Professor Sir Nicholas Shackleton     

PHILIP GIBBARD 《Boreas: An International Journal of Quaternary Research》2006,35(2):385-390

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BLENDING HEIGHTS FOR WINDS OBLIQUE TO CHECKERBOARDS     

J. R. PHILIP 《Boundary-Layer Meteorology》1997,82(2):263-281

Analysis of the two-dimensional checkerboardproblem of many alternating surfaces with different properties andvarious scales and aspect ratios is extended to the general case ofwinds oblique to the surface pattern. Relevant periodic solutions ofa three-dimensional atmospheric convection-diffusion equation arefound, and used to estimate blending heights for both concentrationand flux.Illustrative results show negligible directional effect on blendingheight for X1* (the smaller pattern wavelength) of 10 m, but a ratio of maximum/minimum heights of about 3 to 5 for X1* = 100 m. For X1* = 1000 mthe directional variation is strongly peaked with a maximum/minimum ratio of 8 to 14. At fixed X1* the maximum increases with check aspect ratio. It is associated withthe case where the wind blows along one check diagonal. In thatsingular situation, damping of the dominant harmonic varying normalto the diagonal depends purely on transverse and vertical diffusion:horizontal convection and wind shear play no part.  相似文献   

Sediment suspension under waves and currents: time scales and vertical structure     

PHILIP D. OSBORNE  BRIAN GREENWOOD 《Sedimentology》1993,40(4):599-622

Field measurements of the vertical structure of near-bed suspended sediment concentrations were obtained from arrays of fast response optical backscatter suspended solids sensors to examine the time-dependent response of sediment resuspension to waves and currents and the constraints imposed by bedforms. Data were recorded from both a nonbarred, marine shoreface and a barred lacustrine shoreface, under both shoaling and breaking waves (significant heights of 0·25–1·50m; peak periods of 3 and 8 s) and in water depths of 0·5–5·0 m. Sediment concentrations are positively correlated with increasing elevation above the bed, but lagged in time. The time lag varies directly with separation distance between measurement locations and inversely with the horizontal component of the near-bed oscillatory velocity. Both the presence of wave groups and the settling velocities of the sediment particules in suspension influence the temporal changes in concentration at a given elevation. Sediment concentrations appear to respond more slowly to the incident wind-wave forcing with distance away from the bed as a result of two factors: (1) the sequential increase in concentration induced by a succession of large waves in a group; and (ii) the relative increase in finer sediments with smaller settling velocities. Bedforms interact with the near-bed horizontal currents to impose a distinct constraint upon the timing of suspension events relative to the phase of the fluid motion, and, therefore, the vertical structure of the suspended sediment concentration at a range of time scales. The near-bed concentrations appear to be strongly dependent upon the vertical convection of sediment associated with the ejection from the wave boundary layer of separation vortices generated in the lee of ripple crests. Concentration gradients in the presence of vortex ripples are large, as are the correlation between concentrations measured at different elevations within the fluid.  相似文献   

ENHANCED MIGRATION OF SEISMIC DATA1     

PHILIP M. CARRION 《Geophysical Prospecting》1990,38(7):689-704

The so-called ‘enhanced migration’ which uses diffraction tomography as the ‘repair tool’ for correction of amplitudes (reflection coefficients) of migrated sections is discussed. As with any linearized procedure, diffraction tomography requires knowledge of the initial model. It is suggested that the initial model is taken as the migrated image. It will be demonstrated that diffraction tomography applied to the data residuals improves the amplitudes of the migrated images. Migration is redefined as the reconstruction of the wavefront sets of distributions (reflection interfaces), and the inversion process as tomographic correction of migrated images.  相似文献   

Pressure--Temperature--Time Paths of Regional Metamorphism I. Heat Transfer during the Evolution of Regions of Thickened Continental Crust   总被引：5，自引：0，他引：5  

ENGLAND  PHILIP C.; THOMPSON  ALAN BRUCE 《Journal of Petrology》1984,25(4):894-928

The development of regional metamorphism in areas of thickenedcontinental crust is investigated in terms of the major controlson regional-scale thermal regimes. These are: the total radiogenicheat supply within the thickened crust, the supply of heat fromthe mantle, the thermal conductivity of the medium and the lengthand time scales of erosion of the continental crust. The orogenicepisode is regarded as consisting of a relatively rapid phaseof crustal thickening, during which little temperature changeoccurs in individual rocks, followed by a lengthier phase oferosion, at the end of which the crust is at its original thickness.The principal features of pressure—temperature—time(PTt) paths followed by rocks in this environment are a periodof thermal relaxation, during which the temperature rises towardsthe higher geotherm that would be supported by the thickenedcrust, followed by a period of cooling as the rock approachesthe cold land surface. The temperature increase that occursis governed by the degree of thickening of the crust, its conductivityand the time that elapses before the rock is exhumed sufficientlyto be affected by the proximity of the cold upper boundary.For much of the parameter range considered, the heating phaseencompasses a considerable portion of the exhumation (decompression)part of the PTt path. In addition to the detailed calculationof PTt paths we present an idealized model of the thickeningand exhumation process, which may be used to make simple calculationsof the amount of heating to be expected during a given thickeningand exhumation episode and of the depth at which a rock willstart to cool on its ascent path. An important feature of thesePTt paths is that most of them lie within 50 °C of the maximumtemperature attained for one third or more of the total durationof their burial and uplift, and for a geologically plausiblerange of erosion rates the rocks do not begin to cool untilthey have completed 20 to 40 per cent of the total uplift theyexperience. Considerable melting of the continental crust isa likely consequence of thickening of crust with an averagecontinental geotherm. A companion paper discusses these resultsin the context of attempts to use metamorphic petrology datato give information on tectonic processes.  相似文献   

Pressure--Temperature--Time Paths of Regional Metamorphism II. Their Inference and Interpretation using Mineral Assemblages in Metamorphic Rocks   总被引：1，自引：0，他引：1  

THOMPSON  ALAN BRUCE; ENGLAND  PHILIP C. 《Journal of Petrology》1984,25(4):929-955

A companion paper (England & Thompson, 1984a) investigatesthe pressure-temperature-time (PTt) paths followed by rocksundergoing burial metamorphism in continental thickening events.This paper discusses problems involved in inferring such pathsfrom the petrological data available in metamorphic rocks and—oncesuch paths are determined—how they may be interpretedin terms of the thermal budgets of metamorphism. Each of theprincipal facies series (glaucophane-jadeite, andalusite- sillimaniteand kyanite-sillimanite) may be encountered by rocks involvedin the thickening and erosion of continental crust in a regimeof average continental heat flow. The inference of a minimumthermal budget required for a given metamorphism depends stronglyon a knowledge of the PTt paths followed by rocks during themetamorphism. Discrimination between possible thermal regimesis greatly enhanced if portions of PTt paths, rather than singlePT points, are available, and additional constraint is possibleif these paths are supplemented by geochronological, structuraland heat flow data.  相似文献   

A NEW RECEPTOR MODEL:A DIRECT TRILINEAR DECOMPOSITION FOLLOWED BY A MATRIX RECONSTRUCTION     

PHILIP K.HOPKE 《地理学报(英文版)》1992,(2)

In many cases,monitoring data for ambient airborne particles can be organized in the form of a three-way data table with one way for chemical species,one for sampling periods and one for sites.A directtrilinear decomposition followed by a matrix reconstruction(DTDMR)is developed to analyze such adata table as a whole.The three-way data set is composed into three two-way matrices by a direct trilineardecomposition(DTD).The column vectors of each of the matrices are called‘source profiles’,‘emissionpatterns’and‘site coefficients’respectively.Particulate sources are identified by examining both theirsource profiles and emission patterns.After the sources have been identified,emission patterns and sitecoefficients are used to produce a three-way matrix that gives estimates of mass contributions of sourcesto the samples collected at every site in every period.By simulation study,not only has the method beenverified,but a good indicator has been found that shows the number of factors(i.e.sources)in thesystem.Unlike other receptor models,DTDMR does not require source profile data and does not involvetrial-and-error procedures.Since DTDMR identifies sources based on variations in two dimensions,it hasa higher potential to distinguish two sources that have similar chemical compositions.The DTDMRmodel has provided excellent results with simulated data and has been applied in a real world three-waydata set.  相似文献   

Trace fossils from proglacial lake sediments   总被引：1，自引：0，他引：1  

PHILIP L. GIBBARD  ANTHONY J. STUART 《Boreas: An International Journal of Quaternary Research》1974,3(2):69-74

Trace fossils have been discovered in Middle Pleistocene proglacial lake sediments from St. Albans, Hertfordshire, England. They indicate that this environment was capable of supporting a variety of benthonic animals. The fossils are described and tentatively assigned to several invertebrate groups.  相似文献   

Quaternary chronostratigraphy: the nomenclature of terrestrial sequences     

PHILIP L. GIBBARD  RICHARD G. WEST 《Boreas: An International Journal of Quaternary Research》2000,29(4):329-336

There is a long-standing tradition of dividing Quaternary stratigraphical sequences on the basis of climate. This climatostratigraphical approach, begun on terrestrial sequences in the last century, led to the widespread adoption of glacial, interglacial, stadial and interstadial subdivisions as standard. However, the limitations of the approach resulted in its replacement by local sequences of chronostratigraphical stages from the 1950s. The subsequent establishment of the detail and complexity of ocean-core sequences has encouraged increasing use of the terminology developed for these records to the terrestrial and shallow marine succession. The view is expressed that it is advisable to separate and retain regional chronostratigraphies for each sequence-type, and that these should be correlated using event-based stratigraphy where possible. This should ensure both the highest precision and lack of ambiguity and a securely-based synthesis of the relations between the terrestrial and ocean isotope sequences, a synthesis which is fundamental to understanding the nature and detail of regional and global climate change.  相似文献   

ENVIRONMENTAL MANAGEMENT IN AUSTRALIA 1788–1914     

PHILIP S. CORBET 《New Zealand geographer》1979,35(1):46-47

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