Consider the first-order linear delay differential equation x′(t) + p(t)x(τ(t)) = 0, t ≥ t0, and the second-order linear delay equation x′′(t) + p(t)x(τ(t)) = 0, t ≥ t0, where p and τ are continuous functions on [t0,∞), p(t) > 0, τ(t) is nondecreasing, τ(t) ≤ t for t ≥ t0 and limt→∞ τ(t) = ∞. Several oscillation criteria are presented for the first-order equation when

We reconsider necessary and suffcient conditions for dynamic inefficiency given in Zilcha (1990, 1991) and a critique by Rangazas and Russell (2005). First, we show that the characterization given in Zilcha (1990) for nonstationary economies is correct and complete Zilcha's proof. Second, using this insight, we complement Rangazas and Russell (2005)'s discussion of the counterexamples to Zilcha...

This paper focuses on product portfolio management in a large multinational medical device organisation. The contribution of this research is to provide insights into the nature, composition and decision making processes of product portfolios in a real world setting. The research is important because portfolio management decisions have a significant impact and influence the performance at each ...