5-5′型木质素二聚体高温热解微观化学反应机理研究

选用5-5′键型连接的木质素二聚体为研究对象,基于B3LYP/6-31g基组和密度泛函理论(DFT)对其进行了高温热解微观化学反应机理研究,设计了5-5′型木质素二聚体高温热解反应的5条初反应路径,并在分析初反应结果的基础上设计了7条次反应路径,对每条路径的反应物及其产物进行了结构优化,计算了1500K温度下每条反应路径的热力学及动力学参数。结果表明,5-5′型木质素苯环位上的甲氧基具有很强的活性,甲氧基中O-CH3键以及Caromatic-OCH3键较易断裂;通过计算得出初反应的R3、R4反应焓变较小,分别为192.7kJ/mol和270.5kJ/mol,认为该热解反应的主反应路径以R3及R4为主;该热解反应得到的最终产物有3-4,二羟基甲苯、对羟基甲苯、2-乙烯-4-甲基-3,5-二烯环己酮、甲烷、甲醇及甲醛。     

Synergistic effects of micro-/nano-fillers on conductive and electromagnetic shielding properties of polypropylene nanocomposites

This study presents the synergistic effects of graphene nanosheets (GNSs) and carbon fibers (CFs) additions on the electrical and electromagnetic shielding properties of GNS/CF/polypropylene (PP) composites. These composites were fabricated by the melt blending of different ratios of GNSs and CFs (20:0, 15:5, 10:10, 5:15 and 0:20 wt/wt%) into a PP polymer matrix using a Brabender mixer. Besides, the chemical and crystalline structures and the thermal stability of the resultant GNS/CF/PP composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). FT-IR and XRD showed that with the addition of GNSs content, transmittances at 1373.4?cm^?1 and 1454.4?cm^?1 became smaller and the characteristic peak at 26.82° became stronger. TGA showed that the GNS/CF/PP composite can be used at high temperature below 456°C. Blending 10?wt% CFs and 10?wt% GNSs into the PP polymer resulted in excellent conductivity (0.397 S/cm), which indicated the occurrence of the critical percolation threshold phenomenon, and also reached the maximum electromagnetic shielding effectiveness (EMSE) of 20?dB at 1.28–2.00?GHz. Laminated with five layers of composites, its EMSE achieved 25–38?dB at 0.3–3.0?GHz, corresponding to blocking of 94.38–98.74% electromagnetic waves.     

Optimal classification methods for diagnosing latent skills and misconceptions for option-scored multiple-choice item quizzes

Behaviormetrika - The paper’s extended Diagnostic Classification Modeling setting assumes (a) nominal item (question) coding, thus including multiple-choice (MC) items, and (b)...     

关于Markov过程的强大数定律

本文研究一般马氏过程的强大数定律．     

基于MPC8548的嵌入式设备的光通信接口设计与实现

提出了一种基于PowerPC的光通信接口设计方案,该方案以PowerPC微处理器为核心,通过其集成的三速以太网控制器,实现了1Gb/s的高速以太网协议接口逻辑;文中详细介绍了其硬件结构原理,并在此基础上详细阐述了其在嵌入式Linux操作系统平台上驱动程序的设计思想与具体实现;系统基于嵌入式Linux操作系统平台完成相关驱动软件的开发,实现了数据的高效率采集与高速光纤传输,具有低功耗、高带宽和高集成度等优点;测试结果表明,系统处于全效率运行状态,以太网接口传输速率可以达到1Gb/s左右,满足了系统设计的要求,具有广阔的应用前景.     

基于FPGA的某雷达多功能数字替换板设计

为了提高高技术战争条件下电子装备战场抢修的快捷性、时效性,减少备件携带数量,以某雷达火控计算机中4块数字电路板为背景设计了一种多功能替换版;该替换版以一块FPGA芯片为控制核心,并配以海绵电路区和跳线插座的设计,使得在战场紧急情况下只需更换EPROM存储芯片,并在海绵电路区上焊接相应的集成电路器件以及调整跳线插座来控制信号走向,就可以在短时间内方便快捷地对损坏电路板实施替换;结果证实,该技术可作为一种备用的维修手段,可以在很大程度上提高部队装备战场维修率.     

A novel adaptive steganography based on local complexity and human vision sensitivity

This paper presents a novel adaptive steganographic scheme that is capable of both preventing visual degradation and providing a large embedding capacity. The embedding capacity of each pixel is dynamically determined by the local complexity of the cover image, allowing us to maintain good visual quality as well as embedding a large amount of secret messages. We classify pixels into three levels based on the variance of the local complexity of the cover image. When determining which level of local complexity a pixel should belong to, we take human vision sensitivity into consideration. This ensures that the visual artifacts appeared in the stego image are imperceptible, and the difference between the original and stego image is indistinguishable by the human visual system. The pixel classification assures that the embedding capacity offered by a cover image is bounded by the embedding capacity imposed on three levels that are distinguished by two boundary thresholds values. This allows us to derive a combination ratio of the maximal embedding capacity encountered with at each level. Consequently, our scheme is capable of determining two threshold values according to the desired demand of the embedding capacity requested by the user. Experimental results demonstrated that our adaptive steganographic algorithm produces insignificant visual distortion due to the hidden message. It provides high embedding capacity superior to that offered by a number of existing schemes. Our algorithm can resist the RS steganalysis attack, and it is statistically invisible for the attack of histogram comparison. The proposed scheme is simple, efficient and feasible for adaptive steganographic applications.     

Passive control of uncertain multiple input-delayed systems using reduction method

In order to conveniently analyze stability of uncertain multiple input-delayed closed-loop systems and successfully synthesize passive controllers for a general class of uncertain multiple input-delayed systems with disturbance, the so-called reduction method is applied to the multiple input-delayed systems with parametric uncertainties. A feedback controller associated with the system state and the past control action is designed to guarantee the passivity of the closed-loop systems for all admissible uncertainties. The theoretical findings are illustrated and verified with one numerical example.     

Robust nonlinear power iteration algorithm for adaptive blind separation of independent signals

In this paper, we elaborate an extension of classical power iteration method to nonlinear power iteration for blind separation of multiple independent sources from observed array output signals. The present algorithm, referred to as NPI, considers the estimating of the separating matrix as a nonlinear power iteration problem. By naturally choosing the positive definite normalizer for nonlinear power term, the resulting algorithm not only yields robust convergence behavior but also guarantees the orthonormality of the separating matrix at each iteration. To circumvent the difficulty of solving the inverse square root for the normalizer, an efficient adaptive singular value decomposition (SVD) technique is also adopted to obtain a fast implementation of NPI. The estimation accuracy and convergence speed of the present algorithm are illustrated through simulation results and compared with the existing adaptive algorithms.