The Penrose photoproduction scenario for NGC 4151: A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies

A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus

The Convergence of Health Care Financing Structures: Empirical Evidence from OECD-Countries

In this paper we concentrate on the question whether the financing structure of the health care systems converges. In a world of increasing economic integration convergence in health care financing (HCF) and, hence, decreasing differences in HCF across countries enhance individuals’ (labour) mobility and support harmonization processes. As an indicator for convergence we take the public financing ratio in % of total HCF and in % of GDP. The major finding is that HCF in the OECD countries converged in the time period 1970 – 2005. This conlusion also holds when looking at smaller sub groups of countries and shorter time periods. However, we find evidence that countries do not move towards a common mean and that the rate of convergence is decreasing over time.Convergence, health care system, health care financing

Spectral evolution of active galactic nuclei: A unified description of the X-ray and gamma

A model for spectral evolution is presented whereby active galactic nuclei (AGN) of the type observed individually emerge from an earlier stage at z approx = 4 in which they are the thermal X-ray sources responsible for most of the cosmic X-ray background (CXB). The conjecture is pursued that these precursor objects are initially supermassive Schwarzschild black holes with accretion disks radiating near the Eddington luminosity limit. It is noted that after approx. 10 to the 8th power years these central black holes are spun-up to a canonical Kerr equilibrium state (A/M = 0.998; Thorne 1974) and shown how they then can lead to spectral evolution involving non-thermal emission extending to gamma rays, at the expense of reduced thermal disk radiation. That major portion of the CXB remaining after the contribution of usual AGN are considered, while a superposition of AGN sources at z 1 can account for the gamma ray background. Extensive X-ray measurements carried out with the HEAO 1 and 2 missions as well as gamma ray and optical data are shown to compare favorably with principal features of this model

Optical characteristics of young quasars as sources of the cosmic X-ray background

The sources which dominate the thermal cosmic X-ray background cannot have X-ray spectra similar to the power laws measured for bright active galactic nuclei. The optical consequences of this disparity are pursued by considering a standard model for the photoexcitation and heating of the line emitting gas surrounding a central source (e.g., such as a quasar). The optical line emission to be associated with compact young quasar sources having the same X-ray spectrum as the X-ray background is found to be substantially different from that characteristic of typical quasars. Implications on quasar source counts and the identification of such new objects are discussed

Determinants of Inter-Country Internet Diffusion Rates

This paper employs cross-sectional data from 100 countries to analyze the main determinants of inter-country Internet diffusion rates. We set up an empirical model based on strong theoretical foundations, in which we regress Internet usage on variables that capture social, economic and political differences between these countries. Our results support past findings that economic strength, infrastructure and knowledge of the English language positively affect Internet connectivity. In addition to these indicators, the openness of a country, tertiary enrollment, and income equality are found to also have a significant positive effect on Internet diffusion.internet, technological diffusion, inequality, education, English proficiency

Does going green pay off? The effect of an international environmental agreement on tropical timber trade

Trade-related measures aim to regulate side-effects in international environmental agreements and are expected to positively influence the level of participation in the agreements as well as their degree of stability. In this paper we examine one side-effect of the 1994 International Tropical Timber Agreement - its impact on tropical timber trade. We use a cross-sectional dataset on bilateral trade flows of tropical timber that additionally contains information on trading partners' economic and geographical characteristics. Our empirical specification is based on a gravity equation, which is estimated using Heckman's selection model to address the potentially systematic selection of trading partners. We find significantly positive impacts of the 1994 ITTA on member countries' level of tropical timber trade. Furthermore, poor exporter countries benefit more from this trade enhancing effect than their richer counterparts.International environmental agreements, side benefits, bilateral trade flows, product quality, sample selection