# Laura HernándezUniversité de Cergy-Pontoise · Laboratoire de physique théorique et modélisation

Laura Hernández

PhD - HDR

## About

59

Publications

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456

Citations

Introduction

Associate professor at Cergy Pontoise University since 1993, I did my undergraduate studies at Buenos Aires University, I have obtained my PhD in Physics in 1992 at the Institut National des Sciences Appliquées (INSA) Toulouse, and my HDR (“Habilitation to Conduct Research” French diploma) in 2015, at Cergy Pontoise University.
I'm interested in the study of complexity in Physics, as well as in other fields like Ecology or Social Sciences, with the tools and the point of view of Physics.

Additional affiliations

October 1993 - July 2015

March 1988 - March 1990

## Publications

Publications (59)

Two main procedures characterize the way in which social actors evaluate the qualities of the options in decision-making processes: they either seek to evaluate their intrinsic qualities (individual learners), or they rely on the opinion of the others (social learners). For the latter, social experiments have suggested that the mathematical form of...

Mutualistic relationships, where species interact to obtain mutual benefits, constitute an essential component of natural ecosystems. The use of ecological networks to represent the species and their ecological interactions allows the study of structural and dynamic patterns common to different ecosystems. However, by neglecting the temporal dimens...

We present an extensive study of the joint effects of heterogeneous social agents and their heterogeneous social links in a bounded confidence opinion dynamics model. The full phase diagram of the model is explored for two different network’s topologies and compared to two opposed extreme cases: on one hand, the heterogeneous agents constitute a mi...

Within the framework of Game Theory, contests study decision-making in those situations or conflicts when rewards depend on the relative rank between contenders rather than their absolute performance. By relying on the formalism of Tullock success functions, we propose a model where two contenders fight in a conflict on two fronts with different te...

We study the dynamics of interactions between a traditional medium, the New York Times journal, and its followers in Twitter, using a massive dataset. It consists of the metadata of the articles published by the journal during the first year of the COVID-19 pandemic, and the posts published in Twitter by a large set of followers of the @nytimes acc...

We present an extensive study of the joint effects of heterogeneous social agents and their heterogeneous social links in a bounded confidence opinion dynamics model. The full phase diagram of the model is explored for two different network's topologies and compared to two opposed extreme cases: on one hand heterogeneous agents which constitute a m...

We study the dynamics of interactions between a traditional medium, the New York Times journal, and its followers in Twitter, using a massive dataset. It consists of the metadata of the articles published by the journal during the first year of the COVID-19 pandemic, and the posts published in Twitter by a large set of followers of the @nytimes acc...

Most opinion dynamics models are based on pairwise interactions. However in many real situations, discussions take place within groups of people. Here, we define a higher order Deffuant model by generalizing the original pairwise interaction model for bounded-confidence opinion-dynamics to interactions involving a group of agents of size k. The gen...

We present a study of the evolution of the political landscape during the 2015 and 2019 presidential elections in Argentina, based on data obtained from the micro-blogging platform Twitter. We build a semantic network based on the hashtags used by all the users following at least one of the main candidates. With this network we can detect the topic...

We define a higher order Deffuant model by generalizing the original pairwise interaction model for bounded-confidence opinion-dynamics to interactions involving a group of agents of size k. The generalized model is naturally encoded in a hypergraph. We study this dynamics in different hypergraph topologies, from random hypergraph ensembles, to spa...

We study the influence of hesitating agents in the Axelrod model by introducing an intrinsic noise, which is proportional to the disagreement between the interacting agents, and thus coupled to the dynamics. Our results show that, unlike the effect of the cultural drift where the noise is just controlled by an external parameter, the intrinsic nois...

We study the influence of hesitating agents in the Axelrod model by introducing an intrinsic noise, which is proportional to the disagreement between the interacting agents, and thus coupled to the dynamics. Our results show that, unlike the effect of the cultural drift where the noise is just controlled by an external parameter, the intrinsic nois...

In this work we present results to the problem of the Hegselmann-Krause dynamics in networks obtained by an extensive study of the behavior of the standard order parameter sensitive to the onset of consensus: the normalized size of the giant cluster. This order parameter reveals the nontrivial effect of the network topology on the steady states of...

In this work we present novel results to the problem of the Hegselmann-Krause dynamics in networks obtained by an extensive study of the behavior of the standard order parameter sensitive to the onset of consensus: the normalized size of the giant cluster. This order parameter reveals the non trivial effect of the network topology on the steady sta...

We present a study of the evolution of the political landscape during the 2015 and 2019 presidential elections in Argentina, based on the data obtained from the micro-blogging platform Twitter. We build a semantic network based on the hashtags used by all the users following at least one of the main candidates. With this network we can detect the t...

Abstract Nestedness is a property of interaction networks widely observed in natural mutualistic communities, among other systems. A perfectly nested network is characterized by the peculiarity that the interactions of any node form a subset of the interactions of all nodes with higher degree. Despite a widespread interest on this pattern, no gener...

We study the dynamics of opinion formation in the situation where changing opinion involves a cost for the agents. To do so we couple the dynamics of a heterogeneous bounded confidence Hegselmann–Krause model with that of the resources that the agents invest on each opinion change. The outcomes of the dynamics are non-trivial and strongly depend on...

We study the dynamics of opinion formation in the situation where changing opinion involves a cost for the agents. To do so we couple the dynamics of a heterogeneous bounded confidence Hegselmann-Krause model with that of the resources that the agents invest on each opinion change. The outcomes of the dynamics are non-trivial and strongly depend on...

We perform a detailed study of the Hegselmann-Krause bounded confidence opinion dynamics model with heterogeneousconfidence εi drawn from uniform distributions in different intervals [ε1, εu]. The phase diagram reveals a highly complex andnon-monotonous behaviour, with a re-entrant consensus phase in the region where fragmentation into multiple dis...

Nestedness is a property of interaction networks widely observed in natural mutualistic communities, like plant-pollinators or plant-seed dispersers, among other systems. A perfectly nested network is characterized by the peculiarity that the interactions of any node form a subset of the interactions of all nodes with higher degree. Despite a wides...

We perform a detailed study of the Hegselmann-Krause bounded confidence opinion dynamics model with heterogeneous confidence $\varepsilon_i$ drawn from uniform distributions in different intervals $[\varepsilon_l, \varepsilon_u]$. The phase diagram reveals a highly complex and nonmonotonous behaviour, with a re-entrant consensus phase in the region...

Mutualistic interactions, those that are naturally beneficial for both interacting species, are recurrently found in ecosystems. Observations of natural systems show that if we draw mutualistic relationships as links between species, the resulting mutualistic network of interactions displays a widespread particular ordering called nestedness. In su...

Relations among species in ecosystems can be represented by complex networks where both negative (competition) and positive (mutualism) interactions are concurrently present. Recently, it has been shown that many ecosystems can be cast into mutualistic networks, and that nestedness reduces effective inter-species competition, thus facilitating mutu...

Centralized markets are often considered more efficient than bilateral exchanges because information is public and the same for all the agents. On decentralized markets, where the information is private, the influence of trust on the market outcome has been underlined by many authors. We present an empirical study of the distinctive Boulogne-sur-Me...

SI to introduction, nestedness definition.
Description of a perfectly nested mutualistic ecosystems.
(ZIP)

SI to materials and methods.
Description of different nestedness indices.
(ZIP)

SI to results.
In this supplement we give the nestedness values obtained with different indices for the global period along with details of the daily analyzed matrices and their nestedness index using NIR. We also provide more examples as a complement of the results shown in Figs 2 and 6 of the main text.
(ZIP)

Mutualistic interactions, which are beneficial for both interacting species, are recurrently present in ecosystems. Observations of natural systems showed that, if we draw mutualistic relationships as binary links between species, the resulting bipartite network of interactions displays a widespread particular ordering called nestedness [1]. On the...

Mutualistic interactions, which are beneficial for both interacting species, are recurrently present in ecosystems. Observations of natural systems showed that, if we draw mutualistic relationships as binary links between species, the resulting bipartite network of interactions displays a widespread particular ordering called nestedness. On the oth...

Relations among species in ecosystems can be represented by complex networks where both negative (competition) and positive (mutualism) interactions are concurrently present. Recently , it has been shown that many ecosystems can be cast into mutualistic networks, and that nestedness reduces effective intra-species competition, thus facilitating mut...

Centralized markets are often considered as being more efficient than bilateral exchanges, based on the fact that information is uniformly spread among all the agents. However, the influence of trust on the outcome of decentralized markets has been underlined by many authors. We present an empirical study of the distinctive Boulogne-sur-Mer fish ma...

Complex Systems are usually defined as systems where the collective behavior of their parts entails the emergence of properties that can hardly, if not at all, be inferred from the properties of those parts. They usually present nonlinear interactions, multiscale phenomena and feedback loops. Complex Systems are then, ubiquitous, appear at differen...

We study an opinion formation model by the means of a co-evolving complex
network where the vertices represent the individuals, characterised by their
evolving opinions, and the edges represent the interactions among them. The
network adapts to the spreading of opinions in two ways: not only connected
agents interact and eventually change their thi...

Elections constitute a paradigm of decision-making problems that have puzzled experts of different disciplines for decades. We study two decision-making problems, where groups make decisions that impact only themselves as a group. In both studied cases, participation in local elections and the number of democratic representatives at different scale...

Elections constitute a paradigm of decision making problems that have puzzled
experts of different disciplines for decades. We study two decision making
problems, where groups make decisions that only impact themselves as a group.
In both studied cases, participation to local elections and the number of
democratic representatives at different scale...

Starting from Axelrod's model of cultural dissemination, we introduce a
rewiring probability, enabling agents to cut the links with their unfriendly
neighbors if their cultural similarity is below a tolerance parameter. For low
values of tolerance, rewiring promotes the convergence to a frozen monocultural
state. However, intermediate tolerance val...

We investigate how the pattern of contacts between species in mutualistic
ecosystems is affected by the phylogenetic proximity between the species of
each guild. We develop a dynamical model geared to establish the role of such
proximity in the emergence of a nested pattern of contacts. We also define a
parameter that provides a direct measure of t...

Community ecologists are principally occupied with the proposition that
natural assemblages of species exhibit orderliness and with identifying its
causes. Plant-pollinator networks exhibit a variety of orderly properties, one
of which is 'nestedness'. Nestedness has been attributed to various causes, but
we propose a further influence arising from...

We investigate how the pattern of contacts between species in mutualistic ecosystems is affected by the phylogenetic proximity between the species of each guild. We develop several theoretical tools to measure that effect and we use them to examine some real mutualistic sytems. We aim at establishing the role of such proximity in the emergence of a...

Bipartite graphs have received some attention in the study of social networks and of biological mutualistic systems. A generalization of a previous model is presented, that evolves the topology of the graph in order to optimally account for a given contact preference rule between the two guilds of the network. As a result, social and biological gra...

In this work we present a dynamical model that succesfully describes the organization of mutualistic ecological systems. The main characteristic of these systems is the nested structure of the bipartite adjacency matrix describing their interactions. We introduce a nestedness coefficient, as an alternative to the Atmar and Patterson temperature, co...

We apply the Wang–Landau method to the study of the critical behavior of the three-dimensional random field Ising model with a bimodal probability distribution. For high values of the random field intensity we find that the energy probability distribution at the transition temperature is double peaked, suggesting that the phase transition is of fir...

We discuss the recent application to strongly disordered systems of the Critical Minimum Energy Subspace (CMES) method, used to limit the energy subspace of the Wang-Landau sampling. We compare with our results on the 3D Random Field Ising Model obtained by a multi-range Wang-Landau simulation in the whole energy range. We point out at some problem...

A Monte Carlo simulation of the critical behaviour of a quite realistic FeBr2 model in a magnetic field has been performed. Two regions of different critical behaviour have been found in the temperature-field (T,H)-plane. At high temperature a region of continuous phase transitions is found with a crossover to a region of first-order (metamagnetic)...

We have studied by Monte Carlo simulations the thermal behaviour of a small (N=13 particles) cluster described by a Heisenberg model, including nearest-neighbour ferromagnetic interactions and radial surface anisotropy, in an applied magnetic field. We have studied three different lattice structures: hexagonal close packed, face centered cubic and...

In order to search for the origin of the deviation of the critical exponents of a FeCl2 model from the three-dimensional (3D) Ising universality class, we have systematically studied by standard and histogram Monte Carlo simulations the influence of different features of that model such as the frustrating in-plane interaction, the super-exchange in...

The critical behavior of the random-field Ising model with a bimodal field distribution is studied using standard and histogram Monte Carlo calculations. It is definitely found that the transition is second order for weak fields while it becomes first order for higher fields. The existence of this crossover, discovered here in Monte Carlo simulatio...

The critical behavior of the RFIM has been a subject of controversy for a long time. After the qualitative analysis of Imry and Ma and the rigorous proof given by Imbrie, it is nowadays accepted that the lower critical dimension of the system is d1=2. Though some general results exist in the mean field approach, the nature of the transition for the...

In a previous work, a realistic three‐dimensional 3‐D Ising model of FeCl 2 was studied. It consists of triangular lattice planes stacked along the c axis of the crystal, with the following interactions: a nearest neighbor (nn) ferromagnetic one competing with a next‐nearest‐neighbor (nnn) antiferromagnetic interaction, which causes some degree of...

A Monte Carlo study of a quite realistic model of FexMg1-xCl2 (a diluted anisotropic antiferromagnet in a field) has been performed in the strong concentration limit (x=0.9, 0.8, and 0.7). Simulations of field cooling (FC) and heating (FH) processes as well as isothermal field cycles are presented. A modification to the standard Metropolis algorith...

A Monte Carlo simulation of the critical behavior of a quite realisticL model of FeCl2 in a magnetic field has been performed. Our results show, in agreement with previous experimental ones, that in the temperature-field phase space, two regions of highly different critical behavior may be recognized. For values of temperature T higher than a certa...

A Monte Carlo simulation on a two-dimensional Ising-like model with competing two- and four-spin interactions was performed. We studied the magnetization (both global and by column), susceptibility, energy, specific heat, correlation functions, and structure factors of this model for small values of x, the ratio of the interaction constants, paying...