13,161 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
Teleparallel origin of the Fierz picture for spin-2 particle
A new approach to the description of spin-2 particle in flat and curved
spacetime is developed on the basis of the teleparallel gravity theory. We show
that such an approach is in fact a true and natural framework for the Fierz
representation proposed recently by Novello and Neves. More specifically, we
demonstrate how the teleparallel theory fixes uniquely the structure of the
Fierz tensor, discover the transparent origin of the gauge symmetry of the spin
2 model, and derive the linearized Einstein operator from the fundamental
identity of the teleparallel gravity. In order to cope with the consistency
problem on the curved spacetime, similarly to the usual Riemannian approach,
one needs to include the non-minimal (torsion dependent) coupling terms.Comment: 5 pages, Revtex4, no figures. Accepted for publication in Phys. Rev.
Gravitation and Duality Symmetry
By generalizing the Hodge dual operator to the case of soldered bundles, and
working in the context of the teleparallel equivalent of general relativity, an
analysis of the duality symmetry in gravitation is performed. Although the
basic conclusion is that, at least in the general case, gravitation is not dual
symmetric, there is a particular theory in which this symmetry shows up. It is
a self dual (or anti-self dual) teleparallel gravity in which, due to the fact
that it does not contribute to the interaction of fermions with gravitation,
the purely tensor part of torsion is assumed to vanish. The ensuing fermionic
gravitational interaction is found to be chiral. Since duality is intimately
related to renormalizability, this theory may eventually be more amenable to
renormalization than teleparallel gravity or general relativity.Comment: 7 pages, no figures. Version 2: minor presentation changes,
references added. Accepted for publication in Int. J. Mod. Phys.
Development of a molecular method for the identification of clone varieties of Coffea canephora via PCR.
Conilon coffee belongs to the Coffea canephora species, which is a diploid (2n = 2 Ă— = 22), perennial, allogamous plant with a high genetic variability. Consequently, a plantation established from seeds will likely have plants with highly diversified characteristics. Accordingly, the production of cuttings is of great value for the success of crop implementation. Using clones produced from superior genotypes instead of seeds has some advantages such as lower implementation costs, higher productivity, higher uniformity of maturation, better grain quality, differentiated cycle of maturation and staggered harvest scheduling. Brazil is an important coffee producer, and the development of new varieties is important to maintain or even increase its production
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