δ-SHOCK MAINTENANCE MODEL FOR AN IMPROVING SYSTEM UNDER PARTIAL SUM PROCESS. INTERNATIONAL JOURNAL OF MATHEMATICS (IJMM), [S. l.], v. 1, n. 1, p. 1–11, 2020. Disponível em: https://iaeme-library.com/index.php/IJMM/article/view/IJMM_01_01_001.. Acesso em: 30 mar. 2026.