Formula 1 , εz=0\varepsilon_{z}=0εz=0, and σz≠0\sigma_{z} \neq 0σz=0. σz≠0\sigma_{z} \neq 0σz=0 Formula 2 , σz=0\sigma_{z}=0σz=0, and εz≠0\varepsilon_{z} \neq 0εz=0. εz≠0\varepsilon_{z} \neq 0εz=0 Found in January