混凝土缺陷信号变分模态分解与超声成像方法

混凝土的强散射特性限制了其中缺陷声波成像的分辨率。该文采用一种依据变分模态分解与全聚焦成像相结合的方法,将接收信号分解成多个本征模态函数,计算各本征模态函数与激励信号的相关系数,对信号加权重构以实现对特征信号的提取,从而提高成像算法对混凝土缺陷间散射波互干扰的鲁棒性。通过设置对比试验,研究了不同缺陷混凝土结构中该信号处理方式对于成像结果的影响。试验结果表明,该方法对于弱散射及散射干扰具有更好的鲁棒性,相比基于原始数据的成像方法能够更好地还原混凝土内部结构。

Orbital angular momentum conversion of acoustic vortex beams via planar lattice coupling

Orbital angular momentum(OAM)conversion is critical in understanding interactions between a structural sound field and a planar lattice.Herein,we explore the evolution of a monochromatic acoustic vortex beam(AVB)that is scattered by a phononic crystal(PnC)or a correlated random lattice.The phenomenon is ascribed to the enhanced orbit–orbit angular momentum coupling induced by the band structure.By modifying the coupling condition,accurate and continuous micromanipulation of AVBs can be achieved,including the transverse/lateral gravity shift,the dynamics of the phase singularities,and the spatial distribution of acoustic pressure,etc.This research provides insight to the inhomogeneous coupling of AVBs with both propagating Bloch waves and localized Anderson modes,and may facilitate development of novel OAM-based acoustic devices for active sound field manipulation.

宁波市发展地摊经济的优劣势分析及其对策研究

在发展地摊经济的同时,我国的经济逐渐开始复苏,但是其市场竞争模式也给传统市场带来了挑战。因此,在这样的背景下,本文通过探究宁波市地摊经济的优势和劣势等内容,对其特点以及相关的应对对策进行了整合。并针对消费者的权益难以保障、消费者的防疫意识淡薄、政府对品质难以把控、收益附有季节性波动、地摊商品存在隐患等问题提出可行性对策。以期为我国地摊经济的发展并对其他城市地摊经济发展有一定的借鉴之处。