高温、高压、高应变速率动态过程晶体塑性有限元理论模型及其应用

对于高温、高压、高应变速率加载条件下的材料冲击变形行为,动态晶体塑性模型能够直接反映晶体中塑性滑移的各向异性及其对温度、压力和微观组织结构的依赖性,因而广泛应用于材料的动态冲击力学响应、微观结构演化以及动态损伤破坏的模拟。本文综述了高压冲击下动态晶体塑性有限元的理论模型,主要包括变形运动学、包含状态方程的超弹性本构模型和晶体塑性本构模型,涉及位错滑移、相变、孪生等塑性变形机制,以及层裂、绝热剪切带等动态破坏方式。     

Spectral approximation for drainage of an Elastico‐viscous liquid and error analysis

A Fourier‐Galerkin spectral method is proposed and used to analyze a system of quasilinear partial differential equations governing the drainage of liquids of the Oldroyd four‐constant type. It is shown that, Fourier‐Galerkin approximations are convergent with spectral accuracy. An efficient and accurate algorithm based on the Fourier‐Galerkin approximations to the system of quasilinear partial differential equations are developed and implemented. Numerical results indicating the high accuracy and effectiveness of this algorithm are presented. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 28: 492–505, 2012     

Identifying the viscoelastic properties of soft matter from the indentation response of a hard film-soft substrate system

The indentation technique is widely used in measuring the mechanical properties of soft matter at the microscale or nanoscale,but still faces challenges by these unique properties as well as the consequent strong surface adhesion, including the strong nonlinear effect, unclear judgment of the contact point, difficulties in estimating the contact area, and the risk of the indenter piercing the sample. Here we propose a two-step method to solve these problems: lay a hard film on a soft matter, and obtain the viscoelastic properties of this soft matter through the indentation response of this composite structure. We first establish a theoretical indentation model of the hard film-soft substrate system based on the theory of plates, elastic-viscoelastic correspondence principle and Boltzmann superposition principle. To verify the correctness of this method, we measure the mechanical properties of the methyl vinyl silicone rubber(MVSR) covered by a Cu nanofilm. Finally, we test the effectiveness and error sensitivity of this method with the finite element method(FEM). The results show that our method can accurately measure the mechanical properties of soft matter, while effectively circumventing the problems of the traditional indentation technique.     

The first excited single-proton resonance in ~(15)F by complex-scaled Green's function method

The complex-scaled Green's function(CGF)method is employed to explore the single-proton resonance in 15F.Special attention is paid to the first excited resonant state 5/2+,which has been widely studied in both theory and experiments.However,past studies generally overestimated the width of the 5/2+state.The predicted energy and width of the first excited resonant state 5/2+by the CGF method are both in good agreement with the experimental value and close to Fortune's new estimation.Furthermore,the influence of the potential parameters and quadruple deformation effects on the resonant states are investigated in detail,which is helpful to the study of the shell structure evolution.     

湍流大气传输中跟踪抖动对远场影响的仿真研究

分析了跟踪抖动对湍流大气传输远场光斑的影响。基于麦克斯韦电磁场理论,采用大气相干长度对大气湍流进行描述,推导了发射光束因跟踪抖动导致光轴偏离的远场表达式。在此基础上,利用相位屏法模拟抖动引起的倾斜相位和大气折射率起伏引起的相位调制,并采用低频补偿的功率谱反演法对传输过程进行了数值仿真。分析了不同跟踪抖动、湍流强度条件下远场光斑质心脱靶量的变化,以及不同尺寸模拟目标的回波概率。分析结果表明,在传输距离为10 km时,强湍流造成的远场光斑脱靶量可达几十μrad;当跟踪抖动较大时,湍流强弱对脱靶量影响差别很小。最后,对一定尺寸的模拟目标,从探测回波概率的角度给出了发射系统跟踪抖动量的控制范围。     

概率盒框架下混合认知不确定声场的响应预测

针对含概率盒-证据混合认知不确定参数声场的响应预测问题,提出了一种概率盒框架下的改进区间蒙特卡洛方法。该方法首先将混合认知不确定参数转换为纯概率盒形式,然后结合有限元方法推导出混合认知不确定声场的盖根鲍尔多项式代理模型,再采用蒙特卡洛方法求解代理模型得到声压响应。以含概率盒-证据混合认知不确定参数的二维管道声场模型和卡车乘客舱声腔模型为例,计算结果表明混合认知不确定参数影响下的声压响应为概率盒形式,其包括声压响应极值和相应的概率信息,并且所提方法较常规混合离散方法效率更优,较基于一阶摄动法的区间蒙特卡洛方法准确性更高。研究结果表明:所提方法可以有效预测混合认知不确定声场的声压响应,并可进行声学性能的风险和保守估计。     

An asymptotic method for calculating limits of maximal means

For a continuous almost periodic function , we show that the function

具有未知源的某些非线性伪抛物型方程的反问题

考 虑具有未 知源项的 某些非 线性伪 抛物 型方程 的反演 问题． 首先 将伪抛 物型 方程初 边值问 题化为非线 性发展方 程 Ｃｏｕｃｈ ｙ 问题,然 后,利用半 群理论,论 证发展 方程反问 题解的存 在唯一 性,最后, 利用不 动点方法得到 伪抛物型方程反 问题的可解性     

A novel two-dimensional SiO sheet with high-stability,strain tunable electronic structure,and excellent mechanical properties

Using the structure search of particle swarm optimization(PSO) algorithm combined with density functional theory(DFT), we conduct a systematic two-dimensional(2D) material research on the SiO and discover a P2 monolayer structure.The phonon spectrum shows that the 2D P2 is dynamic-stable under ambient pressure. Molecular dynamics simulations show that 2D P2 can still exist stably at a high temperature of 1000 K, indicating that 2D P2 has application potential in high-temperature environments. The intrinsic 2D P2 structure has a quasi-direct band gap of 3.2 e V. The 2D P2 structure can be transformed into a direct band gap semiconductor by appropriate strain, and the band gap can be adjusted to the ideal band gap of 1.2 e V–1.6 e V for photovoltaic materials. These unique properties of the 2D P2 structure make it expected to have potential applications in nanomechanics and nanoelectronics.     

Crystal growth,structure and optical properties of Pr~(3+) -doped yttria-stabilized zirconia single crystals

The development of blue semiconductor light-emitting diodes(LEDs) has produced potential applications for Prdoped materials that can absorb blue light, especially crystals, and we now report structure and optical properties for high-quality Pr-doped single crystals of yttria-stabilized zirconia(YSZ) grown by the optical floating zone(FZ) method.X-ray diffraction(XRD) and Raman spectroscopy showed that all of the single crystal samples were in the cubic phase,whereas the corresponding ceramic samples contained a mixture of monoclinic and cubic phases. X-ray photoelectron spectroscopy(XPS) and electron paramagnetic resonance(EPR) spectroscopy showed that Pr was present as the Pr~(3+) ion in ceramic rods and single crystals after heating to high temperatures. The absorption and photoluminescence excitation(PLE) spectra of the Pr-doped YSZ crystals measured at room temperature showed strong absorption of blue light, while their photoluminescence(PL) spectra showed five emission peaks at 565 nm, 588 nm, 614 nm, 638 nm, and 716 nm under450 nm excitation. The optimum luminescence properties were obtained with the crystal prepared using 0.15 mol% Pr_6O_(11),and those with higher concentrations showed evidence of quenching of the luminescence properties. In addition, the color purity of Pr-doped YSZ single crystal reached 98.9% in the orange–red region.