共查询到20条相似文献,搜索用时 421 毫秒
1.
2.
3.
4.
5.
提出矩形波导近似,并分别采用Marcatili法和有效折射率法进行计算,得出了数值结果,并将其与大块光学材料近似、修正耦合波理论和微扰法以及精确求解特征方程的结果进行比较. 相似文献
6.
7.
超声平面波经颅成像时,由于颅骨对超声传播的影响引起图像质量下降,需要对颅骨造成的超声相位畸变进行校正。为此,该文研究了两种相位补偿方法:基于近似射线声学的理论方法和基于时间反转的数值计算方法,并利用数值仿真对比了两种方法的补偿和成像效果。结果表明:无论使用近似射线法还是时间反转法,都能够有效地校正因颅骨造成的相位畸变;时间反转法成像的精度和结果要好于近似射线法,但所需的计算资源和时间都要远远大于近似射线法;两种方法与平面波相干复合方法结合都能够一定程度上提高成像的对比度和分辨率。该研究结果为超声经颅脑成像方法研究和设备研发提供了理论指导和技术支持。 相似文献
8.
9.
在改进的平均原子模型的基础上,在中心场近似下用分波法来处理部分自由电子密度分布函数,提高了电子波函数、电子占据数等原子参数的计算精度.通过平均近似处理,给出了劈裂的能带.通过使用分波法来准确计算贵金属Au的电子状态方程. 相似文献
10.
利用泛函分析理论中的迭代法,分别计算了平行平板双电层在高、中、低电位下的相互作用能,并以数值法所得结果为参照,在各电位下分别与Debye-Hückel线性近似法、Langmuir近似法所得的结果进行比较.结果表明,DH线性近似法和Langmuir近似法均只能分别局限于极低或极高电位,而泛函迭代法不但有简单的解析表达式,而且在各种电位下都能得到较满意的结果. 相似文献
11.
Dehua Chen Hui Wang Xianglin Yang 《International Journal of Infrared and Millimeter Waves》1999,20(8):1533-1540
Based on the wave theory of light and taken the random polarizations of signal and crosstalk into consideration, bit error rate (BER) and power penalties (PP) of optical cross-connects are calculated using the so-called saddlepoint approximation which is improved. The calculated results agree well with the results of experiment and Gauss approximation, shown highly calculated precision of the improved saddlepoint approximation. We also show that BER and PP for systems with random-polarizations are much smaller than that for systems with matched-polarizations when the number N of crosstalk is large, and the conclusion of near-worst-case operation is true only for N<3, so the impact of random signal and crosstalk polarizations on optical cross-connects must be considered in the design for lightwave networks. 相似文献
12.
13.
H. Fehske D. Ihle J. Loos U. Trapper H. Büttner 《Zeitschrift für Physik B Condensed Matter》1994,94(1-2):91-100
On the basis of the Holstein-Hubbard model the formation of polarons at finite densities is investigated by means of a variational approach appropriate for describing squeezing and correlation effects. An effective Hubbard model for the polarons is derived, where the correlations are treated within the slave-boson saddlepoint approximation. For low enough phonon frequencies, with increasing coupling an abrupt self-trapping transition from light to heavy polarons is found. With increasing density the squeezing effect increases, and the transition is shifted to higher couplings. In the case of an effective Coulomb repulsion, the self-trapping transition is shifted to lower couplings with increasing Hubbard interaction, and the effective polaron mass below the transition is enhanced. In the heavy polaron regime, the frequency-dependent polaron hopping conductivity is calculated. There occur qualitative finite-density and correlation effects on the zero-temperature absorption spectrum which are discussed with respect to their possible relevance to the midinfrared absorption in high-T
c
superconductors. 相似文献
14.
V. P. Zavarzina V. E. Pafomov V. A. Sergeev 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(5):583-586
Differential cross sections and longitudinal momentum distributions of observed particles are calculated for stripping reactions that result from diffractive interaction between halo nuclei and targets. The applicability of different analytic methods of calculation is considered. The advantages of an improved approximation of small target radius are demonstrated for valent halo nucleon absorption radii of 2–4 fm in describing momentum distributions in particular. 相似文献
15.
The Feshbach-Rubinow approximation and its improved versions have been applied to the H2+ ion system.The ground-state energies are calculated with these different methods.The best ground-state energy obtained is only 2% higher than the experimental result.Given the simplicity of the method,this accuracy is quite remarkable.It is shown that the screening effect plays a less significant role and the effective potential between the two protons is probably of most importance in this problem. 相似文献
16.
The effect of a polarizable impurity atom on the frequency of optical vibrations of a polar crystal is calculated. The impurity-lattice interaction is treated by considering lattice polarization as discrete in contrast to earlier methods based on continuum approximation. In the appropriate limit, our result goes over exactly to the result of earlier approximation. 相似文献
17.
18.
刘之景 《核聚变与等离子体物理》1999,19(2):79-82
使用双撞近似和托马斯-费米近似计算了类氢离子Li^2+和C^5+与中性原子H和He碰撞的电荷剥离截面。计算结果表明,总截面主要处在0.35-10的速度范围,这些载面与ToshzoShirai等人计算的结果符合得较好。 相似文献
19.
20.
在改进的Hartree-Fock-Slater原子模型的基础上,在中心场近似下用含能带效应的全动态电子判据处理自由电子与束缚电子的密度分布,提高了电子波函数、电子占据数等原子参数的计算精度.通过平均近似处理,给出了劈裂的能带,从而改善了物质电子状态方程的计算精度.结果部分详细计算了W元素的原子能量、电子压强、熵、定容热容及其它热力学参数 相似文献