39,747 research outputs found
Composite Learning Control With Application to Inverted Pendulums
Composite adaptive control (CAC) that integrates direct and indirect adaptive
control techniques can achieve smaller tracking errors and faster parameter
convergence compared with direct and indirect adaptive control techniques.
However, the condition of persistent excitation (PE) still has to be satisfied
to guarantee parameter convergence in CAC. This paper proposes a novel model
reference composite learning control (MRCLC) strategy for a class of affine
nonlinear systems with parametric uncertainties to guarantee parameter
convergence without the PE condition. In the composite learning, an integral
during a moving-time window is utilized to construct a prediction error, a
linear filter is applied to alleviate the derivation of plant states, and both
the tracking error and the prediction error are applied to update parametric
estimates. It is proven that the closed-loop system achieves global
exponential-like stability under interval excitation rather than PE of
regression functions. The effectiveness of the proposed MRCLC has been verified
by the application to an inverted pendulum control problem.Comment: 5 pages, 6 figures, conference submissio
Sound radiation characteristics of a box-type structure
The finite element and boundary element methods are employed in this study to investigate the sound radiation characteristics of a box-type structure. It has been shown [T.R. Lin, J. Pan, Vibration characteristics of a box-type structure, Journal of Vibration and Acoustics, Transactions of ASME 131 (2009) 031004-1–031004-9] that modes of natural vibration of a box-type structure can be classified into six groups according to the symmetry properties of the three panel pairs forming the box. In this paper, we demonstrate that such properties also reveal information about sound radiation effectiveness of each group of modes. The changes of radiation efficiencies and directivity patterns with the wavenumber ratio (the ratio between the acoustic and the plate bending wavenumbers) are examined for typical modes from each group. Similar characteristics of modal radiation efficiencies between a box structure and a corresponding simply supported panel are observed. The change of sound radiation patterns as a function of the wavenumber ratio is also illustrated. It is found that the sound radiation directivity of each box mode can be correlated to that of elementary sound sources (monopole, dipole, etc.) at frequencies well below the critical frequency of the plates of the box. The sound radiation pattern on the box surface also closely related to the vibration amplitude distribution of the box structure at frequencies above the critical frequency. In the medium frequency range, the radiated sound field is dominated by the edge vibration pattern of the box. The radiation efficiency of all box modes reaches a peak at frequencies above the critical frequency, and gradually approaches unity at higher frequencies
Coinvasion-Coexistence Traveling Wave Solutions of an Integro-Difference Competition System
This paper is concerned with the traveling wave solutions of an
integro-difference competition system, of which the purpose is to model the
coinvasion-coexistence process of two competitors with age structure. The
existence of nontrivial traveling wave solutions is obtained by constructing
generalized upper and lower solutions. The asymptotic and nonexistence of
traveling wave solutions are proved by combining the theory of asymptotic
spreading with the idea of contracting rectangle
Spin tunneling properties in mesoscopic magnets: effects of a magnetic field
The tunneling of a giant spin at excited levels is studied theoretically in
mesoscopic magnets with a magnetic field at an arbitrary angle in the easy
plane. Different structures of the tunneling barriers can be generated by the
magnetocrystalline anisotropy, the magnitude and the orientation of the field.
By calculating the nonvacuum instanton solution explicitly, we obtain the
tunnel splittings and the tunneling rates for different angle ranges of the
external magnetic field ( and ). The
temperature dependences of the decay rates are clearly shown for each case. It
is found that the tunneling rate and the crossover temperature depend on the
orientation of the external magnetic field. This feature can be tested with the
use of existing experimental techniques.Comment: 27 pages, 4 figures, accepted by Euro. Phys. J.
A Photo-detachment Study of Binding Energies of La-
Among the three candidates for negative ion laser cooling, La- is the most promising due to the strong transitions between its bound states. A direct energy calculation at the valence level [1] had been applied to La-. However, a comparison with the most recent experimental study [2] has shown there exists a range of disagreement of 17 ~ 90 meV in the energy values relative to the ground state. This research is a computational effort to determine the energies using a different method. By reproducing the photo-detachment cross section of La- and then lining it up with the experimental plot, the amount of shifts needed for the excited states and the ground states can be determined. In doing so, the main sources to the above-mentioned discrepancies can be identified, e.g. the differing amount of missing correlation energy in the ground state and the excited states. This presentation will be a summary of the progress that has been made toward the goal. [1] S. M. O\u27Malley and D. R. Beck, Phys. Rev. A 79, 023622 (2009). [2] C. W. Walter, et al, Phys. Rev. Lett. 113, 063001 (2014)
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