Biomedical subjects

L H Monteiro

Publications and source records attributed to L H Monteiro.

5 recordsLinked to original sources

PubMed2001

The oxygen gain of diving insects.

The gas gill of diving insects allows gas exchange with the surrounding water, thus extending diving time. Incompressible gas gills can potentially last indefinitely underwater, but compressible gas gills have a definite lifetime. Theoretical models of a dive event have reached opposite conclusions about the oxygen gain (G, the ratio between the duration of the diving event and the time that the initial oxygen content of the bubble would allow the insect to stay underwater). While some authors claim that G has a fixed value independently of the parameters of the dive (e.g. oxygen consumption rate) others claim the contrary. However, these claims are based on numerical solutions of the models. In this study we offer an analytical solution to the problem. The analysis of a model with constant area for gas exchange demonstrates that G cannot have a fixed value, for a fixed gain would imply in a P(O(2)) inside the bubble different from the one occurring as a result of physical constraints of the gas exchange process.

Algorithms↗

PubMed2000

A condition for successful escape of a mutant after primary HIV infection.

Cytotoxic T lymphocytes (CTLs) vigorously restrict primary human immunodeficiency virus (HIV) infection. However, the frequently erroneous process of viral replication favors the creation of mutants not recognizable by primary CTLs. Variants that tolerate the mutations may have selective advantage and may increase in abundance, until the immune system reacts against them. Therefore, such variants represent a way of propagating the viremia. With the aid of a simple mathematical model, here we estimate the intensity of CTL cross-reactivity against different strains of HIV in a typical progressor. We show that below a critical intensity of cross-reactivity, the concentration of a mutant created at primary peak grows and causes a secondary peak in viremia. Above this critical intensity, such a mutant strain is prevented from reaching a detectable level. We speculate about how this result may contribute to the design of an anti-HIV vaccine.

Cross Reactions↗

PubMed2000

Kinematics of eye movement.

In a simplified fashion, the motion of the eyeball in its orbit consists of rotations around a fixed point. Therefore, this motion can be described in terms of Euler's angles of rigid body dynamics. However, there is a physiological constraint in the motion of the eye which reduces to two its degrees of freedom, so that one of Euler's angles is not an independent variable. This paper reviews the basic features of the kinematics of the eye and the laws governing its motion.

Eye Movements↗

PubMed1999

Zipf's law organizes a psychiatric ward.

We developed a simple mathematical model based on power law fitting for describing the interactions among patients from a psychiatric ward. First we defined a protocol in order to evaluate in a quantative way the state of the patient, measuring sociability/restlessness through a daily analysis of the behavior and attributing a grade for both parameters, per patient. The grades were checked by two different specialists and a table of incidence was constructed. This table generated power laws for the grades and their variations. We concluded that power laws, like Zipf's law, may be good to explain the data, showing a self-organizing process that indicates a strong interaction component determining the whole behavior. We would like to see more data being collected, in other centers and among normal populations, trying to quantify complex collective behavioral phenomena using self-organizing criticality laws.

Humans↗

PubMed1999

Modeling homopolymer self-replication: implications for early competition.

We start showing that the rate equation for a homopolymer self-replication may be written as being proportional to mbetapGamma with beta=1 and Gamma=1/2, where m is the monomer concentration and p is the homopolymer total concentration (double helices plus isolated strands). With such values for the exponents beta and Gamma, we examine analytically the asymptotic behavior of our model previously proposed for studying the early polymer evolution. In this model, polymers compete for activated monomers carried into the system under a constant flux. Time changes on their concentrations are determined by the reactions of: spontaneous generation of dimers through non-instructed junction of two monomers; ligation among free monomers and polymers at the end of their chains, so that they can extend their sizes; template-instructed synthesis by which polymers with lengths above a length threshold can catalyse the formation of other polymers; and decomposition of all species. We find out that if the monomer flux intensity is "low" (lesser than the decomposition rate constants), dimer is the dominant species. Under a "high" flux (greater than the template-instructed synthesis rate constant), the longest self-replicating species prevails. For a "middle" flux (between "low" and "high"), the shortest self-replicating polymer is the winner. Whatever the flux intensity, all polymer species ever coexist.

Animals↗