Viscoelasticity of nanobubble‐inflated ultrathin polymer films: Justification by the coupling model

The nanobubble inflation method is the only experimental technique that can measure the viscoelastic creep compliance of unsupported ultrathin films of polymers over the glass–rubber transition zone as well as the dependence of the glass transition temperature (T_g) on film thickness. Sizeable reduction of T_g was observed in polystyrene (PS) and bisphenol A polycarbonate by the shift of the creep compliance to shorter times. The dependence of T_g on film thickness is consistent with the published data of free‐standing PS ultrathin films. However, accompanying the shift of the compliance to shorter times, a decrease in the rubbery plateau compliance is observed. The decrease becomes more dramatic in thinner films and at lower temperatures. This anomalous viscoelastic behavior was also observed in poly(vinyl acetate) and poly (n‐butyl methacrylate), but with large variation in the change of either the T_g or the plateau compliance. By now, well established in bulk polymers is the presence of three different viscoelastic mechanisms in the glass–rubber transition zone, namely, the Rouse modes, the sub‐Rouse modes, and the segmental α‐relaxation. Based on the thermorheological complexity of the three mechanisms, the viscoelastic anomaly observed in ultrathin polymer films and its dependence on chemical structure are explained in the framework of the Coupling Model. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

An interlaboratory study of quantitation procedures for the analysis of water and wastewater for organo-chlorine pesticides by gas chromatography–electron capture detector

An interlaboratory study was conducted to assess two widely used procedures for estimating quantitation levels. Six laboratories participated in the analysis of artificially prepared water samples for organo-chlorine compounds by liquid-liquid extraction followed by gas chromatography–electron capture detector using USEPA Method 608. The study consisted of three phases, including six months of results from analyte free samples, the replicate analysis of fortified samples at a single concentration by the laboratory, and finally the analysis of blind fortified samples prepared by a third party. Estimated detection and quantitation limits (Currie's L_C and L_Q and USEPA's MDL and ML) were determined for each laboratory-method-analyte combination and then compared to the observed detection and quantitation limits. The overwhelming majority of analyte free samples had a reported value of zero. As a result, observed quantitation and detection limits were frequently zero. When they were not zero, the observed quantitation limits were sometimes less than the observed detection limits and when they were not, there was no observed fixed ratio between the quantitation and detection limits. The variability between days of analysis and the use of noise reducing techniques proved to be a significant source of the observed non-normal distribution of results from distilled water samples with a concentration of zero. Conventional procedures and their underlying analytical and statistical assumptions did not provide useful predictions of laboratory quantitation based upon the results of this study. Rather than one time statistical determinations, ongoing verification of quantitation limits may be a better approach.     

微柔顺装置及其力学分析

根据微装配及柔性铰链的特点，提出了微柔顺装置(MRCC，Micro Remote Center Compliance)并对其进行了力学分析。由平衡方程和几何相容条件推导出了三个重要的设计参数——位移刚度Kx、角位移刚度KФ和中心距L的表达式。讨论并示例了柔性铰链的刚度系数、结构参数、位置参数对Kx、KФ和L的影响，分析结果表明，位置参数中的转角θ对Kx、KФ和L影响最大，而且要同时获得Kx、KФ和L的最佳值是不可能的，只能在设计微RCC时综合考虑，选择合适的θ值。     

一个临床试验模型中的参数检验和估计改进

讨论有不服从发生时，临床试验数据EV模型中的参数估计和检验问题．在以前结果的基础上，文中给出模型中公共参数的一个改进估计，提出了一个药物治疗效果的检验方法．最后通过模拟研究考察上述估计和检验的效果。     

三质点共线碰撞问题的理论分析

以三质点弹性碰撞系统为例，考虑质点之间相互作用时局部的接 触变形信息，并基于矩阵函数理论得到了三质点弹性碰撞系统Hamilton空间中的严格理论 解. 基于理论分析结果，详细讨论了不同质点之间的质量比以及接触刚度比对质点碰撞后的 动力学行为的影响，包括可能产生的不同分离模式，接触点的分离次序，以及由此可能导致 的内碰撞现象等.     

Investigation of the linear flow regime of commercial polymers by numerical conversion of MVM creep measurements

A new experimental and numerical method has been developed to characterize the terminal flow behavior of polydisperse, commercial grade polymer melts over a wide dynamic range of time/frequency scales. Experimentally, an MVM rheometer specifically designed for long time scale (t 10⁴ s) creep measurements is used to measure the creep compliance of three commercial polymers: two high density polyethylenes and one polystyrene. The long time scale MVM creep data are complemented in the short time scale regime by creep data from an industrial plate-plate rheometer. The time-dependent creep data is combined and converted to a discrete retardation spectra using a nonlinear regularization algorithm to address the ill-posed nature of the interconversion. The retardation spectrum is analytically converted to dynamic moduli and compared with independently measured dynamic moduli. In the overlapping frequency region, calculations and measurements show excellent agreement and the combined data span a much larger dynamic range than either independent data set. The calculated and measured dynamic moduli data are combined and a retardation spectrum with a vastly expanded dynamic range is generated. Combining long time scale MVM creep compliance data and dynamic moduli data exploits the intrinsic sensitivities of controlled strain and controlled stress rheological experiments and is a powerful means to greatly expand the experimentally accessible dynamic range of time/frequency. This approach is particularly useful for commercial polymers with broad molecular weight distributions and commensurately large distributions of relaxation times.     

狭长结构拓扑优化

通常的拓扑优化是在给定区域内，通过设计材料分布实现结构拓扑形式优化。对于设计区域的长和宽相近的平面问题，现行的方法可得到清晰的拓扑。但是，狭长结构的设计域具有大的长宽比。为了保证基结构包含足够多的拓扑形式，宽度方向要求有一定量的有限元分割，从而导致整体网格数和设计变量多、问题求解困难。本文提出了通过基本结构拼装的狭长结构拓扑优化方法，建立了以最小平均柔顺性密度为目标、同时设计材料分布和设计域几何尺度的基本结构的拓扑优化问题的数学提法和求解方法。利用所提出的问题提法和求解方法，设计了狭长悬臂梁的拓扑形式，讨论了危险截面的弯矩与剪力的相对值以及材料体积约束对拓扑形式的影响。数值结果表明，不同的弯矩与剪力的相对数值对应不同的拓扑形式，随着相对数值的增加，梁的拓扑形式由类桁架结构逐渐变成竖直立板加强的框架式结构。     

上覆单相弹性层的饱和地基上刚性圆板的扭转振动分析

采用解析的方法研究了上覆单相弹层的饱和地基上刚性圆板的扭转振动。首先运用积分变换技术分别求解了单相弹性介质和饱和介质情况时的控制方程，然后按混合边值条件建立了上覆单相弹性层的饱和地基上刚性圆板扭转振动的对偶积分方程，并把对偶积分方程化为易于数值求解的第二类Fredholm积分方程，并给出了数值算例。     

卸载柔度法测定JR阻力曲线的微机自动化系统

本文依据我国有关试验规范,在国内广泛引进的日本岛津(Shimadzu)DSS—25T 型电子万能试验机上,研制配备了用微型计算机实现的单试样卸载柔度法的加、卸载控制与数据采集、处理的自动化系统。全部实验结果由打印机直接输出,可以大幅度地提高测试效率,试验精度也得到改善。     

Generating line spectra from experimental responses. Part I: Relaxation modulus and creep compliance

We describe a recursive computer algorithm which generates line spectra from relaxation modulus or creep compliance data without producing negative spectrum lines. We apply the algorithm here to data read from mathematical models for the relaxation modulus. Since these data were thus free of the usual experimental error, we could use a relatively simple form of the basic algorithm that is applicable also to smoothed data. The spectra faithfully reproduced the input functions and may serve for data storage as well as for predicting other experimental responses.