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251.
A series of first principles calculations have been carried out to study structural, electronic properties of BaSxSe1−x alloys. We have used the local density as well as the generalized gradient approximations for the exchange-correlation potential. The structural properties of these materials, in particular the composition dependence to the lattice constant and bulk modulus, are found to be linear. It is also found linear relationship between theoretical band gaps and 1/a2 (where a is lattice constant). 相似文献
252.
We develop an anisotropic perfectly matched layer (PML) method for solving the time harmonic electromagnetic scattering problems in which the PML coordinate stretching is performed only in one direction outside a cuboid domain. The PML parameters such as the thickness of the layer and the absorbing medium property are determined through sharp a posteriori error estimates. Combined with the adaptive finite element method, the proposed adaptive anisotropic PML method provides a complete numerical strategy to solve the scattering problem in the framework of FEM which produces automatically a coarse mesh size away from the fixed domain and thus makes the total computational costs insensitive to the choice of the thickness of the PML layer. Numerical experiments are included to illustrate the competitive behavior of the proposed adaptive method. 相似文献
253.
254.
In this article, Lagrange interpolation by polynomials in several variables is studied. Particularly on the sufficiently intersected algebraic manifolds, we discuss the dimension about the interpolation space of polynomials. After defining properly posed set of nodes (or PPSN for short) along the sufficiently intersected algebraic manifolds, we prove the existence of PPSN and give the number of points in PPSN of any degree. Moreover, in order to compute the number of points in PPSN concretely, we propose the operator ? k with reciprocal difference. 相似文献
255.
Xiangyu Cui Li Duan Jiaan Yan 《The Journal of the Operational Research Society》2015,66(10):1646-1655
Investigating the inverse problem of the classical Markowitz mean-variance formulation: Given a mean-variance pair, find initial investment levels and their corresponding portfolio policies such that the given mean-variance pair can be realized, we reveal that any mean-variance pair inside the reachable region can be achieved by multiple portfolio policies associated with different initial investment levels. Therefore, in the mean-variance world for a market of all risky assets, the common belief of monotonicity: ‘The larger you invest, the larger expected future wealth you can expect for a given risk (variance) level’ does not hold, which stimulates us to extend the classical two-objective mean-variance framework to an expanded three-objective framework: to maximize the mean and minimize the variance of the final wealth as well as to minimize the initial investment level. As a result, we eliminate from the policy candidate list the set of pseudo efficient policies that are efficient in the original mean-variance space, but inefficient in this newly introduced three-dimensional objective space. 相似文献
256.
三元黄铜矿结构(也称类金刚石结构)半导体是一类具有热电转换潜力的新型热电材料. 本次工作中采用电负性更小的Mn元素替换CuInTe2黄铜矿结构半导体中的Cu元素, 设计制备贫Cu化合物Cu1-xInMnxTe2. 研究表明, 当Mn含量较低时, Mn优先占位在In 位置产生受主缺陷MnIn-. 因此随着Mn含量的增大, 载流子浓度和电导率均得到改善. 但当Mn含量进一步增大后, Mn可同时占位在In位置和Cu位置, 除产生受主缺陷MnIn-外, 还能产生施主缺陷MnCu+. 由于两类极性相反的缺陷之间的湮灭现象, 使得缺陷浓度及载流子浓度开始降低, 晶格结构畸变有变小趋势, 因此在高温下晶格热导率仅略有提高. 研究结果表明, 在某一特定的Mn含量(x=0.05)时, 材料具有最优的热电性能(ZT=0.84@810.0 K), 这一性能约是未掺杂CuInTe2的2倍. 相似文献
257.
Siqi Shi Yuanhao Tang Lixia Cui Peijuan Li Hua Zhang Liquan Chen 《Journal of Physics and Chemistry of Solids》2010,71(5):788-5145
Atomic and electronic structures of CeO2 (1 1 1), (1 1 0) and (1 0 0) surfaces are investigated using the first-principles density functional theory taking into account the on-site Coulomb interaction. Both the stoichiometric and O-deficient surfaces are examined in order to clarify the overall features. The CeO2 (1 1 1) is found to be the most stable surface, followed by the (1 1 0) and (1 0 0) surfaces, consistent with experimental observations. Three surfaces exhibit different features of relaxation. Large relaxations are found at the (1 1 0) and (1 0 0) surfaces, while very small changes are observed at the (1 1 1) surface. It is found that the O-vacancy occurs more readily at the (1 1 0) surface as compared with the (1 1 1) surface. Furthermore, the formation energies of the O-vacancy in the surfaces are lower than that in the bulk. The energetically favorable O-vacancy locates in the second O-atomic layer for the (1 1 1) while at the surface layer for the (1 1 0). The excess electrons left with the removal of the O atom are distributed in the first two layers with certain (a considerable) fraction filling the Ce-4f states. 相似文献
258.
Peng-Xiang Li Meng-Wu Zhang You-Min Xi Wen-Tian Cui 《Computational & Mathematical Organization Theory》2009,15(3):169-190
This paper discusses chain of command networks that are most likely to exhibit the scale-free (SF) property in organizational
networks, explaining why organizational networks do not show SF distributions. We propose an evolving hierarchical tree network
model without explicit preferential attachment. The model simulates several kinds of chain of command networks with the span
of control ranging from extreme homogeneity to extreme heterogeneity. In addition to traditional degree distribution, a new
kind of cumulative-outdegree distribution p(K
cum
=k
cum
) is introduced and discussed that gives a probability that a randomly selected node has exactly k
cum
children nodes. Theoretical analysis and simulation results show that even if the network size is large enough to meet the
demand of large-scale networks, the SF property can emerge only when a hierarchical tree lies in two extreme situations: (1)
the exact same span of control exists at all levels of an organization; (2) the node outdegree (i.e. span of control) distribution
obeys a power-law distribution. The empirical investigations show that real organization networks are between the two extreme
situations. This is why organizational networks in reality do not show an SF degree distribution or SF cumulative-outdegree
distribution. This finding shows that the SF property is the consequence of extreme situations, even though it is very common
in nature and in society. In fact, the SF property is of no value in the study of problems in organizations. 相似文献
259.
Time-gated luminescence detection technique using lanthanide complexes as luminescent probes is a useful and highly sensitive
method. However, the effective application of this technique is limited by the lack of the target-responsive luminescent lanthanide
complexes that can specifically recognize various analytes in aqueous solutions. In this work, a dual-functional ligand that
can form a stable complex with Tb3+ and specifically recognize Hg2+ ions in aqueous solutions, N,N,N
1
,N
1
-{[2,6-bis(3′-aminomethyl-1′-pyrazolyl)-4-[N,N-bis(3″,6″-dithiaoctyl)-aminomethyl]- pyridine]} tetrakis(acetic acid) (BBAPTA), has been designed and synthesized. The luminescence
of its Tb3+ complex is weak, but can be effectively enhanced upon reaction with Hg2+ ions in aqueous solutions. The luminescence response investigations of BBAPTA-Tb3+ to various metal ions indicate that the complex has a good luminescence sensing selectivity for Hg2+ ions, but not for other metal ions. Thus a highly sensitive time-gated luminescence detection method for Hg2+ ions was developed by using BBAPTA-Tb3+ as a luminescent probe. The dose-dependent luminescence enhancement of the probe shows a good linearity with a detection
limit of 17 nM for Hg2+ ions. These results demonstrated the efficacy and advantages of the new Tb3+ complex-based luminescence probe for the sensitive and selective detection of Hg2+ ions. 相似文献
260.
By using elementary symmetric functions, this paper presents an explicit representation for the Lagrangian numerical differentiation formula as well as the error estimate for local approximation. And we also point out that the numerical differentiation formula constructed by Li [J.P. Li, General explicit difference formulas for numerical differentiation, J. Comput. Appl. Math. 183 (2005) 29-52] is actually a special case of the Lagrangian numerical differentiation formula to approximate the values of the derivatives at the nodes. 相似文献