Brădeanu, Cristina, and Doina Brădeanu. “ Application of the Ritz Variational Method for the Problem of Heat Conduction through Non-Convex Thick Plates”.
Rev. Anal. Numér. Théor. Approx., vol. 22, no. 1, Feb. 1993, pp. 23-37,
https://ictp.acad.ro/jnaat/journal/article/view/1993-vol22-no1-art2.