General analysis of the measurements of the lateral crystal lattice moduli of semicrystalline polymers by x-ray diffraction and the application to nylon 6

A mathematical representation based on a linear elastic theory is proposed by which one may investigate the dependences of molecular orientation and crystallinity on the crystal lattice moduli and linear thermal expansion coefficients in the direction perpendicular to the chain axis as commonly measured by x-ray diffraction. In the theoretical calculation, a previously introduced model was employed in which oriented crystalline phase is surrounded by oriented amorphous phase and the strains of the two phases at the boundary are identical. The mathematical analysis indicated that the lateral crystal lattice moduli and linear thermal coefficients as measured by x-ray diffraction may be different from the intrinsic crystal moduli and linear thermal coefficients of a crystal unit cell, depending on the structure of the polymer solid. The numerical calculation was applied to nylon 6. As a result, it may be confirmed that the lateral crystal lattice moduli measured by x-ray diffraction are sensitive to the morphology of the bulk speciments and close to the intrinsic crystal moduli if the morphology of the test specimen can be represented by a parallel model with respect to the original stretching longitudinal direction.     

In situ friction study of Ag Underpotential deposition (UPD) on Au(111) in aqueous electrolyte

The electrodeposition of silver on Au(111) was investigated using lateral force microscopy (LFM) in Ag⁺ containing sulfuric acid. Friction force images show that adsorbed sulfate forms structure ( on Au(111) prior to Ag underpotential deposition (UPD) and structure ( ) on a complete monolayer or bilayer of Ag. Variation of friction with normal load shows a non-monotonous dependence, which is caused by increasing penetration of the tip into the sulfate adlayer. In addition, the friction force is influenced by the varying coverage and mobility of Ag atoms on the surface. Before Ag coverage reaches the critical value, the deposited silver atoms may be mobile enough to be dragged by the movement of AFM tip. Possible penetration of the tip into the UPD layer at very high loads is discussed as a model for self-healing wear. However, when the coverage of Ag is close to 1, the deposited Ag atoms are tight enough to resist the influence of the AFM tip and the tip penetrates only into the sulfate adlayer.     

斜拉桥中斜拉索的面内外耦合内共振分析

研究了桥面侧振引起的斜拉索非线性振动问题。基于Hamilton原理建立了拉索的非线性振动控制方程,并利用多尺度法得到了斜拉索振动方程的二阶近似解。通过具体算例分析了斜拉索面内一阶模态与面外一阶模态相互耦合发生内共振的可能性,讨论了拉索倾斜角对拉索振动的影响,比较了在零初始条件和非零初始条件下拉索振动响应的区别。研究发现:拉索内共振发生在一定的激励频率和激励幅值区域内;改变倾斜角度,会影响拉索发生内共振时激励频率区域的大小;初始条件的不同,拉索的振动形式会相差很大。     

舰载机拦阻钩索滑摆动载荷特性研究

针对舰载机钩偏着舰时拦阻钩沿拦阻索侧向滑摆运动,运用仿真与理论分析结合的方法,通过调整拦阻钩侧向动载荷的振动频率范围,具体研究了飞机机身动载荷特性。结果表明,在2 Hz, 10 Hz,20 Hz 等振动频率附近,机身会受到严重的载荷情况。结论可供机体结构刚度、钩头减摆等性能优化设计参考。     

侧向冲击载荷下钢管混凝土结构的动力响应及参数分析

采用刚塑性结构模态分析法和数值模拟方法,对侧向冲击载荷作用下的圆截面钢管混凝土结构进行了塑性动力分析。将钢管混凝土等效为刚塑性地基梁模型,给出了钢管混凝土构件跨中侧向变形的模态解析解,得到了冲击载荷作用下影响结构最终侧向变形的无量纲参数。利用ABAQUS/Explicit软件建立了钢管混凝土结构在侧向冲击作用下的动态响应数值模型并进行了计算分析,将理论预测值和数值模拟结果与试验结果进行了交叉对比。结合量纲分析和数值模型对影响构件最终变形的几何、物理参数及初始冲量进行了分析。结果表明：理论预测值和数值模拟结果与试验结果吻合较好,结构的塑性变形与理论假定的塑性铰分布一致。构件几何参数中,长径比和径厚比对其侧向最终变形有较大影响;冲击头相对宽度可改变构件的变形模态;相比于几何参数,钢管和混凝土芯层的物理参数对构件跨中挠度的影响较小;结构的侧向变形与初始冲量成二次幂相关。最后给出了理论分析参数的适用范围。刚塑性响应模态解可较好地预测钢管混凝土结构在侧向冲击载荷作用下的塑性变形行为。

     

三向受压混凝土的动态特性研究

为探究混凝土在三向受压状态下的动态特性,利用自行研制的大型多功能三轴材料试验机,进行不同应变速率(10-5/s、10-4/s、10-3/s、10-2/s)下混凝土不同定侧压比(1∶1、2∶1、3∶1、4∶1)的动态真三轴抗压试验,研究了混凝土在动态抗压下的强度和变形特性.结果表明:混凝土在三向受压状态下表现出明显的应变...     

基于自适应侧抑制网络的红外弱小目标检测

为了提高远距离红外弱小目标的检测效率,提出了一种基于自适应侧抑制网络的复杂背景下的红外弱小目标检测方法。该方法建立了改进的侧抑制网络数学模型,利用各向异性滤波来自适应地确定侧抑制网络的抑制系数,不需要人为干预,实现了侧抑制网络与各向异性高斯滤波的有机结合。同时,在各向异性高斯滤波器两轴确定方面进行了改进,两轴分别采用对比度尺度模型和强度尺度传播模型来独立确定。通过与传统弱小目标检测方法的对比实验,验证了方法的有效性。     

超低温度系数的光子晶体光纤Sagnac压力传感器

提出了一种基于光子晶体光纤Sagnac干涉仪的横向压力传感器。使用的光子晶体光纤为低双折射光纤,首先预先在Saganc环中的光子晶体光纤上施加初始压力,使Sagnac干涉仪产生正弦干涉光谱,然后再将被测物体放在光子晶体光纤上,由于被测物体重力的作用,Saganc干涉仪输出的光谱产生移动,实现横向压力传感测量。传感器具有高灵敏度0.529 nm/(N·mm)及超低的温度系数-0.4 pm/℃,其环境温度的影响可以忽略。     

Efficiently Synthesizing Lacto-Ganglio-Series Gangliosides by Using a Glucosyl Ceramide Cassette Approach: The Total Synthesis of Ganglioside X2

The first total synthesis of the hybrid ganglioside X2, which consisted of a highly branched octasaccharide and ceramide moieties, was accomplished by using a glucosyl ceramide cassette approach. With a disaccharyl donor, the heptasaccharide could not be constructed by glycosylation of the C4 hydroxy group of galactose at the reducing end of the pentasaccharide. In contrast, through an alternative approach with two branched glycan units, a GM2-core trisaccharide, and a lacto-ganglio tetrasaccharide, the heptasaccharyl donor could be prepared and subsequently joined with a glucosyl ceramide cassette to afford the protected ganglioside, X2. Finally, global deprotection completed the synthesis, thus affording the pure ganglioside X2.