Ion acoustic solitary waves in magnetized anisotropic nonextensive plasmas

The nonlinear propagation of ion-acoustic (IA) electrostatic solitary waves (SWs) is studied in a magnetized electron–ion (e–i) plasma in the presence of pressure anisotropy with electrons following Tsallis distribution. The Korteweg–de Vries (KdV) type equation is derived by employing the reductive perturbation method (RPM) and its solitary wave (SW) solution is determined and analyzed. The effect of nonextensive parameter q, parallel component of anisotropic ion pressure p 1, perpendicular component of anisotropic ion pressure p 2, obliqueness angle θ, and magnetic field strength Ω on the characteristics of SW structures is investigated. The present investigation could be useful in space and astrophysical plasma systems.

An investigation on AC loss reduction for permanent-magnet wind power generator with superconducting windings

High temperature superconducting (HTS) tapes could be introduced into large scale wind power generators in order to improve the power density. However, the alternating current (AC) loss of HTS tapes will cause the reduction of efficiency. On the basis of analytical and numerical model calculations, this paper presents an optimal design of the HTS armature winding aiming at lower AC loss. The main contribution of this work is that the relationship between the installation parameters and the AC loss of such HTS armature windings has been figured out based on the analysis of the shape feature of the HTS tape and the external magnetic field. When the tape is placed along a particular direction where the perpendicular component of external magnetic field has the lowest amplitude, the AC loss is the smallest. The modified installation location and angle are found based on the proposed generator. These results are verified using finite element method (FEM).

Aerodynamic investigation on shifted-back vertical stroke plane of flapping wing in forward flight

In order to properly understand aerodynamic characteristics in a flapping wing in forward flight, additional aerodynamic parameters apart from those in hover—an inclined stroke plane, a shifted-back stroke plane, and an advance ratio—must be comprehended in advance. This paper deals with the aerodynamic characteristics of a flapping wing in a shifted-back vertical stroke plane in freestream. A scaled-up robotic arm in a water towing tank was used to collect time-varying forces of a model flapping wing, and a semi-empirical quasi-steady aerodynamic model, which can decompose the forces into steady, quasi-steady, and unsteady components, was used to estimate the forces of the model flapping wing. It was found that the shifted-back stroke plane left a part of freestream as a non-perpendicular component, giving rise to a time-course change in the aerodynamic forces during the stroke. This also brought out two quasi-steady components (rotational and added-mass forces) apart from the steady one, even the wing moved with a constant stroke velocity. The aerodynamic model underestimated the actual forces of the model flapping wing even it can cover the increasingly distributed angle of attack of the vertical stroke plane with a blade element theory. The locations of the centers of pressure suggested a greater pressure gradient and an elongated leading-edge vortex along a wingspan than that of the estimation, which may explain the higher actual force in forward flight.

Dynamic resistance measurements in a GdBCO-coated conductor

Dynamic resistance is a phenomenon which occurs when a superconducting wire carries dc transport current whilst experiencing an alternating magnetic field. This situation occurs in a range of HTS machinery applications, where dynamic resistance can lead to large parasitic heat loads and potential quench events. Here, we present dynamic resistance measurements of a 5-mm-wide Fujikura coated conductor wire at 77 K. We report experimental values obtain through varying the field angle (the angle between magnetic field and normal vector of the conductor wide-face), the dc current levels, and the magnetic field amplitude, and frequency. We show that the dynamic resistance in perpendicular magnetic field can be predicted by using a simple analytical equation. We also show that across the range of field angles measured here the dynamic resistance is dominated by the perpendicular component of the applied magnetic field. © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Dynamic resistance measurements in a GdBCO-coated conductor

Dynamic resistance is a phenomenon which occurs when a superconducting wire carries dc transport current whilst experiencing an alternating magnetic field. This situation occurs in a range of HTS machinery applications, where dynamic resistance can lead to large parasitic heat loads and potential quench events. Here, we present dynamic resistance measurements of a 5-mm-wide Fujikura coated conductor wire at 77 K. We report experimental values obtain through varying the field angle (the angle between magnetic field and normal vector of the conductor wide-face), the dc current levels, and the magnetic field amplitude, and frequency. We show that the dynamic resistance in perpendicular magnetic field can be predicted by using a simple analytical equation. We also show that across the range of field angles measured here the dynamic resistance is dominated by the perpendicular component of the applied magnetic field. © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Структурные особенности и магнитные свойства пленок Co-W

The structure and magnetic properties of thin polycrystalline Co100-xWx (0<x>30) films deposited by magnetron sputtering on glass substrates, including those containing buffer layers Ta, W and Ru, have been investigated. It was found that pure Co films are non-single-phase and contain hpc and fcc crystal modifications. Doping leads to an increase in the concentration of the fcc phase and enhance the texture (111), and subsequently to the amorphization of the films. Buffer layers had a certain influence on the depth and concentration localization of these transformations. A characteristic feature of the magnetism of Co-W films is a significant perpendicular component in the macroscopic magnetic anisotropy, which leads to a "trance critical" magnetic state. It was shown that its source was a textured fcc phase, the crystal anisotropy of which was enhanced by the doping of cobalt with tungsten.

Topology of Coronal Magnetic Fields: Extending the Magnetic Skeleton Using Null-like Points

Many phenomena in the Sun’s atmosphere are magnetic in nature and study of the atmospheric magnetic field plays an important part in understanding these phenomena. Tools to study solar magnetic fields include magnetic topology and features such as magnetic null points, separatrix surfaces, and separators. The theory of these has most robustly been developed under magnetic charge topology, where the sources of the magnetic field are taken to be discrete, but observed magnetic fields are continuously distributed, and reconstructions and numerical simulations typically use continuously distributed magnetic boundary conditions. This article investigates the pitfalls in using continuous-source descriptions, particularly when null points on the $z=0$ z = 0 plane are obscured by the continuous flux distribution through, e.g., the overlap of non-point sources. The idea of null-like points on the boundary is introduced where the parallel requirement on the field $B_{\parallel }=0$ B ∥ = 0 is retained but the requirement on the perpendicular component is relaxed, i.e. $B_{\perp }\ne 0$ B ⊥ ≠ 0 . These allow the definition of separatrix-like surfaces which are shown (through use of a squashing factor) to be a class of quasi-separatrix layer, and separator-like lines which retain the x-line structure of separators. Examples are given that demonstrate that the use of null-like points can reinstate topological features that are eliminated in the transition from discrete to continuous sources, and that their inclusion in more involved cases can enhance understanding of the magnetic structure and even change the resulting conclusions. While the examples in this article use the potential approximation, the definition of null-like points is more general and may be employed in other cases such as force-free field extrapolations and MHD simulations.

The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence

© 2018, The Author(s). Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 μV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, B⊥, measured at any point on the surface of a high-temperature superconducting tape abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field, Ba. In all experimental data presented here Ic,B is found to be significantly (10–30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 µV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.

The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence

© 2018, The Author(s). Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 μV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, B⊥, measured at any point on the surface of a high-temperature superconducting tape abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field, Ba. In all experimental data presented here Ic,B is found to be significantly (10–30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 µV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.

Landau–Kelly representation of statistical thermodynamics of a quantum plasma and electron emission from metals

We have investigated the influence of a strong magnetic field on various aspects of a quantum Fermi plasma. Due to the strong magnetic field, the distribution function becomes anisotropic. First, we consider non-degenerate quantum, Landau and Kelly distribution function. It was found that the adiabatic equation is similar to the adiabatic equation for a Maxwell distribution function, when we include the magnetic field in the energy expression. Using the Kelly distribution for a degenerate, quantum Fermi gas, parallel and perpendicular components of the pressure were derived. It was found that perpendicular component of pressure never becomes zero and three-dimensional system always stay three-dimensional. Lastly, we investigated electron emission from metals and have shown the influence of the magnetic field. We calculated thermionic emission, the so-called Richardson effect. In addition, we investigate the influence of external electromagnetic radiation on the electron current density (Hallwachs effect) from metals.