For Wireless Sensor Networks (WSNs), the Voronoi partition of a region is a challenging problem owing to the limited sensing ability of each sensor and the distributed organization of the network. In this paper, an algorithm is proposed for each sensor having a limited sensing range to compute its limited Voronoi cell autonomously, so that the limited Voronoi partition of the entire WSN is generated in a distributed manner. Inspired by Graham’s Scan (GS) algorithm used to compute the convex hull of a point set, the limited Voronoi cell of each sensor is obtained by sequentially scanning two consecutive bisectors between the sensor and its neighbors. The proposed algorithm called the Boundary Scan (BS) algorithm has a lower computational complexity than the existing Range-Constrained Voronoi Cell (RCVC) algorithm and reaches the lower bound of the computational complexity of the algorithms used to solve the problem of this kind. Moreover, it also improves the time efficiency of a key step in the Adjust-Sensing-Radius (ASR) algorithm used to compute the exact Voronoi cell. Extensive numerical simulations are performed to demonstrate the correctness and effectiveness of the BS algorithm. The distributed realization of the BS combined with a localization algorithm in WSNs is used to justify the WSN nature of the proposed algorithm.

In this paper, we propose a connectivity-preserving flocking algorithm for multi-agent systems in which the neighbor set of each agent is determined by the hybrid metric-topological distance so that the interaction topology can be represented as the range-limited Delaunay graph, which combines the properties of the commonly used disk graph and Delaunay graph. As a result, the proposed flocking algorithm has the following advantages over the existing ones. First, range-limited Delaunay graph is sparser than the disk graph so that the information exchange among agents is reduced significantly. Second, some links irrelevant to the connectivity can be dynamically deleted during the evolution of the system. Thus, the proposed flocking algorithm is more flexible than existing algorithms, where links are not allowed to be disconnected once they are created. Finally, the multi-agent system spontaneously generates a regular quasi-lattice formation without imposing the constraint on the ratio of the sensing range of the agent to the desired distance between two adjacent agents. With the interaction topology induced by the hybrid distance, the proposed flocking algorithm can still be implemented in a distributed manner. We prove that the proposed flocking algorithm can steer the multi-agent system to a stable flocking motion, provided the initial interaction topology of multi-agent systems is connected and the hysteresis in link addition is smaller than a derived upper bound. The correctness and effectiveness of the proposed algorithm are verified by extensive numerical simulations, where the flocking algorithms based on the disk and Delaunay graph are compared.

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With the development of the dye industry, dye wastewater emissions have increased dramatically. The presence of dyes in untreated effluents is unfriendly to the environment, for example, coloring water bodies, disturbing the aquatic system, being chronic and acute toxicities to human beings, etc. So dye-containing wastewater requires treatment before disposal. The most common techniques for removing dyes include membrane separation [1, 2], advanced oxidation [3, 4], and biological treatment [5, 6], etc. However, there are certain disadvantages of these techniques such as high cost or secondary pollution. The adsorption technique is considered to be an effective method for wastewater treatment, especially with activated carbon due to its high adsorption capacity [7-12]. However, the high initial and regeneration cost of activated carbon limits its use [13, 14]. Hence, many investigators are studying for the alternate adsorbents that are equivalent to activated carbon, but inexpensive and abundant. These include: shell [15, 16], sludge [17], slag [18], palm fruit bunch [19], and straw [20]. As the product of coal gasification at medium temperature, semi-coke is the raw material of certain industries such as ferroalloy, calcium carbide and so on. During the transportation and production process, a large amount of semi-coke powder with particle size less than 3 mm is produced. This powder becomes solid waste for not meeting the production process requirements. So semi-coke powder is cheap and available, and moreover it has some beneficial properties in preparation of activated carbon. As solid waste, semi-coke powder is harmful to the environment. When it is prepared to be activated carbon it becomes

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