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In this paper the problem of stability of the zero solution of singularly perturbed system of linear differential equation with state delays is investigated. We show that if the zero solution of reduced subsystem and the one of the fast subsystem are exponentially stable, then the zero solution of the given singularly perturbed system of differential equations is also exponentially stable. Estimates of the block components of the fundamental matrix solution are derived. These estimates are used to obtain asymptotic expansions on unbounded interval for the solutions of this class of singularly perturbed systems.

The year 2020 will remain in the memory of all mankind as the year of the COVID-19 pandemic. The pandemic has affected the world economy, caused more than a million deaths in 2020 alone, changed the way people work and learn and, last but not least, changed the way people interact in society. Social distancing, along with wearing a face mask, is the best solution to prevent the spread of COVID-19 virus. What happens when in certain spaces social distance is difficult and can be accidentally violated without intention? In the absence of widely available tests, not only for people but also for surfaces or indoor air, the risk of contamination is very difficult to assess. This paper proposes a simple method, with low cost and widely implementable, to warn of respecting the density of people in a room. It proposes a dual monitoring system based on Internet of Things (IoT) to assess the indoor air quality and risk of COVID-19 transmission.

The success of UML and more generally, of the model driven approach, has led to a proliferation of models, representing various systems, but the description of large applications may actually be composed of several system models. Therefore, the challenge is to determine how to compose independent system models, in order to build large applications.We present in this paper the software federation approach developed by our team. A federation relies on the concept of a domain, which describes a specific application domain, represented with a specific metamodel. Building a software federation means composing independently developed domains, by composing their meta-models.The UML standard, which is well supported by tools, has been found convenient for describing our metamodels, but it turns out that it does not contain sufficient modelling capabilities for the composition of these models. This paper analyses the need for model composition, the available UML concepts related to model composition and proposes an UML profile allowing the composition of models in software federations.

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