Field Tunable Polaritonic Band Gaps in Fibonacci Piezoelectric Superlattices

The Fibonacci piezoelectric superlattices(FPSs) with an external dc electric field is presented, in which the dc electric field can tune the bandwidth of polaritonic band gaps(PBGs) continuously and reversibly via the electrooptic effect. The absolute bandwidths of two major PBGs of the FPSs around ω= 7.5 GHz and ω = 12.5 GHz can be broadened from 0.022 GHz to 0.74 GHz and from 0.02 GHz to 0.82 GHz with the dc electric field increasing from 0 to 1.342 × 10~6 V/m, respectively. The corresponding relative bandwidths of the two major PBGs are widened from 0.28% to 9.2% and from 0.18% to 6.35%, respectively. The general mechanism for the bandwidth tunability is that the coupling strength between the lattice vibration and electromagnetic waves is capable of being altered by the dc electric field via the electro-optic effect. Thus the properties can be applied to construct microwave switchings or field tunable bulk acoustic filters.     

钢管混凝土柱断面界面剥离缺陷检测试验研究

提出一种基于压电陶瓷激励与传感技术的钢管混凝土柱界面粘结缺陷检测方法。将嵌入式压电功能元和粘贴在钢管外壁的压电陶瓷片分别作为驱动器和传感器,比较不同频率简谐信号下传感器测量幅值,发现界面剥离区域传感器测量信号幅值明显小于无剥离区域传感器信号幅值,探讨了不同激励频率下所定义的损伤指标的变化。     

Boundary-Dependent Chaotic Regions for a Bose-Einstein Condensate Interacting with Laser Field

Spatial chaos of a Bose Einstein condensate perturbed by a weak laser standing wave and a weak laser δ pulse is studied. By using the perturbed chaotic solution we investigate the new type of Melnikov chaotic regions, which depend on an integration constant co determined by the boundary conditions. It is shown that when the │co│ values are small, the chaotic region corresponds to small values of laser wave vector k, and the chaotic region for the larger h values is related to the large │co│ values. The result is confirmed numerically by finding the chaotic and regular orbits on the Poincarg section for the two different parameter regions. Thus, for a fixed co the adjustment of k from a small value to large value can transform the chaotic region into the regular one or on the contrary, which suggests a feasible method for eliminating or generating Melnikov chaos.     

两分量BEC精确Floquet解的弱驱动不稳定性分析

研究了两分量玻色．爱因斯坦凝聚系统（BEC）的精确Floquet态的不稳定性问题．将两分量玻色一爱因斯坦系统囚禁于一个光格势中,同时用一个可随时间周期调节的激光驻波驱动,可得到精确的Floquet态．应用李雅普诺夫稳定性标准和线性稳定性分析方法,如果驱动场的强度小于光格势强度的两倍时,系统将发生相的blowing-up现象而导致不稳定,将这种不稳定性称之为弱驱动不稳定性．通过调节驱动场强度可避免这种不稳定性。