733 research outputs found
The Dipole Coupling of Atoms and Light in Gravitational Fields
The dipole coupling term between a system of N particles with total charge
zero and the electromagnetic field is derived in the presence of a weak
gravitational field. It is shown that the form of the coupling remains the same
as in flat space-time if it is written with respect to the proper time of the
observer and to the measurable field components. Some remarks concerning the
connection between the minimal and the dipole coupling are given.Comment: 10 pages, LaTe
The local structure of OH species on the V2O3(0 0 0 1) surface: a scanned-energy mode photoelectron diffraction study
Scanned-energy mode photoelectron diffraction (PhD), using O 1s photoemission, together with multiple-scattering simulations, have been used to investigate the structure of the hydroxyl species, OH, adsorbed on a V2O3(0 0 0 1) surface. Surface OH species were obtained by two alternative methods; reaction with molecular water and exposure to atomic H resulted in closely similar PhD spectra. Both qualitative assessment and the results of multiple-scattering calculations are consistent with a model in which only the O atoms of outermost layer of the oxide surface are hydroxylated. These results specifically exclude significant coverage of OH species atop the outermost V atoms, i.e. in vanadyl O atom sites. Ab initio density-functional theory cluster calculations provide partial rationalisation of this result, which is discussed the context of the general understanding of this system
Statistical methods for estimating historical fire frequency from multiple fire-scar data
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
Stochastic Model for Surface Erosion Via Ion-Sputtering: Dynamical Evolution from Ripple Morphology to Rough Morphology
Surfaces eroded by ion-sputtering are sometimes observed to develop
morphologies which are either ripple (periodic), or rough (non-periodic). We
introduce a discrete stochastic model that allows us to interpret these
experimental observations within a unified framework. We find that a periodic
ripple morphology characterizes the initial stages of the evolution, whereas
the surface displays self-affine scaling in the later time regime. Further, we
argue that the stochastic continuum equation describing the surface height is a
noisy version of the Kuramoto-Sivashinsky equation.Comment: 4 pages, 7 postscript figs., Revtex, to appear in Phys. Rev. Let
Design features of the upcoming Coastal and Ocean Basin in Ostend, Belgium, for marine renewable energy applications
The new Coastal and Ocean Basin (COB) located at the Greenbridge Science Park in Ostend, Belgium is under construction since February 2017. The laboratory will provide a versatile facility that will make a wide range of physical modelling studies possible, including the ability to generate waves in combination with currents and wind at a wide range of model scales. The facility is serving the needs in Flanders, Belgium, in the fields of mainly offshore renewable energy and coastal engineering. The COB will allow users to conduct tests for coastal and offshore engineering research and commercial projects. The basin will have state-of-the-art generating and absorbing wavemakers, a current generation system, and a wind generator. It will be possible to generate waves and currents in the same, opposite and oblique directions. The basin is expected to be operational in 2019. This paper presents an overview of the basin’s capabilities, the ongoing work, and selected results from the design of the COB
Gamma rays from the annihilation of singlet scalar dark matter
We consider an extension of the Standard Model by a singlet scalar that
accounts for the dark matter of the Universe. Within this model we compute the
expected gamma ray flux from the annihilation of dark matter particles in a
consistent way. To do so, an updated analysis of the parameter space of the
model is first presented. By enforcing the relic density constraint from the
very beginning, the viable parameter space gets reduced to just two variables:
the singlet mass and the higgs mass. Current direct detection constraints are
then found to require a singlet mass larger than 50 GeV. Finally, we compute
the gamma ray flux and annihilation cross section and show that a large
fraction of the viable parameter space lies within the sensitivity of
Fermi-GLAST.Comment: 13 pages, 5 figures. v2: minor modifications to text and figures;
main results unchanged. v3: some references adde
Determining the WIMP mass using the complementarity between direct and indirect searches and the ILC
We study the possibility of identifying dark matter properties from
XENON-like 100 kg experiments and the GLAST satellite mission. We show that
whereas direct detection experiments will probe efficiently light WIMPs, given
a positive detection (at the 10% level for GeV), GLAST
will be able to confirm and even increase the precision in the case of a NFW
profile, for a WIMP-nucleon cross-section
pb. We also predict the rate of production of a WIMP in the next generation of
colliders (ILC), and compare their sensitivity to the WIMP mass with the XENON
and GLAST projects.Comment: 32 pages, new figures and a more detailed statistical analysis. Final
version to appear in JCA
Dog ownership and physical activity: A review of the evidence
Background: Dog walking is a strategy for increasing population levels of physical activity (PA). Numerous cross-sectional studies of the relationship between dog ownership and PA have been conducted. The purpose was to review studies comparing PA of dog owners (DO) to nondog owners (NDO), summarize the prevalence of dog walking, and provide recommendations for research. Methods: A review of published studies (1990-2010) examining DO and NDO PA and the prevalence of dog walking was conducted (N = 29). Studies estimating the relationship between dog ownership and PA were grouped to create a pointestimate using meta-analysis. Results: Most studies were conducted in the last 5 years, were cross-sectional, and sampled adults from Australia or the United States. Approximately 60% of DO walked their dog, with a median duration and frequency of 160 minutes/week and 4 walks/week, respectively. Meta-analysis showed DO engage in more walking and PA than NDO and the effect sizes are small to moderate (d = 0.26 and d = 0.16, respectively). Three studies provided evidence of a directional relationship between dog ownership and walking. Conclusions: Longitudinal and interventional studies would provide stronger causal evidence for the relationship between dog ownership and PA. Improved knowledge of factors associated with dog walking will guide intervention research
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