Digital video steganalysis using motion vector recovery-based features

As a novel digital video steganography, the motion vector (MV)-based steganographic algorithm leverages the MVs as the information carriers to hide the secret messages. The existing steganalyzers based on the statistical characteristics of the spatial/frequency coefficients of the video frames cannot attack the MV-based steganography. In order to detect the presence of information hidden in the MVs of video streams, we design a novel MV recovery algorithm and propose the calibration distance histogram-based statistical features for steganalysis. The support vector machine (SVM) is trained with the proposed features and used as the steganalyzer. Experimental results demonstrate that the proposed steganalyzer can effectively detect the presence of hidden messages and outperform others by the significant improvements in detection accuracy even with low embedding rates.     

融合黄金正弦算法和纵横交叉策略的秃鹰搜索算法

针对传统秃鹰搜索算法（BES）存在容易陷入局部最优、收敛速度慢等缺点,提出一种融合黄金正弦算法（Gold-SA）和纵横交叉策略的秃鹰搜索算法（GSCBES）。首先,在传统BES的搜索阶段设置基于惯性权重的位置更新公式;然后,在捕食猎物阶段引入Gold-SA;最后,引入纵横交叉策略对全局最优和种群进行修正。对11个Benchmark函数和CEC2014函数进行仿真实验并使用Wilcoxon秩和检验的方式评估所提算法的寻优能力,结果表明,所提算法收敛更快;同时,使用所提算法对反向传播（BP）神经网络模型的权值和阈值进行赋值,并将优化的BP神经网络模型用于空气质量的预测中,平均绝对误差（MAE）、均方根误差（RMSE）、均方误差（MSE）、平均绝对百分比误差（MAPE）值均小于BP神经网络模型以及基于粒子群优化（PSO）的BP神经网络模型,预测精确度有所提高。     

隐曲面变换中纹理映射的研究

曲面映射有多种应用,纹理映射、多通道变形和曲面分析。给定一个4维的隐函数,在两个隐曲面之间定义一个变形,提出一种在形变中产生纹理迁移的映射算法,通过在4维上的四面体超曲面求解两个偏微分方程来得到这种算法。求解第一个PDE产生一个矢量场,指出如何从源曲面上指向目标曲面。求解第二个PDE,生成沿着矢量场的位置标签,这样目标曲面就由源曲面上的唯一的位置所标记。     

Effect of photostablizers on surface color and mechanical property of wood-flour/HDPE composites after weathering

The effects of photostabilizers of ultraviolet absorbers (UVA), hindered amine light stabilizer (HALS) and pigment on surface color change and mechanical properties of weathered wood-flour/ polyethylene (HDPE) composites were investigated. After being added UVA with high UV absorbance, the WPC exhibites better ability to resist color fading and mechanical property loss. High molecular weight HALS is found to be the most effective in controlling long term fading and yellowing changes. Pigments cover the composites for remaining the original color after weathering regardless of less contribution to mechanical property. Addition of photostabilizer and pigment together show great synergism in decreasing color fading and flexural property loss.     

CAN总线位定时和同步的研究与设计

在CAN规范中,位定时和同步机制是既重要又难于理解的环节之一,它不仅关系到对规范其他相关内容的理解,甚至能对节点开发的成功与否产生直接的影响.因此介绍了位时间(周期)的组成与结构,总结并归纳位定时的作用;在此基础上,给出硬同步和重同步的定义,重点分析硬同步和重同步的机理,并给出它们相应的图解,形象而又清晰地表明其本质;以独立CAN控制器为例,详细说明在一般开发和工程实际中,位定时参数设置和计算的一般方法及步骤.     

LNG点供行业现状及前景展望

受低油价的影响并得益于国家强力推进"煤改气"工程,综合经济性明显的LNG点供项目逐渐成为投资、建设的热点。但由于目前LNG点供项目存在着设计规范和行业标准缺失、违规建设及手续不全等诸多问题,特别是对城市燃气企业特许经营权造成了巨大的冲击,致使地方政府和管道燃气企业对其抱有抵触心态。为此,通过多方走访调研,总结了LNG点供项目商务模式、建设模式、运营模式、投资模式、合同模式、计量模式等方面较为成功的经验,分析了LNG点供项目发展的政策环境,梳理了其发展的制约因素。最后,结合我国油气改革的形势,展望了LNG点供行业的发展前景:(1)LNG气化站设计、建设方面规范缺失的局面有望在近期内得到极大的改善;(2)在目前低油价水平下,LNG点供项目很可能会在更大的范围内普及;(3)从长远来看,管道气仍应是主要的供气方式,LNG点供可作为前者的补充,将目标市场锁定在管道不发达的城镇、农村,以气化居民、工商业用户为主。     

An Ultrathin Flexible 2D Membrane Based on Single‐Walled Nanotube–MoS2 Hybrid Film for High‐Performance Solar Steam Generation

Solar steam generation is achieved by localized heating system using various floating photothermal materials. However, the steam generation efficiency is hindered by the difficulty in obtaining a photothermal material with ultrathin structure yet sufficient solar spectrum absorption capability. Herein, for the first time, an ultrathin 2D porous photothermal film based on MoS₂ nanosheets and single‐walled nanotube (SWNT) films is prepared. The as‐prepared SWNT–MoS₂ film exhibits an absorption of more than 82% over the whole solar spectrum range even with an ultrathin thickness of ≈120 nm. Moreover, the SWNT–MoS₂ film floating on the water surface can generate a sharp temperature gradient due to the localized heat confinement effect. Meanwhile, the ultrathin and porous structure effectively facilitates the fast water vapor escaping, consequently an impressively high evaporation efficiency of 91.5% is achieved. Additionally, the superior mechanical strength of the SWNT–MoS₂ film enables the film to be reused for atleast 20 solar illumination cycles and maintains stable water productivity as well as high salt rejection performance. This rational designed hybrid architecture provides a novel strategy for constructing 2D‐based nanomaterials for solar energy harvesting, chemical separation, and related technologies.     

层状金属复合材料加工技术研究现状

概述了层状金属复合材料的爆炸焊接复合法、轧制复合法和爆炸-轧制复合法3种加工技术。介绍了爆炸焊接复合的机理研究及布药、起爆方式、炸药配制、参数选择等工艺技术研究;论述了轧制复合法的热轧复合、等辊径等辊速冷轧复合、等辊径等辊速冷轧复合的技术现状;探讨了爆炸-轧制复合技术的关键是爆炸焊接参数的选择、金属层之间均匀的牵引力、轧制工艺参数确定等。指出了层状金属复合材料加工技术的发展方向是:使材料结构复杂化,提高损伤容限,实现复合材料的韧化;功能一体化,结构材料和功能材料的相互渗透、综合集成;高性能化,进一步提高比强度、比模量;智能化,材料、结构和电子相互融合;低成本化,从过去主要关心性能与质量转到降低成本,强调低成本生产技术。     

纤维素纳米晶/环氧树脂复合材料的制备及性能研究

以过硫酸铵氧化微晶纤维素得到纤维素纳米晶(CNC),与二乙烯三胺在N,N-二甲基甲酰胺(DFM)中发生缩合接枝反应,制备胺化纤维素纳米晶(ACNC)。采用溶液共混法,分别将CNC和ACNC与环氧树脂复合得到纤维素纳米晶/环氧树脂复合膜,纤维素纳米晶不仅起到增强剂的作用,还起到固化交联剂的作用,进而改善环氧树脂的性能。利用万能力学试验机、动态热机械性能、环境扫描电子显微镜、热重分析等对复合材料的性能加以表征分析。结果证明,当CNC和ACNC的添加量均为0.1%时,环氧树脂复合膜的机械强度最大;纤维素纳米晶的加入不仅能够提高环氧树脂的力学性能,还能显著改善其柔韧性,ACNC对环氧树脂复合膜的增强作用高于CNC,CNC的增韧作用强于ACNC。