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Biomedical subjects

A Pelizzola

Publications and source records attributed to A Pelizzola.

At least 19 recordsLinked to original sources
PubMed2004

Two-dimensional lattice-fluid model with waterlike anomalies.

We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

Journal Article↗
PubMed2003

Fluctuation mediated interaction and phase separation of nanoparticles in a liquid crystal solvent.

Water-in-oil microemulsions of nanodroplets in the isotropic phase of a thermotropic liquid crystal exhibit, with decreasing temperature and in anticipation of a demixing transition, enhanced correlation in fluctuations of both molecular orientation and droplet concentration. Mean field modeling of this pretransition behavior, on the basis of a lattice in which the nanodroplets are introduced as holes, shows that the observed interdroplet attractive interaction is produced by the disordering effect of the droplets on the liquid crystal and mediated solely by paranematic fluctuations.

Journal Article↗
PubMed2001

Bethe approximation for a model of polymer solvation.

The phase diagram of a recently proposed model for the solvation of monomers and polymers in water is studied in the homopolymer case, and several thermodynamic quantities are computed by means of pair approximation of the cluster variation method, i.e., the Bethe approximation. The model takes into account the water degrees of freedom in a simplified way, so that they can be integrated out analytically. The resulting effective Hamiltonian contains only a temperature-dependent water-monomer interaction and its phase diagram can be easily studied thanks to the simplicity of the Bethe approximation and exhibits, for a hydrophobic polymer, both cold and warm unfolding transitions in a wide region of the parameter space. This suggests that the present one might be a toy-model description of the phase behavior observed experimentally in water solutions of hydrophobic polymers, such as poly-N-isopropylacrylamide (PNIPAM), as well as a step to understand the mechanism of cold unfolding in proteins.

Journal Article↗
PubMed2000

Cluster-variation-Pade-approximant method for the simple cubic Ising model

The cluster-variation-Pade-approximant method is a recently proposed tool, based on the extrapolation of low- and high-temperature results obtained with the cluster-variation method, for the determination of critical parameters in Ising-like models. Here the method is applied to the three-dimensional simple cubic Ising model, and new results, obtained with an 18-site basic cluster, are reported. Other techniques for extracting nonclassical critical exponents are also applied and their results compared with those by the cluster-variation-Pade-approximant method.

Journal Article↗
PubMed2000

Herringbone ordering and lattice distortions in a planar-molecule model for langmuir monolayers

A model of planar molecules, made up of "atoms" interacting by Lennard-Jones potentials and arranged to mimic the cross section of alkyl chains, is used to study the problem of backbone plane ordering in Langmuir monolayers. It is shown that two minima of the interaction energy are reached if molecules lie on the sites of a centered rectangular lattice in a herringbone configuration with two different dihedral angles. These orientationally ordered phases can be related to the so-called herringbone and pseudoherringbone structures, whose lattice distortions qualitatively agree with those determined by means of grazing incidence x-ray diffraction experiments on Langmuir monolayers. A third energy minimum is obtained for a configuration of parallel molecules on an oblique lattice, which has also been observed in some experiments. The competition between the three phases is investigated, upon varying geometric parameters of the model molecules and surface pressure. The effect of temperature is analyzed in a mean field approximation, by taking into account the orientational entropy contribution on a lattice system with variable unit cell parameters. In this framework the transition to an orientationally disordered phase is also pointed out.

Journal Article↗
PubMed1993

[Practical device to reduce the tidal volume in mechanical ventilation, for neonatal and pediatric anesthesia].

The authors propose a new device for controlled mechanical ventilation during general anaesthesia in pediatric and neonatal patients. This device can reduce TV delivered by an adult ventilator to small values. The device consists of: a small volume box (about 1.3 1); a disposable breathing circuit composed of a bag to put in the box, connecting tubes, a non rebreathing duckbill valve placed at the endotracheal tube; a monitoring system for pressure and expired volume. The authors tested the device according to ISO Standards. Performance during waveform tests and expiratory resistance agree with ISO request. During volume performance tests the device was able to deliver a minimum TV of 10 ml in all ISO Standard requested sets.

Anesthesia, General↗
PubMed1988

A new active model lung.

A new model lung with the capacity for simulated spontaneous breathing is described. It consists of a modified commercial mechanical ventilator (Kontron ABT 4100), connected in parallel to a compliant system, a cylindric acrylic box with a latex thin membrane substituting for the top. Volume and compliance of the model are 2500 ml and 50 ml cmH2O-1, respectively. The modified ventilator simulates physiologic inspiratory flow at a rate of 10 to 30 min-1 and tidal volume up to 1000 ml, with an inspiratory to expiratory time ratio continuously variable between 1:4 and 4:1. The model has been tested under different respiratory assist techniques, connected either to continuous positive airway pressure proved to be reliable, versatile and bearing satisfactory resemblance to human ventilatory physiology.

Humans↗