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Aiming to tackle high accuracy indoor positioning for smart mobiles under dense NLOS (Non-line-of-sight) environment with low anchor deployment density, acoustic fingerprint method is studied in this paper. Considering the properties of the cheap commercial off-the-shelf acoustic components, a TOA based acoustic fingerprint indoor positioning architecture is proposed, and the positioning methods based on decision tree with bagging, BP neural network and weighted K nearest neighbor algorithm are analyzed and evaluated respectively, and called TOA-DTB, TOA-ANN and TOA-WKNN correspondingly. The experiment results show that the TOA-DTB method is superior to TOA-WKNN and TOA-ANN in complex indoor scenarios. By only using 2 Anchors in dense NLOS environment, the probability of positioning error less than 54 cm is 90%, probability of positioning error less than 38 cm is 80%, less than 30 cm is 64%. Thus, the proposed method can meet the needs of accurate indoor positioning for smart mobiles in dense NLOS environment with low anchor deployment density, which means a high values for real application and promotion.

A new anode material, Fe3S4, shows superior electrochemical performance and a novel mechanism for sodium storage., Transition metal dichalcogenide materials have been considered as promising anode materials for rechargeable sodium-ion batteries because of their high specific capacity and low cost. Here, we demonstrate an iron sulfide Fe3S4 as a new anode material for a rechargeable sodium-ion battery. The involved conversion mechanism has been proved when the as-prepared Fe3S4 was used as the host material for sodium storage. Remarkably, a compound FeSx with quantum size generated by conversion reaction overcame the kinetic and thermodynamic constraints of chemical conversion to achieve superior cycling and rate capability. As a result, the as-prepared Fe3S4 electrode delivers a high reversible specific capacity of 548 mA h g–1 at 0.2 A g–1, together with an excellent cycling stability of 275 mA h g–1 after 3500 cycles at 20 A g–1.

Graphene quantum dots (GQDs) possess unique photoelectronic properties ascribed to quantum confinement and edge effects, which have evoked important development and wide application in the optoelectronic field. Doping GQDs with heteroatoms can further modulate the energy band structure and thus produce unexpected properties. Herein, we obtained fluorine-doped GQDs (F-GQDs) by adopting an effective preparation technique, which includes the treatment of the as-prepared reaction precursor, fluorinated carbon fibers, with ultrasonic liquid phase exfoliation. The proposed method is simple, handy, and low-cost, opening up an alternate approach to prepare F-GQDs. Through multiple characterization techniques, the effective incorporation of fluorine in GQDs was confirmed, and the as-prepared F-GQDs exhibit excellent photoelectrical properties and good ultraviolet absorption performances. Accordingly, we have fabricated a vertical photovoltaic UV detector based on F-GQDs. The unoptimized device has an exceptionally...