14,602 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
Physical parameters of three field RR Lyrae stars
This work was partially supported by DGAPA–Universidad Nacional Autonoma de Mexico through project IN104612.Stromgren uvby - beta photometry of the stars classified as RR Lyrae stars RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their iron abundance, temperature, gravity and absolute magnitude. The stability of the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is addressed. The reddening of each star is estimated from the Stromgren colour indices and reddening sky maps. The results of three approaches to the determination of [Fe/H], T-eff and log(g) are discussed: Fourier light curve decomposition, the Preston Delta S index and the theoretical grids on the (b - y)(o) - c(10) plane.Peer reviewe
Controlled generation of large volumes of atmospheric clouds in a ground-based environmental chamber
Atmospheric clouds were generated in a 23,000 cubic meter environmental chamber as the first step in a two part study on the effects of contaminants on cloud formation. The generation procedure was modeled on the terrestrial generation mechanism so that naturally occurring microphysics mechanisms were operative in the cloud generation process. Temperature, altitude, liquid water content, and convective updraft velocity could be selected independently over the range of terrestrially realizable clouds. To provide cloud stability, a cotton muslin cylinder 29.3 meters in diameter and 24.2 meters high was erected within the chamber and continuously wetted with water at precisely the same temperature as the cloud. The improved instrumentation which permitted fast, precise, and continual measurements of cloud temperature and liquid water content is described
Off-Mass-Shell N Scattering and
We adapt the off-shell N amplitude of the Tucson-Melbourne three-body
force to the half-off-shell amplitude of the pion rescattering contribution to
near threshold. This {\em pion} rescattering contribution,
together with the impulse term, provides a good description of the data when
the half-off-shell amplitude is linked to the phenomenological invariant
amplitudes obtained from meson factory N scattering data.Comment: 3 pages, contributed to STORRI99, Bloomington, Indiana, September
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