16,892 research outputs found
Towards an exact orbital-free single-particle kinetic energy density for the inhomogeneous electron liquid in the Be atom
Holas and March (Phys. Rev. A51, 2040 (1995)) wrote the gradient of the
one-body potential V(r) in terms of low-order derivatives of the idempotent
Dirac density matrix built from a single Slater determinant of Kohn-Sham
orbitals. Here, this is first combined with the study of Dawson and March (J.
Chem. Phys. 81, 5850 (1984)) to express the single-particle kinetic energy
density of the Be atom ground-state in terms of both the electron density n(r)
and potential V(r). While this is the more compact formulation, we then, by
removing V(r), demonstrate that the ratio t(r)/n(r) depends, though
non-locally, only on the single variable n'(r)/n(r), no high-order gradients
entering for the spherical Be atom.Comment: Submitted to Journal of Mathematical Chemistr
Gap anisotropy in the angle-resolved photoemission spectroscopy of Bi_2Sr_2CaCu_2O_{8+\delta}
The gap anisotropy in BiSrCaCuO is revisited in the
framework of a d-wave scenario in view of the recent angle-resolved
photoemission experiment. Based on a tight-binding fit to the normal state
dispersion, a detail analysis on the effects of the inclusion of the next
harmonic in the d-wave has been presented. Significant effect has been observed
in the superconducting T. The density of states is linear at the nodes with
enhanced weight, caused by a marked increase in the low energy excitaions which
affect the thermodynamics considerably. The slope of the curve in
the low temperature regime increases and the specific heat reflects the
enhanced entropy at low temperatures. The leading edge of the ARPES energy
distribution curves have been calculated and found to shift towards higher
energy. The effect of scattering by non-magnetic impurities in this context is
also outlined.Comment: 8 pages, 7 figures (akw.eps and edc.eps in one panel
Measuring Omega_0 with higher-order Quasar-Galaxy Correlations induced by Weak Lensing
Via the magnification bias, gravitational lensing by large-scale structures
causes angular cross-correlations between distant quasars and foreground
galaxies on angular scales of arc minutes and above. We investigate the
three-point cross-correlation between quasars and galaxy pairs measurable via
the second moment of the galaxy counts around quasars and show that it reaches
the level of a few per cent on angular scales near one arc minute. Combining
two- and three-point correlations, a skewness parameter can be defined which is
shown to be virtually independent on the shape and normalisation of the
dark-matter power spectrum. If the galaxy bias is linear and deterministic, the
skewness depends on the cosmic matter density parameter Omega_0 only;
otherwise, it can be used to probe the linearity and stochasticity of the bias.
We finally estimate the signal-to-noise ratio of a skewness determination and
find that around twenty thousand distant quasars e.g. from the Sloan Digital
Sky Survey should suffice for a direct measurement of Omega_0.Comment: 11 pages, 6 figures, submitted to Astronomy and Astrophysic
Cosmological Information from Quasar-Galaxy Correlations induced by Weak Lensing
The magnification bias of large-scale structures, combined with galaxy
biasing, leads to a cross-correlation of distant quasars with foreground
galaxies on angular scales of the order of arc minutes and larger. The
amplitude and angular shape of the cross-correlation function w_QG contain
information on cosmological parameters and the galaxy bias factor. While the
existence of this cross-correlation has firmly been established, existing data
did not allow an accurate measurement of w_QG yet, but wide area surveys like
the Sloan Digital Sky Survey now provide an ideal database for measuring it.
However, w_QG depends on several cosmological parameters and the galaxy bias
factor. We study in detail the sensitivity of w_QG to these parameters and
develop a strategy for using the data. We show that the parameter space can be
reduced to the bias factor b, Omega_0 and sigma_8, and compute the accuracy
with which these parameters can be deduced from SDSS data. Under reasonable
assumptions, it should be possible to reach relative accuracies of the order of
5%-15% for b, Omega_0, and sigma_8. This method is complementary to other
weak-lensing analyses based on cosmic shear.Comment: 11 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
Relating language examinations to the common European framework of reference for languages: learning, teaching, assessment (CEFR): a manual
Performance Analysis of Urban Cleaning Devices Using Human–Machine Interaction Method
Presently, several jobs require the collaboration of humans and machines to perform
different services and tasks. The ease and intuitiveness of the worker when using each machine
will not only improve the worker’s experience but also improve the company’s productivity and
the satisfaction that all users have. Specifically, electromechanical devices used to provide cleaning
services require complex interactions. These interactions determine the usability and performance of
devices. Therefore, devices must have appropriate ergonomic arrangements for human–machine
interactions. Otherwise, the desired performance cannot be achieved. This study analyzes the
performance of an urban cleaning device (pressure washer on a power take-off van) using human–
machine interaction method. The method measures visceral and behavioral levels (set by Norman)
and service times. Using these measurements, the usability of the pressure washer is determined
according to different factors that facilitate the operator’s well-being in the working environment.
A pressure washer from Feniks Cleaning and Safety, Limited Company, has been studied. Sixteen
errors related to ergonomics, usability and safety were identified in this machine, which operates in
more than 40 locations in Spain. Therefore, this study provides valuable information on the usability
and performance of pressure washers, as well as possibilities for improvement
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Eyewitness suggestibility across presentation modalities
Misleading post-event information--Cognitive processing differences
CAD and creativity: does the computer really help?
We are frequently told by its exponents that computeraided design (CAD) liberates designers and gives them new ways of envisioning their work, but is this really true? CAD in architecture is examined to see to what extent it has enhanced creativity in design. This is partly
done by applying a test of creativity advanced by contemporary architect Herman Hertzberger. In this analysis, CAD is found somewhat wanting,
and some suggestions are made as to why this might be so
Bayesian detection of piecewise linear trends in replicated time-series with application to growth data modelling
We consider the situation where a temporal process is composed of contiguous
segments with differing slopes and replicated noise-corrupted time series
measurements are observed. The unknown mean of the data generating process is
modelled as a piecewise linear function of time with an unknown number of
change-points. We develop a Bayesian approach to infer the joint posterior
distribution of the number and position of change-points as well as the unknown
mean parameters. A-priori, the proposed model uses an overfitting number of
mean parameters but, conditionally on a set of change-points, only a subset of
them influences the likelihood. An exponentially decreasing prior distribution
on the number of change-points gives rise to a posterior distribution
concentrating on sparse representations of the underlying sequence. A
Metropolis-Hastings Markov chain Monte Carlo (MCMC) sampler is constructed for
approximating the posterior distribution. Our method is benchmarked using
simulated data and is applied to uncover differences in the dynamics of fungal
growth from imaging time course data collected from different strains. The
source code is available on CRAN.Comment: Accepted to International Journal of Biostatistic
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