3,495 research outputs found
A topological approximation of the nonlinear Anderson model
We study the phenomena of Anderson localization in the presence of nonlinear
interaction on a lattice. A class of nonlinear Schrodinger models with
arbitrary power nonlinearity is analyzed. We conceive the various regimes of
behavior, depending on the topology of resonance-overlap in phase space,
ranging from a fully developed chaos involving Levy flights to pseudochaotic
dynamics at the onset of delocalization. It is demonstrated that quadratic
nonlinearity plays a dynamically very distinguished role in that it is the only
type of power nonlinearity permitting an abrupt localization-delocalization
transition with unlimited spreading already at the delocalization border. We
describe this localization-delocalization transition as a percolation
transition on a Cayley tree. It is found in vicinity of the criticality that
the spreading of the wave field is subdiffusive in the limit
t\rightarrow+\infty. The second moment grows with time as a powerlaw t^\alpha,
with \alpha = 1/3. Also we find for superquadratic nonlinearity that the analog
pseudochaotic regime at the edge of chaos is self-controlling in that it has
feedback on the topology of the structure on which the transport processes
concentrate. Then the system automatically (without tuning of parameters)
develops its percolation point. We classify this type of behavior in terms of
self-organized criticality dynamics in Hilbert space. For subquadratic
nonlinearities, the behavior is shown to be sensitive to details of definition
of the nonlinear term. A transport model is proposed based on modified
nonlinearity, using the idea of stripes propagating the wave process to large
distances. Theoretical investigations, presented here, are the basis for
consistency analysis of the different localization-delocalization patterns in
systems with many coupled degrees of freedom in association with the asymptotic
properties of the transport.Comment: 20 pages, 2 figures; improved text with revisions; accepted for
publication in Physical Review
Searching for the Next Yukawa Phase of QCD
QCD predicts that the interactions between quarks and gluons change from a
confining to a screened Yukawa form above a critical temperature
MeV. In this talk, I review some of the key observables in heavy ion reactions
which are being used to search for this new partonic Yukawa phase at SPS and
RHIC. These include collective observables such as ,
meson interferometry, jet quenching, and suppression.Comment: 24 pages (PTPTex style files included) with 26 eps,ps figures using
epsf,psfig. To appear in Proc. of 14th Nishinomiya-Yukawa Memorial Symposium
Nov. 1999, Japan; updated with a critique of the CERN press release Feb. 8,
200
4D electron imaging: principles and perspectives
In this perspective we highlight developments and concepts in the field of 4D electron imaging. With spatial and temporal resolutions reaching the picometer and femtosecond, respectively, the field is now embracing ultrafast electron diffraction, crystallography and microscopy. Here, we overview the principles involved in the direct visualization of structural dynamics with applications in chemistry, materials science and biology. The examples include the studies of complex isolated chemical reactions, phase transitions and cellular structures. We conclude with an outlook on the potential of the approach and with some questions that may define new frontiers of research
Statistical Physics of Vehicular Traffic and Some Related Systems
In the so-called "microscopic" models of vehicular traffic, attention is paid
explicitly to each individual vehicle each of which is represented by a
"particle"; the nature of the "interactions" among these particles is
determined by the way the vehicles influence each others' movement. Therefore,
vehicular traffic, modeled as a system of interacting "particles" driven far
from equilibrium, offers the possibility to study various fundamental aspects
of truly nonequilibrium systems which are of current interest in statistical
physics. Analytical as well as numerical techniques of statistical physics are
being used to study these models to understand rich variety of physical
phenomena exhibited by vehicular traffic. Some of these phenomena, observed in
vehicular traffic under different circumstances, include transitions from one
dynamical phase to another, criticality and self-organized criticality,
metastability and hysteresis, phase-segregation, etc. In this critical review,
written from the perspective of statistical physics, we explain the guiding
principles behind all the main theoretical approaches. But we present detailed
discussions on the results obtained mainly from the so-called
"particle-hopping" models, particularly emphasizing those which have been
formulated in recent years using the language of cellular automata.Comment: 170 pages, Latex, figures include
Desorption of CO from Ru(001) induced by near-infrared femtosecond laser pulses
Irradiation of a Ru(001) surface covered with CO using intense femtosecond laser pulses (800 nm, 130 fs) leads to desorption of CO with a nonlinear dependence of the yield on the absorbed fluence (100–380 J/m2). Two-pulse correlation measurements reveal a response time of 20 ps (FWHM). The lack of an isotope effect together with the strong rise of the phonon temperature (2500 K) and the specific electronic structure of the adsorbate–substrate system strongly indicate that coupling to phonons is dominant. The experimental findings can be well reproduced within a friction-coupled heat bath model. Yet, pronounced dynamical cooling in desorption, found in the fluence-dependence of the translational energy, and in a non-Arrhenius behavior of the desorption probability reflect pronounced deviations from thermal equilibrium during desorption taking place on such a short time scale
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