In a paper published in Acta Mathematica Scientia, a mathematics team led by H.-L. Li in Capital Normal University investigated the linear stability/instability of the planar Couette flow to the two-dimensional compressible Euler-Euler system for (ρ, u) and (n, v) with the sound speeds c₁ and c₂ respectively coupled each other through the drag force on T×R. It is shown in general for the different sound speeds c₁≠c₂ that the perturbations of the densities (ρ, n) and the velocities (u, v) demonstrate the stability in any fixed finite time interval (0, T], besides, excluding the zero mode, the densities (ρ, n) and the irrotational components of the velocities (u, v) obey the algebraic time-growth rates, while the rotational components of the velocities (u, v) exhibit the algebraic time-decay rates due to the inviscid damping. For the case of same sound speeds c₁=c₂ (same sound speeds), it is proved that the relative velocity u − v decays faster than those of the velocities u, v caused by the inviscid damping, but the linear instability of the densities (ρ, n) and the irrotational components of the velocities (u, v) is also shown for some large time in spite of the inviscid damping.

A web-based method developed by a Stanford-led team was shown to mitigate political polarization on X, the platform formerly known as Twitter, by nudging antidemocratic and extremely negative partisan posts lower in a user’s feed. The tool, which is independent of the platform, has the potential to give users more say over what they see on social media.