52,724 research outputs found

    A Survey of Positioning Systems Using Visible LED Lights

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    © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe

    Shaping of molecular weight distribution by iterative learning probability density function control strategies

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    A mathematical model is developed for the molecular weight distribution (MWD) of free-radical styrene polymerization in a simulated semi-batch reactor system. The generation function technique and moment method are employed to establish the MWD model in the form of Schultz-Zimmdistribution. Both static and dynamic models are described in detail. In order to achieve the closed-loop MWD shaping by output probability density function (PDF) control, the dynamic MWD model is further developed by a linear B-spline approximation. Based on the general form of the B-spline MWD model, iterative learning PDF control strategies have been investigated in order to improve the MWD control performance. Discussions on the simulation studies show the advantages and limitations of the methodology

    Optical control of the spin state of two Mn atoms in a quantum dot

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    We report on the optical spectroscopy of the spin of two magnetic atoms (Mn) embedded in an individual quantum dot interacting with either a single electron, a single exciton and single trion. As a result of their interaction to a common entity, the Mn spins become correlated. The dynamics of this process is probed by time resolved spectroscopy, that permits to determine the optical orientation time in the range of a few tens of nsns. In addition, we show that the energy of the collective spin states of the two Mn atoms can be tuned through the optical Stark effect induced by a resonant laser field

    Quantum kk-core conduction on the Bethe lattice

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    Classical and quantum conduction on a bond-diluted Bethe lattice is considered. The bond dilution is subject to the constraint that every occupied bond must have at least k−1k-1 neighboring occupied bonds, i.e. kk-core diluted. In the classical case, we find the onset of conduction for k=2k=2 is continuous, while for k=3k=3, the onset of conduction is discontinuous with the geometric random first-order phase transition driving the conduction transition. In the quantum case, treating each occupied bond as a random scatterer, we find for k=3k=3 that the random first-order phase transition in the geometry also drives the onset of quantum conduction giving rise to a new universality class of Anderson localization transitions.Comment: 12 pgs., 6 fig

    Pinned Low Energy Electronic Excitation in Metal Exchanged Vanadium Oxide Nanoscrolls

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    We measured the optical properties of mixed valent vanadium oxide nanoscrolls and their metal exchanged derivatives in order to investigate the charge dynamics in these compounds. In contrast to the prediction of a metallic state for the metal exchanged derivatives within a rigid band model, we find that the injected charges in Mn2+^{2+} exchanged vanadium oxide nanoscrolls are pinned. A low-energy electronic excitation associated with the pinned carriers appears in the far infrared and persists at low temperature, suggesting that the nanoscrolls are weak metals in their bulk form, dominated by inhomogeneous charge disproportionation and Madelung energy effects.Comment: 4 figure

    Closed-loop control strategy with improved current for a flashing ratchet

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    We show how to switch on and off the ratchet potential of a collective Brownian motor, depending only on the position of the particles, in order to attain a current higher than or at least equal to that induced by any periodic flashing. Maximization of instant velocity turns out to be the optimal protocol for one particle but is nevertheless defeated by a periodic switching when a sufficiently large ensemble of particles is considered. The protocol presented in this article, although not the optimal one, yields approximately the same current as the optimal protocol for one particle and as the optimal periodic switching for an infinite number of them.Comment: 4 pages, 4 figure

    Evolution of Magnetism in Single-Crystal Honeycomb Iridates

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    We report the successful synthesis of single-crystals of the layered iridate, (Na1−x_{1-x}Lix_{x})2_2IrO3_3, 0≤x≤0.90\leq x \leq 0.9, and a thorough study of its structural, magnetic, thermal and transport properties. The new compound allows a controlled interpolation between Na2_2IrO3_3 and Li2_2IrO3_3, while maintaing the novel quantum magnetism of the honeycomb Ir4+^{4+} planes. The measured phase diagram demonstrates a dramatic suppression of the N\'eel temperature, TNT_N, at intermediate xx suggesting that the magnetic order in Na2_2IrO3_3 and Li2_2IrO3_3 are distinct, and that at x≈0.7x\approx 0.7, the compound is close to a magnetically disordered phase that has been sought after in Na2_2IrO3_3 and Li2_2IrO3_3. By analyzing our magnetic data with a simple theoretical model we also show that the trigonal splitting, on the Ir4+^{4+} ions changes sign from Na2_2IrO3_3 and Li2_2IrO3_3, and the honeycomb iridates are in the strong spin-orbit coupling regime, controlled by \jeff=1/2 moments.Comment: updated version with more dat
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