Backreaction in Acoustic Black Holes

The backreaction equations for the linearized quantum fluctuations in an acoustic black hole are given. The solution near the horizon, obtained within a dimensional reduction, indicates that acoustic black holes, unlike Schwarzschild ones, get cooler as they radiate phonons. They show remarkable analogies with near-extremal Reissner-Nordstrom black holes.Comment: 4 pages, revtex, 1 figure. revised version, published in pr

The Holographic Interpretation of Hawking Radiation

Holography gives us a tool to view the Hawking effect from a new, classical perspective. In the context of Randall-Sundrum braneworld models, we show that the basic features of four-dimensional evaporating solutions are nicely translated into classical five-dimensional language. This includes the dual bulk description of particles tunneling through the horizon.Comment: 10 pages, 1 figure, Honorable Mention in the Gravity Research Foundation Essay Competition 200

Momentum distribution and coherence of a weakly interacting Bose gas after a quench

We consider a weakly interacting uniform atomic Bose gas with a time-dependent nonlinear coupling constant. By developing a suitable Bogoliubov treatment we investigate the time evolution of several observables, including the momentum distribution, the degree of coherence in the system, and their dependence on dimensionality and temperature. We rigorously prove that the low-momentum Bogoliubov modes remain frozen during the whole evolution, while the high-momentum ones adiabatically follow the change in time of the interaction strength. At intermediate momenta we point out the occurrence of oscillations, which are analogous to Sakharov oscillations. We identify two wide classes of time-dependent behaviors of the coupling for which an exact solution of the problem can be found, allowing for an analytic computation of all the relevant observables. A special emphasis is put on the study of the coherence property of the system in one spatial dimension. We show that the system exhibits a smooth "light-cone effect," with typically no prethermalization.Comment: 24 pages, 12 figure

Verification Results for Age-Structured Models of Economic-Epidemics Dynamics

In this paper we propose a macro-dynamic age-structured set-up for the analysis of epidemics/economic dynamics in continuous time. The resulting optimal control problem is reformulated in an infinite dimensional Hilbert space framework where we perform the basic steps of dynamic programming approach. Our main result is a verification theorem which allows to guess the feedback form of optimal strategies. This will be a departure point to discuss the behavior of the models of the family we introduce and their policy implications

Theoretical and experimental study on mechanical characterisation of a water drop impact on a solid surface

The drop impact phenomenon can be used to study many agricultural aspects related to the rainfall, runoff and irrigation, such as the stability of aggregated and the detachment of fine particles. The aim of this study was to study experimentally and numerically the water drop impact on a solid wall. In a first phase a simple experimental apparatus and basic theoretical concepts were used to investigate the influence of the drop speed on the impact pressure. In the second section, a finite element model able to reproduce the complex phenomenon observed in the experimental phase, was developed. The pressure values obtained by experimental measurement are similar to those calculated on the base of the energy conservation principle (average percentage difference of 15.6%). Numerical model was useful to obtain important information on pressure profile inside the drop and the impact pressure during the splash, at present hard to achieve experimentally. The model was used to estimate also an almost realistic dynamic behaviour of the spreading drop

Costs and structure of technology in the Italian water industry

WP 14/1997; This paper analyses from an empirical point of view the technology underlying the Water industry. First, we study the impact of environmental and quality factors on the production process. Second, different functional forms are analysed in order to represent the technology. Overall results show that the coefficient of hedonic variables are significant and that the best functional form turns to be the transcendental logarithmic one. Finally, evidence on return to scale depends on the functional form adopted and on the inclusion of hedonic variables

La funzione di costo nel servizio idrico. Un contributo al dibattito sul metodo normalizzato per la determinazione della tariffa del servizio idrico integrato

WP 03/1996; Nel processo di riorganizzazione del servizio idrico italiano, imposto dalla ‘Legge Galli', il Comitato per la Vigilanza sull'uso delle Risorse Idriche presso il Ministero del Tesoro ha proposto la formulazione di un metodo normalizzato per la determinazione della tariffa. Il presente lavoro ha sottoposto ad esame tale metodo in merito alla definizione di una funzione di costo operativo del servizio acque potabili. L'analisi ha inteso verificare la capacità interpretativa della forma funzionale proposta e la significatività delle variabili esplicative. I risultati confermano, in generale, la validità della proposta ma indicano l'esigenza di migliorare la capacità esplicativa del modello considerando variabili rappresentative della produttività e del costo del lavor

Before and after privatization: a comparison between competitive firms

WP 02/1998; The analysis regarding the results of firms privatized mainly during the Eighties within competitive sectors confirms the superiority of private control. The comparison between suitable control samples shows an improvement in profitability associated to a clear progress in labour productivity. However, for many firms, this recovery was still insufficient to guarantee an active and lasting presence on the market. This evolution questions the functioning of the market, the selectivity of the financial operators and the incentive system used in the past as an industrial policy tool