Showing papers by "Southeast University published in 2003"

An overview of operators for aggregating information

Abstract: In this work, we first make a survey of the existing main aggregation operators and then propose some new aggregation operators such as the induced ordered weighted geometric averaging (IOWGA) operator, generalized induced ordered weighted averaging (GIOWA) operator, hybrid weighted averaging (HWA) operator, etc., and study their desirable properties. Finally, we briefly classify all of these aggregation operators. © 2003 Wiley Periodicals, Inc.

Global asymptotic stability of a general class of recurrent neural networks with time-varying delays

Abstract: In this paper, the existence and uniqueness of the equilibrium point and its global asymptotic stability are discussed for a general class of recurrent neural networks with time-varying delays and Lipschitz continuous activation functions. The neural network model considered includes the delayed Hopfield neural networks, bidirectional associative memory networks, and delayed cellular neural networks as its special cases. Several new sufficient conditions for ascertaining the existence, uniqueness, and global asymptotic stability of the equilibrium point of such recurrent neural networks are obtained by using the theory of topological degree and properties of nonsingular M-matrix, and constructing suitable Lyapunov functionals. The new criteria do not require the activation functions to be differentiable, bounded or monotone nondecreasing and the connection weight matrices to be symmetric. Some stability results from previous works are extended and improved. Two illustrative examples are given to demonstrate the effectiveness of the obtained results.

Structural color and the lotus effect.

Abstract: The study of biological microstructure is one of the most important research areas in biomimicry.[1–3] Microstructure plays many important roles in living things.[2,3] For example, the charming blue color of the Morpho sulkowskyi butterfly originates from light diffraction and scattering, which results from the ordered microstructure of its scales. This form of color is usually known as structural color, which is utilized by animals both for protection and as a warning. Today, the study of structural color has been extended from biology to optics.[4–6] As well as affecting coloration, microstructure also plays an important role in self-cleaning.[2, 7] For the butterfly, the specific nanostructure enhances the hydrophobicity of its wings, which allows droplets of water to be dispersed more easily. During this process, dust particles on the surface of the wings are removed. This phenomenon is known as the “lotus effect”, which is not only very useful for natural species, but also for materials applications, such as for decoration where a natural force might be used to clean a surface. It would be interesting to discover whether it is possible to design a material that incorporates both structural color and the lotus effect, thus mimicking the wings of a butterfly. Such a material should be of great biological and technological importance. In this paper, we will show one approach to fabricating such a biomimetic decorative material by taking advantage of a nanostructured inverse opal surface. Inverse opal is a solid material that consists of a threedimensional network.[6,8–10] Orderedmonodisperse air spheres throughout the network contribute to an optical stop band, the position of which can be tuned by careful control of the periodicity of the air spheres. Colors can be observed by the naked eye when the stop band falls in the visible region. As a consequence of its unique optical properties, inverse opal has been regarded as a new-generation decorative material, in addition to its application as a photonic crystalline material.[6,11] Recently, we realized that inverse opal might also be incorporated into the design of a hydrophobic material. The solid material network of inverse opal contributes a rough surface composed of well-ordered meshes. According to the Cassie–Baxter law, the intrinsic wettability of the solid material can be greatly reduced.[12] Such a decorative material, which exhibits both structural color and the lotus effect, would be environmentally friendly and energy-efficient. For practical applications, a convenient method of fabricating a uniform inverse opal film over a large area is required. In addition, the rough inverse opal surface needs to be further optimized to imbue the surface with superhydrophobic character. We describe here the development of a dipping method that can be used to meet these criteria, and which can derive uniform inverse opal films with a nanostructured surface. The procedure for the fabrication is as follows: First, submicron-sized monodisperse polystyrene spheres and nanosized particles were ultrasonically dispersed into deionised water. A glass substrate was then immersed into the solution and withdrawn at a constant speed. It is known that a mixture of spheres with different sizes cannot be used to fabricate colloidal crystals with long-range structural order by such a deposition method,[13–15] as phase separation occurs, or an amorphous structure is formed. In our experiment, we found that this conclusion is only partially correct. A structure with long-range order can be derived when the ratio of the diameters of the spheres falls into a particular regime. Figure 1a shows an image of a structure composed of monodisperse spheres, while Figure 1b–d displays three images of structures composed of spheres of two sizes, with diameter ratios of 0.94, 0.34, and 0.07, respectively. The structure formed by the spheres of varying size depends on the diameter ratio. A structure with long-range order can be observed in films composed of monodisperse spheres, however, such order is absent in films composed of spheres of two sizes, where the diameter ratio is larger than 0.15. Usually, the particles form a structure with discernible separation when the ratio between the two types of sphere is larger than 0.5 (Figure 1b), while the domains formed by different types of particles are separated when the ratio is smaller than this value (Figure 1c). When the diameter ratio between the [7] W. P. Rothwell, W. Shen, J. H. Lunsford, J. Am. Chem. Soc. 1984, 106, 2452 – 2453. [8] Each unit cell of CHA contains 36 T sites and three cages. The HSAPO-34 used has one Si, five P, and six Al atoms per cage. [9] J. F. Haw, P. W. Goguen, T. Xu, T. W. Skloss, W. Song, Z. Wang, Angew. Chem. 1998, 110, 993 – 995; Angew. Chem. Int. Ed. 1998, 37, 948 – 949.

Visible-light responsive cerium ion modified titania sol and nanocrystallites for X-3B dye photodegradation

Abstract: The cerium ion (Ce4+) modified titania sol and nanocrystallites were prepared by chemical coprecipitation–peptization and hydrothermal synthesis methods, respectively. XRD patterns show that Ce4+-TiO2 sol particles had anatase semicrystalline structure. And the calcined Ce4+-TiO2 powder was composed of predominant anatase titania and crystalline cerium titanate (11.18 wt.% CexTi(1−x)O2). AFM micrograph shows that ultrafine particles were well dispersed in sol system and average particle size was about 10 nm. Ce4+-TiO2 nanocrystallites have grown into 70 nm in mean size. The difference in calculated particle size (2.41 nm for sol particle and 4.53 nm for crystallite) by XRD Scherrer’s formula was mainly due to aggregation effect of nanoparticles. The experimental results exhibit that Ce4+-TiO2 sol and nanocrystallites can effectively photodegrade reactive brilliant red dye (X-3B) with the dye/Ce4+-TiO2/visible-light reaction system. Moreover, photocatalytic reaction also can carry out in hydrosol reaction system as well as in suspension reaction system. And Ce4+-TiO2 sol has shown higher efficiency than nanocrystallites in respect of photocatalytic activity. Meanwhile, dye photodegradation mechanisms involving photolysis, photocatalysis, photosensitized photocatalysis and interband photocatalysis were proposed regarding different photocatalytic reaction system.

Finite-difference frequency-domain algorithm for modeling guided-wave properties of substrate integrated waveguide

Abstract: In multilayer microwave integrated circuits such as low-temperature co-fired ceramics or multilayered printed circuit boards, waveguide-like structures can be fabricated by using periodic metallic via-holes referred to as substrate integrated waveguide (SIW). Such SIW structures can largely preserve the advantages of conventional rectangular waveguides such as high-Q factor and high power capacity. However, they are subject to leakage due to periodic gaps, which potentially results in wave attenuation. Therefore, such a guided-wave modeling problem becomes a very complicated complex eigenvalue problem. Since the SIW are bilaterally unbounded, absorbing boundary conditions should be deployed in numerical algorithms. This often leads to a difficult complex root-extracting problem of a transcend equation. In this paper, we present a novel finite-difference frequency-domain algorithm with a perfectly matched layer and Floquet's theorem for the analysis of SIW guided-wave problems. In this scheme, the problem is converted into a generalized matrix eigenvalue problem and finally transformed to a standard matrix eigenvalue problem that can be solved with efficient subroutines available. This approach has been validated by experiment.

Microstructure and mechanical properties of Mg–Al based alloy with calcium and rare earth additions

Abstract: Effects of calcium and rare earth additions to alloy AZ91 on the microstructure and mechanical properties were investigated. The results indicated that small amounts of calcium addition to AZ91 did not cause the formation of any new phases in the microstructure, but refined the as-cast microstructure and increased the thermal stability of the β phase so that the yield strength and creep resistance of the alloy were significantly improved. Additions of lanthanum-rich misch metal (MM) resulted in the formation of needle-shaped particles, which showed very high thermal stability and did not dissolve into the matrix after the solution treatment at 420 °C for 20 h. The strength as well as creep resistance of the alloy at elevated temperatures was remarkably increased when MM was added combined with calcium. The highest creep resistance was obtained from the alloy with 3% of MM and 0.3% of calcium addition and its steady state creep rate reached as low as 2.69×10 −8 s −1 , one order of magnitude lower than that of alloy AZ91 without MM and calcium additions.

Semi-active control of structures incorporated with magnetorheological dampers using neural networks

Abstract: Semi-active control of buildings and structures with magnetorheological (MR) dampers for earthquake hazard mitigation represents a relatively new research area. In this paper, the Bingham model of MR damper is introduced, and the formula relating the yielding shear stress and the control current of MR dampers is put forward that matches the experimental data. Then an on-line real-time control method for semi-active control of structures with MR dampers is proposed. This method considers the time-delay problem of semi-active control, which can solve distortion of the responses of structures. Finally, through a numerical example of a three-storey reinforced concrete structure, a comparison is made between controlled structure and uncontrolled structure. The calculated results show that MR dampers can reduce the seismic responses of structures effectively. Moreover, the on-line real-time control method is compared with the traditional elastoplastic time-history analysis method, and the efficacy of the on-line real-time control method is demonstrated. In addition, the Levenberg–Marquardt algorithm is used to train the on-line control neural network, and studies show that the algorithm has a very fast convergence rate.

Qualitative analysis of a ratio-dependent predator–prey system with diffusion

Abstract: Ratio-dependent predator–prey models are favoured by many animal ecologists recently as they better describe predator–prey interactions where predation involves a searching process. When densities of prey and predator are spatially homogeneous, the so-called Michaelis–Menten ratio-dependent predator–prey system, which is an ordinary differential system, has been studied by many authors. The present paper deals with the case where densities of prey and predator are spatially inhomogeneous in a bounded domain subject to the homogeneous Neumann boundary condition. Its main purpose is to study qualitative properties of solutions to this reaction-diffusion (partial differential) system. In particular, we will show that even though the unique positive constant steady state is globally asymptotically stable for the ordinary-differential-equation dynamics, non-constant positive steady states exist for the partial-differential-equation model. This demonstrates that stationary patterns arise as a result of diffusion.

Structural vibration control by shape memory alloy damper

Abstract: A damper device based on shape memory alloy (SMA) wires is developed for structural control implementation. The design procedures of the SMA damper are presented. As a case study, eight such SMA dampers are installed in a frame structure to verify the effectiveness of the damper devices. Experimental results show that vibration decay of the SMA damper controlled frame is much faster than that of the uncontrolled frame. The finite-element method is adopted to conduct the free and forced vibration analysis of the controlled and uncontrolled frame. The experimental and numerical results illustrate that the developed SMA dampers are very effective in reducing structural response and have great potential for use as efficient energy dissipation devices with the advantages of good control of force and no lifetime limits, etc.

Finite time synchronization of chaotic systems

Abstract: Using finite time control techniques, continuous state feedback control laws are developed to solve the synchronization problem of two chaotic systems. We demonstrate that these two chaotic systems can be synchronized in finite time. Examples of Duffing systems, Lorenz systems are presented to verify our method.

Asynchronous-pulse ultrasonic spray pyrolysis deposition of CuxS (x=1, 2) thin films

Abstract: Nanocrystalline CuxS (x=1, 2) thin films were deposited by asynchronous-pulse ultrasonic spray pyrolysis (APUSP) technique on glass from CuCl2 and thiourea at relatively low temperature without any complexing agent. The deposited films chemically close to CuS were found to be polycrystalline phases, while the Cu2S films were a mixture of amorphous and polycrystalline as well. The crystalline phase of particles was highly depended on the molar ratio of thiourea to CuCl2 and the pyrolysis temperature. The growth of CuxS thin films was controlled successfully by the improved APUSP method. Characterization of the films has been carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XRD and XPS analysis showed stoichiometric CuxS (covellite CuS and chalcolite Cu2S). Raman shifts of the films were measured at 474 cm−1 (CuS) and 472 cm−1 (Cu2S).

An Approach to Improving Consistency of Fuzzy Preference Matrix

Abstract: Based on the transfer formulas of fuzzy preference matrix and multiplicative preference matrix, this paper presents an approach to improving consistency of fuzzy preference matrix and gives a practical iterative algorithm to derive a modified fuzzy preference matrix with acceptable consistency. By using two criteria, we can judge whether the modification is acceptable or not. Finally, a numerical example is given to show the feasibility and effectiveness of the algorithm.

Model reference adaptive control of continuous-time systems with an unknown input dead-zone

Abstract: The adaptive control of continuous-time linear dynamic systems preceded by an unknown dead-zone in state space form is discussed. A lemma to simplify the error equation between the plant and the matching reference model is introduced which allows the development of a robust adaptive control scheme by involving the dead-zone inverse terms. This adaptive control law ensures global stability of the entire system and achieves the desired tracking precision even when the slopes of the dead-zone are unequal. Simulations performed on a typical linear system illustrate and clarify the validity of this approach.

Epoxy asphalt concrete paving on the deck of long-span steel bridges

Abstract: It is the first systematic research in the world on the composition design of epoxy asphalt concrete as paving material. Material characteristics and service performance of mixture, fatigue resistance characteristics of epoxy asphalt concrete by the fatigue test of complex beam have also been described. This research indicates that epoxy asphalt concrete is a good type of paving material. Research results have been applied successfully in the paving of steel deck of the Second Nanjing Yangtze River Bridge (SNYRB). It provides a new paving type for long-span steel bridges of China and has a bright application prospect.

Cultural Differences in E-Commerce: A Comparison between the U.S. and China

Abstract: This paper discusses the importance of identifying cultural problems of the online globalization and points out that payment and logistic systems and language are the primary factors that every firm should take into account in the process of their online globalization. Next, the paper identifies the characteristics and trends of the Internet and e-commerce in China. In the third part, the paper differentiates e-commerce in the U.S. with China through analyzing Internet users’ behaviors especially their attitudes toward different payment systems in these two countries. Finally, it discusses how to remove language barriers to enhance net growth. In conclusion, this paper will suggest some recommendations on how to expand business via the Internet by reducing the gap between the two cultures.