川藏铁路石灰石粉–水泥基材料抗低温硫酸盐侵蚀研究

为研究川藏铁路掺石灰石粉混凝土抗低温硫酸盐侵蚀性能,通过对低温硫酸盐溶液浸泡侵蚀和电脉冲低温硫酸盐侵蚀作用下掺不同石灰石粉的水泥基材料的外观侵蚀变化等级、质量评价参数、抗压强度评价参数、孔隙特征以及侵蚀产物的测试,研究了低温环境下石灰石粉掺量对水泥基材料硫酸盐侵蚀行为的影响规律,并建立非单调Wiener随机过程模型对低温环境下石灰石粉-水泥基材料硫酸盐侵蚀服役寿命进行了预测。结果表明:（1）低温环境下硫酸盐浸泡侵蚀反应缓慢,侵蚀周期内,石灰石粉-水泥基试件外观未出现可见剥落、质量持续增加;强度先提高后降低,在侵蚀120d时出现转折;孔隙先细化后劣化,在侵蚀90d时出现转折;在侵蚀180d时有少量碳硫硅钙石生成。（2）电脉冲加速了低温环境下石灰石粉-水泥基硫酸盐侵蚀反应,电脉冲低温硫酸盐侵蚀60d时,试件表面开始剥落,质量和强度下降,内部孔隙劣化。石灰石粉掺量越多,碳硫硅钙石侵蚀破坏就越严重,石灰石粉掺量为40%的试件在侵蚀60d时就有碳硫硅钙石生成,而石灰石粉掺量为10%、20%的试件在侵蚀90d才生成碳硫硅钙石。（3）基于Wiener随机过程的可靠性寿命退化分析表明,电脉冲低温硫酸盐侵蚀作用下掺10%、20%和40%石灰石粉-水泥基材料室内加速侵蚀寿命分别为265d、130d及105d。     

界面电荷对圆柱形高kVDMOS的影响仿真研究

相比于传统VDMOS,超结耐压层结构和高k介质耐压层结构VDMOS能实现更高的击穿电压和更低的导通电阻.通过仿真软件,对3D圆柱形高k VDMOS具有、不具有界面电荷下的各种结构参数对电场分布、击穿电压和比导通电阻的影响进行了系统总结.研究和定性分析了击穿电压和比导通电阻随参数的变化趋势及其原因.对比导通电阻和击穿电压...     

基于响应面法的复式钢箱提篮拱地震可靠度分析

地震可靠度是桥梁抗震研究中的重要问题.基于随机分析的响应面理论和规范反应谱法,提出了一种分析具有随机结构参数的桥梁地震可靠度的方法,研究了复式钢箱提篮拱桥在地震激励下,结构设计基准期内的可靠度.分析时考虑了结构参数和场地土的随机性,分别计算了钢箱提篮拱桥主、副拱肋在多遇地震、设防地震和罕遇地震作用下的失效概率,得到了主、副拱肋在设计基准期内,按规范"三水准设防标准"条件下的地震可靠度.计算结果表明,该桥设计满足抗震规范要求.     

UTR*-Tree:受限网络中移动对象不确定轨迹索引模型

受限网络中移动对象不确定轨迹的有效索引是移动对象数据库中的研究重点.针对现有方法的不足,提出了一种新的不确定轨迹索引结构UTR~*-Tree.该索引结构采用静态和动态相结合存储管理移动对象,将变化极小的受限道路网络作为静态部分使用2维空间R~*-Tree进行管理;将移动对象位置则作为动态信息采用R~*-Tree和Hash数组协同管理.借助该结构,移动对象数据库不仅可以快速地处理对移动对象过去可能位置的查询,而且能够对其现在及将来的可能位置进行高效的查询处理.实验结果表明同目前有代表性的轨迹索引结构UTR-Tree相比,该索引结构在维护性能上提高了一个数量级,在查询性能上平均提高了约25%.     

Optimisation of two-step sintering parameters to produce bioactive and dense zirconia-hydroxyapatite composite ceramics

3Y-TZP along with Hydroxyapatite (HAp) are common bioceramics used in bone tissue engineering scaffolds to yield better patient outcomes and faster healing times. However, significant differences in thermal expansion of these ceramics result in challenges to co-sintering these materials without losing functionality and strength. In this work, a two-step sintering (TSS) process was utilised to co-sinter composites using (1-x)3Y-TZP and xHAp where x varies between 20 and 80 wt%. A peak temperature of 1300 °C, a plateau temperature of 1175 °C, a holding time of 600 min and heating rate of 10 °C/min were the optimum TSS conditions for all compositions. The TSS process produced specimens with grain sizes between 0.5 and 1.2 µm and a compression strength between 88 and 176 MPa. The similarity in compression strength of these zirconia-hydroxyapatite composites with natural bone and the retention of HAp make them suitable for bone tissue engineering applications in load bearing areas.     

Effects of doping cations on the densification and microstructure of flash-sintered α-Al2O3

The effects of dopants with different valences on the flash sintering behavior of α-Al₂O₃ are investigated. The results indicate that regardless of their valence and ionic radius, all the tested dopants reduce the onset temperature more effectively compared to undoped Al₂O₃. Interestingly, the relative density and grain size of the flash-sintered samples exhibit an inverse linear relationship. The data for the samples doped with non-trivalent cations fall on a different line than those for the samples doped with trivalent cations and the undoped samples. Dopants have an effect on the flash sintering behavior of Al₂O₃ because flash sintering increases the solubility of the dopants in alumina, creating more point defects, and thereby increasing the electrical conductivity of the material. The mechanisms for point defect generation in trivalent and non-trivalent dopants are different.