@article{wang_2005,  title={Perturbations around black holes},  volume={35},  ISSN={0103-9733},  url={https://doi.org/10.1590/S0103-97332005000700002},  DOI={10.1590/S0103-97332005000700002},  number={4b},  journal={Brazilian Journal of Physics},  publisher={Sociedade Brasileira de Física},  author={Wang, Bin},  year={2005},  month={Dec},  pages={1029–1037} }