Denotational, Causal, and Operational Determinism in Event Structures

Determinism is a theoretically and practically important concept in labelled transition systems and trees. We study its generalisation to event structures. It turns out that the result depends on what characterising property of tree determinism one sets out to generalise. We present three distinct notions of event structure determinism, and show that none of them shares all the pleasant properties of the one concept for trees

The Joys of Graph Transformation

We believe that the technique of graph transformation offers a very natural way to specify semantics for languages that have dynamic allocation and linking structure; for instance, object-oriented programming languages, but also languages for mobility. In this note we expose, on a rather informal level, the reasons for this belief. Our hope in doing this is to raise interest in this technique and so generate more interest in the fascinating possibilities and open questions of this area.\u

The Problem of Low and Unequal Voter Turnout - and What We Can Do About It. IHS Political Science Series No. 54, February 1998

Low voter turnout has become a serious problem in most democracies, not only in the United States but also in many West European countries – and even in a traditionally high-turnout country like Austria where turnout has also been declining in recent years. There are five reasons why we should be concerned about this problem: 1. Low turnout means low participation by less privileged citizens, who are already at a disadvantage in terms of other forms of political participation. 2. Unequal participation means unequal influence. 3. Actual turnout tends to be lower than the official turnout figures suggest. 4. Turnout in elections other than those at the national level tends to be particularly low. 5. Turnout is declining in most countries. The problem of low and unequal turnout can be solved by a number of institutional mechanisms such as proportional representation, concurrent and infrequent elections, weekend instead of weekday voting, and compulsory voting. The last of these – mandatory voting – is especially strong and effective, and also morally justified

Financial Shocks, Financial Frictions and Financial Intermediaries in DSGE Models: Comments on the Recent Literature

The aim of this work is to compare and contrast different ways of modeling financial shocks and financial intermediaries in the Dynamic Stochastic General Equilibrium models (DSGE models) and to discuss the empirical evidence on the importance of modeling financial sector and financial shocks in the economy. The analysis is based on four papers on the matter Jerman and Quiadrini (2009),Christiano, Motto and Rostagno (2006), Goodfriend and McCallum (2007), and Gertler and Kiyotaki (2009)Financial frictions; Financial Intermediaries; Financial shocks; DSGE models.

An Analytical Solution for the Interest Rate Reaction Function in a Neo- Keynesian Economy Using the Undetermined Coefficients Method

In this research note I propose the use of the undetermined coefficients method as an alternative approach to solve the Central Bank optimization problem in a neo-keynesian economy. The advantage of using this method is that it provides a theory as to how rational expectations are constructed, and how shocks in the economy are propagated, in order to find an analytical solution for the interest rate reaction function in an economy with a forward-looking behavior.undetermined coefficients method; neo-keynesian; rational expectations; interest rate; foward-looking; central bank optimization; new keynesian

Graph attribution through sub-graphs

We offer an alternative to the standard formalisation of attributed graphs. We propose to represent an attributed graph as a graph with a marked sub-graph, in which the sub-graph represents the data domain, rather than as a tuple of graph and algebra. This is a general construction which can be shown to preserve adhesiveness of categories; it has the advantage of uniformity and gives more flexibility in defining data abstractions. We show equivalence of our formalisation with the standard one, under a suitable encoding of algebras as graphs

Punishment in Public Goods games leads to meta-stable phase transitions and hysteresis

The evolution of cooperation has been a perennial problem in evolutionary biology because cooperation can be undermined by selfish cheaters who gain an advantage in the short run, while compromising the long-term viability of the population. Evolutionary game theory has shown that under certain conditions, cooperation nonetheless evolves stably, for example if players have the opportunity to punish cheaters that benefit from a public good yet refuse to pay into the common pool. However, punishment has remained enigmatic because it is costly, and difficult to maintain. On the other hand, cooperation emerges naturally in the Public Goods game if the synergy of the public good (the factor multiplying the public good investment) is sufficiently high. In terms of this synergy parameter, the transition from defection to cooperation can be viewed as a phase transition with the synergy as the critical parameter. We show here that punishment reduces the critical value at which cooperation occurs, but also creates the possibility of meta-stable phase transitions, where populations can "tunnel" into the cooperating phase below the critical value. At the same time, cooperating populations are unstable even above the critical value, because a group of defectors that are large enough can "nucleate" such a transition. We study the mean-field theoretical predictions via agent-based simulations of finite populations using an evolutionary approach where the decisions to cooperate or to punish are encoded genetically in terms of evolvable probabilities. We recover the theoretical predictions and demonstrate that the population shows hysteresis, as expected in systems that exhibit super-heating and super-cooling. We conclude that punishment can stabilize populations of cooperators below the critical point, but it is a two-edged sword: it can also stabilize defectors above the critical point.Comment: 22 pages, 9 figures. Slight title change, version that appears in Physical Biolog