93,285 research outputs found
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 () and the nematic-to-smectic-A
() temperatures. For Si surfaces with coverages between 47 and
nm, reentrant wetting behavior is observed twice as we increase the
temperature, with separate coexistence behaviors near and .
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
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