Experimental study and electromechanical model analysis of the nonlinear deformation behavior of IPMC actuators

This paper develops analytical electromechanical formulas to predict the mechanical deformation of ionic polymer–metal composite(IPMC) cantilever actuators under DC excitation voltages. In this research, IPMC samples with Pt and Ag electrodes were manufactured, and the large nonlinear deformation and the effect of curvature on surface electrode resistance of the IPMC samples were investigated experimentally and theoretically. A distributed electrical model was modified for calculating the distribution of voltage along the bending actuator. Then an irreversible thermodynamic model that could predict the curvature of a unit part of an IPMC actuator is combined with the electrical model so that an analytical electromechanical model is developed. The electromechanical model is then validated against the experimental results obtained from Pt-and Ag-IPMC actuators under various excitation voltages. The good agreement between the electromechanical model and the actuators shows that the analytical electromechanical model can accurately describe the large nonlinear quasi-static deflection behavior of IPMC actuators.     

通气法控制超空泡流动的实验研究

在高速水洞中运用人工通气方法进行了航行体模型超空泡形态特性的系列实验研究.获得了不同通气流量、不同空化数和不同弗鲁德数下的空泡形态,建立了以弗鲁德数为参数的空泡几何特征参数与空化数的对应关系、空化数与通气流量系数之间的对应关系.验证了空化数是决定空泡尺度的主要无因次参数,通过改变通气流量可以有效地调控空化数,进而达到控制空泡形态的目的.文中同时给出了通气流量系数的实验曲线拟合公式,并与国外的相关实验和公式进行了比较,两者基本一致.所得结论对进一步的水下超高速航行体空泡形态控制技术研究具有参考价值.     

关于刚体角速度定义的一个注解

给出了一种角速度定义方法. 这种方法基于固连坐标系基矢量和单位矢量的导数给出,但避免使用角速度矩阵概念. 另外从刚体上速度分布的角度,用速度场旋度的方法解释角速度. 可以帮助学生从另外一个角度来理解角速度概念.     

Experimental investigation and modeling of the tension behavior of polycarbonate with temperature effects from low to high strain rates

The effects of strain rate and temperature on the tension stress–strain responses of polycarbonate are experimentally investigated over a wide range of strain rates (0.001–1700 s⁻¹) and temperatures (0–120 °C). A modified split Hopkinson tension bar is used for high-rate uniaxial tension tests. Experimental results indicate that the stress–strain responses of polycarbonate at high strain rates exhibit the nonlinear characteristics including the obvious yielding and strain softening. The tension behavior is strongly dependent on the strain rate and temperature. The values of yield stress and strain at yield present a dramatic increase at higher strain rates and decrease with the increase in temperature. Moreover, there exists a significant rate-sensitivity transition in the polycarbonate tension yield behavior. Based on the experimental investigation, a physically based three-dimensional elastoplastic constitutive model for the finite deformation of glassy polymers is used to characterize the rate-temperature dependent yield and post-yield behavior of polycarbonate when subjected to tension loading. The model results are shown close to the experimental data within the investigated strain-rate and temperature ranges.     

Initial step of anthracene‐sensitized photoacid generation from diphenyliodonium hexafluorophosphate in an epoxy matrix studied by steady‐state and laser‐flash photolyses

The anthracene‐sensitized photodecomposition of diphenyliodonium hexafluorophosphate was studied in an epoxy matrix. From steady‐state photolysis, the generation of protons, which are considered to be the actual initiators of the polymerization of epoxides, was confirmed. In addition, 9‐phenylanthracene was detected as a main product from anthracene. From time‐resolved laser‐flash photolysis, a broad absorption band with a peak at about 500 nm was observed that was thought to be due to the precursor of 9‐phenylanthracene. On the basis of these results, we propose electron transfer from anthracene in the excited singlet state to the diphenyliodonium cation as the initial step of photoacid generation. This process is followed by fast chemical reactions, which generate 9‐phenylanthracene and protons, and back electron transfer from the diphenyliodine radical to the anthracene cation radical. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2937–2946, 2001     

On the relation between complexity and uncertainty

In practical problem situations data are usually inherently unreliable. A mathematical representation of uncertainty leads to stochastic optimization problems. In this paper the complexity of stochastic combinatorial optimization problems is discussed. Surprisingly, certain stochastic versions of NP-hard determinstic combinatorial problems appear to be solvable in polynomial time.     

Lowest energy electronic transition in aqueous Cl(-) salts: Cl(-) → (H2O)6 charge transfer transition

We use UV resonance Raman spectroscopy to probe the lowest energy allowed electronic transitions of aqueous solutions containing Cl(-) salts. We show that the waters hydrating the Cl(-) are involved in charge transfer transitions that transfer electron density from Cl(-) to the water molecules. These charge transfer transitions cause significant change in the H-O-H bond angle in the excited state, which results in a strong enhancement of the preresonance Raman intensity of the water bending modes. Our work gives the first insight into the lowest allowed electronic transition of hydrated Cl(-).     

Diastereoselective and enantioselective capture of chiral zinc enolate using nitroolefins: a rapid access to chiral γ-nitro carbonyl compounds

Highly diastereoselective and enantioselective catalytic capture of chiral zinc enolates using nitroolefins as electrophiles is described. The tandem products γ-nitro ketones were obtained in good yields with high diastereoselectivities and enantioselectivities. The γ-nitro ketones were readily hydrogenated to the optically enriched and diastereomerically pure chiral pyrrolidines with four contiguous stereocentres under mild conditions.