共查询到20条相似文献,搜索用时 671 毫秒
1.
G. Carbone B. Lorenz B. N. J. Persson A. Wohlers 《The European physical journal. E, Soft matter》2009,29(3):275-284
In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem.
Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic
contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction,
while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding
on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory. 相似文献
2.
Detecting and quantifying temporal correlations in stochastic resonance via information theory measures 总被引:1,自引:0,他引:1
O. A. Rosso C. Masoller 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):37-43
We show that Information Theory quantifiers are suitable tools for detecting and for quantifying noise-induced temporal correlations
in stochastic resonance phenomena. We use the Bandt & Pompe (BP) method [Phys. Rev. Lett. 88, 174102 (2002)] to define a probability distribution, P, that fully characterizes temporal correlations. The BP method is
based on a comparison of neighboring values, and here is applied to the temporal sequence of residence-time intervals generated
by the paradigmatic model of a Brownian particle in a sinusoidally modulated bistable potential. The probability distribution
P generated via the BP method has associated a normalized Shannon entropy, H[P], and a statistical complexity measure, C[P],
which is defined as proposed by Rosso et al. [Phys. Rev. Lett. 99, 154102 (2007)]. The statistical complexity quantifies not only randomness but also the presence of correlational structures,
the two extreme circumstances of maximum knowledge (“perfect order") and maximum ignorance (“complete randomness") being regarded
an “trivial", and in consequence, having complexity C = 0. We show that both, H and C, display resonant features as a function
of the noise intensity, i.e., for an optimal level of noise the entropy displays a minimum and the complexity, a maximum.
This resonant behavior indicates noise-enhanced temporal correlations in the sequence of residence-time intervals. The methodology
proposed here has great potential for the precise detection of subtle signatures of noise-induced temporal correlations in
real-world complex signals. 相似文献
3.
C. Caroli P. Nozières 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):233-246
Velocity independent dry friction of a slider upon a base is due to an hysteretic response of relative displacement to a tangential driving force F. We show that the purely elastic model for multistability considered in a previous publication is in no way essential: multistability
arises just as well from adhesion. We emphasize the physical consequences of multistability for dynamic/static, a.c./d.c.
friction. When the slider is moved from rest by an amount the transition from the zero force static configuration to dynamic behaviour is progressive, spreading on a range equal to
the width of the hysteresis cycle. When is small, an elastic restoring force ensues, in agreement with observations. The competition of that elastic pinning with
bulk elasticity generates a screening length which we believe is the natural size of Burridge Knopoff blocks. We then study the effect of elastic interactions between
asperities: it is weak for dilute asperities, but its long range makes it important. In lowest order the interaction mediated
displacement of a given asperity has logarithmically divergent fluctuations: they become comparable to the asperity radius
when the slider size reaches another characteristic “Larkin length”, which for dilute micronic asperities is exponentially large. We give arguments suggesting that individually monostable asperities
display collective multistability on scales larger than . For individually multistable sites we show that elastic interactions give rise to cascade processes in which the spinodal
jump of a given asperity triggers the jump of others. We estimate the size of these cascades that should show up in the noise
spectrum.
Received: 3 February 1998 / Accepted: 19 March 1998 相似文献
4.
T. Boutreux H.A. Makse P.-G. de Gennes 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):105-115
We present the generalization of the minimal model for surface flows of granular mixtures, proposed by Boutreux and de Gennes
[J. Phys. I France 6, 1295 (1996)]. The minimal model was valid for grains differing only in their surface properties. The present model also
takes into account differences in the size of the grains. We apply the model to study segregation in two-dimensional silos
of mixtures of grains differing in size and/or surface properties. When the difference in size is small, the model predicts
that a continuous segregation appears in the static phase during the filling of a silo. When the difference in size is wide,
we take into account the segregation of the grains in the rolling phase, and the model predicts complete segregation and stratification
in agreement with experimental observations.
Received 9 September 1998 and Received in final form 4 November 1998 相似文献
5.
J. Dunkel W. Ebeling U. Erdmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):511-524
We investigate the stochastic dynamics of an one-dimensional ring with N self-driven Brownian particles. In this model neighboring particles interact via conservative Morse potentials. The influence of the surrounding heat bath is modeled by Langevin-forces (white noise) and
a constant viscous friction coefficient γ. The Brownian particles are provided with internal energy depots which may lead to active motions of the particles. The depots
are realized by an additional nonlinearly velocity-dependent friction coefficient γ
1(v) in the equations of motions. In the first part of the paper we study the partition functions of time averages and thermodynamical
quantities (e.g. pressure) characterizing the stationary physical system. Numerically calculated non-equilibrium phase diagrams are represented.
The last part is dedicated to transport phenomena by including a homogeneous external force field that breaks the symmetry
of the model. Here we find enhanced mobility of the particles at low temperatures.
Received 21 July 2001 相似文献
6.
The dynamic structure factor S(q, ω) of a harmonically trapped Bose gas has been calculated well above the Bose-Einstein condensation temperature by treating
the gas cloud as a canonical ensemble of non-interacting classical particles. The static structure factor is found to vanish
s8 q
2 in the long-wavelength limit. We also incorporate a relaxation mechanism phenomenologically by including a stochastic friction
force to study S(q, ω). A significant temperature dependence of the density fluctuation spectra is found. The Debye-Waller factor has been calculated
for the trapped thermal cloud as a function of q and the number N of atoms. A substantial difference is found for small- and large-N clouds. 相似文献
7.
S. Risau-Gusman G. Abramson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):515-520
We analyze general two-species stochastic models, of the
kind generally used for the study of population dynamics. Although
usually defined a priori, the deterministic version of these
models can be obtained as the infinite volume limit of many
stochastic models (which are necessarily defined by more parameters
than the deterministic one). It is known that damped oscillations in
a deterministic model usually correspond to oscillatory-like
fluctuations in their deterministic counterparts. The quality of
these “oscillations" depends on details of each stochastic model.
We show, however, that the parameters of the deterministic system
are generally enough to obtain very good bounds for the quality of
“oscillations" in any of its stochastic counterparts. These
bounds are shown to depend on only one dimensionless parameter. 相似文献
8.
A. L. Dantas A. S. Carriço N. S. Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):581-585
We calculate the dynamical response of a group of
non-interacting magnetic grains dispersed in a medium that imposes
on them an uniaxial anisotropy. Numerical results are obtained for
a collection of grains that has its volume distribution given by a
Gaussian function centered in the average volume V0, and has a
width σV0. We assume that the only effect of the medium
on the particles is the anisotropy imposed on the grains to study
the influence of the volume distribution (σ and V0) on
the effective permeability. The results are analyzed through the
calculation of numerical values for the components of the magnetic
permeability and also by the analysis of the combined effect of
the external dc magnetic field and the width of the volume
distribution on the skin depth. 相似文献
9.
D. Staresinic A. Borovac K. Biljakovic H. Berger F. Levy J.W. Brill 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):425-429
We report on measurements of the voltage dependence of the complex shear compliance of two crystals of the charge-density-wave
(CDW) conductor NbSe3, for torsional frequencies between 1 Hz and 71 Hz. For both samples, there is a frequency independent, ∼1% increase of the magnitude of the compliance when the voltage exceeds the threshold for CDW depinning, but the internal
friction has a striking sample dependence which we do not understand. For one sample, there is a frequency independent decrease
in internal friction with CDW depinning, suggesting that the elastic changes are not relaxational and might reflect changes
in the screening of the crystal strain by the CDW. For the second sample, the sign and magnitude of the change in internal
friction is strongly frequency dependent, which we associate with a change in screening due to the finite electron diffusion
time. The second sample also exhibits a frequency dependent peak in internal friction near threshold that may reflect relaxation
of the CDW phase.
Received 14 August 2001 and Received in final form 3 October 2001 相似文献
10.
L. Gauvin J. Vannimenus J.-P. Nadal 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(2):293-304
The collective behavior in a variant of Schelling’s segregation model is characterized with methods borrowed from statistical
physics, in a context where their relevance was not conspicuous. A measure of segregation based on cluster geometry is defined
and several quantities analogous to those used to describe physical lattice models at equilibrium are introduced. This physical
approach allows to distinguish quantitatively several regimes and to characterize the transitions between them, leading to
the building of a phase diagram. Some of the transitions evoke empirical sudden ethnic turnovers. We also establish links
with ‘spin-1’ models in physics. Our approach provides generic tools to analyze the dynamics of other socio-economic systems. 相似文献
11.
E. Heinsalu M. Patriarca F. Marchesoni 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):19-22
We study the effects of the confining conditions on the
occurrence of stochastic resonance (SR) in continuous bistable
systems. We model such systems by means of double-well potentials
that diverge like |x|q for |x|↦∞. For super-harmonic
(hard) potentials with q > 2 the SR peak sharpens with increasing q, whereas for sub-harmonic (soft) potentials, q < 2, it
gets
suppressed. 相似文献
12.
D. Helbing A. F. Johansson 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(4):549-562
Daganzo’s criticisms of second-order fluid approximations of traffic flow [C. Daganzo, Transpn. Res. B. 29, 277 (1995)] and Aw and Rascle’s proposal how to overcome them [A. Aw, M. Rascle, SIAM J. Appl. Math. 60, 916 (2000)] have stimulated an intensive scientific activity in the field of traffic modeling. Here, we will revisit their
arguments and the interpretations behind them. We will start by analyzing the linear stability of traffic models, which is
a widely established approach to study the ability of traffic models to describe emergent traffic jams. Besides deriving a
collection of useful formulas for stability analyses, the main attention is put on the characteristic speeds, which are related
to the group velocities of the linearized model equations. Most macroscopic traffic models with a dynamic velocity equation
appear to predict two characteristic speeds, one of which is faster than the average velocity. This has been claimed to constitute a theoretical inconsistency. We will carefully discuss arguments
for and against this view. In particular, we will shed some new light on the problem by comparing Payne’s macroscopic traffic
model with the Aw-Rascle model and macroscopic with microscopic traffic models. 相似文献
13.
A. B. Shapoval M. G. Shnirman 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):399-403
This paper considers a one-parameter family of sand-piles.
The family exhibits the crossover
between the models with deterministic and stochastic relaxation.
The mean pile height is used to describe the crossover.
The height densities corresponding to the models with relaxation
of both types approach one another as the parameter increases.
Relaxation is supposed to deal
with the local losses of grains by a fixed amount.
In that case the densities show a step-like behaviour
in contrast to the peaked shape
found in the models with the local loss of grains down
to a fixed level
[S. Lübeck, Phys. Rev. E 62, 6149 (2000)].
A spectral approach based on the long-run properties of the pile height
considers the models with deterministic and random relaxation
more accurately and
distinguishes between the two cases for admissible parameter values. 相似文献
14.
On the properties of small-world network models 总被引:7,自引:0,他引:7
A. Barrat M. Weigt 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):547-560
We study the small-world networks recently introduced by Watts and Strogatz [Nature 393, 440 (1998)], using analytical as well as numerical tools. We characterize the geometrical properties resulting from the
coexistence of a local structure and random long-range connections, and we examine their evolution with size and disorder
strength. We show that any finite value of the disorder is able to trigger a “small-world” behaviour as soon as the initial
lattice is big enough, and study the crossover between a regular lattice and a “small-world” one. These results are corroborated
by the investigation of an Ising model defined on the network, showing for every finite disorder fraction a crossover from
a high-temperature region dominated by the underlying one-dimensional structure to a mean-field like low-temperature region.
In particular there exists a finite-temperature ferromagnetic phase transition as soon as the disorder strength is finite.
[0.5cm]
Received 29 March 1999 and Received in final form 21 May 1999 相似文献
15.
S. Aumaître S. Fauve S. McNamara P. Poggi 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):449-460
We consider three examples of dissipative dynamical systems involving many degrees of freedom, driven far from equilibrium
by a constant or time dependent forcing. We study the statistical properties of the injected and dissipated power as well
as the fluctuations of the total energy of these systems. The three systems under consideration are: a shell model of turbulence,
a gas of hard spheres colliding inelastically and excited by a vibrating piston, and a Burridge-Knopoff spring-block model.
Although they involve different types of forcing and dissipation, we show that the statistics of the injected power obey the
“fluctuation theorem" demonstrated in the case of time reversible dissipative systems maintained at constant total energy,
or in the case of some stochastic processes. Although this may be only a consequence of the theory of large deviations, this
allows a possible definition of “temperature" for a dissipative system out of equilibrium. We consider how this “temperature"
scales with the energy and the number of degrees of freedom in the different systems under consideration.
Received 26 June 2000 and Received in final form 24 October 2000 相似文献
16.
S. Lahiri A. M. Jayannavar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(1):87-92
We investigate the total entropy production of a Brownian particle in a driven bistable system. This system exhibits the phenomenon
of stochastic resonance. We show that in the time-periodic steady state, the probability density function for the total entropy
production satisfies Seifert’s integral and detailed fluctuation theorems over finite time trajectories. 相似文献
17.
M. Kuperman D. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):387-391
We analyze the phenomenon of stochastic resonance in an Ising-like system on a small-world network. The system, which is subject
to the combined action of noise and an external modulation, can be interpreted as a stylized model of opinion formation by
imitation under the effects of a “fashion wave”. Both the amplitude threshold for the detection of the external modulation
and the width of the stochastic-resonance peak show considerable variation as the randomness of the underlying small-world
network is changed.
Received 19 December 2001 相似文献
18.
S. Alfarano T. Lux F. Wagner 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(2):183-187
The present paper expands on recent attempts at
estimating the parameters of simple interacting-agent models of
financial markets [S. Alfarano, T. Lux, F. Wagner, Computational Economics 26, 19 (2005); S. Alfarano, T. Lux, F. Wagner, in Funktionsf?higkeit und
Stabilit?t von Finanzm?rkten, edited by W. Franz, H. Ramser,
M. Stadler (Mohr Siebeck, Tübingen, 2005), pp. 241–254]. Here we
provide additional evidence by (i) investigating a large sample of
individual stocks from the Tokyo Stock Exchange, and (ii)
comparing results from the baseline noise trader/fundamentalist
model of [S. Alfarano, T. Lux, F. Wagner, Computational Economics 26, 19 (2005)] with those obtained from an even
simpler version with a preponderance of noise trader behaviour. As
it turns out, this somewhat more parsimonious “maximally skewed”
variant is often not rejected in favor of the more complex
version. We also find that all stocks are dominated by noise
trader behaviour irrespective of whether the data prefer the
skewed or the baseline version of our model. 相似文献
19.
20.
Tanaka Y 《The European physical journal. E, Soft matter》2005,18(1):95-103
We study experimentally the impact of spherical gel balls on a rigid substrate, where the balls largely deform like a pancake
at high impact velocities. In our previous study (Y. Tanaka, Y. Yamazaki, K. Okumura, Europhys. Lett. 63, 149 (2003)), we measured the contact time τf and maximally deformed size versus impact velocity and explained the behaviors at the scaling level. In this study, we further measure τm, the time required to reach the maximum deformation (from the initial contact), and the restitution coefficient e. We also make a static experiment where we obtain the force-deformation curve of the gel balls up to fairly large deformations
to explain the data on the impact. We propose two phenomenological treatments going beyond the scaling argument, one for intermediate
impact velocities and the other for large velocities; the former is based on the static experiment while the latter on a Lagrangian
constructed from appropriate constraints. Results from these treatments reproduce the experimental behavior of τm. 相似文献