Showing papers by "Beihang University published in 2005"

Improved particle swarm optimization combined with chaos

Abstract: As a novel optimization technique, chaos has gained much attention and some applications during the past decade. For a given energy or cost function, by following chaotic ergodic orbits, a chaotic dynamic system may eventually reach the global optimum or its good approximation with high probability. To enhance the performance of particle swarm optimization (PSO), which is an evolutionary computation technique through individual improvement plus population cooperation and competition, hybrid particle swarm optimization algorithm is proposed by incorporating chaos. Firstly, adaptive inertia weight factor (AIWF) is introduced in PSO to efficiently balance the exploration and exploitation abilities. Secondly, PSO with AIWF and chaos are hybridized to form a chaotic PSO (CPSO), which reasonably combines the population-based evolutionary searching ability of PSO and chaotic searching behavior. Simulation results and comparisons with the standard PSO and several meta-heuristics show that the CPSO can effectively enhance the searching efficiency and greatly improve the searching quality.

Dynamic flight stability of a hovering bumblebee

Abstract: The longitudinal dynamic flight stability of a hovering bumblebee was studied using the method of computational fluid dynamics to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. For the longitudinal disturbed motion, three natural modes were identified: one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. The unstable oscillatory mode consists of pitching and horizontal moving oscillations with negligible vertical motion. The period of the oscillations is 0.32 s (approx. 50 times the wingbeat period of the bumblebee). The oscillations double in amplitude in 0.1 s; coupling of nose-up pitching with forward horizontal motion (and nose-down pitching with backward horizontal motion) in this mode causes the instability. The stable fast subsidence mode consists of monotonic pitching and horizontal motions, which decay to half of the starting values in 0.024 s. The stable slow subsidence mode is mainly a monotonic descending (or ascending) motion, which decays to half of its starting value in 0.37 s. Due to the unstable oscillatory mode, the hovering flight of the bumblebee is dynamically unstable. However, the instability might not be a great problem to a bumblebee that tries to stay hovering: the time for the initial disturbances to double (0.1 s) is more than 15 times the wingbeat period (6.4 ms), and the bumblebee has plenty of time to adjust its wing motion before the disturbances grow large.

Mode-independent robust stabilization for uncertain Markovian jump nonlinear systems via fuzzy control

Abstract: This paper is concerned with the robust-stabilization problem of uncertain Markovian jump nonlinear systems (MJNSs) without mode observations via a fuzzy-control approach. The Takagi and Sugeno (T-S) fuzzy model is employed to represent a nonlinear system with norm-bounded parameter uncertainties and Markovian jump parameters. The aim is to design a mode-independent fuzzy controller such that the closed-loop Markovian jump fuzzy system (MJFS) is robustly stochastically stable. Based on a stochastic Lyapunov function, a robust-stabilization condition using a mode-independent fuzzy controller is derived for the uncertain MJFS in terms of linear matrix inequalities (LMIs). A new improved LMI formulation is used to alleviate the interrelation between the stochastic Lyapunov matrix and the system matrices containing controller variables in the derivation process. Finally, a simulation example is presented to illustrate the effectiveness of the proposed design method.

Orientation and size dependence of the elastic properties of zinc oxide nanobelts

Abstract: Molecular dynamics simulations are performed to characterize the response of zinc oxide (ZnO) nanobelts to tensile loading. The ultimate tensile strength (UTS) and Young's modulus are obtained as functions of size and growth orientation. Nanobelts in three growth orientations are generated by assembling the unit wurtzite cell along the [0001], , and crystalline axes. Following the geometric construction, dynamic relaxation is carried out to yield free-standing nanobelts at 300 K. Two distinct configurations are observed in the [0001] and orientations. When the lateral dimensions are above 10 A, nanobelts with rectangular cross-sections are seen. Below this critical size, tubular structures involving two concentric shells similar to double-walled carbon nanotubes are obtained. Quasi-static deformations of belts with and orientations consist of three stages, including initial elastic stretching, wurtzite-ZnO to graphitic-ZnO structural transformation, and cleavage fracture. On the other hand, [0001] belts do not undergo any structural transformation and fail through cleavage along (0001) planes. Calculations show that the UTS and Young's modulus of the belts are size dependent and are higher than the corresponding values for bulk ZnO. Specifically, as the lateral dimensions increase from 10 to 40 A, decreases between 38–76% and 24–63% are observed for the UTS and Young's modulus, respectively. This effect is attributed to the size-dependent compressive stress induced by tensile surface stress in the nanobelts. and nanobelts with multi-walled tubular structures are seen to have higher values of elastic moduli (~340 GPa) and UTS (~36 GPa) compared to their wurtzite counterparts, echoing a similar trend in multi-walled carbon nanotubes.

Shape memory effect in Cu nanowires.

Abstract: A rubber-like pseudoelastic behavior is discovered in single-crystalline face-centered-cubic (FCC) Cu nanowires in atomistic simulations. Nonexistent in bulk Cu, this phenomenon is associated primarily with a reversible crystallographic lattice reorientation driven by the high surface-stress-induced internal stresses due to high surface-to-volume ratios at the nanoscale level. The temperature-dependence of this behavior leads to a shape memory effect (SME). Under tensile loading and unloading, the nanowires exhibit recoverable strains up to over 50%, well beyond the typical recoverable strains of 5−8% for most bulk shape memory alloys (SMAs). This behavior is well-defined for wires between 1.76 and 3.39 nm in size over the temperature range of 100−900 K.

A hybrid collaborative filtering method for multiple-interests and multiple-content recommendation in E-Commerce ☆

Abstract: Recommender systems apply knowledge discovery techniques to the problem of making personalized recommendations for products or services during a live interaction. These systems, especially collaborative filtering based on user, are achieving widespread success on the Web. The tremendous growth in the amount of available information and the kinds of commodity to Web sites in recent years poses some key challenges for recommender systems. One of these challenges is ability of recommender systems to be adaptive to environment where users have many completely different interests or items have completely different content (We called it as Multiple interests and Multiple-content problem). Unfortunately, the traditional collaborative filtering systems can not make accurate recommendation for the two cases because the predicted item for active user is not consist with the common interests of his neighbor users. To address this issue we have explored a hybrid collaborative filtering method, collaborative filtering based on item and user techniques, by combining collaborative filtering based on item and collaborative filtering based on user together. Collaborative filtering based on item and user analyze the user-item matrix to identify similarity of target item to other items, generate similar items of target item, and determine neighbor users of active user for target item according to similarity of other users to active user based on similar items of target item. In this paper we firstly analyze limitation of collaborative filtering based on user and collaborative filtering based on item algorithms respectively and emphatically make explain why collaborative filtering based on user is not adaptive to Multiple-interests and Multiple-content recommendation. Based on analysis, we present collaborative filtering based on item and user for Multiple-interests and Multiple-content recommendation. Finally, we experimentally evaluate the results and compare them with collaborative filtering based on user and collaborative filtering based on item, respectively. The experiments suggest that collaborative filtering based on item and user provide better recommendation quality than collaborative filtering based on user and collaborative filtering based on item dramatically.

Transformations for a generalized variable-coefficient nonlinear Schrodinger model from plasma physics, arterial mechanics and optical fibers with symbolic computation

Abstract: Describing space and laboratory plasmas, arterial mechanics and optical fibers, a generalized variable-coefficient nonlinear Schrodinger model is hereby under investigation. Four transformations have been constructed from such a model to the known standard and cylindrical nonlinear Schrodinger equations with the relevant constraints on the variable coefficients presented. Symbolic computation is performed. Specialities of those transformations are discussed. Analytic solutions of such a generalized variable-coefficient model can be obtained via those transformations from the analytic solutions of the standard and cylindrical ones.

An improved robust fuzzy-PID controller with optimal fuzzy reasoning

Abstract: Many fuzzy control schemes used in industrial practice today are based on some simplified fuzzy reasoning methods, which are simple but at the expense of losing robustness, missing fuzzy characteristics, and having inconsistent inference. The concept of optimal fuzzy reasoning is introduced in this paper to overcome these shortcomings. The main advantage is that an integration of the optimal fuzzy reasoning with a PID control structure will generate a new type of fuzzy-PID control schemes with inherent optimal-tuning features for both local optimal performance and global tracking robustness. This new fuzzy-PID controller is then analyzed quantitatively and compared with other existing fuzzy-PID control methods. Both analytical and numerical studies clearly show the improved robustness of the new fuzzy-PID controller.

Spherical nebulons and Bäcklund transformation for a space or laboratory un-magnetized dusty plasma with symbolic computation

Abstract: Plasmas and dust are a couple of the ubiquitous elements of the Universe. The nonlinear dust-acoustic-wave propagation in a space or laboratory un-magnetized dusty plasma is hereby considered, which is described by a spherical Kadomtsev-Petviashvili equation. By virtue of computerized symbolic computation, we obtain the analytically-expressed spherical nebulons and an auto-Backlund transformation for the electrostatic potential in such a plasma. With figures, we discuss the features of the nebulon structures, and propose some (3+1)-dimensional, possibly-observable nebulonic effects for the future space/laboratory plasma experiments.

Collaboration between industry and research institutes/universities on industrial innovation in Beijing, China

Abstract: Most R&D resources in China were allocated to public research institutes/universities until the economic transition of the mid 1990s. To maximize the return from these resources, it is important to have a healthy collaboration between industry and research institutes/universities on industrial innovation. This paper examines that relationship and discusses some empirical evidence on its efficiency with particular reference to industry in Beijing. Following a survey of 950 industrial enterprises, the influences of the collaboration relationship on industrial innovation were analyzed. The main findings indicate that the technology novelty of industrial innovation is positively related to that relationship, i.e. the more the collaboration, the higher the technology novelty of the innovation. However, the collaboration relationship is less efficient in terms of economic performance indicators such as innovation sales and profit ratios, to measure innovation. Moreover, the collaboration relationship i...

A computational study of the aerodynamics and forewing-hindwing interaction of a model dragonfly in forward flight

Abstract: SUMMARY The aerodynamics and forewing-hindwing interaction of a model dragonfly in forward flight are studied, using the method of numerically solving the Navier-Stokes equations. Available morphological and stroke-kinematic parameters of dragonfly (Aeshna juncea) are used for the model dragonfly. Six advance ratios (J; ranging from 0 to 0.75) and, at each J, four forewing-hindwing phase angle differences (γd; 180°, 90°, 60° and 0°) are considered. The mean vertical force and thrust are made to balance the weight and body-drag, respectively, by adjusting the angles of attack of the wings, so that the flight could better approximate the real flight. At hovering and low J (J=0, 0.15), the model dragonfly uses separated flows or leading-edge vortices (LEV) on both the fore- and hindwing downstrokes; at medium J (J=0.30, 0.45), it uses the LEV on the forewing downstroke and attached flow on the hindwing downstroke; at high J (J=0.6, 0.75), it uses attached flows on both fore- and hindwing downstrokes. (The upstrokes are very lightly loaded and, in general, the flows are attached.) At a given J, at γd=180°, there are two vertical force peaks in a cycle, one in the first half of the cycle, produced mainly by the hindwing downstroke, and the other in the second half of the cycle, produced mainly by the forewing downstroke; atγ d=90°, 60° and 0°, the two force peaks merge into one peak. The vertical force is close to the resultant aerodynamic force [because the thrust (or body-drag) is much smaller than vertical force (or the weight)]. 55-65% of the vertical force is contributed by the drag of the wings. The forewing-hindwing interaction is detrimental to the vertical force (and resultant force) generation. At hovering, the interaction reduces the mean vertical force (and resultant force) by 8-15%, compared with that without interaction; as J increases, the reduction generally decreases (e.g. at J=0.6 and γd=90°, it becomes 1.6%). A possible reason for the detrimental interaction is as follows: each of the wings produces a mean vertical force coefficient close to half that needed for weight support, and a downward flow is generated in producing the vertical force; thus, in general, a wing moves in the downwash-velocity field induced by the other wing, reducing its aerodynamic forces.

Disclosure and Determinants Studies: An Extension Using the Divisive Clustering Method (DIV)

Abstract: Past accounting research contains an extensive range of disclosure and determinants studies. But these studies have one major methodological drawback: the disclosure analysis is often restricted to determination of the disclosure index, i.e. the sum of disclosed items, weighted or unweighted. The disclosure profile (which reflects the structure of published information) is generally not part of the research design. The objective of this paper is to introduce a divisive (descendant) clustering method, which splits the sample into homogeneous sub-groups corresponding to disclosure patterns (or profiles), for clearer determination of the financial characteristics of each group. This methodology is illustrated by a study of disclosure on provisions by large French firms. The results show that the disclosure pattern is related to provision intensity, size, leverage and market expectation, but not to profit, return and industry. This new research method is a valuable complementary tool for expanding on disclosure and determinants studies, moving from disclosure levels to disclosure patterns.

Adaptive knot placement in B-spline curve approximation

Abstract: An adaptive knot placement algorithm for B-spline curve approximation to dense and noisy data points is presented in this paper. In this algorithm, the discrete curvature of the points is smoothed to expose the characteristics of the underlying curve. With respect to the integration of the smoothed curvature, knots are placed adaptively to satisfy a heuristic rule. Several experimental results are included to demonstrate the validity of this algorithm.

Integrated scheduling of daily work activities and morning–evening commutes with bottleneck congestion

Abstract: Previous analysis of bottleneck congestion and departure time choice have focused on the trade-off between queuing delay cost and early/late arrival penalty for a given work start schedule.The actual scheduling of travel and work activities may well depend on some other important factors, such as the travel cost of the after-work trip, the work duration and the utility variation of different work times.This paper attempts to link the home-to-work and work-to-home trip schedules via the work duration.The morning home-to-work and evening work-to-home travel costs are calculated by the bottleneck queuing models and each individuals work utility is determined according to his/her work start time and end time with a predetermined marginal timing utility function.Travelers make a tradeoff between travel cost minimization and stay-at-home and work utility maximization in choosing their travel and activity schedules.A discrete choice model is used to predict the dynamic evolution process and stationary distribution of individual schedule patterns.After specifying various kinds of timing utility functions with different degrees of flexibility in work hour schemes, a set of numerical experiments are conducted and some meaningful observations are made from the experiment results, particularly on the effect of flexible work hours on traffic congestion mitigation. � 2004 Elsevier Ltd. All rights reserved.

Towards quantitative understanding of formation and stability of Ge hut islands on Si(001).

Abstract: We analyze Ge hut island formation on Si(001), using first-principles calculations of energies, stresses, and their strain dependence of $\mathrm{Ge}/\mathrm{Si}(105)$ and $\mathrm{Ge}/\mathrm{Si}(001)$ surfaces combined with continuum modeling. We give a quantitative assessment on strain stabilization of Ge(105) facets, estimate the critical size for hut nucleation or formation, and evaluate the magnitude of surface stress discontinuity at the island's edge and its effect on island stability.

Stability of the car-following model on two lanes.

Abstract: In the case of two-lane traffic, vehicle drivers always worry about the lane changing actions from neighbor lane. This paper studies the stability of a car-following model on two lanes which incorporates the lateral effects in traffic. The stability condition of the model is obtained by using the linear stability theory. The modified Korteweg-de Vries equation is constructed and solved, and three types of traffic flows in the headway-sensitivity space--stable, metastable, and unstable--are classified. Both analytical and simulation results show that the anxiousness about lane changing from neighbor lane indeed has influence upon people's driving behavior and the consideration of lateral effects could stabilize the traffic flows on both lanes.