29,811 research outputs found
A new formulation of compartmental epidemic modelling for arbitrary distributions of incubation and removal times
The paradigm for compartment models in epidemiology assumes exponentially
distributed incubation and removal times, which is not realistic in actual
populations. Commonly used variations with multiple exponentially distributed
variables are more flexible, yet do not allow for arbitrary distributions. We
present a new formulation, focussing on the SEIR concept that allows to include
general distributions of incubation and removal times. We compare the solution
to two types of agent-based model simulations, a spatially homogeneous one
where infection occurs by proximity, and a model on a scale-free network with
varying clustering properties, where the infection between any two agents
occurs via their link if it exists. We find good agreement in both cases.
Furthermore a family of asymptotic solutions of the equations is found in terms
of a logistic curve, which after a non-universal time shift, fits extremely
well all the microdynamical simulations. The formulation allows for a simple
numerical approach; software in Julia and Python is provided.Comment: 21 pages, 11 figures. v2 matches published version: improved
presentation (including title, abstract and references), results and
conclusions unchange
Mid-Infrared Observations of Planetary Nebulae detected in the GLIMPSE 3D Survey
We present mapping, profiles and photometry for 24 planetary nebulae (PNe)
detected in the GLIMPSE 3D mid-infrared (MIR) survey of the Galactic plane. The
PNe show many of the properties observed in previous studies of these sources,
including evidence for longer wave emission from outside of the ionised zones,
a likely consequence of emission from polycyclic aromatic hydrocarbons (PAHs)
within the nebular photo-dissociation regimes (PDRs). We also note variations
in 5.8/4.5 and 8.0/4.5 microns flux ratios with distance from the nuclei;
present evidence for enhanced MIR emission in the halos of the sources; and
note evidence for variations in colour with nebular evolution.Comment: 35 pages, 28 figures, Accepted for publication in Revista Mexicana de
Astronomia y Astrofisica (RevMexAA). 61 pages in arXi
Partial dynamical symmetry as a selection criterion for many-body interactions
We propose the use of partial dynamical symmetry (PDS) as a selection
criterion for higher-order terms in situations when a prescribed symmetry is
obeyed by some states and is strongly broken in others. The procedure is
demonstrated in a first systematic classification of many-body interactions
with SU(3) PDS that can improve the description of deformed nuclei. As an
example, the triaxial features of the nucleus 156Gd are analyzed.Comment: 5 pages, 3 figures, Phys. Rev. C, in pres
Intrinsic structure of two-phonon states in the interacting boson model
A general study of excitations up to two-phonon states is carried out using
the intrinsic-state formalism of the Interacting Boson Model (IBM). Spectra and
transitions for the different dynamical symmetries are analyzed and the
correspondence with states in the laboratory frame is established. The
influence of multi-phonon states is discussed. The approach is useful in
problems where the complexity of the IBM spectrum renders the analysis in the
laboratory frame difficult.Comment: 22 pages, TeX (ReVTeX). 7 eps figures. Submitted to Nucl. Phys.
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