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排序方式: 共有73条查询结果,搜索用时 31 毫秒
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.
The phase β-K0.25Pb0.75F1.75 previously found in the KF-PbF2 system appears to be metastable at low temperatures relative to a mixture of orthorhombic PbF2 and a new phase suspected to be KPbF3 II. KPbF3 II transforms to KPbF3 I at 298.5°C at atmospheric pressure. The KPbF3 II/I transition line rises with pressure, but the substance appears to reversibly disproportionate above ~360°C, 5 kbar, possibly to a mixture of PbF2 and K4PbF6. Instead of β-K0.25Pb0.75F1.75, a mixture with this composition yielded, in addition to weak heat events due to the KPbF3 II/I transition, strong heat events at 254.5°C and atmospheric pressure (thermal hysteresis ~13°C) which were ascribed to the PbF2 orthorhombic/cubic transition. This transition rises with pressure to 673°C at 37.8 kbar. 相似文献
3.
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
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E. J. Janse van Rensburg E. Orlandini D. W. Sumners M. C. Tesi S. G. Whittington 《Journal of statistical physics》1996,85(1-2):103-130
We consider a discrete ribbon model for double-stranded polymers where the ribbon is constrained to lie in a three-dimensional lattice. The ribbon can be open or closed, and closed ribbons can be orientable or nonorientable. We prove some results about the asymptotic behavior of the numbers of ribbons withn plaquettes, and a theorem about the frequency of occurrence of certain patterns in these ribbons. We use this to derive results about the frequency of knots in closed ribbons, the linking of the boundary curves of orientable closed ribbons, and the twist and writhe of ribbons. We show that the centerline and boundary of a closed ribbon are both almost surely knotted in the infinite-n limit. For an orientable ribbon, the expectation of the absolute value of the linking number of the two boundary curves increases at least as fast as n, and similar results hold for the twist and writhe. 相似文献
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S.M.M. Coelho F.D. Auret G. Myburg P.J. Janse van Rensburg W.E. Meyer 《Physica B: Condensed Matter》2009,404(22):4389-4392
Inductively coupled plasma (ICP) etching has been used primarily on compound semiconductors. There are however compelling reasons to study the effects of ICP etching on Ge. Pd Schottky barrier diodes (SBDs) were resistively evaporated onto Ge (1 1 1) that was ICP etched at a rate of 60 Å per minute for three or ten minute intervals. Although plasma cleaning is known to introduce defects that were observed with DLTS, the diodes exhibited excellent current-voltage characteristics when cooled down to 80 K. Current-temperature (IT) scans that were recorded from 20 K up to 300 K after cooling under reverse bias showed no effect of recombination/generation (RG). On the other hand, IT scans that were recorded after cooling under zero or forward bias clearly exhibited RG effects in the 100-240 K temperature range. This effect was found to be completely reversible. In addition, ICP etching leads to superior devices when compared to devices manufactured by RF sputter deposition. 相似文献
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van Vuuren Nadia Janse van Rensburg Helena D. Janse Terre’Blanche Gisella Legoabe Lesetja J. 《Molecular diversity》2022,26(4):2211-2220
Molecular Diversity - In a pilot study, eleven pyrrolopyridine and pyrrolopyrimidine derivatives (specifically, 7-azaindole and 7-deazapurine derivatives) were synthesised by Suzuki cross-coupling... 相似文献