Thin-thick coexistence behavior of 8CB liquid crystalline films on silicon

The wetting behavior of thin films of 4'-n-octyl-4-cyanobiphenyl (8CB) on Si is investigated via optical and x-ray reflectivity measurement. An experimental phase diagram is obtained showing a broad thick-thin coexistence region spanning the bulk isotropic-to-nematic ($T_{IN}$) and the nematic-to-smectic-A ($T_{NA}$) temperatures. For Si surfaces with coverages between 47 and $72\pm3$ nm, reentrant wetting behavior is observed twice as we increase the temperature, with separate coexistence behaviors near $T_{IN}$ and $T_{NA}$. For coverages less than 47 nm, however, the two coexistence behaviors merge into a single coexistence region. The observed thin-thick coexistence near the second-order NA transition is not anticipated by any previous theory or experiment. Nevertheless, the behavior of the thin and thick phases within the coexistence regions is consistent with this being an equilibrium phenomenon.Comment: 4 pages, 3 figure

Minimal mechanisms for vegetation patterns in semiarid regions

The minimal ecological requirements for formation of regular vegetation patterns in semiarid systems have been recently questioned. Against the general belief that a combination of facilitative and competitive interactions is necessary, recent theoretical studies suggest that, under broad conditions, nonlocal competition among plants alone may induce patterns. In this paper, we review results along this line, presenting a series of models that yield spatial patterns when finite-range competition is the only driving force. A preliminary derivation of this type of model from a more detailed one that considers water-biomass dynamics is also presented. Keywords: Vegetation patterns, nonlocal interactionsComment: 8 pages, 4 figure

Preface "Nonlinear processes in oceanic and atmospheric flows"

Nonlinear phenomena are essential ingredients in many oceanic and atmospheric processes, and successful understanding of them benefits from multidisciplinary collaboration between oceanographers, meteorologists, physicists and mathematicians. The present Special Issue on ``Nonlinear Processes in Oceanic and Atmospheric Flows'' contains selected contributions from attendants to the workshop which, in the above spirit, was held in Castro Urdiales, Spain, in July 2008. Here we summarize the Special Issue contributions, which include papers on the characterization of ocean transport in the Lagrangian and in the Eulerian frameworks, generation and variability of jets and waves, interactions of fluid flow with plankton dynamics or heavy drops, scaling in meteorological fields, and statistical properties of El Ni\~no Southern Oscillation.Comment: This is the introductory article to a Special Issue on "Nonlinear Processes in Oceanic and Atmospheric Flows'', published in the journal Nonlinear Processes in Geophysics, where the different contributions are summarized. The Special Issue itself is freely available from http://www.nonlin-processes-geophys.net/special_issue103.htm

LYING ABOUT WHAT YOU KNOW OR ABOUT WHAT YOU DO?

We compare communication about private information to communication about actions in a one-shot 2-person public good game with private information. The informed player, who knows the exact return from contributing and whose contribution is unobserved, can send a message about the return or her contribution. Theoretically, messages can elicit the uninformed player's contribution, and allow the informed player to free-ride. The exact language used is not expected to matter. Experimentally, however, we find that free-ride depends on the language: the informed player free-rides less-and thereby lies less frequently-when she talks about her contribution than when she talks about the return. Further experimental evidence indicates that it is the promise component in messages about the contribution that leads to less free-ride and less lying. © 2013 by the European Economic Association

Numerical Study of a Lyapunov Functional for the Complex Ginzburg-Landau Equation

We numerically study in the one-dimensional case the validity of the functional calculated by Graham and coworkers as a Lyapunov potential for the Complex Ginzburg-Landau equation. In non-chaotic regions of parameter space the functional decreases monotonically in time towards the plane wave attractors, as expected for a Lyapunov functional, provided that no phase singularities are encountered. In the phase turbulence region the potential relaxes towards a value characteristic of the phase turbulent attractor, and the dynamics there approximately preserves a constant value. There are however very small but systematic deviations from the theoretical predictions, that increase when going deeper in the phase turbulence region. In more disordered chaotic regimes characterized by the presence of phase singularities the functional is ill-defined and then not a correct Lyapunov potential.Comment: 20 pages,LaTeX, Postcript version with figures included available at http://formentor.uib.es/~montagne/textos/nep

Losses for microwave transmission in metamaterials for producing left-handed materials: The strip wires

This paper shows that the effective dielectric permitivity for the metamaterials used so far to obtain left-handed materials, with strip wires 0.003cm thick, is dominated by the imaginary part at 10.6- 11.5 GHz frequencies, where the band pass filter is, and therefore there is not propagation and the wave is inhomogeneous inside the medium. This is shown from finite-differences time-domain calculations using the real permitivity values for the Cu wires. For thicker wires the losses are reduced and the negative part of the permitivity dominates. As the thickness of the wires is critical for the realization of a good transparent left- handed material we propose that the strip wires should have thickness of 0.07-0.1cm and the split ring resonators 0.015-0.03c

The ages of very cool hydrogen-rich white dwarfs

The evolution of white dwarfs is essentially a cooling process that depends primarily on the energy stored in their degenerate cores and on the transparency of their envelopes. In this paper we compute accurate cooling sequences for carbon-oxygen white dwarfs with hydrogen dominated atmospheres for the full range of masses of interest. For this purpose we use the most accurate available physical inputs for both the equation of state and opacities of the envelope and for the thermodynamic quantities of the degenerate core. We also investigate the role of the latent heat in the computed cooling sequences. We present separately cooling sequences in which the effects of phase separation of the carbon-oxygen binary mixture upon crystallization have been neglected, and the delay introduced in the cooling times when this mechanism is properly taken into account, in order to compare our results with other published cooling sequences which do not include a treatment of this phenomenon. We find that the cooling ages of very cool white dwarfs with pure hydrogen atmospheres have been systematically underestimated by roughly 1.5 Gyr at log(L/Lo)=-4.5 for an otherwise typical 0.6 Mo white dwarf, when phase separation is neglected. If phase separation of the binary mixture is included then the cooling ages are further increased by roughly 10%. Cooling tracks and cooling isochrones in several color-magnitude diagrams are presented as well.Comment: 8 Pages; ApJ, accepted for publicatio