Testing Photons Coupled to Weyl Tensor with Gravitational Time Advancement

Classical Solar System tests of photons coupled to Weyl tensor with two polarizations were studied in a recent work. A coupling strength parameter α in this model was firstly obtained as |α|<4×10¹¹ m² by using available datasets in the Solar System. In this paper, a new test called by gravitational time advancement is proposed and investigated to test such the coupling. This new test, which is quite different from Shapiro time delay, depends strongly on round-trip proper time span (not coordinate time one) of flight of radio pulses between an observer on the Earth and a distant spacecraft. For ranging a spacecraft getting far away from the Sun, two special cases (the superior/inferior conjunctions) are used to analyse the observability in the advancement contributed by the Weyl coupling. We found that the situation of the inferior conjunction is more suitable for detecting the advancement caused by such the Weyl coupling. In either case, two kinds of polarizations make the advancement in the model smaller or larger than the one of general relativity. Although the observability in the advancement could be out of the reach of already existing technology, the implement of planetary laser ranging and optical clocks might provide us more insights on such the Weyl coupling in the near future.     

考虑边聚类与扩散特性的信息传播网络结构优化算法

优化网络结构以促进信息在网络中传播一直是复杂网络研究的重点,网络中边的聚类特性和扩散特性对信息传播具有重要作用. K-truss分解算法是一种利用边的聚类特性识别网络关键节点的算法,然而K-truss算法会受到网络中局部聚类结果 (即相互连接的假核结构)的影响,而这些假核结构里的节点对信息扩散能力通常较弱.为此,本文提出一种衡量边扩散特性的指标,研究发现一些位于网络边缘的边具有很好的扩散性,但这类边的聚类很低,并不利于信息传播.通过同时考虑边的聚类特性和扩散特性之间的制约关系,提出一种信息传播网络结构优化算法.为了验证所提算法的有效性,使用该算法对四个真实的网络进行结构优化,并使用经典的独立级联模型来验证网络结构优化前后信息传播的有效范围.结果表明:使用提出的算法优化后的网络拓扑可以有效提高信息传播范围;并且,优化后的网络其叶子节点数目降低、聚类系数降低以及平均路径长度降低.     

流体/准饱和多孔介质中伪Scholte波的传播特性

研究流体/多孔介质界面Scholte波的传播特性对于水下勘探、地震工程等领域具有重要意义.本文基于Biot理论和等效流体模型,采用势函数方法,推导了描述有限厚度流体/准饱和多孔半空间远场界面波的特征方程和位移、孔压计算公式.在此基础上,分别以砂岩和松散沉积土为例,研究了流体/硬多孔介质和流体/软多孔介质两种情况下,可压缩流体层厚度和多孔介质饱和度对伪Scholte波传播特性的影响.结果表明：多孔介质软硬程度显著影响界面波的种类、相速度、位移和水压力分布;有限厚度流体/饱和多孔半空间界面处伪Scholte波相速度与界面波波长和流体厚度的比值有关;孔隙水中溶解的少量气体对剪切波的相速度的影响不大,对压缩波相速度、伪Scholte波相速度和孔隙水压力分布影响显著.     

Improved quadratic isogeometric element simulation of one-dimensional elastic wave propagation with central difference method

Two improved isogeometric quadratic elements and the central difference scheme are used to formulate the solution procedures of transient wave propagation problems. In the proposed procedures, the lumped matrices corresponding to the isogeometric elements are obtained. The stability conditions of the solution procedures are also acquired. The dispersion analysis is conducted to obtain the optimal Courant-Friedrichs-Lewy (CFL) number or time-step sizes corresponding to the spatial isogeometric elements. The dispersion analysis shows that the isogeometric quadratic element of the fourth-order dispersion error (called the isogeometric analysis (IGA)-f quadratic element) provides far more desirable numerical dissipation/dispersion than the element of the second-order dispersion error (called the IGA-s quadratic element) when appropriate time-step sizes are selected. The numerical simulations of one-dimensional (1D) transient wave propagation problems demonstrate the effectiveness of the proposed solution procedures.     

Propagations of Airy Beams and Nonlinear Accelerating Optical Beams in Photorefractive Crystals with Asymmetric Nonlocality

The impact of the asymmetric nonlocal diffusion nonlinearity of Airy beams and nonlinear accelerating beams supported by photorefractive crystals is addressed. It is revealed how the asymmetric nonlocal response alters the evolution of these optical beams. It is found that the evolution of these beams presents a bending action under the influence of the diffusion nonlinearity. It is also shown that nonlinear accelerating beams can exist in photorefractive crystals with asymmetric nonlocality. These accelerating solutions have the same Airy‐like tail, and accelerate along parabolic trajectories. Soliton states are formed in the interaction of both in‐phase and out‐of‐phase Airy beams and nonlinear accelerating beams and also present a bending action because of the action of diffusion nonlinearity.     

非常规态型近场动力学热黏塑性模型及其应用

在非常规态型近场动力学(non-ordinary state-based peridynamics, NOSB-PD) 理论框架下构建了考虑应变率效应、塑性硬化、热软化效应和材料断裂特征的非局部三维热黏塑性固体本构模型以及相应的非局部空间积分型数值算法, 并应用于金属类材料和构件在冲击载荷作用等工况下的高应变率热黏塑性变形与破坏分析. 通过对经典含初始裂纹Kalthoff-Winkler板冲击试验进行三维近场动力学模拟, 可得到裂纹的起裂角度、扩展路径、扩展速度以及裂纹扩展过程中靶板等效应力和温度分布, 所得结果与已有试验结果和其他数值方法结果吻合较好. 在此基础上, 应用该模型分析了不同冲击速度作用下金属靶板的变形与裂纹扩展过程, 结果表明: 该模型能较好地模拟不同冲击速度(应变率)情况下靶板的变形与破坏全过程. 随着冲击速度变化, 初始裂纹的起裂时间、扩展方向和扩展速度呈一定规律变化. 冲击速度越低, 起裂时间越晚(直至冲击速度低于某值时初始裂纹不扩展), 裂纹扩展速度峰值越低, 冲击过程中靶板温度峰值越低, 完全扩展所需时间越长.      

AC-current-induced magnetization switching in amorphous microwires

We studied the influence of AC current flowing through microwires, on magnetization dynamics. We used a previously developed Sixtus-Tonks modified setup to evaluate the domain wall (DW) velocity within the microwire. However, instead of a magnetizing solenoid, we used a current flowing through the microwire. We observed that the AC current flowing through the annealed Co-rich microwire leads to remagnetization by fast domain wall propagation. The estimated DW velocity was approximately 4.5 km/s, which is similar to and even higher than that reported for the magnetic-field-driven domain wall propagation in Fe- and Co-rich microwires. We measured the DW velocity under tensile stress, and found that the DW velocity decreases under applied stress. An observed DW propagation induced by the current flowing through the microwire is explained considering the influence of an Oersted magnetic field on the outer domain shell. This field has a circular easy magnetization direction and magnetostatic interaction between the outer circumferentially magnetized shell and the inner axially magnetized core.     

Four-wave mixing and six-wave mixing in a four-level confined atomic system

We have investigated coexisting four-wave mixing and six-wave mixing (SWM) in ultra-thin, micrometre and long vapour cells. There exists competition between Dicke-narrowing features and polarization interference in the micrometre cell. The oscillation behaviour of SWM signal intensities and linewidths results from destructive interference. With a larger destructive interference, the SWM signal in ultra-thin cells shows a narrow spectrum, in contrast to the long cell case. Due to the Dicke-narrowing features, a narrow spectrum can be obtained, and such spectra can be used for high precision measurements and metrological standards.     

Fractional Fourier transform of Lorentz beams

This paper introduces Lorentz beams to describe certain laser sources that produce highly divergent fields. The fractional Fourier transform (FRFT) is applied to treat the propagation of Lorentz beams. Based on the definition of convolution and the convolution theorem of the Fourier transform, an analytical expression for a Lorentz beam passing through a FRFT system has been derived. By using the derived formula, the properties of a Lorentz beam in the FRFT plane are illustrated numerically.     

基于遗传算法的近红外光谱橄榄油产地鉴别方法研究

提出了一种应用近红外光谱技术快速无损鉴别橄榄油产地的新方法。采用近红外光谱仪获取三种不同产地的橄榄油各30个样本的光谱漫反射特征曲线,利用全局搜索算法-遗传算法提取特征波长,即从光谱751个波长数据提取9个特征波长数据,并将其作为主成分分析法的输入变量,运用主成分分析法建立分析校正模型。结果表明,主成分1和2累计可信度已达99.130%,对不同产地的橄榄油有很好的聚类作用,同时也说明遗传算法抽取特征波长方法正确。将提取到的六种主成分作为BP神经网络的输入变量,品种类型作为神经网络的输出变量,建立3层人工神经网络模型,对30个未知橄榄油产地进行预测,预测结果准确率达100％。该方法能快速无损地检测橄榄油产地,同时也为其他油类产地鉴别提供了一种新方法。