Quasi-Lagrangian diagnostics of a Mediterranean cyclone: Isentropic results     

Prof. Dr. D. R. Johnson  D. K. Hill 《Meteorology and Atmospheric Physics》1987,36(1-4):118-140

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Nitrate Distribution in the Ground Water of the Alliston Region of Ontario, Canada   总被引：3，自引：0，他引：3  

A. R. Hill 《Ground water》1982,20(6):696-702

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A comparison of solute-transport solution techniques and their effect on sensitivity analysis and inverse modeling results   总被引：1，自引：0，他引：1  

Mehl S  Hill MC 《Ground water》2001,39(2):300-307

Five common numerical techniques for solving the advection-dispersion equation (finite difference, predictor corrector, total variation diminishing, method of characteristics, and modified method of characteristics) were tested using simulations of a controlled conservative tracer-test experiment through a heterogeneous, two-dimensional sand tank. The experimental facility was constructed using discrete, randomly distributed, homogeneous blocks of five sand types. This experimental model provides an opportunity to compare the solution techniques: the heterogeneous hydraulic-conductivity distribution of known structure can be accurately represented by a numerical model, and detailed measurements can be compared with simulated concentrations and total flow through the tank. The present work uses this opportunity to investigate how three common types of results--simulated breakthrough curves, sensitivity analysis, and calibrated parameter values--change in this heterogeneous situation given the different methods of simulating solute transport. The breakthrough curves show that simulated peak concentrations, even at very fine grid spacings, varied between the techniques because of different amounts of numerical dispersion. Sensitivity-analysis results revealed: (1) a high correlation between hydraulic conductivity and porosity given the concentration and flow observations used, so that both could not be estimated; and (2) that the breakthrough curve data did not provide enough information to estimate individual values of dispersivity for the five sands. This study demonstrates that the choice of assigned dispersivity and the amount of numerical dispersion present in the solution technique influence estimated hydraulic conductivity values to a surprising degree.  相似文献   

An archaeomagnetic investigation of a Roman amphorae workshop in Albinia (Italy)     

Mimi J. Hill  Philippe Lanos  Annick Chauvin  Daniele Vitali  Fanette Laubenheimer 《Geophysical Journal International》2007,169(2):471-782

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Investigating the ancient Martian magnetic field using microwaves   总被引：1，自引：0，他引：1  

John Shaw  Mimi J. Hill  Steven J. Openshaw 《Earth and Planetary Science Letters》2001,190(3-4):103-109

The new microwave palaeointensity technique has been used to investigate samples from the Martian meteorite Nakhla. This technique is a promising new way to obtain absolute palaeointensity information regarding the ancient Martian magnetic field as recorded by the Martian meteorites. Assuming that a part of the magnetic remanence is of thermal origin and originating on Mars the two samples studied yield estimates of 4 μT for the Martian magnetic field at 1.35 Ga.  相似文献   

Mineral chemistry of a zircon-bearing, composite, veined and metasomatised upper-mantle peridotite xenolith from kimberlite   总被引：4，自引：0，他引：4  

J. Dawson  P. Hill  P. Kinny 《Contributions to Mineralogy and Petrology》2001,140(6):720-733

Zircon-bearing veins in a harzburgite xenolith from kimberlite have imposed Ca-metasomatism on the harzburgite wall rock, in addition to adding K, Fe, Ti and OH. The zircon, previously dated to have an age similar to that of the xenolith-hosting kimberlite, shows higher Y, Nb, Ba, REE, Th and U contents than other mantle-derived zircons. Peripheral alteration of the zircon to baddeleyite and zirconolite, and alteration of vein ilmenite to perovskite suggest reaction with an evolving carbonatitic kimberlite melt. The high Cr₂O₃ content (0.77 wt%) of the zirconolite extends the compositional range of terrestrial zirconolite.  相似文献   

Poikilitic chromfite in komatiitic cumulates     

Dr. S. J. Barnes  Dr. R. E. T. Hill 《Mineralogy and Petrology》1995,54(1-2):85-92

Summary Chromite is a widespread accessory mineral in olivine-rich cumulates derived from komatiitic lavas. The distribution and crystal habit of chromfite is related to the degree of differentiation of the parent magma as reflected in the composition of cumulus olivine. Cumulates with olivine forsterite content greater than 93 mol percent typically contain no chromfite at all, while chromfite forms clusters of disseminated euhedral grains in cumulates with forsterite less than 91 mol percent. In the forsterite 91–93 interval, chromite may develop lobate interstitial habits. In the Six Mile Well ultramafic complex in the Yakabindie region of the Agnew-Wiluna greenstone belt, and in other olivine-rich komatiitic units within this belt, chromfite shows well developed poikilitic textures enclosing olivine.The absence of intercumulus silicate phases in these rocks and the low normative chromfite content of the parent magma make it impossible for these chromfite grains to have crystallised from intercumulus trapped liquid. These rocks must be cotectic chromite-olivine adcumulates, owing their unusual texture to differing relative rates of nucleation and growth of chromfite and olivine, crystallising togetherin situ. This observation provides further evidence for a cumulus origin for oikocrysts in layered intrusions, and casts doubt on the usefulness of cumulus terminology.

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Poikilitischer Chromit in komatiitischen Kumulaten

Zusammenfassung Chromit ist in Olivin-reichen Kumulaten, die von komatiitischen Laven abstammen, ein häufiges akzessorisches Mineral. Die Verteilung und der Kristallhabitus von Chromit hängt vom Grad der Differentiation des Stammagmas, der in der Zusammensetzung der Kumulus-Olivine zum Ausdruck kommt, ab. Für Kumulate mit Olivinen mit einem Forsterit-Gehalt von über 93 mol.% ist es charakteristisch, daß sie überhaupt keinen Chromit enthalten, während Chromit in Kumulaten mit Olivinen mit weniger als 90 mol.% Forsterit Cluster aus fein verteilten, idiomorphem Körnern bildet. Im Intervall Forsterit 90–93 kann Chromit lobate, interstitielle Formen ausbilden. Im ultramafischen Komplex Six Mile Well in der Yakabindie-Region des Agnew-Wiluna-Grünsteingürtels und in anderen Olivin-reichen komatiitischen Einheiten in diesem Gürtel zeigen die Chromite gut entwickelte poikilitische Texturen mit eingeschlossenen Olivinen.Da silikatische Interkumulus-Phasen in diesen Gesteinen fehlen und der normative Chromitgehalt des Stammagmas niedrig ist, können diese Chromitkörner nicht aus einer Interkumulus-Schmelze auskristallisiert sein. Diese Gesteine müssen daher kotektische Chromit-Olivin-Adkumulate sein, die ihre ungewöhnliche Textur den variierenden relativen Keimbildungs- und Wachstumsraten von Chromit und Olivin, die gemeinsam in situ kristallisierten, verdanken. Diese Beobachtung stellt einen weiteren Beweis für die Entstehung von Oikokristallen als Kumulusphase in geschichteten Intrusionen dar und läßt die Zweckmäßigkeit der Kumulus-Terminologie als zweifelhaft erscheinen.

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With 5 Figures  相似文献   

Sakmarian geography     

Dorothy Hill 《International Journal of Earth Sciences》1959,47(2):590-629

The known palaeontological and stratigraphical evidence is used as a basis for the construction of maps of the continents showing the extent of their inundation by the sea in Sakmarian time in the Upper Palaeozoic. In the northern hemisphere apart from India the evidence is sufficiently reliable to give reasonable maps, and the great extent of the inundations suggests that the climate would be considerably modified from that of today; no undoubted Sakmarian glacials occur there. In Southern continents and India, the Gondwana biogeographical province has made correlation with the northern continents controversial, but reasons are given for assuming that Gondwana glacial deposits were at least in part Sakmarian; the resultant maps show that the Gondwana land surfaces were but little reduced in area, and that the main glacials (except for India) lie within a belt between 40 S and 20 S. Present lack of knowledge of Sakmarian conditions in Antarctica makes reconstructions of climatic belts too hazardous for possible use in enunciating or checking hypotheses of continental drift and polar wandering.  相似文献   

Theory of the electromagnetic transient response of the ionosphere for plane wave excitation     

David A. Hill  James R. Wait 《Pure and Applied Geophysics》1971,90(1):169-186

Summary The reflection and transmission of a transient plane wave by an ionosphere with a linear electron density profile and constant collision frequency are calculated. The exact frequency domain solution is inverted numerically, and the resultant reflected and transmitted waveforms are found to satisfy causality. A linearly varying, nondispersive dielectric half-space is also considered, but the nonphysical nature of the model causes the reflected waveform to be noncausal. Using convolution the waveforms for a step modulated sinusoid excitation are also obtained from the impulse response of the ionosphere. The results provide insight into the physical mechanism involved in the ionospheric propagation of HF electromagnetic pulsed signals.  相似文献   

Subsurface electric fields of a grounded cable of finite length for both frequency and time domain     

David A. Hill  James R. Wait 《Pure and Applied Geophysics》1973,111(1):2324-2332

Summary The subsurface electric fields of a current-carrying cable are examined for both steady-state and transient situations. Closed form expressions are obtained for two of the electric field components, and a numerical integration is used to obtain the third component. Waveforms for a stepfunction current excitation are displayed. The results have possible application to pulsed downlink communication in mine rescue operations.  相似文献