Parameter estimation during the cooling of mold

Luiz F. S. Ferreira2^{2}, Thomas Pierre1,^{1,\star}, Helcio R. B. Orlande2^{2}, Leonardo Antonio Bermeo Varo3^{3}
^{\star} :
1^{1} Université Bretagne Sud
2^{2} Université Fédérale de Rio de Janeiro
3^{3} Université Santiago de Cali
Mots clés : micro-organisms detection; flash method; inverse methods; infrared thermography; lumped system; MCMC; parameter estimation
Résumé :

Microbiology standard procedures for the detection of bacteria or other micro-organisms in liquid or gas media usually require incubation of the samples for few days. For example, in the standard test for the bacterial filtration efficiency of medical face masks [1], air with dispersed Staphylococcus aureus is flown for 2 minutes through a cascade impactor containing plates with a culture medium. Despite this short time required to collect the samples, the plates need to be incubated at 37±2 ^{\circ}C for 20 to 52 hours (usually 48 hours in practice) in order to allow sufficient growth of the bacteria colonies for visual detection and counting. The COVID-19 pandemic unequivocally revealed the major importance of such filtration test and the need to expedite the whole procedure. This research project is aimed at the fast detection of micro-organisms by thermal excitation and measurements. In this paper, we present preliminary results obtained with mold, which was grown on a plate with culture media of the same type that is used for the bacterial filtration tests described above. The plate was thermally excited with a light pulse from a photograph flash. The temperature of the plate containing the mold was then measured with an infrared camera made by FLIR (model SC660). The spatial resolution of the camera was determined. Also, the relation between digital level counts and the temperature measured by the camera was linear, as expected for small temperature variations like those imposed by the light pulse. Temperature variations during the cooling period after the light pulse were used for the solution of a parameter estimation problem, by modeling the mold as a lumped system. The lumped model parameter was estimated by stochastic simulations with the Metropolis-Hastings algorithm of the Markov Chain Monte Carlo (MCMC) method. Results are presented for mold of different types and sizes.


[1] Medical face masks - Requirements and test methods, European standard EN 14683:2019+AC:2019

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