 (o with diaeresis) is used in some publications to show that a vowel is pronounced separately and is done in Dutch.
In languages without such vowels, the character is known as an "o with diaeresis" and denotes a syllable break, wherein its pronunciation remains an unmodified o. Some writers and publications, such as The New Yorker, use it in English words such as zoology and cooperate to indicate that the second vowel is pronounced separately. This is also done in Dutch. 
