Highly Stable Graphene‐Based Multilayer Films Immobilized via Covalent Bonds and Their Applications in Organic Field‐Effect Transistors

Highly stable graphene oxide (GO)‐based multilayered ultrathin films can be covalently immobilized on solid supports through a covalent‐based method. It is demonstrated that when (3‐aminopropyl) trimethoxysilane (APTMS), which works as a covalent cross‐linking agent, and GO nanosheets are assembled in an layer‐by‐layer (LBL) manner, GO nanosheets can be covalently grafted on the solid substrate successfully to produce uniform multilayered (APTMS/GO)N films over large‐area surfaces. Compared with conventional noncovalent LBL films constructed by electrostatic interactions, those assembled using this covalent‐based method display much higher stability and reproducibility. Upon thermal annealing‐induced reduction of the covalent (APTMS/GO)N films, the obtained reduced GO (RGO) films, (APTMS/RGO)N, preserve their basic structural characteristics. It is also shown that the as‐prepared covalent (APTMS/RGO)N multilayer films can be used as highly stable source/drain electrodes in organic field‐effect transistors (OFETs). When the number of bilayers of the (APTMS/RGO)N film exceeds 2 (ca. 2.7 nm), the OFETs based on (APTMS/RGO)N electrodes display much better electrical performance than devices based on 40 nm Au electrodes. The covalent protocol proposed may open up new opportunities for the construction of graphene‐based ultrathin films with excellent stability and reproducibility, which are desired for practical applications that require withstanding of multistep post‐production processes.     

A Versatile Fluoro‐Containing Low‐Bandgap Polymer for Efficient Semitransparent and Tandem Polymer Solar Cells

The versatility of a fluoro‐containing low band‐gap polymer, poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b’]dithiophene)‐alt‐4,7‐(5‐fluoro‐2,1,3‐benzothia‐diazole)] (PCPDTFBT) in organic photovoltaics (OPVs) applications is demonstrated. High boiling point 1,3,5‐trichlorobenzene (TCB) is used as a solvent to manipulate PCPDTFBT:[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) active layer morphology to obtain high‐performance single‐junction devices. It promotes the crystallization of PCPDTFBT polymer, thus improving the charge‐transport properties of the active layer. By combining the morphological manipulation with interfacial optimization and device engineering, the single‐junction device exhibits both good air stability and high power‐conversion efficiency (PCE, of 6.6%). This represents one of the highest PCE values for cyclopenta[2,1‐b;3,4‐b’]dithiophene (CPDT)‐based OPVs. This polymer is also utilized for constructing semitransparent solar cells and double‐junction tandem solar cells to demonstrate high PCEs of 5.0% and 8.2%, respectively.     

A spatiotemporal super-resolution algorithm for a hybrid stereo video system

This paper presents a spatiotemporal super-resolution method to enhance both the spatial resolution and the frame rate in a hybrid stereo video system. In this system, a scene is captured by two cameras to form two videos, including a low spatial resolution with high-frame-rate video and a high spatial resolution with low-frame-rate video. For the low-spatial-resolution video, the low-resolution frames are spatially super-resolved by the high-resolution video via the stereo matching, the bilateral overlapped block motion estimation, and the adaptive overlapped block motion compensation algorithms, while for the low-frame-rate video, those missed frames are interpolated using the high-resolution frames obtained by fusing the disparity compensation and the motion compensation frame rate up-conversion. Experimental results demonstrate that the proposed mixed spatiotemporal super-resolution method has a more significant contribution to both the subjective and objective qualities than the pure spatial super-resolution or the frame rate up-conversion.     

Truthful budget constrained auction for device-to-device relaying packet allocation

Taking advantage of peer-to-peer transmission underlying cellular networks, device-to-device (D2D) communications offer various benefits such as coverage extension, traffic offloading, and improved energy efficiency. In this paper, we focus on a promising scenario where a D2D local area network is formed to relay packets for an out-of-coverage source device. A one-sided auction model is formulated from a unique perspective in which the source device decides the allocation of its packets among the helpers and charges reserve payments to the helpers according to their bids. The winning helpers only collect rewards from the source’s deposit at the base station when the assigned packets are successfully relayed. In this model, we further take into account the budget constraints of the helpers to capture the helpers’ resource limits and the risks that the helpers are willing to take. Based on this model, we propose three auction mechanisms targeting economic properties such as individual rationality, efficiency, and truthfulness. An enhanced Martello & Toth algorithm is first developed for the VCG-based auction to determine packet allocation that optimizes the source’s quality of service. The probabilistic entrance auction mechanism uses sequential second price auction to achieve a low computational cost. The randomized mechanism involves a randomization over the above two mechanisms to satisfy certain requirement for social welfare while minimizing the computational time. We also conduct extensive simulations to examine the performance of the proposed mechanisms.     

气溶胶及能见度变化对标准大气中远红外传输的影响分析

红外制导系统发现、识别和跟踪目标主要依据背景、目标物辐射特性和对比特性信息。气溶胶及其能见度变化是大气环境中影响红外辐射传输的主要因素之一。以标准大气为例,开展了气溶胶及其能见度变化对中、远红外光谱区间（3～5mm,8～12mm）大气透过率和目标背景对比度的影响分析,重点分析了标准大气中相同能见度不同气溶胶类型及同气溶胶类型不同能见度对中远红外传输特性的影响。结果显示：大气透过率对目标背景对比度的理论计算值有重要影响。在其他大气条件既定情况下,气溶胶及其能见度变化对两波段的透过特性和目标识别效果影响明显,且以8～12mm波段的好于3～5mm的。同能见度不同气溶胶类型下的透过率和目标背景对比度差异较大,需要考虑气溶胶的影响。在中远红外区间,3.4～4.2mm和9.5～12mm波段内的透过率和目标背景对比度平均值相对较大,变化振幅小,可作为武器使用理想波段加以选择应用。     

Electrical Percolation Behavior in Silver Nanowire–Polystyrene Composites: Simulation and Experiment

The design and preparation of isotropic silver nanowire‐polystyrene composites is described, in which the nanowires have finite L/D (< 35) and narrow L/D distribution. These model composites allow the L/D dependence of the electrical percolation threshold, ?_c, to be isolated for finite‐L/D particles. Experimental ?_c values decrease with increasing L/D, as predicted qualitatively by analytical percolation models. However, quantitative agreement between experimental data and both soft‐core and core–shell analytical models is not achieved, because both models are strictly accurate only in the infinite‐L/D limit. To address this analytical limitation, a soft‐core simulation method to calculate ?_c and network conductivity for cylinders with finite L/D are developed. Our simulated ?_c results agree strongly with our experimental data, suggesting i) that the infinite‐aspect‐ratio assumption cannot safely be made for experimental networks of particles with L/D < 35 and ii) in predicting ?_c, the soft‐core model makes a less significant assumption than the infinite‐L/D models do. The demonstrated capability of the simulations to predict ?_c in the finite‐L/D regime will allow researchers to optimize the electrical properties of polymer nanocomposites of finite‐L/D particles.     

Hierarchical Asymptotic Methods in the Theory of Cluster Free Electron Lasers

We describe an algorithm for the hierarchic method of averaged characteristics and discuss a practical application of this concept. The application of this method opens new prospects for the solutions of many difficult electrodynamic problems, which, until recently, were considered “unsolved”. We illustrate this method with the example of the effect of plural multi-harmonic parametric resonance of electron-beam waves. This effect can take place within high-current electron beams in the case of the realization of two-stream instability. The considered relativistic beam-model is treated as a model for the transit section of relevant klystron Cluster Two-stream Free Electron Laser (CTSFEL).     

Speech Enhancement Algorithm Based on MMSE Short Time Spectral Amplitude in Whispered Speech

An improved method based on minimum mean square error-short time spectral amplitude （MMSE-STSA） is proposed to cancel background noise in whispered speech. Using the acoustic character of whispered speech, the algorithm can track the change of non-stationary background noise effectively. Compared with original MMSE-STSA algorithm and method in selectable mode Vo-coder （SMV）, the improved algorithm can further suppress the residual noise for low signal-to-noise radio （SNR） and avoid the excessive suppression. Simulations show that under the non-stationary noisy environment, the proposed algorithm can not only get a better performance in enhancement, but also reduce the speech distortion.     

数据城域网安全防护体系部署及解决方案研究

以中国移动数据城域网为例,分析了数据城域网的网络结构、承载业务及面临的主要安全威胁,构建了包含安全域划分及边界整合、设备安全配置、专业安全防护手段建设和信息安全管理平台建设4个层面内容的安全防护体系,并针对中国移动某省数据城域网的现状给出了多层次、阶梯式、分阶段的安全防护建设方案,解决了原有网络安全系统存在的各部分相对独立、关联性不强以及无相互补充、统一协调的防护体系问题。     

多用户MC DS-CDMA系统中的时频域信道估计方法

该文提出了一种用于多用户MC DS-CDMA系统的信道估计方法,该方法在平均时域估计的基础上迭代一次平均频域信道估计,较好地改善了信道估计的性能。仿真结果表明,经过平均时域信道估计方法能较大程度地滤除多址干扰(MAI)和噪声,提高信道估计的准确性。再经过迭代一次平均频域信道估计,系统的误码率(BER)性能还可进一步改善,经过两次信道估计,系统取得的性能已很接近理想估计的性能。