Effect of weld characteristics on the formability of welded tubes in NC bending process

The weld profiles, weld width, weld positions, and mechanical property changes in the weld and heat-affected zones (HAZ) are the most important parameters that influence the potential formability of the welded tube. To investigate the effect of weld characteristics on the forming behaviors of the welded tube, finite element models which consider the geometric profile and mechanical properties of the weld and HAZ are employed. The results show that (1) the mechanical constitutive relation of the weld region determined by the microhardness empirical formula obviously decreases the tangent strain, thickness strain, and cross-sectional deformation ΔD in the weld and HAZ as compared with that determined by the improved rule of mixtures, which is contrary to the hoop strain, and the predicted results determined by the improved rule of mixtures are much closer to the experimental ones; (2) different weld and HAZ widths determined by the microhardness profile and metallographic section have a little effect on the tangent strain, thickness strain, and ΔD distribution; (3) the implementation of weld profile and material properties decreases the wall variation of the weld region as the weld line locates on the outside and inside. On the contrary, both the weld profile and weld material properties increase the maximum ΔD. The sectorial weld profile has a stronger effect on the wall variation and maximum ΔD than the hourglass profile; and (4) the same weld and HAZ volume have a stronger effect on wall thinning and ΔD.     

Fractionation and characterization of ɛ-poly-l-lysine from Streptomyces albulus CGMCC 1986

ɛ-Poly-l-lysine (ɛ-PLL) produced by Streptomyces albulus CGMCC 1986 was fractionated using ultra-filtration technique with 2 and 5 kDa cut-offs of membrane. The number-average molecular weight of each fraction was determined by ¹H nuclear magnetic resonance (NMR) method. The number-average molecular weights of the cutoffs of 5 and 2 kDa and the filtrate are 4,230.95, 3,687.80, and 1,900.82 Da, respectively. ¹H NMR indicates the chemical shifts of α-H, β-H, γ-H, δ-H, and ɛ-H are very similar to all the fractions. Fourier transform-infrared (FTIR) spectra showed that the ɛ-PLL solid samples obtained by freeze-drying at pH 5 with molecular weights higher than 2 kDa take on a β-turn conformation, however, the fraction with molecular weight smaller than 2 kDa adopts random coil structure. The antibacterial test proved that the fraction between 2 and 5 kDa of membranes behaves the highest antibacterial activity than other fractions for the test strains of Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Escherichia coli, and Shigella.     

京沪高速铁路无锡西桥段跨锡澄高速公路桥水中墩钢板桩围堰的设计与施工

京沪高速铁路无锡西桥段跨锡澄高速公路桥深基坑的施工方案设计、施工进行了总结，对以后同类型桥梁的施工有一定的借鉴意义。     

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH₃)₂]⁺was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

矩阵损失下受约回归系数的可容许线性估计

讨论带有齐次线性等式约束的线性模型:Y=Xβ+ε,ε～(0, σ_V),Hβ=0,在矩阵损失下,我们给出 Sβ的估计 LY(LY+a)在齐次线性(非齐次线性)估计类中可容许的充要条件.     

N型渐开线少齿差行星传动啮合效率的精确计算法

本文全面考虑了齿轮传动的实际啮合情况,推导出计算N型渐开线少齿差行星传动啮合效率的新公式.公式精确、简便、避免了传统的潜在功率法误差放大的缺点.     

除氧器焊接补强计算

计算了除氧器焊接补强时产生的温度场并确定了焊接时其塑性区范围。用有限元法计算得出纵、横焊缝由于补强在原焊缝处及其附近引起的残余应力。通过对残余应力分布状况的分析给出了加强板的适宜宽度和厚度以及加强板的合理布置方案。     

强化工程监理制度以确保高速公路质量

本文介绍了关于高速公路建设中的监理工作,国际贷款的高速公路必须实行监理工程师制度.采用工程质量控制、合同管理、进度控制、投资控制等措施.按照 FIDIC 条款进行监理,是保证高速公路工程质量关键.     

零知识证明的新进展

本文介绍零知识证明方面的两个最新成果，多验证者的广播式证明协议（ＭＶＢＩＰ）与非交互式的知识的零知识证明（ＮＩＺＫＰＫ），给出它们的定义和主要结论，以及在密码体制设计中的应用。     

斜轧线接触矫直辊的设计与调整探讨

线接触矫直辊在实际操作参数与设计给定参数产生偏差时，其线接触特征受到破坏，最终影响矫直效果。本文采用数理分析，探讨了当某一参数在调整中产生偏差时，该偏差和其他参数对线接触破坏程度的影响，并提出了线接触矫直辊设计和调整要点。