In this paper‎, ‎we study the class of rings in which every $P$-flat‎ ‎ideal is flat and which will be called $PFF$-rings‎. ‎In particular‎, ‎Von Neumann regular rings‎, ‎hereditary rings‎, ‎semi-hereditary ring‎, ‎PID and arithmetical rings are examples of $PFF$-rings‎. ‎In the context domain‎, ‎this notion coincide with‎ ‎Pr"{u}fer domain‎. ‎We provide necessary and sufficient conditions for‎...

The annual attack rate for influenza in children is high, the highest of any age group. It is estimated that 10% to 40% of children are infected with influenza each winter, a figure similar to the attack rate reported for children during the 2009 H1N1 pandemic.1–4 Children with underlying medical conditions bear a disproportionate burden of influenza-related morbidity and mortality.5–7 Two stud...