南水北调中线受水区分布式水文模型子流域划分研究

从空间尺度上对分布式水文模拟进行了分类,提出了区域分布式水文模拟的概念.根据区域分布式水文模拟的特点,提出了针对不完整流域进行分布式水文模拟时,研究范围的确定原则.同时通过引入流域入口点,实现了一种基于Pfafstetter编码规则的区域分布式水文模型子流域划分方法,并成功应用到南水北调中线受水区.另外,在该方法中还包括了对狭长子流域的进一步自动细分及根据水文站、水库位置进一步细分子流域的功能.     

The ground movement,strata fracturing and changes in permeability due to deep longwall mining

This is an emperical study of the sub-surface deformation caused by retreating longwall mining. The strata movement was monitored by a multi-wire borehole instrumentation system consisting of mechanical anchors installed at different horizons in a borehole drilled over a longwall panel. The anchors were connected to the suspended weights on the surface by a system of pulleys and wires, and the movement of these weights was monitored during mining. Changes in strata bulk permeability were measured by packer tests before and after mining. Strata fracturing due to mining was estimated by comparing pre-mining fractures with post-mining fractures. The observed vertical strains in the overburden were generally small, varying between 0.5 and 4 mm/m. Tensile strains in the overburden extending from the surface to 112m depth Tensile strains in the overburden extending from the surface to 112m depth were less than 0.5 mm/m. There were increases in the number of fractures and permeability in the strata. However, no correlation was observed between fracturing and changes in permeability.     

Meso-damage evolution and mechanical characteristics of low-porosity sedimentary rocks under uniaxial compression

Low pore sedimentary rocks (from Guangxi, China) were subjected to uniaxial compression loading experiment under different initial stresses. The rock samples were investigated by nuclear magnetic resonance before and after the loading. The relationships between the mesoscopic rock damage and macroscopic mechanical parameters were established, and the initial damage stress of the low-porosity sedimentary rock was determined. The results showed that this type of rock has the initial stress of damage. When the initial loading stress is lower than the initial stress of damage, the T₂ spectrum area of the rock sample gradually decreases, and the primary pores of the rock are further closed under the stress. The range of the initial stress of damage for this type of rock is 8-16 MPa. When the loading stress exceeds the initial stress of damage, the T₂ spectrum area gradually increases, indicating that the porosity of the rock increases and microscopic damage of the rock appears. The rock damage degree is defined, and the nonlinear function between the rock damage degree and the initial loading stress is established.     

Surface microstructure and abrasion resistance of concrete

The influence of several surface finishing techniques on the abrasion resistance of concrete specimens of various mix compositions has been measured by means of a rolling-wheel apparatus. Microstructural features of the cement matrix components of the exposed surfaces have been studied by mercury intrusion porosimetry and microhardness determinations. The results indicate that different methods of surface finishing produce substantially different microstructural characteristics within a surface zone of a few mm maximum thickness. For the systems investigated, it was found that the abrasion resistance was determined largely by the pore structure of this surface zone.     

How influential is the role of oligotrophication on the integrity of fish assemblages in the littoral zone?

Food web theory predicts that one of the consequences of oligotrophication is the decline in fisheries following the establishment of nutrient-deficient conditions and low biogenic production. However, emerging evidence suggests that more complex trophic interactions, induced by plankton composition, dietary diversification, temporal and spatial heterogeneity, variations in fish age and size structure can lead to ecosystem responses that deviate from theoretical predictions; especially in the shallow littoral zone. In this study, two end-to-end modelling strategies are used to characterize potential food web structural shifts and overall ecosystem productivity in response to oligotrophication. Our modelling strategy draws upon empirical and theoretical evidence from the Bay of Quinte, a semi-enclosed embayment in northeastern Lake Ontario that has been subjected to phosphorus (P) abatement strategies in the 1970s. We first show that the role of food abundance has been a primary factor shaping fish production, but the fish community gradually responded to the reduced availability of pelagic staples of their diet by displaying greater reliance upon alternative sources, including benthic and other autochthonous (or even allochthonous) food items. Our analysis further suggests that degree of diet overlap between competing trophic guilds can significantly modulate realized biomass levels. The composition of the autotrophic community is another major confounding factor that can induce significant variations from the predicted food web productivity patterns in response to oligotrophication. Overall, our analysis suggests that the proposed reduction of the ambient total phosphorus levels may not necessarily trigger a significant decline in fish biomass in the Bay of Quinte.     

A comparative Appraisal of Classical and Holistic Water Scarcity Indicators

Water Resources Management - Precise measurement of water scarcity is a prerequisite to effective resource management. Researchers have developed a range of water scarcity indicators. However, no...     

A modified stereographic projection approach and a free software tool for kinematic analysis of rock slope toppling failures

Bulletin of Engineering Geology and the Environment - Toppling failure is one of the common instability modes of rock slopes. Up to date, the stereographic projection approach is still an...