Search results for " Fisica Matematica"

The completion of a C*-algebra with a locally convex topology

2006

There are examples of C*-algebras A that accept a locally convex *-topology t coarser than the given one, such that Ae[t] (the completion of A with respect to t) is a GB*-algebra. The multiplication of A[t] may be or not be jointly continuous. In the second case, Ae[t] may fail being a locally convex *-algebra, but it is a partial *-algebra. In both cases the structure and the representation theory of Ae[t] are investigated. If A[t+] denotes the t-closure of the positive cone A+ of the given C*-algebra A, then the property A[t]+ \cap (−A[t]+) = {0} is decisive for the existence of certain faithful *-representations of the corresponding *-algebra Ae[t].

Extension of representations in quasi *-algebras

2009

Let $(A, A_o)$ be a topological quasi *-algebra, which means in particular that $A_o$ is a topological *-algebra, dense in $A$. Let $\pi^o$ be a *-representation of $A_o$ in some pre-Hilbert space ${\cal D} \subset {\cal H}$. Then we present several ways of extending $\pi^o$, by closure, to some larger quasi *-algebra contained in $A$, either by Hilbert space operators, or by sesquilinear forms on ${\cal D}$. Explicit examples are discussed, both abelian and nonabelian, including the CCR algebra.

Second sound propagation in laminar and turbulent superfluid 4He via extended thermodynamics

2012

In this work, previous results on the complex propagation of second sound in laminar and turbulent superfluid 4He are reported. Furthermore the case of inhomogeneous superfluid turbulence is examined and, in particular, the wave propagation is investigated in the presence of an anisotropic vortex tangle. Two cases of physical interest are considered: wave front collinear and orthogonal to the heat flux.

Speeds of discontinuity waves in turbulent superfluids

2012

In this work, using a hydrodynamical model previously formulated, the possible modes of propagation of discontinuity waves in turbulent superfluids are studied in the nonlinear regimes. The field equations are written down, then the wave speeds are determined in a constant state.

Large number asympotics for dispersed, non regular distributions of inclusions in a fluid

We shall describe the large number asymtpotics for systems consisting in a fluid surrounding a non regular distributions of inclusions. The fluid satisfies a given boundary (or initial-boundary) value problem (involving a second order operator of divergence form) in a perforated domain and the holes in the domain are occupied by the inclusions; fluid and inclusions are coupled by the boundary conditions only. These systems are meant as models at some "microscopic" scale for describing, in a suitable asymptotics, the behaviour at a macroscopic level of composite media. We shall give a general overview of the results about the homogenized limit of such a kind of systems obtained in previous w…

Matter-wave dark solitons in boxlike traps

2017

Motivated by the experimental development of quasihomogeneous Bose-Einstein condensates confined in boxlike traps, we study numerically the dynamics of dark solitons in such traps at zero temperature. We consider the cases where the side walls of the box potential rise either as a power law or a Gaussian. While the soliton propagates through the homogeneous interior of the box without dissipation, it typically dissipates energy during a reflection from a wall through the emission of sound waves, causing a slight increase in the soliton's speed. We characterize this energy loss as a function of the wall parameters. Moreover, over multiple oscillations and reflections in the boxlike trap, the…

Studies in thermal and dynamical duality

2011

Applications of topological *-algebras of unbounded operators to modified quons

2002

In this paper we discuss some applications of topological *-algebras of unbounded operators to what we call Modified Quons (MQ). In particular, the existence of the thermodynamical limit for some models of free and interacting modified quons is proved in the same framework proposed by the author in a recent paper for ordinary bosons.

States and representations of CQ∗ -algebras

1994

A class of quasi *-algebras which exhibits some analogy with C*-algebras is studied. The extension of some properties of C*-algebras which are relevant for physical applications (such as the GNS-representation) is discussed. Quasi *-algebras of linear operators in rigged Hilbert space are shown to be typical examples of the developed framework.

Nonlocal and rotational effects in superfluid turbulence

2008

We discuss phenomenological equations for the evolution of vortex tangle in counterflow superfluid turbulence, which takes into account the influence of the non local effects, both in absence and in the presence of rotation.