Analysis of a robust and energy efficient transmission scheduling protocol in single‐hop ad hoc networks

A fully connected one‐hop ad hoc network constitutes a basic unit for managing self‐organizing networks such as IEEE 802.11 and 802.15.3 networks. Since energy efficiency is a critical issue in ad hoc networks, we develop an energy‐saving framework that includes scheduling for node‐to‐node direct communication. The scheduling is performed by a coordinator that is selected by some simple rule. We enhance IEEE 802.11 protocol by using our proposed framework, and analyze its energy efficiency in transmitting and receiving data. Through mathematical analysis, we confirm that our enhanced protocol significantly saves energy compared to the IEEE 802.11 protocol. We also investigate the robustness of our algorithm by covering the cases of uncooperative users, system malfunctioning, and channel errors. The numerical results confirm that our protocol works well under these hostile environments and maintains its advantage over the conventional scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

Modeling the level of contamination of Staphylococcus aureus in ready-to-eat kimbab in Korea

The risk of Staphylococcus aureus in ready-to-eat kimbab (rice rolled in laver) sold in Korea was evaluated by a mathematical modeling approach. Four nodes were constructed from preparation at retail to consumption. A predictive microbial growth model and survey data were combined with probabilistic modeling to simulate the level of S. aureus in a single kimbab at the time of consumption. We estimated the mean level of S. aureus to be 2.92 log CFU/g for a typical kimbab (150 to 200 g each) at the time of consumption. Our model also showed that 29.73% of the kimbabs had > or = 100,000 S. aureus CFU/g, which poses some risk of illness, since some level of enterotoxin would be expected from toxigenic strains. However, because of the lack of dose-response models for staphylococcal enterotoxin, the final level of S. aureus in the kimbabs could not be used to estimate how many people would become ill from eating them. Correlation sensitivity results showed that consumer eating patterns and initial contamination levels at retail stores were the most significant risk factors for illness and that temperature control under 10 degrees C was a critical control point in kimbab retail establishments to prevent the growth of S. aureus.