1,194 research outputs found

    MULTI-BAND ELECTRICAL CONDUCTION

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    Scattering amplitudes arising from lattice vibrations are calculated for electrons in a transition metal, with special reference to nickel. The potential in the crystal is treated as a deformable potential, with corrections to adjust the zero of potential and to include effects of the redistribution of charge during lattice vibration.</p

    Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities

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    The coronal magnetic field is the primary driver of solar dynamic events. Linear and circular polarization signals of certain infrared coronal emission lines contain information about the magnetic field, and to access this information, either a forward or an inversion method must be used. We study three coronal magnetic configurations that are applicable to polar-crown filament cavities by doing forward calculations to produce synthetic polarization data. We analyze these forward data to determine the distinguishing characteristics of each model. We conclude that it is possible to distinguish between cylindrical flux ropes, spheromak flux ropes, and sheared arcades using coronal polarization measurements. If one of these models is found to be consistent with observational measurements, it will mean positive identification of the magnetic morphology that surrounds certain quiescent filaments, which will lead to a greater understanding of how they form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis

    Vitamin D status and associated genetic polymorphisms in a cohort of UK children with non -alcoholic fatty liver disease

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    Background: Vitamin D deficiency has been associated with non-alcoholic fatty liver disease (NAFLD). However, the role of polymorphisms determining vitamin D status remains unknown. Objectives: To determine in UK children with biopsy-proven NAFLD: (i) vitamin D status throughout a 12-month period; (ii) interactions between key vitamin D-related genetic variants (NADSYN1/DHCR7, VDR, GC, CYP2R1) and disease severity. Methods: In 103 pediatric patients with NAFLD, serum 25-hydroxyvitamin D (25OHD) levels and genotypes were determined contemporaneously to liver biopsy and examined in relation to NAFLD activity score and fibrosis stage. Results: Only 19.2% of children had adequate vitamin D status; most had mean 25OHD levels considered deficient (<25nmol/l, 25.5%) or insufficient (<50nmol/l, 55.3%). Patients had significantly lower 25OHD levels in winter months (95%CI: 22.7-31.2nmol/l) when compared to spring (30.5-42.1nmol/l; P=0.0089), summer (36.3-47.2nmol/l; P<0.0001) and autumn (34.2-47.5nmol/l; P=0.0003). Polymorphisms in the NADSYN1/DHCR7 (rs3829251, rs12785878), and VDR (rs2228570) genes were independently associated with increased steatosis; while a GC variant (rs4588) was associated with increased inflammation in liver biopsies. Conclusions: Children with NAFLD in the UK have particularly low winter vitamin D status; with vitamin D insufficiency prevalent throughout the year. Polymorphisms in the vitamin D metabolic pathway are associated with histological severity of pediatric NAFLD

    On the structure and evolution of a polar crown prominence/filament system

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    Polar crown prominences are made of chromospheric plasma partially circling the Suns poles between 60 and 70 degree latitude. We aim to diagnose the 3D dynamics of a polar crown prominence using high cadence EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304 and 171A and the Ahead spacecraft of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195A. Using time series across specific structures we compare flows across the disk in 195A with the prominence dynamics seen on the limb. The densest prominence material forms vertical columns which are separated by many tens of Mm and connected by dynamic bridges of plasma that are clearly visible in 304/171A two-color images. We also observe intermittent but repetitious flows with velocity 15 km/s in the prominence that appear to be associated with EUV bright points on the solar disk. The boundary between the prominence and the overlying cavity appears as a sharp edge. We discuss the structure of the coronal cavity seen both above and around the prominence. SDO/HMI and GONG magnetograms are used to infer the underlying magnetic topology. The evolution and structure of the prominence with respect to the magnetic field seems to agree with the filament linkage model.Comment: 24 pages, 14 figures, Accepted for publication in Solar Physics Journal, Movies can be found at http://www2.mps.mpg.de/data/outgoing/panesar

    Final State Interactions in Hypernuclear Decay

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    We present an update of the One-Meson-Exchange (OME) results for the weak decay of s- and p-shell hypernuclei (Ref. Phys. Rev. C {\bf 56}, 339 (1997)), paying special attention to the role played by final state interactions between the emitted nucleons. The present study also corrects for a mistake in the inclusion of the KK and KK^* exchange mechanisms, which substantially increases the ratio of neutron-induced to proton-induced transitions, Γn/Γp\Gamma_n/\Gamma_p. With the most up-to-date model ingredients, we find that the OME approach is able to describe very satisfactorily most of the measured observables, including the ratio Γn/Γp\Gamma_n/\Gamma_p.Comment: 20 pages, 2 eps figure

    Observations of Coronal Mass Ejections with the Coronal Multichannel Polarimeter

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    The Coronal Multichannel Polarimeter (CoMP) measures not only the polarization of coronal emission, but also the full radiance profiles of coronal emission lines. For the first time, CoMP observations provide high-cadence image sequences of the coronal line intensity, Doppler shift and line width simultaneously in a large field of view. By studying the Doppler shift and line width we may explore more of the physical processes of CME initiation and propagation. Here we identify a list of CMEs observed by CoMP and present the first results of these observations. Our preliminary analysis shows that CMEs are usually associated with greatly increased Doppler shift and enhanced line width. These new observations provide not only valuable information to constrain CME models and probe various processes during the initial propagation of CMEs in the low corona, but also offer a possible cost-effective and low-risk means of space weather monitoring.Comment: 6 figures. Will appear in the special issue of Coronal Magnetism, Sol. Phy

    New sources and stability of resistance to aphids in cowpea germplasm across locations in Uganda

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    Open Access ArticleThe cowpea aphid (Aphis craccivora Koch) is an economically important pest, whose feeding effects cause stunting, delayed flower initiation and yield reduction in cowpea (Vigna unguiculata L. Walp). Host plant resistance offers an alternative for controlling aphids; while simultaneously reducing reliance on chemical pesticides. The objective of this study was to evaluate a multi-parent advanced generation inter-cross (MAGIC) population of cowpea against aphids, across cowpea growing regions in Uganda. The study was arranged in alpha lattice design, with two replicates in three locations over two seasons (2018B and 2019A). Results revealed significant effects (P<0.001) for the main treatment effects, genotype x location and location x season interaction for both infestation and damage. The genotype x season interaction was significant (P<0.01) for both aphid infestation and damage; while the three-way interaction was only significant (P<0.001) for aphid infestation, but not for damage. The study identified five new resistant and stable genotypes from the MAGIC panel, including MAGIC131, MAGIC-132, MAGIC149, MAGIC170 and MAGIC280; and one resistant parent, SUVITA-2. The study further revealed MAGIC-125, MAGIC-171, MAGIC153, MAGIC-333, MAGIC177, MAGIC-292, MAGIC282, MAGIC249, MAGIC162, SEC 4W * SEC 5T, NAROCOWPEA 4, MAGIC-204, MAGIC-039, MAGIC060, MAGIC-097, NAROCOWPEA 3, MAGIC-233, MAGIC090 and MU 9 to be moderately resistant and high yielding genotypes. The above genotypes are recommended for use in the cowpea breeding programme, to develop improved resistant lines against aphids in Uganda

    Physics of Solar Prominences: II - Magnetic Structure and Dynamics

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    Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape

    Origins of the Ambient Solar Wind: Implications for Space Weather

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    The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure
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