Hello @Anton
It is possible to create the block using "block mask" techniques. However, I think the authors probably (and simply) used the Fcn block. However, the block has become obsolete since R2020b, if I remember correct.
Nevertheless, the expression 
can be easily constructed using basic blocks like the Trigonometric Function block and the Gain block.
can be easily constructed using basic blocks like the Trigonometric Function block and the Gain block.
By the way, why is the Gravity (physics) described like a sine wave? Sometimes, do not 100% trust the works or results in some Journal papers. Trust your guts instead.
