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41.
Multichannel and omnidirectional transmission can be realized in one-dimensional periodic metamaterial layers, where double-negative materials and single-negative materials are alternately stacked. The proposed structures can produce as many resonance transmission modes as desired by adjusting the number of the periods. Such transmission modes with perfect transmission are robust against incident angles and polarizations. The frequencies and frequency intervals of these modes can be tuned by changing the thicknesses of the metamaterial layers. Composite right/left-handed transmission lines with lumped elements (capacitors and inductors) were used to verify the characteristics of the considered system. Our findings provide an efficient way to select useful multiple channel signals from all directions, and it is useful in optoelectronic device applications. 相似文献
42.
Xe‐Qin Ran Ji‐Kang Feng Wai‐Yeung Wong Ai‐Min Ren Guijiang Zhou Chia‐Chung Sun 《Journal of Physical Organic Chemistry》2012,25(12):1351-1358
A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2‐phenylpyridine) with various main group moieties in [Ir(ppy‐X)2(acac)] (X = POPh2, SO2Ph, GePh3, OPh, OPh(CF3)3, SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time‐dependent density functional theory (TD‐DFT) and Hartree–Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD‐DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground‐ and excited‐state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light‐emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron‐injection and electron‐transporting features. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
43.
In this paper, we consider approximation algorithms for optimizing a generic multi-variate homogeneous polynomial function,
subject to homogeneous quadratic constraints. Such optimization models have wide applications, e.g., in signal processing,
magnetic resonance imaging (MRI), data training, approximation theory, and portfolio selection. Since polynomial functions
are non-convex, the problems under consideration are all NP-hard in general. In this paper we shall focus on polynomial-time
approximation algorithms. In particular, we first study optimization of a multi-linear tensor function over the Cartesian
product of spheres. We shall propose approximation algorithms for such problem and derive worst-case performance ratios, which
are shown to be dependent only on the dimensions of the model. The methods are then extended to optimize a generic multi-variate
homogeneous polynomial function with spherical constraint. Likewise, approximation algorithms are proposed with provable approximation
performance ratios. Furthermore, the constraint set is relaxed to be an intersection of co-centered ellipsoids; namely, we
consider maximization of a homogeneous polynomial over the intersection of ellipsoids centered at the origin, and propose
polynomial-time approximation algorithms with provable worst-case performance ratios. Numerical results are reported, illustrating
the effectiveness of the approximation algorithms studied. 相似文献
44.
Shaoxiang Chen Guillermo Gallego Michael Z.F. Li Bing Lin 《European Journal of Operational Research》2010
In this paper, we study a two-flight model where there are two flights between two cities in a day (e.g., one departs at 9:00 am and another at 11:00 am) and booking requests in each fare class arrive according to a random process. There are three types of booking requests: the first and second types are respectively for the first and the second flight only; whereas the third type is flexible and willing to take either flight. Upon receiving a booking request, the airline has to decide whether to accept it, and in case a third type is accepted, which flight to accommodate it. This paper uncovers the structure of optimal booking policies through four monotone switching curves. We also present an extension of the basic model to multiple-flight case. Finally, a numerical example is used to illustrate the derivation and the dynamics of the optimal booking policies. 相似文献
45.
In this paper,we are interested in HSS preconditioners for saddle point lin- ear systems with a nonzero(2,2)-th block.We study an approximation of the spectra of HSS preconditioned matrices and use these results to illustrate and explain the spectra obtained from numerical examples,where the previous spectral analysis of HSS precon- ditioned matrices does not cover. 相似文献
46.
The notions of exhausters were introduced in (Demyanov, Exhauster of a positively homogeneous function, Optimization 45, 13–29
(1999)). These dual tools (upper and lower exhausters) can be employed to describe optimality conditions and to find directions
of steepest ascent and descent for a very wide range of nonsmooth functions. What is also important, exhausters enjoy a very
good calculus (in the form of equalities). In the present paper we review the constrained and unconstrained optimality conditions
in terms of exhausters, introduce necessary and sufficient conditions for the Lipschitzivity and Quasidifferentiability, and
also present some new results on relationships between exhausters and other nonsmooth tools (such as the Clarke, Michel-Penot
and Fréchet subdifferentials). 相似文献
47.
ZHONG Wei-Rong SHAO Yuan-Zhi BIE Meng-Jie HE Zhen-Hui 《理论物理通讯》2008,50(9):793-796
Understanding the cause of the synchronization of population evolution is an important issue for ecological improvement. Here we present a Lotka-Volterra-type model driven by two correlated environmental noises and show, via theoretical analysis and direct simulation, that noise correlation can induce a synchronization of the mutualists. The time series of mutual species exhibit a chaotic-like fluctuation, which is independent of the noise correlation, however, the chaotic fluctuation of mutual species ratio decreases with the noise correlation. A quantitative parameter defined for characterizing chaotic fluctuation provides a good approach to measure when the complete synchronization happens. 相似文献
48.
The Grammian determinant solutions of the non-isospectral modified Kadomtsev-Petviashvili (mKP) equation are presented. Moreover, a new non-isospectral coupled system is constructed by using the Pfaffianization procedure. Furthermore, Gramm-type Pfaffian solutions of the non-isospectral coupled system are obtained. 相似文献
49.
Wing Hong Chan Albert Wai Ming LeeYiu Sing Lam Jian Zhong Lu 《Microchemical Journal》2002,72(2):201-207
A fast responsive sodium ion selective fluorescent optode membrane mounted on an optical fiber has been developed. The sensing membrane contained fluorescein octadecyl ether octadecyl ester (FODEE), potassium tetrakis(4-chlorophenyl) borate (KTpClPB) and a calix[4]arene tetraester in a plasticized poly(vinyl chloride) (PVC) matrix. It exhibited a reversible response to Na+ in 0.5 mol/l of HCl in the concentration range of 1.0×10−6 to 0.1 mol/l. The selectivity, response time, reproducibility and lifetime of the optode membrane were discussed. The practical use of this sensor was demonstrated by real sample analysis in complex sample solutions such as beverage and urine samples. 相似文献
50.
A new procedure called ‘source generation’ is applied to the pfaffianized KP equation. As a result, the pfaffianized-KP equation with self-consistent sources (ESCS) is obtained. This coupled system cannot only be reduced to the pfaffianized KP equation, but also reduced to the KP equation with self-consistent sources (KPESCS). So the pfaffianized-KP ESCS can be viewed as a pfaffian version of the KPESCS, which indicates the commutativity of the ‘source generation’ procedure and pfaffianization. 相似文献