镍基单晶合金蠕变变形过程的描述

基于强化相γ’的筏化－解筏和粗化的细观过程,本文推导了一组用于描述基单在合金蠕变变形过程的蠕变方程,并在９５０℃和７６０℃标定了国产ＤＤ３镍基单晶合金不同晶体取向的模型参数,与实验结果比较,所提模型可以准确地描述蠕变的主要阶段。     

Focusing subwavelength grating coupler for mid-infrared suspended membrane waveguide

A mid-infrared (mid-IR)-focusing subwavelength grating (SWG) coupler and suspended membrane waveguide (SMW) on a silicon-on-insulator wafer are studied. For a transverse-electric mode uniform SWG, finite-difference time-domain simulation predicts 44.2% coupling efficiency with 1 dB bandwidth of about 220 nm and backreflection of 0.78% at 2.75 μm. Then the uniform SWG is curved to a focusing SWG using a phase-matching formula. The SMWs are analyzed by the finite element method and fabricated. An Er3+-Pr3+ co-doped mid-IR fiber laser is used for device characterization. The fabricated mid-IR SWG coupler has 24.7% coupling efficiency.     

A generalized Borgonovo's importance measure for fuzzy input uncertainty

In this work, the way in which fuzzy uncertainty in a model's output is apportioned to fuzzy uncertainty in model inputs is studied through a sensitivity analysis. Here, an optimization technique is employed to obtain the membership functions of the fuzzy structural response, for which a global sensitivity indicator is introduced to measure the influence of fuzzy input uncertainty on fuzzy output uncertainty. The global sensitivity indicator is the important measure of the fuzzy input uncertainty, which extends Borgonovo's measure. In this study, the mathematical properties of the important measure of the fuzzy input uncertainty are discussed and proved. The results of numerical examples and engineering examples show that the proposed importance measure can effectively describe the effect of fuzzy input uncertainty on fuzzy structural response. When the sensitivity indicator is larger, the basic fuzzy-valued variable becomes more important. The sensitivity indicators of the fuzzy structural response can give an essential importance sequence of all the basic fuzzy-valued variables and identify key contributing fuzzy-valued variables. The sensitivity indicators can provide the availability guidance to reduce the number of basic variables and optimize the fuzzy response model.     

Reliability sensitivity by method of moments

Based on the available methods of moments for structural system reliability assessment and point estimate methods for the first few moments of performance functions, an effective method is proposed to analyze reliability sensitivity of a structural system. The proposed method for analyzing reliability sensitivity includes two steps. Firstly, the reliability sensitivity, usually measured by partial differential of the failure probability _Pf$P_f$ with respect to distribution parameter θ$\theta$ of the basic random variable is derived according to the moment based reliability assessment. The derived expression of ∂_Pf/∂θ$\partial P_f/\partial \theta$ is related to the derivative of the performance function moment α$\alpha$ with respect to θ$\theta$. Secondly, by using the integral formulation between α$\alpha$ and the probability density function (PDF) of the basic random variable, ∂α/∂θ$\partial \alpha /\partial \theta$ could be derived as an expectation of a transformed performance function, and the expectation could be approximated by the point estimate methods. Through the two steps above, the reliability sensitivity can be obtained easily. The obvious advantages of the proposed method include independence of the explicit expression of the performance function, no limitations on the types of PDF of the basic random variables, wide applicability for multiple failure modes and high efficiency for low and medium dimensional problem, which are illustrated by the given examples. However, the efficiency of this method decreases as the dimension of the basic random variables increase, therefore, it is not suitable for the high dimensional problems.     

三维弹塑性受剪板表面裂纹的可靠性分析计算

本文建立了受剪应力表面裂纹塑性失稳扩展的可靠性分析模型。采用三维弹塑性模型对其综合变量Ｊ积分进行了计算，分析了在不同的无量纲裂纹尺寸和外载应力情况下，裂纹失稳扩展的失效概率分布规律，为工程检测和维修提供指导。     

A new algorithm for variance based importance analysis of models with correlated inputs

Importance analysis is aimed at finding the contributions of the inputs to the output uncertainty. For structural models involving correlated input variables, the variance contribution by an individual input variable is decomposed into correlated contribution and uncorrelated contribution in this study. Based on point estimate, this work proposes a new algorithm to conduct variance based importance analysis for correlated input variables. Transformation of the input variables from correlation space to independence space and the computation of conditional distribution in the process ensure that the correlation information is inherited correctly. Different point estimate methods can be employed in the proposed algorithm, thus the algorithm is adaptable and evolvable. Meanwhile, the proposed algorithm is also applicable to uncertainty systems with multiple modes. The proposed algorithm avoids the sampling procedure, which usually consumes a heavy computational cost. Results of several examples in this work have proven the proposed algorithm can be used as an effective tool to deal with uncertainty analysis involving correlated inputs.     

Inhibition of cyclodextrins on the activity of α-amylase

α-amylase activity influences both flour fermentation process and the quality of the fermented products due to its ability of breaking starch into smaller units. The inhibition of cyclodextrins on α-amylase activity was investigated in this paper. Experiment results showed that hydrophobic cavity size was an intrinsic factor during the inhibition processing. Among three types of cyclodextrin (α-, β- and γ-), β-type exhibited the most significant inhibitory activity toward α-amylase. The optimal inhibitory parameters were indicated to be pH 5.9, concentration of β-cyclodextrins 1 mmol/L, reaction temperature 45 °C and reaction time 60 min. Results suggested that the endogenous fluorescence of α-amylase was inhibited by cyclodextrins. Circular dichroism spectrum indicated that the secondary structure of α-amylase, including α-helices, β-sheets and random coils, was changed by cyclodextrins. All the results in this paper aim to provide a further understanding for α-amylase in the industry application.     

Higher-Order Logic Formalization of Conformal Geometric Algebra and its Application in Verifying a Robotic Manipulation Algorithm

Conformal geometric algebra (CGA) is an advanced geometric language used in solving three-dimensional Euclidean geometric problems due to its simple, compact and coordinate-free formulations. It promises to stimulate new methods and algorithms in all areas of science dealing with geometric properties, especially for engineering applications. This paper presents a higher-order logic formalization of CGA theories in the HOL-Light theorem prover. First, we formally define the classical algebraic operations and representations of geometric entities in the new framework. Second, we use these results to reason about the correctness of operation properties and geometric features such as the distance between the geometric entities and their rigid transformations in higher-order logic. Finally, in order to demonstrate the practical effectiveness and utilization of this formalization, we use it to formally model the grasping algorithm of a robot based on the conformal geometric control technique and verify the property that whether the robot can grasp firmly or not.     

Springtail-inspired Light-driven Soft Jumping Robots Based on Liquid Crystal Elastomers with Monolithic Three-leaf Panel Fold Structure

Jump is an important form of motion that enables animals to escape from predators, increase their range of activities, and better adapt to the environment. Inspired by springtails, we describe a light-driven soft jumping robot based on a double-folded liquid crystal elastomer (LCE) ribbon actuator with a monolithic three-leaf panel fold structure. This robot can achieve remarkable jumping height, jumping distance, and maximum take-off velocity, of up to 87 body length (BL), 65 BL, and 930 BL s⁻¹, respectively, under near-infrared light irradiation. Further, it is possible to control the height, distance, and direction of jump by changing the size and crease angle of the double-folded LCE ribbon actuators. These robots can efficiently jump over obstacles and can jump continuously, even in complex environments. Our simple design strategy improves the performance of jumping actuators and we expect it to have a wide-ranging impact on the strength, continuity, and adaptability of future soft robots.     

基于区间模型的结构非概率可靠性优化

采用区间变量描述不确定参数,研究了结构非概率可靠性优化问题。基于区间模型描述不确定信息这一前提,针对Elishakoff的非概率可靠性指标,给出了其几何解释和求解方法。建立了以结构重量为目标函数、以非概率可靠性指标为约束条件的非概率可靠性优化模型。算例分析表明:该非概率可靠性优化方法能够考虑不确定信息的影响,对结构重量进行合理分配。该方法为结构非概率可靠性优化提供了一种新的思路。