Recent in-situ and remote observations suggest that the transport regime associated with shock accelerated particles may be anomalous i.e., the Mean Square Displacement (MSD) of such particles scales non-linearly with time. We use self-consistent, hybrid PIC plasma simulations to simulate a quasi-parallel shock with parameters compatible with heliospheric shocks, and gain insights about the particle transport in such a system. For suprathermal particles interacting with the shock we compute the MSD separately in the upstream and downstream regions. Tracking suprathermal particles for sufficiently long times up and/or downstream of the shock poses problems in particle plasma simulations, such as statistically poor particle ensembles and trajectory fragments of variable length in time. Therefore, we introduce the use of time-averaged mean square displacement (TAMSD), which is based on single particle trajectories, as an additional technique to address the transport regime for the upstream and downstream regions. MSD and TAMSD are in agreement for the upstream energetic particle population, and both give a strong indication of superdiffusive transport, consistent with interplanetary shock observations. MSD and TAMSD are also in reasonable agreement downstream, where indications of anomalous transport are also found. TAMSD shows evidence of heterogeneity in the diffusion properties of the downstream particle population, ranging from subdiffusive behaviour of particles trapped in the strong magnetic field fluctuations generated at the shock, to superdiffusive behaviour of particles transmitted and moving away from the shock.

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Energetic particles are ubiquitous in the interplanetary space and their transport properties are strongly influenced by the interaction with magnetic field fluctuations. Numerical experiments have shown that transport in both the parallel and perpendicular directions with respect to the background magnetic field is deeply affected by magnetic turbulence spectral properties. Recently, making use of a numerical model with three dimensional isotropic turbulence, the influence of turbulence intermittency and magnetic fluctuations on the energetic particle transport was investigated in the solar wind context. Stimulated by this previous theoretical work, here we analyze the parallel transport of supra-thermal particles upstream of interplanetary shock waves by using in situ particle flux measurements; the aim was to relate particle transport properties to the degree of intermittency of the magnetic field fluctuations and to their relative amplitude at the energetic particle resonant scale measured in the same regions. We selected five quasi-perpendicular and five quasi-parallel shock crossings by the ACE satellite. The analysis clearly shows a tendency to find parallel superdiffusive transport at quasi-perpendicular shocks, with a significantly higher level of the energetic particle fluxes than those observed in the quasi-parallel shocks. Furthermore, the occurrence of anomalous parallel transport is only weakly related to the presence of magnetic field intermittency.

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We study the transport of energetic particles accelerated at three different shock events observed in the solar wind by the ACE spacecraft. We consider particle propagation for a quasi-parallel, an oblique, and a quasi-perpendicular shock. The transport regime is deduced from the shape of the energetic particle profiles upstream of the shock, and for these events the profiles are well-fitted by power-laws with slope β. This corresponds to a superdiffusive transport with the anomalous diffusion exponent α = 2 − β when β < 1, and to normal diffusion when β ≥ 1. We checked the resonant turbulence level upstream of the shocks, finding that this is statistically constant, so that the transport regime is not expected to change with the shock distance. For the three shocks under study, particle transport upstream of the shock is mostly superdiffusive, although the superdiffusive character appears to diminish with the increase of the shock normal angle θ Bn . We discuss possible interpretations of these results.

This is the first of three papers where we present the applicable potential of an original construction process for steel space grids, named PREMIT System. After a general introduction, we explain the geometrical and structural characteristics of the proposed System. We carry out a morphological study of the principal typological schemes to which it is possible to extend the applicable field of the System. Moreover, we deduce some useful criteria for the static-economic valuation through a comparative analysis among the more frequently employed geometrical shapes.

Interplanetary shocks are large-scale heliospheric structures often caused by eruptive phenomena at the Sun, and represent one of the main sources of energetic particles. Several interplanetary (IP) shock crossings by spacecraft at 1 au have revealed enhanced energetic-ion fluxes that extend far upstream of the shock. Surprisingly, in some shock events ion fluxes with energies between 100 keV and about 2 MeV acquire similar values (which we refer to as “overlapped” fluxes), corresponding to flat energy spectra in that range. In contrast, closer to the shock the fluxes are observed to depend on energy. In this work, we analyze three IP-shock-related energetic particle events observed by the Advanced Composition Explorer spacecraft where flat ion energy spectra were observed upstream of the shock. We interpret these observations via a velocity-filter mechanism for particles in a given energy range. In particular, ions with velocity parallel to the local magnetic field larger than the speed of the upstream plasma, in the reference frame of the shock, can easily propagate back upstream, while lower-energy ions tend to be confined to the shock front, thus reducing their fluxes far upstream and giving rise to flat energy spectra. The velocity-filter mechanism has been corroborated from observations of particle flux anisotropy by the Solid-State Telescope of Wind/3DP.

In the field of civil and industrial buildings and, particularly, dealing with coverings of wide areas, space truss structures are spreading more and more. Modern tridimensional steel systems are made up to the modular aggregation of standardized structural single or multiple elements, coordinated in space in accordance with rational geometric criteria, mass produced on an industrial scale and designed for a fine and functional architecture. Concerning these structures, the paper presents basic qualitative and performance characteristics, main typologies for the applications and, lastly, some among the most significant structural systems patented by Italian production.