4,236 research outputs found
Regularity of Bound States
We study regularity of bound states pertaining to embedded eigenvalues of a
self-adjoint operator , with respect to an auxiliary operator that is
conjugate to in the sense of Mourre. We work within the framework of
singular Mourre theory which enables us to deal with confined massless
Pauli-Fierz models, our primary example, and many-body AC-Stark Hamiltonians.
In the simpler context of regular Mourre theory our results boils down to an
improvement of results obtained recently in \cite{CGH}.Comment: 70 page
Self-consistent massive disks in triaxial dark matter halos
Galactic disks in triaxial dark matter halos become deformed by the
elliptical potential in the plane of the disk in such a way as to counteract
the halo ellipticity. We develop a technique to calculate the equilibrium
configuration of such a disk in the combined disk-halo potential, which is
based on the method of Jog (2000) but accounts for the radial variation in both
the halo potential and the disk ellipticity. This crucial ingredient results in
qualitatively different behavior of the disk: the disk circularizes the
potential at small radii, even for a reasonably low disk mass. This effect has
important implications for proposals to reconcile cuspy halo density profiles
with low surface brightness galaxy rotation curves using halo triaxiality. The
disk ellipticities in our models are consistent with observational estimates
based on two-dimensional velocity fields and isophotal axis ratios.Comment: ApJ, in pres
Reduced dimensionality spin-orbit dynamics of CH3 + HCl reversible arrow CH4 Cl on ab initio surfaces
A reduced dimensionality quantum scattering method is extended to the study of spin-orbit nonadiabatic transitions in the CH3 + HCl reversible arrow CH4 + Cl(P-2(J)) reaction. Three two-dimensional potential energy surfaces are developed by fitting a 29 parameter double-Morse function to CCSD(T)/IB//MP2/cc-pV(T+d)Z-dk ab initio data; interaction between surfaces is described by geometry-dependent spin-orbit coupling functions fit to MCSCF/cc-pV(T+d)Z-dk ab initio data. Spectator modes are treated adiabatically via inclusion of curvilinear projected frequencies. The total scattering wave function is expanded in a vibronic basis set and close-coupled equations are solved via R-matrix propagation. Ground state thermal rate constants for forward and reverse reactions agree well with experiment. Multi-surface reaction probabilities, integral cross sections, and initial-state selected branching ratios all highlight the importance of vibrational energy in mediating nonadiabatic transition. Electronically excited state dynamics are seen to play a small but significant role as consistent with experimental conclusions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3592732
Exploratory studies to inform full-scale evaluations of complex public health interventions: the need for guidance
No abstract available
Oxygen in Open Cluster Dwarfs: Pleiades and M34
We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] lambda6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]6300=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]Trip at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures
Two-photon photoassociation spectroscopy of CsYb: Ground-state interaction potential and interspecies scattering lengths
We perform two-photon photoassociation spectroscopy of the heteronuclear CsYb molecule to measure the binding energies of near-threshold vibrational levels of the X 2+ 1/2 molecular ground state. We report results for 133Cs170Yb, 133Cs173Yb, and 133Cs174Yb, in each case determining the energy of several vibrational levels including the least-bound state. We fit an interaction potential based on electronic structure calculations to the binding energies for all three isotopologs and find that the ground-state potential supports 77 vibrational levels. We use the fitted potential to predict the interspecies s-wave scattering lengths for all seven Cs+Yb isotopic mixtures
Dancing to the Partisan Beat: A First Analysis of Political Communication on TikTok
TikTok is a video-sharing social networking service, whose popularity is
increasing rapidly. It was the world's second-most downloaded app in 2019.
Although the platform is known for having users posting videos of themselves
dancing, lip-syncing, or showcasing other talents, user-videos expressing
political views have seen a recent spurt. This study aims to perform a primary
evaluation of political communication on TikTok. We collect a set of US
partisan Republican and Democratic videos to investigate how users communicated
with each other about political issues. With the help of computer vision,
natural language processing, and statistical tools, we illustrate that
political communication on TikTok is much more interactive in comparison to
other social media platforms, with users combining multiple information
channels to spread their messages. We show that political communication takes
place in the form of communication trees since users generate branches of
responses to existing content. In terms of user demographics, we find that
users belonging to both the US parties are young and behave similarly on the
platform. However, Republican users generated more political content and their
videos received more responses; on the other hand, Democratic users engaged
significantly more in cross-partisan discussions.Comment: Accepted as a full paper at the 12th International ACM Web Science
Conference (WebSci 2020). Please cite the WebSci version; Second version
includes corrected typo
Criteria for the use of omics-based predictors in clinical trials.
The US National Cancer Institute (NCI), in collaboration with scientists representing multiple areas of expertise relevant to 'omics'-based test development, has developed a checklist of criteria that can be used to determine the readiness of omics-based tests for guiding patient care in clinical trials. The checklist criteria cover issues relating to specimens, assays, mathematical modelling, clinical trial design, and ethical, legal and regulatory aspects. Funding bodies and journals are encouraged to consider the checklist, which they may find useful for assessing study quality and evidence strength. The checklist will be used to evaluate proposals for NCI-sponsored clinical trials in which omics tests will be used to guide therapy
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