The depolarization properties of powerful radio sources: breaking the radio power versus redshift degeneracy     

J. A. Goodlet  C. R. Kaiser  P. N. Best  J. Dennett-Thorpe 《Monthly notices of the Royal Astronomical Society》2004,347(2):508-540

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HST and UKIRT imaging observations of z∼ 1 6C radio galaxies – I. The data     

K. J. Inskip  P. N. Best  M. S. Longair  S. Rawlings  H. J. A. Röttgering  S. Eales 《Monthly notices of the Royal Astronomical Society》2003,345(4):1365-1380

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On determining the geometric and kinematic characteristics of coherent flow structures over a gravel bed: a new approach using combined PLIF‐PIV     

R.J. Hardy  J.L. Best  D.R. Parsons  G.M. Keevil 《地球表面变化过程与地形》2011,36(2):279-284

In gravel‐bed rivers, the microtopography of the bed is known to exert a significant influence on the generation of turbulent flow structures that owe their origin to fluid shear generated near the bed. Although field and laboratory measurements have indicated that flows over gravel beds contain a range of coherent flow structures, the kinematic and dynamic properties of these structures are still poorly understood. This paper describes a new experimental methodology to quantify simultaneously both the kinematic and dynamic characteristics of coherent flow structures based upon combined planar laser‐induced fluorescence and particle imaging velocimetry (PLIF‐PIV). The results confirm that the primary generative mechanism of coherent flow structures is at the bed, where merging hairpin vortices form around bed clasts and generate larger‐scale fluid motions that advect downstream. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Joint elastic‐electrical effective medium models of reservoir sandstones     

Angus I. Best  Lucy M. MacGregor  Jeremy Sothcott  Tim A. Minshull 《Geophysical Prospecting》2011,59(4):777-786

Improvements in the joint inversion of seismic and marine controlled source electromagnetic data sets will require better constrained models of the joint elastic‐electrical properties of reservoir rocks. Various effective medium models were compared to a novel laboratory data set of elastic velocity and electrical resistivity (obtained on 67 reservoir sandstone samples saturated with 35 g/l brine at a differential pressure of 8 MPa) with mixed results. Hence, we developed a new three‐phase effective medium model for sandstones with pore‐filling clay minerals based on the combined self‐consistent approximation and differential effective medium model. We found that using a critical porosity of 0.5 and an aspect ratio of 1 for all three components, the proposed model gave accurate model predictions of the observed magnitudes of P‐wave velocity and electrical resistivity and of the divergent trends of clean and clay‐rich sandstones at higher porosities. Using only a few well‐constrained input parameters, the new model offers a practical way to predict in situ porosity and clay content in brine saturated sandstones from co‐located P‐wave velocity and electrical resistivity data sets.  相似文献   

Observations of fluid‐dependent shear‐wave splitting in synthetic porous rocks with aligned penny‐shaped fractures‡     

Philip Tillotson  Angus Ian Best  Jeremy Sothcott  Clive McCann  Wang Shangxu  Xiang‐Yang Li 《Geophysical Prospecting》2011,59(1):111-119

P‐ and S‐wave velocity and attenuation coefficients (accurate to ±0.3% and ±0.2 dB/cm, respectively) were measured in synthetic porous rocks with aligned, penny‐shaped fractures using the laboratory ultrasonic pulse‐echo method. Shear‐wave splitting was observed by rotating the S‐wave transducer and noting the maximum and minimum velocities relative to the fracture direction. A block of synthetic porous rock of fracture density 0.0201 ± 0.0068 and fracture size 3.6 ± 0.38 mm (measured from image analysis of X‐ray CT scans) was sub‐sampled into three 20–30 mm long, 50 mm diameter core plugs oriented at 0°, 45° and 90° to the fracture normal (transversely isotropic symmetry axis). Full waveform data were collected over the frequency range 500–1000 kHz for both water and glycerin saturated cores to observe the effect of pore fluid viscosity at 1 cP and 100 cP, respectively. The shear‐wave splitting observed in the 90° core was 2.15 ± 0.02% for water saturated and 2.39 ± 0.02% for glycerin saturated, in agreement with the theory that suggests that the percentage splitting should be 100 times the fracture density and independent of the saturating fluid. In the 45° core, by contrast, splitting was 0.00 ± 0.02% for water saturation and ?0.77 ± 0.02% for glycerin saturation. This dependence on fracture orientation and pore fluid viscosity is consistent with the poro‐visco‐elastic theory for aligned, meso‐scale fractures in porous rocks. The results suggest the possible use of shear‐ or converted‐wave data to discriminate between fluids on the basis of viscosity variations.  相似文献   

Awards presented by the International Association of Sedimentologists at the 18th International Sedimentological Congress,Mendoza, Argentina
Citation of John Bridge for the Sorby Medal     

Jim Best  Rudy Slingerland 《Sedimentology》2011,58(3):824-826

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Quantification of the relation between surface morphodynamics and subsurface sedimentological product in sandy braided rivers     

Natalie O. Parker  Gregory H. Sambrook Smith  Philip J. Ashworth  James L. Best  Stuart N. Lane  Ian A. Lunt  Christopher J. Simpson  Roberte. Thomas 《Sedimentology》2013,60(3):820-839

This study uses digital elevation models and ground‐penetrating radar to quantify the relation between the surface morphodynamics and subsurface sedimentology in the sandy braided South Saskatchewan River, Canada. A unique aspect of the methodology is that both digital elevation model and ground‐penetrating radar data were collected from the same locations in 2004, 2005, 2006 and 2007, thus enabling the surface morphodynamics to be tied explicitly to the associated evolving depositional product. The occurrence of a large flood in 2005 also allowed the influence of discharge to be assessed with respect to the process–product relationship. The data demonstrate that the morphology of the study reach evolved even during modest discharges, but more extensive erosion was caused by the large flood. In addition, the study reach was dominated by compound bars before the flood, but switched to being dominated by unit bars during and after the flood. The extent to which the subsurface deposits (the ‘product’) were modified by the surface morphodynamics (the ‘process’) was quantified using the changes in radar‐facies recorded in sequential ground‐penetrating radar surveys. These surveys reveal that during the large flood there was an increase in the proportion of facies associated with bar margin accretion and larger dunes. In subsequent years, these facies became truncated and replaced with facies associated with smaller dune sets. This analysis shows that unit bars generally become truncated more laterally than vertically and, thus, they lose the high‐angle bar margin deposits and smaller scale bar‐top deposits. In general, the only fragments that remain of the unit bars are dune sets, thus making identification of the original unit barform problematic. This novel data set has implications for what may ultimately become preserved in the rock record.  相似文献   

The nappe pile of eastern Crete   总被引：1，自引：0，他引：1  

A. Baumann  G. Best  W. Gwosdz  H. Wachendorf 《Tectonophysics》1976,30(3-4):T33-T40

In eastern Crete four allochthonous units with different styles of deformation are piled up above the autochthonous Cherty Limestone (“Plattenkalk”). The emplacement of the nappes is discussed. Diapiric uplift of the Cycladic area was accompanied by large-scale gravity sliding in the direction towards the Aegean arc. There is no evidence from geophysical data for the existence of a subduction zone. Therefore, the transport of the eastern Cretan nappes may be better explained by gravity tectonics than by the model of plate tectonics.  相似文献   

Effect of broken clouds on satellite-based columnar water vapor retrieval     

Chylek  P. Borel  C. Davis  A.B. Bender  S. Augustine  J. Hodges  G. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(3):175-178

We investigate the effect of broken clouds on the satellite-based retrieval of columnar water vapor using a near-infrared radiance ratio technique. A typical difference between the retrieval using only pixels directly illuminated by the Sun and pixels with mixed illumination containing direct sunlight as well as cloud shadows is found to be within 3%.  相似文献   

Relations of field line resonances and upstream waves and the winter attenuation of pulsations     

J. Ver  H{o}  I. Best  M. Vellante  H. Lühr  M. de Lauretis  L. Holló  F. Märcz  J. Str  ues  utik 《Annales Geophysicae》1995,13(7):689-697

Using data on the occurrence frequency of geomagnetic pulsations of different periods from three observatories in Central Europe, conclusions are drawn about the occurrence of field line resonances and pulsations directly driven by upstream waves at L-values below 3. It was found that both types occur during the interval studied (first 6 months of the year 1991), but both the occurrence frequency of the two types and the characteristic period of the field line resonance change significantly as compared to other intervals. During Northern winter, pulsation activity is severely damped in solar maximum years, including the year 1991. The decrease in the activity of the pulsations is more significant at shorter periods.  相似文献