Palaeointensity results from Ethiopian basalts: implications for the Oligocene geomagnetic field strength     

Janna Riisager  Mireille Perrin  & Pierre Rochette 《Geophysical Journal International》1999,138(2):590-596

From a large collection of Ethiopian flood basalts (~30  Myr old) sampled for magnetostratigraphy, ⁴⁰Ar/³⁹Ar geochronology and geochemical investigations, 47 samples were selected in order to test their suitability for Thellier palaeointensity experiments. Only 17 samples from eight individual flows yielded reliable palaeointensity estimates, with flow-mean virtual dipole moments ranging from 3.0 to 10.5 × 10²²  A  m² .
  A critical review of the Oligocene palaeointensity data set, including these new Ethiopian data, indicates an Oligocene mean virtual dipole moment of 5.1 ± 2.5 × 10²²  A  m² for the complete data set. After applying mild selection criteria, the reduced data set yields a mean value of only 4.6 ± 1.9 × 10²²  A  m² . This value is significantly lower than the present-day field strength but is higher than the Mesozoic dipole low mean field. This low Oligocene field might be in agreement with the high palaeosecular variation and rather high non-dipole field invoked around 30  Ma. However, the Oligocene data set is largely dependent on the palaeointensity determinations from Armenia, obtained mainly from baked contacts, which show amazingly low dispersion at both flow and between-flow levels. More data are needed to reduce the weight of these determinations on the mean value and avoid a possible bias.  相似文献   

An active wave generating–absorbing boundary condition for VOF type numerical model     

Peter Troch  Julien De Rouck 《Coastal Engineering》1999,38(4):2145

The objective of the present work is to discuss the implementation of an active wave generating–absorbing boundary condition for a numerical model based on the Volume Of Fluid (VOF) method for tracking free surfaces. First an overview of the development of VOF type models with special emphasis in the field of coastal engineering is given. A new type of numerical boundary condition for combined wave generation and absorption in the numerical model VOFbreak² is presented. The numerical boundary condition is based on an active wave absorption system that was first developed in the context of physical wave flume experiments, using a wave paddle. The method applies to regular and irregular waves. Velocities are measured at one location inside the computational domain. The reflected wave train is separated from the incident wave field in front of a structure by means of digital filtering and subsequent superposition of the measured velocity signals. The incident wave signal is corrected, so that the reflected wave is effectively absorbed at the boundary. The digital filters are derived theoretically and their practical design is discussed. The practical use of this numerical boundary condition is compared to the use of the absorption system in a physical wave flume. The effectiveness of the active wave generating–absorbing boundary condition finally is proved using analytical tests and numerical simulations with VOFbreak².  相似文献   

Geophysical and structural signatures of syntectonic batholith construction: the South Mountain Batholith, Meguma Terrane, Nova Scotia   总被引：2，自引：0，他引：2  

K. Benn  W. R. Roest  P. Rochette  N. G. Evans  & G. S. Pignotta 《Geophysical Journal International》1999,136(1):144-158

The Late Devonian South Mountain Batholith is a very large (7000 km²) composite peraluminous granitoid complex situated within the Meguma Terrane of the northern Appalachians. It is made up of two suites of granodioritic to leucogranitic plutons emplaced at approximately 380–370 Ma during the Acadian Orogeny, i.e. during the collision of Gondwana with the eastern margin of North America. A significant geophysical and geological database makes the South Mountain Batholith a type example of a very large syntectonic batholith emplaced within a collisional orogen. Gravity models reveal the plutons have flat or gently dipping floors at approximately 7.0 km depth and aspect ratios >6:1. They are underlain by deeper (>10 km) elongate northeast–southwest-trending roots that may indicate magma feeder zones. Dyke transport of granitic magma and the progressive construction of plutons by sheet injections are supported by field observations and by mapping of the anisotropy of magnetic susceptibility at the pluton scale. The very narrow deformation aureole within the country rocks suggests lateral spreading of the plutons was not the main space creation mechanism during emplacement; space was mostly created by vertical displacements of country rocks. The data are consistent with a laccolithic model for syntectonic batholith assembly. The laccolithic plutons may have been emplaced at the base of the Meguma Supergroup metasedimentary rocks, suggesting a maximum thickness of approximately 7.0 km for the supracrustal rocks in the Meguma Terrane.  相似文献   

The Integration of Scene Understanding within a Geographic Information System: A Prototype Approach for Agricultural Applications     

Mark Gahegan  & Julien Flack 《Transactions in GIS》1999,3(1):31-49

This paper describes progress towards engineering a combined GIS and image understanding system, designed to analyse remotely-sensed imagery in a task-oriented manner, with the task and contextual parameters being supplied by the GIS. The overall aim is to evaluate some of the more recent developments in the field of computer vision and to show how they may be integrated (along with more traditional methods of image interpretation) to improve system performance in terms of object recognition and extraction. Three aspects are reported: (1) Development of a formal notation as the basis of describing the process of transforming data from low level image representations to high level object representations; (2) Design of collaborating low and high level image processes used in this abstraction process and their control via Process Networks encapsulated into frames ; and (3) Use of Dempster-Shafer Decision Theory as the basis for combining different types of evidence to improve the recognition of objects in the scene. Some sample results are presented to illustrate the issues raised and mechanisms for the co-operative processing of data are suggested.  相似文献   

Perspectives of a visible instrument on the VLTI     

Florentin Millour  Denis Mourard  Julien Woillez  Philippe Berio  Andrea Chiavassa  Orlagh Creevey  Eric Lagadec  Marc-Antoine Martinod  Anthony Meilland  Nicolas Nardetto  Karine Perraut  Philippe Stee 《Experimental Astronomy》2018,46(3):497-509

In this paper we present the most promising science cases for a new generation visible instrument on the VLTI and the conceptual idea for the instrumental configuration. We also present a statistical study of the potential targets that may be accessible for the different classes of objects and for the required spectral resolutions.  相似文献   

Modelling of drainage dynamics influence on sediment routing system in a fold‐and‐thrust belt     

Marc Viaplana‐Muzas  Julien Babault  Stphane Dominguez  Jean Van Den Driessche  Xavier Legrand 《Basin Research》2019,31(2):290-310

Drainage networks link erosional landscapes and sedimentary basins in a source‐to‐sink system, controlling the spatial and temporal distribution of sediment flux at the outlets. Variations of accumulation rates in a sedimentary basin have been classically interpreted as changes in erosion rates driven by tectonics and/or climate. We studied the interactions between deformation, rainfall rate and the intrinsic dynamics of drainage basins in an experimental fold‐and‐thrust belt subjected to erosion and sedimentation under constant rainfall and shortening rates. The emergence of thrust sheets at the front of a prism may divert antecedent transverse channels (perpendicular to the structural grain) leading to the formation of longitudinal reaches, later uplifted and incorporated in the prism by the ongoing deformation. In the experiments, transverse incisions appear in the external slopes of the emerging thrust sheets. Headward erosion in these transverse channels results in divide migration and capture of the uplifted longitudinal channels located in the inner parts of the prism, leading to drainage network reorganization and modification of the sediment routing system. We show that the rate of drainage reorganization increases with the rainfall rate. It also increases in a nonlinear way with the rate of uplift. We explain this behaviour by an exponent > 1 on the slope variable in the framework of the stream power erosion model. Our results confirm the view that early longitudinal‐dominated networks are progressively replaced by transverse‐dominated rivers during mountain building. We show that drainage network dynamics modulate the distribution of sedimentary fluxes at the outlets of experimental wedges. We propose that under constant shortening and rainfall rates the drainage network reorganization can also modulate the composition and the spatial distribution of clastic fluxes in foreland basins.  相似文献   

Numerical implementation and sensitivity analysis of a wave energy converter in a time-dependent mild-slope equation model     

Charlotte Beels  Peter Troch  Griet De Backer  Marc Vantorre  Julien De Rouck 《Coastal Engineering》2010

Several Wave Energy Converters (abbreviated as WECs) have intensively been studied and developed during the last decade and currently small farms of WECs are getting installed. WECs in a farm are partly absorbing, partly redistributing the incident wave power. Consequently, the power absorption of each individual WEC in a farm is affected by its neighbouring WECs. The knowledge of the wave climate around the WEC is needed to predict its performance in the farm. In this paper a technique is developed to implement a single and multiple WECs based on the overtopping principle in a time-dependent mild-slope equation model. So far, the mild-slope equations have been widely used to study wave transformations around coastal and offshore structures, such as breakwaters, piles of windmills and offshore platforms. First the limitations of the WEC implementation are discussed through a sensitivity analysis. Next the developed approach is applied to study the wave height reduction behind a single WEC and a farm. The wake behind an isolated WEC is investigated for uni- and multidirectional waves; it is observed that an increase of the directional spread leads to a faster wave redistribution behind the WEC. Further the wake in the lee of multiple WECs is calculated for two different farm lay-outs, i.e. an aligned grid and a staggered grid, by adapting the performance of each WEC to its incident wave power. The evolved technique is a fast tool to find the optimal lay-out of WECs in a farm and to study the possible influence on surrounding activities in the sea.  相似文献   

New sedimentological and palynological data from the Yarkand-Fergana Basin(Kyrgyz Tian Shan): Insights on its Mesozoic paleogeographic and tectonic evolution     

Julien Morin  Marc Jolivet  Dave Shaw  Sylvie Bourquin  Elena Bataleva 《地学前缘(英文版)》2021,12(1):183-202

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