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1.
Disease spreading in structured scale-free networks 总被引:2,自引:0,他引:2
Y. Moreno A. Vázquez 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):265-271
We study the spreading of a disease on top of structured scale-free networks recently introduced. By means of numerical simulations
we analyze the SIS and the SIR models. Our results show that when the connectivity fluctuations of the network are unbounded
whether the epidemic threshold exists strongly depends on the initial density of infected individuals and the type of epidemiological
model considered. Analytical arguments are provided in order to account for the observed behavior. We conclude that the peculiar
topological features of this network and the absence of small-world properties determine the dynamics of epidemic spreading.
Received 16 October 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: yamir@ictp.trieste.it 相似文献
2.
R. Percacci A. Vespignani 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):411-414
Measurements and data analysis have proved very effective in the study of the Internet's physical fabric and have shown heterogeneities
and statistical fluctuations extending over several orders of magnitude. Here we focus on the relationship between the Round-Trip-Time
(RTT) and the geographical distance. We define dimensionless variables that contain information on the quality of Internet
connections finding that their probability distributions are characterized by a slow power-law decay signalling the presence
of scale-free features. These results point out the extreme heterogeneity of Internet delay since the transmission speed between
different points of the network exhibits very large fluctuations. The associated scaling exponents appear to have fairly stable
values in different data sets and thus define an invariant characteristic of the Internet that might be used in the future
as a benchmark of the overall state of “health” of the Internet.
Received 25 January 2003 Published online 7 May 2003 相似文献
3.
The epidemic spread and immunizations in geographically embedded scale-free (SF) and Watts-Strogatz (WS) networks are numerically investigated. We make a realistic assumption that it takes time which we call the detection time, for a vertex to be identified as infected, and implement two different immunization strategies: one is based on connection neighbors (CN) of the infected vertex with the exact information of the network structure utilized and the other is based on spatial neighbors (SN) with only geographical distances taken into account. We find that the decrease of the detection time is crucial for a successful immunization in general. Simulation results show that for both SF networks and WS networks, the SN strategy always performs better than the CN strategy, especially for more heterogeneous SF networks at long detection time. The observation is verified by checking the number of the infected nodes being immunized. We found that in geographical space, the distance preferences in the network construction process and the geographically decaying infection rate are key factors that make the SN immunization strategy outperforms the CN strategy. It indicates that even in the absence of the full knowledge of network connectivity we can still stop the epidemic spread efficiently only by using geographical information as in the SN strategy, which may have potential applications for preventing the real epidemic spread. 相似文献
4.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
5.
W. Ebeling H. Hache M. Spahn 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):265-272
Applying Gibb's geometrical methods to the thermodynamics of H-plasmas we explore the landscape of the free energy as a function
of the degrees of ionization and dissociation. Several approximations for the free energy are discussed. We show that in the
region of partial ionization/dissociation the quantum Debye-Hückel approximation (QDHA) yields a rather good but still simple
representation which allows to include magnetic field and fluctuation effects. By using relations of Onsager-Landau-type the
probability of fluctuations and ionization/dissociation processes are described. We show that the degrees of ionization/dissociation
are probabilistic quantities which are subject to a relatively large dispersion. Magnetic field effects are studied.
Received 10 September 2002 / Received in final form 26 November 2002 Published online 11 February 2003 相似文献
6.
7.
S.C. Manrubia U. Bastolla A.S. Mikhailov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):497-508
Systems of globally coupled logistic maps (GCLM) can display complex collective behaviour characterized by the formation of
synchronous clusters. In the dynamical clustering regime, such systems possess a large number of coexisting attractors and
might be viewed as dynamical glasses. Glass properties of GCLM in the thermodynamical limit of large system sizes N are investigated. Replicas, representing orbits that start from various initial conditions, are introduced and distributions
of their overlaps are numerically determined. We show that for fixed-field ensembles of initial conditions all attractors
of the system become identical in the thermodynamical limit up to variations of order 1/, and thus replica symmetry is recovered for N→∞. In contrast to this, when fluctuating-field ensembles of initial conditions are chosen, replica symmetry remains broken
in the thermodynamical limit.
Received 9 July 2001 相似文献
8.
D.F. Zheng P.M. Hui K.F. Yip N.F. Johnson 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):213-218
We present generalized dynamical models describing the sharing of information, and the corresponding herd behavior, in a population
based on the recent model proposed by Eguıluz and Zimmermann (EZ) [Phys. Rev. Lett. 85, 5659 (2000)]. The EZ model, which is a dynamical version of the herd formation model of Cont and Bouchaud (CB), gives a
reasonable model for the formation of clusters of agents and for actions taken by clusters of agents. Both the EZ and CB models
give a cluster size distribution characterized by a power law with an exponent -5/2. By introducing a size-dependent probability
for dissociation of a cluster of agents, we show that the exponent characterizing the cluster size distribution becomes model-dependent
and non-universal, with an exponential cutoff for large cluster sizes. The actions taken by the clusters of agents generate
the price returns, the distribution of which is also characterized by a model-dependent exponent. When a size-dependent transaction
rate is introduced instead of a size-dependent dissociation rate, it is found that the distribution of price returns is characterized
by a model-dependent exponent while the exponent for the cluster-size distribution remains unchanged. The resulting systems
provide simplified models of a financial market and yield power law behaviour with an easily tunable exponent.
Received 31 December 2001 相似文献
9.
J.-M. Courty A. Heidmann M. Pinard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):399-408
Thermal noise of a mirror can be reduced by cold damping. The displacement is measured with a high-finesse cavity and controlled
with the radiation pressure of a modulated light beam. We establish the general quantum limits of noise in cold damping mechanisms
and we show that the optomechanical system allows to reach these limits. Displacement noise can be arbitrarily reduced in
a narrow frequency band. In a wide-band analysis we show that thermal fluctuations are reduced as with classical damping whereas
quantum zero-point fluctuations are left unchanged. The only limit of cold damping is then due to zero-point energy of the
mirror.
Received 1st August 2001 and Received in final form 12 October 2001 相似文献
10.
P. Stein N. Aßfalg H. Finkelmann P. Martinoty 《The European physical journal. E, Soft matter》2001,4(3):255-262
We investigate the behavior of the complex shear modulus of a series of elastomers including mono-domain and poly-domain liquid
crystal samples, and a non-mesomorphic sample. We find that the dynamics of the glass transition are strongly modified by
the nematic order. This result explains why the truly elastic response of liquid crystal elastomers can only be observed in
the isotropic phase at very high temperatures and at very low frequencies. Between the elastic regime and the glassy state,
the elastomers have a visco-elastic regime, which is characterized by a Rouse-like behavior for mono-domain and poly-domain
samples, and by a Zimm-like behavior for the non-mesomorphic sample. We also show that the mono-domain sample exhibits marked
anisotropy of the shear-modulus G
′. This anisotropy, which is observed for the first time, is a function of frequency and is inverted between low and high frequencies,
due to relaxation effects of the orientational order.
Received 28 January 2000 and Received in final form 16 October 2000 相似文献
11.
R. Monasson 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):555-567
The spectral properties of the Laplacian operator on “small-world” lattices, that is mixtures of unidimensional chains and
random graphs structures are investigated numerically and analytically. A transfer matrix formalism including a self-consistent
potential à la Edwards is introduced. In the extended region of the spectrum, an effective medium calculation provides the density of states
and pseudo relations of dispersion for the eigenmodes in close agreement with the simulations. Localization effects, which
are due to connectivity fluctuations of the sites are shown to be quantitatively described by the single defect approximation
recently introduced for random graphs.
Received 23 March 1999 相似文献
12.
The spatial confinement of a fluctuation spectrum leads to forces at the confining boundaries. While electromagnetic (EM)
fluctuations lead to the well-known dispersion forces, the acoustic analogy has widely been neglected. We show that the strength
of the forces resulting from confined acoustic modes may be of the same order of magnitude as van der Waals forces. Additionally,
the predicted scaling behavior is identical to the non-retarded case of the EM fluctuations. Our results suggest that dewetting
experiments using polymer films are strongly influenced by the acoustic dispersion forces.
Received 5 March 2002 and Received in final form 21 May 2002 相似文献
13.
V. Bernard N. Kaiser U.-G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):209-216
We investigate near-threshold neutral pion photoproduction off protons to fourth order in heavy-baryon chiral perturbation
theory in the light of the new data from MAMI. We show that the unitarity cusp at the secondary π+
n threshold is in agreement with expectations from the final-state theorem. We also analyze the fourth-order corrections to
the P-wave low-energy theorems and show that potentially large Δ isobar contributions are cancelled by sizeable pion loop effects.
This solidifies the parameter-free third-order predictions, which are in good agreement with the data.
Received: 25 May 2001 / Accepted: 21 June 2001 相似文献
14.
V.S. Gerdjikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):237-241
We compare the Hamiltonian properties of the N-soliton solutions of the NLSE in the adiabatic approximation and show how it matches the Hamiltonian formulation for the
complex Toda chain which describes the adiabatic N-soliton interactions.
Received 21 October 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: gerjikov@inrne.bas.bg 相似文献
15.
D.H. Zanette 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):623-628
A dynamical model for the distribution of resources among competing agents is studied. The model is exactly solvable in the
case of global competition, which leads to the accumulation of all the resources by the agent with the highest performance.
On the other hand, local competition allows for a wider resource distribution, with a much weaker correlation with individual
performances. Multiplicative processes give rise to almost-ordered spatial structures, through the enhancement of random fluctuations.
Received 17 August 2000 and Received in final form 1st November 2000 相似文献
16.
Slow dynamics of density fluctuations near the colloidal glass transition is discussed from a new viewpoint by numerically
solving a nonlinear stochastic diffusion equation for the density fluctuations recently proposed by one of the present authors
(MT). The effects of spatial heterogeneities on the dynamics of density fluctuations are then investigated in an equilibrium
system. The spatial heterogeneities are generated by the nonlinear density fluctuations, while in a nonequilibrium system
they are described by a nonlinear deterministic equation for the average number density. The dynamics of equilibrium density
fluctuations is thus shown to be quite different from that of nonequilibrium ones, leading to a logarithmic decay followed
by less distinct α- and β-relaxation processes.
Received 9 March 2002 and Received in final form 19 September 2002 相似文献
17.
The lifetime of the soliton in the improved Davydov model at the biological temperature 300 K for protein molecules 总被引:7,自引:0,他引:7
Pang Xiao-feng 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):297-316
We study the effects of quantum fluctuations and thermal perturbations on the lifetime of the soliton in the improved Davydov
model proposed by us with two-quanta and with an added interaction. By using quantum perturbation theory, we compute the soliton
lifetime for a wide ranges of parameter values relevant for protein molecules. The lifetime of the new soliton at the biological
temperature 300 K is of the order of 10-10 second or τ/τ≥ 500 for parameters appropriate to α-helical protein molecules. This shows clearly that the new soliton in the improved model
is a viable mechanism for the bio-energy transport in the α-helix region of proteins.
Received 7 January 1999 and Received in final form 16 August 2000 相似文献
18.
K. Broderix M. Weigt A. Zippelius 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):441-455
We consider the gelation of particles which are permanently connected by random crosslinks, drawn from an ensemble of finite-dimensional
continuum percolation. To average over the randomness, we apply the replica trick, and interpret the replicated and crosslink-averaged
model as an effective molecular fluid. A Mayer-cluster expansion for moments of the local static density fluctuations is set
up. The simplest non-trivial contribution to this series leads back to mean-field theory. The central quantity of mean-field
theory is the distribution of localization lengths, which we compute for all connectivities. The highly crosslinked gel is
characterized by a one-to-one correspondence of connectivity and localization length. Taking into account higher contributions
in the Mayer-cluster expansion, systematic corrections to mean-field can be included. The sol-gel transition shifts to a higher
number of crosslinks per particle, as more compact structures are favored. The critical behavior of the model remains unchanged
as long as finite truncations of the cluster expansion are considered. To complete the picture, we also discuss various geometrical
properties of the crosslink network, e.g. connectivity correlations, and relate the studied crosslink ensemble to a wider class of ensembles, including the Deam-Edwards
distribution.
Received on 24 April 2002 Published online 14 October 2002
RID="a"
ID="a"deceased
RID="b"
ID="b"e-mail: weigt@theorie.physik.uni-goettingen.de 相似文献
19.
A.T. Bernardes D. Stauffer J. Kertész 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):123-127
The network of Barabasi and Albert, a preferential growth model where a new node is linked to the old ones with a probability
proportional to their connectivity, is applied to Brazilian election results. The application of the Sznajd rule, that only
agreeing pairs of people can convince their neighbours, gives a vote distribution in good agreement with reality
Received 19 September 2001 and Received in final form 2 November 2001 相似文献
20.
I.I. Satija 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):345-348
Disordered systems exhibiting exponential localization are mapped to anisotropic spin chains with localization length being
related to the anisotropy of the spin model. This relates localization phenomenon in fermions to the rotational symmetry breaking
in the critical spin chains. One of the intriguing consequence is that the statement of Onsager universality in spin chains
implies universality of the localized fermions where the fluctuations in localized wave functions are universal. We further
show that the fluctuations about localized nonrelativistic fermions describe relativistic fermions. This provides a new approach
to understand the absence of localization in disordered Dirac fermions. We investigate how disorder affects well known universality
of the spin chains by examining the multifractal exponents. Finally, we examine the effects of correlations on the localization
characteristics of relativistic fermions.
Received 28 September 2001 / Received in final form 30 November 2001 Published online 2 October 2002
RID="a"
ID="a"e-mail: isatija@nickel.nist.gov 相似文献