Ultrafast dynamics of three types of simultaneous shockwaves and filament attenuation in femtosecond laser multi-pulse ablation of PMMA

Cylindrical shockwaves inside polymethyl methacrylate(PMMA) generated simultaneously with two hemispherical shockwaves induced by a femtosecond Gaussian beam laser were investigated using an ultrafast pump–probe imaging technique. The evolutions of these three shockwaves with probe delay and incident pulse number have been systematically analyzed. The plasma intensity and filament length in the center of cylindrical shockwave both decayed with pulse number. Moreover, the self-focused filament moved downstream towards the output surface with an increased pulse number. The experimental results and mechanism illustrated that energy deposition was suppressed by a degraded nonlinear effect due to a pre-ablated structure in multi-pulse irradiation.     

一种快速且全局收敛的BP神经网络学习算法

目前误差反向传播(BP)算法在训练多层神经网络方面有很多成功的应用.然而,BP算法也有一些不足:收敛缓慢和易陷入局部极小点等.提出一种快速且全局收敛的BP神经网络学习算法,并且对该优化算法的全局收敛性进行分析和详细证明.实证结果表明提出的算法比标准的BP算法效率更高且更精确.     

两粒子XXZ海森堡系统中的量子纠缠动力学

研究了考虑内禀退相干情况下,两粒子XXZ海森堡系统中量子纠缠在各种外界因素影响下的动态演化规律。研究发现无论系统的初态是否处于最大纠缠态,内禀退相干都会对系统纠缠的含时演化有明显的抑制作用。如果系统的初态为纠缠态|ψ(0)〉=c|01〉+d|10〉,系统的纠缠与各向异性参数和外加磁场没有关系,却受到Dzyaloshinskii-Moriya(DM)相互作用程度和内禀退相干因素的明显影响;如果系统的初态为纠缠态|ψ(0)〉=a|00〉+b|11〉,系统的纠缠与DM相互作用大小和各向异性参数无关,纠缠程度不仅要受到内禀退相干因素的影响,还会被外加磁场进一步削弱。     

压缩真空态的激发态下介观耦合电路的量子效应

通过量子化电容耦合电路和对角化电路哈密顿量,研究了介观电路在压缩真空态的激发态下的量子力学效应.     

ICP-AES测定葡萄糖酸钙中Pb、As、Cd等9个杂质元素

本文应用ICP-AES直接测定了葡萄糖酸钙中的Pb、As、Cd等9个杂质元素,对样品的消解方法、基体和酸介质的影响等进行了讨论.用基体匹配法消除钙基体的干扰,9个杂质元素测定的测定范围为:Pb 0.0008%-0.08%,Cu、Mg 0.0001%-0.01%,其余元素0.0003%-0.03%.加标回收率为95.8%-100.0%,相对标准偏差为0.16%-3.61%.     

ICP-AES测定汽车催化剂中的助剂元素

试样用HCl-H2O2高温高压密闭溶解处理,不溶渣再用HF-HNO3-HCl-H2SO4高温高压密闭溶解二次处理后,ICP-AES同时测定汽车催化剂中的助剂元素La、Ba、Zr、Ti、Ce。方法的加标回收率和相对标准偏差分别为96.2%—100.4%和0.36%—1.15%,结果满意。     

建筑设计艺术中的"梦幻曲"——浅析建筑设计中的非理性成分

通过理性与非理性概念的简要比较,结合相关的建筑设计作品,分析了非理性成分在建筑设计以及城市设计中的表现形式.论证了非理性成分在建筑设计中的现实意义及发展趋势,它的进一步发展将对当代的建筑潮流的发展产生深远的影响.     

Transparent and Ultra-lightweight Design for Ultra-Broadband Asymmetric Transmission of Airborne Sound

Acoustic one-way manipulations have recently attracted significant attention due to the deep implications in many diverse fields such as biomedical imaging and treatment.However,the previous mechanisms of asymmetric manipulation of airborne sound need to use elaborate heavyweight structures and only work in certain frequency ranges.We propose a mechanism for designing an ultra-lightweight and optically transparent structure with asymmetric transmission property for normally incident plane waves.Instead of fabricating solids into complicated artificial structures with limited bandwidth and heavy weight,we simply use xenon to fill a spatial region of asymmetric shape which allows the incident plane wave to pass along one direction while reflecting the reversed wave regardless of frequency.We demonstrate both analytically and numerically its effectiveness of producing highly-asymmetric transmission within an ultra-broad band.Our design offers new possibility for the design of one-way devices and may have far-reaching impact on various scenarios such as noise control.     

显微镜自动对焦方法研究综述

自动对焦是全自动显微镜的关键技术,决定着显微镜成像的精确性和实时性。对焦方法包括主动式和被动式两种,主动式是指基于数字图像处理的对焦方法,被动式是指基于光学离焦量检测的对焦方法。介绍了两种方法的原理和研究现状,通过比较其优缺点,总结出基于离焦误差检测的主动式对焦方法具有更高的精度和速度,更适用于全自动显微镜系统。     

矩形波导中宽带非对称声传输

目前已有的非对称性声传输模型大部分局限于二维模式,无法直接应用于三维实际系统,针对这一问题,文中研究了通过内置非对称几何结构来实现声单向传输的三维管道模型。该几何结构体内引入天然材料——氙气,利用氙气与空气两种天然气体折射率的差异以及结构的不对称,实现声波在管道中的非对称传输,即当声波正向入射时,可通过管道内结构到达另一侧;而当反向入射时,声波无法通过内置的非对称结构。理论计算结果和仿真结果表明声波在三维矩形波导管中的非对称声传输效果和结构的厚度相关:当结构厚度较薄时,可在较宽频带范围内实现声波的非对称传输。此外,该矩形波导设计具有结构简单、透明超轻等特点,为设计新型声波非对称传输器件提供了相应的理论参考。