Mirjana Brdar

Isotherms for the adsorption of Cu(II) onto lignin: Comparison of linear and non-linear methods

Equilibrium studies were carried out for the adsorption of Cu(II) onto Kraft lignin as an adsorbent. The experimental data were fitted to the Freundlich, Langmuir and Redlich-Peterson isotherms by linear and non-linear method. Comparison of linear and non-linear regression method was given in selecting the optimum isotherm for the experimental data. The coefficient of correlation r2 and Chi-square test χ2 was used to select the best linear theoretical isotherm. The best linear model is Redlich-Peterson isotherm model, where r2=0,985 and χ2=0,02. In order to predict the error ERRSQ, HYBRD, MPSD, ARE and EABS were used. Moreover, by minimizing these error functions the optimal values of parameters and also the optimum isotherm was found. The Redlich-Peterson isotherm was found to be the best representative for adsorption of Cu(II) on the adsorbent in the cases when ERRSQ, HYBRD, MPSD functions were used. There coefficients of determination are 0.986, 0.985, 0.984, respectively and Chi-square is 0.02 in all cases. Freundlich isotherms which were obtained by minimization of the ERRSQ, HYBRD, MPSD, ARE and EABS function showed very good agreement with experimental data. In all cases the coefficients of determination are greater than 0.91. Besides, it was observed that non-linear isotherm models were better for representation of equilibrium data than linearized models.

A singularly perturbed problem with two parameters on a Bakhvalov-type mesh

A singularly perturbed problem with two small parameters is considered. On a Bakhvalov-type mesh we prove uniform convergence of a Galerkin finite element method with piecewise linear functions. Arguments in the error analysis include interpolation error bounds for a Clement quasi-interpolant as well as discretization error estimates in an energy norm. Numerical experiments support theoretical findings.

On graded meshes for a two-parameter singularly perturbed problem

A one-dimensional reaction-diffusion-convection problem is numerically solved by a finite element method on two layer-adapted meshes, Duran-type mesh and Duran-Shishkin-type mesh, both defined by recursive formulae. Robust error estimates in the energy norm are proved. Numerical results are given to illustrate the parameter-uniform convergence of numerical approximations.

A fixed point theorem for a special class of probabilistic contraction

AbstractIn this paper, a special class of probabilistic contraction will be considered. Using the theory of countable extension of t-norms, we proved a fixed point theorem for such a class of mappings f : S → S, where (S,F,T) is a Menger space. Mathematics Subject Classification (2000) 54H25, 47H10

A singularly perturbed problem with two parameters in two dimensions on graded meshes

Abstract A numerical approximation of a convection–reaction–diffusion problem by standard bilinear finite elements is considered. Using Duran–Lombardi and Duran–Shishkin type meshes we prove first order error estimates in an energy norm. Numerical examples confirm our theoretical results and show smaller errors compared to the well-known Shishkin mesh.