Genesis of indifference thresholds and infinitely many indifference points in discrete time infinite horizon optimisation problems

This article investigates the discrete time indifference-attractor bifurcation of infinite horizon continous-time optimal control problems with a single state variable. We show that these bifurcations are linked to a heteroclinic bifurcation scenario of the state-costate equations, and we analyse the consequences for the optimal solutions. In particular, we can characterise the bifurcation value at which indifference thresholds appear by a geometric condition, and we find that for certain parameter values, there are countably infinitely many indifference points. We apply our results to a modified version of the shallow lake pollution management problem.

Optimal Management with Potential Regime Shifts

We analyze how the threat of a potential future regime shift affects optimal management. We use a simple general growth model to analyze four cases that involve combinations of stock collapse versus changes in system dynamics, and exogenous versus endogenous probabilities of regime shift. Prior work has focused on stock collapse with endogenous probabilities and reaches ambiguous conclusions about the effect of potential regime shift on optimal management. We show that all other cases yield unambiguous results. In particular, with endogenous probability of regime shift that affects system dynamics the potential for regime shift causes optimal management to become precautionary.

The Size of Stable International Environmental Agreements in the case of Stock Pollution

Most of the literature on stability of International Environmental Agreements is essen- tially static and can therefore not identify changes in the size of the stable coalition in connection with changes in the stock of pollutants. This is a relevant issue because most global pollution problems are dynamic with stock externalities. This paper shows that the incentives for membership indeed change with changes in the stock of pollutants and that technology choice is an important factor when considering the consequences.

Loss of Estrus and Concealed Ovulation in Human Evolution: A Reevaluation.

Accounts ofhuman evolution tend to highlight a number ofsignificant characteristics as critical in defining humanity including bipedalism (Jolly 1970, Lovejoy 1981, Wheeler 1984), enlarged brains (Falk 1990, Foley 1996), hairlessness (Morris 1963, Schwartz and Rosenblum 1980), and language (pinker and Bloom 1990, Dunbar 1996). Less frequently, scholars have focused on the unique aspects of human sexuality. In this paper, I seek to demonstrate that sexual swellings are not the norm among alloprimates and that the prevailing absence ofestrus among female humans is better viewed as a derived trait which is no more unique than that of any other primate. As such, I would argue, current theories of the loss of human estrus should be reevaluated

Orthotopic liver transplantation in U.S. veterans under primary tacrolimus immunosupression.

The evolution and refinement of surgical techniques, per ioperative patient care, and immunosuppression hav~ estab~ished orthoto~ic li~er transplantation (OLTX) as a ~ighly successful therapeutic modality for patients wrth end-stage hver disease. In February 1989,Tacrohmus (Prograf®, formerly FK 506)was first used successfully at the University of Pittsburgh Medical Center to treat patients with rejection refractory to cyclosporine-based immunosuppression." Clinical trials utilizing Tacrolimus in solid organ transplantation followed, and in April of 1994 it was approved for use by the Food and Drug Administration