two-phase-percolative composites of R-ZnO/PVDF, the three-phase-percolative (R-ZnO/(BT + PVDF)) composites showed enhanced dielectric constant and decreased dielectric loss. The percolation theory was used to explain the experimental results. The increased percolation threshold was studied in detail, and the thermal stability was also investigated. © 2010 American Chemical Society.

Zheng Y.F.,Peking University | Gu X.N.,Beihang University | Witte F.,Charite - 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.

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.

Ling Z.,Beihang University
International Journal of Digital Content Technology and its Applications | Year: 2012

In this paper, it involves some deficiency in the relationship between teacher's human resource management practices and overall performance of sports universities, human resource management system transmission mechanism as well as the representative of the survey questionnaire. We will overcome shortcomings and problems in the next research. This study also found that the affective commitment of teachers in the current teacher's human resources management system has a negative correlation between service performance and social research. For example, some sports universities has given more emotional concern on teachers that have a certain development potential, or have made outstanding achievements in scientific research, but still facing the problem of brain drain, so the role of current emotional commitment mechanisms on the retention of staff is limited.

Zhao L.,Beihang University
Wuli Xuebao/Acta Physica Sinica | Year: 2012

The traditional terrain contour matching (TERCOM) algorithm has worse reliability when velocity error or course error is larger. The extend Kalman filtering (EKF) algorithm based BUAA inertial terrain aided navigation (BITAN) algorithm fails to correctly position, leading to a decline of robustness when large initial position error or altimeter noise error occurs. In this paper, we introduce a Robust BUAA inertial terrain aided navigation (RBITAN) algorithm, which is an improved algorithm of BITAN. In the RBITAN algorithm a searching mode approach is designed by the statistic properties of mean absolute difference algorithm, mean square difference algorithm and cross correlation algorithm. The RBITAN gathers the advantages of both the TERCOM algorithm and the BITAN algorithm, and it adopts EKF based BITAN algorithm as the tracking approach. The algorithm is verified by both real digital altitude model and flight-test data. Compared with the BITAN algorithm, the RBITAN algorithm is robust, for it can achieve accurate positioning and tolerate large initial position error or altimeter noise error. © 2012 Chinese Physical Society.

Zhang Q.,Beihang University
Journal of Computer Science and Technology | Year: 2012

Abstract Developed from the dynamic causality diagram (DCD) model, a new approach for knowledge representation and reasoning named as dynamic uncertain causality graph (DUCG) is presented, which focuses on the compact representation of complex uncertain causalities and efficient probabilistic inference. It is pointed out that the existing models of compact representation and inference in Bayesian Network (BN) is applicable in single-valued cases, but may not be suitable to be applied in multi-valued cases. DUCG overcomes this problem and beyond. The main features of DUCG are: 1) compactly and graphically representing complex conditional probability distributions (CPDs), regardless of whether the cases are single-valued or multi-valued; 2) able to perform exact reasoning in the case of the incomplete knowledge representation; 3) simplifying the graphical knowledge base conditional on observations before other calculations, so that the scale and complexity of problem can be reduced exponentially; 4) the efficient two-step inference algorithm consisting of (a) logic operation to find all possible hypotheses in concern for given observations and (b) the probability calculation for these hypotheses; and 5) much less relying on the parameter accuracy. An alarm system example is provided to illustrate the DUCG methodology. © 2012 Springer Science+Business Media, LLC & Science Press, China.

Jin D.,Beihang University
International Journal of Digital Content Technology and its Applications | Year: 2012

Sewage treatment cost function model, support the important means of cost control and decision making. As environment the understanding and the understanding of the system of transport quantitative description pollutants environment has become an increasingly complex models. In addition, the construction of urban sewage treatment plants in many as models also include the understanding of the problems such as decision-making, solve the results of the analysis and assessment, policy makers need to use the experience and knowledge, because knowledge of the limitations of cognitive ability, will take a lot of uncertainty. Therefore, the author of this article, and consider the risk factors under the prerequisite of the equipment life cycle cost theory, the value of the research methods, such as engineering and technology to comprehensive and accurate control of uncertainty, ensure the integrity and rigorous study process.

Cheng M.,Beijing University of Chemical Technology | Liu Q.,Beijing University of Chemical Technology | Ju G.,Beijing University of Chemical Technology | Zhang Y.,Beijing University of Chemical Technology | And 2 more authors.
Advanced Materials | Year: 2014

Superhydrophobic to neutral water droplets, superhydrophilic to acidic or basic. This double transition of surface wettability in response to a single stimulus - pH - is demonstrated for the first time. The smart surface is composed of a rough gold surface modified with a self-assembled monolayer (SAM) containing three thiols, HS(CH2)11CH3, HS(CH2)10COOH, and HS(CH2)11NH 2. A ternary diagram is generated that describes wettability as a function of the SAM composition and the pH of the surrounding solution. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lang B.,Beihang University
Tongxin Xuebao/Journal on Communications | Year: 2010

Based on the research fruit of social trust in sociology, the semantics, properties and elements of trust in the context of access control of distributed systems were defined. By combining fuzzy set theory with probability theory, a mathematical definition of trust was given, a quantified trust degree representation model including an integrated trust evaluation model and a trust calculating algorithm was established. The model integrates multiple elements of trust, and is in accordance with the decreasing and enhancing rules of the recommended trust.

Zhang Q.,Beihang University
Jisuanji Xuebao/Chinese Journal of Computers | Year: 2010

Bayesian Network (BN) is a prominent model to deal with knowledge representation and inference in case of uncertain causalities. This paper discusses the essential difference between single-valued and multi-valued cases. It is pointed out that even a binary child variable can be either single-valued or multi-valued, while the existing compact representations and the corresponding inference algorithms applicable in single-valued cases cannot be simply applied in multi-valued cases. To overcome this problem and others, a new model named as DUCG (Dynamical Uncertain Causality Praph) is presented. By introducing a set of new concepts, DUCG is able to compactly and graphically represent complex conditional probability distributions (CPDs) in different modules, irrespective of whether the cases of the modules are single-valued or multi-valued. The simple connection among separately constructed modules composes a final DUCG. Once the evidence is observed, the first inference step is to simplify the DUCG regardless of queries by applying the 10 rules presented in this paper. The second step is to apply the event outspread algorithm presented in this paper to calculate the updated probabilities of the queries still in concern based on the simplified DUCG, regardless of whether the variables are singly or multiply connected. Sometimes, the qualitative solution can be found by only simplifying DUCG. Correspondingly, the accuracy of parameters is less important in DUCG. Moreover, DUCG enables people to represent the knowledge only in concern but not enough to represent CPDs. In other words, DUCG does not have to represent the joint probability distribution over a set of variables, although it is able to. This incompleteness of representation and flexiable conditional causalities represented in DUCG, in addition to that DUCG is able to deal with the directed cyclic graph (DCG) to be addressed in next paper, etc, makes DUCG beyound BN. The example of an alarm system detecting intruder illustrates the DUCG methodology.

Guo L.,Beihang University
Proceedings of the 30th Chinese Control Conference, CCC 2011 | Year: 2011

This paper addresses the elegant anti-disturbance control (EADC) problem for complex systems with multiple disturbances. First, we briefly review the classical control methodologies for disturbance attenuation and rejection problems. Then, we summarize the recent progresses of disturbance observer based control (DOBC). It is noted that most of above methodologies focus on systems with the single disturbance. To reduce the conservertiveness, we classified and modelled the multiple disturbances, and presented a composite anti-disturbance control with hierarchical achitecture-Composite Hierarchical Anti-Disturbance Control (CHADC). CHADC has two layers: the inner layer includes the disturbance observer and the compensator in feedforward path; the outer layer includes the controller with disturbance attenuation and other performance in feedback path. © 2011 Chinese Assoc of Automati.

Di J.,Jilin University | Zhao Y.,Beihang University | Yu J.,Jilin University
Journal of Materials Chemistry | Year: 2011

Molecular sieves, such as zeolites and mesoporous materials, have been widely used in the fields of catalysis, adsorption, ion-exchange, and are finding new applications in optics, electronics, magnetism, medicine, etc. Molecular sieves with different morphologies or aggregation states, such as spheres, films, and fibers have been prepared to fulfil the need for various applications. Electrospinning offers a simple and straightforward way for generating ultrafine fibers with diameter in the range of nanometres to micrometres from a variety of materials. In recent decades, electrospinning has been introduced to prepare molecular sieve fibers. In this review, fibrous molecular sieves including zeolite fibers, siliceous and nonsiliceous mesoporous fibers prepared by electrospinning are summarized, and their prominent applications in optics, adsorptions, catalysis, etc. are highlighted. © 2011 The Royal Society of Chemistry.

Sun H.,Beihang University | Hou L.,Qufu Normal University
Nonlinear Analysis: Hybrid Systems | Year: 2014

The composite anti-disturbance control problem is developed for discrete-time systems with both time-varying delay and multiple disturbances under actuator failures in this paper. First, depending on the information of actuator failures, the system is transformed into a switched system. Then, considering the switched system, the composite controller is designed via a disturbance observer based control and an exponential l2 - l∞ control method. A disturbance observer is constructed to estimate the disturbances generated by an exogenous system, and the estimated value is introduced into a memory exponential l2 - l∞ state feedback control law, such that, the closed-loop system is asymptotically stable, and different types of disturbances are rejected and attenuated. Third, by resorting to the average dwell time approach and the free-weighting matrix technique, some sufficient criteria for the desired disturbance observer and the state feedback controller are established, and the corresponding solvability conditions using a cone complementarity linearization method are presented. A numerical example is provided to demonstrate the effectiveness of the proposed algorithms finally. © 2014 Elsevier Ltd.

Li G.,Beihang University
IEICE Transactions on Information and Systems | Year: 2014

SUMMARY The large and complicated safety-critical systems today need to keep changing to accommodate ever-changing objectives and environments. Accordingly, runtime analysis for safe reconfiguration or evaluation is currently a hot topic in the field, whereas information acquisition of external environment is crucial for runtime safety analysis. With the rapid development of web services, mobile networks and ubiquitous computing, abundant realtime information of environment is available on the Internet. To integrate these public information into runtime safety analysis of critical systems, this paper brings forward a framework, which could be implemented with open source and cross platform modules and encouragingly, applicable to various safety-critical systems. © 2014 The Institute of Electronics, Information and Communication Engineers.

Yao J.,Nanjing University of Science and Technology | Jiao Z.,Beihang University | Ma D.,Nanjing University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2014

Structured and unstructured uncertainties always exist in physical servo systems and degrade their tracking accuracy. In this paper, a practical method named adaptive robust control with extended state observer (ESO) is synthesized for high-accuracy motion control of a dc motor. The proposed controller accounts for not only the structured uncertainties (i.e., parametric uncertainties) but also the unstructured uncertainties (i.e., nonlinear friction, external disturbances, and/or unmodeled dynamics). Adaptive control for the structured uncertainty and ESO for the unstructured uncertainty are designed for compensating them respectively and integrated together via a feedforward cancellation technique. The global robustness of the controller is guaranteed by a feedback robust law. Furthermore, the controller theoretically guarantees a prescribed tracking performance in the presence of various uncertainties, which is very important for high-accuracy control of motion systems. Extensive comparative experimental results are obtained to verify the high-performance nature of the proposed control strategy. © 1982-2012 IEEE.

In this paper, a root locus approach is developed to investigate near-controllability of a class of discrete-time bilinear systems and new representations of Hermitian matrices are derived. The root locus approach has three merits: firstly, it makes the proof of near-controllability of the systems more simple; secondly, the control inputs that achieve the state transition can be computed in an explicit way and, meanwhile, the number of the required control inputs can be fixed; and thirdly, it leads to a more general conclusion on near-controllability. A numerical example is given to demonstrate the effectiveness of the root locus approach. Finally, the more general conclusion yields new representations of Hermitian matrices. © 2013 The Franklin Institute. Published by Elsevier Ltd. All right sreserved.

Liang B.,Beihang University
Journal of the Royal Society, Interface / the Royal Society | Year: 2013

Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier-Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect.

Chen M.W.,Beihang University
Journal of the Royal Society, Interface / the Royal Society | Year: 2013

Here, we present a detailed analysis of the take-off mechanics in droneflies performing voluntary take-offs. Wing and body kinematics of the insects during take-off were measured using high-speed video techniques. Based on the measured data, the inertia force acting on the insect was computed and the aerodynamic force of the wings was calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. In take-off, a dronefly increases its stroke amplitude gradually in the first 10-14 wingbeats and becomes airborne at about the 12th wingbeat. The aerodynamic force increases monotonously from zero to a value a little larger than its weight, and the leg force decreases monotonously from a value equal to its weight to zero, showing that the droneflies do not jump and only use aerodynamic force of flapping wings to lift themselves into the air. Compared with take-offs in insects in previous studies, in which a very large force (5-10 times of the weight) generated either by jumping legs (locusts, milkweed bugs and fruit flies) or by the 'fling' mechanism of the wing pair (butterflies) is used in a short time, the take-off in the droneflies is relatively slow but smoother.

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.

Liu F.,Beihang University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

On the basis of a quantum mechanical analog of the famous Feynman-Kac formula, we present a method to derive nonequilibrium work equalities for isolated quantum systems, which include the Jarzynski equality and Bochkov-Kuzovlev equality. Compared with other methods in the literature, our method shows a higher similarity in form to the method deriving the fluctuation relations in the classical systems. © 2012 American Physical Society.

Yao J.,Nanjing University of Science and Technology | Jiao Z.,Beihang University | Ma D.,Nanjing University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2014

Continuous friction compensation along with other modeling uncertainties is concerned in this paper, to result in a continuous control input, which is more suitable for controller implementation. To accomplish this control task, a practical method, named as robust integral of the sign of the error controller, is synthesized with a continuous differentiable friction model for high-accuracy motion control of a dc motor. To reduce the noise sensitivity and further improve the tracking accuracy, a desired compensation technique is employed in the proposed controller, in which the model compensation term depends on the reference trajectory only, and its global stability is guaranteed by a proper robust feedback law. Furthermore, the proposed controller theoretically guarantees an asymptotic output tracking performance even in the presence of modeling uncertainties, which is very important for high-accuracy control of motion systems. Comparative experimental results are obtained for the motion control of a dc motor drive system to verify the high-performance nature of the proposed control strategy. © 2014 IEEE.

Yao J.,Nanjing University of Science and Technology | Jiao Z.,Beihang University | Ma D.,Nanjing University of Science and Technology
IEEE Transactions on Industrial Electronics | Year: 2014

In this paper, an output feedback nonlinear control is proposed for a hydraulic system with mismatched modeling uncertainties in which an extended state observer (ESO) and a nonlinear robust controller are synthesized via the backstepping method. The ESO is designed to estimate not only the unmeasured system states but also the modeling uncertainties. The nonlinear robust controller is designed to stabilize the closed-loop system. The proposed controller accounts for not only the nonlinearities (e.g., nonlinear flow features of servovalve), but also the modeling uncertainties (e.g., parameter derivations and unmodeled dynamics). Furthermore, the controller theoretically guarantees a prescribed tracking transient performance and final tracking accuracy, while achieving asymptotic tracking performance in the absence of time-varying uncertainties, which is very important for high-accuracy tracking control of hydraulic servo systems. Extensive comparative experimental results are obtained to verify the high-performance nature of the proposed control strategy. © 1982-2012 IEEE.

Wu X.,Beihang University | Liu H.X.,University of Minnesota
Transportation Research Part C: Emerging Technologies | Year: 2014

Research on using high-resolution event-based data for traffic modeling and control is still at early stage. In this paper, we provide a comprehensive overview on what has been achieved and also think ahead on what can be achieved in the future. It is our opinion that using high-resolution event data, instead of conventional aggregate data, could bring significant improvements to current research and practices in traffic engineering. Event data records the times when a vehicle arrives at and departs from a vehicle detector. From that, individual vehicle's on-detector-time and time gap between two consecutive vehicles can be derived. Such detailed information is of great importance for traffic modeling and control. As reviewed in this paper, current research has demonstrated that event data are extremely helpful in the fields of detector error diagnosis, vehicle classification, freeway travel time estimation, arterial performance measure, signal control optimization, traffic safety, traffic flow theory, and environmental studies. In addition, the cost of event data collection is low compared to other data collection techniques since event data can be directly collected from existing controller cabinet without any changes on the infrastructure, and can be continuously collected in 24/7 mode. This brings many research opportunities as suggested in the paper. © 2014 Elsevier Ltd.

Diallo O.,University of Beira Interior | Rodrigues J.J.P.C.,University of Beira Interior | Sene M.,Ucad | Niu J.,Beihang University
Information Sciences | Year: 2014

Wireless body area networks (WBANs) have received a lot of attention from both academia and industry due to the increasing need of ubiquitous computing for eHealth applications, the continuous advances in miniaturization of electronic devices, and the ultra-low-power wireless technologies. In these networks, various sensors are attached either on clothes, on human body or even implanted under the skin for real-time health monitoring of patients in order to improve their independent daily lives. The energy constraints of sensors, the vital and large amount of data collected by WBAN nodes require powerful and secure storage, and a query processing mechanism that takes into account both real-time and energy constraints. This paper addresses these challenges and proposes a new architecture that combines a cloud-based WBANs with statistical modeling techniques in order to provide a secure storage infrastructure and optimize the real-time user query processing in terms of energy minimization and query latency. Such statistical model provides good approximate answers to queries with a given probabilistic confidence. Furthermore, the combination of the model with the cloud-based WBAN allows performing a query processing algorithm that uses the error tolerance and the probabilistic confidence interval as query execution criterions. The performance analysis and the experiments based on both real and synthetic data sets demonstrate that the new architecture and its underlying proposed algorithm optimize the real-time query processing to achieve minimal energy consumption and query latency, and provide secure and powerful storage infrastructure. © 2014 Elsevier Inc. All rights reserved.