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Epidemic spreading in a finite-precision BA model Ababou, Malika ; Vandewalle, Nicolas ; et al in Physica A: Statistical Mechanics and its Applications (2011) The Barabasi-Albert (BA) model with ﬁnite-precision preferential attachment is used to build a wide range of network structures. Spreading epidemics and collective dynamics are investigated on such ... [more ▼] The Barabasi-Albert (BA) model with ﬁnite-precision preferential attachment is used to build a wide range of network structures. Spreading epidemics and collective dynamics are investigated on such complex networks. Numerical simulations reveal a transition from an exponential scaling to a power law distribution of link numbers per node along with the increase of the tuning parameter ω. The collective synchronization induced by Susceptible- Infected-Recovered-Susceptible (SIRS) epidemiological process is shown to depend on the topological structure of the network. [less ▲] Detailed reference viewed: 137 (16 ULg)Has the world economy reached its globalization limit? ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2010), 389(4), 797-806 The economy globalization measure problem is discussed. Four macroeconomic indices of twenty among the "richest" countries are examined. Four types of "distances" are calculated. Two types of networks are ... [more ▼] The economy globalization measure problem is discussed. Four macroeconomic indices of twenty among the "richest" countries are examined. Four types of "distances" are calculated. Two types of networks are next constructed for each distance measure definition. It is shown that the globalization process can be best characterised by an entropy measure, based on entropy Manhattan distance. It is observed that a globalization maximum was reached during the interval 1970-2000. More recently a deglobalization process has been observed. (C) 2009 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 4 (0 ULg)Dynamic peer-to-peer competition ; ; et al in Physica A: Statistical Mechanics and its Applications (2010), 389(13), 2628-2636 The dynamic behavior of a multiagent system in which the agent size si is variable it is studied along a Lotka-Volterra approach. The agent size has hereby the meaning of the fraction of a given market ... [more ▼] The dynamic behavior of a multiagent system in which the agent size si is variable it is studied along a Lotka-Volterra approach. The agent size has hereby the meaning of the fraction of a given market that an agent is able to capture (market share). A Lotka-Volterra system of equations for prey-predator problems is considered, the competition factor being related to the difference in size between the agents in a one-on-one competition. This mechanism introduces a natural self-organized dynamic competition among agents. In the competition factor, a parameter sigma is introduced for scaling the intensity of agent size similarity, which varies in each iteration cycle. The fixed points of this system are analytically found and their stability analyzed for small systems (with n = 5 agents). We have found that different scenarios are possible, from chaotic to non-chaotic motion with cluster formation as function of the a parameter and depending on the initial conditions imposed to the system. The present contribution aim is to show how a realistic though minimalist nonlinear dynamics model can be used to describe the market competition (companies, brokers, decision makers) among other opinion maker communities. (C) 2010 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 22 (1 ULg)Organization of networks with tagged nodes and biased links: A priori distinct communities The case of intelligent design proponents and Darwinian evolution defenders ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2010), 389(23), 5479-5494 Among the topics of opinion formation it is of interest to observe the characteristics of networks with a priori distinct communities. The citation network(s) between selected members of the ... [more ▼] Among the topics of opinion formation it is of interest to observe the characteristics of networks with a priori distinct communities. The citation network(s) between selected members of the Neocreationist and Intelligent Design and the Darwinian Evolution communities are unfolded through the available internet citations. The resulting adjacency matrix is not symmetric. A generalization of considerations pertaining to the case of networks with tagged nodes and biased links, directed or undirected, is presented. The main characteristic coefficients describing the structure of such networks are outlined. The structural features are discussed searching for statistical aspects of the communities. The degree distributions, each network's assortativity, specific global and local clustering coefficients and the Average Overlap Indices are especially calculated since the distribution of elements in the rectangular submatrices represent inter-community connections. The various closed and open triangles made from nodes, distinguishing the community, are listed. The z-scores of patterns are calculated. One can distinguish between opinion leaders, followers and main rivals and briefly interpret their relationships through intuitively expected behavior in defence of an opinion. Suggestions for more elaborate models describing such communities and their subsequent structures are found in conclusions. (C) 2010 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 9 (0 ULg)Statistical mechanics approach to a reinforcement learning model with memory ; ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2009), 388(9), 1849-1856 We introduce a two-player model of reinforcement learning with memory. Past actions of an iterated game are stored in a memory and used to determine player's next action. To examine the behaviour of the ... [more ▼] We introduce a two-player model of reinforcement learning with memory. Past actions of an iterated game are stored in a memory and used to determine player's next action. To examine the behaviour of the model some approximate methods are used and confronted against numerical simulations and exact master equation. When the length of memory of players increases to infinity the model undergoes ail absorbing-state phase transition. Performance of examined strategies is checked in the prisonor' dilemma game. It turns out that it is advantageous to have a large memory in symmetric games, but it is better to have a short memory in asymmetric ones. (C) 2009 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 12 (0 ULg)Correlation measure to detect time series distances, whence economy globalization ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2008), 387(26), 6584-6594 An instantaneous time series distance is defined through the equal time correlation coefficient. The idea is applied to the Gross Domestic Product (GDP) yearly increments of 21 rich countries between 1950 ... [more ▼] An instantaneous time series distance is defined through the equal time correlation coefficient. The idea is applied to the Gross Domestic Product (GDP) yearly increments of 21 rich countries between 1950 and 2005 in order to test the process of economic globalisation. Some data discussion is first presented to decide what (EKS, GK, or derived) GDP series should be studied. Distances are then calculated from the correlation coefficient values between pairs of series. The role of time averaging of the distances over finite size windows is discussed. Three network structures are next constructed based on the hierarchy of distances. It is shown that the mean distance between the most developed countries on several networks actually decreases in time, -which we consider as a proof of globalization. An empirical law is found for the evolution after 1990 similar to that found, in flux creep. The optimal observation time window size is found similar or equal to 15 years. (c) 2008 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 22 (1 ULg)Risk of population extinction from periodic and abrupt changes of environment ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2008), 387(11), 2526-2534 A simulation model of a population having internal (genetic) structure is presented. The population is subject to selection pressure coming from the environment which is the same in the whole system but ... [more ▼] A simulation model of a population having internal (genetic) structure is presented. The population is subject to selection pressure coming from the environment which is the same in the whole system but changes in time. Reproduction has a sexual character with recombination and mutation. Two cases are considered - oscillatory changes of the environment and abrupt ones (catastrophes). We show how the survival chance of a population depends on the maximum allowed size of the population, the length of the genotypes characterizing individuals, selection pressure and the characteristics of the "climate" changes, either their period of oscillations or the scale of the abrupt shift. (C) 2008 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 8 (0 ULg)Power law for the duration of recession and prosperity in Latin American countries ; ; Ausloos, Marcel in Physica A: Statistical Mechanics and its Applications (2008), 387(25), 6330-6336 Ormerod and Mounfield [P. Ormerod, C. Mounfield, Power law distribution of duration and magnitude of recessions in capitalist economies: Breakdown of scaling, Physica A 293 (2001) 573] and Ausloos et al ... [more ▼] Ormerod and Mounfield [P. Ormerod, C. Mounfield, Power law distribution of duration and magnitude of recessions in capitalist economies: Breakdown of scaling, Physica A 293 (2001) 573] and Ausloos et al. [M. Ausloos, J. Mikievvicz, M. Sanglier, The durations of recession and prosperity: Does their distribution follow a power or an exponential law? Physica A 339 (2004) 548] have independently analyzed the duration of recessions for developed countries through the evolution of the GDP in different time windows. It was found that there is a power law governing the duration distribution. We have analyzed data collected from 19 Latin American countries in order to observe whether such results are valid or not for developing countries. The case of prosperity years is also discussed. We observe that the power law of recession time intervals, see Ref. [1], is valid for Latin American countries as well. Thus an interesting point is discovered: the same scaling time is found in the case of recessions for the three data sets (ca. 1 year), and this could represent a universal feature. Other time scale parameters differ significantly from each other. (C) 2008 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 20 (2 ULg)Multifractal properties of Pyrex and silicon surfaces blasted with sharp particles ; Kraft, Michaël ; in Physica A: Statistical Mechanics and its Applications (2008), 387(8-9), 2083--2090 The blasting of brittle materials with sharp particles is an important fabrication technology in many industrial processes. In particular, for microsystems, it allows the production of devices with ... [more ▼] The blasting of brittle materials with sharp particles is an important fabrication technology in many industrial processes. In particular, for microsystems, it allows the production of devices with feature sizes down to few tens of microns. An important parameter of this process is the surface roughness of post-blasted surfaces. In this work the scaling properties of Pyrex glass and silicon surfaces after bombardment with alumina particles are investigated. The targets were bombarded at normal incidence using alumina particles with two different average sizes, 29 μm and 9 μm. This investigation indicates that the resulting surfaces are multifractal. Applying multifractal detrended fluctuation analysis (MFDFA) allowed us to determine the singularity spectrum of the surfaces. This spectrum did not depend on the target material or on the size of the particles. Several parameters quantifying relevant quantities were determined. It was found that long range correlations are responsible for the observed multifractal behaviour. [less ▲] Detailed reference viewed: 14 (0 ULg)Experimental evidences of a structural and dynamical transition in fish school Becco, Christophe ; Vandewalle, Nicolas ; Delcourt, Johann et al in Physica A: Statistical Mechanics and its Applications (2006), 367 We have developed a video tracking system in order to determine all the trajectories of young fish (Oreochromis niloticus L.) within a school. Both individual and collective behaviours have been studied ... [more ▼] We have developed a video tracking system in order to determine all the trajectories of young fish (Oreochromis niloticus L.) within a school. Both individual and collective behaviours have been studied as a function of the number of fish per unit area. By studying distributions of distances between fish and distributions of relative orientations, structural effects and cooperative motions have been evidenced. Signatures of a phase transition have been found, as predicted by some numerical models. This work opens new perspectives in the study of collective phenomena in biological systems since it is the first time that such measurements are possible. [less ▲] Detailed reference viewed: 174 (55 ULg)Microporous and heterogeneous surface adsorption isotherms arising from Levy distributions Brouers, François ; ; et al in Physica A: Statistical Mechanics and its Applications (2005), 349(1-2), 271-282 We show that for adsorption on heterogeneous and microporous surfaces, the Freundlich isotherm power-law exponent a is directly related to the Levy tail index of the distribution of the Langmuir parameter ... [more ▼] We show that for adsorption on heterogeneous and microporous surfaces, the Freundlich isotherm power-law exponent a is directly related to the Levy tail index of the distribution of the Langmuir parameter b and to the expected value and the variance of the adsorption energy distribution. This allows us to view adsorption at low pressure in these systems as a rare event dominated phenomena. Based on this discussion, a generalized isotherm formulation is proposed and applied to the interpretation of recent data on activated carbons. (C) 2004 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 34 (3 ULg)Bubble and granular flows: differences and similarities Caps, Hervé ; Trabelsi, Samy ; Dorbolo, Stéphane et al in Physica A: Statistical Mechanics and its Applications (2004), 344(3-4), 424-430 We have experimentally studied the dense flow of identical bubbles below planes inclined at an angle theta. The flow is driven by the fast motion of dislocations. As a function of the density of ... [more ▼] We have experimentally studied the dense flow of identical bubbles below planes inclined at an angle theta. The flow is driven by the fast motion of dislocations. As a function of the density of dislocations (controlled by the parameter theta), a transition occurs between a simple collective block motion and a granular-like surface flow regime. (C) 2004 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 34 (6 ULg)From scale invariance to deterministic chaos in DNA sequences: towards a deterministic description of gene organisation in the human genome Nicolay, Samuel ; ; et al in Physica A: Statistical Mechanics and its Applications (2004), 342 We use the continuous wavelet transform to perform a space-scale analysis of the AT and GC skews (strand asymmetries) in human genomic sequences, which have been shown to correlate with gene transcription ... [more ▼] We use the continuous wavelet transform to perform a space-scale analysis of the AT and GC skews (strand asymmetries) in human genomic sequences, which have been shown to correlate with gene transcription. This study reveals the existence of a characteristic scale `c 25 ± 10 kb that separates a monofractal long-range correlated noisy regime at small scales (` ¡ `c ) from relaxational oscillatory behavior at large-scale (` ¿ `c ). We show that these large scale nonlinear oscillations enlighten an organization of the human genome into adjacent domains ( 400 kb) with preferential gene orientation. When using classical techniques from dynamical systems the- ory, we demonstrate that these relaxational oscillations display all the characteristic properties of the chaotic strange attractor behavior observed nearby homoclinic orbits of Shil'nikov type. We discuss the possibility that replication and gene regulation processes are governed by a low-dimensional dynamical system that displays deterministic chaos. c 2004 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 25 (4 ULg)Long lasting instabilities in granular mixtures Caps, Hervé ; ; et al in Physica A: Statistical Mechanics and its Applications (2003), 326(3-4), 313-321 We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and ... [more ▼] We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurrence of instabilities which can last several hours! We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurrence of giant fluctuations in the fraction of grain species along the surface during the unstable periods. (C) 2003 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 10 (4 ULg)Dynamics of crack opening in a one-dimensional desiccation experiment ; Vandewalle, Nicolas in Physica A: Statistical Mechanics and its Applications (2003), 321(3-4), 431-441 We used a simple one-dimensional experiment to investigate the dynamical aspects of crack opening that occurs in clay exposed to shrinkage induced by desiccation. The opening rate of single cracks is ... [more ▼] We used a simple one-dimensional experiment to investigate the dynamical aspects of crack opening that occurs in clay exposed to shrinkage induced by desiccation. The opening rate of single cracks is obtained. A simple model is introduced to account for the observed behavior. Interaction between adjacent cracks is put into evidence and a collective behavior is observed. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 15 (2 ULg)Cascades of popping bubbles Vandewalle, Nicolas ; Caps, Hervé ; Dorbolo, Stéphane in Physica A: Statistical Mechanics and its Applications (2002), 314(1-4), 320-324 We study the intermittent dynamics of collapsing foams. Avalanches of popping bubbles are observed. Although correlations between successive popping bubbles are emphasized, film raptures at the air/foam ... [more ▼] We study the intermittent dynamics of collapsing foams. Avalanches of popping bubbles are observed. Although correlations between successive popping bubbles are emphasized, film raptures at the air/foam interface seem to be independent of the bubble size. Possible mechanisms for cascades of bubble pops are proposed and discussed. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 17 (3 ULg)Patterns in hydraulic ripples with binary granular mixtures Caps, Hervé ; Vandewalle, Nicolas in Physica A: Statistical Mechanics and its Applications (2002), 313(3-4), 357-364 An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of ... [more ▼] An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of phase segregation in those spiral patterns is shown. The relative grain size between sand species is found to be a relevant parameter leading to phase segregation. However, the relative repose angle is an irrelevant parameter. The formation of sedimentary structures is also presented. They result from a ripple climbing process. The "sub-critical" or "super-critical" character of the lamination patterns is shown to depend on the rotation speed of the container. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 14 (1 ULg)Electrical investigations of granular arches Dorbolo, Stéphane ; Vandewalle, Nicolas in Physica A: Statistical Mechanics and its Applications (2002), 311(3-4), 307-312 Compaction dynamics and granular arches have been studied using the electrical resistance of a packing. An exponential decay of the resistance is found whatever the electrical current is. A fluctuation ... [more ▼] Compaction dynamics and granular arches have been studied using the electrical resistance of a packing. An exponential decay of the resistance is found whatever the electrical current is. A fluctuation regime is then encountered. A characteristic relaxation time has been pointed out and is linked to the arch formation in the system. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 12 (5 ULg)Applications of statistical physics - Proceedings of the NATO Advanced Research Workshop held at Technical University of Budapest Hungary, 19-22 May 1999 - Preface ; ; et al in Physica A: Statistical Mechanics and its Applications (1999), 274(1-2), - Detailed reference viewed: 12 (0 ULg)Applications of statistical physics to economic and financial topics Ausloos, Marcel ; Vandewalle, Nicolas ; et al in Physica A: Statistical Mechanics and its Applications (1999), 274(1-2), 229-240 Problems in economy and finance have started to attract the interest of statistical physicists. Fundamental problems pertain to the existence or not of long-, medium-, short-range power-law correlations ... [more ▼] Problems in economy and finance have started to attract the interest of statistical physicists. Fundamental problems pertain to the existence or not of long-, medium-, short-range power-law correlations in economic systems as well as to the presence of financial cycles. Methods like the extended detrented fluctuation analysis, and the multi-affine analysis are recalled emphasizing their value in sorting out correlation ranges and predictability. Among spectacular results, the possibility of crash predictions is indicated. The well known financial analyst technique, the so-called moving average, is shown to raise questions about fractional Brownian motion properties. Finally, the (m,k)-Zipf method and the i-variability diagram technique are presented for sorting out short range correlations. Analogies with other fields of modem applied statistical physics are also presented in view of some universal openess. [less ▲] Detailed reference viewed: 65 (7 ULg) |
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