6,739 research outputs found
Invalidation of the Kelvin Force in Ferrofluids
Direct and unambiguous experimental evidence for the magnetic force density
being of the form in a certain geometry - rather than being the
Kelvin force - is provided for the first time. (M is the
magnetization, H the field, and B the flux density.)Comment: 4 pages, 4 figure
Electromagnetic Force in Dispersive and Transparent Media
A hydrodynamic-type, macroscopic theory was set up recently to simultaneously
account for dissipation and dispersion of electromagnetic field, in
nonstationary condensed systems of nonlinear constitutive relations~\cite{JL}.
Since it was published in the letter format, some algebra and the more subtle
reasonings had to be left out. Two of the missing parts are presented in this
paper: How algebraically the new results reduce to the known old ones; and more
thoughts on the range of validity of the new theory, especially concerning the
treatment of dissipation.Comment: 10 pages, 0 figur
Electromagnetic Force and the Maxwell Stress Tensor in Condensed Systems
While the electromagnetic force is microscopically simply the Lorentz force,
its macroscopic form is more complicated, and given by expressions such as the
Maxwell stress tensor and the Kelvin force. Their derivation is fairly opaque,
at times even confusing, and their range of validity all but a well kept
secret. These circumstances unnecessarily reduce the usefulness and
trustworthiness of some key quantities in macroscopic electrodynamics.
This article presents a thorough yet pedagogical derivation of the Maxwell
stress tensor and electromagnetic force in condensed media. It starts from
universally accepted inputs: conservation laws, thermodynamics and the Maxwell
equations. Simplifications are considered for various limits, especially the
equilibrium, with a range of validity assigned to each expression. Some
widespread misconceptions are scrutinized, and hidden ambiguities in popular
notations revealed.
A number of phenomena typical of strongly polarizable systems, especially
ferrofluid, are then considered. In addition to enhancing the appreciation of
these systems, it helps to solidify the grasp of the introduced concepts and
derived formulas, and it demonstrates the ease with which the Maxwell stress
tensor can be handled, inviting theorists and experimentalists alike to embrace
this useful quantity.Comment: 27 pages, 7 fi
Applying GSH to a Wide Range of Experiments in Granular Media
Granular solid hydrodynamics (GSH) is a continuum-mechanical theory for
granular media, the range of which is shown in this paper. Simple, frequently
analytic solutions are related to classic observations at different shear
rates, including: (i)~static stress distribution, clogging; (ii)~elasto-plastic
motion: loading and unloading, approach to the critical state, angle of
stability and repose; (iii)~rapid dense flow: the -rheology, Bagnold
scaling and the stress minimum; (iv)~elastic waves, compaction, wide and narrow
shear band. Less conventional experiments have also been considered: shear
jamming, creep flow, visco-elastic behavior and nonlocal fluidization. With all
these phenomena ordered, related, explained and accounted for, though
frequently qualitatively, we believe that GSH may be taken as a unifying
framework, providing the appropriate macroscopic vocabulary and mindset that
help one coming to terms with the breadth of granular physics.Comment: arXiv admin note: substantial text overlap with arXiv:1207.128
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