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.
A character study typically refers to a film where the primary  focus is on the evolution of one particular character's  personality, usually the main character. A popular eâ¦xample of the  use of character study in a film was the evolution of the character  of Travis Bickle in Taxi Driver (played by Robert DeNiro.)