Showing papers by "Scuola superiore di Catania published in 2005"

Modeling cascading failures in the North American power grid

Abstract: The North American power grid is one of the most complex technological networks, and its interconnectivity allows both for long-distance power transmission and for the propagation of disturbances. We model the power grid using its actual topology and plausible assumptions about the load and overload of transmission substations. Our results indicate that the loss of a single substation can result in up to $25\%$ loss of transmission efficiency by triggering an overload cascade in the network. The actual transmission loss depends on the overload tolerance of the network and the connectivity of the failed substation. We systematically study the damage inflicted by the loss of single nodes, and find three universal behaviors, suggesting that $40\%$ of the transmission substations lead to cascading failures when disrupted. While the loss of a single node can inflict substantial damage, subsequent removals have only incremental effects, in agreement with the topological resilience to less than $1\%$ node loss.

Quantum Many Particle Systems in Ring-Shaped Optical Lattices

Abstract: In the present work we demonstrate how to realize a 1D closed optical lattice experimentally, including a tunable boundary phase twist. The latter may induce ''persistent currents,'' visible by studying the atoms' momentum distribution. We show how important phenomena in 1D physics can be studied by physical realization of systems of trapped atoms in ring-shaped optical lattices. A mixture of bosonic and/or fermionic atoms can be loaded into the lattice, realizing a generic quantum system of many interacting particles.

Locating critical lines in high-voltage electrical power grids

Abstract: Electrical power grids are among the infrastructures that are attracting a great deal of attention because of their intrinsic criticality. Here we analyze the topological vulnerability and improvability of the spanish 400 kV, the french 400 kV and the italian 380 kV power transmission grids. For each network we detect the most critical lines and suggest how to improve the connectivity.

Collective atomic recoil in a moving Bose-Einstein condensate: From superradiance to Bragg scattering

Abstract: We present the results of an experiment on light scattering from an elongated Bose-Einstein condensate (BEC) interacting with a far-off-resonant pump laser. By collective atomic recoil lasing (CARL) a coherent superposition of two atomic wave packets with different momenta is created. Varying the intensity of a weak counterpropagating laser beam we observe the transition from the pure superradiant regime to the Bragg scattering regime, where Rabi oscillations in a two-level system are observed. The process is limited by the decoherence between the two atomic wave packets. In the superradiant regime the experiment gives evidence of a contribution to decoherence which depends on the initial velocity of the condensate. The system is described by the CARL-BEC model, which is a generalization of the Gross-Pitaevskii model to include the self-consistent evolution of the scattered field and a phase-diffusion decoherence process, which accounts for the observed damping.

Opinion dynamics and decision of vote in bipolar political systems

Abstract: A model of the opinion dynamics underlying the political decision is proposed. The analysis is restricted to a bipolar scheme with a possible third political area. The interaction among voters is local but the final decision strongly depends on global effects such as, for example, the rating of the governments. As in the realistic case, the individual decision making process is determined by the most relevant personal interests and problems. The phenomenological analysis of the national vote in Italy and Germany has been carried out and a prediction of the next Italian vote as a function of the government rating is presented.

Opinion dynamics and decision of vote in bipolar political systems

Abstract: A model of the opinion dynamics underlying the political decision is proposed. The analysis is restricted to a bipolar scheme with a possible third political area. The interaction among voters is local but the final decision strongly depends on global effects such as the rating of the governments. As in the realistic case, the individual decision making process is determined by the most relevant personal interests and problems. The phenomenological analysis of the national vote in Italy and Germany has been carried out and a prediction of the next Italian vote as a function of the government rating is presented.

Robustness of a quantum key distribution with two and three mutually unbiased bases

Abstract: We study the robustness of various protocols for quantum key distributions. We first consider the case of qutrits and study quantum protocols that employ two and three mutually unbiased bases. We then derive the optimal eavesdropping strategy for two mutually unbiased bases in dimension 4 and generalize the result to a quantum key distribution protocol that uses two mutually unbiased bases in arbitrary finite dimensions.

Full characterization of the loading of a magneto-optical trap from an alkali metal dispenser

Abstract: We present an experimental study of the dynamics of a magneto–optical trap (MOT) loaded from an alkali dispenser current controlled source. In our experimental vacuum conditions and for a low trapping force MOT the trap loading process critically depends on the dispensers working regime. This allows to completely characterize the dispensers–MOT system and to determine the best loading conditions.

Climbing obstacles via bio-inspired CNN-CPG and adaptive attitude control

Abstract: A control system based on the principles used by cockroaches to climb obstacles is introduced and applied to a bio-inspired hexapod robot. Cockroaches adaptively use different strategies as functions of the ground morphology and obstacle characteristics. The control system introduced in this paper consists of two parts working in parallel. Locomotion control is performed by a cellular neural network (CNN) playing the role of an artificial central pattern generator (CPG) for the robot, while a new attitude control system has been designed. In order to reproduce the adaptative capabilities of the biological model, the attitude control system is based on a motor map and is aimed at regulating the posture of the robot to allow it to overcome obstacles. In fact, high obstacles require the locomotion gait to be reorganized by changing the posture of the robot to be more effective during the overcoming of the obstacle. Both proprioceptive and exteroceptive information are needed to solve this problem, they constitute the input of the adaptive attitude control. Simulation results illustrating the suitability of the control system are also shown.

Slow light amplification in a non-inverted gain medium

Abstract: We investigate the propagation of a coherent probe light pulse through a three-level atomic medium (in the Λ-configuration) in the presence of a pump laser under the conditions for gain without inversion. When the carrier frequency of the probe pulse and the pump laser are in a Raman configuration, we show that it is possible to amplify a slow propagating pulse. We also analyze the regime in which the probe pulse is slightly detuned from resonance where we observe anomalous light propagation.

Slow Light amplification in a non-inverted gain medium

Abstract: We investigate the propagation of a coherent probe light pulse through a three-level atomic medium (in the $\Lambda$--configuration) in the presence of a pump laser under the conditions for gain without inversion. When the carrier frequency of the probe pulse and the pump laser are in a Raman configuration, we show that it is possible to amplify a slow propagating pulse. We also analyze the regime in which the probe pulse is slightly detuned from resonance where we observe anomalous light propagation.

Olami-Feder-Christensen Model on different Networks

Abstract: We investigate numerically the Self Organized Criticality (SOC) properties of the dissipative Olami-Feder-Christensen model on small-world and scale-free networks. We find that the small-world OFC model exhibits self-organized criticality. Indeed, in this case we observe power law behavior of earthquakes size distribution with finite size scaling for the cut-off region. In the scale-free OFC model, instead, the strength of disorder hinders synchronization and does not allow to reach a critical state.