3,142 research outputs found
A Parallel Decomposition Scheme for Solving Long-Horizon Optimal Control Problems
We present a temporal decomposition scheme for solving long-horizon optimal
control problems. In the proposed scheme, the time domain is decomposed into a
set of subdomains with partially overlapping regions. Subproblems associated
with the subdomains are solved in parallel to obtain local primal-dual
trajectories that are assembled to obtain the global trajectories. We provide a
sufficient condition that guarantees convergence of the proposed scheme. This
condition states that the effect of perturbations on the boundary conditions
(i.e., initial state and terminal dual/adjoint variable) should decay
asymptotically as one moves away from the boundaries. This condition also
reveals that the scheme converges if the size of the overlap is sufficiently
large and that the convergence rate improves with the size of the overlap. We
prove that linear quadratic problems satisfy the asymptotic decay condition,
and we discuss numerical strategies to determine if the condition holds in more
general cases. We draw upon a non-convex optimal control problem to illustrate
the performance of the proposed scheme
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Optically pumped colloidal-quantum-dot lasing in LED-like devices with an integrated optical cavity.
Realization of electrically pumped lasing with solution processable materials will have a revolutionary impact on many disciplines including photonics, chemical sensing, and medical diagnostics. Due to readily tunable, size-controlled emission wavelengths, colloidal semiconductor quantum dots (QDs) are attractive materials for attaining this goal. Here we use specially engineered QDs to demonstrate devices that operate as both a light emitting diode (LED) and an optically pumped laser. These structures feature a distributed feedback resonator integrated into a bottom LED electrode. By carefully engineering a refractive-index profile across the device, we are able to obtain good confinement of a waveguided mode within the QD medium, which allows for demonstrating low-threshold lasing even with an ultrathin (about three QD monolayers) active layer. These devices also exhibit strong electroluminescence (EL) under electrical pumping. The conducted studies suggest that the demonstrated dual-function (lasing/EL) structures represent a promising device platform for realizing colloidal QD laser diodes
Overlapping Schwarz Decomposition for Constrained Quadratic Programs
We present an overlapping Schwarz decomposition algorithm for constrained
quadratic programs (QPs). Schwarz algorithms have been traditionally used to
solve linear algebra systems arising from partial differential equations, but
we have recently shown that they are also effective at solving structured
optimization problems. In the proposed scheme, we consider QPs whose algebraic
structure can be represented by graphs. The graph domain is partitioned into
overlapping subdomains (yielding a set of coupled subproblems), solutions for
the subproblems are computed in parallel, and convergence is enforced by
updating primal-dual information in the overlapping regions. We show that
convergence is guaranteed if the overlap is sufficiently large and that the
convergence rate improves exponentially with the size of the overlap.
Convergence results rely on a key property of graph-structured problems that is
known as exponential decay of sensitivity. Here, we establish conditions under
which this property holds for constrained QPs (as those found in network
optimization and optimal control), thus extending existing work that addresses
unconstrained QPs. The numerical behavior of the Schwarz scheme is demonstrated
by using a DC optimal power flow problem defined over a network with 9,241
nodes
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