221 research outputs found
Parameter estimation for VSI-Fed PMSM based on a dynamic PSO with learning strategies
© 1986-2012 IEEE.A dynamic particle swarm optimization with learning strategy (DPSO-LS) is proposed for key parameter estimation for permanent magnet synchronous machines (PMSMs), where the voltage-source inverter (VSI) nonlinearities are taken into account in the parameter estimation model and can be estimated simultaneously with other machine parameters. In the DPSO-LS algorithm, a novel movement modification equation with variable exploration vector is designed to effectively update particles, enabling swarms to cover large areas of search space with large probability and thus the global search ability is enhanced. Moreover, a Gaussian-distribution-based dynamic opposition-based learning strategy is developed to help the pBest jump out local optima. The proposed DPSO-LS can significantly enhance the estimator model accuracy and dynamic performance. Finally, the proposed algorithm is applied to multiple parameter estimation including the VSI nonlinearities of a PMSM. The performance of DPSO-LS is compared with several existing PSO algorithms, and the comparison results show that the proposed parameters estimation method has better performance in tracking the variation of machine parameters effectively and estimating the VSI nonlinearities under different operation conditions
Elastic-to-plastic crossover below the peak effect in the vortex solid of YBa2Cu3O7 single crystals
We report on transport and ac susceptibility studies below the peak effect in
twinned YBa2Cu3O7 single crystals. We find that disorder generated at the peak
effect can be partially inhibited by forcing vortices to move with an ac
driving current. The vortex system can be additionally ordered below a
well-defined temperature where elastic interactions between vortices overcome
pinning-generated stress and a plastic to elastic crossover seems to occur. The
combined effect of these two processes results in vortex structures with
different mobilities that give place to history effects.Comment: 4 pages, 4 figures. Published in PRB Rapid Comm., February 1, 200
Electrical transport and magnetic properties of nanostructured La0.67Ca0.33MnO3
Nanostructured La0.67Ca0.33MnO3 (NS-LCMO) was formed by pulsed-laser
deposition on the surface of porous Al2O3. The resistance peak temperature (Tp)
of the NS-LCMO increases with increasing average thickness of the films, while
their Curie temperatures (Tc) remain unchanged. The coercive field of the
samples increases with decreasing film thickness and its temperature dependence
can be well described by Hc(T) = Hc(0)[1-(T/TB)1/2]. A large magnetoresistance
and strong memory effect were observed for the NS-LCMO. The results are
discussed in terms of the size effect, Coulomb blockade and magnetic tunneling
effect. This work also demonstrates a new way to get nanostructured manganites
Slow relaxations and history dependence of the transport properties of layered superconductors
We study numerically the time evolution of the transport properties of
layered superconductors after different preparations. We show that, in
accordance with recent experiments in BSCCO performed in the second peak region
of the phase diagram (Portier et al, 2001), the relaxation strongly depends on
the initial conditions and is extremely slow. We investigate the dependence on
the pinning center density and the perturbation applied. We compare the
measurements to recent findings in tapped granular matter and we interpret our
results with a rather simple picture.Comment: 4 pages, 4 fig
History effects and pinning regimes in solid vortex matter
We propose a phenomenological model that accounts for the history effects
observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys.
Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the
model is the assumption that the penetrating ac magnetic field modifies the
vortex lattice mobility, trapping different robust dynamical states in
different regions of the sample. We discuss in detail on the response of the
superconductor to an ac magnetic field when the vortex lattice mobility is not
uniform inside the sample. We begin with an analytical description for a simple
geometry (slab) and then we perform numerical calculations for a strip in a
transverse magnetic field which include relaxation effects. In calculations,
the vortex system is assumed to coexist in different pinning regimes. The
vortex behavior in the regions where the induced current density j has been
always below a given threshold (j_c^>) is described by an elastic Campbell-like
regime (or a critical state regime with local high critical current density,
j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the
critical current density is modified to j_c^) at
regions where vortices have been forced to oscillate by a current density
larger than j_c^>. Experimentally, an initial state with high critical current
density (j_c^>) can be obtained by zero field cooling, field cooling (with no
applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g.
sawtooth) field. We compare our calculations with experimental ac
susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR
Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition
We examine metastable and transient effects both above and below the
first-order decoupling line in a 3D simulation of magnetically interacting
pancake vortices. We observe pronounced transient and history effects as well
as supercooling and superheating between the 3D coupled, ordered and 2D
decoupled, disordered phases. In the disordered supercooled state as a function
of DC driving, reordering occurs through the formation of growing moving
channels of the ordered phase. No channels form in the superheated region;
instead the ordered state is homogeneously destroyed. When a sequence of
current pulses is applied we observe memory effects. We find a ramp rate
dependence of the V(I) curves on both sides of the decoupling transition. The
critical current that we obtain depends on how the system is prepared.Comment: 10 pages, 15 postscript figures, version to appear in PR
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
A study of charged kappa in
Based on events collected by BESII, the decay
is studied. In the invariant mass
spectrum recoiling against the charged , the charged
particle is found as a low mass enhancement. If a Breit-Wigner function of
constant width is used to parameterize the kappa, its pole locates at MeV/. Also in this channel,
the decay is observed for the first time.
Its branching ratio is .Comment: 14 pages, 4 figure
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