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Tile-based streaming techniques have been widely used to save bandwidth in 360${}^{\circ }$∘ video streaming. However, it is a challenge to determine the right tile size which directly affects the bandwidth usage. Moreover, downloading and processing many small tiles consume a large amount of energy on mobile devices. To solve this problem, we propose to encode the video by taking into account the viewing popularity, where the popularly viewed areas are encoded as macrotiles. We propose techniques for identifying and building macrotiles, and adjusting their sizes to take into account practical issues such as head movement randomness. In some cases, the user's viewing area may not be covered by the constructed macrotiles, and then the conventional tiling scheme is used. To support macrotile based 360${}^{\circ }$∘ video streaming, the client selects the right tiles (a macrotile or a set of conventional tiles) with the right quality level to maximize the QoE under bandwidth constraint. We formulate this problem as an optimization problem which is NP-hard, and then propose a heuristic algorithm to solve it. Through extensive evaluations based on real head movement traces, we demonstrate that the proposed algorithm can significantly improve QoE, save bandwidth usage, and reduce energy consumption.

Chemical vapor deposition (CVD)-grown flakes of high-quality monolayers of WS2can be stabilized at elevated temperatures by encapsulation with several layer hexagonal boron nitride (h-BN), but to different degrees in the presence of ambient air, flowing N2, and flowing forming gas (95% N2, 5% H2). The best passivation of WS2at elevated temperature occurs for h-BN-covered samples with flowing N2(after heating to 873 K), as judged by optical microscopy and photoluminescence (PL) intensity after a heating/cooling cycle. Stability is worse for uncovered samples, but best with flowing forming gas. PL from trions, in addition to that from excitons, is seen for covered WS2only for forming gas, during cooling below ∼323 K; the trion has an estimated binding energy of ∼28 meV. It might occur because of doping level changes caused by charge defect generation by H2molecules diffusing between the h-BN and the SiO2/Si substrate. The decomposition of uncovered WS2flakes in air suggests a dissociation and chemisorption energy barrier of O2on the WS2surface of ∼1.6 eV. Fitting the high-temperature PL intensities in air gives a binding energy of a free exciton of ∼229 meV.

In the mouse embryo, the aorta-gonad-mesonephros (AGM) region is considered to be the sole location for intraembryonic emergence of hematopoietic stem cells (HSCs). Here we report that, in parallel to the AGM region, the E10.5–E11.5 mouse head harbors bona fide HSCs, as defined by long-term, high-level, multilineage reconstitution and self-renewal capacity in adult recipients, before HSCs enter the circulation. The presence of hemogenesis in the midgestation head is indicated by the appearance of intravascular cluster cells and the blood-forming capacity of a sorted endothelial cell population. In addition, lineage tracing via an inducible VE-cadherin-Cretransgene demonstrates the hemogenic capacity of head endothelium. Most importantly, a spatially restricted lineage labeling system reveals the physiological contribution of cerebrovascular endothelium to postnatal HSCs and multilineage hematopoiesis. We conclude that the mouse embryonic head is a previously unappreciated site for HSC emergence within the developing embryo.