高T_c超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.     

Quantitative analysis of ethylenediamine in plasma by capillary column gas chromatography

A specific and sensitive method for the determination of ethylenediamine in human plasma is described. The aqueous sample is treated with m-toluoyl chloride, yielding the N,N′-bis(m-toluoyl) derivative of the diamine, which is extracted into dichloromethane and quantitated after “on column” methylation by capillary gas liquid chromatography with alkali flame ionization detection. The corresponding derivative of putrescine serves as internal standard. The assay is reproducible and calibration curves are linear over the concentration range 0.05 to 10 μg · ml^?1. The lower detection limit is about 10 ng · ml^?1. The structures of the compounds of interest eluting from the capillary column are examined by gas liquid chromatography/mass spectrometry. The assay has been applied to the analysis of ethylenediamine in plasma following the administration of aminophylline and ethylenediamine in a cross-over study to patients with bronchopulmonary diseases. The method also proves suitable for measuring other primary and secondary amines and diamines in aqueous solutions by gas liquid chromatography.     

Molecular optimization of multiply-functionalized mesoporous films with ion conduction properties

Sequential processing of multiply functionalized mesoporous films is shown to yield materials that are compositionally and structurally heterogeneous on mesoscopic and molecular length scales, both of which must be controlled to optimize macroscopic ion-conduction properties. Cubic mesoporous silica films prepared from strongly acidic solutions were subsequently functionalized under highly alkaline conditions to incorporate hydrophilic aluminosilica surface moieties, followed by nonaqueous conditions to introduce perfluorosulfonic-acid surface groups. Such sequential combination of individually incompatible steps yielded stable mesoporous films with high surface hydrophilicities and strong acid functionalities that exhibited high proton conductivities (ca. 9 × 10(-2) S/cm) at elevated temperatures (120 °C). Molecular, mesoscopic, and macroscopic properties of the multiply functionalized films were monitored and correlated at each stage of the syntheses by nuclear magnetic resonance (NMR) spectroscopy, small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), elemental analysis, adsorption, and ion conductivity measurements. In particular, variable-temperature solid-state two-dimensional (2D) (27)Al{(1)H}, (29)Si{(1)H}, (27)Al{(19)F}, and (29)Si{(19)F} HETeronuclear chemical-shift CORrelation (HETCOR) NMR spectra reveal separate surface adsorption and grafting sites for the different functional surface species within the mesopore channels. The hydrophilic aluminosilica and acidic fluoro-group loadings and interaction sites are demonstrated to be strongly affected by the different synthesis and functionalization treatments, which must be separately and collectively optimized to maximize the proton conductivities.     

Sensitivity considerations in polarization transfer and filtering using dipole-dipole couplings: implications for biomineral systems

The robustness and sensitivities of different polarization-transfer methods that exploit heteronuclear dipole-dipole couplings are compared for a series of heterogeneous solid systems, including polycrystalline tetrakis(trimethylsilyl)silane (TKS), adamantane, a physical mixture of doubly (13)C,(15)N-enriched and singly (13)C-enriched polycrystalline glycine, and a powder sample of siliceous marine diatoms, Thalossiosira pseudonana. The methods were analyzed according to their respective frequency-matching spectra or resultant signal intensities. For a series of (13)C{(1)H} cross-polarization experiments, adiabatic passage Hartmann-Hahn cross-polarization (APHH-CP) was shown to have several advantages over other methods, including Hartmann-Hahn cross-polarization (HHCP), variable-amplitude cross-polarization (VACP), and ramped-amplitude cross-polarization (RACP). For X-Y systems, such as (13)C{(15)N}, high and comparable sensitivities were obtained by using APHH-CP with Lee-Goldburg decoupling or by using the transferred-echo double resonance (TEDOR) experiment. The findings were applied to multinuclear (1)H, (13)C, (15)N, and (29)Si CP MAS characterization of a powder diatom sample, a challenging inorganic-organic hybrid solid that places high demands on NMR signal sensitivity.