1,537 research outputs found
Universality classes in directed sandpile models
We perform large scale numerical simulations of a directed version of the
two-state stochastic sandpile model. Numerical results show that this
stochastic model defines a new universality class with respect to the Abelian
directed sandpile. The physical origin of the different critical behavior has
to be ascribed to the presence of multiple topplings in the stochastic model.
These results provide new insights onto the long debated question of
universality in abelian and stochastic sandpiles.Comment: 5 pages, RevTex, includes 9 EPS figures. Minor english corrections.
One reference adde
From Minority Games to real markets
We address the question of market efficiency using the Minority Game (MG)
model. First we show that removing unrealistic features of the MG leads to
models which reproduce a scaling behavior close to what is observed in real
markets. In particular we find that i) fat tails and clustered volatility arise
at the phase transition point and that ii) the crossover to random walk
behavior of prices is a finite size effect. This, on one hand, suggests that
markets operate close to criticality, where the market is marginally efficient.
On the other it allows one to measure the distance from criticality of real
market, using cross-over times. The artificial market described by the MG is
then studied as an ecosystem with different_species_ of traders. This clarifies
the nature of the interaction and the particular role played by the various
populations.Comment: 9 pages, 7 figures, to appear in Quantitative Financ
Corrections to scaling in the forest-fire model
We present a systematic study of corrections to scaling in the self-organized
critical forest-fire model. The analysis of the steady-state condition for the
density of trees allows us to pinpoint the presence of these corrections, which
take the form of subdominant exponents modifying the standard finite-size
scaling form. Applying an extended version of the moment analysis technique, we
find the scaling region of the model and compute the first non-trivial
corrections to scaling.Comment: RevTeX, 7 pages, 7 eps figure
Green power grids: How energy from renewable sources affects networks and markets
The increasing attention to environmental issues is forcing the implementation of novel energy models based on renewable sources. This is fundamentally changing the configuration of energy management and is introducing new problems that are only partly understood. In particular, renewable energies introduce fluctuations which cause an increased request for conventional energy sources to balance energy requests at short notice. In order to develop an effective usage of low-carbon sources, such fluctuations must be understood and tamed. In this paper we present a microscopic model for the description and for the forecast of short time fluctuations related to renewable sources in order to estimate their effects on the electricity market. To account for the inter-dependencies in the energy market and the physical power dispatch network, we use a statistical mechanics approach to sample stochastic perturbations in the power system and an agent based approach for the prediction of the market players' behavior. Our model is data-driven; it builds on one-dayahead real market transactions in order to train agents' behaviour and allows us to deduce the market share of different energy sources. We benchmarked our approach on the Italian market, finding a good accordance with real data
Crack roughness and avalanche precursors in the random fuse model
We analyze the scaling of the crack roughness and of avalanche precursors in
the two dimensional random fuse model by numerical simulations, employing large
system sizes and extensive sample averaging. We find that the crack roughness
exhibits anomalous scaling, as recently observed in experiments. The roughness
exponents (, ) and the global width distributions are found
to be universal with respect to the lattice geometry. Failure is preceded by
avalanche precursors whose distribution follows a power law up to a cutoff
size. While the characteristic avalanche size scales as , with a
universal fractal dimension , the distribution exponent differs
slightly for triangular and diamond lattices and, in both cases, it is larger
than the mean-field (fiber bundle) value
Internet of robotic things : converging sensing/actuating, hypoconnectivity, artificial intelligence and IoT Platforms
The Internet of Things (IoT) concept is evolving rapidly and influencing newdevelopments in various application domains, such as the Internet of MobileThings (IoMT), Autonomous Internet of Things (A-IoT), Autonomous Systemof Things (ASoT), Internet of Autonomous Things (IoAT), Internetof Things Clouds (IoT-C) and the Internet of Robotic Things (IoRT) etc.that are progressing/advancing by using IoT technology. The IoT influencerepresents new development and deployment challenges in different areassuch as seamless platform integration, context based cognitive network integration,new mobile sensor/actuator network paradigms, things identification(addressing, naming in IoT) and dynamic things discoverability and manyothers. The IoRT represents new convergence challenges and their need to be addressed, in one side the programmability and the communication ofmultiple heterogeneous mobile/autonomous/robotic things for cooperating,their coordination, configuration, exchange of information, security, safetyand protection. Developments in IoT heterogeneous parallel processing/communication and dynamic systems based on parallelism and concurrencyrequire new ideas for integrating the intelligent “devices”, collaborativerobots (COBOTS), into IoT applications. Dynamic maintainability, selfhealing,self-repair of resources, changing resource state, (re-) configurationand context based IoT systems for service implementation and integrationwith IoT network service composition are of paramount importance whennew “cognitive devices” are becoming active participants in IoT applications.This chapter aims to be an overview of the IoRT concept, technologies,architectures and applications and to provide a comprehensive coverage offuture challenges, developments and applications
Optimizing interpolation of shoot density data from a Posidonia oceanica seagrass bed
A case study on the optimization of Posidonia oceanica density interpolation, using a data set from a large meadow at Porto Conte Bay (NW Sardinia, Italy), is presented. Ordinary point kriging, cokriging and a weighted average based on inverse square distance were used to interpolate density data measured in 36 sampling stations. The results obtained from different methods were then compared by means of a leave-one-out cross-validation procedure. The scale at which interpolation was carried out was defined on the basis of the Hausdorff dimension of the variogram. Optimizing spatial scale and data points search strategy allowed obtaining more accurate density estimates independently of the interpolation method
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