移动场景下的节点高效寻路RPL路由算法优化

在低功耗有损网络(low power and lossy networks)中,现有的移动性支持路由算法存在控制消息冗余,应用场景不具有普适应,网络丢包率和移动节点能耗较高等问题.针对这些问题,提出一种移动场景下的节点高效寻路RPL路由算法(efficient pathfinding RPL routing algorithm for nodes in mobile scenarios,MSE-RPL).该算法提出的优化思路如下:首先,精简了移动节点的控制消息,并采用自适应黑名单机制建立备选父节点集,从而降低了移动节点的能耗;其次,基于移动节点的移动速度和方向,从备选父节点集中选择移出通信范围预估时间最短的节点作为最优父节点,不但适用于随机移动场景,还降低了平均端到端时延;最后,在链路中断前,利用DIS计时器及时通告DIS消息以快速重构拓扑,降低了丢包率.仿真结果表明,MSE-RPL算法在平均端到端时延、移动节点能耗、丢包率等性能指标方面均有明显改善.

Evolution of dielectric loss-dominated electromagnetic patterns in magnetic absorbers for enhanced microwave absorption performances

As the growing criterion of electromagnetic wave (EMW) absorption materials, micro/nano-scale magnetic materials are drawing more and more attention for their unique features compared to bulky absorbers. Generally, the complex permeability of micro/nano-scale magnetic absorbers varies in a relatively narrow range, whatever for the storage of magnetic energy or the dissipation of magnetic energy. If so, how the small variation of permeability affects the ultimate performances is still unclear. Here, a strategy of electromagnetic parameters regulation for the magnetic materials is applied to understand the loss contribution in micro/nanoscale magnetic absorbers. After analyzing the evolution of electromagnetic maps of ten ferrosoferric oxide samples, it can be found that the dissipation contribution of permeability for magnetic materials is weaker than that of permittivity, in spite of its significant role in determining the impedance matching characteristics. In summary, this work systematically explores the loss contribution in micro/nano-magnetic absorbers for the first time, which is of great importance in designing and optimizing the microwave absorption properties of magnetic absorbers.

Atomically dispersed Au_1 catalyst towards efficient electrochemical synthesis of ammonia

Tremendous efforts have been devoted to explore energy-efficient strategies of ammonia synthesis to replace Haber-Bosch process which accounts for 1.4% of the annual energy consumption. In this study, atomically dispersed Au_1 catalyst is synthesized and applied in electrochemical synthesis of ammonia under ambient conditions. A high NH＋4 Faradaic efficiency of 11.1 % achieved by our Au_1 catalyst surpasses most of reported catalysts under comparable conditions. Benefiting from efficient atom utilization, an NH＋4 yield rate of 1,305 μg h-1 mg-1Au has been reached, which is roughly 22.5 times as high as that by sup- ported Au nanoparticles. We also demonstrate that by employing our Au_1 catalyst, NH＋4 can be electro- chemically produced directly from N_2 and H_2 with an energy utilization rate of 4.02 mmol kJ-1. Our study provides a possibility of replacing the Haber-Bosch process with environmentally benign and energy-efficient electrochemical strategies.

In Situ Exfoliation and Pt Deposition of Antimonene for Formic Acid Oxidation via a Predominant Dehydrogenation Pathway

Direct formic acid fuel cell(DFAFC)has been considered as a promising energy conversion device for stationary and mobile applications.Advanced platinum(Pt)electrocatalysts for formic acid oxidation reaction(FAOR)are critical for DFAFC.However,the oxidation of formic acid on Pt catalysts often occurs via a dual pathway mechanism,which hinders the catalytic activity owing to the CO poisoning.Herein,we directly exfoliate bulk antimony to 2D antimonene(Sb)and in situ load Pt nanoparticles onto antimonene sheets with the assistance of ethylenediamine.According to the Bader charge analysis,the charge transfer from antimonene to Pt occurs,confirming the electronic interaction between Pt and Sb.Interestingly,antimonene,as a cocatalyst,alters the oxidation pathway for FAOR over Pt catalyst and makes FAOR follow the more efficient dehydrogenation pathway.The density functional theory(DFT)calculation demonstrates that antimonene can activate Pt to be a lower oxidative state and facilitate the oxidation of HCOOH into CO_(2) via a direct pathway,resulting in a weakened intermediate binding strength and better CO tolerance for FAOR.The specific activity of FAOR on Pt/Sb is 4.5 times,and the mass activity is 2.6 times higher than the conventional Pt/C.