1,029 research outputs found
Molecular mode-coupling theory for supercooled liquids: Application to water
We present mode-coupling equations for the description of the slow dynamics
observed in supercooled molecular liquids close to the glass transition. The
mode-coupling theory (MCT) originally formulated to study the slow relaxation
in simple atomic liquids, and then extended to the analysis of liquids composed
by linear molecules, is here generalized to systems of arbitrarily shaped,
rigid molecules. We compare the predictions of the theory for the -vector
dependence of the molecular nonergodicity parameters, calculated by solving
numerically the molecular MCT equations in two different approximation schemes,
with ``exact'' results calculated from a molecular dynamics simulation of
supercooled water. The agreement between theory and simulation data supports
the view that MCT succeeds in describing the dynamics of supercooled molecular
liquids, even for network forming ones.Comment: 22 pages 4 figures Late
Influence of retardation effects on 2D magnetoplasmon spectrum
Within dissipationless limit the magnetic field dependence of magnetoplasmon
spectrum for unbounded 2DEG system found to intersect the cyclotron resonance
line, and, then approaches the frequency given by light dispersion relation.
Recent experiments done for macroscopic disc-shape 2DEG systems confirm theory
expectations.Comment: 2 pages,2 figure
The surface science of quasicrystals
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
(Some figures in this article are in colour only in the electronic version
A mode-coupling theory for the glassy dynamics of a diatomic probe molecule immersed in a simple liquid
Generalizing the mode-coupling theory for ideal liquid-glass transitions,
equations of motion are derived for the correlation functions describing the
glassy dynamics of a diatomic probe molecule immersed in a simple glass-forming
system. The molecule is described in the interaction-site representation and
the equations are solved for a dumbbell molecule consisting of two fused hard
spheres in a hard-sphere system. The results for the molecule's arrested
position in the glass state and the reorientational correlators for
angular-momentum index and near the glass transition are
compared with those obtained previously within a theory based on a
tensor-density description of the molecule in order to demonstrate that the two
approaches yield equivalent results. For strongly hindered reorientational
motion, the dipole-relaxation spectra for the -process can be mapped on
the dielectric-loss spectra of glycerol if a rescaling is performed according
to a suggestion by Dixon et al. [Phys. Rev. Lett. {\bf 65}, 1108 (1990)]. It is
demonstrated that the glassy dynamics is independent of the molecule's inertia
parameters.Comment: 19 pages, 10 figures, Phys. Rev. E, in prin
Profiling the educational value of computer games
There are currently a number of suggestions for educators to include computer games in formal teaching and learning contexts. Educational value is based on claims that games promote the development of complex learning. Very little research, however, has explored what features should be present in a computer game to make it valuable or conducive to learning. We present a list of required features for an educational game to be of value, informed by two studies, which integrated theories of Learning Environments and Learning Styles. A user survey showed that some requirements were typical of games in a particular genre, while other features were present across all genres. The paper concludes with a proposed framework of games and features within and across genres to assist in the design and selection of games for a given educational scenari
Test of the semischematic model for a liquid of linear molecules
We apply to a liquid of linear molecules the semischematic mode-coupling
model, previously introduced to describe the center of mass (COM) slow dynamics
of a network-forming molecular liquid. We compare the theoretical predictions
and numerical results from a molecular dynamics simulation, both for the time
and the wave-vector dependence of the COM density-density correlation function.
We discuss the relationship between the presented analysis and the results from
an approximate solution of the equations from molecular mode-coupling theory
[R. Schilling and T. Scheidsteger, Phys. Rev. E 56 2932 (1997)].Comment: Revtex, 10 pages, 4 figure
Probing the Sensitivity of Electron Wave Interference to Disorder-Induced Scattering in Solid-State Devices
The study of electron motion in semiconductor billiards has elucidated our
understanding of quantum interference and quantum chaos. The central assumption
is that ionized donors generate only minor perturbations to the electron
trajectories, which are determined by scattering from billiard walls. We use
magnetoconductance fluctuations as a probe of the quantum interference and show
that these fluctuations change radically when the scattering landscape is
modified by thermally-induced charge displacement between donor sites. Our
results challenge the accepted understanding of quantum interference effects in
nanostructures.Comment: 8 pages, 5 figures, Submitted to Physical Review
Molecular mode-coupling theory applied to a liquid of diatomic molecules
We study the molecular mode coupling theory for a liquid of diatomic
molecules. The equations for the critical tensorial nonergodicity parameters
and the critical amplitudes of the - relaxation
are solved up to a cut off = 2 without any
further approximations.
Here are indices of spherical harmonics. Contrary to previous studies,
where additional approximations were applied, we find in agreement with
simulations, that all molecular degrees of freedom vitrify at a single
temperature . The theoretical results for the non ergodicity parameters
and the critical amplitudes are compared with those from simulations. The
qualitative agreement is good for all molecular degrees of freedom. To study
the influence of the cut off on the non ergodicity parameter, we also calculate
the non ergodicity parameters for an upper cut off . In addition we
also propose a new method for the calculation of the critical nonergodicity
parameterComment: 27 pages, 17 figure
In-medium nucleon-nucleon potentials in configuration space
Based on the thermodynamic Green function approach two-nucleon correlations
in nuclear matter at finite temperatures are revisited. To this end, we derive
phase equivalent effective -space potentials that include the effect of the
Pauli blocking at a given temperature and density. These potentials enter into
a Schr\"odinger equation that is the -space representation of the
Galitskii-Feynman equation for two nucleons. We explore the analytical
structure of the equation in the complex -plane by means of Jost functions.
We find that despite the Mott effect the correlation with deuteron quantum
numbers are manifested as antibound states, i.e., as zeros of the Jost function
on the negative imaginary axis of the complex momentum space. The analysis
presented here is also suited for Coulombic systems.Comment: 6 pages, 1 table, 4 figure
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