地质雷达数值模拟中有损耗介质吸收边界条件的实现

利用时间域有限差分(FDTD)法将麦克斯韦方程进行离散化,可以对地质雷达进行数值模拟。利用完全匹配层(PML)作为吸收边界条件可以有效地吸收向外的电磁波,从而大大提高了计算效率。对于有损耗介质的情况,采用扩张坐标系下改正的麦克斯韦方程,只要扩张变量满足一定的关系,同样可有效地吸收向外的电磁波, 这种吸收边界条件称为通用完全匹配层。     

城市化:相变与自组织临界性

城市化的本质是一种自组织临界相变过程 ,在时间和空间上分别联系着自组织临界性(SOC)和空间复杂性。城市化过程作为SOC有 3个方面的标志 :时间方向的 1/ f涨落、空间方面的分形结构和等级方式的Zipf定律 ,其共性是无标度性。分形中心地景观和位序 -规模分布分别是城市化自组织临界过程在空间和等级两个领域的实证判据。在城市化的临界相变过程中 ,城市体系通常演化为无标度网络 ,而位序 -规模法则乃是空间领域的无标度性在等级领域的结构性“投影”。基于SOC思想研究城市化过程有助于理解自组织城市网络的复杂空间动力学 ,从而为发展城市演化的模拟实验方法提供理论思路     

1736～1999年西安与汉中地区年冬季平均气温序列重建

基于现代气象资料所建立的西安、汉中地区冬季降雪天数与年冬季平均气温之间的相关关系,根据清代档案所记载的西安与汉中地区冬季降雪日数,恢复了西安与汉中地区1736～1910年的年冬季平均气温,重建了1736～1999年西安与汉中地区年冬季平均气温序列。序列分析表明,这两个地区年冬季平均气温变化趋势一致:18世纪和20世纪为暖期,19世纪为冷期,且20世纪的增暖趋势明显。与利用树轮重建的镇安初春(3～4月)温度序列对比分析表明:西安、汉中地区冬季平均气温与镇安初春温度的低频变化趋势基本一致,但镇安较西安与汉中有明显的位相提前。     

颗粒破碎效应对堆石坝应力变形的影响

颗粒破碎对堆石体的变形有重大影响,颗粒破碎除与母岩强度有关外,与应力状态密切相关,高堆石坝堆石体的大部分变形正是高应力场下颗粒破碎的反映。沈珠江院士提出的南水双屈服面模型虽可以较全面地反映堆石体的变形特性,但未充分考虑颗粒破碎引起的剪缩特性,因此坝体变形计算结果往往偏小,适用于中低堆石坝的分析中。本文的计算方法在南水双屈服面模型的基础上,考虑了堆石体在一定应力状态下颗粒破碎引起的应变,较真实地反映了堆石体的变形特性,可为堆石坝尤其是高堆石坝的应力变形研究提供更为合理的结果。     

Error assessment of grid-based direct solar radiation models

This research assessed two grid-based direct solar radiation models, ESRI’s Solar Analyst (SA) and Kumar’s model (KM), using artificial surfaces. Mathematically derived radiation on the surfaces was compared with grid-based model results. While both models showed good consistency with theoretical derivations, they both underestimated direct radiation at daily, most seasonal, and annual scales. KM performed better than SA at all the scales except at annual scale and in the summer. Horizon angle calculation and numerical integration are the common error sources in both models. Interpolation in horizontal angles and the use of a sky size parameter are the additional error sources in SA. Larger errors were found in SA when the sky size parameter and modeling time interval were not compatible. Overall, KM is a better choice for direct solar radiation modeling as it is more accurate and computationally efficient, easier to understand, and needs fewer parameters.     

Prediction of base flows from basin characteristics: a case study from Zimbabwe / Prévision de débits de base à partir de caractéristiques du bassin: une étude de cas au Zimbabwe

Abstract

Abstract Base flows make up the flows of most rivers in Zimbabwe during the dry season. Prediction of base flows from basin characteristics is necessary for water resources planning of ungauged basins. Linear regression and artificial neural networks were used to predict the base flow index (BFI) from basin characteristics for 52 basins in Zimbabwe. Base flow index was positively related to mean annual precipitation (r = 0.71), basin slope (r = 0.76), and drainage density (r = 0.29), and negatively related to mean annual evapotranspiration (r = –0.74), and proportion of a basin with grasslands and wooded grasslands (r = –0.53). Differences in lithology did not significantly affect BFI. Linear regression and artificial neural networks were both suitable for predicting BFI values. The predicted BFI was used in turn to derive flow duration curves of the 52 basins and with R ² being 0.89–0.99.     

Early Carnian anoxic event as recorded in the southern Tethyan margin,Tunisia: an overview

Considerable attention has been given to the Carnian (Late Triassic) Pluvial and Reingraben events associated with organic-rich shale accumulation in the Germanic basin, Alps, southern Appenines as well as in northwestern Tethyan margins. Less interest has been shown to the southern Tethyan portion represented by the northern margin of Africa, including Tunisia. Tunisian basins represented by the Tellian domain, Tunisian trough, the ‘Dorsale’, and the North–South Axis (NOSA) belong to the southern Tethyan margin, where northern and central areas record the early Carnian anoxic event within an extensive carbonate platform. This short-lived (~2 million year) period of anoxia ranges within the Aonoides to Austriacum ammonite zones, and corresponds in Tunisia generally to intermediate to shallow water environments marked by organic-rich black limestone, dolomite, and shale. Interestingly, toward the south, the dysaerobic conditions in the Jeffara–southern Dahar basin appear to have prevailed locally also in the early Carnian. Here we review evidence of early Carnian anoxia in Tunisia based on the analysis of more than 17 Triassic sections and wireline logs from several petroleum exploration wells penetrating the black dolomites, limestones, and shales. In addition, biostratigraphic and complete geochemical reviews have been undertaken from published papers and unpublished internal reports to better assess this important and promising hydrocarbon source interval.     

Late Jurassic–Early Cretaceous tectonic evolution of the Great Xing’an Range: geochronological and geochemical evidence from granitoids and volcanic rocks in the Erguna Block,NE China

ABSTRACT

The late Mesozoic magmatic record within the Erguna Block is critical to evaluate the tectonic history and geodynamic evolution of the Great Xing’an Range, NE China. Here, we provide geochronological and geochemical data on Late Jurassic–Early Cretaceous plutonic-volcanic rocks in the northern Erguna Block and discuss their origin within a regional tectonic framework. Late Mesozoic magmatism in the Erguna Block can be divided into two major periods: Late Jurassic (162–150 Ma) and Early Cretaceous (140–125 Ma). Late Jurassic quartz monzonite and dacite show adakite characteristics such as high Al₂O₃, high Sr, and steeply fractionated REE patterns. Contemporary granitoids and rhyolites are also characterized by strong enrichment of light rare earth elements (LREE) and significant depletion in heavy rare earth elements (HREE), but with more pronounced negative Eu anomalies. Early Cretaceous trachytes and monzoporphyries exhibit moderate LREE enrichment and relatively flat HREE distributions. Coeval granites and rhyolites have transitional signatures between A-type and fractionated I-type felsic rocks. Both Late Jurassic and Early Cretaceous rocks have distinctive negative Nb, Ta, and Ti anomalies, and positive zircon ε_Hf(t) values, suggesting that these magmas were derived from partial melting of Meso-Neoproterozoic accreted lower crust, although melting occurred at a variety of crustal levels. The transition from adakite to non-adakite magmatism reflects continued crustal thinning from Late Jurassic to Early Cretaceous. Our data, together with recently reported isotopic data for plutonic and volcanic rocks, as well as geochemical data, in NE China, suggest that Late Jurassic–Early Cretaceous magmatism in the Erguna Block was possibly induced by post-collisional extension after closure of the Mongol-Okhotsk Ocean.     

大兴安岭北段旁开门金(银)矿床地球化学特征及成因

旁开门金(银)矿床地处爱辉—呼玛成矿带,矿床主体赋存于侏罗系甘河组火山岩中,矿体主要以脉状形式产出,严格受硅化角砾岩带控制。区内甘河组玄武安山岩、安山岩、流纹岩属过铝高钾钙碱性系列,玄武岩和石英斑岩属过铝质钾玄系列,它们均来源于地幔岩浆,为同源岩浆分异的产物。矿石中流体包裹体发育较差,以气液两相包裹体为主,仅见少量含子矿物三相包裹体。气液两相包裹体均一温度为268.8～331.6℃,盐度(w(NaCl))为8.67%～13.11%,含子矿物三相包裹体均一温度为288.8～313.3℃,盐度为37.32%～39.23%;表明成矿流体为中温、中—高盐度的热液体系。根据流体包裹体氢、氧同位素分析结果推断其为岩浆流体与大气降水混合热液。矿床形成于早白垩世由挤压转变为伸展环境,成矿物质来源于深部岩浆及火山岩地层,成矿温度为中温,成矿深度属浅成,其成因类型为浅成中温热液矿床。     

蒙古国塔南凹陷南屯组水下扇的沉积演化特征

利用基于Wheeler变换的数据驱动倾角导向体生成的非线性年代地层切片,研究蒙古国塔南凹陷下白垩统南屯组水下扇的沉积演化特征。基于沉积学的理论指导,通过单井相、连井相标定,结合地震反演、地震属性等技术,进行等时地层单元的沉积相分析;基于相控应用年代地层切片技术研究沉积演化特征。结果表明:塔南凹陷南屯组SQ21时期发育近岸水下扇及远岸水下扇,水下扇的沉积演化规模随着水体的加深先扩张后萎缩,到最大湖泛时期基本消失;切片中水道显示远岸水下扇是近岸水下扇二次搬运至同生断裂再次滑塌而成。