125 research outputs found
Comisso critico: il problema del romanzo italiano
No full textGiovanni Comisso (1895-1969) è una figura poliedrica, che merita di essere ripresa in esame anche da punti di vista meno noti. L’«italiano errante per l’Italia» (come suona un suo emblematico titolo) ha infatti trovato il tempo per riflettere, da critico, sulla nostra tradizione letteraria e sulla sua difficile convivenza con il più moderno dei generi, il romanzo. Sulla base degli articoli critici di Comisso, il contributo prova a ricostruire una mappa delle predilezioni dello scrittore, in particolare per quanto riguarda la narrativa italiana dell'Ottocento (con speciale attenzione a Leopardi, Verga e Nievo) e i possibili sviluppi futuri della forma romanzo
Modelling 3D Dynamic Cloud Fields to Investigate the Performance of FSO SatCom Systems
No full textWith increasing data rate requirements on SatCom systems there is a push to use higher frequency carriers. Although free space optical communications would meet these demands, they are severely limited by the weather conditions affecting the ground stations. Therefore, it is important to model these phenomena to predict the possibility of link outages so that an appropriate fade mitigation technique can be applied. This contribution aims to extend a model in the literature (Stochastic Model of Clouds) to include the time variability of the cloud field. The temporal evolution is studied using satellite observations and is introduced into the model by inputting ERA5 data chronologically, which has been linearly interpolated to a temporal resolution of 1 minute. The new model is then used to study the effect of site diversity for the mitigation of cloud attenuation on a GEO-Earth optical link operating at 1.55 mu mathrm{m}
Nonlinear response of a neoclassical four-field magnetic reconnection model to localized current drive
No full textIn tokamaks magnetic islands arise from an unstable process of tearing and reconnecting of helical field lines across rational surfaces. After a linear stage the magnetic instability develops through three characteristic nonlinear stages where increasingly complex topological alterations occur in the form of the magnetic islands.
The problem of response of reconnection process to the injection of an external current suitably localized is addressed using a four-field model in a plane slab plasma, with a novel extension to account consistently of the relevant neoclassical effects, such as bootstrap current and pressure anisotropy. The results found have implications on the interpretation of the possible mechanism of present day experimental results on neoclassical tearing modes as well as on the concepts for their control or
avoidance
Sustainable Simultaneous Communications in Ad-Hoc Networks Using Smart Antenna Systems
No full textThis article proposes an analytical model for evaluating the number of simultaneous communications that can be sustained by an ad-hoc network in which the nodes are equipped with fully adaptive smart antennas. The presented mathematical framework adopts realistic models for the antenna radiation pattern and the channel behavior, and is able to take into account the network topology and the characteristics of the medium access control (MAC) protocol in the spatial domain. The model is employed to investigate the impact of the spatial channel model and of the angular spread on network performance. Additionally, this article examines the influence of the transmission policy of the control and data packets of the MAC layer on the number of simultaneous communications
Performance Comparison of Advanced Antenna Systems for Wireless Mesh Routers in an Outdoor Environment
No full textFast gyrofluid reconnection in high temperature plasmas
No full textThe nonlinear evolution of collisionless magnetic reconnection in the presence of a strong guide field is analyzed on the basis of a gyrofluid model for compressible plasmas. It is found that, in a certain regime of plasma parameters, ion gyration contributes to generate two distinctive nonlinear acceleration phases of the growth rate. Furthermore, in the advanced nonlinear phase, finite values of the ion Larmor radius are identified to be responsible for a splitting of the narrow layer structures of ion guiding-center parallel velocity and density perturbations around the magnetic equilibrium null line
Two-dimensional effects in the problem of tearing modes control by electron cyclotron current drive
No full textThe design of means to counteract robustly the classical and neoclassical tearing modes in a tokamak by localized injection of an external control current requires an ever growing understanding of the physical process, beyond the Rutherford-type zero-dimensional models. Here a set of extended magnetohydrodynamic nonlinear equations for four continuum fields is used to investigate the two-dimensional effects in the response of the reconnecting modes to specific inputs of the localized external current. New information is gained on the space- and time-dependent effects of the external action on the two-dimensional structure of magnetic islands, which is very important to formulate applicable control strategies.</jats:p
Formation of plasmoid chains in fusion relevant plasmas
No full textThe formation of plasmoid chains is explored for the first time within the context of the Taylor problem, in which magnetic reconnection is driven by a small amplitude boundary perturbation in a tearing-stable slab plasma equilibrium. Numerical simulations of a magnetohydrodynamical model of the plasma show that for very small plasma resistivity and viscosity, the linear inertial phase is followed by a nonlinear Sweet-Parker evolution, which gives way to a faster reconnection regime characterized by a chain of plasmoids instead of a slower Rutherford phas
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