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F Gulminelli

Publications and source records attributed to F Gulminelli.

9 recordsLinked to original sources
PubMed2004

Exact pairing correlations for one-dimensionally trapped fermions with stochastic mean-field wave functions.

The canonical thermodynamic properties of a one-dimensional system of interacting spin-1/2 fermions with an attractive zero-range pseudopotential are investigated within an exact approach. The density operator is evaluated as the statistical average of dyadics formed from a stochastic mean-field propagation of independent Slater determinants. For a harmonically trapped Fermi gas and for fermions confined in a 1D-like torus, we observe the transition to a quasi-BCS state with Cooper-like momentum correlations and an algebraic long-range order. For a few trapped fermions in a rotating torus, a dominant superfluid component with quantized circulation can be isolated.

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PubMed2003

Influence of the coulomb interaction on the liquid-gas phase transition and nuclear multifragmentation.

The liquid-gas phase transition is analyzed from the topologic properties of the event distribution in the observables space. A multicanonical formalism allows one to directly relate the standard phase transition with neutral particles to the case where the nonsaturating Coulomb interaction is present, and to interpret the Coulomb effect as a deformation of the probability distributions and a rotation of the order parameter. This formalism is applied to a statistical multifragmentation model and consequences for the nuclear multifragmentation phase transitions are drawn.

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PubMed2003

Transient backbending behavior in the Ising model with fixed magnetization.

The physical origin of the backbendings in the equations of state of finite but not necessarily small systems is studied in the Ising model with fixed magnetization (IMFM) by means of the topological properties of the observable distributions and the analysis of the largest cluster with increasing lattice size. Looking at the convexity anomalies of the IMFM thermodynamic potential, it is shown that the order of the transition at the thermodynamic limit can be recognized in finite systems independently of the lattice size. General statistical mechanics arguments and analytical calculations suggest that the backbending in the caloric curve is a transient behavior which should not converge to a plateau in the thermodynamic limit, while the first-order transition (in the Ehrenfest sense) is still signaled by a discontinuity in the magnetization equation of state.

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PubMed2002

Failure of thermodynamics near a phase transition.

In the vicinity of a first-order phase transition, the equation of state might be different when the extensive variable is controlled instead of the intensive one, violating the uniqueness of thermodynamics. A sufficient condition for this nonequivalence to survive at the thermodynamical limit is worked out for classical systems. If energy consists of a kinetic and a potential part, the microcanonical ensemble does not converge towards the canonical ensemble when the kinetic heat capacity is larger than the modulus of the negative interaction heat capacity.

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PubMed2001

Topology of event distributions as a generalized definition of phase transitions in finite systems.

We propose a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. This generalizes the definitions based on the curvature anomalies of thermodynamical potentials, provides a natural definition of order parameters, and can be related to the Yang-Lee theorem in the thermodynamical limit. It is directly operational from the experimental point of view. It allows to study phase transitions in Gibbs equilibria as well as in other ensembles such as the Tsallis ensemble.

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PubMed2000

Caloric curves and energy fluctuations in the microcanonical liquid-Gas phase transition

In this paper we study a microcanonical lattice gas model with a constrained average volume. We show that the caloric curve explicitly depends on the considered transformation of the volume with the excitation energy and so does not bear direct information on the characteristics of the phase transition. Conversely, partial energy fluctuations are demonstrated to be a direct measure of the equation of state. Since the heat capacity has a negative branch in the phase transition region, the presence of abnormally large kinetic energy fluctuations is a signal of the liquid-gas phase transition.

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