A perturbative approach to the time-dependent Karmarkar condition Megandhren Govender, Wesley Govender, Kevin P Reddy and Sunil D Maharaj Eur. Phys. J. C, 81 2 (2021) 177 Published online: 22 February 2021 DOI: 10.1140/epjc/s10052-021-08961-9