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排序方式: 共有147条查询结果,搜索用时 62 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.
B. T. Sutcliffe 《Theoretical chemistry accounts》1974,33(3):201-214
It is shown that in the LCAO-MO-SCF problem, if the molecular orbital orthonormality constraints are introduced in the manner first suggested by Fletcher, then the Hessian of the problem is singular. It is suggested that this singularity may well account for the slow convergence observed using direct energy minimization methods to solve the SCF problem. Ways of avoiding the consequences of this singularity are discussed. 相似文献
3.
A number of recent papers have considered ways in which molecular structure may be calculated when both the electrons and the nuclei are treated from the outset as quantum particles. This is in contrast to the conventional approach in which the nuclei initially have their positions fixed and so merely provide a potential for electronic motion. The usual approach is generally assumed to be justified by the 1927 work of Born and Oppenheimer. In this paper we discuss what precisely might be anticipated in the way of molecular structure from a mathematical consideration of the spectral properties of the full Coulomb Hamiltonian, to what extent the very idea of molecular structure might be dependent upon treating the nuclei simply as providing a potential and the extent to which the work of Born and Oppenheimer can be used to support this position. 相似文献
4.
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
5.
Prof. I. G. Csizmadia Prof. M. C. Harrison Prof. B. T. Sutcliffe 《Theoretical chemistry accounts》1966,6(3):191-216
This paper (Part I) describes the theoretical and computational bases of some non-empirical calculations on small organic molecules to be reported in later papers (Parts II et seq). Approximate solutions for the usual fixed nucleus electronic Hamiltonian, in the term of wave functions composed of Slater determinants, are discussed, with particular emphasis on their computational utility. Possible choices of basis functions, from which to form the determinants are examined, and the advantages of Gaussian type functions (GTF) centered on the component atoms are pointed out. Some of the properties of molecules which can be calculated using such approximate wave functions are outlined. Finally an attempt is made to discuss the current limitations of non-empirical calculations of the type described here, and some guesses are made about their future. Brief outlines as a set of appendices are given of the mathematical formalism and computational details of the calculations. 相似文献
6.
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8.
A computational study is made of the effect of basis set upon the energy, properties and inversion barrier of the phosphine molecule. The calculations are performed at both the SCF and CI level. The flexibility of the double zeta basis is discussed in the light of the results. 相似文献
9.
Under sections 73 and 74 of the revised Canadian Environmental Protection Act (CEPA 1999), Environment Canada and Health Canada must "categorize" and "screen" about 23,000 substances on the Domestic Substances List (DSL) for persistence (P), bioaccumulation (B), and inherently toxic (iT) properties. Since experimental data for P, B and iT are only available for a few DSL substances, a workshop was held to address issues associated with the use of Quantitative Structure-Activity Relationships (QSARs) to categorize these substances. This paper describes the results of an 11-12 November 1999 International Workshop sponsored by Environment Canada to discuss potential uses and limitations of QSARs to categorize DSL substances as either persistent or bioaccumulative and iT to non-human organisms and to recommend future research needed to develop methods for predicting the P, B and iT of difficult-to-model substances. 相似文献
10.
A.H. Khan S. Celotto L. Tunna W. ONeill C.J. Sutcliffe 《Optics and Lasers in Engineering》2007,45(6):709-718
This paper reports on etching rates and hole quality for nanosecond laser percussion drilling of 200-μm thick 316L stainless steel performed with micro supersonic gas jets. The assist-gas jets were produced using nozzles of 200, 300 and 500 μm nominal throat diameters. Air and oxygen were used separately for the process gas in the drilling trials and the drilling performance was compared to drilling in ambient conditions. The highest etch rate of 1.2 μm per pulse was obtained in the ambient atmosphere condition, but this was reduced by about 50% with assist-air jets from the 200 μm nozzle. Increasing the jet diameter and/or using oxygen assist gas also decreased the etching rate and increased the hole diameter. The 200 μm nozzle using air-assist jets produced the least amount of recast and gave the best compromise for etching rate. A combination of plasma shielding and different gas dynamic conditions inside the holes and at the surface are correlated to the observations of different drilling rates and hole characteristics. 相似文献