30,060 research outputs found
Collective Influence of Multiple Spreaders Evaluated by Tracing Real Information Flow in Large-Scale Social Networks
Identifying the most influential spreaders that maximize information flow is
a central question in network theory. Recently, a scalable method called
"Collective Influence (CI)" has been put forward through collective influence
maximization. In contrast to heuristic methods evaluating nodes' significance
separately, CI method inspects the collective influence of multiple spreaders.
Despite that CI applies to the influence maximization problem in percolation
model, it is still important to examine its efficacy in realistic information
spreading. Here, we examine real-world information flow in various social and
scientific platforms including American Physical Society, Facebook, Twitter and
LiveJournal. Since empirical data cannot be directly mapped to ideal
multi-source spreading, we leverage the behavioral patterns of users extracted
from data to construct "virtual" information spreading processes. Our results
demonstrate that the set of spreaders selected by CI can induce larger scale of
information propagation. Moreover, local measures as the number of connections
or citations are not necessarily the deterministic factors of nodes' importance
in realistic information spreading. This result has significance for rankings
scientists in scientific networks like the APS, where the commonly used number
of citations can be a poor indicator of the collective influence of authors in
the community.Comment: 11 pages, 4 figure
Entrograms and coarse graining of dynamics on complex networks
Using an information theoretic point of view, we investigate how a dynamics
acting on a network can be coarse grained through the use of graph partitions.
Specifically, we are interested in how aggregating the state space of a Markov
process according to a partition impacts on the thus obtained lower-dimensional
dynamics. We highlight that for a dynamics on a particular graph there may be
multiple coarse grained descriptions that capture different, incomparable
features of the original process. For instance, a coarse graining induced by
one partition may be commensurate with a time-scale separation in the dynamics,
while another coarse graining may correspond to a different lower-dimensional
dynamics that preserves the Markov property of the original process. Taking
inspiration from the literature of Computational Mechanics, we find that a
convenient tool to summarise and visualise such dynamical properties of a
coarse grained model (partition) is the entrogram. The entrogram gathers
certain information-theoretic measures, which quantify how information flows
across time steps. These information theoretic quantities include the entropy
rate, as well as a measure for the memory contained in the process, i.e., how
well the dynamics can be approximated by a first order Markov process. We use
the entrogram to investigate how specific macro-scale connection patterns in
the state-space transition graph of the original dynamics result in desirable
properties of coarse grained descriptions. We thereby provide a fresh
perspective on the interplay between structure and dynamics in networks, and
the process of partitioning from an information theoretic perspective. We focus
on networks that may be approximated by both a core-periphery or a clustered
organization, and highlight that each of these coarse grained descriptions can
capture different aspects of a Markov process acting on the network.Comment: 17 pages, 6 figue
Submodular Inference of Diffusion Networks from Multiple Trees
Diffusion and propagation of information, influence and diseases take place
over increasingly larger networks. We observe when a node copies information,
makes a decision or becomes infected but networks are often hidden or
unobserved. Since networks are highly dynamic, changing and growing rapidly, we
only observe a relatively small set of cascades before a network changes
significantly. Scalable network inference based on a small cascade set is then
necessary for understanding the rapidly evolving dynamics that govern
diffusion. In this article, we develop a scalable approximation algorithm with
provable near-optimal performance based on submodular maximization which
achieves a high accuracy in such scenario, solving an open problem first
introduced by Gomez-Rodriguez et al (2010). Experiments on synthetic and real
diffusion data show that our algorithm in practice achieves an optimal
trade-off between accuracy and running time.Comment: To appear in the 29th International Conference on Machine Learning
(ICML), 2012. Website:
http://www.stanford.edu/~manuelgr/network-inference-multitree
Modeling the structure and evolution of discussion cascades
We analyze the structure and evolution of discussion cascades in four popular
websites: Slashdot, Barrapunto, Meneame and Wikipedia. Despite the big
heterogeneities between these sites, a preferential attachment (PA) model with
bias to the root can capture the temporal evolution of the observed trees and
many of their statistical properties, namely, probability distributions of the
branching factors (degrees), subtree sizes and certain correlations. The
parameters of the model are learned efficiently using a novel maximum
likelihood estimation scheme for PA and provide a figurative interpretation
about the communication habits and the resulting discussion cascades on the
four different websites.Comment: 10 pages, 11 figure
When resources collide: Towards a theory of coincidence in information spaces
This paper is an attempt to lay out foundations for a general theory of coincidence in information spaces such as the World Wide Web, expanding on existing work on bursty structures in document streams and information cascades. We elaborate on the hypothesis that every resource that is published in an information space, enters a temporary interaction with another resource once a unique explicit or implicit reference between the two is found. This thought is motivated by Erwin Shroedingers notion of entanglement between quantum systems. We present a generic information cascade model that exploits only the temporal order of information sharing activities, combined with inherent properties of the shared information resources. The approach was applied to data from the world's largest online citizen science platform Zooniverse and we report about findings of this case study
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Carbon Catcher Design Report
Overview. The design of the overall Carbon Catcher project can be separated into four distinct systems, each of which is assigned a specialized committee. The committee names and responsibilities are listed below:
Air Mover
The overall goal for the Air Mover committee is the design of the turbine assembly. As the overall goal of the project is to collect and separate carbon dioxide from the air, one of the most important parts is to actually get the air to pass through the carbon-catching
membrane. Passive air would not give a significant enough yield rate to make the carbon dioxide collection rate impactful, thus air must be sucked through a vacuum/turbine.
Membrane
The goal of Membrain is to create a membrane that can filter out CO2 through various methods. These methods are limited, due to there being such variety, to certain techniques and membrane material types that have been decided, prior, by the committee. Most membranes will be geared towards utilizing temperature and pressure along with gaseous speed and flow rate. In addition, examining certain treatments, such as regeneration of material, and replacements will be looked into as well, to see how it fares in sustainability.
Carbon Storer
The Carbon Storer committee will design a store and transport system for fluid CO2 after it is extracted from the atmosphere. Primary considerations include geological solutions, cost-effective materials, and analysis methods to improve overall capacity and efficiency. Additionally, the committee will select an environmentally and economically sustainable method of recycling the captured CO2.
PyControl
The PyControl committee will design a series of sensors and actuators, which will primarily support the sequestration and pipeline systems present in the Carbon Storer Committee and direct air capture system in Air Mover. The design can be broken into four control layers: Input/Output, Field Controllers, Data, and Supervisory.
Goal
The overarching goal of Carbon Catcher is to design a cost-effective, scalable atmospheric carbon dioxide removal system that is capable of being deployed in a variety of urban environments and may fit a variety of different customer requirements or requests
Online reverse discourses? Claiming a space for trans voices
In recent years, online media have offered to trans people helpful resources to create new political, cultural and personal representations of their biographies. However, the role of these media in the construction of their social and personal identities has seldom been addressed. Drawing on the theoretical standpoint of positioning theory and diatextual discourse analysis, this paper discusses the results of a research project about weblogs created by Italian trans women. In particular, the aim of this study was to describe the ways online resources are used to express different definitions and interpretation of transgenderism, transsexuality and gender transitioning. We identified four main positioning strategies: \u201cTransgender\u201d, \u201cTranssexual before being a woman\u201d, \u201cA woman who was born male\u201d and \u201cJust a normal woman\u201d. We conclude with the political implications of the pluralization of narratives about gender non-conformity. Specifically, we will highlight how aspects of neoliberal discourses have been appropriated and rearticulated in the construction of gendered subjectivities
Line graphs as social networks
The line graphs are clustered and assortative. They share these topological
features with some social networks. We argue that this similarity reveals the
cliquey character of the social networks. In the model proposed here, a social
network is the line graph of an initial network of families, communities,
interest groups, school classes and small companies. These groups play the role
of nodes, and individuals are represented by links between these nodes. The
picture is supported by the data on the LiveJournal network of about 8 x 10^6
people. In particular, sharp maxima of the observed data of the degree
dependence of the clustering coefficient C(k) are associated with cliques in
the social network.Comment: 11 pages, 4 figure
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