Du chaos deterministe au bruit dans des systèmes optiques avec retard

An optical device with a variational structure driven by a delayed feedback, F(x(t — d)) = sinAx(t — d) is shown to display high dimensional chaos with dimension increasing linearly with two parameters, the delay d and the feedback frequency A . For large delay d and large frequency A, the system is shown to display Gaussian-Markovian statistics like a system driven b y a white noise. Decreasing the frequency A leads to effects very similar to those of a colored noise, and decreasing the dela y leads to quite special phenomena like phase transitions, giving rise to new peaks in the probability distribution . An analytica l description using the tools of stochastic equations agrees with the numerical results .Un système optique possédant une structure variationnelle, et forcé par une rétro-injection retardée, F(x(t - d)) = sin Ax(t- d), émet un signal lumineux chaotique dont la dimension croit linéairement avec deux paramètres, le retard d et la fréquence A. Pour de grandes valeurs du retard et de la fréquence, le signal émis a une statistique Gaussienne et Markovienne, comme la solution d'une équation de Langevin forcée par un bruit blanc. Lorsqu'on diminue la valeur du paramètre A, la statistique est modifiée comme celle d'une équation de Langevin forcée par un bruit coloré. Lorsqu'on diminue le retard, de nouveaux pics apparaissent dans la distribution de probabilité, comme dans les transitions de phase induites par du bruit coloré. Une description analytique utilisant les méthodes des signaux aléatoires permet d'interpréter les résultats numériques

INP1 involvement in pollen aperture formation is evolutionarily conserved and may require species-specific partners

Pollen wall exine is usually deposited non-uniformly on the pollen surface, with areas of low exine deposition corresponding to pollen apertures. Little is known about how apertures form, with the novel Arabidopsis INP1 (INAPERTURATE POLLEN1) protein currently being the only identified aperture factor. In developing pollen, INP1 localizes to three plasma membrane domains and underlies formation of three apertures. Although INP1 homologs are found across angiosperms, they lack strong sequence conservation. Thus, it has been unclear whether they also act as aperture factors and whether their sequence divergence contributes to interspecies differences in aperture patterns. To explore the functional conservation of INP1 homologs, we used mutant analysis in maize and tested whether homologs from several other species could function in Arabidopsis. Our data suggest that the INP1 involvement in aperture formation is evolutionarily conserved, despite the significant divergence of INP1 sequences and aperture patterns, but that additional species-specific factors are likely to be required to guide INP1 and to provide information for aperture patterning. To determine the regions in INP1 necessary for its localization and function, we used fragment fusions, domain swaps, and interspecific protein chimeras. We demonstrate that the central portion of the protein is particularly important for mediating the species-specific functionality.Funding was provided to AAD by the US National Science Foundation (MCB-1517511) and to VNSS by the Spanish Ministry of Economy and Competitiveness (CGL2015-70290-P). PL was supported by the China Scholarship Council. SB-MS was supported by the University of Granada, Spain (grant Cei BioTic). We thank the Arabidopsis Biological Resource Center (OSU) and the Maize Genetics Cooperation Stock Center (USDA/ ARS) for seed stocks, Priscila Rodriguez Garcia (OSU) for help with characterizing Arabidopsis–tomato INP1 chimeras, and Jay Hollick (OSU) for advice on all things maize

Chaos and the Quantum Phase Transition in the Dicke Model

We investigate the quantum chaotic properties of the Dicke Hamiltonian; a quantum-optical model which describes a single-mode bosonic field interacting with an ensemble of $N$ two-level atoms. This model exhibits a zero-temperature quantum phase transition in the N \go \infty limit, which we describe exactly in an effective Hamiltonian approach. We then numerically investigate the system at finite $N$ and, by analysing the level statistics, we demonstrate that the system undergoes a transition from quasi-integrability to quantum chaotic, and that this transition is caused by the precursors of the quantum phase-transition. Our considerations of the wavefunction indicate that this is connected with a delocalisation of the system and the emergence of macroscopic coherence. We also derive a semi-classical Dicke model, which exhibits analogues of all the important features of the quantum model, such as the phase transition and the concurrent onset of chaos.Comment: 51 pages, 15 figures, late

Equatorial aperture pattern in monocots: Same definition rules as in eudicots? The example of two species of Pontederiaceae

International audiencePontederia cordata L. and Eichhornia paniculata (Spreng.) Solms (Pontederiaceae, monocots) produce disulculate pollen grains. The formation of intersporal callose walls was followed in these two species by staining callose during male meiosis. A new type of cytokinesis that ends with the formation of conspicuous callose knobs at future aperture sites was observed. This observation indicates that the formation of the disulculate pattern is linked to cytokinesis. Thus, equatorial aperture patterns of monocots and aperture patterns of eudicots appear to be defined by similar mechanisms

Links between early pollen development and aperture pattern in monocots

International audienc

SPATIOTEMPORAL INSTABILITIES IN A SATURABLE HOMOGENEOUSLY BROADENED RING CAVITY

L'influence des effets transverses dus à la diffraction libre sur la dynamique nonlinéaire d'une cavité haute finesse est étudiée dans différentes configurations optiques. La nature des deux premières bifurcations semble être très robuste mais le seuil d'apparition du chaos est fortement diminué.The influence of transverse effects caused by free-space propagation on the nonlinear dynamics of a high finesse ring cavity is investigated for different optical configurations. The nature of the first two Hopf bifurcations is found to be robust against significative transverse effects but the threshold for chaos is lowered with respect to the plane wave case

Multiple Developmental Pathways Leading to a Single Morph: Monosulcate Pollen (Examples From the Asparagales)

International audienc