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We will give sufficient conditions for the existence of positive periodic solutions for $ x''(t)+ax'(t)=r(t)x^{\alpha}(t)-s(t)x^{\beta}(t)$ by means of topological arguments. Our main motivation comes from a problem related with the valveless pumping phenomenon [see J. A. Cid, G. Propst and M. Tvrdy, On the pumping effect in a pipe/tank flow configuration with friction, to appear in Phys. D]. |
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