Astrometric binaries and their role in double star astronomy     

T. Herczeg 《Astrophysics and Space Science》1985,110(1):133-134

  相似文献   

A two degree-of-freedom earthquake model with static/dynamic friction   总被引：3，自引：0，他引：3  

Jeffrey Nussbaum  Andy Ruina 《Pure and Applied Geophysics》1987,125(4):629-656

Can a simple multi-block-spring model with total symmetry make interesting predictions for fault behaviour? Our model consists of a symmetric, slowly driven, two degree-of-freedom block-spring system with static/dynamic friction. The simple friction law and slow driving rate allow the state of this fourth order system to be described between slip events by a single variable, the difference in the stretch of the driving springs. This stretch difference measures the locked-in stress and is closely related to fault stress inhomogeneity. In general,smoothing is not observed. A spatially homogeneous stress state is found to almost always be unstable, in that the system tends toward an inhomogeneous state after many slip events. The system evolves either to a cycle that alternates between two types of earthquakes, or to a cycle with repeating but identical asymmetric earthquakes. One type of alternating earthquake solution is structurally unstable, which implies a great sensitivity to model perturbations. For this simple model, spatial asymmetry necessarily occurs, despite the symmetry in the model, thus suggesting that spatial structure in seismicity patterns may be a consequence of earthquake dynamics, not just fault heterogeneity.  相似文献   

Modeling outflow from the Ernest Henry Fe oxide Cu–Au deposit: implications for ore genesis and exploration     

Geordie Mark  Andy Wilde  Nicholas H.S. Oliver  Patrick J. Williams  Chris G. Ryan 《Journal of Geochemical Exploration》2005,85(1):921-46

The Ernest Henry Fe oxide Cu–Au (IOCG) deposit (>ca. 1.51 Ga) is hosted by breccia produced during the waning stages of an evolving hydrothermal system that formed a number of tens of metres to a kilometre scale, pre- and syn-ore alteration halos, although no demonstrable patterns have been attributed to fluids expelled through the outflow zones. However, the recognition of a population of hypersaline fluid inclusions representing the ‘spent’ fluids after Cu–Au deposition at Ernest Henry provides the basis to model the geochemical characteristics of the deposit's outflow zones. Geochemical modeling at 300 °C was undertaken at both high and low fluid/rock ratios via FLUSH models involving three host rock types: (1) granite, (2) calc–silicate rock, and (3) graphitic schist. In models run at high fluid/rock ratios, all rock types are essentially fluid-buffered, and produce an albite–quartz–hematite–barite-rich assemblage, although in low fluid–rock environments, the pH, redox, and geochemical character of the host rock exerts a greater influence on the mineralogy of the alteration assemblages (e.g., andradite, Fe–chlorite, and magnetite). Significant sulphide mineralization was predicted in graphitic schist where sphalerite occurred in both low- and high-porosity models, which indicates the possibility of an association between high-temperature IOCG mineralization and lower temperature base metal mineralization.Cooling experiments (from 300 to 100 °C) using the ‘spent fluids’ predict early high-T (300–200 °C) Na-, Ca-, Fe-, and Mn-rich, magnetite-bearing hydrothermal associations, whereas with cooling to below 200 °C, and with progressive fluid–rock interaction, the system produces rhodochrosite-bearing, hematite–quartz–muscovite–barite-rich assemblages. These results show that the radical geochemical and mineralogical changes associated with cooling and progressive fluid influx are likely to be accompanied by major transformations in the geophysical expression (e.g., spectral and magnetic character) of the alteration in the outflow zone, and highlight the potential link between magnetite- and hematite-bearing IOCG hydrothermal systems.  相似文献   

Thérèse Mound: a case study of coral bank development in the Belgica Mound Province,Porcupine Seabight     

Ben De Mol  Max Kozachenko  Andy Wheeler  Hugo Alvares  Jean-Pierre Henriet  Karine Olu-Le Roy 《International Journal of Earth Sciences》2007,96(1):103-120

High-resolution seismic profiles, swath bathymetry, side-scan sonar data and video imageries are analysed in this detailed study of five carbonate mounds from the Belgica mound province with special emphasis on the well-surveyed Thérèse Mound. The selected mounds are located in the deepest part of the Belgica mound province at water depths of 950 m. Seismic data illustrate that the underlying geology is characterised by drift sedimentation in a general northerly flowing current regime. Sigmoidal sediment bodies create local slope breaks on the most recent local erosional surface, which act as the mound base. No preferential mound substratum is observed, neither is there any indication for deep geological controls on coral bank development. Seismic evidence suggests that the start-up of the coral bank development was shortly after a major erosional event of Late Pliocene–Quaternary age. The coral bank geometry has been clearly affected by the local topography of this erosional base and the prevailing current regime. The summits of the coral banks are relatively flat and the flanks are steepest on their upper slopes. Deposition of the encased drift sequence has been influenced by the coral bank topography. Sediment waves are formed besides the coral banks and are the most pronounced bedforms. These seabed structures are probably induced by bottom current up to 1 m/s. Large sediment waves are colonised by living corals and might represent the initial phase of coral bank development. The biological facies distribution of the coral banks illustrate a living coral cap on the summit and upper slope and a decline of living coral populations toward the lower flanks. The data suggest that the development of the coral banks in this area is clearly an interaction between biological growth processes and drift deposition both influenced by the local topography and current regime.  相似文献   

Equipped to deal with uncertainty in climate and impacts predictions: lessons from internal peer review   总被引：1，自引：0，他引：1  

Anna Wesselink  Andrew Juan Challinor  James Watson  Keith Beven  Icarus Allen  Helen Hanlon  Ana Lopez  Susanne Lorenz  Friederike Otto  Andy Morse  Cameron Rye  Stephane Saux-Picard  David Stainforth  Emma Suckling 《Climatic change》2015,132(1):1-14

  相似文献   

Upscaling unsaturated hydraulic parameters for flow through heterogeneous anisotropic sediments     

Andy L. Ward  Z. Fred ZhangGlendon W. Gee 《Advances in water resources》2006

We compare two methods for determining the upscaled water characteristics and saturation-dependent anisotropy in unsaturated hydraulic conductivity from a field-scale injection test. In both approaches an effective medium approximation is used to reduce a porous medium of M textures to an equivalent homogenous medium. The first approach is a phenomenological approach based on homogenization and assumes that moisture-based Richards’ equation can be treated like the convective–dispersive equation (CDE). The gravity term, dK_z(θ)/d(θ), analogous to the vertical convective velocity in the CDE, is determined from the temporal evolution of the plume centroid along the vertical coordinate allowing calculation of an upscaled K_z(θ). As with the dispersion tensor in the CDE, the rate of change of the second spatial moment in 3D space is used to calculate the water diffusivity tensor, D(θ), from which an upscaled K(θ) is calculated. The second approach uses the combined parameter scale inverse technique (CPSIT). Parameter scaling is used first to reduce the number of parameters to be estimated by a factor M. Upscaled parameters are then optimized by inverse modeling to produce an upscaled K(θ) characterized by a pore tortuosity–connectivity tensor, L. Parameters for individual textures are finally determined from the optimized parameters by inverse scaling using scale factors determined a priori. Both methods produced upscaled K(θ) that showed evidence of saturation dependent anisotropy. Flow predictions with the STOMP simulator, parameterized with upscaled parameters, were compared with field observations. Predictions based on the homogenization method were able to capture the mean plume behavior but could not reproduce the asymmetry caused by heterogeneity and lateral spreading. The CPSIT method captured the effects of heterogeneity and anisotropy and reduced the mean squared residual by nearly 90% compared to local-scale and upscaled parameters from the homogenization method. The Pacific Northwest National Laboratory is operated for the US Department of Energy by Battelle under Contract DE-AC05-76RL01830.  相似文献   

Mesozoic–Tertiary exhumation history of the Altai Mountains, northern Xinjiang, China: New constraints from apatite fission track data   总被引：3，自引：1，他引：2  

Wanming Yuan  Andy Carter  Jinquan Dong  Zengkuan Bao  Yinchang An  Zhaojie Guo 《Tectonophysics》2006,412(3-4):183-193

This study uses apatite fission track (FT) analysis to constrain the exhumation history of bedrock samples collected from the Altai Mountains in northern Xinjiang, China. Samples were collected as transects across the main structures related to Palaeozoic crustal accretion events. FT results and modeling identify three stages in sample cooling history spanning the Mesozoic and Tertiary. Stage one records rapid cooling to the low temperature part of the fission track partial annealing zone circa 70 ± 10 °C. Stage two, records a period of relative stability with little if any cooling taking place between 75 and 25–20 Ma suggesting the Altai region had been reduced to an area of low relief. Support for this can be found in the adjacent Junngar Basin that received little if any sediment during this interval. Final stage cooling took place in the Miocene at an accelerated rate bringing the sampled rocks to the Earth's surface. This last stage, linked to the far field effects of the Himalayan collision, most likely generated the surface uplift and relief that define the present-day Altai Mountains.  相似文献   

River–groundwater connectivity in a karst system,Wellington, New South Wales,Australia     

Mohammadreza Keshavarzi  Andy Baker  Bryce F. J. Kelly  Martin S. Andersen 《Hydrogeology Journal》2017,25(2):557-574

The characterization of river–aquifer connectivity in karst environments is difficult due to the presence of conduits and caves. This work demonstrates how geophysical imaging combined with hydrogeological data can improve the conceptualization of surface-water and groundwater interactions in karst terrains. The objective of this study is to understand the association between the Bell River and karst-alluvial aquifer at Wellington, Australia. River and groundwater levels were continuously monitored, and electrical resistivity imaging and water quality surveys conducted. Two-dimensional resistivity imaging mapped the transition between the alluvium and karst. This is important for highlighting the proximity of the saturated alluvial sediments to the water-filled caves and conduits. In the unsaturated zone the resistivity imaging differentiated between air- and sediment-filled karst features, and in the saturated zone it mapped the location of possible water- and sediment-filled caves. Groundwater levels are dynamic and respond quickly to changes in the river stage, implying that there is a strong hydraulic connection, and that the river is losing and recharging the adjacent aquifer. Groundwater extractions (1,370 ML, megalitres, annually) from the alluvial aquifer can cause the groundwater level to fall by as much as 1.5 m in a year. However, when the Bell River flows after significant rainfall in the upper catchment, river-leakage rapidly recharges the alluvial and karst aquifers. This work demonstrates that in complex hydrogeological settings, the combined use of geophysical imaging, hydrograph analysis and geochemical measurements provide insights on the local karst hydrology and groundwater processes, which will enable better water-resource and karst management.  相似文献   

Geoarchaeology: Exploration,environments, resources     

Andy J. Howard 《Geoarchaeology》2000,15(8):822-824

  相似文献