International Journal of Modern Physics C

We introduce a time-frequency transform based on Gabor functions whose parameters are given by the Fourier transform of the analyzed signal. At any given frequency, the width and the phase of the Gabor function are obtained, respectively, from the magnitude and the phase of the signal's corresponding Fourier component, yielding an analyzing kernel which is a representation of the signal's content at that particular frequency. The resulting Gabor transform tunes itself to the input signal, allowing the accurate detection of time and frequency events, even in situations where the traditional Gabor and S-transform approaches tend to fail. This is the case, for instance, when considering the time-frequency representation of electroencephalogram traces (EEG) of epileptic subjects, as illustrated by the experimental study presented here.

A new optimization technique for evaluating the complex effective relative permittivity and permeability of elementary sub-slab whose thickness equals to the constant of a unit cell of a slab metamaterial is developed. The objective of the technique is based on a numerical solving of appropriate minimization problem for a cascaded network representation of the slab metamaterial utilizing the Effective Medium Theory (EMT) and the definition of S- and T-parameters of the metamaterials considered as a four-pole network. The technique is tested using the open source FDTD software package and the optimization technique obtained [O. Rybin and M. Raza, Int. J. Appl. Electrom. Mech.32, 207 (2010)].

With more attentions drawn to transportation, we find that it is available to analyze transportation system by using weighted networks. Distinguishing from traditional method, we introduce a dynamic weighted network model with evolutional size and weight. Additionally, the expected strength allocation vector of the model consists of a deterministic component reflecting preferential attachment and a random component, which can characterize the realistic network better. In this paper, we obtain the degree and strength distributions of the weighted network and we conclude that the network has scale-free characteristics.

Originally, the color-gradient model proposed by Rothman and Keller (R–K) was unable to simulate immiscible two-phase flows with different densities. Later, a revised version of the R–K model was proposed by Grunau et al. [D. Grunau, S. Chen and K. Eggert, Phys. Fluids A: Fluid Dyn. 5, 2557 (1993).] and claimed it was able to simulate two-phase flows with high-density contrast. Some studies investigate high-density contrast two-phase flows using this revised R–K model but they are mainly focused on the stationary spherical droplet and bubble cases. Through theoretical analysis of the model, we found that in the recovered Navier–Stokes (N–S) equations which are derived from the R–K model, there are unwanted extra terms. These terms disappear for simulations of two-phase flows with identical densities, so the correct N–S equations are fully recovered. Hence, the R–K model is able to give accurate results for flows with identical densities. However, the unwanted terms may affect the accuracy of simulations significantly when the densities of the two fluids are different. For the simulations of spherical bubbles and droplets immersed in another fluid (where the densities of the two fluids are different), the extra terms may not be important and hence, in terms of surface tension, accurate results can be obtained. However, generally speaking, the unwanted term may be significant in many flows and the R–K model is unable to obtain the correct results due to the effect of the extra terms. Through numerical simulations of parallel two-phase flows in a channel, we confirm that the R–K model is not appropriate for general two-phase flows with different densities. A scheme to eliminate the unwanted terms is also proposed and the scheme works well for cases of density ratios less than 10.

Recommender systems have developed rapidly and successfully. The system aims to help users find relevant items from a potentially overwhelming set of choices. However, most of the existing recommender algorithms focused on the traditional user-item similarity computation, other than incorporating the social interests into the recommender systems. As we know, each user has their own preference field, they may influence their friends' preference in their expert field when considering the social interest on their friends' item collecting. In order to model this social interest, in this paper, we proposed a simple method to compute users' social interest on the specific items in the recommender systems, and then integrate this social interest with similarity preference. The experimental results on two real-world datasets Epinions and Friendfeed show that this method can significantly improve not only the algorithmic precision-accuracy but also the diversity-accuracy.

Simulation of complex scenarios and multi-direction pedestrian flow is a main challenge to microscopic model of pedestrian movement. It is an issue to simulate real pedestrian traffic with great fidelity while keeping its computational cost at an acceptable level. This paper reports on an improved floor field model called vector floor field model to simulate pedestrian flows in some basic scenarios. In this model, vectorization of static floor field and dynamic floor field are used to indicate preference directions and the pedestrian flow tendency, respectively. Pedestrian transition depends on both their preference directions and tendency. The simulations in some basic scenarios are conducted, quantitative comparison to the record of practical experiments and standard floor field model is given as well, and the results indicate the effectivity of this model. An adjusted static vector floor field is also proposed to simulate pedestrian flow in turning scenario. The vector floor field model is also sufficient to simulate some essential features in pedestrian dynamic, such as lane formation. This model can be widely used in the simulation of multi-direction pedestrian at turning, crossing and other junctions.

Little work has been done before in the study of separating pedestrian flow interlaced. Under open boundaries, the interaction of separating pedestrian flow interlaced in a T-shaped structure was simulated, using a modified multi-field cellular automaton updating synchronously. The free-jammed phase transition diagram of pedestrian flow and principles of the pedestrian interference were obtained. The movement of pedestrians is free flow in the low entrance density. While it is a complete jammed flow with the entrance density increasing to a certain level and little difference existing between the left moving probability and the right moving probability. Thus, the dominant factor influencing pedestrian flow is the interference of opposite pedestrian flows due to changing movement directions. And it is changing to an incomplete jammed flow with this difference increasing. Thus, the dominant factor is changing to the interference of the coincident pedestrian flow and the limitation of the bottleneck.

In this paper, a novel dynamic system, the fractional-order complex Chen system, is presented for the first time. Dynamic behaviors of system are studied analytically and numerically. Different routes to chaos are shown, and diverse kinds of motions are identified and exhibited by means of bifurcation diagram, portrait phase and the largest Lyapunov exponent. Secondly, an application to digital secure communication based on the novel system is proposed, in which security is enhanced by continually switching different orders of derivative in an irregular pattern. Furthermore, making full use of the advantage of high-capacity transmission of complex system, the improved digital secure communication scheme is achieved based on hybrid synchronization in coupled fractional-order complex Chen system, that means anti-synchronization in real part of state variables and projective synchronization in imaginary part, respectively. The corresponding numerical simulations demonstrate the effectiveness and feasibility of the proposed schemes.