806 research outputs found
Driven linear modes: Analytical solutions for finite discrete systems
We have obtained exact analytical expressions in closed form, for the linear
modes excited in finite and discrete systems that are driven by a spatially
homogeneous alternating field. Those modes are extended for frequencies within
the linear frequency band while they are either end-localized or end-avoided
for frequencies outside the linear frequency band. The analytical solutions are
resonant at particular frequencies, which compose the frequency dispersion
relation of the finite system.Comment: 4 pages, 3 figures, submitted to Phys. Rev.
Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation
We have studied by muon spin resonance ({\mu}SR) the helical ground state and
fluctuating chiral phase recently observed in the MnGe chiral magnet. At low
temperature, the muon polarization shows double period oscillations at short
time scales. Their analysis, akin to that recently developed for MnSi [A. Amato
et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field
distribution induced by the Mn helical order at the muon site. The refined muon
position agrees nicely with ab initio calculations. With increasing
temperature, an inhomogeneous fluctuating chiral phase sets in, characterized
by two well separated frequency ranges which coexist in the sample. Rapid and
slow fluctuations, respectively associated with short range and long range
ordered helices, coexist in a large temperature range below T = 170 K. We
discuss the results with respect to MnSi, taking the short helical period,
metastable quenched state and peculiar band structure of MnGe into account.Comment: 13 pages, 11 figure
Pattern formation and localization in the forced-damped FPU lattice
We study spatial pattern formation and energy localization in the dynamics of
an anharmonic chain with quadratic and quartic intersite potential subject to
an optical, sinusoidally oscillating field and a weak damping. The
zone-boundary mode is stable and locked to the driving field below a critical
forcing that we determine analytically using an approximate model which
describes mode interactions. Above such a forcing, a standing modulated wave
forms for driving frequencies below the band-edge, while a ``multibreather''
state develops at higher frequencies. Of the former, we give an explicit
approximate analytical expression which compares well with numerical data. At
higher forcing space-time chaotic patterns are observed.Comment: submitted to Phys.Rev.
Multicomponent analysis of T1 relaxation in bovine articular cartilage at low magnetic fields
European Unionâs Horizon 2020 Research and Innovation Programme; Grant/Award number 668119 (project âIDentIFYâ).Peer reviewedPublisher PD
Spatial patterns of desynchronization bursts in networks
We adapt a previous model and analysis method (the {\it master stability
function}), extensively used for studying the stability of the synchronous
state of networks of identical chaotic oscillators, to the case of oscillators
that are similar but not exactly identical. We find that bubbling induced
desynchronization bursts occur for some parameter values. These bursts have
spatial patterns, which can be predicted from the network connectivity matrix
and the unstable periodic orbits embedded in the attractor. We test the
analysis of bursts by comparison with numerical experiments. In the case that
no bursting occurs, we discuss the deviations from the exactly synchronous
state caused by the mismatch between oscillators
Recent NMR investigations on molecular dynamics of polymer melts in bulk and in confinement
Polymer dynamics in the melt state cover a wide range in time and frequency, for both molecular weights below and above the entanglement length. Nuclear Magnetic Resonance (NMR) offers a number of techniques that cover a broad section of this frequency range, with frequency dependent (i.e., magnetic field dependent) relaxometry providing the widest window. Combining fast field cycling techniques with frequency-temperature superposition has recently improved the understanding of polymer melt dynamics from the local to global range. At the same time, a detailed theoretical approach that separates intra- and intermolecular contributions to relaxation times has been developed. These methods are shown to improve the description of segmental dynamics in polymers, being related to time-dependent diffusion coefficients, and to distinguish between these two different relaxation contributions for a number of model compounds. The findings represent the foundation for a more thorough understanding of polymers under external restrictions and bear potential to provide a conceptually new access to biopolymer dynamics and interactions. © 2013 Elsevier Ltd
Condensation in Globally Coupled Populations of Chaotic Dynamical Systems
The condensation transition, leading to complete mutual synchronization in
large populations of globally coupled chaotic Roessler oscillators, is
investigated. Statistical properties of this transition and the cluster
structure of partially condensed states are analyzed.Comment: 11 pages, 4 figures, revte
Critical behavior of the Coulomb-glass model in the zero-disorder limit: Ising universality in a system with long-range interactions
The ordering of charges on half-filled hypercubic lattices is investigated
numerically, where electroneutrality is ensured by background charges. This
system is equivalent to the Ising lattice model with
antiferromagnetic interaction. The temperature dependences of specific
heat, mean staggered occupation, and of a generalized susceptibility indicate
continuous order-disorder phase transitions at finite temperatures in two- and
three-dimensional systems. In contrast, the susceptibility of the
one-dimensional system exhibits singular behavior at vanishing temperature. For
the two- and three-dimensional cases, the critical exponents are obtained by
means of a finite-size scaling analysis. Their values are consistent with those
of the Ising model with short-range interaction, and they imply that the
studied model cannot belong to any other known universality class. Samples of
up to 1400, , and sites are considered for dimensions 1 to 3,
respectively.Comment: revtex-file + 14 figures -> 10 pages; two references added, typos
correcte
A Tool to Recover Scalar Time-Delay Systems from Experimental Time Series
We propose a method that is able to analyze chaotic time series, gained from
exp erimental data. The method allows to identify scalar time-delay systems. If
the dynamics of the system under investigation is governed by a scalar
time-delay differential equation of the form ,
the delay time and the functi on can be recovered. There are no
restrictions to the dimensionality of the chaotic attractor. The method turns
out to be insensitive to noise. We successfully apply the method to various
time series taken from a computer experiment and two different electronic
oscillators
The HSE hybrid functional within the FLAPW method and its application to GdN
We present an implementation of the Heyd-Scuseria-Ernzerhof (HSE) hybrid
functional within the full-potential linearized augmented-plane-wave (FLAPW)
method. Pivotal to the HSE functional is the screened electron-electron
interaction, which we separate into the bare Coulomb interaction and the
remainder, a slowly varying function in real space. Both terms give rise to
exchange potentials, which sum up to the screened nonlocal exchange potential
of HSE. We evaluate the former with the help of an auxiliary basis, defined in
such a way that the bare Coulomb matrix becomes sparse. The latter is computed
in reciprocal space, exploiting its fast convergence behavior in reciprocal
space. This approach is general and can be applied to a whole class of screened
hybrid functionals. We obtain excellent agreement of band gaps and lattice
constants for prototypical semiconductors and insulators with
electronic-structure calculations using plane-wave or Gaussian basis sets. We
apply the HSE hybrid functional to examine the ground-state properties of
rocksalt GdN, which have been controversially discussed in literature. Our
results indicate that there is a half-metal to insulator transition occurring
between the theoretically optimized lattice constant at 0 K and the
experimental lattice constant at room temperature. Overall, we attain good
agreement with experimental data for band transitions, magnetic moments, and
the Curie temperature.Comment: 13 pages, 4 figures, 6 table
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