“…Elliptic equations involving Laplacian operator on bounded domains with mixed boundary conditions arise in real applications, for example, in hydrodynamics; see [1,2]. Generally, nonlinear problems subject to various boundary conditions appear in many different branches of the applied sciences, including physics (e.g., steady-state heat flux modeling), chemistry (e.g., Keller-Segel model for parabolic equations in chemotaxis), biology (e.g., Gierer-Meinhardt system in the formation of biological models), and engineering.…”