1,721,323 research outputs found
A General Discrete Time Model of Population Dynamics in the Presence of an Infection
No full textWe present a set of difference equations which generalizes that proposed in the work of G. Izzo and A. Vecchio (2007) and represents the discrete counterpart of a larger class of continuous model concerning the dynamics of an infection in an organism or in a host population. The limiting behavior of this new discrete model is studied and a threshold parameter playing the role of the basic reproduction number is derived
Permanence and global stability of a class of discrete epidemic models
Full text linkIn this paper we investigate the permanence of a system and give a sufficient condition for the endemic equilibrium to be globally asymptotically stable, which are the remaining problems in our previous paper (G. Izzo, Y. Muroya, A. Vecchio, A general discrete time model of population dynamics in the presence of an infection, Discrete Dyn. Nat. Soc. (2009), Article ID 143019, 15 pages. doi:10.1155/2009/143019.
Nonlinear stability of direct quadrature methods for Volterra integral equations
No full textAn important topic in the numerical analysis of Volterra integral equations is the stability theory. The main results known in the literature have been obtained on linear test equations or, at least, on nonlinear equations with convolution kernel. Here, we consider Volterra integral equations with Hammerstein nonlinearity, not necessarily of convolution type, and we study the error equation for Direct Quadrature methods with respect to bounded perturbations. For a class of Direct Quadrature methods, we obtain conditions on the stepsize h for the numerical solution to behave stably and we report numerical examples which show the robustness of this nonlinear stability theory
Occurrence of aflatoxins in feedstuff, sheep milk and dairy products in Western Sicily
No full textSamples of feedstuffs (15), milk (40), and cheese (30) coming from sheep and dairy farms (23) or market in Western
Sicily were analyzed for their respective content of aflatoxin B1 (AFB1) and M1 (AFM1) to evidence any possible indirect
mycotoxin contamination risk to the consumer. Analyses using HPLC and fluorescence detection were performed after
immunoaffinity column sample extraction and cleanup; AFM1 was detected in 30% of the milk samples at levels ranging
from 4 to 23 ng/l and in 13% of the cheeses from 21 to 101 ng/kg; in the feed the AFB1 ranged from <10 to 769 ng/kg.
None of the contaminated samples exceeded the legal limits set down by the European Union for milk (50 ng/l) and feed
(5 μg/kg ), or that in force in the Netherlands for cheese (200 ng/k
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