基于非下采样Contourlet变换的伪Zernike矩水印算法研究

方案以非下采样Contourlet变换及伪Zernike矩知识为基础,利用非下采样Contourlet变换提取出低频区域,在此区域采用量化调制伪Zernike矩的幅值将水印信息嵌入.由于非下采样Contourlet变化有很好的平移不变性和抗噪性,而伪Zernike矩具有旋转不变性,还具有对噪声不敏感的特性,两者结合是一个较好的抗几何攻击方法.仿真实验表明,该算法不仅具有较好的透明性,而且对常规信号处理和一般性几何攻均具有较好的鲁棒性.     

天花板水电站厂房布置与结构设计

天花板水电站厂房位于峡谷地区,河谷偏窄,地质条件较差,机组安装高程低,设计校核尾水位高.厂房设计时采取厂区建筑物紧凑布置、因地制宜的原则,在尾水渠布置、主机间整体稳定、尾水挡水结构、出线布置设计和边坡开挖支护设计上采取有针对性的措施,较好地解决了存在的问题.实践证明,天花板水电站厂房设计方案合理,为电站的顺利发电奠定了良好的基础.     

计算机网络攻击分析及防范技术

本文主要阐述计算机信息网络攻击和入侵的特点、方法以及其安全防范手段和技术。分析了计算机网络信息安全的基本对策     

Er3+/Yb3+掺杂NaGd(WO4)2粉体的制备与发光性能

采用水热法成功制备了Er~(3+)/Yb~(3+)双掺杂的NaGd(WO_4)_2纳米粉体,研究了不同络合剂、水热温度对样品形貌和结构的影响。测量了不同Er~(3+)掺杂浓度样品的可见上转换和近红外发射光谱。结果表明:在980nm LD激发下,可观测到样品强烈的绿色上转换发光,对应Er~(3+)的~2H_(11/2)→~4I_(15/2)(530nm)和~4S_(3/2)→~4I_(15/2)(552nm)跃迁,以及较弱的红色上转换和近红外发光,分别对应Er~(3+)的~4F_(9/2)→4I15/2(656nm)和~4I_(13/2)→~4I_(15/2)(1 532nm)跃迁。且随着Er~(3+)掺杂浓度的增加,样品的上转换红绿光和1.54μm附近的近红外光均呈现出先增大后减小的趋势。样品的激发和发射光谱显示,在378nm处的激发峰最强,对应Er~(3+)的~4I_(15/2)→~4 G_(11/2)能级跃迁,最强发射峰位于552nm。根据泵浦功率与发光强度的关系可以得出,红光和绿光的发射主要为双光子吸收过程,但红光还包含了一定的单光子吸收成分。     

利用吸附技术提取盐湖卤水中锂的研究进展

综述了无机吸附剂提取盐湖卤水中锂的研究进展。详细叙述了铝基吸附剂,层状离子交换吸附剂,钛基、锑基和锰基锂离子筛的提锂原理及发展现状,并根据物质结构特点指出了各类吸附剂的优势以及在提锂过程中存在的不足,提出了相应的改进方向。作为一种新型、高效、绿色的提锂剂,锰基吸附材料的发展前景被普遍看好,重点讨论了锰基吸附材料制备手段及掺杂改性研究,并对其发展进行了展望。     

挤压Mg-4.5Zn-0.75Y合金的热变形行为

为了研究只含准晶相Mg-Zn-Y合金的高温力学性能并获得其较优的加工参数,本文首先制备了含有I-Phase的挤压Mg-4.5Zn-0.75Y(原子数分数/%,下同)合金,并在Gleeble-3500热/力模拟实验机上对其高温变形行为进行了研究,实验温度为300、350、400℃,应变速率为0.01、0.1、1 s~(-1).在此基础上,建立了该合金的流变应力本构方程及DMM加工图,并结合压缩后的显微组织制定较优的加工工艺参数.结果表明:应变速率和加工温度对流变应力有显著的影响;挤压Mg-4.5Zn-0.75Y合金的平均变形激活能和应力指数分别为107.95 kJ/mol和3.996 6;挤压Mg-4.5Zn-0.75Y合金具有较好的热塑性,在实验条件下并没有发生失稳现象,说明准晶相的存在提高了合金的变形能力;压缩后的显微组织显示,当温度为300~350℃、应变速率0.1~1s~(-1)时,合金压缩后为均匀细小的等轴晶;综合Mg-4.5Zn-0.75Y合金的加工图与压缩后的显微组织图,确定了该合金热加工的较优工艺参数为:θ=300~350℃;ε·=0.1~1s~(-1).     

Modeling arbitrary crack propagation in coupled shell/solid structures with X‐FEM

In this paper, the extended finite element method (X‐FEM) formulation for the modeling of arbitrary crack propagation in coupled shell/solid structures is developed based on the large deformation continuum‐based (CB) shell theory. The main features of the new method are as follows: (1) different kinematic equations are derived for different fibers in CB shell elements, including the fibers enriched by shifted jump function or crack tip functions and the fibers cut into two segments by the crack surface or connecting with solid elements. So the crack tip can locate inside the element, and the crack surface is not necessarily perpendicular to the middle surface. (2) The enhanced CB shell element is developed to realize the seamless transition of crack propagation between shell and solid structures. (3) A revised interaction integral is used to calculate the stress intensity factor (SIF) for shells, which avoids that the auxiliary fields for cracks in Mindlin–Reissner plates cannot satisfy exactly the equilibrium equations. Several numerical examples, including the calculation of SIF for the cracked plate under uniform bending and crack propagation between solid and shell structures are presented to demonstrate the performance of the developed method. Copyright © 2015 John Wiley & Sons, Ltd.     

Engineering a Hollow Carbon Sphere-Based Triphase Microenvironment for Enhanced Enzymatic Reaction Kinetics and Bioassay Performance

Electrochemical bioassays based on oxidase reactions are frequently used in biological sciences and medical industries. However, the enzymatic reaction kinetics are severely restricted by the poor solubility and slow diffusion rate of oxygen in conventional solid‒liquid diphase reaction systems, which inevitably compromises the detection accuracy, linearity, and reliability of the oxidase-based bioassay. Herein, an effective solid‒liquid‒air triphase bioassay system is provided that uses hydrophobic hollow carbon spheres (HCSs) as oxygen nanocarriers. The oxygen stored in the cavity of HCS can rapidly diffuse to the oxidase active sites through the mesoporous carbon shell, providing sufficient oxygen for oxidase-based enzymatic reactions. As a result, the triphase system can significantly improve the enzymatic reaction kinetics and obtain a 20-fold higher linear detection range than the normal diphase system. Other biomolecules can also be determined using this triphase technique, and the triphase design strategy offers a new route to address the gas deficiency problem in catalytic reactions that involve gas consumption.     

O-二酸单酯-N,N双长链烷基壳寡糖的制备及表征

壳寡糖与月桂醛反应生成Schiff碱,再用NaBH4还原合成N,N-双十二烷基化壳寡糖,然后在均相条件下与酸酐反应制备了含有不同亲水基团的新型双亲性壳寡糖衍生物:O-丁烯二酸单酯-N,N-双十二烷基壳寡糖(OBDCS)、O-丁二酸单酯-N,N-双十二烷基壳寡糖(OSDCS)和O-邻苯二甲酸单酯-N,N-双十二烷基壳寡糖(OPDCS)。用红外光谱、核磁共振和元素分析等方法对产物的结构进行了表征,并试验了其溶解性能。结果表明,改性产物的溶解性能明显优于未改性的N,N-双十二烷基壳寡糖,拓宽了壳寡糖的应用范围。