AN IMPROVED DOUBLE HETEROGENEITY MODEL FOR PEBBLE-BED REACTORS IN DRAGON-5

In pebble-bed reactors, the fuel is contained in small grains, which are included in a graphite matrix. Some burnable poison particles may also be present. In this work, an additional ’double heterogeneity’ model is introduced in the DRAGON5 lattice code. The model is based on the legacy work of She (INET) and has been improved to overcome intrinsic limitations. It is based on a simplified physical model whereas the two already existing models were based on the collision probability analysis or on renewal theory. The advantage of this new model is its simplicity to implement. The theory shows that the correction suggested in the original model should not be arbitrary, but a constant equivalent particle fraction of 0.63. Numerical comparison between the models is generally good. However it does not support the theory of a constant equivalent fraction. Additional work is needed to reduce the discrepancy between the models in some cases.

Social Models for Dealing with Inequalities

This chapter compares social models in Europe and Latin America. The goal is to study the interaction between two institutions: on the one hand, pre-distributive (ex ante) institutions, such as the structure and coverage of collective bargaining and, on the other hand, post-distributive (ex post) institutions, such as unemployment protection and social policy. Pre-distributive institutions are important for correcting inequalities in the labour market, because they introduce guidelines for egalitarian wage structures. Post-distributive institutions help to mitigate inequalities generated in the labour market.The methodology is based on statistical analysis of a series of indicators related to pre and post-distributive policies. The results present three types of model: (1) coordinated economies, typical of neo-corporatist Scandinavian countries; (2) mixed economies, typical of Mediterranean systems, and (3) uncoordinated economies, which equate to liberalism and the Latin American ‘structural heterogeneity’ model. It is neo-corporatist coordinated economies that generate the most pre and post-distributive equality. In turn, uncoordinated economies, and Latin American ones in particular, generate more inequalities due to highly informal employment and the weakness of their post-distributive institutions.

Modeling Three-Dimensional Anisotropic Structures of Reservoir Lithofacies Using Two-Dimensional Digital Outcrops

Reservoir heterogeneity is a key geological problem that restricts oil and gas exploration and development of clastic rocks from the early to late stages. Existing reservoir heterogeneity modeling methods such as multiple-point geostatistics (MPS) can accurately model the two-dimensional anisotropic structures of reservoir lithofacies. However, three-dimensional training images are required to construct three-dimensional reservoir lithofacies anisotropic structures models, and the method to use reservoir heterogeneity model of fewer-dimensional to obtain a three-dimensional model has become a much-focused research topic. In this study, the outcrops of the second member of Qingshuihe Formation (K1q2) in the northwestern margin of the Junggar Basin, which are lower cretaceous rocks, were the research target. The three-dimensional reservoir heterogeneity model of the K1q2 outcrop was established based on the unmanned aerial vehicle (UAV) digital outcrops model and MPS techniques, and the “sequential two-dimensional conditioning data” (s2Dcd) method was modified based on a sensitivity parameter analysis. Results of the parametric sensitivity analysis revealed that the isotropic multigrid simulations demonstrate poor performance because of the lack of three-dimensional training images, conditioning data that are horizontally discrete and vertically continuous, and distribution of lithofacies that are characterized by large horizontal continuities and small thicknesses. The reservoir lithofacies anisotropic structure reconstructions performed well with anisotropic multigrids. The simulation sequence of two-dimensional surfaces for generating the three-dimensional anisotropic structure of reservoir lithofacies models should be reasonably planned according to the actual geological data and limited hard data. In additional to this, the conditional probability density function of each two-dimensional training image should be fully utilized. The simulation results using only one two-dimensional section will have several types of noises, which is not consistent with the actual geological background. The anisotropic multigrid simulations and two-dimensional training image simulation sequence, proposed in this paper as “cross mesh, refinement step by step”, effectively reduced the noise generated, made full use of the information from the two-dimensional training image, and reconstructed the three-dimensional reservoir lithofacies anisotropic structures models, thus conforming to the actual geological conditions.

Asthma in children treated with paracetamol versus ibuprofen: A systematic review and meta-analysis of randomised controlled trials

Background: Paracetamol and ibuprofen are the most commonly used medications for fever and pain management in children. While the efficacy appears similar with both drugs, there are contradictory findings related to adverse events. In particular, incidence of asthma among children taking paracetamol compared to ibuprofen, remain unsettled. Methods: We conducted a meta-analysis of randomized controlled trials (RCTs) that compared asthma in children taking paracetamol versus ibuprofen. A comprehensive search was conducted in five databases. RCTs reporting on cases of asthma in infants or children after the administration of paracetamol or ibuprofen were included. The pooled effect size was estimated using the inverse variance heterogeneity model. Results: Five RCTs with 85095 children were included in the analysis. The pooled estimate (RR 1.04; 95%CI 0.84-1.29) revealed no difference in the risk of developing asthma or presenting an exacerbation of asthma in children who received paracetamol compared to ibuprofen. When the analysis was restricted to RCTs that examined the incidence of asthma, the pooled estimate remained similar (RR 1.03; 95%CI 0.64-1.67). Additional bias adjusted quality effect sensitivity model yielded similar results (RR 1.03; 95%CI 0.84-1.28). Conclusion: Ibuprofen and paracetamol have similar tolerance and safety profiles in terms of incidence of asthma in children.

Leisure Time Physical Activity Reduces the Risk for Stroke in Adults: A Reanalysis of a Meta-Analysis Using the Inverse-Heterogeneity Model

Objective. Apply more robust and additional analyses to a previous meta-analysis that reported statistically significant associations between leisure time physical activity (LTPA) and stroke. Methods. A reanalysis of a previous meta-analysis that included nine prospective cohort studies representing 269,594 men and women 25-84 years of age and in which the association between LTPA and incident stroke was examined. Follow-up periods ranged from 7.7 to 32.0 years. Relative risks (RR) from each study were pooled using the inverse-heterogeneity model. Heterogeneity was examined using the Q statistic, inconsistency using I2, and small-study effects using Doi plots and the LFK index. Influence and cumulative meta-analysis were also conducted. Results. Using low LTPA as the reference, moderate LTPA was associated with a statistically significant reduction in the risk for stroke in men (RR = 0.79, 95% CI = 0.65 to 0.95) and a trend in women (RR = 0.88, 95% CI = 0.78 to 1.0). High LTPA was associated with a statistically significant reduction in the risk for stroke in both men (RR = 0.72, 95% CI = 0.60 to 0.86) and women (RR = 0.78, 95% CI = 0.66 to 0.92). No statistically significant heterogeneity was observed and inconsistency was low. However, potential small-study effects were observed. With each study deleted once, results remained statistically significant. Cumulative meta-analysis demonstrated stability in results since at least 2005. Conclusions. Leisure time physical activity is associated with a reduced risk of stroke in both men and women. However, the small-study effects observed suggest the possibility that results may be exaggerated.