High-temperature structural phase transitions in neighborite: a high-resolution neutron powder diffraction investigation     

Kevin S. Knight  G. David Price  John A. Stuart  Ian G. Wood 《Physics and Chemistry of Minerals》2015,42(1):45-52

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The role of negative CO2 emissions for reaching 2 °C—insights from integrated assessment modelling     

Detlef P. van Vuuren  Sebastiaan Deetman  Jasper van Vliet  Maarten van den Berg  Bas J. van Ruijven  Barbara Koelbl 《Climatic change》2013,118(1):15-27

Limiting climate change to 2 °C with a high probability requires reducing cumulative emissions to about 1600 GtCO₂ over the 2000–2100 period. This requires unprecedented rates of decarbonization even in the short-run. The availability of the option of net negative emissions, such as bio-energy with carbon capture and storage (BECCS) or reforestation/afforestation, allows to delay some of these emission reductions. In the paper, we assess the demand and potential for negative emissions in particular from BECCS. Both stylized calculations and model runs show that without the possibility of negative emissions, pathways meeting the 2 °C target with high probability need almost immediate emission reductions or simply become infeasible. The potential for negative emissions is uncertain. We show that negative emissions from BECCS are probably limited to around 0 to 10 GtCO₂/year in 2050 and 0 to 20 GtCO₂/year in 2100. Estimates on the potential of afforestation options are in the order of 0–4 GtCO₂/year. Given the importance and the uncertainty concerning BECCS, we stress the importance of near-term assessments of its availability as today’s decisions has important consequences for climate change mitigation in the long run.  相似文献   

Characterizing parameter sensitivity and uncertainty for a snow model across hydroclimatic regimes     

Minxue He  Terri S. Hogue  Kristie J. FranzSteven A. Margulis  Jasper A. Vrugt 《Advances in water resources》2011,34(1):114-127

The National Weather Service (NWS) uses the SNOW17 model to forecast snow accumulation and ablation processes in snow-dominated watersheds nationwide. Successful application of the SNOW17 relies heavily on site-specific estimation of model parameters. The current study undertakes a comprehensive sensitivity and uncertainty analysis of SNOW17 model parameters using forcing and snow water equivalent (SWE) data from 12 sites with differing meteorological and geographic characteristics. The Generalized Sensitivity Analysis and the recently developed Differential Evolution Adaptive Metropolis (DREAM) algorithm are utilized to explore the parameter space and assess model parametric and predictive uncertainty. Results indicate that SNOW17 parameter sensitivity and uncertainty generally varies between sites. Of the six hydroclimatic characteristics studied, only air temperature shows strong correlation with the sensitivity and uncertainty ranges of two parameters, while precipitation is highly correlated with the uncertainty of one parameter. Posterior marginal distributions of two parameters are also shown to be site-dependent in terms of distribution type. The SNOW17 prediction ensembles generated by the DREAM-derived posterior parameter sets contain most of the observed SWE. The proposed uncertainty analysis provides posterior parameter information on parameter uncertainty and distribution types that can serve as a foundation for a data assimilation framework for hydrologic models.  相似文献   

Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco,NE Venezuela     

Maarten Van Daele  Aurélien van Welden  Jasper Moernaut  Christian Beck  Franck Audemard  Javier Sanchez  François Jouanne  Eduardo Carrillo  Gustavo Malavé  Andrés Lemus  Marc De Batist 《Marine Geology》2011,279(1-4):37-51

The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic–stratigraphic units were identified in the upper ~ 200 m of the sedimentary infill. Detailed seismic–stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.  相似文献   

The emerging water crisis in Bulgaria     

C. Gregory Knight  Stefan B. Velev  Marieta P. Staneva 《GeoJournal》1995,35(4):415-423

Climatic records for the last 15 years indicate that Bulgaria is experiencing a period of exceptionally low precipitation. During 1993, significant water supply problems emerged, approaching crisis proportions in Sofia, the nation's capital, by the end of 1994. The record-setting drought of 1993 can be explained from a synoptic climatic perspective. Whether consequences of the continuing drought could have been foreseen is arguable. That these consequences were fully realized only in 1994 may be understood through examination of Bulgarian water use since the end of the socialist era in 1989. If Bulgaria had experienced the same levels of industrial activity and irrigation as occurred in 1989, the current situation would have been national catastrophe, a situation that could quickly emerge in coming years should climatic patterns persist.  相似文献   

Geography in Burundi*     

Jean-Pierre Ndayishimiye  Jean-Etienne Bidou  C. Gregory Knight 《The Professional geographer》1992,44(2):219-223

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Statehood: A politico-geographic and legal perspective     

David B. Knight Dr. 《GeoJournal》1992,28(3):311-318

The political geographical literature of focuses on the State yet little attention has been placed on the basic criteria and attributes of statehood. This paper presents a linked politico-geographic and legal perspective on statehood. The criteria and attributes identified and discussed are: a particular defined territory; a permanent resident population; a constituted effective government; independence; sovereignty; recognition; permanence; the capacity to enter into relations with other States; a State apparatus; a circulation system; and an organized economy. Certain conceptualizations and the importance of discourse are discussed.  相似文献   

Extinguishing Petroleum Vapor Intrusion and Methane Risks for Slab-on-ground Buildings: A Simple Guide     

Gregory B. Davis  John H. Knight  John L. Rayner 《Ground Water Monitoring & Remediation》2021,41(2):61-72

The occurrence of aerobic biodegradation in the vadose zone between a subsurface source and a building foundation can all-but eliminate the risks from methane and petroleum vapor intrusion (PVI). Understanding oxygen availability and the factors that affect it (e.g., building sizes and their distribution) are therefore critical. Uncovered ground surfaces allow oxygen access to the subsurface to actively biodegrade hydrocarbons (inclusive of methane). Buildings can reduce the net flux of oxygen into the subsurface and so reduce degradation rates. Here we determine when PVI and methane risk is negligible and/or extinguished; defined by when oxygen is present across the entire sub-slab region of existing or planned slab-on-ground buildings. We consider all building slab sizes, all depths to vapor sources and the effect of spacings between buildings on the availability of oxygen in the subsurface. The latter becomes critical where buildings are in close proximity or when increased building density is planned. Conservative assumptions enable simple, rapid and confident screening should sites and building designs comply to model assumptions. We do not model the aboveground “building” processes (e.g., air exchange), and assume the slab-on-ground seals the ground surface so that biodegradation of hydrocarbons is minimized under the built structure (i.e., the assessment remains conservative). Two graphs represent the entirety of the outcomes that allow simple screening of hydrocarbon vapors based only on the depth to the source of vapors below ground, the concentration of vapors within the source, the width of the slab-on-ground building, and the gap between buildings; all independent of soil type. Rectangular, square, and circular buildings are considered. Comparison with field sites and example applications are provided, along with a simple 8-step screening guide set in the context of existing guidance on PVI assessment.  相似文献   

Assessment of NMR Logging for Estimating Hydraulic Conductivity in Glacial Aquifers     

Alexander K. Kendrick  Rosemary Knight  Carole D. Johnson  Gaisheng Liu  Steven Knobbe  Randall J. Hunt  James J. Butler Jr. 《Ground water》2021,59(1):31-48

Glacial aquifers are an important source of groundwater in the United States and require accurate characterization to make informed management decisions. One parameter that is crucial for understanding the movement of groundwater is hydraulic conductivity, K. Nuclear magnetic resonance (NMR) logging measures the NMR response associated with the water in geological materials. By utilizing an external magnetic field to manipulate the nuclear spins associated with ¹H, the time-varying decay of the nuclear magnetization is measured. This logging method could provide an effective way to estimate K at submeter vertical resolution, but the models that relate NMR measurements to K require calibration. At two field sites in a glacial aquifer in central Wisconsin, we collected a total of four NMR logs and obtained measurements of K in their immediate vicinity with a direct-push permeameter (DPP). Using a bootstrap algorithm to calibrate the Schlumberger-Doll Research (SDR) NMR-K model, we estimated K to within a factor of 5 of the DPP measurements. The lowest levels of accuracy occurred in the lower-K (K < 10⁻⁴ m/s) intervals. We also evaluated the applicability of prior SDR model calibrations. We found the NMR calibration parameters varied with K, suggesting the SDR model does not incorporate all the properties of the pore space that control K. Thus, the expected range of K in an aquifer may need to be considered during calibration of NMR-K models. This study is the first step toward establishing NMR logging as an effective method for estimating K in glacial aquifers.  相似文献   

Introducing Middle School Students to the Spatial Sciences through a Community Atlas Project     

Michael Ferber  Timothy A. Warner  Eric Pyle  Tina Knight 《国际地球制图》2013,28(1):75-80

Abstract

A community atlas is an effective method of promoting student‐centered, learning oriented instruction. It provides an integrated framework for teaching thematic interdisciplinary material and promotes collaborative work by students, whose efforts can be shared amongst themselves and with the community. This paper describes community atlas projects from three West Virginia middle schools, in which 320 students and five teachers participated. Younger and less structured students responded with more enthusiasm to the open‐ended nature of the assignment. Self‐disciplined students produced effective web pages combining images, maps, and non‐spatial information such as demographic tables and local perceptions. Although this project was a collaboration between a university and local middle schools, sufficient resources are available for teachers to implement community atlases without specialized assistance.  相似文献