Transition from hexagons to optical turbulence

4 pages, 3 figures.-- PACS nrs.: 42.65.Sf, 47.20.Ky, 47.54.+r, 89.75.Kd.We characterize the different dynamical regimes and bifurcations in the transition from a stationary hexagonal pattern to optical turbulence. In order to characterize the bifurcations we perform linear stability analysis of stationary hexagonal patterns and Floquet analysis of oscillating hexagons. The interplay between space and time leads to a series of bifurcations showing spatial-period multiplying and quasiperiodicity.The authors acknowledge financial support from the MCyT (Spain, Project Nos. PB97-0141-C02-02, BFM2000-1108, and BFM2001-0341-C02-02).Peer reviewe

Investigation of the influence of active dopant and co-dopant on the luminescent properties of the phosphor based on calcium aluminate

In the present study the luminescent properties of calcium aluminate activated by Eu3+ and Dy3+ions are investigated. The phosphor on the basis of calcium aluminate was obtained via citric-nitrate sol gel method using a microwave radiation. It was determined by X-ray diffraction method and by electron microprobe analysis that rare earth elements (REE) ions incorporate into lattice of calcium aluminate and don't form own phases. Luminescent properties of calcium aluminate activated by REE ions were studied by spectrofluorimeter. Luminescent spectrum of Ca0,95Eu0,05Al2O4 contains five bands groups of emission between 580-710 nm which correspond to 5D0 - 7Fj transitions of Eu3+(λ=254 nm). Present maxima lie in the red area of the spectrum and determine the obtainment of red glow phosphor. Excitation spectrum of Ca0,95Dy0,05Al2O4 contains two bands with maxima at 240 and 380 nm. Exciting the sample by the far ultraviolet (240 nm), two bands with maxima at 420 and 490 nm conditioning a blue glow of phosphor under overlapping of violet (4G11/2 - 6H15/2 transition of Dy3+) and blue-green (4F9/2 - 6H15/2 transition of Dy3+) radiations, respectively, were observed. Exciting the sample by the near ultraviolet (380 nm), one intense band at 420 nm and bright violet glowing were observed. Emission spectrum of the phosphor obtaining by co-activation of calcium aluminate by two test REE ions is identical to the emission spectrum of calcium aluminate activated by Dy3+ ions. Transitions of Eu3+ in this case are not observed. Nevertheless, the increase of band intensity conditioning more bright violet glowing was observed

Arbuscular Mycorrhizal Fungal Networks Vary throughout the Growing Season and between Successional Stages

To date, few analyses of mutualistic networks have investigated successional or seasonal dynamics. Combining interaction data from multiple time points likely creates an inaccurate picture of the structure of networks (because these networks are aggregated across time), which may negatively influence their application in ecosystem assessments and conservation. Using a replicated bipartite mutualistic network of arbuscular mycorrhizal (AM) fungal-plant associations, detected using large sample numbers of plants and AM fungi identified through molecular techniques, we test whether the properties of the network are temporally dynamic either between different successional stages or within the growing season. These questions have never been directly tested in the AM fungal-plant mutualism or the vast majority of other mutualisms. We demonstrate the following results: First, our examination of two different successional stages (young and old forest) demonstrated that succession increases the proportion of specialists within the community and decreases the number of interactions. Second, AM fungal-plant mutualism structure changed throughout the growing season as the number of links between partners increased. Third, we observed shifts in associations between AM fungal and plant species throughout the growing season, potentially reflecting changes in biotic and abiotic conditions. Thus, this analysis opens up two entirely new areas of research: 1) identifying what influences changes in plant-AM fungal associations in these networks, and 2) what aspects of temporal variation and succession are of general importance in structuring bipartite networks and plant-AM fungal communities