A comparison of semi-analytic and smoothed particle hydrodynamics galaxy formation     

A. J. Benson  F. R. Pearce  C. S. Frenk  C. M. Baugh  A. Jenkins 《Monthly notices of the Royal Astronomical Society》2001,320(2):261-280

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A determination of the intensity of the ancient lunar magnetic field     

W. A. Gose  D. W. Strangway  G. W. Pearce 《Earth, Moon, and Planets》1973,7(1-2):196-201

Thermal demagnetization of lunar breccia 15498,36 shows that the natural remanent magnetization is a simple thermoremanence carried by metallic iron. Using the classical Thellier-Thellier method the strength of the magnetizing field at the time of sample formation was found to be 2100 ±80 gammas.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.  相似文献   

Simulations of galaxy formation in a cosmological volume   总被引：1，自引：0，他引：1  

F.R. Pearce  A. Jenkins  C.S. Frenk  S.D.M. White  P.A. Thomas  H.M.P. Couchman  J.A. Peacock  G. Efstathiou 《Monthly notices of the Royal Astronomical Society》2001,326(2):649-666

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Copper oxidation state in chalcopyrite: Mixed Cu d and d characteristics     

C.I. Pearce  D.J. Vaughan  G. van der Laan 《Geochimica et cosmochimica acta》2006,70(18):4635-4642

The determination of the oxidation states of copper and iron in sulfides, and chalcopyrite (CuFeS₂) in particular, using 2p X-ray photoemission spectroscopy (XPS) and L_2,3-edge X-ray absorption spectroscopy (XAS) is revisited. Reassessment of the published spectra derived by these methods produces consistent results and reveals the ‘d count’ in the copper compounds to be intermediate between d⁹ and d¹⁰. Nevertheless, these covalent copper compounds can be divided into those nominally monovalent and those nominally divalent. The Fe L_2,3-edge XAS of chalcopyrite, along with Mössbauer data, confirm the presence of high-spin Fe³⁺. Chalcopyrite, despite recent published reports to the contrary, clearly belongs to the monovalent copper class.  相似文献   

A re-interpretation of the recent stratigraphical history of Utopia Planitia,Mars: Implications for late-Amazonian periglacial and ice-rich terrain     

R.J. Soare  F. Costard  G.D. Pearce  A. Séjourné 《Planetary and Space Science》2012,60(1):131-139

Utopia Planitia, one of the great northern plains of the Mars, is a region where landscape modification by cold-climate processes, i.e. glacial and periglacial, is thought to be widespread. In the middle latitudes of this region a metres-thick mantle, possibly comprising an ice-dust admixture, has been reported; the occurrence of putative periglacial landforms such as flat-floored (thermokarst-like) depressions, small-sized (possibly thermal-contraction) polygons and polygon trough/junction pits also has been noted. Recently, some workers have suggested that the location of the putative periglacial landforms in mid Utopia Planitia is synonymous with that of the mantle and that the former evolve as the latter degrades. By contrast, preliminary work by others has proposed that this synonymy is misperceived, for two reasons: first, the putative periglacial landforms often are observed in areas of Utopia Planitia where the mantle is absent; second, in areas where the two landscape types are observed concurrently, the putative periglacial landforms either underlie the mantle and, stratigraphically, must predate the mantle, or they are adjacent to the mantle and at a lower datum of elevation. If the geological evolution of Utopia Planitia is to be constrained properly, then each of these hypotheses must be explored.Towards this end, we have mapped the location and distribution of the mantle and putative periglacial landforms across a broad latitudinal and longitudinal swath of the Utopia Planitia and its margins (～55°–125°E and ～30°–60°N). This map incorporates all the relevant images of these features and provides a regional scale of analysis. Previous discussions and/or maps of cold-climate landscapes in Utopia Planitia have been much narrower in latitudinal and longitudinal focus. An evaluation of high-resolution images containing the mantle material and putative periglacial landforms, underpinned by the MOLA-based topographic profiles, comprises a local scale of analysis. This too has not been developed fully in earlier work.Using the map, high-resolution photogeological evidence and the MOLA topographic profiles, we show three things. First, in mid Utopia Planitia the reach of the putative periglacial landforms extends well beyond the location of the possible dust-ice mantle. Second, the latter overprints the former in all observed instances and, consequently, the former cannot be a product of the latter. Third, perhaps the origin and evolution of the putative periglacial landscapes in mid Utopia Planitia is not as recent as some workers have proposed.  相似文献   

Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble   总被引：2，自引：0，他引：2  

B.?Etschmann  J.?BruggerEmail author  M.?A.?Pearce  C.?Ta  D.?Brautigan  M.?Jung  A.?Pring 《Contributions to Mineralogy and Petrology》2014,168(2):1045

Limestone dolomitization is an example of a fluid-induced mineralogical transformation that commonly affects extensive rock volumes. To understand the mechanisms enabling these efficient replacement reactions, we investigated experimentally the dolomitization of a fractured calcite marble under flow-through conditions at mild hydrothermal conditions. Contrary to most earlier studies of coupled dissolution reprecipitation reactions that were conducted using small, individual grains, in this study, the integrity of the rock was preserved, so that the experiment explored the links between flow in a fracture and fluid–rock interaction. In these experiments, grain boundaries acted as microreactors, in which a Mg-poor ‘protodolomite’ formed initially, and then transformed into dolomite. The difficulty in nucleating dolomite played a key role in controlling the evolution of the porosity, by allowing for (1) initial dissolution along grain boundaries, and (2) formation of coarse porosity at the reaction interface. This porosity evolution not only enabled the reaction to progress efficiently, but also controlled the mineralogy of the system, as shown by brucite replacing calcite near the fracture once the fluid along calcite grain boundaries became sufficiently connected to the fluid flowing through the fracture. This study illustrates the role of grain boundaries, porosity evolution and nucleation in controlling reaction progress as well as the nature and textures of the products in pervasive mineralogical transformations.  相似文献   

The Hillarys Transect (2): Validation of satellite-derived sea surface temperature in the Indian Ocean off Perth,Western Australia     

B. McAtee  A. Pearce  M. Lynch  J. Davies  M. Boterhoven  B. Osborne 《Continental Shelf Research》2007

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Intra-crater glacial processes in central Utopia Planitia, Mars     

Geoffrey Pearce  Gordon R. Osinski  Richard J. Soare 《Icarus》2011,212(1):86-95

We describe and interpret a series of previously unidentified glacial-like lobes (34-43°N; 107-125°E) that were discovered as part of a survey of large (D > 5 km) impact craters in Utopia Planitia, one of the great northern plains of Mars. The lobes have characteristics that are consistent with a glacial origin. Evidence includes curvilinearity of form, lineations and ridges, and surface textures that are thought to form by the sublimation of near-surface volatiles. The lobes display morphologies that range from wedge-shaped to near-circular to elongate. The flow directions are towards the northern walls in the case of craters with large single lobes, and in all directions in the case of the largest (D > 30 km) craters. Concentric crater fill is also interspersed within craters of our study region, with such craters having much higher filling rates than those with flow lobes. We suggest that the impact crater population in south-west Utopia Planitia demonstrates a spectrum of glacial modifications, from low levels of filling in the case of craters with elongate lobes at one extreme, to concentric crater fill in highly-filled craters at the other.  相似文献   

Parameter tests within cosmological simulations of galaxy formation     

Scott T. Kay  F. R. Pearce  A. Jenkins  C. S. Frenk  S. D. M. White  P. A. Thomas  H. M. P. Couchman 《Monthly notices of the Royal Astronomical Society》2000,316(2):374-394

Numerical simulations of galaxy formation require a number of parameters. Some of these are intrinsic to the numerical integration scheme (e.g., the time-step), while others describe the physical model (e.g., the gas metallicity). In this paper we present results of a systematic exploration of the effects of varying a subset of these parameters on simulations of galaxy formation. We use N -body and 'Smoothed Particle Hydrodynamics' techniques to follow the evolution of cold dark matter and gas in a small volume. We compare a fiducial model with 24 different simulations, in which one parameter at a time is varied, focusing on properties such as the relative fraction of hot and cold gas, and the abundance and masses of galaxies. We find that for reasonable choices of numerical values, many parameters have relatively little effect on the galaxies, with the notable exception of the parameters that control the resolution of the simulation and the efficiency with which gas cools.  相似文献   

Using regional geophysical databases to facilitate the identification of surface reflections on P seismograms     

David Bowers  Robert G. Pearce  Alan Douglas 《Geophysical Journal International》2000,142(3):915-924

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