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Vehicular ad hoc networks (VANETs) are a type of mobile ad hoc network that forms a unified wireless communication network between vehicles and roadside nodes. Roadside units (RSUs), as the infrastructure and key component of VANETs, play a critical role in improving the performance of VANETs. Their deployment can effectively improve the communication performance of the network. The goal of the RSU deployment (RSUD) problem is to install as few RSUs as possible on both sides of roads or intersections so that they can cover most areas and achieve better communication performance. This paper proposes a multi-objective optimization model to solve the RSUD problem using the characteristics of RSUDs on urban roads. Our optimized target includes three performance indicators, which are the deployment cost of RSUs, their coverage area, and communications. Since these three indicators cannot achieve consensus, this paper proposes a multi-objective evolutionary algorithm, the NSGA-II Pareto optimal solution, to solve the RSUD problem. The simulation results show the effectiveness of the multi-objective model and method. Finally, we present an experiment featuring RSU deployment that is based on a real traffic environment and uses OpenStreetMap; this experiment proves that our proposed method is practical.

Metal-organic frameworks, an emerging class of porous material, have developed rapidly in recent years. In order to clarify the application of metal-organic frameworks in the field of environmental science, 1386 articles over the last 20 years were obtained from Scopus and analysed by the bibliometric method. And the collaboration between countries, institutions and authors and the co-occurrence of keywords were also conducted using VOS viewer. The results indicated that this area of research has entered a fast-developing stage. The number of articles published has grown from 7 articles in 1999 to 378 articles in 2018. The most productive country was China with 626 articles published. The most productive institution was the Chinese Academy of Sciences, and the most productive author was Jhung SH from Kyungpook National University of South Korea. Although metal-organic frameworks have been widely used in adsorption and catalytic degradation of pollutants from the environment, the removal mechanism of pollutants by MOFs, the stability improvement and the cost reduction of metal-organic frameworks are still the main challenges for their practical applications.

The present study focuses on the effect of Ca-alginate gel on aerobic sludge granulation. Three sequencing batch reactors (SBRs) seeded with different mixtures of Ca-alginate gel and activated sludge with the fraction (weight/weight of dry biomass) of 0%, 5.5%, and 15.5%, respectively. The granulation time of 14 days was obtained with 5.5% additive, while 32 days were needed to adapt aerobic granules developed with 0% Ca-alginate gel. Full granulation was achieved in the trial with 15.5% additive from the 20th day. Comparing with granules in reactor 1, the granules cultivated with Ca-alginate gel exhibited attributes of much faster settling velocities, higher biomass retention, greater mechanical strength, and better nutrient-removing capability. The alginate-metal gel may be the structural polymer of aerobic granules and offer bacteria the inhabitancy and protection, which is beneficial to retain more biomass and improve the efficiency of wastewater treatment.