1,128 research outputs found
Insights into the room temperature magnetism of ZnO/Co3O4 mixtures
The origin of room temperature (RT) ferromagneticlike behavior in ZnO-based
diluted magnetic semiconductors is still an unclear topic. The present work
concentrates on the appearance of RT magnetic moments in just mixed ZnO/Co3O4
mixtures without thermal treatment. In this study, it is shown that the
magnetism seems to be related to surface reduction of the Co3O4 nanoparticles,
in which, an antiferromagnetic Co3O4 nanoparticle (core) is surrounded by a
CoO-like shell. This singular superficial magnetism has also been found in
other mixtures with semiconductors such as TiO2 and insulators such as Al2O3
Reforming of Diesel Fuel for Hydrogen Production over Catalysts Derived from LaCo0.8M0.2O3 (M = Ni, Ru, Fe, Ga)
On random graphs and the statistical mechanics of granular matter
The dynamics of spins on a random graph with ferromagnetic three-spin
interactions is used to model the compaction of granular matter under a series
of taps. Taps are modelled as the random flipping of a small fraction of the
spins followed by a quench at zero temperature. We find that the density
approached during a logarithmically slow compaction
- the random-close-packing density - corresponds to a dynamical phase
transition. We discuss the the role of cascades of successive spin-flips in
this model and link them with density-noise power fluctuations observed in
recent experiments.Comment: minor changes, to appear in EP
An invariant distribution in static granular media
We have discovered an invariant distribution for local packing configurations
in static granular media. This distribution holds in experiments for packing
fractions covering most of the range from random loose packed to random close
packed, for beads packed both in air and in water. Assuming only that there
exist elementary cells in which the system volume is subdivided, we derive from
statistical mechanics a distribution that is in accord with the observations.
This universal distribution function for granular media is analogous to the
Maxwell-Boltzmann distribution for molecular gasses.Comment: 4 pages 3 figure
Heterogeneities in systems with quenched disorder
We study the strong role played by structural (quenched) heterogeneities on
static and dynamic properties of the Frustrated Ising Lattice Gas in two
dimensions, already in the liquid phase. Differently from the dynamical
heterogeneities observed in other glass models in this case they may have
infinite lifetime and be spatially pinned by the quenched disorder. We consider
a measure of local frustration, show how it induces the appearance of spatial
heterogeneities and how this reflects in the observed behavior of equilibrium
density distributions and dynamic correlation functions.Comment: 8 page
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