Integro-difference equations for interacting species and the Neolithic transition

We introduce a set of sequential integro-difference equations to analyze the dynamics of two interacting species. Firstly, we derive the speed of the fronts when a species invades a space previously occupied by a second species, and check its validity by means of numerical random-walk simulations. As an example, we consider the Neolithic transition: the predictions of the model are consistent with the archaeological data for the front speed, provided that the interaction parameter is low enough. Secondly, an equation for the coexistence time between the invasive and the invaded populations is obtained for the first time. It agrees well with the simulations, is consistent with observations of the Neolithic transition, and makes it possible to estimate the value of the interaction parameter between the incoming and the indigenous populations

Fronts from integrodifference equations and persistence effects on the Neolithic transition

We extend a previous model of the Neolithic transition in Europe [J. Fort and V. Méndez, Phys. Rev. Lett. 82, 867 (1999)] by taking two effects into account: (i) we do not use the diffusion approximation (which corresponds to second-order Taylor expansions), and (ii) we take proper care of the fact that parents do not migrate away from their children (we refer to this as a time-order effect, in the sense that it implies that children grow up with their parents, before they become adults and can survive and migrate). We also derive a time-ordered, second-order equation, which we call the sequential reaction-diffusion equation, and use it to show that effect (ii) is the most important one, and that both of them should in general be taken into account to derive accurate results. As an example, we consider the Neolithic transition: the model predictions agree with the observed front speed, and the corrections relative to previous models are important (up to 70%)

Improvement of heat-induced gel properties of porcine plasma

L'objectiu és millorar els gels de plasma porcí induïts per calor a pH àcid utilitzant transglutaminasa microbiana (MTGasa). El tractament millora textura i CRA dels gels a pH 5,5, però les millores no són suficients per recuperar les pèrdues degut a l'acidificació. L'estructura globular de les proteïnes dificulta l'atac enzimàtic. La reactivitat de l'enzim no millora amb l'addició de cisteïna a plasma amb MTGasa. El tractament del plasma amb MTGasa sota alta pressió (HP) millora la duresa dels gels. No obstant, la CRA només millora lleugerament. La duresa es pot incrementar mantenint les solucions de plasma pressuritzat sota refrigeració, encara que no millora la CRA. Es pot concloure que les pèrdues en la textura dels gels de plasma induïts per calor a pH àcid es poden recuperar parcialment tractant amb MTGasa, especialment afegint cisteïna o sota HP. Encara que la CRA només es veu lleugerament millorada en el segon cas.