2,974 research outputs found

    Recent Breakthroughs on Angle-of-Arrival Estimation for Millimeter-Wave High-Speed Railway Communication

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    © 2019 IEEE. With significantly improved efficiency, largescale hybrid antenna arrays with tens to hundreds of antennas have great potential to support millimeter-wave (mmWave) communication for high-speed railway (HSR) applications. The significant beamforming gains rely on fast and accurate estimation of the angle-of-arrival (AoA), but this can be impeded by the high train speed, the cost/energy oriented design of arrays, and the severe attenuation of mmWave signals. This article reviews these challenges, and discusses the limitations of existing AoA estimation techniques under hybrid antenna array settings. The article further reveals a few recent theoretical breakthroughs that can potentially enable fast and reliable estimation, even based on severely attenuated signals. Under a speed setting of 500 km/h, a performance study is carried out to confirm the significant improvements of estimation accuracy and subsequent beamforming gains as the results of the breakthroughs

    Angle-Resolved Photoemission Spectroscopy of Tetragonal CuO: Evidence for Intralayer Coupling Between Cupratelike Sublattices

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    We investigate by angle-resolved photoemission the electronic structure of in situ grown tetragonal CuO, a synthetic quasi-two-dimensional edge-sharing cuprate. We show that, in spite of the very different nature of the copper oxide layers, with twice as many Cu in the CuO layers of tetragonal CuO as compared to the CuO2 layers of the high-T-c cuprates, the low-energy electronic excitations are surprisingly similar, with a Zhang-Rice singlet dispersing on weakly coupled cupratelike sublattices. This system should thus be considered as a member of the high-T-c cuprate family, with, however, interesting differences due to the intralayer coupling between the cupratelike sublattices.open1199sciescopu

    Molecular evolution of psbA gene in ferns: unraveling selective pressure and co-evolutionary

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    Background: The photosynthetic oxygen-evolving photo system II (PS II) produces almost the entire oxygen in the atmosphere. This unique biochemical system comprises a functional core complex that is encoded by psbA and other genes. Unraveling the evolutionary dynamics of this gene is of particular interest owing to its direct role in oxygen production. psbA underwent gene duplication in leptosporangiates, in which both copies have been preserved since. Because gene duplication is often followed by the non-fictionalization of one of the copies and its subsequent erosion, preservation of both psbA copies pinpoint functional or regulatory specialization events. The aim of this study was to investigate the molecular evolution of psbA among fern lineages. Results: We sequenced psbA, which encodes D1 protein in the core complex of PSII, in 20 species representing 8 orders of extant ferns; then we searched for selection and convolution signatures in psbA across the 11 fern orders. Collectively, our results indicate that: (1) selective constraints among D1 protein relaxed after the duplication in 4 leptosporangiate orders; (2) a handful positively selected codons were detected within species of single copy psbA, but none in duplicated ones; (3) a few sites among D1 protein were involved in co-evolution process which may intimate significant functional/structural communications between them. Conclusions: The strong competition between ferns and angiosperms for light may have been the main cause for a continuous fixation of adaptive amino acid changes in psbA, in particular after its duplication. Alternatively, a single psbA copy may have undergone bursts of adaptive changes at the molecular level to overcome angiosperms competition. The strong signature of positive Darwinian selection in a major part of D1 protein is testament to this. At the same time, species own two psbA copies hardly have positive selection signals among the D1 protein coding sequences. In this study, eleven co-evolving sites have been detected via different molecules, which may be more important than others.We thank Dr. Yefu Wang at State Key Laboratory of Virology, College of Life Sciences, Wuhan University, China, for the guidance for wording, and we also thank Bo Wang and Dr. Lei Gao at the Wuhan Botanical Garden, Chinese Academy of Sciences, China, for the experimental assistance. We thank Dr. Jianqiang Li at the Wuhan Botanical Garden, Chinese Academy of Sciences, China, for the advices on species sampling. We appreciate two anonymous reviewers and other editors for their helpful suggestions. The present work was financially supported by the National Nature Science Foundation of China (No. 30970290, 31070594), and by the Knowledge Innovation Program of the Chinese Academy of Sciences (No. KSCX2-EW-J-20, KSCX2-YW-Z-0940). Dr. Mario A. 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    Methyl 8-hydroxy-(S)-3-methyl-1-oxoisochromane-5-carboxylate (5-methoxycarbonylmellein)

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    The title compound, C12H12O5, exists as two independent, relatively planar molecules in the asymmetric unit; these differ in the orientation of the ester group

    7,8-dihydroxy-3-methyl-10-oxo-1H,10H-pyrano[4,3-b]chromene-9-carboxylic acid

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    The structure of the title compound, anhydrofulvic acid, C14H10O7, a yellow acidic metabolite isolated from Paecilomyces sp. was determined by X-ray analysis. The chromone ring system is essentially planar, with the carboxylic acid group coplanar with the ring

    Effect of Prestrain on Hydrogen-Induced Delayed Cracking for Medium Mn Steels

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    Medium Mn steels are a class of the new-generation ultra-high-strength materials used in automotives. However, despite excellent ductility, they may suffer from delayed cracking and thus cause serious concerns. In this study, several medium Mn steels were tested with different prestrain and hydrogen charging conditions. The interaction and synergistic effects of prestrain and hydrogen content on hydrogen-induced delayed cracking behavior are investigated. The threshold stress of hydrogen-induced cracking (HIC) decreased during dynamic hydrogen charging under a constant load. In the process of dynamic hydrogen charging, for M7B and M10B steels, the normalized stress intensity factor σ/σb and the corresponding threshold stress σHIC decreased sharply as prestrain increased. This is because the volume fraction of retained austenite decreased with an increase in prestrain. Similarly, σHIC was reduced and the critical hydrogen content dropped drastically with increasing prestrain. For M7C, the influence of prestrain on threshold stress and hydrogen concentration was less than that of M7B. This is because the different treatment processes leads to a different stability of the retained austenite. By observing the SEM fractographs, the fracture surface of medium Mn steels showed different fracture characteristics, such as dimple fractures and intergranular and transgranular modes

    8-Hydroxy-(S)-3-methyl-1-oxoisochromane-5-carboxylic acid(5-carboxymellein)

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    The molecules of the title compound, C11H10O5, are linked by a hydrogen bond involving the acid H and the carbonyl O atom of the dihydroisocoumarin unit into a linear chain running along the b axis of the monoclinic unit cell

    7-methoxy-4,6-dimethyl-3H-isobenzofuran-1-one

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    The title compound, C11H12O3, exists as a nearly planar molecule, the dihedral angle between the five- and six-membered rings being 1.9 (2)degrees
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