3,251 research outputs found

    Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

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    The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion

    Phase Modulated Thermal Conductance of Josephson Weak Links

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    We present a theory for quasiparticle heat transport through superconducting weak links. The thermal conductance depends on the phase difference (ϕ\phi) of the superconducting leads. Branch conversion processes, low-energy Andreev bound states near the contact and the suppression of the local density of states near the gap edge are related to phase-sensitive transport processes. Theoretical results for the influence of junction transparency, temperature and disorder, on the phase modulation of the conductance are reported. For high-transmission weak links, D1D\to 1, the formation of an Andreev bound state at ϵb=Δcos(ϕ/2)\epsilon_{\text{\tiny b}}=\Delta\cos(\phi/2) leads to suppression of the density of states for the continuum excitations that transport heat, and thus, to a reduction in the conductance for ϕπ\phi\simeq\pi. For low-transmission (D1D\ll 1) barriers resonant scattering at energies ϵ(1+D/2)Δ\epsilon\simeq(1+D/2)\Delta leads to an increase in the thermal conductance as TT drops below TcT_c (for phase differences near ϕ=π\phi=\pi).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for Ricatti amplitude

    Choice of Steel Material to Avoid Brittle Fracture for Hollow Section Structures

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    European cold-formed hollow sections in general exhibit better toughness properties than required by EN 10219. However, limits in applying the toughness related rules for the choice of steel material in EN 1993 1 10 to cold-formed hollow sections still constitute barriers to free marketing. By requests from European producers a conservative assessment procedure has been developed which is based on toughness measurements and a concept using effective strains. Due to the cold-forming process such plastic strains may occur in the bent areas of the profiles associated with a noticeable reduction in material toughness. For the degradation of these toughness properties an appropriate temperature shift Delta Tcf has been derived for both circular and rectangular hollow sections. In order to guarantee the proper application of this temperature shift Table 2.1 in EN 1993 1 10 had to be extended to lower temperatures down to -120 °C.JRC.G.5-European laboratory for structural assessmen