Wireless sensor networks provide a wide range of applications, such as environment surveillance, hazard monitoring, traffic control, and other commercial or military applications. The quality of service provided by a sensor network relies on its coverage, i.e., how well an event can be tracked by sensors. This paper studies how to optimally deploy new sensors in order to improve the coverage of an existing network. The best-and worst-case coverage problems that are related to the observability of a path are addressed and formulated into computational geometry problems. We prove that there exists a duality between the two coverage problems, and then solve the two problems together. The presented placement algorithm is shown to deploy new nodes optimally in polynomial time.
The proliferation of Internet technology and balance of composition in major feature of many visual products have been advantageous for businesses and changed the distribution channels through which industries reach their consumers. The intensive development of Internet technology and the increasing popularity of online shopping have further changed customers’ purchasing behaviors and the methods by which companies disseminate their video advertisements. The main research question that this study intends to answer is, “What do users do when a YouTube advertisement appears? Do they avoid or confront them?” The aim of this study is to explore the perceptions and related behaviors of international purchasing and consumers’ trust of YouTube advertisements. Statistical analyses focus on the demographics of a sample population in Thailand. The findings are based on data obtained by a questionnaire, the results of which were analyzed by t-test and multiple regression. The results indicate that YouTube advertising has a significant effect on behavioral trends. Moreover, the subjects in the sample reported that they are more likely to avoid YouTube ads than confront them. The study subjects have low satisfaction with YouTube advertising, and males have significantly lower satisfaction than females. This study also analyzes the reliability of trust perception toward purchasing. The results indicate that the reliability is greater than 90% at an α level of 5% and a 95% confidence interval.
Among security problems of sensor networks, the wormhole attack is especially a serious one because its launch is rather easy and the detection is very difficult. Beside the malicious wormholes built deliberately by attackers, this paper presents another type of wormholes: natural wormholes according to the "shortcut" property of wormholes. Natural wormholes are critical links formed by the topological result of deployment. Both types of wormholes are harmful to normal network operations and need to be identified and repaired to avoid severe damages. This paper presents two novel distributed algorithms using only local connectivity information for detecting both types of wormholes. Unlike the previous approaches, the proposed solution requires no special hardware to get location information or time synchronization.
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