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Biomedical subjects

G Oster

Publications and source records attributed to G Oster.

At least 127 records · Page 7Linked to original sources
PubMed1977

The dynamics of density dependent population models.

The dynamics of density-dependent population models can be extraordinarily complex as numerous authors have displayed in numerical simulations. Here we commence a theoretical analysis of the mathematical mechanisms underlying this complexity from the viewpoint of modern dynamical systems theory. After discussing the chaotic behavior of one-dimensional difference equations we proceed to illustrate the general theory on a density-dependent Leslie model with two age classes. The pattern of bofurcations away from the equilibrium point is investigated and the existence of a "strange attractor" is demonstrated--i.e. an attracting limit set which is neither an equilibrium nor a limit cycle. Near the strange attractor the system exhibits essentially random behavior. An approach to the statical analysis of the dynamics in the chaotic regime is suggested. We then generalize our conclusions to higher dimensions and continuous models (e.g. the nonlinear von Foerster equation).

Ecology↗
PubMed1977

Trypsin-like activity in the vaginal epithelial cells of the rat.

Rat vaginal epithelial cells have trypsin-like activity as shown by the formation of a colored product when the cells are incubated with alpha-N-methyl alpha-N-toxyl-L-lysine beta-naphthol ester and hexazotized pararosanilin. This enzyme activity in vaginal smears is maximal at proestrus, i.e., the day in the 5-day estrus cycle when plasma estrogen is maximal. Only the rounded nucleated epithelial cells present at late diestrus, proestrus and early estrus demonstrate the trypsin-like enzyme activity. These are the cells that stain blue in the Papanicolaou method. Preincubation of cell suspensions with the serine protease inhibitor, p-nitrophenyl p-guanidino benzoate, prevented the enzyme staining reaction, further demonstrating the trypsin-like nature of the cellular enzyme. The advantages of this enzyme staining technique over the fibrin plate method for the demonstration of trypsin-like enzymes in cells are increased resolution and ability to show trypsin inhibitor effects.

Animals↗
PubMed1977

A simplified determination of the urinary luteinizing hormone surge using the hemagglutination inhibition test.

The hemagglutination-inhibition test for urinary luteinizing hormone (LH) has been modified so that the test for LH surge can be assayed in 1 day. A first morning voided urine specimen submitted to the laboratory can be analyzed in 5 hours by ordinary bench procedures. This modification involves a 20-fold reduction, as compared with the older procedure, of the duration of incubation of the urine-antiserum mixture. Another modification is the choice of aliquots which are adaptable to automatic pipetting. Only a single dilution of urine is necessary to determine LH surge for the anticipation of ovulation. Daily LH determinations on 12 normally menstruating women (av. cycle 28.18 days) reveal consistent patterns. For the 40 cycles studied LH surge occurred 14.29 days (av.) prior to the onset of the next menstruation and coincided with the rise in basal body temperature. One woman with an unusually high incidence of familial twinning showed two large LH surges in each consecutive cycle.

Adult↗
PubMed1976

Competition between phenotypes.

We present two models for phenotypic-dependent interspecific competition. In both cases the survivorship of individuals of one population depends on the entire phenotypic distribution of the other species. The first model considers a continuously varying metric trait, with assortative or random mating; the second model examines a character controlled by two alleles at a single locus. Pursuing the notion that each population maximizes its mean fitness we define a vector-optimum strategy using the concepts of cooperative and competitive optima. It is found that the dynamical constraints placed on the equations of motion by Mendelian genetics often prevent a population from evolving to a strategic optimum. However, for the single locus case with complete dominance, the competitive optimum always coincides with some dynamical equilibrium on the Hardy-Weinberg manifold.

Alleles↗
PubMed1975

[Tachycardia caused by reciprocal rhythm between normal pathways and a rapid atrial-His pathway].

Report of one unhabitual case of reciprocal rhythm with anterograde conduction through James' fibres and retrograde conduction through the normal nodal pathways. The reality of an anterograde nodal short-circuit is indicated by many arguments, and in particular by the presence of a double ventricular response, after induced atrial premature beats reaching the ventricle once by the rapid pathway and the second time by the slow pathway.

Bundle of His↗
PubMed1974

Shape transformation of erythrocytes determined by light scattering changes associated with relaxation of particle orientation.

Dilute suspensions of normal erythrocytes exhibit a pearl-like sheen (nacre) when subjected to flow. This results from the asymmetric form (biconcave disc) of these cells. Upon cessation of flow, the nacreous effect decays in 2-3 min, corresponding to the time required for the discs to achieve random orientations by rotatory Brownian motion. The degree of nacre can be measured by comparing the intensity of scattered red light at an angle of 45 degrees for the flowing system to that when the effect has disappeared. Since the phenomenon is critically dependent on red cell shape, it is possible to quantify the extent of erythrocyte disc-to-sphere transformation induced by detergents, low salt concentrations, or metabolic depletion.

Erythrocytes↗