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Chao Zhou,Yibing Liu,Zhiyong Ma 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.1
Under rain-wind conditions, rain-wind induced aerodynamic instability phenomenon often occurs on high-voltage transmission lines. Like the effects of any other oscillations, this kind of vibration intensifies the fatigue of high-voltage conductors, especially on line supportsor clamps. The presence of raindrops and wind associated with electric field maybe the main cause of this phenomenon. On rainydays, raindrops hit the transmission line and suspends to the high-voltage conductor. The suspended raindrops form upper rivulet andlower rivulet and take an elliptical arch shape along the surface of the high-voltage conductor by action of the wind, if rainfall is sufficient. Moreover, the rivulets are enlarged as a cone shape with the electric field of high-voltage conductor. The upper rivulet’s effect onthe original cross-section formation of the high-voltage conductor and its movement are likely to be the cause of aerodynamic instability. The objective of this paper is to validate a two-dimensional model to investigate the effects of different parameters (electric field strength,wind velocity, frequency and damping ratio of the dynamic system) on aerodynamic stability of the conductor. The Lyapunov stabilitytheory is applied to the model to derive the criterion for the instable angle of the rivulet. Moreover, an experimental conductor modelwith a moveable artificial upper rivulet is set-up and tested in a wind tunnel. The theoretical results are in good agreement with the experimentaldata. The model enable better comprehension of the rain-wind induced aerodynamic instability on the conductor.
Hongmei Xu,Libin Wang,Jian Huang,YanQing Zhang,Feng Ma,Jianmin Wang,WenChun Xu,XueMei Zhang,YiBing Yin,KaiFeng Wu 한국미생물학회 2015 The journal of microbiology Vol.53 No.2
Pneumococcal asymptomatic colonization of the respiratory tracts is a major risk for invasive pneumococcal disease. We have previously shown that pneumococcal wall teichoic acid (WTA) was involved in pneumococcal infection of sepsis and adherence to epithelial and endothelial cells. In this study, we investigated the contribution of pneumococcal WTA to bacterial colonization and dissemination in murine models. The result showed that nasopharynx colonizing D39 bacterial cells have a distinct phenotype showing an increased exposure of teichoic acids relative to medium-grown bacteria. The WTA-deficient mutants were impaired in their colonization to the nasopharynx and lungs, and led to a mild inflammation in the lungs at 36 h post-inoculation. Pretreatment of the murine nares with WTA reduced the ability of wild type D39 bacteria to colonize the nasopharynx. In addition, the WTA-deficient strain was impaired in its ability to invade the blood and brain following intranasal administration. WTA-deficient D39 strain was reduced in C3 deposition but was more susceptible to the killing by the neutrophils as compared with its parent strain. Our results also demonstrated that the WTA enhanced pneumococcal colonization and dissemination independently of the host strains. These results indicate that WTA plays an important role in pneumococcal pathogenesis, both in colonization and dissemination processes.