共查询到20条相似文献,搜索用时 15 毫秒
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A large body of conspicuous publications [1] in recent years asserts that the high temperature approximation (HTA), a mostly tested and most widely used assumption in NMR spectroscopy and MRI technology, is invalid for concentrated samples in high magnetic fields such as for a proton COSY spectrum of water [1]. 相似文献
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Examination of Validity of Paraxial Approximation in Second Harmonic Generation Microscopy under Low Numerical Aperture 下载免费PDF全文
By using a vectorial approach, the validity of paraxial approximation in second harmonic generation (SHG) microscopy under low numerical aperture (NA) is examined when the sample is a collagen fibril. Due to the larger value of dzzz and tensorial nature of SHG, the component Ez of the focused fieM may have strong effect on the radiation pattern of SHG. Numerical results indicate that when the value of NA exceeds 0.3, the effect of Ez can not be neglected, which results in the invalidation of paraxial approximation in SHG microscopy despite the fact that SHG microscopy is still under low NA focusing. 相似文献
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在强激光场中,通过Kramers-Henneberger(KH)变换和高频近似可以将狄拉克方程的求解从一个含时问题转换成一个稳态问题来研究。以氢原子为例,详细研究了相对论框架下该稳态问题中的有效库仑势的特点,并和非相对论框架下的结果进行了比较。研究发现,由于相对论有效质量的引入,有效库仑势的分布范围并不像非相对论条件下随着激光场强度的增强单调变大,而是增加到一定值后不再变化。另外,通过比较偶极近似和非偶极近似下有效库仑势的分布,发现对高频强场,偶极近似不再适用。 相似文献
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The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three-dimensional nondipole ab initio wave packet calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization effect in the photoelectron spectrum. 相似文献
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E. A. Volkova A. M. Popov O. V. Smirnova O. V. Tikhonova 《Journal of Experimental and Theoretical Physics》1997,84(4):658-664
We use the Kramers-Henneberger approximation to investigate the phenomenon of stabilization of quantum systems with short-range
potentials in a strong electromagnetic field. We identify the physical limits imposed on our investigation by the use of this
approximation, and the ranges of parameter values of the system and external field that lead to stabilization. We analyze
the dependence of the stabilization threshold on the frequency of the laser light. The conclusions obtained from our analytic
investigation are confirmed by numerical calculations.
Zh. éksp. Teor. Fiz. 111, 1194–1206 (April 1997) 相似文献
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Doklady Physics - The smallness parameter determining the possibility of application of the n-vicinity method for calculating the free energy of a spin system has been found. The types of spin... 相似文献
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Validity of the Debye approximation 总被引:4,自引:0,他引:4
Sheppard CJ 《Optics letters》2000,25(22):1660-1662
The validity of the Debye approximation is reexamined. It is shown that for paraxial systems with strong aberrations the Debye approximation may not be valid, even for systems with a large Fresnel number. The particular case of spherical aberration is considered. Extension to high-aperture systems is discussed. 相似文献
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In the previous paperi[1], we have studied a class of nonlinear stochastic dynamical systems using the stochastic adiabatic approximation. A closed evolution equation for the slow variable ut is obtained. In the present study, we use the methods proposed by the authors in Refs. [2] and [3] to treat the closed ut equation which is derived by means of the new eliminating technique developed in Ref. [1] recently. Two important stochastic dynamical models, the simplified single-mode laser model and the stochastic Haken model, are treated concretely. The coupling effect of the additive and the multiplicative noise is found. 相似文献
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Youngsub Yoon 《General Relativity and Gravitation》2013,45(2):373-386
In 1996, Rovelli suggested a connection between black hole entropy and the area spectrum. Using this formalism and a theorem we prove in this paper, we briefly show the procedure to calculate the quantum corrections to the Bekenstein–Hawking entropy. One can do this by two steps. First, one can calculate the “naive” black hole degeneracy without the projection constraint (in case of the $U(1)$ symmetry reduced framework) or the $SU(2)$ invariant subspace constraint (in case of the fully $SU(2)$ framework). Second, then one can impose the projection constraint or the $SU(2)$ invariant subspace constraint, obtaining logarithmic corrections to the Bekenstein–Hawking entropy. In this paper, we focus on the first step and show that we obtain infinite relations between the area spectrum and the naive black hole degeneracy. Promoting the naive black hole degeneracy into its approximation, we obtain the full solution to the infinite relations. 相似文献
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Approximate susceptibilities of simple cubic S=∞ Heisenberg and Ising antiferromagnets are calculated by using the new expansion method reported previously for the case of a square-plane S=∞ Heisenberg antiferromagnet. The present method gives a good approximation to the susceptibilities of both of the Heisenberg and Ising antiferromagnets above the Néel temperature. 相似文献
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Christoph Gugg Hansjörg Kielhöfer Michael Niggemann 《Communications in Mathematical Physics》2002,230(1):181-199
We prove mathematical approximation results for the (hyperviscous) Burgers equation driven by additive Gaussian noise. In
particular we show that solutions of ``approximating equations' driven by a discretized noise converge towards the solution
of the original equation when the discretization parameter gets small. The convergence takes place in the expected value of
arbitrary powers of certain norms; i.e., all moments of the difference of the solutions tend to zero in certain function spaces.
For the hyperviscous Burgers equation, these results are applied to justify the approximation of certain correlation functions
that play a major role in statistical turbulence theory.
Received: 10 October 2001 / Accepted: 21 May 2002 Published online: 6 August 2002 相似文献
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Approximate susceptibilities of square-plane S = ∞ XY and Ising antiferromagnets are calculated by using the new expansion method reported previously for the case of a square-plane S = ∞ Heisenberg antiferromagnet. The convergence of the new expansion is examined and it is shown that the present method gives a good approximation to the susceptibilities of all of the Heisenberg, XY and Ising antiferromagnets even below the temperature range where the result exhibits a pronounced broad maximum. 相似文献