The primary purpose of this article is to conduct the Fourier Nonlinear Unit Root Test to check Purchasing Power Parity (PPP) for seven cryptocurrencies traded in seventeen countries from 2010 to 2021. The unit root test provides moderate support to the PPP hypothesis when we use each...

The goal of this paper is to search for conclusive evidence against the stationarity of the global air surface temperature, which is one of the most important indicators of climate change. For this purpose, possible long-range dependencies are investigated in the frequency-domain. Since...