Biomedical subjects

J P Badiali

Publications and source records attributed to J P Badiali.

7 recordsLinked to original sources

PubMed2006

Maximum entropy approach to power-law distributions in coupled dynamic-stochastic systems.

Statistical properties of coupled dynamic-stochastic systems are studied within a combination of the maximum information principle and the superstatistical approach. The conditions at which the Shannon entropy functional leads to power-law statistics are investigated. It is demonstrated that, from a quite general point of view, the power-law dependencies may appear as a consequence of "global" constraints restricting both the dynamic phase space and the stochastic fluctuations. As a result, at sufficiently long observation times the dynamic counterpart is driven into a nonequilibrium steady state whose deviation from the usual exponential statistics is given by the distance from the conventional equilibrium.

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PubMed2006

On a mechanism of low-pressure insertion of chain molecules into crystalline matrices.

A microscopic mechanism of low-pressure insertion and separation of chain-like molecules in host matrices is proposed. It is shown that the intramolecular correlations combined to appropriate host activities are responsible for a low-pressure condensation of chain molecules. This allows to recover a fine structure of the isotherms and to explain recent experiments on the insertion of C(2)H(2) and CO(2) guest species into metal-organic microporous materials. We argue that the mechanism should be dominant in low-dimensional host geometries, where the effects related to the chain conformations or reorientations are strongly suppressed and the major factors are the chain connectivity and the segment packing.

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PubMed2006

Negative linear compressibility in confined dilatating systems.

The role of a matrix response to a fluid insertion is analyzed in terms of a perturbation theory and Monte Carlo simulations applied to a hard sphere fluid in a slit of fluctuating density-dependent width. It is demonstrated that a coupling of the fluid-slit repulsion, spatial confinement, and the matrix dilatation acts as an effective fluid-fluid attraction, inducing a pseudocritical state with divergent linear compressibility and noncritical density fluctuations. An appropriate combination of the dilatation rate, fluid density, and the slit size leads to the fluid states with negative linear compressibility. It is shown that the switching from positive to negative compressibility is accompanied by an abrupt change in the packing mechanism.

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PubMed2005

Contact conditions for the charge in the theory of the electrical double layer.

In this paper, from the Born-Green-Yvon equations of the liquid-state theory, we derive a general expression for the charge-density contact value at charged interfaces. This relation is discussed, in particular, for symmetrical electrolytes. We emphasize an essential coupling between the electric properties and the density profile. Limiting behavior at small and large charges at the interface is discussed.

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PubMed1999

Fractal behavior in quantum statistical physics.

The properties of an ideal gas of spinless particles are investigated by using the path integral formalism. It is shown that the quantum paths exhibit a fractal character which remains unchanged in the relativistic domain provided the creation of new particles is avoided, and the Brownian motion remains the stochastic process associated with the quantum paths. These results are obtained by using a special representation of the Klein-Gordon wave equation. On the quantum paths the relation between velocity and momentum is not the usual one. The mean square value of the velocity depends on the time needed to define the velocity and its value shows the interplay between pure quantum effects and thermodynamics. The fractal character is also investigated starting from wave equations by analyzing the evolution of a Gaussian wave packet via the Hausdorff dimension. Both approaches give the same fractal character in the same limit. It is shown that the time that appears in the path integral behaves like an ordinary time, and the key quantity is the time interval needed for the thermostat to give to the particles a thermal action equal to the quantum of action. Thus, the partition function calculated via the path integral formalism also describes the dynamics of the system for short time intervals. For low temperatures, it is shown that a time-energy uncertainty relation is verified at the end of the calculations. The energy involved in this relation has not a thermodynamic meaning but results from the fact that the particles do not follow the equations of motion along the paths. The results suggest that the density matrix obtained by quantification of the classical canonical distribution function via the path integral formalism should not be totally identical to that obtained via the usual route.

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PubMed1999

Electrostatics of a modulated membrane with specific adsorption.

We present a simple model for the electrostatic properties of a modulated membrane separating two different electrolyte solutions. The model is based on an extension to linear Gouy-Chapman theory. Starting from a Hamiltonian which contains a singular part for the surface contributions, we obtain within the mean-field approach a set of equations which allows us to study the equilibrium between the diffuse and singular parts of the charge carriers. It is shown that the interface modulation leads to a higher potential of zero charge compared to the flat system. The value of this effect depends on the interplay between the height and the characteristic length of the interface modulation and the Debye lengths on both sides, even if the adsorption occurs only on one side of the interface. In the latter case, the side where no adsorption occurs locally exhibits a diffuse charge distribution, which averages to zero, but which makes a contribution to the overall potential drop across the interface. We also calculate the electrostatic contribution to the elastic bending modulus of the membrane and show that specific adsorption of ions can destabilize the flat interface.

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PubMed1999

Structural rearrangement of solid surfaces due to competing adsorbate-substrate interactions.

Employing a generalized lattice gas theory and the Brownian dynamics simulation, we show that the competing displacive interaction in an adsorbate may cause a continuous distortive transition in the underlying substrate. The threshold for the transition is determined by the competition of the substrate rigidity and the quasielastic energy induced by the adsorbate. In the presence of a strong pinning and repulsive lateral interaction, the resulting structure appears as a compromise between the square lattice of the substrate and the hexagonal arrangement of the adsorbate. For hexagonal substrate lattices the simulation demonstrates that various adsorbate structures (from honeycomb lattices to quasicrystalline pentagonal configurations) may be observed, depending on the effective radii of interaction. Due to the long-ranged coupling the substrate may acquire a substructure induced by the adsorbate. This paper represents a generalization of the work published in Phys. Rev. Lett. 81, 3904 (1998).

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