The requirement of precious platinum (Pt) based materials as electrocatalysts and the sluggish kinetics of oxygen reduction reaction (ORR) in a cathode have significantly impeded the commercialization of proton exchange membrane fuel cells. Much effort has been directly made to search for high performance Pt-free cathode catalysts. Chalcogenides are promising alternatives because of their moderate electrocatalytic activities and good selectivity toward ORR in acidic and basic media. The carbon supported binary cobalt selenide (CoSe 2 /C), nickel selenide (NiSe 2 /C) and ternary cobalt-nickel selenide (Co-Ni-Se/C) nanoparticles were prepared by a simple microwave synthesis route without or with heat treatment. The microstructure, electrocatalytic activities and stabilities of CoSe 2 /C, NiSe 2 /C and Co-Ni-Se/C catalysts were studied in 0.1 mol/L HClO 4 or KOH solutions. The single cell performances of the as-prepared catalysts were further investigated and compared.
FeSiAl is a commonly used soft magnetic material because of its high resistivity, low core loss, and low cost. In order to systematically study the effect of epoxy resin (EP) on the insulated coating and pressing effect of FeSiAl magnetic powders, six groups of composite powders and their corresponding soft magnetic powder cores (SMPCs) were prepared by changing the content of EP, and the soft magnetic properties of the powders and SMPCs were characterized. The results showed that FeSiAl powders exhibited good sphericity and morphology. The Ms of FeSiAl/EP composite powders was between 117.4-124.8 emu·g-1 after adding (0.3, 0.5, 0.7, 1, 1.5, and 2 wt. %) EP. The permeability μe of SMPCs increased first and then decreased with the increase in EP content. Among them, when the EP content was 1 wt. %, the corresponding SMPCs had the highest μe and excellent DC bias performance (63%, 100 Oe). In the whole test frequency range (50~1000 kHz), SMPCs with 1 wt. % EP content had the lowest core loss (1733.9 mW·cm-3 at 20 mT and 1000 kHz). After that, the loss separation study in the low-frequency range (50~250 kHz) was conducted, and the hysteresis loss and eddy current loss of SMPCs with 1 wt. % EP content were also the lowest. In addition, SMPCs also exhibited the best overall performance when the EP content was 1 wt. %. The results of this study can guide the design of composite insulation coating schemes and promote the development of soft magnetic materials for medium and high frequency applications.
This paper proposes a cloud rendering framework for three-degree-of-freedom-oriented standalone virtual reality headset which worked on wireless network to solve the shortcomings of VR devices using cables connections and insufficient local rendering capabilities. This framework not only solves the problem of the VR experience being affected by cables, but also improves the image quality of the standalone headset. In this solution, we use the standalone headset as the client, the Unreal Engine 4(UE4) as the rendering engine and the server combining Asynchronous TimeWarping (ATW) and Fixed Foveated Rendering (FFR) technology to achieve cloud rendering. The results show that the solution can support the 2560×1440 resolution. Experiments show that the framework can significantly improve the image quality of the standalone headset, and it can also maintain a frame rate of 70Hz.
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