If V is a faithful module for a nite group G over a eld of characteristic p > 0, then the ring of invariants need not be Cohen-Macaulay if p divides the order of G. In this article the cohomology of G is used to study the question of Cohen-Macaulayness of the invariant ring. Let R = S(V) be the polynomial ring on which G acts. Then the main result can be stated as follow: If H r (G; R) 6 = 0 fo...

In this paper, we investigate the maximal Cohen-Macaulay property of tensor products modules, and then give criteria for projectivity modules in terms vanishing Ext modules. One applications shows that Auslander-Reiten conjecture holds normal rings.

This paper shows that Cohen-Macaulay algebras can be algebraically approximated in such a way their Cohen-Macaulayness and minimal Betti numbers are preserved. is achieved by showing finitely generated modules over power series rings manner preserves diagrams of initial exponents numbers. These results also applied to obtain an approximation result for flat homomorphisms from algebras.

Let be a commutative Noetherian ring and let I be a proper ideal of . D’Anna and Fontana in [6] introduced a new construction of ring,  named amalgamated duplication of along I. In this paper by considering the ring homomorphism , it is shown that if , then , also it is proved that if , then there exists  such that . Using this result it is shown that if is generically Cohen-Macaulay (resp. gen...