The algebra of adjacency patterns: Rees matrix semigroups with reversion

We establish a surprisingly close relationship between universal Horn classes of directed graphs and varieties generated by so-called adjacency semigroups which are Rees matrix semigroups over the trivial group with the unary operation of reversion. In particular, the lattice of subvarieties of the variety generated by adjacency semigroups that are regular unary semigroups is essentially the same as the lattice of universal Horn classes of reflexive directed graphs. A number of examples follow, including a limit variety of regular unary semigroups and finite unary semigroups with NP-hard variety membership problems.Comment: 30 pages, 9 figure

Clarifying the origin of near-infrared electroluminescence peaks for nanocrystalline germanium in metal-insulator-silicon structures

10.1063/1.1793348Applied Physics Letters85122349-2351APPL

Mapping of γ/δ T cells reveals Vδ2+ T cells resistance to senescence

10.1016/j.ebiom.2018.11.053EBioMedicine3944-5