1,409,278 research outputs found
Dissociation of hydrogen molecules on the clean and hydrogen-preadsorbed Be(0001) surface
Using first-principles calculations, we systematically study the potential
energy surfaces and dissociation processes for hydrogen molecules on the clean
and hydrogen-preadsorbed Be(0001) surfaces. It is found that the most
energetically favored dissociation channel for H2 molecules on the clean Be
surface is at the surface top site, with the minimum energy barrier of 0.75 eV.
It is further found that after dissociation, hydrogen atoms do not like to
cluster with each other, as well as to penetrate into subsurface sites. For the
hydrogen-preadsorbed Be(0001) surface, the smallest dissociation energy barrier
for H2 molecules is found to be 0.50 eV, which is smaller than the dissociation
energy barrier on a clean Be(0001) surface. The critical dependence of the
dissociation energy barriers for H2 molecules on their horizontal distances
from the preadsorbed hydrogen atom is revealed. Our studies well describe the
adsorption behaviors of hydrogen on the Be(0001) surface.Comment: 17 pages, 9 figure
Adsorption and diffusion of H2O molecule on the Be(0001) surface: A density-functional theory study
Using first-principles calculations, we systematically study the adsorption
behavior of a single molecular HO on the Be(0001) surface. We find that
the favored molecular adsorption site is the top site with an adsorption energy
of about 0.3 eV, together with the detailed electronic structure analysis,
suggesting a weak binding strength of the HO/Be(0001) surface. The
adsorption interaction is mainly contributed by the overlapping between the
and states of the top-layer Be atom and the molecular orbitals 1
and 3 of HO. The activation energy for HO diffusion on the
surface is about 0.3 eV. Meanwhile, our study indicates that no dissociation
state exists for the HO/Be(0001) surface.Comment: 10 pages, 4 figure
Birhythmicity, Synchronization, and Turbulence in an Oscillatory System with Nonlocal Inertial Coupling
We consider a model where a population of diffusively coupled limit-cycle
oscillators, described by the complex Ginzburg-Landau equation, interacts
nonlocally via an inertial field. For sufficiently high intensity of nonlocal
inertial coupling, the system exhibits birhythmicity with two oscillation modes
at largely different frequencies. Stability of uniform oscillations in the
birhythmic region is analyzed by means of the phase dynamics approximation.
Numerical simulations show that, depending on its parameters, the system has
irregular intermittent regimes with local bursts of synchronization or
desynchronization.Comment: 21 pages, many figures. Paper accepted on Physica
Amplification of MHD waves in swirling astrophysical flows
Recently it was found that helical magnetized flows efficiently amplify
Alfv\'en waves (Rogava et al. 2003, A&A, v.399, p.421). This robust and
manifold nonmodal effect was found to involve regimes of transient algebraic
growth (for purely ejectional flows), and exponential instabilities of both
usual and parametric nature. However the study was made in the incompressible
limit and an important question remained open - whether this amplification is
inherent to swirling MHD flows per se and what is the degree of its dependence
on the incompressibility condition. In this paper, in order to clear up this
important question, we consider full compressible spectrum of MHD modes:
Alfv\'en waves (AW), slow magnetosonic waves (SMW) and fast magnetosonic waves
(FMW). We find that helical flows inseparably blend these waves with each other
and make them unstable, creating the efficient energy transfer from the mean
flow to the waves. The possible role of these instabilities for the onset of
the MHD turbulence, self-heating of the flow and the overall dynamics of
astrophysical flows are discussed.Comment: 8 pages, 9 figures, accepted for publication (18.03.2003) in the
"Astronomy and Astrophysics
Bifurcations in nonlinear models of fluid-conveying pipes supported at both ends
Stationary bifurcations in several nonlinear models of fluid conveying pipes
fixed at both ends are analyzed with the use of Lyapunov-Schmidt reduction and
singularity theory. Influence of gravitational force, curvature and vertical
elastic support on various properties of bifurcating solutions are
investigated. In particular the conditions for occurrence of supercritical and
subcritical bifurcations are presented for the models of Holmes, Thurman and
Mote, and Paidoussis.Comment: to appear in Journal of Fluids and Structures; 6 figure
A method to discern complexity in two-dimensional patterns generated by coupled map lattices
Complex patterns generated by the time evolution of a one-dimensional
digitalized coupled map lattice are quantitatively analyzed. A method for
discerning complexity among the different patterns is implemented. The
quantitative results indicate two zones in parameter space where the dynamics
shows the most complex patterns. These zones are located on the two edges of an
absorbent region where the system displays spatio-temporal intermittency.Comment: 3 pages, 3 figures; some information about the authors:
http://add.unizar.es/public/100_16613/index.htm
Dynamics of elastically strained islands in presence of an anisotropic surface energy
The equilibrium solutions and coarsening dynamics of strained semi-conductor
islands are investigated analytically and numerically. We develop an analytical
model to study the effect of surface energy anisotropy on the dynamics
coarsening of islands. We propose a simple model to explain the effect of this
anisotropy on the coarsening time. We find that the anisotropy slows down the
coarsening. This effect is rationalised using a quasi-analytical description of
the island profile
Argentina
After decades of being a marginal player in the GATT trade negotiations, Argentina decided to participate actively in the Uruguay Round. This chapter measures the imbalance between the concessions given and received and concludes that the value of the first are far more important than the second. I discusss the economic consequence of this imbalance, and the prospects that the outcome of the Doha Round can be more balanced outcome for Argentina.Argentina, GATT, Uruguay Round, Reciprocity, Intellectual Property
Palinología e importancia paleoambiental de la Formación Tunal (Daniano) en su localidad tipo, Quebrada el Chorro (Salta, Argentina).
The palynologic investigation of samples from the Tunal Formation at El Chorro creek (Salta, Argentina) resulted in the recovery of terrestrial assemblages of pollen and spores associated with freshwater algae (Pediastrum spp. and Scenedesmus sp.). Of the 43 species of sporomorphs identified for the Tunal Formation so far, 28 species are cited here for the first time. The spores and pollen indicate a Danian age at the type locality. Sedimentary proxidata including abundant evaporites suggest intervals of at least seasonal arid environmental conditions. In contrast, the palynologic assemblages recovered from the organic rich dark shales indicate the presence of swampy areas and forests surrounding them. The dominance of Verrustephanoporites simplex Leidelmeyer (corresponding to the modern Phyllostylon, Ulmaceae) indicates abundant seasonal rainfalls, warm humid conditions and subtropical climate.La investigación palinológica de muestras extraídas de la Formación Tunal en la quebrada El Chorro (Salta, Argentina) resultó en la recuperación de una asociación de polen y esporas, juntamente con algas de agua dulce (Pediastrum spp. y Scenedesmus sp.). De las 43 especies de esporomorfos identificadas hasta el momento para la Formación Tunal, 28 se citan aquí por primera vez. Las esporas y polen indican edad Daniana en la localidad tipo. Los proxidata sedimentarios incluyendo abundantes evaporitas, sugieren intervalos al menos estacionales de condiciones ambientales áridas. Por otro lado, las asociaciones palinológicas recuperadas de las pelitas oscuras ricas en materia orgánica indican la presencia de áreas anegadas y selvas en sus alrededores. En las últimas, el predominio de Verrustephanoporites simplex Leidelmeyer (que se corresponde con el actual Phyllostylon, Ulmaceae) indica abundantes lluvias estacionales, condiciones cálido-húmedas y clima subtropicalFil: Volkheimer, Wolfang. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Novara, Martin Guillermo. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; ArgentinaFil: Narvaez, Paula Liliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Marquillas, Rosa Argentina. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta; Argentin
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