Data compression for the First G-APD Cherenkov Telescope

The First Geiger-mode Avalanche photodiode (G-APD) Cherenkov Telescope (FACT) has been operating on the Canary island of La Palma since October 2011. Operations were automated so that the system can be operated remotely. Manual interaction is required only when the observation schedule is modified due to weather conditions or in case of unexpected events such as a mechanical failure. Automatic operations enabled high data taking efficiency, which resulted in up to two terabytes of FITS files being recorded nightly and transferred from La Palma to the FACT archive at ISDC in Switzerland. Since long term storage of hundreds of terabytes of observations data is costly, data compression is mandatory. This paper discusses the design choices that were made to increase the compression ratio and speed of writing of the data with respect to existing compression algorithms. Following a more detailed motivation, the FACT compression algorithm along with the associated I/O layer is discussed. Eventually, the performances of the algorithm is compared to other approaches.Comment: 17 pages, accepted to Astronomy and Computing special issue on astronomical file format

Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope

The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of the performance of silicon photo detectors in Cherenkov Astronomy. For more than two years it is operated on La Palma, Canary Islands (Spain), for the purpose of long-term monitoring of astrophysical sources. For this, the performance of the photo detectors is crucial and therefore has been studied in great detail. Special care has been taken for their temperature and voltage dependence implementing a correction method to keep their properties stable. Several measurements have been carried out to monitor the performance. The measurements and their results are shown, demonstrating the stability of the gain below the percent level. The resulting stability of the whole system is discussed, nicely demonstrating that silicon photo detectors are perfectly suited for the usage in Cherenkov telescopes, especially for long-term monitoring purpose

FACT -- The G-APD revolution in Cherenkov astronomy

Since two years, the FACT telescope is operating on the Canary Island of La Palma. Apart from its purpose to serve as a monitoring facility for the brightest TeV blazars, it was built as a major step to establish solid state photon counters as detectors in Cherenkov astronomy. The camera of the First G-APD Cherenkov Telesope comprises 1440 Geiger-mode avalanche photo diodes (G-APD), equipped with solid light guides to increase the effective light collection area of each sensor. Since no sense-line is available, a special challenge is to keep the applied voltage stable although the current drawn by the G-APD depends on the flux of night-sky background photons significantly varying with ambient light conditions. Methods have been developed to keep the temperature and voltage dependent response of the G-APDs stable during operation. As a cross-check, dark count spectra with high statistics have been taken under different environmental conditions. In this presentation, the project, the developed methods and the experience from two years of operation of the first G-APD based camera in Cherenkov astronomy under changing environmental conditions will be presented.Comment: Proceedings of the Nuclear Science Symposium and Medical Imaging Conference (IEEE-NSS/MIC), 201

Der diskrete Charme der Bourgeoisie - Ein Beitrag zur Soziologie des modernen Wirtschaftsbürgertums

Entgegen der These der Auflösungserscheinungen des Bürgertums stellt der Autor die Annahme auf den Prüfstand, dass wir es nach wie vor mit gesellschaftlichen Fraktionierungen bürgerlicher Lebensweisen zu tun haben. Am Beispiel autobiographischer Schriften von deutschen Topmanagern stellt der Text ein modernes Verständnis des Wirtschaftsbürgertums vor, das organisational (durch die Karrieremechanismen der Organisation) und institutionell (im Feld der Wirtschaft) verankert ist. Die moderne Sozialformation des Wirtschaftsbürgertums ist nur noch auf der Grundlage von Organisationen denkbar. Sie lässt sich, jenseits von Klasse und Stand, als Positionselite beschreiben. Anhand der Autobiographien lässt sich die Reproduktion dieser Elite auf Basis einer engen Verknüpfung zwischen familialer Herkunft, an organisationale Karrieren gebundene Leistungsbereitschaft und hoher formaler Bildung nachzeichnen. Die Abgrenzung in der Statusreproduktion zwischen Bildungs- und Wirtschaftsbürgertum weist der Autor am jeweiligen Verhältnis zur Bildung nach; zwar können beide einen hohen Bildungsgrad in Form von Bildungspatenten nachweisen, doch im Falle des Wirtschaftsbürgertums herrscht ein instrumentelles Verhältnis zur Bildung vor. Der hohe Bildungsgrad folgt hier dem Bedürfnis, den Status mittels formaler Bildung abzusichern und damit die Gefahr der eigenen Austauschbarkeit - als Personal der Organisation - zu kompensieren. Der Text macht außerdem generationale Effekte sichtbar; insbesondere indem er darlegt, inwieweit der "moderne Manager" einerseits in der Betonung seines Status seinen Vorgängern gleicht und sich doch gleichzeitig in der Art der Unternehmensführung abgrenzt - indem er bspw. die Managementkonzepte seiner Zeit aufgreift

Calibration and performance of the photon sensor response of FACT - the first G-APD Cherenkov telescope

The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of the performance of silicon photo detectors in Cherenkov Astronomy. For more than two years it is operated on La Palma, Canary Islands (Spain), for the purpose of long-term monitoring of astrophysical sources. For this, the performance of the photo detectors is crucial and therefore has been studied in great detail. Special care has been taken for their temperature and voltage dependence implementing a correction method to keep their properties stable. Several measurements have been carried out to monitor the performance. The measurements and their results are shown, demonstrating the stability of the gain below the percent level. The resulting stability of the whole system is discussed, nicely demonstrating that silicon photo detectors are perfectly suited for the usage in Cherenkov telescopes, especially for long-term monitoring purpose.A. Biland, T. Bretz, J. Buß, V. Commichau, L. Djambazov, D. Dorner, S. Einecke, D. Eisenacher, J. Freiwald, O. Grimm, H. von Gunten, C. Haller, C. Hempfling, D. Hildebrand, G. Hughes, U. Horisberger, M.L. Knoetig, T. Krähenbühl, W. Lustermann, E. Lyard, K. Mannheim, K. Meier, S. Mueller, D. Neise, A.-K. Overkemping, A. Paravac, F. Pauss, W. Rhode, U. Röser, J.-P. Stucki, T. Steinbring, F. Temme, J. Thaele, P. Vogler, R. Walter and Q. Weitze

Design and Operation of FACT -- The First G-APD Cherenkov Telescope

The First G-APD Cherenkov Telescope (FACT) is designed to detect cosmic gamma-rays with energies from several hundred GeV up to about 10 TeV using the Imaging Atmospheric Cherenkov Technique. In contrast to former or existing telescopes, the camera of the FACT telescope is comprised of solid-state Geiger-mode Avalanche Photodiodes (G-APD) instead of photomultiplier tubes for photo detection. It is the first full-scale device of its kind employing this new technology. The telescope is operated at the Observatorio del Roque de los Muchachos (La Palma, Canary Islands, Spain) since fall 2011. This paper describes in detail the design, construction and operation of the system, including hardware and software aspects. Technical experiences gained after one year of operation are discussed and conclusions with regard to future projects are drawn.Comment: Corresponding authors: T. Bretz and Q. Weitze

Making Deservingness of the Unemployed Conditional: Changes in Public Support for the Conditionality of Unemployment Benefits

Since the 1990s, stricter conditions for the (long‐term) unemployed to receive benefits have been on the ‘activation’ agenda. However, policymakers are constrained in their reform efforts by the economic and fiscal situation, the pre‐existing institutional contexts and public opinion. This cross‐national and longitudinal study investigates whether the social legitimacy of benefit obligations for the unemployed is affected by the changing economic situation and the varying institutional context. We use data from the European Values Survey, a repeated cross‐sectional survey that was conducted in 1990, 1999 and 2008 in 23 European countries. Support for the conditionality of unemployment benefits is measured with an item that asks whether people who are unemployed should have to take any job available. We find that the main economic indicators – economic growth and the unemployment rate – are significantly related to support for conditionality. People living in wealthier countries are more likely to be in favour of conditionality, whereas a high unemployment rate reduces such support. With regard to institutional features, we find some support for the assumption that people in welfare states with more generous social policies prefer stricter conditionality for access, in order to protect the generous benefits against any misuse

Making Deservingness of the Unemployed Conditional: Changes in Public Support for the Conditionality of Unemployment Benefits

Since the 1990s, stricter conditions for the (long‐term) unemployed to receive benefits have been on the ‘activation’ agenda. However, policymakers are constrained in their reform efforts by the economic and fiscal situation, the pre‐existing institutional contexts and public opinion. This cross‐national and longitudinal study investigates whether the social legitimacy of benefit obligations for the unemployed is affected by the changing economic situation and the varying institutional context. We use data from the European Values Survey, a repeated cross‐sectional survey that was conducted in 1990, 1999 and 2008 in 23 European countries. Support for the conditionality of unemployment benefits is measured with an item that asks whether people who are unemployed should have to take any job available. We find that the main economic indicators – economic growth and the unemployment rate – are significantly related to support for conditionality. People living in wealthier countries are more likely to be in favour of conditionality, whereas a high unemployment rate reduces such support. With regard to institutional features, we find some support for the assumption that people in welfare states with more generous social policies prefer stricter conditionality for access, in order to protect the generous benefits against any misuse