Modeling the diffusion-erosion crossover dynamics in drug release.

A computational model is proposed to investigate drug delivery systems in which erosion and diffusion mechanisms are participating in the drug release process. Our approach allowed us to analytically estimate the crossover point between those mechanisms through the value of the parameter b (b_{c}=1) and the scaling behavior of parameter τ on the Weibull function, exp[-(t/τ)^{b}], used to adjust drug release data in pharmaceutical literature. Numerical investigations on the size dependence of the characteristic release time τ found it to satisfy either linear or quadratic scaling relations on either erosive or diffusive regimes. Along the crossover, the characteristic time scales with the average coefficient observed on the extreme regimes (i.e., τ∼L^{3/2}), and we show that this result can be derived analytically by assuming an Arrhenius relation for the diffusion coefficient inside the capsule. Based on these relations, a phenomenological expression for the characteristic release in terms of size L and erosion rate κ is proposed, which can be useful for predicting the crossover erosion rate κ_{c}. We applied this relation to the experimental literature data for the release of acetaminophen immersed in a wax matrix and found them to be consistent with our numerical results.

Desempenho em confinamento e componentes do peso vivo de cordeiros mestiços de três grupos genéticos / Performance in feedlot and non carcass components in crossbred lambs from three genetic groups

Este trabalho teve como objetivo avaliar o desempenho em confinamento e a produção de carcaça e de componentes não carcaça de cordeiros dos grupos genéticos Texel x Hampshire Down (THD), Texel x Ile de France (TIF) e Texel x Suffolk (TS). Foram utilizados 17 cordeiros castrados, sendo seis THD, seis TIF e cinco TS, com idade de 120 dias e peso vivo médio inicial de 31,0±3,2kg. Os cordeiros foram confinados por um período de 51 dias, quando receberam diariamente ração concentrada comercial com 18 por cento PB e 74 por cento NDT, na proporção de 1,5 por cento do peso vivo, mais cana-de-açúcar picada in natura à vontade. Não houve diferenças significativas (P>0,05) para ganho de peso, peso final e escores de condição corporal entre os grupos genéticos; porém, cordeiros TS tiveram maiores (P<0,05) consumos de MS do que cordeiros THD e TIF. As médias para consumo de MS, como percentagem do peso vivo, foram: 3,9; 3,6 e 3,2 por cento, respectivamente, para TS, THD e TIF. Não houve diferença (P>0,05) entre os grupos genéticos para conversão alimentar. Pesos e rendimentos de carcaça quente também foram similares entre os grupos genéticos. Para os componentes não carcaça, houve diferenças (P<0,05) para percentagem de intestino vazio e peso de coração, em que o grupo TS apresentou valores maiores. Conclui-se que, na produção de carne ovina, qualquer um dos grupos genéticos estudados pode ser utilizado, pois todos apresentaram desempenho e produção de componentes do peso vivo semelhantes.

The objective of this research was to evaluate the performance in feedlot and the production of carcass and non-carcass components of lambs from the genetic groups Texel x Hampshire Down (THD), Texel x Ile de France (TIF) and Texel x Suffolk (TS). Seventeen castrated lambs were used, being six THD, six TIF and five TS. The average age and weight at the beginning of the experiment were, respectively, 120 days and 31.0±3.2kg. Lambs were fed lot for 51 days, where they received a daily commercial concentrate ration (18 percent CP and 74 percent TDN), in the proportion of 1.5 percent of body weight, and had free access to chopped in natura sugar cane. There was no significant difference (P>0.05) for weight gain, final weight and body condition score among the genetic groups. However, TS lambs presented greater (P<0.05) dry matter intake than THD and TIF lambs. Averages for DM intake as percentage of body weight were 3.9, 3.6 and 3.2 percent, respectively, for TS, THD and TIF. There was no difference (P>0.05) among genetic groups for feed conversion. Weights and dressing percentages of hot carcass were also similar among genetic groups. There were few differences among genetic groups for non-carcass components. TS lambs presented greater (P<0.05) percentages of intestines and weights of heart than the other lambs. It can be concluded that in the lamb production any of the genetic groups studied can be used, for their performance and the production of live weight components were quite similar.

Frustration and anomalous behavior in the Bell-Lavis model of liquid water.

We have reconsidered the Bell-Lavis model of liquid water and investigated its relation to its isotropic version, the antiferromagnetic Blume-Emery-Griffiths model on the triangular lattice. Our study was carried out by means of an exact solution on the sequential Husimi cactus. We show that the ground states of both models share the same topology and that fluid phases (gas and low- and high-density liquids) can be mapped onto magnetic phases (paramagnetic, antiferromagnetic, and dense paramagnetic, respectively). Both models present liquid-liquid coexistence and several thermodynamic anomalies. This result suggests that anisotropy introduced through orientational variables play no specific role in producing the density anomaly, in agreement with a similar conclusion discussed previously following results for continuous soft core models. We propose that the presence of liquid anomalies may be related to energetic frustration, a feature common to both models.