Effects of Density and Viscosity in Modeling Heat as a Groundwater Tracer

Decoupled simulation of groundwater flow and heat transport assuming constant fluid density and viscosity is computationally efficient and simple. However, by neglecting the effects of variable density and viscosity, numerical solution of heat transport may be inaccurate. This study investigates the conditions under which the density and viscosity effects on heat transport modeling can be neglected without any significant loss of computational accuracy. A cross-section model of aquifer-river interactions at the Hanford 300 Area in Washington State was employed as the reference frame to quantify the role of fluid density and viscosity in heat transport modeling. This was achieved by comparing the differences in simulated temperature distributions with and without considering variable density and viscosity, respectively. The differences between the two sets of simulations were found to be minor under the complex field conditions at the Hanford 300A site. Based on the same model setup but under different prescribed temperature gradients across the simulation domain, a series of heat transport scenarios were further examined. When the maximum temperature difference across the simulation domain is within 15°C, the mean discrepancy between the simulated temperature distributions with and without considering the effects of variable density and viscosity is approximately 2.5% with a correlation coefficient of above 0.8. Meanwhile, the speedup in runtime is roughly 225% when the maximum temperature difference is at 15°C. This work provides some quantitative guidelines for when heat transport may be simulated by assuming constant density and viscosity as a reasonable compromise between accuracy and efficiency.     

Effectiveness of grass strips in trapping suspended sediments from runoff

Little information is available concerning the performance of grass strips for erosion control from steep cropland. An experiment was conducted on 5‐m‐long grass strips with slopes of 3°～15° that were subjected to silt laden runoff and simulated rainfall, to investigate the sediment trapping processes. The grass strips had three treatments including intact grass control (C), no litter (dead grass material covering the soil surface was removed) (NL), and no litter or leaves (only 2～3 cm grass stems and roots were reserved) (NLL). Generally the grass strips had a high effectiveness in trapping sediment from steep cropland runoff. Sediment trapping efficiency (STE) decreased with increasing slope gradient, and even for a 15° slope, STE was still more than 40%. Most sediment deposited in the backwater region before each grass strips. The removal of grass litter or/and leaves had no significant influence on STE. The sediment median size (D₅₀) in inflow was greater than that in outflow, and the difference (ΔD₅₀) decreased with increasing slope. A positive power relationship between STE and ΔD₅₀ can be obtained. Grass strips were more effective in trapping sediments coarser than 10 or 25 µm, but sediments finer than 1 µm were more readily removed from runoff than particles in the range of 2 to approximately 10 µm. Grass litter had less influence on flow velocity than leaves because the deposited sediment partially covered the litter layer. Mean flow velocity and its standard deviation were negatively correlated with STE, and they can help make good estimation of STE. Results from this study should be useful in planting and managing forage grass to effectively conserve soil loss by runoff from steep slopes on the Loess Plateau of China. Copyright © 2010 John Wiley & Sons, Ltd.     

汶川地震发震构造应力场分析

通过对汶川8级地震区的地震震源机制资料进行分析,得到了该区域内地震震源机制分布及分类特点,讨论了断裂重新滑动型地震的发震构造应力场的校对问题,提出了使用地震学的定标率来区分破裂型地震和滑动型地震的方法,并给出了汶川地震发震构造应力场的分布,结合龙门山断裂带的几何特征,分析了孕育和发生8级地震的构造原因。     

��������ķ������Ȩ����Ӧ���о�

???????????????????У?????????????????????????????????????????????????????????????????????????????????????GPS??InSAR?????????????е??????÷?????????????????????????????????Ч????????????????????????????     

Last glacial climate variations on the tropical Leizhou Peninsula,South China

Two cores were recovered from raised peat bogs on the tropical northern Leizhou Peninsula, south China. Multiple sediment variables including organic matter (OM) content, the stable carbon isotope signature of OM, low-frequency magnetic susceptibility and degree of humification, indicate that the regional paleoclimate played an important role in determining the nature of peat that accumulated. Based on comparison with other climate proxies, the bulk peat δ¹³C record was interpreted as an indicator of variation in the East Asian (EA) summer monsoon, and to a lesser extent, the Indian summer monsoon, during the last glacial period between ~49 and 10 cal ka BP. More negative bulk δ¹³C values reflect wetter and warmer conditions, and thus a strong EA summer monsoon. More positive values indicate drier and cooler conditions. A warm and wet period occurred between ~46 and 28 cal ka BP, implying a strengthening of the EA summer monsoon. A climate shift occurred at ~22 cal ka BP and the driest and coldest period appeared between ~19 and 16 cal ka BP, suggesting weakening of the EA summer monsoon. After ~12 cal ka BP, climate shifted towards wetter and warmer conditions again. It has been suggested that variations in orbitally induced solar insolation played a role in the last glacial climate of the study region. Several millennial—scale arid and cold phases characterized by C4 plants, or by more positive δ¹³C values during periods when C3 plants dominated, show agreement with the Greenland GISP2 ice core and the Chinese stalagmite records. Interactions between high northern latitude cold air advection and summer moisture transported across the tropical ocean, and the migration of the mean position of the Intertropical Convergence Zone (ITCZ) would have favored these millennial–scale phases. Additionally, changes in heat transport to the North Atlantic would also have influenced climate in the region.     

江西省空间运输联系演化特征

利用1990年以来江西省交通运输及相关统计数据,在分析和评价全省各地市客、货运量状况的基础上,运用地域非均衡系数、区域位势商指标,对江西省客、货流运输联系的空间演化特征及趋势进行了探讨。研究表明,全省在交通运输业快速发展的同时,客、货运输在空间分布上已由低水平的集中趋向均衡发展,客运的廊道效应初显,在京九铁路、浙赣铁路、昌九高速、赣粤高速沿线地区客流较为集中;货运重心南移,极化效应减弱,随着全省各地市的资源优势开始转为经济优势,货运地位出现有序演变。结合江西省经济发展所处阶段,对其运输化发展阶段进行了初步的分析和讨论。     

大地电场观测各类干扰源的调研与分析

收集整理大地电场观测的各类干扰及变化原因,通过详尽的调研和相关分析研究,提出其常规干扰变化的识别方法,以及为提高大地电场观测资料的质量而采取的干扰抑制技术,并针对各类干扰源的机理,改进和完善现有的大地电场观测技术,提高资料的稳定性和可靠性。     

Characteristics of Seismic Activity in a 3-Dimensional Space before the Wen'an Earthquake,Hebei Province by Relocation of Small Earthquakes in the China's Capital Area

Characteristics of seismic activity before the M5.1 earthquake in Wen'an,Hebei Province on July 4,2006 are analyzed by relocation of small earthquakes in the China's capital area,and some results are obtained as follows:① The seismic activity of M L ≥3.0 in the middle part of the Hebei plain seismic belt displayed a feature of strengthening (lasting 43 months) quiescence (17 months) five years before the Wen'an earthquake.Simultaneously,the strain release curve showed a variation process of accelerating-flatting.② A seismogenic gap in a three-dimensional space,located at the depth of 15km ～ 20km,with 70km long in latitude direction and 90km long in longitude orientation,was formed by M≥2.0 earthquakes four years prior to the Wen'an earthquake.The initial rupture point of the Wen'an earthquake is situated at the bottom of the gap.③ The focal depths of earthquakes with M L ≥2.0 in the middle part of the Hebei plain seismic belt gradually increased from 10km to 30km during the period from April,2003 to October,2004.Meanwhile,the seismic activity obviously strengthened in the middle and lower crust (from 20km to 30km in depth).     

自流井水温固体潮效应及其应变响应能力

井水温度观测是一项重要的地震前兆观测手段,旨在捕捉地震孕育过程中的应力-应变信息。水温固体潮效应作为地壳应力-应变信息的真实反映和地震前兆观测的干扰因素,具有重要的研究意义。本文首先依据对自流井中热状态的分析,认为自流井水温固体潮效应可能主要存在两种机制,即热传导机制和热对流机制;据此,推导出热传导机制中水温与固体潮体应变变化的定量关系;最后以流量相对较大的本溪自流井为例进行分析。结果表明,本溪井水温固体潮效应是热传导机制和热对流机制共同作用的结果,其中,热传导机制起主要作用。