782 research outputs found
Editorial: Coauthors gone bad; how to avoid publishing conflict and a proposed agreement for co-author teams
World Vaping Day: Contextualizing Vaping Culture in Online Social Media Using a Mixed Methods Approach
Few studies have demonstrated the use of mixed methods research to contextualize health topics using primary data from social media. To address this gap in the methodological literature, we present research about electronic nicotine delivery systems, using Twitter data from “World Vaping Day.” To engage with the quantitative breadth and qualitative depth of 5,149 collected tweets, we utilized a convergent parallel mixed methods framework, integrating thematic prevalence estimates with phenomenological contextualization. Sentiment was more positive than negative across all categories except policy related. A total of 23% of tweets were promotional and relatively few tweets related to tobacco use (4.9%) or health concerns (4.2%). Salient themes included modifying or upgrading electronic nicotine delivery systems devices, and general mistrust of public health advocates and tobacco companies. </jats:p
Hierarchy and Wave Functions in a Simple Quantum Cosmology
Astrophysical observations indicate the expansion of the universe is
accelerating. Applying the holographic entropy conjecture to the cosmological
horizon in an accelerating universe suggests the universe has only a finite
number of degrees of freedom. This is consistent with a closed universe arising
from a quantum fluctuation, with zero total quantum numbers. If space-time has
eleven dimensions, and the universe began as a closed force-symmetric
ten-dimensional space with characteristic dimension L, seven of the space
dimensions must have collapsed to generate the three large space dimensions we
see. The holographic conjecture then suggests the initial length scale L must
be roughly twenty orders of magnitude larger than the Planck length.
Accordingly, the nuclear force must be roughly forty orders of magnitude
stronger than gravity, possibly resolving the force hierarchy problem. A
wavefunction for the radius of curvature of the universe can be obtained from
the Schrodinger equation derived by Elbaz and Novello. The product of this
wavefunction and its complex conjugate can be interpreted as the probability
density for finding a given radius of curvature in one of the infinity of
measurements of the radius of curvature possible (in principle) at any location
in a homogeneous isotropic universe.Comment: 4 pages, no figures, abstract corrected to insert omitted word
On the Accuracy of the Semiclassical Trace Formula
The semiclassical trace formula provides the basic construction from which
one derives the semiclassical approximation for the spectrum of quantum systems
which are chaotic in the classical limit. When the dimensionality of the system
increases, the mean level spacing decreases as , while the
semiclassical approximation is commonly believed to provide an accuracy of
order , independently of d. If this were true, the semiclassical trace
formula would be limited to systems in d <= 2 only. In the present work we set
about to define proper measures of the semiclassical spectral accuracy, and to
propose theoretical and numerical evidence to the effect that the semiclassical
accuracy, measured in units of the mean level spacing, depends only weakly (if
at all) on the dimensionality. Detailed and thorough numerical tests were
performed for the Sinai billiard in 2 and 3 dimensions, substantiating the
theoretical arguments.Comment: LaTeX, 31 pages, 14 figures, final version (minor changes
Correlation Widths in Quantum--Chaotic Scattering
An important parameter to characterize the scattering matrix S for
quantum-chaotic scattering is the width Gamma_{corr} of the S-matrix
autocorrelation function. We show that the "Weisskopf estimate" d/(2pi) sum_c
T_c (where d is the mean resonance spacing, T_c with 0 <= T_c <= 1 the
"transmission coefficient" in channel c and where the sum runs over all
channels) provides a very good approximation to Gamma_{corr} even when the
number of channels is small. That same conclusion applies also to the
cross-section correlation function
Dynamical effects of the neutrino gravitational clustering at Planck angular scales
We study the CMB anisotropy induced by the non-linear perturbations in the
massive neutrino density associated to the non-linear gravitational clustering
proceses. Our results show that for the neutrino fraction in agreement with
that indicated by the astroparticle and nuclear physics experiments and a
cosmological accreting mass comparable with the mass of known clusters, the
angular resolution and the sensitivity of the CMB anisotropy measurements from
the Planck surveyor will allow the detection of the dynamical effects of the
neutrino gravitational clustering.Comment: 40 pages and 12 figures, submitted to ApJ (14 March 2002
Ultra-light Axions: Degeneracies with Massive Neutrinos and Forecasts for Future Cosmological Observations
A generic prediction of string theory is the existence of many axion fields.
It has recently been argued that many of these fields should be light and, like
the well known QCD axion, lead to observable cosmological consequences. In this
paper we study in detail the effect of the so-called string axiverse on large
scale structure, focusing on the morphology and evolution of density
perturbations, anisotropies in the cosmic microwave background and weak
gravitational lensing of distant galaxies. We quantify specific effects that
will arise from the presence of the axionic fields and highlight possible
degeneracies that may arise in the presence of massive neutrinos. We take
particular care understanding the different physical effects and scales that
come into play. We then forecast how the string axiverse may be constrained and
show that with a combination of different observations, it should be possible
to detect a fraction of ultralight axions to dark matter of a few percent.Comment: 24 pages, 16 figures, this version: corrected typos, some comments
added, matches published versio
Molecules in external fields: a semiclassical analysis
We undertake a semiclassical analysis of the spectral properties (modulations
of photoabsorption spectra, energy level statistics) of a simple Rydberg
molecule in static fields within the framework of Closed-Orbit/Periodic-Orbit
theories. We conclude that in addition to the usual classically allowed orbits
one must consider classically forbidden diffractive paths. Further, the
molecule brings in a new type of 'inelastic' diffractive trajectory, different
from the usual 'elastic' diffractive orbits encountered in previous studies of
atomic and analogous systems such as billiards with point-scatterers. The
relative importance of inelastic versus elastic diffraction is quantified by
merging the usual Closed Orbit theory framework with molecular quantum defect
theory.Comment: 4 pages, 3 figure
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