Geological setting of the Rapu Rapu gold-rich volcanogenic massive sulfide deposits,Albay Province,Philippines     

Ross?L.?SherlockEmail author  Timothy?J.?Barrett  Peter?D.?Lewis 《Mineralium Deposita》2004,39(1):122-122

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Inversion of Thick-Target Bremsstrahlung Spectra from Nonuniformly Ionised Plasmas     

Brown  John C.  McArthur  Guillian K.  Barrett  Richard K.  McIntosh  Scott W.  Emslie  A. Gordon 《Solar physics》1998,179(2):379-404

The effects of non-uniform plasma target ionisation on the spectrum of thick-target HXR bremsstrahlung from a non-thermal electron beam are analysed. In particular the effect of the target ionisation structure on beam collisional energy losses, and hence on inversion of an observed photon spectrum to yield the electron injection spectrum, is considered and results compared with those obtained under the usual assumption of a fully ionised target.The problem is formulated and solved in principle for a general target ionisation structure, then discussed in detail for the case of a step function distribution of ionisation with column depth as an approximation to the sharp coronal–chromospheric step structure in solar flare plasmas. It is found that such ionisation structure has very dramatic effects on derivation of the thick-target electron injection spectrum F₀(E₀) as compared with the result F*₀(E ₀) obtained under the usual assumption of a fully ionised target: (a) Inferred F*₀ contain more electrons than F ₀ and in some cases include electrons at energies where none are actually present. Although the total (energy-integrated) beam fluxes in the two cases do not differ by a factor of more than A_ee/A_eH, the spectral shapes can differ greatly over finite energy intervals resulting in the danger of misleading results for total fluxes obtained by extrapolation. (b) The unconstrained mathematical solution for F₀ for any photon spectrum is never unique, while that for F*₀ is unique. When the physical constraint F₀ 0 is added, for some photon spectra solutions for F₀ may not exist or may not be unique. (This is not an effect of noise but of real analytic ambiguity.) (c) For data corresponding to F*₀ with a low-energy cut-off, or a cut-off or rapid enough exponential decline at high energies, a unique solution F₀ does exist and we obtain a recursive summation for its evaluation.Consequently, in future work on the inversion of HXR bremsstrahlung spectra it will be vital for algorithms to include the effects of target ionisation if spurious results on thick-target electron spectra are not to be inferred. Finally it is pointed out that the depth of the transition zone, and its evaporative evolution during flares may be derivable from its effect on the HXR spectrum.  相似文献   

Using GIS to Investigate Spatial and Temporal Variations in Upland Rainfall     

Emma JS Ferranti  J Duncan Whyatt  Roger J Timmis  Gemma Davies 《Transactions in GIS》2010,14(3):265-282

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The mineralogy,petrology, and composition of anomalous eucrite Emmaville          下载免费PDF全文

T. J. Barrett  D. W. Mittlefehldt  R. C. Greenwood  B. L. A. Charlier  S. J. Hammond  D. K. Ross  M. Anand  I. A. Franchi  F. A. J. Abernethy  M. M. Grady 《Meteoritics & planetary science》2017,52(4):656-668

The Emmaville eucrite is a relatively poorly studied basaltic achondrite with an anomalous oxygen isotope signature. In this study, we report comprehensive mineralogical, petrographic, and geochemical data from Emmaville in order to understand its petrogenesis and relationship with the basaltic eucrites. Emmaville is an unusually fine‐grained, hornfelsic‐textured metabasalt with pervasive impact melt veins and mineral compositions similar to those of typical basaltic eucrites. The major and trace element bulk composition of Emmaville is also typical of a basaltic eucrite. Three separated individual lithologies were also analyzed for O isotopes; a dark gray fraction (E1), a shocked lithology (E2), and a lighter gray portion (E3). Fractions E1 and E2 shared similar O isotope compositions to the bulk sample (E‐B), whereas the lighter gray portion (E3) is slightly elevated in Δ¹⁷O and significantly elevated in δ¹⁸O compared to bulk. No evidence for any exogenous material is observed in the thin sections, coupled with the striking compositional similarity to typical basaltic eucrites, appears to preclude a simple impact‐mixing hypothesis. The O‐isotopes of Emmaville are similar to those of Bunburra Rockhole, A‐881394, and EET 92023, and thus distinct from the majority of the HEDs, despite having similarities in petrology, mineral, and bulk compositions. It would, therefore, seem plausible that all four of these samples are derived from a single HED‐like parent body that is isotopically distinct from that of the HEDs (Vesta) but similar in composition.  相似文献   

Reintroduced large wood modifies fine sediment transport and storage in a lowland river channel          下载免费PDF全文

Chris Parker  Alexander J. Henshaw  Gemma L. Harvey  Carl D. Sayer 《地球表面变化过程与地形》2017,42(11):1693-1703

This paper explores changes in suspended sediment transport and fine sediment storage at the reach and patch scale associated with the reintroduction of partial large wood (LW) jams in an artificially over‐widened lowland river. The field site incorporates two adjacent reaches: a downstream section where LW jams were reintroduced in 2010 and a reach immediately upstream where no LW was introduced. LW pieces were organized into ‘partial’ jams incorporating several ‘key pieces’ which were later colonized by substantial stands of aquatic and wetland plants. Reach‐scale suspended sediment transport was investigated using arrays of time‐integrated suspended sediment samplers. Patch‐scale suspended sediment transport was explored experimentally using turbidity sensors to track the magnitude and velocity of artificially generated sediment plumes. Fine sediment storage was quantified at both reach and patch scales by repeat surveys of fine sediment depth. The results show that partial LW jams influence fine sediment dynamics at both the patch and reach scale. At the patch‐scale, introduction of LW led to a reduction in the concentration and increase in the time lag of released sediment plumes within the LW, indicating increased diffusion of plumes. This contrasted with higher concentrations and lower time lags in areas adjacent to the LW; indicating more effective advection processes. This led to increased fine sediment storage within the LW compared with areas adjacent to the LW. At the reach‐scale there was a greater increase in fine sediment storage through time within the restored reach relative to the unrestored reach, although the changes in sediment transport responsible for this were not evident from time‐integrated suspended sediment data. The results of the study have been used to develop a conceptual model which may inform restoration design. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

How Does Large Flaring Activity from the Same Active Region Produce Oppositely Directed Magnetic Clouds?     

Louise K. Harra  Nancy U. Crooker  Cristina H. Mandrini  Lidia van Driel-Gesztelyi  Sergio Dasso  Jingxiu Wang  Heather Elliott  Gemma Attrill  Bernard V. Jackson  Mario M. Bisi 《Solar physics》2007,244(1-2):95-114

We describe the interplanetary coronal mass ejections (ICMEs) that occurred as a result of a series of solar flares and eruptions from 4 to 8 November 2004. Two ICMEs/magnetic clouds occurring from these events had opposite magnetic orientations. This was despite the fact that the major flares related to these events occurred within the same active region that maintained the same magnetic configuration. The solar events include a wide array of activities: flares, trans-equatorial coronal loop disappearance and reformation, trans-equatorial filament eruption, and coronal hole interaction. The first major ICME/magnetic cloud was predominantly related to the active region 10696 eruption. The second major ICME/magnetic cloud was found to be consistent with the magnetic orientation of an erupting trans-equatorial filament or else a rotation of 160° of a flux rope in the active region. We discuss these possibilities and emphasize the importance of understanding the magnetic evolution of the solar source region before we can begin to predict geoeffective events with any accuracy.  相似文献   

Interpreting the Viking Age to Medieval period transition in Norse Orkney through cultural soil and sediment analyses     

Ian A. Simpson  James H. Barrett  Karen B. Milek 《Geoarchaeology》2005,20(4):355-377

The transition from the Viking Age (ca. A.D. 800–1050) to the Medieval period (ca. A.D. 1050–1500) saw the development of widening trade activities that incorporated peripheral North Atlantic polities into mainstream Europe and contributed to the intensification of marineresource exploitation and agricultural production in these localities. As yet, there is only limited understanding of these intensification processes and their interrelationships, particularly at a local, site‐based level. Through the micromorphological analysis of cultural soils and sediments at Quoygrew, Westray, Orkney, we explore the characteristics of farming and fishing activity during the Viking Age–Medieval transition period and establish their chronological relationships. The study demonstrates: (1) that intensification took place from ca. A.D. 966–1162 on an already existing Viking Age settlement, (2) that intensification of fishing activity occurred prior to the intensification of arable agriculture, and (3) that the Quoygrew site continued throughout this period as an economically diverse permanent settlement. When viewed in a wider North Atlantic context, these findings indicate that intensification of different economic activities proceeded at different rates and that intensification of specialized economic activities during the transition from the Viking Age to the Medieval period was dependent on existing knowledge of local environments. © 2005 Wiley Periodicals, Inc.  相似文献   

Two Tales of a City: detecting socio-economic disadvantage in an ‘advantaged’ Australian urban centre     

Xavier Goldie  Isabel Kakuk  Gemma Wood 《The Australian geographer》2014,45(4):521-540

Understanding the distribution of socio-economic status (SES) within and between communities of varying spatial scales is vital for equitable and effective resource delivery and policy development. In Australia, the Socio-economic Indexes for Areas (SEIFA) have been used extensively for these purposes, in both research and government service delivery. As area-based averages, however, their use in these areas is potentially confounded by the ecological fallacy and the modifiable areal unit problem (MAUP), statistical issues which have widespread implications for the use of spatial data. The Socio-economic Index for Individuals (SEIFI) is an individual-based index developed by the ABS to quantify SES at an individual level for 15–64 year-old Australians. Previous work investigated the potential disparities between these area- and individual-level indices, showing that considerable disparities exist, particularly in the Australian Capital Territory (ACT). Using spatial autocorrelation and pair-wise proportion analyses, we show that there was considerable diversity in individual-level SES at a very fine level of geography in 2006, a unique pattern in Australia. We also show that the SES ranking of areas within the ACT is, in many instances, not indicative of the proportions of individuals living within that area experiencing high levels of relative socio-economic disadvantage. We show that between 65–95 per cent of the ACT's disadvantaged population are masked within areas ranked as advantaged, depending on the index and level of spatial aggregation. Our results suggest that the use of SEIFA as a proxy for individual level disadvantage is highly problematic at both a theoretical and practical level, and necessitates further development of an individual- or household-level index as part of the regular suite of socio-economic indices produced by the ABS.  相似文献   

Imaging the recent sediment dynamics of the Galicia Bank region (Atlantic,NW Iberian Peninsula)     

Gemma Ercilla  David Casas  Juan T. Vázquez  Jorge Iglesias  Luís Somoza  Carmen Juan  Teresa Medialdea  Ricardo León  Ferran Estrada  Soledad García-Gil  Marcel.lí Farran  Fernando Bohoyo  Margarita García  Adolfo Maestro  ERGAP Project  Cruise Teams 《Marine Geophysical Researches》2011,32(1-2):99

Multibeam bathymetry, high resolution multi-channel, and very high resolution single-channel (3.5 kHz) seismic records were used to depict the complex geomorphology that defines the Galicia Bank region (Atlantic, NW Iberian Peninsula). This region (≈620–5,000 m water depth) is characterized by a great variety of features: structural features (scarps, highs, valleys, fold bulges), fluid dynamics-related features (structural undulations and collapse craters), mass-movement features (gullies, channels, mass-flow deposits, slope-lobe complexes, and mass-transport deposits), bottom-current features (moats, furrows, abraded surface, sediment waves, and drifts), (hemi)pelagic features, mixed features (abraded surfaces associated to mixed sediments) and bioconstructions. These features represent architectural elements of four sedimentary systems: slope apron, contouritic, current-controlled (hemi)pelagic, and (hemi)pelagic. These systems are a reflection of different sedimentary processes: downslope (mass transport, mass flows, turbidity flows), alongslope (bottom currents of Mediterranean Outflow Water, Labrador Sea Water, North Atlantic Deep Water, and Lower Deep Water), vertical settling, and the interplay between them. The architectural and sediment dynamic complexities, for their part, are conditioned by the morphostructural complexity of the region, whose structures (exposed scarps and highs) favor multiple submarine sediment sources, affect the type and evolution of the mass-movement processes, and interact with different water masses. This region and similar sedimentary environments far from the continental sediment sources, as seamounts, are ideal zones for carrying out submarine source-to-sink studies, and can represent areas subject to hazards, both geologic and oceanographic in origin.  相似文献   

Sediment waves and depositional implications for fine-grained rocks in the Cerro Toro Formation (upper Cretaceous), Silla Syncline, Chile   总被引：1，自引：0，他引：1  

Kirt M. Campion  Barrett T. Dixon 《Marine and Petroleum Geology》2011,28(3):761-784

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