单晶和多晶纯铝蠕变过程中的内耗

研究了单晶和多晶纯铝蠕变过程中的低频内耗. 在单晶纯铝中观察到: 内耗在蠕变初期单调下降, 在蠕变第一阶段后期出现了一个显著的时间内耗峰, 在蠕变第二阶段内耗趋于稳定值. 多晶纯铝在类似实验条件下则不出现时间内耗峰. 文中分析了出现时间内耗峰的条件和原因, 认为它是由于蠕变第一阶段中运动位错的阻尼系数逐渐增大所引起的. 文中还从蠕变过程中位错运动的微观机制出发, 推导出了蠕变过程中内耗的表达式, 满意地解释了实验结果. 关键词：     

Particle size analysis by sedimentation field flow fractionation. Performance and application

Recently commercial equipment using sedimentation field flow fractionation (SFFF) has become available for analysis of particulate materials in the sub-micron range. This paper describes the DuPont instrument and discusses its performance. A particular study is described on the comparison of the SFFF technique with that of quasi-elastic light scattering (QELS). The paper concludes that the instrument is capable of measuring particle size distributions with high resolution and precision, provided that no particles above the upper size limit — about 1 μm — are present.     

Electron spin resonance study of γ-irradiated poly(acrylic acid)

Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH₃? CH? CH₂ ～ and/or ～ CH₂? CH? CH₂ ～. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the C_α? C_β bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.     

Regular variation of order 1 nonlinear AR-ARCH models

We prove both geometric ergodicity and regular variation of the stationary distribution for a class of nonlinear stochastic recursions that includes nonlinear AR-ARCH models of order 1. The Lyapounov exponent for the model, the index of regular variation and the spectral measure for the regular variation all are characterized by a simple two-state Markov chain.     

On the persistence of elliptic lower-dimensional tori in Hamiltonian systems under the first Melnikov condition and Rüssmann’s non-degeneracy condition

In this paper we formulate a theorem on the persistence of elliptic lower-dimensional invariant tori for nearly integrable analytic Hamiltonian systems under the first Melnikov condition and Rüssmann’s non-degeneracy condition, and give the measure estimates of parameters for the non-resonance conditions under Rüssmann’s non-degeneracy condition, which is essential for the proof of our result.     

Relative versions of some star-selection principles

We introduce some relative versions of star selection principles first considered in [5], [11]. Some of the work extends results from [4], [5] and gives some examples.      

UV–visible emission in Tb–Yb codoped tellurite glass on 980-nm excitation

UV–visible upconversion emission from terbium in a Tb–Yb codoped tellurite glass has been observed on 980-nm excitation. The ultraviolet and violet upconversion emissions involve three photons and the blue, green, yellow, and red emissions arise due to two incident photons. The mechanism involved in these emissions is discussed. The effects of doping concentration and of the sample temperature on the upconversion emissions have also been studied. PACS 74.25.Gz; 42.70.Hj; 73.61.Jc; 76.30.Kg; 42.70.Ce     

Kaon production from 1 to 40 AGeV

Kaon production is studied within the Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) model. Results are compared with experiment and with other models. The influence of the kaon potential on the kaon azimuthal distributions at SIS energies is considered. We also discuss the role of the many-body collisions at high-density phase of reaction.     

Domain morphology in ultrathin ferromagnetic films with perpendicular magnetization

We determine the minimal domain structure for the equilibrium thickness of stripes as well as for the minimal energy of the domain configuration in ultrathin films of ferromagnetically coupled spins, where the easy direction of magnetization is perpendicular to the film. It is found that the equilibrium thickness of stripes and walls depend on the exchange energy. The normalized anisotropy, f, depends on interplay between the magnetic and anisotropy energies and is almost independent of the exchange energy inside the wall. The results are compared with the experimental data for thin Ag/Fe/Ag (0 0 1) films and a good coincidence is obtained between both results.