Interaction and superconducting transition in alkali-doped C_(60)

The intermolecular interactions in alkali-doped C60 solids, A3-x-yA'xA"yC60(A, A', A" =alkali; x y ≤3), have been calculated, and their correlations with the structures and the superconducting transition temperaturesTc have also been investigated. It is found that the variations of the lattice constants a0 of A3-x-yA'x A"yC60 solids and the superconducting transition temperatures Tc can be satisfactorily explained from the viewpoint of interaction. It is shown that the relationship of Tc with interaction is much closer than that of Tc with lattice constant a0. Therefore, we can say it is the physical factors such as interaction, other than the geometrical structure factors such as a0, that should be reasonably taken as the primitive cause of the sudden change of superconductivity from pristine C60 to its alkali-doped compounds and of the variation of Tc among superconductors of A3-x-yA'xA'yC60.     

Mixing of low-frequency Raman-active phonons studied by femtosecond pump–probe spectroscopy

We report an optical study of the superconducting transition in the YBa₂Cu₃O_7−x films on MgO substrate carried out by femtosecond pump–probe spectroscopy. In both the normal and the superconducting state, we have observed the transient time-resolved reflectivity caused by the oscillations associated with two A_1g metal-ion modes. Temporal interference between the modes is modified below the phase transition, which also appeared in an altered relative intensity of the modes in the Fourier transformed spectra.     

Charge localization in organic conductors (TM)X: The influence of anion ordering

An investigation of the different contributions leading to charge localization in a 1/2 or 1/4 filled band 1D conductor has been conducted through a study of transport properties in the solid solution [(TMTSF)_1-x (TMTTF) _x]₂ReO₄. The existence of an ordering transition of the anions allows to identify two contributions to the electronic potential with wave vector 4k_F. A dominant on-site 4k_F potential besides the bond contribution is revealed when Umklapp scattering is pertinent via the weakening of the localization arising at the (0, 1/2, 1/2) anion ordering which is stabilized under pressure in the compound [(TMTSF) _0.5 (TMTTF)_0.5]₂ReO₄ at variance with the enhancement of localization observed in the homomolecular (TMTTF)₂ReO ₄ material. Received: 13 May 1998 / Revised: 8 July 1998 / Accepted: 9 July 1998     

高温超导体磁通动力学的一些重要进展

简要回顾了近１０年来,高温超导体磁通动力学领域中理论和实验上的一些重要进展。在理论领域中,Ｆｉｓｈｅｒ等人提出的涡旋玻璃理论改变了人们对磁通运动耗散的认识,因此在此着重介绍。在涡旋态的相图方面,尽管目前还没有彻底弄清楚,但理论和实验研究均展示出了非常丰富的物理内容。还对实验中所发现的一些重要或反常的现象进行了介绍。并对高温超导体的应用和所存在的物理问题和了简单的概述。     

Harmonic generation in superconducting Bi(Pb)SrCaCuO thick films

We present a detailed study of harmonic generation in Bi(Pb)SrCaCuO superconducting thick film prepared by screen printing technique. A comparative study of amplitude of harmonics of two films of different J_c have been carried out. The variation of amplitudes of the harmonics are studied as a function of magnitude of ac and dc field. The temperature dependence of amplitude of third harmonic (V³) is studied with increasing amplitude as well as frequency of ac field. These results are analyzed in the frame work of critical state model. V₃ -T curve also indicates the presence of two phases in Bi(Pb)SrCaCuO film.     

带时变增长率、迁移率、波动率的种群变动模型与生物防治最小成本的确定方法

用回归方法确定种群数量增长率、迁移率与波动率的最优拟合曲线,求解带时变漂移串与波动串的It(?)随机微分方程,建立有迁移行为的害虫种群的数量变动模型,进而给出确定生物防治最小成本的计算方法,指出了确定模型中参数的统计方法。     

Synthesis and Self-Association of Stimuli-Responsive Diblock Copolymers by Living Cationic Polymerization

The living cationic polymerization of several functional monomers in the presence of an added base is investigated as a possible preparation of a new series of water-soluble or stimuli-responsive copolymers. Under appropriate conditions, the polymerization allows the selective preparation of polymers with various shapes and different sequence distributions of monomer units, including stimuli-responsive block copolymers, gradient copolymers, poly(vinyl alcohol) graft copolymers, and star-shaped polymers. The stimuli-induced self-association of the diblock copolymers is also examined. An aqueous solution of the diblock copolymer with a thermo-sensitive segment undergoes rapid physical gelation upon warming to the critical temperature to give a transparent gel, and returns sensitively to the solution state upon cooling. The sharp transition of stimuli-responsive segments with highly controlled primary structure turns out to play an important role in the self-association. Small-angle neutron scattering, dynamic light scattering, and electron microscopy studies reveal that the physical gelation involves a thermosensitive micellization of diblock copolymers (core size: 18-20 nm) and subsequent micelle macrolattice formation (bcc symmetry). Based on the gelation mechanism, several stimuli-responsive gelation systems are achieved using other stimuli such as the addition of a selective solvent or compound, cooling, pH change, and irradiation with ultraviolet light.     

阳离子色谱法测定溴棕三甲胺含量

建立了用阳离子色谱法测定溴棕三甲胺的方法。在淋洗液为硫酸(3mmol/L)+乙腈(40%),流速为1mL/min,柱温为40℃的色谱条件下,采用MetrosepC4-150阳离子色谱柱,非抑制电导检测器,在1～15mg/L范围内,溴棕三甲胺的浓度与色谱峰面积呈良好线性关系,相关系数为0.999。方法具有快速、简便、灵敏的特点,适用于检测实际样品中溴棕三甲胺的含量。