28,987 research outputs found
Finite-temperature time-dependent variation with multiple Davydov states
The Dirac-Frenkel time-dependent variational approach with Davydov Ans\"atze
is a sophisticated, yet efficient technique to obtain an acuurate solution to
many-body Schr\"odinger equations for energy and charge transfer dy- namics in
molecular aggregates and light-harvesting complexes. We extend this variational
approach to finite temperatures dynamics of the spin-boson model by adopting a
Monte Carlo importance sampling method. In or- der to demonstrate the
applicability of this approach, we compare real-time quantum dynamics of the
spin-boson model calculated with that from numerically exact iterative
quasiadiabatic propagator path integral (QUAPI) technique. The comparison shows
that our variational approach with the single Davydov Ans\"atze is in excellent
agreement with the QUAPI method at high temperatures, while the two differ at
low temperatures. Accuracy in dynamics calculations employing a multitude of
Davydov trial states is found to improve substantially over the single Davydov
Ansatz, especially at low temperatures. At a moderate computational cost, our
variational approach with the multiple Davydov Ansatz is shown to provide
accurate spin-boson dynamics over a wide range of temperatures and bath
spectral densities.Comment: 8 pages, 3 figure
Is attending a mental process?
The nature of attention has been the topic of a lively research programme in psychology for over a century. But there is widespread agreement that none of the theories on offer manage to fully capture the nature of attention. Recently, philosophers have become interested in the debate again after a prolonged period of neglect. This paper contributes to the project of explaining the nature of attention. It starts off by critically examining Christopher Mole’s prominent “adverbial” account of attention, which traces the failure of extant psychological theories to their assumption that attending is a kind of process. It then defends an alternative, process-based view of the metaphysics of attention, on which attention is understood as an activity and not, as psychologists seem to implicitly assume, an accomplishment. The entrenched distinction between accomplishments and activities is shown to shed new light on the metaphysics of attention. It also provides a novel diagnosis of the empirical state of play
Cosmological constraints on the generalized holographic dark energy
We use the Markov ChainMonte Carlo method to investigate global constraints
on the generalized holographic (GH) dark energy with flat and non-flat universe
from the current observed data: the Union2 dataset of type supernovae Ia
(SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data
(OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation
(BAO), and the cosmic microwave background (CMB) data. The most stringent
constraints on the GH model parameter are obtained. In addition, it is found
that the equation of state for this generalized holographic dark energy can
cross over the phantom boundary wde =-1.Comment: 14 pages, 5 figures. arXiv admin note: significant text overlap with
arXiv:1105.186
WHAM Observations of H-alpha Emission from High Velocity Clouds in the M, A, and C Complexes
The first observations of the recently completed Wisconsin H-Alpha Mapper
(WHAM) facility include a study of emission lines from high velocity clouds in
the M, A, and C complexes, with most of the observations on the M I cloud. We
present results including clear detections of H-alpha emission from all three
complexes with intensities ranging from 0.06 R to 0.20 R. In every observed
direction where there is significant high velocity H I gas seen in the 21 cm
line we have found associated ionized hydrogen emitting the H-alpha line. The
velocities of the H-alpha and 21 cm emission are well correlated in every case
except one, but the intensities are not correlated. There is some evidence that
the ionized gas producing the H-alpha emission envelopes the 21 cm emitting
neutral gas but the H-alpha "halo", if present, is not large. If the H-alpha
emission arises from the photoionization of the H I clouds, then the implied
Lyman continuum flux F_{LC} at the location of the clouds ranges from 1.3 to
4.2 x 10^5 photons cm^{-2} s^{-1}. If, on the other hand, the ionization is due
to a shock arising from the collision of the high-velocity gas with an ambient
medium in the halo, then the density of the pre-shocked gas can be constrained.
We have also detected the [S II] 6716 angstrom line from the M I cloud and have
evidence that the [S II] to H-alpha ratio varies with location on the cloud.Comment: 32 pages, 18 figures, to appear in ApJ (Sept. 10, 1998
On low temperature kinetic theory; spin diffusion, Bose Einstein condensates, anyons
The paper considers some typical problems for kinetic models evolving through
pair-collisions at temperatures not far from absolute zero, which illustrate
specific quantum behaviours. Based on these examples, a number of differences
between quantum and classical Boltzmann theory is then discussed in more
general terms.Comment: 25 pages, minor updates of previous versio
Learning Optimal Deep Projection of F-FDG PET Imaging for Early Differential Diagnosis of Parkinsonian Syndromes
Several diseases of parkinsonian syndromes present similar symptoms at early
stage and no objective widely used diagnostic methods have been approved until
now. Positron emission tomography (PET) with F-FDG was shown to be able
to assess early neuronal dysfunction of synucleinopathies and tauopathies.
Tensor factorization (TF) based approaches have been applied to identify
characteristic metabolic patterns for differential diagnosis. However, these
conventional dimension-reduction strategies assume linear or multi-linear
relationships inside data, and are therefore insufficient to distinguish
nonlinear metabolic differences between various parkinsonian syndromes. In this
paper, we propose a Deep Projection Neural Network (DPNN) to identify
characteristic metabolic pattern for early differential diagnosis of
parkinsonian syndromes. We draw our inspiration from the existing TF methods.
The network consists of a (i) compression part: which uses a deep network to
learn optimal 2D projections of 3D scans, and a (ii) classification part: which
maps the 2D projections to labels. The compression part can be pre-trained
using surplus unlabelled datasets. Also, as the classification part operates on
these 2D projections, it can be trained end-to-end effectively with limited
labelled data, in contrast to 3D approaches. We show that DPNN is more
effective in comparison to existing state-of-the-art and plausible baselines.Comment: 8 pages, 3 figures, conference, MICCAI DLMIA, 201
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