I considered some properties of the van der Pol equation d^2 x/dt^2 +mu (x^2-1)+x=0. During the consideration, I made some animations for understanding its limit cycle solutions. I opened two animations which I made in youtube. One is its shape in real space and the other is the one in phase space.
As already known, earthquakes and disasters attacked about a half part of Japan. I and my family are alive but so many people, mainly north-east part of Japan, were dead and much people alive there are suffer from lack of water, food, wear, and so on now. The current situation is terrible and I have no word to describe it correctly.
The disaster also affects my activities. Some events relating to my research and some my lectures were suspended or canceled.
How do I live well in such a situation? I have no answer now but I think that I have to spend my life time meaningfully as possible as I can.