Use Of Extended Sources Research Articles

QGP hydrodynamical study using energy-momentum in-medium deposition by an extended source.

The quark-gluon plasma (QGP) is created under extreme conditions, such as the ones prevailing in heavy ion collisions. The characterization of the QGP can be done using high-pT probes such as the partons that are created through hard scatterings in the fireball. These fast-moving partons lose energy and momentum along their traveled path through the medium. The parton deposition of energy-momentum creates an in-medium disturbance that can be described using approximations within relativistic hydrodynamics in a defined regime of the QGP evolution. Based on earlier research in this field, we study the use of extended sources that depend on the location of the parton-jet in the initial stages of the QGP evolution. We explore this approach as a way to complement the current numerical landscape of hydrodynamical QGP studies and to eventually generate initial conditions that can be used as input of hydrodynamical numerical simulations.

Monte Carlo analysis of the influence of germanium dead layer thickness on the HPGe gamma detector experimental efficiency measured by use of extended sources

We have carried out a study to figure out the influence of crystal inactive-layer thickness on gamma spectra measured by an HPGe detector. The thickness of this dead layer (DL) is not known (no information about it was delivered by the manufacturer) due to the existence of a transition zone where photons are increasingly absorbed. To perform this analyses a virtual model of a Canberra HPGe detector was produced with the aid of MCNPX 2.7 code.The main objective of this work is to produce an optimal modeling for our GPGe detector. To this end, the study included the analysis of the total inactive germanium layer thickness and the active volume that are needed in order to obtain the smallest discrepancy between calculated and experimental efficiencies. Calculations and measurements were performed for all of the radionuclides included in a standard calibration gamma cocktail solution. Different geometry sources were used: a Marinelli and two other new sources represented as S(1) and S(2). The former was used for the determination of the active volume, whereas the two latter were used for the determination of the face and lateral DL, respectively. The model was validated by comparing calculated and experimental full energy peak efficiencies in the 50–1900keV energy range. the results show that the insertion of the DL parameter in the modeling is absolutely essential to reproduce the experimental results, and that the thickness of this DL varies from one position to the other on the detector surface.

Perturbative versus lattice QCD energy density correlators at high temperatures

Correlators of magnetic and electric field energy density are investigated for SU( N c ) gauge theory at high temperatures T. A separations z ⩽ 2/ T the correlators are shown to be dominated by a power-law behavior even for finite gluon screening masses. This continuum behavior is well approximated on current 4 × 16 3-lattices in the perturbative limit and leads to a considerable overestimate of screening masses deduced from fitting the lattice correlators with conventional exponential forms. The use of extended sources and sinks to enhance the signal improves the situation for screening masses m ⪢ T but leads to a largely uncontrolled error for masses less than T. In fact, we show that recent lattice QCD data of Grossmann et al., from which a magnetic screening mass m M ∼ 2.9 T was deduced, may even be consistent with a vanishing actual magnetic screening mass.

Astigmatism in reflector antennas: measurement and correction

Investigates astigmatism is Cassegrain antennas from cross scans through in-and-out-of-focus diffraction images of extended radio sources. The use of extended sources is of interest for large (mm-wavelength) telescopes where the bright planets subtend a substantial fraction of the beam. The experimental and theoretical results presented refer to the IRAM 30-m telescope and measurements at 7.3 mm-1.3 mm wavelength; however, extrapolation to other telescopes is evident. The authors report on an experiment to correct the astigmatism (phase) at a position close to the focal plane of the telescope, i.e. the flat surface of the corotating Nasmyth mirror. >

Partial Coherence and Practical Radiometry

A review is presented of recent claims on the effects of partial coherence in radiometric measurements, particularly in relation to spectral irradiance intercomparisons. It is shown that for practical sources typically used in radiometric laboratories, effects claimed to be due to partial coherence are equivalent to those of diffraction and interference associated with the use of extended sources. The relative importance of these effects may then be estimated using existing literature on diffraction corrections in radiometry. Estimates of the importance of coherence may be made from comparison of coherence dimensions with aperture sizes; where small apertures are used, coherence theory may be required to superimpose correlated fields.