Superconductivity and normal state resistivity of Ba0.6K0.4BiO3: an optical phonon approach

We discuss the nature of the pairing mechanism and the physical properties associated with the normal as well as the superconducting state of cubic perovskites Ba_0.6K_0.4BiO₃using the strong coupling theory. An interaction potential which includes the Coulomb, electron–optical phonon and electron–plasmon interactions is developed to elucidate the superconducting state. A model dielectric function is constructed with these interactions fulfilling thef-sum rule. The screening parameter (μ^* = 0.26) infers the poor screening of charge carriers. The electron–optical phonon strength (λ) estimated as 0.98 is consistent with an attractive electron–electron interaction and supports the moderate to strong coupling theory. The superconducting transition temperature of Ba_0.6K_0.4BiO₃is then estimated as 32 K. Ziman's formula of resistivity is employed to analyse and compare this with the temperature-dependent resistivity of a single crystal. The estimated contribution from the electron–optical phonon together with the residual resistivity clearly infers a difference when a comparison is made with experimental data. The subtracted data infer a quadratic temperature dependence in the temperature domain (30 ≤ T ≤ 200 K). The quadratic temperature dependence of ρ [ = ρ_exp − (ρ₀ + ρ_e–ph)] is understood in terms of 3D electron–electron inelastic scattering. The presence of these el–el and el–ph interactions allows a coherent interpretation of the physical properties. Analysis reveals that a moderate to strong coupling exists in the Ba_0.6K_0.4BiO₃system and the coupling of electrons with the high-energy optical phonons of the oxygen breathing mode will be a reason for superconductivity. The implications of the above analysis are discussed.     

光声光谱法研究光学薄膜的吸收特性

本文以“一维热流活塞模型”为基础,推导出薄膜光声表达式,光声信号的幅值正比于吸收率.测量了透明基底上光学薄膜的光声吸收谱,实验结果与理论一致.尤其是测量弱吸收薄膜的吸收谱时,具有较高的灵敏度和实用性.     

双甲基丙烯酰氧苯基丙烷与苯乙烯共聚物的光学性能

标题共聚物的耐冲击性与丙烯酸酯均聚物相比有明显改善,但随着双烯单体含量的降低,共聚物的耐热性和表面硬度有所下降。丙烯酸酯含量为70%的共聚物的吸收紫外光能力最强(<370nm全吸收),含量为5%～10%的共聚物耐吸水性、耐酸耐碱性及耐冲击性最好。     

Nanoscale organization of the pathogen receptor DC-SIGN mapped by single-molecule high-resolution fluorescence microscopy.

DC-SIGN, a C-type lectin exclusively expressed on dendritic cells (DCs), plays an important role in pathogen recognition by binding with high affinity to a large variety of microorganisms. Recent experimental evidence points to a direct relation between the function of DC-SIGN as a viral receptor and its spatial arrangement on the plasma membrane. We have investigated the nanoscale organization of fluorescently labeled DC-SIGN on intact isolated DCs by means of near-field scanning optical microscopy (NSOM) combined with single-molecule detection. Fluorescence spots of different intensity and size have been directly visualized by optical means with a spatial resolution of less than 100 nm. Intensity- and size-distribution histograms of the DC-SIGN fluorescent spots confirm that approximately 80 % of the receptors are organized in nanosized domains randomly distributed on the cell membrane. Intensity-size correlation analysis revealed remarkable heterogeneity in the molecular packing density of the domains. Furthermore, we have mapped the intermolecular organization within a dense cluster by means of sequential NSOM imaging combined with discrete single-molecule photobleaching. In this way we have determined the spatial coordinates of 13 different individual dyes, with a localization accuracy of 6 nm. Our experimental observations are all consistent with an arrangement of DC-SIGN designed to maximize its chances of binding to a wide range of microorganisms. Our data also illustrate the potential of NSOM as an ultrasensitive, high-resolution technique to probe nanometer-scale organization of molecules on the cell membrane.     

椭圆法用于阳极溶出伏安法测定微量银

用新物理量Ｖｏｐ的椭圆法对阳极溶出伏安法分析的含银离子浓度为１０＾５－１０＾－９ｍｏｌ／Ｌ的一系列溶液进行了研究。结果表明：光学方法与电化学方法所得分析结果相同；椭圆法可检测的浓度下限比电化学方法低一个数量级以上。而且测量的相对平均偏差也小于电化学方法。     

Spectral and photochemical characteristics of CdSe nanoparticles stabilized in polymer-containing media

The optical characteristics of CdSe nanoparticles, produced in aqueous solutions and polymer films in the reaction of cadmium chloride and sodium selenosulfate, were studied. The main parameters that make it possible to vary the forbidden band width were identified. The absorption, photoluminescence, Raman, and nonstationary decolorization spectra of CdSe nanoparticles of various sizes were analyzed. It was demonstrated that under the conditions of pulsed irradiation the CdSe nanoparticles are capable of accumulating excess electrons and inducing redox transformations in components of the solution (oxygen, methylviologen, and sulfite ions). __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 150–155, May–June, 2006.     

非线性光学材料──水草酸铵

一水草酸铵（简称ＡＯＭ）是一种优良的电光晶体￣［１］。文献￣［１，２］报道了该晶体的晶体结构，化学式为（ＮＨ＿４）＿２Ｃ＿２Ｏ＿２·Ｈ＿２Ｏ，属正交晶系，Ｐ２２２空间群，晶胞参数ａ＝０．８０３５ｎｍ，ｂ＝１。０３１ｎｍ，ｃ＝０．３８０１ｎｍ，ｚ＝２。本文拟报道ＡＯＭ单晶生长，热化学分析，透过波段以及非线性光学性质的初步研究。     

1，2—二氯丙烷裂解反应光窗结焦机理的研究

有机化合物在光窗上的结焦严重地影响激光引发化学反应及光学原位实时探测。本文报道在1，2－二氯丙烷反应系统中，光窗结焦现象同时存在于激光引发反应及热反应过程中，对光窗在300℃条件 下的结焦机理研究表明，少量氧气在光窗结焦过程中起关键作用。结焦前驱体的红外光谱研究表明，前驱体的可能结构为1－丙炔－1，3－二醇的缩聚体。该化合物极易通过缩聚反应形成更大的分子，最终导致光 窗结焦。对系统及反应物进行彻底除氧，光窗结焦现象大为改善。     

一种主链含非线性光学活性基团聚合物的合成

把非线性光学(NLO)发色基团引入到聚合物主链中,既可以增大聚合物中NLO基团的含量,从而提高聚合物的宏观NLO系数,又能够提高NLO聚合物的极化稳定性。本文报道一种由酚酞环氧树脂(PPh)与对硝基苯胺(NA)得到的NLO聚合物的合成及其极化松弛。 所用酚酞环氧树脂系自制,环氧值0.427。对硝基苯胺北京化工厂产,分析纯。N,N-二甲基甲酰胺为中国医药公司售品,化学纯,用前减压蒸馏精制,乙醇、丙酮均为北京化工厂生产,分析纯。在氮气保护下将等当量的PPh与NA溶于DMF中于150℃反应6～8小时后,倒     

含吩噻嗪金属配合物的合成及非线性光学性质研究

本文报道了一种新的配体:10-乙基-3-甲酰吩噻嗪缩肼基二硫代甲酸甲酯(HL)及其金属配合物的合成。采用了元素分析、质谱、核磁共振、红外光谱对配体及其金属配合物进行了表征。此外,并应用紫外、荧光和Z-扫描技术,测定了配体及其金属配合物的荧光最佳发射波长(λ_max^em)、荧光量子产率(Φ_f)、寿命(τ)和非线性光学性质。结果表明它们在DMF溶液中都能发射出较强的橄榄色荧光,配体及其金属配合物都有双光子吸收,并且金属配合物的非线性光学效应比配体明显增强。用半经验量子化学方法(RHF/PM3)计算结果与实验值较为吻合。