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Bredehoeft JD 《Ground water》2003,41(5):571-577
Today, models are ubiquitous tools for ground water analyses. The intent of this paper is to explore philosophically the role of the conceptual model in analysis. Selection of the appropriate conceptual model is an a priori decision by the analyst. Calibration is an integral part of the modeling process. Unfortunately a wrong or incomplete conceptual model can often be adequately calibrated; good calibration of a model does not ensure a correct conceptual model. Petroleum engineers have another term for calibration; they refer to it as history matching. A caveat to the idea of history matching is that we can make a prediction with some confidence equal to the period of the history match. In other words, if we have matched a 10-year history, we can predict for 10 years with reasonable confidence; beyond 10 years the confidence in the prediction diminishes rapidly. The same rule of thumb applies to ground water model analyses. Nuclear waste disposal poses a difficult problem because the time horizon, 1000 years or longer, is well beyond the possibility of the history match (or period of calibration) in the traditional analysis. Nonetheless, numerical models appear to be the tool of choice for analyzing the safety of waste facilities. Models have a well-recognized inherent uncertainty. Performance assessment, the technique for assessing the safety of nuclear waste facilities, involves an ensemble of cascading models. Performance assessment with its ensemble of models multiplies the inherent uncertainty of the single model. The closer we can approach the idea of a long history with which to match the models, even models of nuclear waste facilities, the more confidence we will have in the analysis (and the models, including performance assessment). This thesis argues for prolonged periods of observation (perhaps as long as 300 to 1000 years) before a nuclear waste facility is finally closed. 相似文献
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J.D. Bredehoeft 《Ground Water Monitoring & Remediation》1994,14(1):95-100
The United Stales, both the private and the public sector, is currently spending approximately $10 billion annually on environmental cleanup. In 1991. the Waste Management Research and Educational Institute at the University of Tennessee, Knoxville completed an exhaustive study that estimated if we continue to pursue current policies the total cost of the cleanup will be approximately $750 billion — in 1990 dollars. This suggests that given current technology and the current rate of expenditure, cleanup will take 75 years - well into the latter half of the next century.
The legacy of environmental problems associated with our weapons complex is enormous. The Tennessee group estimated that one-third of the total cost of cleanup — approximately $240 billion — will be borne by the Department of Energy (DOR). Currently, approximately one-half of the annual expenditures for cleanup conies from DOE —$5 billion, one-third of the DOE budget.
In contrast, the amount of funds for basic research on environmental cleanup problems is small. The federal government spends less than $100 million annually for basic research — less than 1 percent of the total annual expenditure of $10 billion. This level of funding for basic research seems shortsighted given the current status of cleanup technologies and the expected long duration of the problem. 相似文献
The legacy of environmental problems associated with our weapons complex is enormous. The Tennessee group estimated that one-third of the total cost of cleanup — approximately $240 billion — will be borne by the Department of Energy (DOR). Currently, approximately one-half of the annual expenditures for cleanup conies from DOE —$5 billion, one-third of the DOE budget.
In contrast, the amount of funds for basic research on environmental cleanup problems is small. The federal government spends less than $100 million annually for basic research — less than 1 percent of the total annual expenditure of $10 billion. This level of funding for basic research seems shortsighted given the current status of cleanup technologies and the expected long duration of the problem. 相似文献
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The water budget myth revisited: why hydrogeologists model 总被引：26，自引：0，他引：26
Bredehoeft JD 《Ground water》2002,40(4):340-345
Within the ground water community, the idea persists that if one can estimate the recharge to a ground water system, one then can determine the size of a sustainable development. Theis addressed this idea in 1940 and showed it to be wrong-yet the myth continues. The size of a sustainable ground water development usually depends on how much of the discharge from the system can be "captured" by the development. Capture is independent of the recharge; it depends on the dynamic response of the aquifer system to the development. Ground water models were created to study the response dynamics of ground water systems; it is one of the principal reasons hydrogeologists model. 相似文献
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JD Kubicki 《Geochemical transactions》2000,1(1):41-6
Molecular simulations (energy minimizations and molecular dynamics) of an n-hexane soot model developed by Smith and co-workers (M. S. Akhter, A. R. Chughtai and D. M. Smith, Appl. Spectrosc., 1985, 39, 143; ref. 1) were performed. The MM+ (N. L. Allinger, J. Am. Chem. Soc., 1977, 395, 157; ref. 2) and COMPASS (H. Sun, J. Phys. Chem., 1998, 102, 7338; ref. 3) force fields were tested for their ability to produce realistic soot nanoparticle structure. The interaction of pyrene with the model soot was simulated. Quantum mechanical calculations on smaller soot fragments were carried out. Starting from an initial 2D structure, energy minimizations are not able to produce the observed layering within soot with either force field. Results of molecular dynamics simulations indicate that the COMPASS force field does a reasonably accurate job of reproducing observations of soot structure. Increasing the system size from a 683 to a 2732 atom soot model does not have a significant effect on predicted structures. Neither does the addition of water molecules surrounding the soot model. Pyrene fits within the soot structure without disrupting the interlayer spacing. Polycyclic aromatic hydrocarbons (PAH), such as pyrene, may strongly partition into soot and have slow desorption kinetics because the PAH-soot bonding is similar to soot–soot interactions. Diffusion of PAH into soot micropores may allow the PAH to be irreversibly adsorbed and sequestered so that they partition slowly back into an aqueous phase causing dis-equilibrium between soil organic matter and porewater. 相似文献
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JD Klein AE Bester-van der Merwe ML Dicken A Emami-Khoyi KL Mmonwa 《African Journal of Marine Science》2019,41(1):115-118
Genomic data can be a useful tool in the management and conservation of biodiversity. Here, we report the development of genomic resources for the spotted ragged-tooth shark Carcharias taurus using genome-wide DNA data from Illumina next-generation sequencing. We explored two commonly used genetic marker types: microsatellites and mitochondrial DNA. A total of 4 394 putative microsatellites were identified, of which 10 were tested on 24 individuals and found to have ideal properties for population genetic analyses. Additionally, we reconstructed the first complete mitochondrial genome of a South African spotted ragged-tooth shark, and highlight the most informative gene regions to facilitate future primer design. The data reported here may serve as a resource for future studies and can ultimately be applied in the sustainable conservation and fisheries management of this apex predator. 相似文献
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Ground water systems can be categorized with respect to quantity into two groups: (1) those that will ultimately reach a new equilibrium state where pumping can be continued indefinitely and (2) those in which the stress is so large that a new equilibrium is impossible; hence, the system has a finite life. Large ground water systems, where a new equilibrium can be reached and in which the pumping is a long distance from boundaries where capture can occur, take long times to reach a new equilibrium. Some systems are so large that the new equilibrium will take a millennium or more to reach a new steady-state condition. These large systems pose a challenge to the water manager, especially when the water manager is committed to attempting to reach a new equilibrium state in which water levels will stabilize and the system can be maintained indefinitely. 相似文献