ADVANCES IN PHYSICS

 Advances In Physics, Volume 55, Numbers 1-2, January-April 2006
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LA eng
AU Namiko Mitarai, Franco Nori
TE Wet granular materials
RE Most studies on granular physics have focused on dry granular
   media, with no liquids between the grains. However, in geology
   and many real world applications (e.g. food processing,
   pharmaceuticals, ceramics, civil engineering, construction, and
   many industrial applications), liquid is present between the
   grains. This produces inter-grain cohesion and drastically
   modifies the mechanical properties of the granular media (e.g.
   the surface angle can be larger than 90 degrees). Here we
   present a review of the mechanical properties of wet granular
   media, with particular emphasis on the effect of cohesion. We
   also list several open problems that might motivate future
   studies in this exciting but mostly unexplored field.
PP 1-45
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LA eng
AU Matthias Eschrig
TE The effect of collective spin-1 excitations on electronic
   spectra in high-T_{c} superconductors
RE We review recent experimental and theoretical results on the
   interaction between single-particle excitations and collective
   spin excitations in the superconducting state of high- T_{c}
   cuprates. We concentrate on the traces that sharpen features in
   the magnetic-excitation spectrum (measured by inelastic neutron
   scattering) and imprint in the spectra of single-particle
   excitations (measured, e.g. by angle-resolved photoemission
   spectroscopy, tunnelling spectroscopy, and indirectly also by
   optical spectroscopy). The ideal object to obtain a quantitative
   picture for these interaction effects is a spin-1 excitation
   around 40 meV, termed `resonance mode'. Although the total
   weight of this spin-1 excitation is small, the confinement of
   its weight to a rather narrow momentum region around the
   antiferromagnetic wavevector makes it possible to observe strong
   self-energy effects in parts of the electronic Brillouin zone.
   Notably, the sharpness of the magnetic excitation in energy has
   allowed these self-energy effects to be traced in the
   single-particle spectrum rather precisely. Namely, the doping
   and temperature dependence together with the characteristic
   energy and momentum behaviour of the resonance mode has been
   used as a tool to examine the corresponding self-energy effects
   in the dispersion and in the spectral line-shape of the
   single-particle spectra, and to separate them from similar
   effects due to the electron-phonon interaction. This leads to
   the unique possibility to single out the self-energy effects due
   to the spin-fermion interaction and to directly determine the
   strength of this interaction in high-T_{c} cuprate
   superconductors. The knowledge of this interaction is important
   for the interpretation of other experimental results as well as
   for the quest for the still unknown pairing mechanism in these
   interesting superconducting materials.
PP 47-183
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LA eng
AU Michael Zaiser
TE Scale invariance in plastic flow of crystalline solids
RE From the traditional viewpoint of continuum plasticity, plastic
   deformation of crystalline solids is, at least in the absence of
   so-called plastic instabilities, envisaged as a smooth and
   quasi-laminar flow process. Recent theoretical and experimental
   investigations, however, demonstrate that crystal plasticity is
   characterized by large intrinsic spatio-temporal fluctuations
   with scale-invariant characteristics: In time, deformation
   proceeds through intermittent bursts with power-law size
   distributions; in space, deformation patterns and
   deformation-induced surface morphology are characterized by
   long-range correlations, self-similarity and/or self-affine
   roughness. We discuss this scale-invariant behaviour in terms of
   robust scaling associated with a non-equilibrium critical point
   (`yielding transition').
PP 185-245
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