Biomedical subjects

M P Almeida

Publications and source records attributed to M P Almeida.

6 recordsLinked to original sources

PubMed2002

Extended phase-space dynamics for the generalized nonextensive thermostatistics.

We apply a variant of the Nosé thermostat to derive the Hamiltonian of a nonextensive system that is compatible with the canonical ensemble of the generalized thermostatistics of Tsallis. This microdynamical approach provides a deterministic connection between the generalized nonextensive entropy and power-law behavior. For the case of a simple one-dimensional harmonic oscillator, we confirm by numerical simulation of the dynamics that the distribution of energy H follows precisely the canonical q statistics for different values of the parameter q. The approach is further tested for classical many-particle systems by means of molecular dynamics simulations. The results indicate that the intrinsic nonlinear features of the nonextensive formalism are capable of generating energy fluctuations that obey anomalous probability laws. For q<1 a broad distribution of energy is observed, while for q>1 the resulting distribution is confined to a compact support.

Journal Article↗

PubMed2001

Observation of image transfer and phase conjugation in stimulated down-conversion.

We observe experimentally the transfer of angular spectrum and image formation in the process of stimulated parametric down-conversion. Images and interference patterns can be transferred from either the pump or the auxiliary laser beams to the stimulated down-converted one. The stimulated field propagates as the complex conjugate of the auxiliary laser. The phase conjugation is observed through intensity pattern measurements.

Journal Article↗

PubMed1999

Scaling behavior in a proportional voting process.

We perform a statistical analysis on the proportional elections held in Brazil in October 1998. We show that the distribution of votes among candidates for the whole country follows a power law N(v) is proportional to v(-alpha), with alpha=1.00+/-0.02, extending over two orders of magnitude. The voting distributions for several states of the federation also display scale-invariant behavior with alpha approximately equal to 1. We argue that this particular voting system can be modeled as a typical multiplicative process in which the choice of the candidate is governed by a product of probabilities.

Journal Article↗

PubMed1999

Fluid flow through ramified structures.

We investigate the fluid flow through two-dimensional ramified structures by direct simulation of the Navier-Stokes equations. We show that for trees with n generations, the flow distribution strongly depends on the Reynolds number Re. Specifically, for a tree without loops the flow becomes highly heterogeneous at high Re. For a tree with loops, on the other hand, the flow distribution tends to be more uniform at increased Re conditions. We show that these apparently contradictory behaviors have the same origin, namely, the effect of inertia on the momentum transport in the channels of the ramified geometry. In order to simulate the propagation of the flow imbalance throughout the tree without loops, we develop a simple model that incorporates the basic fluid dynamics features of the system. For large trees, the results of the model indicate that the distribution of flow at the outlet branches can be described by a self-affine landscape. Finally, we argue that the nonuniform partitioning of flow found for the structure without loops may contribute to the morphogenesis and functioning of the bronchial tree.

Journal Article↗

PubMed1994

Vincristine in steroid-resistant nephrotic syndrome.

The therapeutic response to vincristine was examined in seven children (aged 2-15 years) with corticosteroid-resistant (CR) nephrotic syndrome (NS) with focal and segmental glomerulosclerosis (FGS). Five were also resistant to cyclophosphamide. Vincristine was given weekly (1.5 mg/m2 intravenously) for 8 weeks. Simultaneously, prednisone (60 mg/m2 per day, orally) was given for 4 weeks and then gradually tapered. Two of these patients had a complete and stable remission; in five no benefit was observed. It was not possible to identify any characteristics to predict the response to vincristine. Although there is a case for trying vincristine therapy in CR NS with FGS, the results of this study are not encouraging and a better understanding of its action and indications is necessary.

Administration, Oral↗

PubMed1975

Radioimmunoassay for desmethylimipramine.

This paper describes the production of antibodies against demethyl-imipramine (DMI). By using antisera, a radioimmunoassay was developed capable of detecting 0.2 ng of DMI which is linear up to 25 ng. The assay has been applied for the measurement of DMI in rat plasma and brain. The assay might find application especially when only limited amounts of blood, plasma or tissue are available.

Animals↗