Bound states for massive Dirac fermions in graphene in a magnetic step field

We calculate the spectrum of massive Dirac fermions in graphene in the presence of an inhomogeneous magnetic field modeled by a step function. We find an analytical universal relation between the bandwidths and the propagating velocities of the modes at the border of the magnetic region, showing how, by tuning the mass term, one can control the speed of these traveling edge states. Graphic Abstract

Chemical disorder induced positive magnetoimpedance in La0.7Pb0.3Mn0.35Fe0.65O3- and La0.7Pb0.3Mn0.3Fe0.7O3- manganites

We report structural, magnetic and magnetoimpedance properties of La0.7Pb0.3Mn0.35Fe0.65O3- and La0.7Pb0.3Mn0.3Fe0.7O3- manganites. Bulk samples were prepared by solid state method. Rietveld refinement of the X-ray diffraction pattern shows the crystallization of these samples in trigonal crystal system. Fe doping at Mn site in La0.7Pb0.3MnO3 increases the lattice parameters and induces oxygen non stoichiometry in the lattice of La0.7Pb0.3Mn0.35Fe0.65O3-and La0.7Pb0.3Mn0.3Fe0.7O3-. La0.7Pb0.3Mn0.3Fe0.7O3-composition shows ~180% positive magnetoimpedance at 1Tesla magnetic field while La0.7Pb0.3Mn0.35Fe0.65O3- shows ~75% positive magnetoimpedance at 320K. Magnetization versus applied magnetic field measurement curves show the magnetic moment of La0.7Pb0.3Mn0.35Fe0.65O3-and La0.7Pb0.3Mn0.3Fe0.7O3-do not saturate up to 2 tesla magnetic field at 300K. Fe doping at Mn site in these manganites created chemically modified systems where the origin of positive magnetoimpedance is found due to the presence of magnetic region inside of the nonmagnetic regions. Huge positive magnetoimpedance in 65% and 70% Fe doped manganites originated by maxwell wagner effect due to the chemical disorder induced by Fe in manganite lattice.

Field Weakening Operation Control Strategies of PMSM Based on Feedback Linearization

Based on current research into the mathematical model of the permanent magnet synchronous motor (PMSM) and the feedback linearization theory, a control strategy established upon feedback linearization is proposed. The Lie differential operation is performed on the output variable to obtain the state feedback of the nonlinear system, and the dynamic characteristics of the original system are transformed into linear dynamic characteristics. A current controller based on the input–output feedback linearization algorithm is designed to realize the input–output linearization control of the PMSM. The current controller decouples the d–q axis current from the flux linkage information of the motor and outputs a control voltage. When the motor speed reaches above the base speed, the field-forward and straight-axis current components are newly distributed to achieve field weakening control, which can realize the smooth transition between the constant torque region and weak magnetic region. Simulation and experimental results show the feasibility and viability of the strategy.

Study on Magnetic Flux Weakening Control Strategy of Interior Permanent Magnet Synchronous Motor

When the maximum ratio of torque to current strategy is used for IPMSM flux weakening speed regulation, it is needed to solve nonlinear High-Order equations determining the direct and quadrature axis current given value. Facing this problem, the paper used the curve fitting and obtained the given current, improved the control accuracy of the system. At the same time, in the weak magnetic high speed zone, proposed a new over-modulation control algorithm, which through the optimization of voltage vector and phase, achieved a natural transition of different modulation region, increased the output voltage of the inverter, and enhanced the stator voltage and output torque when motor runs at a certain speed given value, expanded steady weak magnetic region of IPMSM when the load torque is certain.

Coronal Holes in Global Complexes of Activity

We propose a new concept that considers the global complexes of activity as a combination of global and local fields. Traditionally, the complexes of activity have been identified from observations of active regions (ARs). Here, we show that a complex of activity comprises both (AR) and coronal holes (CHs). Our analysis is based on observations of magnetic fields of various scales, SOHO/MDI data, and UV observations of CH. The analysis has corroborated the existence of complexes of activity that involve AR and equatorial CH. Both AR and CH are embedded in an extended magnetic region dominated by the magnetic field of one sign, but not strictly unipolar. It is shown that the evolution of CH and AR is a single process. The relationship between the fields of various scales in the course of a cycle is discussed.