86,113 research outputs found

    Bounded perturbation resilience of projected scaled gradient methods

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    We investigate projected scaled gradient (PSG) methods for convex minimization problems. These methods perform a descent step along a diagonally scaled gradient direction followed by a feasibility regaining step via orthogonal projection onto the constraint set. This constitutes a generalized algorithmic structure that encompasses as special cases the gradient projection method, the projected Newton method, the projected Landweber-type methods and the generalized Expectation-Maximization (EM)-type methods. We prove the convergence of the PSG methods in the presence of bounded perturbations. This resilience to bounded perturbations is relevant to the ability to apply the recently developed superiorization methodology to PSG methods, in particular to the EM algorithm.Comment: Computational Optimization and Applications, accepted for publicatio

    Gate-controlled generation of optical pulse trains using individual carbon nanotubes

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    We report on optical pulse-train generation from individual air-suspended carbon nanotubes under an application of square-wave gate voltages. Electrostatically-induced carrier accummulation quenches photoluminescence, while a voltage sign reversal purges those carriers, resetting the nanotubes to become luminescent temporarily. Frequency domain measurements reveal photoluminescence recovery with characteristic frequencies that increase with excitation laser power, showing that photoexcited carriers quench the emission in a self-limiting manner. Time-resolved measurements directly confirm the presence of an optical pulse train sychronized to the gate voltage signal, and flexible control over pulse timing and duration is demonstrated.Comment: 4 pages, 4 figure

    Residual proton-neutron interactions and the NpNnN_{\rm p} N_{\rm n} scheme

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    We investigate the correlation between integrated proton-neutron interactions obtained by using the up-to-date experimental data of binding energies and the NpNnN_{\rm p} N_{\rm n}, the product of valence proton number and valence neutron number with respect to the nearest doubly closed nucleus. We make corrections on a previously suggested formula for the integrated proton-neutron interaction. Our results demonstrate a nice, nearly linear, correlation between the integrated p-n interaction and NpNnN_{\rm p} N_{\rm n}, which provides us with a firm foundation of the applicability of the NpNnN_{\rm p} N_{\rm n} scheme to nuclei far from the stability line.Comment: four pages, three figures, Physical Review C, in pres
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