Meandering Spiral Waves Induced by Time-Periodic Coupling Strength

Effects of time-periodic coupling strength （TPCS） on spiral waves dynamics are studied by numerical computations and mathematical analyses. We find that meandering or drifting spirals waves, which are not observed for the case of constant coupling strength, can be induced by TPCS. In particular, a transition between outward petal and inward petal meandering spirals is observed when the period of TPCS is varied. These two types of meandering spirals are separated by a drifting spiral, which can be induced by TPCS when the period of TPCS is very close to that of rigidly rotating spiral. Similar results can be obtained if the coupling strength is modulated by a rectangle wave. Furthermore, a kinetic model for spiral movement suggested by Diet al., [Phys. Rev. E 85 （2012） 046216] is applied for explaining the above findings. The theoretical results are in good qualitative agreement with numerical simulations.     

非手性的酞菁铜分子在Bi(111)表面上的手性特征

利用低温扫描隧道显微镜（LT-STM）研究了酞菁铜（CuPc）分子在Bi（111）表面上的吸附和手性自组装结构。由于较弱的分子-衬底相互作用,我们发现在液氮温度（78 K）下吸附在Bi（111）表面上的单个CuPc分子围绕着分子中心发生旋转,直到遇到其他分子形成团簇为止。随着分子覆盖度的增加,CuPc分子形成了自组装分子单层。高分辨STM图表明,非手性的CuPc分子出现了手性特征：两个相对的酞菁基团发生了弯曲。当覆盖度超过一个分子层,酞菁铜分子的吸附取向由“平躺”转变到“站立”姿态。我们认为,酞菁铜分子的手性起源是由两种因素共同导致的结果：一种是分子-衬底之间的非对称电荷转移,另一种是相邻分子间的非对称性的范德华力作用。