These are decimal numbers, and dots above some of the digits make them recurring decimals. One dot means the digit under it repeats infinitely. In other words, it goes on forever (and ever and ever).

Abstract: Using a 1550 nm array-based single-photon LiDAR system, we demonstrated depth profiling of both static and dynamic targets up to a distance of 10 kilometers. The system comprises a 1550 nm ...

The array can be shown as 5 groups of 3 showing that 5 x 3 = 15. Or it could be shown as 3 groups of 5 showing that 3 x 5 = 15. This demonstrates that multiplication is commutative. Image caption, ...