13,132 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
Mixed action computations on fine dynamical lattices
We report on our first experiences in simulating Neuberger valence fermions
on CLS configurations with light sea quark masses and small lattice
spacings. Valence quark masses are considered that allow to explore the
matching to (partially quenched) chiral perturbation theory both in the
- and -regimes. The setup is discussed, and first results are
presented for spectral observables.Comment: 7 pages. Presented at the XXVII International Symposium on Lattice
Field Theory, July 26-31, 2009, Peking University, Beijing, Chin
Observation of magnetization reversal in epitaxial Gd0.67Ca0.33MnO3 thin films
High quality epitaxial thin films of Gd0.67Ca0.33MnO3 have been deposited
onto (100) SrTiO3 substrates by pulsed-laser deposition. Enhanced properties in
comparison with bulk samples were observed. The magnetic transition temperature
(Tc) of the as-grown films is much higher than the corresponding bulk values.
Most interestingly, magnetization measurements performed under small applied
fields, exhibit magnetization reversals below Tc, no matter whether the film is
field-cooled (FC) or zero-field-cooled (ZFC). A rapid magnetization reversal
occurs at 7 K when field cooled, while as for the ZFC process the magnetization
decreases gradually with increasing temperatures, taking negative values above
7 K and changing to positive values again, above 83 K. In higher magnetic
fields the magnetization does not change sign. The reversal mechanism is
discussed in terms of a negative exchange f-d interaction and magnetic
anisotropy, this later enhanced by strain effects induced by the lattice
mismatch between the film and the substrate.Comment: 16 pages, 4 figure
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