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41.
A strong coupling expansion for a two‐band Hubbard model on two sites with nearly degenerate states is considered. A comparative analysis is performed for different schemes of perturbation theory which are applicable to systems with nearly degenerate states. A fourth order approach which builds on a four‐dimensional low‐energy subspace with nearly degenerate states captures accurately the transition from an antiferromagnetic to a ferromagnetic ground state at large on‐site Coulomb interaction. 相似文献
42.
《Optimization》2012,61(2):135-158
Parametric and nonparametric sufficient optimality conditions are established for a class of nonsmooth generalized fractional programming problems containing ρ-univex functions. Subsequently, these optimality criteria are utilized as a basis for construction of two parametric and four parameter–free duality models and proving appropriate duality theorems 相似文献
43.
SUPER EFFICIENCY IN THE NEARLY CONE-SUBCONVEXLIKE VECTOR OPTIMIZATION WITH SET-VALUED FUNCTIONS 总被引:5,自引:0,他引:5
Some properties for convex cones are discussed, which are used to obtain an equivalent condition and another important property for nearly cone-subconvexlike setvalued functions. Under the nearly cone-subconvexlikeness, some characterizations of the super efficiency are given in terms of scalarization and Lagrangian multipliers. Related results are generalized. 相似文献
44.
A. Taa 《Mathematical Methods of Operations Research》2005,62(2):187-209
In this paper we consider vector optimization problems where objective and constraints are set-valued maps. Optimality conditions
in terms of Lagrange-multipliers for an ɛ-weak Pareto minimal point are established in the general case and in the case with
nearly subconvexlike data. A comparison with existing results is also given. Our method used a special scalarization function,
introduced in optimization by Hiriart-Urruty. Necessary and sufficient conditions for the existence of an ɛ-weak Pareto minimal
point are obtained. The relation between the set of all ɛ-weak Pareto minimal points and the set of all weak Pareto minimal
points is established. The ɛ-subdifferential formula of the sum of two convex functions is also extended to set-valued maps
via well known results of scalar optimization. This result is applied to obtain the Karush–Kuhn–Tucker necessary conditions,
for ɛ-weak Pareto minimal points 相似文献
45.
Aparna Mehra 《Journal of Mathematical Analysis and Applications》2002,276(2):815-832
In this paper, we establish a scalarization theorem and a Lagrange multiplier theorem for super efficiency in vector optimization problem involving nearly convexlike set-valued maps. A dual is proposed and duality results are obtained in terms of super efficient solutions. A new type of saddle point, called super saddle point, of an appropriate set-valued Lagrangian map is introduced and is used to characterize super efficiency. 相似文献
46.
We present new insights into the Nearly Constant Loss (NCL) effect, which are based on a study of conductivity as a function of temperature and frequency in 0.3Na2O · 0.7B2O3 and 0.5AgI · 0.5AgPO3 glasses. In these systems, the ionic conductivity has been measured over a temperature range from 4 K to 475 K and in a frequency range from a few mHz to a few MHz. The conductivity spectra taken at various temperatures have then been mapped on to a representation of conductivity versus temperature (or inverse temperature) at fixed frequency. Indeed, such plots are often published in studies of the NCL effect. For a given system and a given frequency, an equivalent mapping is achieved by using suitable scaled model conductivity spectra derived from the MIGRATION concept. This enables us to identify, at fixed frequency, the temperature of transition from the ionic conductivity caused by the “ordinary” correlated hopping motion of the mobile ions (now known as the “first” universality) to the classical NCL behaviour (which Nowick termed “new” or “second” universality). We describe the details of our procedure and show that insights emerge with regard to both the high-frequency plateau of the conductivity component due to “ordinary” hopping and the NCL effect itself. 相似文献
47.
Hiroyuki Takano Koichi IzumiyaNaokazu Kumagai Koji Hashimoto 《Applied Surface Science》2011,257(19):8171-8176
The active catalysts for methane formation from the gas mixture of CO2 + 4H2 with almost 100% methane selectivity were prepared by reduction of the oxide mixture of NiO and ZrO2 prepared by calcination of aqueous ZrO2 sol with Sm(NO3)3 and Ni(NO3)2. The 50 at%Ni-50 at%(Zr-Sm oxide) catalyst consisting of 50 at%Ni-50 at%(Zr + Sm) with Zr/Sm = 5 calcined at 650 or 800 °C showed the highest activity for methanation. The active catalysts were Ni supported on tetragonal ZrO2, and the activity for methanation increased by an increase in inclusion of Sm3+ ions substituting Zr4+ ions in the tetragonal ZrO2 lattice as a result of an increase in calcination temperature. However, the increase in calcination temperature decreased BET surface area, metal dispersion and hydrogen uptake due to grain growth. Thus, the optimum calcination temperature existed. 相似文献
48.
三维变系数热传导问题边界元分析中几乎奇异积分计算 总被引:2,自引:2,他引:0
在边界积分的数值计算过程中,当源点离积分单元很近时,边界积分就会具有几乎奇异性,此时不能直接用高斯数值积分公式计算几乎奇异积分。本文以三维非均质热传导问题为例,介绍了一种计算几乎奇异边界积分的新方法。首先,采用Newton-Raphson迭代算法确定积分单元上离源点最近的点;然后,将积分单元上任意一点的坐标在最近点处展开成泰勒级数,并计算源点到积分单元任意点的距离;最后,将距离函数代入几乎奇异边界积分中,并运用指数变换方法导出积分单元上几乎奇异积分的计算公式。文中给出了两个非均质热传导问题的算例来验证所述方法的正确性、有效性和稳定性。 相似文献
49.
50.
We classify flat strict nearly Kähler manifolds with (necessarily) indefinite metric. Any such manifold is locally the product of a flat pseudo-Kähler factor of maximal dimension and a strict flat nearly Kähler manifold of split signature (2m, 2m) with m ≥ 3. Moreover, the geometry of the second factor is encoded in a complex three-form $\zeta \in \Lambda^3 (\mathbb{C}^m)^*We classify flat strict nearly K?hler manifolds with (necessarily) indefinite metric. Any such manifold is locally the product
of a flat pseudo-K?hler factor of maximal dimension and a strict flat nearly K?hler manifold of split signature (2m, 2m) with m ≥ 3. Moreover, the geometry of the second factor is encoded in a complex three-form . The first nontrivial example occurs in dimension 4m = 12.
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