具有规则表面织构的超高分子量聚乙烯髋臼表面温度分析

就人工关节中广泛使用的超高分子量聚乙烯(UHMWPE)髋臼在运行中的瞬态表面温度场进行了理论计算,与理想光滑表面对比考察了微球表面织构对接触压力分布的影响及其引起的表面温度变化.结果表明,基于光滑表面计算得到的髋臼表面温度偏低,而基于规则织构表面计算得到的温度与文献值接近;髋臼表面温度随摩擦系数和载荷增加而升高,随关节摆动而呈现周期性变化.     

Dynamics of a stochastic rumor propagation model incorporating media coverage and driven by Lévy noise

With the development of information technology, rumors propagate faster and more widely than in the past. In this paper, a stochastic rumor propagation model incorporating media coverage and driven by Lévy noise is proposed. The global positivity of the solution process is proved, and further the basic reproductive number R₀ is obtained. When R₀ < 1, the dynamical process of system with Lévy jump tends to the rumor-free equilibrium point of the deterministic system, and the rumor tends to extinction; when R₀ > 1, the rumor will keep spreading and the system will oscillate randomly near the rumor equilibrium point of the deterministic system. The results show that the oscillation amplitude is related to the disturbance of the system. In addition, increasing media coverage can effectively reduce the final spread of rumors. Finally, the above results are verified by numerical simulation.     

Rayleigh Scattering for An Electromagnetic Anisotropic Medium Sphere

Based on the scales theory of electromagnetic waves, the analytical expression of electrical fields inside an anisotropic medium sphere is studied. Differential scattering cross section and radar cross section （RCS） for an anisotropic spherical target are presented. The correctness of the obtained results is tested. The simulation results show that the scattering of an anisotropic sphere has the property of a dipole radiation under the condition of Rayleigh scattering. The larger the dielectric constant is, the stronger the dipole scattering is. Anisotropy in magnetism only has an effect on differential RCS. These results provide a theoretical base for the identification of anisotropic targets.     

退火温度和溅射时间对磁控溅射法制备Mg2Si薄膜的影响

采用磁控溅射法和原位退火工艺在钠钙玻璃衬底上制备 Mg2Si 薄膜。首先在钠钙玻璃衬底上交替溅射沉积两层Si、Mg 薄膜,冷却至室温后原位退火4 h,制备出一系列 Mg2Si 薄膜样品。通过 X 射线衍射仪(XRD) 、 扫描电子显微镜(SEM)对所得薄膜样品的晶体结构和表面形貌进行表征, 讨论了退火温度和溅射Si/Mg/Si/Mg 时间对制备 Mg2Si 薄膜的影响。结果表明,采用磁控溅射法在钠钙玻璃衬底上交替溅射两层Si、Mg 薄膜, 通过原位退火方式成功制备出单一相的 Mg2Si 薄膜,溅射Si/Mg/Si/Mg 的时间为12.5/9/12.5/9 min,退火温度为550 ℃ 时,制备的 Mg2Si 薄膜结晶度最好,连续性和致密性最强。这对后续 Mg2Si 薄膜器件的设计与制备提供了重要的参考。 积两层Si、Mg 薄膜, 冷却至室温后原位退火4 h, 制备出一系列 Mg2Si 薄膜样品. 通过 X 射线衍射仪(XRD) 、 扫描 电子显微镜(SEM)对所得薄膜样品的晶体结构和表面形貌进行表征, 讨论了退火温度和溅射Si/Mg/Si/Mg 时间 对制备 Mg2Si 薄膜的影响. 结果表明, 采用磁控溅射法在钠钙玻璃衬底上交替溅射两层Si、Mg 薄膜, 通过原位退火 方式成功制备出单一相的 Mg2Si 薄膜, 溅射Si/Mg/Si/Mg 的时间为12.5/9/12.5/9 min, 退火温度为550 ℃ 时, 制 备的 Mg2Si 薄膜结晶度最好, 连续性和致密性最强. 这对后续 Mg2Si 薄膜器件的设计与制备提供了重要的参考.     

室温离子液体法合成新型三维共价有机骨架材料

采用室温离子热法合成了一种氟取代的具有五重贯穿金刚石拓扑结构的三维共价有机骨架材料(COFs), 记为JUC-515. 与高温溶剂热法不同的是, 室温离子液体法具有反应温度和压力低、 反应时间短、 操作简单、 无需催化剂和不产生有机蒸汽污染等优势. 制备的材料具有高度结晶性、 较大的孔隙率和良好的CO₂选择性吸附性能.     

冬小麦冻害胁迫高光谱分析与冻害严重度反演

对冬小麦冻害严重度的精确反演是及时采取补救措施降低损失的关键,同时及时预测产量损失对政府职能部门也具有积极意义。针对冬小麦冻害群体严重度评估方法在经典统计反演模型存在估算效果不理想的情况下,以冬小麦为试验对象,首先对冬小麦冠层光谱反射率数据进行重采样平滑处理,再用主成分分析(PCA)技术对高光谱数据进行分析,进一步实现综合原始光谱主成分信息作为自变量参与冬小麦冻害严重度反演过程,最后采用决定系数R2、均方根误差RMSE、准确度Accuracy三种模型精度验证方法对模型进行评价。结果显示,基于主成分分析法建立冬小麦冻害严重度模型精度分别达0.697 5,0.184 2和0.697 5;同时对反演模型进行验证,其精度也分别达到0.630 9,0.350 3和1.339 6。因此,该方法能有效地对冬小麦冻害严重度进行快速、精确的反演。     

海洋平台的时域低阶建模与主动控制研究

以海洋平台为对象, 开展时域低阶建模与主动控制的研究. 首先采用OKID(observer/Kalman filter identification)辨识方法, 根据系统的输入和输出时间历程数据计算出系统的Markov参数, 然后采用特征系统实现方法(eigensystemrealization algorithm, ERA)建立起一个阶数较低的系统状态空间模型, 随后基于该低阶模型采用LQG (linear quadratic Gaussian)控制方法进行控制律的设计, 最后将该控制律引入到系统的有限元模型中进行反馈闭环控制, 验证控制律的有效性. 数值仿真结果显示, 所给方法是有效和可行的.      

Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations

Several rocksalt Sr₄X₃N (X=,O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr₄X₃N possibly have higher Curie temperatures and have more stable half metallicity than the Sr₄X₃C. Their crystal-cell magnetic moments are all 1.00 μ_B. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp² hybridized orbitals in the Sr₄X₃N. Then two Sr-5s and three N-2p electrons enter into three sp² hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp² hybridized orbitals.