37,441 research outputs found

    Polarization Induced Switching Effect in Graphene Nanoribbon Edge-Defect Junction

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    With nonequilibrium Green's function approach combined with density functional theory, we perform an ab initio calculation to investigate transport properties of graphene nanoribbon junctions self-consistently. Tight-binding approximation is applied to model the zigzag graphene nanoribbon (ZGNR) electrodes, and its validity is confirmed by comparison with GAUSSIAN03 PBC calculation of the same system. The origin of abnormal jump points usually appearing in the transmission spectrum is explained with the detailed tight-binding ZGNR band structure. Transport property of an edge defect ZGNR junction is investigated, and the tunable tunneling current can be sensitively controlled by transverse electric fields.Comment: 18 pages, 8 figure

    The correlations between the twin kHz QPO frequencies of LMXBs

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    We analyzed the recently published kHz QPO data in the neutron star low-mass X-ray binaries (LMXBs), in order to investigate the different correlations of the twin peak kilohertz quasi-eriodic oscillations (kHz QPOs) in bright Z sources and in the less luminous Atoll sources. We find that a power-law relation \no\sim\nt^{b} between the upper and the lower kHz QPOs with different indices: b≃b\simeq1.5 for the Atoll source 4U 1728-34 and b≃b\simeq1.9 for the Z source Sco X-1. The implications of our results for the theoretical models for kHz QPOs are discussed.Comment: 6 pages, accepted by MNRA
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