An extreme value analysis of the flow of Burbage Brook     

J. H. Barrett 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(3):151-165

An extreme value analysis of the flow of Burbage Brook is carried out by modelling peaks over a high threshold. The aims are to illustrate recently developed statistical techniques and to report on interesting features of the flow of the brook over a 58-year period. Peak flows are found to show marked seasonal variation and a downward trend. Then-year return level is estimated for various values ofn, and the reliability of the estimates is assessed.  相似文献   

Adapting visual methods: action research with Kampala street children   总被引：3，自引：0，他引：3  

Lorraine Young  & Hazel Barrett 《Area》2001,33(2):141-152

The paper examines the use of four visual 'action' methods for eliciting information from street children about their interactions with the socio-spatial environment. These methods were adapted and used to encourage child-led activities and minimize researcher input. The advantages and constraints associated with the successful implementation of visual methods with children are examined, followed by a brief examination of the 'real' and ethical considerations surrounding their use. The paper concludes that visual methods allow a high level of child-led participation in research, as well as providing a stimulus for eliciting further oral material.  相似文献   

Elemental concentrations and their distribution in two bituminous coals of different paleoenvironments     

L.A. Harris  H.E. Barrett  O.C. Kopp 《International Journal of Coal Geology》1981,1(3):175-193

The vertical distributions of major and minor elements in two high-volatile bituminous coals of Eastern Tennessee are compared. The coals studied are the Pewee, deposited in a fresh-water environment, and the Upper Grassy Spring, previously thought to be influenced by a late incursion of marine water.X-ray fluorescence analyses were performed on a continuous series of specimens obtained from full-face channel samples representing the entire thickness of each seam. Correlation coefficients (r) for all element pairs show high positive correlations for element pairs normally associated with clay minerals. Equally good correlations were observed for (Si, Ti) and (Al, Ti), suggesting that titanium is associated with clay minerals in both coals. Strontium and phosphorous showed a high positive r factor for both the Upper Grassy Spring and the Pewee.Major differences were found to exist in the concentrations and distributions of sulfur, iron, and arsenic in the Upper Grassy Spring and Pewee seams. The Upper Grassy Spring contains an order of magnitude more sulfur than the Pewee as well as several times as much iron and arsenic. The element concentrations and especially their distributions in the Upper Grassy Spring suggest an earlier time for the marine incursion than previously reported. In fact, there is evidence that this coal deposit may have been influenced by marine conditions from its inception.  相似文献   

Strontium and oxygen isotopic composition of some basalts from Hole 504B,Costa Rica Rift,DSDP Legs 69 and 70     

T.J. Barrett  H. Friedrichsen 《Earth and Planetary Science Letters》1982,60(1):27-38

Seventeen whole-rock samples, generally taken at 25–50 m intervals from 5 to 560 m sub-basement in Hole 504B, drilled in 6.2 m.y. old crust, were analysed for⁸⁷Sr/⁸⁶Sr ratios, Sr and Rb concentrations, and¹⁸O/¹⁶O ratios. Sr isotope ratios for 8 samples from the upper 260 m of the hole range from 0.70287 to 0.70377, with a mean of 0.70320. In the 330–560 m interval, 5 samples have a restricted range of 0.70255–0.70279, with a mean of 0.70266, the average value for fresh mid-ocean ridge basalts (MORB). In the 260–330 m interval, approximately intermediate Sr isotopic ratios are found.δ¹⁸O values (‰) range from 6.4 to 7.8 in the upper 260 m, 6.2–6.4 in the 270–320 m interval, and 5.8–6.2 in the 320–560 m interval. The values in the upper 260 m are typical for basalts which have undergone low-temperature seawater alteration, whereas the values for the 320–560 m interval correspond to MORB which have experienced essentially no oxygen isotopic alteration.The higher⁸⁷Sr/⁸⁶Sr and¹⁸O/¹⁶O ratios in the upper part of the hole can be interpreted as the result of a greater overall water/rock ratio in the upper part of the Hole 504B crust than in the lower part. Interaction of basalt with seawater(⁸⁷Sr/⁸⁶Sr=0.7091) increased basalt⁸⁷Sr/⁸⁶Sr ratios and produced smectitic alteration products which raised whole-rock δ¹⁸O values. Seawater circulation in the lower basalts may have been partly restricted by the greater number of relatively impermeable massive lava flows below about 230 m sub-basement. These flows may have helped to seal off lower basalts from through-flowing seawater.  相似文献   

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   

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   

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   

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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River forecasts may ease the water crisis of the 1990s     

Curtis B. Barrett 《Environmental Geology》1990,15(1):1-3

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