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While traditional multimedia applications such as games and videos are still popular, there has been a significant interest in the recent years towards new 3D media such as 3D immersion and Virtual Reality (VR) applications, especially 360 VR videos. 360 VR video is an immersive spherical video where the user can look around during playback. Unfortunately, 360 VR videos are extremely bandwidth intensive, and therefore are difficult to stream at acceptable quality levels.In this paper, we propose an adaptive bandwidth-efficient 360 VR video streaming system using a divide and conquer approach. We propose a dynamic view-aware adaptation technique to tackle the huge bandwidth demands of 360 VR video streaming. We spatially divide the videos into multiple tiles while encoding and packaging, use MPEG-DASH SRD to describe the spatial relationship of tiles in the 360-degree space, and prioritize the tiles in the Field of View (FoV). In order to describe such tiled representations, we extend MPEG-DASH SRD to the 3D space of 360 VR videos. We spatially partition the underlying 3D mesh, and construct an efficient 3D geometry mesh called hexaface sphere to optimally represent a tiled 360 VR video in the 3D space. Our initial evaluation results report up to 72% bandwidth savings on 360 VR video streaming with minor negative quality impacts compared to the baseline scenario when no adaptations is applied.

Virtual Reality (VR) devices are becoming accessible to a large public, which is going to increase the demand for 360°VR videos. VR videos are often characterized by a poor quality of experience, due to the high bandwidth required to stream the 360°video. To overcome this issue, we spatially divide the VR video into tiles, so that each temporal segment is composed of several spatial tiles. Only the tiles belonging to the viewport, the region of the video watched by the user, are streamed at the highest quality. The other tiles are instead streamed at a lower quality. We also propose an algorithm to predict the future viewport position and minimize quality transitions during viewport changes. The video is delivered using the server push feature of the HTTP/2 protocol. Instead of retrieving each tile individually, the client issues a single push request to the server, so that all the required tiles are automatically pushed back to back. This approach allows to increase the achieved throughput, especially in mobile, high RTT networks. In this paper, we detail the proposed framework and present a prototype developed to test its performance using real-world 4G bandwidth traces. Particularly, our approach can save bandwidth up to 35% without severely impacting the quality viewed by the user, when compared to a traditional non-tiled VR streaming solution. Moreover, in high RTT conditions, our HTTP/2 approach can reach 3 times the throughput of tiled streaming over HTTP/1.1, and consistently reduce freeze time. These results represent a major improvement for the e cient delivery of 360°VR videos over the Internet.

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Nd2Fe14B hard magnetic nanoparticles were synthesized by chemical synthesis techniques. Nd−Fe−B gel was prepared using NdCl3·6H2O, FeCl3·6H2O, H3BO3, citric acid, and ethylene glycol (EG) by a Pechini type sol−gel method. This gel was subsequently annealed to produce mixed oxide powders. Nd2Fe14B nanoparticles were prepared from these oxides by a reduction−diffusion process. The phase analysis, structure, and magnetic properties were determined by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM) techniques. The mechanism of Nd2Fe14B formation was investigated by differential scanning calorimetry (DSC), XRD, and thermodynamic free energy change data. Our experimental and modeling results showed that the reduction−diffusion of the Nd−Fe−B mixed oxide was a three step process. The reduction of Fe2O3 to Fe and B2O3 to B occurred at 300 °C. NdH2 and Fe was formed from Nd2O3 and NdFeO3 at 620 °C. The Nd2Fe14B phase was formed from NdH2, Fe, and B at 692 °C. The coercivity of as-synthesized powder was 6.1 kOe. The Henkel plot showed that this powder was exchange coupled; removal of CaO by washing led to dipolar interactions and a decrease in coercivity.