Modelling water infiltration in cracked paddy field soil

Periodic paddy field flooding is a major source of groundwater recharge. Many paddy fields thus are used as groundwater recharge ponds after harvesting the first crop of the summer. Following rice harvesting, paddy field surfaces may crack into fissures as a result of drainage and exposure to sunlight. Field observation indicates that applying precipitation to the paddy field can increase the rate of infiltration. To quantitatively evaluate the amount of infiltration in a cracked paddy field, this study sets up a simple soil crack model to simulate the field infiltration process. A three‐dimensional groundwater model FEMWATER is adopted to simulate water movement in the paddy field subjected to various crack conditions. Using the field and laboratory data of irrigation water requirements, soil physical properties, hydraulic conductivities and soil profiles obtained from Ten‐Chung, FEMWATER simulates the water movement in the dry cracked paddy. Simulation results show that if the cracks develop extensively and penetrate the ploughed soil, the infiltration rate may increase significantly. The infiltration fluxes of crack with depths of 80, 60 and 27·5 cm are 18·77, 14·50 and 8·06 times higher than that of 20 cm, respectively. The simulation results of cracks with 80 cm depth correlated closely with field observations. The results of the study elucidate the processes of unsaturated water movement in a dry cracked paddy field. Copyright © 2004 John Wiley & Sons, Ltd.     

Geostatistical analysis and conditional simulation for estimating the spatial variability of hydraulic conductivity in the Choushui River alluvial fan,Taiwan

This work evaluated the spatial variability and distribution of heterogeneous hydraulic conductivity (K) in the Choushui River alluvial fan in Taiwan, using ordinary kriging (OK) and mean and individual sequential Gaussian simulations (SGS). A baseline flow model constructed by upscaling parameters was inversely calibrated to determine the pumping and recharge rates. Simulated heads using different K realizations were then compared with historically measured heads. A global/local simulated error between simulated and measured heads was analysed to assess the different spatial variabilities of various estimated K distributions. The results of a MODFLOW simulation indicate that the OK realization had the smallest sum of absolute mean simulation errors (SAMSE) and the SGS realizations preserved the spatial variability of the measured K fields. Moreover, the SAMSE increases as the spatial variability of the K field increases. The OK realization yields small local simulation errors in the measured K field of moderate magnitude, whereas the SGS realizations have small local simulation errors in the measured K fields, with high and low values. The OK realization of K can be applied to perform a deterministic inverse calibration. The mean SGS method is suggested for constructing a K field when the application focuses on extreme values of estimated parameters and small calibration errors, such as in a simulation of contaminant transport in heterogeneous aquifers. The individual SGS realization is useful in stochastically assessing the spatial uncertainty of highly heterogeneous aquifers. Copyright © 2004 John Wiley & Sons, Ltd.     

Image registration for the underwater inspection using the maximum a posteriori technique

Describes an image registration method for underwater inspection tasks. A remotely operated vehicle equipped with a video camera and a scanning sonar is used as the testbed vehicle. Each image of the underwater scene is saved along with the video camera's position and orientation. The images are then combined to create a large composite picture of the underwater structure being inspected. This method is based upon a maximum a posteriori estimation technique and provides smooth and robust estimates of image shifts. Our results demonstrate the feasibility of this highly promising underwater inspection procedure.     

区域地理信息系统在农业中的应用——以福建省浦城县为例

本文应用系统分析的理论和方法，建立了浦城县地理信息系统，分析了信息系统的结构、功能及信息管理过程，并在系统的支持下对浦城县农业发展战略进行决策研究，提出了一系列分析意见，开辟了地理信息系统应用的新领域。     

一颗与众不同的脉冲星Geminga

最近，一个困扰人们达十几年之久的γ射线源Ｇｅｍｉｎｇａ被证认为Ｘ、γ射线脉冲星，其光学对应体也被确定为一颗光谱偏蓝的２５等星。对Ｇｅｍｉｎｇａ脉冲星的确证说明存在着一类没有射电辐射的脉冲单星。     

2008年汶川8.0级地震孕震机理研究

用三维流变非连续变形与有限元相结合（DDA+FEM）的方法,在青藏高原及邻近地区三维构造块体相互制约的大背景中,考虑了龙门山断裂带东西两侧地势、地壳厚度和分层的明显变化,及断裂带东侧四川盆地及鄂尔多斯块体坚硬地壳阻挡的影响,通过用GPS资料做位移速率边界约束和震源机制约束,计算得到研究区的速度场和应力场与该地区GPS测量结果和震源机制分布结果基本一致.在此基础上,模拟计算现今构造块体边界断层上表征剪应力及法向应力等综合影响的危险度分布.结果表明,上、中地壳层危险度分布中危险度较高的地段多数与近几十年来发生的七级以上大震区域基本一致.包括2008年汶川8.0级等大震的发震断层.通过分别对龙门山断裂带东西两侧的两种不同构造格局进行试算表明,龙门山断裂带东西两侧地势、地壳厚度、分层与物性明显变化对汶川大震的孕育发生均起了关键性作用.计算得到的应变率强度分布图可见,高原东部整个边缘地带均接近应变率强度的陡变带.其中以龙门山断裂带上的陡变最为明显,西侧应变率强度是东侧的近4倍,而且断裂带东侧应变率强度等值线衰减比西侧快.反映了汶川大震逆冲型发震断层地区独特的特征.此外,由计算得到的应变能密度分布图可见,龙门山断裂带在上、中地壳层中均位于宽度相同、其走向与龙门山断裂带走向一致的高应变能密度带中,在上地壳层这个带的东西两侧则是应变能密度较低的地区,而在中地壳层,其强度在断裂带东侧逐渐向东衰减,西侧应变能密度高,而东侧应变能密度较低.表明在印度板块强烈推挤作用和高原各构造块体相互制约及龙门山断裂带东西两侧特殊构造环境中,高原地壳物质向东水平运动,受到龙门山断裂带东侧介质刚性强度较大的四川盆地阻挡,使得汶川大震发震断层在大震前已积累了相当水平的应变能,并同时处于力学上的不稳定状态.     

Synchronous structure control of superlarge ore deposits

The control of synchronous structures on formation of superlarge stratabound ore deposits is immense. Based on studies of ore deposits in South Qiniing, northern Guangdong, Langshan and other areas, three new ideas in comparison with examples of ore control of synchronous structures both in China and abroad are proposed: (i) multiorder ore control of synchronous structures, which means that synchronous structures of different orders display different controls on ore deposits; (ii) synchronous structures in different stages of basin evolution display different controls on basin fluid system and ore-forming system; (iii) synchronous strurture accompanying hydrothermal mineralization as a preexisting weak surface in earth crust often reactivate in later tcctono-thermal event to be a channelway for magma or thermal fluids which superimposed on and reformed preexisting ore beds to form large or superlarge composite ore deposits.     

加密自动站资料在强对流天气分析预报中的应用

利用常规分析资料、雷达产品和太原地面加密自动站资料,对2008年6月28日出现在太原地区的一次强对流天气过程进行了分析,结果发现:①高空冷涡和中低空暖湿气团配置为此次强对流天气提供了有利的环流背景条件。②雷达回波的形状、结构、VIL均显示出强对流特征,速度辐合区与地面中尺度辐合线相对应,垂直方向存在强烈的风切变。③逐小时变温场显示出冷空气入侵路径、强度,负变温中心未来成为强对流天气区。④地面中尺度辐合线是强对流发生的触发机制,逐小时变压场的负中心与随后出现的灾害性天气区有效对应。⑤对流发生前,单站气象要素出现显著的不连续变化,气压和湿度呈同位相变化,与气温变化则反位相,3者在对流发生前1h同步出现谷(峰)值,灾害天气出现在之后的要素陡升(降)时段内。     

Simulating the effect of hydrate dissociation on wellhead stability during oil and gas development in deepwater

It is well known that methane hydrate has been identified as an alternative resource due to its massive reserves and clean property. However, hydrate dissociation during oil and gas development (OGD) process in deep water can affect the stability of subsea equipment and formation. Currently, there is a serious lack of studies over quantitative assessment on the effects of hydrate dissociation on wellhead stability. In order to solve this problem, ABAQUS finite element software was used to develop a model and to evaluate the behavior of wellhead caused by hydrate dissociation. The factors that affect the wellhead stability include dissociation range, depth of hydrate formation and mechanical properties of dissociated hydrate region. Based on these, series of simulations were carried out to determine the wellhead displacement. The results revealed that, continuous dissociation of hydrate in homogeneous and isotropic formations can causes the non-linear increment in vertical displacement of wellhead. The displacement of wellhead showed good agreement with the settlement of overlying formations under the same conditions. In addition, the shallower and thicker hydrate formation can aggravate the influence of hydrate dissociation on the wellhead stability. Further, it was observed that with the declining elastic modulus and Poisson’s ratio, the wellhead displacement increases. Hence, these findings not only confirm the effect of hydrate dissociation on the wellhead stability, but also lend support to the actions, such as cooling the drilling fluid, which can reduce the hydrate dissociation range and further make deepwater operations safer and more efficient.