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

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

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

Projectivity and Birational Geometry of Bridgeland moduli spaces

We construct a family of nef divisor classes on every moduli space of stable complexes in the sense of Bridgeland. This divisor class varies naturally with the Bridgeland stability condition. For a generic stability condition on a K3 surface, we prove that this class is ample, thereby generalizing a result of Minamide, Yanagida, and Yoshioka. Our result also gives a systematic explanation of the relation between wall-crossing for Bridgeland-stability and the minimal model program for the moduli space. We give three applications of our method for classical moduli spaces of sheaves on a K3 surface: 1. We obtain a region in the ample cone in the moduli space of Gieseker-stable sheaves only depending on the lattice of the K3. 2. We determine the nef cone of the Hilbert scheme of n points on a K3 surface of Picard rank one when n is large compared to the genus. 3. We verify the "Hassett-Tschinkel/Huybrechts/Sawon" conjecture on the existence of a birational Lagrangian fibration for the Hilbert scheme in a new family of cases.Comment: v2: 50 pages, exposition substantially improved based on referee's comments. Accepted for publication in Journal of the AM

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.

On a Graph-Based Semantics for UML Class and Object Diagrams

In this paper we propose a formal extension of type graphs with notions that are commonplace in the UML and have long proven their worth in that context: namely, inheritance, multiplicity, containment and the like. We believe the absence of a comprehensive and commonly agreed upon formalisation of these notions to be an important and, unfortunately, often ignored omission. Since our eventual aim (shared by many researchers) is to give unambiguous, formal semantics to the UML using the theory of graphs and graph transformation, in this paper we propose a set of definitions to repair this omission. With respect to previous work in this direction, our aim is to arrive at more comprehensive and at the same time simpler definitions.\u