You might want to open two files in two separate windows to compare them. Also, if you want to edit two files simultaneously, you need to open them separately. That is why you can change Notepad ...

Abstract: During the last decade, possibilities to realize new phenomena and create new applications by varying system properties in time have gained increasing attention in many research fields.

Abstract: Sixth-generation (6G) mobile communication networks are expected to have dense infrastructures, large antenna size, wide bandwidth, cost-effective hardware, diversified positioning methods, ...