摘要 :
This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty ass...
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This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport.
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摘要 :
Objective: To evaluate the role of transoesophageal echocardiography and problems related to safety during the surgical repair of congenital cardiac malformations in children. Methods: We examined the transoesophageal recordings m...
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Objective: To evaluate the role of transoesophageal echocardiography and problems related to safety during the surgical repair of congenital cardiac malformations in children. Methods: We examined the transoesophageal recordings made in 350 children with congenital cardiac diseases, aged from 2 months to 17 years and 9 months, with a median age of 2.7 years, tracings having been taken both before and after cardiopulmonary bypass. All patients had been scanned by transthoracic echocardiography before the operative procedures. Results: Preoperative transoesophageal echocardiography added additional findings, or changed the diagnoses made using transthoracic echocardiography, in 33 cases (9.4%), among which the findings had therapeutic significance in 23 cases (6.6%) that altered the planned surgical procedures. Residual problems or sequels were detected by postoperative transoesophageal echocardiography in 57 cases (16.3%), with 13 patients (3.7%) requiring instant intervention or return to bypass for modifications of the surgical procedures. We encountered no severe complications due to the performance of transoesophageal echocardiography. Mild complications occurred in only 2 patients (0.6%). Conclusions: Transoesophageal echocardiography is a useful tool with which to determine the strategies for treatment in the perioperative period, and to improve the quality of surgical procedures in children with congenital cardiac diseases. Complications were few, but still deserved careful attention to detail.
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