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71.
本文应用指数三分性和不变流形的局部几何表示方法,给出异宿流形上的轨道当两个奇点经历超;临界分支和摄动时保存和横截的条件. 相似文献
72.
Thaleia Zariphopoulou 《Mathematical Methods of Operations Research》1999,50(2):271-296
We study a generalization of the Merton's original problem of optimal consumption and portfolio choice for a single investor
in an intertemporal economy. The agent trades between a bond and a stock account and he may consume out of his bond holdings.
The price of the bond is deterministic as opposed to the stock price which is modelled as a diffusion process. The main assumption
is that the coefficients of the stock price diffusion are arbitrary nonlinear functions of the underlying process. The investor's
goal is to maximize his expected utility from terminal wealth and/or his expected utility of intermediate consumption. The
individual preferences are of Constant Relative Risk Aversion (CRRA) type for both the consumption stream and the terminal
wealth. Employing a novel transformation, we are able to produce closed form solutions for the value function and the optimal
policies. In the absence of intermediate consumption, the value function can be expressed in terms of a power of the solution
of a homogeneous linear parabolic equation. When intermediate consumption is allowed, the value function is expressed via
the solution of a non-homogeneous linear parabolic equation. 相似文献
73.
本文用Melnikov函数方法讨论了一类扩张了的软弹簧型Duffing方程(k=1,2,3,…)在周期激励下的紊动现象.给出了出现二阶同宿切的条件.文中所采用的方法对于不能给出并宿轨道的显式的系统的研究是非常有用的. 相似文献
74.
Martin Fuchs 《manuscripta mathematica》1991,72(1):131-140
Given a smooth domain Ω in ℝ
m+1 with compact closure and a smooth integrable functionh: ℝ
m+1→ℝ satisfyingh(x)≥H
∂Ω
(x) on ∂Ω whereH
∂ω denotes the mean curvature of ∂Ω calculated w.r.t. the interior unit normal we show that there is a setA⊂ℝ
m+1 with the properties
andH
∂A=h on ∂A. 相似文献
75.
ABSTRACTWe theoretically investigated the influences of the magnetic field and light polarisation on the electronic and optical properties of a GaAs/GaAlAs pseudo-elliptic quantum ring, modelled by an outer ellipsis and an inner circle, in the presence of the Rashba and Dresselhaus spin–orbit interactions and Zeeman effect. We show that Aharonov-Bohm oscillations of the energy spectrum are not affected by the presence of the Zeeman effect alone but, in the presence of Rashba and Dresselhaus spin–orbit couplings, the periodicity of certain levels becomes hardly definite. The Zeeman effect generally enhances/diminishes the separation levels produced by Rashba/Dresselhaus interactions (SOI) and when both types of SOI are considered, the effect depends on their relative strength. The magnetic field can trigger spin-flip for each type of spin–orbit interaction and Zeeman effect or their combination through anticrossings in the energy spectra. Our results reveal that the absorption spectra are very sensitive to the magnetic field and light polarisation. For all polarisations considered, the magnetic field increment leads to the redshift or blueshift of some particular peaks (an effect of this ring geometry) and a better separation of the peaks. The x-polarised light determines spectra with many small, but separated peaks while the circular polarised light leads to spectra with large peaks of high amplitude. 相似文献
76.
We investigate the coherent control of spin tunneling for a spin–orbit (SO) coupled boson trapped in a driven triple well. In the high-frequency limit, the quasienergies of the system are obtained analytically and the fine energy band structures are shown. By regulating the driving parameters, we reveal that the directed spin-flipping or spin-conserving tunneling of an SO-coupled boson occurs along different pathways and in different directions. The analytical results are demonstrated by numerical simulations and good agreements are found. Further, an interesting scheme of quantum spin tunneling switch with or without spin-flipping is presented. The results may have potential applications in the design of spintronic devices. 相似文献
77.
We consider the dynamics and formation of vortices from ring dark solitons in a two-dimensional Bose–Einstein condensate with the Rashba spin–orbit coupling based on the time-dependent coupled Gross–Pitaevskii equation. Compared with previous results, the system exhibits complex dynamical behaviors in the presence of the spin–orbit coupling. With the modulation of the spin–orbit coupling, not only the lifetime of ring dark solitons is greatly prolonged, but also their attenuation kinetics is significantly affected. For two shallow ring dark solitons with the equal strength of the spin–orbit coupling, the radius of ring dark solitons increases to a maximum value over time and then shrinks into a minimum value. Due to the effect of the snake instability, ring dark solitons split into a series of ring-like clusters of vortex pairs, which perform complex oscillations. This indicates that the system is strongly dependent on the presence of the spin–orbit coupling. Furthermore, the effect of different initial modulation depths on the dynamics of ring dark solitons is investigated. 相似文献
78.
Ordered Sr2CrReO6 has been synthesized recently. It is measured to be ferrimagnetic semiconductor, in contrary to the previous reports of metallic properties. To solve the discrepancy, we have investigated the compound by using the density functional theory. The semiconducting behavior is reproduced by including the electron correlation and spin–orbit coupling simultaneously. The calculated band gap is 0.22 eV, close to the experimental value of 0.21 eV. A large orbital moment of 0.69µB is found for Re, which is caused by the Coulomb‐enhanced spin–orbit coupling. By applying pressure, a semiconductor to half‐metal transition is observed through 5% volume compression.
79.
The optical absorption spectra (d-d transition bands) and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is Ri?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni2+ center in Ca3Sc2Ge3O12 crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni2+ ion in the octahedral site of Ga3Sc2Ge3O12 is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d8 ions in octahedral lattices. 相似文献
80.
We prove that there exists a maximal ideal of a BCI-algebra X in which each subalgebra is an ideal.AMS Subject Classification (1991): 06F35, 03G25.The second author was supported by the LG Yonam Foundation (1995). 相似文献