Search results for " Fisica Matematica"

Exact Solutions of the Two Dimensional Boussinesq and Dispersive Water Waves Equations

2010

In this paper two-dimensional Boussinesq and dispersive water waves equations are investigated in exact solutions. The Exp-function method is used for seeking exact solutions of the equations through symbolic computation.

Dynamics of mean-field spin models from basic results in abstract differential equations

1992

The infinite-volume limit of the dynamics of (generalized) mean-field spin models is obtained through a direct analysis of the equations of motion, in a large class of representations of the spin algebra. The resulting dynamics fits into a general framework for systems with long-range interaction: variables at infinity appear in the time evolution of local variables and spontaneous symmetry breaking with an energy gap follows from this mechanism. The independence of the construction of the approximation scheme in finite volume is proven. © 1992 Plenum Publishing Corporation.

A duality-invariant Einstein-Planck relation and its consequences on micro-black holes.

2013

We discuss the consequences of a duality-invariant Einstein–Planck (DIEP) relation on the equation of state of micro black holes. The results are analogous to those obtained from the "world-crystal" model, but with some significative differences, as for instance a limiting vanishing value for temperature for very small black holes. The model leads to a total evaporation of micro black holes but with the final stage being very slow.

Non-equilibrium temperature of well-developed quantum turbulence

2009

Abstract A non-equilibrium effective temperature of quantum vortex tangles is defined as the average energy of closed vortex loops. The resulting thermodynamic expressions for the entropy and the energy in terms of the temperature of the tangle are confirmed by a microscopic analysis based on a potential distribution function for the length of vortex loops. Furthermore, these expressions for the entropy and energy in terms of temperature are analogous to those of black holes: this may be of interest for establishing further connections between topological defects in superfluids and cosmology.

Fractal dimension of superfluid turbulence : A random-walk toy model

2021

This paper deals with the fractal dimension of a superfluid vortex tangle. It extends a previous model [J. Phys. A: Math. Theor. {\bf 43}, 205501 (2010)] (which was proposed for very low temperature), and it proposes an alternative random walk toy model, which is valid also for finite temperature. This random walk model combines a recent Nemirovskii's proposal, and a simple modelization of a self-similar structure of vortex loops (mimicking the geometry of the loops of several sizes which compose the tangle). The fractal dimension of the vortex tangle is then related to the exponents describing how the vortex energy per unit length changes with the length scales, for which we take recent pr…

Complex singularity analysis for vortex layer flows

2021

We study the evolution of a 2D vortex layer at high Reynolds number. Vortex layer flows are characterized by intense vorticity concentrated around a curve. In addition to their intrinsic interest, vortex layers are relevant configurations because they are regularizations of vortex sheets. In this paper, we consider vortex layers whose thickness is proportional to the square-root of the viscosity. We investigate the typical roll-up process, showing that crucial phases in the initial flow evolution are the formation of stagnation points and recirculation regions. Stretching and folding characterizes the following stage of the dynamics, and we relate these events to the growth of the palinstro…

Stock markets and quantum dynamics: A second quantized description

2009

In this paper we continue our description of stock markets in terms of some non-abelian operators which are used to describe the portfolio of the various traders and other observable quantities. After a first prototype model with only two traders, we discuss a more realistic model of market involving an arbitrary number of traders. For both models we find approximated solutions for the time evolution of the portfolio of each trader. In particular, for the more realistic model, we use the stochastic limit approach and a fixed point like approximation. © 2007 Elsevier B.V. All rights reserved

Three-dimensional features in burning plasmas

2019

A next major step in the research toward magnetic fusion energy production is to carry out experimental campaigns exploring regimes with relevant amount of fusion power. So far, the theoretical knowledge of the path toward a fusion burning plasma has been acquired mainly by performing numerical studies in 0 or 1-1.5 dimensions. Due to the marked anisotropy of magnetically confined plasmas, however, three-dimensional effects might play a role. In particular, the drastic change in magnetic topology associated with reconnecting modes on selected rational magnetic surfaces [1] may decrease the thermal electron conductivity parallel to the magnetic field lines, with a consequent impact on the el…

Importance and Unpredictability of Self-organization Processes in Fusion Burning Plasmas

Self-organization processes are considered to have an important role in well confined plasmas produced by present day experiments where the heating source is externally applied. The observation of ``Profile Consistency'' [1] is viewed as a manifestation of the presence of these processes. In the case of fusion burning plasmas close to self-sustainment (ignition) most of the heating due to fusion products is strongly dependent on the evolution of both the plasma temperature and density profiles. Therefore, self-organization is expected to be of considerably greater importance than in the case of non-reacting plasmas. This fact involves a significant degree of unpredictability on the outcome …

Mode-particle Interactions as Sources of Gamma-ray Bubbles in the Galaxy

A plasma outflow coming from the center of Our Galaxy is simulated by an ion beam reaching a nearly stationary magnetic field that can excite lower hybrid waves efficiently in the rarefied plasma (10-2-10-4 cm-3) surrounding the whole galaxy. The electrostatic lower hybrid waves are driven to instability via Cerenkov interaction. In this work we derive (by using a fluid model) the relevant dispersion relation and the expression for the growth rate by solving the dispersion relation both analytically and numerically. Parametric studies show that the growth rate of the instability increases with the beam density. The instability is found to have the maximum growth rate when the perpendicular …