Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.     

Peculiarities of isotopic temperatures obtained from p + A collisions at 1 GeV

Nuclear temperatures were extracted from fragment yields obtained in inclusive measurements of p+A collisions at 1 GeV. All thermometers based on double-isotopic yield-ratios provide temperatures T ≃ 4 MeV nearly independent on the target mass.     

不同波长下氩原子高阶阈上电离的类共振增强结构

利用量子S-矩阵理论, 借助一致近似方法, 研究了波长分别为800, 1300与2000 nm的强激光场下氩原子高阶阈上电离光电子能谱的类共振增强结构. 结果表明: 在近红外和中红外波段的强激光场下, 阈上电离光电子能谱中均会出现类共振增强结构, 而出现的光强正好满足通道关闭条件, 从而进一步证实了类共振增强的通道关闭机理解释; 发现随着激光波长和光强的增加, 光电子能谱中类共振增强和抑制会交替出现, 该原因可能是电子返回次数不同的“量子轨道”间的相干叠加, 这可以解释实验观察到的长波长下出现的类共振增强能量范围展宽的现象. 研究表明, 在中红外波段的强激光场下, 也会出现与近红外波段类似的type-Ⅰ和type-Ⅱ类共振增强结构.