On dependent items in series in different environments

The Accelerated Life Model (ALM) and the proportional hazards (PH) model are very popular in reliability theory and applications as tools for modeling an impact of another environment on reliability characteristics of items defined for some baseline environment. These models were extensively studied for single items or systems. However, generalizations of the ALM and the PH model to the case of possibly dependent items were not considered in reliability literature as a tool for modeling the impact of environment. In this note, we suggest and discuss possible approaches for defining bivariate ALM and PH models and consider several examples.