Dynamical friction force exerted on spherical bodies     

O. Esquivel †  B. Fuchs 《Monthly notices of the Royal Astronomical Society》2007,378(3):1191-1195

We present a rigorous calculation of the dynamical friction force exerted on a spherical massive perturber moving through an infinite homogenous system of field stars. By calculating the shape and mass of the polarization cloud induced by the perturber in the background system, which decelerates the motion of the perturber, we recover Chandrasekhar's drag force law with a modified Coulomb logarithm. As concrete examples, we calculate the drag force exerted on a Plummer sphere or a sphere with the density distribution of a Hernquist profile. It is shown that the shape of the perturber only affects the exact form of the Coulomb logarithm. The latter converges on small scales because encounters of the test and field stars with impact parameters less than the size of the massive perturber become inefficient. We confirm in this way the earlier results based on the impulse approximation of small angle scatterings.  相似文献   

Tectono‐sedimentary evolution of lower to middle Miocene half‐graben basins related to an extensional detachment fault (western Crete,Greece)     

Markus Seidel  Eberhard Seidel  Bernhard Stckhert 《地学学报》2007,19(1):39-47

Crustal extension in the overriding plate at the Aegean subduction zone, related to the rollback of the subducting African slab in the Miocene, resulted in a detachment fault separating high‐pressure/low‐temperature (HP‐LT) metamorphic lower from non‐metamorphic upper tectonic units on Crete. In western Crete, detachment faulting at deeper crustal levels was accompanied by structural disintegration of the hangingwall leading to the formation of half‐graben‐type sedimentary basins filled by alluvial fan and fan‐delta deposits. The coarse‐grained clastic sediments in these half‐grabens are exclusively derived from the non‐metamorphic units atop the detachment fault. Being in direct tectonic contact with HP‐LT metamorphic rocks of the lower tectonic units today, the basins must have formed in the period between c. 20 and 15 Ma, prior to the exposure of the HP‐LT metamorphic rocks at the surface, and juxtaposed with the latter during ongoing deformation.  相似文献   

Singular value decomposition and cluster analysis as regression diagnostics tools for geodetic applications     

Markus Vennebusch  Axel Nothnagel  Hansjörg Kutterer 《Journal of Geodesy》2009,83(9):877-891

It is well known that high-leverage observations significantly affect the estimation of parameters. In geodetic literature, mainly redundancy numbers are used for the detection of single high-leverage observations or of single redundant observations. In this paper a further objective method for the detection of groups of important and less important (and thus redundant) observations is developed. In addition, the parameters which are predominantly affected by these groups of observations are identified. This method thus complements other diagnostics tools, such as, e.g., multiple row diagnostics methods as described in statistical literature (see, e.g., Belsley et al. in Regression diagnostics: identifying influential data and sources of collinearity. Wiley, New York, 1980). The method proposed in this paper is based on geometric aspects of adjustment theory and uses the singular value decomposition of the design matrix of an adjustment problem together with cluster analysis methods for regression diagnostics. It can be applied to any geodetic adjustment problem and can be used for the detection of (groups of) observations that significantly affect the estimated parameters or that are of negligible impact. One of the advantages of the proposed method is the improvement of the reliability of observation plans and thus the reduction of the impact of individual observations (and outliers) on the estimated parameters. This is of particular importance for the very long baseline interferometry technique which serves as an application example of the regression diagnostics tool.  相似文献   

Wide-angle vibroseis test across the Rhine graben   总被引：1，自引：0，他引：1  

B. Damotte  K. Fuchs  E. Lüschen  F. Wenzel  R. Schlich  G. Toreilles 《Geophysical Journal International》1987,89(1):313-318

Summary. As a joint operation of ECORS and DEKORP, a deep wide-angle seismic experiment using vibrators was carried out in the autumn of 1984. The object was to get information on the deep crust under the Rhine graben without crossing through sedimentary layers. Offsets were in the range of 50 to 89 km. In the first phase, two vibration points were executed in the Vosges mountains. A signal was received in the Black Forest from solely the farthest VP. In the second phase, fourteen VPs were executed in the Black Forest. No stacking or correlation was performed in the field in France. The quality of the results is good only if an equalization is applied before vertical stacking and correlation in the computing centre.  相似文献   

Numerical and Experimental Analysis of A Ducted Propeller Designed by A Fully Automated Optimization Process Under Open Water Condition     

余龙  Markus DRUCKENBROD  Martin GREVE  王珂琦  Moustafa ABDEL-MAKSOUD 《海洋工程》2015,29(5):733-744

A fully automated optimization process is provided for the design of ducted propellers under open water conditions, including 3D geometry modeling, meshing, optimization algorithm and CFD analysis techniques. The developed process allows the direct integration of a RANSE solver in the design stage. A practical ducted propeller design case study is carried out for validation. Numerical simulations and open water tests are fulfilled and proved that the optimum ducted propeller improves hydrodynamic performance as predicted.  相似文献   

Advancing the interdisciplinary dialogue on climate justice     

Dominic Roser  Christian Huggel  Markus Ohndorf  Ivo Wallimann-Helmer 《Climatic change》2015,133(3):349-359

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Variability of high rainfalls and related synoptic situations causing heavy floods at the northern foothills of the Tatra Mountains     

Tadeusz Niedźwiedź  Ewa Łupikasza  Iwona Pińskwar  Zbigniew W. Kundzewicz  Markus Stoffel  Łukasz Małarzewski 《Theoretical and Applied Climatology》2015,119(1-2):273-284

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Sedimentary evolution of a late Pleistocene wetland indicating extreme coastal uplift in southern Tanzania     

Markus Reuter  W.E. Piller 《Quaternary Research》2010,73(1):136-142

Facies analyses of Pleistocene deposits from southern coastal Tanzania (Lindi District) document that sediments formed in a wetland evolving on a coastal terrace in the Lindi Fracture Zone foreland. The exposed succession shows a marked sedimentary change from tidal to terrestrial facies. ¹⁴C analyses on gastropod shells indicate the emergence of the Lindi coast at ∼ 44 ¹⁴C ka BP. Emergence and subsequent elevation of terraces to 21 m above present-day sea level was linked to the falling eustatic sea level prior to the last glacial maximum, and to a periodic elevation due to extensional tectonic episodes in the eastern branch of the East African Rift System (EARS). Since ∼ 44 ¹⁴C ka BP tectonic uplift at the coast was 80-110 m, comparable to that in the extreme uplift areas of the EARS.  相似文献   

Preface: special section of papers dealing with overdeepened basins and valleys in the alpine realm     

Markus Fiebig  Frank Preusser  Kurt Decker  Christian Schlüchter 《Swiss Journal of Geoscience》2010,103(3):327-328

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Hydrostatic pore water pressure revisited     

Simon A. Stewart  Markus Albertz 《Basin Research》2023,35(1):172-186

Hydrostatic or “normal” pressure can be easily visualized as a water column with pressure given by ρgh and any departures classified as abnormal pressure. This is the basis for commonly used hydrostatic pressure depth trends in sedimentary basins that are constructed on assumptions of constant gradients and are datumed at mean sea level or ground level. But the straightforward water column concept does not upscale in a simple way to sedimentary basins where the zones of interest are several thousands of metres below the land or sea surface. Sedimentary basins are heterogeneous, including stacked, confined reservoirs and variations in pore water composition. It is possible to construct pressure-depth profiles that honour the geology and hydrostratigraphy of a basin and these give different hydrostatic baselines from simple constant gradients hung from familiar local datums such as ground level. Key steps are using a reservoir-specific datums such as the water table or potentiometric surface relevant to that unit, then building a pressure-depth trend that represents the pore fluid salinity variation and density profile throughout the reservoir unit. At a given depth, this version of hydrostatic may predict pressures several hundred psi different from a single density gradient hung from a datum local to the well, and exhibit a notched profile reflecting the geological and hydrological stratigraphy. This construct redefines normal and abnormal pore fluid pressures in sedimentary basins. The impacts of this alternative approach to sedimentary basin hydrostatics, even if data are limited and pressure profiles have to be framed probabilistically, extend to many aspects of studying and interacting with fluid systems in sedimentary basins including basin modelling, petroleum systems analysis, well planning and well operations.  相似文献