798 research outputs found

    First time evidence of pronounced plateaus right above the Coulomb barrier in 8Li + 4He fusion

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    We investigate unprecedented experimental information on the fusion reaction induced by the radioactive projectile 8 Li on a 4 He gas target, at center-of-mass energies between 0.6 and 5 MeV. The main issue is the tendency of the dimensionless fusion cross section σfπƛ2 to form well visible plateaus alternated to steep rises. This finding is likely to be the most genuine consequence of the discrete nature of the intervening angular momenta observed so far in fusion reactions right above the Coulomb barrier. A partial-wave analysis, exclusively based on a pure quantal penetration fusion model and sensitive to the interaction potential, identifies a remarkably low-height barrier

    Assessing the effect of tsunami-induced vertical loads on RC frames

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    The increasing number of people, structures and economic activities being exposed to tsunami hazards makes it important to estimate the effects of this hazard on coastal developments. Tsunami onshore flow generates significant loading on buildings and infrastructure, which can lead to structural failure. Literature works recently proposed a non-linear static analysis method, called Variable Depth Pushover (VDPO), for assessing the performance of buildings under the lateral pressures induced by a tsunami onshore flow. This methodology was developed under the assumption that the building is watertight. However, in the case of buildings with breakaway cladding (e.g., masonry infills), the water flow passing through the building induces vertical loads on horizontal structural members, due to uplift and buoyancy pressures, that should be considered during the analysis. Thus, to address this phenomenon, in this paper a numerical investigation is performed considering a combination of tsunami-induced horizontal and vertical loads on a case-study reinforced concrete (RC) moment-resisting frame with breakaway infills, typical of Mediterranean construction. The building model is subjected to a VDPO analysis that applies different types and sizes of vertical loading on the horizontal elements of the building, as the tsunami inundation depth increases. From the results of this analysis, the effects of tsunamiinduced vertical load components on the case-study building in terms of damage propagation and failure mode are discussed, and the significance of considering vertical loading is proven

    Strong enhancement of extremely energetic proton production in central heavy ion collisions at intermediate energy

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    The energetic proton emission has been investigated as a function of the reaction centrality for the system 58Ni + 58Ni at 30A MeV. Extremely energetic protons (EpNN > 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons thus indicating the onset of a mechanism beyond one and two-body dynamics.Comment: 5 pages, 2 figures, submitted to Physical Review Letter

    Solving the large discrepancy between inclusive and exclusive measurements of the 8Li+4He→11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n reaction cross section at astrophysical energies

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    A solution of the large discrepancy existing between inclusive and exclusive measurements of the 8Li+4He→11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n reaction cross section at Ecm<3E_{cm} <3 MeV is evaluated. This problem has profound astrophysical relevance for this reaction is of great interest in Big-Bang and r-process nucleosynthesis. By means of a novel technique, a comprehensive study of all existing 8Li+4He→11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n cross section data is carried out, setting up a consistent picture in which all the inclusive measurements provide the reliable value of the cross section. New unambiguous signatures of the strong branch pattern non-uniformities, near the threshold of higher 11B{}^{11}{\rm B} excited levels, are presented and their possible origin, in terms of the cluster structure of the involved excited states of 11B{}^{11}{\rm B} and 12B{}^{12}{\rm B} nuclei, is discussed.Comment: 5 pages, 4 figures, 1 tabl

    Prompt dipole radiation in fusion reactions

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    The prompt gamma ray emission was investigated in the 16A MeV energy region by means of the 36,40Ar+96,92Zr fusion reactions leading to a compound nucleus in the vicinity of 132Ce. We show that the prompt radiation, which appears to be still effective at such a high beam energy, has an angular distribution pattern consistent with a dipole oscillation along the symmetry axis of the dinuclear system. The data are compared with calculations based on a collective bremsstrahlung analysis of the reaction dynamics

    Stabilization of linear carbon structures in a solid Ag nanoparticle assembly

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    Linear sp carbon nanostructures are gathering interest for the physical properties of one-dimensional (1D) systems. At present, the main obstacle to the synthesis and study of these systems is their instability. Here we present a simple method to obtain a solid system where linear sp chains (i.e. polyynes) in a silver nanoparticle assembly display a long term stability at ambient conditions. The presence and the behavior of linear carbon is investigated by Surface Enhanced Raman Scattering (SERS) exploiting the plasmon resonance of the silver nanoparticles assembly. This model system opens the possibility to investigate an intriguing form of carbon nanostructures
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