Topographic gravitational potential up to second-order derivatives: an examination of approximation errors caused by rock-equivalent topography (RET)   总被引：3，自引：2，他引：1  

Michael Kuhn  Christian Hirt 《Journal of Geodesy》2016,90(9):883-902

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Settling-velocity distributions and sorting processes on a longitudinal dune: A case study     

Daniel Hartmann  Christian Christiansen 《地球表面变化过程与地形》1988,13(7):649-656

The processes acting on a longitudinal dune are inferred from the response in the area size-sorting characteristics of the sediment of the active layer. The sediment size distributions are determined by settling and are best described by a log-hyperbolic model which provides the most information on size-sorting processes. Size-sorting characteristics are markedly different across the low round-crested part of the dune from cross-sections of the high more sharp-crested part. This results in changes in textural parameters along the lee-side consistent with changes in the lee-side separation vortex. This is the first time that the effect of wind speed up on the lee-side is observed to be reflected in the sediment; it can only be detected with the very sensitive log-hyperbolic parameters.  相似文献   

Dating of mine waste in lacustrine sediments using cesium-137     

W. C. Rember  T. W. Erdman  M. L. Hoffmann  V. E. Chamberlain  K. F. Sprenke 《Environmental Geology》1993,22(3):242-245

For over a century Medicine Lake in northern Idaho has received heavy-metal-laden tailings from the Coeur d'Alene mining district. Establishing the depositional chronology of the lake bottom sediments provides information on the source and rate of deposition of the tailings. Cesium-137, an isotope produced in the atmosphere by nuclear bomb tests, was virtually absent in the environment prior to 1951, but reached its apex in 1964. Our analysis of cesium-137 in the sediments of Medicine Lake revealed that 14 cm of fine-grained tailings were deposited in the lake from 1951 to 1964 and tailing deposition downstream was greatly reduced by the installation of tailings dams in the district in 1968. Cesium-137 analysis is accomplished by a fairly simple gamma-ray counting technique and should be a valuable tool for analyzing sedimentation in any lacustrine environment that was active during the 1950s and 1960s.  相似文献   

Explorations into the formal structure of drainage basins     

Christian Werner 《地球表面变化过程与地形》1994,19(8):747-762

Every basin of higher than first order is drained by a channel network composed of two subnetworks. Their basins are separated by a drainage divide line, called the basin divider, which is the primary organizing feature of the main basin. Each basin of magnitude n contains n – 1 subnetworks of higher order, and is therefore organized by a set of n – 1 dividers. The dividers and the basin boundary are interconnected in a graph called the divider network of the basin; in graph-theoretic terms this network forms a tree and has the same magnitude and link numbers as the channel network draining the basin. While the subbasins and subnetworks of a drainage basin form a nesting hierarchy, the corresponding dividers do not; indeed, any two dividers share at most one node in common, and whether they do so is independent of whether the corresponding subbasins are nesting or disjoint. However, the dividers of nesting basins are linked by recursive relationships which permit the derivation of a set of algebraic equations; these equations relate the dividers of a basin to other basin components; for example, their combined length is equal to half the length of all first-order basin boundaries minus the length of the main basin boundary. The second part of the paper explores the dependence of the divider length on other basin parameters. The expected length, as predicted by the assumption of topological randomness, is clearly rejected by the data. An alternative approach (regression) is based on the observed magnitudes of the subbasins separated by each divider, and is reasonably successful in estimating divider length. The last section introduces the concept of the standardized basin defined by a boundary length of unity; the estimated lengths of the basin divider and the basin boundary permit an approximate reconstruction of the idealized basin shape and the location of the divider in it.  相似文献   

Reply to 'Can magnetic-force microscopy determine micromagnetic structures?' by Grütter and Allenspach     

W. Williams  V. Hoffmann  F. Heider  T. Göddenhenrich  C. Heiden 《Geophysical Journal International》1994,116(2):506-507

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Tidal river sediments in the Washington,D.C. area. III. Biological effects associated with sediment contamination     

Christian E. Schlekat  Beth L. McGee  Eli Reinharz  David J. Velinsky  Terry L. Wade 《Estuaries and Coasts》1994,17(2):334-344

Sediment toxicity and benthic macroinvertebrate community structure were measured as one component of a study cohceived to determine the distribution and effect of sediment contamination in tidal freshwater portions of the Potomac and Anacostia rivers in the Washington, D.C., area. Samples were collected at 15 sites. Analyses included a partial life cycle (28 d) whole sediment test using the amphipod Hyalella azteca (Talitridae) and an assessment of benthic community structure. Survival and growth (as estimated by amphipod length) were experimental endopoints for the toxicity test. Significant mortality was observed in 5 of 10 sites in the lower Anacostia River basin and at the main channel Potomac River site. Sublethal toxicity, as measured by inhibition of amphipod growth, was not observed. Toxicity test results were in general agreement with synoptically measured sediment contaminant concentrations. Porewater total ammonia (NH₃+NH₄ ⁺) appears to be responsible for the toxicity of sediments from the Potomac River, while correlation analysis and simultaneously extracted metals: acid volatile sulfide (SEM∶AVS) results suggest that the toxicity associated with Anacostia River sediments was due to organic compounds. Twenty-eight macroinvertebrate taxa were identified among all sites, with richness varying from 5 to 17 taxa per site. Groups of benthic assemblages identified by group-average cluster analysis exhibited variable agreement with sediment chemical and sediment toxicity results. Integration of toxicological, chemical, and ecological components suggests that adverse environmental effects manifest in the lower Anacostia River benthos result from chemical contamination of sediment.  相似文献   

Influence of bottom topography roughness on the jet and inertial recirculation of a mid-latitude gyre     

Bernard Barnier  Christian Le Provost 《Dynamics of Atmospheres and Oceans》1993,18(1-2)

Several numerical experiments are conducted to examine the influence of mesoscale, bottom topography roughness on the inertial circulation of a wind-driven, mid-latitude ocean gyre. The ocean model is based on the quasi-geostrophic formulation, and is eddy-resolving as it features high vertical and horizontal resolutions (six layers and a 10 km grid). An antisymmetrical double-gyre wind stress curl forces the baroclinic modes and generates a strong surface jet. In the case of a flat bottom, inertia and inverse energy cascade force the barotropic mode, and the resulting circulation features strong, barotropic, inertial gyres. The sea-floor roughness inhibits the inertial circulation in the deep layers; the barotropic component of the flow is then forced by eddy-topography interactions, and its energy concentrates at the scales of the topography. As a result, the baroclinicity of the flow is intesified: the barotropic mode is reduced with regard to the baroclinic modes, and the bottom flow (constrained by the mesoscale sea-floor roughness) is decoupled from the surface flow (forced by the gyre-scale wind). Rectified, mesoscale bottom circulation induces an interfacial form stress at the thermocline, which enhances horizontal shear instability and opposes the eastward penetration of the jet. The mean jet is consequently shortened, but the instantaneous jet remains very turbulent, with meanders of large meridional extent. The sea-floor roughness modifies the energy pathways, and the eddies have an even more important role in the establishment of the mean circulation: below the thermocline, rectification processes are dominant, and eddies transfer energy toward permanent mesoscale circulations strongly correlated with topography, whereas above the thermocline mean flow and eddy generation are influenced by the mean bottom circulation through interfacial stress. The topography modifies the vorticity of the barotropic and highest baroclinic modes. Vorticity accumulates at the small topographic scales, and the vorticity content of the highest modes, which is very weak in the flat-bottom case, increases significantly. Few changes occur in surface-intensified modes. In the deep layers of the model, the inverse correlation between relative vorticity and topography at small scales ensures the homogenization of the potential vorticity, which mainly retains the largest scales of the bottom flow and the scale of β.  相似文献   

Development of a High Magnification Enlarger     

R P Dubey  N D Christian  K D Mallick 《Journal of the Indian Society of Remote Sensing》1991,19(4):277-286

Visual interpretation forms the basis for many operational applications of remote sensing. Suitable enlargement of remotely sensed data by optical projection is a basic requirement for visual interpretation. High Magnification Enlarger (HME) is a versatile interpretation aid developed for achieving wide-ranging scale transfer and variable-magnification display from a standard 24 cm format transparency. It operates on the principle of optical projection and is configured as a vertical column mounted unit. Low-distortion, high-quality enlarging lenses coupled with accuracy of alignment ensure accurate reproduction of the scale and the finer details from the input image transparency. Maximum user convenience is achieved by motorization of various controls.  相似文献   

Cloudphysical parameters in dependence on height above cloud base in different clouds     

H. -E. Hoffmann  R. Roth 《Meteorology and Atmospheric Physics》1989,41(4):247-254

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Heavy metal pollution in the Arcachon Basin (France) : Bonding states     

Christian Carruesco  Yvon Lapaquellerie 《Marine pollution bulletin》1985,16(12):493-497

Information available (since 1977) from a great many recent surveys on the Arcachon Basin has enabled us to determine three characteristic environments and study the behaviour of heavy metals (Ni, Cu, Zn, Pb, Cd, Hg). The relationship between heavy metals and grain-size fractions has been determined after having specified whether metals were preferentially organically or inorganically bound. This study has allowed us to establish the origin (natural or anthropogenic) of metallic enrichment and assess the extent of pollution.  相似文献