Multifractal analysis and randomness of almost periodic forced two-level systems

Numerical results of multifractal analysis of the (quantum) dynamics of forced two-level systems under some almost periodic time dependence are reported. The aims are to check the presence of multifractal characteristics of these systems, and also to inspect if different degrees of aperiodicities in the force are transferred to the system dynamics. Although the dynamics present signatures of the randomness of the perturbation, it does not follow strictly its autocorrelation type. The wavelet transform is the tool used to carry out the multifractal analysis.     

Dynamics of non-Newtonian droplets

We study the impact and subsequent retraction dynamics of aqueous liquid droplets upon high-speed impact on hydrophobic surfaces. Often a spectacular "rebound" of the droplet can be observed: after the impact and expansion, the drop retracts rapidly, leading to ejection of part of the material from the surface. We show how non-Newtonian flow properties can be used to slow down the retraction sufficiently to completely inhibit rebound. The slowing down is due to non-Newtonian normal stresses generated near the moving contact line of the droplet. We provide a quantitative theory for the slowing down, and show that the non-Newtonian effects profoundly change the contact line dynamics.     

X-ray induced luminescence of LiNbO3

X-ray induced luminescence has been observed in pure as well as Ni, Cu and Eu-doped LiNbO₃. The emission spectrum for both, pure congruently grown and doped samples, consists of a well-defined band peaked at ≈425 nm. The shape and height of this band is also independent of the amount of radiation-induced coloring in the crystal. It has been concluded that the emission corresponds to an intrinsic and bulk recombination process.     

Luminescence spectra of lead-doped NaCl,KCl and KBr

The luminescence spectra of lead-doped NaCl, KCl and KBr have been systematically investigated. Special attention has been paid to the effects of concentration and thermal history of the crystals. In the three systems, the emission spectra for A and C band excitation consists mainly of two well-defined emission bands whose energy separation is ～0.7 eV. It has been concluded that none of the bands can be attributed to a single type of lead center but are both typical of Pb²⁺ luminescence. In fact, their behavior can be correlated with that found for most monovalent ions and interpreted in a similar way. The excitation spectra for the two emissions have shown that the A-band is complex. One of the components appearing in very low doped and quenched samples is ascribed to dipoles, whereas additional side bands are attributed to complexes or small aggregates involving Pb²⁺ ions.     

Adaptation to synchronization in phase-oscillator networks

We introduce an adaptation algorithm by which an ensemble of coupled oscillators with attractive and repulsive interactions is induced to adopt a prescribed synchronized state. While the performance of adaptation is controlled by measuring a macroscopic quantity, which characterizes the achieved degree of synchronization, adaptive changes are introduced at the microscopic level of the interaction network, by modifying the configuration of repulsive interactions. This scheme emulates the distinct levels of selection and mutation in biological evolution and learning.     

Lifetime of thermally fixed holograms in LiNbO3 crystals doped with Mg and Fe

Decays of thermally fixed holograms in LiNbO₃ crystals doped with 5.5 mol. % of Mg and 0.1 mol. % of Fe were measured at different temperatures. The analysis showed that the time decay is a thermally activated single process. The thermal activation energy depends on the Mg impurity and hydrogen concentration. Samples with moderate hydrogen concentration show an activation energy of 1.16 eV. Extrapolated room temperature hologram lifetimes as long as 540 years were determined. Samples with large amount of hydrogen impurity showed a lower activation energy and also lower room temperature lifetime. PACS 42.40.Eq; 42.40.Ln; 42.70.Nq