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Design of Power-Splitter With Selectable Splitting-Ratio Using Angled and Cascaded MMI-Coupler
A concept of power splitter with selectable splitting-ratios is proposed based on two multimode interference (MMI) sections connected by a phase-shifting region, in which phase-matching conditions can be fulfilled by using a simple angled section or alternatively using matched phase-shifters. The design example of an asymmetrical splitter (10 : 90) is optimized by using the transfer matrix method and three-dimensional full-vectorial beam propagation method. The numerical results reveal that a simple 1.2° angled section can yield a 10 : 90 splitter with an insertion loss of 0.74 dB and a total length of 192 μm. It is also shown that, for the cascaded MMI couplers based splitter, a more compact length of 58 μm with a lower insertion loss of 0.41 dB can be achieved. The fabrication tolerances are also investigated for the proposed asymmetrical power splitter
Relation of SiO maser emission to IR radiation in evolved stars based on the MSX observation
Based on the space MSX observation in bands A(8m), C(12m),
D(15m) and E(21m), and the ground SiO maser observation of evolved
stars by the Nobeyama 45-m telescope in the v=1 and v=2 J=1-0 transitions, the
relation between SiO maser emission and mid-IR continuum radiation is analyzed.
The relation between SiO maser emission and the IR radiation in the MSX bands
A, C, D and E is all clearly correlated. The SiO maser emission can be
explained by a radiative pumping mechanism according to its correlation with
infrared radiation in the MSX band A.Comment: 11 pages, 4 figures, to appear in ApJ
Bounded perturbation resilience of projected scaled gradient methods
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
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