This paper presents the results of an experimental study of the bacterial-mediated biodegradation of linear low density polyethylene (LLDPE) by Serratia marcescens subsp. marcescens (S. marcescens marcescens) bacterium without prior exposure of the LLDPE to thermooxidative aging. Degradation promoted by supernatant from S. marcescens marcescens was also studied, and compared to that promoted by direct exposure to S. marcescens marcescens cells. The results show that the cell-free extracts degrade LLDPE faster than the S. marcescens marcescens. The mechanisms of degradation are also elucidated via Scanning Electron Microscopy, Differential Scanning Calorimetry and Fourier Transform Infra-Red Spectroscopy. These methods show that the S. marcescens marcescens and its supernatant both degrade LLDPE. There was also an increase in the concentrations of the carbonyl groups (new peaks) after the microbial degradation of LLDPE. The degradation process results in the formation and growth of microvoids. The latter are also found to coalesce to form larger defects with increasing exposure to supernatant/cell-free extracts or S. marcescens marcescens.
This paper presents the results of a study on the reliability and performance of the solar-powered street lighting systems installed at the African University of Science and Technology (AUST) in Nigeria, a hot and humid environment. The technical performance of the systems was studied using the following performance indicators: system energy yield, capture loss, as well as the system performance ratio while the reliability of the systems was examined using a model developed from the findings from the maintenance and fault diagnosis of the systems. The model was used to predict the total failure and survival probability of the systems using the Weibull distribution. The performance evaluation during the monitored period (February 2012 to January 2015) indicated that the performance ratios of the systems vary from 70% to 89% and the energy yields of the systems ranging from 2.87 h/day to 5.57 h/day. The results from the reliability analysis also showed that when the stress concentration factor around the notch between the cable terminals in the charge controller increases, the charge controller will become overheated, which in turn affected other components of the systems. The implications of this study are also discussed for the design and development of future solar-powered street lighting systems.
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