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891.
It is known that shape preserving approximation has lower rates than unconstrained approximation. This is especially true for copositive and intertwining approximations. ForfLp, 1p<∞, the former only has rateω(f, n−1)p, and the latter cannot even be bounded byC fp. In this paper, we discuss various ways to relax the restrictions in these approximations and conclude that the most sensible way is the so-calledalmostcopositive/intertwining approximation in which one relaxes the restriction on the approximants in a neighborhood of radiusΔn(yj) of each sign changeyj. 相似文献
892.
Ravi P. Agarwal X.H. Tang Z.C. Wang 《Journal of Mathematical Analysis and Applications》1999,240(2):1
In this paper, we shall consider a class of neutral differential equations of the form
where τ (0, ∞), σ [0, ∞), Q(t) C([t0, ∞), R + ), r(t) C([t0, ∞), (0, ∞)) with r(t) nondecreasing on [t0 − τ, ∞). We shall show that all positive solutions of ( * ) can be classified into four types, A, B, C, and D, and we shall obtain sufficient and necessary conditions for the existence of A-type, B-type, and D-type positive solutions of ( * ), respectively. A sufficient condition for the existence of C-type positive solutions of ( * ) is also given. Finally, we shall offer a sharp oscillation result for all solutions of ( * ). Our results generalize and improve those established in B. Yang and B. G. Zhang (Funkcial. Ekvac.39 (1996), 347–362). 相似文献
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893.
894.
895.
We consider the design criteria of a chemical mixing device based on a chaotic flow, with an emphasis on the steady-state devices. The merit of a reactor, defined as the Q-factor, is related to the physical dimension of the device and the molecular diffusivity of the reactants through the local Lyapunov exponents of the flow. The local Lyapunov exponent can be calculated for any given flow field and it can also be measured in experimental situations. Easy-to-compute formulae are provided to estimate the Q-factor given either the exact spatial dependence of the local Lyapunov exponent or its probability distribution function. The requirements for optimization are made precise in the context of local Lyapunov exponents. (c) 1999 American Institute of Physics. 相似文献
896.
Wang H.-D. Li Y.-T. Ma P.-H. Zeng X.-C. 《Journal of Thermal Analysis and Calorimetry》2002,69(2):575-581
A complex of N,N'-ethylenebis(salicylideneiminato)diaquochromium(III) nitrate, [Cr(salen)(H2O)2]NO3 was characterized and its decomposition mechanism was studied by TG. The IR spectrum and X-ray analysis were examined for the complex. The non-isothermal kinetic data were analyzed by means of the Achar method and the Coats—Redfern method. The most probable kinetic model function was suggested by comparison of the kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
897.
898.
899.
Purification and magnetic properties of carbon nanotubes 总被引:7,自引:0,他引:7
S. Bandow S. Asaka X. Zhao Y. Ando 《Applied Physics A: Materials Science & Processing》1998,67(1):23-27
Received: 5 January 1998 相似文献
900.
用分子束外延方法在GaAs(100)衬底上生长了Zn1-xMgxSySe1-y四元半导体合金薄膜.用X-射线衍射方法确定了外延层的结构和晶格常数.测量了这些样品在平行和垂直两种不同几何配置下的拉曼散射光谱并对其特性做了研究。从实验上观察到了四类不同的晶格振动模:类ZnSe的TO和LO模以及类ZnS和类MgS的LO模,实验发现:在ZnSe和ZnSSe中加入Mg使得类ZnSe的TO和LO模的振动频率下降;同时,也使类ZnS模的频率随S的增加率减小。 相似文献