Photons can hide where they have been

Recently,the nested Mach–Zehnder interferometer[Phys.Rev.Lett.111,240402(2013)]was modified by adding Dove prisms in a paper[Quantum Stud.:Math.Found.2,255(2015)],and an interesting result is that,after the Dove prisms were inserted,a signal at the first mirror of the nested interferometer was obtained.But,according to the former original paper,the photons have never been present near that mirror.In this work,we interpret this result naturally by resorting to the three-path interference method.Moreover,we find that even though the photons have been somewhere,they can hide the trace of being there.     

Spatially modulated polarimetry based on a vortex retarder and Fourier analysis

We report a spatially modulated polarimetry scheme by using a zero-order vortex half-wave retarder(ZVHR)and a spatial Fourier analysis method.A ZVHR is employed to analyze the input polarized light and convert it into a vectorial optical field,and an analyzer is set after the ZVHR to form an hourglass intensity pattern due to the spatial polarization modulation.Then,the input light’s Stokes parameters can be calculated by spatial Fourier analysis of the hourglass pattern with a single shot.The working principle of the polarimeter has been analyzed by the Stokes-Mueller formalism,and some quantitative measuring experiments of different polarization states have been demonstrated.The experimental results indicate that the proposed polarimeter is accurate,robust,and simple to use.     

Highly transparent ceramics for the spectral range from 1.0 to 60.0μm based on solid solutions of the system AgBr-AgI-TlI-TlBr

The article is devoted to the technology for obtaining optical ceramics of Ag Br-Tl I and Ag Br-Tl Br_0.46I_0.54 systems and manufacturing samples with different compositions.The new heterophase crystal ceramics are transparent without absorption windows in the spectral range from 1.0 to 60.0μm.In the ceramics’transparency spectra based on the Ag Br-Tl I and Ag Br-Tl Br_0.46I_0.54 systems fusibility diagrams,with an increase in the thallium halides mass fraction,as well as the replacement of the bromine ion with iodine,the maximum transparency shifts to a long infrared region.     

NO分子宏观气体热力学性质的理论研究

采用量子统计系综理论,研究了基态NO分子宏观气体摩尔熵、摩尔内能、摩尔热容等热力学性质.首先应用课题组前期建立的变分代数法(variational algebraic method, VAM)计算获得了基态NO分子的完全振动能级,得到的VAM振动能级作为振动部分,结合欧拉-麦克劳林渐进展开公式的转动贡献,应用于经典的热力学与统计物理公式中,从而计算得到了1000-5000 K温度范围内NO宏观气体的摩尔内能、摩尔熵和摩尔热容.将不同方法计算得到的摩尔热容结果分别与实验值进行比较,结果表明基于VAM完全振动能级获得的结果优于其他方法获得的理论结果.振动部分采用谐振子模型对无限能级求和计算热力学性质的方法有一定的局限性,应当使用有限的完全振动能级进行统计求和.     

三维位势问题的梯度边界积分方程的新解法

三维位势问题的边界元分析中,关于坐标变量的边界位势梯度的计算是一个困难的问题. 已有一些方法着手解决这个问题,然而,这些方法需要复杂的理论推导和大量的数值计算. 本文提出求解一般边界位势梯度边界积分方程的辅助边值问题法. 该方法构造了与原边界值问题具有相同解域的辅助边值问题,该辅助边值问题具有已知解,因此通过求解此辅助边值问题,可获得梯度边界积分方程对应的系统矩阵,然后将此系统矩阵应用于求解原边值问题,求解过程非常简单,只需求解一个线性系统即可获得原边值问题的解. 值得注意的是,在求解原边值问题时,不再需要重新计算系统矩阵,因此辅助边值问题法的效率并不很差. 辅助边值问题法避免了强奇异积分的计算,具有数学理论简单、程序设计容易、计算精度高等优点,为坐标变量梯度边界积分方程的求解提供了一个新的途径. 3个标准的数值算例验证了方法的有效性.      

四连杆膝关节假肢的动力学建模与分析

相比于单轴式膝关节,四连杆膝关节具有更好的仿生特性和运动安全性,因而在下肢假肢研究中得到广泛关注. 本研究以一款四连杆膝关节被动假肢为研究对象,主要关注足-地交互作用力以及膝关节单边接触力等强非线性因素对下肢假肢步态的影响. 为此,采用 Kelvin-Voigt 模型和库伦模型描述足-地接触力和摩擦力,并采用 Kelvin-Voigt 模型描述膝关节单边接触力,从而基于第一类拉格朗日方程建立假肢动力学模型. 本研究以步态实验测得的髋关节运动数据为模型的驱动信号,针对假肢的步态特征进行了数值分析. 计算结果显示,当膝关节液压阻尼器的刚度较小时,强非线性作用力会使假肢产生显著的亚谐波响应,进而导致步态周期失谐. 进一步研究发现,提胯行为能够避免步态周期失谐,这也为残疾人行走时的提胯等代偿行为提供了一种新的力学解释. 为了评价假肢步态与健康人实测步态的一致性,本研究进一步定义了步态相关系数并分析了膝关节液压阻尼器刚度、阻尼参数对相关系数的影响. 结果表明,通过合理的刚度、阻尼参数设计,两者步态的相关系数可达到 0.9 以上,这为四连杆膝关节被动假肢进一步优化提供了理论支撑.      

松木-聚氯乙烯复合材料催化热解特性的研究

通过热重法研究了松木与聚氯乙烯复合材料的催化热解特性,结果表明聚氯乙烯脱氯阶段与松木的纤维素、半纤维素热分解阶段温度区间重合,二者共热解时存在协同效应,并且HCl的释放对纤维素的脱水反应能够产生催化作用,HCl释放也对木质素的热分解及碳化反应有着明显的催化作用,导致二者共热解制备的碳化物产率提高,约为29.61%。并且利用元素分析仪、扫描电镜和能谱仪对成碳材料进行表征分析,结果表明成碳材料表面粗糙呈现多孔结构,其碳元素含量较高达到74.67%。     

Hierarchical structure observation and nanoindentation size effect characterization for a limnetic shell

In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.     

Graphene-nickel nitride hybrids supporting palladium nanoparticles for enhanced ethanol electrooxidation

Electrocatalysts for ethanol oxidation reaction(EOR)are generally limited by their poor durability because of the catalyst poisoning induced by the reaction intermediate carbon monoxide(CO).Therefore,the rapid oxidation removal of CO intermediates is crucial to the durability of EOR-based catalysts.Herein,in order to effectively avoiding the catalyst CO poisoning and improve the durability,the graphene-nickel nitride hybrids(AG-Ni₃N)were designed for supporting palladium nanoparticles(Pd/AG-Ni₃N)and then used for ethanol electrooxidation.The density functional theory(DFT)calculations demonstrated the introduction of AG-Ni₃N depresses the CO absorption and simultaneously promotes the adsorption of OH species for CO oxidation removal.The fabricated Pd/AG-Ni₃N catalyst distinctively exhibits excellent electroactivity with the mass catalytic activity of 3499.5 m A mg^-1 on EOR in alkaline media,which is around 5.24 times higher than Pd/C(commercial catalyst).Notably,the Pd/AG-Ni₃N hybrids display excellent stability and durability after chronoamperometric measurements with a total operation time of 150,000 s.