441,153 research outputs found

    Some new less conservative criteria for impulsive synchronization of a hyperchaotic Lorenz system based on small impulsive signals

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    In this Letter the issue of impulsive Synchronization of a hyperchaotic Lorenz system is developed. We propose an impulsive synchronization scheme of the hyperchaotic Lorenz system including chaotic systems. Some new and sufficient conditions on varying impulsive distances are established in order to guarantee the synchronizability of the systems using the synchronization method. In particular, some simple conditions are derived for synchronizing the systems by equal impulsive distances. The boundaries of the stable regions are also estimated. Simulation results show the proposed synchronization method to be effective. (C) 2009 Elsevier Ltd. All rights reserved

    The B\to D_s^{(*)}\eta^{(\prime)} decays in the perturbative QCD

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    In this paper, we calculate the branching ratios for B+Ds+η,B+Ds+ηB^+\to D_s^+\eta, B^+\to D_s^+\eta^{\prime}, B+Ds+ηB^+\to D_s^{*+}\eta and B+Ds+η B^+\to D_s^{*+}\eta^{\prime} decays by employing the perturbative QCD (pQCD) factorization approach. Under the two kinds of ηη\eta-\eta^{\prime} mixing schemes, the quark-flavor mixing scheme and the singlet-octet mixing scheme, we find that the calculated branching ratios are consistent with the currently available experimental upper limits. We also considered the so called "fDsf_{D_s} puzzle", by using two groups of parameters about the Ds()D^{(*)}_s meson decay constants, that is fDs=241f_{D_s}=241 MeV, fDs=272f_{D^*_s}=272 MeV and fDs=274f_{D_s}=274 MeV, fDs=312f_{D^*_s}=312 MeV, to calculate the branching ratios for the considered decays. We find that the results change 30%30\% by using these two different groups of paramters.Comment: 12 pages, 1 figure. Typos removed, minor correction

    Transplanted olfactory ensheathing cells promote regeneration of cut adult rat optic nerve axons

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    Transplantation of olfactory ensheathing cells into spinal cord lesions promotes regeneration of cut axons into terminal fields and functional recovery. This repair involves the formation of a peripheral nerve-like bridge in which perineurial-like fibroblasts are organized into a longitudinal stack of parallel tubular channels, some of which contain regenerating axons enwrapped by Schwann-like olfactory ensheathing cells. The present study examines whether cut retinal ganglion cell axons will also respond to these cells, and if so, whether they form the same type of arrangement. In adult rats, the optic nerve was completely severed behind the optic disc, and a matrix containing cultured olfactory ensheathing cells was inserted between the proximal and distal stumps. After 6 months, the transplanted cells had migrated for up to 10 mm into the distal stump. Anterograde labeling with cholera toxin B showed that cut retinal ganglion cell axons had regenerated through the transplants, entered the distal stump, and elongated for 10 mm together with the transplanted cells. Electron microscopy showed that a peripheral nerve-like tissue had been formed, similar to that seen in the spinal cord transplants. However, in contrast to the spinal cord, the axons did not reach the terminal fields, but terminated in large vesicle-filled expansions beyond which the distal optic nerve stump was reduced to a densely interwoven mass of astrocytic processes