元件与模式相对重要度对静强度可靠度的影响分析

本文通过研究指出,在运用增量载荷法寻找每级可能破坏元件时,必须考虑每个元件变异系数的影响,以避免漏掉极限承载能力很大但可靠度很低的失效模式;同时指出,结构失效的各个模式对系统可靠性的影响不仅与其本身发生失效的概率有关,而且与这个模式的重要程度有关,并提出了采用加权系数来计及每个失效模式的重要程度对结构系统可靠性影响的方法;最后用算例说明了本文方法的合理性。     

对数梯度材料泊松比不为零时的裂纹尖端场

严格地求出了当泊松比不为零时对数梯度材料的裂纹尖端场. 虽然在本构方程中对数项为\exp(ax), 但严格地证明了在最后应力的表达式中, 它却变为\exp(ax/2+ak_{1}^{1 / 2}y/2-kr/2) 与\exp(ax/2-ak_{1}^{1/2} y/2-kr/2). 对于数值解法, 若考虑了此种严格关系, 将会很容易地解释其结果.     

Theoretical Calculations on the Second-order Nonlinear Optical Property of Chiral Bis-corroles

The second-order nonlinear optical (NLO) properties of 5,10,15-triphenylcorrole (TPC), 5,10,15,20-tetraphenylporphyrin (TPP) and L-amino acid bridged bis-corroles 1, 2, 3 and 4 have been calculated by using TDHF/PM3 method based on the RHF/6-31G (TPC and TPP) or semiempirical PM3 (1, 2, 3, 4) optimized geometries. Calculation results showed TPC and TPP have C1 and D2h symmetry, respectively when N-H protons are localized on the nitrogen atoms. TPC is the second-order NLO active chromophore due to the cancellation of centrosymmetrical structure and its first hyperpolarizability β increases to 11.524×10-30 esu. Under electrical dipole approximation, β values of bis-corroles 1, 2, 3 and 4 vary from 9.831×10-30 to 14.221×10-30 esu, and no much improvement in the first hyperpolarizability was observed as compared to TPC monomer. However, β values of bis-corroles 1, 2, 3 and 4 are improved by about 4 times as compared to their bis-porphyrin counterparts. The analysis of β components indicates that β of this kind of bis-corroles is mainly contributed from its radial component βr. With the variation of amino acid side chains, βHRS, β, βxyz, βr and βa of bis-corroles change remarkably. Chiral L-amino acid bridged bis-corroles 2, 3 and 4 have a right-handed helix structure, and their chiral component βxyz matches βxyz ∝ r2ζ/L4 (helix parameters), showing the second-order chiral NLO response of these bis-corroles could be described by one-electron helical model theory. It was found that the radial component βr of chiral helix bis-corroles also matches β r ∝ r2ζ/L4.     

中国区域全要素能源效率及节能减排潜力分析—基于非期望产出的SBM模型

运用DEA-SBM模型测度了碳排放约束下1999年-2010年中国30省、市、区及四大区域的全要素能源效率,并利用变异系数及K-Means聚类分析考察了区域全要素能源效率的差异,最后对各省份及区域的节能减排潜力进行了测度分析.研究结果表明:不考虑碳排放约束的各省份的全要素能源效率被高估,绿色能源效率总体均值呈现U型趋势;绿色能源效率的区域格局按照由东向西递减.四大区域的变异系数差异较大,均呈现收敛趋势;由聚类分析结果可知处于高效区的省份全部为东部沿海省份;中效区的省份大多是中部省市及东北老工业基地,而西部区域的各省份多数处于低效区;不同省份的节能减排的潜力差异较大,西部区域的节能减排潜力最高,其次为中部和东北部,东部的节能减排潜力最低.     

Homotopy method for a mean curvature-based denoising model

Variational image denoising models based on regularization of gradients have been extensively studied. The total variation model by Rudin, Osher, and Fatemi (1992) [38] can preserve edges well but for images without edges (jumps), the solution to this model has the undesirable staircasing effect. To overcome this, mean curvature-based energy minimization models offer one approach for restoring both smooth (no edges) and nonsmooth (with edges) images. As such models lead to fourth order (instead of the usual second order) nonlinear partial differential equations, development of fast solvers is a challenging task. Previously stabilized fixed point methods and their associated multigrid methods were developed but the underlying operators must be regularized by a relatively large parameter. In this paper, we first present a fixed point curvature method for solving such equations and then propose a homotopy approach for varying the regularized parameter so that the Newton type method becomes applicable in a predictor-corrector framework. Numerical experiments show that both of our methods are able to maintain all important information in the image, and at the same time to filter out noise.     

Omni-total variation algorithm for the restoration of all-focused catadioptric image

In this paper, we present a novel omni-total variation (Omni-TV) algorithm for the restoration of defocus blur to obtain all-focused catadioptric image. Catadioptric omni-directional imaging systems usually consist of conventional cameras and curved mirrors for capturing 360° field of view. Mirror curvature in the catadioptric camera often leads to noticeable blurring artifacts in omni-directional imaging. The problem becomes more severe when high resolution sensor is introduced. In an omni-directional image, two points near each other may not be close to one another in the 3D scene. Traditional gradient computation cannot be directly applied to omni-directional image processing. Thus, an omni-gradient computing method combined with the characteristics of catadioptric imaging is proposed, in which an Omni-TV minimization is used as the constraint for deconvolution regularization. The proposed method is vital for improving catadioptric omni-directional imaging quality and promoting applications in related fields like omni-directional video and image processing.     

球谐函数法解点源辐射传输方程的P3近似及其在生物组织中的应用

辐射传输方程在球坐标下的P3近似是一个非线性微分方程组,其齐次解为球Bessel函数.需要将球Bessel函数分解为指数函数,才能用参数变异法求出它的特解.由于球Bessel函数在r=0的奇异性,无法利用Marshak和其它近似边界条件,因此直接利用能量守恒,和当介质的吸收系数比约化散射系数小得多时P3近似等于P1近似这个特点,确定全解中的常数.比较Monte Carolo模拟和P3近似理论的解析解发现,P3近似能处理约化散射系数与吸收系数之比介于2~10之间的生物组织.     

浙江省水域系统时空变化特征及驱动力分析

基于浙江省1980—2020年8期土地利用数据,分析了浙江省不同时期水域系统时空格局、水面率、转换趋势、景观格局等特征,揭示了水域系统面积变化的驱动因素。结果表明：（1）浙江省水域面积总体呈增加趋势,河流、滩地面积缩减,湖泊、水库坑塘、滩涂面积增加。水域系统转移集中于河流、湖泊和沿海一侧。（2）浙江省水域景观格局MPS、NP、LST、FRA、CCONTAG指数上升,PD、ED、LPI、COHESION、AI指数下降,突出反映了水域景观破碎化、离散化、复杂化。（3）不同地级市水域系统面积存在差异,杭州市的河流、水库坑塘面积最大,嘉兴市和湖州市的湖泊面积最大,宁波市的滩涂面积最大,绍兴市的滩地面积最大。各流域水域系统大多以水库坑塘为主,面积呈增加趋势,其他地类面积变化较小。（4）浙江省水域系统与人为活动（GDP、农林牧渔总产值、人口密度）关系密切,自然因素对水域影响较为稳定,年均降水量的影响大于年均温度的影响。     

文化传播模型中的非平衡相变

采用Monte Carlo数值模拟的方法研究了社会体系中文化突变对文化传播的作用.文化突变机制的引入,使得文化传播模型展示出丰富的相变行为.随着文化突变参量的变化,在一定条件下,体系出现从无序到有序和从有序到无序的相变.在相变点的邻域内,文化畴大小的概率分布函数p(s)与文化畴大小s成幂指数关系,p(s)～s-τ.此外,通过引入系统平均学习概率,研究了文化的突变机制和学习机制的联系.研究表明,个体文化突变可以增加整个体系文化交流的机会.     

Rank-one theorem and subgraphs of BV functions in Carnot groups

We prove a rank-one theorem à la G. Alberti for the derivatives of vector-valued maps with bounded variation in a class of Carnot groups that includes Heisenberg groups ${\mathbb{H}}^n$ for $n\ge 2$. The main tools are properties relating the horizontal derivatives of a real-valued function with bounded variation and its subgraph.