Towards a precise determination of the topological susceptibility in the SU(3) Yang-Mills theory

An ongoing effort to compute the topological susceptibility for the SU(3) Yang-Mills theory in the continuum limit with a precison of about 2% is reported. The susceptibility is computed by using the definition of the charge suggested by Neuberger fermions for two values of the negative mass parameter s. Finite volume and discretization effects are estimated to meet this level of precision. The large statistics required has been obtained by using PCs of the INFN-GRID. Simulations with larger lattice volumes are necessary in order to better understanding the continuum limit at small lattice spacing values.Comment: 8 pages, 2 figures, The XXVII International Symposium on Lattice Field Theory - LAT2009,July 26-31 2009,Peking University, Beijing, Chin

La disciplina degli scarichi di acque reflue industriali

La tesi ricostruisce la disciplina riguardante gli scarichi di acque reflue industriali, ripercorrendo, anzitutto, le principali tappe della normativa in materia di tutela delle acque dall’inquinamento. In particolare, si rileva come, rispetto alla prima legge in materia (l. n. 319/1976, c.d. legge Merli), il legislatore adotti, a partire dal d.lgs. n. 152/1999 (c.d. Testo Unico delle acque), un approccio completamente nuovo, volto a regolare in modo organico non un singolo settore, ma l’intero ciclo delle acque, soprattutto attraverso il criterio del collegamento dei limiti di emissione degli scarichi agli obiettivi di qualità dei corpi idrici. Tale approccio integrato alla tutela delle acque sarà consacrato dalla Direttiva 2000/60/CE (c.d. Direttiva Acque) e confermato dalla normativa vigente, contenuta nel d.lgs. n. 152/2006 (c.d. Codice dell’ambiente). Nella trattazione, si descrive il percorso evolutivo della nozione di «scarico» e si delineano le diverse tipologie di acque reflue, con particolare riguardo alla definizione di «acque reflue industriali» e alla questione, molto dibattuta, dell’assimilabilità delle acque meteoriche di dilavamento ai reflui industriali. In seguito, si individuano le norme sui divieti di scarico, nonché sugli scarichi contenenti sostanze pericolose. Si ricostruisce poi il sistema autorizzatorio, anche con riferimento alle discipline dell’AIA e dell’AUA. Infine, si conclude con la descrizione dell’attività di controllo e del relativo regime sanzionatorio

Large statistics study of the topological charge distribution in the SU(3) gauge theory

We present preliminary results for a high statistics study of the topological charge distribution in the SU(3) Yang-Mills theory obtained by using the definition of the charge suggested by Neuberger fermions. We find statistical evidence for deviations from a gaussian distribution. The large statistics required has been obtained by using PCs of the INFN-GRID.Comment: Talk given at the 24th International Symposium on Lattice Field Theory (Lattice 2006), Tucson, Arizona, 23-28 Jul 200

Remarks on the Gauge Dependence of the RI/MOM Renormalization Procedure

The RI/MOM non-perturbative renormalization scheme is studied on the lattice in SU(3) quenched QCD with Wilson fermions. The gauge dependence of some fermion bilinear renormalization constants is discussed by comparing data which have been gauge-fixed in two different realizations of the Landau gauge and in a generic covariant gauge. The very good agreement between the various sets of results and the theory indicates that the numerical uncertainty induced by the lattice gauge-fixing procedure is moderate and below the statistical errors.Comment: 11 pages, 3 figure

The String Tension in Gauge Theories

A review article on string tension concept and their relevance as non-perturbative quantity on the study of quark confinement in lattice gauge theories. A detailed description of a variety of methods to measure the string tension on the lattice and an indication of the most promising developments is proposed.Comment: Postscript file, 46 pages and 14 figure

High Strain Rate Dynamic Response of Aluminum 6061 Micro Particles at Elevated Temperatures and Varying Oxide Thicknesses of Substrate Surface

Cold spray is a unique additive manufacturing process, where a large number of ductile metal micro particles are deposited to create new surface coatings or free-standing structures. Metallic particles are accelerated through a gas stream, reaching velocities of over 1 km/s. Accelerated particles experience a high-strain-rate microscopic ballistic collisions against a target substrate. Large amounts of kinetic energy results in extreme plastic deformation of the particles and substrate. Though the cold spray process has been in use for decades, the extreme material science behind the deformation of particles has not been well understood due to experimental difficulties arising from the succinct spatial (10 μm) and temporal scales (10 ns). In this study, using a recently developed micro-ballistic method, the advanced laser induced projectile impact test (α-LIPIT), the dynamic behavior of micro-particles during the collision is precisely defined. We observe single aluminum 6061 alloy particles, approximately 20μm in diameter, impact and rebound off of a rigid target surface over a broad range of impact speeds, temperatures, and substrate oxide film thicknesses. Through observation of the collisions, we extract characteristic information of the dynamic response of particles as well as the relationship with various parameters (e.g. surrounding temperature, particle diameter, oxide thickness, and impact velocity). By impacting a polished aluminum 6061 alloy substrate we are able to mimic the collision events that occur during cold spray deposition. The connection between the temperature increase and the oxide thickness plays a role in theorizing the cause of unexpected phenomena, such as increased rebound energies at higher temperatures. Highly-controlled single particle impacts results, are provided to calibrate and improve computational simulations as well. This, in turn, can provide insight into the underlying material science behind the cold spray process

Glueballs and mesons in the superfluid phase of two-color QCD

QCD with two colors undergoes a transition to a superfluid phase with diquark condensate when the quark chemical potential equals half the pion mass. We investigate the gluonic aspects of the transition by inspecting the behavior of the glueball correlators evaluated via a multi-step smearing procedure for several values of chemical potential ranging between zero and the saturation threshold. The results are based on an analysis of 0++ glueball correlators, on a sample of 40000 independent configurations on each parameter set. The amplitudes of the correlators peak for \mu = m_\pi/2,indicating that the superfluid phase transition affects the gluonic sector as well. The mass of the fundamental state decreases in the superfluid phase, and the amplitude of the propagators drops, suggesting a reduction of the gluon condensate, in agreement with model calculations. The analysis of the smearing dependence of the results helps disentangling the role of long and short distance phenomena at the superfluid transition.Comment: 7 pages, 5 figures, talk presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4, 2007, Regensburg,German

SU(2) Glueballs, diquarks and mesons in dense matter

We present preliminary results from a high statistics study of 2-color QCD at low temperature and non-zero baryon density. The simulations are carried out on a 6^3*12 lattice and use a standard hybrid molecular dynamics algorithm for staggered fermions for two values of quark mass. Observables include glueball correlators evaluated via a multi-step smearing procedure as well as scalar and vector mesons and diquarks.Comment: Poster presented at Lattice 2003 (Non zero temperature and density), 3 pages, 4 figure

The String Tension in Gauge Theories: a Suggestion for a New Measurement Method

We discuss a new method for testing confinement and measuring the string tension (in the Coulomb gauge). Our numerical simulations demonstrate that the problems related to Gribov copies are not harmful and that the method is effective in the case of pure gauge Q.C.D.. We discuss the relevance of the method for studying gauge theories coupled to fermionic matter.Comment: 9 pages, Latex style, 4 postscript figures appended, ROMA 92-90