22,354 research outputs found
Statistical distributions in the folding of elastic structures
The behaviour of elastic structures undergoing large deformations is the
result of the competition between confining conditions, self-avoidance and
elasticity. This combination of multiple phenomena creates a geometrical
frustration that leads to complex fold patterns. By studying the case of a rod
confined isotropically into a disk, we show that the emergence of the
complexity is associated with a well defined underlying statistical measure
that determines the energy distribution of sub-elements,``branches'', of the
rod. This result suggests that branches act as the ``microscopic'' degrees of
freedom laying the foundations for a statistical mechanical theory of this
athermal and amorphous system
Bond patterns and charge order amplitude in 1/4-filled charge-transfer solids
Metal-insulator transition accompanied by charge-ordering has been widely
investigated in quasi-one-dimensional conductors, including in particular
organic charge-transfer solids. Among such materials the 1/4-filled band
charge-transfer solids are of strong interest, because of the commensurate
nature of the charge-ordering in these systems. The period-four charge-order
pattern ...1100... here is accompanied by two distinct bond distortion
patterns, giving rise to bond-charge-density waves (BCDW) of types 1 and 2.
Using quantum Monte Carlo methods, we determine the phase diagram within the
extended Hubbard Hamiltonian that gives both types 1 and 2 BCDW in the
thermodynamic limit. We further investigate the effect of electron-electron and
electron-phonon interactions on the amount of charge disproportionation. Our
results show that between these two bond patterns, one (BCDW2) in general
coexists with a large magnitude charge order, which is highly sensitive to
electron-phonon interactions, while the other (BCDW1) is characterized by weak
charge order. We discuss the relevance of our work to experiments on several
1/4-filled conductors, focusing in particular on the materials (EDO-TTF)_2X and
(DMEDO-TTF)_2X with large amplitude charge-order.Comment: 7 pages, 8 figure
Gauged Thirring Model in the Heisenberg Picture
We consider the (2+1)-dimensional gauged Thirring model in the Heisenberg
picture. In this context we evaluate the vacuum polarization tensor as well as
the corrected gauge boson propagator and address the issues of generation of
mass and dynamics for the gauge boson (in the limits of QED and Thirring
model as a gauge theory, respectively) due to the radiative corrections.Comment: 14 pages, LaTex, no figure
Curso sobre o uso de técnicas de manejo e cultivo orgânico do solo em pequenas propriedades.
bitstream/item/133222/1/ID-39100.pd
Dynamical Lorentz and CPT symmetry breaking in a 4D four-fermion model
In a 4D chiral Thirring model we analyse the possibility that radiative
corrections may produce spontaneous breaking of Lorentz and CPT symmetry. By
studying the effective potential, we verified that the chiral current
may assume a nonzero vacuum expectation
value which triggers the Lorentz and CPT violations. Furthermore, by making
fluctuations on the minimum of the potential we dynamically induce a bumblebee
like model containing a Chern-Simons term.Comment: Small modifications in the text and new references added, 12 pages, 4
figures, revtex4. To appear in Phys. Rev.
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