The topographic bias by analytical continuation in physical geodesy

This study emphasizes that the harmonic downward continuation of an external representation of the Earth’s gravity potential to sea level through the topographic masses implies a topographic bias. It is shown that the bias is only dependent on the topographic density along the geocentric radius at the computation point. The bias corresponds to the combined topographic geoid effect, i.e., the sum of the direct and indirect topographic effects. For a laterally variable topographic density function, the combined geoid effect is proportional to terms of powers two and three of the topographic height, while all higher order terms vanish. The result is useful in geoid determination by analytical continuation, e.g., from an Earth gravity model, Stokes’s formula or a combination thereof.     

Comparison of Galerkin-type discretization techniques for two-phase flow in heterogeneous porous media

A comparison of Standard Galerkin, Petrov-Galerkin, and Fully-Upwind Galerkin methods for the simulation of two-phase flow in heterogeneous porous media is presented. On the basis of the coupled pressure-saturation equations, a generalized formulation for all three finite element methods is derived and analysed. For flow in homogeneous media, the Petrov-Galerkin method gives excellent results. But this method fails miserably for problems with heterogeneous media. This is because it is not able to capture correctly processes that take place at interfaces when, for instance, the capillary pressure-saturation relationship after Brooks and Corey is assumed. The Fully-Upwind Galerkin method is superior to the Petrov-Galerkin approach because it is able to give correct results for flow in homogeneous and heterogeneous media for the two models of van Genuchten and Brooks-Corey. The widely used formulation which is correct for the homogeneous case cannot be used for heterogeneous media. Instead the straightforward approach of gradp_c in combination with a chord-slope technique must be utilized.     

Oxygen and Carbon Isotopes of Cold-water Corals—Reconstructing Paleotemperature Changes and Calcification Mechanism

Cold-water corals represent an intriguing paleoceanographic archive with a great potential to reconstruct high-resolution paleoenvironmental changes. Compared to those of shallow-water corals, proxies derived from cold-water corals have been complicated by biologically mediated vital effects. The oxygen and carbon stable isotope compositions of cold-water coral skeletons are more depleted than the expected carbonate-seawater equilibrium values by 4‰~6‰ and about 10‰, respectively. Therefore, it is necessary to correct for the vital effects before using δ¹⁸O as a temperature proxy. The principles and methods of reconstructing paleotemperature variations of intermediate and deep oceans using oxygen and carbon isotopes of cold-water corals are reviewed, as well as three existing cold-water coral calcification models and their advantages and disadvantages. It is suggested that further micro-scales analysis and targeted experiments are required to clarify the calcification processes of cold-water corals.     

Node-centered finite volume discretizations for the numerical simulation of multiphase flow in heterogeneous porous media

Three node-centered finite volume discretizations for multiphase porous media flow are presented and compared. By combination of these methods two additional discretization methods are generated. The ability of these schemes to describe flows at textural interfaces of different geologic formations is investigated. It was found that models with nonzero-entry pressures for the capillary pressure-saturation relationship in conjunction with the Box discretization may give rise to spurious oscillations for flows around low permeable lenses. Furthermore, the applicability and sensitivity of the discretization methods with regard to the used computational grids is discussed. The schemes are used for the numerical study of two-phase flow in porous media with zones of different material properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Discrete Wavenumber Boundary Element Method for study of the 3-D response 2-D scatterers

A mathematical formulation of the 2·5D elastodynamic scattering problem is presented and validated. The formulation is a straightforward extension of the Discrete Wave number Boundary Integral Equation Method (DWBIEM) originally proposed by Kawase¹ for 2D scattering problems and subsequently extended to the 3D problem by Kim and Papageorgiou.² It is demonstrated that the Green's function which is appropriate for a boundary formulation of the 2·5D elastodynamic scattering problem is the one corresponding to a unit force moving on a straight line with constant velocity. Such a Green's function is derived in the present study. The formulation may be used to study the wavefields in models of sedimentary deposits (e.g. valleys) or topography (e.g. canyons or ridges) with a 2D variation in structure but obliquely incident plane waves. The advantage of a 2·5D formulation is that it provides the means for calculations of 3D wavefields in scattering problems by requiring a storage comparable to that of the corresponding 2D calculations. © 1998 John Wiley & Sons, Ltd.     

西南岩溶地下水资源开发利用效应与潜力分析

西南岩溶地区面积78万km2,地下水系统包括裸露岩溶水系统和覆盖-埋藏型岩溶水系统两大类。由于降水丰富、地下岩溶发育,西南岩溶地下水资源丰富,在43万km2调查区内,具有地下水天然资源量1762.82×108m3/a,岩溶地下水允许开采资源量615.70×108m3/a。近年来,通过开展水文地质调查,在地下河、表层岩溶水和蓄水构造岩溶水打井开采方面均取得重要进展,产生了显著的经济和生态环境效应。但由于西南地区岩溶水开发难度大,区域经济落后,西南岩溶地下水的开发利用程度普遍较低,已开采量为98.32×108m3/a,仅占允许开采量的15.97%,剩余地下水潜力资源量517.38×108m3/a。     

The “Zero-order Model” revisited: Paul Schindler's influence on the development of trace metal scavenging models

In 1975 Paul Schindler produced the first oceanic trace metal scavenging model to explicitly include the role of surface chemistry as a control on trace metal water column residence times. The eighteen years that have elapsed since the publication of Schindler's seminal paper have seen the development of a variety of oceanic scavenging models; yet, the fundamental insight of his Zero-order Model remains the benchmark. This paper describes the role of Paul Schindler's work on surface chemistry in providing a framework for the current generation of trace element scavenging models.     

高山峡谷区影响土壤测量找矿效果的元素表生活动特性研究

研究发现，高山峡谷区内土壤中元素的表生活动以表生富集作用为主，元素表征富集作用的程度、富集层位和粒级等受矿化作用和自然风化作用双重影响。非矿化地段土壤中元素的表生富集程度较矿化带处土壤中元素表生富集程度更强；矿化带处B层土壤比A层土壤中元素的富集强度稍大，元素明显地富集在粗粒级组分中；近矿（化）带的非矿化地段，A、B两层土壤仍受到矿化组分的影响，A层土壤比B层土壤受到的影响更加明显，粗粒级组分比细粒级组分反映敏感，C层土壤中元素在细粒级组分中轻微富集。根据本次研究结果，调整了高山峡谷区土壤测量工作方法，经试点测量验证，找矿效果良好。     

Improvement in the performance of solar adaptive optics

Adaptive optics （AO）, which provides diffraction limited imaging over a field-of-view （FOV）, is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor （WFS） is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors （DMs）. This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope （pointing toward zenith） is related to atmospheric anisoplanatism. We theoretically quantify the performance of the to- mographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10＂ - 80＂ diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric prop- erties at ground level, and present the optimum DM conjugate altitudes for different observation sites.