Insight into excess pore pressure generation leading to liquefaction of sand with stress history under saturated and unsaturated conditions

Assessments of the liquefaction resistance of clean sand still involve considerable uncertainties, which are a current research topic in the field of soil liquefaction. The factors considered and discussed in this study include the loading history, degree of saturation, and partial drainage. The effects of each of these factors on pore pressure generation and liquefaction resistance have been studied for decades in the laboratory, and empirical relationships have been derived. In this paper, an attempt is made to explain these effects using the unique index of volumetric strain. A pore pressure generation model is developed which is similar to that of Martin et al. (1975), but based on stress-controlled triaxial tests. The model is verified through comparisons of its results with those of laboratory tests. It is confirmed that the plastic volumetric strain that has accumulated in sand, either by drained or undrained cyclic loading, dominates the increase in the liquefaction resistance of the sand. However, the plastic volumetric strain caused by overconsolidation is less effective in reducing the volumetric strain potential for subsequent cyclic shearing, thus enhancing its resistance to liquefaction. The model provides a better understanding of the physical processes leading to the liquefaction of saturated and unsaturated sand with and without stress history.     

3-RRR球面并联机构的工作空间分析及结构优化

根据Kutzbach-Grübler修正公式分析了球面3-RRR并联机构的自由度个数以及性质,采用哈密顿"四元数"对关节矢量进行描述并建立了逆运动学数学模型,找出了动平台运动时连杆之间、连杆与电机主轴相互之间的碰撞干涉条件。根据运动学逆解以及碰撞干涉条件,基于Mathematica软件完成了可达工作空间的分析,绘制了球面并联机构的工作空间形状,给出了工作空间的极限位置。以工作空间的最大化为目标对并联机构进行了结构优化设计,使动平台实现了完整的球面工作空间。     

线型低密度聚乙烯溶液接枝聚甲基丙烯酸甲酯

用溶液接枝聚合的方法在线型低密度聚乙烯(LLDPE)上接枝聚合极性单体甲基丙烯酸甲酯(MMA)制备LLDPE-g-PMMA,研究了反应时间、单体用量和引发剂用量对接枝反应的影响。结果表明,随着引发剂和单体量的增加,聚合物的接枝率增加,当引发剂质量分数为0.48%,单体比率为150%时,接枝率将达到26.1%。利用红外光谱(FTIR)、核磁共振碳波谱仪(13C-NMR)对其进行结构表征,证明PMMA分子链被接枝聚合到LLDPE上。使用X射线衍射仪(XRD)、差示扫描量热仪(DSC)对接枝聚合物的结晶性能进行了分析,发现接枝聚合没有改变晶型,但结晶焓由61.39 J/g降低到47.18 J/g。     

海上平台电气设备的防爆与防护等级分类

海洋石油平台上电气设备的防爆防护工作是非常重要的,这关系着平台操作人员的自身安全,以及平台甚至整个油田的安全生产。中国海油提出并已执行的＂五想五不干＂,也都是基于安全的考虑,最大限度避免人员伤亡、财产损失。因此在平台设计、建造、投产以及后期改造过程中,都要注意电气设备的防爆与防护。     

宅基地置换小区居民满意度评价体系研究

在我国城市化快速推进的过程中,随着我国城市郊区宅基地置换工程的实施和完善,急需一套完整的宅基地置换小区规划效果评价体系。该文针对我国已经成功规划建设的宅基地置换小区,构建了一套宅基地置换小区居民满意度评价体系,该评价体系主要从定量、定性相结合的角度进行综合评价,通过量化、动态检测我国宅基地置换工程的实施成效,填补了规划效果评价领域里的技术空白,具有一定的实际意义与推广价值。     

Inhibition of Bacillus cereus spore outgrowth and multiplication by chitosan

Bacillus cereus is an endospore-forming bacterium able to cause food-associated illness. Different treatment processes are used in the food industry to reduce the number of spores and thereby the potential of foodborne disease. Chitosan is a polysaccharide with well-documented antibacterial activity towards vegetative cells. The activity against bacterial spores, spore germination and subsequent outgrowth and growth (the latter two events hereafter denoted (out)growth), however, is poorly documented. By using six different chitosans with defined macromolecular properties, we evaluated the effect of chitosan on Bacillus cereus spore germination and (out)growth using optical density assays and a dipicolinic acid release assay. (Out)growth was inhibited by chitosan, but germination was not. The action of chitosan was found to be concentration-dependent and also closely related to weight average molecular weight (M_w) and fraction of acetylation (F_A) of the biopolymer. Chitosans of low acetylation (F_A = 0.01 or 0.16) inhibited (out)growth more effectively than higher acetylated chitosans (F_A = 0.48). For the F_A = 0.16 chitosans with medium (56.8 kDa) and higher M_w (98.3 kDa), a better (out)growth inhibition was observed compared to low M_w (10.6 kDa) chitosan. The same trend was not evident with chitosans of 0.48 acetylation, where the difference in activity between the low (19.6 kDa) and high M_w (163.0 kDa) chitosans was only minor. In a spore test concentration corresponding to 10²-10³ CFU/ml (spore numbers relevant to food), less chitosan was needed to suppress (out)growth compared to higher spore numbers (equivalent to 10⁸ CFU/ml), as expected. No major differences in chitosan susceptibility between three different strains of B. cereus were detected. Our results contribute to a better understanding of chitosan activity towards bacterial spore germination and (out)growth.     

胰蛋白酶水解酪蛋白进程研究

研究了碱性务件下胰蛋白酶对酪蛋白的水解，用甲醛固定法对蛋白质的水解度进行测定，并用水解度（DH）表征其反应历程。分析了底物浓度、酶浓度、时间、pH和温度对DH、水解速度的影响。     

四组分混纺针织纱的开发实践

探讨改性涤纶纤维、丝麻改性粘胶纤维、粘胶纤维、精梳棉四组分混纺纱的生产要点。介绍了改性涤纶纤维、丝麻改性粘胶纤维的性能特点,并与普通粘胶纤维、普通涤纶纤维性能进行了对比。重点论述了原料选配、原料预处理、各工序工艺优化配置等技术措施。认为:优选各项技术措施后,可以确保纺纱顺利,开发出的四组分混纺纱的质量水平能满足最终产品要求。     

超细旦丙纶梳棉工艺研究

根据超细旦丙纶纤维的纺纱特性，对梳棉工序的纺纱工艺进行了研究。认为纺超细旦丙纶纤维时，应减少梳棉喂入量，降低刺辊分梳强度，增强锡林刺辊间的转移能力，增加道夫转移率，减少纤维的平均梳理时间并选择适宜的针布等。     

斜轴式高效混料机关键技术参数分析

在综合分析传统混料机的基础上,对所设计的新型斜轴式高效混料机关键技术进行参数分析。根据斜轴式混料机新型的逆向搅拌原理即搅拌筒体和搅拌轴逆向旋转,利用AUTOCAD画出二维原理图。采用DEM离散元分析方法,使用Solid Works为三维建模软件,将模型导入EDEM中,运用Hertz Mindlin(no lips)无滑动接触模型,模拟仿真混料机筒体倾斜角度、搅拌轴位置以及搅拌叶片长度变化对混合效果的影响,重点介绍简化三维模型的导入、定义仿真参数及后处理图表的分析技术。此方法分析为同类混料机的设计改进提供了方法,具有较高的实用价值。