Numerical Analysis of MHD Accelerator with Non-Equilibrium Air Plasma

Magnetohydrodynamic （MHD） accelerator is proposed as a next generation propulsion system. It can be used to increase the performance of a propulsion system. The objective of this study is to investigate the performance of MHD accelerator using non-equilibrium air plasma as working gas. In this study, the fundamental performance of MHD accelerator such as flow performance and electrical performance is evaluated at different levels of applied magnetic field using I-D numerical simulation. The numerical simulation is developed based on a set of differential equations with MHD approximation. To solve this set of differential equations the MacCormack scheme is used. A specified channel designed and developed at NASA Marshall Space Flight Centre is used in the numerical simulation. The composition of the simulated air plasma consists of seven species, namely, N2, N, O2, O, NO, NO＋, and e-. The performance of the non-equilibrium MHD accelerator is also compared with the equilibrium MHD accelerator.

QuantiFERON~-TB Gold试验在结核病接触者筛查和活动性结核病预测中的应用

目的:评估QuantiFERON-TBGold(QFT-G)试验在筛查结核病(TB)接触者、以及评估其发展为活动性结核病的风险方面的效果。方法:收集公共卫生中心结核病密切接触者接受QFT-G试验2年后,临床进展为活动性结核病的资料。结果:3102例观察的接触者中,有419例QFT-G阳性,其中323例开始异烟肼(INH)治疗。419例中的20例(4.8%)发展为结核病。在平均随访的1.6年时间里,2683例QFT-G-阴性人群中,19例被诊断为结核病(0.7%)。QFT-G对于检测可能发展为活动性结核病的接触者的敏感性估计为51%,对于进行异烟肼治疗估计的敏感性为64%。在QFT-G阴性接触者中,所有发展为结核病的都是高度传染病例的接触者。没有进行大规模的结核分枝杆菌素皮肤试验。结论:QFT-G阳性接触者中结核病发病率比QFT-G阴性接触者要高,但是QFT-G阴性接触者中的结核病病例数也是不可忽视的,尤其是具有高传染性结核病例的接触者。