研究现今地壳运动和强震机理的一种方法

本文阐述了地壳形变与密度变化耦合运动的基本理论,分析了地壳形变与密度变化耦合运动引起的重力时间变化.断层位错运动是地壳形变与密度变化耦合运动的特殊形式.利用重复重力观测数据,选用稳健算法反演研究了1985-2002年滇西地震实验场主要断裂运动的时间分布和强震响应特征,获得了不同类型强震孕育过程图像.     

触发闪电环境下地网冲击接地电阻特征分析

基于触发闪电技术,研究了2019年夏季8次触发闪电44次回击、5次初始连续电流脉冲（ICCP）和24次M分量对冲击接地电阻的影响,探索了冲击接地电阻随雷电流注入的动态变化规律。结果发现：闪电放电ICCP、M分量和回击过程冲击接地电阻均小于工频接地电阻,ICCP和叠加在回击回落之后连续电流上的M分量冲击接地电阻略大于回击过程,平均值分别为11.2Ω和10.8Ω。叠加在回击下降沿上的M分量冲击接地电阻平均值7.8Ω,明显小于回击过程,最小值可达2.4Ω。ICCP和M分量冲击接地电阻随电流增加而减小,回击过程与电流峰值没有明显的相关性。叠加在回击下降沿上的M分量冲击接地电阻随雷电流峰值、背景电流值的增加呈指数衰减关系,还与之前回击电流峰值成一定的反比例关系。随着闪电回击电流的注入,冲击接地电阻呈现动态变化过程,小电流在回击峰值下降后出现一个缓慢增长的过程,大电流在回击峰值下降后出现一个快速下降的过程。闪电不同物理过程火花和电感效应的作用是不同的,两者共同作用决定了土壤的电离程度,从而决定了冲击接地电阻的大小和变化。     

Urban shrinkage and growth: Measurement and determinants of economic resilience in the Pearl River Delta

Journal of Geographical Sciences - In the aftermath of the global financial crisis of 2008, China witnessed gradual shrinkage of cities in the Pearl River Delta (PRD). In this study, we introduce...     

Heliospheric magnetic fields, energetic particles, and the solar cycle

The heliosphere is the region filled with magnetized plasma of mainly solar origin. It extends from the solar corona to well beyond the planets, and is separated from the interstellar medium by the heliopause. The latter is embedded in a complex and still unexplored boundary region. The characteristics of heliospheric plasma, fields, and energetic particles depend on highly variable internal boundary conditions, and also on quasi-stationary external ones. Both galactic cosmic rays and energetic particles of solar and heliospheric origin are subject to intensity variations over individual solar cycles and also from cycle to cycle. Particle propagation is controlled by spatially and temporally varying interplanetary magnetic fields, frozen into the solar wind. An overview is presented of the main heliospheric components and processes, and also of the relevant missions and data sets. Particular attention is given to flux variations over the last few solar cycles, and to extrapolated effects on the terrestrial environment.     

A possible explanation for the radio afterglow of GRB 980519: the dense medium effect

GRB 980519 is characterized by its rapidly declining optical and X-ray afterglows. Explanations of this behaviour include models invoking a dense medium environment, which makes the shock wave evolve quickly into the subrelativistic phase, a jet-like outflow, and a wind-shaped circumburst medium environment. Recently, Frail et al. found that the latter two cases are consistent with the radio afterglow of this burst. Here, by considering the transrelativistic shock hydrodynamics, we show that the dense medium model can also account for the radio light curve quite well. The potential virtue of the dense medium model for GRB 980519 is that it implies a smaller angular size of the afterglow, which is essential for interpreting the strong modulation of the radio light curve. Optical extinction arising from the dense medium is not important if the prompt optical–UV flash accompanying the γ -ray emission can destroy dust by sublimation out to an appreciable distance. Comparisons with some other radio afterglows are also discussed.     

A self-similar solution for spherically symmetric gravitational collapse

A model of gas-dynamical flow during gravitational collapse is analyzed mathematically by assuming its spherical symmetry and self-similarity. A shock wave diverging from the center emerges in this model. The physical requirements imposed on the post-shock flow at the center for the specified parameters at infinity unambiguously determine the shock front and the flow behind it.     

Sputtering of grains in C-type shocks

Sputtering yields are reported for the release of Mg, Fe, Si and O under impact of He, C, O, Si and Fe on grain material composed of Mg- and Fe-bearing silicates. The yields were derived using the trim code, which simulates the results of the transport of ions in matter by means of classical Monte Carlo techniques. The energetics of the sputtering process are a key factor in the sputtering calculations, and so detailed determinations have been made of the energy with which atoms are bound to the lattice, using solid-state simulation programs. The probability of ejection of an atom is computed at a given energy, for a number of angles of incidence, and integrated to obtain the mean yield at that energy. These numerical results are then fitted with a simple function of energy for convenience in subsequent applications.
A grid of C-type shock models has been computed, using our new sputtering yields, for pre-shock densities in the range 10⁴ n _H n (H)+2 n (H₂)10⁶ cm⁻³ and shock speeds 20 v _s45 km s⁻¹. Sputtered fractions can be high, exceeding 50 per cent for shock speeds in excess of approximately 40 km s⁻¹. The column densities of Si and SiO were also computed, for comparison with observations.     

克氏原螯虾热休克蛋白70 ku类似物基因的cDNA分析

根据已测序的克隆号PCI246基因序列设计2条引物,用快速扩增cDNA末端技术扩增克氏原螯虾(Procambarus clarkii)70 ku热休克蛋白同类物基因cDNA的5'端片段和3'端片段,测序得到1 184 bp基因片段,包含该基因的完整3'端,GenBank登录号AY357302,与GenBank序列号AB016836家蚕(Bombyx mori)的70 ku热休克蛋白同类物mRNA的部分片段83%同源。和果蝇(Drosophila melanogaster)的热休克蛋白同类物3的同源性最高(GenBank的登录号分别是NP_727 563,NP_511 132,NP_727 564,NP_727 565),为85%。     

大黄鱼雌核发育二倍体的人工诱导

采用紫外线照射对大黄鱼(Pseudosciaena crocea Richardson)精子遗传物质进行完全灭活,灭活后精子与卵子受精获得雌核发育单倍体受精卵,再通过冷休克对单倍体受精卵进行倍性恢复,成功诱导出大黄鱼雌核发育二倍体。实验结果表明:(1)在紫外照射过程中照射剂量与大黄鱼精子和卵子受精后其成活率和孵化率呈现出明显的Hertwig效应,紫外照射时间超过2 min(剂量>2 400 ergs/mm2),可使大黄鱼精子遗传物质完全灭活。大黄鱼雌核发育诱导中精子遗传灭活的最适紫外照射时间为2.5 min(剂量为3 000 ergs/mm2);(2)冷休克法可成功抑制大黄鱼受精卵第二极体排放,诱导效果受处理时刻、处理时间和处理温度三因素的影响。综合雌核发育二倍体的诱导率、处理后受精卵早期胚胎存活率和仔鱼孵化率等因素,较适合的染色体加倍条件为23℃培育水温下授精后2 min,在3-4℃海水中处理10 min。