39,620 research outputs found
Application of an adaptive blade control algorithm to a gust alleviation system
The feasibility of an adaptive control system designed to alleviate helicopter gust induced vibration was analytically investigated for an articulated rotor system. This control system is based on discrete optimal control theory, and is composed of a set of measurements (oscillatory hub forces and moments), an identification system using a Kalman filter, a control system based on the minimization of the quadratic performance function, and a simulation system of the helicopter rotor. The gust models are step and sinusoidal vertical gusts. Control inputs are selected at the gust frequency, subharmonic frequency, and superharmonic frequency, and are superimposed on the basic collective and cyclic control inputs. The response to be reduced is selected to be that at the gust frequency because this is the dominant response compared with sub- and superharmonics. Numerical calculations show that the adaptive blade pitch control algorithm satisfactorily alleviates the hub gust response. Almost 100% reduction of the perturbation thrust response to a step gust and more than 50% reduction to a sinusoidal gust are achieved in the numerical simulations
Thermoelectric coefficients and the figure of merit for large open quantum dots
We consider the thermoelectric response of chaotic or disordered quantum dots
in the limit of phase-coherent transport, statistically described by random
matrix theory. We calculate the full distribution of the thermoelectric
coefficients (Seebeck and Peltier ), and the thermoelectric figure of
merit , for large open dots at arbitrary temperature and external magnetic
field, when the number of modes in the left and right leads ( and
) are large. Our results show that the thermoelectric coefficients
and are maximal when the temperature is half the Thouless energy, and the
magnetic field is negligible. They remain small, even at their maximum, but
they exhibit a type of universality at all temperatures, in which they do not
depend on the asymmetry between the left and right leads , even though they depend on .Comment: 25 pages [final version - minor typos fixed
Case of Almost Redundant Components in 3 alpha Faddeev Equations
The 3 alpha orthogonality condition model using the Pauli-forbidden bound
states of the Buck, Friedlich and Wheatly alpha alpha potential can yield a
compact 3 alpha ground state with a large binding energy, in which a small
admixture of the redundant components can never be eliminated.Comment: Revtex V4.0, 4 pages, no figure
Intersecting D-brane states derived from the KP theory
A general scheme to find tachyon boundary states is developed within the
framework of the theory of KP hierarchy. The method is applied to calculate
correlation function of intersecting D-branes and rederived the results of our
previous works as special examples. A matrix generalization of this scheme
provides a method to study dynamics of coincident multi D-branes.Comment: 10 page
Stabilization mechanism of edge states in graphene
It has been known that edge states of a graphite ribbon are zero-energy,
localized eigen-states. We show that next nearest-neighbor hopping process
decreases the energy of the edge states at zigzag edge with respect to the
Fermi energy. The energy reduction of the edge states is calculated
analytically by first-order perturbation theory and numerically. The resultant
model is consistent with the peak of recent scanning tunneling spectroscopy
measurements.Comment: 4 pages, 2 figures, final version to appear in Applied Physics
Letter
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