24,686 research outputs found
Angular Momentum of a Brane-world Model
In this paper we discuss the properties of the general covariant angular
momentum of a five-dimensional brane-world model. Through calculating the total
angular momentum of this model, we are able to analyze the properties of the
total angular momentum in the inflationary RS model. We show that the
space-like components of the total angular momentum of are all zero while the
others are non-zero, which agrees with the results from ordinary RS model.Comment: 8 pages; accepted by Chinese Physics
Satisfactory optimization design for fractional order PID controller
Copyright © 2019 ASME. This paper presents a new parameters optimization approach for fractional order PID controllers, which uses a satisfactory optimization model. To fulfill different design performance specfications and constrains of systems, the application of multi-criterion satisfactory optimization to fractional control systems is considered. At the same time, the performance of fractional control systems controlled by fractional order controller and integer order controller is discussed. The simulation illustrates the effectiveness of the proposed method and the superiority of the fractional order controller in both time domain and frequency domain
Parameter Setting Strategy for the Controller of the DFIG Wind Turbine Considering the Small-Signal Stability of Power Grids
Due to the increasing penetration of the wind generation, the stability, especially the small-signal stability, of the power grid is much related to it. Currently, few studies considered the impact of the parameter settings of the wind turbine controller on the small-signal stability of the grid under the full range of wind conditions. In this paper, we propose a framework for deriving a set of controller parameters by interiorizing their impact on the power system stability, based on an analytic model of a 15th-order single DFIG-infinite grid connection under all wind speeds. The study results on a real wind turbine show that the controller parameters optimized for a specific wind speed may not feasible for other operational conditions yet the proposed framework can obtain a set of parameters guaranteeing the power system stability under all wind speeds
Doping evolution of spin and charge excitations in the Hubbard model
To shed light on how electronic correlations vary across the phase diagram of
the cuprate superconductors, we examine the doping evolution of spin and charge
excitations in the single-band Hubbard model using determinant quantum Monte
Carlo (DQMC). In the single-particle response, we observe that the effects of
correlations weaken rapidly with doping, such that one may expect the random
phase approximation (RPA) to provide an adequate description of the
two-particle response. In contrast, when compared to RPA, we find that
significant residual correlations in the two-particle excitations persist up to
hole and electron doping (the range of dopings achieved in the
cuprates). These fundamental differences between the doping evolution of
single- and multi-particle renormalizations show that conclusions drawn from
single-particle processes cannot necessarily be applied to multi-particle
excitations. Eventually, the system smoothly transitions via a
momentum-dependent crossover into a weakly correlated metallic state where the
spin and charge excitation spectra exhibit similar behavior and where RPA
provides an adequate description.Comment: 5 pages, 4 figures, plus supplementary materia
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