109,611 research outputs found
Stability of Model Predictive Control with Soft Constraints
We derive stability conditions for Model Predictive Control (MPC) with hard constraints on the inputs and "soft" constraints on the outputs for an infinitely long output horizon. We show that with state feedback MPC is globally asymptotically stabilizing if and only if all the eigenvalues of the open loop system are in the closed unit disk. With output feedback the eigenvalues must be strictly inside the unit circle. The on-line optimization problem defining MPC can be posed as a finite dimensional quadratic program even though the output constraints are specified over an infinite horizon
First-principles materials design of high-performing bulk photovoltaics with the LiNbO structure
The bulk photovoltaic effect is a long-known but poorly understood
phenomenon. Recently, however, the multiferroic bismuth ferrite has been
observed to produce strong photovoltaic response to visible light, suggesting
that the effect has been underexploited as well. Here we present three polar
oxides in the LiNbO structure that we predict to have band gaps in the 1-2
eV range and very high bulk photovoltaic response: PbNiO,
MgZnPbO, and LiBiO. All three have band gaps determined
by cations with electronic configurations, leading to conduction
bands composed of cation -orbitals and O -orbitals. This both
dramatically lowers the band gap and increases the bulk photovoltaic response
by as much as an order of magnitude over previous materials, demonstrating the
potential for high-performing bulk photovoltaics
Высшее образование в Китае
Данная статья посвящена особенностям высшего образования в Китае. Автор делает акцент на отличительных чертах обучения в университетах Китая и студенческой жизни.The article is devoted to the features of higher education in China. The author focuses on the distinctive features of studying at Chinese universities and student life
Constrained Stabilization of Discrete-Time Systems
Based on the growth rate of the set of states reachable with unit-energy inputs, we show that a discrete-time controllable linear system is globally controllable to the origin with constrained inputs if and only if all its eigenvalues lie in the closed unit disk. These results imply that the constrained Infinite-Horizon Model Predictive Control algorithm is globally stabilizing for a sufficiently large number of control moves if and only if the controlled system is controllable and all its eigenvalues lie in the closed unit disk.
In the second part of the paper, we propose an implementable Model Predictive Control algorithm and show that with this scheme a discrete-time linear system with n poles on the unit disk (with any multiplicity) can be globally stabilized if the number of control moves is larger than n. For pure integrator systems, this condition is also necessary. Moreover, we show that global asymptotic stability is preserved for any asymptotically constant disturbance entering at the plant input
Projector operators for the no-core shell model
Projection operators for the use within ab initio no-core shell model, are
suggested.Comment: 3 page
Chirality Dependence of the -Momentum Dark Excitons in Carbon Nanotubes
Using a collection of twelve semiconducting carbon nanotube samples, each
highly enriched in a single chirality, we study the chirality dependence of the
-momentum dark singlet exciton using phonon sideband optical spectroscopy.
Measurements of bright absorptive and emissive sidebands of this finite
momentum exciton identify its energy as 20 - 38 meV above the bright singlet
exciton, a separation that exhibits systematic dependencies on tube diameter,
family, and semiconducting type. We present calculations that explain
how chiral angle dependence in this energy separation relates to the Coulomb
exchange interaction, and elaborate the dominance of the phonon
sidebands over the zone-center phonon sidebands over a wide range of
chiralities. The Kataura plot arising from these data is qualitatively well
described by theory, but the energy separation between the sidebands shows a
larger chiral dependence than predicted. This latter observation may indicate a
larger dispersion for the associated phonon near the point than expected
from finite distance force modeling.Comment: 24 pages, 12 figures, 1 table; slight title change, Figures 1 and 11
added, reference added, presentation improved throughout documen
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