A Simple Particle Action from a Twistor Parametrization of AdS_5

The SO(4,2) isometries of AdS_5 are realized non-linearly on its horospherical coordinates (x^m,\rho). On the other hand, Penrose twistors have long been known to linearly realize these symmetries on 4-dimensional Minkowski space, the boundary of AdS_5, parametrized by x^m. Here we extend the twistor construction and define a pair of twistors, allowing us to include a radial coordinate in the construction. The linear action of SO(4,2) on the twistors induces the correct isometries of AdS_5. We apply this new construction to the study of the dynamics of a massive particle in AdS_5. We show that in terms of the twistor variables the action takes a simple form of a 1-dimensional gauge theory. Our result might open up the possibility to find a simple worldvolume action also for the string propagating on AdS_5.Comment: 11 pages, LaTe

Transmitting shocks to the economy: The contribution of interest and exchange rates and the credit channel

Understanding the transmission channels of shocks is critical for successful policy response. This paper develops a dynamic general equilibrium model to assess the relative importance of the interest rate, the exchange rate and the credit channels in transmitting shocks in an open economy. The relative contribution of each channel is determined by comparing the impulse responses when the relevant channel is suppressed with the impulse responses when all three channels are operating. The results suggest that all three channels contribute to business cycle fluctuations and the transmission of shocks to the economy. But the magnitude of the impact of the interest rate channel crucially depends on the inflation process and the structure of the economy.Transmission channels, open economy, general equilibrium model

How many jobs? A leading indicator model of New Zealand employment

This paper constructs a composite index of leading indicators of New Zealand employment. The choice of variables and their weights in the composite index are determined by their concordance with employment. The composite index is included in an indicator model to forecast quarterly employment growth. The indicator model explains about 67 percent of the quarterly variation in employment, in sample, and correctly predicted the direction of next period employment almost 80 percent of the time, out of sample.Composite index of leading indicators, forecasting, employment

Managing evolution and change in web-based teaching and learning environments

The state of the art in information technology and educational technologies is evolving constantly. Courses taught are subject to constant change from organisational and subject-specific reasons. Evolution and change affect educators and developers of computer-based teaching and learning environments alike – both often being unprepared to respond effectively. A large number of educational systems are designed and developed without change and evolution in mind. We will present our approach to the design and maintenance of these systems in rapidly evolving environments and illustrate the consequences of evolution and change for these systems and for the educators and developers responsible for their implementation and deployment. We discuss various factors of change, illustrated by a Web-based virtual course, with the objective of raising an awareness of this issue of evolution and change in computer-supported teaching and learning environments. This discussion leads towards the establishment of a development and management framework for teaching and learning systems

Modal logics for reasoning about object-based component composition

Component-oriented development of software supports the adaptability and maintainability of large systems, in particular if requirements change over time and parts of a system have to be modified or replaced. The software architecture in such systems can be described by components and their composition. In order to describe larger architectures, the composition concept becomes crucial. We will present a formal framework for component composition for object-based software development. The deployment of modal logics for defining components and component composition will allow us to reason about and prove properties of components and compositions