In this paper, we propose a novel 3D sensing model for the sensor placement optimization problem given a three dimensional environment. The model take into account the angles of a sensor, the distance between the sensor and a given point in the terrain, the Line-of-Sight (visibility) capability, the constraints of the terrain and the number of sensors needed to maximize the coverage over the terrain. In order to generate optimal solutions to the model, we firstly present a novel Line-of-Sight (LoS) method aiming to determine the number of obstacles between a given sensor and a point in the region of interest using the ideas of adaptive lengths and linear regression. Secondly, we propose a modification of PSO algorithm, where particles (sensors) update their velocity by using only local information coming from their neighbors. The comparison and analyses of experimental results reveal that optimal solutions achieved from the 3D sensing model are better than those of the related work.

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In this paper, the authors present the expression of triggered earthquakes at some hydropower reservoirs in Vietnam. The results indicate that: (1) The triggered earthquakes of magnitude M > 4.0 have occurred at the Hoa Binh, Song Tranh 2 and Son La hydropower reservoirs. All these reservoirs are more than 90 m deep and located on gneiss, granite or limestone rocks; (2) Triggered earthquakes at the Hoa Binh, Song Tranh 2 and Son La hydropower reservoirs are the rapid ones. The earthquake frequency has close ties with the water level change; (3) Vp/Vs ratio can be used as the main factor determining the triggered earthquake source. The natural earthquake sources interconnecting with the reservoir and having the Vp/Vs ratio of 1.63-1.69 have the highest risk of triggered earthquake occurrence and (4) There is no risk of triggered earthquake occurrence at Hoa Binh hydropower reservoir, the magnitude of 4.9 is the maximum. Triggered earthquakes in the Song Tranh 2 reservoir continue occurring with the magnitude of smaller than 4.7. In the Son La reservoir, triggered earthquakes have a magnitude of 4.3.

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