429,042 research outputs found
Multilevel compression of random walks on networks reveals hierarchical organization in large integrated systems
To comprehend the hierarchical organization of large integrated systems, we
introduce the hierarchical map equation, which reveals multilevel structures in
networks. In this information-theoretic approach, we exploit the duality
between compression and pattern detection; by compressing a description of a
random walker as a proxy for real flow on a network, we find regularities in
the network that induce this system-wide flow. Finding the shortest multilevel
description of the random walker therefore gives us the best hierarchical
clustering of the network, the optimal number of levels and modular partition
at each level, with respect to the dynamics on the network. With a novel search
algorithm, we extract and illustrate the rich multilevel organization of
several large social and biological networks. For example, from the global air
traffic network we uncover countries and continents, and from the pattern of
scientific communication we reveal more than 100 scientific fields organized in
four major disciplines: life sciences, physical sciences, ecology and earth
sciences, and social sciences. In general, we find shallow hierarchical
structures in globally interconnected systems, such as neural networks, and
rich multilevel organizations in systems with highly separated regions, such as
road networks.Comment: 11 pages, 5 figures. For associated code, see
http://www.tp.umu.se/~rosvall/code.htm
Consensus-based approach to peer-to-peer electricity markets with product differentiation
With the sustained deployment of distributed generation capacities and the
more proactive role of consumers, power systems and their operation are
drifting away from a conventional top-down hierarchical structure. Electricity
market structures, however, have not yet embraced that evolution. Respecting
the high-dimensional, distributed and dynamic nature of modern power systems
would translate to designing peer-to-peer markets or, at least, to using such
an underlying decentralized structure to enable a bottom-up approach to future
electricity markets. A peer-to-peer market structure based on a Multi-Bilateral
Economic Dispatch (MBED) formulation is introduced, allowing for
multi-bilateral trading with product differentiation, for instance based on
consumer preferences. A Relaxed Consensus+Innovation (RCI) approach is
described to solve the MBED in fully decentralized manner. A set of realistic
case studies and their analysis allow us showing that such peer-to-peer market
structures can effectively yield market outcomes that are different from
centralized market structures and optimal in terms of respecting consumers
preferences while maximizing social welfare. Additionally, the RCI solving
approach allows for a fully decentralized market clearing which converges with
a negligible optimality gap, with a limited amount of information being shared.Comment: Accepted for publication in IEEE Transactions on Power System
Hierarchical self-organization of non-cooperating individuals
Hierarchy is one of the most conspicuous features of numerous natural,
technological and social systems. The underlying structures are typically
complex and their most relevant organizational principle is the ordering of the
ties among the units they are made of according to a network displaying
hierarchical features. In spite of the abundant presence of hierarchy no
quantitative theoretical interpretation of the origins of a multi-level,
knowledge-based social network exists. Here we introduce an approach which is
capable of reproducing the emergence of a multi-levelled network structure
based on the plausible assumption that the individuals (representing the nodes
of the network) can make the right estimate about the state of their changing
environment to a varying degree. Our model accounts for a fundamental feature
of knowledge-based organizations: the less capable individuals tend to follow
those who are better at solving the problems they all face. We find that
relatively simple rules lead to hierarchical self-organization and the specific
structures we obtain possess the two, perhaps most important features of
complex systems: a simultaneous presence of adaptability and stability. In
addition, the performance (success score) of the emerging networks is
significantly higher than the average expected score of the individuals without
letting them copy the decisions of the others. The results of our calculations
are in agreement with a related experiment and can be useful from the point of
designing the optimal conditions for constructing a given complex social
structure as well as understanding the hierarchical organization of such
biological structures of major importance as the regulatory pathways or the
dynamics of neural networks.Comment: Supplementary videos are to be found at
http://hal.elte.hu/~nepusz/research/supplementary/hierarchy
Pattern Formation, Spatial Externalities and Regulation in Coupled Economic-Ecological Systems
We develop a novel theoretical framework for studying ecosystems in which interacting state variables which are affected by management decisions diffuse in space. We identify (i) mechanisms creating spatial patterns when economic agents maximize profit at each site by ignoring the impact of their actions on other sites and (ii) a diffusion induced externality. Pattern formation mechanisms and externalities create a divergence in the spatiotemporal structures emerging under private or social objectives We develop optimal regulation which internalize the spatiotemporal externalities. Our theory is applied to the management and regulation of a semi-arid system. Supporting numerical simulations are also presented.Economic-Ecological Systems, Pattern Formation, Reaction-Diffusion, Diffusion Instability, Spatial Externalities, Regulation
Generalized Opinion Dynamics from Local Optimization Rules
We study generalizations of the Hegselmann-Krause (HK) model for opinion
dynamics, incorporating features and parameters that are natural components of
observed social systems. The first generalization is one where the strength of
influence depends on the distance of the agents' opinions. Under this setup, we
identify conditions under which the opinions converge in finite time, and
provide a qualitative characterization of the equilibrium. We interpret the HK
model opinion update rule as a quadratic cost-minimization rule. This enables a
second generalization: a family of update rules which possess different
equilibrium properties. Subsequently, we investigate models in which a external
force can behave strategically to modulate/influence user updates. We consider
cases where this external force can introduce additional agents and cases where
they can modify the cost structures for other agents. We describe and analyze
some strategies through which such modulation may be possible in an
order-optimal manner. Our simulations demonstrate that generalized dynamics
differ qualitatively and quantitatively from traditional HK dynamics.Comment: 20 pages, under revie
Mining dense substructures from large deterministic and probabilistic graphs
Graphs represent relationships. Some relationships can be represented as a deterministic graph while others can only be represented by using probabilities. Mining dense structures from graphs help us to find useful patterns in these relationships having applications in wide areas like social network analysis, bioinformatics etc. Arguably the two most fundamental dense substructures are Maximal Cliques and Maximal Bicliques. The enumeration of both these structures are central to many data mining problems. With the advent of “big data”, real world graphs have become massive. Recently systems like MapReduce have evolved to process such large data. However using these systems to mine dense substrucures in massive graphs is an open question. In this thesis, we present novel parallel algorithms using MapReduce for the enumeration of Maximal Cliques / Bicliques in large graphs. We show that our algorithms are work optimal and load balanced. Further, we present a detailed evaluation which shows that the algorithm scales to large graphs with millions of edges and tens of millions of output structures. Finally we consider the problem of Maximal Clique Enumeration in an Uncertain Graph, which is a probability distribution on a set of deterministic graphs. We define the notion of a maximal clique for an uncertain graph, give matching upper and lower bounds on the number of such structures and present a near optimal algorithm to mine all maximal cliques
Understanding the structure and processes of primary health care for young indigenous children
INTRODUCTION: Primary health care organisations need to continuously reform to more effectively address current health challenges, particularly for vulnerable populations. There is growing evidence that optimal health service structures are essential for producing positive outcomes.
AIM: To determine if there is an association between process of care indicators (PoCIs) for important young indigenous child health and social issues and: (i) primary health-care service and child characteristics; and (ii) organisational health service structures.
METHODS: This was a cross-sectional study of 1554 clinical child health audits and associated system assessments from 74 primary care services from 2012 to 2014. Composite PoCIs were developed for social and emotional wellbeing, child neurodevelopment and anaemia. Crude and adjusted logistic regression models were fitted, clustering for health services. Odds ratios and 95% confidence intervals were derived.
RESULTS: Overall, 32.0% (449) of records had a social and emotional wellbeing PoCI, 56.6% (791) had an anaemia PoCI and 49.3% (430) had a child neurodevelopment PoCI. Children aged 12–23 months were significantly more likely to receive all PoCIs compared to children aged 24–59 months. For every one point increase in assessment scores for team structure and function (aOR 1.14, 95% CI 1.01–1.27) and care planning (aOR 1.14, 95% CI 1.01–1.29) items, there was a 14% greater odds of a child having an anaemia PoCI. Social and emotional wellbeing and child neurodevelopment PoCIs were not associated with system assessment scores.
DISCUSSION: Ensuring young indigenous children aged 24–59 months are receiving quality care for important social and health indicators is a priority. Processes of care and organisational systems in primary care services are important for the optimal management of anaemia in indigenous children
Enhancing topology adaptation in information-sharing social networks
The advent of Internet and World Wide Web has led to unprecedent growth of
the information available. People usually face the information overload by
following a limited number of sources which best fit their interests. It has
thus become important to address issues like who gets followed and how to allow
people to discover new and better information sources. In this paper we conduct
an empirical analysis on different on-line social networking sites, and draw
inspiration from its results to present different source selection strategies
in an adaptive model for social recommendation. We show that local search rules
which enhance the typical topological features of real social communities give
rise to network configurations that are globally optimal. These rules create
networks which are effective in information diffusion and resemble structures
resulting from real social systems
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