4,115 research outputs found
Temporal Networks
A great variety of systems in nature, society and technology -- from the web
of sexual contacts to the Internet, from the nervous system to power grids --
can be modeled as graphs of vertices coupled by edges. The network structure,
describing how the graph is wired, helps us understand, predict and optimize
the behavior of dynamical systems. In many cases, however, the edges are not
continuously active. As an example, in networks of communication via email,
text messages, or phone calls, edges represent sequences of instantaneous or
practically instantaneous contacts. In some cases, edges are active for
non-negligible periods of time: e.g., the proximity patterns of inpatients at
hospitals can be represented by a graph where an edge between two individuals
is on throughout the time they are at the same ward. Like network topology, the
temporal structure of edge activations can affect dynamics of systems
interacting through the network, from disease contagion on the network of
patients to information diffusion over an e-mail network. In this review, we
present the emergent field of temporal networks, and discuss methods for
analyzing topological and temporal structure and models for elucidating their
relation to the behavior of dynamical systems. In the light of traditional
network theory, one can see this framework as moving the information of when
things happen from the dynamical system on the network, to the network itself.
Since fundamental properties, such as the transitivity of edges, do not
necessarily hold in temporal networks, many of these methods need to be quite
different from those for static networks
A Methodology for Information Flow Experiments
Information flow analysis has largely ignored the setting where the analyst
has neither control over nor a complete model of the analyzed system. We
formalize such limited information flow analyses and study an instance of it:
detecting the usage of data by websites. We prove that these problems are ones
of causal inference. Leveraging this connection, we push beyond traditional
information flow analysis to provide a systematic methodology based on
experimental science and statistical analysis. Our methodology allows us to
systematize prior works in the area viewing them as instances of a general
approach. Our systematic study leads to practical advice for improving work on
detecting data usage, a previously unformalized area. We illustrate these
concepts with a series of experiments collecting data on the use of information
by websites, which we statistically analyze
The role of constraints in expert memory
A great deal of research has been devoted to developing process models of expert memory. However, K. J. Vicente and J. H. Wang (1998) proposed (a) that process theories do not provide an adequate account of expert recall in domains in which memory recall is a contrived task and (b) that a product theory, the constraint attunement hypothesis (CAH), has received a significant amount of empirical support. We compared 1 process theory (the template theory; TT; F. Gobet & H. A. Simon, 1996c) with the CAH in chess. Chess players (N = 36) differing widely in skill levels were required to recall briefly
presented chess positions that were randomized in various ways. Consistent with TT, but inconsistent
with the CAH, there was a significant skill effect in a condition in which both the location and distribution of the pieces were randomized. These and other results suggest that process models such as TT can provide a viable account of expert memory in chess
New Multiplier Sequences via Discriminant Amoebae
In their classic 1914 paper, Polya and Schur introduced and characterized two
types of linear operators acting diagonally on the monomial basis of R[x],
sending real-rooted polynomials (resp. polynomials with all nonzero roots of
the same sign) to real-rooted polynomials. Motivated by fundamental properties
of amoebae and discriminants discovered by Gelfand, Kapranov, and Zelevinsky,
we introduce two new natural classes of polynomials and describe diagonal
operators preserving these new classes. A pleasant circumstance in our
description is that these classes have a simple explicit description, one of
them coinciding with the class of log-concave sequences.Comment: 11 pages, 6 figures. Submitted for publicatio
Social dilemmas, time preferences and technology adoption in a commons problem
Agents interacting on a body of water choose between technologies to catch fish. One is harmless to the resource, as it allows full recovery; the other yields high immediate catches, but low(er) future catches. Strategic interaction in one 'objective'resource game may induce several 'subjective' games in the class of social dilemmas. Which unique 'subjective'game is actually played depends crucially on how the agents discount their future payo¤s. We examine equilibrium behavior and its consequences on sustainability of the common-pool resource system under exponential and hyperbolic discounting. A sufficient degree of patience on behalf of the agents may lead to equilibrium behavior averting exhaustion of the resource, though full restraint (both agents choosing the ecologically or environmentally sound technology) is not necessarily achieved. Furthermore, if the degree of patience between agents is sufficiently dissimilar, the more patient is exploited by the less patient one in equilibrium. We demonstrate the generalizability of our approach developed throughout the paper. We provide recommendations to reduce the enormous complexity surrounding the general cases
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