5,892 research outputs found
Small-amplitude solitons in a nonlocal sine-Gordon model
It is shown that small amplitude solitons of a nonlocal sine-Gordon model corresponding to different frequencies of the
carrier wave can create coupled states. The effect is due to a change of the dispersion originated by a nonlocal nonlinearity.
Within the framework of the multiscale expansion such pulses are described by a system of nonlinear Schtidinger equations
which possesses coupled mode solutions in the form of running localized waves (breathers). Such breathers consist of
modes with different frequencies and are characterized by two internal frequencies.info:eu-repo/semantics/publishedVersio
Using synchronization to improve earthquake forecasting in a cellular automaton model
A new forecasting strategy for stochastic systems is introduced. It is
inspired by the concept of anticipated synchronization between pairs of chaotic
oscillators, recently developed in the area of Dynamical Systems, and by the
earthquake forecasting algorithms in which different pattern recognition
functions are used for identifying seismic premonitory phenomena. In the new
strategy, copies (clones) of the original system (the master) are defined, and
they are driven using rules that tend to synchronize them with the master
dynamics. The observation of definite patterns in the state of the clones is
the signal for connecting an alarm in the original system that efficiently
marks the impending occurrence of a catastrophic event. The power of this
method is quantitatively illustrated by forecasting the occurrence of
characteristic earthquakes in the so-called Minimalist Model.Comment: 4 pages, 3 figure
Experimental evidence on the development of scale invariance in the internal structure of self-affine aggregates
It is shown that an alternative approach for the characterization of growing
branched patterns consists of the statistical analysis of frozen structures,
which cannot be modified by further growth, that arise due to competitive
processes among neighbor growing structures. Scaling relationships applied to
these structures provide a method to evaluate relevant exponents and to
characterize growing systems into universality classes. The analysis is applied
to quasi-two-dimensional electrochemically formed silver branched patterns
showing that the size distribution of frozen structures exhibits scale
invariance. The measured exponents, within the error bars, remind us those
predicted by the Kardar-Parisi-Zhang equation.Comment: 11 pages, 4 figure
Three-dimensional numerical simulation of 1GeV/Nucleon U92+ impact against atomic hydrogen
The impact of 1GeV/Nucleon U92+ projectiles against atomic hydrogen is
studied by direct numerical resolution of the time-dependent wave equation for
the atomic electron on a three-dimensional Cartesian lattice. We employ the
fully relativistic expressions to describe the electromagnetic fields created
by the incident ion. The wave equation for the atom interacting with the
projectile is carefully derived from the time-dependent Dirac equation in order
to retain all the relevant terms.Comment: 12 pages and 7 figures included in the tex
Scale free networks by preferential depletion
We show that not only preferential attachment but also preferential depletion
leads to scale-free networks. The resulting degree distribution exponents is
typically less than two (5/3) as opposed to the case of the growth models
studied before where the exponents are larger. Our approach applies in
particular to biological networks where in fact we find interesting agreement
with experimental measurements. We investigate the most important properties
characterizing these networks, as the cluster size distribution, the average
shortest path and the clustering coefficient.Comment: 8 pages, 4 figure
Periodically modulated geometric and electronic structure of graphene on Ru(0001)
We report here on a method to fabricate and characterize highly perfect,
periodically rippled graphene monolayers and islands, epitaxially grown on
single crystal metallic substrates under controlled UHV conditions. The
periodicity of the ripples is dictated by the difference in lattice parameters
of graphene and substrate, and, thus, it is adjustable. We characterize its
perfection at the atomic scale by means of STM and determine its electronic
structure in the real space by local tunnelling spectroscopy. There are
periodic variations in the geometric and electronic structure of the graphene
monolayer. We observe inhomogeneities in the charge distribution, i.e a larger
occupied Density Of States at the higher parts of the ripples. Periodically
rippled graphene might represent the physical realization of an ordered array
of coupled graphene quantum dots. The data show, however, that for rippled
graphene on Ru(0001) both the low and the high parts of the ripples are
metallic. The fabrication of periodically rippled graphene layers with
controllable characteristic length and different bonding interactions with the
substrate will allow a systematic experimental test of this fundamental
problem.Comment: 12 pages. Contribution to the topical issue on graphene of
Semiconductor Science and Technolog
Translationally invariant nonlinear Schrodinger lattices
Persistence of stationary and traveling single-humped localized solutions in
the spatial discretizations of the nonlinear Schrodinger (NLS) equation is
addressed. The discrete NLS equation with the most general cubic polynomial
function is considered. Constraints on the nonlinear function are found from
the condition that the second-order difference equation for stationary
solutions can be reduced to the first-order difference map. The discrete NLS
equation with such an exceptional nonlinear function is shown to have a
conserved momentum but admits no standard Hamiltonian structure. It is proved
that the reduction to the first-order difference map gives a sufficient
condition for existence of translationally invariant single-humped stationary
solutions and a necessary condition for existence of single-humped traveling
solutions. Other constraints on the nonlinear function are found from the
condition that the differential advance-delay equation for traveling solutions
admits a reduction to an integrable normal form given by a third-order
differential equation. This reduction also gives a necessary condition for
existence of single-humped traveling solutions. The nonlinear function which
admits both reductions defines a two-parameter family of discrete NLS equations
which generalizes the integrable Ablowitz--Ladik lattice.Comment: 24 pages, 4 figure
Turbulent Control of the Star Formation Efficiency
Supersonic turbulence plays a dual role in molecular clouds: On one hand, it
contributes to the global support of the clouds, while on the other it promotes
the formation of small-scale density fluctuations, identifiable with clumps and
cores. Within these, the local Jeans length \Ljc is reduced, and collapse
ensues if \Ljc becomes smaller than the clump size and the magnetic support
is insufficient (i.e., the core is ``magnetically supercritical''); otherwise,
the clumps do not collapse and are expected to re-expand and disperse on a few
free-fall times. This case may correspond to a fraction of the observed
starless cores. The star formation efficiency (SFE, the fraction of the cloud's
mass that ends up in collapsed objects) is smaller than unity because the mass
contained in collapsing clumps is smaller than the total cloud mass. However,
in non-magnetic numerical simulations with realistic Mach numbers and
turbulence driving scales, the SFE is still larger than observational
estimates. The presence of a magnetic field, even if magnetically
supercritical, appears to further reduce the SFE, but by reducing the
probability of core formation rather than by delaying the collapse of
individual cores, as was formerly thought. Precise quantification of these
effects as a function of global cloud parameters is still needed.Comment: Invited review for the conference "IMF@50: the Initial Mass Function
50 Years Later", to be published by Kluwer Academic Publishers, eds. E.
Corbelli, F. Palla, and H. Zinnecke
Coulomb explosion sputtering of selectively oxidized Si
We have studied multiply charged Arq+ ion induced potential sputtering of a
unique system comprising of coexisting Silicon and Silicon oxide surfaces. Such
surfaces are produced by oblique angle oxygen ion bombardment on Si(100), where
ripple structures are formed and one side of each ripple gets more oxidized. It
is observed that higher the potential energy of Arq+ ion, higher the sputtering
yield of the non conducting (oxide) side of the ripple as compared to the
semiconducting side. The results are explained in terms of Coulomb explosion
model where potential sputtering depends on the conductivity of the ion impact
sites.Comment: 9 pages and 3 figure
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