A statistical analysis of hard X-Ray solar flares     

G. Pearce  A. K. Rowe  J. Yeung 《Astrophysics and Space Science》1993,208(1):99-111

In this study we perform a statistical study on, 8319 X-Ray solar flares observed with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission satellite (SMM). The events are examined in terms of the durations, maximum intensities, and intensity profiles. It is concluded that there is no evidence for a correlation between flare intensity, flare duration, and flare asymmetry. However, we do find evidence for a rapid fall-of in the number of short-duration events.  相似文献   

Stable clustering, the halo model and non-linear cosmological power spectra     

R. E. Smith  J. A. Peacock  A. Jenkins  S. D. M. White  C. S. Frenk  F. R. Pearce  P. A. Thomas  G. Efstathiou  H. M. P. Couchman 《Monthly notices of the Royal Astronomical Society》2003,341(4):1311-1332

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Evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A in the large magellanic cloud     

G. Pearce  K. Turner  C. G. Rushworth 《Astrophysics and Space Science》1992,196(2):337-343

We investigate the evaporation and condensation of corundum and silicon carbide grains around the supernova SN1987A. We predict the time after outburst of the interaction of the condensed dust with pre-existing dust, with a view to undertaking observations with future instrumentation such as the Infra-Red Space Observatory.  相似文献   

Tephrochronology,magnetostratigraphy and mammalian faunas of Middle and Early Pleistocene sediments at two sites on the Old Crow River,northern Yukon Territory,Canada     

John A. Westgate  G. William Pearce  Shari J. Preece  Charles E. Schweger  Richard E. Morlan  Nicholas J.G. Pearce  T. William Perkins 《Quaternary Research》2013,79(1):75-85

Alluvial and lacustrine sediments exposed beneath late Pleistocene glaciolacustrine silt and clay at two sites along the Old Crow River, northern Yukon Territory, are rich in fossils and contain tephra beds. Surprise Creek tephra (SZt) occurs in the lower part of the alluvial sequence at CRH47 and Little Timber tephra (LTt) is present near the base of the exposure at CRH94. Surprise Creek tephra has a glass fission-track age of 0.17 ± 0.07 Ma and Little Timber tephra is 1.37 ± 0.12 Ma. All sediments at CRH47 have a normal remanent magnetic polarity and those near LTt at CRH94 have a reversed polarity — in agreement with the geomagnetic time scale. Small mammal remains from sediments near LTt support an Early Pleistocene age but the chronology is not so clear at CRH47 because of the large error associated with the SZt age determination. Tephrochronological and paleomagnetic considerations point to an MIS 7 age for the interglacial beds just below SZt at CRH47 and at Chester Bluffs in east-central Alaska, but mammalian fossils recovered from sediments close to SZt suggest a late Irvingtonian age, therefore older than MIS 7. Further studies are needed to resolve this problem.  相似文献   

Using Mg Isotopes to Trace Cyanobacterially Mediated Magnesium Carbonate Precipitation in Alkaline Lakes   总被引：1，自引：0，他引：1  

Liudmila S. Shirokova  Vasileios Mavromatis  Irina A. Bundeleva  Oleg S. Pokrovsky  Pascale B��n��zeth  Emmanuelle G��rard  Christopher R. Pearce  Eric H. Oelkers 《Aquatic Geochemistry》2013,19(1):1-24

This study assesses the potential use of Mg isotopes to trace Mg carbonate precipitation in natural waters. Salda Lake (SW Turkey) was chosen for this study because it is one of the few modern environments where hydrous Mg carbonates are the dominant precipitating minerals. Stromatolites, consisting mainly of hydromagnesite, are abundant in this lake. The Mg isotope composition of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments were measured. Because Salda Lake is located in a closed basin, mass balance requires that the Mg isotopic offset between Lake Salda water and precipitated hydromagnesite be comparable to the corresponding offset between Salda Lake and its water inputs. This is consistent with observations; a ??²⁶Mg offset of 0.8?C1.4??? is observed between Salda Lake water and it is the incoming streams and groundwaters, and precipitated hydromagnesite has a ??²⁶Mg 0.9?C1.1??? more negative than its corresponding fluid phase. This isotopic offset also matches closely that measured in the laboratory during both biotic and abiotic hydrous Mg carbonate precipitation by cyanobacteria (Mavromatis, V., Pearce, C., Shirokova, L. S., Bundeleva, I. A., Pokrovsky, O. S., Benezeth, P. and Oelkers, E.H.: Magnesium isotope fractionation during inorganic and cyanobacteria-induced hydrous magnesium carbonate precipitation, Geochim. Cosmochim. Acta, 2012a. 76, 161?C174). Batch reactor experiments performed in the presence of Salda Lake cyanobacteria and stromatolites resulted in the precipitation of dypingite (Mg₅(CO₃)₄(OH)₂·5(H₂O)) and hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) with morphological features similar to those of natural samples. Concurrent abiotic control experiments did not exhibit carbonate precipitation demonstrating the critical role of cyanobacteria in the precipitation process.  相似文献   

The Last Piece Is You     

Margaret Wickens Pearce 《The Cartographic journal》2014,51(2):107-122

Abstract

This article presents the cartographic outcome of a 3-year collaboration with Penobscot Nation Cultural & Historic Preservation to map the traditional place names of Penobscot territory in the state of Maine. After a consideration of the challenges of mapping Indigenous place names, I describe my cartographic contribution to the project, to transform the map design using the tools of narrativity and translation. Initial insights about Penobscot place names then led to wider insights regarding Indigenous place names and traditional cartography, through a comparison to similar practices in the place name traditions of other communities. I then explain how these insights influenced the design of the map itself.  相似文献   

Revisiting the Borrobol Tephra          下载免费PDF全文

Ewa M. Lind  Carl Lilja  Stefan Wastegård  Nicholas J. G. Pearce 《Boreas: An International Journal of Quaternary Research》2016,45(4):629-643

The Borrobol Tephra has been identified as one of the key tephra horizons for the Lateglacial time period but it also exemplifies many of the promises and problems of tephrochronology. Additional horizons with similar major element composition and approximately the same age have been identified around the North Atlantic region. Here, we revisit the Borrobol Tephra identified at two Swedish sites, Hässeldala port and Skallahult, and also the Borrobol type‐site in Scotland. We present the first set of minor element data (trace and rare earth analyses) along with new analyses of major elements from these three sites. The analysed minor and the trace elements have a similar signature; however, the glass from the Scottish type‐site seems to imply two populations. To answer if this truly represents two populations, or if it reflects magmatic differentiation additional and larger data sets of minor elements are needed. The new major elements are compared to other Borrobol‐type tephras identified in the North Atlantic region. Our results are in line with earlier investigations, which showed no differences in major elements. Further, comparison of minor elements from glass analyses from our sites with those for eruptions associated with Icelandic central volcanoes implies an Icelandic origin for the Borrobol‐type tephras.  相似文献   

Nature versus nurture: the curved spine of the galaxy cluster X-ray luminosity–temperature relation     

W. G. Hartley  L. Gazzola  F. R. Pearce  S. T. Kay  P. A. Thomas 《Monthly notices of the Royal Astronomical Society》2008,386(4):2015-2021

The physical processes that define the spine of the galaxy cluster X-ray luminosity–temperature ( L – T ) relation are investigated using a large hydrodynamical simulation of the universe. This simulation models the same volume and phases as the millennium simulation and has a linear extent of  500  h ⁻¹ Mpc  . We demonstrate that mergers typically boost a cluster along but also slightly below the L – T relation. Due to this boost, we expect that all of the very brightest clusters will be near the peak of a merger. Objects from near the top of the L – T relation tend to have assembled much of their mass earlier than an average halo of similar final mass. Conversely, objects from the bottom of the relation are often experiencing an ongoing or recent merger.  相似文献   

Phylogeny of the Sepia officinalis species complex in the eastern Atlantic extends the known distribution of Sepia vermiculata across the Benguela upwelling region     

AJE Healey  NJ McKeown  WM Potts  CL de Beer  W Sauer  PW Shaw 《African Journal of Marine Science》2017,39(3):307-313

Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks.  相似文献   

First National Conference on marine bioinvasions, Massachusetts Institute of Technology, Cambridge, Massachusetts, 24-27 January 1999     

Pearce JB 《Marine pollution bulletin》2001,42(1):77-78

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