+}
+
+@article{ref227,
+ author = {Mihaela Cardei and
+ David MacCallum and
+ Maggie Xiaoyan Cheng and
+ Manki Min and
+ Xiaohua Jia and
+ Deying Li and
+ Ding-Zhu Du},
+ title = {Wireless Sensor Networks with Energy Efficient Organization},
+ journal = {Journal of Interconnection Networks},
+ volume = {3},
+ number = {3-4},
+ year = {2002},
+ pages = {213-229},
+}
+
+@inproceedings{ref228,
+ author = {D. Zorbas and D. Glynos and P. Kotzanikolaou and C. Douligeris},
+ title = {B\{GOP\}: an adaptive coverage algorithm for wireless sensor networks},
+ booktitle = {Proceedings of the 13th European Wireless Conference},
+ series = {EW'07},
+ year = {2007},
+ location = {Paris, France},
+
+}
+
+@inproceedings{ref229,
+ title={A near optimal algorithm for lifetime optimization in wireless sensor networks},
+ author={Deschinkel, Karine and Hakem, Mourad},
+ booktitle={SENSORNETS 2013, 2nd Int. Conf. on Sensor Networks},
+ pages={197--202},
+ year={2013}
