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排序方式: 共有973条查询结果,搜索用时 15 毫秒
91.
This paper deals with the second term asymptotic behavior of large solutions to the problems Δu=b(x)f(u), x∈Ω, subject to the singular boundary condition u(x)=∞, x∈∂Ω, where Ω is a smooth bounded domain in RN, and b(x) is a non-negative weight function. The absorption term f is regularly varying at infinite with index ρ>1 (that is limu→∞f(ξu)/f(u)=ξρ for every ξ>0) and the mapping f(u)/u is increasing on (0,+∞). Our analysis relies on the Karamata regular variation theory. 相似文献
92.
This paper is devoted to the long time behavior for the Drift-diffusion semi-conductor equations. It is proved that the dynamical system has a compact, connected and maximal attractor when the mobilities are constants and generation-recombination term is the Auger model; as well as the semigroup S(t) defined by the solutions map is differential. Moreover the upper bound of Hausdorff dimension for the attractor is given. 相似文献
93.
史美华 《高校应用数学学报(A辑)》2003,18(1):99-104
研究了和式∑↑n≤x(n/ψ(n))^r的渐近公式中的误差项E(x;r)的加权平方积分均值。其中,r是正整数,ψ(n)是Dedekind函数。 相似文献
94.
从等离子体动力学方程出发,采用玻尔兹曼碰撞项,在粒子分布函数偏离麦克斯韦分布甚小的情况下,作三级矩近似得到了等离子体迁移方程组。迁移方程组中忽略时间微分项后,得出了电子-离子等离子体的张量形式迁移系数,以及与磁场方向成平行(∥)、垂直(⊥)和交叉方向的迁移系数。导出的结果和文献[1]采用朗道碰撞项得出的结果进行了比较。结果表明,迁移系数和等离子体参数的依赖关系是一致的,但对磁场B和离子电荷Z_i值取定时,个别迁移系数要差一倍。此外,导出的迁移系数形式比文献[1]的要简单些。 相似文献
95.
解决了一类带阻尼项的三阶脉冲微分方程的非振动解与其一阶、二阶导数的符号关系,用迭代法得到其振动性与渐近性的判别准则,并举例说明准则的有效性. 相似文献
96.
97.
爆破工程中,信号趋势项的准确去除对提高爆破振动信号分析的精度具有重要意义。针对经验模态分解(empirical mode decomposition,EMD)识别法存在的模态混叠和端头效应等缺陷,提出了基于变分模态分解(variational mode decomposition,VMD)去除信号趋势项的方法,即VMD法。叙述了VMD法识别爆破信号趋势项原理,并进行了仿真实验,结果表明:趋势项频率对分解效果的影响相对较小,当趋势项频率处于1~5 Hz之间时,频率对分解效果的影响基本保持不变;振幅对分解效果影响显著,且振幅越小,VMD法的分解效果越差。当趋势项振幅超过原始爆破信号最大振幅的1/3时,VMD法分解效果较好。最后,应用VMD法和EMD法对含有趋势项的实测爆破振动信号进行处理,认为相比于EMD法,VMD法处理后的信号基本一致且不存在端点效应,在爆破信号趋势项去除领域中具有更加广泛的适用性。
相似文献98.
Ernesto Sánchez‐Mendoza Jesús Hernández‐Trujillo 《Magnetic resonance in chemistry : MRC》2010,48(11):866-872
The indirect vicinal proton–proton coupling constants for pyrrole, furan, thiophene and 15 related heteroaromatic compounds were calculated using the Khon–Sham approximation. An analysis of the four Ramsey contributions to the coupling constants was carried out showing that the Fermi contact term is always positive and dominant, although the remaining contributions have a nonnegligible net negative contribution. The trends observed for the proton–proton coupling constants were rationalized in terms of the properties of the electron density. It was found that electron delocalization between the corresponding hydrogen atoms plays a major role on the observed behavior with the charges of the carbon atoms bonded to them and the accompanying geometric variations being also of importance in the coupling mechanism. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
99.
Characteristic formulations for boundary conditions have demonstrated their effectiveness to handle inlets and outlets, especially to avoid acoustic wave reflections. At walls, however, most authors use simple Dirichlet or Neumann boundary conditions, where the normal velocity (or pressure gradient) is set to zero. This paper demonstrates that there are significant differences between characteristic and Dirichlet methods at a wall and that simulations are more stable when using walls modelled with a characteristic wave decomposition. The derivation of characteristic methods yields an additional boundary term in the continuity equation, which explains their increased stability. This term also allows to handle the two acoustic waves going towards and away from the wall in a consistent manner. Those observations are confirmed by stability matrix analysis and one‐ and two‐dimensional simulations of acoustic modes in cavities. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
100.
We propose a model based on the optimal weighted combinational forecasting with constant terms,give formulae of the weights and the average errors as well as a rela- tion of the model and the corresponding model without constant terms,and compare these models.Finally an example was given,which showed that the fitting precision has been enhanced. 相似文献