The derivative operator will usually be written as 
irrespective of whether x is a vector or scalar. If x is a vector,
then the whole symbol is written as bold, e.g
. Exceptions occur to this convention
when the derivative is with respect to 
(position), in which case
the symbol 
is often used, and when the derivative is with respect
to time, when Newton's convention of placing a dot over the symbol is
often used.
With integrals, a volume integral will be written as 
. This is sometimes written as 
by
other authors.