Composite operators from the operator product expansion: what can go wrong?

The operator product expansion is used to compute the matrix elements of composite renormalized operators on the lattice. We study the product of two fundamental fields in the two-dimensional sigma-model and discuss the possible sources of systematic errors. The key problem turns out to be the violation of asymptotic scaling.Comment: Lattice 99 (Improvement and Renormalization), 3 pages, 3 eps figure

Measuring and modelling Internet diffusion using second level domains: the case of Italy

The last 10 years witnessed an exponential growth of the Internet. According to Hobbes' Internet Timeline, the Internet hosts are about 93 million, while in 1989 they were 100,000. The same happens for second level domain names. In July 1989 the registered domains were about 3,900 while they were over 2 million in July 2000. This paper reports about the construction of a database containing daily observations on registrations of second level domain names underneath the it ccTLD in order to analyse the diffusion of Internet among families and businesses. The section of the database referring to domains registered by individuals is analysed. The penetration rate over the relevant population of potential adopters is computed at highly disaggregated geographical level (province). A concentration analysis is carried out to investigate whether the geographical distribution of Internet is less concentrated than population and income suggesting a diffusive effect. Regression analysis is carried out using demographic, social, economic and infrastructure indicators. Finally we briefly describe the further developments of our research. At the present we are constructing a database containing domains registered by firms together with data about the registrants; the idea is to use this new database and the previous one in order to check for the existence of power laws both in the number of domains registered in each province and in the number of domains registered by each firm.Domain names, Internet metrics, Diffusion, Power laws, Zipf s law

Experimental Characterization and Numerical Investigation on the Azzone Visconti Bridge in Lecco (Italy)

AbstractThe paper presents the results of a numerical investigation on the Azzone Visconti Bridge in Lecco (Italy). Starting from the historical data and from an extensive mechanical characterization of both the soil constituting the riverbed and of the masonry constituting the piers, the aim of the analyses is to predict the behaviour of the structure under the testing loading scheme prescribed by the current Italian Code. A finite element structural model has been conceived, and three different models describing the mechanical behaviour of the foundation have been implemented. Limited differences are observed in terms of absolute vertical settlement of the bridge, but important effects are highlighted in terms of stress redistribution within the piers

Prácticas científicas actuales de los académicos formadores de licenciados en Nutrición de la Universidad Nacional del Litoral y la Universidad Nacional de Salta, su relación con la incorporación a la vida académica

Son exiguos y recientes los estudios referentes a los académicos formadores de LN, particularmente en lo concerniente a las características de su incorporación a la vida académica y al desarrollo de sus prácticas científicas actuales, situación que motivó el presente trabajo. Objetivo: Asociar las prácticas científicas de los académicos formadores de LN de la UNL y la UNSa con su incorporación a la vida académica. Diseño Metodológico: estudio cuanti - cualitativo, descriptivo, transversal y correlacional. Universo: docentes de la Licenciatura en Nutrición de la UNL y UNSa categorizados en el PROINCE. Muestra: 23 y 16 docentes categorizados de la UNL y UNSa respectivamente. Instrumento: cuestionario. Para analizar existencia de asociación se aplicó la prueba de chi cuadrado. Resultados: predominio de mujeres que al momento de la incorporación eran mayoritariamente solteras, sin personas a cargo y menores de 35 años. Su primer cargo fue interino y previo a la implementación del PROINCE (1994). Actualmente en la UNL predominan directores de proyectos de investigación a diferencia de la UNSa. La producción científica se ve reflejada en publicaciones en memorias de congresos y revistas nacionales. En lo referente a la formación de recursos humanos se destaca la dirección de tesis de grado siendo escasa la dirección de posgrado y becarios. Conclusión: existe relación entre la mayoría de las dimensiones que caracterizan las prácticas actuales y determinadas características que presentaban los académicos al momento de su incorporación a la vida académica

Fourth-order dispersion mediated modulation instability in dispersion oscillating fibers

We investigate the role played by fourth-order dispersion on the modulation instability process in dispersion oscillating fibers. It not only leads to the appearance of instability sidebands in the normal dispersion regime (as in uniform fibers), but also to a new class of large detuned instability peaks that we ascribe to the variation of dispersion. All these theoretical predictions are experimentally confirmed. (C) 2013 Optical Society of Americ

Uso delle gallerie per la stabilizzione di versanti in frana

L'uso del sottosuolo per la gestione idrogeologica del territorio e per la bonifica delle frane è una so-luzione efficace ed ampiamente utilizzata nel mondo. Nel lavoro dopo un inquadramento generale dell'argomento vengono illustrati alcuni casi studio di particolare interesse

Interconnection of Discrete-Time Dissipative Systems

Strictly proper discrete-time systems cannot be passive. For passivity-based control to be exploited nevertheless, some authors introduce virtual outputs, while others rely on continuous-time passivity and then apply discretization techniques that preserve passivity in discrete-time. Here we argue that quadratic supply rates incorporate and extend the effect of virtual outputs, allowing one to exploit dissipativity properties directly in discrete-time. We derive local dissipativity conditions for a set of nonlinear systems interconnected with arbitrary topology, so that the overall network is guaranteed to be stable. For linear systems, we develop dissipative control conditions that are linear in the supply rate. To demonstrate the validity of our methods, we provide numerical examples in the context of islanded microgrids