Optimizing Computational Mission Operation by Periodic Backups and Preventive Replacements

2018 ◽  
Vol 48 (9) ◽  
pp. 1505-1520 ◽  
Author(s):  
Gregory Levitin ◽  
Liudong Xing ◽  
Yuanshun Dai
Keyword(s):  

Subject COVID-19 impact on Chad. Significance Chad has a relatively low number of confirmed COVID-19 cases but appears quite vulnerable to the impact of the pandemic, especially the economic impact. The country’s highly rural and youthful demography may help to slow the spread and keep the death rate low. Yet low oil prices, a return to recession and a new wave of sector-specific protests could pose major challenges for the government. Impacts Chad's epidemic appears unlikely to affect France’s Sahel counterterrorism mission Operation Barkhane, headquartered in Chad. A bottom-up revolution appears unlikely, and no major rebel challengers appear poised to take advantage of COVID-19 and associated crises. President Idriss Deby's government appears unlikely to fall in the short term -- French backing will continue to ensure his survival.


Author(s):  
Filipe Dias ◽  
José Páscoa ◽  
Carlos Xisto

In hypersonic flight of reentry vehicles the radio blackout is a typical problem, in particular because it arises during a critical mission operation point. To mitigate this radio blackout the magnetic window concept is proposed. In this work a numerical model is presented to accurately simulate the effect of a magnetic field interacting with ionized plasma surrounding the vehicle. The numerical model is based on the MHD flow equations. Initially, the code is validated for pure hypersonic gas dynamics. Diverse high resolution spatial discretisation schemes, within a Finite Volume framework, are analyzed for robustness. Afterwards, the numerical code is further validated for MHD flows using the well-known Hartmann case. A very good comparison between numerical and analytical results is verified. This allows a proper validation of the method in terms of Lorentz force, in particular under low-magnetic Reynolds number conditions. A very tough test-case is finally computed, being typical of a reentry capsule geometry. The accuracy of the model is then verified for different applied magnetic fields.


2016 ◽  
Vol 20 (3) ◽  
pp. 238-245
Author(s):  
Seheon Song ◽  
SangIl Lee ◽  
JaeHyun Park

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