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51.
Mathematical Geosciences - 相似文献
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Wyatt Mark C. Holland Wayne S. Greaves Jane S. Dent William R. F. 《Earth, Moon, and Planets》2003,92(1-4):423-434
Debris disks are found around some 15% of main sequencestars and their dust is thought to be continuallyreplenished in collisions between planetesimals inextrasolar Kuiper belts.While they were discovered in 1984 by IRAS, it is onlywith more recent imaging that their true nature has beenrevealed. This paper discusses recent debris disk images andtheir impact on our understanding of extrasolar systems.Importantly these images confirm the extrasolar Kuiper belthypothesis for most (but not all) debris diskcandidates and show that the planetesimals within thesedisks must have grown to at least a few km.Asymmetries in imaged disk structures also provide informationabout the planetary systems orbiting inside these planetesimalbelts. The impact of debris disk studies on our understandingof the evolution of our own Kuiper belt, as well as theirpotential to solve puzzles such as the origin of the missingmass and the outer edge of the Kuiper belt, is alsodiscussed. 相似文献
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Prediction of Resource Volumes at Untested Locations Using Simple Local Prediction Models 总被引:1,自引:1,他引:0
This paper shows how local spatial nonparametric prediction models can be applied to estimate volumes of recoverable gas resources
at individual undrilled sites, at multiple sites on a regional scale, and to compute confidence bounds for regional volumes
based on the distribution of those estimates. An approach that combines cross-validation, the jackknife, and bootstrap procedures
is used to accomplish this task. Simulation experiments show that cross-validation can be applied beneficially to select an
appropriate prediction model. The cross-validation procedure worked well for a wide range of different states of nature and
levels of information. Jackknife procedures are used to compute individual prediction estimation errors at undrilled locations.
The jackknife replicates also are used with a bootstrap resampling procedure to compute confidence bounds for the total volume.
The method was applied to data (partitioned into a training set and target set) from the Devonian Antrim Shale continuous-type
gas play in the Michigan Basin in Otsego County, Michigan. The analysis showed that the model estimate of total recoverable
volumes at prediction sites is within 4 percent of the total observed volume. The model predictions also provide frequency
distributions of the cell volumes at the production unit scale. Such distributions are the basis for subsequent economic analyses.
相似文献
Emil D. AttanasiEmail: |
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The primary objectives of this research were to (1) investigate empirical methods for establishing regional trends in unconventional
gas resources as exhibited by historical production data and (2) determine whether or not incorporating additional knowledge
of a regional trend in a suite of previously established local nonparametric resource prediction algorithms influences assessment
results. Three different trend detection methods were applied to publicly available production data (well EUR aggregated to
80-acre cells) from the Devonian Antrim Shale gas play in the Michigan Basin. This effort led to the identification of a southeast–northwest
trend in cell EUR values across the play that, in a very general sense, conforms to the primary fracture and structural orientations
of the province. However, including this trend in the resource prediction algorithms did not lead to improved results. Further
analysis indicated the existence of clustering among cell EUR values that likely dampens the contribution of the regional
trend. The reason for the clustering, a somewhat unexpected result, is not completely understood, although the geological
literature provides some possible explanations. With appropriate data, a better understanding of this clustering phenomenon
may lead to important information about the factors and their interactions that control Antrim Shale gas production, which
may, in turn, help establish a more general protocol for better estimating resources in this and other shale gas plays. 相似文献
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Rural household demographics, livelihoods and the environment 总被引:8,自引:0,他引:8
Alex de Sherbinin Leah K. VanWey Kendra McSweeney Rimjhim Aggarwal Alisson Barbieri Sabine Henry Lori M. Hunter Wayne Twine Robert Walker 《Global Environmental Change》2008,18(1):38-53
This paper reviews and synthesizes findings from scholarly work on linkages among rural household demographics, livelihoods and the environment. Using the livelihood approach as an organizing framework, we examine evidence on the multiple pathways linking environmental variables and the following demographic variables: fertility, migration, morbidity and mortality, and lifecycles. Although the review draws on studies from the entire developing world, we find the majority of microlevel studies have been conducted in either marginal (mountainous or arid) or frontier environments, especially Amazonia. Though the linkages are mediated by many complex and often context-specific factors, there is strong evidence that dependence on natural resources intensifies when households lose human and social capital through adult morbidity and mortality, and qualified evidence for the influence of environmental factors on household decision-making regarding fertility and migration. Two decades of research on lifecycles and land cover change at the farm level have yielded a number of insights about how households make use of different land-use and natural resource management strategies at different stages. A thread running throughout the review is the importance of managing risk through livelihood diversification, ensuring future income security, and culture-specific norms regarding appropriate and desirable activities and demographic responses. Recommendations for future research are provided. 相似文献