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Prieto-Castrillo F.,New England Complex Systems Institute | Astillero A.,University of Extremadura | Boton-Fernandez M.,Research Center for Energy
Journal of Grid Computing | Year: 2015

In this work we present analytic expressions for the expected values of the performance metrics of parallel applications when the distributed computing infrastructure has a complex topology. Through active probing tests we analyse the structure of a real distributed computing environment. From the resulting network we both validate the analytic expressions and explore the performance metrics under different conditions through Monte Carlo simulations. In particular we gauge computing paradigms with different hierarchical structures in computing services. Fully decentralised (i.e., peer-to-peer) environments provide the best performance. Moreover, we show that it is possible to improve significantly the parallel efficiency by implementing more intelligent configurations of computing services and task allocation strategies (e.g., by using a betweenness centrality measure). We qualitatively reproduce results of previous works and provide closed-form solutions that link topology, application’s structure and allocation parameters when job dependencies and a complex network structure are considered. © 2014, Springer Science+Business Media Dordrecht. Source


Pacilio M.,Azienda Ospedaliera San Camillo Forlanini | Amato E.,Messina University | Lanconelli N.,University of Bologna | Basile C.,Azienda Ospedaliera San Camillo Forlanini | And 9 more authors.
Physics in Medicine and Biology | Year: 2015

This study compares 3D dose distributions obtained with voxel S values (VSVs) for soft tissue, calculated by several methods at their current state-of-the-art, varying the degree of image blurring. The methods were: 1) convolution of Dose Point Kernel (DPK) for water, using a scaling factor method; 2) an analytical model (AM), fitting the deposited energy as a function of the source-target distance; 3) a rescaling method (RSM) based on a set of high-resolution VSVs for each isotope; 4) local energy deposition (LED). VSVs calculated by direct Monte Carlo simulations were assumed as reference. Dose distributions were calculated considering spheroidal clusters with various sizes (251, 1237 and 4139 voxels of 3 mm size), uniformly filled with 131I, 177Lu, 188Re or 90Y. The activity distributions were blurred with Gaussian filters of various widths (6, 8 and 12 mm). Moreover, 3D-dosimetry was performed for 10 treatments with 90Y derivatives. Cumulative Dose Volume Histograms (cDVHs) were compared, studying the differences in D95%, D50% or Dmax (ΔD95%, ΔD50% and ΔDmax) and dose profiles. For unblurred spheroidal clusters, ΔD95%, ΔD50% and ΔDmax were mostly within some percents, slightly higher for 177Lu with DPK (8%) and RSM (12%) and considerably higher for LED (ΔD95% up to 59%). Increasing the blurring, differences decreased and also LED yielded very similar results, but D95% and D50% underestimations between 30-60% and 15-50%, respectively (with respect to 3D-dosimetry with unblurred distributions), were evidenced. Also for clinical images (affected by blurring as well), cDVHs differences for most methods were within few percents, except for slightly higher differences with LED, and almost systematic for dose profiles with DPK (-1.2%), AM (-3.0%) and RSM (4.5%), whereas showed an oscillating trend with LED. The major concern for 3D-dosimetry on clinical SPECT images is more strongly represented by image blurring than by differences among the VSVs calculation methods. For volume sizes about 2-fold the spatial resolution, D95% and D50% underestimations up to about 60 and 50% could result, so the usefulness of 3D-dosimetry is highly questionable for small tumors, unless adequate corrections for partial volume effects are adopted. © 2015 Institute of Physics and Engineering in Medicine. Source

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