990 research outputs found
Decay of Correlations in a Topological Glass
In this paper we continue the study of a topological glassy system. The state
space of the model is given by all triangulations of a sphere with nodes,
half of which are red and half are blue. Red nodes want to have 5 neighbors
while blue ones want 7. Energies of nodes with other numbers of neighbors are
supposed to be positive. The dynamics is that of flipping the diagonal between
two adjacent triangles, with a temperature dependent probability. We consider
the system at very low temperatures.
We concentrate on several new aspects of this model: Starting from a detailed
description of the stationary state, we conclude that pairs of defects (nodes
with the "wrong" degree) move with very high mobility along 1-dimensional
paths. As they wander around, they encounter single defects, which they then
move "sideways" with a geometrically defined probability. This induces a
diffusive motion of the single defects. If they meet, they annihilate, lowering
the energy of the system. We both estimate the decay of energy to equilibrium,
as well as the correlations. In particular, we find a decay like
Bursty egocentric network evolution in Skype
In this study we analyze the dynamics of the contact list evolution of
millions of users of the Skype communication network. We find that egocentric
networks evolve heterogeneously in time as events of edge additions and
deletions of individuals are grouped in long bursty clusters, which are
separated by long inactive periods. We classify users by their link creation
dynamics and show that bursty peaks of contact additions are likely to appear
shortly after user account creation. We also study possible relations between
bursty contact addition activity and other user-initiated actions like free and
paid service adoption events. We show that bursts of contact additions are
associated with increases in activity and adoption - an observation that can
inform the design of targeted marketing tactics.Comment: 7 pages, 6 figures. Social Network Analysis and Mining (2013
Correlated dynamics in egocentric communication networks
We investigate the communication sequences of millions of people through two
different channels and analyze the fine grained temporal structure of
correlated event trains induced by single individuals. By focusing on
correlations between the heterogeneous dynamics and the topology of egocentric
networks we find that the bursty trains usually evolve for pairs of individuals
rather than for the ego and his/her several neighbors thus burstiness is a
property of the links rather than of the nodes. We compare the directional
balance of calls and short messages within bursty trains to the average on the
actual link and show that for the trains of voice calls the imbalance is
significantly enhanced, while for short messages the balance within the trains
increases. These effects can be partly traced back to the technological
constrains (for short messages) and partly to the human behavioral features
(voice calls). We define a model that is able to reproduce the empirical
results and may help us to understand better the mechanisms driving technology
mediated human communication dynamics.Comment: 7 pages, 6 figure
Spatiotemporal correlations of handset-based service usages
We study spatiotemporal correlations and temporal diversities of
handset-based service usages by analyzing a dataset that includes detailed
information about locations and service usages of 124 users over 16 months. By
constructing the spatiotemporal trajectories of the users we detect several
meaningful places or contexts for each one of them and show how the context
affects the service usage patterns. We find that temporal patterns of service
usages are bound to the typical weekly cycles of humans, yet they show maximal
activities at different times. We first discuss their temporal correlations and
then investigate the time-ordering behavior of communication services like
calls being followed by the non-communication services like applications. We
also find that the behavioral overlap network based on the clustering of
temporal patterns is comparable to the communication network of users. Our
approach provides a useful framework for handset-based data analysis and helps
us to understand the complexities of information and communications technology
enabled human behavior.Comment: 11 pages, 15 figure
High resolution dynamical mapping of social interactions with active RFID
In this paper we present an experimental framework to gather data on
face-to-face social interactions between individuals, with a high spatial and
temporal resolution. We use active Radio Frequency Identification (RFID)
devices that assess contacts with one another by exchanging low-power radio
packets. When individuals wear the beacons as a badge, a persistent radio
contact between the RFID devices can be used as a proxy for a social
interaction between individuals. We present the results of a pilot study
recently performed during a conference, and a subsequent preliminary data
analysis, that provides an assessment of our method and highlights its
versatility and applicability in many areas concerned with human dynamics
Strange Attractors in Dissipative Nambu Mechanics : Classical and Quantum Aspects
We extend the framework of Nambu-Hamiltonian Mechanics to include dissipation
in phase space. We demonstrate that it accommodates the phase space
dynamics of low dimensional dissipative systems such as the much studied Lorenz
and R\"{o}ssler Strange attractors, as well as the more recent constructions of
Chen and Leipnik-Newton. The rotational, volume preserving part of the flow
preserves in time a family of two intersecting surfaces, the so called {\em
Nambu Hamiltonians}. They foliate the entire phase space and are, in turn,
deformed in time by Dissipation which represents their irrotational part of the
flow. It is given by the gradient of a scalar function and is responsible for
the emergence of the Strange Attractors.
Based on our recent work on Quantum Nambu Mechanics, we provide an explicit
quantization of the Lorenz attractor through the introduction of
Non-commutative phase space coordinates as Hermitian matrices in
. They satisfy the commutation relations induced by one of the two
Nambu Hamiltonians, the second one generating a unique time evolution.
Dissipation is incorporated quantum mechanically in a self-consistent way
having the correct classical limit without the introduction of external degrees
of freedom. Due to its volume phase space contraction it violates the quantum
commutation relations. We demonstrate that the Heisenberg-Nambu evolution
equations for the Quantum Lorenz system give rise to an attracting ellipsoid in
the dimensional phase space.Comment: 35 pages, 4 figures, LaTe
Nonlinear analysis of biomagnetic signals recorded from uterine myomas
OBJECTIVE: To determine if there is any non-linearity in the biomagnetic recordings of uterine myomas and to find any differences that may be present in the mechanisms underlying their signal dynamics. METHODS: Twenty-four women were included in the study. Sixteen of them were characterised with large myomas and 8 with small ones. Uterine artery waveform measurements were evaluated by use of Pulsatility Index (PI) (normal value PI<1.45). RESULTS: Applying nonlinear analysis to the biomagnetic signals of the uterine myomas, we observed a clear saturation value for the group of large ones (mean = 11.35 ± 1.49) and no saturation for the small ones. CONCLUSION: The comparison of the saturation values in the biomagnetic recordings of large and small myomas may be a valuable tool in the evaluation of functional changes in their dynamic behavior
Emergence of Bursts and Communities in Evolving Weighted Networks
Understanding the patterns of human dynamics and social interaction, and the
way they lead to the formation of an organized and functional society are
important issues especially for techno-social development. Addressing these
issues of social networks has recently become possible through large scale data
analysis of e.g. mobile phone call records, which has revealed the existence of
modular or community structure with many links between nodes of the same
community and relatively few links between nodes of different communities. The
weights of links, e.g. the number of calls between two users, and the network
topology are found correlated such that intra-community links are stronger
compared to the weak inter-community links. This is known as Granovetter's "The
strength of weak ties" hypothesis. In addition to this inhomogeneous community
structure, the temporal patterns of human dynamics turn out to be inhomogeneous
or bursty, characterized by the heavy tailed distribution of inter-event time
between two consecutive events. In this paper, we study how the community
structure and the bursty dynamics emerge together in an evolving weighted
network model. The principal mechanisms behind these patterns are social
interaction by cyclic closure, i.e. links to friends of friends and the focal
closure, i.e. links to individuals sharing similar attributes or interests, and
human dynamics by task handling process. These three mechanisms have been
implemented as a network model with local attachment, global attachment, and
priority-based queuing processes. By comprehensive numerical simulations we
show that the interplay of these mechanisms leads to the emergence of heavy
tailed inter-event time distribution and the evolution of Granovetter-type
community structure. Moreover, the numerical results are found to be in
qualitative agreement with empirical results from mobile phone call dataset.Comment: 9 pages, 6 figure
Dynamical Patterns of Cattle Trade Movements
Despite their importance for the spread of zoonotic diseases, our
understanding of the dynamical aspects characterizing the movements of farmed
animal populations remains limited as these systems are traditionally studied
as static objects and through simplified approximations. By leveraging on the
network science approach, here we are able for the first time to fully analyze
the longitudinal dataset of Italian cattle movements that reports the mobility
of individual animals among farms on a daily basis. The complexity and
inter-relations between topology, function and dynamical nature of the system
are characterized at different spatial and time resolutions, in order to
uncover patterns and vulnerabilities fundamental for the definition of targeted
prevention and control measures for zoonotic diseases. Results show how the
stationarity of statistical distributions coexists with a strong and
non-trivial evolutionary dynamics at the node and link levels, on all
timescales. Traditional static views of the displacement network hide important
patterns of structural changes affecting nodes' centrality and farms' spreading
potential, thus limiting the efficiency of interventions based on partial
longitudinal information. By fully taking into account the longitudinal
dimension, we propose a novel definition of dynamical motifs that is able to
uncover the presence of a temporal arrow describing the evolution of the system
and the causality patterns of its displacements, shedding light on mechanisms
that may play a crucial role in the definition of preventive actions
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