778 research outputs found
Magnetism in Rare Earth Quasicrystals: RKKY Interactions and Ordering
We study magnetism in simple models for rare earth quasicrystals by means of
a two-step theoretical approach. First, we compute RKKY interactions from a
tight-binding Hamiltonian defined on a two-dimensional quasiperiodic tiling.
Second, we examine the statistical mechanics of Ising spins coupled via these
interactions using Monte Carlo simulations. We find the emergence of strongly
coupled spin clusters with significantly weaker inter-cluster coupling, and a
transition to a low-temperature phase that has long-range order evidenced by a
finite domain wall tension.Comment: restructuring of paper and update of numerical results, 5 pages, 4
figure
Quantum Diffusion in Separable d-Dimensional Quasiperiodic Tilings
We study the electronic transport in quasiperiodic separable tight-binding
models in one, two, and three dimensions. First, we investigate a
one-dimensional quasiperiodic chain, in which the atoms are coupled by weak and
strong bonds aligned according to the Fibonacci chain. The associated
d-dimensional quasiperiodic tilings are constructed from the product of d such
chains, which yields either the square/cubic Fibonacci tiling or the labyrinth
tiling. We study the scaling behavior of the mean square displacement and the
return probability of wave packets with respect to time. We also discuss
results of renormalization group approaches and lower bounds for the scaling
exponent of the width of the wave packet.Comment: 6 pages, 4 figures, conference proceedings Aperiodic 2012 (Cairns
Determination of the laser-induced damage threshold of polymer optical fibers
Investigating the properties of manufactured polymer optical fibers is essential to determine proper areas of application. Using pulsed laser radiation, especially with respect to laser activity in optical fibers, the maximum acceptable transmittable energy without inducing damage is of particular interest. Therefore, this work is related to laser-induced damage in polymer optical fibers at a wavelength of 532 nm and a pulse duration of 7.3 ns. In particular, the influence of the coupling condition on the transmittable pulse energy and the damage behavior applying an R-on-1 test procedure are analyzed in this study. The obtained results give information about the long-Term behavior and will be used to optimize the manufacturing process. © COPYRIGHT SPI
Wave Functions, Quantum Diffusion, and Scaling Exponents in Golden-Mean Quasiperiodic Tilings
We study the properties of wave functions and the wave-packet dynamics in
quasiperiodic tight-binding models in one, two, and three dimensions. The atoms
in the one-dimensional quasiperiodic chains are coupled by weak and strong
bonds aligned according to the Fibonacci sequence. The associated d-dimensional
quasiperiodic tilings are constructed from the direct product of d such chains,
which yields either the hypercubic tiling or the labyrinth tiling. This
approach allows us to consider rather large systems numerically. We show that
the wave functions of the system are multifractal and that their properties can
be related to the structure of the system in the regime of strong quasiperiodic
modulation by a renormalization group (RG) approach. We also study the dynamics
of wave packets to get information about the electronic transport properties.
In particular, we investigate the scaling behaviour of the return probability
of the wave packet with time. Applying again the RG approach we show that in
the regime of strong quasiperiodic modulation the return probability is
governed by the underlying quasiperiodic structure. Further, we also discuss
lower bounds for the scaling exponent of the width of the wave packet and
propose a modified lower bound for the absolute continuous regime.Comment: 25 pages, 13 figure
On the Representation Theory of an Algebra of Braids and Ties
We consider the algebra introduced by F. Aicardi and J.
Juyumaya as an abstraction of the Yokonuma-Hecke algebra. We construct a tensor
space representation for and show that this is faithful. We use
it to give a basis for and to classify its irreducible
representations.Comment: 24 pages. Final version. To appear in Journal of Algebraic
Combinatorics
Genetic partitioning of interleukin-6 signalling in mice dissociates Stat3 from Smad3-mediated lung fibrosis
Idiopathic pulmonary fibrosis (IPF) is a fatal disease that is unresponsive to current therapies and characterized by excessive collagen deposition and subsequent fibrosis. While inflammatory cytokines, including interleukin (IL)-6, are elevated in IPF, the molecular mechanisms that underlie this disease are incompletely understood, although the development of fibrosis is believed to depend on canonical transforming growth factor (TGF)-β signalling. We examined bleomycin-induced inflammation and fibrosis in mice carrying a mutation in the shared IL-6 family receptor gp130. Using genetic complementation, we directly correlate the extent of IL-6-mediated, excessive Stat3 activity with inflammatory infiltrates in the lung and the severity of fibrosis in corresponding gp130757F mice. The extent of fibrosis was attenuated in B lymphocyte-deficient gp130757F;µMT−/− compound mutant mice, but fibrosis still occurred in their Smad3−/− counterparts consistent with the capacity of excessive Stat3 activity to induce collagen 1α1 gene transcription independently of canonical TGF-β/Smad3 signalling. These findings are of therapeutic relevance, since we confirmed abundant STAT3 activation in fibrotic lungs from IPF patients and showed that genetic reduction of Stat3 protected mice from bleomycin-induced lung fibrosis
- …