The Evolution of Conflict under Inertia

In Norman (2003), the introduction of individual strategy switching costs, and thus inertia, into stochastic evolutionary coordination games was found inter alia to strengthen the mixed-strategy equilibrium as a short- to medium-run equilibrium. This paper considers the impact of such switching costs on the conflict scenario of Hawk-Dove games. The "attractive" mixed-strategy equilibrium of Hawk-Dove games represents a far better candidate for long-run equilibrium than its unstable counterpart in coordination games, and yet robust selection results have proved elusive, with conditions on the selection dynamics generally being required. Such a condition remains a necessity in the switching cost model with state-independent mutations. However, a more realistic model of state-dependent mutations driven by stochastic switching costs overcomes this problem, and identifies a threshold mean switching cost, above which the mixed-strategy equilibrium is selected in the long run for a wide class of switching cost distributions.

The Evolution of Coordination under Inertia

This paper models the phenomenon of inertia driven by individual strategy switching costs in a stochastic evolutionary context. Kandori, Mailath, and Rob's (1993) model of a finite population of agents repeatedly playing a 2x2 symmetric coordination game is extended to allow for such inertia. Taking noise to the limit, a number of new short- to medium-run equilibria emerge, centred around the mixed-strategy equilibrium. Thus, unusually, an evolutionary model is seen to provide some justification for the controversial concept of mixed-strategy equilibrium. However, Kandori, Mailath, and Rob's long-run selection of the risk-dominant equilibrium continues to hold, both under fixed-rate mutations and under state-dependent mutations driven by stochastic switching costs. The key to this is the satisfaction of Blume's (1999) "skew-symmetry" of the noise process, which is shown to be crucial even under simultaneous strategy revisions. In fact, the presence of the new short-run equilibria can under certain conditions serve to reduce the expected waiting time before the risk-dominant equilibrium is reached - an instance of Ellison's (2000) idea that evolution is more rapid when it can proceed via a series of small "steps" between extremes. This suggests inertia to be a surprisingly efficient phenomenon, and also serves to moderate the force of the Ellison (1993) critique of excessively long transition times in models with vanishing noise.

Step-by-Step Evolution with State-Dependent Mutations

This paper considers the extension of Ellison's (2000) "Radius-Modified Coradius" Theorem from the uniform-mutations case to a general stochastic setting. A modified theorem is presented, with a crucial role now played by the most probable evolutionary paths between states. The form of such paths is liable to change outside of the uniform mutations case, with concomitant effects on both long-run selection and expected waiting times. An algorithm for finding these paths is offered, and used to demonstrate the continued optimality of "step-by-step" evolution.

Co-movement of Australian State Business Cycles

We use a variety of techniques to examine the nature and degree of co-movement among Australian state business cycles. Our results indicate that these cycles move quite closely together, with particularly strong links between the cycles of the larger states. This finding is robust to a range of statistical measures. We also use an unobserved components model to attempt to distinguish the sources of this co-movement. An implication of our model is that the major source of cyclical fluctuation in state activity is shocks that are common to all states. Region-specific shocks appear to have a moderate influence on cyclical fluctuations, while spillovers of such shocks from one state to another seem to play only a minor role. These findings are consistent with the results of recent studies for the United States, Canada and Europe, where common shocks have also been found to dominate regional cyclical activity.business cycles; concordance; unobserved components

An evaluation of weld metal nitrogen retention and properties in 316NL austenitic stainless steel

A series of tests were conducted using varying levels of nitrogen and helium in a conventional argon shielding gas when welding 316LN austenitic stainless steel. The outcome was that a 15 per cent nitrogen addition to the argon shielding gas had the most significant effect on increasing the weld metal nitrogen. Subsequent additions of helium to the argon 15 per cent nitrogen shielding gas had very little overall benefit. Increasing the nitrogen content of the weld metal had the consequential effects of decreasing the ferrite content and the hardness. As a result of solid solution strengthening, the yield strength increased with increase in nitrogen content. There was an increase in impact toughness as the nitrogen content increased. This was related to the decreased ferrite content associated with the strong austenetizing potential of nitrogen. It was also shown that an almost fully austenitic weld metal could still have very good toughness. In combination with these effects there was no loss in corrosion resistance. The addition of nitrogen to a conventional argon shielding gas presents attractive cost and quality benefits over the established requirement to over alloy the weld filler material with expensive alloys such as nickel