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In this present work, cement slurry flowing in well annuli with narrow or varied radial sizes is investigated, whose purpose is to precisely calculate the equivalent circulating density (ECD) during well cementing in the petroleum industry. The theoretical Metzner-Reed (MR) method and the direct numerical simulation (DNS) are applied to calculate the cementing ECD for different types of cement slurries by considering both the Bingham and Power-Law rheological models. The cementing ECD calculated by the theoretical MR method is verified to be in accordance with the DNS result. Moreover, for the narrow annulus, the cementing ECD is demonstrated to be sensitive to the rheological model. In addition, based on the obtained DNS results, the accuracies of the cementing ECD calculated by three commercial software, including DRILL BENCH (DB), LANDMARK (LM), and PVI, are compared, to determine their corresponding adaptability for different rheological models. According to the detailed comparisons, LM shows the highest accuracy in calculating the cementing ECD for the Power-Law fluid, while PVI is optimal for the Bingham fluid. However, sharp fluctuations of the calculation errors are observed when DB is applied. [ABSTRACT FROM AUTHOR]

Carbon footprint (CF) and inequality reductions were two of the most important sustainable development goals. However, there was a lack of understanding of the latest equality of carbon footprint across regions. Based on the multi-regional input-output table and the China Family Panel Studies survey data of 17 provinces, this paper examined the evolution of carbon footprint and inequality in China. The results showed a stark disparity between regions and a declined inequality in the last few years. Specifically, the CF per capita in northern provinces (Liaoning, Shanxi, Heilongjiang, Shandong and Shaanxi) exceeded the average level in 2017. From 2015 to 2017, the carbon inequality showed a downward trend, with a national CF-Gini coefficient decrease from 0.31 to 0.28. Meanwhile, the gap between CF per capita in urban areas and rural areas was declining, with a growth rate at 18% and 32% from 2015 to 2017, respectively. In addition, CF per capita from various consumption categories indicated that household equipment and daily necessities, residential, transportation and communication were the three most important sources, with a downward trend from 2015 to 2017. This study would provide policymakers with deep insights into policies to achieve just transition. [ABSTRACT FROM AUTHOR]

The dynamics of a self-propelled capsule robot for small-bowel endoscopy driven by its internal vibro-impact excitation is studied in this paper. Due to its complex anatomy, the frictional environment in the small bowel is uncertain, so this work aims to maintain the progression of the robot at a desired velocity in the presence of such an uncertainty by using a new optimisation method. The optimisation method consists of the Six Sigma and the Multi-Island Genetic algorithms, and its reliability analysis is carried out with the consideration of parametric and environmental uncertainties by using the Monte Carlo algorithm. In total, five different motions of the capsule, including fast, slow, forward, backward and hovering, are optimised. Extensive numerical studies show that the five desired motions can be fulfilled by various combinations of system and control parameters. Experimental verification is also carried out using a capsule prototype to demonstrate the efficacy of the proposed method. A mismatch between the numerical optimisation and the experimental results for the backward motion of the prototype was observed. However, optimisations for forward and hovering motions show good agreements with experimental observations. Potentially, the proposed approach can be used for optimising various progressive robots in different scales with multiple control objectives and constraints. [Display omitted] • The dynamics of a capsule robot for small-bowel endoscopy is studied. • Robot's velocity is optimised in the presence of frictional uncertainty. • It combines various optimisation algorithms with a reliability analysis. • Numerical and experimental results are compared to validate its efficacy. • It suits for the robots with multiple control objectives and constraints. [ABSTRACT FROM AUTHOR]