Relativistic Hydrodynamics in Isotropic and Anisotropic Cosmological Backgrounds

A seguito di recenti risultati nel campo dell’Astrofisica, con questo elaborato ci si propone di approfondire il ruolo della viscosità in una classe di modelli cosmologici. La discussione ha lo scopo di generalizzare delle tecniche applicate con successo nello studio dei fluidi ideali a sistemi dove anche la viscosità é un parametro che necessita di essere largamente preso in considerazione. Nello specifico, ci si serve di strumenti computazionali e geometrici e di teoria delle equazioni differenziali alle derivate parziali per comprendere, da un punto di vista matematico, come associare le Equazioni di Einstein ai fluidi in specifici background cosmologici. Questo elaborato parte dallo studio dei fluidi ideali in un background di tipo FLRW al fine di generalizzarlo a fluidi viscosi che scorrono in un background di tipo Bianchi I. Infine si indicano alcuni problemi ancora aperti relativi al caso dissipativo e le possibili strategie risolutive di tali questioni.

Analisi della traduzione delle battute nella serie tv The Big Bang Theory

Questo elaborato tratta della traduzione dello humour. Lo humour fino a poco tempo fa era visto come trascurabile e intraducibile. Per questo motivo l'elaborato si concentra sulle varie strategie che si possono utilizzare per tradurre lo humour e spiega inoltre che in alcune circostanze, come in serie TV e film, la sua traduzione sia necessaria per la comprensione di essi.

Conditional entropy and predictability for non-reversible Markov systems

The purpose of this thesis is to clarify the role of non-equilibrium stationary currents of Markov processes in the context of the predictability of future states of the system. Once the connection between the predictability and the conditional entropy is established, we provide a comprehensive approach to the definition of a multi-particle Markov system. In particular, starting from the well-known theory of random walk on network, we derive the non-linear master equation for an interacting multi-particle system under the one-step process hypothesis, highlighting the limits of its tractability and the prop- erties of its stationary solution. Lastly, in order to study the impact of the NESS on the predictability at short times, we analyze the conditional entropy by modulating the intensity of the stationary currents, both for a single-particle and a multi-particle Markov system. The results obtained analytically are numerically tested on a 5-node cycle network and put in correspondence with the stationary entropy production. Furthermore, because of the low dimensionality of the single-particle system, an analysis of its spectral properties as a function of the modulated stationary currents is performed.

Numerical study on viscoelastic behavior of polypropylene fiber reinforced concrete subjected to temperature variations using LDPM theory

This thesis is focused on the viscoelastic behavior of macro-synthetic fiber-reinforced concrete (MSFRC) with polypropylene studied numerically when subjected to temperature variations (-30 oC to +60 oC). LDPM (lattice discrete particle model), a meso-scale model for heterogeneous composites, is used. To reproduce the MSFRC structural behavior, an extended version of LDPM that includes fiber effects through fiber-concrete interface micromechanics, called LDPM-F, is applied. Model calibration is performed based on three-point bending, cube, and cylinder test for plain concrete and MSFRC. This is followed by a comprehensive literature study on the variation of mechanical properties with temperature for individual fibers and plain concrete. This literature study and past experimental test results constitute inputs for final numerical simulations. The numerical response of MSFRC three-point bending test is replicated and compared with the previously conducted experimental test results; finally, the conclusions were drawn. LDPM numerical model is successfully calibrated using experimental responses on plain concrete. Fiber-concrete interface micro-mechanical parameters are subsequently fixed and LDPM-F models are calibrated based on MSFRC three-point bending test at room temperature. Number of fibers contributing crack bridging mechanism is computed and found to be in good agreement with experimental counts. Temperature variations model for individual constituents of MSFRC, fibers and plain concrete, are implemented in LDPM-F. The model is validated for MSFRC three-point bending stress-CMOD (crack mouth opening) response reproduced at -30 oC, -15 oC, 0 oC, +20 oC, +40 oC and +60 oC. It is found that the model can well describe the temperature variation behavior of MSFRC. At positive temperatures, simulated responses are in good agreement. Slight disagreement in negative regimes suggests an in-depth study on fiber-matrix interface bond behavior with varying temperatures.