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BackgroundMotility of flagellated bacteria depends crucially on their organelles such as flagella and pili, as well as physical properties of the external medium, such as viscosity and matrix elasticity. We studied the motility of wild-type and two mutant strains of Caulobacter crescentus swarmer cells in two different types of media: a viscous and hyperosmotic glycerol-growth medium mixture and a viscoelastic growth medium, containing polyethylene glycol or polyethylene oxide of different defined sizes.ResultsFor all three strains in the medium containing glycerol, we found linear drops in percentage of motile cells and decreases in speed of those that remained motile to be inversely proportional to viscosity. The majority of immobilized cells lost viability, evidenced by their membrane leakage. In the viscoelastic media, we found less loss of motility and attenuated decrease of swimming speed at shear viscosity values comparable to the viscous medium. In both types of media, we found more severe loss in percentage of motile cells of wild-type than the mutants without pili, indicating that the interference of pili with flagellated motility is aggravated by increased viscosity. However, we found no difference in swimming speed among all three strains under all test conditions for the cells that remained motile. Finally, the viscoelastic medium caused no significant change in intervals between flagellar motor switches unless the motor stalled.ConclusionHyperosmotic effect causes loss of motility and cell death. Addition of polymers into the cell medium also causes loss of motility due to increased shear viscosity, but the majority of immobilized bacteria remain viable. Both viscous and viscoelastic media alter the motility of flagellated bacteria without affecting the internal regulation of their motor switching behavior.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0322-3) contains supplementary material, which is available to authorized users.

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To evaluate the safety of emergency training for industrial accident scenarios, an approach combining analytic hierarchy process (AHP) and gray-fuzzy evaluation is proposed. According to the characteristics of industrial emergency training scenarios, a safety evaluation index system for this training is constructed from four aspects: human, machine, environment, and management. The index weight is established using the AHP and the evaluation model is established base of the gray-fuzzy evaluation method. Based on the combination of the two methods, the quantitative results on training safety was obtained and the most important factor that have the greatest impact on training safety was found. Using this new assessment method, the safety of an industrial accident training scenario for a domestic emergency training facility are assessed, the defects in its emergency capacity are determined, and measures and suggestions are recommended to provide scientific and effective basis for improving emergency capacity.

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Mine road dust is an important source of dust in mine operations. The dust produced on the road surface is a great hazard to the workers. Aiming at the road dust of an open-pit mine, this paper conducts physical and chemical analysis of a dust suppressant prepared by using sodium polyacrylate as a binder, sodium carbonate as a moisture absorbent, polyethylene glycol as a water-retaining agent, and alkyl glycoside as a surfactant. Characterization of characteristics and dust suppression performance. The results show that the dust suppressant has a pH of 11.03, a viscosity of 18.5 mPa•s, and a surface tension of 28.1 mN/m. The content of heavy metal ions contained is less than the maximum concentration de ned by the national standard. Under the same temperature condition, the greater the humidity, the stronger the hygroscopicity, especially when the humidity is 30%, where the better hygroscopic effect than water is obvious. The dust suppressant also has good anti-evaporation properties and it keeps at 4-5% moisture content after 10 days at a normal temperature. Compared with water, the dust suppressant has better resistance to wind erosion and compression. Under the same conditions, the loss rate of water is 2 times that of the dust suppressant and the pressure of the dust suppressant sample is about 3 times that of water. The dust suppressant has a much higher dust removal e ciency for all dust and respirable dust than water under the same conditions. Finally, the test results and mechanism of the dust suppression effect of the dust suppressant are described and analyzed, which shows that the dust suppressant studied in this paper has good performance and is suitable for road dust prevention.