Unique achondrite Northwest Africa 11042: Exploring the melting and breakup of the L chondrite parent body

Northwest Africa (NWA) 11042 is a heavily shocked achondrite with medium‐grained cumulate textures. Its olivine and pyroxene compositions, oxygen isotopic composition, and chromium isotopic composition are consistent with L chondrites. Sm‐Nd dating of its primary phases shows a crystallization age of 4100 ± 160 Ma. Ar‐Ar dating of its shocked mineral maskelynite reveals an age of 484.0 ± 1.5 Ma. This age coincides roughly with the breakup event of the L chondrite parent body evident in the shock ages of many L chondrites and the terrestrial record of fossil L chondritic chromite. NWA 11042 shows large depletions in siderophile elements (<0.01×CI) suggestive of a complex igneous history involving extraction of a Fe‐Ni‐S liquid on the L chondrite parent body. Due to its relatively young crystallization age, the heat source for such an igneous process is most likely impact. Because its mineralogy, petrology, and O isotopes are similar to the ungrouped achondrite NWA 4284 (this work), the two meteorites are likely paired and derived from the same parent body.     

广州城市流浪乞讨者的空间管治与日常生活实践

以广州流浪乞讨者为研究对象,通过深度访谈等质性研究方法,解读针对流浪乞讨者的空间管治政策与手段,分析流浪乞讨者的日常生活实践与生境协商。研究发现：在地方城市政策对流动性与公共秩序限制的双重压力下,在流浪乞讨者的日常生活实践中,不仅有针对管治行动者而刻意为之的特殊营建,亦有基于程式化生活流程对自我身份认同的重塑与真情实感的展演。地方政府基于空间目标的救助与真实存在的日常生活实践存在着一种张力。研究关注了城市边缘群体日常生活对地理意义的主动塑造过程,对全面理解并规范管理中国城市流浪乞讨现象具有借鉴意义。     

地球化学揭示早—中侏罗世陆相地层气候环境变化特征——以滇中川街盆地老文村剖面为例

侏罗纪温室气候是中生代以来重要的气候变暖事件,全球关于该事件的研究主要集中在海相地层中,关于陆相地层的研究较少,滇中禄丰川街盆地沉积了完整的侏罗纪地层,为研究侏罗纪温室地球气候环境提供了良好的载体。本次工作通过对川街盆地早—中侏罗世陆相红层的岩石地层、微量元素地球化学研究认为,滇中地区早侏罗世早期主要为高温、湿润的气候环境,早侏罗世晚期气候波动剧烈且频繁,湖泊盐度急剧上升,气温缓慢下降,在即将进入中侏罗世时气温骤然上升,水体盐度快速降低,发生“T—OAE事件”,之后则保持较为稳定的高温、干燥的气候环境。通过对滇中侏罗纪恐龙埋藏层位的研究发现,早侏罗世晚期气候环境的突变层位与该层位位置相当,沉积特征及地球化学特征表明恐龙的集群性埋藏与该事件有着密不可分的关系。     

Matter-wave interference in an axial triple-well optical dipole trap

This paper proposes a scheme of axial triple-well optical dipole trap by employing a simple optical system composed of a circular cosine grating and a lens. Three optical wells separated averagely by ～37 μm were created when illuminating by a YAG laser with power 1 mW. These wells with average trapping depth ～0.5 μK and volume ～74 μm³ are suitable to trap and manipulate an atomic Bose--Einstein condensation (BEC). Due to a controllable grating implemented by a spatial light modulator, an evolution between a triple-well trap and a single-well one is achievable by adjusting the height of potential barrier between adjacent wells. Based on this novel triple-well potentials, the loading and splitting of BEC, as well as the interference between three freely expanding BECs, are also numerically stimulated within the framework of mean-field treatment. By fitting three cosine functions with three Gaussian envelopes to interference fringe, the information of relative phases among three condensates is extracted.     

南极树粉孢属真菌胞外多糖的分离纯化及结构表征

研究南极树粉孢属(Oidiodendron truncatum)真菌所产胞外多糖的理化性质和结构特征。采用阴离子交换柱层析和凝胶柱层析对南极树粉孢属(Oidiodendron truncatum)真菌胞外多糖进行了系统的分离纯化,从中得到4个均一的组分(AFW1,AFW2,AFS1和AFS2),并结合红外、气质及核磁等技术对它们的结构进行了解析。结果表明:AFW1和AFW2为中性多糖,AFS1和AFS2中含有少量的蛋白;AFW1和AFS1是由甘露糖、葡萄糖和半乳糖3种单糖组成的结构复杂的杂多糖;AFW2和AFS2则仅由葡萄糖组成,其中AFW2属线性(-1,6-葡聚糖,而AFS2属于C-3位有分支的α-1,6-葡聚糖。     

上扬子陆块西南缘早—中元古代造山运动的地质记录

早—中元古代,上扬子陆块西南缘发育有河口群—大红山群、东川群、昆阳群—会理群为代表的3套浅变质火山-沉积岩系.已有的岩石学、地球化学、年代同位素数据指示了其大地构造格架及其演化史.在早—中元古代地层所夹的火山岩中,获得了4组SHRIMP U-Pb岩浆锆石年龄:1800～1600Ma、1600～1300Ma、1300～1100Ma、1100～1000Ma.结合沉积相、常量、微量、稀土元素地球化学分析,证明了上扬子陆块西南缘在早—中元古代也相应历经了4个演化阶段.1800～1600Ma,在大红山地区、河口地区、东川汤丹地区形成近东西向的裂谷盆地.1600～1300Ma,在东川因民地区表现为—被动陆缘下的伸张环境.1300～1100Ma,在菜籽园—麻塘地区为板内裂谷-洋盆,老武山地区为裂谷盆地.1100～1000Ma阶段,菜籽园-麻塘裂谷-洋盆向北俯冲或向北向南双向俯冲,在北边的天宝山地区和南边的富良棚地区形成火山岛弧,同时在扬子西缘也出现了1.0Ga左右(1007±14～1014±8 Ma)的同造山或同碰撞型花岗岩,表明此时康滇地区已经拼贴到一起,并与整个上扬子陆块Rodinia超大陆形成同步.     

Correction of common lead in U-Pb analyses that do not report 204 Pb

During the Early-Middle Proterozoic era, three major lithostratigraphic unit associations, namely Hekou-Dahongshan, Dongchuan, and Kunyang-Huili Groups, were established for the metamorphosed volcanic-sedimentary rocks exposed in the southwestern Yangtze Block (SWYB). The integration of petrology, geochemistry and geochronology constrains tectonic framework and evolution of the SWYB, in which four sets of SHRIMP U-Pb zircon ages were obtained from the volcanic rocks interbedded within the Middle Proterozoic successions: 1800–1600 Ma, 1600–1300 Ma, 1300–1100 Ma, and 1100–1000 Ma. Major and trace elemental analysis indicate that four key tectonic evolutionary stages, each coinciding with the above radiometric age set, of the SWYB during the Early-Middle Mesoproterozoic. The SWYB was characterized by an east-westerly trending rift in the Hekou, Dongshan, and Dongchuan areas, and separate basin-forming events during 1800–1600 Ma and 1600–1300 Ma, respectively. In the SWYB, an intracontinental rift basin and a rift basin occurred in the Caiziyuan-Matang and Laowushan areas, respectively in 1300–1100 Ma ago. During 1100–1000 Ma, the SWYB was characterized by the closure of the Caiziyuan-Matang rift-ocean basin, collision between the Huili Blocks and Kunyang Blocks, and presence of volcanic arcs in the Tianbaoshan and Fulingpen areas. Accordingly, the SWYB represents a new basin that records the relatively complete assembly process of the Rodina during the Early-Middle Mesoproterozoic era.     

Real-time monitoring and early warning of landslides at relocated Wushan Town,the Three Gorges Reservoir,China

A special monitoring and warning system has been established and improved in the Three Gorges Reservoir area since 1999. It is necessary to develop a real-time monitoring system on landslides because there are dense populations centered in the reservoir area and geo-hazards may be triggered by a 30-m water level fluctuation between 145 and 175 m in elevation during reservoir operation; the regular monitoring could not be suitable to the early warning on landslides. Since 2003, the authors have carried out a real-time monitoring and early warning project on landslides at the relocated Wushan town in the Three Gorges Reservoir area. The monitoring station includes Global Positioning System with high-accuracy double frequency to monitor ground displacement, time domain reflection technology, and immobile borehole, inclinometer to monitor deep displacement, piezometer to monitor pore water pressure, and precipitation and reservoir water level monitoring. Compared with traditional methods, the real-time monitoring is continuous and traceable in the acquisition process, and the cycle of data acquisition is very short, usually within hours, minutes, or even shorter. Based on the landslide monitoring experience at the Three Gorges Reservoir area, the early warning criteria on landslide are established in which the critical situation is classified into four levels: blue, yellow, orange, and red, respectively, expressed by no, slight, moderate, and high risk situation. Comprehensive judgment from multimonitoring data of Yuhuangge landslide in this area since 2004 suggested that the new Wushan town will be at the blue early warning level, although some monitoring data of individual displacement at deep borehole showed that the displacement was increased by 5 mm in 5 months with an average velocity of 1.0 mm/month, and the data of BOTDR also showed an obvious dislocation along a stairway on the landslide.     

Combined refraction and diffraction models for sea waves over complicated topography and with currents in shallow water

-Combined refraction and diffraction models in the form of linear parabolic approximation are derived through smallparameter method. More strictly theoretical basis and more accuracy in the models than Lozano's (1980) are obtained. Some theoretical defects in Liu's model (1985) with consideration of current are not only found but also eliminated. More strict and accurate models are, therefore, presented in this paper.The calculation results and analysis in applying the models to actual wave field with consideration of bottom friction will be given in the following paper.     

ZnO压敏陶瓷冲击老化的电子陷阱过程研究

使用8/20 μs脉冲电流发生器对普通商用ZnO陶瓷压敏电阻片进行了最多5000次的冲击试验.测量了冲击前后试样的电气性能和介电特性,分析了冲击后小电流区的U-I特性和损耗角正切值tanδ随脉冲大电流的不断作用而发生的变化.实验发现压敏电压U1mA随冲击次数的增加经历增大—稳定—减小三个过程.认为正反偏Schottky势垒的中性费米能级的变化是影响样品小电流区的最根本原因.本文提出用试样的非线性系数α作为老化特征参数比传统的U