Records of the Moon‐forming impact and the 470 Ma disruption of the L chondrite parent body in the asteroid belt from U‐Pb apatite ages of Novato (L6)     

Qing‐Zhu Yin  Qin Zhou  Qiu‐Li Li  Xian‐Hua Li  Yu Liu  Guo‐Qiang Tang  Alexander N. Krot  Peter Jenniskens 《Meteoritics & planetary science》2014,49(8):1426-1439

Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U‐Pb isotope systematics of coarse Cl‐apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U‐Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U‐Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon‐forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar‐Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.  相似文献   

大震前P波出射角和方位角的异常变化     

郭瑞芝  冯德益  陈化然 《大地测量与地球动力学》1995,(3)

给出了数字化地震记录Ｐ波初始部分平均出射角和方位角的分析处理方法，研究了山西大同ＭＬ＝６．１级地震以及唐山ＭＬ＝５．６级地震前出射角与方位角出现的异常变化，并对地震前地震波动力学特征的这一类前兆异常现象进行了初步讨论。  相似文献   

FEM for Stability Analysis Against Overturning of Portal Water Injection Sheet Pile     

LIU Lingyun GUO Haiyan SUN Qi 《中国海洋大学学报(英文版)》2006,5(3):269-272

Portal water injection sheet pile （PWISP）, as a retaining wall, appeared in seashore engineering in 2000. Although there have been many systematic methods addressing the issue, there are very few focusing on the new structure because of the difficulties in defining the earth pressure between the two piles. A new method is proposed in this paper to obtain the earth pressure between the PWISPs. Stability analysis against overturning follows as a consequence. Using Finite Element Analysis （FEA） software ANSYS, both the nonlinear characteristics of the soil and those of the contact elements are taken into account to obtain the earth pressure distribution on the contact surface. Based on the results of the FEA, Rankin＇s theory and the slip plane theory, the formula of the earth pressure on the inner surfaces between the piles is given. Assuming the PWISP as the analysis object and the earth pressure as an outside force acting upon it, the equation of stability against overturning of the PWISP is presented. Finally, some parameters are discussed about the stability of the PWISP against overturning, such as the embedded depth of the front pile, the distance between the two rows of piles, the internal friction angle and the cohesion of the earth. The results show that the increase of the cohesion and the internal friction angle will decrease the distance and the embedded depth, and therefore enhance the stability against overturning. Specifically, when the distance is 1/3-2/3 of the maximal excavation depth, the two rows of piles give the best performance in stability.  相似文献   

Variations mechanism in entropy of wave height field and its relation with thermodynamic entropy     

郭佩芳侯一筠  钱成春周良民 《中国海洋湖沼学报》2006,24(1):65-68

  相似文献   

通往诚信之路:从"政府监管"到"市场激励"     

李国  张永清 《成都信息工程学院学报》2005,20(3):362-364

从市场机制对诚信建构的作用说起，通过对我国现行会计监管方式和实施机制的分析，认为现行会计监管方式难以实现其预定的目标。同时笔者对此问题的解决做出了思考。  相似文献   

变质岩的变质序列分析──以辽河群为例     

郭洪方 《国土资源》1994,(Z1)

通过对辽河群岩石中主要变质矿物的观察和研究，以岩石的变形历史作为变质结晶作用的相对时标，确定了矿物生长的时序特征及其演化过程。发现变质与变形既是有密切联系的又是各自独立的地质作用，辽河期的变形作用存在明显的３个变形幕，而辽河期的变质作用是个连续的完整的过程，无明显的热波动。变质作用高峰和变形作用高峰存在时间差。  相似文献   

Topographic zonation of infiltration in the hilly loess region,north china     

Gang Li  Shiu Hung Luk  Qiang Guo Cai 《水文研究》1995,9(2):227-235

Field infiltration tests using portable rainfall infiltrometers were conducted in the Wangjiagou experimental basin in the hilly loess region of north China. Based on data collected at 27 sites, a topographic zonation of infiltration characteristics was observed. The average steady infiltration rate and the average ponding time decreased from the hilltop to the hillslope and further decreased to the gully wall. Such a zonation is closely related to the variations of topography, soil and land use conditions in the study area. A general infiltration model is proposed. Collected field data are used to establish the applicability of the proposed model in the study area.  相似文献   

语用迁移与跨文化交际能力的培养     

郭遂红 《广东海洋大学学报》2002,22(2):78-81

随着我国改革开放的进展 ,跨国度、跨文化之间的交往越来越频繁。由于文化因素上的差异 ,交际行为在不同的文化中往往产生不同的意义 ,语用迁移难免会造成理解失误或交际失败。因而外语教学在培养学生整体语言技能的同时 ,应注意文化因素的渗透 ,提高学生的跨文化交际能力  相似文献   

The spectra of gamma-ray bursts and emission features     

Shi Tianyi  Guo Qiushuang 《Astrophysics and Space Science》1990,167(2):317-327

We present a new two-component method of fitting spectra of cosmic gamma-ray bursts, to get some information about the emission regions through this kind of fit. Our results support the existence of structure in the thin emission sheet. The peak appearing at about 780 ke V in the spectrum of GB 781119³ seems not to be a one-photon annihilation line.Project supported by the National Nature Science Foundation of China.  相似文献   

解流体动力弥散问题的等参数溶质质量均衡近似有限元法     

郭东屏 《地球科学与环境学报》1990,(3)

本文根据流体动力弥散理论,按地下水中溶质局部质量守恒原理,采用非线性基函数,对单元内的渗透速度和弥散系数作了平均化近似处理,导出了求解流体动力弥散问题的另一种新的数值法——等参数溶质质量均衡近似有限元法。与作者在文献〔1〕中给出的较精确的算法相比,虽不甚精细,但计算工作量大为减小,并保持了文献〔1〕中方法的主要优点,比较简便易行。  相似文献