Time filter

Source Type

Latresne, France

Lappa M.,Telespazio
Journal of Fluid Mechanics | Year: 2013

The present analysis extends the author's earlier work (Lappa, Phys. Fluids, vol. 25, 2003, 012101; Lappa, Chaos, vol. 23, 2003, 013105) on the properties of patterns formed by the spontaneous accumulation and ordering of solid particles in certain types of flow (with a toroidal structure and a travelling wave propagating in the azimuthal direction) by considering the potential impact of 'vibrations' (g-jitters) on such dynamics. It is shown that a kaleidoscope of possible variants exist whose nature and variety calls for a concerted analysis using the tools of computational fluid dynamics in synergy with dimensional arguments and existing theories on the effect of periodic accelerations on fluid systems. A possible categorization of the observed phenomena is introduced according to the type and scale of 'defects' displayed by the emerging particle aggregates with respect to unperturbed (vibration-less) conditions. It is shown that the resulting degree of 'turbulence' depends essentially on the direction (φ), amplitude (γ) and frequency (π{variant}) of the applied inertial disturbance. A range of amplitudes and frequencies exist where the formation of recognizable particle structures is prevented. A quantitative map (in the γ-π{variant}) for their occurrence is derived with the express intent of supporting the optimization of future experiments to be performed in space. © 2013 Cambridge University Press. Source

A completely new phenomenon of particle accumulation in vibrated non-isothermal monodisperse suspensions of solid spheres (in a liquid) is analyzed. For the first time evidence is provided for this case that even in situations in which particle-particle hydrodynamic interactions are negligible (dilute systems), intriguing nonlinear effects can lead to the irreversible formation of well-defined particulate structures over "long" temporal scales, i.e., times much larger than the period of the applied vibrations. The long-range translational ordering is produced by the delicate interplay between convective effects (of thermovibrational nature) and the (inertial) response of each isolated particle to the time-periodic acceleration. A new family of particle attractors in the physical space is identified with the topological dimension being essentially a function of the "symmetry properties" of the considered vibrated system and related geometrical constraints. © 2014 AIP Publishing LLC. Source

Lappa M.,Telespazio
Physics of Fluids | Year: 2014

The present analysis extends earlier theories on patterns formed by the spontaneous accumulation and ordering of solid particles in certain types of flow by considering the case in which the particle carrier flow has the typical features of a "standing wave." For the first time an explanation for this phenomenon is elaborated through arguments based on the interplay between vorticity and wave-interference dynamics (following a deductive approach after the so-called phase-locking or "resonance" model originally introduced by Pushkin et al. [Phys. Rev. Lett. 106, 234501 (2011)] and later variants developed by Lappa [Phys. Fluids 25(1), 012101 (2013) and Chaos 23(1), 013105 (2013)]). The results of dedicated numerical simulations are used in synergy with available experimental work. An interesting analogy is proposed with the famous Chladni's series of experiments on patterns formed by sand on vibrating plates. © 2014 AIP Publishing LLC. Source

Giuliano R.,Consorzio University Industria | Neri A.,Consorzio University Industria | Valletta D.,Telespazio
WIFS 2012 - Proceedings of the 2012 IEEE International Workshop on Information Forensics and Security | Year: 2012

This contribution is focused on securing end-to-end unicast communications in heterogeneous sensor networks comprising satellite links, while maintaining effective network performance. The proposed protocol extends the LOCKSAT (LOCal Key Synchronization and generation for data security in sATellite communication) key management procedure, and is able to guarantee a frequent key renewal while overcoming limitations of both sensor and satellite segment. Effectiveness of the solution is assessed through a test bed including real and simulated satellite links. © 2012 IEEE. Source

Rochwerger B.,IBM | Breitgand D.,IBM | Epstein A.,IBM | Hadas D.,IBM | And 11 more authors.
Computer | Year: 2011

As demand for cloud services grows, the increases in cost and complexity for the cloud provider could become a major obstacle. Technologies developed under the Reservoir research project help cloud providers deal with complexity and scalability issues. © 2011 IEEE. Source

Discover hidden collaborations