ADAPTIVE MANAGEMENT OF HARVEST RATES IN THE PRESENCE OF A RISK AVERSE UTILITY FUNCTION

Previous research on adaptive harvest strategies has suggested that it should rarely be optimal to introduce deliberate, probing variations in harvest rates in order to reduce uncertainty about production parameters, when there is strong aversion to the risk of low catches. Here we show that this suggestion is incorrect for cases where the stock dynamics can be approximated by a simple power model and the objective is to maximize the sum over time of discounted logarithms of catches. In such cases, the objective function has a simple form that permits easy comparison between passively adaptive (certainty equivalent or cautious) versus actively adaptive policies involving probing variation in harvest rates. Probing is favored when there is high uncertainty about the power parameter that represents density dependence in the stock dynamics.     

Energy-dependent cross sections for the tritium-methane hot atom reactions

Using classical Monte Carlo trajectory methods, we have fitted a new kind of empirical potential energy hypersurface to combined experimental observations on the tritium-methane hot atom reactions. All channels (including Walden inversion) are now present and the degree of uniqueness is apparently high. We present our predicted cross sections as a function of tritium energy for the abstraction, inverting substituting, and total substitution reactions.     

Cation transport at 25°c from binary Tl+Mn+ and K+Mn+ nitrate mixtures in a H2OCHCl3H2O liquid membrane system containing a series of macrocyclic polyether carriers

Carrier-mediated cation fluxes were determined using a H₂OCHC1₃H₂O liquid merebrane system for TlNO₃ and for binary mixtures of either TlNO₃ or KNO₃ with alkali metal ions, alkaline earth metal ions, and Pb²⁺ (in the case of TlNO₃). Both macrocyclic polyether and cryptand ligands were used as carriers. In Tl⁺Mⁿ⁺ mixtures, selective transport of Tl⁺ was found over all cations studied, except in the cases of Ag⁺ by 2.2 and of Pb²⁺ by 18C6, DC18C6, ClDKP18C6, and 2.2. Generally, K⁺ was transported selectively from K⁺Mⁿ⁺ mixtures, except in the cases of K⁺Tl⁺ mixtures in which Tl⁺ was transported selectively in all cases. A model relating cation flux to log K(CH₃OH) for Mⁿ⁺—macrocycle interaction and to ion-partitioning between the organic and aqueous phases was successful in rationalizing selective cation transport in most of the systems studied.     

Combined deuterium labeling and appearance potential measurements to uncover competing reaction mechanisms in the electron-impact-induced loss of water from cyclohexanol

The appearance potentials for loss of H₂O and DOH from the constitutional isomers 3,5-dideuterocyclohexanol and 4,4- dideuterocyclohexannol show, in agreement with proposals based on stereoselectivites, that 1,3 loss of water is energetically more costly than 1,4 loss of water.     

Short distance Regge singularities. Renormalized gluon ladder in QCD

It is shown that the renormalized gluon ladder gives rise to an accumulation of Regge poles at j = +1. This approximation is obtained by reordering the perturbation expansion of the Bethe-Salpeter kernel using the renormalization group. The existence of this accumulation is shown to be independent of the gauge. The relevance of this result for the problem of the Pomeron is discussed briefly.