3,364 research outputs found

    Coronal propagation of solar flare particles observed by satellite

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    Propagation of solar flare particles in corona was studied using the satellite data at the geostationary orbit. by selecting very fast rise time events only, the interplanetary propagation were assumed to be scatter free arrival. The results show that the propagation in corona does not depend on particle energy in 4 to 500 MeV protons, and the time delays from optical flare do not depend on the distance between the flare site and the base of the interplanetary magnetic field which connects to the Earth

    The origin of HE0107-5240 and the production of O and Na in extremely metal-poor stars

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    We elaborate the binary scenario for the origin of HE0107-5240, the most metal-poor star yet observed ([Fe/H] = -5.3), using current knowledge of the evolution of extremely metal-poor stars. From the observed C/N value, we estimate the binary separation and period. Nucleosynthesis in a helium convective zone into which hydrogen has been injected allows us to discuss the origin of surface O and Na as well as the abundance distribution of s-process elements. We can explain the observed abundances of 12C, 13C, N, O, and Na and predict future observations to validate the Pop III nature of HE0107-5240.Comment: 4 pages, 3 figures, proceedings of the conference, "Nuclei in the Cosmos VIII", Nuclear Physics A in pres

    Carbon burning in intermediate mass primordial stars

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    The evolution of a zero metallicity 9 M_s star is computed, analyzed and compared with that of a solar metallicity star of identical ZAMS mass. Our computations range from the main sequence until the formation of a massive oxygen-neon white dwarf. Special attention has been payed to carbon burning in conditions of partial degeneracy as well as to the subsequent thermally pulsing Super-AGB phase. The latter develops in a fashion very similar to that of a solar metallicity 9 M_s star, as a consequence of the significant enrichment in metals of the stellar envelope that ensues due to the so-called third dredge-up episode. The abundances in mass of the main isotopes in the final ONe core resulting from the evolution are X(^{16}O) approx 0.59, X(^{20}Ne) approx 0.28 and X(^{24}Mg) approx 0.05. This core is surrounded by a 0.05 M_s buffer mainly composed of carbon and oxygen, and on top of it a He envelope of mass 10^{-4} M_sComment: 11 pages, 11 figures, accepted for publication in A&

    Evolution of Low- and Intermediate-Mass Stars with [Fe/H] <= -2.5

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    We present extensive sets of stellar models for 0.8-9.0Msun in mass and -5 <= [Fe/H] <= -2 and Z = 0 in metallicity. The present work focuses on the evolutionary characteristics of hydrogen mixing into the He-flash convective zones during the core and shell He flashes which occurs for the models with [Fe/H] <~ -2.5. Evolution is followed from the zero age MS to the TPAGB phase including the hydrogen engulfment by the He-flash convection during the RGB or AGB phase. There exist various types of mixing episodes of how the H mixing sets in and how it affects the final abundances at the surface. In particular, we find H ingestion events without dredge-ups that enables repeated neutron-capture nucleosynthesis in the He flash convective zones with 13 C(a,n)16 O as neutron source. For Z = 0, the mixing and dredge-up processes vary with the initial mass, which results in different final abundances in the surface. We investigate the occurrence of these events for various initial mass and metallicity to find the metallicity dependence for the He-flash driven deep mixing (He-FDDM) and also for the third dredge-up (TDU) events. In our models, we find He-FDDM for M <= 3Msun for Z = 0 and for M <~ 2Msun for -5 <~ [Fe/H] <~ -3. On the other hand, the occurrence of the TDU is limited to the mass range of ~1.5Msun to ~5Msun for [Fe/H] = -3, which narrows with decreasing metallicity. The paper also discusses the implications of the results of model computations for observations. We compared the abundance pattern of CNO abundances with observed metal-poor stars. The origins of most iron-deficient stars are discussed by assuming that these stars are affected by binary mass transfer. We also point out the existence of a blue horizontal branch for -4 <~ [Fe/H] <~ -2.5.Comment: 19 pages, 12 figures, accepted by MNRA

    A predictive model of energy savings from top of rail friction control

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    In this paper the authors present a predictive model of train energy requirements due to the application of a top of rail friction modifier (TOR-FM) versus dry wheel / rail conditions. Using the VAMPIRE® Pro simulation package, train energy requirements are modeled for two sets of TOR-FM frictional conditions, one using full Kalker coefficients and the other by using a Kalker factor of 18%. Both scenarios use a top of rail saturated coefficient of friction of 0.35. Under both TOR-FM frictional conditions, train energy savings are shown for complete laps of the Transportation Technology Center Inc.’s (TTCI) Transit Test Track (TTT) loop, and also when isolating only the tangent section of the loop. However, the magnitude of energy savings varies greatly depending on the Kalker coefficient factor used, highlighting the need to model this relationship as accurately as possible. These simulation results are compared with data obtained from a field study, in which train energy savings of 5.3% (lap) and 7.8% (tangent) are shown due to the application of TOR-FM

    Impacts of reduction of deep levels and surface passivation on carrier lifetimes in p-type 4H-SiC epilayers

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    Impacts of reduction of deep levels and surface passivation on carrier lifetimes in p-type 4H-SiC epilayers are investigated. The authors reported that the carrier lifetime in n-type epilayers increased by reduction of deep levels through thermal oxidation and thermal annealing. However, the carrier lifetimes in p-type epilayers were not significantly enhanced. In this study, in order to investigate the influence of surface passivation on the carrier lifetimes, the epilayer surface was passivated by different oxidation techniques. While the improvement of the carrier lifetime in n-type epilayers was small, the carrier lifetime in p-type epilayers were remarkably improved by appropriate surface passivation. For instance, the carrier lifetime was improved from 1.4 μs to 2.6 μs by passivation with deposited SiO2 annealed in NO. From these results, it was revealed that surface recombination is a limiting factor of carrier lifetimes in p-type 4H-SiC epilayers