Expert Systems Applied to Spacecraft Fire Safety Unclad Prepared for Lewis Research Center under Purchase Order C-32000-m
SUMMARY E x p e r t systems a r e p r o b l e m-s o l v i n g programs t h a t combine a knowledge base and a r e a s o n i n g mechanism t o s i m u l a t e a human " e x p e r t. " The development o f an e x p e r t system t o manage f i r e s a f e t y i n s p a c e c r a f t , i n p a r t i c u l a r t h e NASA Space S t a t i o n Freedom, i s d i f f i c u l t b u t c l e a r l y advantageous i n t h e l o n g-t e r m. The r e p o r t d i s c u s s e s some needs i n l o w-g r a v i t y f l a m m a b i l i t y c h a r a c t e r i s t i c s , v e n t i
Fire behavior and risk analysis in spacecraft
Practical risk management for present and future spacecraft, including space stations, involves the optimization of residual risks balanced by the spacecraft operational, technological, and economic limitations. Spacecraft fire safety is approached through three strategies, in order of risk: (1) control of fire-causing elements, through exclusion of flammable materials for example; (2) response to incipient fires through detection and alarm; and (3) recovery of normal conditions through extinguishment and cleanup. Present understanding of combustion in low gravity is that, compared to normal gravity behavior, fire hazards may be reduced by the absence of buoyant gas flows yet at the same time increased by ventilation flows and hot particle expulsion. This paper discusses the application of low-gravity combustion knowledge and appropriate aircraft analogies to fire detection, fire fighting, and fire-safety decisions for eventual fire-risk management and optimization in spacecraft.
Optimized Delivery System Achieves Enhanced Endomyocardial Stem Cell Retention
Background—Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention. Methods and Results—Stem cell retention was simulated in silico using 1- and 3-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol, a nickel and titanium alloy displaying shape memory and superelasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real-time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared with a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle without effect on biocompatibility or safety. Conclusions—Modeling-guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention.