2000 Mathematics Subject Classification: 16N80, 16S70, 16D25, 13G05.We construct some new examples showing that Heyman and Roos construction of the essential closure in the class of associative rings can terminate at any finite or the first infinite ordinal.

We identify some situations where mappings related to left centralizers, derivations and generalized $(\alpha ,\beta )$-derivations are free actions on semiprime rings. We show that for a left centralizer, or a derivation $T$, of a semiprime ring $R$ the mapping $\psi R\to R$ defined by $\psi \left(x\right)=T\left(x\right)x-xT\left(x\right)$ for all $x\in R$ is a free action. We also show that for a generalized $(\alpha ,\beta )$-derivation $F$ of a semiprime ring $R,$ with associated $(\alpha ,\beta )$-derivation $d,$ a dependent element $a$ of $F$ is also a dependent element of $\alpha +d.$ Furthermore, we prove that for a centralizer $f$ and...

Let $R$ be a prime ring with its Utumi ring of quotients $U$ and extended centroid $C$. Suppose that $F$ is a generalized derivation of $R$ and $L$ is a noncentral Lie ideal of $R$ such that $F\left(u\right){[F\left(u\right),u]}^n=0$ for all $u\in L$, where $n\ge 1$ is a fixed integer. Then one of the following holds: (1) ...

Let $R$ be a prime ring with center $Z\left(R\right)$ and $I$ a nonzero right ideal of $R$. Suppose that $R$ admits a generalized reverse derivation $(F,d)$ such that $d\left(Z\right(R\left)\right)\ne 0$. In the present paper, we shall prove that if one of the following conditions holds: (i) $F\left(xy\right)\pm xy\in Z\left(R\right)$, (ii) $F\left(\right[x,y\left]\right)\pm \left[F\right(x),y]\in Z\left(R\right)$, (iii) $F\left(\right[x,y\left]\right)\pm \left[F\right(x),F(y\left)\right]\in Z\left(R\right)$, (iv) $F(x\circ y)\pm F\left(x\right)\circ F\left(y\right)\in Z\left(R\right)$, (v) $\left[F\right(x),y]\pm [x,F(y\left)\right]\in Z\left(R\right)$, (vi) $F\left(x\right)\circ y\pm x\circ F\left(y\right)\in Z\left(R\right)$ for all $x,y\in I$, then $R$ is commutative.

In this paper we investigate $3$-prime near-rings with derivations satisfying certain differential identities on Jordan ideals, and we provide examples to show that the assumed restrictions cannot be relaxed.

Let M be a 2 and 3-torsion free prime Γ-ring, d a nonzero derivation on M and U a nonzero Lie ideal of M. In this paper it is proved that U is a central Lie ideal of M if d satisfies one of the following (i) d(U)⊂ Z, (ii) d(U)⊂ U and d²(U)=0, (iii) d(U)⊂ U, d²(U)⊂ Z.