2,060 research outputs found
Front Propagation in Chaotic and Noisy Reaction-Diffusion Systems: a Discrete-Time Map Approach
We study the front propagation in Reaction-Diffusion systems whose reaction
dynamics exhibits an unstable fixed point and chaotic or noisy behaviour. We
have examined the influence of chaos and noise on the front propagation speed
and on the wandering of the front around its average position. Assuming that
the reaction term acts periodically in an impulsive way, the dynamical
evolution of the system can be written as the convolution between a spatial
propagator and a discrete-time map acting locally. This approach allows us to
perform accurate numerical analysis. They reveal that in the pulled regime the
front speed is basically determined by the shape of the map around the unstable
fixed point, while its chaotic or noisy features play a marginal role. In
contrast, in the pushed regime the presence of chaos or noise is more relevant.
In particular the front speed decreases when the degree of chaoticity is
increased, but it is not straightforward to derive a direct connection between
the chaotic properties (e.g. the Lyapunov exponent) and the behaviour of the
front. As for the fluctuations of the front position, we observe for the noisy
maps that the associated mean square displacement grows in time as in
the pushed case and as in the pulled one, in agreement with recent
findings obtained for continuous models with multiplicative noise. Moreover we
show that the same quantity saturates when a chaotic deterministic dynamics is
considered for both pushed and pulled regimes.Comment: 11 pages, 11 figure
Talking about routines in the field: the emergence of organizational capabilities in a new cellular phone network company
No abstract availabl
Specifying and analysing reputation systems with coordination languages
Reputation systems are nowadays widely used to support decision making in networked systems. Parties in such systems rate each other and use shared ratings to compute reputation scores that drive their interactions. The existence of reputation systems with remarkable differences calls for formal approaches to their analysis. We present a verification methodology for reputation systems that is based on the use of the coordination language Klaim and related analysis tools. First, we define a parametric Klaim specification of a reputation system that can be instantiated with different reputation models. Then, we consider stochastic specification obtained by considering actions with random (exponentially distributed) duration. The resulting specification enables quantitative analysis of properties of the considered system. Feasibility and effectiveness of our proposal is demonstrated by reporting on the analysis of two reputation models
Truthful Learning Mechanisms for Multi-Slot Sponsored Search Auctions with Externalities
Sponsored search auctions constitute one of the most successful applications
of microeconomic mechanisms. In mechanism design, auctions are usually designed
to incentivize advertisers to bid their truthful valuations and to assure both
the advertisers and the auctioneer a non-negative utility. Nonetheless, in
sponsored search auctions, the click-through-rates (CTRs) of the advertisers
are often unknown to the auctioneer and thus standard truthful mechanisms
cannot be directly applied and must be paired with an effective learning
algorithm for the estimation of the CTRs. This introduces the critical problem
of designing a learning mechanism able to estimate the CTRs at the same time as
implementing a truthful mechanism with a revenue loss as small as possible
compared to an optimal mechanism designed with the true CTRs. Previous work
showed that, when dominant-strategy truthfulness is adopted, in single-slot
auctions the problem can be solved using suitable exploration-exploitation
mechanisms able to achieve a per-step regret (over the auctioneer's revenue) of
order (where T is the number of times the auction is repeated).
It is also known that, when truthfulness in expectation is adopted, a per-step
regret (over the social welfare) of order can be obtained. In
this paper we extend the results known in the literature to the case of
multi-slot auctions. In this case, a model of the user is needed to
characterize how the advertisers' valuations change over the slots. We adopt
the cascade model that is the most famous model in the literature for sponsored
search auctions. We prove a number of novel upper bounds and lower bounds both
on the auctioneer's revenue loss and social welfare w.r.t. to the VCG auction
and we report numerical simulations investigating the accuracy of the bounds in
predicting the dependency of the regret on the auction parameters
A Software Suite for the Control and the Monitoring of Adaptive Robotic Ecologies
Adaptive robotic ecologies are networks of heterogeneous robotic devices (sensors, actuators, automated appliances) pervasively embedded in everyday environments, where they learn to cooperate towards the achievement of complex tasks. While their flexibility makes them an increasingly popular way to improve a system’s reliability, scalability, robustness and autonomy, their effective realisation demands integrated control and software solutions for the specification, integration and management of their highly heterogeneous and computational constrained components. In this extended abstract we briefly illustrate the characteristic requirements dictated by robotic ecologies, discuss our experience in developing adaptive robotic ecologies, and provide an overview of the specific solutions developed as part of the EU FP7 RUBICON Project
All Optical Switch of Vacuum Rabi Oscillations: The Ultrafast Quantum Eraser
We study the all-optical time-control of the strong coupling between a single
cascade three-level quantum emitter and a microcavity. We find that only
specific arrival-times of the control pulses succeed in switching-off the Rabi
oscillations. Depending on the arrival times of control pulses, a variety of
exotic non-adiabatic cavity quantum electrodynamics effects can be observed. We
show that only control pulses with specific arrival times are able to suddenly
switch-off and -on first-order coherence of cavity photons, without affecting
their strong coupling population dynamics. Such behavior may be understood as a
manifestation of quantum complementarity
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