排序方式: 共有74条查询结果,搜索用时 15 毫秒
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为解决大规模无约束优化问题,该文结合WYL共轭梯度法和谱共轭梯度法,给出了一种WYL型谱共轭梯度法.在不依赖于任何线搜索的条件下,该方法产生的搜索方向均满足充分下降性,且在强Wolfe线搜索下证明了该方法的全局收敛性.与WYL共轭梯度法的收敛性相比,WYL型谱共轭梯度法推广了线搜索中参数σ的取值范围.最后,相应的数值结果表明了该方法是有效的. 相似文献
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This paper investigates theoretically the electronic structure and
transport of a two-level quantum dot irradiated under a strong laser
field at low temperatures. Using the method of Keldysh equation of
motion for nonequilibrium Green functions, it examines the
time-averaged density of states and conductance for the system with
photon polarization parallel with and perpendicular to the tunnelling
current direction respectively. It is demonstrated that, by analysing
some numerical examples, more photon sidebands resonance states and
multi- and single-photon transitions are found when diagonal matrix
elements dominate the interaction, while the electronic transitions
due to multiphoton absorption are more or less suppressed when
off-diagonal interaction dominates. 相似文献
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We address velocity-modulation control of electron wave propagation in a normal/ferromagnetic/normal silicene junc tion with local variation of Fermi velocity, where the properties of charge, valley, and spin transport through the junction ar investigated. By matching the wavefunctions at the normal-ferromagnetic interfaces, it is demonstrated that the variation of Fermi velocity in a small range can largely enhance the total conductance while keeping the current nearly fully valley and spin-polarized. Further, the variation of Fermi velocity in ferromagnetic silicene has significant influence on the valley and spin polarization, especially in the low-energy regime. It may drastically reduce the high polarizations, which can b realized by adjusting the local application of a gate voltage and exchange field on the junction. 相似文献
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We study theoretically the low-temperature electronic transport property of a straight quantum wire under the irradiation of a finite-range transversely polarized external terahertz (THz) electromagnetic (EM) field. Using the freeelectron model and the scattering matrix approach, we show an unusual behaviour of the electronic transmission of this system. A sharp step-structure appears in the electronic transmission probability as the EM field strength increases to a threshold value when a coherent EM field is applied. We demonstrate that this effect physically comes from the inelastic scattering of electrons with lateral photons through intersubband transitions. 相似文献
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给出集值映射导数的若干等价命题,这有助于加深对集值映射的导数概念的理解,并给使用带来方便. 相似文献