多年冻土区高温冻土融化固结变形理论研究

为研究多年冻土区高温冻土的变形机制,分析了高温冻土与融土在物理力学性质方面的相似性,基于高温冻土具有未冻水量高、相变剧烈、压缩性大及渗透性相对较高的特点,尝试将其变形机理考虑为固结。在文中提出了一种移动区间法用以计算冻土融化固结,基于孔隙冰、水压力相互转化的融化固结模型,采用移动区间法模拟了融化区及高温冻土区的孔隙水压力变化。数值模拟结果表明:孔隙水压力分布曲线的拐点对应于相变温度,融土区由于渗透系数较大、排水条件好而使得孔隙水压力消散较快,相应的孔隙水压力较小;高温冻土区由于渗透系数相对较小,不能及时排水,因此孔隙水压力较高。

1533年狮子座流星雨亮度的有关研究

根据中国史书和地方志中的记载，１５３３年１０月２３—１１月４日出现的狮子座流星雨，是历史上最盛大的一次流星雨过程。不但出现“天尽赤”、“光著门户”和“唧唧有声”这种空前未有的现象，而且还出现“吓得舟人不敢渡船”的白昼流星雨。本文按历史记载情况，并把它与１８３３年１１月１２日的流星雨比较，估计了流星雨的密度，应用融化理论和能量方程，结合狮子座流星物质的特点，以及大量激流星物质的作用，计算出“天赤”的亮度可达到１ｍ—－１ｍ星等。本文还就本世纪５０年代外国天文学家对这群流星群的物质结构模型、几个主要参数及其曲线做了一些分析和探讨。

Superheating and melting behaviors of Ag clusters with Ni coating studied by molecular dynamics and experiments

Using molecular dynamics with embedded-atom-type interatomicpotentials, we simulated the melting behavior of a spherical Ag3055 cluster coated with Ni. The semi-coherent Ag/Ni interface formed at low temperatures acts as an effective barrier against the surface melting and leads to a substantial superheating of the Ag cluster. The melting point was found to be about 100 K above the equilibrium melting point of the bulk Ag crystal (1230 K±15 K) and about 290 K above that (1040 K) of the free Ag3055 cluster. A superheating of 70 K was observed in the high-temperature differential scanning calorimetry measurement for Ag particles with a mean size of 30 nm embedded in Ni matrix prepared by means of melt-spinning. Melting is initiated locally at the defective interfacial area and then propagates inwards, suggesting a heterogeneously nucleated melting event at the Ag/Ni interface.