Abstract-Efficiency and security are two basic requirements for sensor network design. However, these requirements could be sharply contrary to each other in some scenarios. For example, innetwork data aggregation can significantly reduce communication overhead and thus has been adopted widely as a means to improve network efficiency; however, the adoption of in-network data aggregation may prevent data from being encrypted since it is a prerequisite for aggregation that data be accessible during forwarding. In this paper, we address this dilemma by proposing a family of secret perturbation-based schemes that can protect sensor data confidentiality without disrupting additive data aggregation. Extensive simulations are also conducted to evaluate the proposed schemes. The results show that our schemes provide confidentiality protection for both raw and aggregated data items with an overhead lower than that of existing related schemes.
in Wiley InterScience (www.interscience.wiley.com).The performance of solid-gas reaction heat transformer system using MnCl 2 and CaCl 2 was investigated with the consideration of multistep reactions between CaCl 2 and NH 3 . The reactions between CaCl 2 and NH 3 could be CaCl 2 Á2/4NH 3 and CaCl 2 Á4/ 8NH 3 . The simulated results were verified by the experimental data. From the analysis results, it was concluded that the two reactions between CaCl 2 and NH 3 existed simultaneously. The favored conditions for the simultaneous occurrence of multistep reactions were discussed. The main reaction in the system with the initial state of CaCl 2 Á2NH 3 and CaCl 2 Á4NH 3 were designated as the reaction of CaCl 2 Á2/4NH 3 and CaCl 2 Á4/8NH 3 , respectively. It was concluded that high driving temperature T M , large relative gas volume, and large specific heat transfer area were the favored conditions for the simultaneous occurrence of multistep reactions in the systems both with the initial state of CaCl 2 Á2NH 3 and CaCl 2 Á4NH 3 . High initial charging pressure P 0 was favored for the system with the initial state of CaCl 2 Á2NH 3 , while low P 0 was favored for the system with the initial state of CaCl 2 Á4NH 3 . The impacts of the simultaneous occurrence of multistep reactions on the system performance indicators [temperature lift, specific power, and system coefficient of performance (COP)] were also investigated in this article. It was concluded that the occurrence of the reaction of CaCl 2 Á4/ 8NH 3 for the initial state of CaCl 2 Á2NH 3 led to better system performance, i.e., larger temperature lift, larger specific power, and larger system COP. However, the occurrence of the reaction of CaCl 2 Á2/4NH 3 for the initial state of CaCl 2 Á4NH 3 would lead to lower specific power. The temperature lift and system COP were larger for the initial state of CaCl 2 Á4NH 3 ; while the cycle period was shorter for the initial state of CaCl 2 Á2NH 3 .
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