This article is an amazing example of poor journalism, snake-oil science and bad benchmarking.
Basically three Chemistry majors have "proven" that string concatenation in languages which have immutable strings is O(n^2) in the number of concatenations.
It looks like the authors have not heard about kernel-level page cache. No fsync was ever used in the benchmarks, therefore, it is never actually hitting the disk. The only good thing about this paper is that the Java and Python listings are available at the end, for everyone to identify the basic flaws in this research.
It's actually proving that it is faster to write directly to memory than to do a copy before writing to memory. Nothing really impressive there. :)
Basically three Chemistry majors have "proven" that string concatenation in languages which have immutable strings is O(n^2) in the number of concatenations.