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981.
Feng Wang Jiale Ma Fangyan Xie Linkai Li Jian Chen Jun Fan Ni Zhao 《Advanced functional materials》2016,26(20):3417-3423
The applications of organotin halide perovskites are limited because of their chemical instability under ambient conditions. Upon air exposure, Sn2+ can be rapidly oxidized to Sn4+, causing a large variation in the electronic properties. Here, the role of organic cations in degradation is investigated by comparing methylammonium tin iodide (MASnI3) and formamidinium tin iodide (FASnI3). Through chemical analyses and theoretical calculations, it is found that the organic cation strongly influences the oxidation of Sn2+ and the binding of H2O molecules to the perovskite lattice. On the one hand, Sn2+ can be easily oxidized to Sn4+ in MASnI3, and replacing MA with FA reduces the extent of Sn oxidation; on the other hand, FA forms a stronger hydrogen bond with H2O than does MA, leading to partial expansion of the perovskite network. The two processes compete in determining the material's conductivity. It is noted that the oxidation is a difficult process to prevent, while the water effect can be largely suppressed by reducing the moisture level. As a result, FASnI3‐based conductors and photovoltaic cells exhibit much better reproducibility as compared to MASnI3‐based devices. This study sheds light on the development of stable Pb‐free perovskite optoelectronic devices through new material design. 相似文献
982.
Haitong Sun Zhihua Shi Chunming Zhao Manton J.H. Zhi Ding 《Communications, IEEE Transactions on》2008,56(5):818-827
This work investigates the design of linear precoders for ARQ packet retransmissions in multi-input multi-output (MIMO) systems. We consider transmitter precoder design based on partial MIMO channel information in the form of their covariance feedback. Our objective is to maximize the ergodic mutual information provided by multiple (re)transmissions of a packet subject to transmission power constraint. We propose a set of near-optimal successive linear ARQ precoders for flat fading MIMO channels. This progressive linear ARQ precoder combines the appropriate power loading and the reverse-order pairing of singular values in the current retransmission with previous transmissions. This reverse-order pairing is a special feature unique to our sequential ARQ preceding approach with demonstrated performance gains. 相似文献
983.
基于Kohonen网络的入侵检测方法 总被引:1,自引:0,他引:1
赵玲 《信息安全与通信保密》2005,(3):125-127
本文在自动聚类分析的基础上,根据入侵检测系统收到的网络数据包中的特征数据, 采用Kohonen神经网络方法,确定该数据的状态,判断结果与该数据的真实模式是否相一致。该方 法能实现对入侵检测系统中用户行为的模式识别,而且准确率高。 相似文献
984.
985.
Quality-of-Service (QoS) performance and connection admission control (CAC) for heterogeneous services in wireless multiple access networks are investigated. The heterogeneous services include constant bit rate (CBR), variable bit rate (VBR) and available bit rate (ABR) services. Multiple access control is handled by a polling-based scheme with non-preemptive priority. Tight delay variation (jitter) bounds for CBR connections and delay bounds for VBR connections are derived. A CAC scheme based on the derived bounds is developed. The CAC makes use of user mobility information to reserve an appropriate amount of system resources for potential handoff connections to achieve low handoff connection dropping rate (HCDR). Simulation results show that the proposed CAC scheme can achieve both low HCDR and high resource utilization. 相似文献
986.
本文研究了高温(1300℃)氧化并在一氧化氮(NO)气体中进行氧化后退火方法对4H-SiC 金属-氧化物-半导体(MOS)电容的SiC/SiO2界面特性的影响,主要通过SiC MOS的电容-电压(C-V)特性详细讨论了NO退火时间和温度与SiO2/SiC界面特性的相互关系. 结果表明在NO气体中进行氧化后退火可明显降低界面态密度,并且界面态密度随着温度和时间的增加会进一步降低。 同时,与常规1200℃及以下氧化温度相比,1300℃下热生长的氧化层具有更低的界面态密度且显著缩短了氧化时间,节约了生产成本。 相似文献
987.
重点论述了移动互联网环境下智能管道的网络架构和关键技术,指出"感知、控制、开放"的智能管道能力将成为运营商网络能力提升的主要技术发展方向,感知是智能管道的基础、控制是智能管道的核心、开放是智能管道差异化服务的主要手段。 相似文献
988.
Hierarchical NiMn Layered Double Hydroxide/Carbon Nanotubes Architecture with Superb Energy Density for Flexible Supercapacitors 下载免费PDF全文
Jingwen Zhao Jiale Chen Simin Xu Mingfei Shao Qiang Zhang Fei Wei Jing Ma Min Wei David G. Evans Xue Duan 《Advanced functional materials》2014,24(20):2938-2946
A hierarchical nanostructure composed of NiMn‐layered double hydroxide (NiMn‐LDH) microcrystals grafted on carbon nanotube (CNT) backbone is constructed by an in situ growth route, which exhibits superior supercapacitive performance. The resulting composite material (NiMn‐LDH/CNT) displays a three‐dimensional architecture with tunable Ni/Mn ratio, well‐defined core‐shell configuration, and enlarged surface area. An electrochemical investigation shows that the Ni3Mn1‐LDH/CNT electrode is rather active, which delivers a maximum specific capacitance of 2960 F g–1 (at 1.5 A g–1), excellent rate capability (79.5% retention at 30 A g–1), and cyclic stability. Moreover, an all‐solid‐state asymmetric supercapacitor (SC) with good flexibility is fabricated by using the NiMn‐LDH/CNT film and reduced graphene oxide (RGO)/CNT film as the positive and negative electrode, respectively, exhibiting a wide cell voltage of 1.7 V and largely enhanced energy density up to 88.3 Wh kg–1 (based on the total weight of the device). By virtue of the high‐capacity of pseudocapacitive hydroxides and desirable conductivity of carbon‐based materials, the monolithic design demonstrated in this work provides a promising approach for the development of flexible energy storage systems. 相似文献
989.
990.