We prove that a finite von Neumann algebra $𝒜$ is semisimple if the algebra of affiliated operators $𝒰$ of $𝒜$ is semisimple. When $𝒜$ is not semisimple, we give the upper and lower bounds for the global dimensions of $𝒜$ and $𝒰.$ This last result requires the use of the Continuum Hypothesis.

Let $$𝕂$$ be an algebraically closed field. Consider a finite dimensional monomial relations algebra $$\Lambda =𝕂\Gamma /\phantom{𝕂\Gamma I}I$$ of finite global dimension, where Γ is a quiver and I an admissible ideal generated by a set of paths from the path algebra $$𝕂\Gamma$$ . There are many modules over Λ which may be represented graphically by a tree with respect to a top element, of which the indecomposable projectives are the most natural example. These trees possess branches which correspond to right subpaths of cycles in the quiver. A pattern...

In the first part, we study algebras A such that A = R ⨿ I, where R is a subalgebra and I a two-sided nilpotent ideal. Under certain conditions on I, we show that A is standardly stratified if and only if R is standardly stratified. Next, for $A=\left[\begin{array}{cc}U& 0\\ M& V\end{array}\right]$, we show that A is standardly stratified if and only if the algebra R = U × V is standardly stratified and ${}_{V}M$ is a good V-module.

Let Λ be an artinian ring and let 𝔯 denote its Jacobson radical. We show that a simple module of finite projective dimension has no self-extensions when Λ is graded by its radical, with at most two simple modules and 𝔯⁴ = 0, in particular, when Λ is a finite-dimensional algebra over an algebraically closed field with at most two simple modules and 𝔯³ = 0.