高效半解析方法分析周期正交加筋板的振动-声辐射特性

为了对水下无穷大双周期正交加筋板结构模型在简谐面力激励下的振动响应及声辐射特性进行更为合理的理论预测与分析,建立了加筋板结构的数学模型。结合傅里叶变换、泊松迭加公式及空间波数法,将周期加筋板的振动响应及辐射声压表达为关于结构位移谐波分量的函数方程,对加筋板模型提出了高效分析求解方法并进行了谐波分量截断求解。验证了方法的正确性,并分析了结构的振动特性以及加强筋周期间距和扭矩对辐射声压的影响。结果表明,加强筋的扭转作用影响加筋板结构的振动模态频率,对于较高精度要求的工程应用,加强筋的扭转作用不能忽略。通过调节加强筋周期间距及横截面尺寸,可以降低薄板在较低频域区间的远场辐射声压。     

三角翼涡破裂的高精度数值模拟

采用5阶精度的加权紧致非线性格式(WCNS-E-5)数值模拟65°后掠角尖前缘三角翼的大攻角跨声速绕流流场,考察低耗散、高分辨率的WCNS-E-5格式对于三角翼涡破裂模拟的适用性,及激波旋涡干扰对涡破裂点位置的影响,重点研究三角翼大攻角旋涡破裂点的突然前移.通过求解任意坐标系下的非定常雷诺平均N-S方程,采用WCNS-E-5和SST两方程湍流模型,与试验结果和文献计算结果对比,表明既有高阶精度又能光滑捕捉激波的WCNS格式在模拟三角翼旋涡破裂方面具有一定优势,其数值结果与试验结果吻合较好,三角翼大攻角旋涡破裂点的突然前移是由于跨声速流场的激波旋涡干扰.     

On-axis Gaussian beam scattering by an eccentrically coated conducting cylinder

Based on the generalized Lorenz–Mie theory (GLMT) framework, an exact analytic solution to electromagnetic scattering by an eccentrically coated conducting cylinder is constructed, for oblique incidence of an on-axis Gaussian beam described by a localized beam model. The solution is found by the classical separation of variables technique and the translational addition theorem. For a tightly focused Gaussian beam propagating perpendicularly to the cylinder axis, numerical results of the normalized differential scattering cross section are presented, and the scattering characteristics are discussed concisely.     

Stress boundary layers in the viscoelastic flow past a cylinder in a channel： limiting solutions

The flow past a cylinder in a channel with the aspect ratio of 2:1 for the upper convected Maxwell (UCM) fluid and the Oldroyd-B fluid with the viscosity ratio of 0.59 is studied by using the Galerkin/Least-square finite element method and a p-adaptive refinement algorithm. A posteriori error estimation indicates that the stress-gradient error dominates the total error. As the Deborah number, D_e, approaches 0.8 for the UCM fluid and 0.9 for the Oldroyd-B fluid, strong stress boundary layers near the rear stagnation point are forming, which are characterized by jumps of the stress-profiles on the cylinder wall and plane of symmetry, huge stress gradients and rapid decay of the gradients across narrow thicknesses. The origin of the huge stress-gradients can be traced to the purely elongational flow behind the rear stagnation point, where the position at which the elongation rate is of 1/2D_e approaches the rear stagnation point as the Deborah number approaches the critical values. These observations imply that the cylinder problem for the UCM and Oldroyd-B fluids may have physical limiting Deborah numbers of 0.8 and 0.9, respectively.The project supported by the National Natural Science Foundation of China (50335010 and 20274041) and the MOLDFLOW Comp. Australia.     

低频泥石流特征及其预测初步探讨

同高频泥石流相比,低频泥石流更具有潜在危害性。近年来,低频泥石流的暴发给我国山区人们的生命财产安全、经济发展和社会进步以及山区生态环境带来了极大的影响。本文通过对低频泥石流沟实地考察以及对近年来我国暴发的约30例典型低频泥石流资料进行搜集整理,从其隐蔽性、活动性、规模和破坏性以及灾情等方面探讨了低频泥石流的特征;以茶园沟为例,采用灰色灾变预测方法,建立灰色灾变预测模型对其进行预测,经检验预测结果与实际发生年份一致,并且预测出2042年或2043年前后以及2095年或2096年前后茶园沟发生大规模泥石流的可能性较大;最后,针对低频泥石流的特征,提出了相应的防治建议。     

Gaussian beam scattering by a chiral sphere

Based on the generalized Lorenz–Mie theory that provides the general framework, an analytic solution to Gaussian beam scattering by a chiral sphere is constructed, by expanding the incident Gaussian beam, scattered fields and internal fields in terms of spherical vector wave functions. The unknown expansion coefficients are determined by a system of equations derived from the boundary conditions. For a localized beam model, numerical results of the normalized differential scattering cross section are presented.     

Synthesis,Spectroscopy and Photochemistry of Novel Branched Fluorescent Nitro-Stilbene Derivatives with Benzopheonone Groups

In this article, we presented novel nitro-stilbene derivatives with one or two benzophenone groups as photoinitiators via multi-steps synthesis. The ultraviolet/visible spectroscopy and the emission spectroscopy of the compounds were determined in various solvents. The results showed that the ultraviolet/visible absorption spectroscopy of the derivatives with benzophenone moiety displayed overlap effects of nitro-stilbene and benzophenone parts. In non-polar solvents, the derivatives exhibited strong emission, while they displayed weak emission in modest and strong polar solvents. Dyes-linked benzopheonone groups displayed stronger fluorescence emission than simple chromophore parent molecules. Visible-light photoinitiating effects of the derivatives were investigated extensively. Methyl methacrylate could be photoinitiated efficiently by the derivatives with benzophenone moieties at very low concentration, even at 1 × 10⁻⁵ mol/L. While the photopolymerization efficiency of styrene initiated by the derivatives was lower than that of methyl methacrylate. Our results showed that the dye-linked photoinitators had more efficient photoinitiating than the simple mixture of dye and photoinitator. Furthermore, the derivative with two benzophenone groups displayed more excellent phototiniatiating effects than the derivative with one benzophenone group. Thermodynamics driving for the occurrence of visible-light photoinduced intramolecular electron transfer from chromophore part to benzophenone part was evaluated. Benzopinacol moiety produced in photoreaction was confirmed by nuclear magnetic resonant spectroscopy. Thermal stability of the derivatives was analyzed.     

Characterization of activation energy distribution for ultraviolet irradiation of T-rich oligonucleotide using high-performance liquid chromatography electrospray ionization mass spectrometry tandem mass spectrometry

Exposure to solar UV radiation gives rise to mutations that may lead to skin cancer of human being. Series of experiments were carried out in order to reveal activation energy distribution of DNA mutation caused by UV radiation. The T-rich oligonucleotides were exposed to UV radiation with increasing intensity for different durations. Photoproducts of T-rich oligonucleotide were investigated using ion-pair reversed-phase high-performance liquid chromatography/tandem electrospray ionization mass spectrometry (IP-RP-HPLC/ESI-MS) at room temperature. Two photoproducts of T-rich oligonucleotide were cis-syn cyclobutane pyrimidine dimmer (T[c,s]T) and the pyrimidine(6,4)pyrimidone product (T[6,4]T). Activation energy distribution of DNA mutation was calculated using a commercial kinetics analysis programs by Robert L. Braun and Alan K. Burnham , Lawrance Livermore International Laboratory (version 2.4.1). To use the software for deriving the kinetics parameters, the factor T (temperature) in the software was substituted with k1R, in which k1 is a factor, R is radiation intensity. The activation energy derived ranges from 55 to 110 kJ mol(-1). By the same software, those kinetics parameters were extrapolated to natural UV radiation process to predict DNA damage degree without the DNA repair process.     

基于光纤M-Z干涉仪相干度变化的超窄线宽激光器跳模检测研究

超窄线宽激光器随机发生的跳模现象,作为一种干扰或噪声,是降低光学相干检测系统性能的重要因素。为了有效检测单纵模超窄线宽激光器的模式稳定性,提出一种基于光纤M-Z干涉仪的超窄线宽激光器跳模检测方法,该方法通过在干涉仪内引入相位生成载波(PGC)外调制技术,将激光器跳模过程中光源相干性的变化转化为干涉仪相干度的突变,从而实现对整个跳模过程的实时监测。实验结果表明,该方法在检测灵敏度上有明显优势,能够有效监测跳模的持续时间、模式竞争随时间演化的动态过程等跳模细节,尤其适合用于短直腔激光器的跳模检测,并且能为光纤激光器跳模现象的预测与主动抑制提供重要参考。