11,667 research outputs found
Collective rearrangement at the onset of flow of a polycrystalline hexagonal columnar phase
Creep experiments on polycrystalline surfactant hexagonal columnar phases
show a power law regime, followed by a drastic fluidization before reaching a
final stationary flow. The scaling of the fluidization time with the shear
modulus of the sample and stress applied suggests that the onset of flow
involves a bulk reorganization of the material. This is confirmed by X-ray
scattering under stress coupled to \textit{in situ} rheology experiments, which
show a collective reorientation of all crystallites at the onset of flow. The
analogy with the fracture of heterogeneous materials is discussed.Comment: to appear in Phys. Rev. Let
Electronic Griffiths phase of the d=2 Mott transition
We investigate the effects of disorder within the T=0 Brinkman-Rice (BR)
scenario for the Mott metal-insulator transition (MIT) in two dimensions (2d).
For sufficiently weak disorder the transition retains the Mott character, as
signaled by the vanishing of the local quasiparticles (QP) weights Z_{i} and
strong disorder screening at criticality. In contrast to the behavior in high
dimensions, here the local spatial fluctuations of QP parameters are strongly
enhanced in the critical regime, with a distribution function P(Z) ~
Z^{\alpha-1} and \alpha tends to zero at the transition. This behavior
indicates a robust emergence of an electronic Griffiths phase preceding the
MIT, in a fashion surprisingly reminiscent of the "Infinite Randomness Fixed
Point" scenario for disordered quantum magnets.Comment: 4+ pages, 5 figures, final version to appear in Physical Review
Letter
Memory effects on the statistics of fragmentation
We investigate through extensive molecular dynamics simulations the
fragmentation process of two-dimensional Lennard-Jones systems. After
thermalization, the fragmentation is initiated by a sudden increment to the
radial component of the particles' velocities. We study the effect of
temperature of the thermalized system as well as the influence of the impact
energy of the ``explosion'' event on the statistics of mass fragments. Our
results indicate that the cumulative distribution of fragments follows the
scaling ansatz , where is
the mass, and are cutoff parameters, and is a scaling
exponent that is dependent on the temperature. More precisely, we show clear
evidence that there is a characteristic scaling exponent for each
macroscopic phase of the thermalized system, i.e., that the non-universal
behavior of the fragmentation process is dictated by the state of the system
before it breaks down.Comment: 5 pages, 8 figure
The virtual origin as a first-order correction for the far-field description of laminar jets
The far-field velocity and composition fields of a submerged laminar jet are known to approach a self-similar solution corresponding to the flow induced by a point source of momentum and scalar. Previous efforts to improve this far-field description have introduced a virtual origin for the streamwise coordinate to remedy the singular behavior of the self-similar solution near the jet origin. The purpose of this note is to show, by means of a perturbative analysis of the point-source solution, that this virtual origin is in fact the first-order correction to the leading-order description. The perturbative analysis, which uses the ratio x of the streamwise distance to the length of jet development as an asymptotically large quantity, also indicates that the displaced point source provides the description in the far field with small relative errors of order x-3 for the round jet and of order x-10/3 for the plane jet. The values of the virtual origin are obtained by numerical integration of the boundary-layer equations in the region of jet development, giving values that depend on the shape of the jet velocity profile at the exit
Plurality Voting: the statistical laws of democracy in Brazil
We explore the statistical laws behind the plurality voting system by
investigating the election results for mayor held in Brazil in 2004. Our
analysis indicate that the vote partition among mayor candidates of the same
city tends to be "polarized" between two candidates, a phenomenon that can be
closely described by means of a simple fragmentation model. Complex concepts
like "government continuity" and "useful vote" can be identified and even
statistically quantified through our approach.Comment: 4 pages, 4 figure
Neighborhood properties of complex networks
A concept of neighborhood in complex networks is addressed based on the
criterion of the minimal number os steps to reach other vertices. This amounts
to, starting from a given network , generating a family of networks
such that, the vertices that are steps apart in
the original , are only 1 step apart in . The higher order
networks are generated using Boolean operations among the adjacency matrices
that represent . The families originated by the well known
linear and the Erd\"os-Renyi networks are found to be invariant, in the sense
that the spectra of are the same, up to finite size effects. A further
family originated from small world network is identified
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