3,842 research outputs found
Estimation of Stator Resistance and Rotor Flux Linkage in SPMSM Using CLPSO with Opposition-Based-Learning Strategy
Electromagnetic parameters are important for controller design and condition monitoring of permanent magnet synchronous machine (PMSM) system. In this paper, an improved comprehensive learning particle swarm optimization (CLPSO) with opposition-based-learning (OBL) strategy is proposed for estimating stator resistance and rotor flux linkage in surface-mounted PMSM; the proposed method is referred to as CLPSO-OBL. In the CLPSO-OBL framework, an opposition-learning strategy is used for best particles reinforcement learning to improve the dynamic performance and global convergence ability of the CLPSO. The proposed parameter optimization not only retains the advantages of diversity in the CLPSO but also has inherited global exploration capability of the OBL. Then, the proposed method is applied to estimate the stator resistance and rotor flux linkage of surface-mounted PMSM. The experimental results show that the CLPSO-OBL has better performance in estimating winding resistance and PM flux compared to the existing peer PSOs. Furthermore, the proposed parameter estimation model and optimization method are simple and with good accuracy, fast convergence, and easy digital implementation
Simulating gravitational waves passing through the spacetime of a black hole
We investigate how GWs pass through the spacetime of a Schwarzschild black
hole using time-domain numerical simulations. Our work is based on the
perturbed 3+1 Einstein's equations up to the linear order. We show explicitly
that our perturbation equations are covariant under infinitesimal coordinate
transformations. Then we solve a symmetric second-order hyperbolic wave
equation with a spatially varying wave speed. As the wave speed in our wave
equation vanishes at the horizon, our formalism can naturally avoid boundary
conditions at the horizon. Our formalism also does not contain coordinate
singularities and, therefore, does not need regularity conditions. Then, based
on our code, we simulate both finite and continuous initially plane-fronted
wave trains passing through the Schwarzschild black hole. We find that for the
finite wave train, the wave zone of GWs is wildly twisted by the black hole.
While for the continuous wave train, unlike geometric optics, GWs can not be
sheltered by the back hole. A strong beam and an interference pattern appear
behind the black hole along the optical axis. Moreover, we find that the
back-scattering due to the interaction between GWs and the background curvature
is strongly dependent on the direction of the propagation of the trailing
wavefront relative to the black hole.Comment: 24 pages, 9 figure
Revisiting f(R) gravity models that reproduce CDM expansion
We reconstruct an gravity model that gives rise to the particular
CDM background evolution of the universe. We find well-defined,
real-valued analytical forms for the model to describe the universe both
in the early epoch from the radiation to matter dominated eras and the late
time acceleration period. We further examine the viability of the derived
model and find that it is viable to describe the evolution of the
universe in the past and there does not exist the future singularity in the
Lagrangian.Comment: 7 pages, 2 figures, revised version, accepted for publication in PR
Emergent Mott-insulators at non-integer fillings and devil's staircase induced by attractive interaction in many-body polarons
We investigate the ground state properties of an ultracold atom system
consisting of many-body polarons, quasiparticles formed by impurity atoms in
optical lattices immersing in a Bose-Einstein condensate. We find the
nearest-neighbor attractive interaction between polarons can give rise to rich
physics that is peculiar to this system. In a relatively shallow optical
lattice, the attractive interaction can drive the system being in a self-bound
superfluid phase with its particle density distribution manifesting a
self-concentrated structure. While in a relatively deep optical lattice, the
attractive interaction can drive the system forming the Mott-insulator phase
even though the global filling factor is not integer. Interestingly, in the
Mott-insulator regime, the system can support a series of different
Mott-insulators with their effective density manifesting a devil's staircase
structure with respect to the strength of attractive interaction. Detailed
estimation on relevant experimental parameters shows that these rich physics
can be readily observed in current experimental setups
The imprint of the interaction between dark sectors in large scale cosmic microwave background anisotropies
Dark energy interacting with dark matter is a promising model to solve the
cosmic coincidence problem. We study the signature of such interaction on large
scale cosmic microwave background (CMB) temperature anisotropies. Based on the
detail analysis in perturbation equations of dark energy and dark matter when
they are in interaction, we find that the large scale CMB, especially the late
Integrated Sachs Wolfe effect, is a useful tool to measure the coupling between
dark sectors. We also discuss the possibility to detect the coupling by
cross-correlating CMB maps with tracers of the large scale structure. We
finally perform the global fitting to constrain the coupling by using the CMB
power spectrum data together with other observational data. We find that in the
range, the constrained coupling between dark sectors can solve the
coincidence problem.Comment: 17 pages, 9 figures, revised version, more discussions added,
accepted for publication in PR
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