Owing to its interactive look around nature and very large resolution requirement, providing immersive omnidirectional video (ODV) streaming experiences in virtual reality applications demands cost-effective solutions to meet both the content delivery network and device constraints. In this paper, we introduce an adaptive ODV streaming pipeline that optimizes dynamic adaptive streaming over HTTP representations of ODV content considering their visual attention (VA) maps. The main contribution of this paper is the use of VA maps: 1) to compute a novel objective quality metric that captures the fact that not all of the ODV is actually watched by users: the VA spherical weightedbased objective quality measurement; 2) to define optimal tile representations of the ODV frames, namely, tiling schemes, which are composed of variable-sized and non-overlapping tiles; and 3) to efficiently distribute a given bitrate budget among the set of tiles within a tiling scheme for an ODV. We evaluate the proposed system performance with varying bandwidth conditions and the tracked head orientations from user experiments. Results show that the proposed system significantly outperforms the existing non-tiled and tile-based streaming solutions.

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A theoretical model is proposed to account for the damage and amorphization induced in LiNbO 3 by ion bombardment in the electronic energy-loss regime. It relies on the synergy between the thermal spike generated by electron-phonon interaction and the nonradiative decay of localized ͑self-trapped͒ excitons. Calculations have been carried out to describe the effect of single impact as well as multiple impact ͑high fluence͒ irradiations. In the first case, the defect concentration profile and the radius of the amorphous tracks have been theoretically predicted and they are in good accordance with those experimentally determined. For high fluence irradiations ͑Ն10 13 cm −2 ͒ the model predicts the formation of homogeneous amorphous surface layers whose thickness increases with fluence. The propagation of the crystalline-amorphous boundary has been determined as a function of irradiation fluence. Theoretical predictions are also in good agreement with experimental data on Si-irradiated ͑7.5 and 5 MeV͒ LiNbO 3 outside the region of nuclear collision damage.