Erratum: Luminosity function, sizes and FR dichotomy of radio-loud AGN

This erratum corrects a number of formulae containing mistakes in the paper 'Luminosity function, sizes and FR dichotomy of radio-loud AGN', 2007, MNRAS, v. 381, p.1548. The corrections do not alter any of the conclusions in the original paper.Comment: single page, no figures, erratum to MNRAS, 2007, v. 381, p. 154

Luminosity function, sizes and FR dichotomy of radio-loud AGN

The radio luminosity function (RLF) of radio galaxies and radio-loud quasars is often modelled as a broken power-law. The break luminosity is close to the dividing line between the two Fanaroff-Riley (FR) morphological classes for the large-scale radio structure of these objects. We use an analytical model for the luminosity and size evolution of FRII-type objects together with a simple prescription for FRI-type sources to construct the RLF. We postulate that all sources start out with an FRII-type morphology. Weaker jets subsequently disrupt within the quasi-constant density cores of their host galaxies and develop turbulent lobes of type FRI. With this model we recover the slopes of the power laws and the break luminosity of the RLF determined from observations. The rate at which AGN with jets of jet power $Q$ appear in the universe is found to be proportional to $Q^{-1.6}$. The model also roughly predicts the distribution of the radio lobe sizes for FRII-type objects, if the radio luminosity of the turbulent jets drops significantly at the point of disruption. We show that our model is consistent with recent ideas of two distinct accretion modes in jet-producing AGN, if radiative efficiency of the accretion process is correlated with jet power.Comment: 13 pages, 1 figure, accepted by MNRA

Entropy Evolution of the Gas in Cooling Flow Clusters

We emphasise the importance of the gas entropy in studying the evolution of cluster gas evolving under the influence of radiative cooling. On this basis, we develop an analytical model for this evolution. We then show that the assumptions needed for such a model are consistent with a numerical solution of the same equations. We postulate that the passive cooling phase ends when the central gas temperature falls to very low values. It follows a phase during which an unspecified mechanism heats the cluster gas. We show that in such a scenario the small number of clusters containing gas with temperatures below about 1 keV is simply a consequence of the radiative cooling.Comment: Contribution to Proceedings of `The Riddle of Cooling Flows in Galaxies and Clusters of Galaxies', Charlottesville, VA, USA. May 31 -- June 4, 2003. Editors: Reiprich, T. H., Kempner, J. C., and Soker, N. Requires included style fil

Do Magazines' ”Companion Websites” Cannibalize the Demand for the Print Version?

We analyze the extent to which visits to a magazine's companion website affects total circulation, subscription, kiosk sales and foreign sales using Granger causality tests on the basis of monthly data for the German magazine market spanning the period January 1998 to September 2005. We find evidence for positive effects of website visits on magazine subscription but negative effects on magazine kiosk sales. Contrary to the widespread belief that the Internet will cannibalize print media markets, our results do not, however, provide evidence for website visits adversely affecting total circulation.Granger causality; heterogeneous panel data models; Mean Group Estimation; website visits; magazine circulation

True versus spurious state dependence in firm performance: the case of West German exports

This paper analyzes the persistence of firms’ exporting behavior in a panel of West German manufacturing firms. Dynamic binary choice models allow us to distinguish between true and spurious state dependence in firm performance. Using random effects models as well as a recent fixed effect approach which imposes few restrictions on unobservables, we find robust evidence of state dependence in the current export status of firms. Unobserved permanent firm heterogeneity (“spurious state dependence”) is found to be less important than suggested by earlier studies. The existence of true state dependence in exports has direct economic policy implications: if policy successfully turns non-exporters into exporters, the effect is likely to be lasting.state dependence; export activity; dynamic binary choice models

Do Magazines' "Companion Websites" Cannibalize the Demand for the Print Version?

We analyze the relationship between website visits, magazine demand and the demand for advertising pages using Granger non-causality tests on the basis of an extensive and externally audited quarterly data set for the German magazine market spanning the period I/1998 to II/2004. We use traditional panel data estimators and an estimator suitable for heterogeneity across magazines. We find very robust evidence for positive effects from website visits to circulation. There is no evidence of causality running in the opposite direction. Our findings are contrary to the widespread belief that the Internet will cannibalize print media markets.Granger causality; heterogeneous panel data models; Mean Group Estimation; website visits; magazine circulation