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( Xing Hu ),( Linhua Ma ),( Shaocheng Huang ),( Jinke Huang ),( Kangning Sun ),( Tianyu Huang ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.8
In high diversity node situation, single-channel MAC protocols suffer from many collisions. To solve this problem, the research of multichannel MAC protocol has become a hotspot. And the cyclic quorum-based multichannel (CQM) MAC protocol outperformed others owing to its high frequency utilization. In addition, it can avoid the bottleneck that others suffered from and can be easily realized with only one transceiver. To obtain the accurate performance of CQM MAC protocol, a Markov chain model, which combines the channel hopping strategy of CQM protocol and IEEE 802.11 distributed coordination function (DCF), is proposed. The metrics (throughput and average packet transmission delay) are calculated in performance analysis, with respect to node number, packet rate, channel slot length and channel number. The results of numerical analysis show that the optimal performance of CQM protocol can be obtained in saturation bound situation. And then we obtain the saturation bound of CQM system by bird swarm algorithm (BSA). Finally, the Markov chain model and saturation bound are verified by Qualnet platform. And the simulation results show that the analytic and simulation results match very well.
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A Signal Characteristic Based Cluster Scheme for Aeronautical Ad Hoc Networks
( Yu Tian ),( Linhua Ma ),( Le Ru ),( Hong Tang ),( Bo Song ) 한국인터넷정보학회 2014 KSII Transactions on Internet and Information Syst Vol.8 No.10
Clustering is an effective method for improving the performance of large scale mobile ad hoc networks. However, when the moving speed is very fast, the topology changes quickly, which leads to frequent cluster topology updates. The drastically increasing control overheads severely threaten the throughput of the network. SCBCS (Signal Characteristic Based Cluster Scheme) is proposed as a method to potentially reduce the control overheads caused by cluster formation and maintenance in aeronautical ad hoc networks. Each node periodically broadcasts Hello packets. The Hello packets can be replaced by data packets, which preserve bandwidth. The characteristics of the received packets, such as the Doppler shift and the power of two successive Hello packets, help to calculate the relative speed and direction of motion. Then, the link connection lifetime is estimated by the relative speed and direction of motion. In the clustering formation procedure, the node with the longest estimated link connection time to its one-hop neighbors is chosen as the cluster head. In the cluster maintenance procedure, re-affiliation and re-clustering schemes are designed to keep the clusters more stable. The re-clustering phenomenon is reduced by limiting the ripple effect. Simulations have shown that SCBCS prolongs the link connection lifetime and the cluster lifetime, which can reduce the topology update overheads in highly dynamic aeronautical ad hoc networks.
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YONG DING,SONGYUAN DAI,Litao Jia,YANMEI MA,ZHAOQIAN LI,CHANGNENG ZHANG,JIANXI YAO,LIE MO,LINHUA HU,BING ZHANG,LING JIANG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.5
The sub-microspheres play multiple roles in enhancing dye adsorption and light-scattering toimprove the performance of dye-sensitized solar cells (DSSCs). In this work, the well-de¯ned TiO 2sub-microspheres with anatase granular-like nanocrystals are prepared in high yield by com-bining hydrolytic process with solvothermal treatment. Scanning electron microscopy (SEM) andtransmission electron microscopy (TEM) results indicated that plenty of rhombic nanoparticleswith ? 18 nm diameter having mutual contacts to neighboring nanoparticles were densely self-assembled into sub-microspheres, and abundant mesopores existed in the whole sub-microsphereswith superior light scattering ability. The appropriate pore diameter and relatively high speci¯csurface area of the as-obtained sub-microsphere result in a higher dye adsorption. As expected, byusing the sub-microspheres as a scattering layer, a higher photovoltaic conversion e±ciency of10.15% is obtained for DSSCs.
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Enhanced UV emission and photocatalytic activity due to morphology evolution of ZnO thin films
Zang Aoxin,Chen Keyu,Xu Linhua,Xian Fenglin,Ma Wenyang,Tian Zhen 한국물리학회 2023 Current Applied Physics Vol.54 No.-
Tuning the optical properties of nanomaterials through morphology evolution has attracted extensive attention. In this study, ZnO films were deposited on substrates using sol-gel approach, and ZnO nanocolumn arrays were formed on the film surface induced by doped ions. XRD results show that the nanocolumns all have a growth orientation along the c-axis and good crystallization quality. Compared with pure ZnO film, the ones with nanocolumn arrays on the film surface exhibit higher UV emission efficiency and photocatalytic activity. The enhanced UV emission efficiency is attributed to the higher crystalline quality and fewer surface defects of the nanocolumn arrays. The improved photocatalytic activity is mostly ascribed to two factors: (1) nanocolumns are more conducive to the migration of photogenerated electrons and holes to the photocatalyst surface to participate in redox reactions, (2) the formation of nanocolumn arrays improves light absorption of the ZnO films.
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