Analysis of low-flow characteristics for catchments in Dongjiang Basin, China

Low-flow indices have been determined from long-term daily streamflow data for 13 catchments in Dongjiang Basin in southern China. The Brutsaert-Nieber method was applied to estimate catchment-scale effective groundwater parameters; representative values were 4.5?×?10^?4 m² s^?1 for the hydraulic diffusivity; 3.19?×?10^?5 m² s^?1/2 for the hydraulic desorptivity; 2.27?×?10^?4 m s^?1 for the hydraulic conductivity; and 0.2617 for the drainable porosity. The response constants correlate well with the total stream length and catchment area. Solutions of the linearised Boussinesq equation were used to guide the development of regional multivariate regression models for estimating low-flow indices from the catchment-scale effective parameters. Results showed that these catchments exhibit similar low-flow characteristics. The 7-day lowest average streamflows with return periods of 10 and 2 years (7Q10 and 7Q2) are highly correlated with the catchment-scale response constants. The low-flow ratio Q95/Q50 (ratio of daily streamflow exceeded 95 and 50% of the time, respectively) varied between 0.3 and 0.5, indicating a high proportion of groundwater in the streamflow. The advantage of the regional regression model is its conceptual basis and use of the catchment-scale effective parameters. The method has the potential to be applied to ungauged catchments for estimating low-flow statistics from stream length and catchment area.     

A Further Study on the Mechanism of Airdecking

Airdecking is used in mining for two quite different applications. One is to enhance the fragmentation by amplifying the induced fracturing and the second is for pre-split blasting in which the borehole fracturing is reduced. This paper deals with the first of these effects. A forth coming paper will describe pre-splitting by airdecking. The use of air decks to enhance rock fragmentation and so to reduce explosive costs has been the practice for quite long time. Although a number of studies has been conducted to verify the advantages of blasting with air decks and to investigate the mechanisms involved, the proposed mechanisms still cannot explain clearly the phenomena observed in practice and the design approach adopted for this kind of blasting is still primary based on rules-of-thumb. In this paper, the theory of shock tubes is adopted to (a) investigate the processes of the expanding detonation products, (b) study the interactions between the explosion products and the stemming or bottom of blasthole, and (c) to decide the distribution of the changing pressure of explosion products along blasthole. Numerical simulation and theoretical analyses are then performed to study the physical process of blasting with air decks. Finally, a reasonable value for the airdecking ratio is decided theoretically. It is shown that the pressure-unloading process caused by the propagation of the rarefaction wave and the reflected rarefaction waves in the detonation products plays an important role in the enhanced fragmentation of rock when blasting with air decks. The unloading process can induce tensile stresses of rather high magnitude in the rock mass surrounding blasthole. This favors fracturing of the rock. The reflected shock wave with a magnitude of gas pressure higher than that of the average detonation pressure in a fully charged blasthole acts as the main energy source to break the rock in the air deck and stemming portions. The second and succeeding strain waves induced by the unloading or reloading of the pressurewithin the blasthole also contribute to form the initial fracture network in the rock around the blasthole. It is also revealed that there exists a reasonable range of values for the airdecking ratio. For ANFO, this value varies from 0.13-0.40.     

新疆东准双泉地区与韧-脆性剪切带有关的金矿成矿

[摘要]区域成矿背景分析表明,东准噶尔卡拉麦里地区韧-脆性剪切带形成于陆-陆碰撞体制, 在330 ~265Ma 期间,受挤压伸展体制转换影响,先后经历了韧、脆性构造变形。对与韧-脆性剪切带有 关的金矿石英流体包裹体研究发现,包裹体以气液相为主,均一温度集中在160 ~ 240益,成矿流体盐度 为3. 55 ~4. 5wt%NaCl。成矿流体的氢、氧同位素组成表明成矿流体的水为变质成因水。金属硫化物硫 同位素啄34 S 值为3. 54 ~10. 68译,显然属于混染硫。黄铁矿包裹体氦氩同位素3 He/ 4 He 值为0. 18 ~2. 18 Ra,属幔壳混源。成矿年代学研究表明,双泉金矿成矿时代及控矿构造脆性变形时间为(269依9) Ma ~ (260依4)Ma,金初始富集时间在310Ma 前后,并得到含矿花岗斑岩U-Pb 同位素年龄的支持,该事件在 东准地区均有同位素年龄记录,是区域性的构造岩浆成矿流体热事件。上述资料表明,金矿成矿过程、 成矿流体性质等在时间、空间上严格受韧-脆性剪切构造变形带控制。     

基于贝叶斯网络的地下水环境系统决策管理研究

应用贝叶斯网络解决地下水环境管理中具有不确定性的多目标决策问题,通过对决策变量氮肥施用量以及灌溉模式的调控,减少水中的硝酸盐含量,达到既能有效改善水环境又不至使农民经济利益受到损害的目标。通过分析具体的地下水环境管理系统中变量间的相互关系,构建描述变量间不确定性关系的贝叶斯网络模型,其中包括表示其依赖关系的有向无环图和表示其具体概率依赖程度的条件概率表。并在多个水环境管理目标均达到最优的前提下进行概率推理,得到决策变量氮肥施用量以及灌溉模式取不同值时目标变量的概率分布情况。最终确定出能使所有目标均达到最优的合理的水环境管理决策:(1)使用喷灌,将氮肥施用量控制在0.01~0.03 kg/m2;(2)使用漫灌,将氮肥施用量控制在0.01~0.02 kg/m2。     

U–Pb and Hf-isotope analysis of zircons in mafic xenoliths from Fuxian kimberlites: evolution of the lower crust beneath the North China craton

Mafic xenoliths from the Paleozoic Fuxian kimberlites in the North China craton include garnet granulite, and minor pyroxene amphibolite, metagabbro, anorthosite and pyroxenite. The formation conditions of the amphibolites are estimated at 745–820 °C and 7.6–8.8 Kb (25–30 km); the granulites probably are derived from greater depths in the lower crust. LAM-ICPMS U–Pb dating of zircons from four granulites reveals multiple age populations, recording episodes of magmatic intrusion and metamorphic recrystallisation. Concordant ages and upper intercept ages, interpreted as minimum estimates for the time of magmatic crystallisation, range from 2,620 to 2,430 Ma in three granulites, two amphibolites and two metagabbros. Lower intercept ages, represented by near-concordant zircons, are interpreted as reflecting metamorphic recrystallisation, and range from 1,927 to 1,852 Ma. One granulite contains two metamorphic zircon populations, dated at 1,927±55 Ma and 600–700 Ma. Separated minerals from one granulite and one amphibolite yield Sm–Nd isochron ages of 1,619±48 Ma (¹⁴³Nd/¹⁴⁴Nd)i=0.51078), and 1,716±120 Ma (¹⁴³Nd/¹⁴⁴Nd)i=0.51006), respectively. These ages are interpreted as recording cooling following metamorphic resetting; model ages for both samples are in the range 2.40–2.66 Ga. LAM-MC-ICPMS analyses of zircon show a range in ¹⁷⁶Hf/¹⁷⁷Hf from 0.28116 to 0.28214, corresponding to a range of _Hf from –34 to +12. The relationships between ²⁰⁷Pb/²⁰⁶Pb age and _Hf show that: (1) the granulites, amphibolites and metagabbro were derived from a depleted mantle source at 2.6–2.75 Ga; (2) zircons in most samples underwent recrystallisation and Pb loss for 100–200 Ma after magmatic crystallisation, consistent with a residence in the lower crust; (3) metamorphic zircons in several samples represent new zircon growth, incorporating Hf liberated from breakdown of silicates with high Lu/Hf; (4) in other samples metamorphic and magmatic zircons have identical ¹⁷⁶Hf/¹⁷⁷Hf, and the younger ages reflect complete resetting of U–Pb systems in older zircons. The Fuxian mafic xenoliths are interpreted as the products of basaltic underplating, derived from a depleted mantle source in Neoarchean time, an important period of continental growth in the North China craton. Paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1.8–1.9 Ga, corresponding to the timing of collision between the Eastern and Western Blocks that led to the final assembly of the North China craton. The growth of metamorphic zircon at 600–700 Ma may record an asthenospheric upwelling in Neoproterozoic time, related to uplift and a regional disconformity in the North China craton.     

Subsurface Occurrence of Natural Gas Hydrate in the Nankai Trough Area: Implication for Gas Hydrate Concentration

Abstract. The Nankai Trough runs along the Japanese Islands, where extensive BSRs have been recognized in its forearc basins. High resolution seismic surveys and site-survey wells undertaken by the MITI have revealed the gas hydrate distribution at a depth of about 290 mbsf. The MITI Nankai Trough wells were drilled in late 1999 and early 2000. The highlights were successful retrievals of abundant gas hydrate-bearing cores in a variety of sediments from the main hole and the post survey well-2, keeping the cored gas hydrate stable, and the obtaining of continuous well log data in the gas hydrate-dominant intervals from the main hole, the post survey well-1 and the post survey well-3. Gas-hydrate dominant layers were identified at the depth interval from 205 to 268 mbsf. Pore-space hydrate, very small in size, was recognized mostly filling intergranular pores of sandy sediments. Anomalous chloride contents in extracted pore water, core temperature depression, core observations as well as visible gas hydrates confirmed the presence of pore-space hydrates within moderate to thick sand layers. Gas hydrate-bearing sandy strata typically were 10 cm to a meter thick with porosities of about 40 %. Gas hydrate saturations in most hydrate-dominant layers were quite high, up to 90 % pore saturation.
All the gas hydrate-bearing cores were subjected to X-ray CT imagery measurements for observation of undisturbed sedimentary textures and gas-hydrate occurrences before being subjected to other analyses, such as (1) petrophysical properties, (2) biostratigraphy, (3) geochemistry, (4) microbiology and (5) gas hydrate characteristics.     

加利福尼亚弧-盆-沟体系的地质特征

加利福尼亚中生代弧-盆-沟系的构造和演化模式一向为世人所重视。作者应邀有机会对加州内华达岛弧地块、弗兰西斯科杂岩和大谷弧前盆地进行了实地地质考察。本文仅就这3个岩性-构造单元的一些独特地质特征和地质景观作一简介。     

脉冲星γ射线辐射光度的分析

本文作者在脉冲星γ射线辐射的极冠模型的基础上，考虑光子在磁层中的级联过程，提出了级联过程中能量转化效率的概念并得出了转化效率公式，分析表明，能量转化效率只和磁场强度有关，与周期无关，考虑能量转化效率，我们计算了极冠模型的γ射线辐射光度，得出了可以和观测值比较的结果，本文结果倾向于支持脉冲星γ射线辐射的极冠模型。     

浙江近海夜光藻的分布及其生态学特点

本文利用历次夜光藻调查资料，阐述了其在浙江近岸海域的分布特点，丰度高峰主要出现在春秋季，夏季亦存在暴发性增殖的可能性，冬季则基本见不到夜光藻的踪迹。杭州湾口等水体浑浊区是夜光藻的低丰度区，仅在春夏季有零星出现，这与水体透明度低、悬浮泥沙含量高及强烈的水动力因子等密切相关。在时间尺度上，夜光藻丰度呈上升趋势，根本原因是海域富营养化加剧的结果。     

宇宙常数Λ≠0的平面引力波

本文讨论了宇宙常数Λ≠0时的平面引力波问题。在弱场近似下,得到了平面引力波传播方程及色散方程。通过对Kretschmann曲率标量的讨论发现,不同于Λ=0时h_(μv)仅有横场这一众所周知的结果,Λ<0时不存在一个坐标系,使h_(μv)的标量场、纵场、混合场分量全为零。最后讨论引力波辐射,结论是与Λ=0时无偶极辐射这一结果不同,Λ<0时,混合场的辐射有偶极辐射。