Energy-efficient trajectory planning for amulti-UAV-assisted mobile edge computing system

We study a mobile edge computing system assisted by multiple unmanned aerial vehicles(UAVs),where the UAVs act as edge servers to provide computing services for Internet of Things devices.Our goal is to minimize the energy consumption of this system by planning the trajectories of UAVs.This problem is difficult to address because when planning the trajectories,we need to consider not only the order of stop points(SPs),but also their deployment(including the number and locations)and the association between UAVs and SPs.To tackle this problem,we present an energy-efficient trajectory planning algorithm(TPA)which comprises three phases.In the first phase,a differential evolution algorithm with a variable population size is adopted to update the number and locations of SPs at the same time.In the second phase,the k-means clustering algorithm is employed to group the given SPs into a set of clusters,where the number of clusters is equal to th at of UAVs and each cluster contains all SPs visited by the same UAV.In the third phase,to quickly generate the trajectories of UAVs,we propose a low-complexity greedy method to construct the order of SPs in each cluster.Compared with other algorithms,the effectiveness of TPA is verified on a set of instances at different scales.

A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(Ⅱ) dye for detecting mercury ion

A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye [Ru（Hipdpa）（Hdcb- py）（NCS）2]^-.0.5H^＋ 0.5[N（C4H9）4]＋ Ru（Hipdpa） {where Hdcbpy = monodeprotonted-4,4＇-dicarboxy-2,2＇- bipyridine and Hipdpa = 4-（1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl）-N,N-diphenylaniline} for selective detection of Hg2. is presented. The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement （I/Io = 11 ） and a considerable blue shift in visible absorption and luminescence maxima with the addition of rig2.. The sensitive response of the optical sensor on Hg^2＋ was attributed to the binding of the electron-deficient Hg^2＋ to the electron-rich sulfur atom of the thiocyanate （NCS） ligand in the Ru（Hipdpa）, which led to an increase in the energy gap between the highest occupied molecular orbital （HOMO） and the lowest unoccupied molecular orbital （LUMO）. Accordingly, the blue shift in the absorption spectrum of Ru（Hipdpa） due to the binding of Hg2. was obtained. Ru（Hipdpa） was found to have decreased Hg2~ detection limit and improved linear region as compared to di（tetrabutylammonium） cis-bis（isothiocyanato）bis（2,2＇-bipyridine-4-carboxylic acid-4＇- carboxylate）ruthenium（ll） N719. Moreover, a dramatic color change from pink to yellow was observed, which allowed simple monitoring of Hg^2＋ by either naked eyes or a simple colorimetric reader. Therefore, the proposed sensor can provide potential applications for Hg2＊ detection.