Xi'an, China

Northwestern Polytechnical University is a National Key University, directed by the Ministry of Industry and Information Technology of the People's Republic of China, located in Xi'an, Shaanxi, China. The university emphasizes on the education and research in aeronautical, astronautical and marine engineering. In February 2012, NPU has 13,736 graduate students and 14,395 undergraduate students. Wikipedia.


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Wang Z.,Northwestern Polytechnical University | Wang Z.,Kyushu University | Andrews M.A.,University of Guelph | Wu Z.-X.,Lanzhou University | And 2 more authors.
Physics of Life Reviews | Year: 2015

It is increasingly recognized that a key component of successful infection control efforts is understanding the complex, two-way interaction between disease dynamics and human behavioral and social dynamics. Human behavior such as contact precautions and social distancing clearly influence disease prevalence, but disease prevalence can in turn alter human behavior, forming a coupled, nonlinear system. Moreover, in many cases, the spatial structure of the population cannot be ignored, such that social and behavioral processes and/or transmission of infection must be represented with complex networks. Research on studying coupled disease-behavior dynamics in complex networks in particular is growing rapidly, and frequently makes use of analysis methods and concepts from statistical physics. Here, we review some of the growing literature in this area. We contrast network-based approaches to homogeneous-mixing approaches, point out how their predictions differ, and describe the rich and often surprising behavior of disease-behavior dynamics on complex networks, and compare them to processes in statistical physics. We discuss how these models can capture the dynamics that characterize many real-world scenarios, thereby suggesting ways that policy makers can better design effective prevention strategies. We also describe the growing sources of digital data that are facilitating research in this area. Finally, we suggest pitfalls which might be faced by researchers in the field, and we suggest several ways in which the field could move forward in the coming years. © 2015 Elsevier B.V..


Cui R.,Northwestern Polytechnical University | Cui R.,National University of Singapore | Ge S.S.,National University of Singapore | Voon Ee How B.,National University of Singapore | Sang Choo Y.,National University of Singapore
Ocean Engineering | Year: 2010

This paper is concerned with the leaderfollower formation control of multiple underactuated autonomous underwater vehicles (AUVs). In the proposed leaderfollower control, the follower tracks a reference trajectory based on the leader position and predetermined formation without the need for leader's velocity and dynamics. This is desirable in marine robotics due to weak underwater communication and low bandwidth. A virtual vehicle is constructed such that its trajectory converges to the reference trajectory of the follower. Position tracking control is designed for the follower to track the virtual vehicle using Lyapunov and backstepping synthesis. Approximation-based control technique is employed to handle the model parametric uncertainties and unknown disturbances for the follower. The residual error between vehicles within the formation is proven to converge to a bounded compact set and control performance is guaranteed by suitably choosing the design parameters. Extensive simulations are provided to demonstrate the effectiveness of the approaches presented. © 2010 Elsevier Ltd. All rights reserved.


Ma X.,Northwestern Polytechnical University
Carbohydrate Polymers | Year: 2012

Sodium alginate/Na+-rectorite (SA/Na+REC) intercalated nano-composite microspheres were prepared in an inverse suspension system. The effect of the preparation conditions of SA/Na+REC composite microspheres on adsorption capacity for Basic Blue 9 was investigated. The structure and morphology were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed that the optimal condition was that the amount of Na+-rectorite was 2 wt%, the amount of cross-linker was 0.384% and the amount of the initiator was 8%. SEM showed that it is porous products with spherical particulate surface. XRD showed that intercalation is formed between Na+-rectorite and sodium alginate. The adsorption capacity of SA/Na+REC was investigated in comparison with Na+- rectorite and sodium alginate using different cationic dyes. The SA/Na +REC composite microspheres showed the highest adsorption capacity. The reason lies in the existence of intercalated sodium alginate. It could enlarge the pore structure of microspheres, facilitating the penetration of macromolecular dyes. © 2012 Elsevier Ltd. All rights reserved.


Ren J.,University of Bradford | Ren J.,Northwestern Polytechnical University | Jiang J.,University of Bradford | Vlachos T.,Ionian University
IEEE Transactions on Image Processing | Year: 2010

In this paper, we propose a new method for estimating sub-pixel motion via exploiting the principle of phase correlation in the Fourier domain. The method is based on linear weighting of the height of the main peak on the one hand and the difference between its two neighboring side-peaks on the other. Using both synthetic and real data we show that the proposed method outperforms many established approaches and achieves improved accuracy even in the presence of noisy samples. © 2010 IEEE.


Yang W.,Renewable Energy National Center CENER | Yang W.,Northwestern Polytechnical University | Tavner P.J.,Durham University | Court R.,Renewable Energy National Center CENER
Mechanical Systems and Signal Processing | Year: 2013

Induction generators have been successfully applied to a variety of industries. However, their operation and maintenance in renewable wind and marine energy industries still face challenges due to harsh environments, limited access to site and relevant reliability issues. Hence, further enhancing their condition monitoring is regarded as one of the essential measures for improving their availability. To date, much effort has been made to monitor induction motors, which can be equally applied to monitoring induction generators. However, the achieved techniques still have constrains in particular when dealing with the condition monitoring problems in wind and marine turbine generators. For example, physical measurements of partial discharge, noise and temperature have been widely applied to monitoring induction machinery. They are simple and cost-effective, but unable to be used for fault diagnosis. The spectral analysis of vibration and stator current signals is also a mature technique popularly used in motor/generator condition monitoring practice. However, it often requires sufficient expertise for data interpretation, and significant pre-knowledge about the machines and their components. In particular in renewable wind and marine industries, the condition monitoring results are usually coupled with load variations, which further increases the difficulty of obtaining a reliable condition monitoring result. In view of these issues, a new condition monitoring technique is developed in this paper dedicated for wind and marine turbine generators. It is simple, informative and less load-dependent thus more reliable to deal with the online motor/generator condition monitoring problems under varying loading conditions. The technique has been verified through both simulated and practical experiments. It has been shown that with the aid of the proposed technique, not only the electrical faults but also the shaft unbalance occurring in the generator become detectable despite the external loading conditions. Moreover, the rotor and stator winding faults can be readily discriminated through observing the variation tendencies of the proposed condition monitoring criteria. © 2012 Elsevier Ltd.


Li C.,Xidian University | Zhuang Y.,Xidian University | Di S.,Peking University | Han R.,Northwestern Polytechnical University
IEEE Transactions on Electron Devices | Year: 2013

With the exact solution of the 2-D Poisson's equation in cylindrical coordinates, analytical subthreshold behavior models for junctionless cylindrical surrounding-gate (JLCSG) MOSFETs are developed. Using these analytical models, subthreshold characteristics of JLCSG MOSFETs are investigated in terms of channel electrostatic potential distribution, subthreshold current, and subthreshold slope (SS). It is shown that the electrostatic potential distribution, subthreshold current, and SS predicted by the analytical models are in close agreement with 3-D numerical simulation results without the need of any fitting parameters. These analytical models not only provide useful physical insight into the subthreshold behaviors, but also offer basic design guideline for the nanoscale JLCSG MOSFETs. © 1963-2012 IEEE.


Li H.,Northwestern Polytechnical University | Li H.,University of Victoria | Shi Y.,University of Victoria
Automatica | Year: 2014

This paper studies the robust distributed receding horizon control (DRHC) problem for large-scale continuous-time nonlinear systems subject to communication delays and external disturbances. A dual-mode robust DRHC strategy is designed to deal with the communication delays and the external disturbances simultaneously. The feasibility of the proposed DRHC and the stability of the closed-loop system are analyzed, and the sufficient conditions for ensuring the feasibility and stability are developed, respectively. We show that: (1) the feasibility is affected by the bounds of external disturbances, the sampling period and the bound of communication delays; (2) the stability is related to the bounds of external disturbances, the sampling period, the bound of communication delays and the minimum eigenvalues of the cooperation matrices; (3) the closed-loop system is stabilized into a robust invariant set under the proposed conditions. A simulation study is conducted to verify the theoretical results. © 2014 Elsevier Ltd. All rights reserved.


Li Q.H.,Hong Kong Polytechnic University | Yue T.M.,Hong Kong Polytechnic University | Guo Z.N.,Guangdong University of Technology | Lin X.,Hong Kong Polytechnic University | Lin X.,Northwestern Polytechnical University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2013

Electrospark deposition (ESD) was employed to clad the AlCoCrFeNi high-entropy alloy (HEA) on AISI 1045 carbon steel. The relationship between the microstructure and corrosion properties of the HEA-coated specimens was studied and compared with that of the copper-molded cast HEA material. Two major microstructural differences were found between the cast HEA material and the HEA coatings. First, the cast material comprises both columnar and equiaxed crystals with a columnar-to-equiaxed transition (CET), whereas the HEA coatings consist of an entirely columnar crystal structure. The CET phenomenon was analyzed based on Hunt's criterion. Second, unlike the cast HEA material, there was no obvious Cr-rich interdendritic segregation and nano-sized precipitate distributed within the dendrites of the HEA coating. With regard to corrosion properties, the corrosion current of the HEA-coated specimen was significantly lower than for the 1045 steel and the cast HEA material. This was attributed to the ESD specimen having a relatively high Cr oxide and Al oxide content at the surface. Moreover, for the ESD specimen, the absence of Cr-rich interdendritic phase and second-phase precipitation resulted in a relatively uniform corrosion attack, which is different from the severe galvanic corrosion attack that occurred in the cast specimen. © 2012 The Minerals, Metals & Materials Society and ASM International.


Wen J.,Northwestern Polytechnical University | Tian Z.,Northwestern Polytechnical University | Liu X.,China Institute of Technology | Lin W.,Northwestern Polytechnical University
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | Year: 2013

In this paper, we propose a manifold geometry based projective nonnegative matrix factorization linear dimensionality reduction method, called neighborhood preserving orthogonal projective nonnegative matrix factorization (NPOPNMF), for feature extraction of hyperspectral image. By adding constraints on projective nonnegative matrix factorization (PNMF) that each data point can be represented as a linear combination of its neighbors, NPOPNMF preserves local neighborhood geometrical structure of hyperspectral data in the reduced space, and overcomes the Euclidean limitation of PNMF. The metric structure of original high-dimensional hyperspectral data space is preserved due to the orthogonality of projection matrix. NPOPNMF can be performed in either supervised or unsupervised mode according to the construction of adjacency graph and it can improve the discriminant performance of PNMF. Theoretical analysis and experimental results on hyperspectral data sets demonstrate that the proposed method is an effective and promising method for hyperspectral image feature extraction. © 2008-2012 IEEE.


Zhao Y.,Northwestern Polytechnical University | Duan Z.,Peking University
Nonlinear Dynamics | Year: 2015

This paper studies the distributed finite-time containment control for a group of mobile agents modeled by double-integrator dynamics under multiple dynamic leaders with bounded unknown acceleration inputs. A class of distributed finite-time containment protocols is proposed without relying velocity and acceleration measurements. This kind of protocols can drive the states of the followers to track the convex hull spanned by those of the leaders in finite time under the constraint that the leaders’ acceleration inputs are unknown but bounded for all the followers. Further, by computing the value of the Lyapunov function at the initial point, the finite settling time can also be theoretically estimated for the second-order finite-time containment control problems. Finally, the effectiveness of the results is illustrated by numerical simulation. © 2015 Springer Science+Business Media Dordrecht


Sodium alginate/Na +rectorite-graft-poly acrylic acid (SA/Na +REC-g-PAA) composite superabsorbent was prepared via 60Coγ irradiation in methanol solution and nitrogen protection. The effect of the preparation conditions on graft ratio, graft efficiency and absorption of water were investigated. The structure and morphology were analyzed by IR, XRD, TEM and SEM. The results showed that the optimal condition was that the amount of Na +REC was 2 wt%, the ratio of SA/Na +REC to AA was 10 wt%, total dose was 9.0 kGy and volume ratio of methanol to water was 8:2. SEM showed that it is much easier to obtain porous products through 60Coγ irradiation than chemical initiator. The mechanism of graft copolymerization via 60Coγ irradiation was discussed. The water absorption of the graft copolymer in salt solutions of different ionic strengths was also measured, from which the superabsorbent properties are found to be saline sensitive. Ionic strength markedly decreased the water absorption of the sodium alginate grafted superabsorbent composites. © 2011 Elsevier Ltd. All rights reserved.


Ding J.,Jiangnan University | Shi Y.,University of Victoria | Wang H.,Northwestern Polytechnical University | Ding F.,Jiangnan University
Digital Signal Processing: A Review Journal | Year: 2010

In this paper, we propose a novel identification algorithm for a class of dual-rate sampled-data systems whose input-output data are measured by two different sampling rates. A polynomial transformation technique is employed to derive a mathematical model for such dual-rate systems. The proposed modified stochastic gradient algorithm has faster convergence rate than stochastic gradient algorithms for parameter identification using the dual-rate input-output data. Convergence properties of the algorithm are analyzed. Finally, illustrative and comparison examples are provided to verify the effectiveness and performance improvement of the proposed method. © 2009 Elsevier Inc. All rights reserved.


Yao R.,Northwestern Polytechnical University | Shi Q.,University of Adelaide | Shen C.,University of Adelaide | Zhang Y.,Northwestern Polytechnical University | Van Den Hengel A.,University of Adelaide
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

Despite many advances made in the area, deformable targets and partial occlusions continue to represent key problems in visual tracking. Structured learning has shown good results when applied to tracking whole targets, but applying this approach to a part-based target model is complicated by the need to model the relationships between parts, and to avoid lengthy initialisation processes. We thus propose a method which models the unknown parts using latent variables. In doing so we extend the online algorithm pegasos to the structured prediction case (i.e., predicting the location of the bounding boxes) with latent part variables. To better estimate the parts, and to avoid over-fitting caused by the extra model complexity/capacity introduced by the parts, we propose a two-stage training process, based on the primal rather than the dual form. We then show that the method outperforms the state-of-the-art (linear and non-linear kernel) trackers. © 2013 IEEE.


Yang W.,Renewable Energy National Center CENER | Court R.,Renewable Energy National Center CENER | Jiang J.,Northwestern Polytechnical University
Renewable Energy | Year: 2013

Wind turbines are being increasingly deployed in remote onshore and offshore areas due to the richer wind resource there and the advantages of mitigating the land use and visual impact issues. However, site accessing difficulties and the shortage of proper transportation and installation vehicles/vessels are challenging the operation and maintenance of the giants erected at these remote sites. In addition to the continual pressure on lowering the cost of energy of wind, condition monitoring is being regarded as one of the best solutions for the maintenance issues and therefore is attracting significant interest today. Much effort has been made in developing wind turbine condition monitoring systems and inventing dedicated condition monitoring technologies. However, the high cost and the various capability limitations of available achievements have delayed their extensive use. A cost-effective and reliable wind turbine condition monitoring technique is still sought for today. The purpose of this paper is to develop such a technique through interpreting the SCADA data collected from wind turbines, which have already been collected but have long been ignored due to lack of appropriate data interpretation tools. The major contributions of this paper include: (1) develop an effective method for processing raw SCADA data; (2) propose an alternative condition monitoring technique based on investigating the correlations among relevant SCADA data; and (3) realise the quantitative assessment of the health condition of a turbine under varying operational conditions. Both laboratory and site verification tests have been conducted. It has been shown that the proposed technique not only has a potential powerful capability in detecting incipient wind turbine blade and drive train faults, but also exhibits an amazing ability in tracing their further deterioration. © 2012 Elsevier Ltd.


Li H.,Northwestern Polytechnical University | Li H.,University of Victoria | Shi Y.,University of Victoria
Automatica | Year: 2014

The event-triggered control is of compelling features in efficiently exploiting system resources, and thus has found many applications in sensor networks, networked control systems, multi-agent systems and so on. In this paper, we study the event-triggered model predictive control (MPC) problem for continuous-time nonlinear systems subject to bounded disturbances. An event-triggered mechanism is first designed by measuring the error between the system state and its optimal prediction; the event-triggered MPC algorithm that is built upon the triggering mechanism and the dual-mode approach is then designed. The rigorous analysis of the feasibility and stability is conducted, and the sufficient conditions for ensuring the feasibility and stability are developed. We show that the feasibility of the event-triggered MPC algorithm can be guaranteed if, the prediction horizon is designed properly and the disturbances are small enough. Furthermore, it is shown that the stability is related to the prediction horizon, the disturbance bound and the triggering level, and that the state trajectory converges to a robust invariant set under the proposed conditions. Finally, a case study is provided to verify the theoretical results. © 2014 Elsevier Ltd. All rights reserved.


Ge Y.Y.,Northwestern Polytechnical University
Applied Mechanics and Materials | Year: 2013

For conventional fuzzy path tracking controller need to manually updated the control parameters in order to get better tracking control deficiencies and the lack of robustness of the problem when the control object is disturbed. Parameters self-adjusting tracking algorithm is proposed based on Cerebellum Model Articulation Controller (CMAC) and fuzzy logic composite of the control. The CAMC control logarithm first charged with tracking through learning objects charged with approximation of the object model, to learning cycle worth to control corresponding to the amount of correction corresponding weight value according to the error between input and output of the system and set the learning rate. When the object or environment changes can make the control performance of the system is automatically adjusting within a certain range, since the role of the CAMC. Tracking experiments show that. The tracking control algorithm has high tracking accuracy and good robustness, is conducive to the overall optimization of robot path tracking. © (2013) Trans Tech Publications, Switzerland.


Zhou S.,Northwestern Polytechnical University | Zhang X.,Northwestern Polytechnical University
Construction and Building Materials | Year: 2012

The pozzolanic activity of cattle manure ash (CMA) was determined and compared with fly ash (FA) in this study. X-ray diffraction (XRD) and energy-dispersive analysis (EDA) were used to determine the chemical composition of the CMA and FA. Scanning electron microscope (SEM) images indicated that the microstructure of the CMA is mainly in the shape of floccules. Mortar prism and concrete cube specimens were tested to determine the reactivity of CMA; the compressive strength of CMA mortar was found to be greater than that of FA mortar. The same result was obtained for concrete cube compressive strengths at 7, 28 and 56 days. Tests of electric flux to assess chloride anion penetration resistance of the concrete gave the CMA concrete the highest results for the four materials after 28 days, and least after 180 days. These results indicate that the pozzolanic activity index of CMA exceeds that of FA, indicating that CMA is a suitable replacement for cement in the preparation of concrete. Such a result can assist the cattle raising industry to drastically reduce waste disposal problems. © 2011 Elsevier Ltd. All rights reserved.


Li H.,Northwestern Polytechnical University | Li H.,University of Victoria | Shi Y.,University of Victoria
IEEE Transactions on Automatic Control | Year: 2014

Due to the ubiquitous existence of external disturbances, the design of distributed control algorithms with robustness is an urgent demand for multi-agent system applications. This technical note investigates the robust distributed model predictive control (MPC) problem for a group of nonlinear agents (subsystems) subject to control input constraints and external disturbances. A robustness constraint is proposed to handle the external disturbances. Based on this, a novel robust distributed MPC scheme is designed for the overall agent system. Furthermore, the feasibility of the robust distributed MPC scheme and the robust stability of the overall agent system are analyzed, respectively. The conditions under which the proposed MPC is feasible and the overall agent system is robustly stabilized are established. Finally, the application of the robust distributed MPC to a group of cart-damper-spring systems verifies the theoretical results. © 1963-2012 IEEE.


Benesty J.,University of Québec | Souden M.,Nippon Telegraph and Telephone | Chen J.,Northwestern Polytechnical University
Applied Acoustics | Year: 2013

Conventional multichannel noise reduction techniques are formulated by splitting the processed microphone observations into two terms: filtered noise-free speech and residual additive noise. The first term is treated as desired signal while the second is a nuisance. Then, the objective has typically been to reduce the nuisance while keeping the filtered speech as similar as possible to the clean speech. It turns out that this treatment of the overall filtered speech as the desired signal is inappropriate as will become clear soon. In this paper, we present a new study of the multichannel time-domain noise reduction filters. We decompose the noise-free microphone array observations into two components where the first is correlated with the target signal and perfectly coherent across the sensors while the second consists of residual interference. Then, well-known time-domain filters including the minimum variance distortionless response (MVDR), the space-time (ST) prediction, the maximum signal-to-noise ratio (SNR), the linearly constrained minimum variance (LCMV), the multichannel tradeoff, and Wiener filters are derived. Besides, the analytical performance evaluation of these time-domain filters is provided and new insights into their functioning are presented. Numerical results are finally given to corroborate our study. © 2012 Elsevier Ltd. All rights reserved.


Xu B.,Northwestern Polytechnical University | Yang C.,University of Plymouth | Yang C.,South China University of Technology | Pan Y.,National University of Singapore
IEEE Transactions on Neural Networks and Learning Systems | Year: 2015

This paper studies both indirect and direct global neural control of strict-feedback systems in the presence of unknown dynamics, using the dynamic surface control (DSC) technique in a novel manner. A new switching mechanism is designed to combine an adaptive neural controller in the neural approximation domain, together with the robust controller that pulls the transient states back into the neural approximation domain from the outside. In comparison with the conventional control techniques, which could only achieve semiglobally uniformly ultimately bounded stability, the proposed control scheme guarantees all the signals in the closed-loop system are globally uniformly ultimately bounded, such that the conventional constraints on initial conditions of the neural control system can be relaxed. The simulation studies of hypersonic flight vehicle (HFV) are performed to demonstrate the effectiveness of the proposed global neural DSC design. © 2012 IEEE.


Cui R.,Northwestern Polytechnical University | Ren B.,University of California at San Diego | Ge S.S.,National University of Singapore
IET Control Theory and Applications | Year: 2012

This study is concerned with the synchronised tracking control for multiple agents with high-order dynamics, whereas the desired trajectory is only available for a portion of the team members. Using the weighted average of the neighbours' states as the reference signal, adaptive neural network (NN) control is designed for each agent in both full-state and output feedback cases. It is proved that the adaptive NN control law guarantees that the tracking error of each agent converges to an adjustable neighbourhood of the origin for both cases although some of them do not access the desired trajectory directly. Two simulation examples are provided to demonstrate the performance of the proposed approaches. © 2012 The Institution of Engineering and Technology.


Ma C.,National University of Singapore | Yeo T.S.,National University of Singapore | Tan C.S.,DSO National Laboratories | Li J.-Y.,Northwestern Polytechnical University | Shang Y.,Peking University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2012

A conventional inverse synthetic aperture radar image is a 2-D range-Doppler projection of a target and does not provide 3-D information. Three-dimensional imaging using an interferometric technique cannot separate scatterers that have been projected onto the same range-Doppler unit. Multiple-input-multiple-output (MIMO) radar, however, in addition to having a wide virtual aperture and a high cross-range resolution, could also obtain a target's 3-D image in one snapshot. We discuss in this paper the use of time-domain information to improve MIMO radar's imaging quality. A 3-D image alignment algorithm and a rotation vector estimation method are discussed. Simulation results show that image SNR is improved and cross-range sidelobes are mitigated. © 2012 IEEE.


Li X.,Northwestern Polytechnical University | Zhang L.,Northwestern Polytechnical University | Yin X.,Northwestern Polytechnical University
Journal of Alloys and Compounds | Year: 2010

Polymer-derived nano-sized SiC(BN) was successfully introduced into porous Si3N4 ceramic by precursor infiltration pyrolysis (PIP). After PIP, the porous Si3N4-SiC(BN) ceramic possesses improved mechanical properties and excellent dielectric properties. As the annealing temperature increases from 900 °C to 1800 °C, the mechanical properties of porous Si3N4-SiC(BN) ceramic improve little, the real part and imaginary part of the permittivity of porous Si3N4-SiC(BN) ceramic increase obviously with the dielectric loss increasing gradually over the frequencies ranging from 8.2 GHz to 12.4 GHz. The increase of dielectric loss is due to the dipolar polarization and the increase of grain boundary as the annealing temperature increases. © 2009.


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

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


Grant
Agency: Cordis | Branch: FP7 | Program: CP-FP | Phase: SPA.2011.3.2-02 | Award Amount: 11.78M | Year: 2011

The QB50 Project will demonstrate the possibility of launching a network of 50 CubeSats built by CubeSat teams from all over the world to perform first-class science and in-orbit demonstration in the largely unexplored middle and lower thermosphere. Space agencies are not pursuing a multi-spacecraft network for in-situ measurements in the middle and lower thermosphere because the cost of a network of 50 satellites built to industrial standards would be very high and not justifiable in view of the limited orbital lifetime. No atmospheric network mission for in-situ measurements has been carried out in the past or is planned for the future. A network of satellites for in-situ measurements in the middle and lower thermosphere can only be realised by using very low-cost satellites, and CubeSats are the only realistic option. The Project will demonstrate the sustained availability of a low-cost launch opportunities, for launching small payloads into low-Earth orbit; these could be microsatellites or networks of CubeSats or nanosats or many individual small satellites for scientific, technological, microgravity or biology research. The Project will include the development of a deployment system for the deployment into orbit of a large number of single, double or triple CubeSats. Once the system is developed for QB50 it can be easily adapted to other missions. QB50 will also provide a launch opportunity for key technology demonstration on IOD CubeSats such as formation flying and aerobrakes. All 50 CubeSats will be launched together into a circular orbit at approximately 380 km altitude. Due to atmospheric drag, the orbits of the CubeSats will decay and progressively lower and lower layers of the thermosphere will be explored without the need for on-board propulsion, perhaps down to 200 km. QB50 will be among the first CubeSat networks in orbit.


News Article | February 15, 2017
Site: phys.org

But all bets are off, if the students journey to the center of the Earth, à la Jules Verne's Otto Lidenbrock or if they venture to one of the solar system's large planets, such as Jupiter or Saturn. "That's because extremely high pressure, like that found at the Earth's core or giant neighbors, completely alters helium's chemistry," says Boldyrev, faculty member in USU's Department of Chemistry and Biochemistry. It's a surprising finding, he says, because, on Earth, helium is a chemically inert and unreactive compound that eschews connections with other elements and compounds. The first of the noble gases, helium features an extremely stable, closed-shell electronic configuration, leaving no openings for connections. Further, Boldyrev's colleagues confirmed computationally and experimentally that sodium, never an earthly comrade to helium, readily bonds with the standoffish gas under high pressure to form the curious Na He compound. These findings were so unexpected, Boldyrev says, that he and colleagues struggled for more than two years to convince science reviewers and editors to publish their results. Persistence paid off. Boldyrev and his doctoral student Ivan Popov, as members of an international research group led by Artem Oganov of Stony Brook University, published the pioneering findings in the Feb. 6, 2017, issue of Nature Chemistry. Additional authors on the paper include researchers from China's Nankai University, Center for High Pressure Science and Technology, Chinese Academy of Sciences, Northwestern Polytechnical University, Xi'an and Nanjing University; Russia's Skolkovo Institute of Science and Technology, Moscow Institute of Physics and Technology, Sobolev Institute of Geology and Mineralogy and RUDN University; the Carnegie Institution of Washington, Lawrence Livermore National Laboratory, Italy's University of Milan, the University of Chicago and Germany's Aachen University and Photo Science DESY. Boldyrev and Popov's role in the project was to interpret a chemical bonding in the computational model developed by Oganov and the experimental results generated by Carnegie's Alexander Goncharov. Initially, the Na He compound was found to consist of Na cubes, of which half were occupied by helium atoms and half were empty. "Yet, when we performed chemical bonding analysis of these structures, we found each 'empty' cube actually contained an eight-center, two-electron bond," Boldyrev says. "This bond is what's responsible for the stability of this enchanting compound." Their findings advanced the research to another step. "As we explore the structure of this compound, we're deciphering how this bond occurs and we predicted that, adding oxygen, we could create a similar compound," Popov says. Such knowledge raises big questions about chemistry and how elements behave beyond the world we know. Questions, Boldyrev says, Earth's inhabitants need to keep in mind as they consider long-term space travel. "With the recent discovery of multiple exoplanets, we're reminded of the vastness of the universe," he says. "Our understanding of chemistry has to change and expand beyond the confines of our own planet." Explore further: Scientists discover extraordinary compounds that may be hidden inside Jupiter and Neptune More information: A stable compound of helium and sodium at high pressure, Nature Chemistry, DOI: 10.1038/nchem.2716


News Article | November 16, 2016
Site: www.prweb.com

Rising Media announced the full program for the Inside 3D Printing San Diego event, taking place at the San Diego Convention Center on December 14-15, 2016. Inside 3D Printing is the largest professional 3D printing event worldwide, having hosted 33 events globally since its launch in 2013. This will be the series’ fourth edition in California, with previous events hosted in San Jose and Santa Clara. The Inside 3D Printing San Diego program, which is chaired by Tyler Benster, General Partner, Asimov Ventures, features dedicated conference tracks focused on 3D printing applications in business, manufacturing, medical, and metal; keynote speeches from industry leaders Weidong Huang of Northwestern Polytechnical University, Hod Lipson of Columbia University, and Terry Wohlers of Wohlers Associates, Inc.; a full day of pre-conference workshops on December 13; as well as networking opportunities for additive manufacturing professionals to forge valuable industry connections. “3D printing is undergoing a watershed moment, as big and small companies alike begin to use the technology to manufacture finished goods. Several breakthrough technologies in plastics and metals promise to drive this exponential growth,” said Tyler Benster, conference chair and General Partner, Asimov Ventures. He continued, “We have some surprises in store at Inside 3D Printing San Diego, as several companies emerge from stealth mode to unveil ground-breaking new technology, while other established presenters discuss best practices for emerging business models.” Rising Media also announced The Nature Game, a competition challenging participants to create objects, which are hard or impossible to determine as objects having been created by natural growth or by human 3D design and manufacturing. Inspired by Alan Turing's 1950 Turing Test and developed by Uformia's Turlif Vilbrandt, The Nature Game asks the question, "Can an object be explicitly designed and fabricated by humans that seems to be naturally grown and/or expresses properties and complexity only found in naturally produced objects?" Objects created for The Nature Game will be on display at Inside 3D Printing San Diego where event attendees will have the opportunity to view the objects and guess whether they are human or nature made. "We are now able to understand and control all types of matter at scales beyond our own perception. In the next 30 years, manufacturing systems will communicate and fabricate alongside natural systems and human made objects will no longer stand apart and separated from natural processes,” said Turlif Vilbrandt, CTO, Uformia. San Diego-based bioprinting company Organovo is confirmed to participate and display 3D printed tissue for attendees to view through a microscope at Inside 3D Printing San Diego as part of The Nature Game. For more information, including submission guidelines and deadlines, visit TheNatureGame.org. Also on the program will be the Frontier Tech Showdown, a startup competition for early-stage startups in 3D printing, robotics, and virtual and augmented reality; the Frontier Tech Hackathon hosted by Amazon Alexa; and a special panel aimed at exploring diversity and multiculturalism in frontier technology industries. Inside 3D Printing San Diego is co-located with Rising Media's RoboUniverse and Virtual Reality Summit as the first Frontier Tech Forum. The combined expo hall expects 50+ exhibitors showcasing the latest in frontier tech hardware, services, and software. Prices for Frontier Tech Forum San Diego increase on-site, so register before December 14 to save. For more information and to register, visit inside3dprinting.com/san-diego. If your company is interested in sponsoring or exhibiting at Frontier Tech Forum San Diego or an upcoming event, please contact sponsorship(at)risingmedia(dot)com. About Rising Media Rising Media is a global events and media producer excelling in Internet and technology-related events and content. Events include Inside 3D Printing, RoboUniverse, Virtual Reality Summit, Frontier Tech Forum, Inside Fintech, Data Driven Business, Building Business Capability, Predictive Analytics World, Text Analytics World, eMetrics Summit, Conversion Conference, Email Innovations Summit, AllFacebook Marketing Conference, Search Marketing Expo, Affiliate Management Days, Influencer Marketing Days and Web Effectiveness Conference in the USA, Brazil, United Kingdom, Germany, France, Italy, India, China, Korea, Singapore, Australia. For more information, please visit http://www.risingmedia.com.


Guo Q.,Washington University in St. Louis | Guo Q.,Northwestern Polytechnical University | Beilicke M.,Washington University in St. Louis | Garson A.,Washington University in St. Louis | And 3 more authors.
Astroparticle Physics | Year: 2013

We report on the optimization of the hard X-ray polarimeter X-Calibur for a high-altitude balloon-flight in the focal plane of the InFOClS X-ray telescope from Fort Sumner (NM) in Fall 2013. X-Calibur combines a low-Z scintillator slab to Compton-scatter photons with a high-Z Cadmium Zinc Telluride (CZT) detector assembly to photo-absorb the scattered photons. The detector makes use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of order unity and reaches a sensitivity close to the best theoretically possible. In this paper, we discuss the optimization of the design of the instrument based on Monte Carlo simulations of polarized and unpolarized X-ray beams and of the most important background components. We calculate the sensitivity of the polarimeter for the upcoming balloon flight from Fort Sumner and for additional longer balloon flights with higher throughput mirrors. We conclude by emphasizing that Compton polarimeters on satellite borne missions can be used down to energies of a few keV. © 2012 Elsevier B.V. All rights reserved.


Zhang H.,Northwestern Polytechnical University | Zhang H.,University of Illinois at Urbana - Champaign | Nasrabadi N.M.,U.S. Army | Zhang Y.,Northwestern Polytechnical University | Huang T.S.,University of Illinois at Urbana - Champaign
Pattern Recognition | Year: 2012

We consider the problem of automatically recognizing a human face from its multi-view images with unconstrained poses. We formulate the multi-view face recognition task as a joint sparse representation model and take advantage of the correlations among the multiple views for face recognition using a novel joint dynamic sparsity prior. The proposed joint dynamic sparsity prior promotes shared joint sparsity patterns among the multiple sparse representation vectors at class-level, while allowing distinct sparsity patterns at atom-level within each class to facilitate a flexible representation. Extensive experiments on the CMU Multi-PIE face database are conducted to verify the efficacy of the proposed method. © 2011 Elsevier Ltd All rights reserved.


Zhang H.,University of Illinois at Urbana - Champaign | Nasrabadi N.M.,U.S. Army | Zhang Y.,Northwestern Polytechnical University | Huang T.S.,University of Illinois at Urbana - Champaign
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

We introduce a novel joint sparse representation based multi-view automatic target recognition (ATR) method, which can not only handle multi-view ATR without knowing the pose but also has the advantage of exploiting the correlations among the multiple views of the same physical target for a single joint recognition decision. Extensive experiments have been carried out on moving and stationary target acquisition and recognition (MSTAR) public database to evaluate the proposed method compared with several state-of-the-art methods such as linear support vector machine (SVM), kernel SVM, as well as a sparse representation based classifier (SRC). Experimental results demonstrate that the proposed joint sparse representation ATR method is very effective and performs robustly under variations such as multiple joint views, depression, azimuth angles, target articulations, as well as configurations. © 2012 IEEE.


Zhang X.,Shanghai JiaoTong University | Jiang L.,Shanghai JiaoTong University | Deng J.,Northwestern Polytechnical University | Li S.,University of Michigan | Chen Z.,University of Michigan
IEEE Transactions on Power Electronics | Year: 2014

In this paper, a new topology of a nonisolated boost converter with zero-voltage-switching (ZVS) capabilities is proposed. In order to realize ZVS conditions, the auxiliary circuit only consists of a coupled inductor and a diode, which operates with a zero-current-switching (ZCS) condition. Due to ZVS, the reverse recovery problem of MOSFET antiparallel body diodes can be resolved, and the voltage and current stresses on the switch components are also reduced. The detailed operating analysis of the proposed converter and the design method of the main circuit are presented. With the aim to verify the effectiveness and feasibility of the proposed boost converter, a 500 W experimental prototype is built up, and the related experimental waveforms and the efficiency curve are presented. © 1986-2012 IEEE.


Cui R.,Northwestern Polytechnical University | Gao B.,Northwestern Polytechnical University | Guo J.,Anyang University, China
Autonomous Robots | Year: 2012

This paper investigates the coordination of multiple robots with pre-specified paths, considering motion safety and minimizing the traveling time. A method to estimate possible collision point along the local paths of the robots is proposed. The repulsive potential energy is computed based on the distances between the robots and the potential collision points. This repulsive potential energy is used as the cost map of the probabilistic roadmap (PRM), which is constructed in the coordination space for multiple robots taking into account both motion time cost and safety cost. We propose a search method on the PRM to obtain the Pareto-optimal coordination solution for multiple robots. Both simulation and experimental results are presented to demonstrate the effectiveness of the algorithms. © 2011 Springer-Verlag.


Cui R.,Northwestern Polytechnical University | Guo J.,Anyang University, China | Gao B.,Northwestern Polytechnical University
Robotica | Year: 2013

This paper investigates task allocation for multiple robots by applying the game theory-based negotiation approach. Based on the initial task allocation using a contract net-based approach, a new method to select the negotiation robots and construct the negotiation set is proposed by employing the utility functions. A negotiation mechanism suitable for the decentralized task allocation is also presented. Then, a game theory-based negotiation strategy is proposed to achieve the Pareto-optimal solution for the task reallocation. Extensive simulation results are provided to show that the task allocation solutions after the negotiation are better than the initial contract net-based allocation. In addition, experimental results are further presented to show the effectiveness of the approach presented. © Cambridge University Press 2013.


Peng X.,Northwestern Polytechnical University | Peng X.,Shanghai JiaoTong University | Rehman Z.U.,Northwestern Polytechnical University
Composites Science and Technology | Year: 2011

Stamping is one of the most effective ways to form textile composites in industry for providing high-strength, low-weight and cost-effective products. This paper presents a fully continuum mechanics-based approach for stamping simulation of textile fiber reinforced composites by using finite element (FE) method. A previously developed non-orthogonal constitutive model is used to represent the anisotropic mechanical behavior of textile composites under large deformation during stamping. Simulation are performed on a balanced plain weave composite with 0°/90° and ±45° as initial yarn orientation over a benchmark double dome device. Simulation results show good agreement with experimental output in terms of a number of parameters selected for comparison. The effects of meshing and shear moduli obtained from bias extension test and picture frame test on forming simulation results are also investigated. © 2011 Elsevier Ltd.


Peng X.,Shanghai JiaoTong University | Peng X.,Northwestern Polytechnical University | Ding F.,Northwestern Polytechnical University
Composites Part A: Applied Science and Manufacturing | Year: 2011

A non-orthogonal constitutive model was previously developed to characterize the anisotropic material behavior of woven composite fabrics under large shear deformation. This paper presents a validation of the constitutive model via hemispherical stamping simulation of a square woven composite fabric by a fully continuum mechanics-based approach with finite element (FE) method. The constitutive model is imposed on conventional shell elements to equivalently characterize the global mechanical behavior of woven composite fabric during forming. A balanced plain woven composite is taken as an example. The stamping results from the non-orthogonal model and the corresponding orthogonal constitutive model are compared with experimental data. It is shown that the results predicted by the non-orthogonal model are in a good agreement with the experimental results, while those from the orthogonal model have large discrepancies. The numerical simulation demonstrates the necessity and efficiency of the non-orthogonal constitutive model in capturing the anisotropic material behavior that woven composite fabrics render in forming. © 2010 Elsevier Ltd. All rights reserved.


Ma Y.E.,Northwestern Polytechnical University | Ma Y.E.,Cranfield University | Staron P.,Institute of Materials Research | Fischer T.,Institute of Materials Research | Irving P.E.,Cranfield University
International Journal of Fatigue | Year: 2011

Residual stress fields were measured in three different sizes of Compact-Tension (C(T)) and eccentrically loaded single edge notch (ESE(T)) specimens containing transverse or longitudinal welds. The effect of size on residual stress profiles was studied. Fatigue crack growth tests were carried out with cracks growing into or away from the weld line, as well as growing along the weld centre line. Effects of weld residual stresses on fatigue crack growth rates parallel and perpendicular to the friction stir welds were studied. It was found that compressive residual stresses around the sample notch had significant retarding effects on both crack initiation and crack growth rates for cracks growing towards the weld line. Effects of residual stress on crack growth rates declined with increasing crack length. When cracks grew parallel to the weld line in C(T) samples the crack growth rate was around 20% lower than in parent material. © 2011 Elsevier Ltd. All rights reserved.


Zhang H.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Huang T.S.,University of Illinois at Urbana - Champaign
Pattern Recognition | Year: 2013

We propose a pose-robust face recognition method to handle the challenging task of face recognition in the presence of large pose difference between gallery and probe faces. The proposed method exploits the sparse property of the representation coefficients of a face image over its corresponding view-dictionary. By assuming the representation coefficients are invariant to pose, we can synthesize for the probe image a novel face image which has smaller pose difference with the gallery faces. Furthermore, face recognition in the presence of pose variations is achieved based on the synthesized face image again via sparse representation. Extensive experiments on CMU Multi-PIE face database are conducted to verify the efficacy of the proposed method. © 2012 Elsevier Ltd.


Xu Y.,Northwestern Polytechnical University | Liang X.,China Airborne Missile Academy
International Journal of Digital Content Technology and its Applications | Year: 2011

Active radar/infrared (IR) compound guidance technology has become a hot research content of compound guidance field. According to the characteristics and the engineering application of active radar/IR composite seeker system, in this paper, a distributed flow of information fusion for Radar/IR composite seeker was established. First the observation data of the two seekers were pretreated, including time and space registration and outlier elimination of the observation data. After that, the Federated Filter (FF) was used to setup an information fusion algorithm of radar/IR composite seeker. According to the different characteristics of radar and IR system, the Extended Kalman Filter (EKF) algorithm and the Pseudo-linear Kalman Filter (PLKF) algorithm were used to design radar and IR local filter respectively. The simulation results show that this information fusion algorithm provides significant improvement in the tracking precision of the radar/IR composite seeker system, and it has good real-time performance and stability.


Semlitsch B.,KTH Royal Institute of Technology | Wang Y.,Northwestern Polytechnical University | Mihescu M.,KTH Royal Institute of Technology
Energy Conversion and Management | Year: 2015

Performance optimization regarding e.g. exhaust valve strategies in an internal combustion engine is often performed based on one-dimensional simulation investigation. Commonly, a discharge coefficient is used to describe the flow behavior in complex geometries, such as the exhaust port. This discharge coefficient for an exhaust port is obtained by laboratory experiments at fixed valve lifts, room temperatures, and low total pressure drops. The present study investigates the consequences of the valve and piston motion onto the energy losses and the discharge coefficient. Therefore, Large Eddy Simulations are performed in a realistic internal combustion geometry using three different modeling strategies, i.e. fixed valve lift and fixed piston, moving piston and fixed valve lift, and moving piston and moving valve, to estimate the energy losses. The differences in the flow field development with the different modeling approaches is delineated and the dynamic effects onto the primary quantities, e.g. discharge coefficient, are quantified. Considering the motion of piston and valves leads to negative total pressure losses during the exhaust cycle, which cannot be observed at fixed valve lifts. Additionally, the induced flow structures develop differently when valve motion is taken into consideration, which leads to a significant disparity of mass flow rates evolving through the two individual valve ports. However, accounting for piston motion and limited valve motion, leads to a minor discharge coefficient alteration of about one to two percent. © 2015 Elsevier Ltd. All rights reserved.


Zhang H.,Northwestern Polytechnical University | Zhang H.,University of Illinois at Urbana - Champaign | Yang J.,University of Illinois at Urbana - Champaign | Zhang Y.,Northwestern Polytechnical University | And 2 more authors.
Proceedings of the IEEE International Conference on Computer Vision | Year: 2011

Most previous visual recognition systems simply assume ideal inputs without real-world degradations, such as low resolution, motion blur and out-of-focus blur. In presence of such unknown degradations, the conventional approach first resorts to blind image restoration and then feeds the restored image into a classifier. Treating restoration and recognition separately, such a straightforward approach, however, suffers greatly from the defective output of the ill-posed blind image restoration. In this paper, we present a joint blind image restoration and recognition method based on the sparse representation prior to handle the challenging problem of face recognition from low-quality images, where the degradation model is realistic and totally unknown. The sparse representation prior states that the degraded input image, if correctly restored, will have a good sparse representation in terms of the training set, which indicates the identity of the test image. The proposed algorithm achieves simultaneous restoration and recognition by iteratively solving the blind image restoration in pursuit of the sparest representation for recognition. Based on such a sparse representation prior, we demonstrate that the image restoration task and the recognition task can benefit greatly from each other. Extensive experiments on face datasets under various degradations are carried out and the results of our joint model shows significant improvements over conventional methods of treating the two tasks independently. © 2011 IEEE.


Wang Q.,Anyang University, China | Oganov A.R.,Moscow Institute of Physics and Technology | Oganov A.R.,Northwestern Polytechnical University | Zhu Q.,State University of New York at Stony Brook | Zhou X.-F.,State University of New York at Stony Brook
Physical Review Letters | Year: 2014

Reconstructions of the (110) surface of rutile TiO2 (the dominant surface of this important mineral and catalyst) are investigated using the evolutionary approach, resolving previous controversies. Depending on thermodynamic conditions, four different stable reconstructions are observed for this surface. We confirm the recently proposed "Ti2O3-(1×2)" and "Ti2O-(1×2)" reconstructions and predict two new reconstructions "Ti3O2-(1×2)" and "Ti3O3-(2×1)," which match experimental results. Furthermore, we find that surface electronic states are sensitive to reconstructions and, therefore, depend on thermodynamic conditions. © 2014 American Physical Society.


Zhang H.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Huang T.S.,University of Illinois at Urbana - Champaign
Pattern Recognition | Year: 2013

Sparsity driven classification method has been popular recently due to its effectiveness in various classification tasks. It is based on the assumption that samples of the same class live in the same subspace, thus a test sample can be well represented by the training samples of the same class. Previous methods model the subspace for each class with either the training samples directly or dictionaries trained for each class separately. Although enabling strong reconstructive ability, these methods may not have desirable discriminative ability, especially when there are high correlations among the samples of different classes. In this paper, we propose to learn simultaneously a discriminative projection and a dictionary that are optimized for the sparse representation based classifier, to extract discriminative information from the raw data while respecting the sparse representation assumption. By formulating the task of projection and dictionary learning into an optimization framework, we can learn the discriminative projection and dictionary effectively. Extensive experiments are carried out on various datasets and the experimental results verify the efficacy of the proposed method. © 2012 Elsevier Ltd All rights reserved.


Wang Z.-J.,Chang'an University | Wang Z.-J.,Northwestern Polytechnical University | Li K.-Z.,Northwestern Polytechnical University | Wang C.,Shaanxi Railway Institute
Construction and Building Materials | Year: 2014

Electromagnetic pollution has increasingly attracted attention with the development of electronic technology. Carbon fiber cement based composites are widely used as electromagnetic wave absorbing material. However, freezing-thawing cycles can affect their wave absorbing function. In this paper, specimens of the composites with different carbon fiber (CF) contents were prepared. The reflectivity variation of the composites against the wave was investigated before and after 50 freezing-thawing cycles by Naval Research Laboratory (NRL) testing system in 2.0-18.0 GHz frequency bands. The microstructure and the pore size distribution were analyzed by Scanning Electron Microscopy (SEM) and a pore distribution analyzer. Results show that the reflectivity varies slightly before and after freezing-thawing without any CF. In the lower frequency bands, the reflectivity of the composites with different CF contents increases obviously after freezing-thawing cycles. In the higher frequencies, it decreases first and increases then with the minimum value of -12.5 dB and 2.5 GHz frequency band. When the CF content is higher than 0.2%, freezing-thawing cycles can decrease the wave absorbing property of the composites. The porosity of the composites decreases with the increase of the CF contents. It rises when the CF content is 0.8 wt.%. Lower porosity is beneficial to improve the electromagnetic wave absorbing property for the composites. © 2014 Elsevier Ltd. All rights reserved.


Semlitsch B.,KTH Royal Institute of Technology | Wang Y.,Northwestern Polytechnical University | Mihaescu M.,KTH Royal Institute of Technology
Energy Conversion and Management | Year: 2014

In an internal combustion engine, the residual energy remaining after combustion in the exhaust gasses can be partially recovered by a downstream arranged device. The exhaust port represents the passage guiding the exhaust gasses from the combustion chamber to the energy recovering device, e.g. a turbocharger. Thus, energy losses in the course of transmission shall be reduced as much as possible. However, in one-dimensional engine models used for engine design, the exhaust port is reduced to its discharge coefficient, which is commonly measured under constant inflow conditions neglecting engine-like flow pulsation. In this present study, the influence of different boundary conditions on the energy losses and flow development during the exhaust stroke are analyzed numerically regarding two cases, i.e. using simple constant and pulsating boundary conditions. The compressible flow in an exhaust port geometry of a truck engine is investigated using three-dimensional Large Eddy Simulations (LES). The results contrast the importance of applying engine-like boundary conditions in order to estimate accurately the flow induced losses and the discharge coefficient of the exhaust port. The instantaneous flow field alters significantly when pulsating boundary conditions are applied. Thus, the induced losses by the unsteady flow motion and the secondary flow motion are increased with inflow pulsations. The discharge coefficient decreased about 2% with flow pulsation. A modal flow decomposition method, i.e. Proper Orthogonal Decomposition (POD), is used to analyze the coherent structures induced with the particular inflow and outflow conditions. The differences in the flow field for different boundary conditions suggest to incorporate a modeling parameter accounting for the quality of the flow at the turbocharger turbine inlet in one-dimensional simulations. © 2014 Elsevier Ltd. All rights reserved.


Yuan D.,East China Institute of Technology | Zhang H.,Northwestern Polytechnical University
Applied Catalysis A: General | Year: 2014

Superparamagnetic polymer composite microspheres Fe3O 4/P(GMA-AA-MMA) prepared by an emulsifier free emulsion polymerization using DPE as free radical control agent were used to support palladium nanoparticles. The magnetic catalyst can provide excellent reactivity in the Suzuki coupling reactions of aryl halides with phenylboronic acids under mild condition (at 80 C) in EtOH/H2O (1:1) mixture. Furthermore, the novel catalyst can be conveniently recovered by an external magnet field and reused at least five times without significant loss of its catalytic activity. © 2014 Elsevier B.V.


Zhang H.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Li H.,Northwestern Polytechnical University | Huang T.S.,University of Illinois at Urbana - Champaign
IEEE Transactions on Image Processing | Year: 2012

We propose a new single image super resolution (SR) algorithm via Bayesian modeling with a natural image prior modeled by a high-order Markov random field (MRF). SR is one of the long-standing and active topics in image processing community. It is of great use in many practical applications, such as astronomical observation, medical imaging, and the adaptation of low-resolution contents onto high-resolution displays. One category of the conventional approaches for image SR is formulating the problem with Bayesian modeling techniques and then obtaining its maximum-a-posteriori solution, which actually boils down to a regularized regression task. Although straightforward, this approach cannot exploit the full potential offered by the probabilistic modeling, as only the posterior mode is sought. On the other hand, current Bayesian SR approaches using the posterior mean estimation typically use very simple prior models for natural images to ensure the computational tractability. In this paper, we present a Bayesian image SR approach with a flexible high-order MRF model as the prior for natural images. The minimum mean square error (MMSE) criteria are used for estimating the HR image. A Markov chain Monte Carlo-based sampling algorithm is presented for obtaining the MMSE solution. The proposed method cannot only enjoy the benefits offered by the flexible prior, but also has the advantage of making use of the probabilistic modeling to perform a posterior mean estimation, thus is less sensitive to the local minima problem as the MAP solution. Experimental results indicate that the proposed method can generate competitive or better results than state-of-the-art SR algorithms. © 1992-2012 IEEE.


Zhang H.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Nasrabadi N.M.,U.S. Army | Huang T.S.,University of Illinois at Urbana - Champaign
IEEE Transactions on Systems, Man, and Cybernetics, Part B: Cybernetics | Year: 2012

This paper investigates the joint-structured-sparsity-based methods for transient acoustic signal classification with multiple measurements. By joint structured sparsity, we not only use the sparsity prior for each measurement but we also exploit the structural information across the sparse representation vectors of multiple measurements. Several different sparse prior models are investigated in this paper to exploit the correlations among the multiple measurements with the notion of the joint structured sparsity for improving the classification accuracy. Specifically, we propose models with the joint structured sparsity under different assumptions: same sparse code model, common sparse pattern model, and a newly proposed joint dynamic sparse model. For the joint dynamic sparse model, we also develop an efficient greedy algorithm to solve it. Extensive experiments are carried out on real acoustic data sets, and the results are compared with the conventional discriminative classifiers in order to verify the effectiveness of the proposed method. © 1996-2012 IEEE.


Zhou W.,Shanghai JiaoTong University | Lin X.,Northwestern Polytechnical University | Li J.F.,Shanghai JiaoTong University
Journal of Alloys and Compounds | Year: 2013

The composition dependences of crystallization, microstructure and mechanical properties have been investigated. When the Ag content is in the range of 0-8 at%, the BMGs with two or three-step of crystallization process exhibit remarkable plasticity, of which primary phase is an icosahedral phase. However, when the Ag concentration reaches 12-16 at%, the BMGs with single-step of crystallization mode display relatively limited plasticity, whose precipitation phase is Zr2Cu and/or Zr2Ni intermetallic compounds. Structural analyses reveal that the presence of icosahedral medium-range order clusters, which, in turn leads to the heterogeneity of free volume distribution, is responsible for the improvement of plasticity. The present results suggest that, under appropriate microstructural design by the introduction of icosahedral medium-range order clusters, BMG has extensive application prospect as structural material. © 2012 Elsevier B.V. All rights reserved.


News Article | December 15, 2016
Site: www.eurekalert.org

Medical implants often carry surface substrates that release ac-tive substances or to which biomolecules or cells can adhere better. However, degradable gas-phase coatings for degradable implants, such as surgical suture materials or scaffolds for tis-sue culturing, have been lacking so far. In the journal An-gewandte Chemie, researchers of Karlsruhe Institute of Technol-ogy now present a polymer coating that is degraded in the body together with its carrier. (DOI:10.1002/ange.201609307) "Our new degradable polymer films might be applied for functionali-zation and coating of surfaces in biosciences, medicine, or food packaging," says Professor Joerg Lahann, Co-Director of the Insti-tute of Functional Interfaces of Karlsruhe Institute of Technology (KIT). Together with an international team, he produced polymer films with functional groups as "anchor sites" for fluorescent dyes or biomolecules. For the first time, the researchers present a CVD (chemical vapor deposition) method to produce biodegradable polymers. Via spe-cial side groups, biomolecules or active substances can be at-tached. This opens up new potentials for e.g. coating biodegrada-ble implants. Polymerization by chemical vapor deposition is a sim-ple and widely used method to modify surfaces, by means of which also complex and irregular carrier substrates can be coated homo-geneously with polymers. In CVD polymerization, the initial compounds are evaporated, acti-vated at high temperature, and deposited onto surfaces, where they polymerize. However, so far it has been possible to coat permanent implants only. Coating has been impossible for materials that are to be degraded after fulfilling their tasks, such as surgical suture mate-rials, systems for the controlled release of substances, stents re-leasing medical substances or scaffolds for culturing tissue. Bio-degradable coatings could not be produced by CVD. Now, this gap is closed, as scientists of Karlsruhe Institute of Tech-nology, University of Michigan (Ann Arbor, USA), and Northwestern Polytechnical University (Xi'an, China) for the first time synthesized a CVD polymer with a degradable backbone. The team applied co-polymerization of two special monomer types: The para-cyclophanes usually used for this method were combined with cy-clic ketene acetals. While classical polymers on the basis of para-cyclophanes are linked by carbon-carbon bonds exclusively, ketene acetal is repositioned during polymerization, such that ester bonds (e.g. bonds between carbon and oxygen atoms) are formed in the polymer backbone. Ester bonds can be cleaved in aqueous medi-um. "The degradation rate depends on the ratio of both monomer types and on the side groups of the monomers," Lahann explains. "Polar side groups make the polymer film less water-repellent and acceler-ate degradation, as water can enter more easily. In this way, the degradation rate can be adapted to application." Using cell cultures, the researchers already demonstrated that neither the polymer nor its degradation products are toxic. Xie, F., Deng, X., Kratzer, D., Cheng, K. C. K., Friedmann, C., Qi, S., Solorio, L. and Lahann, J. (2016), Backbone-Degradable Poly-mers Prepared by Chemical Vapor Deposition. Angew. Chem. DOI:10.1002/ange.201609307. Karlsruhe Institute of Technology (KIT) pools its three core tasks of research, higher education, and innovation in a mission. With about 9,300 employees and 25,000 students, KIT is one of the big institutions of research and higher education in natural sciences and engineering in Europe. KIT - The Research University in the Helmholtz Association Since 2010, the KIT has been certified as a family-friendly university.


Han Z.-H.,Northwestern Polytechnical University | Gortz S.,German Aerospace Center
AIAA Journal | Year: 2012

The efficiency of building a surrogate model for the output of a computer code can be dramatically improved via variable-fidelity surrogate modeling techniques. In this article, a hierarchical kriging model is proposed and used for variable-fidelity surrogate modeling problems. Here, hierarchical kriging refers to a surrogate model of a highfidelity function that uses a kriging model of a sampled lower-fidelity function as a model trend. As a consequence, the variation in the lower-fidelity data is mapped to the high-fidelity data, and a more accurate surrogate model for the high-fidelity function is obtained. A self-contained derivation of the hierarchical kriging model is presented. The proposed method is demonstrated with an analytical example and used for modeling the aerodynamic data of an RAE 2822 airfoil and an industrial transport aircraft configuration. The numerical examples show that it is efficient, accurate, and robust. It is also observed that hierarchical kriging provides a more reasonable mean-squared-error estimation than traditional cokriging. It can be applied to the efficient aerodynamic analysis and shape optimization of aircraft or any other research areas where computer codes of varying fidelity are in use. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


Yang X.L.,Shaanxi Normal University | Sun Z.K.,Northwestern Polytechnical University
International Journal of Non-Linear Mechanics | Year: 2010

Analytical derivations and numerical calculations are employed to gain insight into the parametric resonance of a stochastically driven van der Pol oscillator with delayed feedback. This model is the prototype of a self-excited system operating with a combination of narrow-band noise excitation and two time delayed feedback control. A slow dynamical system describing the amplitude and phase of resonance, as well as the lowest-order approximate solution of this oscillator is firstly obtained by the technique of multiple scales. Then the explicit asymptotic formula for the largest Lyapunov exponent is derived. The influences of system parameters, such as magnitude of random excitation, tuning frequency, gains of feedback and time delays, on the almost-sure stability of the steady-state trivial solution are discussed under the direction of the signal of largest Lyanupov exponent. The non-trivial steady-state solution of mean square response of this system is studied by moment method. The results reveal the phenomenon of multiple solutions and time delays induced stabilization or unstabilization, moreover, an appropriate modulation between the two time delays in feedback control may be acted as a simple and efficient switch to adjust control performance from the viewpoint of vibration control. Finally, theoretical analysis turns to a validation through numerical calculations, and good agreements can be found between the numerical results and the analytical ones. © 2010 Elsevier Ltd. All rights reserved.


Song K.,Northwestern Polytechnical University | Liu Y.,Northwestern Polytechnical University | Fu Q.,Northwestern Polytechnical University | Zhao X.,Northwestern Polytechnical University | And 2 more authors.
Optics Express | Year: 2013

We propose a more efficient way to obtain much stronger polarization rotatory power by constructing a composite chiral metamaterial (CCMM) which is achieved via the combination of the cut-wire pairs (CWPs) and a purely chiral metamaterial (PCMM) composed of conjugated gammadion resonators. Owing to the strong coupling between the CWPs and PCMM, the polarization rotation in our CCMM is more gigantic than that of the PCMM. Furthermore, the CCMM proposed in this paper can function as a wide-angle 90° polarization rotator for different substrate permittivity without needing to adjust its geometric parameters. Due to the unique properties, the CCMM may greatly benefit potential applications including designing a tunable 90°-polarization rotator, microwave devices, telecommunication, and so on. © 2013 Optical Society of America.


Zhang W.,Albert Ludwigs University of Freiburg | Zhang W.,Northwestern Polytechnical University | Aljasem K.,Albert Ludwigs University of Freiburg | Zappe H.,Albert Ludwigs University of Freiburg | Seifert A.,Albert Ludwigs University of Freiburg
Optics Express | Year: 2011

An integrated tunable microlens, whose focal length may be varied over a range of 3 to 15mm with total power consumption below 250mW, is presented. Using thermo-pneumatic actuation, this adaptive optical microsystem is completely integrated and requires no external pressure controllers for operation. The lens system consists of a liquid-filled cavity bounded by a distensible polydimethyl-siloxane membrane and a separate thermal cavity with actuation and sensing elements, all fabricated using silicon, glass and polymers. Due to the physical separation of thermal actuators and lens body, temperature gradients in the lens optical aperture were below 4°C in the vertical and 0.2°C in the lateral directions. Optical characterization showed that the cutoff frequency of the optical transfer function, using a reference contrast of 0.2, varied from 30 lines/mm to 65 lines/mm over the tuning range, and a change in the numerical aperture from 0.067 to 0.333. Stable control of the focal length over a long time period using a simple electronic stabilization circuit was demonstrated. © 2011 Optical Society of America.


Xiao F.,Northwestern Polytechnical University | Zhu W.,Monash University | Premaratne M.,Monash University | Zhao J.,Northwestern Polytechnical University
Optics Express | Year: 2014

We propose a method to dynamically control the Fano resonance of a ring/crescent-ring gold nanostructure by spatially changing the phase distribution of a probe Bessel beam. We demonstrate that a highly tunable Fano interference between the quadrupole and bright dipole modes can be realized in the near-infrared range. Even though a complex interference between a broad resonance and a narrower resonance lead to these observations, we show that a simple coupled oscillator model can accurately describe the behavior, providing valuable insights into the dynamics of the system. A further analysis of this structure uncovers a series of interesting phenomena such as anticrossing, sign changing of coupling and the spectral inversion of quadrupole and bright dipole modes. We further show that near field enhancement at Fano resonance can be actively controlled by modulating the phase distribution of the exciting incident Bessel beam.©2014 Optical Society of America.


Gao S.,Northwestern Polytechnical University | Zhong Y.,Curtin University Australia | Shirinzadeh B.,Monash University
Information Sciences | Year: 2010

This paper adopts the concept of random weighting estimation to multi-sensor data fusion. It presents a new random weighting estimation methodology for optimal fusion of multi-dimensional position data. A multi-sensor observation model is constructed for multi-dimensional position. Based on this observation model, a random weighting estimation algorithm is developed for estimation of position data from single sensors. Using the random weighting estimations from each single sensor, an optimization theory is established for optimal fusion of multi-sensor position data. Experimental results demonstrate that the proposed methodology can effectively fuse multi-sensor dimensional position data, and the fusion accuracy is much higher than that of the Kalman fusion method. © 2010 Elsevier Inc. All rights reserved.


Zhu W.,Monash University | Xiao F.,Northwestern Polytechnical University | Kang M.,Tianjin Normal University | Sikdar D.,Monash University | Premaratne M.,Monash University
Applied Physics Letters | Year: 2014

A terahertz fishnet metamaterial, consisting of a gallium arsenide substrate sandwiched between multi-layer graphene-dielectric composites, is theoretically studied. Detailed analysis shows that this metamaterial has a left-handed transmission peak accompanied with an abnormal phase dispersion and a clear negative refractive index which originates from simultaneous magnetic and electric resonances. Our structure is unique because it has no metallic parts to achieve the left-handed properties. The most important utility of this metamaterial comes from the fact that its left-handed features can be dynamically controlled by applying external bias to shift the Fermi level in graphene. © 2014 AIP Publishing LLC.


Xiao J.,Hong Kong University of Science and Technology | Xiao J.,Northwestern Polytechnical University | Ye W.,Hong Kong University of Science and Technology | Cai Y.,Hong Kong University of Science and Technology | Zhang J.,Hong Kong University of Science and Technology
International Journal for Numerical Methods in Engineering | Year: 2012

A precorrected fast Fourier transform (pFFT) accelerated boundary element method (BEM) for large-scale transient elastodynamic analysis is developed and described in this paper. The frequency-domain approach is used. To overcome the 'wrap-around' problem associated with the discrete Fourier transform, the exponential window method (EWM) is employed and incorporated in the frequency-domain BEM. An improved implementation scheme of the pFFT method based on polynomial interpolation technique is developed and applied to accelerate the elastodynamic BEM. This new scheme reduces the memory required to save the convolution matrix by a factor of 8. To further improve the efficiency of the code, a newly developed linear system solver based on the induced dimension reduction method is employed. Its performance is investigated and compared with that of the well-known GMRES. The accuracy and computational efficiency of the method are evaluated and demonstrated by three examples: a classical benchmark, a plate subject to an impact loading and a porous cube with nearly half million DOFs subject to a step traction loading. Both analytical and experimental results are employed to validate the method. It has been found that the EWM can effectively resolve the wrap-around problem and accurate time responses for an arbitrarily chosen time period can be obtained. © 2011 John Wiley & Sons, Ltd.


Asadi M.,Islamic Azad University at Tehran | Xie G.,Northwestern Polytechnical University | Sunden B.,Lund University
International Journal of Heat and Mass Transfer | Year: 2014

An impressive amount of investigations has been devoted to enhancing thermal performance of microchannels. The small size of microchannels and their ability to dissipate heat makes them as one of the best choices for the electronic cooling systems. In this paper, a comprehensive review of available studies regarding single and two-phase microchannels is presented and analyzed. 219 articles are reviewed to identify the heat transfer mechanisms and pressure drops in microchannels. This review looks into the different methodologies and correlations used to predict the heat transfer and pressure drop characteristics of microchannels along the channel geometries and flow regimes. The review shows that earlier studies (from 1982 to 2002) were largely conducted using experimental approaches, and discrepancies between analytical and experimental results were large, while more recent studies (from 2003 to 2013) used numerical simulations, correlations for predicting pressure drop and heat transfer coefficients were considerably more accurate. © 2014 Elsevier Ltd. All rights reserved.


Liu W.,Northwestern Polytechnical University | Yang X.J.,Aeronautical University
Fatigue and Fracture of Engineering Materials and Structures | Year: 2013

The influence of cyclic creep accumulation rate on the damage evolution of MDYB-3 polymethyl methacrylate (PMMA) was experimentally investigated. Fatigue tests were carried out at four stress levels by stress control mode. The steady cyclic creep accumulation stage was observed occupying a substantial proportion of all specimens fatigue processes. Cyclic creep strain growth speed and relaxed modulus degradation rate were deduced as two important indicators for describing the damage evolution characteristics. Linear evolution relations of cyclic creep strain and modulus degradation with cycle times were retrieved from different terms of hysteresis loops. A preliminary model was proposed to be able to estimate the damage extent at different cyclic stress levels. The life predictions by the proposed model were compared with the experiment results and the classical power S-N model, which were demonstrated as a good estimation for the fatigue life. It is feasible to make durability evaluations by the characteristics of steady cyclic creep for multiaxis directed PMMA material. © 2013 Wiley Publishing Ltd.


Xu J.,Northwestern Polytechnical University | Xu J.,Nanjing University of Science and Technology | Xu J.,Nanjing Southeast University
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2016

This later firstly presents a quasi-elliptic bandpass filter (QE-BPF) which consists of a pair of shorted stepped-impedance resonator (SSIR) and a dual-mode resonator (DMR). Then, a 900 MHz switchable bandpass filter (SW-BPF) and a 1250 MHz SW-BPF are designed by loading p-i-n diodes at two open ends of DMR or SSIRs. Finally, a common-T junction constructed by two T-networks is used to combine the above designed 900 and 1250 MHz SW-BPFs to constitute a switchable diplexer. The fabricated QE-BPF, two SW-BPFs and switchable diplexer exhibit wide bandwidth, low insertion loss, sharp passband selectivity, high port isolation and compact size. © 2015 IEEE.


Song S.J.,Northwestern Polytechnical University | Liu F.,Northwestern Polytechnical University | Zhang Z.H.,Baosteel
Acta Materialia | Year: 2014

During solid-state phase transformation, volume misfit between the parent and the product phases leads to strain energy and affects the transformation kinetics. Considering a misfitting spherical inclusion growing/shrinking in a finite elastic-perfectly plastic medium and recognizing the isolated product/present phase as the inclusion at different stages of transformation, complete solutions to the displacement, stress and strain fields for the purely elastic and elastic-plastic accommodations of the transformation misfit are obtained. Then, analytical expressions for the transformed fraction dependences of the total molar accommodation energy and the mechanical driving force at an interphase are presented and incorporated into the transformation kinetics. The present model is evaluated using the austenite-to-ferrite (γ → α) transformation in pure iron with temperature-dependent material properties. During the elastic-plastic accommodation, the elastic strain energies in the matrix and inclusion are negligible compared to the plastic work in the matrix; and meanwhile, the total strain energy is relaxed to a lower value in contrast to the corresponding purely elastic accommodation. Furthermore, during almost the entire process of transformation, the matrix remains completely plastic. The mechanical driving force varies monotonously with the transformed fraction, which counteracts the transformation at the initial stage but favors the transformation at the later stage. Application of the present model in the non-isothermal γ → α transformation of pure iron conducted with a cooling rate of 10 K min-1 is performed, and the effect of the misfit accommodation on the metastable equilibrium temperature is demonstrated. As compared with the chemical driving force, the mechanical driving force is much smaller but has a significant effect on the transformation kinetics. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Sun Z.,Northwestern Polytechnical University | Yang X.,Shaanxi Normal University | Xu W.,Northwestern Polytechnical University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We study the effect of noise recycling on nonequilibrium escape dynamics in a bistable system. For small noise, the non-Markovian problem is reduced to a two-state model with the master equation depending on not only the current state but also the earlier state, based on which we are able to derive the analytical formulas for the switching rate, the autocorrelation function, and the power spectrum density (PSD). Both the theoretical and the numerical results show that, with modulating the time delay in noise recycling, a monotonic PSD may switch to a nonmonotonic one; the amplitude of PSD at resonance frequency exhibits a pronounced maximum at a certain noise level, declaring the onset of stochastic resonance (SR) in the absence of a weak periodic signal. Further, we also demonstrate that the linear response to the external periodic force displays a maximum at a certain level of time delay, displaying the signature of SR. © 2012 American Physical Society.


Liu S.,Northwestern Polytechnical University | Yu P.,Hong Kong University of Science and Technology | Xu K.,Hong Kong University of Science and Technology | Zhong C.,Northwestern Polytechnical University
Journal of Computational Physics | Year: 2014

A unified gas-kinetic scheme (UGKS) is constructed for both continuum and rarefied flow computations. The underlying principle for the development of UGKS is the direct modeling for the gas evolution process from the kinetic to the hydrodynamic scale, which is used in the flux construction across a cell interface. More specifically, the physical process from the kinetic particle free transport to the hydrodynamic pressure wave propagation is recovered in the flux function. In the previous study, the UGKS has been developed mainly for monatomic gas with particle translational motion only. The construction of time evolution solution is based on the BGK, Shakhov, and ES-BGK models. The UGKS has been validated through extensive numerical tests. In this paper, a UGKS for diatomic gas will be constructed, where the gas-kinetic Rykov model with a Landau-Teller-Jeans-type rotational energy relaxation is used in the numerical scheme. The new scheme will be tested in many cases, such as homogeneous flow relaxation, shock structure calculations, hypersonic flow passing a flat plate, and the flow around a blunt circular cylinder. The analytic, DSMC, and experimental measurements will be used for validating the solutions of UGKS. © 2013 Elsevier Inc.


Zhang L.,Harbin Engineering University | Zhang L.,Northwestern Polytechnical University | Zhang K.,Harbin Engineering University | Zhang K.,University of Turku
IEEE Transactions on Neural Networks and Learning Systems | Year: 2013

This brief investigates the controllability and observability of Boolean control networks with (not necessarily bounded) time-variant delays in states. After a brief introduction to converting a Boolean control network to an equivalent discrete-time bilinear dynamical system via the semi-tensor product of matrices, the system is split into a finite number of subsystems (constructed forest) with no time delays by using the idea of splitting time that is proposed in this brief. Then, the controllability and observability of the system are investigated by verifying any so-called controllability constructed path and any so-called observability constructed paths in the above forest, respectively, which generalize some recent relevant results. Matrix test criteria for the controllability and observability are given. The corresponding control design algorithms based on the controllability theorems are given. We also show that the computing complexity of our algorithm is much less than that of the existing algorithms. © 2012 IEEE.


Feng T.,Northwestern Polytechnical University | Wang D.,Monash University
Industrial Management and Data Systems | Year: 2013

Purpose - The purpose of this paper is to investigate the impacts of three types of supply chain involvement (SCI) on three types of new product development (NPD) performance. Design/methodology/approach - To test the research hypotheses, structural equation modeling was conducted using data from 214 Chinese manufacturing companies. Findings - The results reveal that internal involvement is positively associated with customer and supplier involvement. It was also found that three types of SCI influence three types of NPD performance differently. Specifically, internal involvement is important in improving NPD speed, while customer and supplier involvement have significant effects on NPD cost and NPD speed. Moreover, internal and customer involvement enhance market performance indirectly, whereas supplier involvement improves market performance both directly and indirectly. Research limitations/implications - This research examines the relationship between SCI and NPD performance in China. However, the effectiveness of SCI may be contingent on various factors (such as involvement timing, innovation strategy and business environment) and the relationship may be different in other cultural contexts. Practical implications - Managers should adopt a holistic SCI perspective to manage their supply chains when developing new products, to achieve better performance. Originality/value - This study contributes to SCI literature and practices by defining three types of SCI in the context of supply chain, examining the relationships among them and revealing the impacts of different types of SCI on different types of NPD performance. © Emerald Group Publishing Limited.


Wang H.,Northwestern Polytechnical University | Wang H.,German Aerospace Center | Liu F.,Northwestern Polytechnical University | Ehlen G.J.,German Aerospace Center | Herlach D.M.,German Aerospace Center
Acta Materialia | Year: 2013

Because the Cahn-Hillard and Allen-Cahn equations cannot deal with the additional constraints in the multi-phase-field models, several approximate treatments, e.g. a specific partition relation and the condition of equal or unequal diffusion potentials, were proposed. In this paper, the problem is solved successfully by the maximal entropy production principle and a model is developed for rapid solidification of a binary alloy system. Due to the mixture law used to define the free energy density, solute concentration and chemical potential jumps happen at an "imaginary" sharp interface between solid and liquid. The solute diffusions in solid and liquid are described by two independent equations and additional non-linear equations do not need to be employed to fix the solute concentrations of solid and liquid. Application to solute trapping during rapid solidification of Si-9 at.% As alloy shows that a good agreement between the model predictions and the experimental results is obtained. The interface and bulk contributions are decoupled at very low and very high interface velocities and in other cases the interaction between them depends weakly on the interface velocity.


Li J.,Northwestern Polytechnical University | Soh A.K.,Monash University | Wu X.,CAS Institute of Mechanics
Scripta Materialia | Year: 2014

A theoretical model has been developed for nanograin rotation that could be achieved through dislocation climb. The results obtained show that the occurrence of nanograin rotation and the coalescence of grains depend on the external stress level, structure of grain boundary and grain size. Moreover, a critical misorientation parameter that represents the crossover between nanograin rotation and shear-coupled migration of grain boundaries has also been found, based on which a coupling mechanism between nanograin rotation and shear-coupled migration was proposed. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Asadi M.,Islamic Azad University at Tehran | Xie G.,Northwestern Polytechnical University
Journal of Thermal Science and Engineering Applications | Year: 2014

Effects of wavy-fins surface area on thermal-hydraulic performance of a heat exchanger have been observed. First, a new method to calculate the heat transfer area of wavy-fin surfaces is introduced. The results show that the proposed method is accurate enough to be used in the analysis of heat exchanger performance. One of the important aspects of this method is that it is a direct method compared with the experimental method introduced by Kays and London, and thus might be a strong tool in the optimization of heat exchangers based on different objective functions. Effects of some nondimensional parameters, such as amplitude-to-wavelength ratio, fin space ratio, and channel crosssection ratio on the heat transfer characteristics and pressure drop are also investigated. © 2014 by ASME.


Han Z.-H.,Northwestern Polytechnical University | Gortz S.,German Aerospace Center | Zimmermann R.,German Aerospace Center
Aerospace Science and Technology | Year: 2013

Variable-fidelity surrogate modeling offers an efficient way to generate aerodynamic data for aero-loads prediction based on a set of CFD methods with varying degree of fidelity and computational expense. In this paper, direct Gradient-Enhanced Kriging (GEK) and a newly developed Generalized Hybrid Bridge Function (GHBF) have been combined in order to improve the efficiency and accuracy of the existing Variable-Fidelity Modeling (VFM) approach. The new algorithms and features are demonstrated and evaluated for analytical functions and are subsequently used to construct a global surrogate model for the aerodynamic coefficients and drag polar of an RAE 2822 airfoil. It is shown that the gradient-enhanced GHBF proposed in this paper is very promising and can be used to significantly improve the efficiency, accuracy and robustness of VFM in the context of aero-loads prediction. © 2012 Elsevier Masson SAS. All rights reserved.


News Article | December 1, 2016
Site: www.eurekalert.org

Polymerization by chemical vapor deposition (CVD) is a simple method for modifying surfaces by which topologically challenging substrates can be evenly coated with polymers. In the journal Angewandte Chemie, researchers have now introduced the first CVD method for producing degradable polymers. Biomolecules or drugs can be attached by means of special side groups. This introduces new possibilities for applications like the coating of biodegradable implants. In CVD polymerization, the starting compounds are vaporized, activated at high temperature, and deposited onto surfaces, where they polymerize. In medical applications, substrates for implants are coated to allow functional groups to be added as anchors for the attachment of biomolecules or drugs. Until now, however, it has only been possible to coat nondegradable implants, not materials that need to degrade after fulfilling their task, like surgical sutures, systems for controlled drug delivery, drug-eluding stents, or tissue engineering scaffolds. This is because it was previously not possible to make degradable coatings by CVD. Scientists from the University of Michigan (Ann Arbor, USA), Northwestern Polytechnical University (Xi'an, China), and the Karlsruhe Institute of Technology (KIT, Eggenstein-Leopoldshafen, Germany) have now synthesized the first CVD polymer with a degradable backbone. The research team led by Jörg Lahann succeeded by using two special types of monomer: The paracyclophanes usually used for this process were combined with cyclic ketene acetals. While the classic polymers based on paracyclophanes are connected exclusively through carbon-carbon bonds, the ketene acetal converts during the polymerization so that ester bonds (a bond between a carbon and an oxygen atom) are formed within the polymer backbone. Ester bonds can be broken in aqueous environments. "The speed of the degradation depends on the ratio of the two types of monomer as well as their side chains," explains Lahann. "Polar side chains make the polymer film less hydrophobic and accelerate degradation because water can penetrate more easily. The speed of degradation can thus be tailored to the intended use." Tests with cell cultures demonstrated that neither the polymer nor its degradation products are toxic. The team produced polymer films that were equipped with functional side groups that act as "anchor points" for molecules, which can be used to attach fluorescence dyes and biomolecules. "Our new degradable polymer films could find broad application for the functionalization and coating of surfaces in the biological sciences as well as medicine and for food packaging applications," states Lahann. Dr. Lahann is Professor of Chemical Engineering, Materials Science and Engineering and Biomedical Engineering at the University of Michigan. He also serves as the Director of the Biointerfaces Institute at the University of Michigan and the Co-Director of the Institute for Functional Interfaces at the Karlrsruhe Institute of Technology, Germany. He has been selected byTechnology Review as one of the top 100 young innovators and is the recipient of the 2007 Nanoscale Science and Engineering Award as well as a NSF-CAREER award. Since 2011, he has been a fellow of the American Institute of Medical and Biological Engineering.


News Article | December 15, 2016
Site: phys.org

The microscopic fluorescence image reveals structures printed onto the biodegradable coating for test purposes. Credit: KIT Medical implants often carry surface substrates that release ac-tive substances or to which biomolecules or cells can adhere better. However, degradable gas-phase coatings for degradable implants, such as surgical suture materials or scaffolds for tis-sue culturing, have been lacking so far. In the journal An-gewandte Chemie, researchers of Karlsruhe Institute of Technol-ogy now present a polymer coating that is degraded in the body together with its carrier. "Our new degradable polymer films might be applied for functionali-zation and coating of surfaces in biosciences, medicine, or food packaging," says Professor Joerg Lahann, Co-Director of the Insti-tute of Functional Interfaces of Karlsruhe Institute of Technology (KIT). Together with an international team, he produced polymer films with functional groups as "anchor sites" for fluorescent dyes or biomolecules. For the first time, the researchers present a CVD (chemical vapor deposition) method to produce biodegradable polymers. Via spe-cial side groups, biomolecules or active substances can be at-tached. This opens up new potentials for e.g. coating biodegrada-ble implants. Polymerization by chemical vapor deposition is a sim-ple and widely used method to modify surfaces, by means of which also complex and irregular carrier substrates can be coated homo-geneously with polymers. In CVD polymerization, the initial compounds are evaporated, acti-vated at high temperature, and deposited onto surfaces, where they polymerize. However, so far it has been possible to coat permanent implants only. Coating has been impossible for materials that are to be degraded after fulfilling their tasks, such as surgical suture mate-rials, systems for the controlled release of substances, stents re-leasing medical substances or scaffolds for culturing tissue. Bio-degradable coatings could not be produced by CVD. Now, this gap is closed, as scientists of Karlsruhe Institute of Tech-nology, University of Michigan (Ann Arbor, USA), and Northwestern Polytechnical University (Xi'an, China) for the first time synthesized a CVD polymer with a degradable backbone. The team applied co-polymerization of two special monomer types: The para-cyclophanes usually used for this method were combined with cy-clic ketene acetals. While classical polymers on the basis of para-cyclophanes are linked by carbon-carbon bonds exclusively, ketene acetal is repositioned during polymerization, such that ester bonds (e.g. bonds between carbon and oxygen atoms) are formed in the polymer backbone. Ester bonds can be cleaved in aqueous medi-um. "The degradation rate depends on the ratio of both monomer types and on the side groups of the monomers," Lahann explains. "Polar side groups make the polymer film less water-repellent and acceler-ate degradation, as water can enter more easily. In this way, the degradation rate can be adapted to application." Using cell cultures, the researchers already demonstrated that neither the polymer nor its degradation products are toxic. More information: Fan Xie et al, Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition, Angewandte Chemie (2016). DOI: 10.1002/ange.201609307


News Article | December 1, 2016
Site: phys.org

Polymerization by chemical vapor deposition (CVD) is a simple method for modifying surfaces by which topologically challenging substrates can be evenly coated with polymers. In the journal Angewandte Chemie, researchers have now introduced the first CVD method for producing degradable polymers. Biomolecules or drugs can be attached by means of special side groups. This introduces new possibilities for applications like the coating of biodegradable implants. In CVD polymerization, the starting compounds are vaporized, activated at high temperature, and deposited onto surfaces, where they polymerize. In medical applications, substrates for implants are coated to allow functional groups to be added as anchors for the attachment of biomolecules or drugs. Until now, however, it has only been possible to coat nondegradable implants, not materials that need to degrade after fulfilling their task, like surgical sutures, systems for controlled drug delivery, drug-eluding stents, or tissue engineering scaffolds. This is because it was previously not possible to make degradable coatings by CVD. Scientists from the University of Michigan (Ann Arbor, USA), Northwestern Polytechnical University (Xi'an, China), and the Karlsruhe Institute of Technology (KIT, Eggenstein-Leopoldshafen, Germany) have now synthesized the first CVD polymer with a degradable backbone. The research team led by Jörg Lahann succeeded by using two special types of monomer: The paracyclophanes usually used for this process were combined with cyclic ketene acetals. While the classic polymers based on paracyclophanes are connected exclusively through carbon-carbon bonds, the ketene acetal converts during the polymerization so that ester bonds (a bond between a carbon and an oxygen atom) are formed within the polymer backbone. Ester bonds can be broken in aqueous environments. "The speed of the degradation depends on the ratio of the two types of monomer as well as their side chains," explains Lahann. "Polar side chains make the polymer film less hydrophobic and accelerate degradation because water can penetrate more easily. The speed of degradation can thus be tailored to the intended use." Tests with cell cultures demonstrated that neither the polymer nor its degradation products are toxic. The team produced polymer films that were equipped with functional side groups that act as "anchor points" for molecules, which can be used to attach fluorescence dyes and biomolecules. "Our new degradable polymer films could find broad application for the functionalization and coating of surfaces in the biological sciences as well as medicine and for food packaging applications," states Lahann. Explore further: Rapid synthesis of ring-shaped molecules offers a cheap route to a plethora of polymers More information: Fan Xie et al, Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201609307


Song H.Y.,Xi'an Shiyou University | Li Y.L.,Northwestern Polytechnical University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2015

Abstract The effects of amorphous boundary (AB) spacing on the deformation behavior of crystalline/amorphous (C/A) Mg/MgAl nanocomposites under tensile load are investigated using molecular dynamics method. The results show that the plasticity of nano-polycrystal Mg can be enhanced with the introduction of C/A interfaces. For samples 5.2 nm in AB spacing and larger, the superior tensile ductility and nearly perfect plastic flow behavior occur during plastic deformation. The studies indicate that the cooperative interactions between crystalline and amorphous are the main reason for excellent ductility enhancements in C/A Mg/MgAl nanocomposites. © 2015 Elsevier B.V.


Zhao T.F.,Tsinghua University | Zhao T.F.,Northwestern Polytechnical University | Chen C.Q.,Tsinghua University
Mechanics of Materials | Year: 2014

Porous metal fiber sintered sheets (MFSSs) are a type of layered transversely isotropic open cell materials with low relative density (i.e., volume fraction of fibers), high specific stiffness and strength, and controllable precision for functional and structural applications. Based on a non-contact optical full field strain measurement system, the in-plane and transverse shear properties of SMFFs with relative densities ranging from 15% to 34% are investigated. For the in-plane shear, the modulus and strength are found to depend linearly upon the relative density. The associated deformation is mainly due to fiber stretching, accompanied by the direction change of metal fibers. When the shear loading is applied in the transverse direction, the deformation of the material is mainly owing to fiber bending, followed by the separation failure of the fiber joints. Measured results show that the transverse shear modulus and strength have quartic and cubic dependence upon the relative density respectively and are much lower than their in-plane counterparts. Simple micromechanics models are proposed for the in-plane and transverse moduli and strengths of MFSSs in shear. The predicted relationships between the shear mechanical properties of MFSSs and their relative density are obtained and are in good agreement with the measured ones. © 2013 Elsevier Ltd. All rights reserved.


Zhang F.,Northwestern Polytechnical University | Zhao Q.,Tsinghua University | Zhou J.,Tsinghua University | Wang S.,Wuhan Textile University
Optics Express | Year: 2013

In this manuscript, we demonstrate numerically classical analogy of electromagnetically induced transparency (EIT) with a windmill type metamaterial consisting of two dumbbell dielectric resonator. With proper external excitation, dielectric resonators serve as EIT bright and dark elements via electric and magnetic Mie resonances, respectively. Rigorous numerical analyses reveal that dielectric metamaterial exhibits sharp transparency peak characterized by large group index due to the destructive interference between EIT bright and dark resonators. Furthermore, such EIT transmission behavior keeps stable property with respect to polarization and incidence angles. ©2013 Optical Society of America.


Luo Y.H.,Northwestern Polytechnical University | Liu Y.F.,Jilin University
Advanced Materials Research | Year: 2014

It is well-known that sharkskin surface has the effect of inhibiting the occurrence of turbulence and reducing the wall resistance, however, the drag reduction mechanism has developed into an urgent problem to be resolved now. According to the actual circumstance, for purpose of obtaining the best drag-reducing efficiency, the biomimetic sharkskin micro-grooved surface is designed according to the relevant literatures and research achievements, and numerical simulation of the micro flow field on the biomimetic sharkskin surface is carried out comprehensivley, which has the important significance to explain the drag reduction mechanism. © (2014) Trans Tech Publications, Switzerland.


Yuan X.,Xiamen University | Lu Z.,Northwestern Polytechnical University
Reliability Engineering and System Safety | Year: 2014

An efficient methodology is presented to perform the reliability-based optimization (RBO). It is based on an efficient weighted approach for constructing an approximation of the failure probability as an explicit function of the design variables which is referred to as the 'failure probability function (FPF)'. It expresses the FPF as a weighted sum of sample values obtained in the simulation-based reliability analysis. The required computational effort for decoupling in each iteration is just single reliability analysis. After the approximation of the FPF is established, the target RBO problem can be decoupled into a deterministic one. Meanwhile, the proposed weighted approach is combined with a decoupling approach and a sequential approximate optimization framework. Engineering examples are given to demonstrate the efficiency and accuracy of the presented methodology. © 2014 Elsevier Ltd. All rights reserved.


Xu B.,Northwestern Polytechnical University | Xu B.,Nanyang Technological University | Huang X.,China Academy of Launch Vehicle Technology | Wang D.,Nanyang Technological University | Sun F.,Tsinghua University
Asian Journal of Control | Year: 2014

In this paper, the robust adaptive controller is investigated for the longitudinal dynamics of a generic hypersonic flight vehicle. The proposed methodology addresses the issue of controller design and stability analysis with respect to parametric model uncertainty and input saturations for the control-oriented model. The velocity and attitude subsystems are transformed into the linearly parameterized form. Based on the parameter projection estimation, the dynamic inverse control is proposed via the back-stepping scheme. In order to avoid the problem of "explosion of complexity," by introducing a first-order filtering of the synthetic input at each step, the dynamic surface control is designed. The closed-loop system achieves uniform ultimately bounded stability. The compensation design is employed when the input saturations occur. Simulation results show that the proposed approach achieves good tracking performance. © 2013 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society.


Zhang X.,Shanghai Maritime University | Zhang X.,Northwestern Polytechnical University | Dai J.,Zhejiang University | Yu Y.,Shaoxing High School
Information Sciences | Year: 2015

Algebraic structures and lattice structures of rough sets are basic and important topics in rough sets theory. In this paper we pointed out that a basic problem had been overlooked, that is the closeness of union and intersection operations of rough approximation pairs, i.e. (lower approximation, upper approximation). We present that the union and intersection operations of rough approximation pairs are closed for classical rough sets and two kinds of covering based rough sets, but not for twenty kinds of covering based rough sets and the generalized rough sets based on fuzzy approximation space. Moreover, we proved that the union and intersection operations of rough fuzzy approximation pairs are closed and a bounded distributive lattice can be constructed. © 2014 Elsevier Inc. All rights reserved.


Liu Q.,Xiamen University | Gu Y.T.,Queensland University of Technology | Zhuang P.,Xiamen University | Liu F.,Queensland University of Technology | Nie Y.F.,Northwestern Polytechnical University
Computational Mechanics | Year: 2011

This paper aims to develop an implicit meshless approach based on the radial basis function (RBF) for numerical simulation of time fractional diffusion equations. The meshless RBF interpolation is firstly briefed. The discrete equations for two-dimensional time fractional diffusion equation (FDE) are obtained by using the meshless RBF shape functions and the strong-forms of the time FDE. The stability and convergence of this meshless approach are discussed and theoretically proven. Numerical examples with different problem domains and different nodal distributions are studied to validate and investigate accuracy and efficiency of the newly developed meshless approach. It has proven that the present meshless formulation is very effective for modeling and simulation of fractional differential equations. © 2011 Springer-Verlag.


Jin N.,Northwestern Polytechnical University | Yang Y.,Northwestern Polytechnical University | Luo X.,Northwestern Polytechnical University | Xia Z.,University of North Texas
Progress in Materials Science | Year: 2013

Ti-containing films have attracted many interests in last decades due to their specific properties, and can be used in many applications. Chemical vapor deposition (CVD) is an advanced manufacture technique for surface coating currently and has been widely used to prepare various surface coatings and thin films. Therefore, researchers have carried out in depth investigations on CVD Ti-containing films in the last decades. This article reviews the development of CVD Ti-containing films in the last years. Ti-containing films can be classified into pure Ti films, binary films, ternary films and quaternary films by components, and are described with extend discussion about their preparaiton, structures, properties and applications. Otherwise, the techniques based on CVD method and the Ti-precursors for Ti-containing films will be presented in the article. © 2013 Elsevier Ltd. All rights reserved.


Wang J.,Northwestern Polytechnical University | Zhang C.,Northwestern Polytechnical University | Kang F.,Tsinghua University
ACS Applied Materials and Interfaces | Year: 2015

Manganese oxides are promising high-capacity anode materials for lithium-ion batteries (LIBs) yet suffer from short cycle life and poor rate capability. Herein, we demonstrate a facile in situ interfacial synthesis of core-shell heterostructures comprising nitrogen-enriched porous carbon (pN-C) nanocoating and manganese oxide (MnOx) nanotubes. When MnOx/pN-C serves as an anode material for LIBs, the pN-C coating plays multiple roles in substantially improving the lithium storage performance. In combination with the nanosized structure and nanotubular architecture, the MnOx/pN-C nanocomposites exhibit an impressive reversible capacity of 1068 mAh g-1 at 100 mA g-1, a high-rate delivery of 361 mAh g-1 at 8 A g-1, and a stable cycling retention up to 300 cycles. The surface pN-C coating strategy can be extended to design and fabricate various metal oxide nanostructures for high-performance LIBs. © 2015 American Chemical Society.


Li J.,Xi'an Shiyou University | Li J.,Northwestern Polytechnical University | Zhang M.,Xi'an Shiyou University | Luo X.,Northwestern Polytechnical University
Journal of Alloys and Compounds | Year: 2013

Phase stability, elastic and thermodynamic properties, and electronic structure of titanium trialuminide (Al3Ti) with Ll2 and D022 structures under pressure up to 40 GPa have been investigated using first-principles calculations. The equilibrium structure and formation energy show that L12-Al3Ti is stable when the pressure is higher enough, approximately above than 20-30 GPa. The elastic constants, anisotropy index and Debye temperature of both phases increase with the pressure going up, and L12-Al3Ti has better ductility, smaller anisotropy and lower Debye temperature than D022-A13Ti. The pressure-induced Ti-3d delocalization can strengthen its orbital hybridization with Al(s,p), which leads to stronger atomic bonding, and subsequently makes the L12-Al3Ti more stable under high pressure. © 2012 Elsevier B.V. All rights reserved.


Zhang F.,Northwestern Polytechnical University | Kang L.,CNRS Institute of Electronics, Microelectronics and Nanotechnology | Zhao Q.,Tsinghua University | Zhou J.,Tsinghua University | Lippens D.,CNRS Institute of Electronics, Microelectronics and Nanotechnology
New Journal of Physics | Year: 2012

The coupling effects of subwavelength high-permittivity (ε r > 100) arrayed ceramics which exhibit magnetic and electric Mie resonances are investigated by electromagnetic full-wave analysis. Special attention was paid to the symmetry properties of both magnetic- and electric-induced dipoles by varying independently the array periodicity. In agreement with the interactions between electric and magnetic dipoles, it is shown that resonance frequency shifts toward lower (higher) frequencies can be obtained, which depends on the longitudinal (transverse) dipole coupling strengths. Moreover, the emergence of quasi-bound states between tightly coupled basic cells is pointed out for the electric Mie resonances, which shows an unexpected frequency shift with a reverse variation. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Xiao M.,Northwestern Polytechnical University | Li F.,Northwestern Polytechnical University | Zhao W.,Northwestern Polytechnical University | Yang G.,Beijing Institutive of Aeronautical Materials
Materials and Design | Year: 2012

The high-temperature deformation behaviors of as-cast and as-forged TiNiNb shape memory alloy under compression in the temperature range of 923-1323K and strain rate range of 0.01-10s-1 have been investigated with the view to acquiring the optimum hot deformation processing parameters. By the application of orthogonal experiment and variance analysis, the significance of the effects of strain, strain rate, deformation temperature as well as interaction between strain rate and deformation temperature on flow stress are evaluated, and the results indicate that the effect of interaction between strain rate and deformation temperature can be neglected in comparison with other factor. Thereafter, on the basis of the conclusions of orthogonal analysis, a new constitutive equation incorporating the effects of strain, strain rate and deformation temperature has been established. The developed constitutive equation enables to predict the flow stress accurately throughout the entire domain of temperature and strain rate, excepting at 973K in 0.1s-1 and 10s-1 for as-cast TiNiNb alloy and at 923K in 0.1s-1 and 1s-1 for as-forged TiNiNb alloy. © 2011 Elsevier Ltd.


Peng B.,Northwestern Polytechnical University | Fan H.,Northwestern Polytechnical University | Zhang Q.,University of Bedfordshire
Journal of the American Ceramic Society | Year: 2012

Pure perovskite Pb(Mg 1/3Nb 2/3) 1-xTi xO 3 (x = 0, 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were prepared using a two-stage solid state reaction process. With the increase of Ti content, the dielectric tunability and dielectric loss at x = 0.09, 25 kV/cm and 300 K reached a maximum 91% and 0.09, respectively. High dielectric tunability 82% with low dielectric loss 0.007 was obtained at x = 0.05, indicating that it is a promising tunable material. The Lorentz fit of the temperature dependence of the dielectric permittivity and the measurement of the temperature dependence of the depolarization current density showed that polar nanoregions are related to the dielectric tunability properties of these relaxor ferroelectric ceramics . The Landau-Ginsberg-Devonshire and multipolarization-mechanism model fitted results of the electric field dependence of the dielectric permittivity showed that the contribution of the "extrinsic" polarizations including "reorientation of nanopolar clusters" and the "motion of the cluster interphase boundaries or domain-wall motions" to the dielectric tunability properties increased with the increase of Ti content. These results provide a clear understanding to the complicated dielectric response in a family of high-tunability ceramics and a key to the high tunability of ferroelectrics with low loss under dc electric field. © 2012 The American Ceramic Society.


Xu B.,Tsinghua University | Xu B.,ETH Zurich | Xu B.,Northwestern Polytechnical University | Sun F.,Tsinghua University | And 2 more authors.
IET Control Theory and Applications | Year: 2012

In this study, the adaptive Kriging controller is investigated for the longitudinal dynamics of a generic hypersonic flight vehicle. For the altitude subsystem, the dynamics are transformed into the strict-feedback form where the back-stepping scheme is used. The velocity subsystem is transformed into the output-feedback form. Considering the non-linearity of the dynamics, the nominal feedback is included in the controller while Kriging system is used to estimate the uncertainty, which is described as the realisations of Gaussian random functions. To eliminate the infinite increase of the data size, the recursive Kriging algorithm is adopted in this study. Under the proposed controller, the almost surely bounded stability analysis is presented. The simulation study compared with neural back-stepping control is presented to show the effectiveness of the proposed control approach. © 2012 The Institution of Engineering and Technology.


Yue X.-K.,Northwestern Polytechnical University | Dai H.-H.,Northwestern Polytechnical University | Liu C.-S.,National Taiwan University
Nonlinear Dynamics | Year: 2014

A novel optimal scale polynomial interpolation method (OSPIM) is proposed to attack the Duffing oscillator. This method is based on the ideas of multi-scaling and equilibrated matrix, such that the condition number of the coefficient matrix of the polynomial interpolation is minimized. The OSPIM can eliminate the Runge phenomenon, which occurs in the conventional polynomial interpolation, and is well suited for solving nonlinear oscillatory systems. In addition, we further alleviate the ill-posedness of polynomial interpolation by proposing a half-order technique, with which one can use a (Formula presented.)-order polynomial to interpolate as many as (Formula presented.) points. We then employ the half-order OSPIM, i.e., OSPIM(H), as a trial function in conjunction with the simple point-collocation method, to solve the nonlinear Duffing equation. Moreover, the differential transformation method is used for the first time to solve a forced Duffing oscillator to compare with the present method. Finally, illustrative examples verify the accuracy and efficiency of the present method. © 2014 Springer Science+Business Media Dordrecht.


Si S.,Northwestern Polytechnical University | Dui H.,Northwestern Polytechnical University | Zhao X.,Tsinghua University | Zhang S.,Northwestern Polytechnical University | Sun S.,Northwestern Polytechnical University
IEEE Transactions on Reliability | Year: 2012

This paper mainly focuses on the integrated importance measure (IIM) of component states based on loss of system performance. To describe the impact of each component state, we first introduce the performance function of the multi-state system. Then, we present the definition of IIM of component states. We demonstrate its corresponding physical meaning, and then analyze the relationships between IIM and Griffith importance, Wu importance, and Natvig importance. Secondly, we present the evaluation method of IIM for multi-state systems. Thirdly, the characteristics of IIM of component states are discussed. Finally, we demonstrate a numerical example, and an application to an offshore oil and gas production system for IIM to verify the proposed method. The results show that 1) the IIM of component states concerns not only the probability distributions and transition intensities of the states of the object component, but also the change in the system performance under the change of the state distribution of the object component; and 2) IIM can be used to identify the key state of a component that affects the system performance most. © 2006 IEEE.


Zhu Y.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Yuille A.L.,University of California at Los Angeles
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2014

We proposed a deformable patches based method for single image super-resolution. By the concept of deformation, a patch is not regarded as a fixed vector but a flexible deformation flow. Via deformable patches, the dictionary can cover more patterns that do not appear, thus becoming more expressive. We present the energy function with slow, smooth and flexible prior for deformation model. During example-based super-resolution, we develop the deformation similarity based on the minimized energy function for basic patch matching. For robustness, we utilize multiple deformed patches combination for the final reconstruction. Experiments evaluate the deformation effectiveness and super-resolution performance, showing that the deformable patches help improve the representation accuracy and perform better than the state-of-art methods. © 2014 IEEE.


Li Z.,Northwestern Polytechnical University | Li H.,Northwestern Polytechnical University | Zhang S.,Northwestern Polytechnical University | Wang J.,Northwestern Polytechnical University | And 2 more authors.
Corrosion Science | Year: 2012

Two-dimensionally (2D) reinforced C/C-SiC-ZrC composites were prepared by ICVI combined with RMI method. The ablation properties of the composites were tested under an oxyacetylene flame. The results indicate that the temperature of RMI has remarkable effect on the microstructure and ablation properties of C/C-SiC-ZrC composites, the linear and mass ablation rates of the C/C-SiC-ZrC prepared at 2300 °C are greatly reduced compared with those of C/C-SiC-ZrC prepared at 2000 °C and C/C composites. The formation of a dense ZrC-SiC coating and its oxide layer are the reasons for high ablation resistance. © 2012 Elsevier Ltd.


Fan Y.,Northwestern Polytechnical University | Zhang F.,Northwestern Polytechnical University | Zhao Q.,Tsinghua University | Wei Z.,Tongji University | Li H.,Tongji University
Optics Letters | Year: 2014

Coherent perfect absorber (CPA) was proposed as the time-reversed counterpart to laser: a resonator containing lossy medium instead of gain medium can absorb the coherent optical fields completely. Here, we exploit a monolayer graphene to realize the CPA in a nonresonant manner. It is found that quasi-CPA point exists in the terahertz regime for suspending monolayer graphene, and the CPA can be implemented with the assistance of proper phase modulation among two incident beams at the quasi-CPA frequencies. The graphene-based CPA is found of broadband angular selectivity: CPA point splits into two frequency bands for the orthogonal s and p polarizations at oblique incidence, and the two bands cover a wide frequency range starting from zero frequency. Furthermore, the coherent absorption can be tuned substantially by varying the gate-controlled Fermi energy. The findings of CPA with nonresonant graphene sheet can be generalized for potential applications in terahertz/infrared detections and signal processing with two-dimensional optoelectronic materials. © 2014 Optical Society of America


Peng W.,Northwestern Polytechnical University | Zeng W.,Northwestern Polytechnical University | Wang Q.,CAS Shenyang Institute of Metal Research | Yu H.,Northwestern Polytechnical University
Materials and Design | Year: 2013

Hot compression of as-cast Ti60 titanium alloy at the deformation temperatures ranging from 970 to 1120°C with an interval of 30°C, the strain rates ranging from 0.01 to 10.0s-1 and the height reduction of 75% is conducted on a Gleeble-3500 thermo-mechanical simulator. The experimental stress-strain data from hot compression are employed to develop the Arrhenius-type constitutive model incorporating the strain effect and artificial neural network (ANN) model with a back-propagation learning algorithm. The strain compensated constitutive model can track the experimental data across the whole hot working domain other than that at high strain rates (≥1s-1). It is possibly associated with the deformation mechanisms at high strain rates, where microstructure exhibits bands of flow localization and longitudinal cracking, are far different from that at low strain rates (≤0.1s-1) where dynamic recrystallization occurs. Comparison of the predicted results of flow stress based on the ANN model and those acquired from the strain compensated constitutive model has been performed. It is found that the relative error of the ANN model varies from -3.42% to 4.33% while that of the strain compensated constitutive model ranges from -14.65% to 13.63%, and the average absolute relative error is 2.41% and 8.45% corresponding to the ANN model and strain compensated constitutive model, respectively. These results sufficiently indicate that the ANN model is more accurate and efficient in terms of predicting the flow stress of as-cast Ti60 titanium alloy. © 2013.


Li F.,Northwestern Polytechnical University | Li F.,University of Birmingham | Tang L.,University of Birmingham | Zhou W.,Northwestern Polytechnical University | Guo Q.,University of Birmingham
Journal of the American Chemical Society | Year: 2010

The bonding sites for Au-adatom-octanethiolate within the (√3×√3)R30° structure on Au(111) have been investigated with high-resolution scanning tunneling microscopy (STM) imaging. By establishing the relationship between the lateral positions of adsorbates on the top layer of gold and those inside an etch pit, we are able to determine the adsorption configuration with a high degree of accuracy for the elusive (√3×√3)R30° molecular layer. The boundary between adjacent SAM domains is also imaged with molecular resolution that allows the assignment of adsorption site in each domain without ambiguity. The standard (√3×√3)R30° alkanethiol SAM on Au(111) is found to consist of domains with Au-adatom-octanethiolate occupying the fcc hollows site, alongside domains where the hcp hollow site is occupied. © 2010 American Chemical Society.


Zhu Q.,State University of New York at Stony Brook | Zeng Q.,State University of New York at Stony Brook | Zeng Q.,Northwestern Polytechnical University | Oganov A.R.,State University of New York at Stony Brook | Oganov A.R.,Moscow State University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We present a systematic search for low-energy metastable superhard carbon allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an allotrope at 15-20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2H- or 3R-graphite and applying a pressure of 20 GPa, a large variety of intermediate sp3 carbon allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for "superhard graphite," but also predicted two allotropes (X-carbon and Y-carbon) showing unusual types of 5+7 and 4+8 topologies. These superhard carbon allotropes can be classified into five families based on 6 (diamond/lonsdaleite), 5+7 (M- and W-carbon), 5+7 (X-carbon), 4+8 (bct-C 4), and 4+8 (Y-carbon) topologies. This study shows that evolutionary metadynamics is a powerful approach both to find the global minima and systematically search for low-energy metastable phases reachable from given starting materials. © 2012 American Physical Society.


Dai D.-M.,Wenzhou University | Mu D.-J.,Northwestern Polytechnical University
Journal of Convergence Information Technology | Year: 2012

Rough set theory involves techniques for knowledge discovery and data mining. Rough set theory is typically applied within decision systems and offers an alternative to more conventional techniques for classification and rules induction. It is suitable for handling different kinds of uncertainty in dataset. Multilayer neural networks are nonparametric, robust, and generalization capabilities in data-rich environments, multilayer neural networks have been used effectively in a wide range of applications in pattern recognition and data classification. Time series data analysis is an important research domain of financial trading and economics. It is crucial to certain applications of data mining, machine learning, and others in computer science. This type of analysis plays an important role in forecasting future development. In this paper, to inherit the merits of both rough sets and neural networks, an integration model of rough sets and multilayer neural networks is proposed to analyze time-series data, the integration model not only provides efficient information about what is expected to happen, but also reveals how to recover from the abnormal condition with prediction on process time series data. Take stock market for instance, the proposed model shows a greatly improved performance in stock market forecasting compared to other models.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Sevilla M.,CSIC - National Coal Institute | Sevilla M.,University of Nottingham | And 3 more authors.
Advanced Energy Materials | Year: 2011

Cellulose, potato starch, and eucalyptus wood saw dust were transformed into porous carbons with micropore surface areas of up to 2387 m 2/g. The specific capacitance of the produced carbons approaches 236 F/g (100 F/cc) when measured in a symmetric configuration in an organic electrolyte. Charge-discharge tests showed excellent capacitance retention with capacitance of up to 175 F/g at an ultra-high current density of 20 A/g. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Yu Z.-H.,Xi'an University of Science and Technology | Liu L.,Northwestern Polytechnical University | Zhang J.,Northwestern Polytechnical University
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2014

Single crystal superalloys of AM3 with different carbon levels were prepared at withdraw rate of 50 μm/s. The effect of carbon addition on the carbide morphology was investigated. It was found that there were four types of MC-type carbides, acicular, nodular, blocky, and Chinese script-type in the crystals. With an increase in carbon level, the volume fraction of carbide increased significantly while the volume fraction of eutectic decreased significantly. Furthermore, the size of carbide in high level carbon alloy became much larger. © 2014 The Nonferrous Metals Society of China.


Zhou X.-F.,Nankai University | Zhou X.-F.,State University of New York at Stony Brook | Dong X.,Nankai University | Dong X.,State University of New York at Stony Brook | And 6 more authors.
Physical Review Letters | Year: 2014

It has been widely accepted that planar boron structures, composed of triangular and hexagonal motifs are the most stable two-dimensional (2D) phases and likely precursors for boron nanostructures. Here we predict, based on an ab initio evolutionary structure search, a novel 2D boron structure with nonzero thickness, which is considerably, by 50 meV/atom, lower in energy than the recently proposed α-sheet structure and its analogues. In particular, this phase is identified for the first time to have a distorted Dirac cone, after graphene and silicene the third elemental material with massless Dirac fermions. The buckling and coupling between the two sublattices not only enhance the energetic stability, but also are the key factors for the emergence of the distorted Dirac cone. © 2014 American Physical Society.


Hazar S.,Istanbul University | Hazar S.,ENSTA ParisTech | Zaki W.,Khalifa University | Moumni Z.,ENSTA ParisTech | And 2 more authors.
International Journal of Plasticity | Year: 2015

Shape memory alloys experience phase transformation from austenite to martensite around crack tip. When the crack advances, martensitic transformation occurs at the tip and the energy that goes into this transformation results in stable crack growth like in the case of plastic deformation. In literature, steady-state crack growth in elasto-plastic materials with small scale yielding at the crack tip has been successfully modeled using stationary methods. In this work, Mode I steady-state crack growth in an edge-cracked Nitinol plate is modeled using a non-local stationary method (Moumni, 1995). The Zaki-Moumni (ZM) constitutive model is utilized for this purpose. The model is implemented in ABAQUS by means of a user-defined material subroutine (UMAT) to determine transformation zones around the crack tip. Steady-state crack growth is first simulated without considering reverse transformation to calculate the effect of transformation on stress distribution in the wake region, then reverse transformation is taken into account. The effect of reorientation of martensite near the crack tip as a result of non-proportional loading is also studied. The stress distribution and the phase transformation region are compared to results obtained for the case of a static crack. ©2014 Elsevier B.V. All rights reserved.


Chen Z.,Northwestern Polytechnical University | Hao L.,Xi'an University of Science and Technology | Chen C.,Northwestern Polytechnical University
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2012

A fast, facile one-step process was developed to fabricate superhydrophobic surfaces by electrodepositing copper substrate in an electrolyte containing lanthanum chloride (LaCl 3·6H 2O), myristic acid (CH 3(CH 2) 12COOH) and ethanol. Morphology and the chemical structure and composition of the superhydrophobic surface were investigated with SEM, FTIR, XRD, and EDX, respectively. The results indicate that the shortest process for constructing superhydrophobic surface is 1min, the maximum contact angle is 165° and rolling angle is less than 2°. In the process of electrodeposition time, structure of cathodic copper surface transforms from the blossom buds into nanostructure assemblies, flowers and then into nanorods. In addition, the method can be extended to effectively prepare a superhydrophobic surface with rare-earth element on general conductive material. © 2012 Elsevier B.V.


Dai D.-M.,Wenzhou University | Mu D.-J.,Northwestern Polytechnical University
International Journal of Advancements in Computing Technology | Year: 2012

Clustering time series data is often necessary to provide very useful information for the method of real-world data problems arising from many domains. For this reason, the study of clustering distance measures for time series data has proposed an important research in different scientific fields. So a fast approach to K-means clustering for time series data based on symbolic representation has represented, which can efficiently reduce the size of time series data, and improve the efficiency of the clustering algorithm. At the same time, the proposed method can't reduce the effects by using the complex network. In this paper, at first, k-nearest neighbor networks is built based on the similarity of time series data based on symbolic representation, in this process, an objects distance is used to measure the similarity in time series data. For k-nearest neighbor networks, every node represent one the object and each connect denotes neighbor relationship between nodes. What's more, the nodes with high similarity is chosen and used to cluster in time series data. In clustering process, an efficient hierarchical function of distance measure is applied. At last, experimental results are employed to show that efficiency and effectiveness of the proposed algorithm.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Sevilla M.,University of Nottingham | Sevilla M.,CSIC - National Coal Institute | And 3 more authors.
Advanced Functional Materials | Year: 2012

As electrical energy storage and delivery devices, carbon-based electrical double-layer capacitors (EDLCs) have attracted much attention for advancing the energy-efficient economy. Conventional methods for activated carbon (AC) synthesis offer limited control of their surface area and porosity, which results in a typical specific capacitance of 70-120 F g -1 in commercial EDLCs based on organic electrolytes and ionic liquids (ILs). Additionally, typical ACs produced from natural precursors suffer from the significant variation of their properties, which is detrimental for EDLC use in automotive applications. A novel method for AC synthesis for EDLCs is proposed. This method is based on direct activation of synthetic polymers. The proposed procedure allowed us to produce ACs with ultrahigh specific surface area of up to 3432 m 2 g -1 and volume of 0.5-4 nm pores up to 2.39 cm 3 g -1. The application of the produced carbons in EDLCs based on IL electrolyte showed specific capacitance approaching 300 F g -1, which is unprecedented for carbon materials, and 5-8% performance improvement after 10 000 charge-discharge cycles at the very high current density of 10 A g -1. The remarkable characteristics of the produced materials and the capability of the fabricated EDLCs to operate safely in a wide electrochemical window at elevated temperatures, suggest that the proposed synthesis route offers excellent potential for large-scale material production for EDLC use in electric vehicles and industrial applications. A novel method of activated carbon (AC) synthesis for electrical double-layer capacitors (EDLCs) based on direct activation of synthetic polymers polypyrrole is proposed. ACs with high specific surface area are created. The specific capacitance of the produced carbons is very high when measured in a symmetric configuration in an ionic liquid electrolyte. Charge-discharge tests show excellent capacitance retention at an ultrahigh current density. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Chen Z.,Northwestern Polytechnical University | Hao L.,Xi'an University of Science and Technology | Chen A.,Northwestern Polytechnical University | Song Q.,Northwestern Polytechnical University | Chen C.,Northwestern Polytechnical University
Electrochimica Acta | Year: 2012

Superhydrophobic surfaces are commonly prepared by a combination of low surface energy materials and micro/nano structures. In this work, a rapid one-step electrodepositing process is developed to fabricate superhydrophobic cathodic surface by copper plate in an electrolytic solution containing nickel chloride(NiCl 2·6H 2O), myristic acid and ethanol. Scanning electron microscopy (SEM) images, Fourier-transform infrared (FTIR) spectrometer, X-ray diffraction (XRD) and contact angle measurement have been performed to characterize the morphological features, chemical composition and superhydrophobicity property. The results demonstrate that the micro/nano scales cauliflower-like structure are composed of Ni crystals and Ni[CH 3(CH 2) 12COO] 2 crystals. The maximum contact angle is about 164°and rolling angle is less than 2°. The needed electrolytic time is largely shortened to 1 min. This method is rapid, easy and effective, and it will have great prospects for industrial applications. © 2011 Elsevier Ltd. All Rights Reserved.


Li W.,Northwestern Polytechnical University | Vairis A.,Technological Educational Institute of Crete | Preuss M.,University of Manchester | Ma T.,Northwestern Polytechnical University
International Materials Reviews | Year: 2016

Friction welding (FW) is a high quality, nominally solid-state joining process, which produces welds of high structural integrity. Rotary friction welding (RFW) is the most commonly used form of FW, while linear friction welding (LFW) is a relatively new method being used mainly for the production of integrally bladed disc (blisk) assemblies in the aircraft engine industry. Numerous similar and dissimilar joints of structural metallic materials have been welded with RFW and LFW. In this review, the current state of understanding and development of RFW and LFW is presented. Particular emphasis is placed on the process parameters, joint microstructure, residual stresses, mechanical properties and their relationships. Finally, opportunities for further research and development of the RFW and LFW processes are identified. © 2016 Institute of Materials, Minerals and Mining and ASM International Published by Taylor & Francis on behalf of the Institute and ASM International.


Xu B.,Northwestern Polytechnical University | Shi Z.,Northwestern Polytechnical University | Yang C.,University of Plymouth | Wang S.,Yantai Naval Aeronautical and Astronautical University
Nonlinear Dynamics | Year: 2013

Considering the use of digital computers and samplers in the control circuitry, this paper describes the controller design in discrete time for the longitudinal dynamics of a generic hypersonic flight vehicle (HFV) with Neural Network (NN). Motivated by time-scale decomposition, the states are decomposed into slow dynamics of velocity, altitude and fast dynamics of attitude angles. By command transformation, the reference command for γ-θ p -q subsystem is derived from h-γ subsystem. Furthermore, to simplify the backstepping design, we propose the controller for γ-θ p -q subsystem from prediction function without virtual controller. For the velocity subsystem, the throttle setting constraint is considered and new NN adaption law is designed by auxiliary error dynamics. The uniformly ultimately boundedness (UUB) of the system is proved by Lyapunov stability method. Simulation results show the effectiveness of the proposed algorithm. © 2013 Springer Science+Business Media Dordrecht.


Jia W.,Northwestern Polytechnical University | Jia W.,Northwestern Institute for Nonferrous Metal Research | Zeng W.,Northwestern Polytechnical University | Yu H.,Northwestern Polytechnical University
Materials and Design | Year: 2014

The effect of aging temperature between 650°C and 750°C for different aging times on the tensile properties and microstructures of Ti60 alloy were studied. The results show that the strength of the alloy increases first and then decreases with the aging temperature increases from 650°C to 750°C. The reduction of area of the alloy is more sensitive to the aging time than elongation. With increasing aging temperature and time, the volume fracture and grain size of silicides and α2 phase increase gradually. The silicides have the strengthen effect on the Ti60 alloy, but the effect weakens when the silicides grow up. The loss of ductility is mainly attributed to the precipitation of α2 phase after aging treatment. © 2014 Elsevier Ltd.


Cai K.,Osaka City University | Zhang R.,Northwestern Polytechnical University | Wonham W.M.,University of Toronto
IEEE Transactions on Automatic Control | Year: 2015

We identify a new observability concept, called relative observability, in supervisory control of discrete-event systems under partial observation. A fixed, ambient language is given, relative to which observability is tested. Relative observability is stronger than observability, but enjoys the important property that it is preserved under set union; hence there exists the supremal relatively observable sublanguage of a given language. Relative observability is weaker than normality, and thus yields, when combined with controllability, a generally larger controlled behavior; in particular, no constraint is imposed that only observable controllable events may be disabled. We design new algorithms which compute the supremal relatively observable (and controllable) sublanguage of a given language, which is generally larger than the normal counterpart. We demonstrate the new observability concept and algorithms with a Guideway and an AGV example. © 2014 IEEE.


Liu H.,Northwestern Polytechnical University | Cai J.,Northwestern Polytechnical University | Jiang L.,Zhengzhou University of Light Industry
International Journal of Intelligent Systems | Year: 2014

Linguistic fuzzy preference relations are commonly used in decision-making problems. The recent proposal of comparative linguistic expressions has been introduced to deal with the situation that decision makers hesitate among several linguistic terms to express their assessments. To apply this idea to linguistic fuzzy preference relations, we propose the linguistic fuzzy preference relations based on the comparative linguistic expressions. We then transform the linguistic fuzzy preference relations into linguistic 2-tuple fuzzy preference relations, and introduce an iterative method to measure and improve the additive consistency of the linguistic 2-tuple fuzzy preference relations. An illustrative example is finally presented to clarify the computational processes. © 2014 Wiley Periodicals, Inc.


Xu W.,Northwestern Polytechnical University | Wang X.-Y.,Northwestern Polytechnical University | Liu X.-Z.,University of Waterloo
Chinese Physics B | Year: 2015

This paper mainly investigates dynamics behavior of HIV (human immunodeficiency virus) infectious disease model with switching parameters, and combined bounded noise and Gaussian white noise. This model is different from existing HIV models. Based on stochastic Itô lemma and Razumikhin-type approach, some threshold conditions are established to guarantee the disease eradication or persistence. Results show that the smaller amplitude of bounded noise and R¯0 < 1 can cause the disease to die out; the disease becomes persistent if R0 > 1. Moreover, it is found that larger noise intensity suppresses the prevalence of the disease even if R0 > 1. Some numerical examples are given to verify the obtained results. © 2015 Chinese Physical Society and IOP Publishing Ltd.


Zhang H.,Northwestern Polytechnical University | Wipf D.,Microsoft | Zhang Y.,Northwestern Polytechnical University
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2013

This paper presents a robust algorithm for estimating a single latent sharp image given multiple blurry and/or noisy observations. The underlying multi-image blind deconvolution problem is solved by linking all of the observations together via a Bayesian-inspired penalty function which couples the unknown latent image, blur kernels, and noise levels together in a unique way. This coupled penalty function enjoys a number of desirable properties, including a mechanism whereby the relative-concavity or shape is adapted as a function of the intrinsic quality of each blurry observation. In this way, higher quality observations may automatically contribute more to the final estimate than heavily degraded ones. The resulting algorithm, which requires no essential tuning parameters, can recover a high quality image from a set of observations containing potentially both blurry and noisy examples, without knowing a priori the degradation type of each observation. Experimental results on both synthetic and real-world test images clearly demonstrate the efficacy of the proposed method. © 2013 IEEE.


Zhu C.X.,Northwestern Polytechnical University | Zhu W.Q.,Northwestern Polytechnical University | Zhu W.Q.,State Key Laboratory of Fluid Power Transmission and Control | Zhu W.Q.,Zhejiang University
Automatica | Year: 2011

In the present paper, an innovative procedure for designing the feedback control of multi-degree-of-freedom (MDOF) nonlinear stochastic systems to target a specified stationary probability density function (SPDF) is proposed based on the technique for obtaining the exact stationary solutions of the dissipated Hamiltonian systems. First, the control problem is formulated as a controlled, dissipated Hamiltonian system together with a target SPDF. Then the controlled forces are split into a conservative part and a dissipative part. The conservative control forces are designed to make the controlled system and the target SPDF have the same Hamiltonian structure (mainly the integrability and resonance). The dissipative control forces are determined so that the target SPDF is the exact stationary solution of the controlled system. Five cases, i.e., non-integrable Hamiltonian systems, integrable and non-resonant Hamiltonian systems, integrable and resonant Hamiltonian systems, partially integrable and non-resonant Hamiltonian systems, and partially integrable and resonant Hamiltonian systems, are treated respectively. A method for proving that the transient solution of the controlled system approaches the target SPDF as t→∞ is introduced. Finally, an example is given to illustrate the efficacy of the proposed design procedure. © 2010 Elsevier Ltd. All rights reserved.


Sun Q.J.,Northwestern Polytechnical University | Wang G.C.,Nanchang Hangkong University | Li M.Q.,Northwestern Polytechnical University
Materials and Design | Year: 2012

A two-step deformation method was adopted to investigate the superplasticity of Ti-6.5Al-2Zr-1Mo-1V alloy in this work, in which the specified pre-elongation was obtained by the constant velocity in the first step, and then the specimen was deformed to fracture by the maximum m-value method in the second step. The superplastic tensile tests were performed on a SANS CMT4104 electronic tensile testing machine at all temperatures ranging from 1123 to 1223. K and pre-elongations ranging from 100% to 200%, and the maximum elongation-to-failure values between 188% and 1456% were obtained. For comparison, the constant velocity and the maximum m-value methods were also applied separately at 1173. K in the study. The experimental results indicate that the superplasticity of Ti-6.5Al-2Zr-1Mo-1V alloy has been improved greatly by the two-step method compared with these single-step deformation methods. The ductility of the alloy was increased significantly at a pre-elongation of 150% and deformation temperature of 1173. K, at which the maximum elongation of 1456% was attained in the present work. © 2011 Elsevier Ltd.


Jin M.,Northwestern Polytechnical University | Zhao K.,Shaanxi Institute of Zoology | Huang Q.,Northwestern Polytechnical University | Shang P.,Northwestern Polytechnical University
International Journal of Biological Macromolecules | Year: 2014

Recently, a great deal of interest has been developed to isolate and investigate novel bioactive components with health benefit effects from natural resources. The dried root of Astragalus membranaceus, one of the most popular health-promoting herbal medicines, has been used historically as an immunomodulating agent for the treatment of common cold, diarrhea, fatigue and anorexia for more than 2000 years. Modern phytochemistry and pharmacological experiments have proved that polysaccharide is one of the major active ingredients in the root of A. membranaceus with various important bioactivities, such as immunomodulation, antioxidant, antitumor, anti-diabetes, antiviral, hepatoprotection, anti-inflammation, anti-atherosclerosis, hematopoiesis and neuroprotection. The aim of the present review is to summarize previous and current references and give a comprehensive summary regarding the structural features and biological activities of A. membranaceus polysaccharides in order to provide new insight for further development of these macromolecules. © 2013 Elsevier B.V.


Chen L.,University of Ulster | Hoey J.,University of Waterloo | Nugent C.D.,University of Ulster | Cook D.J.,Washington State University | Yu Z.,Northwestern Polytechnical University
IEEE Transactions on Systems, Man and Cybernetics Part C: Applications and Reviews | Year: 2012

Research on sensor-based activity recognition has, recently, made significant progress and is attracting growing attention in a number of disciplines and application domains. However, there is a lack of high-level overview on this topic that can inform related communities of the research state of the art. In this paper, we present a comprehensive survey to examine the development and current status of various aspects of sensor-based activity recognition. We first discuss the general rationale and distinctions of vision-based and sensor-based activity recognition. Then, we review the major approaches and methods associated with sensor-based activity monitoring, modeling, and recognition from which strengths and weaknesses of those approaches are highlighted. We make a primary distinction in this paper between data-driven and knowledge-driven approaches, and use this distinction to structure our survey. We also discuss some promising directions for future research. © 2012 IEEE.


Zhang D.,Northwestern Polytechnical University | Han J.,Northwestern Polytechnical University | Li C.,Northwestern Polytechnical University | Wang J.,Microsoft
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2015

With the goal of effectively identifying common and salient objects in a group of relevant images, co-saliency detection has become essential for many applications such as video foreground extraction, surveillance, image retrieval, and image annotation. In this paper, we propose a unified co-saliency detection framework by introducing two novel insights: 1) looking deep to transfer higher-level representations by using the convolutional neural network with additional adaptive layers could better reflect the properties of the co-salient objects, especially their consistency among the image group; 2) looking wide to take advantage of the visually similar neighbors beyond a certain image group could effectively suppress the influence of the common background regions when formulating the intra-group consistency. In the proposed framework, the wide and deep information are explored for the object proposal windows extracted in each image, and the co-saliency scores are calculated by integrating the intra-image contrast and intra-group consistency via a principled Bayesian formulation. Finally the window-level co-saliency scores are converted to the superpixel-level co-saliency maps through a foreground region agreement strategy. Comprehensive experiments on two benchmark datasets have demonstrated the consistent performance gain of the proposed approach. © 2015 IEEE.


Zhang D.,Orange S.A. | Wang L.,University Pierre and Marie Curie | Xiong H.,University Pierre and Marie Curie | Guo B.,Northwestern Polytechnical University
IEEE Communications Magazine | Year: 2014

With the rapid proliferation of sensor-rich smartphones, mobile crowd sensing has become a popular research field. In this article, we propose a four-stage life cycle (i.e., task creation, task assignment, individual task execution, and crowd data integration) to characterize the mobile crowd sensing process, and use 4W1H (i.e., what, when, where, who, and how) to sort out the research problems in the mobile crowd sensing domain. Furthermore, we attempt to foresee some new research directions in future mobile crowd sensing research. © 2014 IEEE.


He C.,Xi'an Jiaotong University | Zhang W.,Chang'an University | Deng J.,Chang'an University | Deng J.,Northwestern Polytechnical University
Journal of Physical Chemistry C | Year: 2011

The ballistic transport properties of Cu nanowires (NWs) with diameter of 0.2-1.0 nm under electric field (V = 1 V/Å) are reported for future applications as interconnections in microelectronics. Our density-functional calculations show that, under V = 1 V/Å, with the wire diameter increasing, the number of conduction channels of a helical atomic strand increases, whereas the number of a nonhelical atomic strand is constant within the considered size range. The structure, electronic, and charge properties of these two types of Cu NWs exhibit distinctly different behaviors. © 2011 American Chemical Society.


Wang Q.,Northwestern Polytechnical University | Wang Q.,Henan Polytechnic University | Huang Y.,Northwestern Polytechnical University | Miao J.,Henan Polytechnic University | And 2 more authors.
Electrochimica Acta | Year: 2013

The nanocomposites Ce doped SnS2 (CeSnS2) have been synthesized by a hydrothermal route. The CeSnS2 composites exhibit 3D flowerlike structures. The particle sizes of each petal are in the range from 100 to 200 nm with clear lattice fringes. The electrode cycling performance and rate retention ability of CeSnS2 are better than those of SnS 2 as anode electrodes materials for lithium ion batteries. The CeSnS2 compound (Ce of 5 mol%) shows the best reversible capacities and cycling performance among the synthesized CeSnS2 compounds. The reason is that the part of large-radius cerium ions (much larger than that of Sn4+) can be the substitutes for Sn4+ in the SnS 2 lattice. The expansion of the crystal lattice can provide more lattice space for lithium intercalation and de-intercalation, and further improves the cycling performance of CeSnS2. © 2013 Elsevier Ltd. © 2013 Elsevier Ltd. All rights reserved.


Nie Y.,Northwestern Polytechnical University | Cocci R.,University of Massachusetts Amherst | Cao Z.,University of Massachusetts Amherst | Diao Y.,University of Massachusetts Amherst | Shenoy P.,University of Massachusetts Amherst
IEEE Transactions on Knowledge and Data Engineering | Year: 2012

Despite its promise, RFID technology presents numerous challenges, including incomplete data, lack of location and containment information, and very high volumes. In this work, we present a novel data inference and compression substrate over RFID streams to address these challenges. Our substrate employs a time-varying graph model to efficiently capture possible object locations and interobject relationships such as containment from raw RFID streams. It then employs a probabilistic algorithm to estimate the most likely location and containment for each object. By performing such online inference, it enables online compression that recognizes and removes redundant information from the output stream of this substrate. We have implemented a prototype of our inference and compression substrate and evaluated it using both real traces from a laboratory warehouse setup and synthetic traces emulating enterprise supply chains. Results of a detailed performance study show that our data inference techniques provide high accuracy while retaining efficiency over RFID data streams, and our compression algorithm yields significant reduction in output data volume. © 2011 IEEE.


Fan X.L.,Northwestern Polytechnical University | Zhang W.X.,Xi'an Jiaotong University | Wang T.J.,Xi'an Jiaotong University | Sun Q.,Northwestern Polytechnical University
Surface and Coatings Technology | Year: 2012

The objective of this paper is to understand the effect of thermally grown oxide (TGO) on the multiple surface cracking behaviors in an air plasma sprayed (APS) thermal barrier coating system (TBCs). The extended finite element method (XFEM) and periodic boundary conditions are used to investigate the TGO dependences of periodic surface crack driving force and crack propagation path. It is seen that the effect of TGO thickness on the strain energy release rate (SERR) is negligible while ignoring the thickening and elongation strains of the TGO layer. However, the effect of elastic modulus of TGO layer is significant. In particular, for relatively stiff TGO layer the SERR drops to zero as the ratio of surface crack length to coating thickness approximates to one. And vice versa, for a severely damaged TGO layer with relatively compliant modulus, the SERR approaches infinity as surface cracks propagate to the interface. This kind of fracture mechanism is mainly governed by the elastic mismatch across the bimaterial interfaces, which can be used as a guide for the design of good strain-tolerant coating film in APS-TBCs. © 2012 Elsevier B.V.


Jin M.,Northwestern Polytechnical University | Zhao K.,Xi'an Jiaotong University | Huang Q.,Northwestern Polytechnical University | Xu C.,Northwestern Polytechnical University | Shang P.,Northwestern Polytechnical University
Carbohydrate Polymers | Year: 2012

The root of Angelica sinensis (Oliv.) Diels, a well-known Chinese herbal medicine, has been used historically as a tonic, hematopoietic and anti-inflammatory agent for thousands of years. Modern phytochemistry and pharmacological experiments have proved that polysaccharide is one of the major active ingredients in A. sinensis. It has been demonstrated that A. sinensis polysaccharides had various important biological activities, such as hematopoiesis, immunomodulation, antitumor, antioxidant, radioprotection and hypoglycemic activity. The purpose of the present review is to summarize previous and current references regarding extraction and purification techniques as well as structural characterization and biological activities of A. sinensis polysaccharides. © 2012 Elsevier Ltd. All rights reserved.


Kang W.,Northwestern Polytechnical University | Zhang J.-Z.,Xi'an Jiaotong University | Lei P.-F.,Xi'an Jiaotong University | Xu M.,Northwestern Polytechnical University
Journal of Fluids and Structures | Year: 2014

A numerical method for fluid-structure interaction is presented for the analysis of unsteady viscous flow over a locally flexible airfoil. The Navier-Stokes equations are solved by ALE-CBS algorithm, coupling with a structural solver with large deformation. Following the validation of the method, a numerical example for the flight of micro-air vehicles at low Reynolds number is chosen for the computation. The coupling effect of flexible structure with different elastic stiffness on aerodynamic performance is demonstrated. A noticeable camber effect is induced by the deflection of the structure as the elastic stiffness of the structure goes smaller. Moreover, when the vibrating frequencies of the structure with smaller elastic stiffness have a close correlation with the shedding frequencies, the positive impact of the vibration of local flexible surface on the lift of the airfoil is highlighted, which results from the formation of the coherent vortices. © 2014 Elsevier Ltd.


Zang D.,Northwestern Polytechnical University | Wang X.,Northwestern Polytechnical University | Geng X.,Northwestern Polytechnical University | Zhang Y.,Northwestern Polytechnical University | Chen Y.,Xi'an Jiaotong University
Soft Matter | Year: 2013

We investigate the impact dynamics of droplets containing silica nanoparticles and/or poly(ethylene oxide) (PEO) additives by using a high speed camera, and relate the impact behavior to the rheological properties of liquids. For a droplet with both particles and polymer additives, the rebound is damped much faster and the instability behavior is suppressed. Interestingly, the rebound can be inhibited even when impact is at high velocity (1.88 m s -1). The transition from "rebound" to "stick" by enhancing the impact velocity is mainly due to the increase of the friction force of the nanoparticles and polymer aggregates with the substrate. This is confirmed by the increase of the sliding angle with impact velocity. © The Royal Society of Chemistry 2013.


Zhang D.-W.,Northwestern Polytechnical University | Zhang D.-W.,Xi'an Jiaotong University | Yang H.,Northwestern Polytechnical University
International Journal of Advanced Manufacturing Technology | Year: 2013

To explore the metal flow and filling law of large-scale rib-web component local loading forming process is important for fast design of unequal-thickness billet (UTB), parameter optimization and process control of the rib-web component local loading forming process. T-shaped component forming under UTB can reflect the forming characteristics in the large-scale rib-web component forming process. In the forming process by using UTB, the width of local loading changes dynamically, the thickness difference of billet changes notably, and the boundary conditions are very complex. By introducing new assumptions, variables and boundary conditions, a mathematical model for local loading pattern caused by UTB is established by using slab method (SM). Based on the virtualizing experimental data observed by finite element method (FEM), a predicted model for the dynamic width of local loading is established by using polynomial regression and partial least squares (PLS) regression. Comparing with FEM results indicates that the relative differences are less than about 10 % for predicted model of local loading width. Comparing with FEM and physical modeling experimental results indicates that the relative differences are less than about 15 % for SM model. The metal flow, cavity fill, and increased width of local loading under local loading condition are studied by using the mathematical models and numerical simulation, and the results indicate that: the metal flow and deformation pattern under local loading are determined by the thickness of billet and the width of local loading; the increased width of local loading is determined by initial geometric parameters, and the forming parameters such as materials (Ti-6Al-4 V and Ti-6Al-2Zr-1Mo-1 V), loading speed (0.1-1.0 mm/s), temperature (950-970 C), etc. have little influence on it; the value of x k (position of neutral layer) under local loading pattern caused by geometric parameters of billet is less than that caused by geometric parameters of die at initial forming stage. © 2013 Springer-Verlag London.


Li T.,Northwestern Polytechnical University | Sun S.,Northwestern Polytechnical University | Sattar T.P.,London South Bank University | Corchado J.M.,University of Salamanca
Expert Systems with Applications | Year: 2014

During the last two decades there has been a growing interest in Particle Filtering (PF). However, PF suffers from two long-standing problems that are referred to as sample degeneracy and impoverishment. We are investigating methods that are particularly efficient at Particle Distribution Optimization (PDO) to fight sample degeneracy and impoverishment, with an emphasis on intelligence choices. These methods benefit from such methods as Markov Chain Monte Carlo methods, Mean-shift algorithms, artificial intelligence algorithms (e.g.; Particle Swarm Optimization, Genetic Algorithm and Ant Colony Optimization), machine learning approaches (e.g.; clustering, splitting and merging) and their hybrids, forming a coherent standpoint to enhance the particle filter. The working mechanism, interrelationship, pros and cons of these approaches are provided. In addition, approaches that are effective for dealing with high-dimensionality are reviewed. While improving the filter performance in terms of accuracy, robustness and convergence, it is noted that advanced techniques employed in PF often causes additional computational requirement that will in turn sacrifice improvement obtained in real life filtering. This fact, hidden in pure simulations, deserves the attention of the users and designers of new filters. © 2013 Elsevier Ltd. All rights reserved.


Li B.,Xi'an Jiaotong University | Zhao Z.,Northwestern Polytechnical University
EPL | Year: 2014

A pre-stretched dielectric elastomer is capable of large deformation, when subject to voltage. This paper investigates the effect of two types of pre-stretch: by strain and by stress. The difference is compared and discussed using thermodynamics models. The significance of the pre-stretch in actuation is explained by examining the true stress in actuation. Under both pre-stretch strategies, during the actuation, the dielectric elastomer exhibits hysteresis loops due to snap-through but differs in shape and physical quantity. With pre-stretch by strain, the dielectric elastomer features a discontinuous snap in stretch while with the stress the voltage snaps. © CopyrightEPLA, 2014.


Zhang D.-W.,Xi'an Jiaotong University | Zhang D.-W.,Northwestern Polytechnical University | Yang H.,Northwestern Polytechnical University
International Journal of Advanced Manufacturing Technology | Year: 2013

Friction plays an important role in bulk metal-forming process. Especially, it has an important influence on metal flow in the local loading process. In the present study, the influence of friction on the metal flow in local loading forming process of rib-web component was analyzed by using analytical method, numerical simulation, and experiment. Constant shear friction model was employed in the analytical analysis and numerical simulation. Two kinds of local loading experiment were carried out, which differ in the shape of billet. The results in the present study indicated that (a) in local loading state, increasing friction is beneficial to reduce or avoid the occurrence of shearing deformation behavior; (b) the metal flowing into rib cavity would increase if friction factor increases; (c) as the width of local loading increases or thickness difference of variable-thickness region decreases, the friction effect will reduce. © 2013 Springer-Verlag London.


Zhang D.-W.,Northwestern Polytechnical University | Zhang D.-W.,Xi'an Jiaotong University | Yang H.,Northwestern Polytechnical University
International Journal of Advanced Manufacturing Technology | Year: 2013

Large-scale TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy bulkhead is a key lightweight load-bearing structure part in an aircraft, which has a large plane view and has a complex shape with high ribs and thin webs. In its forging process, the forming defects, such as folding and under-filling are prone to occurrence. The near-net shape forming with saving force of this large-scale complex component can be realized with proper preform design combining local loading condition. By analyzing isothermal local loading process characteristic of large-scale bulkhead, it indicates that the simple unequal-thickness billet is suitable for small lot manufacture of large-scale TA15 titanium alloy bulkhead. Considering the geometry and forming characteristics, such as large dimension, complex shape, mass data, etc., a design method of unequal-thickness billet using analytical analysis and numerical simulation is proposed. The preform for a large-scale TA15 titanium alloy bulkhead is designed by the proposed method. The basic three-dimensional shape of billet is determined by the analytical models based on local loading features, and the basic billet is modified according to numerical simulation result and considering the local loading forming characteristic, and then the preform without resulting in folding and under-filling can be obtained after two modifications. © Springer-Verlag London 2012.


Jin M.,Northwestern Polytechnical University | Huang Q.,Northwestern Polytechnical University | Zhao K.,Xi'an Jiaotong University | Shang P.,Northwestern Polytechnical University
International Journal of Biological Macromolecules | Year: 2013

Recently, isolation and investigation of novel ingredients with biological activities and health benefit effects from natural resources have attracted a great deal of attention. The fruit of Lycium barbarum L., a well-known Chinese herbal medicine as well as valuable nourishing tonic, has been used historically as antipyretic, anti-inflammation and anti-senile agent for thousands of years. Modern pharmacological experiments have proved that polysaccharide is one of the major ingredients responsible for those biological activities in L. barbarum. It has been demonstrated that L. barbarum polysaccharides had various important biological activities, such as antioxidant, immunomodulation, antitumor, neuroprotection, radioprotection, anti-diabetes, hepatoprotection, anti-osteoporosis and antifatigue. The purpose of the present review is to summarize previous and current references regarding biological activities as well as potential health benefits of L. barbarum polysaccharides. © 2012 Elsevier B.V.


Qiao J.,Northwestern Polytechnical University | Yang N.,Northwestern Polytechnical University | Gao J.,Xi'an Jiaotong University
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2011

Traffic efficiency is commonly regarded as the most important target for the control of signalized intersections. However, from the fairness point of view, it can be argued that all vehicles at a signalized intersection should have equal passing opportunities. In this correspondence paper, a two-stage fuzzy logic control model for an isolated signalized intersection has been proposed, where both traffic efficiency and fairness have been considered simultaneously. At the first stage, a green-phase selector has been developed to select the subsequent green phase. At the second stage, a green-time adjustor has been proposed to determine the green time for the selected phase. An offline genetic algorithm (GA) has been developed to optimize the fuzzy rules and membership functions of the two controllers. The simulation results demonstrate that the proposed model outperforms the vehicle-actuated control model and the model proposed by Pappis and Mamdani in 1977 in terms of both traffic efficiency and fairness. The performance of the proposed model can be further improved after its rules and membership functions are optimized by using GA. © 2006 IEEE.


Li W.-Y.,Northwestern Polytechnical University | Li C.-J.,Xi'an Jiaotong University
Applied Surface Science | Year: 2010

The ball-milled Fe-Si alloy was used as feedstock for deposition of nanocrystalline Fe-Si by cold spraying process. The microstructure of the as-sprayed nanostructured Fe-Si was characterized by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The grain sizes of the feedstock and as-sprayed deposit were estimated based on X-ray diffraction analysis. The microhardness and coercivity of the deposited Fe-Si alloy were characterized. The results showed that the as-sprayed deposit presented a dense microstructure. The mean grain size of the as-deposited Fe-Si was several tens nanometers and comparable to that of the corresponding milled feedstock. The temperature of driving gas presented little effect on the microstructure of cold-sprayed nanostructured Fe-Si deposit. The mechanical alloying induced oxygen contents up to 8 wt% in the feedstocks and subsequent deposits. The microhardness of the deposit reached about 400 Hv. The deposit achieved a high coercivity up to 190 kA/m indicating the potential possibility for applications to recording materials. © 2009 Elsevier B.V. All rights reserved.


Li W.-Y.,Northwestern Polytechnical University | Li C.-J.,Xi'an Jiaotong University | Liao H.,University of Technology of Belfort - Montbéliard
Applied Surface Science | Year: 2010

The critical velocity for particle deposition in cold spraying is a key parameter, which depends not only on the material type, but also the particle temperature and oxidation condition. The dependency of deposition efficiency of cold spray Cu particles on the particle temperature and surface oxidation was examined. The effect of particle surface oxide scales on the interfacial microstructure and adhesive strength of the cold-sprayed Cu coatings was investigated. The results show that the deposition efficiency significantly increases with increasing the gas temperature but decreases with augmenting the oxygen content of the starting powder. The oxide inclusions at the interfaces between the deposited particles inhibit the effective bonding of fresh metals and remarkably lower the bond strength of the deposited Cu coatings on steel. © 2010 Elsevier B.V. All rights reserved.


Feng T.,Northwestern Polytechnical University | Zhao G.,Xi'an Jiaotong University | Su K.,Northwestern Polytechnical University
International Journal of Production Research | Year: 2014

With the significant increase in the adoption of environmental management systems (EMSs), it is important to evaluate whether EMSs can improve the business value for organisations that adopt them. However, less is known about whether or not EMSs lead to improved firm performance with only few studies evaluating the broad link between an organisations environmental strategies and its business performance. Furthermore, previous studies are inconsistent in their findings about the relationship between environmental strategies and firm performance. We attribute this inconsistency to the misfit between environmental strategies and organisational learning orientation which results in operational inefficiency within the firm. This study tries to find out the proper fit pattern between EMSs and organisational learning orientation by investigating their joint effect on firm performance. Based on survey data from 214 Chinese manufacturing companies, we found that the interactions between EMSs and four dimensions of organisational learning orientation have positive impacts on firm performance. Thus, the proper organisational learning orientation for efficiency and effective EMSs is characterised by high levels of commitment to learning, shared vision, open-mindedness and knowledge sharing. © 2013 Taylor & Francis.


Feng J.,Northwestern Polytechnical University | Che A.,Northwestern Polytechnical University | Wang N.,Xi'an Jiaotong University
International Journal of Production Research | Year: 2014

This paper addresses bi-objective cyclic scheduling in a robotic cell with processing time windows. In particular, we consider a more general non-Euclidean travel time metric where robots travel times are not required to satisfy the well-known triangular inequality. We develop a tight bi-objective mixed integer programming (MIP) model with valid inequalities for the cyclic robotic cell scheduling problem with processing time windows and non-Euclidean travel times. The objective is to minimise the cycle time and the total robot travel distance simultaneously. We propose an iterative ε-constraint method to solve the bi-objective MIP model, which can find the complete Pareto front. Computational results both on benchmark instances and randomly generated instances indicate that the proposed approach is efficient in solving the cyclic robotic cell scheduling problems. © 2013 © 2013 Taylor & Francis.


Feng T.,Northwestern Polytechnical University | Zhao G.,Xi'an Jiaotong University
Industrial Management and Data Systems | Year: 2014

Purpose - The purpose of this paper is to examine the effects of top management support (TMS) and inter-organizational relationships (IORs) on external involvement (EI), and their differences across different ownerships. Design/methodology/approach - To test the research hypotheses, structural equation modeling was conducted using data from 176 Chinese manufacturing firms. Findings - TMS enhances relationship with customers and relationship with suppliers. Relationship with customers increases the degree of customer involvement, while relationship with suppliers increases the degree of supplier involvement. In addition, TMS improves customer involvement while does not improve supplier involvement directly. A further analysis reveals that the relationship between TMS and supplier involvement is partially mediated by relationship with suppliers in Chinese-controlled firms, whereas it is completely mediated by relationship with suppliers in foreign-controlled firms. Moreover, the effect of relationship with suppliers on supplier involvement is stronger in foreign-controlled firms than in Chinese-controlled firms. Research limitations/implications - This study employed perceptual data from a single respondent in each firm. In addition, the data used in this study were collected from one side of the dyad: the manufacturers. Practical implications - Both Chinese-controlled and foreign-controlled firms should get support from top management and develop close relationship with customers and suppliers to improve EI. Originality value - This study extends our knowledge in the field by examining how TMS and prior history of IORs can improve the degree of EI. © Emerald Group Publishing Limited.


Wu H.,Northwestern Polytechnical University | Wu G.,Xi'an Jiaotong University | Wang L.,Northwestern Polytechnical University
Powder Technology | Year: 2015

We reported a facile approach to prepare peculiar porous α-Fe2O3, γ-Fe2O3 and Fe3O4 nanospheres by combining a facile hydrothermal route with a calcination process in Ar or H2 atmosphere. The synthesized monodisperse porous α-Fe2O3 nanospheres with uniform average diameters of ~60nm in fact contained randomly distributed pores. A close view further revealed that there are two types of pores, one is large mesopores (ca. 15-20nm) in the center, and the other is small mesopores (ca. <10nm) in the outside. After calcining in Ar or H2, the obtained α-Fe2O3, γ-Fe2O3 and Fe3O4 nanospheres preserved the similar morphology and particle size as the uncalcined α-Fe2O3 nanospheres, indicating the as-prepared α-Fe2O3 nanospheres are stable under Ar and H2-annealing heat treatment. Comparing with all the paraffin composites, it was found that the porous α-Fe2O3 nanosphere/paraffin composites exhibit a higher permittivity level. A minimum reflection loss (RL) of -25dB was observed at ~13GHz for the porous α-Fe2O3 nanosphere/paraffin composites with a thickness of 3.5mm, and the effective absorption frequency (RL<-10dB) ranged from 9.9 to 15.1GHz. The composites exhibited better absorption properties than the magnetic porous γ-Fe2O3 and Fe3O4 nanosphere/paraffin composites. © 2014 Elsevier B.V.


Liu Y.J.,Northwestern Polytechnical University | Sun Q.,Northwestern Polytechnical University | Fan X.L.,Xi'an Jiaotong University
Computer Methods in Applied Mechanics and Engineering | Year: 2014

A non-intrusive global/local algorithm with non-matching (incompatible) interface is proposed to evaluate the durability of large-scale structures with local nonlinearity both on the basis of local multigrid strategy and the domain decomposition (DD) method, which can serve as an intermediate way to perform analyses of complex structures. The proposed algorithm couples a global linear elastic analysis (on coarse mesh) with a local nonlinear analysis (on fine mesh), which extends the iterative global/local method to treat non-matching partition interfaces. Furthermore, to deal with non-matching interface the framework of localized Lagrange multiplier (LLM) method is introduced, and a feasible but robust data transfer method is established with radial basis function (RBF) interpolation. Aitken's acceleration method is adopted to increase the convergence rate. The convergence property and accuracy of this non-intrusive algorithm are investigated for a two-dimensional model with different interface geometries and interface node allocations. The effect of reduced integration on the convergence rate is also concerned in verification. Then, it is further verified with a three-dimensional model. Numerical results reveal that this non-intrusive algorithm is robust in the non-matching interface data transfer procedure, which is significant in error control during iterations, and it has good performance in both convergence and accuracy. © 2014 Elsevier B.V.


Li W.,Northwestern Polytechnical University | Li W.,University of New South Wales | Wang J.,University of New South Wales
Journal of Navigation | Year: 2013

To improve the computational efficiency and dynamic performance of low cost Inertial Measurement Unit (IMU)/magnetometer integrated Attitude and Heading Reference Systems (AHRS), this paper has proposed an effective Adaptive Kalman Filter (AKF) with linear models; the filter gain is adaptively tuned according to the dynamic scale sensed by accelerometers. This proposed approach does not need to model the system angular motions, avoids the non-linear problem which is inherent in the existing methods, and considers the impact of the dynamic acceleration on the filter. The experimental results with real data have demonstrated that the proposed algorithm can maintain an accurate estimation of orientation, even under various dynamic operating conditions. Copyright © 2012 The Royal Institute of Navigation.


Zhang Y.,Northwestern Polytechnical University | Huang G.Q.,University of Hong Kong | Sun S.,Northwestern Polytechnical University | Yang T.,Northwestern Polytechnical University
Computers and Industrial Engineering | Year: 2014

The lack of timely feedback shopfloor information during manufacturing execution stage leads to significant difficulties in achieving real-time production scheduling. To address this problem, an overall architecture of multi-agent based real-time production scheduling is presented to close the loop of production planning and control. Several contributions are significant. Firstly, wireless devices such as radio frequency identification (RFID) are deployed into value-adding points in a ubiquitous shopfloor environment to form Machine Agent for the collection and processing of real-time shopfloor data. Secondly, Capability Evaluation Agent is designed to optimally assign the tasks to the involved machines at the process planning stage based on the real-time utilization ration of each machine. The third contribution is a Real-time Scheduling Agent for manufacturing tasks scheduling/re-scheduling strategy and methods according to the real-time feedback. Fourthly, a Process Monitor Agent model is designed for tracking and tracing the manufacturing execution based on a critical event structure. Finally, a case is used to demonstrate the proposed multi-agent based real-time production scheduling models and methods. © 2014 Elsevier Ltd. All rights reserved.


Xu B.,Northwestern Polytechnical University | Yang C.,University of Plymouth | Yang C.,Beijing Institute of Technology | Shi Z.,Northwestern Polytechnical University
IEEE Transactions on Neural Networks and Learning Systems | Year: 2014

In this brief, a novel adaptive-critic-based neural network (NN) controller is investigated for nonlinear pure-feedback systems. The controller design is based on the transformed predictor form, and the actor-critic NN control architecture includes two NNs, whereas the critic NN is used to approximate the strategic utility function, and the action NN is employed to minimize both the strategic utility function and the tracking error. A deterministic learning technique has been employed to guarantee that the partial persistent excitation condition of internal states is satisfied during tracking control to a periodic reference orbit. The uniformly ultimate boundedness of closed-loop signals is shown via Lyapunov stability analysis. Simulation results are presented to demonstrate the effectiveness of the proposed control. © 2012 IEEE.


Xie K.,Northwestern Polytechnical University | Wei B.,Northwestern Polytechnical University | Wei B.,University of Delaware
Advanced Materials | Year: 2014

Stretchable energy storage and conversion devices (ESCDs) are attracting intensive attention due to their promising and potential applications in realistic consumer products, ranging from portable electronics, bio-integrated devices, space satellites, and electric vehicles to buildings with arbitrarily shaped surfaces. Material synthesis and structural design are core in the development of highly stretchable supercapacitors, batteries, and solar cells for practical applications. This review provides a brief summary of research development on the stretchable ESCDs in the past decade, from structural design strategies to novel materials synthesis. The focuses are on the fundamental insights of mechanical characteristics of materials and structures on the performance of the stretchable ESCDs, as well as challenges for their practical applications. Finally, some of the important directions in the areas of material synthesis and structural design facing the stretchable ESCDs are discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cao Z.,University of Delaware | Wei B.,University of Delaware | Wei B.,Northwestern Polytechnical University
ACS Nano | Year: 2014

Polymer binders such as poly(vinylidene fluoride) (PVDF) and conductive additives such as carbon black (CB) are indispensable components for manufacturing battery electrodes in addition to active materials. The concept of adhesive conductors employing fragmented carbon nanotube macrofilms (FCNTs) is demonstrated by constructing composite electrodes with a typical active material, LiMn2O4. The adhesive FCNT conductors provide not only a high electrical conductivity but also a strong adhesive force, functioning simultaneously as both the conductive additives and the binder materials for lithium-ion batteries. Such composite electrodes exhibit superior high-rate and retention capabilities compared to the electrodes using a conventional binder (PVDF) and a conductive additive (CB). An in situ tribology method combining wear track imaging and force measurement is employed to evaluate the adhesion strength of the adhesive FCNT conductors. The adhesive FCNT conductors exhibit higher adhesion strength than PVDF. It has further been confirmed that the adhesive FCNT conductor can be used in both cathodes and anodes and is proved to be a competent substitute for polymer binders to maintain mechanical integrity and at the same time to provide electrical connectivity of active materials in the composite electrodes. The organic-solvent-free electrode manufacturing offers a promising strategy for the battery industry. © 2014 American Chemical Society.


Yu L.,Northwestern Polytechnical University | Shi Z.-K.,Northwestern Polytechnical University | Li T.,University of Iowa
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014

A new car-following model is proposed by taking into account two different time delays in sensing headway and velocity. The effect of time delays on the stability analysis is studied. The theoretical and numerical results show that traffic jams are suppressed efficiently when the difference between two time delays decreases and those can be described by the solution of the modified Korteweg-de Vries (mKdV) equation. Traffic flow is more stable with two delays in headway and velocity than in the case with only one delay in headway. The impact of local small disturbance to the system is also studied. © 2013 Elsevier B.V.


Gu J.,Northwestern Polytechnical University | Zhang Q.,Northwestern Polytechnical University | Dang J.,Northwestern Polytechnical University | Xie C.,PLA Fourth Military Medical University
Polymers for Advanced Technologies | Year: 2012

Boron nitride (BN) micro particles modified by silane coupling agent, γ-aminopropyl triethoxy silane (KH550), are employed to prepare BN/epoxy resin (EP) thermal conductivity composites. The thermal conductivity coefficient of the composites with 60% mass fraction of modified BN is 1.052W/mK, five times higher than that of native EP (0.202W/mK). The mechanical properties of the composites are optimal with 10wt% BN. The thermal decomposition temperature, dielectric constant, and dielectric loss increase with the addition of BN. For a given BN loading, the surface modification of BN by KH550 exhibits a positive effect on the thermal conductivity and mechanical properties of the BN/EP composites. © 2011 John Wiley & Sons, Ltd.


Cao Z.,University of Delaware | Wei B.,Northwestern Polytechnical University | Wei B.,University of Delaware
Energy and Environmental Science | Year: 2013

The ever-increasing demand of electricity storage is a growing challenge among a broad range of renewable energy sources. The development of high-energy storage devices has been one of the most important research areas in modern days. In particular, rechargeable batteries and electrochemical capacitors are recognized as the primary power sources for applications from portable electronic devices to electric vehicles. In order to power the emerging flexible/stretchable electronics, power sources themselves must be able to accommodate high levels of deformation and stretchability in addition to high energy and power density, light weight, miniaturization in size, safety qualification, and other significant characteristics. Utilizing carbon nanotubes (CNTs) for various energy storage applications such as electrodes in lithium ion batteries and supercapacitors, are under close scrutiny because of the promising electrochemical performance in addition to their extraordinary tensile strength and flexibility, ultrahigh surface area, and excellent thermal and electrical conductivity. Recently, there has been growing interest in investigating CNT macro-films with large-scale organized nanostructures of desired shape and form and unique and enhanced properties: integrity and stability to realize the scaled-up energy storage devices. In this perspective, research efforts in assembling 2-D CNT macro-films using a chemical vapor deposition method and their applications for different energy storage devices including stretchable supercapacitors, supercapacitors working under extreme conditions such as high temperature and high pressure, and lithium-ion batteries are discussed. In details, this paper provides an original overview involving the effect of compressive stress on the electrochemical behavior of flexible supercapacitors assembled with CNT macro-film electrodes and electrolytes with different anions and cations; the demonstration of the dynamic and galvanic stability of stretchable supercapacitor using buckled CNT macro-films by an in situ dynamic electrochemical testing method; the understandings on the self-discharge mechanisms of CNT macrofilm-based supercapacitors from both electrode and electrolyte aspects; and the investigation of the electrochemical properties of the tandem structure of active materials (e.g. thin porous silicon film and CuO) with CNT macro-films acting as a flexible and adhesive layer between the active layers and current collectors for lithium-ion batteries. Future research on CNT macro-films-based lithium-sulfur batteries and lithium-air batteries is also discussed. © 2013 The Royal Society of Chemistry.


Li C.,Northwestern Polytechnical University | Li Q.,PLA Fourth Military Medical University | Mei Q.,Northwestern Polytechnical University | Lu T.,Northwestern Polytechnical University
Life Sciences | Year: 2015

Herba Epimedii is an important medicinal plant which has been used in various traditional Chinese formulations for thousands of years as well as in modern proprietary traditional Chinese medicine products. It has extensive clinical indications, especially for the treatment of sexual dysfunction and osteoporosis. There have been more than 260 chemical moieties identified in the genus Epimedium most of which belong to flavonoids. Icariin is the most abundant constituent in Herba Epimedii. Icariin is pharmacologically bioactive and demonstrates extensive therapeutic capacities such as osteoprotective effect, neuroprotective effect, cardiovascular protective effect, anti-cancer effect, anti-inflammation effect, immunoprotective effect and reproductive function. Particularly, the significant osteogenic effect of icariin made it a promising drug candidate in bone tissue engineering. The current review paper aims to summarize the literatures reporting the pharmacological effects of icariin. The pharmacokinetic properties of bioactive ingredients in Herba Epimedii have also been discussed. © 2015 Elsevier Inc.


Luo B.C.,University of New South Wales | Luo B.C.,Northwestern Polytechnical University | Wang D.Y.,University of New South Wales | Duan M.M.,Northwestern Polytechnical University | Li S.,University of New South Wales
Applied Physics Letters | Year: 2013

Orientation-engineered 0.5BaZr0.2Ti0.8O 3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on La0.7Sr0.3MnO3-coated SrTiO3 single-crystalline (001), (110), and (111) substrates by off-axis radio-frequency magnetron sputtering. X-ray diffraction confirmed a highly epitaxial growth of all the as-deposited films. It is believed the strong orientation dependence of ferroelectric and piezoelectric properties on the films is attributed to the relative alignment of crystallites and spontaneous polarization vector. The optimal ferroelectric response lies in the [001] direction, whereas a comparatively large effective piezoelectric coefficient d33,eff of 100.1 ± 5 pm/V was attained in [111] BZT-BCT thin film, suggesting its potential application for high-performance lead-free piezoelectric devices. © 2013 AIP Publishing LLC.


Xu Z.-J.,Beijing Institute of Technology | Li Y.-L.,Northwestern Polytechnical University
Acta Mechanica Sinica/Lixue Xuebao | Year: 2011

An elusive phenomenon is observed in previous investigations on dynamic fracture that the dynamic fracture toughness (DFT) of high strength metals always increases with the loading rate on the order of TPa•m 1/2•s-1. For the purpose of verification, variation of DFT with the loading rate for two high strength steels commonly used in the aviation industry, 30CrMnSiA and 40Cr, is studied in this work. Results of the experiments are compared, which were conducted on the modified split Hopkinson pressure bar (SHPB) apparatus, with striker velocities ranging from 9.2 to 24.1 m/s and a constant value of 16.3 m/s for 30CrMnSiA and 40Cr, respectively. It is observed that for 30CrMn-SiA, the crack tip loading rate increases with the increase of the striker velocity, while the fracture initiation time and the DFT simultaneously decrease. However, in the tests of 40Cr, there is also an increasing tendency of DFT, similar to other reports. Through an in-depth investigation on the relationship between the dynamic stress intensity factor (DSIF) and the loading rate, it is concluded that the generally increasing tendency in previous studies could be false, which is induced from a limited striker velocity domain and the errors existing in the experimental and numerical processes. To disclose the real dependency of DFT on the loading rate, experiments need to be performed in a comparatively large striker velocity range. © 2011 The Chinese Society of Theoretical and Applied Mechanics and Springer-Verlag Berlin Heidelberg.


Deqiang S.,Xi'an University of Technology | Weihong Z.,Northwestern Polytechnical University | Yanbin W.,Northwestern Polytechnical University
Composite Structures | Year: 2010

Double-walled hexagonal honeycomb cores (DHHCs) are important cushioning materials and their out-of-plane impact properties depend upon their configuration parameters and impact velocities. In this paper, the reliable finite element (FE) model by using ANSYS/LS-DYNA was designed to investigate the relations between configuration parameters of DHHCs and their out-of-plane dynamic plateau stresses at the impact velocities from 3 to 350. m/s. FE simulations demonstrate, when all configuration parameters are kept constant, mean out-of-plane dynamic plateau stresses are related to impact velocities by conic curves. For a given impact velocity, mean out-of-plane dynamic plateau stresses are related to the ratios between cell wall thickness and edge length and to edge length ratios by power laws. There are complicated relations between mean out-of-plane dynamic plateau stresses and expanding angels, which are discussed in detail. Many empirical expressions on mean out-of-plane dynamic plateau stresses of DHHCs are suggested. © 2010.


Liu Z.-G.,Northwestern Polytechnical University | Liu Z.-G.,CNRS Communication and Information Sciences Laboratories | Pan Q.,Northwestern Polytechnical University | Dezert J.,ONERA | Mercier G.,CNRS Communication and Information Sciences Laboratories
Pattern Recognition | Year: 2014

In this paper we present a new credal classification rule (CCR) based on belief functions to deal with the uncertain data. CCR allows the objects to belong (with different masses of belief) not only to the specific classes, but also to the sets of classes called meta-classes which correspond to the disjunction of several specific classes. Each specific class is characterized by a class center (i.e. prototype), and consists of all the objects that are sufficiently close to the center. The belief of the assignment of a given object to classify with a specific class is determined from the Mahalanobis distance between the object and the center of the corresponding class. The meta-classes are used to capture the imprecision in the classification of the objects when they are difficult to correctly classify because of the poor quality of available attributes. The selection of meta-classes depends on the application and the context, and a measure of the degree of indistinguishability between classes is introduced. In this new CCR approach, the objects assigned to a meta-class should be close to the center of this meta-class having similar distances to all the involved specific classes centers, and the objects too far from the others will be considered as outliers (noise). CCR provides robust credal classification results with a relatively low computational burden. Several experiments using both artificial and real data sets are presented at the end of this paper to evaluate and compare the performances of this CCR method with respect to other classification methods. © 2014 Elsevier Ltd. All rights reserved.


Li C.,Northwestern Polytechnical University | Xu W.,Northwestern Polytechnical University | Feng J.,Polytechnic University of Mozambique | Wang L.,Northwestern Polytechnical University
Physica A: Statistical Mechanics and its Applications | Year: 2013

This paper aims to investigate the stationary probability density functions (PDFs) of a Duffing-Van der Pol vibro-impact system excited by correlated Gaussian white noise. With the help of non-smooth transformation, the stationary PDFs are formulated analytically by the stochastic averaging of energy envelope. The analytical results are verified by numerical simulation results. Stochastic bifurcations for different parameters are considered, and several special PDF forms are observed in this paper. The first form is the shape of the PDF of total energy can be similar to a crater, which has a minimum and a maximum. The second one is the shape of the joint PDF with three peaks, that is to say, the section of joint PDF has three maximum and two minimum. In addition, the influence of the degree of the correlation of Gaussian white noises is explored. © 2012 Elsevier B.V. All rights reserved.


Gao B.,Northwestern Polytechnical University | Gao B.,Polytechnic University of Mozambique | Fan H.,Northwestern Polytechnical University | Zhang X.,Polytechnic University of Mozambique
Journal of Physics and Chemistry of Solids | Year: 2012

Orthorhombic phase MoO 3 (α-MoO 3) nanobelts with uniform diameter are successfully prepared through a hydrothermal synthesis route at a low temperature (180 °C) in the presence of cetyltrimethylammonium bromide (CTAB) using saturated solution of ammonium molybdate tetrahydrate (AHM) as well as nitrate as raw materials, and are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The CTAB plays a key role in the formation of α-MoO 3 nanobelts and the aspect ratio of nanobelts significantly varies with quality of CTAB. The nanobelts with rectangular cross-sections have single crystalline orthorhombic phase structure, preferentially grow in [001] direction. Raman shifts of the α-MoO 3 nanobelts are fully consistent with that of flaky structure; however, intensity ratio of peaks 818.3 cm -1 and 991.2 cm -1 of α-MoO 3 nanobelts remarkably changes comparing with that of lamellar MoO 3. Electrochemical properties of α-MoO 3 single crystal nanobelts synthesized as cathode electrode materials for rechargeable lithium batteries are also measured. It indicates that the α-MoO 3 nanobelts exhibit a better performance than MoO 3 micro flakes. © 2011 Elsevier Ltd. All rights reserved.


Wang W.,Beijing Institute of Technology | Shen J.,Beijing Institute of Technology | Li X.,Northwestern Polytechnical University | Porikli F.,Australian National University
IEEE Transactions on Image Processing | Year: 2015

With ever-increasing volumes of video data, automatic extraction of salient object regions became even more significant for visual analytic solutions. This surge has also opened up opportunities for taking advantage of collective cues encapsulated in multiple videos in a cooperative manner. However, it also brings up major challenges, such as handling of drastic appearance, motion pattern, and pose variations, of foreground objects as well as indiscriminate backgrounds. Here, we present a cosegmentation framework to discover and segment out common object regions across multiple frames and multiple videos in a joint fashion. We incorporate three types of cues, i.e., intraframe saliency, interframe consistency, and across-video similarity into an energy optimization framework that does not make restrictive assumptions on foreground appearance and motion model, and does not require objects to be visible in all frames. We also introduce a spatio-temporal scale-invariant feature transform (SIFT) flow descriptor to integrate across-video correspondence from the conventional SIFT-flow into interframe motion flow from optical flow. This novel spatio-temporal SIFT flow generates reliable estimations of common foregrounds over the entire video data set. Experimental results show that our method outperforms the state-of-the-art on a new extensive data set (ViCoSeg). © 1992-2012 IEEE.


Zhou B.,Northwestern Polytechnical University | McDonnell M.D.,University of South Australia
Physica A: Statistical Mechanics and its Applications | Year: 2015

The problem of optimising the threshold levels in multilevel threshold system subject to multiplicative Gaussian and uniform noise is considered. Similar to previous results for additive noise, we find a bifurcation phenomenon in the optimal threshold values, as the noise intensity changes. This occurs when the number of threshold units is greater than one. We also study the optimal thresholds for combined additive and multiplicative Gaussian noise, and find that all threshold levels need to be identical to optimise the system when the additive noise intensity is a constant. However, this identical value is not equal to the signal mean, unlike the case of additive noise. When the multiplicative noise intensity is instead held constant, the optimal threshold levels are not all identical for small additive noise intensity but are all equal to zero for large additive noise intensity. The model and our results are potentially relevant for sensor network design and understanding neurobiological sensory neurons such as in the peripheral auditory system. © 2014 Elsevier B.V. All rights reserved.


Yu L.,Northwestern Polytechnical University | Li T.,University of Iowa | Shi Z.-K.,Northwestern Polytechnical University
Physica A: Statistical Mechanics and its Applications | Year: 2010

Density waves are investigated analytically and numerically in the optimal velocity model with reaction-time delay of drivers. The stability condition of this model is obtained by using the linear stability theory. The results show that the decrease of reaction-time delay of drivers leads to the stabilization of traffic flow. The Burgers, Korteweg-de Vries (KdV) and modified Korteweg-de Vries (mKdV) equations are derived to describe the density waves in the stable, metastable and unstable regions respectively. The triangular shock waves, soliton waves and kink-antikink waves appearing respectively in the three distinct regions are derived to describe the traffic jams. The numerical simulations are given. © 2010 Elsevier B.V. All rights reserved.


Wang D.,Northwestern Polytechnical University | Wang D.,Northwestern University | Tejerina B.,Equilibrium Energy | Lagzi I.,Northwestern University | And 3 more authors.
ACS Nano | Year: 2011

Selective aggregation and precipitation of like-charged nanoparticles (NPs) covered with carboxylate ligands can be induced by different monovalent cations. The ordering of critical concentrations required for NP precipitation is Cs+≫K+>Li+>Na+> Rb+ and does not correlate with the size of hydrated cations M +, nor can it be predicted by the Hofmeister series. On the other hand, different anions have no effect on the precipitation trends. These observations are rationalized by a theoretical model combining the elements of the DLVO theory with molecular-level calculations. The key component of the model is the cation-specific binding of various metal cations to the carboxylate ligands. © 2011 American Chemical Society.


Liu J.-C.,China University of Mining and Technology | Wang J.-G.,Northwestern Polytechnical University
CMES - Computer Modeling in Engineering and Sciences | Year: 2014

We consider the determination of heat flux within a body from the Cauchy data. The aim of this paper is to seek an approach to solve the onedimensional heat equation in a bounded domain without initial value. This problem is severely ill-posed and there are few theoretic results. A quasi-reversibility regularization method is used to obtain a regularized solution and convergence estimates are given. For numerical implementation, we apply a method of lines to solve the regularized problem. From numerical results, we can see that the proposed method is reasonable and feasible. Copyright © 2014 Tech Science Press.


Luo Y.,Northwestern Polytechnical University | Luo Y.,Chinese University of Hong Kong | Wang M.Y.,Chinese University of Hong Kong | Kang Z.,Dalian University of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2013

By introducing a new reduction parameter into the Kreisselmeier-Steihauser (K-S) function, this paper presents a general K-S formulation providing an approximation to the feasible region restricted by active constraints. The approximation is highly accurate even when the aggregation parameter takes a relatively small value. Numerical difficulties, such as high nonlinearity and serious violation of local constraints that may be exhibited by the original K-S function, are thus effectively alleviated. In the considered topology optimization problem, the material volume is to be minimized under local von Mises stress constraints imposed on all the finite elements. An enhanced aggregation algorithm based on the general K-S function, in conjunction with a " removal and re-generation" strategy for selecting the active constraints, is then proposed to treat the stress constraints of the optimization problem. Numerical examples are given to demonstrate the validity of the present algorithm. It is shown that the proposed method can achieve reasonable solutions with a high computational efficiency in handling large-scale stress constrained topology optimization problems. © 2012 Elsevier B.V.


Kong J.,Northwestern Polytechnical University | Kong M.,Northwestern Polytechnical University | Zhang X.,Northwestern Polytechnical University | Chen L.,Northwestern Polytechnical University | An L.,University of Central Florida
ACS Applied Materials and Interfaces | Year: 2013

In this contribution, we report a novel strategy for the synthesis of nanocrystal-containing magnetoceramics with an ultralow hysteresis loss by the pyrolysis of commercial polysilazane cross-linked with a functional metallopolymer possessing hyperbranched topology. The usage of hyperbranched polyferrocenylcarbosilane offers either enhanced ceramic yield or magnetic functionality of pyrolyzed ceramics. The ceramic yield was enhanced accompanied by a decreased evolution of hydrocarbons and NH3 because of the cross-linking of precursors and the hyperbranched cross-linker. The nucleation of Fe5Si3 from the reaction of iron atoms with Si-C-N amorphous phase promoted the formation of α-Si3N4 and SiC crystals. After annealing at 1300 C, stable Fe3Si crystals were generated from the transformation of the metastable Fe5Si 3 phase. The nanocrystal-containing ceramics showed good ferromagnetism with an ultralow (close to 0) hysteresis loss. This method is convenient for the generation of tunable functional ceramics using a commercial polymeric precursor cross-linked by a metallopolymer with a designed topology. © 2013 American Chemical Society.


Wang K.,Northwestern Polytechnical University | Ma B.,Northwestern Polytechnical University | Wang Y.,Northwestern Polytechnical University | An L.,University of Central Florida
Journal of the American Ceramic Society | Year: 2013

The complex impedance spectra of polymer-derived amorphous silicon oxycarbides synthesized at different temperatures are reported. Analysis of the spectra using equivalent circuit models showed that the conduction of current is dominantly through the matrix and free carbon in series, instead of through the matrix or free carbon only. We found that the conductivity of both matrix and free-carbon phase increases with increasing synthesis temperature, whereas the relaxation time of the matrix is much shorter than that of the free carbon. The results are correlated with the structures of the materials. © 2013 The American Ceramic Society.


Kang Z.,Dalian University of Technology | Luo Y.,Northwestern Polytechnical University | Li A.,University of Reims Champagne Ardenne
Structural Safety | Year: 2011

This paper investigates the formulation and numerical solution of reliability-based optimization of structures exhibiting grouped uncertain-but-bounded variations. Based on the multi-ellipsoid convex model description for grouped uncertain-but-bounded parameters, the mathematical definition of a non-probabilistic reliability index is presented for quantified measure of the safety margin. The optimal design is then formulated as a nested optimization problem. A method based on concerned performance is proposed for regularization of the reliability index constraints. The expensive computation of the non-probabilistic reliability index and its derivative is thus avoided. Numerical examples are given to illustrate the validity and efficiency of the present method. © 2011 Elsevier Ltd.


Kang Z.,Dalian University of Technology | Luo Y.,Northwestern Polytechnical University
Structural and Multidisciplinary Optimization | Year: 2010

For structural systems exhibiting both probabilistic and bounded uncertainties, it may be suitable to describe these uncertainties with probability and convex set models respectively in the design optimization problem. Based on the probabilistic and multi-ellipsoid convex set hybrid model, this paper presents a mathematical definition of reliability index for measuring the safety of structures in presence of parameter or load uncertainties. The optimization problem incorporating such reliability constraints is then mathematically formulated. By using the performance measure approach, the optimization problem is reformulated into a more tractable one. Moreover, the nested double-loop optimization problem is transformed into an approximate single-loop minimization problem by considering the optimality conditions and linearization of the limit-state function, which further facilitates efficient solution of the design problem. Numerical examples demonstrate the validity of the proposed formulation as well as the efficiency of the presented numerical techniques. © 2009 Springer-Verlag.


Zhao D.-L.,Beijing University of Chemical Technology | Luo F.,Northwestern Polytechnical University | Zhou W.-C.,Northwestern Polytechnical University
Journal of Alloys and Compounds | Year: 2010

Microwave absorbing property and complex permittivity of the nano SiC particles doped with nitrogen within the frequency range of 8.2-18 GHz were investigated. The nano SiC particles doped with nitrogen was synthesized from hexamethyldisilazane ((Me3Si)2NH) (Me:CH3) by a laser-induced gas-phase reaction. The complex permittivities of the composites can be tailored by the contents of the nano SiC particles. The real part (ε′) and imaginary part (ε″) of the complex permittivity, and the dielectric dissipation factor (tg δ = ε″/ε′) of the composites increase with the volume filling factor (v) of the nano SiC particles doped with nitrogen. The ε′ and ε″ of the composites can be effectively modeled using second-order polynomials (ε′, ε″ = Av 2 + Bv + C). The ε′ and ε″ of the nano SiC particles doped with nitrogen decrease with frequency. The high ε″ and tg δ of the nano SiC particles doped with nitrogen are believed to be caused by the substitution of nitrogen for carbon in the nanocrystals of SiC. The single layer composites of 7 wt% nano SiC particles doped with nitrogen with a thickness of 2.96 mm achieved a reflection loss below -10 dB (90% absorption) at 9.8-15.8 GHz, and the minimum value was -63.41 dB at 12.17 GHz. The reflection loss calculations show that the prepared nano SiC particles doped with nitrogen are good electromagnetic wave absorbers in the microwave range. © 2009 Elsevier B.V. All rights reserved.


Butt H.S.U.,Northwestern Polytechnical University | Xue P.,Northwestern Polytechnical University | Xue P.,State Key Laboratory of Explosion Science and Technology
International Journal of Impact Engineering | Year: 2014

Test bars made of viscoelastic materials are frequently employed for the testing of soft materials, using split Hopkinson pressure bar (SHPB) techniques, because of their low mechanical impedance. Determination of the propagation coeffi cient for such bars is a critical step for the subsequent evaluation of the material properties of the specimen. This propagation coef ficient may be determined through experiments or using the analytical solutions if the material properties of the bars are known in advance. Contrary to the case of elastic materials, it is difficult to provide generic properties for such materials as these are dependent on the loading rate, environmental history and manufacturing conditions. Many studies may be found in the open literature reporting numerical values of the identi fied parameters for various viscoelastic materials evaluated through the wave propagation experiments. However, the observed scatter among such data in the case of individual materials dictates that the published parameters should be used with caution. Two polymethyl methacrylate (PMMA) bars, used as incident and transmitter bar in an SHPB test setup, are being subjected to the wave propagation testing. Longitudinal strains, generated as a result of axial impact of strikers with two different lengths and recorded at the mid-length of the bars, are used to determine the wave propagation coef ficient. Propagation coefficients are also evaluated using selected material models of PMMA published in the literature. A considerable scatter is found in the evaluated frequency dependent propagation coefficient. The consequence of using such scattered properties for the bars on the results of the stressestrain response of aluminum foam is being investigated. Although, the evaluated dynamic properties of the tested foam are not considerably influenced in quantitative terms, however qualitative differences are observed. © 2013 Elsevier Ltd. All rights reserved.


Luo Y.,Northwestern Polytechnical University | Kang Z.,Dalian University of Technology
Computers and Structures | Year: 2012

This paper presents an efficient topology optimization strategy for seeking the optimal layout of continuum structures exhibiting asymmetrical strength behaviors in compression and tension. Based on the Drucker-Prager yield criterion and the power-law interpolation scheme for the material property, the optimization problem is formulated as to minimize the material volume under local stress constraints. The -relaxation of stress constraints is adopted to circumvent the stress singularity problem. For improving the computational efficiency, a grouped aggregation approach based on the Kreisselmeier- Steinhauser function is employed to reduce the number of constraints without much sacrificing the approximation accuracy of the stress constraints. In conjunction with the adjoint-variable sensitivity analysis, the minimization problem is solved by a gradient-based optimization algorithm. Numerical examples demonstrate the validity of the present optimization model as well as the efficiency of the proposed numerical techniques. Moreover, it is also revealed that the optimal design of a structure with pressure-dependent material may exhibit a considerable different topology from the one obtained with pressure-independent material model. © 2011 Elsevier Ltd. All rights reserved.


Luo Y.,Northwestern Polytechnical University | Li A.,University of Reims Champagne Ardenne | Kang Z.,Dalian University of Technology
Engineering Structures | Year: 2012

The steel-concrete composite beam bonded by adhesive has particular advantages over the traditional composite beam. Based on the experimental push-out test, this paper proposes a three-dimensional nonlinear finite element model for the mechanical behaviour simulation of bonded steel-concrete composite beams. The proposed numerical model is validated through comparisons between numerical results and experimental data. The effects of certain parameters, including the elastic modulus of adhesive, the adhesive layer's thickness, the concrete strength, the bonding strength and the bonding area, are investigated. Numerical results show that the influence of most investigated parameters on the response of the bonded composites is very notable, while that of the adhesive layer's thickness (variation within 3-15. mm) is relatively small. © 2011 Elsevier Ltd.


Yin S.,Dalian University of Technology | Wang X.-F.,Dalian University of Technology | Li W.-Y.,Northwestern Polytechnical University
Surface and Coatings Technology | Year: 2011

In cold spraying, the spraying of certain complicated surfaces may require nozzles with special cross-sections. In this study, numerical investigation is conducted to study the effect of nozzle cross-section shape on gas flow and particle acceleration in cold spraying. The comprehensive comparison between rectangular nozzles and elliptical nozzles indicates that rectangular nozzles result in slightly lower mean particle impact velocity than elliptical nozzles. However, for rectangular nozzles, more particles may achieve relatively high velocity due to the larger sectional area of their potential core. Furthermore, it can also be found from the numerical results that the mean particle impact velocity increases gradually with the decrease in Width/Length ratio (W/L) of the cross-section because of the diminishing bow shock size. However, when reducing the W/L to 0.2, the mean particle impact velocity begins to decrease steeply, which may be attributed to the rather small area of the potential core for the case of W/L = 0.2. Moreover, the systematic study on the powder release position shows that releasing particles from the nozzle inlet can ensure that particles achieve a high impact velocity and temperature. © 2010 Elsevier B.V.


Xu B.,Northwestern Polytechnical University | Ou J.P.,Dalian University of Technology | Jiang J.S.,Northwestern Polytechnical University
Finite Elements in Analysis and Design | Year: 2013

The integrated optimization of structural topology, number and positions of the actuators and control parameters of piezoelectric smart plates is investigated in this paper. Based on the optimal control effect in the independent mode control and singular value decomposition of the distributed matrix of total performance index for all physical control forces for piezoelectric smart plate, a new criterion, where several large values in singular values are selected, is put forward to determine the optimal number of the assigned actuators in the coupled modal space control. Furthermore, the optimal positions of actuators are ascertained by singular value decomposition of the modal distributing matrix. The integrated optimization model, including the optimized objective function, design variables and constraint functions, is built. The design variables include the logic design variables of structural topology, the number and positions of actuators as well as the control design parameters. Some optimal strategies based on genetic algorithm (GA), such as structural connection checking and structural checkerboard checking and repairing technique, are used to guide the optimization process efficiently. The results of two numerical examples show that the proposed approach can produce the optimal solution with clear structural topology and high control performance. © 2012 Elsevier B.V.


Deng Y.,Southwest University | Jiang W.,Northwestern Polytechnical University | Sadiq R.,University of British Columbia
Expert Systems with Applications | Year: 2011

Contaminant intrusion in a water distribution network is a complex but a commonly observed phenomenon, which depends on three elements - a pathway, a driving force and a contamination source. However, the data on these elements are generally incomplete, non-specific and uncertain. In an earlier work, Sadiq, Kleiner, and Rajani (2006) have successfully applied traditional Dempster-Shafer theory (DST) to estimate the "risk" of contaminant intrusion in a water distribution network based on limited uncertain information. However, the method used for generating basic probability assignment (BPA) was not very flexible, and did not handle and process uncertain information effectively. In this paper, a more pragmatic method is proposed that utilizes "soft" computing flexibility to generate BPAs from uncertain information. This paper compares these two methods through numerical examples, and demonstrates the efficiency and effectiveness of modified method. © 2010 Elsevier Ltd. All rights reserved.


Deng Y.,Southwest University | Sadiq R.,University of British Columbia | Jiang W.,Northwestern Polytechnical University | Tesfamariam S.,University of British Columbia
Expert Systems with Applications | Year: 2011

Performing risk analysis can be a challenging task for complex systems due to lack of data and insufficient understanding of the failure mechanisms. A semi quantitative approach that can utilize imprecise information, uncertain data and domain experts' knowledge can be an effective way to perform risk analysis for complex systems. Though the definition of risk varies considerably across disciplines, it is a well accepted notion to use a composition of likelihood of system failure and the associated consequences (severity of loss). A complex system consists of various components, where these two elements of risk for each component can be linguistically described by the domain experts. The proposed linguistic approach is based on fuzzy set theory and Dempster-Shafer theory of evidence, where the later has been used to combine the risk of components to determine the system risk. The proposed risk analysis approach is demonstrated through a numerical example. © 2011 Elsevier Ltd. All rights reserved.


Liu D.,Northwestern Polytechnical University | Li J.,Shanxi University
Information Processing Letters | Year: 2010

Embedding of paths have attracted much attention in the parallel processing. Many-tomany communication is one of the most central issues in various interconnection networks. In this paper, we investigate the problem of many-to-many unpaired n-disjoint path covers in the n-dimensional hypercube Qn and obtain the following result. For any two sets S and T of n vertices in different parts, Qn has many-to-many unpaired n-disjoint (S, T )- path covers except the case that there exists a vertex v such that NQn (v) = S and v / ∈ T or NQn (v) = T and v / ∈ S. © 2010 Elsevier B.V. All rights reserved.


Kong J.,Northwestern Polytechnical University | Wang M.,Northwestern Polytechnical University | Zou J.,University of Central Florida | An L.,University of Central Florida
ACS Applied Materials and Interfaces | Year: 2015

High-temperature stable siliconborocarbonitride (SiBCN) ceramics produced from single-source preceramic polymers have received increased attention in the last two decades. In this contribution, soluble and meltable polyborosilazanes with hyperbranched topology (hb-PBSZ) were synthesized via a convenient solvent-free, catalyst-free and one-pot A2 + B6 strategy, an aminolysis reaction of the A2 monomer of dichloromethylsilane and the B6 monomer of tris(dichloromethylsilylethyl)borane in the presence of hexamethyldisilazane. The amine transition reaction between the intermediates of dichlorotetramethyldisilazane and tri(trimethylsilylmethylchlorosilylethyl)borane led to the formation of dendritic units of aminedialkylborons rather than trialkylborons. The cross-linked hb-PBSZ precursors exhibited a ceramic yield higher 80%. The resultant SiBCN ceramics with a boron atomic composition of 6.0-8.5% and a representative formula of Si1B0.19C1.21N0.39O0.08 showed high-temperature stability and retained their amorphous structure up to 1600 °C. These hyperbranched polyborosilazanes with soluble and meltable characteristics provide a new perspective for the design of preceramic polymers possessing advantages for high-temperature stable polymer-derived ceramics with complex structures/shapes. © 2015 American Chemical Society.


Deng Y.,Northwestern Polytechnical University | Liu Y.,Southwest University | Zhou D.,Northwestern Polytechnical University
Mathematical Problems in Engineering | Year: 2015

A new initial population strategy has been developed to improve the genetic algorithm for solving the well-known combinatorial optimization problem, traveling salesman problem. Based on the k-means algorithm, we propose a strategy to restructure the traveling route by reconnecting each cluster. The clusters, which randomly disconnect a link to connect its neighbors, have been ranked in advance according to the distance among cluster centers, so that the initial population can be composed of the random traveling routes. This process is k-means initial population strategy. To test the performance of our strategy, a series of experiments on 14 different TSP examples selected from TSPLIB have been carried out. The results show that KIP can decrease best error value of random initial population strategy and greedy initial population strategy with the ratio of approximately between 29.15% and 37.87%, average error value between 25.16% and 34.39% in the same running time. © 2015 Yong Deng et al.


Chen Z.,China University of Mining and Technology | Chen Z.,Northwestern Polytechnical University | Liu F.,Northwestern Polytechnical University | Yang X.Q.,China University of Mining and Technology | Shen C.J.,China University of Mining and Technology
Acta Materialia | Year: 2012

The inhibition of grain growth by solute segregation in nanoscale materials has often been described using kinetic models (e.g. Acta Mater 1999;47:2143) or thermokinetic models (e.g. Acta Mater 2009;57:1466), in which constant activation energy and a negligible effect of solute segregation on activation energy were assumed. In this paper, an intact thermokinetic model for nanoscale grain growth was developed by incorporating mixed effects of activation energy and grain boundary (GB) energy. By application of the model to nanoscale grain growth in Ni-P, Pb-Zr, Fe-Zr and Ru-Al alloys, the validity of the present model was confirmed, in combination with verification of the initial condition of GB segregation. On this basis, the increase of activation energy and the decrease of GB energy are interrelated and thus the kinetics and the thermodynamics of normal grain growth are linked. Based on a comparison of three characteristic velocities V TK, V GE and V AE of GB derived from the present thermokinetic model, grain boundary energy model and activation energy model, a mechanism of controlled nanoscale grain growth was proposed, which indicated a transition from a kinetic-controlled to a thermodynamic- controlled process. © 2012 Acta Materialia Inc. Published by Elsevier Ltd.


Yue T.M.,Hong Kong Polytechnic University | Li T.,Kayex An SPX Brand | Lin X.,Northwestern Polytechnical University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2010

A multilayer coating of Ni/Cu/Al was fabricated on magnesium substrates using laser cladding. The solidification behavior and the phase evolution of the compositionally graded coating were studied. The results of the X-ray diffraction (XRD) analysis together with the metallographic study showed that a series of phase evolutions had occurred along the gradient (Mg) → (Mg) + Al 12Mg 17 → (Mg) + Q + λ 2 → λ 1 → λ 1 + γ 1 → γ 1 + (Cu) + λ 1 → (Cu) + λ 1 → (Cu) → (CuNi) → (Ni). The rapid solidification condition had suppressed the invariant reactions that existed in the ternary Mg-Al-Cu alloy system. As a result, many of the predicted Al-rich brittle intermetallic compounds, which are detrimental to the performance of the coating, were not produced. The solidification path during the laser cladding of the Al and Cu layers was determined and the various phases, as predicted by the corresponding phase diagram, agreed well with the experimental results. Finally, the primary arm spacing (PAS) and the solidification morphology of the dendrites in the Cu and Ni layers were analyzed in relation to the solidification conditions. © 2009 The Minerals, Metals & Materials Society and ASM International.


Luo Y.,Northwestern Polytechnical University | Li A.,University of Reims | Kang Z.,Dalian University of Technology
Engineering Structures | Year: 2011

It is meaningful to account for various uncertainties in the optimization design of the adhesive bonded steel-concrete composite beam. Based on the definition of the mixed reliability index for structural safety evaluation with probabilistic and non-probabilistic uncertainties, the reliability-based optimization incorporating such mixed reliability constraints are mathematically formulated as a nested problem. The performance measure approach is employed to improve the convergence and the stability in solving the inner-loop. Moreover, the double-loop optimization problem is transformed into a series of approximate deterministic problems by incorporating the sequential approximate programming and the iteration scheme, which greatly reduces the burdensome computation workloads in seeking the optimal design. The validity of the proposed formulation as well as the efficiency of the presented numerical techniques is demonstrated by a mathematical example. Finally, reliability-based optimization designs of a single span adhesive bonded steel-concrete composite beam with different loading cases are achieved through integrating the present systematic method, the finite element analysis and the optimization package. © 2011 Elsevier Ltd.


Li W.-Y.,Northwestern Polytechnical University | Yin S.,Dalian University of Technology | Wang X.-F.,Dalian University of Technology
Applied Surface Science | Year: 2010

In this study, a systematic examination of the oblique impacting of copper particles in cold spraying was conducted by using the smoothed particle hydrodynamics (SPH) method compared to the Lagrangian method. 3D models were employed owing to the asymmetric characteristic of the oblique impacting. It is found that in the oblique impact, the additional tangential component of particle velocity along the substrate surface could create a tensile force and decrease the total contact area and bonding strength between the particle and the substrate. The simulation results compare fairly well to the experiment results. Meanwhile, the asymmetric deformation can result in the focus of the shear friction on a small contact zone at one side, which may rise the interfacial temperature and thus facilitate the occurrence of the possible shear instability. Therefore, there probably exists an angle range, where the deposition efficiency may be promoted rather than the normal angle. Moreover, the particle deformation behavior simulated by the SPH method is well comparable to that simulated by the Lagrangian method and the experimental results, which indicates the applicability of the SPH method for simulating the impact process in cold spraying besides the previously used Arbitrary Lagrangian Eulerian (ALE) method. © 2010 Elsevier B.V. All rights reserved.


Luo Y.,Northwestern Polytechnical University | Kang Z.,Dalian University of Technology
Structural and Multidisciplinary Optimization | Year: 2013

This paper aims to develop a method that can automatically generate the optimal layout of reinforced concrete structures by incorporating concrete strength constraints into the two-material topology optimization formulation. The Drucker-Prager yield criterion is applied to predict the failure behavior of concrete. By using the power-law interpolation, the proposed optimization model is stated as a minimum compliance problem under the yield stress constraints on concrete elements and the material volume constraint of steel. The ε-relaxation technique is employed to prevent the stress singularity. A hybrid constraint-reduction strategy, in conjunction with the adjoint-variable sensitivity information, is integrated into a gradient-based optimization algorithm to overcome the numerical difficulties that arise from large-scale constraints. It can be concluded from numerical investigations that the proposed model is suitable for obtaining a reasonable layout which makes the best uses of the compressive strength of concrete and the tensile strength of steel. Numerical results also reveal that the hybrid constraint-reduction strategy is effective in solving the topology optimization problems involving a large number of constraints. © 2012 Springer-Verlag.


Li J.,Shanxi University | Wang S.,Shanxi University | Liu D.,Northwestern Polytechnical University | Lin S.,Shanxi University
Information Sciences | Year: 2011

The k-ary n-cube has been one of the most popular interconnection networks for massively parallel systems. In this paper, we investigate the edge-bipancyclicity of k-ary n-cubes with faulty nodes and edges. It is proved that every healthy edge of the faulty k-ary n-cube with fv faulty nodes and fe faulty edges lies in a fault-free cycle of every even length from 4 to kn - 2fv (resp. kn - f v) if k ≥ 4 is even (resp. k ≥ 3 is odd) and fv + fe ≤ 2n - 3. The results are optimal with respect to the number of node and edge faults tolerated. © 2011 Elsevier Inc. All rights reserved.


Xue H.Q.,Northwestern Polytechnical University | Bathias C.,Paris West University Nanterre La Défense
Engineering Fracture Mechanics | Year: 2010

Torsion fatigue tests have been conducted at 20kHz ultrasonic fatigue testing systems, and compared to the torsion fatigue data generated on 35Hz conventional fatigue test machine to determine if there are any frequency effects, for steels including D38MSV5S steel and 100C6 steel. Results indicated that the S-N curves exhibit decrease in fatigue strength beyond 107 cycles. The initiation in the Gigacycle regime is related to defects sometimes located beneath the surface which shows a competition between the maximum shear at the surface and the stress concentration under the surface, even in torsion. © 2010 Elsevier Ltd.


Yao Y.,Northwestern Polytechnical University | Rao L.,General Motors | Liu X.,McGill University
IEEE Transactions on Vehicular Technology | Year: 2013

Vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications are gaining increasing importance in vehicular applications. Dedicated short-range communication (DSRC) is a fundamental set of short-to-medium-range communication channels and a set of protocols and standards that are specifically designed for V2V and V2I communications. IEEE 802.11p is a protocol that has been standardized as the medium access control (MAC) layer of the DSRC standard. Due to the highly dynamic topology and low delay constraints in vehicular ad hoc networks (VANETs), direct (or one-hop) broadcast on the control channel (CCH) is an effective approach to inform the neighborhood of safety-related messages. The 802.11p enhanced distributed channel access (EDCA) mechanism allows four access categories (ACs) in a station for applications with different priorities according to their criticalities for the vehicle's safety. This paper focuses on the analysis of the 802.11p safety-critical broadcast on the CCH in a VANET environment and improves the existing work by taking several aspects into design consideration. Extensive performance evaluations based on the NS-2 simulator help to validate the accuracy of the proposed model and analyze the capabilities and limitations of the standard 802.11p broadcast on the CCH. © 2013 IEEE.


Huang S.-D.,Chinese University of Hong Kong | Wang F.,Chinese University of Hong Kong | Xi H.-D.,Northwestern Polytechnical University | Xia K.-Q.,Chinese University of Hong Kong
Physical Review Letters | Year: 2015

We report the first experimental study of the influences of the thermal boundary condition on turbulent thermal convection. Two configurations were examined: one had a constant heat flux at the bottom boundary and a constant temperature at the top (CFCT cell); the other had constant temperatures at both boundaries (CTCT cell). In addition to producing different temperature stability in the boundary layers, the differences in the boundary condition lead to rather unexpected changes in the flow dynamics. It is found that, surprisingly, reversals of the large-scale circulation occur more frequently in the CTCT cell than in the CFCT cell, despite the fact that in the former its flow strength is on average 9% larger than that in the latter. Our results not only show which aspects of the thermal boundary condition are important in thermal turbulence, but also reveal that, counterintuitively, the stability of the flow is not directly coupled to its strength. © 2015 American Physical Society.


Fan J.,Northwestern Polytechnical University | Wilson M.C.T.,University of Leeds | Kapur N.,University of Leeds
Journal of Colloid and Interface Science | Year: 2011

The motion of droplets on surfaces is crucial to the performance of a wide range of processes; this study examines the initiation of droplet motion through a shearing mechanism generated here by a controlled air flow. Systematic experiments are carried out for a range of fluids and well defined surfaces. A model is postulated that balances surface tension forces at the contact line and the drag force due to the air motion. Experiments reveal that the critical velocity at which droplet motion is initiated depends on the contact angle and the droplet size. Visualizations highlight three modes of motion: (I) the droplet retains a footprint similar to that at the point of motion; (II) a tail exists at the rear of the droplet; (III) a trail remains behind the droplet (that can shed smaller droplets). The predictions of droplet initiation velocity are good for type I motion, in accordance with the assumptions inherent within the model. This model confirms the dominant physics associated with the initiation of droplet motion and provides a useful predictive expression. © 2011 Elsevier Inc.


Liotta L.F.,CNR Institute of Nanostructured Materials | Wu H.,CNR Institute of Nanostructured Materials | Wu H.,Northwestern Polytechnical University | Pantaleo G.,CNR Institute of Nanostructured Materials | Venezia A.M.,CNR Institute of Nanostructured Materials
Catalysis Science and Technology | Year: 2013

Among the possible substitutes for noble metals, cobalt-based catalysts represent promising alternative systems. In recent years, many articles have been devoted to the synthesis, characterization and reactivity of cobalt oxides. This article provides a comprehensive review of the state-of-the-art activities that concentrate on the synthesis, structural properties and catalytic applications of Co3O4 nanocrystals and Co 3O4-MOx binary oxides in CO, CH4 and VOC oxidation at low temperatures. It begins with the major synthetic approaches and basic properties of Co3O4 nanocrystals and Co3O4-MOx binary oxides and subsequently highlights the relationship between the peculiar structure of Co 3O4 nanocrystals and their catalytic activity (or between the redox properties of Co3O4-MOx binary oxides and their catalytic activity). Finally, the active sites and key factors determining the catalytic oxidation over Co3O4 and Co 3O4-MOx are discussed. The perspective with respect to future research on Co3O4 nanocrystals and Co3O4-MOx binary oxides is considered. This journal is © The Royal Society of Chemistry.


Niu W.-N.,Northwestern Polytechnical University | Yadav P.K.,University of Michigan | Adamec J.,University of Nebraska - Lincoln | Banerjee R.,University of Michigan
Antioxidants and Redox Signaling | Year: 2015

Aims: Cystathionine β-synthase (CBS) catalyzes the first and rate-limiting step in the two-step trans-sulfuration pathway that converts homocysteine to cysteine. It is also one of three major enzymes responsible for the biogenesis of H2S, a signaling molecule. We have previously demonstrated that CBS is activated in cells challenged by oxidative stress, but the underlying molecular mechanism of this regulation has remained unclear. Results: Here, we demonstrate that S-glutathionylation of CBS enhances its activity ∼2-fold in vitro. Loss of this post-translational modification in the presence of dithiothreitol results in reversal to basal activity. Cys346 was identified as the site for S-glutathionylation by a combination of mass spectrometric, mutagenesis, and activity analyses. To test the physiological relevance of S-glutathionylation-dependent regulation of CBS, HEK293 cells were oxidatively challenged with peroxide, which is known to enhance the trans-sulfuration flux. Under these conditions, CBS glutathionylation levels increased and were correlated with a ∼3-fold increase in CBS activity. Innovation: Collectively, our results reveal a novel post-translational modification of CBS, that is, glutathionylation, which functions as an allosteric activator under oxidative stress conditions permitting enhanced synthesis of both cysteine and H2S. Conclusions: Our study elucidates a molecular mechanism for increased cysteine and therefore glutathione, synthesis via glutathionylation of CBS. They also demonstrate the potential for increased H2S production under oxidative stress conditions, particularly in tissues where CBS is a major source of H2S. Antioxid. Redox Signal. 22, 350-361. © Copyright 2015, Mary Ann Liebert, Inc. 2015.


Yang H.,CAS Fujian Institute of Research on the Structure of Matter | Yang H.,Northwestern Polytechnical University | Wang F.,CAS Fujian Institute of Research on the Structure of Matter | Kang Y.,CAS Fujian Institute of Research on the Structure of Matter | And 2 more authors.
Chemical Communications | Year: 2012

Corner-sharing assembly of dodecahedral cavities with both paddle-wheel [M 2(CO 2) 4] units and trimeric [M 3(μ 3-OH)(CO 2) 6] units leads to two isomorphous chiral microporous metal-organic frameworks, where the heterometallic framework has high surface area and excellent CO 2/N 2 adsorption selectivity. © 2012 The Royal Society of Chemistry.


Zhao Y.-Q.,Northwestern Polytechnical University | Zhang L.,Hong Kong Polytechnic University | Kong S.G.,Temple University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

This paper proposes a band-subset-based clustering and fusion technique to improve the classification performance in hyperspectral imagery. The proposed method can account for the varying data qualities and discrimination capabilities across spectral bands, and utilize the spectral and spatial information simultaneously. First, the hyperspectral data cube is partitioned into several nearly uncorrelated subsets, and an eigenvalue-based approach is proposed to evaluate the confidence of each subset. Then, a nonparametric technique is used to extract the arbitrarily-shaped clusters in spatial-spectral domain. Each cluster offers a reference spectral, based on which a pseudosupervised hyperspectral classification scheme is developed by using evidence theory to fuse the information provided by each subset. The experimental results on real Hyperspectral Digital Imagery Collection Experiment (HYDICE) demonstrate that the proposed pseudosupervised classification scheme can achieve higher accuracy than the spatially constrained fuzzy c-means clustering method. It can achieve nearly the same accuracy as the supervised K-Nearest Neighbor (KNN) classifier but is more robust to noise. © 2006 IEEE.


Liang C.,Northwest University, China | Zhang Y.,Northwest University, China | Song Q.,Northwestern Polytechnical University
Journal of Machine Learning Research | Year: 2010

Current research on data stream classification mainly focuses on certain data, in which precise and definite value is usually assumed. However, data with uncertainty is quite natural in real-world application due to various causes, including imprecise measurement, repeated sampling and network errors. In this paper, we focus on uncertain data stream classification. Based on CVFDT and DTU, we propose our UCVFDT (Uncertainty-handling and Concept-adapting Very Fast Decision Tree) algorithm, which not only maintains the ability of CVFDT to cope with concept drift with high speed, but also adds the ability to handle data with uncertain attribute. Experimental study shows that the proposed UCVFDT algorithm is efficient in classifying dynamic data stream with uncertain numerical attribute and it is computationally efficient. © 2010 Chunquan Liang, Yang Zhang, and Qun Song.


Samanta S.,University of Toronto | Qin C.,Northwestern Polytechnical University | Lough A.J.,University of Toronto | Woolley G.A.,University of Toronto
Angewandte Chemie - International Edition | Year: 2012

It goes both ways: A thiol-reactive cross-linker based on a bridged azobenzene derivative permits photoreversible control of peptide conformation on irradiation with violet (407a nm) and green (500-550a nm) light (see picture) through isomerization of the cross-linker. The large separation of the absorbance bands of the cis (yellow) and trans (red) isomers enables complete bidirectional photoswitching. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Wei P.,Northwestern Polytechnical University | Lu Z.,Northwestern Polytechnical University | Hao W.,Northwestern Polytechnical University | Feng J.,AVIC Aviation Industry Corporation of China | Wang B.,AVIC Aviation Industry Corporation of China
Computer Physics Communications | Year: 2012

An important problem in structure reliability analysis is how to reduce the failure probability. In this work, we introduce a main and total effect indices framework of global reliability sensitivity. By decreasing the uncertainty of input variables with high main effect indices, the most reduction of failure probability can be obtained. By decreasing the uncertainty of the input variables with small total effect indices (close to zero), the failure probability will not be reduced significantly. The efficient sampling methods for evaluating the main and total effect indices are presented. For the problem with large failure probability, a single-loop Monte Carlo simulation (MCS) is derived for computing these sensitivity indices. For the problem with small failure probability, the single-loop sampling methods combined with the importance sampling procedure (IS) and the truncated importance sampling procedure (TIS) respectively are derived for improving the calculation efficiency. Two numerical examples and one engineering example are introduced for demonstrating the efficiency and precision of the calculation methods and illustrating the engineering significance of the global reliability sensitivity indices. © 2012 Elsevier B.V. All rights reserved.


Li X.,Northwest University, China | Zhang L.,Northwestern Polytechnical University | Yin X.,Northwestern Polytechnical University
Journal of the European Ceramic Society | Year: 2013

Pyrolytic carbon-Si3N4 ceramics (PyC-Si3N4) with gradient PyC distribution (Gradient-PyC-Si3N4) is fabricated by directional oxidation. After directional oxidation for 1.0h, the electromagnetic absorptivity of Gradient-PyC-Si3N4 increases significantly from 0.8 to 50.1% with the obvious reduction of electromagnetic reflectivity from 99.2 to 43.8%. The Gradient-PyC-Si3N4 is a good electromagnetic absorbing material meeting the requirement of self-concealing technology. © 2012 Elsevier Ltd.


Li T.,Northwestern Polytechnical University | Li T.,London South Bank University | Sun S.,Northwestern Polytechnical University | Sattar T.P.,London South Bank University
Electronics Letters | Year: 2013

An adaptive resampling method is provided. It determines the number of particles to resample so that the Kullback-Leibler distance (KLD) between the distribution of particles before resampling and after resampling does not exceed a pre-specified error bound. The basis of the method is the same as Fox's KLD-sampling but implemented differently. The KLD-sampling assumes that samples are coming from the true posterior distribution and ignores any mismatch between the true and the proposal distribution. In contrast, the KLD measure is incorporated into the resampling in which the distribution of interest is just the posterior distribution. That is to say, for sample size adjustment, it is more theoretically rigorous and practically flexible to measure the fit of the distribution represented by weighted particles based on KLD during resampling than in sampling. Simulations of target tracking demonstrate the efficiency of the method. © The Institution of Engineering and Technology 2013.


Li X.,Northwest University, China | Zhang L.,Northwestern Polytechnical University | Yin X.,Northwestern Polytechnical University
Scripta Materialia | Year: 2012

The mechanical properties of porous Si3N4 ceramic are noticeably improved after chemical vapor deposition (CVD) of Si 3N4, BN and B4C coatings. The dielectric constant and loss of porous Si3N4 ceramic remain almost unchanged after CVD of BN, increase slightly after CVD of Si3N 4, but increase greatly after CVD of B4C. Overall, CVD of Si3N4 performs better than CVD of BN and B4C in improving the mechanical properties and keeping the low dielectric constant and loss of porous Si3N4 ceramic. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Li X.,Northwest University, China | Zhang L.,Northwestern Polytechnical University | Yin X.,Northwestern Polytechnical University
Journal of the American Ceramic Society | Year: 2012

Pyrolytic carbon-silicon nitride ceramics with dense silicon nitride coating (PyC-Si 3N 4/Si 3N 4) were fabricated by chemical vapor infiltration of PyC into porous Si 3N 4 ceramics combined with chemical vapor deposition of Si 3N 4 at their surface. The electromagnetic shielding effectiveness (SE) of PyC-Si 3N 4/Si 3N 4 increases with the increase of PyC content and specimen thickness. When the content of PyC is 11.7 vol% and the thickness of specimen is 2.8 mm, the mean total SE of PyC-Si 3N 4/Si 3N 4 reaches 43.2 dB in the frequency range of 8.2-12.4 GHz. Due to the excellent sealing effect of dense Si 3N 4 coating, the mean total SE of PyC-Si 3N 4/Si 3N 4 remains unchanged even after oxidation at 1100°C for 10 h in air. © 2011 The American Ceramic Society.


Li T.,London South Bank University | Li T.,Northwestern Polytechnical University | Sattar T.P.,London South Bank University | Sun S.,Northwestern Polytechnical University
Signal Processing | Year: 2012

A novel resampling algorithm (called Deterministic Resampling) is proposed, which avoids uncensored discarding of low weighted particles thereby avoiding sample impoverishment. The diversity of particles is maintained by deterministically sampling support particles to improve the residual resampling. A proof is given that our approach can be strictly unbiased and maintains the original state density distribution. Additionally, it is practically simple to implement in low dimensional state space applications. The core idea behind our approach is that it is important to (re)sample based on both the weight of particles and their state values, especially when the sample size is small. Our approach, verified by simulations, indicates that estimation accuracy is better than traditional methods with an affordable computation burden. © 2011 Elsevier B.V. All rights reserved.


Gan X.,Columbia University | Gan X.,Northwestern Polytechnical University | Mak K.F.,Columbia University | Gao Y.,Columbia University | And 5 more authors.
Nano Letters | Year: 2012

We demonstrate a large enhancement in the interaction of light with graphene through coupling with localized modes in a photonic crystal nanocavity. Spectroscopic studies show that a single atomic layer of graphene reduces the cavity reflection by more than a factor of one hundred, while also sharply reducing the cavity quality factor. The strong interaction allows for cavity-enhanced Raman spectroscopy on subwavelength regions of a graphene sample. A coupled-mode theory model matches experimental observations and indicates significantly increased light absorption in the graphene layer. The coupled graphene-cavity system also enables precise measurements of graphene's complex refractive index. © 2012 American Chemical Society.


Wang N.,Northwestern Polytechnical University | Kalay Y.E.,Middle East Technical University | Trivedi R.,Iowa State University
Acta Materialia | Year: 2011

A systematic experimental study is carried out to investigate microstructure selection over a very wide range of undercooling at the interface in the Al-Sm system by using a combination of the Bridgman, laser and melt spinning techniques, which give increasing interface undercooling. Eutectic microstructure forms at low undercooling, while metallic glass forms at very large undercooling. Experiments are designed to obtain a sharp transition from the eutectic to glass during the growth of eutectic as the interface undercooling increases with growth. The eutectic spacing at the transition is characterized, and the results are analyzed by using a model of eutectic growth that incorporates non-equilibrium effects at the interface. It is shown that a very large undercooling at the interface, required for glass formation, is obtained due to the combined effects of the sharp decrease in the diffusion coefficient, or the sharp increase in viscosity of the liquid, with undercooling in this system and the large undercooling required for the attachment kinetics at the compound-liquid interface in the eutectic structure. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Aguero J.C.,University of Newcastle | Tang W.,Northwestern Polytechnical University | Yuz J.I.,Federico Santa María Technical University | Delgado R.,University of Newcastle | Goodwin G.C.,University of Newcastle
Automatica | Year: 2012

In this paper we obtain the maximum likelihood estimate of the parameters of discrete-time linear models by using a dual time-frequency domain approach. We propose a formulation that considers a (reduced-rank) linear transformation of the available data. Such a transformation may correspond to different options: selection of time-domain data, transformation to the frequency domain, or selection of frequency-domain data obtained from time-domain samples. We use the proposed approach to identify multivariate systems represented in state-space form by using the Expectation-Maximisation algorithm. We illustrate the benefits of the approach via numerical examples. © 2012 Elsevier Ltd. All rights reserved.


Gao T.,Northwestern Polytechnical University | Gao T.,University of Liège | Zhang W.,Northwestern Polytechnical University | Duysinx P.,University of Liège
International Journal for Numerical Methods in Engineering | Year: 2012

The discrete optimal orientation design of the composite laminate can be treated as a material selection problem dealt with by using the concept of continuous topology optimization method. In this work, a new bi-value coding parameterization (BCP) scheme of closed form is proposed to this aim. The basic idea of the BCP scheme is to 'code' each material phase using integer values of +1 and -1 so that each available material phase has one unique 'code' consisting of +1 and/or -1 assigned to design variables. Theoretical and numerical comparisons between the proposed BCP scheme and existing schemes show that the BCP has the advantage of an evident reduction of the number of design variables in logarithmic form. The benefit is particularly remarkable when the number of candidate materials becomes important in large-scale problems. Numerical tests with up to 36 candidate material orientations are illustrated for the first time to indicate the reliability and efficiency of the BCP scheme in solving this kind of problem. It proves that the BCP is an interesting and valuable scheme to achieve the optimal orientations for large-scale design problems. Besides, a four-layer laminate example is tested to demonstrate that the proposed BCP scheme can easily be extended to multilayer problems. © 2012 John Wiley & Sons, Ltd.


Xu J.,Northwestern Polytechnical University | Xu J.,Nanjing University of Science and Technology
IEEE Microwave and Wireless Components Letters | Year: 2015

This letter presents a novel quasi-elliptic response bandpass filter (BPF) with 3 dB fractional bandwidth of 39.8% for 2.4 GHz WLAN application. Four resonant modes from two stepped-impedance stub loaded shorted stepped-impedance resonators (SISLSSIRs) and one dual-mode shorted stub loaded stepped-impedance resonator (SSLSIR) can constitute an asynchronously tuned coupled-resonator circuit which support a wideband performance. Four transmission zeros (TZs), i.e., one TZ due to the mixed electric and magnetic coupling, one TZ due to the harmonic effects, and another two TZs owing to the cross-couplings, are realized on both sides of the passband, resulting in its quasi-elliptic response performance. The radial stubs and high-impedance open stubs are loaded at the middle position of SISLSSIRs to improve the in-band return loss of BPF. The fabricated filter has a compact size of 0.22λg × 0.22λg and wide upper stopband from 2.62 to 7.69 GHz. Good agreement is shown between the simulated and measured results. © 2015 IEEE.


Li P.,Northwestern Polytechnical University | Yang R.,Northwestern Polytechnical University | Zheng Y.,Northwestern Polytechnical University | Qu P.,Shaanxi Applied Physics Chemistry Research Institute | Chen L.,Northwestern Polytechnical University
Carbon | Year: 2015

A series of specific solvent-free nanofluids with ionically tethered polyether amine terminated polymers were successfully prepared and evaluated based on multiwalled carbon nanotubes (MWCNTs). The newly synthesized sorbents exhibited enhanced carbon dioxide (CO2) capture capacities compared to their corresponding polyether amine and pristine MWCNTs. The effects of polyether amine canopy structure such as amine types, Molecular weight (Mw), Ethylene Oxide/Propylene Oxide (EO/PO), viscosity and melting point on CO2 capture capacities were investigated. It had been demonstrated that the sorbents impregnated with more unprotonated amine groups and higher Mw or EO/PO showed larger CO2 capture capacities and good stabilities over multiple adsorption-desorption cycles. Last but not least, we also demonstrated that the lower melting point and viscosity were beneficial for the CO2 uptake. © 2015 Elsevier Ltd.


Yang Y.,Northwestern Polytechnical University | Qi S.,Northwestern Polytechnical University | Wang J.,Ningxia University
Journal of Alloys and Compounds | Year: 2012

Nanocomposites PPy/NanoG and PPy/Ni/NanoG were prepared via in situ polymerization of pyrrole in the presence of NanoG and nickel-coated graphite nanosheet (Ni/NanoG), respectively. The morphologies and nanostructures of NanoG, Ni/NanoG, PPy, PPy/NanoG and PPy/Ni/NanoG were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Fourier transmission infrared (FTIR) and X-ray diffraction analysis (XRD). Results show that most of PPy chains disperse on NanoG and Ni/NanoG's surfaces for the high aspect ratio (300-500) of NanoG and Ni/NanoG. From the thermogravimetric analysis (TG) it can be seen that the introduction of Ni and NanoG leads the composites PPy/NanoG and PPy/Ni/NanoG to exhibit a better thermal stability than pure PPy. According to the four-point-probe test, the conductivities of the final PPy/NanoG and PPy/Ni/NanoG composites are dramatically increased compared to pure PPy. Measurement of electromagnetic parameters shows that the reflection loss (R) of PPy/Ni/NanoG is below -19 dB at the X band (8.2-12.4 GHz) and the minimum loss value is -23.46 dB at 9.88 GHz. The reflection loss of PPy/NanoG is below -10 dB at 8.2-12.4 GHz and the minimum loss value is -13.44 dB at 10.28 GHz. The microwave absorbing properties of PPy/NanoG and PPy/Ni/NanoG are superior to those of PPy. © 2011 Elsevier B.V. All rights reserved.


Gong X.,Northwestern Polytechnical University | Bansmer S.,TU Braunschweig
Optics Express | Year: 2015

A general approach based on mid-infrared (MIR) laser scanning is proposed to measure the 3-D ice shape no matter whether the ice is composed of clear ice, rime ice, mixed ice, or even supercooled water droplets or films. This is possible because MIR radiation penetrates ice and water only within a depth of less than 10 micrometers. First, an MIR laser point scanning technique is implemented and verified on transparent glass and clear ice. Then, to improve efficiency, an MIR laser line scanning method is developed and validated on different models. At last, several sequential MIR laser line scans are applied to trace the 3-D shape evolution of the continuous ice accretion on an airfoil in an icing wind tunnel. The ice growth process can be well observed in the results. The MIR scan shows a good agreement with the traditional visible laser scan on a plastic replication of the final ice shape made by the mold and casting method. ©2015 Optical Society of America.


Liu T.,Northwestern Polytechnical University | Tian W.,Northwestern Polytechnical University | Zhu Y.,Tongji University | Bai Y.,Northwestern Polytechnical University | And 2 more authors.
Polymer Chemistry | Year: 2014

It is a theoretical and technical challenge to construct well-defined nanostructures such as vesicles from fully hydrophilic homopolymers in pure water. In this paper, we incorporate one terminal alkynyl group into a fully hydrophilic linear or non-linear homopolymer to drive its unusual self-assembly in aqueous solution to form multicompartment vesicles, spherical compound micelles, flower-like complex particles, etc., which have been confirmed by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic/static light scattering (DLS/SLS) and drug encapsulation experiments. The formation of poly(N-isopropyl acrylamide) (NIPAM) and poly[oligo(ethylene glycol) methacrylate] (POEGMA475) self-assemblies is mainly determined by the terminal alkynyl group itself (typically 1-3 wt%) while it is independent of other factors such as traditional hydrophobic-hydrophilic balance. Moreover, upon increasing the chain length of PNIPAM homopolymers, multicompartment vesicles, spherical micelles, and large flower-like complex particles can be obtained during the self-assembly process. In contrast, smaller micelles were formed when the kind of terminal alkynyl group attached to the PNIPAM chain was changed from a propargyl isobutyrate group to a (di)propargyl 2-methylpropionamide group. Particularly, a long chain hyperbranched structure with lots of terminal alkynyl groups induces the formation of vesicles. Also, the encapsulation experiment of doxorubicin hydrochloride was employed to further distinguish vesicular and micellar nanostructures. Additionally, the terminal alkynyl group-driven self-assembly has been applied to hydrophilic POEGMA475 homopolymers to afford similar nanostructures to PNIPAM homopolymers such as multicompartment vesicles and spherical compound micelles. Our study has opened up a new way to prepare hydrophilic homopolymer self-assemblies with tunable morphology. This journal is © the Partner Organisations 2014.


Dai Y.,Northwestern Polytechnical University | Dai Y.,Australian National University | Li H.,NICTA | He M.,Northwestern Polytechnical University
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

The Sturm-Triggs type iteration is a classic approach for solving the projective structure-from-motion (SfM) factorization problem, which iteratively solves the projective depths, scene structure, and camera motions in an alternated fashion. Like many other iterative algorithms, the Sturm-Triggs iteration suffers from common drawbacks, such as requiring a good initialization, the iteration may not converge or may only converge to a local minimum, and so on. In this paper, we formulate the projective SfM problem as a novel and original element-wise factorization (i.e., Hadamard factorization) problem, as opposed to the conventional matrix factorization. Thanks to this formulation, we are able to solve the projective depths, structure, and camera motions simultaneously by convex optimization. To address the scalability issue, we adopt a continuation-based algorithm. Our method is a global method, in the sense that it is guaranteed to obtain a globally optimal solution up to relaxation gap. Another advantage is that our method can handle challenging real-world situations such as missing data and outliers quite easily, and all in a natural and unified manner. Extensive experiments on both synthetic and real images show comparable results compared with the state-of-the-art methods. © 1979-2012 IEEE.


Guo S.,City University of Hong Kong | Hu Q.,Northwestern Polytechnical University | Ng C.,Hong Kong Polytechnic University | Liu C.T.,City University of Hong Kong
Intermetallics | Year: 2013

Metastable solid solutions can form preferably over intermetallic compounds, in cast high-entropy alloys or multi-component alloys with equi- or nearly equi-atomic compositions, due to the entropy contribution at elevated temperatures. Meanwhile, the high mixing entropy also favors the amorphous phase formation. The phase selection between solid solutions and the amorphous phase upon alloying in high-entropy alloys is intriguing. A two-parameter physical scheme, utilizing the atomic size polydispersity and mixing enthalpy, is found to be capable of capturing this phase selection mechanism. © 2013 Elsevier Ltd. All rights reserved.


Wang K.,China Coal Research Institute | Xie H.,Northwestern Polytechnical University
2011 International Conference on Multimedia Technology, ICMT 2011 | Year: 2011

A new global minimization active contour model is proposed, which has three advantages compared to other active contours. Firstly, the energy function of proposed model is convex, so the proposed model is not sensitive to the initial condition because of having no existence of local minimum in the active contour energy; Secondly by combining the gray levels of pixels and texture information of an image, this method can be used for segmentation of a texture image or a none-texture image. Finally, LBP (local binary pattern) is employed to extract texture features, so computation complexity of proposed model is low. The segmentation tests for synthetic and SAR texture images show that the proposed segmentation model is efficient, accurate, fast and robust. © 2011 IEEE.


Ning Y.,Northwestern Polytechnical University | Yao Z.,Northwestern Polytechnical University | Guo H.,Northwestern Polytechnical University | Fu M.W.,Hong Kong Polytechnic University
Journal of Alloys and Compounds | Year: 2014

The electron beam welding (EBW) of Nickel-base superalloys was conducted, and the cylindrical compression specimens were machined from the central part of the electron beam (EB) weldments. The hot deformation behavior of EB weldments was investigated at the temperature of 960-1140 C and the strain rate of 0.001-1.0 s-1. The apparent activation energy of deformation was calculated to be 400 kJ/mol, and the constitutive equation that describes the flow stress as a function of strain rate and deformation temperature was proposed for modeling of the hot deformation process of EB weldments. The processing map approach was adopted to investigate the deformation mechanisms during the hot plastic deformation and to optimize the processing parameters of EB weldments. It is found that the true strain has a significant effect on the efficiency of power dissipation (η). The η value in the safe processing domain (1140 C, 1.0 s-1) increases from 0.32 to 0.55. In the unsafe processing domain (1080 C, 0.001 s-1), however, the η value greatly decreases with the increase of strain. When the strain is 0.40, the efficiency of power dissipation becomes negative. The flow instability is predicted to occur since the instability parameter ξ(ε̇) becomes negative. The hot deformation of EB weldments can be carried out safely in the domain with the strain rate range of 0.1-1.0 s-1 and the temperature range of 960-1140 C. When the height reduction is about 50%, the optimum processing condition is (Topi: 1140 C, ε̇ opi: 1.0 s-1) with the peak efficiency of 0.55 for the processing of EB weldments. © 2013 Published by Elsevier B.V. All rights reserved.


Yue T.M.,Hong Kong Polytechnic University | Xie H.,Hong Kong Polytechnic University | Lin X.,Northwestern Polytechnical University | Yang H.O.,Northwestern Polytechnical University | Meng G.H.,Hong Kong Polytechnic University
Journal of Alloys and Compounds | Year: 2014

The AlCoCrCuFeNi high-entropy alloy (HEA) was fabricated on pure magnesium substrates by means of laser cladding using a direct blown powder method. The coating can be categorised into two layers, a top AlCoCrCuFeNi HEA layer and a lower composite layer that consists of some partially melted HEA powders in an Mg based matrix. A metallurgically bonded interface was obtained between the Mg substrate and the HEA coating, with epitaxial crystals formed at the melting boundary of the substrate. In the solidification of the HEA alloy, some Cu was rejected into the Mg melt, however, no serious dilution of the HEA composition occurred in the top layer of the coating. The phenomenon of Cu rejection was analysed based on Gibbs free energy. Moreover, the solidification behaviour of the HEA was studied using the Kurz-Giovanola-Trivedi and the Gaümann models with modifications for multi-component alloys. © 2013 Elsevier B.V. All rights reserved.


Gao W.,Northwestern Polytechnical University | Liu H.,Northwestern Polytechnical University | Gan B.,Northwestern Polytechnical University | Hu Y.,CNRS Hubert Curien Multi-disciplinary Institute
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

In this paper, we present the design and characteristics of a novel low-noise front-end readout application-specific integrated circuit dedicated to CdZnTe (CZT) detectors for a small animal PET imaging system. A low-noise readout method based on the charge integration and the delayed peak detection is proposed. An eight-channel front-end readout prototype chip is designed and implemented in a 0.35 μm CMOS process. The die size is 2.3 mm ×2.3 mm. The prototype chip is tested in different methods including electronic test, energy spectrum test and irradiation test. The input range of the ASIC is from 2000e- to 180,000e-, reflecting the energy of the gamma ray from 11.2 keV to 1 MeV. The gain of the readout channel is 65 mV/fC at the shaping time of 1 μs. The best test result of the equivalent noise charge (ENC) is 58.9 e- at zero farad plus 5.4 e- per picofarad. The nonlinearity and the crosstalk are less than 3% and less than 2%, respectively, at the room temperature. The static power dissipation is about 3 mW/channel. © 2014 Elsevier B.V.


Yu L.,Northwestern Polytechnical University | Su Z.,Hong Kong Polytechnic University
Mathematical Problems in Engineering | Year: 2012

The present work concerns the estimation of the probability density function (p.d.f.) of measured data in the Lamb wave-based damage detection. Although there was a number of research work which focused on the consensus algorithm of combining all the results of individual sensors, the p.d.f. of measured data, which was the fundamental part of the probability-based method, was still given by experience in existing work. Based on the analysis about the noise-induced errors in measured data, it was learned that the type of distribution was related with the level of noise. In the case of weak noise, the p.d.f. of measured data could be considered as the normal distribution. The empirical methods could give satisfied estimating results. However, in the case of strong noise, the p.d.f. was complex and did not belong to any type of common distribution function. Nonparametric methods, therefore, were needed. As the most popular nonparametric method, kernel density estimation was introduced. In order to demonstrate the performance of the kernel density estimation methods, a numerical model was built to generate the signals of Lamb waves. Three levels of white Gaussian noise were intentionally added into the simulated signals. The estimation results showed that the nonparametric methods outperformed the empirical methods in terms of accuracy. © 2012 Long Yu and Zhongqing Su.


Li H.,Hong Kong Polytechnic University | Li H.,Northwestern Polytechnical University | Fu M.W.,Hong Kong Polytechnic University | Lu J.,Hong Kong Polytechnic University | Yang H.,Northwestern Polytechnical University
International Journal of Plasticity | Year: 2011

Numerous criteria have been developed for ductile fracture (DF) prediction in metal plastic deformation. Finding a way to select these DF criteria (DFCs) and identify their applicability and reliability, however, is a non-trivial issue that still needs to be addressed in greater depth. In this study, several criteria under the categories of 'uncoupled damage criterion' and the 'coupled damage criterion', including the continuum damage mechanics (CDM)-based Lemaitre model and the Gurson-Tvergaard-Needleman (GTN) model, are investigated to determine their reliability in ductile failure prediction. To create diverse stress and strain states and fracture modes, different deformation scenarios are generated using tensile and compression tests of Al-alloy 6061 (T6) with different sample geometries and dimensions. The two categories of criteria are coded into finite element (FE) models based on the unconditional stress integration algorithm in the VUMAT/ABAQUS platform. Through physical experiments, computations and three industrial case studies, the entire correlation panorama of the DFCs, deformation modes and DF mechanisms is established and articulated. The experimental and simulation results show the following. (1) The mixed DF mode exists in every deformation of concern in this study, even in the tensile test of the round bar sample with the smallest notch radius. A decrease of stress triaxiality (η-value) leads to a reduction in the accuracy of DF prediction by the two DFC categories of DFCs, due to the interplay between the principal stress dominant fracture and the shear-stress dominant factor. (2) For deformations with a higher η-value, both categories of DFCs predict the fracture location reasonably well. For those with a lower or even negative η-value, the GTN and CDM-based criteria and some of the uncoupled criteria, including the C&L, Ayada and Oyane models, provide relatively better predictions. Only the Tresca and Freudenthal models can properly predict the shear dominant fracture. The reliability sequence of fracture moment prediction is thus the GTN model, followed by the CDM-based model and the uncoupled models. (3) The applicability of the DFCs depends on the use of suitable damage evolution rules (void nucleation/growth/coalescence and shear band) and consideration of several influential factors, including pressure stress, stress triaxiality, the Lode parameter, and the equivalent plastic strain or shear stress. These parameters determine the deformation mode (shear dominant or maximum principal stress dominant deformation) and, further, the DF mechanism (dimple fracture/shear fracture/mixed fracture). © 2010 Elsevier Ltd. All rights reserved.


Ke S.,Hong Kong Polytechnic University | Fan H.,Northwestern Polytechnical University | Huang H.,Hong Kong Polytechnic University
Applied Physics Letters | Year: 2010

The Vögel-Fulcher (VF) equation ω= ω0 exp [- Ea / kB (Tm - Tf)] was frequently used to describe the dielectric relaxation of relaxor ferroelectrics where ω is the probe frequency at the peak temperature Tm of either the real or imaginary parts of the dielectric constant. We revisited this relation in a typical relaxor lead magnesium niobate and found that the parameters obtained were not physically meaningful. Meaningful results can only be obtained by fitting the VF relation on the characteristic relaxation time τc, whose temperature dependence can be obtained from the Cole-Cole model. The freezing temperature we obtained is 230 K, below which τc becomes temperature independent. © 2010 American Institute of Physics.


Bi X.,University of Pittsburgh | Mao M.,University of Pittsburgh | Wang D.,Northwestern Polytechnical University | Li H.,University of Pittsburgh
IEEE/ACM International Conference on Computer-Aided Design, Digest of Technical Papers, ICCAD | Year: 2013

In this paper, we study the use of multi-level cell (MLC) spin-transfer torque RAM (STT-RAM) in cache design of embedded systems and microprocessors. Compared to the single level cell (SLC) design, a MLC STT-RAM cache is expected to offer higher density and faster system performance. However, the cell design constrains, such as the switching current requirement and asymmetry in write operations, severely limit the density benefit of the conventional MLC STT-RAM. The two-step read/write accesses and inflexible data mapping strategy in the existing MLC STT-RAM cache architecture may even result in system performance degradation. To unleash the real potential of MLC STT-RAM cache, we propose a cross-layer solution. First, we introduce the reverse magnetic junction tunneling (MTJ) into MLC cell design, which offers a more balanced device and design tradeoff and enables 2x storage density than SLC. At architectural level, we propose a cell split mapping method to divide cache lines into fast and slow regions and data migration policies to allocate the frequently-used data to fast regions. Furthermore, an application-aware speed enhancement mode is utilized to adaptively tradeoff cache capacity and speed, satisfying different requirements of various applications. Simulation results show that the proposed techniques can improve the system performance by 10.3% and reduce the energy consumption on cache by 26.0% compared with conventional MLC STT-RAM. © 2013 IEEE.


Liu Y.,Northwestern Polytechnical University | Ning Y.,Northwestern Polytechnical University | Yao Z.,Northwestern Polytechnical University | Fu M.W.,Hong Kong Polytechnic University
Materials and Design | Year: 2014

The deformation behavior of the 1.15C-4.00Cr-3.00V-6.00W-5.00Mo powder metallurgy (PM) high speed steel in hot working process was investigated by the isothermal compression tests carried out at the temperature of 950-1150°C and the strain rate of 0.001-1.0s-1 with the height reduction of 60%. True stress-true strain curves are investigated; the hot deformation activation energy of the steel is determined to be 750kJ/mol, and a constitutive equation is obtained. The processing maps were constructed, identification of the instability region and optimization of hot deformation parameters. It is found that the hot working process of the steel can be carried out safely in the domain of (Td: 1000-1150°C, ε·: 0.006-0.1s-1). To obtain the homogeneous microstructure with fine grains, the hot working process should be carried out at the condition of (Topi: 1050°C, ε·opi: 0.1s-1). The flow instability is expected in the two domains at 1030-1150°C/0.1-1.0s-1 and 1000-1075°C/0.001-0.006s-1. Furthermore, the true strain takes a great effect on processing maps in which the efficiency of power dissipation obviously changes with the increase of strain from 0.05 to 0.90. © 2013 Elsevier Ltd.


Di W.,Purdue University | Zhang L.,Hong Kong Polytechnic University | Zhang D.,Hong Kong Polytechnic University | Pan Q.,Northwestern Polytechnical University
IEEE Transactions on Systems, Man, and Cybernetics Part A:Systems and Humans | Year: 2010

This correspondence paper studies face recognition by using hyperspectral imagery in the visible light bands. The spectral measurements over the visible spectrum have different discriminatory information for the task of face identification, and it is found that the absorption bands related to hemoglobin are more discriminative than the other bands. Therefore, feature band selection based on the physical absorption characteristics of face skin is performed, and two feature band subsets are selected. Then, three methods are proposed for hyperspectral face recognition, including whole band (2D)2PCA, single band (2D)2PCA with decision level fusion, and band subset fusion-based (2D)2PCA. A simple yet efficient decision level fusion strategy is also proposed for the latter two methods. To testify the proposed techniques, a hyperspectral face database was established which contains 25 subjects and has 33 bands over the visible light spectrum (0.40.72 μm). The experimental results demonstrated that hyperspectral face recognition with the selected feature bands outperforms that by using a single band, using the whole bands, or, interestingly, using the conventional RGB color bands. © 2006 IEEE.


Gao T.,Northwestern Polytechnical University | Gao T.,Ege University | Zhang W.,Northwestern Polytechnical University
International Journal for Numerical Methods in Engineering | Year: 2011

This work is focused on the topology optimization of lightweight structures consisting of multiphase materials. Instead of adopting the common idea of using volume constraint, a new problem formulation with mass constraint is proposed. Meanwhile, recursive multiphase materials interpolation (RMMI) and uniform multiphase materials interpolation (UMMI) schemes are discussed and compared based on numerical tests and theoretical analysis. It is indicated that the nonlinearity of the mass constraint introduced by RMMI brings numerical difficulties to attain the global optimum of the optimization problem. On the contrary, the UMMI-2 scheme makes it possible to formulate the mass constraint in a linear form with separable design variables. One such formulation favors very much the problem resolution by means of mathematical programming approaches, especially the convex programming methods. Moreover, numerical analysis indicates that fully uniform initial weighting is beneficial to seek the global optimum when UMMI-2 scheme is used. Besides, the relationship between the volume constraint and mass constraint is theoretically revealed. The filtering technique is adapted to avoid the checkerboard pattern related to the problem with multiphase materials. Numerical examples show that the UMMI-2 scheme with fully uniform initial weighting is reliable and efficient to deal with the structural topology optimization with multiphase materials and mass constraint. Meanwhile, the mass constraint formulation is evidently more significant than the volume constraint formulation. © 2011 John Wiley & Sons, Ltd.


Wang S.,Northwestern Polytechnical University | Wang S.,Hong Kong Polytechnic University | Zhang L.,Hong Kong Polytechnic University | Liang Y.,Northwestern Polytechnical University | Pan Q.,Northwestern Polytechnical University
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2012

In various computer vision applications, often we need to convert an image in one style into another style for better visualization, interpretation and recognition; for examples, up-convert a low resolution image to a high resolution one, and convert a face sketch into a photo for matching, etc. A semi-coupled dictionary learning (SCDL) model is proposed in this paper to solve such cross-style image synthesis problems. Under SCDL, a pair of dictionaries and a mapping function will be simultaneously learned. The dictionary pair can well characterize the structural domains of the two styles of images, while the mapping function can reveal the intrinsic relationship between the two styles' domains. In SCDL, the two dictionaries will not be fully coupled, and hence much flexibility can be given to the mapping function for an accurate conversion across styles. Moreover, clustering and image nonlocal redundancy are introduced to enhance the robustness of SCDL. The proposed SCDL model is applied to image super-resolution and photo-sketch synthesis, and the experimental results validated its generality and effectiveness in cross-style image synthesis. © 2012 IEEE.


Yu Z.,Northwestern Polytechnical University | Nakamura Y.,Kyoto University
ACM Computing Surveys | Year: 2010

Smart meeting systems, which record meetings and analyze the generated audio-visual content for future viewing, have been a topic of great interest in recent years. A successful smart meeting system relies on various technologies, ranging from devices and algorithms to architecture. This article presents a condensed survey of existing research and technologies, including smart meeting system architecture, meeting capture, meeting recognition, semantic processing, and evaluation methods. It aims at providing an overview of underlying technologies to help understand the key design issues of such systems. This article also describes various open issues as possible ways to extend the capabilities of current smart meeting systems. © 2010 ACM.


Ma W.,Northwestern Polytechnical University | Ma W.,Yan'an University | Chen F.,Northwestern Polytechnical University
Catalysis Letters | Year: 2013

The CO oxidation reactivity of negatively and positively charged isolated cuboctahedron (c-Oh) Au13 and Au12Ag nanoparticles is investigated using density functional theory calculations. Charging the nanoparticles modifies the structural stability of the Au13 and Au12Ag nanoparticles as well as the electron distribution in the core and shell atoms. An Ag-doping in gold (Au) clusters improves CO or O 2 adsorption on Au12Ag cluster. For Au13 cluster, CO preadsorption increases the capacity of CO and O2 coadsorption, but the result is opposite for Au12Ag cluster. The neutral Au13 and Au12Ag clusters exhibit relatively poor reactivity for CO oxidation, while the reactivity is enhanced significantly by excess electrons. In comparisons of the results of CO oxidation on Ag- and un-doped Au nanoparticles, we discover Ag-doping in Au cluster surely decreases first energy barrier (Ea), and increases slightly second energy barrier (Eb). This work provides a fundamental insight into how the excess charges affect the adsorption activity and how the Ag-doping in Au clusters adjusts the catalytic activity for Ag- or un-doped c-Oh Au clusters. Graphical Abstract: Reaction pathways for CO + O2 → CO 2 + O associated with Au13 and Au12Ag clusters. Here,*denotes the adsorbed species on an Au13 or Au 12Ag cluster. The reactivity of CO oxidation on Au nanoparticles is enhanced significantly by excess electrons. An Ag-doping in Au cluster improves CO or O2 adsorption on Au12Ag cluster. Ag-doping in Au clusters decreases first energy barrier (Ea), and increases slightly second energy barrier (Eb). Ag-doping in Au nanoparticles weakens C-Au bond at CO + O2 coadsorption state, and strengths CO-O bonds at transition states and intermediate state.[Figure not available: see fulltext.] © 2012 Springer Science+Business Media New York.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Nitta N.,Georgia Institute of Technology | Yushin G.,Georgia Institute of Technology
ACS Nano | Year: 2013

Continuous, smooth, visibly defect-free, lithographically patterned activated carbon films (ACFs) are prepared on the surface of silicon wafers. Depending on the synthesis conditions, porous ACFs can either remain attached to the initial substrate or be separated and transferred to another dense or porous substrate of interest. Tuning the activation conditions allows one to change the surface area and porosity of the produced carbon films. Here we utilize the developed thin ACF technology to produce prototypes of functional electrical double-layer capacitor devices. The synthesized thin carbon film electrodes demonstrated very high capacitance in excess of 510 F g-1 (>390 F cm-3) at a slow cyclic voltammetry scan rate of 1 mV s-1 and in excess of 325 F g-1 (>250 F cm-3) in charge-discharge tests at an ultrahigh current density of 45 000 mA g -1. Good stability was demonstrated after 10 000 galvanostatic charge-discharge cycles. The high values of the specific and volumetric capacitances of the selected ACF electrodes as well as the capacity retention at high current densities demonstrated great potential of the proposed technology for the fabrication of various on-chip devices, such as micro-electrochemical capacitors. © 2013 American Chemical Society.


Chen T.,Northwestern Polytechnical University | Chen T.,Shaanxi University of Technology
Advanced Materials Research | Year: 2014

Gene expression profiles of tumor have the limited amount of samples in comparison to the high dimensionality of the samples;this paper proposed a classification algorithm based on neighborhood rough set to improve classification accuracy.This paper first applied feature filtering method of kruskal-wallis rank sum test to select a set of top-ranked related genes, and then applied neighborhood rough set on these genes to generate a informative genes subset. Finally, SVM was used to classify the GEP data set. The result of the experiment indicates that this method can effectively improve classification accuracy, and it has higher generalization. © (2014) Trans Tech Publications, Switzerland.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Yushin G.,Georgia Institute of Technology
Nano Energy | Year: 2012

The development of energy-sustainable and energy-efficient economy depends on the ability to produce low-cost high-performance renewable materials for electrical energy storage devices. The electrical double layer capacitors (EDLCs) with nanostructured activated carbon (AC) electrodes from natural precursors have attracted considerable attention due to their great cycle stability, combined with moderate cost and attractive overall performance. Such ACs offer high specific surface area, high electrical conductivity, relatively low price, easy and environmental friendly production in large quantities. The recent developments in the synthesis of such AC materials allow for the greatly enhanced specific capacitance in a wide range of electrolytes. This review provides a summary of a recent research progress in synthesis and understanding the critical structure-property relationships for nanostructured ACs and highlights the trends for the future developments of ACs for EDLC applications. © 2012 Elsevier Ltd.


Wan M.,Northwestern Polytechnical University | Altintas Y.,University of British Columbia
International Journal of Machine Tools and Manufacture | Year: 2014

This paper presents the mechanics and dynamics of thread milling operations. The tool follows a helical path around the wall of the pre-machined hole in thread milling, which has varying tool-part engagement and cut area during one threading cycle. The variation of cut area that reflects the kinematics of threading as well as structural vibrations is modeled along the helical, threading path. The mechanics of the process are first experimentally proven, followed by the formulation of dynamic thread milling which is periodic in threading cycle, in a semi-discrete time domain. The stability of the operation is predicted as a function of spindle speed, axial depth of cut, cutter path and tool geometry. The mechanics and stability models are experimentally proven in opening M16×2 threads with a five-fluted helical tool on a Steel AISI1045 workpiece. © 2014 Elsevier Ltd.


Zhong Y.,RMIT University | Gao S.,Northwestern Polytechnical University | Li W.,Northwestern Polytechnical University
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

A new quaternion-based method for the SINS/SAR (strap-down inertial navigation system/synthetic aperture radar) integrated navigation system is presented. This method overcomes the shortcomings due to the linear SINS error model used in the currently existing SINS/SAR integrated navigation systems. A quaternion-based matrix is derived for describing the attitude of SINS. Quaternion-based nonlinear error and observation models are established for the SINS/SAR integrated navigation system. An adaptive unscented particle filtering (UPF) algorithm is developed based on the quaternion-based nonlinear models for optimal data fusion in the SINS/SAR integrated navigation system. Experimental results demonstrate that the proposed quaternion based method can effectively reduce the navigation error and improve the navigational positioning precision. © 2006 IEEE.


Zhang L.,CAS Institute of Process Engineering | Ouyang J.,Northwestern Polytechnical University | Zhang X.,China Three Gorges University
Computer Physics Communications | Year: 2013

The aim of the paper is the development of an efficient numerical algorithm for the solution of magnetohydrodynamics (MHD) flow problems with either fully insulating walls or partially insulating and partially conducting walls. Toward this, we first extend the influence domain of the shape function for the element free Galerkin (EFG) method to have arbitrary shape. When the influence factor approaches 1, we find that the EFG shape function almost has the Delta property at the node (i.e. the value of the EFG shape function of the node is nearly equal to 1 at the position of this node) as well as the property of slices in the influence domain of the node (i.e. the EFG shape function in the influence domain of the node is nearly constructed by different functions defined in different slices). Therefore, for MHD flow problems at high Hartmann numbers we follow the idea of the variational multiscale finite element method (VMFEM) to combine the EFG method with the variational multiscale (VM) method, namely the variational multiscale element free Galerkin (VMEFG) method is proposed. Subsequently, in order to validate the proposed method, we compare the obtained approximate solutions with the exact solutions for some problems where such exact solutions are known. Finally, several benchmark problems of MHD flows are simulated and the numerical results indicate that the VMEFG method is stable at moderate and high values of Hartmann number. Another important feature of this method is that the stabilization parameter has appeared naturally via the solution of the fine scale problem. Meanwhile, because this proposed method is a type of meshless method, it can avoid the need for meshing, a very demanding task for complicated geometry problems. © 2012 Elsevier B.V. All rights reserved.


Lu L.,Georgia Institute of Technology | Li G.Y.,Georgia Institute of Technology | Maaref A.,Huawei | Yao R.,Northwestern Polytechnical University
IEEE Wireless Communications | Year: 2014

With increasing demand to support high-data-rate applications, spectral efficiency is becoming more and more important. To exploit limited spectrum efficiently, techniques, such as cognitive radio, device-to-device communications and heterogeneous networks, have been proposed. They make wireless networks more agile and flexible by allowing users/systems to coexist as a result of careful and dynamic planning. In this article, we provide an overview of opportunistic transmission schemes for the scenarios where some existing users/systems have to be protected while new ones can transmit. Schemes exploiting opportunities on frequency and spatial domains will be investigated. Some practical considerations, potential applications and future research topics will also be discussed. © 2014 IEEE.


Liang Y.,Northwestern Polytechnical University | Chen T.,Northwestern Polytechnical University | Pan Q.,University of Alberta
IEEE Transactions on Automatic Control | Year: 2010

This technical note is concerned with the optimal linear estimation problem in the presence of multiple packet dropouts in both sensor-to-controller and controller-to-actuator channels. The considered stochastic packet dropouts are independent and Bernoulli distributed. Based on a linear packet dropout model with stochastic parameters, a linear-minimum-variance (LMV) filter is proposed using the orthogonality principle. A sufficient condition for convergence of the steady-state LMV filter under a dc controller output is also given. Simulation results show the effectiveness of the proposed filter. © 2006 IEEE.


Lu P.,Iowa State University | Pan B.,Northwestern Polytechnical University | Pan B.,Iowa State University
Journal of Guidance, Control, and Dynamics | Year: 2010

This paper is concerned with ascent guidance of multiple-stage launch vehicles subject to aerodynamic bending- moment constraint. In the first part of the paper, several new developments are made to refine and expand the capability of an optimal endoatmospheric ascent-guidance algorithm. These include new conditions for determining optimal body axes of the vehicle, handling of the aerodynamic bending-moment constraint by automated optimization of gravity-turn trajectory or by optimal closed-loop guidance, and seamless integration of the endoatmospheric guidance algorithm with exoatmospheric ascent-guidance algorithm for the upper stages of a vehicle. An extensive application of these developments using the vehicle and mission data of the Ares I Crew Launch Vehicle constitutes the second part of the paper. Extensive Monte Carlo simulations are conducted to demonstrate the algorithm and compare optimal closed-loop ascent guidance with conventional open-loop ascent guidance. The testing results help answer an age-old question on the comparison of closed-loop and open-loop ascent guidance on performance and constraint enforcement in the presence of winds and dispersions.


Yang H.,Northwestern Polytechnical University | Zhang F.,Georgia Institute of Technology
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2011

This paper presents a novel robust controller design for formation control of autonomous underwater vehicles (AUVs). We consider a nonlinear three-degree-of-freedom dynamic model for the horizontal motion of each AUV. By using the Jacobi transform, the horizontal dynamics of AUVs are explicitly expressed as dynamics for formation shape and formation center, and are further decoupled by feedback control. We treat the coupling terms as perturbations to the decoupled system. An H∞ state feedback controller is designed to achieve robust stability of the closed loop formation and translation dynamics. By incorporating an orientation controller, the formation shape under control converges and the formation center tracks a desired trajectory simultaneously. Simulation results demonstrate the effectiveness of the controllers. © 2011 IEEE.


Trivedi R.,Iowa State University | Wang N.,Northwestern Polytechnical University
Acta Materialia | Year: 2012

The growth of eutectic under large undercooling conditions is important in obtaining nanoscale composite microstructures. Many glass-forming eutectic systems also exhibit a fine rod eutectic microstructure and often show a direct transition from eutectic to glass with increasing undercooling at the interface. A theoretical model of rod eutectic growth is developed in this paper, which quantitatively evaluates the system and growth parameters that will give rise to large undercooling at the interface. In addition to the diffusion and capillary undercooling, the model incorporates the effects of a sharp decrease in the diffusion coefficient that is exhibited by fragile glass-forming systems, the presence of highly nonlinear liquidus lines at large undercooling, and the effects of non-equilibrium at the interface. The results of the model are then discussed to obtain an insight into the system and growth parameters that are critical for obtaining a large undercooling at the eutectic interface, which is important in the design of nanoscale composite materials and in the selection of potential glass-forming systems. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Yang J.,Northwestern Polytechnical University | Vela P.,Georgia Institute of Technology | Teizer J.,Georgia Institute of Technology | Shi Z.,Northwestern Polytechnical University
Journal of Computing in Civil Engineering | Year: 2014

Visual monitoring of construction worksites through the installation of surveillance cameras has become prevalent in the construction industry. These cameras also are useful for automatic observation of construction events and activities. This paper demonstrates the use of a surveillance camera for assessing tower crane activities during the course of a workday. In particular, it seeks to demonstrate that the crane jib trajectory, together with known information regarding the site plans, provides sufficient information to infer the activity states of the crane. The jib angle trajectory is tracked by using two-dimensional to three-dimensional rigid pose tracking algorithms. The site plan information includes a process model for the activities and site layout information. A probabilistic graph model for crane activity is designed to process the track signals and recognize crane activity as belonging to one of two categories: concrete pouring and nonconcrete material movement. The experimental results from a construction surveillance camera show that crane activities are correctly identified. © 2014 American Society of Civil Engineers.


Yang F.,Xidian University | Song J.,Xidian University | Wan S.,Northwestern Polytechnical University | Wu H.R.,RMIT University
IEEE Journal on Selected Topics in Signal Processing | Year: 2012

Packet-layer models are designed to use only the information provided by packet headers for real-time and non-intrusive quality monitoring of networked video services. This paper proposes a content-adaptive packet-layer (CAPL) model for networked video quality assessment. Considering the fact that the quality degradation of a networked video significantly relies on the temporal as well as the spatial characteristics of the video content, temporal complexity is incorporated in the proposed model. Due to very limited information directly available from packet headers, a simple and adaptive method for frame type detection is adopted in the CAPL model. The temporal complexity is estimated using the ratio of the number of bits for coding P and I frames. The estimated temporal complexity and frame type are incorporated in the CAPL model together with the information about the number of bits and positions of lost packets to obtain the quality estimate for each frame, by evaluating the distortions induced by both compression and packet loss. A two-level temporal pooling is employed to obtain the video quality given the frame quality. Using content related information, the proposed model is able to adapt to different video contents. Experimental results show that the CAPL model significantly outperforms the G.1070 model and the DT model in terms of widely used performance criteria, including the Root-Mean-Squared Error (RMSE), the Pearson Correlation Coefficient (PCC), the Spearman Rank Order Correlation Coefficient (SCC), and the Outlier Ratio (OR). © 2007-2012 IEEE.


Qi Y.,Zhejiang University | Bian T.,Zhejiang University | Choi S.-I.,Georgia Institute of Technology | Jiang Y.,Zhejiang University | And 4 more authors.
Chemical Communications | Year: 2014

Pt-Cu alloy concave nanocubes enclosed by high-index {511} facets were synthesized in high yields and exhibited substantially enhanced electrocatalytic properties for methanol oxidation relative to commercial Pt/C. This journal is © The Royal Society of Chemistry 2014.


Liang Y.,Northwestern Polytechnical University | Chen T.,University of Alberta | Pan Q.,Northwestern Polytechnical University
Automatica | Year: 2010

This paper presents a multi-rate filtering problem for a class of networked multi-sensor fusion systems with packet dropouts (PDs): the state evolves according to a linear discrete-time model with norm-bounded unknown inputs (UIs), and its underlying period is h; the p sensors are distributively deployed with different sampling periods n1 h, ..., np h; multi-rate sensor measurements, corrupted by UIs, are subject to stochastic PDs in the transmission to a fusion center for state estimation; the estimation is updated at the period m h. Different from the single-rate estimator design with PDs which are treated as stochastic parameters, a UI observer is proposed where PDs are represented as zero-mean white input noises of the linear time-variant estimation error system. The results on the existence of a stable observer are proposed. Due to insufficient design freedom for absolute error decoupling, we turn to designing an observer-based stochastic H∞ filter. A numerical example of distributive multi-sensor target tracking is given to illustrate the proposed filter. © 2009 Elsevier Ltd. All rights reserved.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Yushin G.,Georgia Institute of Technology
Carbon | Year: 2011

Electrical double layer capacitors (EDLCs) with activated sucrose-derived carbons (ASCs) as electrodes are reported. The carbons were prepared by the pyrolysis of sucrose followed by the activation with CO 2 gas for 1-5 h at 900 °C to tune the pore size distribution and the specific surface area (SSA). The porosity of the ASCs has been characterized using N 2 and CO 2 adsorption measurements. The activation increased the SSA from ∼200 to 3000 m 2 g -1 and produced pores mostly in the 0.4-2 nm range. The pyrolysis of sucrose without CO 2 activation produces a carbon with specific capacitance as low as 4 F g -1, whereas selected ASCs exhibit specific capacitance in excess of 160 F g -1 and excellent frequency response in a two-electrode EDLC cell with 1 M H 2SO 4 electrolyte. The activation time of 4 h resulted in the most promising electrochemical performance. Excellent ASC stability was confirmed by extensive electrochemical characterization after 10,000 charge-discharge cycles. © 2011 Elsevier Ltd. All rights reserved.


Kong J.,Northwestern Polytechnical University | Kong J.,University of Bayreuth | Schmalz T.,University of Bayreuth | Motz G.,University of Bayreuth | Muller A.H.E.,University of Bayreuth
Macromolecules | Year: 2011

We report the synthesis of versatile hyperbranched ferrocene-containing poly(boro)carbosilanes (hb-PBCS) via a convenient "A2 + B 3" approach. Two types of hb-PBCS are obtained by the hydrosilylation of 1,1′-bis(dimethylsilyl)ferrocene (A2) with trivinylmethylsilane (B3) followed by modification with 9-borabicyclo[3.3.1]nonane (9-BBN) and by the hydroboration of 1,1′-bis(dimethylvinylsilyl)ferrocene (A2) with the borane-dimethyl sulfide complex (B3), respectively. Size exclusion chromatography (SEC) results demonstrate that the well-soluble hb-PBCS possess appreciable weight-average molecular weight (Mw,SEC) up to 62-300 g/mol with the polydispersity index (PDI) of 1.95-4.51. The combined characterization by 1H-29Si heteronuclear multiple-bond correlation (HMBC), 11B nuclear magnetic resonance (NMR), and triple-detection SEC (triple-SEC) confirms the remarkable hyperbranched architecture of hb-PBCS with degrees of branching (DB) between 0.47 and 0.79. The Mark-Houwink-Sakurada exponents of hb-PBCS obtained from triple-SEC are significantly lower (α = 0.36-0.47) than that of their linear analogue (α = 0.69). © 2011 American Chemical Society.


Xu B.,Northwestern Polytechnical University | Xie Y.M.,RMIT University
Composite Structures | Year: 2015

In this paper, a method for the concurrent topology optimization of macrostructural material distribution and periodic microstructure under random excitations is proposed. The sensitivity analysis of dynamic response with respect to design variables in two scales, i.e., macro and micro scales, is presented. The corresponding concurrent topology optimization of macrostructure and microstructure is established, where the objective function is to minimize the displacement response mean square (RMS) of the prescribed degree of freedom while volume constraints are applied to the macromaterial distribution and phase materials. The optimization problem is solved using a bi-directional evolutionary structural optimization (BESO) method. Several examples are presented to demonstrate the effectiveness of the proposed method. © 2014 Elsevier Ltd.


Yang F.,Xidian University | Wan S.,Northwestern Polytechnical University | Xie Q.,Huawei | Wu H.R.,RMIT University
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2010

A no-reference (NR) quality measure for networked video is introduced using information extracted from the compressed bit stream without resorting to complete video decoding. This NR video quality assessment measure accounts for three key factors which affect the overall perceived picture quality of networked video, namely, picture distortion caused by quantization, quality degradation due to packet loss and error propagation, and temporal effects of the human visual system. First, the picture quality in the spatial domain is measured, for each frame, relative to quantization under an error-free transmission condition. Second, picture quality is evaluated with respect to packet loss and the subsequent error propagation. The video frame quality in the spatial domain is, therefore, jointly determined by coding distortion and packet loss. Third, a pooling scheme is devised as the last step of the proposed quality measure to capture the perceived quality degradation in the temporal domain. The results obtained by performance evaluations using MPEG-4 coded video streams have demonstrated the effectiveness of the proposed NR video quality metric. © 2006 IEEE.


Yang D.,Orange S.A. | Zhang D.,Orange S.A. | Yu Z.,Orange S.A. | Wang Z.,Northwestern Polytechnical University
HT 2013 - Proceedings of the 24th ACM Conference on Hypertext and Social Media | Year: 2013

Although online recommendation systems such as recommendation of movies or music have been systematically studied in the past decade, location recommendation in Location Based Social Networks (LBSNs) is not well investigated yet. In LBSNs, users can check in and leave tips commenting on a venue. These two heterogeneous data sources both describe users' preference of venues. However, in current research work, only users' check-in behavior is considered in users' location preference model, users' tips on venues are seldom investigated yet. Moreover, while existing work mainly considers social influence in recommendation, we argue that considering venue similarity can further improve the recommendation performance. In this research, we ameliorate location recommendation by enhancing not only the user location preference model but also recommendation algorithm. First, we propose a hybrid user location preference model by combining the preference extracted from check-ins and text-based tips which are processed using sentiment analysis techniques. Second, we develop a location based social matrix factorization algorithm that takes both user social influence and venue similarity influence into account in location recommendation. Using two datasets extracted from the location based social networks Foursquare, experiment results demonstrate that the proposed hybrid preference model can better characterize user preference by maintaining the preference consistency, and the proposed algorithm outperforms the state-of-the-art methods. Copyright 2013 ACM.


Wei L.,Georgia Institute of Technology | Wei L.,Northwestern Polytechnical University | Yushin G.,Georgia Institute of Technology
Journal of Power Sources | Year: 2011

Activated carbons were prepared via a pyrolysis of sucrose followed by activation in the stream of CO2 gas for 2-6 h at 900 °C to tune the pore size distribution (PSD) and increase the specific surface area (SSA). The porosity of the activated sucrose derived carbons (ASCs) has been characterized using N2 sorption measurements. Increasing activation time led to the significant increase in SSA and pore volume of ASCs, among which sucrose derived carbon with 6 h activation time (ASC-6 h) exhibited the highest SSA of 1941 m2 g-1 and the highest micropore volume of 0.87 cm3 g-1. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge cycle tests have been applied to investigate the capacitive performance of the ASC electrodes in ionic liquids (ILs) at room and elevated temperatures. The ASC-6 h electrodes in ethyl-dimethyl-propyl-ammonium bis (trifluoromethylsulfonyl) imide (EdMPNTf2N) showed specific capacitance in excess of 170 F g -1 at 60 °C, whereas the same electrodes in 1-ethyl-3- methylimidazolium tetrafluoroborate (EMImBF4) showed slightly lower capacitance but significantly better rate performance. © 2011 Elsevier B.V. All rights reserved.


Zhang Y.,Northwestern Polytechnical University | Duijster A.,University of Antwerp | Scheunders P.,University of Antwerp
IEEE Transactions on Geoscience and Remote Sensing | Year: 2012

In this paper, a Bayesian restoration technique for multiple observations of hyperspectral (HS) images is presented. As a prototype problem, we assume that a low-spatial-resolution HS observation and a high-spatial-resolution multispectral (MS) observation of the same scene are available. The proposed approach applies a restoration on the HS image and a joint fusion with the MS image, accounting for the joint statistics with the MS image. The restoration is based on an expectation-maximization algorithm, which applies a deblurring step and a denoising step iteratively. The Bayesian framework allows to include spatial information from the MS image. To keep the calculation feasible, a practical implementation scheme is presented. The proposed approach is validated by simulation experiments for general HS image restoration and for the specific case of pansharpening. The experimental results of the proposed approach are compared with pure fusion and deconvolution results for performance evaluation. © 2012 IEEE.


Yang H.,Northwestern Polytechnical University | Zhang F.,Georgia Institute of Technology
Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME | Year: 2012

This paper presents a novel robust controller design for formation control of autonomous underwater vehicles (AUVs). We consider a nonlinear three-degree-of-freedom dynamic model for the horizontal motion of each AUV. By using the Jacobi transform, the horizontal dynamics of AUVs are explicitly expressed as dynamics for formation shape and formation center, and are further decoupled by feedback control. We treat the coupling terms as perturbations to the decoupled system. An H-infinity state feedback controller is designed to achieve robust stability of the closed loop formation and translation dynamics. By incorporating an orientation controller, the formation shape under control converges and the formation center tracks a desired trajectory simultaneously. Simulation results demonstrate the effectiveness of the controllers. © 2012 American Society of Mechanical Engineers.


Zhang D.,Orange S.A. | Guo B.,Orange S.A. | Yu Z.,Northwestern Polytechnical University
Computer | Year: 2011

Social and community intelligence research aims to reveal individual and group behaviors, social interactions, and community dynamics by mining the digital traces that people leave while interacting with Web applications, static infrastructure, and mobile and wearable devices. © 2011 IEEE.


Yang H.,Northwestern Polytechnical University | Zhang F.,Georgia Institute of Technology
Proceedings - IEEE International Conference on Robotics and Automation | Year: 2010

This paper presents a novel approach based on Jacobi shape theory and geometric reduction for formation control of autonomous underwater vehicles (AUVs). We consider a three degree-of-freedom (DOF) dynamic model for the horizontal motion of each AUV that has control inputs over surge force and yaw moment. By using the Jacobi transform, the horizontal dynamics of AUVs are expressed as dynamics for formation shape, formation motion and vehicle orientation. The system decouples when additional symmetries in vehicle design are presented. Hence formation shape controllers, formation motion controllers, and vehicle orientation controllers can be designed separately. This approach reduces the complexity of formation controllers. We use the model for ODIN as an example to demonstrate the controller design process. Simulation results show the effectiveness of the controllers. ©2010 IEEE.


Chen C.,Northwestern Polytechnical University | Chen C.,North Carolina State University | Yuan F.-G.,North Carolina State University
Smart Materials and Structures | Year: 2010

This paper aims to identify impact sources on plate-like structures based on the synthetic time-reversal (T-R) concept using an array of sensors. The impact source characteristics, namely, impact location and impact loading time history, are reconstructed using the invariance of time-reversal concept, reciprocal theory, and signal processing algorithms. Numerical verification for two finite isotropic plates under low and high velocity impacts is performed to demonstrate the versatility of the synthetic T-R method for impact source identification. The results show that the impact location and time history of the impact force with various shapes and frequency bands can be readily obtained with only four sensors distributed around the impact location. The effects of time duration and the inaccuracy in the estimated impact location on the accuracy of the time history of the impact force using the T-R method are investigated. Since the T-R technique retraces all the multi-paths of reflected waves from the geometrical boundaries back to the impact location, it is well suited for quantifying the impact characteristics for complex structures. In addition, this method is robust against noise and it is suggested that a small number of sensors is sufficient to quantify the impact source characteristics through simple computation; thus it holds promise for the development of passive structural health monitoring (SHM) systems for impact monitoring in near real-time. © 2010 IOP Publishing Ltd.


Xu B.,Northwestern Polytechnical University | Zhang Y.,Zhejiang University
Neurocomputing | Year: 2015

This paper describes the back-stepping controller design in discrete time for the longitudinal dynamics of a generic hypersonic flight vehicle with neural networks. For the altitude subsystem, to avoid the causality contradiction, the original system is formulated into a new equivalent prediction model with strict-feedback form from which the virtual control is designed with error feedback and neural approximation via back-stepping. For stability analysis, Lyapunov function is chosen with regard to the novel formulation of new strict-feedback system. Under the proposed controller, the semiglobal uniform ultimate boundedness stability is guaranteed. The step response is presented in the simulation studies to show the effectiveness of the proposed control approach. © 2014 Elsevier B.V.


Xia L.,Northwestern Polytechnical University | Zhu J.,Northwestern Polytechnical University | Zhang W.,Northwestern Polytechnical University | Breitkopf P.,CNRS Roberval Laboratory (Mechanical Research Unit)
Computer Methods in Applied Mechanics and Engineering | Year: 2013

Integrated design of the structure topology and involved component layout is a challenging design issue when compared with traditional topology optimization. In this paper, we propose an implicit modeling approach that works completely on an Eulerian finite element mesh throughout the whole optimization process. To this aim, implicit level-set functions and R-functions are employed to describe geometrical shapes of movable components. In particular, a modified arctan function is adopted to depict the material discontinuity along the interface between the structure domain and each component domain. They are then used for material interpolations and analytical sensitivity analysis w.r.t. both pseudo-density design variables and location design variables related to the host structure and components, respectively. Based on a variety of numerical tests, it is demonstrated that considered design problems with movable components can easily be solved by extending the SIMP material model based topology optimization approach using an Eulerian mesh and the gradient-based optimization algorithm. © 2013 Elsevier B.V.


Chen J.,Northwestern Polytechnical University | Benesty J.,University of Québec | Pan C.,Northwestern Polytechnical University
Journal of the Acoustical Society of America | Year: 2014

Differential microphone array (DMA), a particular kind of sensor array that is responsive to the differential sound pressure field, has a broad range of applications in sound recording, noise reduction, signal separation, dereverberation, etc. Traditionally, an Nth-order DMA is formed by combining, in a linear manner, the outputs of a number of DMAs up to (including) the order of N - 1. This method, though simple and easy to implement, suffers from a number of drawbacks and practical limitations. This paper presents an approach to the design of linear DMAs. The proposed technique first transforms the microphone array signals into the short-time Fourier transform (STFT) domain and then converts the DMA beamforming design to simple linear systems to solve. It is shown that this approach is much more flexible as compared to the traditional methods in the design of different directivity patterns. Methods are also presented to deal with the white noise amplification problem that is considered to be the biggest hurdle for DMAs, particularly higher-order implementations. © 2014 Acoustical Society of America.


Fu M.S.,Northwestern Polytechnical University | Fu M.S.,Zhejiang University | Ni L.,Chang'an University | Du N.,Zhejiang University
Journal of Alloys and Compounds | Year: 2014

Porous hierarchical SnO2 ceramics is achieved by oxidizing the flowerlike SnS2 precursors, which are obtained via hydrothermal reaction between SnCl4 and thioacetamide. The release rate of the sulfur ions from the sulfur source plays the most important role in the formation of flowerlike microstructures which define the morphology of the resulted SnO2. The obtained SnO2 by annealing exhibits a porous hierarchical microstructure with large surface-to-volume ratio because of the large and small pores between and in the flowers. The porous hierarchical SnO2 ceramics shows a promising capacity of 1645.5 mA h g -1 at the current of 100 mA g-1, and remains 660.5 mA h g-1 after 20 cycles when used as anode of lithium-ion batteries. The enhanced cycling performance than SnO2 nanoparticles should be due to that the porous hierarchical microstructure could provide more reaction sites and give channels making Li+ transport more efficiently. © 2013 Elsevier B.V. All rights reserved.


Liu Z.-G.,Northwestern Polytechnical University | Liu Z.-G.,Telecom Bretagne | Dezert J.,ONERA | Pan Q.,Northwestern Polytechnical University | Mercier G.,Telecom Bretagne
Decision Support Systems | Year: 2011

The sources of evidence may have different reliability and importance in real applications for decision making. The estimation of the discounting (weighting) factors when the prior knowledge is unknown have been regularly studied until recently. In the past, the determination of the weighting factors focused only on reliability discounting rule and it was mainly dependent on the dissimilarity measure between basic belief assignments (bba's) represented by an evidential distance. Nevertheless, it is very difficult to characterize efficiently the dissimilarity only through an evidential distance. Thus, both a distance and a conflict coefficient based on probabilistic transformations BetP are proposed to characterize the dissimilarity. The distance represents the difference between bba's, whereas the conflict coefficient reveals the divergence degree of the hypotheses that two belief functions strongly support. These two aspects of dissimilarity are complementary in a certain sense, and their fusion is used as the dissimilarity measure. Then, a new estimation method of weighting factors is presented by using the proposed dissimilarity measure. In the evaluation of weight of a source, both its dissimilarity with other sources and their weighting factors are considered. The weighting factors can be applied in the both importance and reliability discounting rules, but the selection of the adapted discounting rule should depend on the actual application. Simple numerical examples are given to illustrate the interest of the proposed approach. © 2011 Published by Elsevier B.V. All rights reserved.


Chen J.,Northwestern Polytechnical University | Benesty J.,University of Québec
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2012

This paper studies the problem of noise reduction in the short-time Fourier transform (STFT) domain. Traditionally, the STFT coefficients in different frequency bands are assumed to be independent. This assumption holds when the signals are stationary and the fast Fourier transform(FFT) length is sufficiently large. In practice, however, speech is nonstationary and also the FFT length cannot be very large due to practical reasons. So, there always exists some correlation between STFT coefficients from neighboring frequency bands. An important question then arises: how the interband correlation can be used to optimize noise reduction performance? This paper addresses this issue. We discuss two solutions in the framework of the bifrequency spectrum. One considers the cross-correlation between all the frequency bands and the other takes into account only the cross-correlation between neighboring bands. While the former is optimal from a theoretical perspective, the latter is more practical as it is more immune to the error in correlation matrix estimation. © 2012 IEEE.


Benesty J.,University of Québec | Chen J.,Northwestern Polytechnical University
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2012

This paper deals with the problem of binaural noise reduction using an array of microphones. This is a very important problem in applications such as teleconferencing and hearing aids where there is a need to mitigate the noise effect from the noisy signals picked up by multiple microphones and produce two "clean" outputs. The mitigation of the noise should be made in such a way that no audible distortion is added to the two outputs (this is the same as in the single-channel case) and meanwhile the spatial information of the desired sound source should be preserved so that, after noise reduction, the listener will still be able to localize the sound source thanks to his/her binaural hearing mechanism. In this paper, we present a novel approach to this problem where we first form a number of complex input signals from the multiple and real microphone observations. We also merge the two expected real outputs into a complex output signal. The widely linear estimation theory is then used to derive optimal noise reduction filters that can achieve noise reduction while preserving the desired signal (speech) and its spatial information. With this new formulation, the Wiener and minimum variance distortionless response (MVDR) filters are derived. Experiments are provided to justify the effectiveness of these filters. © 2012 IEEE.


Jia W.,Northwestern Polytechnical University | Zhu W.,Northwestern Polytechnical University | Zhu W.,Zhejiang University
Nonlinear Dynamics | Year: 2014

A stochastic averaging method for predicting the response of quasi-integrable and non-resonant Hamiltonian systems to combined Gaussian and Poisson white noise excitations is proposed. First, the motion equations of a quasi-integrable and non-resonant Hamiltonian system subject to combined Gaussian and Poisson white noise excitations is transformed into stochastic integro-differential equations (SIDEs). Then n -dimensional averaged SIDEs and generalized Fokker-Plank-Kolmogrov (GFPK) equations for the transition probability densities of n action variables and n - independent integrals of motion are derived by using stochastic jump-diffusion chain rule and stochastic averaging principle. The probability density of the stationary response is obtained by solving the averaged GFPK equation using the perturbation method. Finally, as an example, two coupled non-linear damping oscillators under both external and parametric excitations of combined Gaussian and Poisson white noises are worked out in detail to illustrate the application and validity of the proposed stochastic averaging method. © 2014 Springer Science+Business Media Dordrecht.


Liu Z.-G.,Northwestern Polytechnical University | Pan Q.,Northwestern Polytechnical University | Dezert J.,ONERA
Knowledge-Based Systems | Year: 2013

A new evidential classifier (EC) based on belief functions is developed in this paper for the classification of imprecise data using K-nearest neighbors. EC works with credal classification which allows to classify the objects either in the specific classes, in the meta-classes defined by the union of several specific classes, or in the ignorant class for the outlier detection. The main idea of EC is to not classify an object in a particular class whenever the object is simultaneously close to several classes that turn to be indistinguishable for it. In such case, EC will associate the object with a proper meta-class in order to reduce the misclassification errors. The full ignorant class is interpreted as the class of outliers representing all the objects that are too far from the other data. The K basic belief assignments (bba's) associated with the object are determined by the distances of the object to its K-nearest neighbors and some chosen imprecision thresholds. The classification of the object depends on the global combination results of these K bba's. The interest and potential of this new evidential classifier with respect to other classical methods are illustrated through several examples based on artificial and real data sets. © 2013 Elsevier B.V. All rights reserved.


Liu H.,Northwestern Polytechnical University | Cai J.,Northwestern Polytechnical University | Martinez L.,University of Jaén
Knowledge-Based Systems | Year: 2013

The uncertainty of decision making problems means that the assessments may be provided by means of continuous intervals. The importance weighted continuous ordered weighted averaging operator has been developed in the case that the values in an interval have associated importance weights. In order to provide better properties of the importance weighted aggregation method, we propose the importance weighted continuous generalized ordered weighted averaging (IW-CGOWA) operator and its attitudinal character. We study the properties of the IW-CGOWA operator and introduce its special cases. We then extend the IW-CGOWA operator to aggregate multiple continuous arguments. A group decision making model based on the IW-CGOWA operator is introduced and a numerical example with a comparative analysis among different aggregation operators is then provided to show the flexibility and generality of the IW-CGOWA operator. © 2013 Elsevier B.V. All rights reserved.


Li S.,University of Michigan | Deng J.,University of Michigan | Deng J.,Northwestern Polytechnical University | Mi C.C.,University of Michigan
IEEE Transactions on Vehicular Technology | Year: 2013

This paper presents the study of a single-stage onboard battery charger for electric vehicle (EV) and plug-in hybrid EV (PHEV) applications. The topology had never been seen in any literature or patents but is employed in the NLG5 charger made by Brusa Elektronik AG. We thoroughly analyzed the topology and thought it would be beneficial to publish it so that advanced work can be done based on the existing structure. The charger directly transfers power from the alternating current (ac) to the battery side; thus, the bulky electrolytic capacitor in a traditional two-stage charger is eliminated. Power factor correction (PFC) is inherently achieved; thus, the control becomes very simple. In addition, all the power switches work at a zero-current switching (ZCS) condition to reduce the switching loss. The charger charges the battery with a sinusoidal-like charging current instead of a constant direct current. However, this current waveform has minimal impact on the battery life and efficiency, as demonstrated by other studies. Hence, having the advantages of high efficiency, compact size, easy control, and no need of an electrolytic capacitor, the topology is suitable for the PHEV and the pure EV onboard charging applications. © 2013 IEEE.


Liu H.,Northwestern Polytechnical University | Rodriguez R.M.,University of Jaén
Information Sciences | Year: 2014

Decision making is a process common to human beings. The uncertainty and fuzziness of problems demand the use of the fuzzy linguistic approach to model qualitative aspects of problems related to decision. The recent proposal of hesitant fuzzy linguistic term sets supports the elicitation of comparative linguistic expressions in hesitant situations when experts hesitate among different linguistic terms to provide their assessments. The use of linguistic intervals whose results lose their initial fuzzy representation was introduced to facilitate the computing processes in which such expressions are used. The aim of this paper is to present a new representation of the hesitant fuzzy linguistic term sets by means of a fuzzy envelope to carry out the computing with words processes. This new fuzzy envelope can be directly applied to fuzzy multicriteria decision making models. An illustrative example of its application to a supplier selection problem through the use of fuzzy TOPSIS is presented. © 2013 Elsevier Inc. All rights reserved.


Liu W.-Y.,Northwestern Polytechnical University | Zhu W.-Q.,Northwestern Polytechnical University | Zhu W.-Q.,Zhejiang University | Xu W.,Northwestern Polytechnical University
Probabilistic Engineering Mechanics | Year: 2013

The asymptotic Lyapunov stability with probability one of n-degree-of-freedom (n-DOF) quasi non-integrable Hamiltonian systems subject to weakly parametric excitations of combined Gaussian and Poisson white noises is studied by using the largest Lyapunov exponent. First, an n-DOF quasi non-integrable Hamiltonian system subject to weakly parametric excitations of combined Gaussian and Poisson white noises is reduced to a one-dimensional averaged Itô stochastic differential equation (SDE) for Hamiltonian by using the stochastic averaging method for quasi non-integrable Hamiltonian systems. Then, the expression for the Lyapunov exponent of the averaged Itô SDE is derived and the approximately necessary and sufficient condition for the asymptotic Lyapunov stability with probability one of the trivial solution of the original system is obtained. Finally, one example is worked out to illustrate the proposed procedure and its effectiveness is confirmed by comparing with Monte Carlo simulation. It is found that analytical and simulation results agree well. © 2013 Elsevier Ltd.


Liu Z.-G.,Northwestern Polytechnical University | Pan Q.,Northwestern Polytechnical University | Dezert J.,ONERA
Pattern Recognition | Year: 2013

The K-nearest neighbor (K-NN) classification method originally developed in the probabilistic framework has serious difficulties to classify correctly the close data points (objects) originating from different classes. To cope with such difficult problem and make the classification result more robust to misclassification errors, we propose a new belief-based K-nearest neighbor (BK-NN) method that allows each object to belong both to the specific classes and to the sets of classes with different masses of belief. BK-NN is able to provide a hyper-credal classification on the specific classes, the rejection classes and the meta-classes as well. Thus, the objects hard to classify correctly are automatically committed to a meta-class or to a rejection class, which can reduce the misclassification errors. The basic belief assignment (bba) of each object is defined from the distance between the object and its neighbors and from the acceptance and rejection thresholds. The bba's are combined using a new combination method specially developed for the BK-NN. Several experiments based on simulated and real data sets have been carried out to evaluate the performances of the BK-NN method with respect to several classical K-NN approaches.


Xuetao S.,Northwestern Polytechnical University | Kezhi L.,Northwestern Polytechnical University | Hejun L.,Northwestern Polytechnical University | Hongying D.,Jinxi Machinery Industries Group Corporation | And 2 more authors.
Carbon | Year: 2010

Carbon/carbon composites doped with zirconium carbide were prepared by a three-step process. Carbon fiber felts were first immersed in a zirconium oxychloride solution, followed by rapid densification using thermal gradient chemical vapor infiltration. The densified carbon/carbon composites were then graphitized at 2500 °C. The phase composition and morphology of the composites were investigated by X-ray diffraction and scanning electron microscopy. The ablation properties were tested in an oxyacetylene torch. The results show that the linear and mass ablation rates of the composites after doping with 4.14 wt.% zirconium carbide decreased by 83.0% and 77.0%, respectively. The ablated surface of the carbon matrix for pure carbon/carbon composites was very smooth and glossy, while that for doped carbon/carbon composites was honeycombed and dim. The bonding between carbon fibers and matrix decreased because of the formation of more zirconium dioxide, resulting in carbon fibers peeling off the matrix and the ablation resistance of carbon fibers could not be brought into play when the zirconium carbide contents achieved 4.14 wt.%. Although mechanical denudation does not seem to play a dominant role, the ablation was mainly controlled by heterogeneous mass transfer. © 2009 Elsevier Ltd. All rights reserved.


Jia W.,Northwestern Polytechnical University | Zhu W.,Northwestern Polytechnical University | Zhu W.,Zhejiang University
Physica A: Statistical Mechanics and its Applications | Year: 2014

A stochastic averaging method for predicting the response of quasi-partially integrable and non-resonant Hamiltonian systems to combined Gaussian and Poisson white noise excitations is proposed. For the case with r(1


Zhang H.,Northwestern Polytechnical University | Chen J.,Northwestern Polytechnical University | Benesty J.,University of Québec
Applied Acoustics | Year: 2015

The performance of differential microphone arrays (DMAs) depends on many factors such as the number of sensors and the array geometry. This paper develops an approach that exploits nonuniform linear geometries and the minimum-norm filter to improve the robustness of DMAs against white noise. Unlike the conventional way that forms an Nth-order DMA by subtractively combining the outputs of two DMAs of order N - 1, this approach works in the short-time Fourier transform (STFT) domain and applies a complex weight to the output of each sensor and then sum the weighted outputs to form the beamforming output in every STFT subband. The minimum-norm filter is obtained by maximizing the white noise gain of the beamformer subject to the so-called fundamental constraints. The nonuniform linear arrays are created by adjusting the interelement spacing according to some rule. We show that the use of nonuniform linear geometries can significantly improve the robustness of DMAs, particularly at low frequencies. We also show that the diagonal loading technique can help improve the robustness of DMA beamformers, though the improvement is not significant. © 2015 Elsevier Ltd. All rights reserved.


Gao W.,University of Nice Sophia Antipolis | Gao W.,Northwestern Polytechnical University | Chen J.,University of Nice Sophia Antipolis | Richard C.,University of Nice Sophia Antipolis | Huang J.,Northwestern Polytechnical University
IEEE Transactions on Signal Processing | Year: 2014

Adaptive filtering algorithms operating in reproducing kernel Hilbert spaces have demonstrated superiority over their linear counterpart for nonlinear system identification. Unfortunately, an undesirable characteristic of these methods is that the order of the filters grows linearly with the number of input data. This dramatically increases the computational burden and memory requirement. A variety of strategies based on dictionary learning have been proposed to overcome this severe drawback. In the literature, there is no theoretical work that strictly analyzes the problem of updating the dictionary in a time-varying environment. In this paper, we present an analytical study of the convergence behavior of the Gaussian least-mean-square algorithm in the case where the statistics of the dictionary elements only partially match the statistics of the input data. This theoretical analysis highlights the need for updating the dictionary in an online way, by discarding the obsolete elements and adding appropriate ones. We introduce a kernel least-mean-square algorithm with ℓ1 -norm regularization to automatically perform this task. The stability in the mean of this method is analyzed, and the improvement of performance due to this dictionary adaptation is confirmed by simulations. © 1991-2012 IEEE.


Sun F.,Northwestern Polytechnical University | Sun F.,University of Technology of Belfort - Montbéliard | Zhang N.,University of Technology of Belfort - Montbéliard | Li J.,Northwestern Polytechnical University | Liao H.,University of Technology of Belfort - Montbéliard
Journal of Power Sources | Year: 2013

Magnesium doped lanthanum silicate with apatite-type structure, as a solid electrolyte for IT-SOFC (intermediate-temperature solid oxide fuel cells), was prepared by solid state sintering. The electrolyte coatings were fabricated by LPPS (Low Pressure Plasma Spraying) and VLPPS (Very Low Pressure Plasma Spraying). Their microstructures and phase composition were characterized by SEM and XRD. The gas permeability of coatings was measured with pure H 2 and O 2 at room temperature. It is shown that dense lanthanum silicate coatings can be obtained by LPPS and VLPPS. Amorphous and trace phases existed in coating deposited by LPPS. Well-crystallized lanthanum silicate coating can be prepared by one step VLPPS. The specific permeability of coating fabricated by VLPPS is 1.79 × 10 -19 m 2. © 2012 Elsevier B.V. All rights reserved.


Gu X.,Northwestern Polytechnical University | Zhu W.,Northwestern Polytechnical University | Zhu W.,Zhejiang University
Journal of Sound and Vibration | Year: 2014

A new stochastic averaging method for predicting the response of vibro-impact (VI) systems to random perturbations is proposed. First, the free VI system (without damping and random perturbation) is analyzed. The impact condition for the displacement is transformed to that for the system energy. Thus, the motion of the free VI systems is divided into periodic motion without impact and quasi-periodic motion with impact according to the level of system energy. The energy loss during each impact is found to be related to the restitution factor and the energy level before impact. Under the assumption of lightly damping and weakly random perturbation, the system energy is a slowly varying process and an averaged Itô stochastic differential equation for system energy can be derived. The drift and diffusion coefficients of the averaged Itô equation for system energy without impact are the functions of the damping and the random excitations, and those for system energy with impact are the functions of the damping, the random excitations and the impact energy loss. Finally, the averaged Fokker-Plank-Kolmogorov (FPK) equation associated with the averaged Itô equation is derived and solved to yield the stationary probability density of system energy. Numerical results for a nonlinear VI oscillator are obtained to illustrate the proposed stochastic averaging method. Monte-Carlo simulation (MCS) is also conducted to show that the proposed stochastic averaging method is quite effective. © 2014 Elsevier Ltd. All rights reserved.


Liu Z.-G.,Northwestern Polytechnical University | Pan Q.,Northwestern Polytechnical University | Dezert J.,ONERA
Neurocomputing | Year: 2014

In this paper, we present a new belief c×. K neighbor (BCKN) classifier based on evidence theory for data classification when the available attribute information appears insufficient to correctly classify objects in specific classes. In BCKN, the query object is classified according to its K nearest neighbors in each class, and c×. K neighbors are involved in the BCKN approach (c being the number of classes). BCKN works with the credal classification introduced in the belief function framework. It allows to commit, with different masses of belief, an object not only to a specific class, but also to a set of classes (called meta-class), or eventually to the ignorant class characterizing the outlier. The objects that lie in the overlapping zone of different classes cannot be reasonably committed to a particular class, and that is why such objects will be assigned to the associated meta-class defined by the union of these different classes. Such an approach allows to reduce the misclassification errors at the price of the detriment of the overall classification precision, which is usually preferable in some applications. The objects too far from the others will be naturally considered as outliers. The credal classification is interesting to explore the imprecision of class, and it can also provide a deeper insight into the data structure. The results of several experiments are given and analyzed to illustrate the potential of this new BCKN approach. © 2014 Elsevier B.V.


Liu Z.-G.,Northwestern Polytechnical University | Pan Q.,Northwestern Polytechnical University | Dezert J.,ONERA
Applied Intelligence | Year: 2014

The classification of imprecise data is a difficult task in general because the different classes can partially overlap. Moreover, the available attributes used for the classification are often insufficient to make a precise discrimination of the objects in the overlapping zones. A credal partition (classification) based on belief functions has already been proposed in the literature for data clustering. It allows the objects to belong (with different masses of belief) not only to the specific classes, but also to the sets of classes called meta-classes which correspond to the disjunction of several specific classes. In this paper, we propose a new belief classification rule (BCR) for the credal classification of uncertain and imprecise data. This new BCR approach reduces the misclassification errors of the objects difficult to classify by the conventional methods thanks to the introduction of the meta-classes. The objects too far from the others are considered as outliers. The basic belief assignment (bba) of an object is computed from the Mahalanobis distance between the object and the center of each specific class. The credal classification of the object is finally obtained by the combination of these bba's associated with the different classes. This approach offers a relatively low computational burden. Several experiments using both artificial and real data sets are presented at the end of this paper to evaluate and compare the performances of this BCR method with respect to other classification methods. © 2013 Springer Science+Business Media New York.


Ren A.,Northwestern Polytechnical University | Wu C.,Northwestern Polytechnical University | Gao Y.,Northwestern Polytechnical University | Yuan Y.,Siemens AG
IEEE Transactions on Antennas and Propagation | Year: 2012

A novel broadband antenna for ultrahigh-frequency (UHF) near-field radio frequency identification (RFID) applications is presented. The antenna is composed of a grounded coplanar waveguide (GCPW), a coplanar stripline (CPS), a lumped balun, multiple resistors, and a finite-sized ground plane. The load impedance is equal to the characteristic impedance of the CPS, hence traveling wave can transmit along the CPS. The proposed antenna structure can produce large currents along the CPS so that a strong and uniform magnetic field distribution is excited in the adjacent region around the antenna. The antenna geometry, design concept, simulated, and measured results are carefully discussed throughout the paper. Measurements show that the antenna operating with a commercial reader demonstrates good performance of tag identification with inductive coupling for near-field RFID applications. In addition, the parametric study is conducted to facilitate the design and optimization processes for engineers. © 2012 IEEE.


Mei S.,Northwestern Polytechnical University | He M.,Northwestern Polytechnical University | Wang Z.,University of Sydney | Feng D.,University of Sydney
IEEE Transactions on Geoscience and Remote Sensing | Year: 2010

Spectral mixture analysis (SMA) has been widely utilized to address the mixed-pixel problem in the quantitative analysis of hyperspectral remote sensing images, in which endmember extraction (EE) plays an extremely important role. In this paper, a novel algorithm is proposed to integrate both spectral similarity and spatial context for EE. The spatial context is exploited from two aspects. At first, initial endmember candidates are identified by determining the spatial purity (SP) of pixels in their spatial neighborhoods (SNs). Several SP measurements are investigated at both intensity level and feature level. In order to alleviate local spectra variability, the average of the pixels in pure SNs are voted as endmember candidates. Then, the spatial connectivity is utilized to merge spatially related endmember candidates by finding connection paths in a graph so that the number of endmember candidates is further reduced, which results in computational efficiency and better performance in SMA by alleviating global spectral variability. Experimental results on both synthetic and real hyperspectral images demonstrate that the proposed SP based EE (SPEE) algorithm outperforms the other popular EE algorithms. It is also observed that feature-level SP measurements are more distinguishable than intensity-level SP measurements to discriminate pure SNs from mixed SNs. © 2006 IEEE.


Yu K.,Henan University of Science and Technology | Yang X.,Northwestern Polytechnical University | Yue Z.,Northwestern Polytechnical University
Structural and Multidisciplinary Optimization | Year: 2011

This study presents a numerical procedure to optimize the cooling passage structure of turbine blade to enhance aerodynamic and heat transfer. Surrogate model based optimization technique is used with Navier-Stokes analysis of fluid flow and heat transfer with RNG k-epsilon transport turbulence model. The objective function is defined as a nonlinear combination of heat transfer and pressure loss with K-S function. Optimal Latin Hypercube Sampling is used to determine the training points as a mean of design of experiment. Two Loops Dynamic Optimization System (TLDOS) is performed to implement the cooling blade optimization. Blade performance improves obviously, especially the kriging model based system. Result shows a significant impact of rib positions for blade heat transfer but slightly for total pressure loss. Numerical simulation proves the feasibility and validity of the TLDOS methods. © 2010 Springer-Verlag.


Wang K.,Chongqing University | Li M.,Northwestern Polytechnical University | Liu Q.,Chongqing University
Materials Characterization | Year: 2016

A TC8 titanium alloy was isothermally compressed at the strain rates of 10–50 s− 1 in the two-phase region of 820–940 °C, and the evolution mechanisms of the primary α and β phases, including grain morphology, dynamic recovery (DRV) and dynamic recrystallization (DRX), were investigated by optical microscopy (OM) and transmission electron microscopy (TEM). OM reveals that the phase content and grain morphology are more significantly influenced by the deformation temperature than the strain rate. The β grains achieve refinement only at 940 °C due to DRX in the β phase. TEM reveals the remarkable variations of the DRX grains, subgrains, sub-boundaries and dislocations morphology with temperature and strain rate related to DRV and DRX in the primary α phase. The DRX in the primary α phase appears most strongly at a middle temperature of 860 °C, and DRV dominates in the primary α phase at 940 °C. While the dominant mechanism varies from DRV to DRX in the β phase as the temperature increases. Finally, the influence mechanism of deformation parameters on the primary α grain morphology is revealed based on the combined effect of DRV and DRX in the primary α phase and diffusion of the β phase. © 2016 Elsevier Inc.


Li Y.,Northwestern Polytechnical University | Gong H.,Northwestern Polytechnical University | Feng D.,University of Sydney | Zhang Y.,Northwestern Polytechnical University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2011

This paper proposes an adaptive method based on the mirror-extended curvelet transform and the improved particle swarm optimization (PSO) algorithm, which reduce speckle noise and enhance edge features and contrast of synthetic aperture radar (SAR) images. First, an improved gain function, which integrates the speckle reduction with the feature enhancement, is introduced to nonlinearly shrink and stretch the curvelet coefficients. Then, a novel objective criterion for the quality of the despeckled and enhanced images is proposed in order to adaptively obtain the optimal parameters in the gain function. Finally, the PSO algorithm is employed as a global search strategy for the best despeckled and enhanced image. In order to increase the convergence speed and avoid the premature convergence, two further improvements for the classic PSO algorithm are presented. That is, a new learning scheme and a mutation operator are introduced. Experimental results demonstrate that the proposed method can efficiently reduce the speckle and enhance the edge features and the contrast of SAR images and outperforms the wavelet- and curvelet-based nonadaptive despeckling and enhancement methods. © 2011 IEEE.


Lou Y.,Northwestern Polytechnical University | Lou Y.,Henan University of Science and Technology | Li Z.,Northwestern Polytechnical University | Chen Q.,Northwestern Polytechnical University
Information Sciences | Year: 2012

Keyword search is a user-friendly mechanism used to retrieve XML data for web and scientific applications. Unlike text data, XML data contain rich semantics, which are obviously useful for information retrieval. It is observed that most existing approaches for XML keyword search either do not consider relevance ranking or perform relevance ranking using traditional text IR techniques. Based on an in-depth analysis of user information need and XML structural semantics, we propose to rank the relevance between a keyword query and an XML fragment by their semantic similarity. We first present a formula to quantify the concept of semantic similarity and then introduce a novel semantic ranking scheme for XML keyword search. Our extensive experiments demonstrate that the proposed scheme outperforms existing approaches in terms of search quality and achieve high efficiency and scalability. © 2011 Elsevier Inc. All rights reserved.


Yao Y.,Northwestern Polytechnical University | Keer L.M.,Northwestern University
Microelectronics Reliability | Year: 2013

Lead free solders are replacing lead rich solders in the electronic industry, the performance and safety of lead free solder interconnects in electric packaging under drop impact becomes a critical concern of semiconductor and electronic product manufacturers. Compared with the lead rich solder alloy, lead free solder alloy typically has higher rigidity and lower ductility. The presence of the Intermetallic Compound (IMC) layer can also affect the drop impact response of the solder interconnect, which may lead to quasi-brittle solder/IMC interfacial fracture. The traditional drop test is expensive and time consuming, and it is quite difficult to observe the full dynamic responses during the drop impact. In the present study, numerical analysis is performed to investigate drop impact effect on ball grid array (BGA) electronic packaging with the intention of predicting the performance of solders under drop impact and providing the fundamental understanding required to design a reliable electric packaging. A three dimensional finite element model is developed to simulate the solder interconnect and electronic packaging failure under board-level drop impact. An impact analysis procedure coupled with sub-modeling technique is established. The Cu6Sn5 and Cu3Sn IMC layers are incorporated in the solder interconnects model; cohesive fracture mechanics based method is applied to predict the crack initiation and propagation near the IMC/solder interface. A lead-free solder alloy constitutive relationship comprising elastic and rate dependent plastic effects is incorporated in the computational model. © 2012 Elsevier Ltd. All rights reserved.


Yao Y.,Northwestern Polytechnical University | Fry J.,Northwestern University | Fine M.E.,Northwestern University | Keer L.M.,Northwestern University
Acta Materialia | Year: 2013

Lead-free solders are replacing lead-rich solders in the electronics industry. Due to the limitation of available experimental data for thermal conductivity of lead-free solder and intermetallic compound (IMC) materials, the Wiedemann-Franz-Lorenz (WFL) relation is presented in this paper as a possible solution to predict thermal conductivity with known electrical conductivity. The method is based upon the fact that heat and electrical transport both involve free electrons. The thermal and electrical conductivities of Cu, Ni, Sn and different Sn-rich lead-free solder and IMC materials are studied by employing the WFL relation. Generally, analysis of the experimental data shows that the WFL relation is obeyed in both solder alloy and IMC materials, especially matching close to the relation for Sn, with a positive deviation from the theoretical Lorenz number. Thus, with the available electrical conductivity data, the thermal conductivity of solder and IMC materials can be obtained based on the proper WFL relation, and vice versa. A coupled thermal-electrical three-dimensional finite element analysis is performed to study the behavior of lead-free solder/IMC interconnects. Solder and IMC material properties predicted using the WFL relation are adopted in the computational model. By applying the WFL relation, the number of experiments required to determine the material properties for different lead-free solder/IMC interconnects can be significantly reduced, which can lead to pronounced savings of time and cost. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.


Han J.,Northwestern Polytechnical University | Zhang D.,Northwestern Polytechnical University | Cheng G.,Northwestern Polytechnical University | Guo L.,Northwestern Polytechnical University | Ren J.,University of Strathclyde
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015

The abundant spatial and contextual information provided by the advanced remote sensing technology has facilitated subsequent automatic interpretation of the optical remote sensing images (RSIs). In this paper, a novel and effective geospatial object detection framework is proposed by combining the weakly supervised learning (WSL) and high-level feature learning. First, deep Boltzmann machine is adopted to infer the spatial and structural information encoded in the low-level and middle-level features to effectively describe objects in optical RSIs. Then, a novel WSL approach is presented to object detection where the training sets require only binary labels indicating whether an image contains the target object or not. Based on the learnt high-level features, it jointly integrates saliency, intraclass compactness, and interclass separability in a Bayesian framework to initialize a set of training examples from weakly labeled images and start iterative learning of the object detector. A novel evaluation criterion is also developed to detect model drift and cease the iterative learning. Comprehensive experiments on three optical RSI data sets have demonstrated the efficacy of the proposed approach in benchmarking with several state-of-the-art supervised-learning-based object detection approaches. © 2014 IEEE.


Song H.-Y.,Northwestern Polytechnical University | Song H.-Y.,University of Posts and Telecommunications | Li Y.-L.,Northwestern Polytechnical University
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2012

The effect of twin spacing and temperature on the deformation behavior of nanotwinned magnesium is investigated using molecular dynamics simulation. The results indicate that there is a pronounced shift in the mechanical behavior of nanotwinned magnesium when twin spacing is smaller than 2.9 nm, and that the yield strength decreases with increasing temperature. The results show that at relatively high temperatures, a strength softening can be observed when twin spacing is larger than 7.8 nm. This study demonstrates that the yield strength is associated with the dislocation storage ability of nanotwinned magnesium and the repulsive force between twin boundaries and dislocations. © 2011 Elsevier B.V. All rights reserved.


Liu D.,Northwestern Polytechnical University | Zhu Z.,Shaanxi University of Science and Technology
Journal of Alloys and Compounds | Year: 2014

Al2O3:Eu3+ samples were synthesized via microwave solvothermal method and thermal decomposition of Eu3+ doped precursors. The sample characterizations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence (PL) spectra. XRD results indicated that Eu3+ doped samples were most of α-Al2O3 phase after being calcined at 1473 K. SEM results showed that the obtained α-Al2O3 based powders via microwave solvothermal method were microspheres with an average diameter about 1.6 μm. PL spectra showed that upon excitation at 393 nm, the orange-red emission bands at the wavelength longer than 560 nm were from 5D0 → 7FJ (J = 1, 2) transitions. The asymmetry ratio of (5D0 → 7F2)/(5D0 → 7F 1) intensity is about 1 and this value suggests that Eu3+ ions occupy the same ratio of symmetry and asymmetry sites. It is shown that the 0.7 mol% of doping concentration of Eu3+ ions in α-Al 2O3:Eu3+ is optimum. According to Dexter's theory, the critical distance between Eu3+ ions for energy transfer was determined to be 18 Å. © 2013 Elsevier B.V. All rights reserved.


Lagzi I.,Northwestern University | Kowalczyk B.,Northwestern University | Wang D.,Northwestern University | Grzybowski B.A.,Northwestern University | Grzybowski B.A.,Northwestern Polytechnical University
Angewandte Chemie - International Edition | Year: 2010

Rhythmic nanoparticles: Chemical oscillations can be coupled to the dynamic self-assembly of nanoparticles. Periodic pH changes translate into protonation and deprotonation of the ligands that stabilize the nanoparticles, thus altering repulsive and attractive interparticle forces. In a continuous stirred-tank reactor, rhythmic aggregation and dispersion is observed; in spatially distributed media, propagation of particle aggregation fronts is seen. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ren J.,University of Strathclyde | Zabalza J.,University of Strathclyde | Marshall S.,University of Strathclyde | Zheng J.,Northwestern Polytechnical University
IEEE Signal Processing Magazine | Year: 2014

With numerous and contiguous spectral bands acquired from visible light (400?1,000 nm) to (near) infrared (1,000?1,700 nm and over), hyperspectral imaging (HSI) can potentially identify different objects by detecting minor changes in temperature, moisture, and chemical content. As a result, HSI has been widely applied in a number of application areas, including remote sensing [1]. HSI data contains two-dimensional (2-D) spatial and one-dimensional spectral information, and naturally forms a three-dimensional (3-D) hypercube with a high spectral resolution in nanometers that enables robust discrimination of ground features. However, new challenges arise in dealing with extremely large data sets. For a hypercube with relatively small spatial dimension of 600 ? 400 pixels at 16 bits-per-band-per-pixel, the data volume becomes 120 MB for 250 spectral bands. In some cases, this large data volume can be linearly increased when multiple hypercubes are acquired across time to monitor system dynamics in consecutive time instants. When the ratio between the feature dimension (spectral bands) and the number of data samples (in vector-based pixels) is vastly different, high-dimensional data suffers from the well-known curse of dimensionality. For feature extraction and dimensionality reduction, principal components analysis (PCA) is widely used in HSI [2], where the number of extracted components is significantly reduced compared to the original feature dimension, i.e., the number of spectral bands. For effective analysis of large-scale data in HSI, conventional PCA faces three main challenges: © 2014 IEEE.


Gao S.,Northwestern Polytechnical University | Zhong Y.,Curtin University Australia | Li W.,Northwestern Polytechnical University
IEEE Sensors Journal | Year: 2011

This paper presents a new data fusion method by adopting random weighting estimation for optimal weighted fusion of multisensor observation data. This method adjusts in real time the weights of individual sensors according to variations in estimated sensor variances to obtain optimal weight distribution. Theories of random weighting estimation are established for optimal data fusion through optimal weighting distribution. Algorithms of random weighting estimation are developed to calculate sensor variances for determination of optimal random weighting factors. The fusion result in least mean square error is achieved directly from multisensor observation data, without requirement of any prior knowledge on unknown parameters. The mean square error estimated by the proposed method is not only smaller than from each individual sensor, but also smaller than by the mean of multisensor observation data. © 2006 IEEE.


Wang H.,University of Sichuan | Geng W.-C.,Northwestern Polytechnical University
Research on Chemical Intermediates | Year: 2011

Monodispersed α-Fe2O3 nanoparticles modified by sodium dodecylbenzene sulfonate (SDBS) surfactant and assisted by glycerol have been successfully synthesized via a hydrothermal process using FeCl 3•6H2O as the starting precursor. These nanoparticles possess good crystallinity and have an average particle size of 100 nm. The as-prepared products are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and a superconducting quantum interference device magnetometer. SDBS and glycerol played an important role in controlling the final morphology of the products. Magnetic hysteresis measurements reveal that monodispersed α-Fe2O3 nanoparticles exhibit normal ferromagnetic behaviors with the remanent magnetization and coercivity of 0.2389 emu/g and 2339.0 Oe at room temperature. © 2011 Springer Science+Business Media B.V.


Wang D.,Northwestern Polytechnical University | Wang D.,Northwestern University | Nap R.J.,Northwestern University | Lagzi I.,Northwestern University | And 4 more authors.
Journal of the American Chemical Society | Year: 2011

Dissociation of ionizable ligands immobilized on nanopaticles (NPs) depends on and can be regulated by the curvature of these particles as well as the size and the concentration of counterions. The apparent acid dissociation constant (pKa) of the NP-immobilized ligands lies between that of free ligands and ligands self-assembled on a flat surface. This phenomenon is explicitly rationalized by a theoretical model that accounts fully for the molecular details (size, shape, conformation, and charge distribution) of both the NPs and the counterions. © 2011 American Chemical Society.


Wang L.,Northwestern Polytechnical University | Yang Z.,Northwestern Polytechnical University | Waters T.P.,University of Southampton
Journal of Sound and Vibration | Year: 2010

Structural damage detection methods based on vibration responses are appealing for a variety of reasons such as their potential to observe damage from sensors placed remote from an unknown damage site. Of particular interest to the authors is online damage detection in which changes in the structure can be flagged up in an automated fashion by permanently installed transducers. In a previous paper by the authors, the inner product vector (IPV) was proposed as a damage detection algorithm which uses cross correlation functions between response measurements. Implicitly assumed in the formulation is that the response quantity is that of displacement resulting from white noise excitation. In this paper, the IPV technique is first reviewed and then generalised to address velocity and acceleration response to band pass white noise excitation. It is shown that the IPV is a weighted summation of the mode shapes, and the effect of some particular measurement noise on the IPV can be adaptively eliminated in the calculation of IPV. Then, the damage detection method based on changes in the IPV is proposed. Finally, damage detection experiments of shear frame structure, honeycomb sandwich composite beam and aircraft stiffened panel are presented to illustrate the feasibility and effectiveness of the proposed method. Crown Copyright © 2010 Published by Elsevier Ltd. All rights reserved.


Gao S.,Northwestern Polytechnical University | Zhong Y.,Curtin University Australia | Li W.,Northwestern Polytechnical University
Aerospace Science and Technology | Year: 2011

This paper presents a new robust adaptive filtering method for SINS/SAR (Strap-down Inertial Navigation System/Synthetic Aperture Radar) integrated navigation system. This method adopts the principle of robust estimation to adaptive filtering of observational data. A robust adaptive filter is developed to adaptively determine the covariance matrix of observation noise, and adaptively adjust the covariance matrix of system state noise according to the adaptive factor constructed based on predicted residuals. Experimental results and comparison analysis demonstrate that the proposed method cannot only effectively resist disturbances due to system state noise and observation noise, but it can also achieve higher accuracy than the adaptive Kalman filtering method. © 2010 Elsevier Masson SAS. All rights reserved.


Kou L.,Nanjing University of Aeronautics and Astronautics | Li C.,Northwestern Polytechnical University | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Guo W.,Nanjing University of Aeronautics and Astronautics
ACS Nano | Year: 2010

We show by first-principles calculations that the magnetic moments of zigzag ZnO nanoribbons can be efficiently modulated by transverse electric fields. Depending on the field direction, the total magnetic moment in a zigzag ZnO nanoribbon can be remarkably enhanced or reduced and even completely quenched with increasing field over a threshold strength. However, in weak electric fields below the threshold, the magnetic moment in the zigzag ZnO nanoribbons nearly remains unchanged, which can be explained in terms of intrinsic transverse electric polarization and quantum confinement effects. The threshold electric field required to modulate the magnetic moment decreases significantly with increasing ribbon width, showing practical importance. © 2010 American Chemical Society.


Hu D.,Northwestern Polytechnical University | Li X.,CAS Xi'an Institute of Optics and Precision Mechanic | Lu X.,CAS Xi'an Institute of Optics and Precision Mechanic
Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition | Year: 2016

In view of the advantages of deep networks in producing useful representation, the generated features of different modality data (such as image, audio) can be jointly learned using Multimodal Restricted Boltzmann Machines (MRB-M). Recently, audiovisual speech recognition based the M-RBM has attracted much attention, and the MRBM shows its effectiveness in learning the joint representation across audiovisual modalities. However, the built networks have weakness in modeling the multimodal sequence which is the natural property of speech signal. In this paper, we will introduce a novel temporal multimodal deep learning architecture, named as Recurrent Temporal Multimodal RB-M (RTMRBM), that models multimodal sequences by transforming the sequence of connected MRBMs into a probabilistic series model. Compared with existing multimodal networks, it's simple and efficient in learning temporal joint representation. We evaluate our model on audiovisual speech datasets, two public (AVLetters and AVLetters2) and one self-build. The experimental results demonstrate that our approach can obviously improve the accuracy of recognition compared with standard MRBM and the temporal model based on conditional RBM. In addition, RTMRBM still outperforms non-temporal multimodal deep networks in the presence of the weakness of long-term dependencies.


Peng B.,Northwestern Polytechnical University | Peng B.,Cranfield University | Fan H.,Northwestern Polytechnical University | Zhang Q.,Cranfield University
Journal of the American Ceramic Society | Year: 2013

Using a sol-gel method Pb0.8Ba0.2ZrO3 (PBZ) thin film with a thickness of ~320 nm was fabricated on Pt(111)/TiO x/SiO2/Si substrate. The analysis results of XRD, SEM, and dielectric properties revealed that this thin film is a (111)-oriented nano-scaled antiferroelectric and ferroelectric two-phase coexisted relaxor. Calculations of dielectric tunability (η) and figure-of-merit (FOM) at room temperature display a maximum value of 75% at E = 560 kV/cm and ~236, respectively. High-temperature stability (η > 75% and FOM > 230 at 560 kV/cm in the range from 300 to 380 K) and high breakdown dielectric strength (leakage current < 1 nA at 598 kV/cm) make the PBZ thin film to be an attractive material for applications of tunable devices. © 2013 The American Ceramic Society.


Fang J.,CAS Xi'an Institute of Optics and Precision Mechanic | Wang Q.,Northwestern Polytechnical University | Yuan Y.,CAS Xi'an Institute of Optics and Precision Mechanic
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014

Visual tracking in condition of occlusion, appearance or illumination change has been a challenging task over decades. Recently, some online trackers, based on the detection by classification framework, have achieved good performance. However, problems are still embodied in at least one of the three aspects: 1) tracking the target with a single region has poor adaptability for occlusion, appearance or illumination change; 2) lack of sample weight estimation, which may cause overfitting issue; and 3) inadequate motion model to prevent target from drifting. For tackling the above problems, this paper presents the contributions as follows: 1) a novel part-based structure is utilized in the online AdaBoost tracking; 2) attentional sample weighting and selection is tackled by introducing a weight relaxation factor, instead of treating the samples equally as traditional trackers do; and 3) a two-stage motion model, multiple parts constraint, is proposed and incorporated into the part-based structure to ensure a stable tracking. The effectiveness and efficiency of the proposed tracker is validated upon several complex video sequences, compared with seven popular online trackers. The experimental results show that the proposed tracker can achieve increased accuracy with comparable computational cost. © 2013 IEEE.


Kou L.,Nanjing University of Aeronautics and Astronautics | Li C.,Northwestern Polytechnical University | Zhang Z.,Nanjing University of Aeronautics and Astronautics | Guo W.,Nanjing University of Aeronautics and Astronautics
Journal of Physical Chemistry C | Year: 2010

We report on the electric-field- and H chemical-absorption-induced band manipulations of armchair ZnO nanoribbons using first-principles calculations. It is shown that the band gap of a semiconducting armchair nanoribbon can be reduced monotonically with increasing transverse field strength, demonstrating a giant Stark effect. The critical field strength to completely close the band gap decreases with increasing ribbon width, while it is almost independent of the stacking thickness. On the other hand, the nanoribbon with the edges fully passivated shows an enhanced gap but a slightly weaker Stark effect. We also observe hydrogentermination-induced metallization of the ribbons when only the edge O atoms are passivated, which results from an n-type doping effect. These findings suggest potential ways of band engineering in armchair ZnO nanoribbons. © 2010 American Chemical Society.


Chen M.,Nanjing University of Aeronautics and Astronautics | Wu Q.-X.,Nanjing University of Aeronautics and Astronautics | Cui R.-X.,Northwestern Polytechnical University
ISA Transactions | Year: 2013

In this paper, the terminal sliding mode tracking control is proposed for the uncertain single-input and single-output (SISO) nonlinear system with unknown external disturbance. For the unmeasured disturbance of nonlinear systems, terminal sliding mode disturbance observer is presented. The developed disturbance observer can guarantee the disturbance approximation error to converge to zero in the finite time. Based on the output of designed disturbance observer, the terminal sliding mode tracking control is presented for uncertain SISO nonlinear systems. Subsequently, terminal sliding mode tracking control is developed using disturbance observer technique f