Offloading technique is an effective approach to migrate tasks from mobile devices to cloud to prolong the battery life. However, it cannot be guaranteed that all devices can successfully offload their tasks to cloud due to the limited network resources, thus offloading decisions should be made to coordinate devices. The existing works focus on how to maximize energy saving for a group of devices instead of the number of mobile devices that benefits from offloading. Therefore, how to maximize the number of energy-saving devices in the multi-user offloading scenario remains a challenging issue to be solved. In this paper, we aim to obtain a beneficial offloading group where all device can offloading tasks simultaneously to achieve energy saving and the number of beneficial offloading devices maximum for the group. In order to get such a group where each device can achieve its own benefit, firstly, we adopt game theory to model each device's demand of saving energy by offloading in OFDM communication system, and formulate multi-user offloading game problem (MUOG). Furthermore, we propose an offloading game mechanism (OGM), including: beneficial offloading threshold (BOT) algorithm and beneficial offloading group (BOG) algorithm. BOT algorithm can obtain the threshold of each device, i.e., the maximum number of mobile devices that the device can tolerate to offload tasks simultaneously while BOG algorithm can obtain a group of beneficial offloading devices. It can be proved that OGM strategy can achieve the Nash equilibrium of MUOG problem so as to obtain the maximum number of beneficial offloading devices. Experimental comparisons verify the number of beneficial offloading users and the overhead of the mechanism among different strategies. The results show that OGM can benefit more devices by offloading to save energy without high overhead compared with other offloading strategies.
Magnetic graphene oxide (MGO) was prepared and used as a catalyst to activate peroxymonosulfate (PMS) for degradation of Coomassie brilliant blue G250 (CBB). The effects of operation conditions including MGO dosage, PMS dosage and initial concentration of CBB were studied. CBB removal could reach 99.5% under optimum conditions, and high removals of 98.4–99.9% were also achieved for other organic dyes with varied structures, verifying the high efficiency and wide applicability of the MGO/PMS catalytic system. The effects of environmental factors including solution pH, inorganic ions and water matrices were also investigated. Reusability test showed that CBB removals maintained above 90% in five consecutive runs, indicating the acceptable recyclability of MGO. Based on quenching experiments, solvent exchange (H2O to D2O) and in situ open circuit potential (OCP) test, it was found that ˙OH, SO4˙− and high-valent iron species were responsible for the efficient degradation of CBB in the MGO/PMS system, while the contributions of O2˙−, 1O2 and the non-radical electron-transfer pathway were limited. Furthermore, the plausible degradation pathway of CBB was proposed based on density functional theory (DFT) calculations and liquid chromatography-mass spectrometry (LC-MS) results, and toxicity variation in the degradation process was evaluated by computerized structure–activity relationships (SARs) using green algae, daphnia, and fish as indicator species.