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Radio Spectra (radio + spectrum)
Selected AbstractsAre radio-loud Broad Absorption Line Quasars young sources?ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009F.M. Montenegro-Montes Abstract Studying Broad Absorption Line Quasars (BAL QSOs) is interesting because they probe the physics of the AGN environment, and because AGN outflows are important ingredients in many recent astrophysical puzzles. In the last decade, a substantial population of radio BAL QSOs was discovered and we have started a characterisation of the radio-loud BAL QSO population studying their radio spectra, radio morphology and polarisation properties. Our high-resolution radio maps show that BAL QSOs are compact radio sources with projected linear sizes below 1 kpc. Most BAL QSOs in our sample are unpolarised or weakly polarised at 8.4 GHz. They display convex radio spectra which typically flatten at low frequencies and become steeper at high frequencies, i.e. above 20 GHz. Many of these characteristics are common to the population of young radio sources, like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources. The above supports the hypothesis that BAL QSOs might be related to the initial stages in the AGN evolution (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] High Frequency Peakers: The faint sampleASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009C. Stanghellini Abstract We present a sample of sources with convex radio spectra peaking at frequencies above a few GHz, known as "High Frequency Peakers" (HFPs). A "bright" sample with a flux density limit of 300 mJy at 5 GHz has been presented by Dallacasa et al. (2000). Here we present the "faint" sample with flux density between 50 and 300 mJy at 5 GHz, restricted to the area around the North Galactic Cap, where the FIRST catalogue is available. The candidates have been observed with the VLA at several frequencies ranging from 1.4 to 22 GHz, in order to derive a simultaneous radio spectrum. The final list of confirmed HFP sources consists of 61 objects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] RubAre symmetric radio spectra of some GPS/HFP sources related to a statistical acceleration mechanism?rikASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009A. Maselli Abstract We present the results of a new spectral analysis of a sample of HFPs. We took from literature simultaneous radio measurements at various epochs and studied the symmetry of flux distribution around the peak frequency by means of a logparabolic fit. We found that a large fraction of spectra are symmetric and propose that this property may be a consequence of statistical acceleration (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Economist as Engineer: Game Theory, Experimentation, and Computation as Tools for Design EconomicsECONOMETRICA, Issue 4 2002Alvin E. Roth Economists have lately been called upon not only to analyze markets, but to design them. Market design involves a responsibility for detail, a need to deal with all of a market's complications, not just its principle features. Designers therefore cannot work only with the simple conceptual models used for theoretical insights into the general working of markets. Instead, market design calls for an engineering approach. Drawing primarily on the design of the entry level labor market for American doctors (the National Resident Matching Program), and of the auctions of radio spectrum conducted by the Federal Communications Commission, this paper makes the case that experimental and computational economics are natural complements to game theory in the work of design. The paper also argues that some of the challenges facing both markets involve dealing with related kinds of complementarities, and that this suggests an agenda for future theoretical research. [source] Strange Bids: Bidding Behaviour in the United Kingdom's Third Generation Spectrum Auction,THE ECONOMIC JOURNAL, Issue 505 2005Tilman Börgers This article studies bidding behaviour in the auction of radio spectrum for third generation mobile telephone services which took place in the UK in the Spring of 2000. We show that several companies' bidding behaviour deviates strongly from straightforward bidding with private values. In particular some companies' evaluation of the added advantage of having a large licence rather than a small licence seemed to change dramatically during the auction. No compelling explanation of this phenomenon seems available at this stage. We conclude that it is less well understood than previously believed how spectrum auctions work. [source] High Frequency Peakers: The faint sampleASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009C. Stanghellini Abstract We present a sample of sources with convex radio spectra peaking at frequencies above a few GHz, known as "High Frequency Peakers" (HFPs). A "bright" sample with a flux density limit of 300 mJy at 5 GHz has been presented by Dallacasa et al. (2000). Here we present the "faint" sample with flux density between 50 and 300 mJy at 5 GHz, restricted to the area around the North Galactic Cap, where the FIRST catalogue is available. The candidates have been observed with the VLA at several frequencies ranging from 1.4 to 22 GHz, in order to derive a simultaneous radio spectrum. The final list of confirmed HFP sources consists of 61 objects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||