Time filter

Source Type

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.

Zhang S.Q.,RWTH Aachen | Zhang S.Q.,Northwestern Polytechnical University | Schmidt R.,RWTH Aachen
Thin-Walled Structures | Year: 2014

A fully geometrically nonlinear finite element (FE) model is developed using large rotation shell theory for static analysis of composite and piezoelectric laminated thin-walled structures. The proposed large rotation theory is based on the first-order shear deformation (FOSD) hypothesis. It has six independent kinematic parameters which are expressed by five mechanical nodal degrees of freedom (DOFs). Linear electro-mechanically coupled constitutive equations with a constant electric field distribution through the thickness of each smart material layer are considered. Eight-node quadrilateral plate/shell elements with five mechanical DOFs per node and one electrical DOF per smart material layer are employed in the FE modeling. The present large rotation FE model is implemented into static analysis of both composite and piezoelectric laminated plates and shells. The equilibrium equation is solved by Newton-Raphson algorithm with system matrices updated in every iteration. The results are compared with those presented in the literature and others calculated by various simplified nonlinear shell theories. They indicate that large rotation theory has to be considered for the calculation of displacements and sensor output voltages of smart structures undergoing large deflections, since other simplified nonlinear theories fail to predict the static response precisely in many cases. © 2013 Elsevier Ltd.

Li P.,University of Technology of Troyes | Chen H.,University of Technology of Troyes | Che A.,Northwestern Polytechnical University
International Journal of Production Research | Year: 2013

For a supply chain modelled as a multi-echelon inventory system, effective management of its inventory at each stock is critical to reduce inventory costs while assuring a given service level to customers. In our previous work, we used the guaranteed-service approach (GSA) to design optimal echelon batch ordering policies for continuous-review serial systems with Poisson customer demand and fixed order costs. The approach assumes that the final customer demand is bounded and each stock has a guaranteed service time in the sense that the demand of its downstream stock can always be satisfied in the service time. This paper extends this work by considering more general assembly systems. We first derive an analytical expression for the total cost of the system in the long run. The problem of finding optimal echelon batch ordering policies for the system can then be decomposed into two independent sub-problems: order size decision sub-problem and reorder point decision sub-problem. We develop efficient dynamic programming algorithms for the two sub-problems. Numerical experiments on randomly generated instances show the effectiveness of the proposed approach. © 152013 © 2013 Taylor & Francis.

Xu C.,Lund University | Xu C.,Northwestern Polytechnical University | Konnov A.A.,Lund University
Energy | Year: 2012

Present work aims at evaluation of contemporary comprehensive detailed kinetic mechanisms for ethylene combustion, including the Konnov mechanism, LLNL nButane mechanism, San Diego (UCSD) mechanism and USC mechanism. These models have been validated by extensive comparison with available experimental data on ethylene ignition and flame propagation. The experimental data from the literature have been carefully examined to accurately assess the models' predicting performance. Noticeable differences in the predictions of ethylene ignition and flame propagation under a variety of conditions have been observed. Moreover, sensitivity analysis has been conducted to identify important reactions for the prediction of ethylene ignition and flames. For ethylene ignition, it was found that C 2H 4 consumption reactions with radicals OH, O and subsequent reactions of vinyl with oxygen have dominant effect on predicted ignition delays. The pathway analysis has also been performed for each mechanism to identify different reaction pathways in ethylene ignition process. For ethylene flames, sensitivity analysis shows that H-O and C 1 chemistry reactions significantly influence the laminar burning velocity in lean ethylene/air flames, while C 2 chemistry reactions become of increasing importance in fuel-rich flames. Furthermore, to better understand the models' predicting behavior, the differences in the reaction rate constants and routes of C 2H 4 and vinyl chemistry have been analyzed and discussed. © 2011 Elsevier Ltd.

Hong Z.,Northwestern Polytechnical University | Hong Z.,University of Bristol | Zhang J.,University of Bristol | Drinkwater B.W.,University of Bristol
Physical Review Letters | Year: 2015

We observe distinct regimes of orbital angular momentum (OAM) transfer from two-dimensional Bessel-shaped acoustic vortices to matter. In a homogeneous diphasic mixture of microparticles and water, slow swirling about the vortex axis is seen. This effect is driven by the absorption of OAM across the mixture, the motion following the OAM density distribution. Larger particles are formed into clusters by the acoustic radiation force, making the mixture nonhomogeneous. Here, the OAM transfer to the microparticle clusters dominates and they spin at high speeds entraining the surrounding fluid. © 2015 American Physical Society.

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.

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.

Sun H.,Northwestern Polytechnical University
International Journal of Internet Manufacturing and Services | Year: 2010

To describe interrelationship among enterprises in offering the product services, concept of product service relationship is proposed. The product service architecture is put forward to explain how product services act in the product structure and lifecycle. And product service network is adopted to model the product service relationship. The problem of how to evaluate the product service relationship is discussed in mathematical language. Two examples are given to validate these theories and methods. The paper points out some meaningful topics for future study about product service relationship. Copyright © 2010 Inderscience Enterprises Ltd.

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.

Guan X.,Northwestern Polytechnical University
AIAA Journal | Year: 2014

The wave drag is an important factor that affects the supersonic flight efficiency and is closely related to the aircraft's cross-sectional area distribution. A reasonable cross-sectional area distribution determines supersonic aircraft wave drag reduction. In this paper, an exploration of the supersonic aircraft wing-body shape parameterization using the class-shape-refinement-transformation technique and the method of extended far-field composite-element (EFCE) supersonic wing-body wave drag optimization are proposed. The method was applied to a supersonic civil transport wing-body shape optimization, yielding a 40.5% reduction of wave drag coefficient. In this way, the goal of reducing the wave drag in sufficient precision without any lift penalty was achieved. The EFCE wave drag optimization method is available in the conceptual design process of supersonic cruise aircraft to achieve high lift-to-drag ratio characteristics in supersonic flight conditions. © 2013 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

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.

Zhao X.,Northwestern Polytechnical University
Journal of Materials Chemistry | Year: 2012

The bottom-up fabrication of facile, lower-cost, larger areas optical metamaterials (OMMs) is expected to provide important benefits for applications in stealth technology and communication networks. Currently available OMMs at optical wavelengths are all composed of periodic structures, and fabricated by top-down approaches of e-beam lithography or focused ion beam technique. Limited by the high cost and extremely small sample volumes size, the fabrication of visible OMMs is still quite challenging on the nanometer scale. The rapid maturation of synthetic methodology in the field of the nanometer scale has lead to the creation of new materials at an incredible rate. In this review, we regard a V-shaped core as an artificial atom and a dendritic cell as an artificial molecule, and address the bottom-up fabrication and performance of optical metamaterials, and with an outlook toward developing devices capable of operating in optical media. © 2012 The Royal Society of Chemistry.

Liu L.,Northwestern Polytechnical University
Zhuzao/Foundry | Year: 2012

This paper reviews the principle, techniques, research statues and current problems of major processing technologies of cast superalloys, such as polycrystalline casting, directional solidification, single-crystal manufacture. The cast structure control and crystal orientation selection during solidification were analyzed. Single-crystal processing including bottom-seeding and spiral selection technique was summarized. The formation mechanism and control methods of typical cast defects in single crystal superalloys were analyzed. Finally, the possible development trends of the superalloy investment casting in future were prospected.

Li C.,Northwestern Polytechnical University | Jin W.,University of Kaiserslautern | Xiang H.,University of Kaiserslautern | Lefkidis G.,University of Kaiserslautern | Hubner W.,University of Kaiserslautern
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Laser-induced ultrafast spin manipulations in positively charged two-magnetic-center molecular ions with a small number of bridging atoms are investigated to explore the role of bridging atoms in the spin switching process and spin transferability between the magnetic centers via the Λ process. Taking O and Mg as examples for bridging atoms, fully ab initio calculations demonstrate that spin flip can be readily achieved on subpicosecond time scales at both magnetic centers of the linear structures composed of two nonidentical magnetic atoms with a single bridging atom in between. Although these two nonmagnetic elements possess completely different chemical and electronic natures, both types of bridging atoms contribute to spin density redistribution at the magnetic atoms, especially for the low-lying triplet states that are suitable to act as initial and final states in the Λ-type process of spin flip or transfer. This also provides a rule of thumb that spins in the linear structures can be flipped more easily since symmetric structures exhibit weaker magnetocrystalline anisotropy. The spin transfer process achieved in the structure [Fe-O(Mg)-Co]+ demonstrates that if both bridging atoms are involved to further lower the symmetry of the linear structures, spin transferability between the Fe and Co atoms can be improved. © 2011 American Physical 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.

Ruan Y.,Northwestern Polytechnical University
Physica Status Solidi (B) Basic Research | Year: 2013

Peri-eutectic transition was investigated in terms of the dependence of crystallization behavior on undercooling in Cu-Ag-Ge ternary alloy composed of (Ag), ζ(Cu5Ge), and ε2(Cu3Ge) phases. (Ag+ε2) pseudobinary eutectic is the product of both peri-eutectic and subsequent pseudobinary eutectic transitions. Nanoscale structure of anomalous (Ag+ε2) pseudobinary eutectic forms at the maximum undercooling, which is ascribed to the independent nucleation and growth from the liquid. The decrease of (Ag+ε2) pseudobinary eutectic at a high undercooling is due to that the phase transition happening at the beginning solidification stage proceeds more thoroughly at a higher undercooling. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

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.

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.

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.

Xu J.,Northwestern Polytechnical University
Applied Computational Electromagnetics Society Journal | Year: 2015

In this paper, a novel dual-wideband bandpass filter (BPF) is presented by using quarterwavelength open stub loaded half-wavelength coupledline. Equivalent voltage-current analysis method is applied to analyze this structure, which shows it has two tunable transmission zeros and dual-wideband frequency response. As an example, a dual-wideband BPF covering 1.228/1.57/6.8 GHz for GPS (Link 1 and Link 2) and RFID applications is designed, fabricated and measured. The fabricated filter has a compact size of 0.043λg × 0.213λg. The measured results show that the fabricated filter has the merits of low insertion loss, good return loss and high band-to-band isolation. The proposed dual-band BPF also has a very simple physical topology and quick design procedure. © 2015 ACES.

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.

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.

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.

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.

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.

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.

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.

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.

Luo Y.,Northwestern Polytechnical University
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics | Year: 2011

Many widely used materials, such as concrete, rocks, ceramics and polymers, have the feature of increasing shear strength as a result of hydrostatic pressure increases. Structures made of these pressure-dependent materials would typically hold the characteristic of better stress limit in tension than in compression. In this case, the von Mises criterion is incompetent while the D-P criterion described in terms of stress invariants is available as one of the simplest plasticity yield models. To take into account the asymmetrical compression and tension behaviors in the conceptual design of continuum structures, a practicable topology optimization strategy for pressure-dependent materials based on D-P yield criterion is presented in this paper. By using the element artificial relative densities as design variables, the optimization problem is formulated as to minimize the total material volume under D-P yield constraints on each element. In this optimization model, the SIMP interpolation for element stiffness and the power-law interpolation for the local stress of porous microstructures are adopted. In order to circumvent the stress singularity phenomenon, the ε-relaxation strategy is applied for relaxing the local yield constraints involved in the low-density elements. In this context, the sensitivity of the element constraints with respect to the design variables is efficiently derived by the adjoint variable method. Then, the optimal design is obtained by employing the gradient-based optimization algorithm. Finally, three numerical examples with different strength limits in compression and tension have been solved to illustrate the validity of the proposed optimization model as well as the efficiency of the numerical techniques. It is observed that the optimal material distribution designed by the present method may have a significant difference compared with one designed by the conventional von Mises stress constraint approach. The obtained optimization solutions are reasonable since they can make the best use of their strength in withstanding the compression. The meaning of the proposed method for pressure-dependent material structures is thus demonstrated.

Wei H.,Northwestern Polytechnical University
Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University | Year: 2015

This paper analyzed the needs for self-service of a company employee in detail. Though there was no login account in the ERP system, it still required the staff to provide self-service of their personal information. To solve this problem, this paper provided the safe and feasible integration of solutions-enterprise portals, EP and ERP, which could satisfy the requirement of single login. This paper carried out a detailed design for system architecture, discussing the authority control scheme and designing and making the codes for the key part of the program. The design of the employee self-service system was based on the B/S operation mode. It used Web Dynpro for Abap technology to develop. The easy-operatablity of program interface was close to that of Windows program, and its interactive performance had absolute advantage over that of the Web program. In addition, based on the premise of ensuring safety and authority-control, the system helped the staffs who had no ERP account protect their personal information in the ERP system. The safeguard measures in promoting the timely transfer of business processes were fairly advanced. ©, 2014, Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University. All right reserved.

Fan H.,Northwestern Polytechnical University | Fang P.,Xian Technological University | Xi Z.,Xian Technological University | Chen W.,Xian Technological University
Solid State Communications | Year: 2012

BaBi 4Ti 4O 15 (BBT) ceramic was synthesized using mixed oxide route and the structural and electrical properties were investigated systematically. The structural studies confirmed it to be an n=4 member of the Aurivillius oxide. A broad dielectric peak with frequency dependent dielectric maximum temperature was observed. The dielectric relaxation obeyed the Vogel-Fulcher relation wherein f 0=8.37E14 Hz, E a=0.13 eV, and T f=608.18 K. The diffuseness parameter γ established the relaxor nature and it was attributed to the A-site cationic disorder. The specimen exhibited the excellent reproducibility in the measurements of displacement current, a remnant polarization of 5.4 μC/cm 2, and a coercive field of 4.03 MV/m. The room temperature piezoelectric coefficient d 33 was found to be 23 pC/N and the field-induced strain S was about 0.018% at the 8 MV/m electric field. © 2012 Elsevier Ltd.

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.

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.

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.

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.

Yin D.-C.,Northwestern Polytechnical University
Progress in Crystal Growth and Characterization of Materials | Year: 2015

The rapid advance in superconducting magnet technology enables more and more applications for the use of high magnetic fields in scientific researches and industrial manufacturing. These applications include material processing, separation, chemical reaction, nuclear fusion, high energy physics, and many more. Generally, a superconducting magnet provides both homogeneous and inhomogeneous magnetic fields simultaneously, and both can affect the samples in the field so that the magnetic field can be utilized for various purposes. A homogeneous or inhomogeneous magnetic field will exert a torque on suspending particles in a solution if the particles have anisotropic magnetic susceptibility, which will further influence the properties of the solution; in an inhomogeneous magnetic field, a repulsive force will act on a diamagnetic solution so that the levels of apparent or effective gravity of the solution can be tuned in a vertical magnetic field. These effects can be utilized to govern the physical and chemical processes in solution like crystallization. In recent years, high magnetic fields have been applied in protein crystallization. It was found that a magnetic field can align the crystals along the field direction, decrease the diffusivity of macromolecules in the solution, and increase the viscosity of the solution; a suitable inhomogeneous magnetic field can damp the natural convection substantially, which resembles the case in a space environment. Both homogeneous and inhomogeneous magnetic fields have been found to improve the quality of some protein crystals. These discoveries showed that the researches on protein crystallization in high magnetic field is potentially valuable, because obtaining high quality protein crystals is important for 3-dimensional structure determination of proteins using X ray crystallography. This paper will review the background and more recent progress and discuss the future perspectives in this research field. © 2015 Elsevier Ltd.

He C.,Xian Jiaotong University | Zhang W.,Changan University | Deng J.,Changan 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.

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.

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.

Xu B.,Northwestern Polytechnical University | Wang D.,Nanyang Technological University | Wang H.,Nanyang Technological University | Zhu S.,Nanyang Technological University
Journal of Intelligent and Robotic Systems: Theory and Applications | Year: 2014

The article investigates the discretetime controller for the longitudinal dynamics of the hypersonic flight vehicle with throttle setting constraint. Based on functional decomposition, the dynamics can be decomposed into the altitude subsystem and the velocity subsystem. Furthermore, the discrete model could be derived using the Euler expansion. For the velocity subsystem, the controller is proposed by estimating the system uncertainty and unknown control gain separately with neural networks. The auxiliary error signal is designed to compensate the effect of throttle setting constraint. For the altitude subsystem, the desired control input is approximated by neural network while the error feedback is synthesized for the design. The singularity problem is avoided. Stability analysis proves that the errors of all the signals in the system are uniformly ultimately bounded. Simulation results show the effectiveness of the proposed controller. © Springer Science+Business Media Dordrecht 2013.

Wei D.,Northwestern Polytechnical University
Mathematical Problems in Engineering | Year: 2015

Navigation with the specific objective can be defined by specifying desired timed trajectory. The concept of desired direction field is proposed to deal with such navigation problem. To lay down a principled discussion of the accuracy and efficiency of navigation algorithms, strictly quantitative definitions of tracking error, actuator effect, and time efficiency are established. In this paper, one vision navigation control method based on desired direction field is proposed. This proposed method uses discrete image sequences to form discrete state space, which is especially suitable for bipedal walking robots with single camera walking on a free-barrier plane surface to track the specific objective without overshoot. The shortest path method (SPM) is proposed to design such direction field with the highest time efficiency. However, one improved control method called canonical piecewise-linear function (PLF) is proposed. In order to restrain the noise disturbance from the camera sensor, the band width control method is presented to significantly decrease the error influence. The robustness and efficiency of the proposed algorithm are illustrated through a number of computer simulations considering the error from camera sensor. Simulation results show that the robustness and efficiency can be balanced by choosing the proper controlling value of band width. © 2015 Dunwen Wei.

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 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.

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.

Xu J.,Northwestern Polytechnical University
Asia-Pacific Microwave Conference Proceedings, APMC | Year: 2016

This paper presents a novel mixed electric and magnetic coupling tri-band bandpass filter (BPF) by using multiple stubs loaded ring resonator. The first three resonant modes of this stubs loaded ring resonator can be separately controlled, resulting in the separately controlled passband frequencies and in-band return losses. Owing to the nature feature of stubs loaded ring resonator, directly coupled configuration and the cancelling effect of mixed electric and magnetic coupling, six transmission zeros can be seen around three passbands, which can improve the band-to-band isolation and passband selectivity significantly. As an example, a secondorder tri-band BPF centered at 0.9 / 2.4 / 3.5 GHz are designed and fabricated. The fabricated tri-band BPF has low insertion loss, good return loss and occupies a compact circuit area of 0.061λ g × 0.157λg. Good agreement between the simulated and measured results is obtained. © IEEE.

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.

Li X.,Nankai University | Shi Y.,Nankai University | Wei M.,Nankai University | Li J.,Northwestern Polytechnical University
Match | Year: 2014

For a given simple graph G, the energy of G, denoted by E(G), is defined as the sum of the absolute values of all eigenvalues of its adjacency matrix, which was defined by I. Gutman. The problem on determining the maximal energy tends to be complicated for a given class of graphs. There are many approaches on the maximal energy of trees, unicyclic graphs and bicyclic graphs, respectively. Let P6,6,6 n denote the graph with n ≥ 20 vertices obtained from three copies of C6 and a path Pn-18 by adding a single edge between each of two copies of C6 to one endpoint of the path and a single edge from the third C6 to the other endpoint of the Pn-18. Very recently, Aouchiche et al. [M. Aouchiche, G. Caporossi, P. Hansen, Open problems on graph eigenvalues studied with AutoGraphiX, Europ. J. Comput. Optim. 1(2013), 181-199] put forward the following conjecture: Let G be a tricyclic graphs on n vertices with n = 20 or n ≥ 22, then ε(G) ≤ ε(P6,6,6 n ) with equality if and only if G ≅ P6,6,6 n . Let G(n; a, b, k) denote the set of all connected bipartite tricyclic graphs on n vertices with three vertex-disjoint cycles Ca, Cb and Ck, where n = 20. In this paper, we try to prove that the conjecture is true for graphs in the class G ε G(n; a, b, k), but as a consequence we can only show that this is true for most of the graphs in the class except for 9 families of such graphs.

Ren S.,Changan University | Zhang T.,Northwestern Polytechnical University
International Journal of Advancements in Computing Technology | Year: 2012

Taking advantage of the feature that the energy of the image would gather and spread on four components (LL 2, LH 2, HL 2 and HH 2) in the sub-image after first-order CL multi-wavelet transform, and Using the advantage of Discrete Cosine Transform in application of information hiding, propose an Information Hiding scheme based on CL multi-wavelet transform and Discrete Cosine Transform (abbreviated as CL-DCT). LL 2 is embedded module of robust parameters (including parity check code of RAID4, optimized code of Chebyshev scrambling and Hash value of embedding information). Embed hiding Information in LH 2 and HL 2 with RAID4 and fragile sign in HH2. Select a different range of DCT coefficients in LH 2, HL 2 and HH 2. Experimental results indicate that the proposed scheme can increase invisibility and robustness separately by 4.71% and 30.26% averagely. In particular, the scheme has better ability against cutting attacks. The scheme has certain ability against steganalysis such as Higher Order Statistics based on wavelet coefficients. Moreover, the scheme has excellent sensitivity of image processing.

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.

Tang X.,Northwestern Polytechnical University
Acta Astronautica | Year: 2016

The main purpose of this work is to provide multiple-interval integral Gegenbauer pseudospectral methods for solving optimal control problems. The latest developed single-interval integral Gauss/(flipped Radau) pseudospectral methods can be viewed as special cases of the proposed methods. We present an exact and efficient approach to compute the mesh pseudospectral integration matrices for the Gegenbauer-Gauss and flipped Gegenbauer-Gauss-Radau points. Numerical results on benchmark optimal control problems confirm the ability of the proposed methods to obtain highly accurate solutions. © 2015 IAA. Published by Elsevier Ltd. All rights reserved.

Xu B.,Northwestern Polytechnical University
JVC/Journal of Vibration and Control | Year: 2015

In this paper, non-probabilistic reliability indices for frequency and static displacement constraints are analyzed based on the ellipse convex model of elastic modulus and mass density. The dynamic non-probabilistic reliability-based topology optimization model of a truss is built, where the cross-sectional areas and nodal topology variables are taken as design variables. The objective is to minimize the structural total mass. Constraints are imposed on static stresses and non-probabilistic reliability indices of static displacement and natural frequency. A genetic algorithm is used as the optimization method to find optimal solutions in the outer loop and an analysis method is adopted to seek non-probabilistic reliability index according to implicit forms of the limit state function in the inner loop. Results of numerical examples show that the optimal mass of a non-probabilistic reliability-based topology optimization is larger than that of the deterministic topology optimization and the optimal mass increases with the increase of the non-probabilistic reliability requirement in order to ensure structural safety. © The Author(s) 2013.

Mahmud K.,Northwestern Polytechnical University
2013 IEEE Global High Tech Congress on Electronics, GHTCE 2013 | Year: 2013

Through the popularity of the conventional PID control system, the implementation of the neural network on PID has gained a special concern in the control technology. Sometimes the traditional PID control technology is less encouraged for its delayed convergence rate and easy to fall into local minimum. So this research analyzed an upgraded BP algorithm and tried to design an implementation process to apply on PID control system. The algorithm convergence speed for the training process is quite good. Moreover, the trained BP neural network has self learning capability and has strong adaptive capability as well. So by applying this in the PID controllers can improve the performance very well. In the paper the PID and BP neural network, control process and control algorithm and the simulation results of neural network based PID control has been analyzed. © 2013 IEEE.

Fu M.S.,Northwestern Polytechnical University | Fu M.S.,Zhejiang University | Ni L.,Changan 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.

Jin W.,University of Kaiserslautern | Li C.,Northwestern Polytechnical University | Lefkidis G.,University of Kaiserslautern | Hubner W.,University of Kaiserslautern
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We present a fully ab initio theory for coherent laser-induced ultrafast spin manipulation on the homodinuclear magnetic clusters FeOFe, FeOOFe, NiONi, and NiOONi. With the oxygen atom(s) bridging the magnetically active centers, the clusters tend to adopt asymmetric geometries due to the Jahn-Teller effect. Therefore they have well-defined spin localization which is required for local spin manipulation. We find that both spin-flip and spin-transfer scenarios can be achieved on the clusters FeOFe and FeOOFe while only spin flip is realized on NiONi and NiOONi, based on which we predict that the Fe-containing clusters are quite promising for logic operations. The different dynamical behavior on these systems is analyzed in detail from the viewpoint of their distinct electronic structures and related spectra. In striving for better magnetization dynamics control, the results obtained on these prototypic systems strongly indicate their great potential in spintronic device design and future practical applications. © 2014 American Physical Society.

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.

Ling L.,Northwestern Polytechnical University
Integrated Ferroelectrics | Year: 2015

It was researched by a CNC spindle system after remanufacturing as the object, used the finite element analysis software ANSYS spindle system.Firstly, the urgency of the remanufacturing spindle and processing is analyzed; secondly it was established by the finite element model and being dynamic performance analysed, it was obtained by first five natural frequencies, vibration type and the largest integrated deformation on the specific conditions and different structural parameters of the spindle system; they are analyzed by the supporting stiffness, the supporting span and other structural parameters of the spindle system low natural vibration characteristics and its antivibration performance. For the spindle system dynamic design and similar components and residual stress VSR process provides a useful analysis of data and feasible method of analysis. Copyright © Taylor & Francis Group, LLC.

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.

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.

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.

Xiao H.,Northwestern Polytechnical University
Mathematical Problems in Engineering | Year: 2015

Numerical studies of microscale shock-vortex interaction were conducted by particle-based direct simulation of Monte Carlo (DSMC). The enstrophy is found to be increased in the strong microscale shock-vortex interaction, which is not observed in the previous DSMC studies within the limited cases. Investigations also show that the increase of the enstrophy results in an increase in dissipation rate during the strong interaction. The incoming Mach number, vortex size, and vortex Mach number turn out to play a critical role in the strength of interaction, which in turn govern the change in the dissipation rate and the increase or decrease in enstrophy during the microscale shock-vortex interaction. It is also observed that the incoming Mach number is the most dominant parameter, followed by vortex size and vortex Mach number, during the microscale shock-vortex interaction. © 2015 Hong Xiao.

Zhang Q.,Northwestern Polytechnical University
Advanced Materials Research | Year: 2011

The research on ceramic matrix composites and their applications in aerospace field were discussed in terms of their advantages and features, fabrication methods, domestic and foreign research progress, difficulties and key technologies to be solved, and future development trends and directions. © (2011) Trans Tech Publications, Switzerland.

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.

Qi L.,Northwestern Polytechnical University | Cai G.Q.,Florida Atlantic University
Nonlinear Dynamics | Year: 2013

Stochastic ecosystems of prey-predator type subjected to colored noises with broad-band spectra are investigated. Nonlinear models are considered for two different scenarios: one is the case of possible abundant prey supply and another is the case of possible large predator population. The stochastic averaging procedure is applied to obtain stationary probability solutions of the nonlinear systems. Two types of colored noise are considered: one is the low-pass filtered noise with the spectrum peak at zero frequency, and another is the randomized harmonic process with the spectrum peak at a nonzero frequency. For either type of the noises, the band width reflecting the level of the noise color can be adjusted using a single parameter. The analytical results are substantiated by those obtained from Monte Carlo simulations. It is found that the noise color has significant effects on the stationary state of the system. A narrower band width leads to a less stable system in the sense that the prey and predator populations deviate farther from the equilibrium point of the system without noise disturbances. © 2013 Springer Science+Business Media Dordrecht.

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..

Shi Z.,Northwestern Polytechnical University
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2015

Considering the relevant effects of the flight attitude to the flight safety, the post stall maneuvering at high angle of attack region, airdropping heavy cargoes at super low-altitude, flight vehicles suffering catastrophe faults and UAV control methods are briefly reviewed in the paper, according to the thirty years flight test experiences. The approach of establishing flight model by handling stability flight test is presented as well as the useful flight model simplification assumptions for controller design. To enhance the robustness of flight controller against uncertainties, eight topics for robust control are suggested. The control problem for transport plane airdropping heavy cargoes at extremely low altitude is described, and the catastrophic models and tolerant control methods are presented with flight vehicles faults. Meanwhile, the importance of flight state measurements to flight control is issued, especially to UAV flight safety. Due to the inaccuracy measurement, certain flight control problem is addressed. Finally, studies of fixed wing or single rotor tactical unmanned aerial vehicles and other high level research vehicles are suggested for some university and institute to replace the study of four rotor steering aircraft with better stability. ©, 2015, AAAS Press of Chinese Society of Aeronautics and Astronautics. All right reserved.

Yu Q.M.,Northwestern Polytechnical University
International Journal of Fracture | Year: 2015

A three-dimensional unit cell model with an inclusion is established, where an interfacial layer between the matrix and inclusion is modeled by a cohesive zone mode. This model is then used to investigate the effect of the stress state of the unit cell on the crack nucleation at the interface and subsequently the void growth, which gives the evolutions of the macro equivalent stress and relative void volume fraction associated with the macro equivalent strain. The interface debonding process indicates that both the stress triaxility and the Lode parameter play a remarkable role in the process and void nucleation and growth. Compared with the model of pure void, the inclusion increases the load carrying capacity and lowers the void growth rate for the same stress triaxiality. Meanwhile the inclusion causes a lag in the expansion of the void due to the interface fracture, which becomes significant as the stress triaxiality increases. The interfacial crack nucleates from different position for different Lode parameter and propagates in different pattern as the Lode parameter changes the principal stresses even for the same stress triaxiality. The two points, where the crack initiates and where the interface is fully debonded, vary with stress triaxiality and Lode parameter, and are getting closer for different Lode parameters when stress triaxiality increases. © 2015, Springer Science+Business Media Dordrecht.

Dong W.,Northwestern Polytechnical University
Advanced Materials Research | Year: 2011

This paper investigates an unconventional honeycomb cellular structure featuring a negative Poisson's ratio with the ability to undergo large overall displacements with limited straining of its solid material in the spanwise direction. Numerical analyses are performed to exploit such properties in the design of a morphing airfoil. The commercial simulation software ANSYS is used to carry on these processes. The cellular structure is designed to satisfy the requirements of configuration changing occurred while wing morphing. Finally, detailed numerical models of the structures are presented as a possible approach to evaluate the stress distribution of the structure. According to simulation results, the airfoil designed in this paper has the property of negative Poisson's ratio, which is useful to the morphing wing aircraft design. © (2011) Trans Tech Publications.

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.

Wang D.,Northwestern Polytechnical University
International Journal of Mechanical Sciences | Year: 2012

The finite element method is applied to the sensitivity analysis of a natural frequency of a general beam carrying a lumped mass with both translational and rotary inertias. By virtue of the characteristics of the shape functions of a higher-order finite beam element of three degrees of freedom per node (namely, the translation, rotation and curvature), successfully formulated is a closed-form solution of the frequency sensitivity with respect to the attachment point of the mass. More importantly, by using the same element model, the first-order derivative of a natural frequency can be evaluated readily with the essential nodal displacements. Numerical results show that the sensitivity can be achieved with excellent precision. For practical calculation of the frequency sensitivity, however, a further investigation is performed with use of the classical finite beam element of two degrees of freedom per node (i.e., the translation and rotation). Two approaches are provided for the curvature approximation at the mass-attached point. Comparison of numerical solutions from the uniform and linearly tapered beams illustrates that the frequency sensitivity can only be appropriately estimated in a more refined mesh scheme with the commonly-used beam element. © 2012 Elsevier Ltd.

Li T.,Northwestern Polytechnical University | Li T.,University of Salamanca | Bolic M.,University of Belgrade | Djuric P.M.,State University of New York at Stony Brook
IEEE Signal Processing Magazine | Year: 2015

Two decades ago, with the publication of [1], we witnessed the rebirth of particle filtering (PF) as a methodology for sequential signal processing. Since then, PF has become very popular because of its ability to process observations represented by nonlinear state-space models where the noises of the model can be non-Gaussian. This methodology has been adopted in various fields, including finance, geophysical systems, wireless communications, control, navigation and tracking, and robotics [2]. The popularity of PF has also spurred the publication of several review articles [2]-[6]. © 1991-2012 IEEE.

Deng Y.,Northwestern Polytechnical University
Mathematical Problems in Engineering | Year: 2015

Threat evaluation is extremely important to decision makers in many situations, such as military application and physical protection systems. In this paper, a new threat assessment model based on interval number to deal with the intrinsic uncertainty and imprecision in combat environment is proposed. Both objective and subjective factors are taken into consideration in the proposed model. For the objective factors, the genetic algorithm (GA) is used to search out an optimal interval number representing all the attribute values of each object. In addition, for the subjective factors, the interval Analytic Hierarchy Process (AHP) is adopted to determine each object's threat weight according to the experience of commanders/experts. Then a discounting method is proposed to integrate the objective and subjective factors. At last, the ideal of Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is applied to obtain the threat ranking of all the objects. A real application is used to illustrate the effectiveness of the proposed model. © 2015 Yong Deng.

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.

Han R.,Northwestern Polytechnical University
2012 10th IEEE International Conference on Semiconductor Electronics, ICSE 2012 - Proceedings | Year: 2012

The device characteristics of Cylindrical surrounding-gate (CSG) 6H-SiC NW FET is investigated in this paper. The results indicate that the surface potential, threshold voltage and the electric characteristics (transfer characteristics and output characteristics) is very sensitive to 6H-SiC nanowire radius, channel length, oxide thickness and temperature. The temperature dependence of CSG 6H-SiC NW FET is also discussed in this paper. When the nanowire radius is decreased, the minimum potential is lowered, the locations of minimum potential moves to the source side and the threshold voltage is increased. When the oxide thickness is increased, the locations of minimum potentials are not changed, but the minimum potentials themselves become larger and the threshold voltage become smaller. The minimum potential increases as the gate length decreases, but the threshold voltage decreased as the gate length decreases. With increasing temperature, the surface potential decreases and the location of minimum potential moves to the source side. The threshold voltage decreases monotonically with temperature. At strong inversion region, the drain current decrease as nanowire radius decreases, but increases as temperature decreases. © 2012 IEEE.

Wang D.,Northwestern Polytechnical University
Journal of Engineering Mechanics | Year: 2012

A hole inside a rectangular thin plate is optimized for maximization of an eigenfrequency of the structure. The shape of the hole is represented by an ellipse parametrization to guarantee a smooth curve along the boundary; and the hole's center position, semiaxes, and rotation are treated as shape design variables. The Rayleigh-Ritz approach is applied to constitute the vibration frequency equation such that an exact procedure can be presented for the frequency sensitivity analysis. The hole shape optimization is performed by using a combined mathematical programming algorithm with different search directions for two sets of design variables in relation to the constraint of the hole's size. In addition, a simple optimality criterion is provided for the optimum profile design of the internal hole of a given area. Several illustrative examples demonstrate the validity and effectiveness of the design sensitivity analysis and the proposed optimization method. © 2012 American Society of Civil Engineers.

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.

Wang D.,Northwestern Polytechnical University
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2012

The free vibration analysis of a uniform beam carrying a lumped mass with the inclusion of both translational and rotary inertias are performed, and a closed-form expression of the frequency sensitivity with respect to the attachment location of the lumped mass is formulated using the discrete method upon the finite element analysis. By virtually introducing additional degrees of freedom at the mass-attached point, the first-order derivative of the natural frequency can be determined straightforwardly. Comparisons of numerical results from two typical examples show that the rotary inertia of a lumped mass may impose important effects on the natural frequency and its sensitivity. Neglecting the rotary inertia may lead to inaccurate or even erroneous solutions of the beam's dynamics. © 2012 American Society of Mechanical Engineers.

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.

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.

Benesty J.,University of Quebec | 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.

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.

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.

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.

Han Z.-H.,Northwestern Polytechnical University
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012

Gradient-based optimization using adjoint method has proved effective for automatic aerodynamic shape optimization via high-fidelity Computational Fluid Dynamics (CFD) methods. Past experience suggests that its optimization efficiency and robustness are crucially affected by the step size along a direction of descending. In this paper, a surrogate modeling method based on gradient-enhanced Kriging is exercised to determinate the step size of adjoint-based optimization and a routine for adjoint-based aerodynamic design has been proposed. Representative results are presented for the inverse design of a RAE 2822 airfoil. It is found that the efficiency as well as robustness of adjoint-based aerodynamic optimization can be dramatically improved. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

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.

Hou X.,Northwestern Polytechnical University
Proceedings of 2011 International Conference on Computer Science and Network Technology, ICCSNT 2011 | Year: 2011

Recently there are many models which make the usage of buildings' shadows to calculate its height, however, they don't care for the universal demand and the method of using coordinates of spatial points is rare. Therefore a comprehensive analysis puts forward, referring how to utilize a single high resolution satellite image to extract construction's height, and models which involve spatial coordinate are provided. © 2011 IEEE.

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.

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.

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 for the uncertain SISO nonlinear system with control singularity and unknown non-symmetric input saturation. The effects of the control singularity and unknown input saturation are combined with the external disturbance which is approximated using the disturbance observer. Under the proposed terminal sliding mode tracking control techniques, the finite time convergence of all closed-loop signals are guaranteed via Lyapunov analysis. Numerical simulation results are given to illustrate the effectiveness of the proposed terminal sliding mode tracking control. © 2012 ISA.

Li B.,Xian 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.

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.

Xu B.,Northwestern Polytechnical University
JVC/Journal of Vibration and Control | Year: 2014

The integrated optimization of structure and control systems is investigated for n interconnected building structures subjected to earthquake. The vibration control model is established for the interconnected building structures, and optimal stiffness and damping parameters of assigned passive controllers are calculated based on LQR algorithm and an equivalent control effect strategy in the frequency domain. The integrated optimization model of structure and control, including design variables, the objective function and constraint function, is built. The design variables are size parameters of structural elements, the parameters of the weighted matrix, and the number and locations of passive controllers. The maximal displacement of the controlled system in the time domain and the energy index in the frequency domain are introduced as the optimized objective functions. A genetic algorithm is adopted to solve this kind of optimization problem with discrete and continuous design variables. The results of a numerical example show that the proposed method is reasonable and effective. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

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.

Benesty J.,University of Quebec | 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.

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.

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.

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.

Zang D.,Northwestern Polytechnical University | Clegg P.S.,University of Edinburgh
Soft Matter | Year: 2013

An emulsion can undergo a catastrophic inversion from water droplets in oil to oil droplets in water driven by a change in the proportions of the two liquids. This can occur without hysteresis in particle-stabilized emulsions, an effect that was first systematically studied in emulsions of water and toluene stabilized by partially hydrophobic silica nanoparticles. Here we study experimentally how emulsions, comprised of these same ingredients, close to the composition at which inversion occurs respond to changes in the emulsification parameters and the quantity of particles. We argue that this inversion is driven by the flow properties of the phases under different mixing conditions. We thus identify the conditions under which a long-lived emulsion containing a high volume-fraction of droplets can form. © 2013 The Royal Society of Chemistry.

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.

Zhang G.,Northwestern Polytechnical University
ICRMS'2011 - Safety First, Reliability Primary: Proceedings of 2011 9th International Conference on Reliability, Maintainability and Safety | Year: 2011

This paper discusses wireless sensor network technology manufacturing equipment in the building air management system for monitoring the application of safety issues. Further analysis of the wireless sensor network architecture that can extend the life of the system and build a common platform of issues is also present in this paper. On this basis, establish security monitoring and management system design, data collection protocols, routing protocols, sensor node scheduling. The paper focuses on the application of the manufacturing process for the assembly of aircraft characteristics build wireless sensor network architecture, and gives the FPGA-based hardware design of sensor nodes. © 2011 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

Yang Z.,Northwestern Polytechnical University | He L.,Singapore University of Technology and Design | Cai L.,University of Victoria | Pan J.,University of Victoria
IEEE Transactions on Wireless Communications | Year: 2014

Synchronization is a pre-requisite for many sensor network applications. However, it remains challenging in sensor networks due to both the limited resources and the dynamic environments. In this paper, we propose a new two-phase clock synchronization scheme. The first one is the external clock synchronization phase, during which nodes update their clock by exchanging timestamp messages with the reference clock. Different from the conventional solutions, we propose to directly remove the clock skew during the external synchronization to achieve a higher synchronization accuracy and lower computational complexity. The second one is the clock self-calibration phase, as the accumulated clock skew will make the synchronized clock drift away again, we need to compensate the clock skew to maintain the clock synchronization accuracy. However, the compensation is non-trivial as the clock skew may not be constant due to the changing environment. Thus we propose the temperature-assisted clock self-calibration (TACSC) to dynamically compensate the clock skew according to the working temperature. Extensive simulation demonstrates that the proposed synchronization scheme can achieve a much lower root mean square error in the external synchronization phase. Furthermore, during the clock self-calibration phase, the TACSC scheme can improve the synchronization accuracy by more than one order of magnitude, which is verified by both simulation and testbed experimentation. © 2002-2012 IEEE.

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.

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.

Wang D.,Northwestern Polytechnical University
Zhendong yu Chongji/Journal of Vibration and Shock | Year: 2010

The dynamic behaviors of a uniform slender beam carrying one or two lumped masses with both translational and rotary inertias were studied. At the same time, the frequency sensitivity was analyzed with respect to the position of the lumped mass attached, and a correct expression of the sensitivity was obtained. Numerical results showed that the rotary inertia of a lumped mass affects the natural frequencies, mode shapes and the design sensitivities noticeably; ignoring the rotary inertia, in some cases, may lead to inaccurate results of the beam vibration analysis.

Xue H.Q.,Northwestern Polytechnical University | Bathias C.,Paris West University Nanterre La Defense
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.

Xu C.,Northwestern Polytechnical University | Chase J.G.,University of Canterbury | Rodgers G.W.,University of Canterbury
Computers and Structures | Year: 2014

Base isolation is an increasingly applied earthquake-resistant design technique in highly seismic areas. Examination of the actual performance of isolated structures in real earthquake has become a critical issue. In this paper, a new computational method for system identification is proposed for obtaining insight into the linear and nonlinear structural properties of based-isolated buildings. A bilinear hysteresis model is used to model the isolation system and the superstructure is assumed linear. The method is based on linear and nonlinear regression analysis techniques. Response time histories are divided into different loading or unloading segments. A one-step multiple linear regression is implemented to simultaneously estimate storey stiffness and damping parameters of the superstructure. A two-step regression-based procedure is proposed to identify the nonlinear physical parameters of the isolation system. First, standard multiple linear regression is implemented to deduce equivalent linear system parameters. Analysis of the varying equivalent linear system parameters with displacement is used to distinguish linear and nonlinear segments. Second, nonlinear regression is applied for the nonlinear segments to obtain nonlinear physical parameters. A 3-storey base-isolated building was simulated to real earthquake ground motions and recorded responses were used to demonstrate the feasibility of the proposed method. Superstructure and isolation bearing properties were identified to within 6% those of actual model value even with a SNR 30 dB signal noise level. The overall method allows the simple, effective analysis of nonlinear base isolated structures. The approach to multi-degree of freedom nonlinear structures could be readily generalised to nonlinear, fixed-base, multi-storey structures. © 2014 Elsevier Ltd. All rights reserved.

Based on the coupled theory, a simple explicit solution of piezoresponse force microscopy (PFM) in determining the effective piezoelectric coefficient for an ultra-thin transversely isotropic piezoelectric film bonded to a rigid conducting substrate is obtained, using the Taylor expansion and homogeneous assumption. And it is found to be exactly the same as the well-known result for the case of piezoelectric thin film clamped between flat rigid electrodes for homogeneous external electric field. The electric charge and the distance from the image charge model are also derived and the influences of the film thickness and substrate permittivity on the effective piezoelectric coefficient are then discussed. The obtained results can be used to quantitatively interpret the PFM signals and directly detect the piezoelectric constant through PFM for an ultra-thin film or supply important information for constructing a reliable formula to describe the thickness effect. © Owned by the authors, published by EDP Sciences, 2016.

Xie G.,Northwestern Polytechnical University
Journal of Electronic Packaging, Transactions of the ASME | Year: 2014

The special issue of the Journal of Electronic Packaging focuses on thermodynamics, flow, and heat transfer in microelectromechanical systems (MEMS) equipment. Thermodynamics, fluid flow, and heat transfer are important physical processes in advanced MEMS and affiliated parts. A better understanding of the mechanisms of thermodynamics, fluid mechanics, and heat transfer in MEMS is needed for advanced MEMS thermal management. MEMS thermal management demands high heat transfer coefficient, low pressure drop penalty, and low load-driven temperature nonuniformity. The articles published in this special issue address a variety of topics, including enhancement of single-phase cooling, analytic and numerical models from microchannel heat sink level to system level, development of three-dimensional multicavity microprocessor chip stacks, and a three-stage design approach for microchannel systems of multicore processors.

Jia X.,Northwestern Polytechnical University
Advanced Materials Research | Year: 2012

In connection with characteristics of complex product development, in order to solve problems of long product development cycle, multi-collaborative firms, difficult to control product quality in manufacturing firms, the approach of complex product lifecycle quality management technology based on the collaboration of 3D virtual product and physical product is put forward. The connotation of complex product lifecycle quality management technology based on 3D product model is analyzed. Complex product lifecycle quality management model based on 3D product model is founded also. Base on 3D virtual product model and PLM technology, key technologies on complex product lifecycle quality management are described in detail. © (2012) Trans Tech Publications, Switzerland.

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.

Deng Y.,Northwestern Polytechnical University
Applied Intelligence | Year: 2015

Dempster-Shafer evidence theory is an efficient tool in knowledge reasoning and decision-making under uncertain environments. Conflict management is an open issue in Dempster-Shafer evidence theory. In past decades, a large amount of research has been conducted on this issue. In this paper, we propose a new theory called generalized evidence theory (GET). In comparison with classical evidence theory, GET addresses conflict management in an open world, where the frame of discernment is incomplete because of uncertainty and incomplete knowledge. Within the presented GET, we define a novel concept called generalized basic probability assignment (GBPA) to model uncertain information, and provide a generalized combination rule (GCR) for the combination of GBPAs, and build a generalized conflict model to measure conflict among evidences. Conflicting evidence can be effectively handled using the GET framework. We present many numerical examples that demonstrate that the proposed GET can explain and deal with conflicting evidence more reasonably than existing methods. © 2015, Springer Science+Business Media New York.

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.

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 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.

Zhang L.,Harbin Engineering University | Zhang L.,Northwestern Polytechnical University | Zhang K.,Harbin Engineering University
International Journal of Robust and Nonlinear Control | Year: 2013

This paper investigates the problems of L2 stability and H ∞ control of switched homogeneous nonlinear systems. This paper gives that if a switched homogeneous nonlinear system with disturbance is internally homogeneously asymptotically stable, then it has a finite L 2 gain, and if a switched homogeneous nonlinear system with disturbance and controls is homogeneously stabilizable under the zero disturbance condition, its H∞ control problem is solvable under some mild conditions, and a homogeneous solution is given. Then, via the semi-tensor product of matrices method, the aforementioned obtained results are transformed to linear-like forms, and the aforementioned obtained Hamilton-Jacobi-Isaacs inequality is transformed to a linear-like matrix inequality, which makes it feasible to compute the solutions by computer. Copyright © 2012 John Wiley & Sons, Ltd.

Zhang X.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2012

Both resting state fMRI (R-fMRI) and task-based fMRI (T-fMRI) have been widely used to study the functional activities of the human brain during task-free and task-performance periods, respectively. However, due to the difficulty in strictly controlling the participating subject's mental status and their cognitive behaviors during fMRI scans, it has been very challenging to tell whether or not an R-fMRI/T-fMRI scan truly reflects the participant's functional brain states in task-free/task-performance. This paper presents a novel approach to characterizing the brain's functional status into task-free or task-performance states. The basic idea here is that the brain's functional state is represented by a whole-brain quasi-stable connectivity pattern (WQCP), and an effective sparse coding procedure was then applied to learn the atomic connectivity patterns (ACP) of both task-free and task-performance states based on training R-fMRI and T-fMRI data. Our experimental results demonstrated that the learned ACPs for R-fMRI and T-fMRI datasets are substantially different, as expected. However, a certain portion of ACPs from R-fMRI and T-fMRI datasets are overlapping, suggesting that those subjects with overlapping ACPs were not in the expected task-free/task-performance states during R-fMRI/T-fMRI scans.

Ge B.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2012

Fiber clustering is an essential step towards brain connectivity modeling and tract-based analysis of white matter integrity via diffusion tensor imaging (DTI) in many clinical neuroscience applications. A variety of methods have been developed to cluster fibers based on various types of features such as geometry, anatomy, connection, or function. However, identification of group-wise consistent fiber bundles that are harmonious across multi-modalities is rarely explored yet. This paper proposes a novel hybrid two-stage approach that incorporates connectional and functional features, and identifies group-wise consistent fiber bundles across subjects. In the first stage, based on our recently developed 358 dense and consistent cortical landmarks, we identified consistent backbone bundles with representative fibers. In the second stage, other remaining fibers are then classified into the existing backbone bundles using their correlations of resting state fMRI signals at the two ends of fibers. Our experimental results show that the proposed methods can achieve group-wise consistent fiber bundles with similar shapes and anatomic profiles, as well as strong functional coherences.

Zhang Y.,Northwestern Polytechnical University
International Journal of Image and Data Fusion | Year: 2012

In this article, a wavelet-based Bayesian fusion framework is presented, in which a low spatial resolution hyperspectral (HS) image is fused with a high spatial resolution multispectral (MS) image by accounting for the joint statistics. Particularly, a zero-mean heavy-tailed model, Gaussian scale mixture model, is employed as the prior, which is believed to be capable of modelling the distribution of wavelet coefficients more accurately than traditional Gaussian model. To keep the calculations feasible, a practical implementation scheme is presented. The proposed approach is validated by simulation experiments for both general HS and MS image fusion as well as the specific case of pansharpening. The experimental results of the proposed approach are also compared with its counterpart, employing a Gaussian prior for performance evaluation. © 2012 Copyright Taylor and Francis Group, LLC.

Li J.,Northwestern Polytechnical University | Chen S.,CAS Institute of Mechanics
Materials Letters | Year: 2014

A theoretical model is proposed to illustrate the cooperative effect of nano-grain rotation and shear-coupled migration of grain boundaries on toughening of nanocrystalline materials. The toughening mechanism is embodied by an effective stress intensity factor near the tip of a mode I crack. The result shows a possibly effective toughening mechanism in nanocrystalline materials. © 2014 Elsevier B.V. All rights reserved.

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 X.,Northwestern Polytechnical University
Lecture Notes in Electrical Engineering | Year: 2011

Professional courses are significant for the undergraduate students. Nowadays the teachers face many problems in teaching reform of professional course. One of them is how to improve the quality of professional course teaching and develop students' specialty ability under the circumstance of class hour decreased. On the basis of analyzing the course contents and teaching features for the professional course of "forming methods of sheet metal for airplane parts", the article focuses on the professional course system, teaching method, and teaching fulfillment combining the course teaching process. Firstly consolidating resources in existence, courses system is constructed according to classroom teaching and experiment teaching. Secondly as one of the most important tools in the modern education revolution, that is multimedia teaching method, is applied to classroom teaching in order to increase the student's direct feeling. Finally the experimental teaching including demonstration teaching is carried out. Preliminary achievements are acquired in teaching practice. The students raise the interest in the professional lesson, expand knowledge range, and improve professional character. © 2012 Springer-Verlag.

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.

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.

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.

Zhao E.,Northwestern Polytechnical University
Applied Mechanics and Materials | Year: 2012

In order to solve the problem of general fins and rudders being lower at low moving speed, the moving mass technical is applied onto AUV, thus to radically solve the weakness of control method with fin and rudder. The space dynamics model of moving mass control is created for AUV. And based on this, the moving mass control system is designed with the sliding mode variable structure control method so as to ensure system tracking error zero convergence. By controlling the moving mass movement with moving mass control system, the attitude of AVU is previously controlled. And simulation result proves that moving mass control system will control the AUV attitude angle precisely and rapidly. © (2012) Trans Tech Publications, Switzerland.

Huang J.,Yale University | Abadi D.J.,Yale University | Ren K.,Northwestern Polytechnical University
Proceedings of the VLDB Endowment | Year: 2011

The generation of RDF data has accelerated to the point where many data sets need to be partitioned across mul-tiple machines in order to achieve reasonable performance when querying the data. Although tremendous progress has been made in the Semantic Web community for achieving high performance data management on a single node, cur-rent solutions that allow the data to be partitioned across multiple machines are highly inecient. In this paper, we introduce a scalable RDF data management system that is up to three orders of magnitude more ecient than popular multi-node RDF data management systems. In so doing, we introduce techniques for (1) leveraging state-of-the-art single node RDF-store technology (2) partitioning the data across nodes in a manner that helps accelerate query pro-cessing through locality optimizations and (3) decomposing SPARQL queries into high performance fragments that take advantage of how data is partitioned in a cluster. © 2011 VLDB Endowment.

Zhang Y.,Northwestern Polytechnical University | Zhang Y.,Virginia Polytechnic Institute and State University | Zhen W.,Virginia Polytechnic Institute and State University | Maechler P.,University of Geneva | Liu D.,Virginia Polytechnic Institute and State University
Journal of Nutritional Biochemistry | Year: 2013

Chronic hyperlipidemia causes β-cell apoptosis and dysfunction, thereby contributing to the pathogenesis of type 2 diabetes (T2D). Thus, searching for agents to promote pancreatic β-cell survival and improve its function could be a promising strategy to prevent and treat T2D. We investigated the effects of kaempferol, a small molecule isolated from ginkgo biloba, on apoptosis and function of β-cells and further determined the mechanism underlying its actions. Kaempferol treatment promoted viability, inhibited apoptosis and reduced caspase-3 activity in INS-1E cells and human islets chronically exposed to palmitate. In addition, kaempferol prevented the lipotoxicity-induced down-regulation of antiapoptotic proteins Akt and Bcl-2. The cytoprotective effects of kaempferol were associated with improved insulin secretion, synthesis, and pancreatic and duodenal homeobox-1 (PDX-1) expression. Chronic hyperlipidemia significantly diminished cyclic adenosine monophosphate (cAMP) production, protein kinase A (PKA) activation, cAMP-responsive element binding protein (CREB) phosphorylation and its regulated transcriptional activity in β-cells, all of which were restored by kaempferol treatment. Disruption of CREB expression by transfection of CREB siRNA in INS-1E cells or adenoviral transfer of dominant-negative forms of CREB in human islets ablated kaempferol protection of β-cell apoptosis and dysfunction caused by palmitate. Incubation of INS-1E cells or human islets with kaempferol for 48. h induced PDX-1 expression. This effect of kaempferol on PDX-1 expression was not shared by a host of structurally related flavonoid compounds. PDX-1 gene knockdown reduced kaempferol-stimulated cAMP generation and CREB activation in INS-1E cells. These findings demonstrate that kaempferol is a novel survivor factor for pancreatic β-cells via up-regulating the PDX-1/cAMP/PKA/CREB signaling cascade. © 2013 Elsevier Inc.

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.

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.

Yang H.,Northwestern Polytechnical University | Wang C.,Georgia Institute of Technology | Zhang F.,Georgia Institute of Technology
IET Control Theory and Applications | Year: 2013

Formation control for a group of autonomous underwater vehicles (AUVs) is challenging due to the complex systems dynamics and time delay in the cooperative feedback loops. This paper introduces a decoupled design procedure, so that formation controllers designed for particle dynamics can be generalised to formation controllers for fully actuated AUVs with six-degree-of-freedom dynamic models for motions in three-dimensional space. The orientation control and the translation control are first decoupled following a standard inner-outer loop approach. Then, a geometric approach is followed to separate the translation dynamics into formation shape dynamics and formation centre dynamics. Coupling terms between the two portions of the dynamics are treated as perturbations and are tolerated by a robust formation-keeping controller. The controller is also robust to constant bounded time delays. This decoupling procedure simplified the entire design process comparing with other existing approaches with similar goals. Both rigorous theoretical analysis and simulation results are presented to justify the effectiveness of this method. © The Institution of Engineering and Technology 2013.

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.

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.

Yuan Y.,CAS Xian Institute of Optics and Precision Mechanic | Zhu G.,CAS Xian Institute of Optics and Precision Mechanic | Wang Q.,Northwestern Polytechnical University
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015

Hyperspectral images have been proved to be effective for a wide range of applications; however, the large volume and redundant information also bring a lot of inconvenience at the same time. To cope with this problem, hyperspectral band selection is a pertinent technique, which takes advantage of removing redundant components without compromising the original contents from the raw image cubes. Because of its usefulness, hyperspectral band selection has been successfully applied to many practical applications of hyperspectral remote sensing, such as land cover map generation and color visualization. This paper focuses on groupwise band selection and proposes a new framework, including the following contributions: 1) a smart yet intrinsic descriptor for efficient band representation; 2) an evolutionary strategy to handle the high computational burden associated with groupwise-selection-based methods; and 3) a novel MTSP-based criterion to evaluate the performance of each candidate band combination. To verify the superiority of the proposed framework, experiments have been conducted on both hyperspectral classification and color visualization. Experimental results on three real-world hyperspectral images demonstrate that the proposed framework can lead to a significant advancement in these two applications compared with other competitors. © 2014 IEEE.

He K.L.,Northwestern Polytechnical University
Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology | Year: 2011

To study possible association between three single nucleotide polymorphisms (-597G/A, -572C/G and -174G/C) of interleukin-6 (IL-6) gene promoter and breast cancer. Genomic DNA was isolated from the venous blood leukocytes from 176 unrelated patients with breast cancer and 200 healthy unrelated females (control group). Polymorphisms of -597G/A, -572C/G and -174G/C, were genotyped by PCR-restriction fragment length polymorphisms (PCR-RFLP). SPSS 11.5 software was employed for statistical analysis and the association of IL-6 polymorphisms with breast cancer was evaluated by x(2); test. There was significant differences in both allele and genotype frequencies of -572C/G in case group compared with control group. The allele G of -572C/G was significantly higher in cancer patients than the controls(x(2);=15.438, P<0.01). There is an association between -572C/G polymorphism and breast cancer risk. The females with G allele of -572C/G are susceptible to breast cancer compared with non-carrying females.

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.

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.

Xu B.,Northwestern Polytechnical University
JVC/Journal of Vibration and Control | Year: 2014

Based on interval analysis and the interval extension method, the upper and lower bounds of feedback performance for optimal control in physical space and in modal space, and static and dynamic characteristics for the smart truss with interval parameters, are analyzed. The first-order and second-order topology optimization models are built, where the cross-section areas, topology variables, control design parameters and the number and placements of actuators are taken as design variables. The objective function to minimize is the total mass, and the constraints are also imposed on the allowable voltages of actuators, static displacements, static stresses, first natural frequency of open-loop system and damping ratio of closed-loop system. Genetic algorithm is used as the optimization method. The solutions of numerical examples show that the optimization model and the proposed method are effective. © The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

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 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.

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.

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.

Li W.-Y.,Northwestern Polytechnical University | Li C.-J.,Xian Jiaotong University | Liao H.,University of Technology of Belfort - Montbeliard
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.

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.

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.

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.

Xie G.,Northwestern Polytechnical University | Xie G.,Lund University | Sunden B.,Lund University
International Journal of Heat and Mass Transfer | Year: 2010

The heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Improved cooling methods are therefore needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to very hot gas flow, and suffers high local thermal loads due to the external tip leakage flow. A common way to cool the tip is to design serpentine passages with 180° turn under the blade tip-cap taking advantage of the three-dimensional turning effect and impingement. Increased internal convective cooling is therefore required to increase the blade tip lifetime. In this paper, augmented heat transfer of a blade tip with internal hemispherical dimples has been investigated numerically. The computational models consist of two-pass channels with 180° turn and arrays of dimples depressed on the internal tip-cap. Turbulent convective heat transfer between the fluid and dimples, and heat conduction within dimples and tip are simultaneously computed. The inlet Reynolds number is ranging from 100,000 to 600,000. Details of the 3D fluid flow and heat transfer over the tip-walls are presented. Comparisons of the overall performance of the models are presented. It is found that due to the combination of turning impingement and dimple-induced advection flow, the heat transfer coefficient of the dimpled tip is up to two times higher than that of a smooth tip with less than 5% pressure drop penalty. It is suggested that the use of dimples is suitable for augmenting blade tip cooling to achieve an optimal balance between thermal and mechanical design requirements. © 2010 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.

Li W.-Y.,Northwestern Polytechnical University | Li C.-J.,Xian 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.

Zhang S.Q.,RWTH Aachen | Zhang S.Q.,Northwestern Polytechnical University | Schmidt R.,RWTH Aachen
Smart Materials and Structures | Year: 2013

A geometrically nonlinear large rotation shell theory is proposed for dynamic finite element (FE) analysis of piezoelectric integrated thin-walled smart structures. The large rotation theory, which has six independent kinematic parameters but expressed by five nodal degrees of freedom (DOFs), is based on first-order shear deformation (FOSD) hypothesis. The two-dimensional (2D) FE model is constructed using eight-node quadrilateral shell elements with five mechanical DOFs per node and one electrical DOF per piezoelectric material layer with linear constitutive equations. The linear and nonlinear dynamic responses are determined by the central difference algorithm (CDA) and the Newmark method. The results are compared with those obtained by simplified nonlinear theories, as well as those reported in the literature. It is shown that the present large rotation theory yields considerable improvement if the structures undergo large displacements and rotations. © 2013 IOP Publishing Ltd.

Luo M.Z.,Northwestern Polytechnical University
Xi bao yu fen zi mian yi xue za zhi = Chinese journal of cellular and molecular immunology | Year: 2012

To investigate the effects of high magneto-gravitational environment on Ca(2+);]/calmodulin (CaM) signal of MG63 osteoblast-like cells. A special designed large gradient high magnetic field could produce three different high magneto-gravitational environments including μg (12 T), 1 g (16 T) and 2 g (12 T). The effects of high magneto-gravitational environments on intracellular free Ca(2+);] concentration ([Ca(2+);](i);) and protein expression including calmodulin (CaM), myosin light chain kinases (MLCK) and phosphorylated Ca(2+);]/CaM dependent protein kinase II(pCaMKII) were measured by Fluo-3/AM or Western blot, respectively. When compared with control group, an increase of [Ca(2+);](i); of MG63 was caused by strong magnetic field; Compared to 2 g, μg decreased [Ca(2+);](i); of MG63. The protein expression of CaM and pCaMKIIof MG63 cells was decreased by simulated weightlessness. [Ca(2+);](i); of MG63 cells was increased by strong magnetic field; simulated weightlessness inhibited Ca(2+);/CaM signaling of MG63 cells.

Feng T.,Northwestern Polytechnical University | Zhao G.,Xian 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.

Liu H.,Northwestern Polytechnical University | Rodriguez R.M.,University of Jaen
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.

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.

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.

Yang C.,University of Plymouth | Li Z.,South China University of Technology | Cui R.,Northwestern Polytechnical University | Xu B.,South China University of Technology
IEEE Transactions on Neural Networks and Learning Systems | Year: 2014

In this paper, automatic motion control is investigated for one of wheeled inverted pendulum (WIP) models, which have been widely applied for modeling of a large range of two wheeled modern vehicles. First, the underactuated WIP model is decomposed into a fully actuated second order subsystem Σa consisting of planar movement of vehicle forward and yaw angular motions, and a nonactuated first order subsystem Σb of pendulum motion. Due to the unknown dynamics of subsystem Σa and the universal approximation ability of neural network (NN), an adaptive NN scheme has been employed for motion control of subsystem Σa. The model reference approach has been used whereas the reference model is optimized by the finite time linear quadratic regulation technique. The pendulum motion in the passive subsystem Σb is indirectly controlled using the dynamic coupling with planar forward motion of subsystem Σa , such that satisfactory tracking of a set pendulum tilt angle can be guaranteed. Rigours theoretic analysis has been established, and simulation studies have been performed to demonstrate the developed method. © 2014 IEEE.

Benesty J.,University of Quebec at Montreal | Chen J.,Northwestern Polytechnical University | Huang Y.,WEVOICE, Inc.
IEEE Transactions on Audio, Speech and Language Processing | Year: 2011

Binaural noise reduction with a stereophonic (or simply stereo) setup has become a very important problem as stereo sound systems and devices are being more and more deployed in modern voice communications. This problem is very challenging since it requires not only the reduction of the noise at the stereo inputs, but also the preservation of the spatial information embodied in the two channels so that after noise reduction the listener can still localize the sound source from the binaural outputs. As a result, simply applying a traditional single-channel noise reduction technique to each channel individually may not work as the spatial effects may be destroyed. In this paper, we present a new formulation of the binaural noise reduction problem in stereo systems. We first form a complex signal from the stereo inputs with one channel being its real part and the other being its imaginary part. By doing so, the binaural noise reduction problem can be processed by a single-channel widely linear filter. The widely linear estimation theory is then used to derive optimal noise reduction filters that can fully take advantage of the noncircularity of the complex speech signal to achieve noise reduction while preserving the desired signal (speech) and spatial information. With this new formulation, the Wiener, minimum variance distortionless response (MVDR), maximum signal-to-noise ratio (SNR), and tradeoff filters are derived. Experiments are provided to justify the effectiveness of these filters. © 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.

Liu D.,Northwestern Polytechnical University
Ceramics International | Year: 2013

Al2O3:Cr3+ samples were synthesized via hydrothermal and microwave solvothermal methods and thermal decomposition of Cr3+ doped precursors. The sample characterizations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD results indicated that Cr3+ doped samples were pure α-Al2O3 phase after being calcined at 1573 K. SEM results showed that the length and diameter of these Cr3+ doped alumina microfibers by hydrothermal route were about 2-5 μm and 100-300 nm, respectively; the obtained α-Al2O3 based powders via the microwave solvothermal method were microspheres with an average diameter about 1-2 μm. PL spectra showed that the Al2O3:Cr3+ samples presented a broad R band at 696 nm. It is shown that the 0.3 mol% of doping concentration of Cr3+ ions in α-Al2O3:Cr3+ is optimum. According to Dexter's theory, the critical distance between Cr 3+ ions for energy transfer was determined to be 24 Å. It is found that the curve followed the single-exponential decay. Furthermore, the luminescence properties of the samples are also dependent on the morphology. © 2012 Elsevier Ltd and Techna Group S.r.l.

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 T.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2011

Study of structural and functional connectivities of the human brain has received significant interest and effort recently. A fundamental question arises when attempting to measure the structural and/or functional connectivities of specific brain networks: how to best identify possible Regions of Interests (ROIs)? In this paper, we present a novel ROI prediction framework that localizes ROIs in individual brains based on learned fiber shape models from multimodal task-based fMRI and diffusion tensor imaging (DTI) data. In the training stage, ROIs are identified as activation peaks in task-based fMRI data. Then, shape models of white matter fibers emanating from these functional ROIs are learned. In addition, ROIs' location distribution model is learned to be used as an anatomical constraint. In the prediction stage, functional ROIs are predicted in individual brains based on DTI data. The ROI prediction is formulated and solved as an energy minimization problem, in which the two learned models are used as energy terms. Our experiment results show that the average ROI prediction error is 3.45 mm, in comparison with the benchmark data provided by working memory task-based fMRI. Promising results were also obtained on the ADNI-2 longitudinal DTI dataset.

Yuan H.,Northwestern Polytechnical University
Journal of Materials Science: Materials in Electronics | Year: 2012

Si doped ZnO (SZO) films with various Si concentrations were deposited by atomic layer deposition at 300 °C using triethyzinc, tris(dimethylamino) silane and H2O2 as the precursors. The influences of Si doping concentration on structural, electrical and optical properties of ZnO films have been investigated. All the films exhibited a highly preferential c-axis orientation. A minimum resistivity of 9.2 × 10-4 ω cm, with a carrier concentration of 4.3 × 1020 cm-3 and a Hall mobility of 15.8 cm2/Vs, was obtained for SZO film prepared with the Si concentration of 2.1 at%. The increase of conductivity with Si doping was attributed to the presence of Si in + 3 valence state acting as donor in ZnO and the increases of oxygen vacancies with Si concentration as proven by XPS measurements. The optical bandgap of SZO films initially increased from 3.25 to 3.55 eV with increasing of Si concentration to 2.1 at%, then decreased with further increase of Si concentration. The blue shift of band gap of SZO films with increasing carrier concentration can be explained by the Burstein-Moss (B-M) effects. © Springer Science+Business Media, LLC 2012.

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.

Lv J.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2010

Recently, inference of functional connectivity between brain regions using resting state fMRI (rsfMRI) data has attracted significant interests in the neuroscience community. This paper proposes a novel fiber-centered approach to study the functional connectivity between brain regions using high spatial resolution diffusion tensor imaging (DTI) and rsfMRI data. We measure the functional coherence of a fiber as the time series' correlation of two gray matter voxels that this fiber connects. The functional connectivity strength between two brain regions is defined as the average functional coherence of fibers connecting them. Our results demonstrate that: 1) The functional coherence of fibers is correlated with the brain regions they connect; 2) The functional connectivity between brain regions is correlated with structural connectivity. And these two patterns are consistent across subjects. These results may provide new insights into the brain's structural and functional architecture.

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.

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.

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

A theoretical model is proposed to illustrate the effect of shear-coupled migration of grain boundaries on the emission of lattice dislocations from a semi-infinite crack tip in nanocrystalline materials. The results obtained show that the shear-coupled migration process is able to considerably enhance the capability of the crack to emit dislocations, thus leading to strong crack blunting. Moreover, the combination of grain boundary migration and dislocation emission can serve as an effective toughening mechanism in nanocrystalline materials. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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.

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.

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.

Pang X.,Northwestern Polytechnical University
Optics Communications | Year: 2015

An investigation is made of the phase properties, especially the Gouy phase of the tightly focused, circularly polarized vortex beams. First two groups of symmetry relations of the focused field are derived, from which the effect of the topological charge on the field can be found easily. By decomposing the electric field into three specific components, the corresponding Gouy phases are defined and their properties are examined in detail. Our result shows that not only the polarization of the incident field or the numerical aperture influence the phase behavior, but also the topological charge gives much contribution to the phase structure near the focus. © 2014 Elsevier B.V. All rights reserved.

Li S.,Northwestern Polytechnical University
Optik | Year: 2015

A novel color-coded sinusoidal fringe pattern for absolute phase measurement is proposed in this letter. We used composited color sinusoidal fringe to calculate the wrapped phases and fringe orders without other assistant gratings. A novel algorithm was used to map wrapped phase to absolute phase. Three different colors were employed to mark to fringe orders, and then 27 fringes could be encoded by 4-bits codeword in three gratings with a phase shift of 2π/3. Gray values of the color-coded sinusoidal fringe are employed to calculate the wrapped phases by phase shift method, and then we used wrapped phases to obtain the lowest bit of codewords. Color information were used to decide three high bits of codewords. With codewords of 4 bits, the fringe orders can be found from a lookup table, and then the wrapped phased could be mapped to absolute phase. Moreover, shortcomings of channels coupling in color grating measurement are also circumvented. The experimental results showed the validity of our algorithm. © 2015 Elsevier GmbH. All rights reserved.

Xie W.,Northwestern Polytechnical University
Journal of Computational Physics | Year: 2015

A multiple-relaxation-time (MRT) lattice Boltzmann (LB) scheme developed for axisymmetric flows recovers the complete continuity and Navier-Stokes equations. This scheme follows the strategy of the standard D2Q9 model by using a single particle distribution function and a simple "collision-streaming" updating rule. The extra terms related to axisymmetry in the macroscopic equations are recovered by adding source terms into the LB equation, which are simple and involve no gradients. The compressible effect retained in the Navier-Stokes equations is recovered by introducing a term related to the reversed transformation matrix for MRT collision operator, so as to produce a correct bulk viscosity, making it suitable for compressible flows with high frequency and low Mach number. The validity of the scheme is demonstrated by testing the Hagen-Poiseuille flow and 3D Womersley flow, as well as the standing acoustic waves in a closed cylindrical chamber. The numerical experiments show desirable stability at low viscosities, enabling to simulate a standing ultrasound field in centimeters space. © 2014 Elsevier Inc.

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.

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.

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.

Wang Y.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2011

Skull-stripping refers to the separation of brain tissue from non-brain tissue, such as the scalp, skull, and dura. In large-scale studies involving a significant number of subjects, a fully automatic method is highly desirable, since manual skull-stripping requires tremendous human effort and can be inconsistent even after sufficient training. We propose in this paper a robust and effective method that is capable of skull-stripping a large number of images accurately with minimal dependence on the parameter setting. The key of our method involves an initial skull-stripping by co-registration of an atlas, followed by a refinement phase with a surface deformation scheme that is guided by prior information obtained from a set of real brain images. Evaluation based on a total of 831 images, consisting of normal controls (NC) and patients with mild cognitive impairment (MCI) or Alzheimer's Disease (AD), from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database indicates that our method performs favorably at a consistent overall overlap rate of approximately 98% when compared with expert results. The software package will be made available to the public to facilitate neuroimaging studies.

Ge B.,Northwestern Polytechnical University
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2011

Fiber clustering is a prerequisite step towards tract-based analysis of white mater integrity via diffusion tensor imaging (DTI) in various clinical neuroscience applications. Many methods reported in the literature used geometric or anatomic information for fiber clustering. This paper proposes a novel method that uses functional coherence as the criterion to guide the clustering of fibers derived from DTI tractography. Specifically, we represent the functional identity of a white matter fiber by two resting state fMRI (rsfMRI) time series extracted from the two gray matter voxels to which the fiber connects. Then, the functional coherence or similarity between two white matter fibers is defined as their rsfMRI time series' correlations, and the data-driven affinity propagation (AP) algorithm is used to cluster fibers into bundles. At current stage, we use the corpus callosum (CC) fibers that are the largest fiber bundle in the brain as an example. Experimental results show that the proposed fiber clustering method can achieve meaningful bundles that are reasonably consistent across different brains, and part of the clustered bundles was validated via the benchmark data provided by task-based fMRI data.

Wang D.,Northwestern Polytechnical University
Structural and Multidisciplinary Optimization | Year: 2014

Procedures for sensitivity analysis of the structural responses, i.e., nodal displacement, mean compliance and local stresses within an element, with respect to the location of an external applied load are developed. This is mainly because the external loads are often of some freedom to change their application positions in the structural preliminary design. Apart from the structural response evaluation, the finite element method is employed in this work for the sensitivity analysis implementation of a plane stress continuum structure. First, an external load is transformed into the equivalent nodal forces such that the influence of an external load shift is represented completely by the magnitude variation of the associated nodal forces, upon which the first- and second-order derivatives of an external load to its location change are performed respectively in a closed form by the aid of the features of the element shape functions. Then, the relevant sensitivities of the structural responses aforementioned are formulated readily with the discrete method. Finally, two typical examples are provided to demonstrate the validity of the sensitivity formulations presented, and the numerical results show a perfect accuracy of calculation of the response sensitivity. © 2014, Springer-Verlag Berlin Heidelberg.

Zuo J.,Northwestern Polytechnical University
IET Radar, Sonar and Navigation | Year: 2013

In particle filter, the use of resampling technique solves the problem of particle degeneracy to some extent, but introduces a new problem of particle impoverishment. To reconcile this dilemma, a dynamic resampling strategy is proposed, where the resampling operation is only performed on part of the particles in a step-by-step manner and the number of resampled particles is determined dynamically by a termination criterion based on the effective sample size. The new-born particles produced by resampling operations are helpful in alleviating particle degeneracy, whereas particles free from being resampled is conducive to improving the diversity of particles. Thus, a tradeoffbetween these two problems can be achieved. Also, two techniques, that is, recursive computation of the effective sample size and improved bisection method, for improving the computational efficiency are proposed. Simulation results conducted on two typical examples show the improved performance of the proposed method. © The Institution of Engineering and Technology 2013.

Ren S.,Changan University | Zhang T.,Northwestern Polytechnical University
International Journal of Digital Content Technology and its Applications | Year: 2012

Using first-order transformation of CL multi-wavelet, carrier image is decomposed into four components of lowest resolution sub-image. These four components are processed by ASA (Annulus Sector Analysis) to obtain embedding areas. Information hiding follows two rules: First, satisfies four components energy distributed feature of CL multi-wavelet first-order sub-images. That means embedding robust parameters in LL 1, embedding the same pre-hiding information in LH 1 and HL 1, embedding fragile identifier in HH 1. Second, use two or more annulus to embed data symmetrically. Moreover, using Chebyshev chaotic map and genetic algorithm to adjust sequence of embedded data and LSB is checked by other bit plane. Experimental results show that the invisibility of this scheme is of 8.75% average increase and excellent perception to distortion. Robustness is improved by 29.24% at least. This scheme has a good robustness against cutting, mean and medium filtering, especially can completely resist rotation.

Dong L.,Central South University | Li X.,Central South University | Xie G.,Northwestern Polytechnical University
Mathematical Problems in Engineering | Year: 2014

This paper presents a three-dimensional analytical solution for acoustic emission source location using time difference of arrival (TDOA) measurements from N receivers, N5. The nonlinear location equations for TDOA are simplified to linear equations, and the direct analytical solution is obtained by solving the linear equations. There are not calculations of square roots in solution equations. The method solved the problems of the existence and multiplicity of solutions induced by the calculations of square roots in existed close-form methods. Simulations are included to study the algorithms' performance and compare with the existing technique. © 2014 Longjun Dong et al.

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.

Wang Q.,Northwestern Polytechnical University | Li X.,CAS Xian Institute of Optics and Precision Mechanic
Neurocomputing | Year: 2014

With the development of multimedia technology, image resizing has been raised as a question when the aspect ratio of an examined image should be displayed on a device with a different aspect ratio. Traditional nonuniform scaling for tackling this problem will lead to distortion. Therefore, content-aware consideration is mostly incorporated in the designing procedure. Such methods generally defines an energy function indicating the importance level of image content. The more important regions would be retained in the resizing procedure and distortion could be avoided consequently. The definition of the related energy function is thus the critical factor that directly influences the resizing results. In this work, we explore the definition of energy function from another aspect, matrix decomposition of Low-rank Representation. In our processing, a feature matrix that reflects the texture prior of object contour is firstly constructed. Then the matrix is decomposed into a low-rank one and sparse one. The energy function for resizing is then inferred from the sparse one. We illustrate the proposed method through seam carving framework and image shrinkage operation. Experiments on a dataset containing 1000 images demonstrate the effectiveness and robustness of the proposed method. © 2014 Elsevier B.V.

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.

Chen J.,Northwestern Polytechnical University | Benesty J.,University of Quebec at Montreal
IEEE Transactions on Audio, Speech and Language Processing | Year: 2013

This paper deals with the problem of noise reduction in stereo sound systems where the objective is not only to reduce noise, but also to preserve the spatial information of both the desired speech and noise sources so that the listener can still localize the speech and noise sources by listening to the enhanced binaural outputs. To achieve this objective, we use the widely linear (WL) framework developed previously and convert the problem of binaural noise reduction into one of monaural filtering with complex signals. We then present a way to decompose both the complex speech and noise signal vectors into two orthogonal components: one correlated and the other uncorrelated with the corresponding current signal sample. With this decomposition, the problem of noise reduction with preservation of the spatial information of speech and noise sources is formulated as an optimization problem with two constraints: one on the desired speech and the other on the preservation of the noise signal. We then derive a WL linearly constrained minimum variance (LCMV) filter, which can take advantage of the statistics and noncircularity of the complex speech signal to achieve noise reduction. In contrast to the WL Wiener and minimum variance distortionless response (MVDR) filters developed previously that can only preserve the characteristics and spatial information of the desired sound source, this new WL LCMV filter has the potential to reduce noise while preserving the characteristics and spatial information of both the desired and noise sources at the same time. Experimental results are provided to justify the claimed merits of the proposed WL LCMV filter. © 2006-2012 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.

Xu J.,Northwestern Polytechnical University
Electronics Letters | Year: 2015

A compact microstrip tri-band lowpass-bandpass filter is described. Two different sets of λ/4 uniform-impedance open stubs generate the desired transmission zeros (TZs) to divide a lowpass frequency response based on a radial stub loaded high-impedance microstrip line into a tri-band lowpass-bandpass frequency response. A lowpass passband with a 3 dB cutoff frequency of 0.66 GHz, and two bandpass passbands centred at 1.57 and 2.45 GHz for global positioning system and wireless local area network applications are obtained in this design. The fabricated tri-band lowpass-bandpass filter occupies a compact circuit area of 0.065 λgc × 0.085 λgc. Seven TZs around the three passbands result in high band-to-band isolation, good passband selectivity and a wide upper stopband. © The Institution of Engineering and Technology 2015.

Wang Q.,Northwestern Polytechnical University | Fang J.,CAS Xian Institute of Optics and Precision Mechanic | Yuan Y.,CAS Xian Institute of Optics and Precision Mechanic
Neurocomputing | Year: 2014

Visual tracking is a central topic in computer vision. However, the accurate localization of target object in extreme conditions (such as occlusion, scaling, illumination change, and shape transformation) still remains a challenge. In this paper, we explore utilizing multi-cue information to ensure a robust tracking. Optical flow, color and depth clues are simultaneously incorporated in our framework. The optical flow can get a rough estimation of the target location. Then the part-based structure is adopted to establish the precise position, combining both color and depth statistics. In order to validate the robustness of the proposed method, we take four video sequences of different demanding situations and compare our method with five competitive ones representing state of the arts. Experiments prove the effectiveness of the proposed method. © 2013 Elsevier B.V.

Ma Y.,Northwestern Polytechnical University
Electronics Letters | Year: 2015

An integrated lossless load current sensing method for buck-boost DC-DC converters is presented. The load current is detected by sensing the average current flowing through the power transistor connected between the inductor and the output capacitor. The circuit is almost independent of voltage and temperature by using a sense resistor method. A second-order on-chip lowpass filter is adopted to average the sensed voltage. The buck-boost converter could automatically switch between heavy and light load modes with a fixed switching current for different input and output voltages. © The Institution of Engineering and Technology 2015.

Tang Z.,Northwestern Polytechnical University
Sensors (Basel, Switzerland) | Year: 2010

We have developed a novel colorimetric sensor based on a digital camera and white LED illumination. Colorimetric sensor arrays (CSAs) were made from a set of six chemically responsive dyes impregnated on an inert substrate plate by solution casting. Six common amine aqueous solutions, including dimethylamine, triethylamine, diisopropylamine, aniline, cyclohexylamine, and pyridine vaporized at 25 °C and six health-related trimethylamine (TMA) concentrations including 170 ppm, 51 ppm, 8 ppm, 2 ppm, 125 ppb and 50 ppb were analyzed by the sensor to test its ability for the qualitative discrimination and quantitative detection of volatile amines. We extracted the feature vectors of the CSA's response to the analytes from a fusional color space, which was obtained by conducting a joint search algorithm of sequential forward selection and sequential backward selection (SFS&SBS) based on the linear discriminant criteria (LDC) in a mixed color space composed of six common color spaces. The principle component analysis (PCA) followed by the hierarchical cluser analysis (HCA) were utilized to discriminate 12 analytes. Results showed that the colorimetric sensor grouped the six amine vapors and five TMA concentrations correctly, while TMA concentrations of 125 ppb and 50 ppb were indiscriminable from each other. The limitation of detection (LOD) of the sensor for TMA was found to be lower than 50 ppb. The CSAs were reusable for TMA concentrations below 8 ppm.

Xu B.,Northwestern Polytechnical University | Xu B.,Nanyang Technological University | Pan Y.,Nanyang Technological University | Wang D.,Nanyang Technological University | Sun F.,Tsinghua University
Neurocomputing | Year: 2014

This paper describes the neural controller design for the longitudinal dynamics of a generic hypersonic flight vehicle (HFV). The dynamics are transformed into the strict-feedback form. Considering the uncertainty, the neural controller is constructed based on the single-hidden layer feedforward network(SLFN). The hidden node parameters are modified using extreme learning machine (ELM) by assigning random values. Instead of using online sequential learning algorithm (OSLA), the output weight is updated based on the Lyapunov synthesis approach to guarantee the stability of closed-loop system. By estimating the bound of output weight vector, a novel back-stepping design is presented where less online parameters are required to be tuned. The simulation study is presented to show the effectiveness of the proposed control approach. © 2013 Elsevier B.V.

Wang Q.,Northwestern Polytechnical University | Yuan Y.,CAS Xian Institute of Optics and Precision Mechanic
Neurocomputing | Year: 2014

An increasing amount of display devices with fixed sizes call for an adaptive strategy for optimal display. For this purpose, content aware image resizing techniques are developed. Previous works mainly lay their attention on the shrinkage operation of the examined image. Less efforts are paid on the expansion manipulation. Though some literatures claim an extension of their shrinkage operation to expanding the image in a similar way, the obtained results are not satisfying. In this paper, a high quality image resizing method is proposed to retain the details when stretching an image. Instead of using interpolation based techniques which are taken for granted by existing methods, an expansion model is first learned from a set of training images. Then the future enlargement is based on this principle. Experiments on two publicly available datasets demonstrate the effectiveness of the presented method. A further extension on video enlargement is also presented as an example. Though the proposed method is formulated in the context of seam carving, it can be readily extended to other techniques such as cropping, segmentation and warping based resizing methods. © 2014.

Li M.,Northwestern Polytechnical University
WIT Transactions on Ecology and the Environment | Year: 2014

Environmental Kuznets curve (EKC) is often used to study the relationship between environmental pollution and economic development, and the results of that research can be mainly summarized as: supporting environmental Kuznets curve and opposing environmental Kuznets curve. In order to better develop and apply EKC theory, this paper firstly analyzes what research has been done on EKC so far by the domestic and foreign scholars and what the research characteristics are. It continues to summarize and review the defects of EKC. Lastly, it suggests some basic train of thoughts for developing EKC theory. © 2013 WIT Press.

Dai H.-H.,Northwestern Polytechnical University | Dai H.-H.,University of California at Irvine | Schnoor M.,University of California at Irvine | Atluri S.N.,University of California at Irvine
CMES - Computer Modeling in Engineering and Sciences | Year: 2012

In this study, the harmonic and 1=3 subharmonic oscillations of a single degree of freedom Duffing oscillator with large nonlinearity and large damping are investigated by using a simple point collocation method applied in the time domain over a period of the periodic solution. The relationship between the proposed collocation method and the high dimensional harmonic balance method (HDHB), proposed earlier by Thomas, Dowell, and Hall (2002), is explored. We demonstrate that the HDHB is not a kind of "harmonic balance method" but essentially a cumbersome version of the collocation method. In using the collocation method, the collocation-resulting nonlinear algebraic equations (NAEs) are solved by the Newton-Raphson method. To start the Newton iterative process, initial values for the N harmonics approximation are provided by solving the corresponding low order harmonic approximation with the aid of Mathematica. We also introduce a generating frequency (wg), where by the response curves are effectively obtained. Amplitude-frequency response curves for various values of damping, nonlinearity, and force amplitude are obtained and compared to show the effect of each parameter. In addition, the time Galerkin method [the Harmonic-Balance method] is applied and compared with the presently proposed collocation method. Numerical examples confirm the simplicity and effectiveness of the present collocation scheme in the time domain. Copyright © 2012 Tech Science Press.

Pang L.,Xidian University | Li H.,Northwestern Polytechnical University | Pei Q.,Xidian University
IET Communications | Year: 2012

Multicasting is an important business in the field of the wireless local area network (WLAN), because the access point (AP) usually has to send the same message to each station (STA) of a specific group, and broadcasting the message to this group is one of the most efficient ways of communication. Chinese WLAN security standard, called WLAN Authentication and Privacy Infrastructure (WAPI), has taken secure multicasting into account, and proposed a Multicast Key Management Protocol (MKMP), in which the multicast session key (MSK) is distributed to each STA over the secure unicast channel built between STA and AP one by one. It is clear that the MSK distribution is very inefficient in performance, especially when the number of STAs is very large. In this study, a new MSK distribution protocol is proposed, and it can be used to substitute the original protocol in WAPI. Analyses show that the proposed protocol can achieve needed security requirements, and is more efficient than the original one in WAPI. Now, WAPI has been in the process of ISO/IEC standard building, and thus the authors think that their proposal can ameliorate WAPI largely and promote its ISO/IEC standard building. © 2012 The Institution of Engineering and Technology.

Yang F.,Xidian University | Wan S.,Northwestern Polytechnical University
IEEE Communications Magazine | Year: 2012

Bitstream-based methods are intuitively suited for quality assessment of networked video services, and are currently under intense investigations in terms of research and standardization activities. This article examines the factors that may affect the quality of the networked video, and reviews the state-of-the-art techniques as well as standardization progress in bitstreambased video quality assessment. According to different levels of access to the bitstream, three types of models are described and compared: the parametric, packet layer, and bitstream-layer models. © 1979-2012 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.

Chen B.,University of Saskatchewan | Shi J.,University of Saskatchewan | Zhang S.,Northwestern Polytechnical University | Wu F.-X.,University of Saskatchewan
Proteomics | Year: 2013

The identification of protein complexes plays a key role in understanding major cellular processes and biological functions. Various computational algorithms have been proposed to identify protein complexes from protein-protein interaction (PPI) networks. In this paper, we first introduce a new seed-selection strategy for seed-growth style algorithms. Cliques rather than individual vertices are employed as initial seeds. After that, a result-modification approach is proposed based on this seed-selection strategy. Predictions generated by higher order clique seeds are employed to modify results that are generated by lower order ones. The performance of this seed-selection strategy and the result-modification approach are tested by using the entropy-based algorithm, which is currently the best seed-growth style algorithm to detect protein complexes from PPI networks. In addition, we investigate four pairs of strategies for this algorithm in order to improve its accuracy. The numerical experiments are conducted on a Saccharomyces cerevisiae PPI network. The group of best predictions consists of 1711 clusters, with the average f-score at 0.68 after removing all similar and redundant clusters. We conclude that higher order clique seeds can generate predictions with higher accuracy and that our improved entropy-based algorithm outputs more reasonable predictions than the original one. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhao B.,Northwestern Polytechnical University
Advanced Materials Research | Year: 2011

The Finite Element Method (FEM) was used for axisymmetric indentation to investigate mechanics properties of piezoelectric solids (PZT-5H). Since piezoelectric materials are usually treated as transversely isotropic elastic materials, a simple linear relationship between indentation load P and indentation displacement h was presented under a cylindrical indenter. Three different cases (uncouple mechanical case, poled substrate-insulating indenter and poled substrate-conducting indenter) were taken into consideration to study indentation responses. The results showed that polarization could more easily damage the poled substrate than the uncoupled case. At the same displacement the highest indentation load existed in the poled/insulating case and the lowest one was in the uncoupled case because of the polarization influence. Electric potential distributions were given to study the direct piezoelectric effects and the electromechanical phenomena. In addition elastic modulus, contact stiffness, and piezoelectric strain constant were calculated directly through the use of the FEM. The determination of the poling direction is another use for the indentation technique, and the discussion of indentation size effect shows that a bigger indenter is followed by a larger indentation load. © (2011) Trans Tech Publications.

Zhang W.,East China University of Science and Technology | Wang S.,East China University of Science and Technology | Kong J.,Northwestern Polytechnical University
Reactive and Functional Polymers | Year: 2012

Amphiphilic hemi-telechelic and telechelic poly(ethylene oxide) (PEO) hybrids based on polyhedral oligmeric silsesquioxane (POSS) were prepared via the copper-catalyzed azide-alkyne "click" reaction. Thermal properties of POSS-PEO were characterized using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The result shows that the thermal properties of telechelic POSS-PEO are effectively enhanced by POSS. The morphology of the POSS-containing PEO hybrid crystals was investigated using polarized optical microscopy (POM), and the results indicate that it is much easier for the POSS in the telechelic POSS-PEO hybrids (T-POSS-PEO) to form quite large aggregates, which act as nucleating agents during the crystallization of the PEO chains. The self-assembly behavior of POSS-PEO in water was also studied using transmission electron microscopy (TEM). The results reveal that hemi-telechelic POSS-PEO hybrids (HT-POSS-PEO) can self-assemble into spherical aggregates, whereas the T-POSS-PEO hybrids self-assemble into ellipsoidal aggregates. © 2012 Elsevier Ltd. All rights reserved.

Wu J.,University of Amsterdam | Wu J.,Northwestern Polytechnical University | Worring M.,University of Amsterdam
IEEE Transactions on Multimedia | Year: 2012

Large video collections such as YouTube contain many different video genres, while in many applications the user might be interested in one or two specific video genres only. Thus, when users are querying the system with a specific semantic concept like AnchorPerson, and MovieStars, they are likely aiming a genre specific instantiation of this concept. Existing methods treat this problem as a classical learning problem leading to unnecessarily complex models. We propose a framework to detect visual-based genre-specific concepts in a more efficient and accurate way. We do so by using a two-step framework distinguishing two different levels. Genre-specific concept models are trained based on a training set with data labeled at video level for genres and at shot level for semantic concepts. In the classification stage, video genre classification is applied first to reduce the entire data set to a relatively small subset. Then, the genre-specific concept models are applied to this subset only. Experiments have been conducted on a small 28-h data set for genre-specific concept detection and a 4168-h (80 031 videos) benchmark data set for genre-specific topic search. Experimental results show that our proposed two-step method is more efficient and effective than existing methods which do not consider the different semantic levels between video genres and semantic concepts for both the indexing and the search tasks. When filtering out 80% of the data set, the average performance loss is about 11.3% for genre-specific concept detection and 31.5% for genre-specific topic search, while the processing speed increases hundreds of times for different video genres. © 2011 IEEE.

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.

Shi J.,Northwestern Polytechnical University
Applied Mathematics and Information Sciences | Year: 2015

Vector sound intensity probe can be used to determine the DOA of a sound source by measuring the three orthogonal components of the sound-intensity vector. Typical vector sound intensity probes are composed of six or four sensors with symmetric structures. Such probes, in our opinion, are still not convenient for engineering implementation. A four-sensor vector sound intensity probe with arbitrary configurations is proposed here. The flexible structure of this probe allows it easily fix in any platform. In this paper, the direction finding algorithm based on this four-sensor probe is investigated first, then the error in direction estimates caused by instrument systematic error in sound intensity measurements are analyzed theoretically. Last, simulation experiments are conducted for testing the performance of DOA estimation based on this probe. © 2015 NSP.

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.

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.

Chen X.-P.,Northwestern Polytechnical University
Engineering Applications of Computational Fluid Mechanics | Year: 2012

Lattice Boltmzann method (LBM) has been developed as an important technique of computational fluid mechanics. Two-dimensional turbulent flow around NACA0012 airfoil, with Re=105 and AOA=4° (angle of attack), is simulated with "multiple-relaxation time" lattice Boltzmann method incorporated with Spalart-Allmaras (SA) turbulence model. From the viewpoint of industrial applications, the related computational aspects are discussed, such as treatments of wall boundary, far field boundary conditions, and the position of the airfoil in the domain. Meanwhile, to balance the computational loads and accuracy of the simulations, grid refinement is applied. According to the results, LBM gives pretty good predictions, and quite flexible domain size can be accepted if the far field boundary condition is well posed. Compared to 3D LES-LBM simulations, two-dimensional LBM with SA turbulent model is of lower computational load, but with good accuracy.

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.

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.

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