Markov chain approach to model intertemporal choices and coverages in air transport markets.

We develop a framework based on discrete-time Markov chains (MCs) to model the Brazilian air transport market networks. Our results suggest that in this market, economic activity explains the centralities of the airports and the players' choices. Periods of economic prosperity affect the air transport networks and they move from a hub-and-spoke topology towards a mixed point-to-point and hub-and-spoke topology. Furthermore, we use the MC transition and stationary probabilities to build geographical subgraphs that reveal (1) the most important routes, (2) the stability of these routes, (3) the most important flights, and (4) the airlines' specific market niches.

[Plasma total anti-oxidant status in young survivors of myocardial infarction]. / Estado anti-oxidante total do plasma em doentes jovens com enfarte do miocárdio.

UNLABELLED: Free oxygen radicals are involved in the endothelial lesion process which leads to the formation of the atheroma plaque and thrombosis. There is some evidence that antioxidant therapy may be beneficial in coronary heart disease prevention. Our objective was to study the plasma total anti-oxidant status in young survivors of acute myocardial infarction. POPULATION: 23 patients, mean age 35.2 years (22-40) admitted for acute myocardial infarction from January 1995 to June 1998 (20 males). RISK FACTORS: Tobacco smoking 22/23, systemic arterial hypertension 4/23, hypercholesterolemia 17/23, positive family history for coronary heart disease 5 patients, previous history of angina 4 patients, none of these patients had diabetes mellitus. The location of the infarct was anterior in 12 patients, inferior in 10 patients and non-Q wave in one patient. Blood samples were drawn after overnight fasting and the plasma total antioxidant status (TAS) was determined by a colorymethric method (Trolox equivalent). The mean time elapsed since the acute myocardial infarction until sample collection was 16.5 +/- 10.7 months. RESULTS: 18 patients had low TAS values, mean 1.23 +/- 0.11 mmol/L (below the reference values: 1.3-1.77 mmol/L). CONCLUSIONS: In this group of patients, the plasma total antioxidant capacity was globally decreased, which may constitute a risk factor for coronary heart disease.