Improved relaxation time coverage in ramp-strain histories

Standard methods for deriving relaxation data from measurements invariably involve some form of ramp-type deformation history, the initial portion of which is typically not employed for modulus evaluation. In fact, the “ten-times-rule” or a variant thereof is widely used at the expense of short term data acquisition. This paper suggests a simple if (not) obvious method to extend the range of relaxation data that can be acquired from a single test at a single temperature. The method draws on new computational developments for inverting ill-conditioned systems of equations which allows the determination of relaxation parameters nearly routinely and trouble-free. We demonstrate this process for extraction of relaxation characterization from ramp strain histories through (a) numerical evaluation with a virtual test sequence, as well as through (b) data measured in the laboratory. Limitations regarding the time range over which the relaxation modulus can be extracted from laboratory measurements in terms of equipment resolution and stability are discussed. With these constraints in mind it appears feasible to extend the time range by three to four decades towards shorter times when compared with the application of the “ten-times-rule”. Similar treatments apply to the acquisition of creep compliance data.     

Heteroepitaxial growth of Zn1−xCdxSe on cleavage-induced GaAs (110) surface in ultra high vacuum

Zn_1−xCd_xSe epitaxial growth by molecular beam epitaxy (MBE) on the GaAs (110) surface cleaved in ultra high vacuum (UHV) was investigated. The growth mode of Zn_1−x Cd_xSe on GaAs (110) was not a simple Stranski–Krastanow type. At initial growth stage, growth mode was two-dimensional type. However, as the growth proceeds three-dimensional island growth and two-dimensional growth modes compete. As a result, two kinds of structures were spontaneously formed on the surface, pyramidal-shaped islands and ridge structures aligned to the [1 0] direction. Anisotropic in-plane strain relaxation on (110) is suggested as the formation mechanism of such structures.     

Phenomenological viscoelasticity of some rice starch gels

The applicability of a powerful but still easy to use technique, based on a phenomenological theory of viscoelasticity, for processing and analyzing dynamic mechanical data of some rice gels was investigated. Based on this theory a continuous relaxation spectra was generated by application of Tikhonov regularization procedure on continuous Maxwell model. Interpretation of relaxation spectra in terms of number of peaks, its peak intensity H(λ) and appearance of its main distribution peak and magnitude of equilibrium elasticity modulus (G_e) of continuous Maxwell model was found to appropriately reflect main peculiarities of the viscoelastic behavior of rice starch gels. An increase in number of peaks in the relaxation spectra was observed for starch gels having higher amylose content indicating the creation of more heterogeneous structure. H(λ) and G_e values also increased with increase in amylose content demonstrating a transition of the system to more stable state like a gel.     

The kinetics of the α relaxation in an amorphous polymer at temperatures close to the glass transition

The kinetics of the α relaxation of a crosslinked copolymer of acrylonitrile and butadiene (T_g = ?7°C) were studied in the temperature range (T_g + 17°C) down to (T_g ? 8°C). The techniques used were shear creep analysed by time-temperature (t-T) superposition and thermal sampling (TS) with correction procedures proposed by McCrum. In this range the kinetics do not follow the compensation rule, as had been proposed in the pioneering TS experiments by Zielinski, Swiderski and Kryszewski and by Lacabanne et al.. The McCrum correction removes a discrepancy between the pioneering TS experiments and the conclusions of classical t-T superposition experiments. The methods of TS and t-T superposition are compared. At low temperatures, below (T_g + 3°C), the TS method is superior: t-T superposition is unreliable due to lack of normalization and to the physical ageing perturbation. At temperatures from (T_g + 3°C) to (T_g + 11°C) t-T superposition is highly reliable since normalization is not required and there is no ageing. At temperatures above (T_g + 11°C) the precision of t-T superposition depends on the validity of the normalization procedure. It has yet to be determined whether or not the compensation rule applies at temperatures below (T_g ? 8°C): the method most likely to settle this important question is TS, mechanical or dielectric variant, with McCrum correction for the distribution of relaxation times.     

μSR技术与穆斯堡尔谱学

本文对近年来发展起来的μSR技术(μ子自旋转动)进行了介绍,并与穆斯堡尔谱学进行了比较,最后讨论了μSR技术在磁学中关于内磁场的测量和自旋动力学方面的研究应用。     

联营市场下的多时段购电交易算法

基于按报价结算和报价曲线为阶梯形递增曲线的市场规则,以最小化购电费用为目标,提出了一种周期内整体优化的购电交易新算法.该算法首先把各机组出力下限松弛为零,然后利用动态经济调度程序得到一个可能不可行的初始最优解,再通过一系列校核和调节过程逐步改善解的可行性.调节过程中始终以购电费用上升最小为目标.通过对比两个算例的计算结果验证了该算法的有效性.     

Simulation study on molecular relaxation in ionomer melts

Relaxation behavior of ionomer molecule in melt state was investigated by Brownian simulation where motion of a bead-rod chain representing a linear ionomer molecule was calculated in two-dimension. Entanglement between the other molecules was assumed by a repulsive interaction between the chain and randomly located entanglement points. Effect of ion aggregates was also introduced by an attractive interaction between the chain and attractive sites randomly dispersed in the simulation box. Relaxation spectra of end-to-end motion and local bond orientation were obtained in equilibrium calculation for various chain lengths. The effect of the attractive site was discussed on the spectrum. It was found that on the end-to-end motion, the longer the chain was, the more discrepant the spectrum was, while on the bond orientation, the shorter it was, the more discrepant the spectrum was. On the basis of these results, a picture to describe the experimental phenomena was proposed.     

Complex permittivity and relaxation processes in CaCu3Ti(4−x)MnxO12

The effects of Mn-doping on CaCu₃Ti₄O₁₂ (CCTO), i.e. the electrical properties of CaCu₃Ti_(4−x)Mn_xO₁₂ were studied in order to get a deep insight into the origin of the colossal dielectric constant of CCTO. It was found that 1 mol% substitution of Mn for Ti decreases the dielectric constant largely to a factor of 1/100, supporting the point of view that the native defects are responsible for the dielectric response of CCTO.     

Dielectric behaviour of BZT-BCT nano pseudobinary system near TCP-assisted morphotopic phase boundary

The present study investigates the comparative dielectric studies in nano pseudobinary system synthesized by conventional and hybrid microwave sintering. The material was formed near Tri Critical Point (TCP)-assisted Morphotropic Phase Boundary (MPB) region from equal weight percentage of Lead Zirconate Titanate (BZT) and Barium Calcium Titanate (BCT) employing high energy ball milling. In the temperature dependent LCR study, a diffused phase transition (DPT) behaviour was identified for both conventional and hybrid microwave sintered samples. In each case, modified Currie-Weiss relation indicates an anomaly in the paraelectric state. Further, another approach using macroscopic composition-fluctuation model also exhibits the anomalous behaviour. Universal dielectric response (UDR) demonstrates that such behaviour is created by a temperature assisted relaxation phenomena by the formation of oxygen vacancies. Beyond 260 °C, microwave sintering creates more oxygen vacancies across grain boundary region as compared to the conventional sintering and in turn plays the key role for enhanced dielectric permittivity.     

Dynamic Viscoelasticity of Wood After Various Drying Processes

In this study, specimens of heartwood from Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) plantation trees were dried by high-temperature drying (HTD), low-temperature drying (LTD), and freeze vacuum drying (FVD), respectively. The dynamic viscoelastic properties of dried and untreated wood specimens with various moisture contents were investigated in the temperature range between ? 120 and 40°C at 1 Hz using a dynamic mechanical analysis (DMA). The results indicated that the relative storage modulus and relative loss modulus were both the highest for HTD wood and the lowest for FVD wood, and that two mechanical relaxation processes developed. The α relaxation process in the higher temperature range was presumably a result of surpassing the glass transition of hemicelluloses with low molecular weight, whereas the β relaxation process occurring in the lower temperature range was most probably due to the motions of both methyl groups in the amorphous region of wood cell wall and adsorbed water molecules in wood. As moisture content increased, the decrease of relative storage modulus with increasing temperature became more dramatic, and the loss peak temperatures of the relaxation processes shifted to lower temperature range. The difference of dynamic mechanical behavior among untreated and dried specimens reduced with the increase of moisture content.