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  • 2015-2019  (3)
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  • 1
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    Data completion with Hilbert transform over plane rectangle: technique renovation for the Grad-Shafranov reconstruction (2017)
    Wiley-Blackwell
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    Publication Date: 2017-04-12
    Description: Hilbert transforms (HT) have first been used to build the essential technique of Grad-Shafranov (GS) reconstruction by Li et al. [2013], where the problem of ill-posedness in GS reconstruction has been thoroughly investigated. In this study, we present an extended Hilbert transform (EHT) over the plane rectangle. In contrast to previous one (HT over the unit circular region), corner singularities are introduced into these new formulae. It's confronted by problems like the integral with both end-point singularities, and the semi-infinite integral with one end-point singularity, as these EHT formulae are used to rebuild the essential technique of GS reconstruction. Two additional mathematic tools are adopted in this study. Firstly, high accuracy quadrature schemes are constructed for those improper integrals based on the double exponential (DE) transformations. Benchmark testing with the analytic solutions on a rectangular boundary has shown the efficiency and robustness of the EHT formulae. Secondly, the data completion or the inverse boundary value problem is solved with the help of a truncated Chebyshev series , which approximates the unknown boundary gradients in very high efficiency under the only assumption that they are Lipschitz continuous on each side of the rectangle. Combining the introduced EHT formulae and the two needed mathematic tools, the essential technique of GS reconstruction is formulated into a linear system of Fredholm equations of the first kind. Then a three-parameter Tikhonov regularization scheme is developed to deal with the ill-posed linear operators appearing in the discretized linear system. This new approach for data completion over the plane rectangle is benchmarked with the analytic solutions. Numerical experiments highlight the efficiency and robustness of the proposed method.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 2
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    Annual and inter-annual variations in global 6.5DWs from 20-110 km during 2002-2016 observed by TIMED/SABER (2017)
    Wiley-Blackwell
    Details
    Publication Date: 2017-08-12
    Description: Using version 2.0 of the TIMED/SABER kinetic temperature data, we have conducted a study on the annual and inter-annual variations of 6.5DWs at 20-110 km, from 52°S-52°N for 2002-2016. First, we obtained global annual variations in the spectral power and amplitudes of 6.5DWs. We found that strong wave amplitudes emerged from 25°S/N-52°S/N, and peaked in the altitudes of the stratosphere, mesosphere and the lower thermosphere. The annual variations in the 6.5DWs are similar in both hemispheres but different at various altitudes. At 40-50 km, the annual maxima emerge mostly in winters. In the MLT, annual peaks occurred twice every half year. At 80-90 km, 6.5DWs appeared mainly in equinoctial seasons and winters. At 100-110 km, 6.5DWs emerged mainly in equinoctial seasons. Second, we continued the study of the inter-annual variations in 6.5DW amplitudes from 2002-2016. Frequency spectra of the monthly mean amplitudes showed that main dynamics in the long-term variations of 6.5DWs were AO and SAO in both hemispheres. In addition, 4-month period signals were noticed in the MLT of the NH. The amplitudes of SAO and AO were obtained using a bandpass filter and were found to increase with altitude, as do the 6.5DW amplitudes. In both hemispheres, the relative importance of SAO and AO changes with altitude. At 40-50 and 100-110 km, AO play a dominant role, while at 80-90 km, they’re weaker than SAO. Our results show that both the annual and inter-annual variations in 6.5DWs are mainly caused by the combined action of SAO and AO.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    Plants send small RNAs in extracellular vesicles to fungal pathogen to silence virulence genes (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-06-08
    Description: Some pathogens and pests deliver small RNAs (sRNAs) into host cells to suppress host immunity. Conversely, hosts also transfer sRNAs into pathogens and pests to inhibit their virulence. Although sRNA trafficking has been observed in a wide variety of interactions, how sRNAs are transferred, especially from hosts to pathogens and pests, is still unknown. Here, we show that host Arabidopsis cells secrete exosome-like extracellular vesicles to deliver sRNAs into fungal pathogen Botrytis cinerea . These sRNA-containing vesicles accumulate at the infection sites and are taken up by the fungal cells. Transferred host sRNAs induce silencing of fungal genes critical for pathogenicity. Thus, Arabidopsis has adapted exosome-mediated cross-kingdom RNA interference as part of its immune responses during the evolutionary arms race with the pathogen.
    Keywords: Botany, Molecular Biology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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