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1.
The $-game 总被引:1,自引:0,他引:1
J. Vitting Andersen D. Sornette 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):141-145
We propose a payoff function extending Minority Games (MG) that captures the competition between agents to make money. In
contrast with previous MG, the best strategies are not always targeting the minority but are shifting opportunistically between
the minority and the majority. The emergent properties of the price dynamics and of the wealth of agents are strikingly different
from those found in MG. As the memory of agents is increased, we find a phase transition between a self-sustained speculative
phase in which a “stubborn majority” of agents effectively collaborate to arbitrage a market-maker for their mutual benefit
and a phase where the market-maker always arbitrages the agents. A subset of agents exhibit a sustained non-equilibrium risk-return
profile.
Received 5 June 2002 / Received in final form 21 November 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: sornette@unice.fr
RID="b"
ID="b"CNRS UMR7536
RID="c"
ID="c"CNRS UMR6622 相似文献
2.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
3.
F. Schweitzer J.A. Hołyst 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(4):723-732
The concept of active Brownian particles is used to model a collective opinion formation process. It is assumed that individuals
in community create a two-component communication field that influences the change of opinions of other persons and/or can
induce their migration. The communication field is described by a reaction-diffusion equation, the opinion change of the individuals
is given by a master equation, while the migration is described by a set of Langevin equations, coupled by the communication
field. In the mean-field limit holding for fast communication we derive a critical population size, above which the community
separates into a majority and a minority with opposite opinions. The existence of external support (e.g. from mass media) changes the ratio between minority and majority, until above a critical external support the supported subpopulation
exists always as a majority. Spatial effects lead to two critical “social” temperatures, between which the community exists
in a metastable state, thus fluctuations below a certain critical wave number may result in a spatial opinion separation.
The range of metastability is particularly determined by a parameter characterizing the individual response to the communication
field. In our discussion, we draw analogies to phase transitions in physical systems.
Received 26 November 1999 相似文献
4.
G.G. Pereira 《The European physical journal. E, Soft matter》2002,7(3):273-289
The inherent nanoscale morphologies of self-organizing diblock copolymer melts are now being investigated for a variety of
technological applications. To obtain global, well-oriented, regular patterns requires suitably confining and aligning the
melt between two flat plates. Here we consider such confinement for an asymmetrical diblock melt, which forms columns of the
minority phase in a matrix of the majority phase. We investigate this system with a combination of numerical simulations and
strong segregation theory and make suggestions as to when perpendicular orientation should prevail over parallel orientation
of the columns.
Received 22 May 2001 and Received in final form 14 February 2002 相似文献
5.
L.Y. Fong K.Y. Szeto 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):569-572
Data mining is performed using genetic algorithm on artificially generated time series data with short memory. The extraction
of rules from a training set and the subsequent testing of these rules provide a basis for the predictions on the test set.
The artificial time series are generated using the inverse whitening transformation, and the correlation function has an exponential
form with given time constant indicative of short memory. A vector quantization technique is employed to classify the daily
rate of return of this artificial time series into four categories. A simple genetic algorithm based on a fixed format of
rules is introduced to do the forecasting. Comparing to the benchmark tests with random walk and random guess, genetic algorithms
yield substantially better prediction rates, between 50% to 60%. This is an improvement compared with the 47% for random walk
prediction and 25% for random guessing method.
Received 29 August 2000 相似文献
6.
M. Kolář F. Slanina 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(3):379-384
We examine a model of biological evolution of Eigen's quasispecies in a so-called holey fitness landscape, where the fitness
of a site is either 0 (lethal site) or a uniform positive constant (viable site). The evolution dynamics is therefore determined
by the topology of the genome space which is modelled by the random Bethe lattice. We use the effective medium and single-defect
approximations to find the criteria under which the localized quasispecies cloud is created. We find that shorter genomes,
which are more robust to random mutations than average, represent a selective advantage which we call “topological”. A way
of assessing empirically the relative importance of reproductive success and topological advantage is suggested.
Received 9 August 2002 / Received in final form 7 November 2002 Published online 14 February 2003
RID="a"
ID="a"e-mail: slanina@fzu.cz 相似文献
7.
A high-density diquark phase seems to be a generic feature of QCD. If so it should also be reproduced by random matrix models.
We discuss a specific one in which the random matrix elements of the Dirac operator are supplemented by a finite chemical
potential and by non-random elements which model the formation of instanton-anti-instanton molecules. Comparing our results
to those found in a previous investigation by Vanderheyden and Jackson we find additional support for our starting assumption,
namely that the existence of a high-density diquark phase is common to all QCD-like model.
Received: 20 February 2001 / Accepted: 24 April 2001 相似文献
8.
9.
V.V. Mourzenko J.-F. Thovert P.M. Adler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):75-85
Two-scale porous media are generated by filtering a Gaussian random correlated field with a random correlated threshold field.
The percolation threshold and the critical exponent ν are derived with the help of a finite-size scaling method. The percolation
threshold for the three-dimensional media is a decreasing function of the variance and correlation length of the threshold
field. A simplified model predicts these trends in 3d; moreover, it suggested some effects in 2d which were all numerically
verified.
Received 17 August 2000 相似文献
10.
F. Thalmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):65-73
The mean field approach of glassy dynamics successfully describes systems which are out-of-equilibrium in their low temperature
phase. In some cases an aging behaviour is found, with no stationary regime ever reached. In the presence of dissipative forces
however, the dynamics is indeed stationary, but still out-of-equilibrium, as inferred by a significant violation of the fluctuation
dissipation theorem. The mean field dynamics of a particle in a random but short-range correlated environment, offers the
opportunity of observing both the aging and driven stationary regimes. Using a geometrical approach previously introduced
by the author, we study here the relation between these two situations, in the pure relaxational limit, i.e. the zero temperature case. In the stationary regime, the velocity (v)-force (F) characteristics is a power law v∼F
4, while the characteristic times scale like powers of v, in agreement with an early proposal by Horner. The cross-over between the aging, linear-response regime and the non-linear
stationary regime is smooth, and we propose a parametrization of the correlation functions valid in both cases, by means of
an “effective time”. We conclude that aging and non-linear response are dual manifestations of a single out-of-equilibrium
state, which might be a generic situation.
Received 7 May 2000 and Received in final form 22 August 2000 相似文献
11.
M. Bauer O. Golinelli 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):339-352
We study both numerically and analytically what happens to a random graph of average connectivity α when its leaves and their
neighbors are removed iteratively up to the point when no leaf remains. The remnant is made of isolated vertices plus an induced
subgraph we call the core. In the thermodynamic limit of an infinite random graph, we compute analytically the dynamics of leaf removal, the number
of isolated vertices and the number of vertices and edges in the core. We show that a second order phase transition occurs
at α = e = 2.718 ... : below the transition, the core is small but above the transition, it occupies a finite fraction of
the initial graph. The finite size scaling properties are then studied numerically in detail in the critical region, and we
propose a consistent set of critical exponents, which does not coincide with the set of standard percolation exponents for
this model. We clarify several aspects in combinatorial optimization and spectral properties of the adjacency matrix of random
graphs.
Received 31 January 2001 and Received in final form 26 June 2001 相似文献
12.
A.N. Ivanov H. Oberhummer N.I. Troitskaya M. Faber 《The European Physical Journal A - Hadrons and Nuclei》2000,7(4):519-535
The Nambu–Jona–Lasinio model of the deuteron suggested by Nambu and Jona–Lasinio (Phys. Rev. 124 (1961) 246) is formulated
from the first principles of QCD. The deuteron appears as a neutron–proton collective excitation, i.e. a Cooper np–pair, induced
by a phenomenological local four–nucleon interaction in the nuclear phase of QCD. The model describes the deuteron coupled
to itself, nucleons and other particles through one–nucleon loop exchanges providing a minimal transfer of nucleon flavours
from initial to final nuclear states and accounting for contributions of nucleon–loop anomalies which are completely determined
by one–nucleon loop diagrams. The dominance of contributions of nucleon–loop anomalies to effective Lagrangians of low–energy
nuclear interactions is justified in the large N
C expansion, where N
C is the number of quark colours.
Received: 10 March 2000 相似文献
13.
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
14.
P. Zieliński W. Schranz D. Havlik A.V. Kityk 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):155-165
A four-state pseudospin model is constructed for the isomorphous phase transition hcp-2↦hcp-1 in pure C70 and in C70-rich mixed crystal C
70(1 - x)
C60x. With the specific anisotropic pseudospin interactions adapted to the C70 crystal the model is equivalent to a two-state Ising model in a temperature-dependent field. Replica symmetric state of the
model is shown to approach the critical point when the width of distribution of random fields and/or of random bonds increases.
The temperature of the phase transition and the phase equilibrium temperature then are practically constant, whereas the experiment
shows their strong decrease with x. The main effect of dilution resides in an x-dependence of the model parameters. Dilatometric data on the hexagonal C
70(1 - x)
C60x are used to fit these parameters. A metastable disordered phase subsisting below the phase transition is discovered in a
range of the model parameters and is shown to be responsible for the macroscopic behaviour of the system. A good agreement
with experimental data is obtained for the spontaneous strain and for the x-dependence of the hysteresis.
Received 20 April 2001 and Received in final form 26 September 2001 相似文献
15.
G.J. Rodgers Y.J. Yap 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):129-132
A model of herding is introduced which is exceptionally simple, incorporating only two phenomena, growth and addition. At
each time step either (i) with probability p the system grows through the introduction of a new agent or (ii) with probability q = 1 - p a free agent already in the system is added at random to a group of size k with rate Ak. Two versions of the model, A
k = k and A
k = 1, are solved and in both versions we find two different types of behaviour. When p > 1/2 all the moments of the distribution of group sizes are linear in time for large time and the group distribution is
power-law. When p < 1/2 the system runs out of free agents in a finite time.
Received 12 February 2002 Published online 9 July 2002 相似文献
16.
M. Leone A. Vázquez A. Vespignani R. Zecchina 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):191-197
We present a detailed study of the phase diagram of the Ising model in random graphs with arbitrary degree distribution. By
using the replica method we compute exactly the value of the critical temperature and the associated critical exponents as
a function of the moments of the degree distribution. Two regimes of the degree distribution are of particular interest. In
the case of a divergent second moment, the system is ferromagnetic at all temperatures. In the case of a finite second moment
and a divergent fourth moment, there is a ferromagnetic transition characterized by non-trivial critical exponents. Finally,
if the fourth moment is finite we recover the mean field exponents. These results are analyzed in detail for power-law distributed
random graphs.
Received 4 April 2002 Published online 19 July 2002 相似文献
17.
R. Paul M. Alava H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):357-367
The random field q-states Potts model is investigated using exact groundstates and finite-temperature transfer matrix calculations. It is found
that the domain structure and the Zeeman energy of the domains resembles for general q the random field Ising case (q = 2). This is also the expected outcome based on a random-walk picture of the groundstate. The domain size distribution is
exponential, and the scaling of the average domain size with the disorder strength is similar for q arbitrary. The zero-temperature properties are compared to the equilibrium spin states at small temperatures, to investigate
the effect of local random field fluctuations that imply locally degenerate regions. The response to field perturbations (`chaos')
and the susceptibility are investigated. In particular for the chaos exponent it is found to be 1 for q = 2,..., 5. Finally for q = 2 (Ising case) the domain length distribution is studied for correlated random fields.
Received 27 August 2002 Published online 19 December 2002
RID="a"
ID="a"e-mail: rieger@lusi-sb.de 相似文献
18.
V.A. Brazhnyi S. Stepanow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):355-362
We consider the adsorption of a random heteropolymer onto an interface within the model of Garel et al. [#!gareletal89!#] by taking into account random self-interactions and ternary repulsive interactions between the monomers.
Within the replica trick and by using a self-consistent preaveraging procedure we map the adsorption problem onto the problem
of binding state of a quantum mechanical Hamiltonian. The analysis of the latter is treated within the variational method
based on the 2nd Legendre transform. Our study reveals a complex behaviour of the localization of the heteropolymer. In particular,
we predict a reentrant localization transition for moderate values of the asymmetry of the distribution function of the monomer
sequences along the heteropolymer.
Received 9 October 2001 and Received in final form 27 February 2002 Published online 6 June 2002 相似文献
19.
H. Portales L. Saviot E. Duval M. Gaudry E. Cottancin J. Lermé M. Pellarin M. Broyer B. Prével M. Treilleux 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):197-200
Low-frequency Raman scattering experiments have been performed on thin films consisting of pure gold or gold-silver alloy
clusters embedded in alumina matrix. It is clearly shown that the quadrupolar vibrational modes are observed by Raman scattering
because of the effect of resonance with the excitation of the electronic surface dipolar plasmon. This is due to the strong
coupling between the collective electronic dipolar excitation and the quadrupolar vibrational modes. This effect of resonance
does not exist with the core electron excitations. The mixing of the conduction electron dipolar excitation (surface plasmon)
with the core electrons leads to the quenching of the resonant Raman scattering.
Received 16 November 2000 相似文献
20.
C.M. Horowitz E.V. Albano 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(4):563-569
The relationship between a microscopic parameter p, that is related to the probability of choosing a mechanism of deposition, and the stochastic equation for the interface's
evolution is studied for two different models. It is found that in one model, that is similar to ballistic deposition, the
corresponding stochastic equation can be represented by a Kardar-Parisi-Zhang (KPZ) equation where both λ and ν depend on
p in the following way: ν(p) = νp and λ(p) = λp
3/2. Furthermore, in the other studied model, which is similar to random deposition with relaxation, the stochastic equation
can be represented by an Edwards-Wilkinson (EW) equation where ν depends on p according to ν(p) = νp
2. It is expected that these results will help to find a framework for the development of stochastic equations starting from
microscopic details of growth models.
Received 26 August 2002 / Received in final form 20 November 2002 Published online 6 March 2003
RID="a"
ID="a"e-mail: ealbano@inifta.unlp.edu.ar 相似文献