Pattern formation and spatial solitons in bistable liquid-crystal microcavities

We report on spatial pattern formation, and appearances of 'optical bullet holes' in single-mode microcavities that are filled with liquid-crystals, when pumped above the cavity resonance frequency. These phenomena only occur beyond the bistability threshold. ©2002 Optical Society of America.

Pattern Recognition With Weighted Complex Networks

In this paper we introduce a weighted complex networks model to investigate and recognize structures of patterns. The regular treating in pattern recognition models is to describe each pattern as a high-dimensional vector which however is insufficient to express the structural information. Thus, a number of methods are developed to extract the structural information, such as different feature extraction algorithms used in pre-processing steps, or the local receptive fields in convolutional networks. In our model, each pattern is attributed to a weighted complex network, whose topology represents the structure of that pattern. Based upon the training samples, we get several prototypal complex networks which could stand for the general structural characteristics of patterns in different categories. We use these prototypal networks to recognize the unknown patterns. It is an attempt to use complex networks in pattern recognition, and our result shows the potential for real-world pattern recognition. A spatial parameter is introduced to get the optimal recognition accuracy, and it remains constant insensitive to the amount of training samples. We have discussed the interesting properties of the prototypal networks. An approximate linear relation is found between the strength and color of vertexes, in which we could compare the structural difference between each category. We have visualized these prototypal networks to show that their topology indeed represents the common characteristics of patterns. We have also shown that the asymmetric strength distribution in these prototypal networks brings high robustness for recognition. Our study may cast a light on understanding the mechanism of the biologic neuronal systems in object recognition as well.

Fractal Pattern Formation In Anodic Bonding Of Pyrex Glass/Al/Si

Anodic bonding of Pyrex glass/Al/Si is an important bonding technique in micro/nanoelectromechanical systems (MEMS/NEMS) industry. The anodic bonding of Pyrex 7740 glass/Aluminum film/Silicon is completed at the temperature from 300 degrees C to 375 degrees C with a bonding voltage between 150 V and 450 V. The fractal patterns are formed in the intermediate Al thin film. This pattern has the fractal dimension of the typical two-dimensional diffusion-limited aggregation (2D DLA) process, and the fractal dimension is around 1.7. The fractal patterns consist of Al and Si crystalline grains, and their occurrences are due to the limited diffusion, aggregation, and crystallization of Si and Al atoms in the intermediate Al layers. The formation of the fractal pattern is helpful to enhance the bonding strength between the Pyrex 7740 glass and the aluminum thin film coated on the crystal silicon substrates.

Role Of Convection Flow On The Pattern Formation In The Drying Process Of Colloidal Suspension

We study the macroscopic drying patterns of aqueous suspensions of colloidal silica spheres. It was found that convection strength can influence pattern formation. Uniformed films are obtained at weaker convection strength. In addition, we make clear that it is not reasonable to discuss individually the effect of temperature and humidity on the colloid self-assembly. The physical mechanism is that these factors have relationship with the evaporation rate, which can affect the convection strength.

圆柱振荡绕流中涡旋运动模式(pattern)的数值模拟

提出并发展的一种基于区域分解思想,综合了解 N—S方程的有限差分法及涡法各自优点的新数值方法,计算了各种 Keulegan-Carpenter 数下(Kc=2～24)振荡流绕圆柱的流动。系统地研究了振荡流中涡旋运动模式随 Kc 数变化的规律,模拟了不对称区、单对涡区(或模向区)、双对涡区(或对角区)和三对涡区四种不同的涡旋运动模式。将计算所得的阻力系数 C_D、惯性系数 C_M与国外近期发表的计算结果进行了比较。

Laser-induced wavy pattern formation in metal thin films

Laser-induced well-ordered and controllable wavy patterns are constructed in the deposited metal thin film. The micrometer-sized structure and orientation of the wavy patterns can be controlled via scanning a different size of rectangle laser spot on the films. Ordered patterns such as aligned, crossed, and whirled wave structures were designed over large areas. This patterning technique may find applications in both exploring the reliability and mechanical properties of thin films, and fabricating microfluidic devices. (C) 2004 American Institute of Physics.

Wave pattern characteristics of a two-phase nozzle flow by shock propagation

In this paper, the wave pattern characteristics of shock-induced two-phase nozzle Hows with the quiescent or moving dusty gas ahead of the incident-shock front has been investigated by using high-resolution numerical method. As compared with the corresponding results in single-phase nozzle flows of the pure gas, obvious differences between these two kinds of flows can be obtained.

A new dynamic model for study of dislocation pattern formation

Based on the principle given in nonlinear diffusion-reaction dynamics, a new dynamic model for dislocation patterning is proposed by introducing a relaxation time to the relation between dislocation density and dislocation flux. The so-called chemical potential like quantities, which appear in the model can be derived from variation principle for free energy functional of dislocated media, where the free energy density function is expressed in terms of not only the dislocation density itself but also their spatial gradients. The Linear stability analysis on the governing equations of a simple dislocation density shows that there exists an intrinsic wave number leading to bifurcation of space structure of dislocation density. At the same time, the numerical results also demonstrate the coexistence and transition between different dislocation patterns.

Statistical description of pattern evolution in damage-fracture

A model of dynamical process and stochastic jump has been put forward to study the pattern evolution in damage-fracture. According to the final states of evolution processes, the evolution modes can be classified as globally stable modes (GS modes) and evolution induced catastrophic modes (ElC modes); the latter are responsible for fracture. A statistical description is introduced to clarify the pattern evolution in this paper. It is indicated that the appearance of fracture in disordered materials should be depicted by probability distribution function.

The mechanism of pattern selection in coupled map lattices

The pattern selection of one-dimensional coupled map lattices is studied in this paper. It is shown by spatiotemporal variable separation that there exists a threshold wavelength in pattern selection which possesses wave-like structures in space and periodic chaotic motion in time.