Transcranial Doppler (TCD), first described in 1982 [1], is a noninvasive ultrasound (US) study that involves the use of a low-frequency (â¤2 MHz) transducer probe to insonate the basal cerebral arteries through relatively thin bone windows.
Details. as.character and is.character are generic: you can write methods to handle specific classes of objects, see InternalMethods. Further, for as.character the default method calls as.vector, so dispatch is first on methods for as.character and then for methods for as.vector.
In information technology today, a character is generally one of a limited number of symbols, including the letters of a particular language's alphabet, the numerals in the decimal number system, and certain special symbols such as the ampersand (&) and atsign (@). Several standards of computer encoding have been developed for characters.