Dilation Theoretic Parametrizations of Positive Matrices with   Applications to Quantum Information
  This paper, dedicated to the memory of late Professor Tiberiu Constantinescu, discusses two parametrizations of positive matrices. The first, called the Schur-Constantinescu parametrization, is used to construct several examples of separable states (e.g., Hankel states). The second, called the Jacobi parametrization, is used to present an alternative to the Bloch sphere representation of qubits. 
M. C. Tseng and V. Ramakrishna