Positive Polynomials on closed boxes
  We present two different proofs that positive polynomials on closed boxes of $\mathbb{R}^2$ can be written as bivariate Bernstein polynomials with strictly positive coefficients. Both strategies can be extended to prove the analogous result for polynomials that are positive on closed boxes of $\mathbb{R}^n$, $n>2$. 
Marcio Alves Diniz and Luis Ernesto Salasar and Rafael Bassi Stern
math.CA