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Based on the daily precipitation data from 53 meteorological stations, 11 extreme precipitation indices were selected, categorized and calculated; the temporal and spatial patterns in these indices and their teleconnections with the large-scale circulations were analyzed by the non-parametric Mann-Kendall test; and Sen's slope estimator and linear regression for the period of 1960-2014 were calculated. The results indicated that all extreme precipitation indices had spatial patterns decreasing from the southeastern to the northwestern parts of the Beijing-Tianjin Sand Source Region (BTSSR), except for the consecutive dry days (CDD), which exhibited a reverse spatial pattern. At the whole-region scale, most extreme precipitation indices showed an insignificant decreasing trend, with exceptions in the intensity indices (RX1day and RX5day) with a statistical significance at the 90% confidence level. The total annual precipitation showed a general shift towards a drier climate in the study area. Spatially, all indices for extreme precipitation showed decreasing trends at most stations, except for simple daily intensity index (SDII) and heavy precipitation days (R10). The change in extreme precipitation may be affected by the El Niño-Southern Oscillation (ENSO), East Asian Summer Monsoon (EASM) and Pacific Decadal Oscillation (PDO). Better understanding of extreme precipitation for the BTSSR may be useful in the regional planning for ecological restoration and water management.

Enzyme-induced carbonate precipitation (EICP) is an emerging biogeotechnical technique that uses free urease to improve soil. Despite its advantages of eliminating complex microbial cultures and reducing reaction byproducts, its efficiency is considered lower than that of microbial induced calcite precipitation (MICP) due to the lack of nucleation sites that induce calcium carbonate deposition. To enhance the strengthening efficiency of EICP for fine-grained soils, an improved EICP method that involves adding an appropriate mass concentration of organic materials (skim milk powder, glutinous rice powder, and brown sugar) into urease solution was proposed and applied to reinforce silt in the Yellow River flood area of China. The preferred concentration and ratio of cementation solution and the optimum concentration of each of the organic materials were determined. Then, the reinforcement effect of the improved EICP at the optimum concentration was compared with the control group, and the reinforcement mechanism for this method was discussed. The results show that after the organic material inclusions, soil strength can be enhanced by 33% compared with EICP-treated soil and is nearly four times higher than that of untreated soil. The superiority of this method over traditional EICP and MICP mainly stems from its ability to provide templates and nucleation sites for calcium carbonate deposition and to improve the size, morphology, and structure of calcium carbonate crystals.

Adhesion hysteresis is defined as the difference between the work needed to separate two surfaces and that originally gained on bringing them together. Adhesion hysteresis is a common phenomenon in most surface/interface interactions. This paper studies the effects of surface roughness on adhesion hysteresis. We assumed that the surface asperity height distribution is Gaussian. Numerical simulations based on Fuller's model showed that adhesion hysteresis depended upon a single dimensionless parameter, the adhesion parameter, which represents the statistical average of a competition between the compressive forces exerted by the higher asperities, which are trying to separate the surfaces, and the adhesion forces of the lower asperities which are trying to hold the surfaces together.