B型套筒角焊缝缺陷相控阵超声检测定量方法

B型套筒修复作为油气管道修复的主要方式之一,在其修复的焊接过程中,该结构的环形角焊缝内部常常出现以气孔、夹渣为代表的孔型缺陷。这类缺陷由于角焊缝特殊的结构,在利用相控阵超声无损检测技术对其检测时,难以对其进行定量分析。通过数值模拟和实验,发现通过相控阵超声扇扫得到缺陷回波信号峰值与孔型缺陷直径呈正相关,为孔型缺陷的定量分析提供了一种可靠的手段。     

基于薄膜编码超表面的宽频超薄声散射体

该文提出了一种基于薄膜编码超表面的宽频超薄声散射体。利用附加质量块的薄膜和空气腔组成的薄膜结构构建了反射声波相位差接近180°的两种共振单元。将两种共振单元按照一定的顺序进行排列,可以组成深亚波长尺寸下的声学超表面。所构建的声学超表面可以产生宽频有效的散射声场。通过有限元仿真软件对多个频率的近场散射声场分布、远场声指向性和扩散系数进行了仿真计算,仿真结果显示,该散射体可以高效地散射入射声波,并且散射效果在一定的频率范围内是宽频有效的。     

Photonic graphene with reconfigurable geometric structures in coherent atomic ensembles

Photonic graphene, possesses a honeycomb-like geometric structure, provides a superior platform for simulating photonic bandgap, Dirac physics, and topological photonics. Here, the photonic graphene with reconfigurable geometric structures is demonstrated in a 5S_1/2 − 5P_3/2 − 5D_5/2 cascade-type ⁸⁵Rb atomic ensembles. A strong hexagonal-coupling field, formed by the interference of three identical coupling beams, is responsible for optically inducing photonic graphene in atomic vapor. The incident weak probe beam experiences discrete diffraction, and the observed pattern at the output plane of vapor cell exhibits a clear hexagonal intensity distribution. The complete photonic graphene geometries from transversely stretched to longitudinally stretched are conveniently constructed by varying the spatial arrangement of three coupling beams, and the corresponding diffraction patterns are implemented theoretically and experimentally to map these distorted geometric structures. Moreover, the distribution of lattice sites intensity in photonic graphene is further dynamically adjusted by two-photon detuning and the coupling beams power. This work paves the way for further investigation of light transport and graphene dynamics.     

机动方舱核爆炸冲击波动力响应和安定性分析

本文以核爆炸当量、高度、距离为参数，采用等超压圆给出了普通方舱和防核加固方舱结构在核冲击波下的安全域。研究了限制舱体倾斜的压力条件。本文还以冲击波压力的时间函数为激励，求解了方舱的动力响应。从试验结果推论和计算模拟两方面，分析了方舱承受冲击波的能力。     

一种变厚度的精化壳体理论及其应用

在Reddy型高阶壳体理论的基础上，采用沿壳体厚度方向的剪切应变呈抛物线分布并且能够满足在壳体的上下表面为零的假设，发展出了一种适合于对变厚度壳体进行非线性分析的方法。该方法利用Ritz原理得到问题的控制方程。通过对一种典型的变厚度壳体结构（子午线轮胎）的结构分析，该方法的计算结果与商用有限元软件的三维分析结果能够很好的吻合。表明了该方法的适用性和有效性。     

弹／粘塑性柱体扭转问题的函数Laplace变换解

在应力Ｌａｐｌａｃｅ变换分析粘塑性轴对称问题基础上，对弹性－弹／粘塑性圆柱体扭转全过程进行分析，根据柱体扭转的应力分布，构造应力函数与位移函数，并对函数进行Ｌａｐｌａｃｅ变换。相应求出圆柱体、空心圆柱体的Ｌａｐｌａｃｅ变换解，以及圆柱体的弹性－粘塑性交界线值     

AFM稳定性研究

“突跳”现象严重影响着原子力显微镜(AFM)的性能。根据W igner-Seitz模型微观连续介质理论,建立了AFM针尖同试样面接触力包含斥力的数学模型;由分析力学的稳定平衡条件,发现了引起AFM“突跳”的本质是不稳定平衡点的存在;通过增加AFM悬臂梁刚度,提出了一种避免AFM“突跳”现象发生的方法,并给出仿真结果。     

Catalytic Asymmetric Inverse‐Electron‐Demand Oxa‐Diels–Alder Reaction of In Situ Generated ortho‐Quinone Methides with 3‐Methyl‐2‐Vinylindoles

The first catalytic asymmetric inverse‐electron‐demand (IED) oxa‐Diels–Alder reaction of ortho‐quinone methides, generated in situ from ortho‐hydroxybenzyl alcohols, has been established. By selecting 3‐methyl‐2‐vinylindoles as a class of competent dienophiles, this approach provides an efficient strategy to construct an enantioenriched chroman framework with three adjacent stereogenic centers in high yields and excellent stereoselectivities (up to 99 % yield, >95:5 d.r., 99.5:0.5 e.r.). The utilization of ortho‐hydroxybenzyl alcohols as precursors of dienes and 3‐methyl‐2‐vinylindoles as dienophiles, as well as the hydrogen‐bonding activation mode of the substrates met the challenges of a catalytic asymmetric IED oxa‐Diels–Alder reaction.     

Hyperbranched Hybridization Chain Reaction for Triggered Signal Amplification and Concatenated Logic Circuits

A hyper‐branched hybridization chain reaction (HB‐HCR) is presented herein, which consists of only six species that can metastably coexist until the introduction of an initiator DNA to trigger a cascade of hybridization events, leading to the self‐sustained assembly of hyper‐branched and nicked double‐stranded DNA structures. The system can readily achieve ultrasensitive detection of target DNA. Moreover, the HB‐HCR principle is successfully applied to construct three‐input concatenated logic circuits with excellent specificity and extended to design a security‐mimicking keypad lock system. Significantly, the HB‐HCR‐based keypad lock can alarm immediately if the “password” is incorrect. Overall, the proposed HB‐HCR with high amplification efficiency is simple, homogeneous, fast, robust, and low‐cost, and holds great promise in the development of biosensing, in the programmable assembly of DNA architectures, and in molecular logic operations.     

Aryne‐Induced Novel Tandem 1,2‐Addition/(3+2) Cycloaddition to Generate Imidazolidines and Pyrrolidines

A new “single‐flask” method was developed for the synthesis of imidazolidines and pyrrolidines with high stereoselectivity. First, a Schiff base was arylated with an aryne. Second, an intramolecular proton transfer took place from the methylene position to the anionic aryne ring. Third, the resultant ylide reacted with a second equivalent of the same Schiff base in situ or an electron‐deficient alkene through a (3+2) cycloaddition. These sequential tandem 1,2‐addition/(3+2) cycloaddition reactions led to the desired heterocycles in 63–88 % yields.