scholarly journals The Steady Currents Driven in a Conducting Sphere Placed in a Rotating Magnetic Field

1984 ◽  
Vol 37 (5) ◽  
pp. 521 ◽  
Author(s):  
WN Hugrass ◽  
HA Kirolous
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Equatorial Plane ◽  
Rotating Magnetic Field ◽  
Toroidal Magnetic Field ◽  
Weakly Nonlinear ◽  
Conducting Sphere

The steady currents (and the associated steady magnetic fields) generated in a conducting sphere placed in a rotating magnetic field are calculated in the weakly nonlinear limit. It is found that the steady driven current has a poloidal and a toroidal component. The steady toroidal magnetic field associated with the driven poloidal current has opposite senses above and below the equatorial plane; the net toroidal flux is zero. The relevance of this result to some recent observations in the Rotamak experiment is discussed.

Frequency-dependent conversion of the torque of a rotating magnetic field on a ferrofluid confined in a spherical cavity

Soft Matter ◽  
2019 ◽  
Vol 15 (44) ◽  
pp. 9018-9030
Author(s):  
Klaus D. Usadel ◽  
Anastasiya Storozhenko ◽  
Igor Arefyev ◽  
Hajnalka Nádasi ◽  
Torsten Trittel ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Nanoparticles ◽  
Magnetic Fields ◽  
Spherical Cavity ◽  
Rotating Magnetic Field ◽  
Rotating Magnetic Fields ◽  
Frequency Dependent

The dynamics of magnetic nanoparticles in rotating magnetic fields is studied both experimentally and theoretically.

Flow Control during Solidification of AlSi-Alloys by Means of Tailored AC Magnetic Fields and the Impact on the Mechanical Properties

2014 ◽  
Vol 790-791 ◽  
pp. 384-389
Author(s):  
Dirk Räbiger ◽  
Bernd Willers ◽  
Sven Eckert
Keyword(s):  
Magnetic Field ◽  
Mechanical Properties ◽  
Grain Size ◽  
Magnetic Fields ◽  
Flow Field ◽  
Phase Distribution ◽  
Solidification Process ◽  
Quantitative Information ◽  
Rotating Magnetic Field ◽  
The Impact

This paper presents an experimental study which in a first stage is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field configurations. Melt stirring has been realized by utilizing a rotating magnetic field. In a second step directional solidification of AlSi7 alloys from a water-cooled copper chill was carried out to verifythe effect of a certain flow field on the solidification process and on the resulting mechanical properties. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were realized. Our results demonstrate the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields show their capability to homogenize both the grain size distribution and the corresponding mechanical properties.

Control of the Macrosegregations during Solidification of a Binary Alloy by Means of a AC Magnetic Field

2006 ◽  
Vol 508 ◽  
pp. 163-168 ◽  
Author(s):  
Xiao Dong Wang ◽  
A. Ciobanas ◽  
Florin Baltaretu ◽  
Anne Marie Bianchi ◽  
Yves Fautrelle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mushy Zone ◽  
Binary Alloy ◽  
Solidification Front ◽  
Laminar Flows ◽  
Rotating Magnetic Field ◽  
Moderate Intensity ◽  
Mushy Region ◽  
Rotating Magnetic Fields

A numerical model aimed at simulating the segregations during the columnar solidification of a binary alloy is used to investigate the effects of a forced convection. Our objective is to study how the segregation characteristics in the mushy zone are influenced by laminar flows driven both by buoyancy and by AC fields of moderate intensity. Various types of magnetic fields have been tested, namely travelling, rotating magnetic field and slowly modulated electromagnetic forces. The calculations have been achieved on two types of alloys, namely tin-lead and aluminiumsilicon. It is shown that the flow configuration changes the segregation pattern. The change comes from the coupling between the liquid flow and the top of the mushy zone via the pressure distribution along the solidification front. The pressure difference along the front drives a mush flow, which transports the solute in the mushy region. Another interesting type of travelling magnetic field has been tested. It consists of a slowly modulated travelling magnetic field. It is shown that in a certain range of values of the modulation period, the channels are almost suppressed. The normal macrosegregation remains, but the averaged segregation in the mushy zone is weaker than in the natural convection case. The optimal period depends on the electromagnetic force strength as well as the cooling rate. The latter phenomenon cannot occur in the case of rotating magnetic fields, since in that configuration the sign of the pressure gradient along the solidification front remains unchanged. Recent solidification experiments with electromagnetic stirring confirm the predicted macrosegregation patterns.

scholarly journals Biochemical and cellular properties of Gluconacetobacter xylinus cultures exposed to different modes of rotating magnetic field

2017 ◽  
Vol 19 (2) ◽  
pp. 107-114 ◽  
Author(s):  
Karol Fijałkowski ◽  
Radosław Drozd ◽  
Anna Żywicka ◽  
Adam F. Junka ◽  
Marian Kordas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Positive Impact ◽  
Biochemical Properties ◽  
Rotating Magnetic Field ◽  
Cellulose Synthesis ◽  
Gluconacetobacter Xylinus ◽  
Biochemical Processes ◽  
Different Types ◽  
The Impact

Abstract The aim of the present study was to evaluate the impact of a rotating magnetic field (RMF) on cellular and biochemical properties of Gluconacetobacter xylinus during the process of cellulose synthesis by these bacteria. The application of the RMF during bacterial cellulose (BC) production intensified the biochemical processes in G. xylinus as compared to the RMF-unexposed cultures. Moreover, the RMF had a positive impact on the growth of cellulose-producing bacteria. Furthermore, the application of RMF did not increase the number of mutants unable to produce cellulose. In terms of BC production efficacy, the most favorable properties were found in the setting where RMF generator was switched off for the first 72 h of cultivation and switched on for the further 72 h. The results obtained can be used in subsequent studies concerning the optimization of BC production using different types of magnetic fields including RMF, especially.

Stabilization of magnetic mirror machine using rotating magnetic field

2018 ◽  
Vol 84 (5) ◽  
Author(s):  
O. Seemann ◽  
I. Be’ery ◽  
A. Fisher
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Collisional Plasma ◽  
Rotating Magnetic Field ◽  
Magnetic Mirror ◽  
Low Density ◽  
Mirror Machine

An increase in symmetry is observed for a low density non-collisional plasma, in a simple magnetic mirror machine, due to the application of external oscillating magnetic fields of 1.5 MHz frequency. The increase in symmetry is attributed to an increase in stability of the flute mode and is dependent on the field’s polarization and trap magnetic field strength.

Semiconductor Crystal Growth by the Vertical Bridgman Process With Transverse Rotating Magnetic Fields

2006 ◽  
Vol 129 (2) ◽  
pp. 241-243 ◽  
Author(s):  
X. Wang ◽  
N. Ma
Keyword(s):  
Magnetic Field ◽  
Crystal Growth ◽  
Magnetic Fields ◽  
Applied Magnetic Field ◽  
Rotating Magnetic Field ◽  
Semiconductor Crystal ◽  
Rotating Magnetic Fields ◽  
Electrically Conducting ◽  
Vertical Bridgman ◽  
Bridgman Process

During the vertical Bridgman process, a single semiconductor crystal is grown by the solidification of an initially molten semiconductor contained in an ampoule. The motion of the electrically conducting molten semiconductor can be controlled with an externally applied magnetic field. This paper treats the flow of a molten semiconductor and the dopant transport during the vertical Bridgman process with a periodic transverse or rotating magnetic field. The frequency of the externally applied magnetic field is sufficiently low that this field penetrates throughout the molten semiconductor. Dopant distributions in the crystal are presented.

scholarly journals The jets of AGN as giant coaxial cables

2018 ◽  
Vol 612 ◽  
pp. A67 ◽  
Author(s):  
Denise C. Gabuzda ◽  
Matt Nagle ◽  
Naomi Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Toroidal Magnetic Field ◽  
Systematic Change ◽  
Physical Mechanisms ◽  
Preferred Direction ◽  
Long Baseline ◽  
Rotation Measure ◽  
Very Long Baseline Array

Context. The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic field, which will give rise to a systematic change in the RM across the jet. Aims. The aim of this study is to identify new AGNs displaying statistically significant transverse RM gradients across their parsec-scale jets, in order to determine how often helical magnetic fields occur in AGN jets, and to look for overall patterns in the implied directions for the toroidal field components and jet currents. Methods. We have carried out new analyses of Faraday RM maps derived from previously published 8.1, 8.4, 12.1 and 15.3 GHz data obtained in 2006 on the NRAO Very Long Baseline Array (VLBA). In a number of key ways, our procedures were identical to those of the original authors, but the new imaging and analysis differs from the original methods in several ways: the technique used to match the resolutions at the different frequencies, limits on the widths spanned by the RM gradients analyzed, treatment of core-region RM gradients, approach to estimation of the significances of the gradients analyzed, and inclusion of a supplementary analysis using circular beams with areas equal to those of the corresponding elliptical naturally weighted beams. Results. This new analysis has substantially increased the number of AGNs known to display transverse RM gradients that may reflect the presence of a toroidal magnetic-field component. The collected data on parsec and kiloparsec scales indicate that the current typically flows inward along the jet axis and outward in a more extended region surrounding the jet, typical to the current structure of a co-axial cable, accompanied by a self-consistent system of nested helical magnetic fields, whose toroidal components give rise to the observed transverse Faraday rotation gradients. Conclusions. The new results presented here make it possible for the first time to conclusively demonstrate the existence of a preferred direction for the toroidal magnetic-field components – and therefore of the currents – of AGN jets. Discerning the origin of this current-field system is of cardinal importance for understanding the physical mechanisms leading to the formation of the intrinsic jet magnetic field, which likely plays an important role in the propagation and collimation of the jets; one possibility is the action of a “cosmic battery”.

scholarly journals Rotation of Liquid Metal Droplets Solely Driven by the Action of Magnetic Fields

2019 ◽  
Vol 9 (7) ◽  
pp. 1421 ◽  
Author(s):  
Jian Shu ◽  
Shi-Yang Tang ◽  
Sizepeng Zhao ◽  
Zhihua Feng ◽  
Haoyao Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Liquid Metal ◽  
Permanent Magnets ◽  
The Self ◽  
Rotating Magnetic Field ◽  
Fluid Mixture ◽  
Cooling Fluid ◽  
Novel Method ◽  
Metal Droplets

The self-rotation of liquid metal droplets (LMDs) has garnered potential for numerous applications, such as chip cooling, fluid mixture, and robotics. However, the controllable self-rotation of LMDs utilizing magnetic fields is still underexplored. Here, we report a novel method to induce self-rotation of LMDs solely utilizing a rotating magnetic field. This is achieved by rotating a pair of permanent magnets around a LMD located at the magnetic field center. The LMD experiences Lorenz force generated by the relative motion between the droplet and the permanent magnets and can be rotated. Remarkably, unlike the actuation induced by electrochemistry, the rotational motion of the droplet induced by magnetic fields avoids the generation of gas bubbles and behaves smoothly and steadily. We investigate the main parameters that affect the self-rotational behaviors of LMDs and validate the theory of this approach. We further demonstrate the ability of accelerating cooling and a mixer enabled by the self-rotation of a LMD. We believe that the presented technique can be conveniently adapted by other systems after necessary modifications and enables new progress in microfluidics, microelectromechanical (MEMS) applications, and micro robotics.

Flow Control Using Alternating Magnetic Fields During Crystal Growth From a Melt

2012 ◽  
Author(s):  
Yue Huang ◽  
Kenneth E. Davis ◽  
Brent C. Houchens
Keyword(s):  
Magnetic Field ◽  
Crystal Growth ◽  
Magnetic Fields ◽  
Flow Control ◽  
Body Force ◽  
Stokes Equations ◽  
Magnetic Reynolds Number ◽  
Rotating Magnetic Field ◽  
Bandgap Energy ◽  
Alternating Magnetic Fields

Flow control during bulk melt crystal growth is desirable for producing ternary alloy semiconductors with tunable lattice parameters and bandgap energy, providing custom materials for specific electro-optical applications. Segregation between constituent elements in the melt, be it through preferential rejection at the growth front or density variations, limits the growth rate and the uniformity in the crystal. External alternating magnetic fields are employed to stir the electrically conducting melt. While mixing is desired, turbulent flow is generally not. Precise control is required to maintain a laminar melt flow while providing sufficient mixing. Stirring via a rotating magnetic field (RMF) and a three-coil traveling magnetic field (TMF) is modeled and compared for a cylindrical melt confined in an ampule. The RMF imposes a body force in the azimuthal direction while the TMF induces primarily radial and axial body forces. The magnetic fields are effectively decoupled from the flow fields due to the small magnetic Reynolds number. Therefore, the magnetic fields are first determined using a finite element solver. The flows are then solved by a spectral element model of the Navier-Stokes equations including an electromagnetic body force term.

Tuning mass transport in magnetic nanoparticle-filled viscoelastic hydrogels using low-frequency rotating magnetic fields

Soft Matter ◽  
2017 ◽  
Vol 13 (36) ◽  
pp. 6259-6269 ◽  
Author(s):  
Shahab Boroun ◽  
Faïçal Larachi
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Mass Transport ◽  
Magnetic Nanoparticle ◽  
Low Frequency ◽  
Rotating Magnetic Field ◽  
Rotating Magnetic Fields ◽  
Rotational Movement

Rotational movement of MNPs in ferrogels in an external rotating magnetic field for tuning mass transport.

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