STRUCTURES IN A MAGNETIC SUSPENSION SUBJECTED TO UNIDIRECTIONAL AND ROTATING FIELD

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2279-2285 ◽  
Author(s):  
P. CARLETTO ◽  
G. BOSSIS ◽  
A. CEBERS
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Thermodynamic Model ◽  
Colloidal Particles ◽  
Average Distance ◽  
Characteristic Size ◽  
Magnetic Suspension ◽  
Order Of Magnitude ◽  
The Magnetic Field ◽  
Rotating Field

Field induced structures are studied inside suspensions of magnetic colloidal particles of micronic size. We have characterized the average distance between aggregates in a thin cell with the magnetic field perpendicular to the plane and also in the presence of a rotating field with the plane of rotation perpendicular to the plane of the cell. The characteristic size of the mesostructure is predicted on the basis of a thermodynamic model. The theory well predicts the experimental results in the uniaxial case but not in the case of ae rotating field; in this last case, the surface tension which is needed to have a good fit is far too low compared to its expected order of magnitude. When the field is uniaxial and sinusoidal we have found a collective instability where all the aggregates are rotating simultaneously in a chaotic way.

scholarly journals Influence of Magnetic Field on Evaporation Rate and Surface Tension of Water

2018 ◽  
Vol 2 (4) ◽  
pp. 68 ◽  
Author(s):  
Emil Chibowski ◽  
Aleksandra Szcześ ◽  
Lucyna Hołysz
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Hydrogen Bonds ◽  
Room Temperature ◽  
Evaporation Rate ◽  
Water Evaporation ◽  
Water Molecules ◽  
Surface Tension Data ◽  
Ring Magnet ◽  
The Magnetic Field

Using neodymium ring magnets (0.5–0.65 T), the experiments on the magnetic field (MF) effects on water evaporation rate and surface tension were performed at room temperature (22–24 °C). In accordance with the literature data, the enhanced evaporation rates were observed in the experiments conducted in a period of several days or weeks. However, the evaporated amounts of water (up to 440 mg over 150 min) in particular experiments differed. The evaporated amounts depended partially on which pole of the ring magnet was directed up. The relatively strong MF (0.65 T) caused a slight decrease in surface tension (−2.11 mN/m) which lasted longer than 60 min and the memory effect vanished slowly. The surface tension data reduced by the MF action are reported in the literature, although contrary results can be also found. The observed effects can be explained based on literature data of molecular simulations and the suggestion that MF affects the hydrogen bonds of intra- and inter-clusters of water molecules, possibly even causing breakage some of them. The Lorentz force influence is also considered. These mechanisms are discussed in the paper.

scholarly journals A Novel Method for Improving Low-Temperature Flotation Performance of Nonpolar Oil in the Molybdenite Flotation

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 609 ◽  
Author(s):  
Wan ◽  
Qu ◽  
Li ◽  
He ◽  
Bu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Surface Tension ◽  
Low Temperature ◽  
Interfacial Tension ◽  
Field Intensity ◽  
Magnetic Field Intensity ◽  
Maximum Surface ◽  
Flotation Recovery ◽  
Flotation Performance ◽  
The Magnetic Field

Nonpolar hydrocarbon oil (NHO) is one of the most extensively used collectors in the flotation of molybdenite due to its excellent selectivity. However, NHO has low sensibility at pulp temperature. At low temperatures (<283 K), although more kerosene is used, the recovery of molybdenite flotation is still lower than at room temperature. In this study, magnetizing treatment, which is an efficient, low-cost, innovative, and environmentally friendly emulsification method, was used to improve the flotation performance of NHO in low-temperature molybdenite flotation. The test results showed that, compared with unmagnetized kerosene (UMK), the optimum dosage of magnetized kerosene (MK) could be reduced by 11% at 298 K. At the same dosage of kerosene, the flotation recovery of MK was 3% higher than UMK at 278 K. The surface tension measurement results showed that the surface tension of MK rose periodically as the magnetic field intensity increased, and there was a maximum surface tension within each period. Further, the magnetic field intensity had the maximum flotation recovery of molybdenite at the maximum surface tension of MK. Combined with the analysis based on the Girifalco–Good theory and the static drop volume method of interfacial tension, the interfacial tension of kerosene–water was shown to decrease with the increase of the surface tension of kerosene. This finding indicates that the dispersibility of kerosene in pulp could be improved by reducing the size of oil droplets, thereby improving the molybdenite flotation recovery of kerosene at low-temperature pulp. It is helpful to improve the flotation recovery of molybdenite using NHO as a collector for low-temperature pulp (<283 K).

End effects in the magnetic field of free electron lasers with sheet electron beams

1990 ◽  
Vol 68 (11) ◽  
pp. 1227-1236
Author(s):  
G. Pocobelli
Keyword(s):  
Magnetic Field ◽  
Free Electron ◽  
Electron Beams ◽  
Field Measurements ◽  
End Effects ◽  
Direction Parallel ◽  
Additional Degree ◽  
Order Of Magnitude ◽  
Three Space ◽  
The Magnetic Field

We calculate the magnetic field of a free-electron-laser's wiggler of a recent design (Granatstein et al. Appl. Phys. Lett. 74, 643 (1985)) using sheet electron beams. We did not assume periodic boundary conditions, as was done in their work, and we obtained analytical expressions in two of the three space variables. We found various irregularities in the field behavior that were dependent on the size of the wiggler in the x direction (parallel to the beam's wide size), and that increased up to a width an order of magnitude greater than the height of the beam channel. These irregularities had been observed in field measurements. A method consisting of making the end magnets thinner worked effectively to reduce the irregularities. We also studied a similar magnetic configuration with free and independent currents and no magnets, and added the additional degree of freedom of programming the currents to further reduce the irregularities.

ON THE THEORY OF ALLOY SOLIDIFICATION IN A MAGNETIC FIELD

1964 ◽  
Vol 42 (11) ◽  
pp. 2238-2258 ◽  
Author(s):  
W. V. Youdelis ◽  
D. R. Colton ◽  
J. Cahoon
Keyword(s):  
Magnetic Field ◽  
Diffusion Rate ◽  
Irreversible Thermodynamic ◽  
Chill Face ◽  
Convective Mixing ◽  
System A ◽  
Aluminium Copper ◽  
Order Of Magnitude ◽  
Chill Cast ◽  
The Magnetic Field

The degree of segregation in unidirectionally solidified ingots, chill-cast in magnetic fields up to 34 kilo-oersteds, has been determined for alloys of the aluminium–copper and bismuth–antimony systems. It is found that the chill-face segregation in aluminium–copper ingots is increased approximately 50% above the no-field ingots for a 34-kilo-oersted field. The effect is independent of field direction. A 13-kilo-oersted field decreases the chill-face segregation by 60% in ingots of the bismuth (rich) – antimony system. A theory based on the diffusion inhibition effect of the magnetic field (previously reported) is presented to explain the segregation change. By applying irreversible thermodynamic principles, it is shown that the segregation changes in the field-solidified ingots are a manifestation of the decreased entropy production of the diffusion, convective mixing, and viscous flow processes of solidification in a magnetic field. For the aluminium–copper ingots there is order-of-magnitude agreement between the observed segregation change and the decreased diffusion rate in the magnetic field.

Characteristics of Ultrasound Propagation in a Magnetic Fluid Under Uniform Magnetic Field

2003 ◽  
Author(s):  
Masaaki Motozawa ◽  
Tatsuo Sawada
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fluid ◽  
Uniform Magnetic Field ◽  
Colloidal Particles ◽  
Magnetic Field Intensity ◽  
Magnetic Field Direction ◽  
Ultrasound Propagation ◽  
Ultrasonic Propagation ◽  
The Magnetic Field

When an external magnetic field is applied to a magnetic fluid, some of the colloidal particles coagulate and form chain-like clusters. Properties of ultrasonic propagation wave are changed by these chain-like clusters. We carried out measurement of the ultrasonic propagation velocity in a magnetic fluid. Measurement were made by changing the magnetic field intensity from 0 mT to 570 mT, and the angle between the magnetic field direction and direction of the ultrasound propagation from 0° to 180°. The ultrasound frequencies were 1 MHz, 2 MHz and 4 MHz. Some of experimental results for the characteristics of ultrasound propagation in a magnetic fluid under a uniform magnetic field were reported.

scholarly journals Wave Energy Dissipation in the Solar Atmosphere

1990 ◽  
Vol 142 ◽  
pp. 266-267
Author(s):  
Zhou Aihua
Keyword(s):  
Magnetic Field ◽  
Heat Conduction ◽  
Transition Region ◽  
Wave Dissipation ◽  
Wave Energy Dissipation ◽  
Wave Heating ◽  
Order Of Magnitude ◽  
Lower Temperature ◽  
The Magnetic Field ◽  
Field Wave

There are two regions of rapid dissipation when Alfvén waves propagate from the transition region to the corona. They occur respectively in a range of several hundred kilometers above the base of the transition region and in the corona at about 1-3Ro. The heating of the atmosphere by wave dissipation could be one order of magnitude larger than heat conduction in the coronal part with a lower temperature and density and stronger magnetic field. Wave heating could also become more important when the magnetic field divergence becomes stronger.

scholarly journals Two-dimensional nonlinear travelling waves in magnetohydrodynamic channel flow

2014 ◽  
Vol 760 ◽  
pp. 387-406 ◽  
Author(s):  
Jonathan Hagan ◽  
Jānis Priede
Keyword(s):  
Magnetic Field ◽  
Linear Stability ◽  
Channel Flow ◽  
Travelling Waves ◽  
Transverse Magnetic ◽  
Travelling Wave ◽  
Linear Stability Theory ◽  
Two Dimensional ◽  
Order Of Magnitude ◽  
The Magnetic Field

AbstractThis study is concerned with the stability of a flow of viscous conducting liquid driven by a pressure gradient in the channel between two parallel walls subject to a transverse magnetic field. Although the magnetic field has a strong stabilizing effect, this flow, similarly to its hydrodynamic counterpart – plane Poiseuille flow – is known to become turbulent significantly below the threshold predicted by linear stability theory. We investigate the effect of the magnetic field on two-dimensional nonlinear travelling-wave states which are found at substantially subcritical Reynolds numbers starting from $\mathit{Re}_{n}=2939$ without the magnetic field and from $\mathit{Re}_{n}\sim 6.50\times 10^{3}\mathit{Ha}$ in a sufficiently strong magnetic field defined by the Hartmann number $\mathit{Ha}$. Although the latter value is a factor of seven lower than the linear stability threshold $\mathit{Re}_{l}\sim 4.83\times 10^{4}\mathit{Ha}$, it is still more than an order of magnitude higher than the experimentally observed value for the onset of turbulence in magnetohydrodynamic (MHD) channel flow.

scholarly journals Observation of Fractal Conductance Fluctuations over Three Orders of Magnitude

1999 ◽  
Vol 52 (5) ◽  
pp. 887 ◽  
Author(s):  
R. P. Taylor ◽  
A. P. Micolich ◽  
R. Newbury ◽  
T. M. Fromhold ◽  
C. R. Tench
Keyword(s):  
Magnetic Field ◽  
Transport Properties ◽  
Field Range ◽  
Magnetic Field Range ◽  
Physical Conditions ◽  
Fractal Behaviour ◽  
Conductance Fluctuations ◽  
Order Of Magnitude ◽  
The Magnetic Field

Fractal magneto-transport properties of mesoscopic semiconductor billiards are highly topical. In these studies, the magnetic field range over which fractal behaviour can be observed is crucial. Previous observations have been limited to approximately one order of magnitude. We present fractal conductance fluctuations observed over three orders of magnitude and discuss the physical conditions required to extend this range.

scholarly journals The skyrmion-bubble transition in a ferromagnetic thin film

2018 ◽  
Vol 4 (5) ◽  
Author(s):  
Anne Bernand-Mantel ◽  
Lorenzo Camosi ◽  
Alexis Wartelle ◽  
Nicolas Rougemaille ◽  
Michaël Darques ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Soliton Solutions ◽  
Perpendicular Magnetic Anisotropy ◽  
Characteristic Size ◽  
Continuous Transformation ◽  
Topological Soliton ◽  
Topological Solitons ◽  
Ferromagnetic Thin Films ◽  
Magnetic Skyrmions ◽  
The Magnetic Field

Magnetic skyrmions and bubbles, observed in ferromagnetic thin films with perpendicular magnetic anisotropy, are topological solitons which differ by their characteristic size and the balance in the energies at the origin of their stabilisation. However, these two spin textures have the same topology and a continuous transformation between them is allowed. In the present work, we derive an analytical model to explore the skyrmion-bubble transition. We evidence a region in the parameter space where both topological soliton solutions coexist and close to which transformations between skyrmion and bubbles are observed as a function of the magnetic field. Above a critical point, at which the energy barrier separating both solutions vanishes, only one topological soliton solution remains, which size can be continuously tuned from micrometer to nanometer with applied magnetic field.

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