How to limit a Julia notebook to a single core?
If the high CPU usage is due to parallelized linear algebra routines, limiting the CPU usage of the linear algebra backend helps. For Julia 1.4 compiled to use BLAS, the following limits it to a single core:
using LinearAlgebra; 
BLAS.set_num_threads(1);

(Many forum posts recommend blas_set_num_threads(1) for older versions of Julia. This seems to have been depricated)