2.4. Statistical analysis
The non-linear regression was computed with theSplus software (AT&T Bell Laboratories, MurrayHill, NJ, USA), the parameters of the regressionwere estimated by the maximum likelihood method.The Gauss–Marquardt algorithm was used in thenumerical process. The linear regression was computed with the general linear model procedure ofSAS software (SAS Institute Inc., Cary, NC, USA).