Parton Interaction Rates in the Quark-Gluon Plasma

The transport interaction rates of elastic scattering processes of thermal partons in the quark-gluon plasma are calculated beyond the leading logarithm approximation using the effective perturbation theory for QCD at finite temperatures developed by Braaten and Pisarski. The results for the ordinary and transport interaction rates obtained from the effective perturbation theory are compared to perturbative approximations based on an infrared cut-off by the Debye screening mass. The relevance of those interaction rates for a quark-gluon plasma possibly formed in ultrarelativistic heavy ion collisions are discussed.Comment: 11 pages, 2 figures (not included), REVTex, UGI-93-0

The aperture array verification system 1 : system overview and early commissioning results

The design and development process for the Square Kilometre Array (SKA) radio telescope’s Low Frequency Aperture Array component was progressed during the SKA pre-construction phase by an international consortium, with the goal of meeting requirements for a critical design review. As part of the development process a full-sized prototype SKA Low ‘station’ was deployed – the Aperture Array Verification System 1 (AAVS1). We provide a system overview and describe the commissioning results of AAVS1, which is a low frequency radio telescope with 256 dual-polarisation log-periodic dipole antennas working as a phased-array. A detailed system description is provided, including an in-depth overview of relevant sub-systems, ranging from hardware, firmware/software, calibration and control sub-systems. Early commissioning results cover initial bootstrapping, array calibration, stability testing, beamforming and on-sky sensitivity validation. Lessons learned are presented, as well as future developments.peer-reviewe