Petrogenesis of the Apollo 14 high-alumina basalts: Implications from ion microprobe analyses     

Justin J. Hagerty  Charles K. Shearer 《Geochimica et cosmochimica acta》2005,69(24):5831-5845

In this study, ion microprobe analyses of individual minerals are used to investigate the petrogenesis of the Apollo 14 high-Al basalts. We use trace element concentrations from individual minerals in the Apollo 14 high-Al basalts to evaluate both endogenic and exogenic models. The data show that if the Apollo 14 high-Al basalts were produced by melting within the lunar mantle, these basalts cannot be related to one another by closed-system fractional crystallization of a single basaltic melt. Rather, the trace element data show that variable amounts of a KREEP component were added to the basalts by either assimilation, mixing into mantle sources, or impact melting. Single-stage assimilation-fractional crystallization models can only explain the data from this study if an excessively large mass of urKREEP is assimilated into the parent magma before olivine crystallization. Alternatively, the trace element data can be explained if the Apollo 14 high-Al basalts were produced by melting multiple Al-rich mantle sources that contain different amounts of urKREEP. Finally, for impact melting to be a relevant process, the data require that multiple large impact melts be formed from mixed KREEP-rich target lithologies. The resulting impact melts must then crystallize to produce basalts with igneous textures, high Al₂O₃ concentrations, uniform major element compositions, and a wide range of incompatible trace element concentrations.  相似文献   

Politicization of research and the relevance of geography: some experiences and reflections for an ongoing debate     

Justin Beaumont  Maarten Loopmans  Justus Uitermark† 《Area》2005,37(2):118-126

In this paper we address the revival of interest in recent years in the relevance of geographical research and highlight problems of politicization faced by researchers through cases of policy-oriented research in the UK and Belgium. We argue that geographers should be aware of the possibilities and constraints for critical engagement in the context of policy-oriented research. We identify at least two important opportunities for researchers to avoid clientelistic relationships with contractors and enhance their political relevance. First, researchers can stick to letter of the contract and maintain academic standards while at the same time interpreting their tasks according to their own ethical and political judgements. Second, relevance can be increased by forming alliances within and beyond the formal hierarchies of the state and the academy. The identification and utilization of these 'spaces of relevance' can be seen as the first step towards an approach that strategically seeks a balance between societal engagement on the one hand and contractual obligations, policy relevance and academic standards on the other.  相似文献   

'How green is my valley?' Desktop geographic information systems as a community-based participatory mapping tool     

Justin Wood 《Area》2005,37(2):159-170

Communities can be encouraged to participate in countryside conservation through mapping, expressing what they feel to be important or distinct locally. Established UK community 'parish map' projects focus on artwork. 'Public participation geographic information systems' potentially offer an alternative community mapping approach. Research sought to compare artwork and GIS mapping and their ease of use. Raster maps, digitizing of features and data table creation encouraged community groups to undertake thematic mapping themselves. Seamless maps removed perceived neighbourhood boundaries. Linking attribute data to maps offers an interactive approach to projects, including internet mapping. Findings indicated that hands-on use of GIS, with support, could benefit and empower community groups when responding to local geographic issues.  相似文献   

Dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth     

Justin Revenaugh  Barry Parsons 《Geophysical Journal International》1987,90(2):349-368

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Hydrogeologic unit flow characterization using transition probability geostatistics   总被引：1，自引：0，他引：1  

Jones NL  Walker JR  Carle SF 《Ground water》2005,43(2):285-289

This paper describes a technique for applying the transition probability geostatistics method for stochastic simulation to a MODFLOW model. Transition probability geostatistics has some advantages over traditional indicator kriging methods including a simpler and more intuitive framework for interpreting geologic relationships and the ability to simulate juxtapositional tendencies such as fining upward sequences. The indicator arrays generated by the transition probability simulation are converted to layer elevation and thickness arrays for use with the new Hydrogeologic Unit Flow package in MODFLOW 2000. This makes it possible to preserve complex heterogeneity while using reasonably sized grids and/or grids with nonuniform cell thicknesses.  相似文献   

Companions of Post-Common Envelope sdB Binaries     

Elizabeth M. Green  Biqing For  Elaina A. Hyde  Ivo R. Seitenzahl  Keith Callerame  Brooke A. White  Corryn N. Young  Christopher S. Huff  Jay Mills  Justin D.R. Steinfadt 《Astrophysics and Space Science》2004,291(3-4):267-274

Preliminary results are presented from two ongoing complementary surveys intended to investigate the nature and characteristics of the optically invisible secondaries in post-common envelope subdwarf B (sdB) binary stars. We obtain precise radial velocities to derive periods and minimum companion masses for bright field sdB stars. These data are combined with light curves to search for eclipses, reflection effects, or ellipsoidal variations. We emphasize the importance of using complete unbiased samples, without which it will not be possible to understand the details of the multiple processes that produce these stars. It remains true that all known secondary companions in short-period sdB binaries are nearly invisible, thus they must be either low mass main sequence (MS) stars or compact objects, e.g., white dwarfs. In our small, nearly-complete sample, white dwarf secondaries outnumber MS secondaries by about a factor of five. Known MS masses in short-period sdB binaries are all surprisingly low, indicating a possible bimodal mass distribution for all MS secondaries in sdB binaries.  相似文献   

Radio continuum surveys     

Justin L. Jonas  Eddie E. Baart 《Astrophysics and Space Science》1995,230(1-2):351-358

The Rhodes University radio astronomy group has been involved in radio continuum mapping of southern extended radio sources since 1976. We describe the various mapping projects undertaken with the HartRAO telescope, particularly the Rhodes/HartRAO 2300 MHz all-sky survey, and speculate on future projects.  相似文献   

The earliest discoveries of dinosaurs: the records re-examined     

Justin B. DelairWilliam A.S. Sarjeant 《Proceedings of the Geologists' Association. Geologists' Association》2002,113(3):185-197

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Book reviews     

Justin Dix  D. H. Tarling  J. H. McD Whitaker  A. J. Barber  Derek W. G. Sears  Olwen Williams-Thorpe  J. C. M. Taylor  P. L. Hancock  S. A. F. Murrell  R. B. J. Smith  Richard Stacey  S. G. Smith 《Surveys in Geophysics》1989,10(1):83-102

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Exploring the causes of an extreme flood event in Central New York,USA     

Peng Gao  Justin J. Hartnett 《自然地理学》2016,37(1):38-55

This study examined the causes of an extreme flood event on 28 June 2013 in Central New York, USA by comparing its hydrological, hydrometeorological, and rainfall-runoff transformation characteristics with those of a typical flood event. Flood frequency analyses showed that the maximum rainfall intensity and the peak discharge of the extreme event had recurrence intervals (RIs) of 8 and 86 years, respectively, while RIs for the typical event were 42 and 11 years, respectively. Their severity diagrams and quantification of their rainfall spatial variations illustrated that the extreme event was spatially localized with high intensities, whereas the typical event was spatially uniform and prolonged. Watershed modeling indicated that the rainfall-runoff transformation was dominated by the infiltration excess process for the extreme flood, while controlled by both infiltration and saturation excess processes for the typical event. These analyses revealed that the upgrade-magnitude conversion pattern of the extreme flood event was induced by the spatial pattern of the rainfall and the “lubricant” effect of the watershed, and emphasized the need for better understanding of such type of extreme events.  相似文献