scholarly journals Taming the Janssen effect

2021 ◽  
Vol 249 ◽  
pp. 08004
Author(s):  
Louison Thorens ◽  
Knut Jørgen Måløy ◽  
Mickaël Bourgoin ◽  
Stéphane Santucci
Keyword(s):  
Magnetic Field ◽  
Radial Force ◽  
Dipole Interactions ◽  
Full Control ◽  
Grain Packing ◽  
Experimental Findings ◽  
The Magnetic Field ◽  
Measured Mass ◽  
Granular Column ◽  
True Mass

We investigate both experimentally and theoretically the apparent mass of a ferromagnetic granular assembly filling a cylindrical container and submitted to a magnetic field B, aligned vertically along the silo. We show that the mass of the ferromagnetic granular column depends strongly on the applied magnetic field. Notably, our measurements deviate strongly from the exponential saturation of the measured mass as a function of the true mass of the grain packing, as predicted by Janssen [H.A. Janssen, Vereins Eutscher Ingenieure Zeitschrift, 1045 (1895)]. In particular, the measured mass of tall columns decreases systematically as the amplitude of the magnetic field increases. We rationalize our experimental findings by considering the induced magnetic dipole-dipole interactions within the whole packing. We show the emergence of a global magnetic radial force along the walls of the silos, fully determined by the external magnetic field. The resulting tunable frictional interactions allows a full control of the effective mass of the ferromagnetic granular column.

scholarly journals Magnetic Janssen effect

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
L. Thorens ◽  
K. J. Måløy ◽  
M. Bourgoin ◽  
S. Santucci
Keyword(s):  
Magnetic Field ◽  
Dynamic Properties ◽  
Radial Force ◽  
Fine Tuning ◽  
Apparent Mass ◽  
Confined Geometries ◽  
Pairwise Interactions ◽  
Janssen Effect ◽  
Lateral Walls ◽  
Granular Column

AbstractA pile of grains, even when at rest in a silo, can display fascinating properties. One of the most celebrated is the Janssen effect, named after the pioneering engineer who explained the pressure saturation at the bottom of a container filled with corn. This surprising behavior arises because of frictional interactions between the grains through a disordered network of contacts, and the vessel lateral walls, which partially support the weight of the column, decreasing its apparent mass. Here, we demonstrate control over frictional interactions using ferromagnetic grains and an external magnetic field. We show that the anisotropic pairwise interactions between magnetized grains result in a radial force along the walls, whose amplitude and direction is fully determined by the applied magnetic field. Such magnetic Janssen effect allows for the fine tuning of the granular column apparent mass. Our findings pave the way towards the design of functional jammed materials in confined geometries, via a further control of both their static and dynamic properties.

JOSEPHSON JUNCTION NETWORK AS A TOOL TO SIMULATE INTERGRAIN SUPERCONDUCTING CHANNELS IN YBCO FILMS

2000 ◽  
Vol 14 (25n27) ◽  
pp. 3068-3073 ◽  
Author(s):  
G. ROTOLI ◽  
C. DE LEO ◽  
G. GHIGO ◽  
L. GOZZELINO ◽  
C. CAMERLINGO
Keyword(s):  
Magnetic Field ◽  
Josephson Junction ◽  
Transport Properties ◽  
Granular Structure ◽  
Current Dependence ◽  
Josephson Junction Network ◽  
Experimental Findings ◽  
Static Conditions ◽  
Vortex Phases ◽  
The Magnetic Field

Recent considerations on the physics of YBa 2 Cu 3 O 7-δ films made possible explaining their transport properties as flow of supercurrents through links between the granular structure of the film. The present work deals with the analysis of the Josephson junction network as a discrete set of parallel junctions (1D array) in quasi-static conditions and is aimed to compare the results of the simulations with the experimental findings, in particular with the plateau-like features in the critical current dependence on the magnetic field. Different regimes and vortex phases have been individuated and discussed.

scholarly journals Magnetic control of polariton spin transport

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
D. Caputo ◽  
E. S. Sedov ◽  
D. Ballarini ◽  
M. M. Glazov ◽  
A. V. Kavokin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spin Transport ◽  
Beat Frequency ◽  
Magnetic Control ◽  
Polarization Pattern ◽  
Spin Degree ◽  
Full Control ◽  
Planar Microcavity ◽  
The Magnetic Field ◽  
Photon Coupling

AbstractPolaritons are hybrid light–matter quasiparticles arising from the strong coupling of excitons and photons. Owing to the spin degree-of-freedom, polaritons form spinor fluids able to propagate in the cavity plane over long distances with promising properties for spintronics applications. Here we demonstrate experimentally the full control of the polarization dynamics of a propagating exciton–polariton condensate in a planar microcavity by using a magnetic field applied in the Voigt geometry. We show the change of the spin-beat frequency, the suppression of the optical spin Hall effect, and the rotation of the polarization pattern by the magnetic field. The observed effects are theoretically reproduced by a phenomenological model based on microscopic consideration of exciton–photon coupling in a microcavity accounting for the magneto-induced mixing of exciton–polariton and dark, spin-forbidden exciton states.

The Nematic Character of a Hidden Ordered State revealed by Magnetic Fields.

2014 ◽  
Vol 1683 ◽  
Author(s):  
Peter S. Riseborough ◽  
S. G. Magalhaes ◽  
E.J. Calegari
Keyword(s):  
Magnetic Field ◽  
Critical Temperature ◽  
Low Temperature ◽  
Applied Field ◽  
Temperature Phase ◽  
Spin Quantization ◽  
Experimental Findings ◽  
Low Temperature Phase ◽  
The Magnetic Field ◽  
Ordered State

ABSTRACTWe examine a novel phase of the underscreened Anderson lattice Model that might pertain to the ”Hidden Ordered” phase of URu2Si2. We show that the system breaks spin-rotational invariance below the critical temperature and spontaneously selects a preferred axis of spin quantization. As a result, the low temperature phase exhibits a magnetic anisotropy, where the electronic properties depend not only on the magnitude of the magnetic field but also on the orientation of the applied field relative to the axis of quantization. The results are discussed in the context of recent experimental findings on URu2Si2.

The decay of wall-bounded MHD turbulence at low

2015 ◽  
Vol 783 ◽  
pp. 605-636 ◽  
Author(s):  
Alban Pothérat ◽  
Kacper Kornet
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Viscous Friction ◽  
Magnetic Reynolds Number ◽  
Two Dimensional ◽  
Mhd Turbulence ◽  
Velocity Gradients ◽  
Two Phases ◽  
Experimental Findings ◽  
The Magnetic Field

We present direct numerical simulations of decaying magnetohydrodynamic (MHD) turbulence at low magnetic Reynolds number. The domain considered is bounded by periodic boundary conditions in the two directions perpendicular to the magnetic field and by two plane Hartmann walls in the third direction. Regimes of high magnetic fields (Hartmann number of up to 896) are reached thanks to a new spectral method using the eigenvectors of the dissipation operator. The decay is found to proceed through two phases: first, energy and integral length scales vary rapidly during a two-dimensionalisation phase extending over approximately a Hartmann friction time. During this phase, the evolution of the former appears significantly more impeded by the presence of walls than that of the latter. Once the large scales are nearly quasi-two-dimensional, the decay results from the competition of a two-dimensional dynamics driven by dissipation in the Hartmann boundary layers and the three-dimensional dynamics of smaller scales. In the later stages of the decay, three-dimensionality subsists under the form of barrel-shaped structures. A purely quasi-two dimensional decay entirely dominated by friction in the Hartmann layers is not reached because of residual dissipation in the bulk. However, this dissipation is not generated by the three-dimensionality that subsists, but by residual viscous friction due to horizontal velocity gradients. In the process, the energy in the velocity component aligned with the magnetic field is found to be strongly suppressed, as is skewness. This result reproduces the experimental findings of Kolesnikov & Tsinober (Fluid Dyn., vol. 9, 1974, pp. 621–624), where, as in the present simulations, Hartmann walls were present.

Formation of chainlike structures in an Mn-89.7 wt%Sb alloy during isothermal annealing process in the semisolid state in a high magnetic field

2009 ◽  
Vol 24 (7) ◽  
pp. 2321-2330 ◽  
Author(s):  
Tie Liu ◽  
Qiang Wang ◽  
Chao Zhang ◽  
Ao Gao ◽  
Donggang Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Magnetic Field ◽  
Isothermal Annealing ◽  
Structural Evolution ◽  
Field Direction ◽  
Semisolid State ◽  
Average Characteristic ◽  
Dipole Interactions ◽  
Characteristic Radius ◽  
The Magnetic Field

This study is concerned with the investigation of the structural evolution occurring during isothermal annealing of an Mn-89.7 wt%Sb alloy in a high magnetic field in the semisolid state. The alloy specimens were isothermally annealed without and with an 11.5-T magnetic field for various annealing times. With the application of the magnetic field, the average characteristic radius of the primary MnSb particles increased with increasing annealing time. The primary MnSb particles were oriented with their c-plane parallel to the imposed field direction. Furthermore, the primary MnSb particles were found to align along the field direction and form chainlike structures eventually. These phenomena were attributed to the attraction and coalescence of the particles induced by the dipole–dipole interactions among them.

Creation of 3-D Crystals from Single Cobalt Nanoparticles in External Magnetic Fields

2001 ◽  
Vol 54 (8) ◽  
pp. 497 ◽  
Author(s):  
Michael Hilgendorff ◽  
Bernd Tesche ◽  
Michael Giersig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Colloidal Dispersions ◽  
Cobalt Nanoparticles ◽  
Dipole Interactions ◽  
Carbon Coated ◽  
Perfect Symmetry ◽  
The Magnetic Field ◽  
Applied External Magnetic Field

Using monodisperse nanocrystalline cobalt (Co) particles in non-polar colloidal dispersions, large areas of symmetric multi-dimensional structures were created using magnetophoretic deposition (MPD). To overcome the van der Waals and magnetic dipole–dipole interactions, the particles were stabilized with hydrophobic amines, phosphines, carboxylates and/or polymers. Depending on the preparation parameters, our particles had either bcc or ε-Co crystalline structures. Using MPD with magnetic fields up to 1 T, it was possible to create two-dimensional (2-D) arrays of near-perfect symmetry up to 1 m2 in size on various substrates, e.g. carbon-coated copper grids, silicon, or glass. Growth of the 2-D crystal was shown to be dependent on the direction of the applied external magnetic field. Three-dimensional (3-D) crystals could be created by increasing the magnetic field strength up to 6 T.

scholarly journals Thermoelectric magnetohydrodynamic effects on the crystal growth rate of undercooled Ni dendrites

2018 ◽  
Vol 376 (2113) ◽  
pp. 20170206 ◽  
Author(s):  
A. Kao ◽  
J. Gao ◽  
K. Pericleous
Keyword(s):  
Magnetic Field ◽  
Strong Dependence ◽  
Convective Transport ◽  
Numerical Code ◽  
Coupled Equations ◽  
Orthogonal Components ◽  
Observed Behaviour ◽  
Experimental Findings ◽  
Tip Velocity ◽  
The Magnetic Field

In the undercooled solidification of pure metals, the dendrite tip velocity has been shown experimentally to have a strong dependence on the intensity of an external magnetic field, exhibiting several maxima and minima. In the experiments conducted in China, the undercooled solidification dynamics of pure Ni was studied using the glass fluxing method. Visual recordings of the progress of solidification are compared at different static fields up to 6 T. The introduction of microscopic convective transport through thermoelectric magnetohydrodynamics is a promising explanation for the observed changes of tip velocities. To address this problem, a purpose-built numerical code was used to solve the coupled equations representing the magnetohydrodynamic, thermal and solidification mechanisms. The underlying phenomena can be attributed to two competing flow fields, which were generated by orthogonal components of the magnetic field, parallel and transverse to the direction of growth. Their effects are either intensified or damped out with increasing magnetic field intensity, leading to the observed behaviour of the tip velocity. The results obtained reflect well the experimental findings. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.

Observing the galactic magnetic field

1967 ◽  
Vol 31 ◽  
pp. 375-380
Author(s):  
H. C. van de Hulst
Keyword(s):  
Magnetic Field ◽  
Fair Agreement ◽  
Solar Neighbourhood ◽  
Galactic Magnetic Field ◽  
The Magnetic Field

Various methods of observing the galactic magnetic field are reviewed, and their results summarized. There is fair agreement about the direction of the magnetic field in the solar neighbourhood:l= 50° to 80°; the strength of the field in the disk is of the order of 10-5gauss.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

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