2,101 research outputs found
Sensor Deployment for Network-like Environments
This paper considers the problem of optimally deploying omnidirectional
sensors, with potentially limited sensing radius, in a network-like
environment. This model provides a compact and effective description of complex
environments as well as a proper representation of road or river networks. We
present a two-step procedure based on a discrete-time gradient ascent algorithm
to find a local optimum for this problem. The first step performs a coarse
optimization where sensors are allowed to move in the plane, to vary their
sensing radius and to make use of a reduced model of the environment called
collapsed network. It is made up of a finite discrete set of points,
barycenters, produced by collapsing network edges. Sensors can be also
clustered to reduce the complexity of this phase. The sensors' positions found
in the first step are then projected on the network and used in the second
finer optimization, where sensors are constrained to move only on the network.
The second step can be performed on-line, in a distributed fashion, by sensors
moving in the real environment, and can make use of the full network as well as
of the collapsed one. The adoption of a less constrained initial optimization
has the merit of reducing the negative impact of the presence of a large number
of local optima. The effectiveness of the presented procedure is illustrated by
a simulated deployment problem in an airport environment
La négociation au travail, sous la direction de Michèle Grosjean et Lorenza Mondada, Lyon : Presses Universitaires de Lyon, 2004, 344 p., ISBN 2-7297-0754-9.
Viscous corrections to anisotropic flow and transverse momentum spectra from transport theory
Viscous hydrodynamics is commonly used to model the evolution of the matter
created in an ultra-relativistic heavy-ion collision. It provides a good
description of transverse momentum spectra and anisotropic flow. These
observables, however, cannot be consistently derived using viscous
hydrodynamics alone, because they depend on the microscopic interactions at
freeze-out. We derive the ideal hydrodynamic limit and the first-order viscous
correction to anisotropic flow (, and ) and momentum spectrum
using a transport calculation. The linear response coefficient to the initial
anisotropy, , depends little on in the ideal
hydrodynamic limit. The viscous correction to the spectrum depends not only on
the differential cross section, but also on the initial momentum distribution.
This dependence is not captured by standard second-order viscous hydrodynamics.
The viscous correction to anisotropic flow increases with , but this
increase is slower than usually assumed in viscous hydrodynamic calculations.
In particular, it is too slow to explain the observed maximum of at
GeV/c.Comment: minor revisio
Robust inference in composite transformation models
The aim of this paper is to base robust inference about a shape parameter indexing a composite transformation model on a quasi- prole likelihood ratio test statistic. First, a general procedure is presented in order to construct a bounded prole estimating function for shape parameters. This method is based on a standard truncation argument from the theory of robustness. Hence, a quasi-likelihood test is derived. Numerical studies and applications to real data show that its use reveals extremely powerful, leading to improved inferences with respect to classical robust Wald and score-type test statistics
A Packet-Switching Strategy for Uncertain Nonlinear Networked Control Systems
International audienceThis paper addresses the problem of stabilizing uncertain nonlinear plants over a shared limited-bandwidth packet-switching network for which both the time between consecutive accesses to each node (MATI) and the transmission and processing delays (MAD) for measurements and control packets are bounded. While conventional control loops are designed to work with circuit-switching networks, where dedicated communication channels provide almost constant bit rate and delay, many networks, such as Ethernet, organize data transmission in packets, carrying larger amount of information at less predictable rates. To avoid the bandwidth waste due to the relatively large overhead inherent to packet transmission, we exploit the packet payload to carry longer control sequences. To this aim we adopt a model-based approach to remotely compute a predictive control signal on a suitable time horizon, which leads to effectively reducing the bandwidth required to guarantee stability. Communications are assumed to be ruled by a rather general protocol model, which encompasses many protocols used in practice. As a distinct improvement over the state of the art, our result is shown to be robust with respect to sector-bounded uncertainties in the plant model. Namely, an explicit bound on the combined effects of MATI and MAD is provided as a function of the basin of attraction and the model accuracy
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