ABSTRACT
Mine water disasters are one of the main disasters threatening safe mine operations. If a fault becomes a water guide channel, it often causes serious water inrush accidents in mining. Therefore, accurate evaluation of fault hydraulic conductivity is very important for the prediction and prevention of mine water disasters. To prevent and control mine water disasters and ensure safe mining of coal seams in the presence of faults, this paper takes the F22 fault in the Jinqiao Coal Mine as an example; proposes three highly applicable fault water conductivity evaluation methods based on analysis of water-rock stress, difference analysis of hydrochemical characteristics, and difference analysis of water pressures for the same aquifer on both sides of the fault; and comprehensively analyzes and evaluates the water conductivity of the F22 fault. The results are as follows: the cross-sectional pressure of the fault is greater than the aquifer water pressure and the plastic deformation strength of mudstone combined. The hydrochemical characteristics of the three-ash aquifers on both sides of the fault are obviously different. The water in the three-ash aquifer on one side of the fault has been drained for a long time, while the water pressure on the other side of the fault has not changed significantly. Based on a comprehensive analysis, it is judged that the F22 fault is not water-conducting. The evaluation results are consistent with geophysical explorations and the actual mine roadway exposure, which verifies the feasibility and rationality of the fault water conductivity evaluation method described above.
ABSTRACT
Bacterial ATP-binding cassette (ABC) importers are primary active transporters that are critical for nutrient uptake. Based on structural and functional studies, ABC importers can be divided into two distinct classes, type I and type II. Type I importers follow a strict alternating access mechanism that is driven by the presence of the substrate. Type II importers accept substrates in a nucleotide-free state, with hydrolysis driving an inward facing conformation. The ribose transporter in Escherichia coli is a tripartite complex consisting of a cytoplasmic ATP-binding cassette protein, RbsA, with fused nucleotide binding domains; a transmembrane domain homodimer, RbsC2; and a periplasmic substrate binding protein, RbsB. To investigate the transport mechanism of the complex RbsABC2, we probed intersubunit interactions by varying the presence of the substrate ribose and the hydrolysis cofactors, ATP/ADP and Mg(2+). We were able to purify a full complex, RbsABC2, in the presence of stable, transition state mimics (ATP, Mg(2+), and VO4); a RbsAC complex in the presence of ADP and Mg(2+); and a heretofore unobserved RbsBC complex in the absence of cofactors. The presence of excess ribose also destabilized complex formation between RbsB and RbsC. These observations suggest that RbsABC2 shares functional traits with both type I and type II importers, as well as possessing unique features, and employs a distinct mechanism relative to other ABC transporters.
