23,632 research outputs found
Hydrophobic interactions with coarse-grained model for water
Integral equation theory is applied to a coarse-grained model of water to
study potential of mean force between hydrophobic solutes. Theory is shown to
be in good agreement with the available simulation data for methane-methane and
fullerene-fullerene potential of mean force in water; the potential of mean
force is also decomposed into its entropic and enthalpic contributions. Mode
coupling theory is employed to compute self-diffusion coefficient of water, as
well as diffusion coefficient of a dilute hydrophobic solute; good agreement
with molecular dynamics simulation results is found
Dissipation Layers in Rayleigh-B\'{e}nard Convection: A Unifying View
Boundary layers play an important role in controlling convective heat
transfer. Their nature varies considerably between different application areas
characterized by different boundary conditions, which hampers a uniform
treatment. Here, we argue that, independent from boundary conditions,
systematic dissipation measurements in Rayleigh-B\'enard convection capture the
relevant near-wall structures. By means of direct numerical simulations with
varying Prandtl numbers, we demonstrate that such dissipation layers share
central characteristics with classical boundary layers, but, in contrast to the
latter, can be extended naturally to arbitrary boundary conditions. We validate
our approach by explaining differences in scaling behavior observed for no-slip
and stress-free boundaries, thus paving the way to an extension of scaling
theories developed for laboratory convection to a broad class of natural
systems
EEG source imaging assists decoding in a face recognition task
EEG based brain state decoding has numerous applications. State of the art
decoding is based on processing of the multivariate sensor space signal,
however evidence is mounting that EEG source reconstruction can assist
decoding. EEG source imaging leads to high-dimensional representations and
rather strong a priori information must be invoked. Recent work by Edelman et
al. (2016) has demonstrated that introduction of a spatially focal source space
representation can improve decoding of motor imagery. In this work we explore
the generality of Edelman et al. hypothesis by considering decoding of face
recognition. This task concerns the differentiation of brain responses to
images of faces and scrambled faces and poses a rather difficult decoding
problem at the single trial level. We implement the pipeline using spatially
focused features and show that this approach is challenged and source imaging
does not lead to an improved decoding. We design a distributed pipeline in
which the classifier has access to brain wide features which in turn does lead
to a 15% reduction in the error rate using source space features. Hence, our
work presents supporting evidence for the hypothesis that source imaging
improves decoding
Dynamic glass transition: bridging the gap between mode-coupling theory and the replica approach
We clarify the relation between the ergodicity breaking transition predicted
by mode-coupling theory and the so-called dynamic transition predicted by the
static replica approach. Following Franz and Parisi [Phys. Rev. Lett. 79, 2486
(1997)], we consider a system of particles in a metastable state characterized
by non-trivial correlations with a quenched configuration. We show that the
assumption that in a metastable state particle currents vanish leads to an
expression for the replica off-diagonal direct correlation function in terms of
a replica off-diagonal static four-point correlation function. A factorization
approximation for this function results in an approximate closure for the
replica off-diagonal direct correlation function. The replica off-diagonal
Ornstein-Zernicke equation combined with this closure coincides with the
equation for the non-ergodicity parameter derived using the mode-coupling
theory.Comment: revised version; to be published in EP
Role of structural relaxations and vibrational excitations in the high-frequency dynamics of liquids and glasses
We present theoretical investigation on the high-frequency collective
dynamics in liquids and glasses at microscopic length scales and terahertz
frequency region based on the mode-coupling theory for ideal liquid-glass
transition. We focus on recently investigated issues from
inelastic-X-ray-scattering and computer-simulation studies for dynamic
structure factors and longitudinal and transversal current spectra: the
anomalous dispersion of the high-frequency sound velocity and the nature of the
low-frequency excitation called the boson peak. It will be discussed how the
sound mode interferes with other low-lying modes present in the system.
Thereby, we provide a systematic explanation of the anomalous sound-velocity
dispersion in systems -- ranging from high temperature liquid down to deep
inside the glass state -- in terms of the contributions from the
structural-relaxation processes and from vibrational excitations called the
anomalous-oscillation peak (AOP). A possibility of observing negative
dispersion -- the {\em decrease} of the sound velocity upon increase of the
wave number -- is argued when the sound-velocity dispersion is dominated by the
contribution from the vibrational dynamics. We also show that the low-frequency
excitation, observable in both of the glass-state longitudinal and transversal
current spectra at the same resonance frequency, is the manifestation of the
AOP. As a consequence of the presence of the AOP in the transversal current
spectra, it is predicted that the transversal sound velocity also exhibits the
anomalous dispersion. These results of the theory are demonstrated for a model
of the Lennard-Jones system.Comment: 25 pages, 22 figure
Structural and Dynamical Anomalies of a Gaussian Core Fluid: a Mode Coupling Theory Study
We present a theoretical study of transport properties of a liquid comprised
of particles uist1:/home/sokrates/egorov/oldhome/Pap41/Submit > m abs.tex We
present a theoretical study of transport properties of a liquid comprised of
particles interacting via Gaussian Core pair potential. Shear viscosity and
self-diffusion coefficient are computed on the basis of the mode-coupling
theory, with required structural input obtained from integral equation theory.
Both self-diffusion coefficient and viscosity display anomalous density
dependence, with diffusivity increasing and viscosity decreasing with density
within a particular density range along several isotherms below a certain
temperature. Our theoretical results for both transport coefficients are in
good agreement with the simulation data
Quantum scissors: teleportation of single-mode optical states by means of a nonlocal single photon
We employ the quantum state of a single photon entangled with the vacuum
(|1,0>-|0,1>), generated by a photon incident upon a symmetric beam splitter,
to teleport single-mode quantum states of light by means of the Bennett
protocol. Teleportation of coherent states results in truncation of their Fock
expansion to the first two terms. We analyze the teleported ensembles by means
of homodyne tomography and obtain fidelities of up to 99 per cent for low
source state amplitudes. This work is an experimental realization of the
quantum scissors device proposed by Pegg, Phillips and Barnett (Phys. Rev.
Lett. 81, 1604 (1998)
Spatial correlations in sheared isothermal liquids : From elastic particles to granular particles
Spatial correlations for sheared isothermal elastic liquids and granular
liquids are theoretically investigated. Using the generalized fluctuating
hydrodynamics, correlation functions for both the microscopic scale and the
macroscopic scale are obtained. The existence of the long-range correlation
functions obeying power laws has been confirmed. The validity of our
theoretical predictions have been verified from the molecular dynamics
simulation.Comment: 34 pages, 12 figure
A spiral-like disk of ionized gas in IC 1459: Signature of a merging collision
The authors report the discovery of a large (15 kpc diameter) H alpha + (NII) emission-line disk in the elliptical galaxy IC 1459, showing weak spiral structure. The line flux peaks strongly at the nucleus and is more concentrated than the stellar continuum. The major axis of the disk of ionized gas coincides with that of the stellar body of the galaxy. The mass of the ionized gas is estimated to be approx. 1 times 10 (exp 5) solar mass, less than 1 percent of the total mass of gas present in IC 1459. The total gas mass of 4 times 10(exp 7) solar mass has been estimated from the dust mass derived from a broad-band color index image and the Infrared Astronomy Satellite (IRAS) data. The authors speculate that the presence of dust and gas in IC 1459 is a signature of a merger event
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