Delineating depth to bedrock beneath shallow unconfined aquifers: a gravity transect across the Palmer River Basin   总被引：1，自引：0，他引：1  

Bohidar RN  Sullivan JP  Hermance JF 《Ground water》2001,39(5):729-736

In view of the increasing demand on ground water supplies in the northeastern United States, it is imperative to develop appropriate methods to geophysically characterize the most widely used sources of ground water in the region: shallow unconfined aquifers consisting of well-sorted, stratified glacial deposits laid down in bedrock valleys and channels. The gravity method, despite its proven value in delineating buried bedrock valleys elsewhere, is seldom used by geophysical contractors in this region. To demonstrate the method's effectiveness for evaluating such aquifers, a pilot study was undertaken in the Palmer River Basin in southeastern Massachusetts. Because bedrock is so shallow beneath this aquifer (maximum depth is 30 m), the depth-integrated mass deficiency of the overlying unconsolidated material was small, so that the observed gravity anomaly was on the order of 1 milligal (mGal) or less. Thus data uncertainties were significant. Moreover, unlike previous gravity studies elsewhere, we had no a priori information on the density of the sediment. Under such circumstances, it is essential to include model constraints and weighted least-squares in the inversion procedure. Among the model constraints were water table configuration, bedrock outcrops, and depth to bedrock from five water wells. Our procedure allowed us to delineate depth to bedrock along a 3.5 km profile with a confidence interval of 1.8 m at a nominal depth of 17 m. Moreover, we obtained a porosity estimate in the range of 39% to 44%. Thus the gravity method, with appropriate refinements, is an effective tool for the reconnaissance of shallow unconfined aquifers.  相似文献   

湿润大气中锋生的非流体静力模拟     

Lofo.  JP 徐明 《气象科技》1992,(6):59-61

1.引言在过去二十年间,大量观测已揭示出伴随锋面系统的带状降水结构.这些研究强调指出,千差万别的天气现象是发生在锋面系统内包含的不同时空尺度上.因此对降水带的理解和预报,是一项困难的工作.半地转理论(Hoskins和Bretherton,1972)是当今全面阐述锋生过程的最合适的基本构想.为改进对锋面的描述,通过显式模拟对流和大尺度气流,用非流体静力云模式(Redelsperger和Sommeria,1986)对由切变引起的锋生,进行二维高分辨率(5km)模拟.模式的  相似文献   

地壳深熔过程中副矿物对铅同位素再分配的影响     

Hogan  JP 杨俊龙 《国外花岗岩类地质与矿产》1992,(2):1-8

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A First Comparison of the Surface Brightness Fluctuation Survey Distances with the Galaxy Density Field: Implications for H0 and Omega     

Blakeslee JP  Davis M  Tonry JL  Dressler A  Ajhar EA 《The Astrophysical journal》1999,527(2):L73-L76

We compare the peculiar velocities measured in the surface brightness fluctuation survey of galaxy distances with the predictions from the density fields of the IRAS 1.2 Jy flux-limited redshift survey and the optical redshift survey (ORS) to derive simultaneous constraints on the Hubble constant H0 and the density parameter beta=Omega0.6&solm0;b, where b is the linear bias. We find that betaI=0.42+0.10-0.06 and betaO=0.26+/-0.08 for the IRAS and ORS comparisons, respectively, and that H0=74+/-4 km s-1 Mpc (with an additional 9% uncertainty due to the Cepheids themselves). The match between predicted and observed peculiar velocities is good for these values of H0 and beta, and although there is covariance between the two parameters, our results clearly point toward low-density cosmologies. Thus, the unresolved discrepancy between the "velocity-velocity" and "density-density" measurements of beta continues.  相似文献   

Education challenges in the North Sea area     

Ducrotoy JP 《Marine pollution bulletin》2003,47(1-6):246-252

This paper introduces the North Sea as a fast evolving coastal ecosystem. The variability of natural conditions relates to the global climatic change and to human disturbances, which originate regionally. Education is an integral part of the strategy to improve environmental awareness. Considering contemporary challenges for educating the wider public about the main issues of environmental concern, attention is paid to various plans, which are being developed in North-Western Europe from primary schools to universities. "Learning for life" relies on an opening of the vocation of traditional universities and on the creation of a European university. Sharing resources in a competitive environment is one response given by British universities in the framework of a Discipline Network in Coastal Sciences and Management in 1996-2000. Networking is truly the key to a fast evolving teaching and learning context, notably in relation to ever developing information and communication technologies. The dissemination of scientific information is primordial in this context; a case study relating to the European project "Marine biodiversity in Europe" (BIOMARE) demonstrates the need for an elaborated strategy leading to socio-economic considerations. Empowering communities and governance are the main possible outcomes of such an enlarged approach to education, involving teachers, students, researchers, professionals, and volunteers. Proposals are made for amplifying the involvement of non-scientists into scientific research and its applications to management. Finally, a case is made for facilitating the mobility of all concerned, with a view to annihilate language and cultural barriers.  相似文献   

Nucleosynthesis and Mixing in Cassiopeia A     

Hughes JP  Rakowski CE  Burrows DN  Slane PO 《The Astrophysical journal》2000,528(2):L109-L113

We present results from the first light observations of the Cassiopeia A supernova remnant (SNR) by the Chandra X-Ray Observatory. Based on representative spectra from four selected regions, we investigate the processes of nucleosynthesis and mixing in Cas A. We make the first unequivocal identification of iron-rich ejecta produced by explosive silicon burning in a young Galactic SNR. Elsewhere in the remnant, we see silicon-rich ejecta from explosive oxygen burning. The Fe-rich ejecta lie outside the Si-rich material, indicating that bulk motions were extensive and energetic enough in Cas A to cause a spatial inversion of a significant portion of the supernova core. It is likely that this inversion was caused by "Fe"-rich ejecta emerging in plumes from the rising bubbles in the neutrino-driven convection layer during the supernova explosion. In addition, the radioactive decay energy from 56Ni may have contributed to the subsequent evolution of the material. We have also discovered faint, well-defined filaments with featureless X-ray spectra that are possibly sites of cosmic-ray acceleration in Cas A.  相似文献   

巴布亚新几内亚波尔盖拉（Porgera）金矿床流体化学及其作用   总被引：1，自引：0，他引：1  

孙希 Rich.  JP 《世界地质》1998,17(1):26-39

巴布亚新几内亚波尔盖拉（Ｐｏｒｇｅｒａ）金矿床是世界的碱性浅成熟液金矿体系（第Ⅱ阶段）的一个实例,同时它经过岩浆热液金成矿的初始阶段（第Ⅰ阶段）,通过这两个成矿阶段矿脉中流体包囊体的气体及离子色谱分析（ＧＣ和ＩＣ）可确定在成矿过程中流体的组分及其参与过程。这些数据资料显示了三种端元组分流体的存在,其中最稀释的一种贯穿了整个成矿过程,被认为是大气起源经过演化的地下水,它的成分包括５００ｍｉＭＮａ＾＋  相似文献   

Temporal survey of petroleum hydrocarbons, organochlorinated compounds and heavy metals in benthic marine organisms from Dhofar, southern Oman     

Fowler SW  Villeneuve JP  Wyse E  Jupp B  de Mora S 《Marine pollution bulletin》2007,54(3):357-367

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法国某热液金矿床中有机质与金的共生关系     

Gate.  JP 吴龙英 《国外地质(成都)》1990,(4):75-81

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犹他州沃萨奇断裂带韦伯段凯斯维尔场地全新世断层活动的重新评价     

McCa.  JP 楚全芝 《地震地质译丛》1995,17(3):17-28

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