高强度低合金铌钒钢板的失效分析

针对高强度低合金铌钒钢板在拉伸试验后出现分层开裂的现象,采用SEM、EDAX进行微观分析,发现试样内部有大量夹杂物存在,这些夹杂物主要含有钙、氧、硫、锰等元素。带有缺陷的钢板若应用到实际工程中,会影响铁塔的寿命。     

流动液体中夹杂物超声去除的影响因素

以高密度聚乙烯（HDPE）颗粒和水形成的悬浮液为研究体系。考察了有无超声波作用下。介质流量、夹杂物数量以及夹杂物的粒径对总去除率、上浮去除率、壁面粘附去除率的影响。实验结果表明，在短时间内（30s)超声波对流动液体中的夹杂物具有明显的去除效果。总去除率达93％。夹杂物的总去除率随着超声波输入电功率的增大而提高；超声波对较多数量或较大粒径的夹杂物去除效果更显著。超声波作用下流动液体中的夹杂物比静止液体中的更容易去除。超声波对流动液体中夹杂物去除效果的去除机理主要是通过气泡捕获夹杂物，超声空化效应产生直接包裹夹杂物的气泡以及通过夹杂物碰撞凝聚使夹杂物容易上浮实现去除。     

A revisit to stochastic near-optimal controls: The critical case

This paper revisits the stochastic near-optimal control problem considered in Zhou (1998), where the stochastic system is given by a controlled stochastic differential equation with the control variable taking values in a general control space and entering both the drift and diffusion coefficients. A necessary condition of near-optimality is derived using Ekeland’s variational principle, spike variation techniques, and some delicate estimates for the state and the adjoint processes. We improve the error bound of order from “almost” ${\epsilon }^{\frac{1}{3}}$ in Zhou (1998) to “exactly” ${\epsilon }^{\frac{1}{3}}$.     

Conformational Modeling of Continuum Structures in Robotics and Structural Biology: A Review

Hyper-redundant (or snakelike) manipulators have many more degrees of freedom than required to position and orient an object in space. They have been employed in a variety of applications ranging from search-and-rescue to minimally invasive surgical procedures, and recently they even have been proposed as solutions to problems in maintaining civil infrastructure and the repair of satellites. The kinematic and dynamic properties of snakelike robots are captured naturally using a continuum backbone curve equipped with a naturally evolving set of reference frames, stiffness properties, and mass density. When the snakelike robot has a continuum architecture, the backbone curve corresponds with the physical device itself. Interestingly, these same modeling ideas can be used to describe conformational shapes of DNA molecules and filamentous protein structures in solution and in cells. This paper reviews several classes of snakelike robots: (1) hyper-redundant manipulators guided by backbone curves; (2) flexible steerable needles; and (3) concentric tube continuum robots. It is then shown how the same mathematical modeling methods used in these robotics contexts can be used to model molecules such as DNA. All of these problems are treated in the context of a common mathematical framework based on the differential geometry of curves, continuum mechanics, and variational calculus. Both coordinate-dependent Euler–Lagrange formulations and coordinate-free Euler–Poincaré approaches are reviewed.     

基于变分贝叶斯逼近的前向仿射变换点集匹配方法研究

本文建立了两个点集线性匹配过程的贝叶斯模型框架,并利用变分贝叶斯逼近方法对模型点集到场景点集的仿射参数进行估计。该模型利用一个有向图对映射参数、隐藏变量、模型与场景点集的关系进行了描述,并基于有向图给出了各个参数和变量后验概率的迭代估计算法。而且该模型还利用了一个带有各向异性协方差矩阵的高斯模型对场景点集的离群点进行了估计和推理。实验结果表明该模型在鲁棒性和匹配精度方面均获得了良好的效果。     

融合全局和局部相关熵的图像分割

目的 针对LCK(local correntropy-based K-means)模型对初始轮廓敏感的问题,提出了新的基于全局和局部相关熵的GLCK(global and local correntropy-based K-means)动态组合模型。方法 首先将相关熵准则引入到CV(Chan-Vese)模型中,得到新的基于全局相关熵的GCK(global correntropy-based K-means)模型。然后,结合LCK模型,提出GLCK组合模型,并给出一种动态组合算法来优化GLCK模型。该模型分两步来完成分割:第1步,用GCK模型分割出目标的大致轮廓;第2步,将上一步得到的轮廓作为LCK模型的初始轮廓,对图像进行精确分割。结果 主观上,对自然图像和人工合成图像进行分割,并同LCK模型、LBF模型以及CV模型进行对比,结果表明本文所提模型的鲁棒性比上述模型都要好;客观上,对BSD库中的两幅自然图像进行分割,并采用Jaccard相似性比率进行定量分析,准确率分别为91.37%和89.12%。结论 本文算法主要适用于分割含有未知噪声及灰度分布不均匀的医学图像及结构简单的自然图像,并且分割结果对初始轮廓具有鲁棒性。     

Evolutionary variational inequality with long-term memory and applications to economic networks

The aim of this paper is to present the relation between an evolutionary variational inequality with long-term memory and Lagrange multipliers. More precisely, we study the oligopolistic market equilibrium problem in which the profit function depends also on previous events of the market by means of a long-term memory which takes into account the previous states of the equilibrium. Moreover, thanks to the variational formulation, we are able to show existence and regularity results for equilibrium solutions. Then, we apply the infinite dimensional duality theory through which we obtain the existence of Lagrange multipliers which are great utility in order to understand the behaviour of the market. Finally, an example is provided, which allows to analyse the influence of the long-term memory on the equilibrium solution.     

基于遗传算法的空间伸展臂展开过程优化控制

针对空间伸展臂展开过程建立多体系统动力学模型,并以控制力为变量建立优化控制模型,通过最优控制力的选取,使空间伸展臂得以平稳、快速展开.为了避免基于梯度的优化方法在寻找最优控制力过程中大量复杂的灵敏度计算,采用遗传算法进行全局寻优.同时,优化迭代过程中动力学方程采用高阶变分数值积分方法求解,具有更高的稳定性.最后,以剪叉式空间伸展臂为例,利用遗传算法对其展开过程进行优化控制.     

An Interacting Multiple Model Approach for State Estimation with Non‐Gaussian Noise Using a Variational Bayesian Method

The conventional interacting multiple models (IMM) approach for a hybrid system under the Gaussian assumption is limited for most real applications due to the noisy measurements often being in the presence of outliers. This paper aims at accommodating the IMM approach to the non‐Gaussian cases where outliers exist. In the proposed IMM algorithm, the Student‐t distribution is used to model the non‐Gaussian measurement noise. At the interaction step, the mixed statistics of the noise parameter under a Bayesian framework are obtained via a Gamma approximation and a recently reported moments matching method. To address the state noise‐coupled intractability in Bayesian filtering, a variational Bayesian method is utilized to approximate the posterior distributions of the noise and state recursively. The proposed algorithm is tested with a maneuvering target tracking example and is shown to be robust to the outliers.     

Compressed sensing of superimposed chirps with adaptive dictionary refinement

The compressed sensing （CS） theory shows that accurate signal reconstruction depends on presetting an appropriate signal sparsifying dictionary. For CS of superimposed chirps, this dictionary is typically taken to be a waveform-matched dictionary formed by blindly diseretizing the frequency-chirp rate plane. However, since practical target parameters do not lie exactly on gridding points of the assumed dictionary, there is always mismatch between the assumed and the actual sparsifying dictionaries, which will cause the performance of conventional CS reconstruction methods to degrade considerably. To address this, we model the waveform- matched sparsifying dictionary as a parameterized one by treating its sampled frequency-chirp rate grid points as the underlying parameters. As a consequence, the sparsifying dictionary becomes refinable and its refinement can be achieved by optimizing the underlying parameters. Based on this, we develop a novel reconstruction algorithm for CS of superimposed chirps by utilizing the variational expectation-maximization （EM） algorithm. By alternating between steps of sparse coefficients estimation and dictionary parameters optimization, the algorithm integrates the process for dictionary refinement into that of signal reconstruction, and thus can achieve sparse reconstruction and dictionary optimization simultaneously. Experimental results demonstrate that the algorithm effectively deals with the performance degradation incurred by dictionary mismatch, and also outperforms the state-of-the-art CS reconstruction methods both in compressing the signal measurements and in suppressing the measurement noise.