A model of COVID-19 pandemic evolution in African countries.

We studied the COVID-19 pandemic evolution in selected African countries. For each country considered, we modeled simultaneously the data of the active, recovered and death cases. In this study, we used a year of data since the first cases were reported. We estimated the time-dependent basic reproduction numbers, R 0 , and the fractions of infected but unaffected populations, to offer insights into containment and vaccine strategies in African countries. We found that R 0 ≤ 4 at the start of the pandemic but has since fallen to R 0 ∼ 1 . The unaffected fractions of the populations studied vary between 1 - 10 % of the recovered cases.

Second-order dissipative fluid dynamics for ultrarelativistic nuclear collisions.

The Müller-Israel-Stewart second-order theory of relativistic imperfect fluids based on Grad's moment method is used to study the expansion of hot matter produced in ultrarelativistic heavy-ion collisions. The temperature evolution is investigated in the framework of the Bjorken boost-invariant scaling limit. The results of these second-order theories are compared to those of first-order theories due to Eckart and to Landau and Lifshitz and those of zeroth order (perfect fluid) due to Euler.