Some sharp inequalities involving Seiffert and other means and their   concise proofs
  In the paper, by establishing the monotonicity of some functions involving the sine and cosine functions, the authors provide concise proofs of some known inequalities and find some new sharp inequalities involving the Seiffert, contra-harmonic, centroidal, arithmetic, geometric, harmonic, and root-square means of two positive real numbers $a$ and $b$ with $a\ne b$. 
Wei-Dong Jiang and Feng Qi
math.CA