340 research outputs found
Dynamics and nonequilibrium states in the Hamiltonian mean-field model: A closer look
We critically revisit the evidence for the existence of quasistationary
states in the globally coupled XY (or Hamiltonian mean-field) model. A
slow-relaxation regime at long times is clearly revealed by numerical
realizations of the model, but no traces of quasistationarity are found during
the earlier stages of the evolution. We point out the nonergodic properties of
this system in the short-time range, which makes a standard statistical
description unsuitable. New aspects of the evolution during the nonergodic
regime, and of the energy distribution function in the final approach to
equilibrium, are disclosed
Dependences of the Casimir-Polder interaction between an atom and a cavity wall on atomic and material properties
The Casimir-Polder and van der Waals interactions between an atom and a flat
cavity wall are investigated under the influence of real conditions including
the dynamic polarizability of the atom, actual conductivity of the wall
material and nonzero temperature of the wall. The cases of different atoms near
metal and dielectric walls are considered. It is shown that to obtain accurate
results for the atom-wall interaction at short separations, one should use the
complete tabulated optical data for the complex refractive index of the wall
material and the accurate dynamic polarizability of an atom. At relatively
large separations in the case of a metal wall, one may use the plasma model
dielectric function to describe the dielectric properties of wall material. The
obtained results are important for the theoretical interpretation of
experiments on quantum reflection and Bose-Einstein condensation.Comment: 5 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A
(special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005
How to suppress undesired synchronization
It is delightful to observe the emergence of synchronization in the blinking
of fireflies to attract partners and preys. Other charming examples of
synchronization can also be found in a wide range of phenomena such as, e.g.,
neurons firing, lasers cascades, chemical reactions, and opinion formation.
However, in many situations the formation of a coherent state is not pleasant
and should be mitigated. For example, the onset of synchronization can be the
root of epileptic seizures, traffic congestion in communication networks, and
the collapse of constructions. Here we propose the use of contrarians to
suppress undesired synchronization. We perform a comparative study of different
strategies, either requiring local or total knowledge of the system, and show
that the most efficient one solely requires local information. Our results also
reveal that, even when the distribution of neighboring interactions is narrow,
significant improvement in mitigation is observed when contrarians sit at the
highly connected elements. The same qualitative results are obtained for
artificially generated networks as well as two real ones, namely, the Routers
of the Internet and a neuronal network
Dependences of the van der Waals atom-wall interaction on atomic and material properties
The 1%-accurate calculations of the van der Waals interaction between an atom
and a cavity wall are performed in the separation region from 3 nm to 150 nm.
The cases of metastable He and Na atoms near the metal,
semiconductor or dielectric walls are considered. Different approximations to
the description of wall material and atomic dynamic polarizability are
carefully compared. The smooth transition to the Casimir-Polder interaction is
verified. It is shown that to obtain accurate results for the atom-wall van der
Waals interaction at shortest separations with an error less than 1% one should
use the complete optical tabulated data for the complex refraction index of the
wall material and the accurate dynamic polarizability of an atom. The obtained
results may be useful for the theoretical interpretation of recent experiments
on quantum reflection and Bose-Einstein condensation of ultracold atoms on or
near surfaces of different nature.Comment: 14 pages, 5 figures, 3 tables, accepted for publication in Phys. Rev.
Simple models of small world networks with directed links
We investigate the effect of directed short and long range connections in a
simple model of small world network. Our model is such that we can determine
many quantities of interest by an exact analytical method. We calculate the
function , defined as the number of sites affected up to time when a
naive spreading process starts in the network. As opposed to shortcuts, the
presence of un-favorable bonds has a negative effect on this quantity. Hence
the spreading process may not be able to affect all the network. We define and
calculate a quantity named the average size of accessible world in our model.
The interplay of shortcuts, and un-favorable bonds on the small world
properties is studied.Comment: 15 pages, 9 figures, published versio
Casearia sylvestris SW. (SALICACEAE) E JACARANDA PUBERULA CHAM. (BIGNONIACEAE): USO POPULAR VERSUS LITERATURA CIENTÍFICA
A utilização de plantas medicinais é notória, entretanto, nem todas possuem ações terapêuticas cientificamente comprovadas. Este artigo é resultado de um levantamento bibliográfico sobre duas árvores medicinais presentes no Parque Ecológico Municipal José Milanese (PEMJM), localizado no Bairro Mina União, no município de Criciúma, Santa Catarina e utilizadas pela população local por apresentarem efeitos terapêuticos. Trata-se de uma revisão de cunho científico sobre os efeitos terapêuticos apontados pela comunidade e posteriormente confrontados em periódicos reconhecidos pela comunidade científica. Foram estudadas Casearia sylvestris Sw.(Salicaceae) e Jacaranda puberula Cham. (Bignoniaceae) nas base de dados eletrônicas Pubmed e Science Direct, cujas informações foram fundamentais para comparar seus possíveis usos medicinais. Pode-se observar que alguns relatos populares vêm ao encontro das informações obtidas nesses bancos de dados, e outras extrapolam as informações populares
Analytical approach to bit-string models of language evolution
A formulation of bit-string models of language evolution, based on
differential equations for the population speaking each language, is introduced
and preliminarily studied. Connections with replicator dynamics and diffusion
processes are pointed out. The stability of the dominance state, where most of
the population speaks a single language, is analyzed within a mean-field-like
approximation, while the homogeneous state, where the population is evenly
distributed among languages, can be exactly studied. This analysis discloses
the existence of a bistability region, where dominance coexists with
homogeneity as possible asymptotic states. Numerical resolution of the
differential system validates these findings.Comment: To appear in Int. J. Mod. Phys.
Condensation in Globally Coupled Populations of Chaotic Dynamical Systems
The condensation transition, leading to complete mutual synchronization in
large populations of globally coupled chaotic Roessler oscillators, is
investigated. Statistical properties of this transition and the cluster
structure of partially condensed states are analyzed.Comment: 11 pages, 4 figures, revte
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