Theoretical calculations of hardness and metallicity for multibond hexagonal 5d transition metal diborides with ReB_2 structure

The hardness, electronic, and elastic properties of 5d transition metal dibofides with ReB2 structure are studied theoretically by using the first principles calculations. The calculated results are in good agreement with the previous experimental and theoretical results. Empirical formulas for estimating the hardness and partial number of effective free electrons for each bond in multibond compounds with metallicity are presented. Based on the formulas, IrB2 has the largest hardness of 21.8 GPa, followed by OsB2 （21.0 GPa） and ReB2 （19.7 GPa）, indicating that they are good candidates as hard materials.

高速PCB差分插入损耗影响因素研究

随着信号速率的提升,板级插入损耗得管控变得越来越重要,我们不能只满足插入损耗越小越好,同时需关注插入损耗的均一性要求;本文主要基于PLTS的测量方法,测试不同PCB结构设计的差分插入损耗变化情况,通过对PCB生产过程中的棕化条件、铜箔类型、阻焊油墨类型、孔径、线宽、线距、背钻残桩、介质厚度、铜厚等关键因子进行研究,为板级插入损耗的有效管控提供了基本的参考。

多连键图法在车辆系统动力学中的应用

本文用多连键图技术来模拟一铁道车辆系统,该系统具有17个自由度。通过编写子程序将非线性的轮轨相互作用力定义为子模型,与系统的键图模型相连接。最后,本文对车辆以恒速在圆曲线轨道上运行的动力学特性进行了简单的分析计算。