环的投射生成元和K0群

设Ｒ是含幺结合环,Ｐｇ（Ｒ）是Ｒ的所有投射生成元的同构类组成的半群,Ｇｒ（Ｐｇ（Ｒ））是Ｐｇ（Ｒ）的Ｇｒｏｔｈｅｎｄｉｅｃｋ群,在本文中我们证明了Ｋ０（Ｒ）＝Ｇｒ（Ｐｇ（Ｒ））。由此我们得到对任意ＶＢＮ环Ｒ,存在环Ｓ满足Ｓ＾２＝Ｓ并且具有Ａｕｔ－Ｐｉｃ性质,最后我们给出了环的一个分类,并且用Ｐｇ（Ｒ）的周期性对它作了描述。     

Morita Equivalence for Factorisable Semigroups

Recall that the semigroups S and R are said to be strongly Morita equivalent if there exists a unitary Morita context (S, R., _S P _R,R Q _S ,〈〉 , ⌈⌉) with 〈〉 and ⌈⌉ surjective. For a factorisable semigroup S, we denote ζ _S = {(s ₁, s ₂) ∈S×S|ss ₁ = ss ₂, ∀s∈S}, S' = S/ζ _S and US-FAct = { _S M∈S− Act |SM = M and SHom _S (S, M) ≅M}. We show that, for factorisable semigroups S and M, the categories US-FAct and UR-FAct are equivalent if and only if the semigroups S' and R' are strongly Morita equivalent. Some conditions for a factorisable semigroups to be strongly Morita equivalent to a sandwich semigroup, local units semigroup, monoid and group separately are also given. Moreover, we show that a semigroup S is completely simple if and only if S is strongly Morita equivalent to a group and for any index set I, S⊗SHom _S (S, ∐ _i∈I S) →∐ _i∈I S, s⊗t·ƒ↦ (st)ƒ is an S-isomorphism. The research is partially supported by a UGC(HK) grant #2160092. Project is supported by the National Natural Science Foundation of China     

Characters and Equivalence Classes of Central Simple Group Graded Algebras

We introduce an equivalence between central simple strongly G-graded algebras. Such classes are associated in a natural way to absolutely irreducible characters of semisimple G-graded algebras. We study invariants of this equivalence relation, and also the structure of certain representatives of the equivalence classes.     

Hermitian Morita Theory and Unitary Groups of Modules over Semisimple Artinian Rings

This article investigates isomorphisms between certain subgroups of the projective unitary groups of hermitian modules over semisimple Artinian rings with anti-structures. These subgroups contain the commutator subgroups of the projective unitary groups. Specifically, the article provides conditions under which these isomorphisms are induced by and the underlying rings are connected by hermitian Morita equivalences (HMEs). This article introduces the hyperbolic length of a module as well as the concept of generalized hyperbolic modules over simple Artinian rings, and over semisimple Artinian rings with anti-structures. The article shows that the stated isomorphisms are induced by HMEs if all the following conditions hold: (a) the hermitian forms are nonsingular and trace valued; (b) the modules in question are generalized hyperbolic; (c) the hyperbolic length equals three or is greater than or equal to five (hyperbolic length is greater than or equal to five in the semisimple case). Significantly, the condition of the hyperbolic length of a module greater than or equal to m is satisfied by a set of modules larger than or equal to those satisfying the condition of the Witt index of the module greater than or equal to m.     

On L-R Smash Products of Hopf Algebras

Let H be a Hopf algebra and A an H-bimodule algebra. This article investigates homological dimensions and Gorenstein dimensions of L-R smash products A?H. Several well-known results are generalized. Moreover, we explore the stability of Gorenstein projective (flat) precovers and Gorenstein injective preenvelopes between the category of left A-modules and the category of left A?H-modules.     

On Almost Unit-Regular Rings

An element a ∈ R is unit-regular provided that there exists an invertible u ∈ R such that a = aua. A ring R is called an almost unit-regular ring provided that for any a ∈ R, either a or 1 ? a is unit-regular. We characterize, in this article, the almost unit-regularity of Morita contexts with zero pairings. We also show that a ring R is unit-regular if and only if M ₂(R) is almost unit-regular. Various examples of such rings are constructed by means of formal triangular matrix rings.     

Lie ideals,Morita context and Generalized (α, β)-Derivations

A classical problem in ring theory is to study conditions under which a ring is forced to become commutative. Stimulated from Jacobson's famous result, several techniques are developed to achieve this goal. In the present note, we use a pair of rings, which are the ingredients of a Morita context, and obtain that if one of the ring is prime with the generalized (α, β)-derivations that satisfy certain conditions on the trace ideal of the ring, which by default is a Lie ideal, and the other ring is reduced, then the trace ideal of the reduced ring is contained in the center of the ring. As an outcome, in case of a semi-projective Morita context, the reduced ring becomes commutative.     

LIE IDEALS, MORITA CONTEXT AND GENERALIZED （α β）-DERIVATIONS

A classical problem in ring theory is to study conditions under which a ring is forced to become commutative. Stimulated from Jacobson＇s famous result, several tech- niques are developed to achieve this goal. In the present note, we use a pair of rings, which are the ingredients of a Morita context, and obtain that if one of the ring is prime with the generalized （α β）-derivations that satisfy certain conditions on the trace ideal of the ring, which by default is a Lie ideal, and the other ring is reduced, then the trace ideal of the reduced ring is contained in the center of the ring. As an outcome, in case of a semi-projective Morita context, the reduced ring becomes commutative.     

Duality for Weakly Co-Hopfian and Generalized Hopfian Modules

Abstract

Duality like connections are established for generalized Hopfian modules and weakly co-Hopfian modules. A generalization of ring Hopficity is also introduced and this concept is studied for matrix rings.