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891.
892.
893.
Joel Brewster Lewis 《Journal of Combinatorial Theory, Series A》2011,118(4):1436-1450
We define a class Ln,k of permutations that generalizes alternating (up-down) permutations and give bijective proofs of certain pattern-avoidance results for this class. As a special case of our results, we give bijections between the set A2n(1234) of alternating permutations of length 2n with no four-term increasing subsequence and standard Young tableaux of shape 〈n3〉, and between the set A2n+1(1234) and standard Young tableaux of shape 〈3n−1,2,1〉. This represents the first enumeration of alternating permutations avoiding a pattern of length four. We also extend previous work on doubly-alternating permutations (alternating permutations whose inverses are alternating) to our more general context.The set Ln,k may be viewed as the set of reading words of the standard Young tableaux of a certain skew shape. In the last section of the paper, we expand our study to consider pattern avoidance in the reading words of standard Young tableaux of any skew shape. We show bijectively that the number of standard Young tableaux of shape λ/μ whose reading words avoid 213 is a natural μ-analogue of the Catalan numbers (and in particular does not depend on λ, up to a simple technical condition), and that there are similar results for the patterns 132, 231 and 312. 相似文献
894.
Stephen M. Lipson Ashley J. Cadby Paul A. Lane Diarmuid F. O’Brien Anna Drury Donald D. C. Bradley Werner J. Blau 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):151-158
Summary. We have investigated the effect of film preparation procedures on the photoluminescence efficiency of the luminescent co-polymer
poly-(m-phenylene-co-2,5-dioctoxy-p-phenylenevinylene) (PmPV). The photoluminescence efficiency of PmPV films improved by up to 50% when the solution was degassed by bubbling argon gas through it prior to spin casting in an inert
atmosphere and baking under vacuum. Photoinduced absorption and doping measurements show that this preparation method reduces
polaron photogeneration, which reduces the photoluminescence (PL) yield through exciton quenching and excited state absorption.
It is proposed that this sample preparation method increases interchain separation, reducing the formation of polarons and
non-radiative quenching routes, thus resulting in increased PL efficiency.
Received June 23, 2000. Accepted (revised) August 3, 2000 相似文献
895.
896.
This work investigates different hemp surface modifications (mercerization, maleated polyethylene (MAPE) addition in solution or in melt blending) to improve the properties of linear medium density polyethylene (LMDPE). From the composites produced, a complete morphological and tensile characterization was performed for a fixed hemp content (30% wt.). The morphological analysis showed that both the direct (melt blending) and solution modifications were able to significantly improve the composites interface quality and therefore the tensile properties (151% increase in modulus and 36% increase in strength over the neat matrix) within the range of conditions tested. 相似文献
897.
Wenden Charles J.A. Soriano Flávio A. Falcão Nascimento J.H. Rodrigues 《Journal of Differential Equations》2013
In this paper we consider a vibrating system of Bresse type, in a one-dimensional bounded domain with nonlinear localized damping mechanisms acting in all the three wave equations. We obtain some rates of decay for its solutions with no restrictions around the coefficients as well as the condition of equal-speed wave propagation. A new result concerning an internal observability for the conservative system was also proved in order to reach the asymptotics above. 相似文献
898.
We consider Schrödinger operators with periodic magnetic field having zero flux through a fundamental cell of the period lattice. We show that, for a generic small magnetic field and a generic small Fermi energy, the corresponding Fermi surface is convex and not invariant under inversion in any point. 相似文献
899.
900.