122 research outputs found
Driving forces in researchers mobility
Starting from the dataset of the publication corpus of the APS during the
period 1955-2009, we reconstruct the individual researchers trajectories,
namely the list of the consecutive affiliations for each scholar. Crossing this
information with different geographic datasets we embed these trajectories in a
spatial framework. Using methods from network theory and complex systems
analysis we characterise these patterns in terms of topological network
properties and we analyse the dependence of an academic path across different
dimensions: the distance between two subsequent positions, the relative
importance of the institutions (in terms of number of publications) and some
socio-cultural traits. We show that distance is not always a good predictor for
the next affiliation while other factors like "the previous steps" of the
career of the researchers (in particular the first position) or the linguistic
and historical similarity between two countries can have an important impact.
Finally we show that the dataset exhibit a memory effect, hence the fate of a
career strongly depends from the first two affiliations
Can extremism guarantee pluralism?
Many models have been proposed to explain opinion formation in groups of
individuals; most of these models study opinion propagation as the interaction
between nodes/agents in a social network. Opinion formation is a complex
process and a realistic model should also take into account the important
feedbacks that the opinions of the agents have on the structure of the social
networks and on the characteristics of the opinion dynamics. In this paper we
will show that associating to different agents different kinds of
interconnections and different interacting behaviours can lead to interesting
scenarios, like the coexistence of several opinion clusters, namely pluralism.
In our model agents have opinions uniformly and continuously distributed
between two extremes. The social network is formed through a social aggregation
mechanism including the segregation process of the extremists that results in
many real communities. We show how this process affects the opinion dynamics in
the whole society. In the opinion evolution we consider the different
predisposition of single individuals to interact and to exchange opinion with
each other; we associate to each individual a different tolerance threshold,
depending on its own opinion: extremists are less willing to interact with
individuals with strongly different opinions and to change significantly their
ideas. A general result is obtained: when there is no interaction restriction,
the opinion always converges to uniformity, but the same is happening whenever
a strong segregation process of the extremists occurs. Only when extremists are
forming clusters but these clusters keep interacting with the rest of the
society, the survival of a wide opinion range is guaranteed.Comment: 20 pages, 10 figure
Can Extremism Guarantee Pluralism?
Many models have been proposed to explain the opinion formation in a group of individuals; most of these models study the opinion propagation as the interaction between nodes/agents in a social network. Opinion formation is a very complex process and a realistic model should also take into account the important feedbacks that the opinions of the agents have on the structure of the social networks and on the characteristics of the opinion dynamics. In this paper we will show that associating to different agents different kind of interconnections and different interacting behaviour can lead to interesting scenarios, like the co-existence of several opinion clusters, namely pluralism. In our model agents have opinions uniformly and continuously distributed between two extremes. The social network is formed through a social aggregation mechanism including the segregation process of the extremists that results in many real communities. We show how this process affects opinion dynamics in the whole society. In the opinion evolution we consider the different predisposition of single individuals to interact and to to modify each other's opinions; we associate to each individual a different tolerance threshold, depending on its own opinion: extremists are less willing to interact with individuals with strongly different opinions and to change significantly their ideas. A general result is obtained: when there is no interaction restriction, the opinion always converges to uniformity, but the same is happening whenever a strong segregation process of the extremists occurs. Only when extremists are forming clusters but these clusters keep interacting with the rest of the society, the survival of a wide opinion range is guaranteed.Extremists, Segregation, Opinion Dynamics
Preferential attachment with partial information
We propose a preferential attachment model for network growth where new
entering nodes have a partial information about the state of the network. Our
main result is that the presence of bounded information modifies the degree
distribution by introducing an exponential tail, while it preserves a power law
behaviour over a finite small range of degrees. On the other hand, unbounded
information is sufficient to let the network grow as in the standard
Barab\'asi-Albert model. Surprisingly, the latter feature holds true also when
the fraction of known nodes goes asymptotically to zero. Analytical results are
compared to direct simulations
Urban skylines from Schelling model
We propose a metapopulation version of the Schelling model where two kinds of
agents relocate themselves, with unconstrained destination, if their local
fitness is lower than a tolerance threshold. We show that, for small values of
the latter, the population redistributes highly heterogeneously among the
available places. The system thus stabilizes on these heterogeneous skylines
after a long quasi-stationary transient period, during which the population
remains in a well mixed phase. Varying the tolerance passing from large to
small values, we identify three possible global regimes: microscopic clusters
with local coexistence of both kinds of agents, macroscopic clusters with local
coexistence (soft segregation), macroscopic clusters with local segregation but
homogeneous densities (hard segregation). The model is studied numerically and
complemented with an analytical study in the limit of extremely large node
capacity.Comment: 16 pages, 10 figure
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
The classical origin of modern mathematics
The aim of this paper is to study the historical evolution of mathematical
thinking and its spatial spreading. To do so, we have collected and integrated
data from different online academic datasets. In its final stage, the database
includes a large number (N~200K) of advisor-student relationships, with
affiliations and keywords on their research topic, over several centuries, from
the 14th century until today. We focus on two different topics, the evolving
importance of countries and of the research disciplines over time. Moreover we
study the database at three levels, its global statistics, the mesoscale
networks connecting countries and disciplines, and the genealogical level
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