Surviving Mass Extinctions through Biomineralized DNA

Even in the worst of conditions, such as those which occurred during mass extinction events, life on Earth never totally stopped. Aggressive chemical and physical attacks able to sterilize or poison living organisms occurred repeatedly. Surprisingly, DNA was not degraded, denatured or modified to the point of losing the capability of transferring the genetic information to the next generations. After the events of mass extinction life was able to survive and thrive. DNA was passed on despite being an extremely fragile biomolecule. The potential implications of hydroxyapatite protection of DNA are discussed in this Concept article including how DNA acts as a template for hydroxyapatite (HAp) formation, how cell death can trigger biomineralization, and how DNA can be successfully released from HAp when the conditions are favorable for life.     

脉冲输入毒素对具有阶段结构的单种群生存影响的研究

研究了一类小容量污染环境中脉冲输入毒素对具有阶段结构的单种群生存问题,分别找到了种群生存与灭绝的阈值,利用不等式放缩技巧,得到了种群灭绝和持久生存的充分条件.利用MATLAB数值仿真,验证了理论结果的正确性,分析了毒素输入量,毒素输入周期及种群成长时间对种群生存的影响.     

捕食者和食饵均带有扩散的随机捕食-食饵模型动力学分析

考虑了斑块环境下捕食者种群和食饵种群分别在n个斑块扩散的随机捕食 食饵模型.利用Lyapunov函数法证明了对任意给定的初始值,随机系统全局正解的存在唯一性,并对其进行了有界性分析.此外给出了食饵种群及整个系统灭绝的充分条件.最后通过数值模拟验证了所得理论的正确性.     

A non-linear model for the dynamics of open cross-section thin-walled beams—Part I: formulation

A non-linear one-dimensional model of inextensional, shear undeformable, thin-walled beam with an open cross-section is developed. Non-linear in-plane and out-of-plane warping and torsional elongation effects are included in the model. By using the Vlasov kinematical hypotheses, together with the assumption that the cross-section is undeformable in its own plane, the non-linear warping is described in terms of the flexural and torsional curvatures. Due to the internal constraints, the displacement field depends on three components only, two transversal translations of the shear center and the torsional rotation. Three non-linear differential equations of motion up to the third order are derived using the Hamilton principle. Taking into account the order of magnitude of the various terms, the equations are simplified and the importance of each contribution is discussed. The effect of symmetry properties is also outlined. Finally, a discrete form of the equations is given, which is used in Part II to study dynamic coupling phenomena in conditions of internal resonance.     

在同位旋空间中正反质子弹性散射的重整化混合圈链图效应

本文采用描述荷电和中性 pion 介子与核子-反核子强相互作用的同位旋SU(2)不变耦合模型,计算出在 pion0 重整化混合圈链图传播下 p pbar -> p pbar 弹性散射微分截面的“精确”解析结果;并且将此结果与在 pion0 树图传播下的微分截面作了对比分析,得到相应的辐射修正重要信息。本文完成的工作对进一步深入研究 pion 介子与核子-反核子强相互作用的同位旋SU(2)不变耦合模型以及深入理论探讨正反质子对撞实验,都将提供理论研究的参考价值。     

金属目标原子晶格结构对其量子雷达散射截面的影响

量子雷达散射截面是描述光量子态照射下目标可见性的重要参数. 本文对量子雷达散射截面的推导进行了扩展, 使其可以应用于非平面凸目标的QRCS计算. 针对面心立方、体心立方以及密排六方三种金属原子晶格所构成的目标的量子雷达散射截面进行了计算, 结果表明不同的原子排列方式下, 目标QRCS主瓣基本不变, 而量子旁瓣在原子排列稀疏的目标中更为明显.     

在容量较小的污染环境中二维捕食系统的持续生存与绝灭

利用极限理论及积分均值法研究了在容量较小的污染环境中毒素对二维Lotka-Volterra捕食被捕食系统持续生存与绝灭的影响,给出了捕食种群与食饵种群弱平均持续生存和绝灭的充分条件.     

独立同分布随机环境中两性Galton-Watson分支过程灭绝概率的渐近行为

本文研究了独立同分布随机环境中的两性Galton-Watson分支过程,在上临界情形下,当k充分大时,qk≤ck<'-α>.     

变刚度梁柱理论及其应用

为解决井斜控制实践中存在的不等截面尺寸梁柱问题, 讨论了典型的变刚度纵横弯曲梁力学 模型. 根据变刚度梁柱变形的挠曲线微分方程和边界条件及连续条件, 得到了梁柱变形和端 部转角的解析计算式, 进而应用梁柱理论叠加原理可解决有集中力作用下的井下控制工具和 带变径稳定器的底部钻具组合(BHA)受力分析问题. 变刚度梁柱理论在BHA力学分析中得到了 成功应用, 为井下控制工具设计、钻具组合优化及井斜控制提供了理论依据.     

Dynamical behavior of a hybrid switching SIS epidemic model with vaccination and Lévy jumps

In this paper, the dynamical behavior of a hybrid switching SIS epidemic model with vaccination and Lévy jumps is considered. Besides a standard geometric Brownian motion, another two driving processes are taken into account: a stationary Poisson point process and a continuous time finite-state Markov chain. Firstly, we establish sufficient conditions for persistence in the mean of the disease. Then we obtain sufficient conditions for extinction of the disease. In addition, we also establish sufficient conditions for the existence of positive recurrence of the solutions to the model by constructing a suitable stochastic Lyapunov function with regime switching.