2,829 research outputs found
Differential Equation Models Derived from an Individual-Based Model Can Help to Understand Emergent Effects
We study a model of primacy effect on individual's attitude. Typically, when receiving a strong negative feature first, the individual keeps a negative attitude whatever the number of moderate positive features it receives afterwards. We consider a population of individuals, which receive the features from a media, and communicate with each other. We observe that interactions favour the primacy effect, compared with a population of isolated individuals. We derive a differential equation system ruling the evolution of probabilities that individuals retain different sets of features. The study of this aggregated model of the IBM shows that interaction can increase or decrease the number of individuals exhibiting a primacy effect. We verify on the IBM that the interactions can decrease the primacy effect in the conditions suggested by the study of the aggregated model. We finally discuss the interest of such a double-modelling approach (using a model of the individual based model) for this application.Primacy Effect, Information Filtering, Agent-Based Model, Aggregated Model, Collective Effects of Interactions, Double-Modelling
The Leviathan model: Absolute dominance, generalised distrust, small worlds and other patterns emerging from combining vanity with opinion propagation
We propose an opinion dynamics model that combines processes of vanity and
opinion propagation. The interactions take place between randomly chosen pairs.
During an interaction, the agents propagate their opinions about themselves and
about other people they know. Moreover, each individual is subject to vanity:
if her interlocutor seems to value her highly, then she increases her opinion
about this interlocutor. On the contrary she tends to decrease her opinion
about those who seem to undervalue her. The combination of these dynamics with
the hypothesis that the opinion propagation is more efficient when coming from
highly valued individuals, leads to different patterns when varying the
parameters. For instance, for some parameters the positive opinion links
between individuals generate a small world network. In one of the patterns,
absolute dominance of one agent alternates with a state of generalised
distrust, where all agents have a very low opinion of all the others (including
themselves). We provide some explanations of the mechanisms behind these
emergent behaviors and finally propose a discussion about their interestComment: Improved version after referees comment
From Aztec diamonds to pyramids: steep tilings
We introduce a family of domino tilings that includes tilings of the Aztec
diamond and pyramid partitions as special cases. These tilings live in a strip
of of the form for some integer , and are parametrized by a binary word that
encodes some periodicity conditions at infinity. Aztec diamond and pyramid
partitions correspond respectively to and to the limit case
. For each word and for different types of boundary
conditions, we obtain a nice product formula for the generating function of the
associated tilings with respect to the number of flips, that admits a natural
multivariate generalization. The main tools are a bijective correspondence with
sequences of interlaced partitions and the vertex operator formalism (which we
slightly extend in order to handle Littlewood-type identities). In
probabilistic terms our tilings map to Schur processes of different types
(standard, Pfaffian and periodic). We also introduce a more general model that
interpolates between domino tilings and plane partitions.Comment: 36 pages, 22 figures (v3: final accepted version with new Figure 6,
new improved proof of Proposition 11
Combining Clustering techniques and Formal Concept Analysis to characterize Interestingness Measures
Formal Concept Analysis "FCA" is a data analysis method which enables to
discover hidden knowledge existing in data. A kind of hidden knowledge
extracted from data is association rules. Different quality measures were
reported in the literature to extract only relevant association rules. Given a
dataset, the choice of a good quality measure remains a challenging task for a
user. Given a quality measures evaluation matrix according to semantic
properties, this paper describes how FCA can highlight quality measures with
similar behavior in order to help the user during his choice. The aim of this
article is the discovery of Interestingness Measures "IM" clusters, able to
validate those found due to the hierarchical and partitioning clustering
methods "AHC" and "k-means". Then, based on the theoretical study of sixty one
interestingness measures according to nineteen properties, proposed in a recent
study, "FCA" describes several groups of measures.Comment: 13 pages, 2 figure
Categorization of interestingness measures for knowledge extraction
Finding interesting association rules is an important and active research
field in data mining. The algorithms of the Apriori family are based on two
rule extraction measures, support and confidence. Although these two measures
have the virtue of being algorithmically fast, they generate a prohibitive
number of rules most of which are redundant and irrelevant. It is therefore
necessary to use further measures which filter uninteresting rules. Many
synthesis studies were then realized on the interestingness measures according
to several points of view. Different reported studies have been carried out to
identify "good" properties of rule extraction measures and these properties
have been assessed on 61 measures. The purpose of this paper is twofold. First
to extend the number of the measures and properties to be studied, in addition
to the formalization of the properties proposed in the literature. Second, in
the light of this formal study, to categorize the studied measures. This paper
leads then to identify categories of measures in order to help the users to
efficiently select an appropriate measure by choosing one or more measure(s)
during the knowledge extraction process. The properties evaluation on the 61
measures has enabled us to identify 7 classes of measures, classes that we
obtained using two different clustering techniques.Comment: 34 pages, 4 figure
Investigation of shear banding in three-dimensional foams
We study the steady flow properties of different three-dimensional aqueous
foams in a wide gap Couette geometry. From local velocity measurements through
Magnetic Resonance Imaging techniques and from viscosity bifurcation
experiments, we find that these foams do not exhibit any observable signature
of shear banding. This contrasts with two previous results (Rodts et al.,
Europhys. Lett., 69 (2005) 636 and Da Cruz et al., Phys. Rev. E, 66 (2002)
051305); we discuss possible reasons for this dicrepancy. Moreover, the foams
we studied undergo steady flow for shear rates well below the critical shear
rate recently predicted (Denkov et al., Phys. Rev. Lett., 103 (2009) 118302).
Local measurements of the constitutive law finally show that these foams behave
as simple Herschel-Bulkley yield stress fluids
Taking into Account the Variations of Neighbourhood Sizes in the Mean-Field Approximation of the Threshold Model on a Random Network
We compare the individual-based \'threshold model\' of innovation diffusion in the version which has been studied by Young (1998), with an aggregate model we derived from it. This model allows us to formalise and test hypotheses on the influence of individual characteristics upon global evolution. The classical threshold model supposes that an individual adopts a behaviour according to a trade-off between a social pressure and a personal interest. Our study considers only the case where all have the same threshold. We present an aggregated model, which takes into account variations of the neighbourhood sizes, whereas previous work assumed this size fixed (Edwards et al. 2003a). The comparison between the aggregated models (the first one assuming a neighbourhood size and the second one, a variable one) points out an improvement of the approximation in most of the value of parameter space. This proves that the average degree of connectivity (first aggregated model) is not sufficient for characterising the evolution, and that the node degree variability has an impact on the diffusion dynamics. Remaining differences between both models give us some clues about the specific ability of individual-based model to maintain a minority behaviour which becomes a majority by an addition of stochastic effects.Aggregate; Individual-Based Model; Innovation Diffusion; Mean Field Approximation; Model Comparison; Social Network Effect
A Universal Model of Commuting Networks
We test a recently proposed model of commuting networks on 80 case studies
from different regions of the world (Europe and United-States) and with
geographic units of different sizes (municipality, county, region). The model
takes as input the number of commuters coming in and out of each geographic
unit and generates the matrix of commuting flows betwen the geographic units.
We show that the single parameter of the model, which rules the compromise
between the influence of the distance and job opportunities, follows a
universal law that depends only on the average surface of the geographic units.
We verified that the law derived from a part of the case studies yields
accurate results on other case studies. We also show that our model
significantly outperforms the two other approaches proposing a universal
commuting model (Balcan et al. (2009); Simini et al. (2012)), particularly when
the geographic units are small (e.g. municipalities).Comment: 11 pages, 5 figure
Activités des formateurs d'enseignants : quelles fonctions pour quels objectifs ?
International audienceL’activité des formateurs constitue un des quatre objets ciblés par la Chaire UNESCO « Former les enseignants au XXIe siècle ». Mieux comprendre leur activité et les dispositifs dans lesquels ils œuvrent est un enjeu clef pour une formation des enseignants de qualité. De nombreux ouvrages ont mis en exergue les convergences à l’échelle internationale concernant la professionnalisation des enseignants et les défis relatifs à leur formation (Altet, Paquay et Perrenoud, 2002 ; Etienne, Altet, Lessard, Paquay et Perrenoud, 2009 ; Paquay, Altet, Charlier et Perrenoud, 1996 ; Perrenoud, Altet, Lessard et Paquay, 2008 ; Tardif, Lessard et Gauthier, 1998). Les efforts réalisés à ce jour s’inscrivent dans une histoire de plus en plus commune et convergente dans la francophonie notamment. Le projet de la Chaire UNESCO insiste sur la nécessité de poursuivre ces débats internationaux en vue d’interroger les conditions qui facilitent ou font obstacle à la formation : « À l’échelle internationale, force est de reconnaître qu’aucun véritable consensus n’est clairement établi entre les chercheurs, les décideurs politiques et les responsables des plans de formation quant aux modalités à proposer pour la professionnalisation des enseignants. C’est pourquoi l’heure nous semble venue de tester à nouveaux frais, et à l’échelle des dix pays partenaires de notre Chaire UNESCO, la pertinence de nouvelles formes d’alternance entre des modalités régulièrement opposées dans les plans de formation, et qui, sous certaines conditions, pourraient contribuer de manière complémentaire au processus complexe de professionnalisation des enseignants : formation en présentiel et formation à distance, autoformation et co-formation, formation à partir de l’activité débutante et formation à partir de l’activité experte, formation disciplinaire et formation transversale » (Projet Chaire UNESCO : « Former les enseignants au XXIe siècle », Luc Ria - lien hypertexte). À l’heure de penser les complémentarités plutôt que les oppositions, l’activité des formateurs est ici envisagée comme un point névralgique à considérer dans la mesure où les principales difficultés inhérentes à la formation se précipitent et se retrouvent en tension au sein même de leur activité quotidienne. C’est le choix opéré pour cette journée de réflexion que de centrer l’attention sur ces acteurs et leurs fonctions, leurs activités ou plus largement leur travail en vue de débattre de la formation des enseignants et de ses objectifs
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