Abstract Waldstrukturen lassen sich mit Methoden der Fernerkundung über grosse Gebiete erfassen. Dabei haben Stereoluftbilder als effiziente Grundlage für die Berechnung von digitalen Oberflächenmodellen erwiesen. Zieht man diesen das Geländemodell ab und eliminiert künstliche Objekte, erhält Vegetationshöhenmodelle. Je nach Auflösung Luftbilder liefern diese in den Vegetationshöhen mehr oder w...

Tests of causality in variance in multiple time series have been proposed recently, based on residuals of estimated univariate models. Although such tests are applied frequently little is known about their power properties. In this paper we show that a convenient alternative to residual based testing is to specify a multivariate volatility model, such as multivariate GARCH (or BEKK), and constr...

The sandwich estimator of variance may be used to create robust Wald-type tests from estimating equations that are sums of K independent or approximately independent terms. For example, for repeated measures data on K individuals, each term relates to a different individual. These tests applied to a parameter may have greater than nominal size if K is small, or more generally if the parameter t...

We extend the Wald cosmic no–hair theorem to a general class of scalar–tensor nonminimally coupled theories of gravity where ordinary matter is also present in the form of a perfect fluid. We give a set of conditions for obtaining a de Sitter expansion independently of any initial conditions, generalizing the treatment of such a problem as given by Wald. Finally we apply the results to some spe...