We examine critically some of the existing descriptions of the envelope of a 1-parameter family of surfaces in 3-space. An old, natural, description is that the envelope is the union of the characteristic curves (defined as the “limit intersection curves” of surfaces from the family). This description fell in disrepute during the 20th century. We claim that this relegation of the limit intersec...

‎The notion of quasi-Einstein metric in physics is equivalent to the notion of Ricci soliton in Riemannian spaces‎. ‎Quasi-Einstein metrics serve also as solution to the Ricci flow equation‎. ‎Here‎, ‎the Riemannian metric is replaced by a Hessian matrix derived from a Finsler structure and a quasi-Einstein Finsler metric is defined‎. ‎In compact case‎, ‎it is proved that the quasi-Einstein met...

In this article, I compare William Faulkner's As I Lay Dying and Sadeq Chubak’s The Patient ‎Stone ‎with respect to the theme of death and from the perspective of Existentialism. I argue that ‎despite ‎Faulkner’s influence on Chubak and similarities in their writings, the Iranian modernist novel ‎presents ‎intellectual and aesthetic nuances catering to the domestic material circumstances of ‎it...

A formal model for diagnostics of biological systems modelled as P systems is presented. We assume the presence of some biologically motivated changes (frequently pathological) in the systems behavior and investigate when these changes could be diagnosed by an external observer by exploiting some techniques originally developed for reasoning on system security.