A First Synoptic Blazar Study Comprising Thirteen Blazars Visible in E>100 GeV Gamma-Rays

Since 2002, the number of detected blazars at E_\gamma > 100 GeV has more than doubled. I study all currently known BL Lac-type objects with published energy spectra. Their intrinsic energy spectra are reconstructed by removing extragalactic background light attenuation effects. The emission properties are then compared and correlated among each other, with X-ray data, and with the individual black hole masses. In addition, I consider temporal properties of the very high energy gamma-ray flux. Key findings concern the flux--black hole mass and variability scale--black hole mass connections and the correlation of the spectral slope and the luminosity. As a specific application, the study allows to constrain the still undetermined redshift of the blazar PG 1553+113.Comment: 4 pages, 4 figures, to appear in the proceedings of the 30th International Cosmic Ray Conference, Merida, July 200

AGN Observations in the GeV/TeV Energy Range with the MAGIC Telescope

MAGIC currently is the largest imaging atmospheric Cerenkov telescope world-wide. Since 2004, gamma-ray emission from several active galactic nuclei in the GeV/TeV energy range has been detected, some of which were newly discovered as very-high energy gamma-ray sources. The gamma-rays are assumed to originate from particle acceleration processes in the AGN jets. We give an overview of the AGN observed and detected by MAGIC, discuss spectral and temporal properties of these and show physics implications of some selected observations.Comment: 7 pages, 8 figures, to appear in the proceedings of Extragalactic Jets: Theory and Observation from Radio to Gamma Ray, Girdwood (AK), May 200

Interpreting Sustainability in Economic Terms: Dynamic Efficiency Plus Intergenerational Equity

Economists have expended considerable effort to develop economically meaningful definitions of the somewhat elusive concept of “sustainability.” We relate such a definition of sustainability to well known concepts from neoclassical economics, in particular, potential Pareto improvements (in the Kaldor-Hicks sense) and inter-personal compensation. In the inter-temporal realm, we find that dynamic efficiency is a necessary but not sufficient condition for a notion of sustainability that has normative standing as a goal for public policy. We define sustainability as dynamic efficiency plus intergenerational equity. Further, we argue that it is not unreasonable for economists to focus on the efficiency element, leaving equity considerations to the political process. The analogy to the relationship between potential Pareto improvements and (intragenerational) transfers can facilitate discussions about sustainability, both within the economics community and as part of an interdisciplinary discourse, and makes the basic concepts easier to operationalize.

Estimating Sensor Motion from Wide-Field Optical Flow on a Log-Dipolar Sensor

Log-polar image architectures, motivated by the structure of the human visual field, have long been investigated in computer vision for use in estimating motion parameters from an optical flow vector field. Practical problems with this approach have been: (i) dependence on assumed alignment of the visual and motion axes; (ii) sensitivity to occlusion form moving and stationary objects in the central visual field, where much of the numerical sensitivity is concentrated; and (iii) inaccuracy of the log-polar architecture (which is an approximation to the central 20°) for wide-field biological vision. In the present paper, we show that an algorithm based on generalization of the log-polar architecture; termed the log-dipolar sensor, provides a large improvement in performance relative to the usual log-polar sampling. Specifically, our algorithm: (i) is tolerant of large misalignmnet of the optical and motion axes; (ii) is insensitive to significant occlusion by objects of unknown motion; and (iii) represents a more correct analogy to the wide-field structure of human vision. Using the Helmholtz-Hodge decomposition to estimate the optical flow vector field on a log-dipolar sensor, we demonstrate these advantages, using synthetic optical flow maps as well as natural image sequences