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Chaotic states induced by resetting process in Izhikevich neuron model

100%

Nobukawa S. , Nishimura H. , Yamanishi T. , Liu J.-Q.

tom Vol. 5, No. 2

109--119

Several hybrid neuron models, which combine continuous spike-generation mechanisms and discontinuous resetting process after spiking, have been proposed as a simple transition scheme for membrane potential between spike and hyperpolarization. As one of the hybrid spiking neuron models, Izhikevich neuron model can reproduce major spike patterns observed in the cerebral cortex only by tuning a few parameters and also exhibit chaotic states in specific conditions. However, there are a few studies concerning the chaotic states over a large range of parameters due to the difficulty of dealing with the state dependent jump on the resetting process in this model. In this study, we examine the dependence of the system behavior on the resetting parameters by using Lyapunov exponent with saltation matrix and Poincar´e section methods, and classify the routes to chaos.

Molecular and morphological evidence for natural hybridization between Primula secundiflora Franchet and P. poissonii Franchet [Primulaceae]

75%

Zhu X. F. , Li Y. , Wu G.-L. , Fang Z.-D. , Li Q.-J. , Liu J.-Q.

2009

tom 51

nr 2

29-36

Natural hybridization occurs commonly in plants and blurs their interspecific delimitation. It is unclear whether spontaneous hybridization occurs in natural populations of Primula in China. In this study we examined natural hybridization between P. secundiflora and P. poissonii based on morphological and molecular analyses of individuals with intermediate morphology. Most morphological characters of these individuals were found to be intermediate between the putative parental species, but plant height and corolla tube length were significantly transgressive. Molecular analyses based on nuclear internal transcribed spacer (ITS) additivity and two types of cloned sequences (each corresponding respectively to one of two parental species) clearly suggested that these individuals result from hybridization between P. secundiflora and P. poissonii. We further used a maternally inherited chloroplast DNA fragment (rpl16 intron) to trace the maternal composition of the hybrids. Among 26 hybrids, ten (two thrums, eight pins) had the P. secundiflora haplotype, while 16 (ten thrums, six pins) possessed the P. poissonii haplotype. These results suggest that both parents served as the mother donors of the hybrids. Reciprocal hybridization between the two species seems to be symmetrical rather than unidirectional