5,892 research outputs found
Bayesian Inversion of Stokes Profiles
[abridged] Inversion techniques are the most powerful methods to obtain
information about the thermodynamical and magnetic properties of solar and
stellar atmospheres. In the last years, we have witnessed the development of
highly sophisticated inversion codes that are now widely applied to
spectro-polarimetric observations. The majority of these inversion codes are
based on the optimization of a complicated non-linear merit function. However,
no reliable and statistically well-defined confidence intervals can be obtained
for the parameters inferred from the inversions. A correct estimation of the
confidence intervals for all the parameters that describe the model is
mandatory. Additionally, it is fundamental to apply efficient techniques to
assess the ability of models to reproduce the observations and to what extent
the models have to be refined or can be simplified. Bayesian techniques are
applied to analyze the performance of the model to fit a given observed Stokes
vector. The posterior distribution, is efficiently sampled using a Markov Chain
Monte Carlo method. For simplicity, we focus on the Milne-Eddington approximate
solution of the radiative transfer equation and we only take into account the
generation of polarization through the Zeeman effect. However, the method is
extremely general and other more complex forward models can be applied. We
illustrate the ability of the method with the aid of academic and realistic
examples. We show that the information provided by the posterior distribution
turns out to be fundamental to understand and determine the amount of
information available in the Stokes profiles in these particular cases.Comment: 15 pages, 12 figures, accepted for publication in A&
Data-driven modelling of biological multi-scale processes
Biological processes involve a variety of spatial and temporal scales. A
holistic understanding of many biological processes therefore requires
multi-scale models which capture the relevant properties on all these scales.
In this manuscript we review mathematical modelling approaches used to describe
the individual spatial scales and how they are integrated into holistic models.
We discuss the relation between spatial and temporal scales and the implication
of that on multi-scale modelling. Based upon this overview over
state-of-the-art modelling approaches, we formulate key challenges in
mathematical and computational modelling of biological multi-scale and
multi-physics processes. In particular, we considered the availability of
analysis tools for multi-scale models and model-based multi-scale data
integration. We provide a compact review of methods for model-based data
integration and model-based hypothesis testing. Furthermore, novel approaches
and recent trends are discussed, including computation time reduction using
reduced order and surrogate models, which contribute to the solution of
inference problems. We conclude the manuscript by providing a few ideas for the
development of tailored multi-scale inference methods.Comment: This manuscript will appear in the Journal of Coupled Systems and
Multiscale Dynamics (American Scientific Publishers
Finite-Size Effects on Traveling Wave Solutions to Neural Field Equations
Neural field equations are used to describe the spatiotemporal evolution of
the activity in a network of synaptically coupled populations of neurons in the
continuum limit. Their heuristic derivation involves two approximation steps.
Under the assumption that each population in the network is large, the activity
is described in terms of a population average. The discrete network is then
approximated by a continuum. In this article we make the two approximation
steps explicit. Extending a model by Bressloff and Newby, we describe the
evolution of the activity in a discrete network of finite populations by a
Markov chain. In order to determine finite-size effects - deviations from the
mean field limit due to the finite size of the populations in the network - we
analyze the fluctuations of this Markov chain and set up an approximating
system of diffusion processes. We show that a well-posed stochastic neural
field equation with a noise term accounting for finite-size effects on
traveling wave solutions is obtained as the strong continuum limit
Rejoinder on: queueing models for the analysis of communication systems
In this rejoinder, we respond to the comments and questions of three discussants of our paper on queueing models for the analysis of communication systems. Our responses are structured around two main topics: discrete-time modeling and further extensions of the presented queueing analysis
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