CHAOTIC MOTIONS AND LIMIT CYCLE FLUTTER OF TWO-DIMENSIONAL WING IN SUPERSONIC FLOW

Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.     

Experimental confirmation of a new reversed butterfly-shaped attractor

This paper reports a new reverse butterfly-shaped chaotic attractor and its experimental confirmation. Some basic dynamical properties, and chaotic behaviours of this new reverse butterfly attractor are studied. Simulation results support brief theoretical derivations. Furthermore, the system is experimentally confirmed by a simple electronic circuit.     

“Butterfly”-like patterns of triblock copolymer gels as observed by small-angle neutron scattering

At high (150-1000%) stretching of a physical gel of a triblock copolymer a “butterfly”-type scattering pattern is observed with a pronounced scattering-free strip perpendicular to the stretching direction. The phenomenon is attributed to the cluster character of the physical network in the gel. Stretching brings endblock domains (junction points of the network) closer to each other in the direction perpendicular to the stretching and leads to formation of a layered structure. High connectivity of the network inside the clusters leads to saturation of the deformation within the clusters as manifested by the scattering-free region in the SANS pattern. © 1996 John Wiley & Sons, Inc.     

Optical Characterization of Iridescent Wings of <Emphasis Type="Italic">Morpho</Emphasis> Butterflies using a High Accuracy Nonstandard Finite-Difference Time-Domain Algorithm

In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with corresponding experimental measurements at normal incidence.     

无限展长后掠翼边界层定常横流不稳定转捩分析

采用γ-Re_θt横流转捩拓展模型对NLF （2）-0415无限展长后掠机翼进行数值模拟,重点分析来流雷诺数、机翼表面粗糙度及后掠角对边界层横流不稳定性的影响.研究发现γ-Re_θt横流转捩拓展模型能够准确预测边界层定常横流不稳定转捩,计算结果与试验数据吻合较好.结果表明来流雷诺数越大、机翼表面越粗糙,横流转捩位置越靠前;随着机翼后掠角的增加,转捩位置先前移随后逐渐靠后.     

基于串联哑铃型微环谐振腔的二维相干光码分多址编解码器

利用微环谐振腔阵列进行光码分多址编解码过程中,微环谐振腔反射谱的自由频谱宽度(FSR)范围制约该系统用户容量的提升.本文提出了一种新型的基于游标效应的串联哑铃型微环谐振腔光编解码器.利用Matlab建立了半径分别为40μm-30μm-40μm的哑铃型微环谐振腔光编解码器模型.详细分析了光反射谱伪模抑制与耦合系数的关系,研究了耦合系数、码片速率对串联哑铃型微环谐振腔光编解码器性能的影响.结果表明,与半径分别为40μm-40μm-40μm的传统串联微环谐振腔编解码器相比,哑铃型微腔编解码器FSR值扩大了4倍.理想情况下,用户容量可呈指数增长.同时,互相关峰值比(P/W)与自相关峰值旁瓣比(P/C)分别提高了约33%和8%.     

Wing characteristics and flapping behavior of flying insects

This paper is concerned with the flapping characteristics and the structure dynamics of insect wings. The flapping behavior of some insects is studied using a threedimensional motion analysis system. The experimental system is composed of two high-speed video cameras, a motion grabber, and a personal computer. The three-dimensional representation of insect flapping can be gained by the system. The extrinsic skeleton vibration produced by insect flapping is examined with the optical displacement detector system. The structural properties of some insect wings are also studied by a three-dimensional, optical shape measurement system. Some functional principles underlying insect wing design are revealed by the measurements of surface roughness and flapping analysis.     

光寻址2×2光学开关及3－D集成光学蝶形互连网络的实现

在光学多级互连网络的实现中，光学２×２开关的构造是至关重要的。本文介绍一种构成光寻址２×２光学开关的方法，该方法是在方解石晶体的双折射性质的基础上，利用普克尔斯只读光调制器（ＰＲＯＭ）来控制入射光的偏振态，从而实现光寻址２×２光学开关，这种开关具有许多优点，并且可以在３－Ｄ方向堆栈集成。利用该开关可以很方便地实现３－Ｄ集成的蝶形互连网络     

Stability and Transition on a Swept Cylinder in a Supersonic Flow

Results of experimental investigations of the evolution of natural disturbances and laminar–turbulent transition in a supersonic boundary layer on the attachment line of a circular cylinder with a sweep angle of 68° and a freestream Mach number M = 2 are presented. The experimental studies are supplemented by calculations of the mean flow and stability characteristics. Flow regimes in the boundary layer on the attachment line are determined by a hotwire technique as functions of the Reynolds number and height of twodimensional roughness elements. The results are compared with NASA (Ames) experiments.