Biomedical subjects

J M Tavares

Publications and source records attributed to J M Tavares.

5 recordsLinked to original sources

PubMed2006

Phase transition in two-dimensional dipolar fluids at low densities.

Monte Carlo computer simulations of a quasi two-dimensional (2D) dipolar fluid at low and intermediate densities indicate that the structure of the fluid is well described by an ideal mixture of self-assembling clusters. A detailed analysis of the topology of the clusters, of their internal energy and of their size (or mass) distributions is used to obtain approximations to their partition functions. Within the scope of these approximations, the results of this work suggest that the 2D dipolar fluid undergoes a phase transition from a dilute phase characterized by a number of disconnected clusters to a condensed phase characterized by a network or spanning (macroscopic) cluster that includes most of the particles in the system.

Journal Article↗

PubMed2006

Diffusion-limited deposition with dipolar interactions: fractal dimension and multifractal structure.

Computer simulations are used to generate two-dimensional diffusion-limited deposits of dipoles. The structure of these deposits is analyzed by measuring some global quantities: the density of the deposit and the lateral correlation function at a given height, the mean height of the upper surface for a given number of deposited particles, and the interfacial width at a given height. Evidences are given that the fractal dimension of the deposits remains constant as the deposition proceeds, independently of the dipolar strength. These same deposits are used to obtain the growth probability measure through the Monte Carlo techniques. It is found that the distribution of growth probabilities obeys multifractal scaling, i.e., it can be analyzed in terms of its f(alpha) multifractal spectrum. For low dipolar strengths, the f(alpha) spectrum is similar to that of diffusion-limited aggregation. Our results suggest that for increasing the dipolar strength both the minimal local growth exponent alpha(min) and the information dimension D(1) decrease, while the fractal dimension remains the same.

Journal Article↗

PubMed2004

Diffusion-limited deposition of dipolar particles.

Deposits of dipolar particles are investigated by means of extensive Monte Carlo simulations. We found that the effect of the interactions is described by an initial, nonuniversal, scaling regime characterized by orientationally ordered deposits. In the dipolar regime, the order and geometry of the clusters depend on the strength of the interactions and the magnetic properties are tunable by controlling the growth conditions. At later stages, the growth is dominated by thermal effects and the diffusion-limited universal regime obtains, at finite temperatures. At low temperatures the crossover size increases exponentially as T decreases and at T=0 only the dipolar regime is observed.

Journal Article↗

PubMed2002

Quasi-two-dimensional dipolar fluid at low densities: Monte Carlo simulations and theory.

We studied a quasi-two-dimensional dipolar fluid in the chaining regime using Monte Carlo canonical simulations and theoretical analyses. The self-assembled clusters were characterized by measuring their internal energy, conformational properties, and equilibrium length distributions. We generalized and used equilibrium polymer theory to describe the structure of the chains and rings observed in the simulations. The scaling forms of the length distribution functions predicted by theory were found to describe adequately the simulation results. Finally, we discuss how this type of analysis may be used to establish the existence and mechanisms of phase transitions in dilute dipolar fluids.

Journal Article↗

PubMed1985

PGE2 gel for enhancement of priming and induction of labour at term in patients with unfavorable cervix.

Fifty women (25 nulliparae and 25 multiparae) with unfavorable cervix at term were enrolled in a clinical experiment to evaluate the safety and efficacy of the intracervical application of 0.5 mg PGE2 gel for cervical softening and eventual induction of labour; duration of pregnancy (38-42 wk) was confirmed by ultrasonic records. Global analysis revealed 48 (96%) vaginal deliveries, 43 (86%) being spontaneous labour and 5 (10%) instrumentally assisted deliveries (forceps). Caesarean section was required in 2 cases (4%). Three patients, having registered no Bishop score (above 5) progress after the first treatment, went into labour upon the second application of PGE2 gel. Mean induction-delivery time was 11 h 50 min for nulliparae and 7 h 50 min for multiparae. Mean ROM/amniotomy-delivery time was 5 h 59 min for nulliparae and 3 h 11 min for multiparae. Four neonates with initial Apgar scores below 7 registered immediately higher values after adequate reanimation manouvres.

Adolescent↗