结构可靠度分析的改进BP神经网络响应面法

对功能函数不能明确表达即具有隐式功能函数的问题进行可靠度分析,常采用响应面法。其中二次多项式响应面法应用较为广泛,采用与此方法相同的思路,人们提出了BP神经网络响应面法。在此基础之上,笔者提出了改进的BP神经网络响应面法。对以上方法计算效果,通过算例进行了对比分析,其中改进BP神经网络响应面法计算精度较好,进行有限元分析次数较少。该方法用于大型复杂结构的可靠度分析,可相应提高工作效率和解题质量,具有一定实际应用价值。     

Review on long-rod penetration at hypervelocity

由高密度金属制成的长杆弹在1.5$\sim$3.0km/s的下具有很强的侵彻和贯穿能力,长杆高速侵彻问题现已成为穿甲侵彻领域的研究热点.本文综述了长杆高速侵彻问题的最新研究进展,首先介绍了长杆高速侵彻的基本概念、研究方法和理论模型;其次重点论述了研究中关注的突出问题与应用, 包括弹靶材料性质、长杆弹头部形状、长径比效应与分段杆设计、陶瓷靶抵抗长杆侵彻与界面击溃和非理想长杆侵彻;最后对未来的研究工作提出一些建议.     

影响内燃机活塞环—缸套擦伤的因素及防擦伤的摩擦学设计

阐述了内燃机活塞环－缸套擦伤的机理。分析了磨合，缸套表面形貌，活塞环外形，活塞组件的热变形与机械变形，润滑油，材料和表面覆层等因素对活塞环擦伤的影响。指出可以采用内燃机强化系数ｐｅｖｍ作为活塞环防擦伤摩擦学设计的判别特征值，从而为从设计上防止活塞环擦伤提供了思路。     

旋转圆板振动的热力控制

本文研究发现,热力对旋转圆盘动力特性有明显影响.可将此特征应用于旋转圆盘振动的热力自适应控制.仿真和试验均表明,这种控制方法对一些结构振动控制将是一种有效的方法.     

各向异性柱体扭转的充分必要的边界积分方程

本文列出各向异性柱体扭转问题无量纲化后的有关方程的边界条件推导和验证了基本解，并指出一些书中基本解列式有误＾［９－１１］，列出了充分必要的边界积分方 程，进行了数据计算，并与习用的边界积分方程所得结果进行了比较，表明在退化值附近，习用的边界积分方程所得的边界剪应力会出现巨大的误差，扭转刚度的误差则要小得多，而充要的边界积分方程计算的结果则如终保持良好的精度，再次显示了它的优点。     

NONLINEAR SATURATION OF BAROCLINIC INSTABILITY IN THE GENERALIZED PHILLIPS MODEL (Ⅰ) -THE UPPER BOUND ON THE EVOLUTION OF DISTURBANCE TO THE NONLINEARLY UNSTABLE BASIC FLOW

On the basis of the nonlinear stability theorem in the context of Arnol’s second theorem for the generalized Phillips model, nonlinear saturation of baroclinic instability in the generalized Phillips model is investigated. By choosing appropriate artificial stable basic flows, the upper bounds on the disturbance energy and potential enstrophy to the nonlinearly unstable basic flow in the generalized Phillips model are obtained, which are analytic completely and without the limitation of infinitesimal initial disturbance.     

Some theoretical problems on variational data assimilation

Theoretical aspects of variational data assimilation (VDA) for a simple model with both global and local observational data are discussed. For the VDA problems with global observational data, the initial conditions and parameters for the model are revisited and the model itself is modified. The estimates of both error and convergence rate are theoretically made and the validity of the method is proved. For VDA problem with local observation data, the conventional VDA method are out of use due to the ill-posedness of the problem. In order to overcome the difficulties caused by the ill-posedness, the initial conditions and parameters of the model are modified by using the improved VDA method, and the estimates of both error and convergence rate are also made. Finally, the validity of the improved VDA method is proved through theoretical analysis and illustrated with an example, and a theoretical criterion of the regularization parameters is proposed.     

Improved charge injection of pentacene transistors by immobilizing DNA on gold source-drain electrodes

The pyrocarbon materials investigated here are examples of disordered graphene-based carbons whose crystallite size L _a ranges from 2 to 5 nm. This L _a size range is between two different Raman behaviors, one for which the D band broadens (for L _a  < 2 nm) and the other for which the D band sharpens (for L _a  > 5 nm) respectively, with increasing L _a . To fully understand the nature of the G band signal, we checked its wavelength behavior from UV to near IR. We demonstrated that the Raman spectrum is well fitted with simply two Lorentzians with various respective contributions centered at the wavenumber of the D band and a Breit–Wigner–Fano shape for the G band. Each intensity contribution for the D band varies linearly with L _a between 2 and 5 nm while the total D band intensity is nearly constant for excitation wavelengths ranging from 0.532 to 0.638 μm. In contrast, the integrated intensity ratio D/G follows the well-known $L_{a}^{-1}$ law. The two subbands building the D band are related to the lifetime of the electrons involved in the double resonance process which can be scattered twice. Their respective occurrences therefore depend on the crystallite size L _a , when below ≈5 nm.     

The statistical sinogram smoothing via adaptive-weighted total variation regularization for low-dose X-ray CT

Though clinically desired, low-dose X-ray computed tomography (CT) images tend to be degraded by the noise-contaminated sinogram data. Preprocessing the noisy sinogram before filtered back-projection (FBP) is an effective way to solve this problem. This paper presents a statistical sinogram smoothing approach for low-dose CT reconstruction. The approach is obtained by minimizing an energy function consisting of an adaptive-weighted total variation (AWTV) regularization term and a data fidelity term based on the Markov random fields (MRF) framework. The AWTV regularization term can make our algorithm automatically adjust the smoothing degree according to the feature and the level of noise of the smoothed pixel. The experimental results indicate that the proposed approach has the excellent performance in visual effects and quantitative analysis.     

266nm下邻二甲苯双光子电离质谱的研究

利用YAG激光器输出的四倍频激光对邻二甲苯分子的多光子电离过程进行了研究,获得了邻二甲苯分子的多光子电离飞行时间质谱（MPI-TOFMS）,其母体离子及碎片离子信号达22种之多。光强指数分析表明母体离子C8H^＋10和主要的碎片离子C7H^＋7、C6H^＋5发生了1＋1共振增强双光子电离（RE2MPI）。