Anul XLVIII 2003

S T U D I A

UNIVERSITATIS BABEŞ-BOLYAI

MATHEMATICA

2

Redacţia: 400084 Cluj-Napoca, Str. M. Kogălniceanu nr. 1 Tel: 405300

SUMAR – CONTENTS – SOMMAIRE

Titu Andreescu, Solutions to the Diophantine equation (x + y + z + t)²= xyzt . . . . . . . . 3

T. Baranyai, Asymtotical Variants of Some Fixed Point Theorems

in Ordered Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Alexandru Bica, A Mathematical Model for the Study of Glycaemic

Homeostasy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Nicoleta Breaz and Daniel Breaz, Fitting of Some Linearisable

Regressional Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

R. G. Buschman, Unitary Products Again . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Sânziana Caraman, Robust Stability of Compact C0-Semigroups

on Banach Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Gh. Coman and I. Todea, Bivariate Shepard Operators

of Abel-Gonciarov-Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 39

Ion Cozac, Shepard Method - from Approximation to Interpolation . . . . . . . . . . .. . . . 49

Nicolae Crainic, On the Necessary and Sufficient Condition

for the Regularity of a Multidimensional Interpolation Scheme . . . . . . . . . . . . . . . . . . 53

Amelia-Anca Holhoş, Applications of Differential Subordination . . . . . . . . . . . . . . . . 61

Teresa Janiak and Elzbieta Luczak-Kumorek, Method on Partial Averaging

for Functional-Differential Equations with Hukuhara’s Derivative . . . . . . . . . . . . . . . 65

Petra Konecna, Polynomial Orbits in Direct Sum of Finite Extension

Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Mokhtar A. Abdel Naby, Mohamed A. Ramadan and Samir T. Mohamed,

Spline Approximation for Solving System of First Order Delay

Differential Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79

Veronica Nechita, On Some Univalence Conditions in the Unit Disk . . . . . . . . . . . . . . 89

Cosmin Pelea, On the Direct Product of Multialgebras . . . . . . . . . . . . . . . . . .. . . . . . . 93

Vasile Pop, A Functional Characterization of the Symmetric-Difference

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Robert Szasz, A New Subclass of Convex Functions . . . . . . . . . . . . . . . . . . . . . . . . . .103

Tran Hung Thao and Christine Thomas-Agnan, Evolution des Cours

Gouvernee par un Processus de Type Arima Fractionnaire . . . . . . . . . . . . . . . . . . . . 107

Book Reviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117