复杂截面RC空间框架结构非线性分析

由于异形柱的截面形状与墙身一致,避免了结构柱在建筑平面中的外凸,增加了建筑可用面积,近年来在结构设计中应用日益广泛.文中运用自编的基于纤维模型柔度法非线性分析程序,对3座底层抽柱的异形柱钢筋混凝土空间框架进行了程序分析,并从骨架曲线和滞回曲线两个方面与试验结果进行了比较,表明骨架曲线计算与试验值吻合得很好,验证了基于纤维模型有限单元柔度法非线性分析程序适用于空间框架,而且对于抽柱的不规则结构也适用.     

A novel clustering-based image segmentation via density peaks algorithm with mid-level feature

Image segmentation is an important and fundamental task in computer vision. Its performance is mainly influenced by feature representations and segmentation algorithms. In this paper, we propose a novel clustering-based image segmentation approach which can be called ICDP algorithm. It is able to capture the inherent structure of image and detect the nonspherical clusters. Compared to the other segmentation methods based on clustering, there are several advantages as follows: (1) Integral channel features are used to clearly and comprehensively represent the input image by naturally integrating heterogeneous sources of information; (2) cluster number can be determined directly and cluster centers are able to be identified automatically; (3) hierarchical segmentation is easy to be achieved via ICDP algorithm. The PSNR and MSE are applied to quantitatively evaluate the segmentation performance. Experimental results clearly demonstrate the effectiveness of our novel image segmentation algorithm.

     

Sentence level topic models for associated topics extraction

In LDA model, independence assumptions in the Dirichlet distribution of the topic proportions lead to the inability to model the connections between topics. Some researchers have attempted to break them and thus obtained more powerful topic models. Following this strategy, by using an association matrix to measure the association between latent topics, we develop an associated topic model (ATM), in which consecutive sentences are considered important and the topic assignments for words are jointly determined by the association matrix and the sentence level topic distributions, instead of the document-specific topic distributions only. This approach gives a more realistic modeling of latent topic connections where the presence of a topic may be connected with the presence of another. We derive a collapsed Gibbs sampling algorithm for inference and parameter estimation for the ATM. The experimental results demonstrate that the ATM gives a more practical interpretation and is capable of learning more associated topics.

     

不同体积无铅微尺度焊点的蠕变力学性能

采用基于动态力学分析仪的精密蠕变试验方法,对比研究了5.34×107 μm3与7.07×106 μm3两种体积相差近一个数量级的无铅Sn-3.0Ag-0.5Cu微尺度焊点的高温蠕变力学行为与蠕变性能.结果表明,所有微尺度焊点的蠕变曲线均呈现初始蠕变、稳态蠕变和加速蠕变阶段.虽然微尺度焊点的体积存在较大差异,但是它们的蠕变激活能与蠕变应力指数均非常接近.此外,在相同的试验温度与拉伸应力作用下,大体积微尺度焊点的稳态蠕变速率相对小体积焊点更大,而蠕变寿命则呈现完全相反的趋势.     

Fabrication of ZrB2 ceramics by reactive hot pressing of ZrB and B

Zirconium diboride (ZrB₂) ceramics were prepared by reactive hot pressing of ZrB+B powder mixture. Formation of a transient liquid due to eutectic reaction of ZrB₂+Zr→L_eu(ZrB2+Zr) at 1661°C following peritectic decomposition of 2ZrB=ZrB₂+Zr at 1250°C during heating up of the ZrB+B mixture facilitated densification. The liquid phase was subsequently eliminated via reaction of B with Zr in the eutectic liquid L_eu(ZrB2+Zr) to result in a dense ZrB₂ ceramic. Full density was reached after reactive hot pressing at 1900°C under 30 MPa for 1 h. The ZrB₂ ceramic had a refined microstructure consisting of grains of <1.5 μm in size and relatively good Vickers hardness (21 ± 2 GPa) and flexural strength (595 ± 63 MPa).     

电迁移对低银无铅微尺度焊点力学行为的影响

研究了电迁移条件下不同电流密度(0.63~1.0×104 A/cm2)和通电时间(0~48 h)对低银无铅Sn-Ag-Cu微尺度焊点的拉伸力学行为的影响. 结果表明,电迁移导致了低银无铅微尺度焊点的抗拉强度显著降低,并且随着电流密度的增加或通电时间的延长,焊点的抗拉强度均呈下降趋势;同时电迁移还导致焊点的拉伸断裂模式发生明显变化,在经历高电流密度或长时间通电的电迁移后,焊点在服役条件下会发生由韧性断裂向脆性断裂的转变. 此外含银量高的微尺度焊点的抗电迁移性能更强.     

High infrared transmission of Y-Yb-doped α-SiAlON

Dense dual Y³⁺-Yb³⁺-doped α-SiAlON ceramic containing extra addition of 2 wt.% Y₂O₃/Yb₂O₃ was fabricated by hot pressing at 1900 °C for 1 h, and its optical transmittance was investigated over the wavelength range 200-6000 nm. The results showed that the addition of 2 wt.% extra liquid phase could effectively promote Y/Yb-α-SiAlONs densification and its assemblage only consisted of single crystallized α-SiAlON phase. The obtained sample had relatively high infrared light transmittance properties. The maximum transmittance in the medium infrared region for 1.0 mm thick specimen could reach around 72% at ~ 2500 nm. It is attributed to the uniform, dense microstructure and few residual intergranular phases.     

电子和光子封装无铅钎料的研究和应用进展

对目前国内外电子和光子封装用无铅钎料研究和应用的新进展和发展趋势进行了回顾、评述和展望,重点评述了无铅钎料的种类和钎焊接头的力学性能、封装结构的可靠性和耐久性,以及目前出现的影响电子封装可靠性的一些新问题(如电迁移和锡须问题).对光子封装钎料和相关钎焊工艺也进行了简要评述.最后,探讨了电子和光子封装无铅钎料及其可靠性和耐久性研究的发展趋势.     

基于内点法考虑风电穿透率的区域间可用输电能力研究

根据鼠笼异步风力发电机（SCIM）无功功率对机端电压和有功功率的表达式,修正了原-对偶内点法中的雅可比矩阵和海森矩阵,协调了算法的计算精度与迭代效率。采用连续潮流法计算了不同节点的穿透功率极限,得到SCIM和恒功率因数控制的双馈感应风力发电机（DFIG）不同穿透率下的可用输电能力（ATC）值。仿真结果表明,联络区域节点接入风电场大幅提升送电区与受电区间的ATC,而对于送电区的风电接入情况结论相反;DFIG的功率因数对ATC有较大的影响;通过合理的补偿措施可解决某些并网方式下算法收敛于局部最优解的问题,多节点电压越限为陷入局部最优的主因。