Unusual N—Alkane Distributions in Extracts from Marine Carbonate Rocks at High Levels of Maturity and Overmaturity

N-alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C₁₇-C₂₁ and C₂₅-C₂₉. In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons (C₂₂₊) with C_21-/C₂₂₊ ratios between 0.50 to 3. 16, and an average value of 1. 34. The n-alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n-alkanes maximizing in the C₂₅-C₂₉ range. These extracts have very high concentrations of waxy hydrocarbons with C_21-/C₂₂₊ ratios all < 1. 0, ranging from 0. 14 to 0. 90 and averaging 0. 36. All of the extracts have a marked odd/even predominance in the high molecular weight n-alkane range regardless of whether they are from shallow or deep cores or out-crop samples. Simulation experiments were performed using typical sapropelic-type kerogens from the immature Sinian Lower Xiamalin Formation carbonate-rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue-green algaeSpirulina subsala. Results indicate that the unusual distribution of n-alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity. This research project was financially supported by the Chinese Academy of Sciences (Grant No. KZCX2-111 ).     

HIV感染地域类型探讨——以中国某地区为例

HIV感染途径不同，使HIV感染对一般人群的威胁产生差异，因而衡量HIV感染流行程度时必须考虑HIV感染途径。选择性传播感染率、静脉吸毒人群感染率和孕妇感染率3项指标来衡量HIV感染流行程度，结合HIV感染途径对一般人群的威胁程度差别，这3项指标对衡量HIV感染流行程度的作用为：孕妇感染率＞性传播感染率＞静脉吸毒人群感染率。综合3项指标的划分标准，从理论上把HIV感染流行程度划分为18个，并用此方法将中国某地区HIV感染流行程度划分出高流行地域、次高流行地域、中度流行地域和低流行地域4个HIV感染地域类型，最后探讨了这4个地域类型的特点和成因。     

烟台第一海水浴场沙源匮乏型海滩地貌和表层沉积物粒度特征

在烟台第一海水浴场,利用经纬仪进行2条海滩横剖面形态测量,并在不同地貌单元采集沉积物样品进行粒度分析。测量显示,该海滩仅有小规模沙坝和沟槽体系。后滨上有风成沉积,但滩肩和海岸沙丘发育均不明显。粒度分析结果表明,海滩沉积物以中砂、粗砂为主,杂以砾或细砂,比山东半岛其他海滩沉积物明显要粗。由陆向海沉积物呈带状分布,平均高潮线附近和沙坝迎水坡侵蚀作用均显著。因此认为缺乏沙源供应的基岩岬湾式海岸是导致沙滩地貌发育不典型、海滩侵蚀作用显著的主要原因。     

1951年以来中国无霜期的变化趋势

准确界定无霜期及初、终霜日的时空变化是减少气候变化对农业生产的危害、有效提升农业适应性的重要内容。根据1951年以来国内824个气象站点日最低气温资料,分析初、终霜日和无霜期在全国的分布特征,采用累积距平和线性倾向估计模拟三者的变化趋势,并对无霜期进行突变检验。结果显示：① 中国无霜期随纬度增加或海拔升高而减少,无霜期的年际波动幅度随纬度增加或随海拔降低而减少。② 中国80%以上区域呈现初霜日推后、终霜日提前和无霜期延长的趋势,且三者的变化幅度均是北方大于南方、东部大于西部。③ 中国多数农区无霜期延长是初霜日推后和终霜日提前共同影响,而西南区和长江中下游区部分地区无霜期延长是初霜日的推后幅度大于终霜日的推后幅度或终霜日的提前幅度大于初霜日的提前幅度。④ 中国过半区域无霜期在1980s和1990s发生突变。突变集中分布在东北区中西部、内蒙及长城沿线区、黄淮海区、青藏区和甘新区;突变时间上,东部农区和西部农区无霜期分别在1980s和1990s突变。     

Torsional response of nonductile structures with soft‐first‐storey

In this paper, torsional response of nonductile structures with soft‐first‐storey subjected to bidirectional ground motions is studied using a simplified two‐storey model with two‐way eccentricities. The stiffness ratio of second storey to first storey is varied to create different levels of soft‐first‐storey effect, while the stiffness eccentricity is varied to create torsional effects. Different overstrength ratios are used in the simplified models to study the response of structure with different structural capacity. Hysteretic model with strength deterioration and stiffness degradation properties is used to capture the deterioration of element stiffness and strength. Ductility capacity of 2.0 is used as the models are for nonductile structures. In general, displacement amplification of irregular model with respect to regular model increases as stiffness ratio increases, while no consistent trend of changes in displacement amplification is found with increase in stiffness eccentricity. It is found that the displacement amplification due to only soft‐first‐storey effect can be conservatively taken as 1.5. Coupling of torsional and soft‐first‐storey effects is more significant in affecting the displacement amplification of elements at flexible side. The trend of changes in displacement amplification of elastic system is similar to that of inelastic system. The displacement amplification of elements at the flexible side is larger than that at the stiff side. The elements at the flexible side in the direction of shorter uncoupled lateral period have larger displacement response than those in the orthogonal direction. Ductility demand–capacity curves subsequently constructed can be used to approximately assess the seismic performance of existing structures and as guidelines for designing structures in Singapore to withstand the maximum credible earthquake considering the coupling of torsional and soft‐first‐storey effects. Copyright © 2014 John Wiley & Sons, Ltd.     

2010年前汛期末华南西部和东部暴雨对比分析

2010年前汛期末期华南出现暴雨过程,暴雨在华南西部与东部有区别,利用NCEP再分析资料和常规观测资料,分析此次暴雨特征与机理。结果表明：对华南整体而言暴雨期间高层受南亚高压东南伸弱脊辐散区影响;中层副热带高压西伸脊先东退、后西伸;暴雨区位于低层相当位温锋区南侧、气流辐合;边界层偏南风急流形成后暴雨发生。分区而言,华南西部两次出现各持续1 d的多站点暴雨时期;每次暴雨站数明显增加之前低层能量大、中低层层结不稳定且整层大气可降水量大;两个多站点暴雨日期之间边界层中尺度偏南风急流有两次明显减弱,低层水汽辐合与上升运动发生明显中断。华南东部多站点暴雨只出现一次但持续3 d,虽然在暴雨前期3个指数条件都没有西部两次暴雨前期好,但是连续3 d多站点暴雨期间较大尺度偏南风边界层急流基本维持,低层水汽辐合与上升运动没有发生明显中断,导致了东部暴雨站点多、强度大、持续时间长。因此对于华南前汛期暖区暴雨而言,边界层偏南风急流的生消活动与水平尺度均很重要。     

山西中部中等地震前地震波异常特征

以山西太原遥测台网7个子台(榆次,东山,平遥,太谷,交城,汾阳,介休)和太原台十几年的地震观测资料为基础,分析几次中等地震前地震波波速比,振幅比,地震波初动符号,S波衰减率,尾波持续时间的异常。结果表明,地震波参数的分析可以提取中等地震前的异常信息,在1991年忻州5．1级地震的前兆异常反映明显。     

1998年临猗5.0级地震Q值的时间变化特征

利用西安数字地震遥测台网记录的数字地震资料,采用P波初动半周期残差法求得了1998年7月临猗5．0级地震前后不同路径的Q值变化,发现在地震发生前Q在87～203之间,震后Q在67～164之间,震前震中区附近出现了明显的高Q值异常。结果表明,地震前的高Q值异常可以作为地震预测的一种手段。     

一次范数最小和选权迭代联合的抗差法

联合一次范数最小和选权迭代法进行抗差估计。使用一次范数进行粗差定位,在确定粗差位置后,对相应的观测值进行降权,以此作为选权迭代法的初始权进行迭代平差,解决初始权不合理导致选权迭代法失效的问题。最后以水准网数据验证了该联合法的正确性。     

近40 a来新疆极地类对流层顶温度变化的若干事实和突变分析

采用1963—2002年新疆12个探空站逐日探测资料．按气候特点和地理分布把新疆划分为阿尔泰山．天山和昆仑山3个研究区域。分析了40a来新疆全年各区极地类对流层顶平均温度变化的若干事实、变化的趋势和变化的空间分布差异,用Mann-Kendall法对其进行了气候突变检验。研究表明：新疆极地类对流层顶平均温度总体呈下降趋势;从年代际变化来看40a共下降了0．5℃,下降速率为0．125℃／（10a）。同时,该层温度于1976年发生了气候突变,皿著水平达5％以上．由此说明新疆近年来高空的一些特性层也同样发生了气候变化。