A data hiding scheme based upon DCT coefficient modification

In this paper, we propose a steganographic scheme based on the varieties of coefficients of discrete cosine transformation of an image. The major problem of hiding data in the high-frequency coefficients of discrete cosine transformation is that rounding errors will be added into the spatial-domain image, and thus cannot be transformed back to the correct modified coefficients of the discrete cosine transformation. To solve this problem, we use integer mapping to implement our discrete cosine transformation. Thus, the image recovered from the modified coefficients can be transformed again to the correct data hidden coefficients.     

热震试验中的纳米5YSZ和8YSZ涂层衍射峰变化

用大气等离子喷涂制备纳米ZrO2-5%Y2O3(5YSZ)和ZrO2-8%Y2O3(8YSZ)热障涂层,用X射线衍射分析涂层晶面峰位偏移和残余应力,对比5YSZ和8YSZ涂层的(111)晶面峰位变化,计算(111)晶面残余应力。结果表明:涂层热震一定次数各晶面峰位向低角度方向偏移,存在残余压应力。随热震次数增加,峰位偏移加大,晶面残余压应力不断累积,直到出现裂纹后不再累积。热震过程5 YSZ涂层晶面残余应力比8YSZ小,5 YSZ涂层比8YSZ热循环性能更好。     

Quantitative relationship model between workload and time pressure under different flight operation tasks

The goal of this study was to establish a quantitative relationship model between workload and task demand under different tasks, when time pressure was set as the main influential factor to the task demand, with three workload measurement parameters. The workload “redline” was also analyzed and determined with the relationship models between the workload measurement parameters and time pressure. The experiment was designed with three different tasks under different time pressures. Three workload measurement parameters (subjective evaluation workload, accuracy and pupil diameter) and the subjective feeling threshold of time pressure were measured experimentally and then used in a comprehensive analysis for the relationship model. The data analysis result showed significant differences in workload under different time pressures, but workload was not affected by the task type. With a time pressure of 0.8, participants felt a sense of time urgency and the accuracy decreased by approximately 85%. The results demonstrate that the subjective evaluation workload, accuracy and pupil diameter can be used as the measurement parameters for the workload under different time pressures and for different tasks. Thus, for a time pressure of 0.8, an accuracy of 80%–85% was determined as the workload “redline”. Linear relationships were found between subjective evaluation workload, and pupil diameter and time pressure, and a quadratic curve relationship was found between accuracy and time pressure. Workload prediction can thus be performed using these relationship models between workload and time pressure.     

考虑桩底土层波动效应的饱和黏弹性半空间中摩擦桩竖向振动

为深化对饱和黏弹性半空间地基中摩擦桩竖向振动特性的认识,基于Boer多孔介质动力控制方程组,考虑桩底土层波动效应,采用Hankel积分变换和微分算子分解理论求解相关方程得到桩底、桩侧反力,进而建立饱和土中桩基竖向振动偏微分方程,结合桩土接触面混合边值条件推导得出了饱和黏弹性半空间地基中摩擦桩桩顶竖向动力阻抗解析表达式。并在此基础上进一步通过数值算例对比分析探讨了液固耦合系数、桩长径比、桩土模量比、地基土黏滞阻尼系数这些重要因素对所得桩顶动力阻抗的影响规律,得到了一些对工程实践有意义的结论。     

三维空间物体任意移动算法研究

为优化3D界面人机交互技术,解决在二维屏幕上利用鼠标控制虚拟三维空间模型的任意移动问题,在研究基于平面的移动算法之后,提出基于坐标轴平面的以及自由移动两种三维空间物体任意移动算法,并且具体实现三种算法,对算法的移动物体精度、速度以及操作简便性等方面进行比较,对3D建模以及可视化具有极其重要的意义。     

隧道照明闭环反馈智慧控制系统

为了解决当前隧道照明中存在的耗电量大,照度测量繁杂,难以实时保证实际照明亮度等问题,设计了一种隧道照明闭环反馈智慧控制系统。该系统能够根据车辆有无、车辆行为信息和环境信息实时调整照明状态实现按需照明;采用摄像机图像亮度测量方法,通过图像灰度与亮度转换来实时获取隧道路面的亮度。为保证照明需求,系统采用PID闭环反馈调节方法,以照明所需亮度和实际测量亮度为基础,实时调节照明系统输出。实验证明,设计的系统安全可靠,自适应性强,具备实时亮度测量和闭环反馈调节功能;实现了按需照明,能保证实际照明亮度实时达到标准要求,同时最大限度地节能降耗;并能在保证行车安全的同时使人眼获得最佳的视觉感受。     

无溶剂环氧煤焦沥青涂层在土壤中的电化学行为

目的研究无溶剂环氧煤焦沥青涂层在饱和水含量土壤中的电化学行为。方法将无溶剂环氧煤焦沥青涂层涂覆在Q235碳钢上,测试不同厚度和不同埋设时间涂层的开路电位和交流阻抗谱图,探索涂层厚度和埋设时间对涂层电化学行为的影响。利用SEM分析基体表面腐蚀产物的元素组成,探索侵蚀性物质是否到达基体表面参与腐蚀历程。结果涂覆200μm厚涂层的Q235碳钢的稳定开路电位约为-0.37 V,与裸Q235钢相比,自腐蚀电位正移了0.28 V。随着涂层厚度的增加,开路电位呈上升趋势,容抗弧半径增大,涂层对侵蚀性溶液的屏蔽阻挡能力提高。随着在土壤中埋设时间的延长,容抗弧半径减小,吸水率增大,涂层的防护性能有所下降,但低频阻抗模值仍高达8.8×107Ω·cm2。能谱分析显示,Q235碳钢表面未出现Cl-等侵蚀性物质。结论无溶剂环氧煤焦沥青涂层在土壤环境中是有效的屏蔽层,可对Q235碳钢基体起到有效的防护作用。     

可重构制造执行系统中的构件复用技术研究

从软件重用角度对可重构制造执行系统及相关构件复用技术进行研究。在提出构件化可重构制造执行系统平台功能架构的基础上,将人工智能的框架表示作为构件的描述方法,在构件库中以框架表示为单元对构件进行分类存储;根据框架表示的继承和关联特性,提出基于规则推理和功能粒度的构件搜索匹配算法;在语义和功能上满足构件在可重构制造执行系统平台上的组装。     

Effects of Anode Arc Root Fluctuation on Coating Quality During Plasma Spraying

To obtain a coating of high quality, a new type of plasma torch was designed and constructed to increase the stability of the plasma arc and reduce the air entrainment into the plasma jet. The torch, called bi-anode torch, generates an elongated arc with comparatively high arc voltage and low arc fluctuation. Spraying experiments were carried out to compare the quality of coatings deposited by a conventional torch and a bi-anode torch. Alumina coatings and tungsten carbide coatings were prepared to appraise the heating of the sprayed particles in the plasma jets and the entrainment of the surrounding air into the plasma jets, respectively. The results show that anode arc root fluctuation has only a small effect on the melting rate of alumina particles. On the other hand, reduced air entrainment into the plasma jet of the bi-anode torch will drastically reduce the decarbonization of tungsten carbide coatings.     

超疏水表面制备技术的研究进展

具有非润湿和自清洁特性的超疏水表面由于其广阔的应用前景而引起人们的极大关注.介绍超疏水状态下Wenzel和Cassie-Baxter 2种接触模型及其相互关系,讨论2种模型下表面微细结构对接触角的影响.从构造表面微细结构和低表面能物质修饰2个方面总结近年来超疏水表面制备技术的研究进展,并对超疏水表面的研究进行展望.