14,930 research outputs found
New family of potentials with analytical twiston-like solutions
In this letter we present a new approach to find analytical twiston models.
The effective two-field model was constructed by a non-trivial combination of
two one field systems. In such an approach we successfully build analytical
models which are satisfied by a combination of two defect-like solutions, where
one is responsible to twist the molecular chain by , while the other
implies in a longitudinal movement. Such a longitudinal movement can be fitted
to have the size of the distance between adjacent molecular groups. The
procedure works nicely and can be used to describe the dynamics of several
other molecular chains.Comment: 7 pages, 3 figure
Dynamical reentrance and geometry imposed quantization effects in Nb-AlOx-Nb Josephson junction arrays
In this paper, we report on different phenomena related to the magnetic
properties of artificially prepared highly ordered (periodic) two-dimensional
Josephson junction arrays (2D-JJA) of both shunted and unshunted Nb-AlOx-Nb
tunnel junctions. By employing mutual-inductance measurements and using a
high-sensitive bridge, we have thoroughly investigated (both experimentally and
theoretically) the temperature and magnetic field dependence of complex AC
susceptibility of 2D-JJA. We also demonstrate the use of the scanning SQUID
microscope for imaging the local flux distribution within our unshunted arrays
Greedy randomized dispatching heuristics for the single machine scheduling problem with quadratic earliness and tardiness penalties
In this paper, we present greedy randomized dispatching heuristics for the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. The several heuristic versions differ, on the one hand, on the strategies involved in the construction of the greedy randomized schedules. On the other hand, these versions also differ on whether they employ only a final improvement step, or perform a local search after each greedy randomized construction. The proposed heuristics were compared with existing procedures, as well as with optimum solutions for some instance sizes. The computational results show that the proposed procedures clearly outperform their underlying dispatching heuristic, and the best of these procedures provide results that are quite close to the optimum. The best of the proposed algorithms is the new recommended heuristic for large instances, as well as a suitable alternative to the best existing procedure for the larger of the middle size instances.scheduling, single machine, early/tardy, quadratic penalties, greedy randomized dispatching rules
Singular diffusion and criticality in a confined sandpile
We investigate the behavior of a two-state sandpile model subjected to a
confining potential in one and two dimensions. From the microdynamical
description of this simple model with its intrinsic exclusion mechanism, it is
possible to derive a continuum nonlinear diffusion equation that displays
singularities in both the diffusion and drift terms. The stationary-state
solutions of this equation, which maximizes the Fermi-Dirac entropy, are in
perfect agreement with the spatial profiles of time-averaged occupancy obtained
from model numerical simulations in one as well as in two dimensions.
Surprisingly, our results also show that, regardless of dimensionality, the
presence of a confining potential can lead to the emergence of typical
attributes of critical behavior in the two-state sandpile model, namely, a
power-law tail in the distribution of avalanche sizes.Comment: 5 pages, 5 figure
Counterions at Charged Cylinders: Criticality and universality beyond mean-field
The counterion-condensation transition at charged cylinders is studied using
Monte-Carlo simulation methods. Employing logarithmically rescaled radial
coordinates, large system sizes are tractable and the critical behavior is
determined by a combined finite-size and finite-ion-number analysis. Critical
counterion localization exponents are introduced and found to be in accord with
mean-field theory both in 2 and 3 dimensions. In 3D the heat capacity shows a
universal jump at the transition, while in 2D, it consists of discrete peaks
where single counterions successively condense.Comment: 4 pages, 3 figures; submitted to Phys. Rev. Lett. (2005
Irreversibility line and low-field grain-boundary pinning in electron-doped superconducting thin films
AC magnetic susceptibilities of electron-doped Pr_{1.85}Ce_{0.15}CuO_4 (PCCO)
and Sm_{1.85}Ce_{0.15}CuO_4 (SCCO) granular thin films have been measured as a
function of temperature and magnetic-field strength. Depending on the level of
homogeneity of our films, two different types of the irreversibility line (IL)
defined as the intergrain-loss peak temperature in the imaginary part of
susceptibility have been found. The obtained results are described via the
critical-state model taking into account the low-field grain-boundary pinning.
The extracted pinning-force densities in more granular SCCO films turn out to
be four times larger than their counterparts in less granular PCCO films
Association between dietary calcium intake and blood pressure among portuguese children
[Resumo][Abstract
Elastic and magnetic effects on the infrared phonon spectra of MnF2
We measured the temperature dependent infrared reflectivity spectra of MnF2
between 4 K and room temperature. We show that the phonon spectrum undergoes a
strong renormalization at TN. The ab-initio calculation we performed on this
compound accurately predict the magnitude and the direction of the phonon
parameters changes across the antiferromagnetic transition, showing that they
are mainly induced by the magnetic order. In this material, we found that the
dielectric constant is mostly from phonon origin. The large change in the
lattice parameters with temperature seen by X-ray diffraction as well as the
A2u phonon softening below TN indicate that magnetic order induced distortions
in MnF2 are compatible with the ferroelectric instabilities observed in TiO2,
FeF2 and other rutile-type fluorides. This study also shows the anomalous
temperature evolution of the lower energy Eu mode in the paramagnetic phase,
which can be compared to that of the B1g one seen by Raman spectroscopy in many
isostructural materials. This was interpreted as being a precursor of a phase
transition from rutile to CaCl2 structure which was observed under pressure in
ZnF2.Comment: 8 pages, 8 figures, updated version accepted in PR
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