工艺参数对磁控溅射WO_3薄膜电致变色性能的影响

本文采用磁控溅射法制备了用于电致变色器件的WO_3薄膜,用X射线衍射仪(XRD)、场发射扫描电镜(FE-SEM)、紫外-可见分光光度计(UV-Vis)对其物相组成、微观形貌以及电致变色性能进行了表征。结果表明:在溅射压强为2 Pa、氩氧比为60:20时所制备的WO_3薄膜厚度适中,且有利于离子的嵌入/脱出,而以此薄膜制备的电致变色器件光调制范围最大,褪色时间最短,着色效率达82.9 cm~2/C。     

遥测射频监视仪中带通滤波器的设计与实现

介绍遥测射频监视仪中的平行耦合线带通滤波器的设计与实现。该遥测射频监视系统的功能是监控2.5GHz载波频率准确性和稳定性。在阐述平行耦合线带通滤波器设计原理基础上,运用ADS综合射频仿真软件对滤波器的各项性能指标进行分析,并插入陷波器用以克服平行耦合线带通滤波器存在寄生通带的弱点。测试结果表明,该滤波器能很好地完成抑制干扰及噪声的功能,确保监视系统的正常工作。     

基于用户偏好的嵌入性网络结构分析

嵌入性是社会网络分析的核心思想,现有的互联网结构研究抛开理论思想只借用社会网络分析方法,不利于从深层次上理解和挖掘用户行为与网络结构之间的关系.本文针对二元关系框架分析互联网深层结构的局限性,构建了基于用户偏好的网络行为分析框架,提出了嵌入性网络结构的观点,分析了用户行为与其所处的互联网及现实社会关系网络之间的双重嵌入关系.从关系性嵌入和结构性嵌入两个维度给出了一系列测度指标和分析方法,为分析互联网深层次的网络结构提供了新的研究思路.     

Switching on Fluorescent Emission by Molecular Recognition and Aggregation Dissociation

A generic and effective approach to “switch on” and enhance the two‐photon fluorescence (TPF) emission of quenched TPF molecules, i.e., fluorene derivatives, is reported in terms of molecular recognition with a decoupling medium. Such a medium, in this case Bombyx mori silk, can recognize TPF molecules and inhibit the aggregation of the TPF molecules. The designed TPF molecules are 2,7‐bis[2‐(4‐nitrophenyl)ethenyl]‐9,9‐dibutylfluorene ( 4NF ) and 2,7‐bis[2‐(4‐nitrophenyl)ethenyl]‐9,9‐dioctylfluorene ( 8NF ), which exhibit suppressed TPF emission owing to molecular‐stacking‐led aggregation in the solid form. Due to the specific recognition between –NO₂ in the quenched fluorescent molecules and –NH groups in silk fibroin molecules, the aggregated molecules of 4NF / 8NF molecules are decoupled. This decoupling gives rise to a significant increase in TPF quantum yields. The mechanism is further confirmed by replacing the terminal group –NO₂ in 8NF with –CH₃ (in 2,7‐bis[2‐(4‐methylphenyl)ethenyl]‐9,9‐dioctylfluorene; 8MF ) to eliminate the possibility of molecular recognition. As predicted, in the case of 8MF the switching‐on effect is eliminated. Completely new TPF silk fibers can additionally be applied in real‐time 3D high‐resolution TPF scaffold bioimaging.     

基于ZigBee无线传感网络技术的污染气体监测系统

无线传感器网络技术已日趋成熟,为了能实时、有效地对污染气体排放企业进行监控,可采用Zigbee技术对污染气体进行自动监测。设计中的无线收发模块采用XBee—PRODigiMesh900芯片,利用单片机作为控制芯片,通过无线通信方式形成的一个多跳自组织网络,将采集的数据经过处理变成串行数据后发送给汇聚节点,再由汇聚节点发送到控制中心。利用NS2进行了网络仿真,通过仿真,网络运行良好,丢包率低,延迟时间短,满足系统自动监测的需求。     

Creating Atomic Ordering in Electrocatalysis

Catalysis always proceeds in a chaotic fashion. Therefore, identifying the working principles of heterogeneous catalysts is a challenging task. Creating atomic order in heterogeneous catalysts simplifies this task and also offers new opportunities for rationally designing active sites to manipulate catalytic performance. The recent rapid advances in heterogeneous electrocatalysis have led to exciting progress in the construction of atomically ordered materials. Here, the latest progress in electrocatalysts with the periodic atomic arrangement, including intermetallic compounds with long-range order and metal atom-array catalysts with short-range order is summarized. The synthesis principles and the intriguing physical and chemical properties of these electrocatalysts are discussed. Furthermore, the compelling prospects of atomically ordered catalysts in the frontier of catalyst research are outlined.     

An efficient and secure cipher scheme for images confidentiality preservation

In this paper, a novel image encryption scheme based on two rounds of substitution–diffusion is proposed. Two main objectives have guided the design of this scheme: (a) robustness against the most known type of attacks (statistical, chosen/known plaintext, ciphertext-only and brute force attacks) and (b) efficiency in terms of computational complexity (i.e., execution time reduction) in order to meet recent mobiles’ applications’ requirements. First, a dynamic key, changed for every input image is generated and used as the basis to construct the substitution and diffusion processes. Then, the encryption process is performed by the transmitter based on a non-linear S-box (substitution) and a matrix multiplication (diffusion), applied on each sub-matrix of the image. At the destination side, decryption is applied in the reverse order. We have conducted several series of experiments to evaluate the effectiveness of the proposed scheme. The obtained results validated the robustness of our scheme against all considered types of attacks and showed an improvement in terms of execution time reduction compared to the recent existed image-encryption schemes.     

Tristable switching of the electrical conductivity through graphene quantum dots sandwiched in multi-stacked poly(methyl methacrylate) layers

Tristable switching nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between multi-stacked poly (methyl methacrylate) (PMMA) layers were fabricated on indium-tin-oxide (ITO)-coated glass substrates by using a solution-processed method. Current-voltage (I-V) curves at 300 K for the silver nanowire/PMMA/GQD/PMMA/GQD/PMMA/ITO/glass devices showed tristable switching currents with high-resistance, intermediate-resistance, and low-resistance states. The device's cycling endurance of the three resistance states remained stable with a distinguishable value for each resistance state over 1000 cycles, and the obtained retention results showed well-distinguished resistance states without degradation for up to 1 × 10⁴ s. Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and ohmic conduction were proposed as the dominant conduction mechanisms for the fabricated NVM devices based on the obtained I-V characteristics. The described energy-band diagrams confirm the proposed conduction band mechanisms.     

Degradable and Fully Recyclable Dynamic Thermoset Elastomer for 3D-Printed Wearable Electronics

Wearable electronics have become an important part of daily lives. However, its rapid development results in the problem of electronic waste (e-waste). Consequently, recyclable materials suitable for wearable electronics are highly sought after. In this study, a conductive recyclable composite (PFBC) is designed based on a dynamic covalently cross-linked elastomer and hierarchical hybrid nanofillers. The PFBC shows excellent wide-ranging properties including processability, elasticity, conductivity, and stability, which are superior to previous materials used for recyclable electronics, and exhibits outstanding mechanical properties and environmental tolerance including high temperature, high humidity, brine, and ethanol owing to its covalent cross-linking. Reversible dissociation of Diels–Alder networks allows for convenient processing and recycling. After three recycles, the toughness of the PFBC remained at 10.1 MJ m⁻³, which is conspicuous among the reported recyclable electronic materials. Three types of PFBC-based wearable electronics including a triboelectric nanogenerator, a capacitive pressure sensor, and a flexible keyboard, are successfully 3D printed with excellent performance. The PFBC possessed both recyclability and degradability, the combination of which provides a new way to reduce e-waste. This is the first work to recycle electronics using direct 3D printing and presents promising new design principles and materials for wearable electronics.     

基于VMD和BP神经网络的轨道病害诊断方法

针对从非线性、非稳态的轨枕振动信号中提取病害特征困难的问题,文中提出一种基于变分模态分解和多尺度排列熵的轨道病害特征提取方法,并采用BP神经网络病害诊断模型进行病害识别.利用变分模态分解方法将采集到的振动加速度信号进行分解,得到若干个本征模态分量.计算这些本征模态分量的多尺度排列熵值,将其作为轨道病害的高维特征向量,以...