The spiral forces of phase singularities are demonstrated experimentally and numerically by presenting the generation and propagation dynamics of multiple optical vortices embedded in a Gaussian beam.The results reveal that the energy flow established by certain phase singularity will perform the characteristics of force on other singularities whose direction is determined by the sign of the topological charge.The force is confirmed by the fluid-like motions of multi-vortex beams,i.e.singularities undergo rotation(annihilation) with each other when they involve identical(opposite) topological charges.This force mechanism may help develop an intuitive understanding of multi-vortex motion and presents a new viewpoint from which to study the dynamics of singularities.
文件复制技术是把负载分散在复制节点上,避免服务器超载,减少服务器响应延迟和查询路径的长度,以达到较高查询率的有效方法。因此文件复制节点的选择就成为了首要考虑的问题。P2P文件共享系统因为节点的加入和离开,甚至节点失效造成拓扑结构会不断地变换,选择一个文件处理性能好,抖动性弱的节点作为复制节点就显得非常重要。提出一种新的文件复制节点选择算法NDC(New Dynamic and Capacity Algorithm),通过在复制节点的选取上考虑抖动性因素,减少节点离开或者失效造成较长的通信延迟和用户体验的降级,提高文件击中率。由于网络的热点文件不断变化,会出现不同倾斜查询的情况,对NPC处理倾斜性查询文件的能力进行了分析。通过在P2Psim上进行的大量实验表明,NPC算法选出的节点处理文件性能好,抖动性弱,可以提供更精确的文件复制节点。
