Desempenho do modelo estocástico na média-variância para o mercado brasileiro de ações

Os modelos de média-variância deotimização de carteira apresentam questionamentos em relação ao seu efetivo desempenho devido ao chamado erro de estimação.Em consequência, a otimização estocástica vem aumentando sua importância pois permite à possibilidade da inclusão da incerteza na estimativa dos parâmetros. Neste estudo foi avaliado o desempenho do modelo de otimização de carteira proposto por Bonami e Lejeune (2009), e reformulado por Filomena e Lejeune (2012), no mercado brasileiro de ações. Ambos os modelos podem ser caracterizados como versões probabilísticas do modelo clássico de média-variância proposto por Markowitz (1952). O modelo de Filomena e Lejeune (2012) apresentou desempenho médio superior aos benchmarks IBRX-50 e IBOVESPA. No entanto, o mesmo apresentou resultados viáveis em apenas 12,5% dos 64 cenários de teste. Embora isto possa ser considerado uma limitação do modelo,também pode ser analisado como um benefício para os investidores, pois oferece pontos de entrada e saída do mercado de ações.The estimation error is a well-documented problem of the mean-variance optimization models. Therefore, stochastic optimization has increased its importance on portfolio optimization given its ability to include uncertainty as a parameter. In this study, the performance of the model proposed by Filomenaand Lejeune (2012), a reformulated version of a previous model developed by Bonami and Lejeune (2009), was evaluated for the Brazilian stock market. Both models can be characterized as probabilistic versions of the classical model developed by Markowitz (1952). The performance of the model was superior when compared to the market benchmarks IBRX-50 and IBOVESPA. However, it presented feasibility in just 12,5% of the 64 test cases. Although this can initially be seen as a strong limitation for the practical use of the model, this can be considered as a very important pragmatic information for investors, since the model provides possible entry and exit points on the stock market

Virulence in Murine Model Shows the Existence of Two Distinct Populations of Brazilian Vaccinia virus Strains

Brazilian Vaccinia virus had been isolated from sentinel mice, rodents and recently from humans, cows and calves during outbreaks on dairy farms in several rural areas in Brazil, leading to high economic and social impact. Some phylogenetic studies have demonstrated the existence of two different populations of Brazilian Vaccinia virus strains circulating in nature, but little is known about their biological characteristics. Therefore, our goal was to study the virulence pattern of seven Brazilian Vaccinia virus strains. Infected BALB/c mice were monitored for morbidity, mortality and viral replication in organs as trachea, lungs, heart, kidneys, liver, brain and spleen. Based on the virulence potential, the Brazilian Vaccinia virus strains were grouped into two groups. One group contained GP1V, VBH, SAV and BAV which caused disease and death in infected mice and the second one included ARAV, GP2V and PSTV which did not cause any clinical signals or death in infected BALB/c mice. The subdivision of Brazilian Vaccinia virus strains into two groups is in agreement with previous genetic studies. Those data reinforce the existence of different populations circulating in Brazil regarding the genetic and virulence characteristics

Purified cellulose, soybean hulls and citrus pulp as a source of fiber for weaned piglets

Dietary fiber is an important component, which has a direct effect on intake, digestion, and absorption of nutrients; and also alters intestinal microbiota and morphology according to solubility. One digestibility trial and one performance experiment were performed to evaluate the effects of sources of fiber in diets for 21 day weaned piglets. The experimental diets used in both trials consisted of a control diet and diets with purified cellulose, soybean hulls or citrus pulp as a main source of dietary fiber. To evaluate the digestibility of nutrients (Assay 1), the total feces and urine collection method was used. The fiber sources did not affect nutrient digestibility, except for soluble fiber, which increased with the inclusion of citrus (Citrus sinensisL.) pulp. To evaluate performance, morphophysiology and microbiology of the digestive tract of weaned piglets, a total of 32 castrated male piglets was used. Slaughter of animals was implemented at 35 and 50 days of age. The use of soybean (Glycine max L.) hulls and citrus pulp in diets increased the number of goblet cells and the density of villi in the jejunum. The viscosities of stomach and cecum contents increased due to the addition of citrus pulp. Soybean hulls and the citrus pulp included in diets reduced the occurrence of E. coli in the small intestines of piglets slaughtered at 35 days of age. Among the fiber sources, purified cellulose in piglet diets promotes better performance of animals, due to the modulation of the small intestine microbiota, with lower E. coli occurrence resulting in higher villus density