949 research outputs found
On the Purity of the free boundary condition Potts measure on random trees
We consider the free boundary condition Gibbs measure of the Potts model on a
random tree. We provide an explicit temperature interval below the
ferromagnetic transition temperature for which this measure is extremal,
improving older bounds of Mossel and Peres. In information theoretic language
extremality of the Gibbs measure corresponds to non-reconstructability for
symmetric q-ary channels. The bounds are optimal for the Ising model and appear
to be close to what we conjecture to be the true values up to a factor of
0.0150 in the case q = 3 and 0.0365 for q = 4. Our proof uses an iteration of
random boundary entropies from the outside of the tree to the inside, along
with a symmetrization argument.Comment: 14 page
Direct data-driven control of constrained linear parameter-varying systems: A hierarchical approach
In many nonlinear control problems, the plant can be accurately described by
a linear model whose operating point depends on some measurable variables,
called scheduling signals. When such a linear parameter-varying (LPV) model of
the open-loop plant needs to be derived from a set of data, several issues
arise in terms of parameterization, estimation, and validation of the model
before designing the controller. Moreover, the way modeling errors affect the
closed-loop performance is still largely unknown in the LPV context. In this
paper, a direct data-driven control method is proposed to design LPV
controllers directly from data without deriving a model of the plant. The main
idea of the approach is to use a hierarchical control architecture, where the
inner controller is designed to match a simple and a-priori specified
closed-loop behavior. Then, an outer model predictive controller is synthesized
to handle input/output constraints and to enhance the performance of the inner
loop. The effectiveness of the approach is illustrated by means of a simulation
and an experimental example. Practical implementation issues are also
discussed.Comment: Preliminary version of the paper "Direct data-driven control of
constrained systems" published in the IEEE Transactions on Control Systems
Technolog
Collective periodicity in mean-field models of cooperative behavior
We propose a way to break symmetry in stochastic dynamics by introducing a
dissipation term. We show in a specific mean-field model, that if the
reversible model undergoes a phase transition of ferromagnetic type, then its
dissipative counterpart exhibits periodic orbits in the thermodynamic limit.Comment: 19 pages, 3 figure
Least costly energy management for series hybrid electric vehicles
Energy management of plug-in Hybrid Electric Vehicles (HEVs) has different
challenges from non-plug-in HEVs, due to bigger batteries and grid recharging.
Instead of tackling it to pursue energetic efficiency, an approach minimizing
the driving cost incurred by the user - the combined costs of fuel, grid energy
and battery degradation - is here proposed. A real-time approximation of the
resulting optimal policy is then provided, as well as some analytic insight
into its dependence on the system parameters. The advantages of the proposed
formulation and the effectiveness of the real-time strategy are shown by means
of a thorough simulation campaign
New activity pattern in human interactive dynamics
We investigate the response function of human agents as demonstrated by
written correspondence, uncovering a new universal pattern for how the reactive
dynamics of individuals is distributed across the set of each agent's contacts.
In long-term empirical data on email, we find that the set of response times
considered separately for the messages to each different correspondent of a
given writer, generate a family of heavy-tailed distributions, which have
largely the same features for all agents, and whose characteristic times grow
exponentially with the rank of each correspondent. We furthermore show that
this universal behavioral pattern emerges robustly by considering weighted
moving averages of the priority-conditioned response-time probabilities
generated by a basic prioritization model. Our findings clarify how the range
of priorities in the inputs from one's environment underpin and shape the
dynamics of agents embedded in a net of reactive relations. These newly
revealed activity patterns might be present in other general interactive
environments, and constrain future models of communication and interaction
networks, affecting their architecture and evolution.Comment: 15 pages, 7 figure
Application of optimal data-based binning method to spatial analysis of ecological datasets
Investigation of highly structured data sets to unveil statistical
regularities is of major importance in complex system research. The first step
is to choose the scale at which to observe the process, the most informative
scale being the one that includes the important features while disregarding
noisy details in the data. In the investigation of spatial patterns, the
optimal scale defines the optimal bin size of the histogram in which to
visualize the empirical density of the pattern. In this paper we investigate a
method proposed recently by K.~H.~Knuth to find the optimal bin size of an
histogram as a tool for statistical analysis of spatial point processes. We
test it through numerical simulations on various spatial processes which are of
interest in ecology. We show that Knuth optimal bin size rule reducing noisy
fluctuations performs better than standard kernel methods to infer the
intensity of the underlying process. Moreover it can be used to highlight
relevant spatial characteristics of the underlying distribution such as space
anisotropy and clusterization. We apply these findings to analyse cluster-like
structures in plants' arrangement of Barro Colorado Island rainforest.Comment: 49 pages, 25 figure
Il testamento di Marino Foscari
Si fornisce l'edizione, accompagnata da uno studio linguistico e storico del testo, della cedola testamentaria in volgare del veneziano Marino Foscari della contrada di S. Pantalon, anteriore al novembre 1291, dunque una delle pi\uf9 antiche rimasteci
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