An artificial neural network (ANN) procedure that uses the scores of a principal component model as input data was tested for calibration in the resolution of binary mixtures from kinetic measurements. The results thus obtained are compared with those provided by partial least-squares (PLS) regression and principal component regression (PCR). The ANN was first applied to simulated single wavelength kinetic curves. The effect of experimental variability was considered by assuming rate constants to fit a normal distribution curve. An amount of instrumental noise was also added to the simulated curves. Both linear and nonlinear systems were tested. Non-linearity was assumed to result from interactions between analytes and modeled by introducing a multiplicative term in the rate equation. The results provided by the three methods on linear systems were comparable; in the presence of interactions between analytes, however, the ANN method clearly outperformed the other two. The ANN method was also used to resolve mixtures of Fe(III), Co(II), and Zn(II) by displacement from their EGTA complexes with 4-(2-pyridylazo)resorcinol (PAR) using a stopped-flow injection assembly including a diode array detector. Preliminary experiments revealed the Co(II) and Zn(II) displacement reactions to be pseudo-first-order and that of Fe(III) to be a multistep process that departed from the linear behavior of the other two. Again, the results obtained with ANN were better than those provided by PCR and PLS.

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Partial least squares (PLS) regression and an artificial neural network (ANN) were tested as calibration procedures for the kinetic-spectrophotometric determination of binary mixtures when the concentration of the reagent is much lower than the concentration of the analytes. The two calibration methods were first applied to computer-simulated kinetic-spectrophotometric data. The spectra of the reaction products (PI, P2) were represented by Gaussian bands with the same bandwidth and the effect of spectral overlap and experimental noise was studied. If both spectra are identical, the mixture cannot be resolved. However, if they are not, then it is possible to quantify simultaneously both analytes by measuring the absorbance at several wavelengths and times. It was found that the precision of the results depends fundamentally on the noise level in the rate constants. Both mathematical procedures were applied to the determination of benzylamine-butylamine mixtures using salicylaldehyde as chromogenic reagent. ANNs outperformed the PLS results giving a relative standard error of prediction of about 4% for the whole set of mixtures.

a b s t r a c tThe effects of the inclusion of raw glycerin (GLYC) and lecithin in the diet on egg production, egg quality and total tract apparent retention (TTAR) of dietary components was studied in brown egg-laying hens from 23 to 51 wk of age. The experimental design was completely randomized with six diets combined as a 2 × 3 factorial with two levels of GLYC (0 vs. 70 g/kg) and three animal fat to lecithin ratios (40:0, 20:20 and 0:40 g/kg). Each treatment was replicated eight times and the experimental unit was a cage with ten hens. Production was recorded by replicate every 28-d period and cumulatively. For the entire experiment, the inclusion of GLYC in the diet hindered feed conversion ratio per kilogram of eggs (2.071 vs. 2.039; P < 0.05) but did not affect any of the other production or egg quality traits studied. The replacement of animal fat by lecithin (40:0, 20:20 and 0:40 g/kg) increased egg weight (60.1, 60.7 and 61.8 g, respectively; P < 0.001) and egg mass production (56.8, 57.5 and 58.8 g/d, respectively; P < 0.01) and improved yolk color as measured by the DSM color fan (9.2, 9.2 and 9.5, respectively; P < 0.001) and feed conversion ratio per kilogram of eggs (2.072, 2.068 and 2.027, respectively; P < 0.05). Feed intake, egg production and body weight gain, however, were not affected. The inclusion of GLYC in the diet did not affect nutrient retention but lecithin inclusion improved TTAR of dry matter (P < 0.05), organic matter (P < 0.05), ether extract (P < 0.001) and gross energy (P < 0.001). In summary, the inclusion of 70 g glycerol/kg diet hindered feed conversion ratio per kilogram of eggs but did not affect any other production or digestibility trait. The replacement of animal fat by lecithin improved egg weight, egg yolk color and nutrient digestibility. Consequently, lecithin can be used as a lipid source in laying hen diets with beneficial effects on egg production.

The chain of events leading to the manifestation of the biological action of somatostatin are described. Internalization is mediated by cytoskeletal proteins in the presence of calmodulin. Transduction of the somatostatin message at the membrane level takes place through inhibition of cyclic AMP accumulation and blockade of cytosol calcium increases. The influence of central and peripheral factors upon these processes is discussed and the importance of the Ni/Ns components is stressed. Thus, somatostatin also suppresses phosphoinositide turnover and stimulates soluble phosphodiesterase, thus reinforcing its negative effect on cyclase generation.