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1.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
2.
Alberti G Brunet E Dionigi C Juanes O de La Mata MJ Rodríguez-Ubis JC Vivani R 《Angewandte Chemie (International ed. in English)》1999,38(22):3351-3353
The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space. 相似文献
3.
High-performance liquid chromatographic methods for the separation and quantitation of phospholipids were developed and shown to give sensitive, reliable measurements of tissue phospholipids, including difficult-to-resolve pairs such as choline plasmalogen (plasmenylcholine) and phosphatidylcholine, choline glycerophospholipids and sphingomyelin, phosphatidylinositol and phosphatidylserine, and phosphatidylserine and lysophosphatidylethanolamine. Separations of most phospholipids including those mentioned above are more complete than in existing procedures, and require only 40 min per injection. Utilization of the hexane-2-propanol-water system has an advantage over separation techniques that employ acidic solvents in that the plasmalogens are not hydrolyzed and a less degradative environment for labile lipids is provided. Further, a rapid high-performance liquid chromatographic procedure for the separation of intact ethanolamine plasmalogen (plasmenylethanolamine) from phosphatidylethanolamine was developed. Previous procedures have required derivatized samples or acid hydrolysis of the plasmalogen vinyl ether linkage. A slight modification of the primary method (method I) increases the resolution of lysophosphatidylethanolamine from other classes (method II). A third modification (method III) can replace the standard silicic acid column separation of lipids into neutral, glycolipid, and phospholipid fractions. 相似文献
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A new method of HPLC column retentivity testing utilizes polymeric probes instead of conventional sets of low molar mass substances. The procedure allows at least semiquantitative, separate and independent evaluation of adsorption and partition properties of column packings. In this present work, the method is applied for comparison of the polar interactivities of selected silica gel C18 HPLC columns. It is shown that free silanols which remained on the surface of the end-capped silica C18 column packings are accessible for interaction with highly polar macromolecules. High molar mass polymeric test probes are adsorbed on the surface silanols and their retention volumes increase. As result, deviations from regular size-exclusion chromatographic (SEC) behavior are observed. The extent of retention volume changes depends on both the nature of polymer probes and on column packing type. Adsorption of macromolecules can be suppressed by addition of a highly polar substance to the mobile phase. The amount of polar additive which is needed to attain regular SEC elution of the polymer probe depends on the column packing type and can be used as a characteristic of silanophilic column interactivity. Courses of dependences of retention volumes on sizes of macromolecules indicate the presence of "U-turn" adsorption which allows two and more silanols situated among C18 groups to be occupied simultaneously with the same macromolecule. 相似文献
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R.S. Howard C.H. Dugan 《Journal of Quantitative Spectroscopy & Radiative Transfer》1973,13(12):1553-1557
We report on measurements of collision broadening of the electric quadrupole transition λ5577.35 Å in oxygen by argon, krypton and xenon. The broadening constant (linewidth added per unit atom density) was found to be: (4.3 ± 2.3) × 10-21 cm-1 atom-1 cm3 for argon (reported earlier), (8.0 ± 1.7) × 10-21 cm-1 atom-1 cm3 for krypton, and (10.0 ± 2.0) × 10-21 cm-1 atom-1 cm3 for xenon. We discuss some experimental problems associated with these measurements. 相似文献