The calculation of critical amplitudes in SU(2) lattice gauge theory
We calculate the critical amplitudes of the Polyakov loop and its susceptibility at the deconfinement transition of (3 + 1)-dimensional SU(2) gauge theory. To this end we study the corrections due to irrelevant exponents in the scaling functions. As a guiding line for determining the critical amplitudes we use envelope equations which we derive from the finite site scaling formulae of the observables. We have produced new high precision data on N-sigma(3) x 4 lattices for N-sigma = 12, 18, 26 and 36, With these data we find different corrections to the asymptotic scaling behaviour above and below the transition. Our result for the universal ratio of the susceptibility amplitudes is C+/C- = 4.72(11) and thus in excellent agreement with a recent measurement for the 3d Ising model. (C) 1999 Published by Elsevier Science B.V.
Universal amplitude ratios in the three-dimensional Ising model
We present a high precision Monte Carlo study of various universal amplitude ratios of the three-dimensional Ising spin model. Using state of the art simulation techniques we study the model close to criticality in both phases. Great care is taken to control systematic errors due to finite size effects and correction to scaling terms. We obtain , and . Our results are compatible with those obtained by field theoretic methods applied to the theory and high- and low-temperature series expansions of the Ising model. The mismatch with a previous Monte Carlo study by Ruge et al remains to be understood.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%