488 research outputs found
Consistency of Spectral Hypergraph Partitioning under Planted Partition Model
Hypergraph partitioning lies at the heart of a number of problems in machine
learning and network sciences. Many algorithms for hypergraph partitioning have
been proposed that extend standard approaches for graph partitioning to the
case of hypergraphs. However, theoretical aspects of such methods have seldom
received attention in the literature as compared to the extensive studies on
the guarantees of graph partitioning. For instance, consistency results of
spectral graph partitioning under the stochastic block model are well known. In
this paper, we present a planted partition model for sparse random non-uniform
hypergraphs that generalizes the stochastic block model. We derive an error
bound for a spectral hypergraph partitioning algorithm under this model using
matrix concentration inequalities. To the best of our knowledge, this is the
first consistency result related to partitioning non-uniform hypergraphs.Comment: 35 pages, 2 figures, 1 tabl
Probabilistic Inference of Twitter Users' Age based on What They Follow
Twitter provides an open and rich source of data for studying human behaviour
at scale and is widely used in social and network sciences. However, a major
criticism of Twitter data is that demographic information is largely absent.
Enhancing Twitter data with user ages would advance our ability to study social
network structures, information flows and the spread of contagions. Approaches
toward age detection of Twitter users typically focus on specific properties of
tweets, e.g., linguistic features, which are language dependent. In this paper,
we devise a language-independent methodology for determining the age of Twitter
users from data that is native to the Twitter ecosystem. The key idea is to use
a Bayesian framework to generalise ground-truth age information from a few
Twitter users to the entire network based on what/whom they follow. Our
approach scales to inferring the age of 700 million Twitter accounts with high
accuracy.Comment: 9 pages, 9 figure
Analysis and Control of Socio-Cultural Opinion Evolution in Complex Social Systems
The overarching goal of this thesis is to further our understanding about opinion evolution in networked societies. Such insights can be used in a variety of fields such as economy, marketing, transportation, egress, etc. Three main subjects build up this interdisciplinary research: Sociology, Statistical Mechanics, and Network Sciences. In this thesis, for macrolevel (or society-level) analyses, techniques from statistical mechanics have been borrowed to mathematically model the opinion dynamic on different network topologies based on different interaction models. Also, for micro-level (individual-level) analyses, Individual Decision Making Algorithms (IDMA) have been designed. To account for both macro-level and micro-level dynamics, these two regimes are combined resulting in a more accurate model for opinion propagation. Assessing the controllability of such dynamics through experiments in presence of actual humans is the part of this thesis
Horizontal visibility graphs transformed from fractional Brownian motions: Topological properties versus Hurst index
Nonlinear time series analysis aims at understanding the dynamics of
stochastic or chaotic processes. In recent years, quite a few methods have been
proposed to transform a single time series to a complex network so that the
dynamics of the process can be understood by investigating the topological
properties of the network. We study the topological properties of horizontal
visibility graphs constructed from fractional Brownian motions with different
Hurst index . Special attention has been paid to the impact of Hurst
index on the topological properties. It is found that the clustering
coefficient decreases when increases. We also found that the mean
length of the shortest paths increases exponentially with for fixed
length of the original time series. In addition, increases linearly
with respect to when is close to 1 and in a logarithmic form when
is close to 0. Although the occurrence of different motifs changes with ,
the motif rank pattern remains unchanged for different . Adopting the
node-covering box-counting method, the horizontal visibility graphs are found
to be fractals and the fractal dimension decreases with . Furthermore,
the Pearson coefficients of the networks are positive and the degree-degree
correlations increase with the degree, which indicate that the horizontal
visibility graphs are assortative. With the increase of , the Pearson
coefficient decreases first and then increases, in which the turning point is
around . The presence of both fractality and assortativity in the
horizontal visibility graphs converted from fractional Brownian motions is
different from many cases where fractal networks are usually disassortative.Comment: 12 pages, 8 figure
Singular Structure and Enhanced Friedel Oscillations in the Two-Dimensional Electron Gas
We calculate the leading order corrections (in ) to the static
polarization , with dynamically screened interactions, for the
two-dimensional electron gas. The corresponding diagrams all exhibit singular
logarithmic behavior in their derivatives at and provide significant
enhancement to the proper polarization particularly at low densities. At a
density of , the contribution from the leading order {\em fluctuational}
diagrams exceeds both the zeroth order (Lindhard) response and the self-energy
and exchange contributions. We comment on the importance of these diagrams in
two-dimensions and make comparisons to an equivalent three-dimensional electron
gas; we also consider the impact these finding have on computed
to all orders in perturbation theory
Impact of edge-removal on the centrality betweenness of the best spreaders
The control of epidemic spreading is essential to avoid potential fatal
consequences and also, to lessen unforeseen socio-economic impact. The need for
effective control is exemplified during the severe acute respiratory syndrome
(SARS) in 2003, which has inflicted near to a thousand deaths as well as
bankruptcies of airlines and related businesses. In this article, we examine
the efficacy of control strategies on the propagation of infectious diseases
based on removing connections within real world airline network with the
associated economic and social costs taken into account through defining
appropriate quantitative measures. We uncover the surprising results that
removing less busy connections can be far more effective in hindering the
spread of the disease than removing the more popular connections. Since
disconnecting the less popular routes tend to incur less socio-economic cost,
our finding suggests the possibility of trading minimal reduction in
connectivity of an important hub with efficiencies in epidemic control. In
particular, we demonstrate the performance of various local epidemic control
strategies, and show how our approach can predict their cost effectiveness
through the spreading control characteristics.Comment: 11 pages, 4 figure
Networks in Financial Markets
The thesis applies methods from network sciences to four economic topics: herding in financial markets; corporate board networks; contagion in global financial markets; the Italian overnight loan market
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