11,221 research outputs found

    Frequency and time profiles of metric wave isolated Type I solar noise storm bursts at high spectral and temporal resolution

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    Type I noise storms constitute a sizeable faction of the active-Sun radio emission component. Observations of isolated instances of such bursts, in the swept-frequency-mode at metric wavelengths, have remained sparse, with several unfilled regions in the frequency coverage. Dynamic spectra of the burst radiation, in the 30 - 130 MHz band, obtained from the recently commissioned digital High Resolution Spectrograph (HRS) at the Gauribidanur Radio Observatory, on account of the superior frequency and time resolution, have unravelled in explicit detail the temporal and spectral profiles of isolated bursts. Apart from presenting details on their fundamental emission features, the time and frequency profile symmetry, with reference to custom-specific Gaussian distributions, has been chosen as the nodal criterion to statistically explain the state of the source regions in the vicinity of magnetic reconnections, the latent excitation agent that contributes to plasma wave energetics, and the quenching phenomenon that causes damping of the burst emission.Comment: 9 pages 7 black and white / grey-scale figures (inclusive of 3 composite). MNRAS - accepte

    A Unified treatment of small and large- scale dynamos in helical turbulence

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    Helical turbulence is thought to provide the key to the generation of large-scale magnetic fields. Turbulence also generically leads to rapidly growing small-scale magnetic fields correlated on the turbulence scales. These two processes are usually studied separately. We give here a unified treatment of both processes, in the case of random fields, incorporating also a simple model non-linear drift. In the process we uncover an interesting plausible saturated state of the small-scale dynamo and a novel analogy between quantum mechanical (QM) tunneling and the generation of large scale fields. The steady state problem of the combined small/large scale dynamo, is mapped to a zero-energy, QM potential problem; but a potential which, for non-zero mean helicity, allows tunneling of bound states. A field generated by the small-scale dynamo, can 'tunnel' to produce large-scale correlations, which in steady state, correspond to a force-free 'mean' field.Comment: 4 pages, 1 figure, Physical Review Letters, in pres

    Dynamic Response of Vertical and Batter Piles

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    The lateral forced vibration test was carried out on driven cast in-situ concrete vertical piles of 500 mm diameter in a petrochemical complex site in Paradip, India. The site predominantly consists of silty sand for the top 3 m with shear wave velocity of 200 m/s and it is followed by clayey sand with shear velocity increases from 415 m/s to 460 m/s over pile termination depth of about 17 m . The piles were subjected to a sinusoidal lateral force with magnitude of 0.3 kN to 9.5 kN in the frequency range of 5 to 30 Hz. A 3D finite element analysis was carried out on vertical piles using ABAQUS and its results are validated with the field test results. Finite element analysis was extended to batter piles (10˚and 20˚) subjected to lateral dynamic load and it was found that the peak displacement amplitude of batter piles is 15 to 25% less than the same that of vertical piles indicating better performance of batter piles under lateral dynamic loading

    Young\u27s modulus of [111] germanium nanowires

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    This paper reports a diameter-independent Young’s modulus of 91.9 ± 8.2 GPa for [111] Germaniumnanowires (Ge NWs). When the surface oxide layer is accounted for using a core-shell NW approximation, the YM of the Ge core approaches a near theoretical value of 147.6 ± 23.4 GPa. The ultimate strength of a NW device was measured at 10.9 GPa, which represents a very high experimental-to-theoretical strength ratio of ∌75%. With increasing interest in this material system as a high-capacity lithium-ion battery anode, the presented data provide inputs that are essential in predicting its lithiation-induced stress fields and fracture behavior
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