1,258 research outputs found
Connections of activated hopping processes with the breakdown of the Stokes-Einstein relation and with aspects of dynamical heterogeneities
We develop a new extended version of the mode-coupling theory (MCT) for glass
transition, which incorporates activated hopping processes via the dynamical
theory originally formulated to describe diffusion-jump processes in crystals.
The dynamical-theory approach adapted here to glass-forming liquids treats
hopping as arising from vibrational fluctuations in quasi-arrested state where
particles are trapped inside their cages, and the hopping rate is formulated in
terms of the Debye-Waller factors characterizing the structure of the
quasi-arrested state. The resulting expression for the hopping rate takes an
activated form, and the barrier height for the hopping is ``self-generated'' in
the sense that it is present only in those states where the dynamics exhibits a
well defined plateau. It is discussed how such a hopping rate can be
incorporated into MCT so that the sharp nonergodic transition predicted by the
idealized version of the theory is replaced by a rapid but smooth crossover. We
then show that the developed theory accounts for the breakdown of the
Stokes-Einstein relation observed in a variety of fragile glass formers. It is
also demonstrated that characteristic features of dynamical heterogeneities
revealed by recent computer simulations are reproduced by the theory. More
specifically, a substantial increase of the non-Gaussian parameter, double-peak
structure in the probability distribution of particle displacements, and the
presence of a growing dynamic length scale are predicted by the extended MCT
developed here, which the idealized version of the theory failed to reproduce.
These results of the theory are demonstrated for a model of the Lennard-Jones
system, and are compared with related computer-simulation results and
experimental data.Comment: 13 pages, 5 figure
Nearest neighbor embedding with different time delays
A nearest neighbor based selection of time delays for phase space
reconstruction is proposed and compared to the standard use of time delayed
mutual information. The possibility of using different time delays for
consecutive dimensions is considered. A case study of numerically generated
solutions of the Lorenz system is used for illustration. The effect of
contamination with various levels of additive Gaussian white noise is
discussed.Comment: 4 pages, 5 figures, updated to final versio
Gating of high-mobility two-dimensional electron gases in GaAs/AlGaAs heterostructures
We investigate high-mobility two-dimensional electron gases in AlGaAs
heterostructures by employing Schottky-gate-dependent measurements of the
samples' electron density and mobility. Surprisingly, we find that two
different sample configurations can be set in situ with mobilities diering by a
factor of more than two in a wide range of densities. This observation is
discussed in view of charge redistributions between the doping layers and is
relevant for the design of future gateable high-mobility electron gases
Occupation, social support and quality of life in persons with schizophrenic or affective disorders
Abstract. : Background: : Most people suffering from severe mental illness (SMI) lack paid employment. This study investigates the relationship between work status and objective as well as subjective quality of life (QoL) in people with SMI. Methods: : The sample consists of 261 subjects (102 women, 159 men) aged 35 (men) and 38 (women) years on average, of whom 158 suffer from a schizophrenic disorder (ICD-10: F2) and 103 were diagnosed as having an affective disorder (ICD-10: F3). Subjective QoL was assessed with the WHOQOL-BREF scale. Results: : Subjects with an occupation in general have a larger social network at their disposal and receive more social support. With regard to income, few (12%) of the subjects with a job on the open labour market live below the poverty level, but many (28-38%) of those engaged in sheltered or other work-like activities do. Occupation ameliorates satisfaction with life domains referring to social integration (social relationships, environment), whereas the individual's well-being (psychological, physical) is hardly affected. Social support is an important mediator of the relationship between occupation and subjective QoL. Income is weakly and negatively related to subjective QoL. Conclusion: : Supportive relationships to colleagues at the workplace mainly explain the better subjective QoL of SMI people with an occupation.When designing specific employment possibilities for people with SMI, we should take notice of the social support dimension at the workplace. Mentally ill people have a substantial poverty risk, even when they are working. In particular, payment for sheltered work should be ameliorate
Evidence of secondary relaxations in the dielectric spectra of ionic liquids
We investigated the dynamics of a series of room temperature ionic liquids
based on the same 1-butyl-3-methyl imidazolium cation and different anions by
means of broadband dielectric spectroscopy covering 15 decades in frequency
(10^(-6)-10^9 Hz), and in the temperature range from 400 K down to 35 K. An
ionic conductivity is observed above the glass transition temperature T_{g}
with a relaxation in the electric modulus representation. Below T_{g}, two
relaxation processes appear, with the same features as the secondary
relaxations typically observed in molecular glasses. The activation energy of
the secondary processes and their dependence on the anion are different. The
slower process shows the characteristics of an intrinsic Johari-Goldstein
relaxation, in particular an activation energy E_{beta}=24k_{B}T_{g} is found,
as observed in molecular glasses.Comment: Major revision, submitted to Phys. Rev. Let
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.
Magnetic Miniband Structure and Quantum Oscillations in Lateral Semiconductor Superlattices
We present fully quantum-mechanical magnetotransport calculations for
short-period lateral superlattices with one-dimensional electrostatic
modulation. A non-perturbative treatment of both magnetic field and modulation
potential proves to be necessary to reproduce novel quantum oscillations in the
magnetoresistance found in recent experiments in the resistance component
parallel to the modulation potential. In addition, we predict oscillations of
opposite phase in the component perpendicular to the modulation not yet
observed experimentally. We show that the new oscillations originate from the
magnetic miniband structure in the regime of overlapping minibands.Comment: 6 pages with 4 figure
Network synchronization of groups
In this paper we study synchronized motions in complex networks in which
there are distinct groups of nodes where the dynamical systems on each node
within a group are the same but are different for nodes in different groups.
Both continuous time and discrete time systems are considered. We initially
focus on the case where two groups are present and the network has bipartite
topology (i.e., links exist between nodes in different groups but not between
nodes in the same group). We also show that group synchronous motions are
compatible with more general network topologies, where there are also
connections within the groups
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